Electromagnetic continuous reactive compensation and harmonic suppression system control strategy

Abstract

The invention discloses a control strategy of an electromagnetic continuous reactive compensation and harmonic suppression system (EVC-PPF) based on an electromagnetic reactive compensator (EVC) and a passive power filter (PPF), and the control strategy mainly comprises a reactive compensation and harmonic suppression main circuit, a measurement module, a signal processing module, a power calculation module, a central control module, an angle calculation module and a driving module. According to the control strategy, the voltage at the two ends of the EVC-PPF compensation capacitor is changed by controlling the phase shift angle synthesis amplitude of the RPST and the voltage with the adjustable phase, and then continuous adjustment of reactive compensation is achieved. The system has the advantages of reliability, stability, easy maintenance, good economical efficiency, no harmonic wave introduction, no need of excessive inductance and the like, and can solve the power quality problem caused by the fact that a large amount of distributed new energy is merged into a power grid.

Description

Technical Field

[0001] The present invention belongs to the field of reactive power compensation and harmonic suppression, and in particular relates to a novel reactive power compensation and harmonic suppression system containing distributed new energy. Background Art

[0002] my country is vigorously developing distributed energy, and the power flow of the power grid has become more complex from simple, and the difficulty of voltage control has gradually increased. With the development of science and technology, new nonlinear loads such as new energy vehicles in the system have gradually increased, and the demand for reactive power has also gradually increased. The voltage in the new distribution network fluctuates frequently and there are a large number of nonlinear loads, which puts higher requirements on the dynamic reactive power compensation and harmonic suppression capabilities of the power system.

[0003] Active Power Filter (APF) eliminates harmonics by injecting current opposite to the harmonic current into the system. Passive Power Filter (PPF) achieves harmonic suppression by shunting the harmonic current. It has low cost, simple and reliable structure. It can not only be used for filtering, but also for certain reactive power compensation of the system.

[0004] Synchronous condenser (SC) is the earliest reactive power compensation device. This device has a slow response speed, limited phase regulation capability, and large losses and noise during operation. Therefore, it is gradually replaced by parallel capacitors. Parallel capacitors have lower losses and cost advantages, but they can only provide fixed reactive power. Against the background of the rapid development of power electronics technology, static var compensators (SVC) with thyristors inside have emerged. SVC has two control modes, namely thyristor switching capacitor (TSC) and thyristor controlled reactor (TCR). TSC realizes reactive power compensation by controlling the number of capacitors put into use, but cannot achieve continuous compensation; TCR can realize continuous regulation of reactive power, and will generate a large number of harmonics during operation, and the size of the harmonics is related to the trigger angle; although combining TCR with TSC can achieve continuous reactive power regulation, there is still a harmonic problem. Compared with SVC, the static synchronous compensator (STATCOM) using fully controlled power electronic devices has fast compensation capability and still injects less harmonics into the system. The economic problems of this equipment will become more serious as the reactive compensation capacity increases.

[0005] Traditional reactive power compensation and harmonic suppression systems often use a combination of parallel capacitors and passive power filters. This structure is simple, reliable and cost-effective, but has the disadvantages of poor performance and easy resonance. The combination of active power filters and static synchronous compensators has better reactive power compensation and filtering effects, but both APF and STATCOM are composed of inverters, which have the problems of poor economy and low system reliability.

[0006] The current reactive power compensation and harmonic suppression systems cannot meet the requirements of high efficiency, economy and stability at the same time. Therefore, it is necessary to invent a new reactive power compensation and harmonic suppression system based on electromagnetic reactive power compensator (EVC) and PPF. This system has good regulation ability and wide applicability. It can use the leakage reactance of the phase-shifting transformer to reduce the reactor required by the system, the required inductance is small, and there is no resonance problem. It has the advantages of reliability, easy maintenance, cost-effectiveness, no introduction of unnecessary harmonics into the system, and relatively stable under impact. Summary of the invention

[0007] The present invention is to provide a control strategy for an electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC, and the control strategy is modularized, mainly including: reactive power compensation and harmonic suppression main circuit; measurement module; signal processing module; power calculation module; central control module; angle calculation module; driving module. The three-phase voltage of the grid connection point, the three-phase compensation current of the reactive power compensator, the three-phase current of the secondary capacitor, the three-phase load current, and the three-phase filter current are obtained through the measurement module. The dq decomposition is performed through the signal processing module to obtain the corresponding dq components. The actual reactive power compensated by the electromagnetic reactive power compensator is obtained through the power calculation module, and the actual value and the reference value are passed through the central control module to obtain the secondary capacitor voltage reference value, and the phase shift angle is obtained in the angle calculation module, and finally the control is completed through the driving module.

[0008] This reactive power compensation and harmonic suppression system can realize bidirectional continuous reactive power regulation, has good dynamic regulation characteristics, effectively reduces the harmonic content of the system, and has stable and good control performance. It is mainly composed of passive filters and electromagnetic reactive power compensators, which are relatively low in cost and have good economic benefits. This system is a passive electromagnetic structure, the durability and reliability of the rotary phase-shifting transformer are very high, and the passive filter structure is simple and has high reliability. This reactive power compensation and harmonic suppression system does not rely on power electronic components and does not generate additional harmonics. Compared with the SVC type regulation system, this system can use its own leakage reactance to reduce the reactance required by the system, and does not require excess inductance to eliminate the harmonics generated by itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1Electrical wiring diagram of a new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC

[0010] Figure 2 Single-phase equivalent circuit for connecting a new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC to the power grid

[0011] Figure 3 The control strategy diagram of the new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC is shown in Figure 2.

[0012] The symbols in the accompanying drawings are explained as follows: C is the three-phase capacitor; K represents the transformation ratio of the rotary phase-shifting transformer; α1 and α2 represent the phase shift angles of the two rotary phase-shifting transformers respectively; is the compensation current; is the current flowing through the capacitor; the two variables and represents the secondary voltage of two rotating phase-shifting transformer devices, and and They correspond to the primary currents of the two devices respectively; is the load-side current of the power system, It represents the voltage at the point where the electromagnetic reactive power compensator is connected in parallel with the power grid. is the primary side voltage; is the voltage across the capacitor; Z l is the equivalent impedance of the power supply; Total current of reactive power compensation and harmonic suppression system; is the filter current; Q is the total reactive power compensation; Q f The reactive power compensated by the passive filtering system; Q Z I is the compensation amount of electromagnetic reactive compensator; Labc is the three-phase load current; I fabc is the three-phase filter current; U sabc is the three-phase voltage on the grid side; I zabc is the three-phase compensation current; I cabc is the three-phase capacitor current; C5, L5, R5 represent the capacitor, inductor and resistor of the 5th order single tuned filter respectively; C7, L7, R7 represent the capacitor, inductor and resistor of the 7th order single tuned filter respectively; C 11 , L 11 , R 11 Respectively represent the capacitance, inductance and resistance of the 11th order single tuned filter; C 13 , L 13 , R 13 They represent the capacitance, inductance and resistance of the 13th-order single-tuned filter respectively; C′, L′, R′ represent the capacitance, inductance and resistance of the secondary high-pass filter respectively.

[0016] The numbers of the components in the accompanying drawings are as follows: 101 and 102 are two rotating phase-shifting transformers respectively; 301 is a 5th-order single-tuned filter; 302 is a 7th-order single-tuned filter; 303 is an 11th-order single-tuned filter; 304 is a 13th-order single-tuned filter; 305 is a second-order high-pass filter. DETAILED DESCRIPTION

[0013] The present invention proposes a control strategy for an electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC, which is modularly designed and mainly includes a reactive power compensation and harmonic suppression main circuit; a measurement module; a signal processing module; a power calculation module; a central control module; an angle calculation module; and a drive module.

[0014] See also Figure 1 , Figure 1 The electrical wiring diagram of the new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC is shown in Figure 1. The EVC-PPF mainly includes two rotating phase-shifting transformers, a three-phase compensation capacitor, four single-tuned filters and a second-order high-pass filter. The electromagnetic reactive power compensator is composed of three-phase power capacitors and two rotating phase-shifting transformers. The primary windings of the two rotating phase-shifting transformers are connected in parallel after three-phase star connection and connected to the grid at the same time; the secondary windings of the two rotating phase-shifting transformers are connected in series in the order of head to tail connection, among which the primary (or secondary) winding connection of one rotating phase-shifting transformer is reverse sequence connection, and the primary (or secondary) winding connection of the other rotating phase-shifting transformer is positive sequence connection. After the secondary windings are connected in series, the three-phase ends are short-circuited, and the first end forms a star connection, and is connected in parallel with the three-phase power capacitor of the three-phase star connection; the PPF part is composed of capacitors, inductors and resistors connected in series and parallel. The electromagnetic reactive power compensator and the passive filter are connected in parallel to the system. When the harmonic current on the load side flows through the parallel connection point, the passive filter group filters out the harmonics to prevent the harmonics from flowing into the power grid and reactive power compensation equipment. In addition, the passive filter group can also compensate for a part of the fixed reactive power.

[0015] See also Figure 2 , Figure 2 It is a single-phase equivalent circuit for connecting a new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC to the power grid.

[0016] To explain the filtering and compensation principle of EVC-PPF in detail, the single-phase equivalent circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system is used to illustrate its working principle.

[0017] The nth order impedance expression of a single tuned filter is:

[0018]

[0019] In the formula, ω n is the nth harmonic angular frequency, ω n =nω1, ω1 is the fundamental angular frequency.

[0020] Easy to know When , its impedance is equal to R and is purely resistive, and the filter impedance value is the smallest.

[0021] The nth order impedance expression of the second-order high-pass filter is:

[0022]

[0023] Reactive power Q generated by the reactive compensator c Generated by the compensation capacitor C, its size is linearly related to the square of the capacitor voltage and the capacitance value, and can be expressed as:

[0024] Q c =U c 2 ωC

[0025] Reactive power Q LRPST Through the equivalent inductance L RPST Absorption can be expressed as:

[0026] Q LRPST =I Z 2 ωL RPST

[0027] Therefore, taking the absorbed reactive power as positive, the reactive power Q compensated by the electromagnetic reactive compensator is the difference between the reactive power absorbed by the inductor and the reactive power emitted by the capacitor, that is,

[0028] Q Z =Q LRPST -Q C

[0029] Reactive power compensation and harmonic suppression The reactive power Q of the system compensation includes Q f and Q Z The two parts, with the absorption of reactive power as positive, can be expressed as follows:

[0030] Q=Q Z -Q f

[0031] Primary current of rotating phase-shifting transformer and The secondary current It can be expressed as

[0032]

[0033] The compensation current It can be expressed as

[0034]

[0035] The number of turns of the windings on the primary and secondary sides is equal, and the primary voltage only changes phase after passing through the rotary phase-shifting transformer, that is, K RPST =1, the phase shift angles α1 and α2 of the two rotating phase-shifting transformers are in opposite directions, so α1=-α2=α, then Can be simplified to

[0036]

[0037] Similarly, the voltage has the following relationship

[0038]

[0039] In summary, the reactive power Q of reactive power compensation and harmonic suppression system compensation can be expressed as

[0040]

[0041] See also Figure 3 , Figure 3 This is the control strategy diagram of the new reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC.

[0042] The main circuit consists of the grid side, the load side, a passive filter group and an electromagnetic reactive compensator; the measurement module obtains the load current I Labc 、Filter current I fabc , three-phase voltage U at the grid connection point sabc , three-phase compensation current I zabc and three-phase capacitor current I cabc In the signal processing module, the three-phase voltage at the grid point is first obtained through a phase locked loop (PLL) PLL , this voltage is taken as the d-axis, and other currents are converted to U based on this coordinate sd , U sq ,I zd ,I zq The actual value of reactive power Q compensated by the electromagnetic reactive compensator is obtained through the instantaneous reactive power theory in the power calculation module. Z It can be expressed as

[0043]

[0044] Compare it with the reference value Q+Q f Input to the central control module, and achieve tracking regulation through PI regulation to obtain the reference value Q of the reactive power emitted by the capacitor cref , the reactive power Q generated by the capacitor crefThe reactive component I cqref There is the following relationship

[0045] Q cref =3I cqref 2 / 2ωC

[0046] The capacitor current is tracked by the PI regulator, and the dq components are converted into phase angle values. The volt-ampere characteristics of the capacitor are as follows:

[0047]

[0048] Get the secondary capacitor voltage reference value U cref The angle calculation module obtains the rotation angle α according to the phase-shifting and voltage-regulating principle of the rotating phase-shifting transformer, and finally inputs the input into the driving module to drive the RPST to rotate to complete the continuous control adjustment.

Claims

1. The control strategy of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) based on the electromagnetic reactive power compensator (EVC) and passive power filter (PPF) is modularized on the basis of the reactive power compensation and harmonic suppression main circuit, including signal transmission, measurement, calculation, closed-loop regulation, drive control, etc. include: Measurement module, signal processing module, power calculation module, central control module, angle calculation module and drive module; the main circuit consists of the grid side, load side, passive filter group and electromagnetic reactive power compensator; the measurement module obtains the load current I Labc 、Filter current I fabc , three-phase voltage U at the grid connection point sabc , three-phase compensation current I zabc and three-phase capacitor current I cabc In the signal processing module, the three-phase voltage at the grid connection point is first obtained through a phase-locked loop (PLL) PLL , this voltage is taken as the d-axis, and other currents are converted to U based on this coordinate sd , U sq ,I zd ,I zq ; The actual value of reactive power Q compensated by the electromagnetic reactive compensator is obtained through the instantaneous reactive power theory in the power calculation module Z ; compare it with the reference value Q+Q f Input to the central control module, and achieve tracking regulation through PI regulation to obtain the reference value Q of the reactive power emitted by the capacitor cref , the capacitor current is tracked by the PI regulator, the dq component is converted into an angle value, and the secondary capacitor voltage reference value U is obtained according to the volt-ampere characteristic of the capacitor. cref The angle calculation module obtains the rotation angle α according to the phase-shifting and voltage-regulating principle of the rotating phase-shifting transformer, and finally inputs the angle into the driving module to drive the rotating phase-shifting transformer to a predetermined position to complete continuous control and regulation.

2. According to the control strategy of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC as described in claim 1, It is characterized in that The electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) consists of two parts: a passive power filter and an electromagnetic reactive power compensator; the electromagnetic reactive power compensator consists of a three-phase power capacitor and two rotating phase-shifting transformers. The primary windings of the two rotating phase-shifting transformers are connected in parallel after three-phase star connection and connected to the grid at the same time; the secondary windings of the two rotating phase-shifting transformers are connected in series in a head-to-tail order, among which the primary (or secondary) winding connection of one rotating phase-shifting transformer is reversed, and the secondary winding connection of the other rotating phase-shifting transformer is reversed. The secondary (or secondary) side winding connection is a positive sequence connection. After the secondary side windings are connected in series, the three-phase ends are short-circuited, the first end forms a star connection, and is connected in parallel with the three-phase power capacitor of the three-phase star connection; the rotary phase-shifting transformer is mainly composed of a primary winding, a secondary winding, a servo motor, an iron core magnetic circuit, and a worm gear mechanism, etc. The primary side of the rotary phase-shifting transformer is connected to a power supply, and the secondary side is connected to a power capacitor; the method is characterized in that reactive compensation is achieved through an electromagnetic reactive compensator and a passive power filter, and harmonic suppression is achieved through a passive power filter.

3. According to the control strategy of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) based on PPF and EVC as described in claim 1, It is characterized in that The rotating phase-shifting transformer rotates at an angle of α. Since the three-phase windings are connected in positive and negative directions respectively, the two rotating phase-shifting transformers form magnetic fields in opposite directions, generating output voltages with equal amplitudes and opposite angles. According to the principle of vector synthesis, the two voltage phasors are synthesized in series to form an amplitude- and phase-adjustable voltage on both sides of the three-phase power capacitor. By adjusting the voltage across the three-phase capacitor, the reactive power Q emitted by the three-phase capacitor in the electromagnetic reactive compensator can be continuously adjusted. c ; Reactive power compensation and harmonic suppression system The reactive power Q compensated by the system consists of three parts: The reactive power Q emitted by the capacitor in the electromagnetic reactive compensator c , the reactive power Q absorbed by the equivalent inductance in the electromagnetic reactive compensator LRPST and the fixed reactive power Q emitted by the passive filter f .

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