Control method of active part of hybrid active power filter

Abstract

This invention provides a control method for the active section of a hybrid power active filter. By employing a three-phase fictitious and improved symmetrical component method, it can perform electrical quantity calculations under severely asymmetrical three-phase nonlinear load conditions, extracting the zero-sequence current component, which contains zero-sequence harmonic currents. Furthermore, due to the use of a triangular wave comparison control method, the resulting PWM pulse signal contains fewer harmonics. Using this PWM pulse signal to control the active section of the hybrid power active filter enables effective control and accurate filtering of zero-sequence harmonic currents. In summary, the control method of this invention enables the hybrid power active filter to accurately filter zero-sequence harmonic currents under severely asymmetrical three-phase nonlinear load conditions, achieving an ideal filtering effect.

Description

Technical Field

[0001] This invention belongs to the field of active power filter design technology, specifically relating to a control method for the active part of a hybrid power active filter. Background Technology

[0002] With the widespread application of numerous nonlinear loads (such as electric arc furnaces, frequency converters, rolling mills, medium-frequency induction heating furnaces, and high-speed rail traction substations) in power distribution systems, severe harmonic pollution has been caused. This severe harmonic pollution shortens the lifespan of both power distribution and consumer equipment and poses a series of serious hazards to the power grid. The connection of numerous single-phase nonlinear loads to three-phase four-wire power distribution systems results in severe asymmetry, generating not only large amounts of 5th and 7th harmonic currents but also a significant amount of third-order (and multiples of 3) harmonic currents. How to detect and mitigate these harmonic currents has become a hot topic in current power quality management.

[0003] While some harmonic detection and classification techniques exist in the existing technology, none of these methods are applicable to situations with severely unbalanced three-phase loads. Therefore, their scope of application is narrow and they cannot effectively solve the aforementioned harmonic pollution problems in reality. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and its purpose is to provide a harmonic current control method applicable to severe three-phase load asymmetry. The invention adopts the following technical solution:

[0005] This invention provides a control method for the active section of a hybrid power active filter, characterized by comprising: step S1, sampling the active section of the hybrid power active filter to obtain the load current of each phase; step S2, performing three-phase fictitious analysis on the load current of each phase to obtain fictitious three-phase currents for each phase; step S3, extracting the zero-sequence current component from the fictitious three-phase current of each phase using an improved symmetrical component method; step S4, merging the zero-sequence current components of the three phases to obtain the zero-sequence current component on the neutral load side; and step S5, obtaining a PWM pulse signal based on the triangular wave comparison control method and the zero-sequence current component on the neutral load side, and using the PWM pulse signal to control the active section.

[0006] The control method for the active section of the hybrid power active filter provided by this invention may also have the following technical features: In step S1, the instantaneous voltage value of the first phase is obtained by sampling; step S3 includes the following sub-steps: Step S3-1, analyzing the fictitious three-phase current of each phase using the symmetrical component method to obtain the fictitious zero-sequence current of each phase; Step S3-2, obtaining the effective voltage value of each phase based on the fictitious zero-sequence current of each phase; Step S3-3, performing a cross-sectional analysis on the instantaneous voltage value and the effective voltage value of each phase. Step S3-4: Compare the virtual zero-sequence current of each phase to 0 to obtain the second pulse sequence of each phase; Step S3-5: Based on the first pulse sequence and the second pulse sequence of each phase, obtain the third pulse sequence of each phase; Step S3-6: Based on the third pulse sequence of each phase and a predetermined filtering algorithm, obtain the filtering pulse of each phase; Step S3-7: Based on the filtering pulse of each phase and the virtual zero-sequence current of each phase, obtain the zero-sequence current component of each phase.

[0007] The control method for the active section of the hybrid power active filter provided by this invention may also have the following technical feature, wherein the first pulse sequence is represented as:

[0008]

[0009] Where u a(k) Let u be the instantaneous value of the voltage. ar(k) The effective value of the voltage.

[0010] The second pulse sequence is represented as follows:

[0011]

[0012] In the formula, i a0(k) For the fictitious zero-sequence current,

[0013] The third pulse sequence is represented as follows:

[0014] k a2(k) =k a1(k) *s a1(k)

[0015] The screening pulse is represented as:

[0016] k a(k) =k a2(k) +k a2(k-512) ,

[0017] In the formula, k a2(k-512) The pulse sequence obtained by delaying the third pulse sequence by half a fundamental period.

[0018] The control method for the active section of the hybrid power active filter provided by this invention may also have the following technical feature, wherein, in steps S3-7, the zero-sequence current component of each phase is obtained according to the following formula:

[0019] i a2(k) =k a(k) *i a0(k) .

[0020] The control method for the active section of the hybrid power active filter provided by the present invention may also have the following technical features, wherein step S5 includes the following sub-steps: step S5-1, comparing the zero-sequence current component on the neutral load side with the actual output current of the active section to obtain the error between the two; step S5-2, amplifying the error through an amplifier; step S5-3, comparing the amplified error with a predetermined triangular wave signal to obtain the PWM pulse signal; step S5-4, using the PWM pulse signal to control the IGBT power switch in the active section, thereby realizing the control of the active section.

[0021] Invention Function and Effect

[0022] The control method for the active section of the hybrid active power filter according to the present invention, by employing a three-phase fictitious and improved symmetrical component method, can perform electrical quantity calculations under severely asymmetrical three-phase nonlinear load conditions, extracting the zero-sequence current component, which contains zero-sequence harmonic current. Furthermore, by employing a triangular wave comparison control method, the resulting PWM pulse signal contains fewer harmonics. Using this PWM pulse signal to control the active section of the hybrid active power filter enables effective control and accurate filtering of zero-sequence harmonic current. In summary, the control method of the present invention enables the hybrid active power filter to accurately filter zero-sequence harmonic current under severely asymmetrical three-phase nonlinear load conditions, achieving an ideal filtering effect. Attached Figure Description

[0023] Figure 1 This is a flowchart of the control method for the active part of the hybrid power active filter in an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the main circuit structure of the hybrid filter in an embodiment of the present invention;

[0025] Figure 3 This is the zero-sequence equivalent circuit diagram of the hybrid filter in this embodiment of the invention;

[0026] Figure 4 This is a schematic diagram of the circuit structure of the phase-locked loop circuit in an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of the overall control hardware structure of the hybrid filter in an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of the control structure of the active part of the filter in an embodiment of the present invention;

[0029] Figure 7 This is a waveform diagram of the instantaneous voltage value, effective voltage value, and first pulse sequence of phase A in an embodiment of the present invention;

[0030] Figure 8 This is a waveform diagram of the virtual zero-sequence current and the second pulse sequence of phase A in an embodiment of the present invention;

[0031] Figure 9 This is a waveform diagram of the first pulse, second pulse, and third pulse of phase A in an embodiment of the present invention;

[0032] Figure 10 This is a waveform diagram of the third pulse and the screening pulse of phase A in an embodiment of the present invention;

[0033] Figure 11 This is a waveform diagram of the virtual zero-sequence current, screening pulse, and actual zero-sequence current of phase A in an embodiment of the present invention;

[0034] Figure 12 The waveforms of the actual zero-sequence current of the three phases and the zero-sequence current on the neutral load side in this embodiment of the invention are shown.

[0035] Figure 13 This is a simulation model diagram of the hybrid filter in an embodiment of the present invention;

[0036] Figure 14 This is a waveform diagram of the neutral load side current when the three-phase load is unbalanced in an embodiment of the present invention;

[0037] Figure 15 This is a waveform diagram of the output current of the active part when the three-phase load is unbalanced in an embodiment of the present invention;

[0038] Figure 16 This is the waveform and spectrum of the current on the load side of phase A when the three-phase load is unbalanced in an embodiment of the present invention;

[0039] Figure 17 This is the waveform and spectrum of the current on the A-phase system side when the three-phase load is unbalanced in an embodiment of the present invention. Detailed Implementation

[0040] To make the technical means, creative features, objectives and effects of this invention easy to understand, the control method of the active part of the hybrid power active filter of this invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0041] <Example>

[0042] This embodiment provides a control method for the active part of a hybrid power active filter, used to control the active part of the hybrid power active filter (hereinafter referred to as the hybrid filter) so that the hybrid filter can achieve better filtering effect.

[0043] Figure 2 This is the main circuit structure diagram of the hybrid filter in this embodiment.

[0044] like Figure 2 As shown, the main circuit of the hybrid filter includes a passive section consisting of a 5th-order passive filter (with inductor L5 and capacitor C5) and a 7th-order passive filter (with inductor L7 and capacitor C7) connected in a star configuration, and an active section consisting of an IGBT capacitor half-bridge. One end of the AC side of the active section of the filter is connected to the neutral point of the passive section, and the other end is connected to the neutral line. Since the active section of the hybrid source filter operates in a zero-sequence loop and there is no usable power supply, an external DC power supply is required. This DC power supply can be obtained by rectifying an AC power supply through an AC inductor and an isolation transformer; or it can be provided by a switching power supply with current limiting function, and the DC voltage U d Continuously adjustable within the range of 0-300V.

[0045] Figure 3 This is the zero-sequence equivalent circuit diagram of the hybrid filter in this embodiment.

[0046] like Figure 3 As shown, the hybrid filter in non-zero sequence is a star-connected single-tuned fifth and seventh order passive filter bank; the simplified circuit in zero sequence is as follows: Figure 3 As shown in (a), i s0 X is the current on the neutral system side. s0 For the system-side zero-sequence equivalent impedance, i f0 For the current on the neutral filter side, i z0 For the current on the neutral load side, i d C is the charging current of the DC power supply. d1 and C d2 This is the DC-side capacitor of the filter.

[0047] Since the zero-sequence current flowing through the active section of the filter is primarily reactive, with very little active component—the limited active component mainly used to overcome losses from parasitic resistance in the zero-sequence loop—the DC power required for the active section of the filter is very small. The actual measured AC current is no greater than 0.2A (220V). Therefore, the influence of the DC power supply can be ignored in the following analysis. Figure 3 (b) and Figure 3(c) The circuit topology is shown when IGBT switches S1 and S2 are turned on respectively.

[0048] For hybrid filters, the higher the system-side zero-sequence impedance, the better the filter's filtering effect on zero-sequence harmonic currents. Therefore, in the analysis... Figure 2 When considering the zero-sequence equivalent circuit of the filter shown, only Δ-Y needs to be taken into account. n0 The scenario involves a distribution transformer with specific wiring configuration. In this case, the zero-sequence reactance X of the distribution system... s0 It's very small, and since the filter's control objective is to filter out all zero-sequence harmonic currents, it can be approximated as... Figure 2 middleu r The voltage is considered to be 0, so the capacitor C d1 Voltage U on Cd1 and capacitor C d2 Voltage U on Cd2 Only the zero-sequence reactance of the filter branch needs to be overcome. Since the zero-sequence harmonic currents above the 21st order are very small, they can be ignored. The following formula gives the 3rd to 21st order zero-sequence harmonic voltages generated when 3rd to 21st order zero-sequence harmonic currents flow through the passive part of the filter:

[0049]

[0050] The following formula gives the capacitance C d1 DC voltage U on Cd1 and capacitor C d2 DC voltage U on Cd2 DC voltage U d For U Cd1 and U Cd2 sum:

[0051]

[0052] Passive filters are widely used in power distribution systems due to their large capacity, low cost, and good filtering effect on fifth-order and higher harmonic currents. However, for passive filter banks that have been grouped, when switching on, the fifth-order passive filter branch should be switched on first, followed by the seventh-order passive filter branch; when disconnecting, the seventh-order passive filter branch should be disconnected first, followed by the fifth-order passive filter branch. When the number of fifth-order passive filter branches u = 6 and the number of seventh-order passive filter branches v = 2, the operating modes of the passive part of the filter can be obtained as shown in Table 1.

[0053] Table 1. Operating Modes of the Passive Component of the Filter

[0054]

[0055] For ease of description, in this embodiment, the capacitors of each passive filter branch are designed to have equal capacitance, where C is the capacitance of each branch.

[0056] For operating modes 1-3, the zero-sequence impedance of the passive filter can be obtained as follows:

[0057]

[0058] In the formula, 3n represents the zero-sequence harmonic order, and n = 1, 2, 3, ...

[0059] For operating modes 4 to 8, the zero-sequence reactance X of the passive filter can be derived. f0 for:

[0060]

[0061] Figure 4 This is a schematic diagram of the phase-locked loop circuit in this embodiment.

[0062] like Figure 4 As shown, in this embodiment, in order to overcome problems such as voltage and current frequency jitter and phase jump in AC systems, the following method is adopted: Figure 5 The phase-locked loop (PLL) circuit shown is implemented using a CD4046 PLL chip and an FPGA (FPGA programmable logic device). Phase A voltage ua passes through a low-pass filter circuit composed of operational amplifiers (op-amps) to generate a voltage signal ua1. This signal is then shaped into a square wave by an op-amp shaping circuit and sent to pin 14 of the CD4046 PLL chip for 90° phase locking. The CD4046 PLL circuit generates high-frequency pulses of approximately 410kHz, which are then fed into the FPGA. The FPGA chip's 8x prescaler divides the pulses, resulting in a frequency of approximately 51.2kHz, equivalent to locking 1024 pulses per fundamental cycle. The overall control hardware structure of the filter using the PLL circuit is as follows: Figure 6 As shown, it uses a 32-bit DSP chip TMS320F28335 and three 14-bit synchronous sampling ADC chips AD7865. The 10-bit angle pulse signal output by the phase-locked loop circuit can be read at any time by the DSP chip. The ADC start pulse signal output by the phase-locked loop circuit controls the three AD7865 chips to start conversion simultaneously. The sampling frequency is 1024 points per fundamental period.

[0063] Figure 5 This is a schematic diagram of the overall control hardware structure of the hybrid filter in this embodiment.

[0064] like Figure 5As shown, the filter control program includes control programs for the active and passive parts of the filter. The passive part control program is responsible for calculating the reactive power demand of the load and determining the number of passive filter branches to be switched. With the cooperation of the phase-locked loop circuit, the active part of the filter uses the improved symmetrical component method to control the three-phase load current i. za 、i zb 、i zc Extract the command current signal i z And the actual output current i of the active part of the filter. f0 The comparison is performed, and a PWM signal pulse is generated through a triangular wave comparator to control the operation of the IGBT power switch in the active part of the filter.

[0065] Nonlinear load current i under three-phase four-wire conditions za 、i zb 、i zc In addition to positive and negative sequence current components, it also includes a zero-sequence current component. When the three-phase load is severely unbalanced, the zero-sequence current components in the three-phase load current are inconsistent, and the conventional symmetrical component method cannot directly extract the zero-sequence current component of the neutral load side from the three-phase load current. This embodiment provides an improved symmetrical component method, which can quickly and accurately extract the zero-sequence current component of the neutral load side from the three-phase load current.

[0066] Based on the above settings, the control method in this embodiment will be described in detail below.

[0067] Figure 1 This is a flowchart of the control method for the active part of the hybrid power active filter in this embodiment.

[0068] like Figure 1 As shown, the control method for the active section of the hybrid power active filter is mainly based on the improved symmetrical component method, and specifically includes the following steps:

[0069] Step S1: Sample the active part of the hybrid filter to obtain the load current of each phase.

[0070] Figure 6 This is a schematic diagram of the control structure of the active part of the filter in this embodiment.

[0071] like Figure 6 As shown, in this embodiment, the three-phase voltage sampling value u is obtained by sampling through AD7865 with the cooperation of the phase-locked loop circuit. a(k) u b(k) u c(k) and three-phase load current sampling value i za(k) 、i zb(k) 、i zc(k)That is, the instantaneous values ​​of voltage and current, where k is the sampling point at the current moment.

[0072] Step S2: Perform three-phase simulation on the load current of each phase to obtain virtual three-phase current and virtual three-phase voltage.

[0073] In this embodiment, for ease of description, the three phases are referred to as phase A, phase B, and phase C, respectively. Since the three phases are assumed and the subsequent zero-sequence current calculation is the same, only phase A will be used as an example for detailed explanation below. The cases of phase B and phase C can be deduced by analogy.

[0074] Step S3: Obtain the zero-sequence current component of each phase based on the improved symmetrical component method and the virtual three-phase current of each phase.

[0075] Step S3 specifically includes the following sub-steps:

[0076] Step S3-1: Analyze the virtual three-phase current of each phase using the symmetrical component method to obtain the virtual zero-sequence current of each phase.

[0077] In this embodiment, the load-side current i of phase A at the current sampling time is... za(k) By performing a three-phase simulation and applying the symmetrical component method, the zero-sequence current i of the virtualized phase A can be obtained. a0(k) :

[0078] i a0(k) =i za(k) +i za(k-341) +i za(k-683)

[0079] Step S3-2: Obtain the effective voltage value of each phase based on the virtual three-phase voltage of each phase.

[0080] In this embodiment, the effective voltage value U of phase A can be calculated using the following formula. ar(k) :

[0081]

[0082] Step S3-3: Compare the instantaneous voltage value and the effective voltage value of each phase to obtain the first pulse sequence of each phase.

[0083] Figure 7 This is a waveform diagram of the instantaneous voltage value, effective voltage value, and first pulse sequence of phase A in this embodiment.

[0084] like Figure 7 As shown, in this embodiment, the instantaneous voltage value u of phase A is... a(k) and the effective value of phase A voltage u ar(k) By comparison, the first pulse sequence s of phase A can be obtained. a(k) as follows:

[0085]

[0086] Step S3-4: Compare the virtual zero-sequence current of each phase with 0 to obtain the second pulse sequence of each phase.

[0087] Figure 8 This is a waveform diagram of the virtual zero-sequence current and the second pulse sequence of phase A in this embodiment.

[0088] like Figure 8 As shown, in this embodiment, the virtualized zero-sequence current i of phase A is... a0(k) Comparing with 0, we obtain the pulse sequence k. a1 (k):

[0089]

[0090] Step S3-5: Based on the first pulse sequence and the second pulse sequence of each phase, obtain the third pulse sequence of each phase.

[0091] Figure 9 This is a waveform diagram of the first pulse, second pulse, and third pulse of phase A in this embodiment.

[0092] like Figure 9 As shown, in this embodiment, the first pulse sequence s of phase A is... a(k) and the second pulse sequence k of phase A a1(k) Multiplying them together yields the third pulse sequence k of phase A. a2(k) :

[0093] k a2(k) =k a1(k) *s a1(k)

[0094] Steps S3-6: Based on the third pulse sequence of each phase and the predetermined filtering algorithm, obtain the filtering pulse for each phase.

[0095] Figure 10 This is a waveform diagram of the third pulse and the screening pulse of phase A in this embodiment.

[0096] like Figure 10 As shown, in this embodiment, the third pulse sequence k of phase A is... a2(k) Delaying by half a fundamental period yields k a2(k-512) Then put k a2(k) With k a2(k-512) By merging, the filtering pulse k can be obtained. a(k) as follows:

[0097] k a(k) =k a2(k) +k a2(k-512)

[0098] Step S3-7: Based on the screening pulse of each phase and the virtual zero-sequence current of each phase, obtain the actual zero-sequence current component of each phase.

[0099] Figure 11 This is a waveform diagram of the virtual zero-sequence current, screening pulse, and actual zero-sequence current of phase A in this embodiment.

[0100] like Figure 11 As shown, in this embodiment, the screening pulse k of phase A is... a(k) With virtualized A zero-sequence current i a0(k) Multiplying them together, we obtain the actual zero-sequence current i of phase A. a2(k) :

[0101] i a2(k) =k a(k) *i a0(k)

[0102] As described above, the actual zero-sequence current of phase A is obtained through the above steps. Similarly, the actual zero-sequence current i of phase B can be obtained using a similar method. b2(k) and the actual zero-sequence current i of phase C c2(k) .

[0103] Step S4: Combine the actual zero-sequence current components of the three phases to obtain the zero-sequence current component on the neutral load side.

[0104] Figure 12 This is a waveform diagram of the actual zero-sequence current of the three phases and the zero-sequence current on the neutral load side in this embodiment.

[0105] like Figure 12 As shown, in this embodiment, the zero-sequence current i on the neutral load side is obtained according to the following formula. z(k) :

[0106] i z(k) =i a2(k) +i b2(k) +i c2(k)

[0107] Step S5: Obtain the PWM pulse signal based on the triangular wave comparison control method and the zero-sequence current component on the neutral load side, and use the PWM pulse signal to control the active part of the hybrid filter.

[0108] Step S5 specifically includes the following sub-steps:

[0109] Step S5-1: Compare the zero-sequence current component on the neutral load side with the actual output current of the active part of the hybrid filter to obtain the error between the two.

[0110] Step S5-2: Amplify the error using an amplifier.

[0111] Step S5-3: Compare the amplified error with the predetermined triangular wave signal to obtain the PWM pulse signal.

[0112] Step S5-4: Use PWM pulse signals to control the IGBT power switches in the active section of the hybrid filter, thereby achieving control of the active section.

[0113] To verify the correctness and effectiveness of the above control method, simulation verification was performed on the control method in this embodiment.

[0114] Figure 13 This is a simulation model diagram of the hybrid filter in this embodiment.

[0115] like Figure 13 As shown, in this embodiment, according to Figure 2 The main circuit structure of the hybrid filter shown was used to build a simulation model of the system on the PSIM9.1.1 simulation software platform. Simulation experiments of the hybrid filter were then conducted on this platform under three-phase balanced and severely unbalanced conditions. Figure 13 In the simulation, the harmonic source consists of three single-phase rectifier loads, which are mainly used to generate third harmonic currents. It is powered by a three-phase 380V AC power supply. The simulation parameters are shown in Table 2.

[0116] Table 2 System Simulation Parameters

[0117]

[0118] Figure 14 This is a waveform diagram of the neutral load side current when the three-phase load is unbalanced in this embodiment.

[0119] Figure 15 This is a waveform diagram of the output current of the active part when the three-phase load is unbalanced in this embodiment.

[0120] like Figure 14 and Figure 15 As shown, the waveforms of the two basically cancel each other out.

[0121] When the three-phase load is unbalanced, the neutral current changes from a peak of approximately 330A to approximately 18A, affecting the neutral system side current i. s0 FFT analysis revealed that the dominant components were the fundamental current (6.1 A) and the fifth harmonic current (7.9 A), while the third harmonic current was only about 2.1 A. The high neutral-line system current is0 was caused by the asymmetry of the three-phase load, indicating that the hybrid filter has a more significant filtering effect when the three-phase load is severely asymmetrical.

[0122] Figure 16 This is the waveform and spectrum of the current on the load side of phase A when the three-phase load is unbalanced in this embodiment; Figure 17 This is the waveform and spectrum of the current on the A-phase system side when the three-phase load is unbalanced in this embodiment.

[0123] like Figure 16 As shown, the current i za The third harmonic current is approximately 100 amps, the fifth harmonic current is approximately 58 amps, the seventh harmonic current is approximately 25 amps, and the ninth harmonic current is approximately 8.3 amps. Figure 17 When the three-phase rectified load is unbalanced, the current i on the A-phase system side is... sa The waveform and spectrum show that the current i sa The third harmonic current is approximately 29 amps, the fifth harmonic current is approximately 1.8 amps, and other harmonics are negligible. The situation for phases B and C is basically similar to that for phase A. Therefore, the hybrid filter can also achieve good filtering results when the three-phase rectified load is severely unbalanced.

[0124] A prototype based on the above control method was applied to a power distribution station in a large residential community in Fuzhou in May 2019. Tables 3 and 4 show the on-site harmonic detection results after the prototype was applied to the power distribution station. The system-side current measured with a clamp meter was approximately 1850A, the DC voltage on the filter's DC side was measured to be 250V with a multimeter, and the current supplied by the DC power supply was measured to be 0.2A with a clamp meter. The estimated power of the DC power supply was approximately 50 watts, which mainly compensates for the resistive losses in components such as the power transformer, reactor, capacitor, and IGBT.

[0125] Table 3 shows the detection results of major harmonic currents in the centerline.

[0126]

[0127] Table 4. Results of Three-Phase Main Harmonics Detection

[0128]

[0129]

[0130] As can be seen from Table 3, the active part of the hybrid filter achieves a filtering effect of over 91% on the third harmonic current on the neutral line and over 87% on the ninth harmonic current. This indicates that the active part of the filter has a good filtering effect on the third and ninth zero-sequence harmonics. As for the fifth and seventh harmonic currents on the neutral line, they are caused by a certain degree of asymmetry in the three-phase load of the substation.

[0131] As shown in Table 4, the hybrid filter achieves a filtering effect of over 72% for the 5th harmonic current, over 70% for the 7th harmonic current, over 68% for the 11th harmonic current, and over 65% for the 13th harmonic current. The filtering performance of the passive part of the filter indicates that the design parameters of the passive filter bank and the corresponding control method of the active part meet the filtering requirements and achieve the ideal filtering effect.

[0132] Functions and effects of the embodiments

[0133] According to the control method of the active section of the hybrid power active filter provided in this embodiment, due to the adoption of a three-phase fictitious and improved symmetrical component method, electrical quantity calculations can be performed under the condition of severe asymmetry in three-phase nonlinear loads, extracting the zero-sequence current component, which contains zero-sequence harmonic current. Furthermore, due to the adoption of the triangular wave comparison control method, the obtained PWM pulse signal contains fewer harmonics. Using this PWM pulse signal to control the active section of the hybrid power active filter can achieve effective control and accurately filter out zero-sequence harmonic current. In summary, the control method of the present invention enables the hybrid power active filter to accurately filter out zero-sequence harmonic current under the condition of severe asymmetry in three-phase nonlinear loads, achieving an ideal filtering effect.

[0134] In the embodiments, the simulation and field application results both confirmed the feasibility and effectiveness of the control method. Under the condition of severe asymmetry of three-phase nonlinear load, it not only accurately filters out zero-sequence harmonic current, but also filters out most of the 5th and 7th harmonic currents.

[0135] The above embodiments are only used to illustrate specific implementations of the present invention, and the present invention is not limited to the scope of the description of the above embodiments.

Claims

1. A control method for the active section of a hybrid power active filter, characterized in that, include: Step S1: Sample the active part of the hybrid power active filter to obtain the load current of each phase; Step S2: Perform three-phase simulation on the load current of each phase to obtain the virtual three-phase current of each phase; Step S3: Obtain the zero-sequence current component of each phase based on the improved symmetrical component method and the virtual three-phase current of each phase. Step S4: Combine the zero-sequence current components of the three phases to obtain the zero-sequence current component on the neutral load side. Step S5: Obtain a PWM pulse signal based on the triangular wave comparison control method and the zero-sequence current component on the neutral load side, and use the PWM pulse signal to control the active part. In step S1, the instantaneous voltage value of the first phase is also obtained through sampling. In step S2, the virtual three-phase voltage of each phase is also obtained through the three-phase simulation. Step S3 includes the following sub-steps: Step S3-1: Analyze the virtual three-phase current of each phase using the symmetrical component method to obtain the virtual zero-sequence current of each phase. Step S3-2: Obtain the effective voltage value of each phase based on the virtual three-phase voltage of each phase; Step S3-3: Compare the instantaneous voltage value of each phase with the effective voltage value of each phase to obtain the first pulse sequence of each phase; Step S3-4: Compare the virtual zero-sequence current of each phase with 0 to obtain the second pulse sequence of each phase; Step S3-5: Based on the first pulse sequence and the second pulse sequence of each phase, obtain the third pulse sequence of each phase; Steps S3-6: Based on the third pulse sequence of each phase and the predetermined filtering algorithm, obtain the filtering pulse for each phase; Step S3-7: Obtain the zero-sequence current component of each phase based on the screening pulse of each phase and the virtual zero-sequence current of each phase. Step S5 includes the following sub-steps: Step S5-1: Compare the zero-sequence current component on the neutral load side with the actual output current of the active part to obtain the error between the two. Step S5-2: Amplify the error using an amplifier; Step S5-3: Compare the amplified error with the predetermined triangular wave signal to obtain the PWM pulse signal; Step S5-4: Use the PWM pulse signal to control the IGBT power switch in the active part, thereby realizing the control of the active part.

2. The control method for the active section of the hybrid power active filter according to claim 1, characterized in that: in, The first pulse sequence is represented as: Where u a(k) Let u be the instantaneous value of the voltage. ar(k) The effective value of the voltage. The second pulse sequence is represented as follows: In the formula, i a0(k) The virtual zero-sequence current, The third pulse sequence is represented as follows: k a2(k) =k a1(k) *s a1(k) The screening pulse is represented as: k a(k) =k a2(k) +k a2(k-512) , In the formula, k a2(k-512) The pulse sequence obtained by delaying the third pulse sequence by half a fundamental period.

3. The control method for the active part of the hybrid power active filter according to claim 2, characterized in that: in, In steps S3-7, the zero-sequence current component of each phase is obtained according to the following formula: i a2(k) =k a(k) *i a0(k) 。

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