Hybrid active filter and control method and control system thereof

Abstract

The invention discloses a hybrid active filter and a control method and a control system thereof. After a single-phase fault is detected, the hybrid active filter device is reconstructed into a three-phase four-switch hybrid active filter to compensate for load harmonic current and reactive power, and the compensation effect is almost unaffected; after a two-phase fault is detected, the normal bridge arm is controlled to operate uninterruptedly, and the faulty bridge arm compensates for fixed reactive power and suppresses harmonic current to a certain extent; after a three-phase fault is detected, the hybrid active filter device is reconstructed into a passive filter to suppress harmonics and compensate for reactive power, thereby improving the stability of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of current conversion in electrical engineering, and in particular to a hybrid active filter and a control method and a control system thereof. Background Art

[0002] With the widespread application of power electronics technology in the fields of flexible DC transmission, flexible AC transmission, distributed generation, etc., the power grid may have serious power quality problems such as voltage flicker, harmonic distortion, and reactive power impact. Hybrid active power filter (HAPF) can achieve excellent filtering effect while reducing system cost, so it is widely used in power systems to manage power quality. As the core component of active filtering equipment, power semiconductor devices have attracted much attention for their reliability. When a device fails and the control mode does not change, it cannot effectively compensate for system harmonics. At this time, the device is equivalent to a harmonic source, which will cause the power quality of the power grid to deteriorate. Therefore, it is of great practical significance to study the fault-tolerant control strategy suitable for hybrid active filters.

[0003] In recent years, related research in the field of inverter fault-tolerant control is as follows: "Fault-tolerant control method for single-tube open-circuit fault of three-phase two-level PMSM drive inverter" (publication number: CN113794407A, publication date: December 14, 2021), which only gives the voltage vector action time redistribution strategy under single-tube open-circuit fault to reduce the time and amplitude of speed and torque fluctuations, and does not give the control strategy under other faults. "A protection circuit and method with high-speed detection of IGBT short-circuit fault" (publication number: CN 109375087A, publication date: October 11, 2018) can only detect IGBT short-circuit fault according to the designed hardware circuit and make corresponding protection, without considering how to detect when the bridge arm has an open-circuit fault. "A real-time detection method and system for open-circuit fault of three-phase voltage source inverter" (publication number: CN 112198458A, publication date: September 7, 2020) does not give the control algorithm after the IGBT fault.

[0004] CN102570465A discloses a hybrid active power filter and an SVPWM method based on the filter. This solution cannot achieve fault-tolerant control of the hybrid active power filter, and its SVPWM method is complex and difficult to implement. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a hybrid active filter and a control method and a control system thereof to improve the operating reliability of the hybrid active filter when a bridge arm fails, in view of the deficiencies in the prior art.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a hybrid active filter, including an active filter and a passive filter; the input side of the passive filter is connected to a three-phase power grid, and the output side is connected to the active filter; the active filter includes a DC side capacitor; the DC side capacitor is connected in parallel with the three-phase bridge arm; the midpoint of each phase bridge arm is connected to one end of a contactor; the other ends of all contactors are connected to the negative electrode of the DC side capacitor.

[0007] In the present invention, each phase bridge arm is connected to a contactor. When a phase or two phase bridge arms fail, the corresponding contactor is closed. At this time, the normal bridge arm is not affected, and the faulty bridge arm can use a passive filter to suppress harmonics and perform fixed reactive power compensation; when all three phase bridge arms fail, the circuit is reconstructed into a passive filter, and the passive filter can suppress harmonics and compensate for reactive power on the hybrid active filter. Therefore, the present invention improves the operating reliability of the hybrid active filter by introducing a contactor at each phase bridge arm.

[0008] In order to further improve the reliability and safety of the hybrid active filter, each phase bridge arm includes an upper switch device and a lower switch device connected in series, and the upper switch device is connected to the positive electrode of the DC side capacitor through a fuse.

[0009] The passive filter includes an inductor and a capacitor tuned to fifth order; the inductor and the capacitor are connected.

[0010] The present invention also provides a control method for the hybrid active filter, comprising the following steps:

[0011] When a phase of the active filter fails, the contactor connected to the bridge arm of the phase is closed, and the trigger signal of the switch device of the phase is controlled to be 0;

[0012] When two phases of the active filter fail, the contactors connected to the bridge arms of the two phases are closed, and the trigger signals of the switch devices of the two phases are controlled to be 0;

[0013] When all three phases of the active filter fail, the contactors connected to all bridge arms are closed, and the trigger signals of all switch devices of the active filter are controlled to be 0.

[0014] When a single-phase or two-phase fault occurs in the hybrid active filter, the present invention changes the circuit topology by closing the contactor, and controls the normal bridge arm to run uninterruptedly at the same time, and the faulty bridge arm relies on the passive filter to achieve harmonic suppression and reactive power compensation. When a three-phase bridge arm fault occurs in the hybrid active filter, the circuit is reconstructed into a passive filter, and the passive filter is relied on to achieve harmonic suppression and reactive power compensation, thereby improving the operating reliability of the hybrid active filter.

[0015] The method of the present invention further comprises:

[0016] The three-phase current reference value of the active filter is calculated from the sampled load current and the common coupling point voltage; the common coupling point is the connection point between the passive filter and the three-phase power grid;

[0017] The three-phase current reference value of the active filter and the actual value of the three-phase output current are compared and modulated through a hysteresis loop to obtain a control signal of the active filter switch device.

[0018] The control method of the present invention is simple and easy to implement.

[0019] The active filter three-phase current reference value The calculation formula is:

[0020]

[0021] in, is the load harmonic active power, is the load harmonic reactive power, Q LC is the fixed reactive power, v α 、v β The voltage obtained by Clarke transformation of the common coupling point voltage.

[0022] In the present invention, Where V is the effective value of the line voltage at the common coupling point, X LC is the fundamental impedance of the passive filter.

[0023] Clarke transformation matrix T adc-αβ for:

[0024] The present invention also provides a control system for a hybrid active filter, which comprises a memory and a processor; the memory stores a computer program / instruction; when the processor executes the computer program / instruction, the steps of controlling the above method of the present invention are implemented.

[0025] Compared with the prior art, the present invention has the following beneficial effects: after a bridge arm fails, the remaining two bridge arms form a three-phase four-switch hybrid active filter, and the compensation effect of the hybrid active filter device is close to that when no failure occurs; after two bridge arms fail at the same time, the operation of the normal bridge arm is not affected, and the faulty bridge arm can suppress harmonics and compensate for fixed reactive power by relying on the passive filter; after all bridge arms fail, the entire device acts as a passive filter to suppress harmonics in the power grid and compensate for reactive power. Therefore, the present invention greatly improves the operational reliability of the hybrid active filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A hybrid active filter circuit topology with fault tolerance function in the present invention;

[0027] FIG2( a ) is a diagram showing the working mode of the hybrid active filter under a single-phase fault condition in the present invention, assuming that the fault is in phase c;

[0028] FIG2( b ) is a diagram showing the working mode of the hybrid active filter under the condition of two-phase faults occurring simultaneously in the present invention, assuming that phases b and c fail simultaneously;

[0029] FIG2( c ) is a diagram showing the operating mode of the hybrid active filter under the condition of three-phase simultaneous faults in the present invention;

[0030] Figure 3 It is the grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power simulation waveform when the hybrid active filter is working normally;

[0031] Figure 4 It is the grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power simulation waveform before and after the hybrid active filter has a phase C fault;

[0032] Figure 5 It is the grid-side voltage, grid-side current, inverter output current, load current, grid-side reactive power simulation waveform before and after the hybrid active filter b and c two phases fail at the same time;

[0033] Figure 6 It is the simulation waveform of grid-side voltage, grid-side current, inverter output current, load current and grid-side reactive power before and after the three-phase a, b and c of the hybrid active filter fail simultaneously. DETAILED DESCRIPTION

[0034] like Figure 1 As shown, the hybrid active filter of the embodiment of the present invention includes an active inverter and a passive filter, and the passive filter includes three branches, each branch includes an L tuned to the fifth order. x and C x , x = a, b, c; the active filter is a voltage source inverter, including a DC side voltage stabilizing capacitor to keep the DC side voltage constant; the three-phase power switch (three-phase bridge arm) uses an insulated gate bipolar transistor (IGBT), with T x , Indicates that each phase bridge arm includes an upper switch tube T x And the lower switch In addition, each phase bridge arm is also equipped with a fuse FU x With contactor KM x , fuse FU x Used to prevent short circuit faults in each phase; contactor KM xOne end is connected to the midpoint of the bridge arm, and the other end is connected to the negative electrode of the capacitor. After a fault is detected, the faulty bridge arm is cut off and the normally open contact of the contactor is turned on at the same time, so that the passive filter of this phase continues to operate.

[0035] Another embodiment of the present invention provides a fault-tolerant control method for the hybrid active filter, which can realize the hybrid active filter in Figure 2(a) to Figure 2(c) The three fault conditions shown in the figure are stable operation, namely single-phase bridge arm fault working mode (Figure 2(a)), two-phase bridge arm simultaneous fault mode Figure 2(b) , three The phase bridge arm simultaneous failure mode is shown in Figure 2(c). The specific implementation steps are as follows:

[0036] S1, for the three-phase current i of the hybrid active filter a, b, c cx , load current i Lx , common coupling point voltage v x Take samples;

[0037] When the hybrid active filter is in a fault-free state, according to the instantaneous power theory, the load current i Lx and the voltage at the common coupling point v x Calculate the inverter a, b, c three-phase current reference value

[0038] For a three-phase three-wire system, the detected voltage and current are transformed by Clarke to obtain the instantaneous values ​​under the αβ axis of the two-phase stationary coordinate system. The transformation relationship is as follows:

[0039] [v r (t)] r＝α、β =T abc-αβ ·[v x (t)] x＝a、b、c (1)

[0040] [i r (t)] r＝α、β =T abc-αβ ·[i x (t)] x＝a、b、c (2)

[0041] Among them, the Clarke transformation matrix T adc-αβ for:

[0042]

[0043] In the obtained v r 、i r (r = α, β), the three-phase instantaneous active power and reactive power can be calculated, where Represents the load fundamental active power; Represents the load harmonic active power; Represents the fundamental reactive power of the load; Represents the load harmonic reactive power.

[0044]

[0045]

[0046] Control the entire HAPF to compensate for harmonic active power, harmonic reactive power, and a fixed fundamental reactive power, i.e. compensation and fixed reactive power Q LC . Reactive power Q LC The calculation is as follows: The value is the reactive power that the three-phase LC can provide, where V is the effective value of the line voltage at the common coupling point, and X is LC is the fundamental impedance of LC:

[0047]

[0048] The power to be compensated is converted into the compensation current in the two-phase stationary coordinate system by equation (7):

[0049]

[0050] The power to be compensated They are:

[0051]

[0052]

[0053] Finally, the compensation current in the abc coordinate system can be obtained by the conversion in the αβ coordinate system:

[0054]

[0055] According to the corresponding fault-tolerant control strategy, when a single-phase, two-phase or three-phase fault occurs in the hybrid active filter, the trigger signal of the power switch device of that phase is controlled to be "0", and the normally open contact of the contactor of that phase is closed. At this time, the three-phase current reference value is still calculated according to the three-phase instantaneous power theory;

[0056] When one of the three phases a, b, and c fails or two phases fail at the same time, the normally open contact of the faulty phase contactor is closed, and the trigger signal of the switch device of the corresponding bridge arm is controlled to be "0", so that the circuit is reconstructed into a three-phase two-switch hybrid active filter. At this time, the normal bridge arm can compensate for the harmonics of the system, and the faulty bridge arm can use a passive filter tuned to the fifth order to suppress the harmonics and compensate for the fixed reactive power.

[0057] When faults occur in phases a, b, and c, the three-phase contactors are all closed and the trigger signals of all switch tubes are controlled to be "0". At this time, the circuit is reconstructed into a passive filter to suppress harmonics and compensate for reactive power in the system.

[0058] S2. According to the calculated reference value of the bridge arm current, the control signal of the active filter switch device is obtained through the hysteresis comparison modulation strategy (see: Xia Yu. Guangxi University 2017.06. Master's thesis).

[0059] The following verifies that the embodiment of the present invention can enable the normal bridge arm to continue to operate and the faulty bridge arm to function as a passive filter to perform harmonic suppression and reactive power compensation when a single-phase, two-phase, or three-phase fault occurs in the hybrid active filter.

[0060] System parameters and hybrid active filter parameters:

[0061] Grid voltage V sx =220V, system inductance L s =20mH, inductor L tuned to the fifth order x =5mH, C x =80μF, DC side voltage V dc =100V.

[0062] The following are the simulation results of the above parameters, and the corresponding results are summarized in Table 1:

[0063] Table 1 Simulation compensation results of HAPF fault-tolerant control method (i.e., control method of the embodiment of the present invention)

[0064]

[0065]

[0066] Figure 3 The grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power waveforms are shown in Table 1 and Figure 3 It can be seen that under ideal conditions, that is, when no fault occurs, the instantaneous power theory can be used to compensate the three-phase reactive power from 1298Var, 1299Var, 1297Var before compensation to 42.35Var, 45.62Var, 48.88Var respectively; the three-phase power factor is also compensated from 0.95 to 1.00; the three-phase harmonic current distortion rate THD at the power supply is isx(%) are 1.94%, 1.92%, and 1.94%, respectively, all meeting IEEE Std 519-2014. Using the fault-tolerant control method of the embodiment of the present invention, the current distortion rate and power factor in the case of a single-phase fault are approximately equal to those in the case of no fault; in the case of a multi-phase fault, harmonics can be suppressed to a certain extent and reactive power can be compensated. The specific analysis is as follows:

[0067] A) Single-phase IGBT failure

[0068] Figure 4 The grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power waveforms when phase c fails. Figure 4 As shown in Table 1, using the fault-tolerant control method of the embodiment of the present invention, the operation of the circuit is not affected by the fault phase, and the fault phase can continue to suppress harmonic current and compensate reactive power. c Closed, the c-phase passive filter operates normally, and the three-phase reactive power at the power supply is approximately at the same level as the three-phase reactive power when no fault occurs; the power factor PF of the c-phase is still 1.00, which is approximately equal to that under normal compensation of the HAPF device; the THD after the fault isx (%) are 1.94%, 1.90%, and 2.00%, respectively, all of which can meet IEEE Std 519-2014. From this analysis, it can be seen that the fault-tolerant control method of the embodiment of the present invention can greatly improve the stability of the device when a single-phase fault occurs, and the harmonic suppression and reactive power compensation of the fault phase are not much different from those of the normal operation of the HAPF device.

[0069] B) When two-phase IGBT fails

[0070] Figure 5 is the grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power waveform when phase b and phase c fail. After using the fault-tolerant control method of the embodiment of the present invention, KM b , KM c Closed, the passive filters of phases b and c operate normally. Figure 5 As can be seen from Table 1, the three-phase reactive power at the power supply is approximately at the same level as the three-phase reactive power without fault, and the reactive power compensation of the fault phase is not affected; THD after the fault isx(%) are 1.43%, 15.50%, and 15.60% respectively, phase a meets IEEE Std 519-2014, and phases b and c are significantly reduced compared to 26.67% and 26.67% before compensation, indicating that the fault phase can suppress harmonics to a certain extent. From this analysis, it can be seen that the fault-tolerant control method of the embodiment of the present invention makes the reactive power compensation of the fault phase not much different from the normal operation of the HAPF (hybrid active power filter) device when a two-phase fault occurs, and harmonics can be suppressed by a passive filter.

[0071] C) When all three-phase IGBTs fail

[0072] Figure 6 The grid-side voltage, grid-side current, inverter output current, load current, and grid-side reactive power waveforms are shown below when all three phases a, b, and c are faulty. a , KM b , KM c All are closed, and the entire HAPF device continues to operate as a passive filter. Figure 6 As shown in Table 1, the three-phase reactive power at the power supply before and after the fault is not much different, and the reactive power compensation is not affected by the fault; after the circuit stabilizes, the THD isx (%) are 17.07%, 17.65%, and 17.28% respectively, which are significantly reduced compared with 26.67%, 26.67%, and 26.67% before compensation, and can suppress harmonic current to a certain extent. From this analysis, it can be seen that after a three-phase fault occurs, the HAPF device can still compensate for fixed reactive power, suppress harmonics, and improve the operating reliability of the device.

[0073] The above simulation results verify that the hybrid active filter can ensure that the normal bridge arm is not affected when a single-phase, two-phase, or three-phase fault occurs, and the faulty bridge arm acts as a passive filter to suppress harmonics and compensate for reactive power, which verifies the effectiveness of the hybrid active inverter fault-tolerant topology and its corresponding control strategy proposed in the present invention.

Claims

1. A control method for a hybrid active filter, the hybrid active filter comprising an active filter and a passive filter; the passive filter input side is connected to a three-phase power grid, and the output side is connected to the active filter; the active filter comprises a DC side capacitor; the DC side capacitor is connected in parallel with a three-phase bridge arm; the midpoint of each phase bridge arm is connected to one end of a contactor; the other ends of all contactors are connected to the negative electrode of the DC side capacitor; characterized in that, The following steps are involved: When a phase of the active filter fails, the contactor connected to the bridge arm of that phase is closed. Control the trigger signal of the phase switch device to be 0; When two phases of the active filter fail, the contactors connected to the bridge arms of the two phases are closed, and the trigger signals of the switch devices of the two phases are controlled to be 0; When all three phases of the active filter fail, the contactors connected to all bridge arms are closed. Control the trigger signal of all switch devices of the active filter to 0; The three-phase current reference value of the active filter is calculated from the sampled load current and the common coupling point voltage; the common coupling point is the connection point between the passive filter and the three-phase power grid; Comparing and modulating the three-phase current reference value of the active filter with the actual value of the three-phase output current through a hysteresis loop to obtain a control signal of the active filter switch device; The active filter three-phase current reference value The calculation formula is: in, is the load harmonic active power, is the load harmonic reactive power, Q LC is the fixed reactive power, v α 、v β The voltage value obtained after Clarke transformation of the common coupling point voltage.

2. The method according to claim 1, characterized in that Where V is the effective value of the line voltage at the common coupling point, X LC is the fundamental impedance of the passive filter.

3. The method according to claim 1, characterized in that Clarke transformation matrix T adc-αβ for:

4. The method according to claim 1, characterized in that: Each phase bridge arm comprises an upper switch device and a lower switch device connected in series, and the upper switch device is connected to the positive electrode of the DC side capacitor through a fuse.

5. The method according to claim 1, characterized in that The passive filter includes an inductor and a capacitor tuned to fifth order; the inductor and the capacitor are connected.

6. A control system for a hybrid active filter, characterized in that: The invention comprises a memory and a processor; the memory stores a computer program / instruction; when the processor executes the computer program / instruction, the steps of the method according to any one of claims 1 to 5 are implemented.

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