Electromagnetic continuous reactive compensation and harmonic suppression system topology circuit

Abstract

The invention discloses a topological circuit of an electromagnetic type continuous reactive power compensation and harmonic suppression system (EVC-PPF), which is composed of an electromagnetic type reactive power compensator (EVC) and a passive power filter (PPF), and the topological circuit is mainly composed of a single tuned filter, a second-order high-pass filter, a rotation phase-shifting transformer and a three-phase capacitor, and is characterized in that the single tuned filter, the second-order high-pass filter, the rotation phase-shifting transformer and the three-phase capacitor are connected in series, and the single tuned filter, the second-order high-pass filter, the rotation phase-shifting transformer and the three-phase capacitor are connected in series. The filter forms a low-resistance channel to realize a filtering function by using resonance characteristics, and can compensate reactive power for a system; the electromagnetic reactive power compensator uses the electromagnetic induction principle and the vector synthesis principle to control the voltage at the two ends of the capacitor so as to realize bidirectional continuous reactive power compensation. The system has the advantages of being reliable and easy to maintain, simple to control, good in economical efficiency, capable of achieving large capacity, free of harmonic wave introduction, free of excessive inductance and the like, and can solve the electric energy 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] In order to achieve the dual carbon goals, China is actively promoting the development of distributed energy to meet the needs of users with smaller electricity demand. However, this distributed energy is greatly affected by external environmental factors. When they are incorporated into the power grid, they will produce significant voltage fluctuations and randomness, which poses a challenge to the system's dynamic reactive power compensation capabilities. In addition, a large number of distributed energy devices are connected to the power grid through power electronic equipment, which has led to the increasingly serious problem of harmonic pollution. At the same time, a large number of nonlinear loads in the industrial field have also begun to enter the power grid, which further increases the demand for the power system's dynamic reactive power compensation and harmonic suppression capabilities.

[0003] Active Power Filter (APF) eliminates harmonics by introducing current opposite to the harmonic current. Passive Power Filter (PPF) achieves the purpose of harmonic suppression by dispersing the harmonic current. It has low cost and simple structure, and can be used for filtering and also for a certain degree of reactive power compensation of the system.

[0004] As one of the early reactive power compensation devices, synchronous compensators (SC) have been gradually replaced by shunt capacitors due to their slow response speed, limited phase regulation capability, high energy consumption and noise during operation. Although shunt capacitors have advantages in reducing energy consumption and costs, they can only provide fixed reactive power.

[0005] With the rapid progress of power electronics technology, a new type of equipment called static var compensator (SVC) has emerged. SVC is mainly composed of built-in thyristors, and its control methods include thyristor switching capacitor (TSC) and thyristor controlled reactor (TCR). Among them, thyristor switching capacitor achieves reactive power compensation by adjusting the number of capacitors put into use, but it cannot compensate continuously. On the other hand, thyristor controlled reactor can achieve continuous regulation of reactive power, but a large number of harmonics will be generated during operation, and the size of the harmonics is closely related to its triggering angle. Although combining TCR with TSC can achieve continuous regulation of reactive power to a certain extent, it still faces the challenge of harmonic problems.

[0006] Compared with static synchronous compensators, static synchronous compensators (STATCOMs) built with fully controlled power electronic devices can achieve rapid compensation functions and introduce relatively few harmonics. However, with the substantial increase in reactive power compensation capacity, the economic challenges faced by this equipment are also increasing.

[0007] Traditional reactive power compensation and harmonic suppression systems usually rely on a combination of shunt capacitor banks and passive power filters. This design is simple, reliable and cost-effective, but their performance is not ideal and they are prone to resonance. Combining active power filters and static synchronous compensators can effectively improve the effects of reactive power compensation and filtering, but both of them include inverters, which affects the economy and stability of the system.

[0008] The reactive power compensation and harmonic suppression systems currently on the market are difficult to meet the requirements of high efficiency, economy and stability at the same time. Therefore, it is particularly important to develop a new reactive power compensation and harmonic suppression system. Summary of the invention

[0009] The present invention aims to provide a topological circuit of an electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) composed of a passive power filter (PPF) and an electromagnetic reactive power compensator (EVC), which combines the characteristics of PPF, which is simple and reliable, economical and capable of reactive power compensation, and the compensation characteristics of EVC, which is low in cost, does not generate harmonics, and can be continuously adjusted and stable.

[0010] In the present invention, the EVC part adjusts the voltage amplitude and phase on both sides of the compensation capacitor by changing the phase shift angle of the two RPSTs, thereby affecting the reactive power emitted by the compensation capacitor. When the reactive power generated by the power capacitor is higher than the reactive power absorbed by the equivalent inductor, the reactive compensator will emit reactive power. On the contrary, if the reactive power generated by the power capacitor is lower than the reactive power absorbed by the equivalent inductor, the reactive compensator will absorb reactive power. The PPF part utilizes the resonant characteristics to construct a low-impedance path at a specific frequency to achieve filtering, and adopts a combination of a single-tuned filter and a second-order high-pass filter. The single-tuned filter is used to filter out the 5th, 7th, 11th, and 13th harmonic currents with large content, and the second-order high-pass filter is used to filter out the 17th and above harmonics.

[0011] Compared with the traditional combination of shunt capacitors and passive power filters, EVC-PPF has a bidirectional continuous compensation function. Compared with the currently widely used combination of static VAR compensators and filter inductors, EVC-PPF not only does not inject additional harmonics into the power grid, but also requires less inductance. Compared with the combination of active power filters and static synchronous compensators, EVC-PPF does not require expensive investment, and its control method is simpler and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The structure diagram of electromagnetic reactive power compensator

[0013] Figure 2 The working principle diagram of single tuned filter

[0014] Figure 3 The working principle diagram of the second-order high-pass filter

[0015] Figure 4 It is the topology circuit of electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF)

[0016] Figure 5 It is the single-phase equivalent circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF)

[0017] The symbols in the accompanying drawings are as follows: RPST In order to consider the equivalent connection inductance of the internal inductance of the rotating phase-shifting transformer, C is the compensation capacitor; K represents the transformation ratio of the rotating phase-shifting transformer; α1 and α2 represent the phase shift angles of the two rotating phase-shifting transformers respectively; is the compensation current; is the current flowing through the capacitor; and Represents the secondary voltage of two rotating phase-shifting transformer devices, 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; E s is the system power supply electromotive force; Z l is the equivalent impedance of the power supply; u a 、u b 、u c are the three-phase voltages at the points where the reactive power compensation and harmonic suppression systems are connected to the power grid; i La 、i Lb 、i Lc They are the three-phase currents on the load side; is the voltage at the point where it is connected to the grid; is the filter current; is the compensation current; is the secondary side capacitor current; Q is the total reactive power compensation; Q f The reactive power compensated by the passive filtering system; Q Z is the compensation amount of electromagnetic reactive power compensator; C5, L5, R5 represent the capacitance, inductance and resistance of 5th order single tuned filter respectively; C7, L7, R7 represent the capacitance, inductance and resistance of 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.

[0018] The numbers of the components in the accompanying drawings are as follows: 501 is a 5th-order single-tuned filter; 502 is a 7th-order single-tuned filter; 503 is an 11th-order single-tuned filter; 504 is a 13th-order single-tuned filter; 505 is a second-order high-pass filter; 601 is a rotating phase-shifting transformer 1; 602 is a rotating phase-shifting transformer 2. DETAILED DESCRIPTION

[0019] The present invention proposes a topological circuit of an electromagnetic type continuous reactive power compensation and harmonic suppression system (EVC-PPF), which mainly comprises an electromagnetic type reactive power compensator, a single tuned filter and a second order high pass filter.

[0020] See also Figure 1 , Figure 1 The electromagnetic reactive compensator structure diagram of the present invention. The electromagnetic reactive compensator is composed 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, wherein 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 head end forms a star connection, and is connected in parallel with the three-phase power capacitor of the three-phase star connection;

[0021] See also Figure 2 , Figure 2The figure is a working principle diagram of the single tuned filter in the present invention. The circuit is mainly composed of a resistor, a capacitor and a reactor in series. When the single tuned filter is placed in the main circuit, if the frequency of the harmonic current is close to it, it behaves as a resistor. The corresponding harmonic current is filtered out at this frequency, and the harmonic current entering the power system is significantly reduced, and finally the effective suppression of harmonics is achieved.

[0022] See also Figure 3 , Figure 3 The working principle diagram of the second-order high-pass filter in the present invention. When f<f0 (cut-off frequency), the filter will work under high impedance, and low-order harmonics will have difficulty passing through. When f>f0, the filter will construct a low-impedance path, which can effectively absorb high-order harmonics.

[0023] See also Figure 4 , Figure 4 It is the topological circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) in the present invention; when the harmonic current on the load side flows through the parallel access 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 to the passive filter group being able to compensate for a part of the fixed reactive power, by adjusting the voltage on both sides of the capacitor, bidirectional continuous compensation of the reactive power of the load can be achieved.

[0024] See also Figure 5 , Figure 5 It is a single-phase equivalent circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) in the present invention.

[0025] 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.

[0026] The nth order impedance expression of a single tuned filter is:

[0027]

[0028] In the formula, ω n is the nth harmonic angular frequency, ω n =nω1, ω1 is the fundamental angular frequency.

[0029] Easy to know When , its impedance is equal to R and is purely resistive, and the filter impedance value is the smallest.

[0030] The nth order impedance expression of the second-order high-pass filter is:

[0031]

[0032] Reactive power Q generated by the reactive compensator cProduced by the compensation capacitor C, it can be expressed as:

[0033] Q c =U c 2 ωC

[0034] Reactive power Q LRPST The absorption and equivalent inductance L RPST It can be expressed as:

[0035] Q LRPST =I Z 2 ωL RPST

[0036] The reactive power Q compensated by the electromagnetic reactive compensation equipment is obtained by the difference between the reactive power absorbed by the inductor and the reactive power emitted by the capacitor, that is,

[0037] Q Z =Q LRPST -Q C

[0038] Reactive power compensation and harmonic suppression The reactive power Q compensated by the system is Q f and Q Z Composition can be expressed as:

[0039] Q=Q Z -Q f

[0040] Through the transformation ratio characteristics of the phase-shifting transformer, the primary side voltage of the rotating phase-shifting transformer With the secondary voltage and have

[0041]

[0042] The voltage across the capacitor is given by and Synthesized into

[0043]

[0044] Primary current of rotating phase-shifting transformer and The secondary current It can be expressed as

[0045]

[0046] The compensation current It can be expressed as

[0047]

[0048] The phase shift angles of the two rotating phase-shifting transformers are α1 = -α2 = α, then and for

[0049]

[0050]

[0051] 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, then

[0052]

[0053]

[0054] In summary, the reactive power Q of reactive power compensation and harmonic suppression system compensation can be expressed as

[0055]

Claims

1. The topological circuit of the electromagnetic continuous reactive compensation and harmonic suppression system (EVC-PPF) based on the electromagnetic reactive compensator (EVC) and the passive power filter (PPF) is mainly composed of two parts: the electromagnetic reactive compensator and the passive power filter; the passive power filter includes four single-tuned filters and a second-order high-pass filter, wherein the single-tuned filter is composed of three-phase resistors, three-phase capacitors and three-phase inductors in series, and the second-order high-pass filter is composed of three-phase resistors and three-phase inductors in parallel and three-phase capacitors in series; the electromagnetic reactive 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 are 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, wherein, The primary (or secondary) side winding connection of one rotary phase-shifting transformer is reverse sequence connection, and the primary (or secondary) side winding connection of another rotary phase-shifting transformer is positive sequence connection. After the secondary side 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 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. The primary side of the rotary phase-shifting transformer is connected to the power supply, and the secondary side is connected to the power capacitor; The method is characterized in that reactive power compensation is achieved through an electromagnetic reactive power compensator and a passive power filter, and harmonic suppression is achieved through a passive power filter.

2. The topology circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) according to claim 1 is characterized in that: Two rotating phase-shifting transformers are coaxially connected and share a driving motor. When the shaft is pushed to rotate to an angle of α, the excitation currents generated by the two rotating phase-shifting transformers in their respective cores will form excitation magnetic fields with opposite directions due to the positive and reverse sequence wiring of the three-phase windings, thereby obtaining output voltages of two rotating phase-shifting transformers with equal amplitudes and opposite phase shift angles. According to the principle of vector synthesis, by adjusting the phase shift angle of the rotating phase-shifting transformer, two voltage phasors are synthesized in series to form a voltage with adjustable size and phase on both sides of the three-phase power capacitor. By adjusting the voltage across the three-phase capacitor, the reactive power emitted by the three-phase capacitor can be continuously adjusted. Combined with the reactive power emitted by the passive filter group and the reactive power absorbed by the rotating phase-shifting transformer itself, the EVC-PPF can achieve bidirectional continuous reactive power regulation.

3. The topology circuit of the electromagnetic continuous reactive power compensation and harmonic suppression system (EVC-PPF) according to claim 1 is characterized in that: The single-tuned filter and the second-order high-pass filter are three-phase correspondingly connected in parallel with the electromagnetic reactive compensator and connected to the grid point together; the single-tuned filter exhibits low resistance at a specific frequency, and the harmonic current is filtered out at this frequency, and the harmonic current entering the system is significantly reduced; the second-order high-pass filter exhibits higher impedance at low frequencies and forms a low-resistance channel at high frequencies, so it can effectively absorb high-order harmonics; this filter can not only filter out harmonics, but also provide fixed reactive power.

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