Installation of fcu. Filter compensating devices (FKU). Static compensating devices for industrial plants

Filter compensating devices (FCD) are designed to reduce harmonic voltage distortion and compensate for reactive power of consumer loads in power supply networks of industrial enterprises and in electrical networks.

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Power higher harmonic filters is important for optimizing the costs of industrial enterprises, as well as increasing the stability of their work and reducing risks. The use of power filters makes it possible to achieve higher industrial performance, as well as to use additional load on the network, which can be quite important during expansion. Power filters for enterprises in most situations have a payback period of less than a year, which makes their use economically justified and necessary.

The structure of the standard designation of the filter compensating device is deciphered as follows:

An example of recording the designation of a PKU of the 13th harmonic with a voltage of 10 kV, a power of 3000 kvar, climatic version and placement category - U3: “Filter compensating device FKU-13-10-3000 UZ GOST 13109-97.”

Harmonic filters are designed individually for each individual application. This guarantees the ability to achieve the highest parameters for filtering higher harmonics and power factor correction of the PKU.

DATA REQUIRED FOR THE DESIGN OF HIGH HARMONIC FILTERS (HHF).

1. Rated voltage.
2. Required reactive power compensation at the fundamental frequency.
3. Values ​​of currents of harmonic components of a nonlinear load to be filtered or information on harmonic-generating loads.
4. Network short circuit power.
5. Required power quality parameters at the non-linear load power buses (or at another junction point).
6. Environmental conditions (indoor or outdoor installation, temperature range).
7. Additional requirements (dimensions, protection, etc.)

High harmonic filters consist of capacitors connected in series with an inductance. The inductance is selected such that the filter is a low-impedance series resonant circuit at the harmonic frequency. This ensures that the main part of the harmonic component of the current passes through the filter. Capacitors produce reactive power at the fundamental frequency.

NPC ENERCOM-SERVICE LLC has experience in manufacturing higher harmonic filters for voltage 0.4; 6.3; 10 and 35 kV for enterprises of the metallurgical, electrochemical industries and for power grids of near and far abroad countries. Qualified specialists can conduct a network survey to identify the harmonic composition of its operating parameters and draw up technical specifications for equipment design.

EXAMPLES OF FCU MANUFACTURED BY SPC "ENERCOM-SERVICE" LLC
FOR DIFFERENT APPLICATIONS AND VOLTAGES.

1. Basic technical data and characteristics

note: the busbar is not shown in the top view

General view of FKU-13-10-3000 U3

Capacitor battery

Dry filter reactor

Current transformer

General view of FKU-2-35-43000 U1

Static compensating devices for industrial enterprises.

The widespread use of thyristor electric drives, rectifier electrolysis plants, powerful electric arc furnaces, rolling mills and other electricity consumers with sharply variable loads and non-sinusoidal current is accompanied by significant consumption of reactive power and distortion of the supply voltage, which can lead to an increase in electricity losses and deterioration and disruption of the normal functioning of the electricity consumer . Such consumers include primarily metallurgical plants, chemical enterprises, non-ferrous metallurgy enterprises, pulp and paper enterprises, enterprises for electrochemical processing of metals and precious stones, enterprises with electric arc and resistance welding, ordinary enterprises using gas discharge lamps for lighting, oil and gas enterprises and coal industries, irrigation enterprises with electric motors of various types, and other enterprises.

To compensate reactive power and improve power factor, filtering higher harmonics current, reducing voltage fluctuations and improving power quality parameters, static compensating devices are used:

• capacitor units (increasing power factor);
• filter-compensating installations (increasing power factor and filtering higher current harmonics);
• static thyristor reactive power compensators (increasing power factor, filtering higher current harmonics, reducing voltage asymmetry and stabilizing voltage).

The use of static compensating devices allows:

• significantly reduce the reactive power load and higher harmonics current of transformers supplying consumers, which makes it possible to connect additional load;
• improve voltage quality indicators and, thereby, increase the quality of products and the productivity of the technological process of the electricity consumer.

For example, the use of SVC at a metallurgical plant increased the load power factor from 0.7 to 0.97, reduced supply voltage fluctuations by 3 times, and reduced the time of one metal melt from 150 minutes. up to 130 min. and specific energy consumption per ton of smelted steel by 4%, and also reduced the consumption of graphite materials. In general, the payback period for static compensating devices averages from 0.5 to 1 year.

If necessary, SPC "enercomserv" LLC can carry out a set of works on the implementation of the STC, starting with surveying electrical networks, performing the necessary measurements to determine the type, power and connection points of the STC, selecting circuits and equipment parameters, their regulation laws, and supplying STC equipment " turnkey”, its installation, commissioning, start-up testing, as well as personnel training and further servicing of the equipment.

Product designations:

• Filter-compensating device FKU-5-10-5400 U3 YUPIN.673842.014
• Filter-compensating device FKU-5-10-5400 U3 YUPIN.673842.014-01
• Filter-compensating device FKU-5-10-7200 UHL1 YUPIN.673842.015
• Filter-compensating device FKU-10-18000 U3
• Design of power filters USFM 0.4-5/7-450 U3
• Control, regulation and protection system for compensating device SURZA KU

Additional information

In order to organically meet these requirements, the power supply system must be uninterrupted and as reliable as possible. Installation power filters is one of the most effective and high-quality ways to reduce the impact on the network of arc steel furnaces, welding production, valve converters, widely implemented in industrial power supply for technical efficiency of production.

The invention relates to the field of electrical engineering. The device provides adjustment of reactive power by switching two or more branches, each of which is equipped with a switch for connection to the supply network and contains capacitor banks, resistors, and reactors that perform filtering and compensation functions. The device also contains one or more active elements. The capacitor banks of the device are connected to the ground through a common active element by means of a corresponding number of medium-voltage switches or through individual active elements and implement only the compensation function. Filtering functions are performed only by the active element; For this purpose, the active element equation system, in addition to the usual set of functional blocks, is equipped with three specific functional blocks implemented in software: damping block D, balance block B, selective harmonic suppression block S, generating reference voltages, the sum of which forms the main converter control variable. The technical result is the use of the same type of interchangeable capacitor banks, the absence of energy-dissipating resistors, and the absence of tuned resonant circuits. 1 salary f-ly, 13 ill.

Drawings for RF patent 2521428

The claimed technical solution relates to electrical engineering, mainly to high-voltage direct current power transmission (HVDC - High Voltage DC Transmission) (or direct current inserts) with adjustable transmitted power and is intended to compensate for reactive power and improve the harmonic composition of the voltage and current of the supply network.

In direct current transmissions of the electric power industry at present, the main technical means are network-driven current converters - converters (line commutated converter, LCC) with thyristor valves. The grid-driven converter consumes reactive power from the alternating current (AC) network and injects higher current harmonics into it. The consumed reactive power changes when regulating the transmitted power.

To compensate for reactive power and improve the harmonic composition of the voltage and current of the supply network, a filter-compensating device (FCD) is used, connected to the AC side, composed of two or more three-phase branches, each of which is equipped with a switch for connection to the supply network

Until recently, circuits composed of passive elements of electrical circuits were used for filtering in converter installations: inductances L, capacitances C and resistors R. The use of passive filters in AC power networks is associated with a fundamental contradiction. In a good electrical power filter, power losses should be zero or at least small. On the other hand, filters made of reactive elements have a long time to establish transient oscillations, so that during repeated disturbances such filters may not be installed at all. This contradiction cannot be eliminated by remaining in the class of passive circuits. You can only choose an acceptable compromise solution, damping the reactive LC circuits with resistors R so that the power losses are not too large and the settling time is acceptable.

The second problem in constructing a PKU is caused by combining the filtering function with the reactive power adjustment function. To adjust the reactive power, the set of capacitors is divided into separate capacitor banks, connected to the AC (alternating current) network separately. When the transmitted power decreases, the batteries are disconnected from the network, and when the transmitted power increases, they are connected again. The number of separately switched batteries Nq is determined by the permissible reactive power imbalance and the transient voltage deviation during switching.

This tuning q-partition defines only the first dimension of the partition. The second dimension is the partition into filtering branches. The LCC current spectrum contains a number of canonical harmonics: 11, 13, 23, 25, 35, 37, 47, 49

Non-canonical harmonics 3, 5, 7 must also be taken into account. Thus, the capacitors must be distributed along the resonant branches (H-partitioning). The combination of partitions by harmonics and partitions by adjusting reactive power leads to very complex PKUs, with a large number of branches.

The experience of creating acceptable compromise PCFs with passive elements is summarized in the CIGRE recommendations (WG 14.30, No. 139, April 1999 - ). An idea of ​​modern practice is also given by the construction of the PKU on the Ballia - Bhiwadi transmission (R-K. Chauhan, M. Kuhnand etc. -). The resulting PKU system is extremely complex, and this is typical.

Thus, the disadvantages of passive filters appear in two situations:

When the requirement for high-quality filtration is combined with the need to adjust reactive power,

When the reactive power required for the system is less than that obtained under the filtration conditions.

Both of these situations are currently gaining increasing importance. The first of them is due to the increasing requirements for gear flexibility. The second situation is associated with the growing use of series-compensated transmission lines and capacitor-commutated valve converters (CCC circuits). In this regard, the increasing use of hybrid filters is expected, with the help of which filtering problems are solved more efficiently. Improvement of power transistors (increase in unit power, reduction of dynamic and static losses), as well as improvement of signal processors (increase in speed, increase in bit depth) are additional factors in favor of increasing the use of active filters.

The creation of insulated gate bipolar transistors (IGBTs) paved the way for the implementation of powerful pulse-width modulation (PWM) voltage converters (Voltage Sourced Converter (VSC), which have already become a staple in adjustable electric drives and uninterruptible power supply systems. nutrition. The rapid progress of IGBTs has opened up the possibility of using this type of converters in the power industry, where they compete with traditional LCC systems and open up new possibilities for building flexible power control systems in AC (alternating current) systems (FACTS). Of decisive importance for expanding the applications of VSC systems in the electric power industry is the invention of the modular multilevel circuit (Modular Multilevel Converter, MMC) by R. Marquardt (Markwardt R., 2002 -). Modular multi-level circuits allow you to raise the voltage and power class of voltage converters and at the same time improve dynamic capabilities and reduce power losses

In energy filters, the active element is connected to the system through a capacitor bank and is shunted by a reactor or a more complex passive circuit, thus forming a hybrid filter. The DC link of the active element contains a capacitive energy storage device, but is not connected to an energy source or consumer.

The idea of ​​using a PWM converter as an active element of an electric power filter was expressed by one of the first L. Guigi (Guigi, 1976 - ).

A known hybrid filter circuit (see Fig. 1) for alternating current networks (Sadek, Pereira, 2002 - ). In it, the active element is connected as an auxiliary device to a two-frequency damped filter 12, 24 (canonical harmonic filtering: 11, 13, 23, 25) to improve its characteristics. The filter output is shunted by an additional LC circuit tuned to the fundamental harmonic; this circuit does not participate in filtration, but reduces the load on the active element in stationary modes.

In April 2003, CIGRE Working Group WG 14.28 issued Paper 223 on Active Filtration in HVDC. The bulk of Recommendation 223 is devoted to filtering in DC circuits. The application of the Sadek-Pereira scheme is given as an application in the AS network. This scheme was tested at the Tjele (Eitra) converter station in Denmark as a demonstration project in 1998

A filter-compensating device (see Fig. 2) used in the Neptune project (Neptune Regional Transmission System, 2007) is also known (which is a development of a technical solution.

The disadvantage of technical solutions is the use of auxiliary resonant circuits and damping resistors introduced into the active filter circuit and connected parallel to the input of the active element - a modular multilevel PWM converter (PWM-MMC). This significantly complicates and increases the cost of the PKU as a whole, causing additional energy losses. Another disadvantage is the installation of several active filters in parallel branches, because when adjusting the reactive power (when the transmitted power decreases, the capacitor banks are disconnected from the network, and when the transmitted power increases, they are connected again), it is possible to disconnect the branch containing the active filter, which reduces the economic efficiency of its use.

The problem to be solved by the proposed technical solution is to ensure:

Use of the same type of interchangeable capacitor banks (homogeneous PKU);

No energy dissipating resistors;

Lack of tuned resonant circuits.

When solving the problem, the achieved technical result is:

Simplification of the PKU circuit (homogeneous PKU), radical reduction in the number of PKU branches for the conditions of reactive power regulation by switching batteries. The consequence of this should be a reduction in the area occupied by the PKU and an increase in this regard in the competitiveness of the LCC system with the system of an alternative technical solution (HVDS-lights) - voltage converters with transistors (Voltage Sourced Converter, VSC);

Reducing power losses of the PKU due to damping with virtual resistors instead of damping with real resistors (the function is performed by the active element control system without the involvement of any hardware);

Simplification of PKU settings during commissioning and restructuring when changing the parameters of the AC network. In the proposed homogeneous PKU, all settings and rearrangements are carried out exclusively by adjusting the active element control program,

which ultimately can significantly reduce capital and operating costs while increasing reliability and ease of maintenance.

The main essence of this technical solution is the use of a three-component active element control algorithm (DBS algorithm: D - damping; B - balance, S - selective harmonic suppression), which allows the full potential of active filtering to be realized. Based on the DBS algorithm it is possible to:

Implementation of damping of transient vibrations without the use of resistors;

Complete absorption of higher harmonics without the use of tuned resonant circuits.

Modular multilevel converters (MMCs) are now manufactured as highly reliable devices, and the requirement to ensure operation without an active element has become irrelevant.

In accordance with the proposed technical solution, the above problem is solved by the fact that in the known filter-compensating device of a complete converter installation for transmitting direct current energy based on a network-driven valve (thyristor) current converter (LCC) with adjustable transmitted power, adjusting the reactive power by switching two or more branches, each of which is equipped with a switch for connection to the supply network and contains capacitor banks, resistors, and reactors that perform filtering and compensation functions; The filter-compensating device also contains one or more active elements (voltage converter with high-frequency width modulation, current and voltage sensors), according to the claimed technical solution:

where: Nq - number of capacitor banks,

Block B - balance (bal),

vz=vdemp+vbal+vsel, and:

vdemp(t)=Rae·iae(t),

and consists of several software modules (subblocks):

Proportional-integral power regulator (PI regulator), acting as a function of the energy accumulated by capacitors, effectively bringing the energy Ed to a given value Ez:

.,

Where; - energy setting; - energy accumulated by capacitors, p - Laplace operator, Kd, ​​td - gain and time constant of the PI controller, Pbal - power reference;

Module for calculating (based on the balance power regulator determined) the complex amplitude of the balance voltage component Vbal,norm, normal to the mains voltage vector:

,

vbal(t)=Vbal,norm·j·e j

where e j is the rotating unit voltage;

Block S is formed using feedback on the network current is with the participation of the network voltage vs in the formation of this connection and consists of several software modules (subblocks):

Module for selective selection of complex amplitudes, higher harmonics, using the expression:

where k is the harmonic number, is the complex amplitude of the k-th harmonic of the network current is, e j·k· is the rotating unit unit of the k-th harmonic of the network current;

,

where: p - Laplace operator, - integrator time constant;

Module for generating the k-th harmonic voltage of the converter based on the obtained value of the complex voltage amplitude:

and subsequent summation:

,

11, 13; -23, 25; -35, 37 ,

5, -7; -17, 19; .

This problem is also solved by the fact that in the known filter-compensating device, a current-limiting reactor is introduced into the circuit of capacitor banks, the reactance of which is determined by the condition of limiting the amplitude of the transient current when switching the capacitor banks.

The following illustrations are provided for clarification.

Figure 1 shows a diagram of a hybrid filter for alternating current networks (Sadek, Pereira, 2002 - ).

Figure 2 shows a diagram of the filter-compensating device used in the Neptune project (Neptune Regional Transmission System, 2007) (.

Figure 3 shows a simplified single-line diagram of a filter-compensating device consisting of untuned capacitor banks of the same type and an active element with a three-component voltage regulator.

Figure 4 shows a diagram of the construction of a modular multilevel converter from similar modules (voltage converters).

Figure 5 a) and b) shows equivalent circuits that explain the principle of operation of damping feedback.

Figure 6 shows a block diagram of the balance block of the general circuit of a homogeneous PKU with an active element.

Figure 7 shows an equivalent circuit to illustrate the operation of the balance unit.

Figure 8 shows an equivalent circuit to illustrate the operation of the selective harmonic suppression unit.

Figure 9 shows a functional diagram of a voltage calculator for selective suppression of harmonics based on the measured current of the slave converter (direct connection, feedforward).

Figure 10 shows a block diagram of a regulator for selective suppression of the kth harmonic of the mains current.

Figure 11 shows a block diagram of a calculator for the component of selective suppression of harmonics using feedback on the network current.

Figures 12 and 13 show graphs of the PKU operation obtained by mathematical modeling:

Fig. 12. Graphs of operation of a homogeneous PKU and its active element at rated transmitted power.

Fig. 13. Current at the converter output and line current when the transmitted power decreases with the third battery of the PKU disconnected.

The design of the proposed technical solution - a filter-compensating device made of untuned same-type capacitor banks and an active element with a three-component voltage regulator - in its static state can be described using the illustrations presented in Fig. 3, 4, 5, 6, 7, 8, 9 , 10, 11, 12, 13.

Figure 3 shows a simplified single-line diagram of a filter-compensating device consisting of untuned capacitor banks of the same type and an active element with a three-component voltage regulator. The filter-compensating device (FCU) is connected on the AC side between AC buses 1 and the secondary winding of transformer 2, to the primary windings of which a network-driven converter 3 is connected, which consumes reactive power from the AC network (AC network - alternate current) and injects higher harmonics of the current flow into it.

The set of capacitors required to operate on the network of the converter 3 driven by it is divided into Nq similar batteries 4 for each three-phase branch of the network. If Q sum is the reactive power required at the highest transmitted power, then the power of each battery is:

Q k =Q sum /N q , k=1, 2 N q .

Each battery 4 (with admittance Yo) is connected to busbars 1 of the AC network through a high-voltage switch 5 and grounded through reactor 6 (with reactance X 0). The connection nodes of the battery 4 and the grounding reactor 6 are connected to the busbars 7 of the active element 8 through medium-voltage switches 9.

If it is necessary to reduce or increase reactive power, any of the identical capacitor banks 4 of a homogeneous PKU can be disconnected or connected. It is advisable to connect capacitor banks 4 at the moments when the voltage crosses zero, using the modern level of synchronization of switching of high-voltage switches 5 and 9. Filtering of higher harmonics of the current in a homogeneous PKU using the active element 8 can be done through all capacitor banks 4 connected to the AC network or through part these batteries.

The splitting factor Nq of a set of capacitors into capacitor banks is determined in the usual way by the network modes: the permissible compensation error and the permissible change in the AC network voltage with a step change in reactive power.

The power converting part of the active element 8 is a high-frequency pulse-width modulation (PWM) PWM voltage converter 10, which is connected to the busbars 7 directly or through an isolation transformer. The width modulation ripples of the PWM converter 10 are filtered directly at the output of the PWM converter 10 using a broadband filter consisting of inductance 11 (Lae) and capacitance 12 (Cae) and do not penetrate into the AC network due to the high modulation frequency (at the same time on the network frequency s reactance s·Lae and admittance s·Cae of the filter are negligible).

A modular multilevel voltage converter (MMC) can be used as a PWM converter 10 of the active element 8 in a homogeneous PKU. It is equipped with the usual set of blocks for operating in the PWM servo converter mode: auxiliary power supplies, transistor drivers, current and voltage sensors (not shown in Fig. 3) and modulator 13 (mdl). In addition to the listed non-specific hardware and functional blocks, for operation as part of the PKU, the control system of the active element 8 is equipped with three specific functional blocks to generate a three-component MMC voltage setting with their corresponding feedbacks:

damping block 14 - D (demp),

balance block 15 - B (balance),

selective harmonic suppression block 16 - S (select).

The output signals of blocks 14, 15, 16: vdemp, vbal, vsel are respectively summed by adder 17. This three-component sum is the voltage setting vz(t):

is the main control variable of PWM converter 10.

Each of the blocks 14, 15, 16 has its own feedback connections and performs its function in a set of filtering tasks.

The damping unit 14 receives a feedback signal from the output current sensor 18 iae of the active element 8.

The balance block 15 receives feedback signals from the voltage sensor 19 of the storage capacitors 20 of the direct voltage links of the PWM converter 10 and from the mains voltage sensor 21 vs.

The selective harmonic suppression unit 16 receives feedback signals from the network current sensor 22 is and from the network voltage sensor 21 vs.

The modular multilevel PWM converter 10 is made up of modules 23 of the same type (see Fig. 4), each of which is a voltage converter capable of operating in width modulation mode (PWM converter). Modules 23 are connected in series via AC voltage ports w and z.

Figure 5 a) and b) shows equivalent circuits that explain the principle of operation of damping feedback. Figure 5 a) shows a simplified equivalent circuit diagram of the system shown in Figure 3. Some new conventions have been introduced. The network-driven current converter 3 is represented in the equivalent circuit by a current source iw(t) 24, the AC network is represented by a three-terminal network Zs 25 and emf. networks us(t) 26, and PWM converter 10 with modulator 13 are presented in the form of block 27. In Fig. 5 b) the same circuit is presented with a virtual resistor Rae 28. In the equivalent circuit in Fig. 5 b) with a virtual resistor 28 only two feedback links remain.

Figure 6 shows a block diagram of the balance block 15 of the general circuit of a homogeneous PKU with an active element 8. The circuit contains: multiplication blocks 29, 30, 31 and division 32, 33, functional block 34, adder 35, regulator 36, synchronization block 37, block 38 selection of magnitude module. The input signals of block 15 are:

Signal vs from sensor 21 mains voltage vs,

Signal Ez - sets the energy of storage capacitors 20.

Figure 7 shows the equivalent circuit of the filter-compensating device shown in Figure 3. The designations in the diagram correspond to the designations in Fig. 5: the network-driven current converter 3 is represented in an equivalent circuit by a current source iw(t) 24, the AC network is represented by a three-terminal network Zs 25; further designations: capacitor banks 4, grounding reactor 6, active element 8.

Figure 8 shows an equivalent circuit to illustrate the operation of the selective harmonic suppression unit. The designations in the diagram correspond to the designations in Fig.7. Virtual resistor Rae and emf source. vsel are part of the active element 8.

Figure 9 shows a functional diagram of a voltage calculator for selective suppression of harmonics based on the measured current of the slave converter 3 (direct connection, feedforward). The circuit contains multiplication blocks 39, 50, integrators 51 54, adder 55.

Figure 10 shows a block diagram of a regulator for selective suppression of the kth harmonic of the mains current. The diagram shows: network current sensor 22 is, multiplication units 56, 57, 58, integrator 59, kth harmonic voltage source 60, element 61 corresponding to the value of the stationary transfer characteristic of the system at the kth harmonic frequency.

Figure 11 shows a block diagram of a calculator for the selective harmonic suppression component vsel using feedback on the network current is. The circuit contains a synchronization and conversion block 62, multiplication blocks 63, 80, integrators 81 86, adder 87.

The device works as follows

In the proposed homogeneous PKU (see Fig. 3), the active element 8 is used as the main filtering device. Auxiliary resonant circuits and damping resistors used in the well-known PKU circuit with an active element (Sadek, Pereira, 2002 -) are excluded. Both functions:

Damping

Selective filtering

in a homogeneous PKU are completely assigned to the control system of the active element 8 and are performed by it without the use of any hardware.

The output voltage vae of the tracking PWM converter 10 with a correctly constructed modulator 13 reproduces at its output to the AC power network the variable from the control system - voltage reference - vz:

At a sufficiently high modulation frequency, PWM pulsations are eliminated by a very light filter (consisting of inductance 11 (Lae) and capacitance 12 (Cae)), the lag of the output relative to the input is negligible, so this kind of PWM converter 10 acts as a signal repeater (accurate to scale) from the control system to the power circuit, and implements equality (2) quite accurately.

PWM converter 10 (see Fig. 4) is a controlled element that does not accumulate or dissipate energy (non-energetic, non-dissipative); the power of the AC port (w-z) is identical to the power of the DC port (dp-dm)

where vae and iae are the current and voltage of the AC port (w-z), vd and id are the current and voltage of the DC port (dp-dm),

and the voltage and current transfer coefficient is set by the control system that generates the switching function of the transistors s(t)

The value of the switching function, locally averaged over the modulation period, can smoothly change in the range [-1, 1], and accordingly, the voltage of the PWM converter 10 can be smoothly changed by the control system in the range [-vd, vd]. With a correctly constructed modulator 13, the switching function s(t) generated by it has a locally averaged value

In this case, the locally averaged voltage of the PWM converter 10 coincides with the reference signal

which is what is required to use it as an active filter element. Equalities (3 7) describe the modules 23 of the multi-level scheme, and after obvious expansions of the interpretation - and the entire modular multi-level scheme as a whole.

As noted above, to generate a three-component voltage reference of the PWM converter 10 in accordance with expression (I):

vz=vdemp+vsel+vbal

the control system of the active element 8 (see Fig. 3) is equipped with three specific DBS functional blocks (blocks 14, 15, 16).

Let's move on to a description of their work.

The damping (D - damp) block 14 uses proportional feedback with gain Rae to produce the first of three components:

which acts exactly like a resistor Rae introduced into the output circuit of the active element 8. Proportional feedback on the output current of the active element 8 creates a virtual damping resistor Rae. This virtual resistor dampens transient network oscillations no worse than a real resistor. Having an active element 8, there is no need to introduce real damping resistors into the filtering circuit. They are not used in homogeneous PKU.

To clarify the physical essence of the processes in the system presented in Fig. 3, it is useful to collapse the damping feedback (D-demp) in the equivalent circuit and transfer its action to the power electrical circuit, where this connection is represented by a resistor Rae (virtual). The damping feedback convolution process is illustrated using Fig. 5 a) and b). Figure 5 a) shows a simplified equivalent circuit of a system containing a homogeneous PKU with block 27 (performing the role of an active element in the equivalent circuit), and in which block 27 is covered by three DBS feedback loops (damp, balance, select). The network-driven current converter 3 is represented in the equivalent circuit in Fig. 5 a) and b), by the current source iw(t), and the AC network is represented by a three-terminal network Zs 25 and emf. network us(t) 26. The remaining designations are the same as in Fig.3. In Fig. 5 b) the same circuit as in Fig. 5 a) is presented with a virtual resistor Rae 28. In the equivalent circuit in Fig. 5 b) with a virtual resistor Rae 28, only two feedbacks remain, B and S. These Feedback to the current of block 27 (active element) does not directly respond. Thus, the synthesis task is divided into two parts. The virtual resistor Rae 28 is selected to best dampen transient vibrations. The remaining two components BS act on the damped system through virtual resistor 28.

Let's move on to a description of the operation of balance block 15 - B (balance).

When operating as part of an active element 8, the PWM converter 10 does not transfer energy from one network to another, and the storage capacitors 20 of the PWM converter 10 may not be connected to a DC voltage source or drain, i.e. left to be "suspended" or "floating". As a consequence of this, the task arises of maintaining the power balance of the storage capacitors 20. For the operation of the PWM converter 10, it is necessary that the voltages vd of the storage capacitors 20 be kept in the vicinity of a given level vdz:

and for this it is necessary that at any sufficiently long time interval Td the average power of the PWM converter 10 (and active element 8) be zero

.

This equality must be fulfilled against the background of the active element 8 fulfilling its essential duties: damping transient oscillations and absorbing higher current harmonics. The specificity of the conditions for using the active element 8 in an AC network filter makes it possible: without any disruption of the filtering, a fundamental harmonic voltage with an arbitrary amplitude and phase can be added to the output voltage of the active element 8. The complex amplitude of the fundamental voltage harmonic of the active element 8 is a free parameter. It is this that is used as a parameter for regulating the power balance Pd of storage capacitors 20 of the active element 8.

The voltages vd of these capacitors are described by the nonlinear differential equation

.

where C is the capacitance of capacitors 20.

However, if we go to the accumulated energy

,

the equation becomes linear

Let us highlight the balance component Pbal in power Pd:

where Pd" are other components. To regulate an object with equation (11), a proportional-integral power regulator 36 (PI regulator) is used (see Fig. 6).

where: p - Laplace operator; Ez-set the energy of storage capacitors 20; Kd, td - gain and time constant of the PI controller.

With suitable parameters, such a regulator effectively brings the energy Ed to a given value Ez.

As shown in Fig. 6, the input of the functional block 34 receives the signal vd from the voltage sensor 19 of the storage capacitors 20, then a difference (Ez-Ed) is formed at the output of the adder 35, which is fed to the input of the regulator 36.

Next, the power value Pbal determined by the regulator 36 must be converted into a complex amplitude of the balance voltage vbal, and then into a sinusoidal variable of the network frequency vbal(t) so as to realize the required balance power Pbal.

The balance power is equal to the scalar product of complex amplitudes, sinusoidal functions of voltage and current (vbal, ibal).

Using the equivalent circuit (see Fig. 7) of the system presented in Fig. 3, an expression was obtained for the complex amplitude of the balance current ibal:

where is the complex amplitude of the network voltage vs, yo is the conductivity of the block of capacitor banks 4, ho is the reactance of the grounding reactor 6, .

Substituting the last expression into (13) gives

where - is the mains voltage module vs, Vbal, norm - the balance voltage component normal to the mains voltage vector.

The tangential component of the vector does not affect the power of the balance. The component Vbal,tan can be taken to be zero or something else; it does not affect balancing. From formula (15) the normal component of the balance amplitude is calculated from the required power Pbal

The calculation of Vbal,norm is implemented (see Fig. 6) using a multiplication block 29 and a division block 32. In this case, the module voltage of the network vs is calculated using the synchronization block 37 and the module calculation block 38. Block 37 converts the triple of phase voltages of a three-phase network into one complex variable of the form:

consisting of a complex amplitude and a rotating unit amplitude vector (unit vector) e j· .,

Division block 33 calculates the values ​​of the rotating unit vector e j· mains voltage, and then, using multiplication blocks 30 and 31, a sinusoidal variable is formed - balance voltage vbal - the second of the three components of expression (1):

After connecting the damping component vdemp and the balance component vbal of the voltage adjuster of the active element 8, the equivalent circuit of the AC network, together with the compensating capacitors 4 and the active element 8, form a power electrical circuit that is heavily damped with the help of virtual resistors without the use of real energy-dissipating resistors for damping. In a simplified form, without taking into account the filter (Lae, Cae) of high-frequency width modulation pulsations, which is unimportant here, this circuit is presented in Fig. 8. The active element 8 is represented in it by a damping resistor Rae and an emf source. vsel, designed to absorb higher harmonics of current iw.

The spectrum of the current sent to the network by the network-driven converter 3 is discrete

Accordingly, the component of selective harmonic absorption vsel is formed as the sum

Each of the higher harmonics of the current iw k, under the action of the harmonic of the output voltage vaek of the active element 8, must be completely drawn into the PKU (into the active element 8), so that it should be:

and accordingly for voltage:

To satisfy these conditions, the complex amplitude of voltage harmonics vsel() must be

, k·Iw k ,

In this case, a current harmonic k with a complex amplitude flows through the active element 8

The functional diagram of the selective harmonic suppression calculator operating according to formulas (21-24) is shown in Fig.9.

The canonical harmonics of the 12-pulse circuit of the network-driven current converter 3 are of the order

k: -11, 13; -23, 25; -35, 37;

where negative numbers correspond to reverse-rotating harmonics. Complex variables with unit amplitude e j·k· (orts) are obtained from a synchronization block (not shown in Fig. 9), in which, as a result of processing the mains voltage vs(), the ort e j· is first obtained, and then other necessary orts are calculated from it. The complex current amplitudes of the slave converter are isolated by synchronous filtering by multiplying in multiplication blocks 39, 42, 45, 48 by the reverse-rotating unit unit e -j·k· and subsequent filtering using a low-pass filter performed on integrators 51 54. Further using blocks By multiplying 40, 43, 46, 49, the complex voltage amplitudes of the harmonics are calculated, and then in multiplication blocks 41, 44, 47, 50 by multiplying by the corresponding unit unit e j·k· the voltage harmonic vsel k is obtained. Adder 55 allows you to obtain the final signal vsel.

The synthesized selective suppression evaluator select operates on top of the damping component demp and does not disrupt the damping. At the same time, with precisely known impedance parameters and precise calculations, it completely absorbs the harmonics of the network-driven converter 3 into the circuit of the compensating device.

The current iw() of the network-driven converter 3 is almost independent of the behavior of the active element 8. Because of this, the selective suppression computer operating on this current, shown in Fig. 9, is a feedforward system, and shares the advantages and disadvantages inherent systems with direct communication. The advantage is that the problem of sustainability is eliminated; direct connections cannot be the cause of self-oscillations. The disadvantage is the preservation of any resulting error, both the error of the initial data and the error of each calculation step, and as a result - low accuracy. Because of this, feed-forward systems are used only in rare cases. The vsel calculator according to the circuit in Fig. 9 is discussed above only to illustrate the action of the active element 8 in the filter-compensating device.

When implementing the vsel calculator in a homogeneous PKU in accordance with the declared technical proposal, feedback is used, i.e. communication based on the measured current of the alternating current network is(), as shown in the general diagram of a homogeneous PKU (Fig. 3).

The construction of a system for selective suppression of mains current harmonics is() proposed here is based on the principle of quasi-stationarity. It is significant that the select system operates against the background of the closed-loop broadband damping feedback demp, which was discussed above. Under the influence of damping, after sufficiently short periods of time or with sufficiently slow changes in conditions, the AC network current consists of the same harmonics that are generated by the network-driven converter 3:

wherein the complex amplitudes of the mains current harmonics are related to the complex amplitudes of the current harmonics of the network-driven converter 3 and the complex amplitudes of the voltage harmonics by the coefficients of the stationary transfer characteristics of the system:

Y(j·) is the stationary transfer characteristic of the complete equivalent circuit of the system from the voltage of the active element to the mains current; Y k =Y(j·k);

G(j·) is the stationary transfer characteristic of the complete equivalent circuit of the system from the current of the network-driven converter to the line current; G k =G(j·k).

It is assumed that the complex amplitude transfer equation is satisfied satisfactorily under almost stationary conditions, when the complex amplitudes are slowly varying functions of time , , . Considering (25) as an equation of the control object, it is easy to select a controller for it. The target control function is to obtain zero values ​​of all mains current harmonics, i.e. the given value for the complex amplitude of each harmonic is zero,

The best controller for these conditions is an integrator

where is the integrator time constant.

The equation for the complex amplitude of the mains current harmonic is obtained as follows:

The variable on the right side of the equation (disturbing variable) is almost independent of harmonic suppression processes, as mentioned earlier, and is constant in steady-state conditions, so the right-hand side of the equation in steady-state conditions becomes zero

.

Accordingly, the complex amplitude of the selectively suppressed harmonic of the network current tends to zero exponentially with the time constant

As one would expect from an integral regulator, the error (in this case, the mains current harmonic) is completely eliminated.

The equations of the system for selective suppression of mains current harmonics (25, 26) are complex. The slowly changing variables , , included in them are complex-valued. The coefficients of the equations Y k and G k are also complex. This in itself is only of a technical nature. It is not difficult to expand equations (25, 26) into the corresponding expressions for 2-vectors with real values

x=x d +j x q col(x d ,x q).

This is not done only because complex-valued formulas express the essence shorter and more clearly. More attention should be paid to another circumstance. The coefficient Y k of the plant equation (25) contains hidden parameters of the AS network in which the PKU operates as a whole, and the regulator for selective suppression of harmonic k in particular. Network parameters are known only imprecisely, and these parameters may change. When considering the sensitivity of the selective harmonic suppression system to the error in knowledge about the line, it is necessary to distinguish between the parameter Y k determined by the line of equation (25) and the expected value of this parameter Y k used in the control system of the active element, equation (26) will then become

When substituting it into (25), a complex multiplier will appear in the equations of the closed-loop system, equal to the ratio of the true and estimated parameter

.

This complex multiplier modifies the controller time constant, turning it into a complex number. The transition component of the closed-loop control system (28) is modified as follows:

where for brevity it is written

The last expression describes a damped harmonic oscillation with a damping time constant and natural frequency

The transient component ceases to be damped only if the phase error reaches critical values

The modulus error does not affect stability; it only changes the tempo. This leads to an important conclusion: the system for selective suppression of mains current harmonics with integral feedback is robust. It remains stable in a wide range of discrepancies between the parameters of the AS network and the expected ones. Stability is lost only when the feedback direction changes, when the divergence vector goes beyond quadrants I, IV of the complex plane (the real component of the divergence vector becomes negative).

The structure of the regulator for selective suppression of the kth harmonic of the mains current, operating according to equations (25, 26), is illustrated by the diagram in Fig. 10.

The controller itself only works with complex amplitudes, . The current amplitude is extracted from the current i(·) measured by the sensor 22 by multiplying using the multiplication unit 56 by the k-th back-rotating unit unit e -j·k· . To obtain the complex voltage amplitude, the output variable of the complex integrator is multiplied by the estimated complex coefficient - transfer resistance from the voltage of the active element 8 to the network current at the k-th harmonic frequency. Based on the obtained value of the complex voltage amplitude, the task of the k-th harmonic voltage Vk of the active element 8 is restored by multiplication using the multiplication block 58 by the k-th rotating unit unit e j·k·.

Construction of a complete circuit of the component vsel(·) calculator, i.e. the component of selective suppression of harmonics is produced by summing regulators of the type shown in Fig. 10 for the entire set of selected harmonics; one regulator for each of the harmonics to be suppressed. This construction is shown in Fig. 11.

The list of suppressed harmonics contains, firstly, the canonical harmonics

11, 13; -23, 25; -35, 37 .

In addition to the canonical harmonics, the current of the grid-driven converter contains residual amounts of non-canonical harmonics

5, -7; -17, 19; .

They are generated by no-load currents of converter transformers and inaccuracies in valve control. Their amplitude is usually small, but a decrease in their level may be necessary. In a homogeneous PCU with an active element controlled by a three-component DBS algorithm, no additional equipment is required to absorb non-canonical harmonics. It is enough to include in the functional diagram and program of the selective harmonic suppression block 16 (select) the branches corresponding to these non-canonical harmonics, as shown in Fig. 11.

When considering the functional diagram of the 16 select block, the phenomenon of harmonic superposition should be taken into account. In Fig. 11, the values ​​Is 11, Is 13 are recorded at the inputs of integrators 81 86.

In reality, with a current of the form

for example, at the input of integrator 82 after multiplication (using multiplication block 66) by e -j·13· the sum is obtained:

Is 1 e -j 12 +Is 11 e -j 24 +Is 13 +Is 23 e -j 36 + ,

in which harmonics of 12, 24 and 36 times the frequency are mixed into the complex amplitude Is 13. To avoid interference, the time constant of the integrators 81 86 must be chosen large enough to attenuate the lowest frequency combination harmonics. In the above example, the lowest frequency of them is the 12th harmonic. To reduce it, it is not necessary to slow down the process of selective harmonic suppression too much. Even without special measures, a selective harmonic suppression system can be quite dynamic.

Concluding the description of the selective suppression system with feedback on the mains current, we note that when using it, the accuracy of suppression of higher harmonics of the mains current is determined solely by the accuracy of the measurements. Other errors, including errors in information about the parameters of the AC network, are completely suppressed by integral feedback regulators.

The operation of the inventive filter-compensating device is illustrated by process graphs (Fig. 12 - Fig. 13) obtained using the ELTRAN model. ELTRAN (, ) is a universal system for modeling valve converters of any configuration and purpose. Along with the power part of the converter, the ELTRAN model also displays its control system, as well as, if necessary, external circuits adjacent to the converter. All these features were needed in this case. The implemented model, firstly, displays in detail all the power circuits of the complete rectifier-converter unit (CRCU), a simplified single-line diagram of which is presented in Fig. 3, including:

Twelve-pulse network-driven current converter 3, with individual representation of each valve;

Converter three-winding transformer 2, displaying the configuration of the magnetic circuit specific to converter transformers and taking into account the phenomena of its saturation;

Capacitor banks 4, switches 5 and grounding reactors 6, as well as auxiliary RC circuits for limiting current surges when switching batteries 4;

AC network 1 in the form of a four-bar equivalent circuit of the transmission line, as well as reactance and emf. adjacent substation;

Modular five-level PWM voltage converter 10 with individual representation of IGBTs and storage capacitors 20 (active element 8);

Filter Lae 11, Cae 12 high-frequency pulsations of width modulation.

Together with the power circuit, the control system of the active element 8 using the DBS algorithm, with all its functional blocks and feedback loops, is also displayed in detail.

The model also displays the synchronization system and control system of the network-driven current converter 3. Model parameters: power - P N = 500 MW, network voltage AC-V N = 400 kV.

The total reactive power of the FKU required for the operation of the KVPU is

Q SUM 330 Mvar.

The capacitor banks of the PKU are divided into 3 blocks of the same type (Nq=3); The power of each battery is

The simulated CVPU provides for operation with a change in the transmitted power R. To adjust the reactive power with wide-range control of the transmitted power, switching of capacitor banks is required. In the framework of the study, the synchronous switching mode is considered as the main switching mode. Modern high-voltage switch technology makes synchronous switching possible. The synchronization functions are shown in the model used.

The synthesized ELTRAN model of the CVPU with the composition and functions described above is used to solve a wide range of problems in the design of real objects.

Only individual simulation results related directly to a homogeneous PKU and its active element are presented here.

In Fig. 12. graphs of the operation of a homogeneous PKU and its active element 8 in steady state at rated transmitted power are presented. The graphs are located on 4 diagrams (1 - top diagram, 4 - bottom diagram).

The first diagram shows:

U LMA - phase voltage of network 1 (it is also the voltage of the network winding of converter transformer 2),

IA - trapezoidal phase current of network-driven converter 3 (it is also the current of the network winding of converter transformer 2)

IAs is the phase current entering the network.

The current of the slave converter is much ahead of the mains voltage: the slave converter consumes reactive power to switch its valves. The filter-compensating device adds a lagging current to the slave converter current and thereby shifts the mains current. In addition, the PKU absorbs the higher harmonics of the driven converter current. As a result, the current entering the network becomes sinusoidal, with a small shift relative to the voltage. Visually, in the graphs, distortions of the mains current and mains voltage are completely invisible. In the first diagram, some overcompensation in reactive power is noticeable: the incoming network current lags behind the network voltage. This is due to the fact that the installed power of the PKU batteries is selected with some excess based on the transfer of increased power of 1.1·P N .

The second diagram shows one variable - UAF - phase voltage on the busbars 7 of the active element 8 (see Fig. 3), which is the voltage of the active element after filtering by the filter Lae 11, Cae 12 high-frequency pulsations of width modulation. Such a filter, as noted above, is part of the active element. The voltage of the active element, as can be seen from the graph, is dominated by the 11th and 13th harmonics, which together give a characteristic beat shape. Other harmonics are not visible in the voltage graph of the active element. To isolate them, special signal processing is required.

The third diagram shows: KUA - phase voltage of the PWM converter 10 (coinciding in shape with the output voltage of the modular multi-level PWM converter 10 - the base part of the active element 8). Width modulation is high frequency. The level of the locally averaged voltage of the converter on the graph is visible only as a thickening/dilution of the switching lines.

The fourth (bottom) diagram shows:

ILAIN - active element current 8,

ILAF is the current of the grounding reactors 6, which shunt the active element,

ICAF - total current of capacitor bank 4.

In the current of the active element, the 11th and 13th harmonics are primarily visible and, in addition to them, the fundamental harmonic with the mains frequency. Width modulation pulsations are noticeable in it, which are visible as some “wooliness” of the current line. The amplitude of these pulsations is small and the frequency is high, and they are completely absorbed by the filter capacitors of the active element. As already noted, width modulation pulsations do not penetrate into the output voltage of the active element.

From consideration of Fig. 12 it follows that the PKU provides compensation and effective filtering.

Transient processes caused by switching of capacitor banks during adjustment of the reactive power of the PKU are a common phenomenon for KVPU with grid-driven converters. These processes are also considered using the ELTRAN model. Switching is carried out synchronized: turning on the switch upon an incoming command is delayed so that the moment the contact closes occurs at the moment the voltage passes through zero. Such control has been mastered by modern technology of high-voltage switches. It reduces transient oscillations in the network and pulse overloads of capacitor banks and the switches themselves, without requiring significant costs.

One of the typical transient processes is shown in Fig. 13, which shows graphs of the process of reducing the transmitted power, accompanied by the shutdown of one of the three capacitor banks of the PKU. The diagram shows the current at the output of converter 3 (It - stepped curve) and the line (network) current (IL - smooth curve) with a decrease in the transmitted power, accompanied by disconnection of the third battery of the PKU.

As the transmitted power decreases, the reactive power Q of the network-driven converter 3 decreases, an excess of reactive power of the network QL occurs, and the reactive power control system initiates the shutdown of the third battery of the PKU. The transient process, caused by a decrease in transmitted power and the battery disconnection initiated by it, ends with the establishment of a new mode in 100 ms.

In Fig. 13, voltage distortion during the transient process is almost invisible. This is a positive consequence of two circumstances. First, synchronizing switches minimizes the disturbance effect of switching on the system. Secondly, virtual resistors formed by subsystem D of the three-component DBS control system provide intensive damping of the system. The effect of the selective harmonic suppression system is also noticeable, providing complete suppression of mains current harmonics.

The quality of operation of a homogeneous PKU and its DBS control system in regulating the transmitted power is quite satisfactory.

The completed study of the KVPU modes with a standard network-driven converter and a homogeneous PKU revealed that the required installed power of the active element is 1.2-1.4% of the throughput power of the KVPU. This value is insignificant, so the cost of the active element does not make any significant contribution to the cost of the CVPU, and losses in the active element are insensible among the losses in the CVPU. Complicating a homogeneous CVPU with resonant circuits in order to reduce the power of the active element is unjustified.

The advantages of a homogeneous PKU with an active element, the current state of the art of MMC converters, as well as the sophistication of the DBS algorithm make it possible to offer a homogeneous PKU for all modern HVDC projects with slave current converters. The state of the art is ripe for this next step in the development of HVDC-LCC.

Thus, with the above design of the inventive device, the main functions are ensured - regulation of reactive power when using the same type of interchangeable capacitor banks, complete absorption of higher harmonics without the use of tuned resonant circuits, damping of transient vibrations without the use of energy dissipating resistors.

Based on the above, the following tasks:

Simplification of the PKU circuit due to a radical reduction in the number of PKU branches for the conditions of regulating reactive power by switching batteries,

Reducing the level of power losses of the PKU due to damping with virtual resistors instead of damping with real resistors (the function is performed by the active element control system without the involvement of any hardware),

Simplification of PKU settings during commissioning and restructuring when changing the parameters of the AS network, which is achieved solely by adjusting the active element control program, have been effectively solved.

Sources of information

1. CIGREWorking Group 14.30. Filter Switching and Reactive Power Management. Section 8. No. 139 - Guide to the specification and design evaluation of AC filters for HVDC systems. April 1999

2. R.K. Chauhan, M. Kuhn, D. Kumar, A. Kolz, P. Riedel - BasicDesignAspectsofBallia-Bhiwadi 2500MWHVDCPowerTransmissionSystem, 2009

3. Marquardt Rainer (DE) - Current rectification circuit for voltage source inverters with separate energy stores replaces phase blocks with energy storing capacitors. Publication number DE 10103031, 2002-07-25

4. L. Gyugyi, V.R. Pelly - Static Power Frequency Changers - Theory, Performance, & Application. New York: J. Wiley, 1976

5. Sadek Kadry (DE), Pereira Marcos (DE) - Siemens AG (DE) - Hybrid filter for an alternating current network. Publication number US 6385063, 2002-05-07

7. CIGRE IEC/PAS 62544 - Active filters in HVDC applications. Publicly available specification, pre-standard, 2008-02, page 43-44

8. Marcos Pereira, Aplicaç o de Novos Filtros Ativos AC de Pot nca Plena - IEE/PES T&D 2010 Latin America. S o Paulo, Brasil, Novembro 2010. (Siemens AG 2010 Energy Sector. [email protected]).

9. Mustafa G.M. - Matrices for describing the topology of transformers. "Electricity" No. 10, 1977, pp. 34-39

10. Mustafa G.M., Sharanov I.M. - Mathematical modeling of thyristor converters. “Electricity” No. 1, 1978, pp. 40-45

FORMULA OF THE INVENTION

1. Filter-compensating device of a complete converting installation for direct current energy transmission based on a network-driven valve (thyristor) current converter (line commutated converter, LCC) with adjustable transmitted power, adjusting reactive power by switching two or more branches, each of which is equipped with a switch for connection to the power supply network and contains capacitor banks, resistors, and reactors that perform filtering and compensation functions; The filter-compensating device also contains one or more active elements (voltage converter with high-frequency width modulation, current and voltage sensors), characterized in that:

Capacitor banks implement only the compensation function and are identical with reactive power Qk equal to the Nqth fraction of the largest total transmitted reactive power Qsum:

where Nq is the number of capacitor banks,

The capacitor banks are connected to ground through a common active element by means of a corresponding number of medium-voltage switches or through individual active elements,

In a filter-compensating device, the filtering functions are performed only by the active element(s); for this purpose, the control system of the active element (PWM converter), in addition to the usual set of functional blocks of the PWM converter, is equipped with three specific functional blocks implemented in software (with the corresponding them with feedback):

Block D - damping (demp),

Block B - balance (bal),

Block S - selective harmonic suppression (sel),

generating reference voltages, the sum of which forms the main converter control variable - voltage reference vz(t) (function of time):

vz=vdemp+vbal+vsel, and:

Block D is formed using broadband (for example, proportional with gain Rae) feedback on the output current of the converter iae(t) in accordance with the equality:

vdemp(t)=Rae·iae(t),

and, representing a virtual resistor Rae, dampens transient oscillations of the network in the same way as a real resistor Rae included in the output circuit of the converter; in this case, the value of the gain Rae is selected so as to best dampen transient vibrations; the remaining two blocks B and S act on the damped system through the virtual resistor Rae;

Block B is formed using feedback on the voltages vd of the storage capacitors of the DC links of the converter with the participation of the mains voltage vs in this feedback, performs the task of maintaining the power balance Pd, and, consequently, the voltages vd of the storage capacitors in the vicinity of a given level vdz:

Module for calculating (based on the balance power regulator determined) the complex amplitude of the balance voltage component Vbal, norm, normal to the mains voltage vector:

,

where is the complex amplitude of the network voltage, yo is the conductivity of the capacitor bank block,

Balance voltage generation module - as a sinusoidal variable of the fundamental frequency, orthogonal to the mains voltage in accordance with the expression:

vbal(t)=Vbal, norm·j·e j ,
- rotating unit unit of the k-th harmonic of the network current;

Module for regulating complex amplitudes of higher voltage harmonics vsel, i.e. component of selective suppression of harmonics (sel), using an integral regulator for each selectively suppressed higher harmonic of the current, which, based on the complex amplitude of the harmonic current, generates a complex amplitude for setting the voltage of this harmonic, and in the formation of setting the complex amplitudes of the voltages of the higher harmonics of the converter (active element) a complex coefficient equal to the value of the stationary transfer characteristic of the system at the kth harmonic frequency:
for the entire set of selected harmonics, and the set of suppressed harmonics contains the canonical harmonics

11, 13; -23, 25; -35, 37 ,

and may also contain individual non-canonical harmonics, for example:

5, -7; -17, 19; .

2. The filter-compensating device according to claim 1, characterized in that a current-limiting reactor is introduced into the circuit of capacitor banks, the reactance of which is determined by the condition of limiting the amplitude of the transient current when switching the capacitor banks.

With modern technological developments, many industrial enterprises use many different converters. During operation, these converters create current and voltage ripples in the circuit, which leads to the occurrence of higher current harmonics in the network.

Their presence in the network degrades its quality and has a bad effect on the operation of all equipment, and can lead to failures in various systems. This can lead to emergency shutdowns of consumers and false alarms of various electronic devices and devices. Also, the presence of harmonics causes heating in electric motors, cables, etc. It is necessary to minimize their influence on the circuit. For this purpose, a filter-compensating device (FCU) is used.

The filter-compensating device consists of an L-C filter that is adjusted to a specific network harmonic. Usually these are the 5th, 7th, 11th harmonics, as the most pronounced ones. Also, enterprises can often install filter-compensating devices tuned to various harmonics. Below is a diagram of the PKU.

To correctly select a filter-compensating device, you need to study which harmonics most influence the quality of the network and its power. Based on these data, the filter is calculated and selected.

Their main advantage is that they not only act as a filter, but also compensate for reactive power. Just like they can be automatic and automatically regulate reactive power.

When the static load predominates (paper machine, fan load), unregulated PCDs are used, which are connected to the circuit and operate in static mode.

If dynamic load predominates (rolling mills, lifting machines, etc.), adjustable ones are used. When the completion of the operating cycle of any device changes, the balance of reactive power changes. Since the PKU not only compensates for the reactive component, but also acts as a filter in the circuit, accordingly, disconnecting it from the network does not make sense. To do this, connect a decompensator, which maintains the power balance in the circuit.

It is most advisable to install a filter-compensating device at voltages of 6 kV, 10 kV. Since when low-voltage consumers operate, a different spectrum of harmonics arises on the low-voltage side. It is not economically feasible to compensate them on the low voltage side, therefore installing a filter to each consumer is expensive. High-voltage consumers create a smaller spectrum of distortion (3, 5, 7, 11 harmonics), therefore, both from a technical and economic point of view, it is easier to compensate for this spectrum on the 6 kV, 10 kV side than the much wider spectrum on the 0.4 kV side, 0.6 kV.

They can be installed both indoors and outdoors. They are usually installed on the GPP and connected to the buses via an individual switch. Below are the placement methods: indoors and outdoors:

Compensators placed indoors require ventilation. In certain cases (depending on the type of production and location of the room), air filters are required for ventilation. A certain temperature regime must be maintained in the room, which leads to additional financial costs.

The PKU must be fenced and access can only be made after the capacitors have been discharged. They must be equipped with capacitor voltage sensors for the safety of operating personnel. If the capacitors are not discharged to the permissible value, repair work or maintenance is prohibited.

The Elektrointer company offers devices used for reactive power compensation in 0.4 kV networks. Reactive power increases electricity losses; if compensation devices are not present in the network, losses can reach 50% of average consumption. In addition, it reduces the quality of power supply: generator overloads, heat losses, changes in frequency and amplitude occur. 0.4 kV filter compensating devices will be a profitable solution to the problem.

Advantages of capacitor units

Capacitor units have become the most effective way to compensate for reactive power. Properly selected capacitors can reduce the reactive power received from the network, which reduces energy losses. Capacitor installations have several advantages:

• Quick installation, no complicated maintenance required. Such compensatory installations do not require an additional foundation.
• Minimum active power losses. Innovative cosine capacitors provide inherent losses of no more than 0.5 W per 1000 VAr.
• Possibility of connection anywhere in the power supply network. Such installations produce minimal noise during operation.

Compensation can be individual or group: in the first case, reactive power is compensated where it occurs, in the second, the action of the compensator extends to several consumers.

Ordering electrical equipment from the manufacturer

JSC "Electrointer" offers to purchase reactive power compensation units in an assortment; the equipment is selected taking into account the personal requirements of the customer. Call our numbers and discuss the terms of purchase with specialists: favorable prices and convenient terms of cooperation are guaranteed.

Filter compensating devices are high-tech equipment for preventing harmonic distortions of current parameters in industrial systems and on power lines. The use of such devices makes it possible to stabilize the parameters of the power grid, protect expensive equipment from voltage surges and improve the quality of the supplied resource. By preventing the formation of higher order harmonics, filter compensating units increase the capacity of electrical networks. The coefficient of nonlinear distortion is reduced, which makes it possible to reduce the cost of servicing electrical systems by an order of magnitude.

The Megavar company has been working successfully in this area for a long time. We design and create equipment of any level. Depending on the needs of your production, we will select and sell the most suitable filter compensating capacitors. High voltage systems are especially susceptible to non-linear loads. Higher-order harmonics in such power networks are dangerous because they can lead not only to electricity losses, but also to damage to industrial equipment.

To choose the most efficient system, it is necessary to understand the specifics of production organization, the parameters and architecture of existing networks, provide for their modernization, etc. Our specialists will analyze the task and offer an installation with maximum efficiency that fully meets the customer’s requirements and the capabilities of industrial power networks. By following the advice of professionals, you can not only optimize your equipment, but also extend the life of filter-compensating units.

Advantages of Megavar LLC products

• Variety of models. The company's product range includes filter compensating units (FCUs) designed for voltages from 6.3 to 35 kV. We produce models with a capacity of 450-10 thousand kVar.
• Adaptation to climatic conditions. Our plants are used in both temperate and cold climates. The catalog presents climatic versions U1, U3 and HL1).
• High quality and reliability. To produce filter compensating devices, we use only proven components from European and domestic suppliers.
• Safety. The installations of Megavar LLC reduce the percentage of harmonic currents to a safe level, preventing emergency shutdowns and protecting expensive equipment.

Design of filter compensating installations "Megavar"

Despite all its diversity, the PKU device is universal. The design of each model includes: an input cell in a metal case, current-limiting reactors (a separate element for each phase), high-voltage capacitors and current transformers. The cell consists of a disconnector, ammeter and filter protection. Each reactor limits the current in one of the phases.

In the general case, a PKU consists of a set of parallel-connected filters that partially compensate for the deficiency of reactive power and partially localize harmonic oscillations occurring in the system.

Climate control may include elements such as fluorescent lamps, powder fire extinguisher, heating and ventilation systems. The main parameters of filter compensating devices are reflected in the marking of the PKU. First of all, the harmonic number is indicated (from 3 to 25), then the rated voltage, then the reactive power of the system (in kVar). The last 2-3 digits of the marking indicate the climate version.

Where and why are filter compensating units PKU used?

In systems with nonlinear loads (inverters, rectifiers, transformers, power electronics, etc.), in addition to active energy, reactive energy arises. In the first case, energy is spent on heat generation, mechanical work and other “useful” load. In the second, part of the resource disappears into nowhere; it is “useless” energy, which deteriorates the quality of the transmitted resource. The ratio of active and reactive powers determines cos ϕ power factor. The higher this indicator, the more efficient the system, the more economically it uses electricity and the safer the processes occurring.

Filter capacitors (high voltage) allow you to compensate for network reactive power and increase the overall power factor. This can be done in different ways, but capacitor units have a number of advantages:

• Simplicity. With easy installation, capacitors require almost no maintenance.
• Economical. The low cost of individual elements turns the purchase of PKU into a profitable acquisition for organizations of any level.
• Self-sufficiency. During the operation of capacitor units, the active energy remains unchanged. PKUs do not increase the active load, but stabilize it.
• Long service life. With the right approach, capacitor units will last up to 20 years.

The phase shift between current and power leads to the formation of harmonic distortion, electrical noise and resonance phenomena. Uncontrolled loads reduce system efficiency; higher order harmonics can lead to breakdown or emergency shutdown. Filter compensating devices will also help to avoid negative consequences. The implementation of such systems increases the power factor, system reliability, reduces energy losses and prevents the occurrence of higher harmonics.