Harmonic suppression method and system for hybrid active power filtering system

Abstract

The invention discloses a hybrid active power filter system harmonic suppression method and system, and the method comprises the steps: taking the size of load harmonic and the impedance of a power grid as the input of a particle swarm optimization method, and obtaining the optimal value of a passive power filter capacitor and the optimal value of an inductor; extracting a load harmonic current ILoadh after the capacitance and inductance of the passive power filter are optimized, taking the load harmonic current ILoadh as the input of a repetitive controller and an additional damping controller, and superposing the output of the repetitive controller and the output of the additional damping controller to obtain a final harmonic compensation reference current Icxref of the active power filter; and taking the harmonic compensation reference current Icxref of the active power filter as the input of a proportional resonance controller, performing PWM (Pulse Width Modulation) on the output of the proportional resonance controller, generating a driving signal, and controlling the on-off of a switching tube of the active power filter. Harmonic amplification can be effectively eliminated, fundamental frequency resonance is suppressed, and the overall performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a harmonic suppression method and system for a hybrid active power filter system, which are used to achieve low inverter capacity requirements, wide-range reactive power compensation and harmonic suppression, eliminate the current amplification problem of a passive power filter (PPF), and improve the system stability. Background Art

[0002] The existing power filtering technologies have the following problems:

[0003] 1. Traditional hybrid active power filter (HAPF):

[0004] 1) The parameters of the passive power filter (PPF) are fixed, and it is easy to cause harmonic current amplification when acting together with the active power filter (APF), resulting in the triggering of overcurrent protection. Forcing the APF to exit the operation will lead to incomplete harmonic suppression;

[0005] 2) It is necessary to independently measure the PPF current and the load current. The cost of the sensors is high, and the total current detection may cause system instability.

[0006] 2. Traditional APF coupling impedance structure:

[0007] 1) When using a fixed coupling impedance (such as L-type, LC-type), the inverter capacity requirement is high, and the reactive power compensation range is limited;

[0008] 2) Although the adaptive impedance (IA) inverter expands the compensation range, it still needs to bear part of the reactive current, resulting in capacity pressure.

[0009] 3. Defects in control strategies:

[0010] 1) The existing damping control mainly aims at harmonic resonance, and the suppression of fundamental frequency resonance is insufficient. However, the fundamental frequency resonance is often the main reason for the HAPF resonance;

[0011] 2) There is a lack of global optimization design for the coordinated control of the PPF and the inverter.

[0012] Although the existing solutions (such as TCLC-HAPF, adaptive control strategies) can partially alleviate the problems, they do not fundamentally solve the inverter capacity optimization problem and the system stability problem of the HAPF. Therefore, there is an urgent need for a coordinated design method for the HAPF that can achieve low capacity, high stability and wide-range compensation. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a harmonic suppression method and system for a hybrid active power filter system, eliminate harmonic amplification, suppress fundamental frequency resonance, and improve the overall performance in view of the deficiencies of the existing technologies.

[0014] To solve the above technical problems, the technical solution adopted by the present invention is: a method for suppressing harmonics in a hybrid active power filter system. The hybrid active power filter system includes an injection-type adaptive impedance unit and a hybrid active filter unit; the injection-type adaptive impedance unit and the hybrid active filter unit are connected in parallel to the power grid; the hybrid active filter unit includes an active power filter and a passive power filter; the active power filter is connected to the injection-type adaptive impedance unit through a filtering inductor, and the passive power filter is connected to the power grid; the method includes the following steps:

[0015] Taking the load harmonic magnitude and the grid impedance as the inputs of the particle swarm optimization method to obtain the optimal values of the capacitance and inductance of the passive power filter;

[0016] Extracting the load harmonic current I after optimizing the capacitance and inductance of the passive power filter Loadh and using the load harmonic current I Loadh as the inputs of the repetitive controller and the additional damping controller, and superimposing the outputs of the repetitive controller and the additional damping controller to obtain the final harmonic compensation reference current I of the active power filter cx_ref ;

[0017] Using the harmonic compensation reference current I of the active power filter cx_ref as the input of the proportional resonance controller, performing PWM modulation on the output of the proportional resonance controller to generate a driving signal, and controlling the on-off of the switching tubes of the active power filter.

[0018] The method of the present invention further includes: calculating the equivalent impedance X of the injection-type adaptive impedance unit by the following formula TCR : and represent the load-side current and the grid-side harmonic voltage after delay respectively, v x is the voltage at the point of common coupling, i Lx is the load-side current. According to the mapping table between α x and the equivalent reactance X TCR , the firing angle α x is further obtained, and using the firing angle α x to generate a PWM signal to control the on-off of the thyristors of the injection-type adaptive impedance unit.

[0019] The method of the present invention further includes:

[0020] Switching the impedance mode of the active power filter according to the load harmonic characteristics, and the specific implementation process includes:

[0021] For the specific-order harmonics compensated by the passive power filter, the active power filter is equivalent to an LC filter; for the other-order harmonics uncompensated by the passive power filter, the active power filter is equivalent to a virtual resistor.

[0022] When the active power filter is equivalent to an LC filter, L v = 0.98L PPF and C v = 0.98C PPF ; L v and C v are the inductor and capacitor of the active power filter respectively; L PPF and C PPF are the optimal values of the capacitor and inductor of the passive power filter respectively.

[0023] The discrete transfer function G RC (z) of the repetitive controller is expressed as: where N is the number of sampling times, Q(z) is the auxiliary compensator, K rc is the adjustable gain of the repetitive control, z m is the phase lead compensator, S(z) is the second-order Butterworth low-pass filter, and z is the complex variable of the z-transform in the discrete domain.

[0024] The additional damping controller processes the load harmonic current I Loadh through the following steps:

[0025] Transform the current of the active power filter into the d-q coordinate system and extract the DC component using the average low-pass filter;

[0026] Compensate the high-frequency oscillation component in the d-q coordinate system through the transfer function G dq_damp (s) to generate the damping signal Δ idq_damp ;

[0027] After inverse-transforming the damping signal Δi dq_damp to the a-b-c coordinate system, the output of the additional damping controller is obtained.

[0028] R v and C v are the virtual resistor and virtual capacitor respectively, and s is the Laplace operator.

[0029] For any phase of the injection-type adaptive impedance unit, it includes a first branch and a second branch connected in parallel. The first branch includes a first inductor and a switch tube module connected in series with the first inductor. The switch tube module includes two switch tubes connected in parallel; the second branch includes a first capacitor; the output ends of the first branch and the second branch are both connected to a second capacitor through a second inductor.

[0030] Through the above method, it is possible to eliminate potential resonance and harmonic amplification between the APF and the IACI, and between the APF and the PPF.

[0031] First, suppress the fundamental frequency resonance existing between the APF and the IACI through additional damping control. In the d-q coordinate system, introduce damping through the transfer function This design is equivalent to adding a negative resistance characteristic at the fundamental frequency to offset the original positive feedback oscillation trend of the system. Through repetitive control technology Precisely track periodic harmonics. Its low-pass filter S(z) suppresses high-frequency noise and avoids interfering with the fundamental frequency control loop. After inverse-transforming the damping signal to the a-b-c coordinate system, it is superimposed on the reference current to change the phase and amplitude of the APF output current, destroying the phase condition of the fundamental frequency resonance. Finally, the suppression of the fundamental frequency resonance is achieved.

[0032] Secondly, eliminate harmonic amplification when the APF and the PPF work together through an intelligent impedance switching strategy. First, use the particle swarm optimization (PSO) algorithm to set the parameters of the PPF to the optimized PPF parameters to ensure that its impedance is inductive at harmonic frequencies, avoid forming a parallel resonance with the grid impedance, and thus block the harmonic current amplification path. At the same time, in cooperation with the intelligent impedance switching strategy, for the harmonics compensated by the PPF, the APF is equivalent to an LC filter; for the uncompensated harmonics, the APF is equivalent to a virtual resistor. By changing the equivalent impedance characteristic of the APF, block the positive feedback loop of the harmonic current between the APF and the PPF. When the APF is equivalent to an LC filter, its parameters are set as L v = 0.98L PPF 、C v = 0.98C PPF . By slightly reducing the resonance frequency, avoid coinciding with the inherent resonance point of the PPF, destroy the harmonic amplification condition, and finally achieve the suppression of harmonic amplification.

[0033] As an inventive concept, the present invention also provides a harmonic suppression system for a hybrid active power filter system, including a memory, a processor, and a computer program stored on the memory; the processor executes the computer program to implement the steps of the above method.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. Capacity reduction: Simulation and experiments show that the proposed method can reduce the inverter capacity requirement by 30% compared with the traditional LC type, and the total current distortion rate THD ≤ 5%.

[0036] 2. Wide-range compensation: The reactive power compensation range is extended to ±50% of the rated capacity, and the power factor PF ≥ 0.98.

[0037] 3. Improved stability: The PPF harmonic magnification ratio ≤ 0.2, and the fundamental frequency harmonic amplitude attenuation ≥ 20 dB. Description of the Drawings

[0038] Figure 1 It is the overall system structure diagram, including IACI, HAPF, and the control module;

[0039] Figure 2 It is the working principle of the IACI-APF inverter, where IAIC is used to provide reactive current, and APF is used to provide harmonic compensation current;

[0040] Figure 3 It is the IACI equivalent circuit;

[0041] Figure 4 It is the schematic diagram of the reactive power compensation IACI control principle;

[0042] Figure 5 It is the schematic diagram of the comprehensive control principle of the inverter virtual impedance self-switching;

[0043] Figure 6 It is the schematic diagram of the additional damping control principle;

[0044] Figure 7 It is the design flow chart of the optimal PPF parameters;

[0045] Figure 8 It is the PCC voltage v coupling different types of impedance units x , grid current i sx , load current i Lx , compensation current i cx , inverter current i ix , load capacity S L , inverter capacity S i and the waveforms of the source side current THD; (a) L-APF type; (b) LC-APF type; (c) IACI-APF type proposed by the present invention;

[0046] Figure 9 It is the PCC voltage v x , grid current i sx , inverter current i ix and inverter capacity S i simulation waveforms with and without additional damping control. Detailed Implementation Manner

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0048] In this text, terms such as "first", "second", and other similar terms do not imply any order, quantity, or importance, but are only used to distinguish different elements. In this text, terms such as "a", "an", and other similar terms do not mean that there is only one of the described things, but mean that the relevant description only refers to one of the things, and the thing may have one or more. In this text, terms such as "comprising", "including", and other similar terms are intended to represent logical relationships and should not be regarded as representing spatial structural relationships. For example, "A includes B" is intended to mean that logically B belongs to A, rather than meaning that B is located inside A in space. Additionally, the meanings of terms such as "comprising", "including", and other similar terms should be regarded as open-ended rather than closed-ended. For example, "A includes B" is intended to mean that B belongs to A, but B does not necessarily constitute all of A, and A may also include other elements such as C, D, E, etc.

[0049] Embodiment 1

[0050] Main circuit: Injection-type adaptive impedance (IACI) unit: It includes capacitor CIA, thyristor-controlled reactor (TCR), and L1-C1 fundamental frequency resonance circuit, and is used for wide-range reactive power compensation.

[0051] Hybrid active power filter (HAPF) unit: It is composed of a parallel connection of APF and PPF. APF is connected to IACI through Lf instead of the power grid to reduce voltage stress.

[0052] PPF optimization design: The particle swarm optimization (PSO) algorithm is used to optimize the L PPF and C PPF of PPF. The objective function is to minimize the harmonic content of the grid current, and the constraint conditions include power factor PF≥0.98 and resonance frequency lower than 99% of the rated harmonic frequency.

[0053] Injection-type coupling impedance IACI control: Based on the TCR triggering angle αx, the equivalent reactance LTCR is adjusted to achieve dynamic reactive power compensation; the relationship between X TCR and αx is mapped through a look-up table (LUT) to ensure that V x +I cxf X TCR =0, reducing the voltage stress of the inverter.

[0054] Additional damping control: In the d-q coordinate system, the DC component of the inverter current is extracted through a moving average filter (MAF); a series virtual resistor R v and capacitor C v are used to suppress fundamental frequency resonance, and the transfer function is:

[0055]

[0056] Inverter virtual impedance self-switching control: For the harmonics compensated by the PPF (such as the 5th harmonic), the APF is equivalent to a virtual LC filter, and the resonance frequency is set to 97% of the target harmonic frequency; for the uncompensated low-order harmonics (such as the 7th, 11th, and 13th harmonics), the APF is equivalent to a virtual resistor.

[0057] Global cooperative control: The outer loop uses a repetitive controller (RC) in parallel with a proportional controller and virtual impedance self-switching control to compensate for harmonic currents; the inner loop realizes current tracking through a proportional-resonant (K p_in ) controller and combines with PWM to generate drive signals.

[0058] The specific implementation process of this embodiment includes:

[0059] S1. Optimize the parameters of the passive power filter (PPF) through the particle swarm optimization (PSO) algorithm

[0060] The function of the PPF is to filter out harmonics. It has a relatively large filtering capacity and can withstand large harmonic currents, but its parameters are fixed. The design of the PPF parameters needs to comprehensively consider various factors, so the PSO algorithm is used for comprehensive calculation. Taking the magnitude of the load harmonics and the grid impedance as inputs, and minimizing the total harmonic distortion rate (THD) of the grid current as the objective function, combined with the constraint conditions (the power factor PF ≥ 0.98 after compensation, the resonance frequency of the PPF is lower than 99% of the rated harmonic frequency), the optimal inductance value L PPF and capacitance value C PPF of the PPF are optimized. The PPF designed according to the optimal values is connected in parallel to the grid. where M is to minimize the total harmonic distortion rate (THD) of the grid power, I Sn and I Ln are the nth harmonic currents of the grid and the load respectively.

[0061] S2. Generate the reference current of the active power filter (APF) based on the optimized PPF parameters

[0062] The APF extracts the load harmonic current I Loadh filtered by the above PPF in real time and inputs it to the repetitive controller (RC) and the additional damping control module, where:

[0063] The repetitive controller passes through the discrete transfer function Track the periodic harmonic components.

[0064] The additional damping control transforms the inverter current into the d-q coordinate system. After extracting the DC component through a moving average filter (MAF), a virtual resistor R is connected in series v with the capacitor C v to generate a damping signal to suppress the fundamental frequency resonance;

[0065] The virtual impedance self-switching control extracts the harmonic voltage at the point of common coupling (PCC) through a notch filter and passes it through the self-switching impedance part (G ss ).

[0066] Superimpose the output of the repetitive controller and the damping signal to generate the final APF harmonic compensation reference current I cx_ref .

[0067] S3. Dynamically adjust the reactive power compensation ability of the injection-type adaptive impedance (IACI)

[0068] Between the APF and the power grid, an IACI module is connected in series. This module can, on the basis of the APF filtering out harmonics, also achieve wide-range reactive power compensation. According to the voltage V at the point of common coupling (PCC) x and the load reactive power Q L , through the preset firing angle α x and the equivalent reactance X TCR lookup table (LUT), adjust the firing angle α of the thyristor-controlled reactor (TCR) x so that the equivalent impedance of the IACI satisfies X TCR =-V x / I cxf to achieve wide-range reactive power compensation.

[0069] In the embodiment of the present invention, an IACI circuit module is connected in series between the APF and the power grid. This module can increase the reactive power compensation range of the APF while not interfering with the APF harmonic compensation. However, it is found in the application that resonance may also occur between the IACI and the APF. Therefore, the above method is used to achieve wide-range reactive power compensation.

[0070] S4. Drive the APF to track the reference current and suppress harmonics

[0071] Input the APF reference current I generated in step S2 cx_ref into the proportional-resonant (K p_in ) controller, combine it with pulse width modulation (PWM) to generate a drive signal, control the APF to output the compensation current I cx , and at the same time switch the APF virtual impedance mode according to the load harmonic characteristics.

[0072] For the harmonics compensated by the PPF (such as the 5th harmonic), the APF is equivalent to a virtual LC filter with parameters L v = 0.98L PPF , C v = 0.98C PPF .

[0073] For the uncompensated low-order harmonics (such as the 7th, 11th, and 13th harmonics), the APF is equivalent to a virtual resistor R SI , and its value is dynamically adjusted according to the load harmonic compensation rate K c .

[0074] S5. Real-time monitoring and protection:

[0075] Monitor the amplitude of the PPF current. If it exceeds the threshold, switch the APF to the virtual resistor mode to avoid the risk of overcurrent.

[0076] Parameter settings

[0077] · Grid parameters: Line voltage 10 kV, frequency 50 Hz, grid inductance L s = 0.2 mH.

[0078] · HAPF parameters: After optimization by PSO, L PPF = 5.28 mH, C PPF = 81.7 μF.

[0079] · Control parameters: Proportional coefficient K p = 1.5, Krc = 3, Rv = 15 Ω, Cv = 0.03 F.

[0080] Experimental verification

[0081] · Simulation platform: Build an HAPF model based on MATLAB / Simulink. The load includes a linear load (parallel capacitor) and a nonlinear load (rectifier bridge). Compare the performance of the proposed hybrid active power filter (HAPF) with that of the traditional coupled inductor L-type and inductor-capacitor LC-type.

[0082] · Experimental results:

[0083] 1) The THD of the grid current is reduced from 27% to 4.5%, and the PPF current does not diverge;

[0084] 2) The capacity of the APF inverter is reduced by 28% compared with the traditional L-type, and the fundamental frequency harmonic amplitude attenuation is ≥ 25 dB.

[0085] Figure 3 Shows the equivalent circuit model of the dynamically adjustable injection-type adaptive impedance (IACI) at harmonic frequencies. Its core purpose is to illustrate how the IACI avoids harmonic pollution of the power grid generated by the TCR through circuit design.

[0086] Figure 3 The "v" in x represents the harmonic voltage on the grid side, and "L" s represents the equivalent inductance on the grid side. The harmonic current source (i TxIh ) represents the characteristic harmonics generated by the TCR. According to the KCL (Kirchhoff's Current Law), the harmonic current i TxIh generated by the TCR will only IA be shunted between the capacitor C fh and the fundamental resonance circuit L fh -C IA . The parallel capacitor C fh -C fh presents a low impedance at harmonic frequencies and provides the main path for harmonic current. The series L IA -C fh fundamental frequency resonance circuit has an impedance close to zero at the fundamental frequency (50 Hz) to support reactive power compensation, but presents a high impedance at harmonic frequencies, forming a barrier to block the flow of harmonics to the grid, so that most of the harmonic current returns locally through C fh , and a very small part flows into the grid through L

[0087] Figure 4 -C Lx , thus realizing harmonic isolation and reducing system complexity without affecting the fundamental reactive power function. x , respectively, after a delay of π / 2, and jointly pass through the power and voltage calculation link to obtain the load reactive power q Lx , and at the same time obtain the equivalent voltage V x . The calculation expression of this link is where and represent the load side current and the grid side harmonic voltage after delay respectively, and the meanings of other symbols are the same as before. Then, the fundamental reactive power of the load is obtained through the low-pass filter LPF . After that, according to the look-up table (LUT), the trigger angle α x can be obtained. Finally, by comparing α x with the phase angle θ x of the voltage at the PCC, a thyristor control trigger signal can be generated, and the phase angle θ x can be obtained by using a phase-locked loop (PLL).

[0088] Figure 5 For the schematic diagram of the integrated control of the virtual impedance self-switching of the inverter, first, the compensation current i cx , the load current i Lx , and the voltage v x at the PCC are used to extract their respective harmonic components icxh , i Lxh and v xh . i cxh i is Lxh subjected to negative feedback and then repetitive control G RC and proportional controller K p_out , v xh is subjected to self - switching impedance part G SS . The signals processed by these three are superimposed and subjected to negative - feedback regulation with the current signal after additional damping. Through output regulation coefficient K p_in it is output to the PWM signal generator to obtain a trigger signal for controlling the devices in the APF inverter. The specific connection forms of each link can be seen in Figure 6 .

[0089] Figure 6 shows the block diagram of the repetitive control with an additional damping strategy. Its core objective is to suppress the fundamental - frequency resonance between the inverter and the IACI while achieving harmonic compensation. This control strategy consists of a compensation - current outer loop and an inverter - current inner loop: the outer loop regulates the harmonic components of the compensation current through proportional controller K p_out and parallel repetitive controller G RC (s); the inner loop achieves fast tracking of the inverter current through proportional controller K p_in and a delay link; the additional - damping control part converts the inverter current to the d - q coordinate system through Park transformation, extracts the DC component using a moving - average filter (MAF), processes it through virtual resistor R v and capacitor C v , and then reconstructs it into a three - phase signal through inverse Park transformation and superimposes it on the reference current, thereby suppressing the fundamental - frequency resonance between the inverter and the IACI while effectively compensating for load harmonics and reactive power, and finally forming a complete closed - loop control system.

[0090] Figure 8 For the PCC voltage v x , of different types of inverters, grid current i sx , load current i Lx , compensation current i cx , inverter current i ix , load capacity S L , inverter capacity S iAnd the waveforms of the source - side current THD. Before 100 ms, only the nonlinear load is applied. After 100 ms, the linear load is added. According to the grid - current waveforms and THD, all these types of inverters can guarantee the reactive - power and harmonic - compensation performance. When the nonlinear load is applied, the THDs of the grid current compensated by the L - type, LC - type, and IACI - APF - type coupling impedance units are 2.78%, 4.21, and 1.07% respectively. After adding the linear load, the THDs of the grid current compensated by the L - type, LC - type, and IACI - APF - type coupling impedance units are 2.15%, 2.21%, and 0.72% respectively. Through comprehensive comparison, it is found that the L - type requires the largest capacity, the LC - type can only guarantee a small capacity under small loads, while the proposed IACI - type can perform effective reactive - power compensation in a wide range and still meet the requirements with a very small capacity under large loads. Moreover, the adaptive impedance can not only withstand the fundamental - frequency voltage stress but also block the reactive current from flowing to the APF, avoiding unnecessary capacity waste.

[0091] Figure 9 For the PCC voltage v x 、grid current i sx 、inverter current i ix and inverter capacity S i simulation waveforms. Before and after 100 milliseconds are with and without damping control respectively. When the damping control exists, the fundamental - frequency component of the APF inverter current is very small. When the additional damping control is removed, the fundamental - frequency component of the APF inverter current and the inverter - capacity requirement increase.

[0092] Embodiment 2

[0093] Embodiment 2 of the present invention provides a suppression system corresponding to Embodiment 1 above, including a memory, a processor, and a computer program stored on the memory; the processor executes the computer program on the memory to implement the steps of the method in Embodiment 1 above.

[0094] In some implementations, the memory may be a high - speed random - access memory (RAM: Random Access Memory), and may also include non - volatile memory, such as at least one disk memory.

[0095] In other implementations, the processor may be a central - processing unit (CPU), a digital - signal processor (DSP), or various types of general - purpose processors, which are not limited herein.

[0096] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present application.

[0097] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A method for suppressing harmonics in a hybrid active power filter system, wherein the hybrid active power filter system comprises an injection type adaptive impedance unit and a hybrid active filter unit; the injection type adaptive impedance unit and the hybrid active filter unit are connected to a power grid in parallel; the hybrid active filter unit comprises an active power filter and a passive power filter; the active power filter is connected to the injection type adaptive impedance unit via a filter inductor, and the passive power filter is connected to a power grid; the method is characterized in that: The method comprises the following steps: The load harmonics and grid impedance are used as inputs of the particle swarm optimization method to obtain the optimal values ​​of the passive power filter capacitor and inductor. Extract the load harmonic current I after optimizing the passive power filter capacitance and inductance Loadh , the load harmonic current I Loadh As the input of the repetitive controller and the additional damping controller, the outputs of the repetitive controller and the additional damping controller are superimposed to obtain the final active power filter harmonic compensation reference current I cx_ref ; The active power filter harmonic compensation reference current I cx_ref As the input of the proportional resonant controller, the output of the proportional resonant controller is PWM modulated to generate a drive signal to control the on and off of the active power filter switch tube.

2. The method for harmonic suppression of a hybrid active power filter system according to claim 1, characterized in that: The equivalent impedance X of the injection-type adaptive impedance unit is calculated using the following formula: TCR : and Respectively represent the load side current and grid side harmonic voltage after delay, v x is the voltage at the common coupling point, i Lx is the load side current, according to α x With equivalent reactance X TCR The mapping table between them further obtains the trigger angle α x , using the trigger angle α x Generate PWM signal to control the on and off of the thyristor of the injection type adaptive impedance unit.

3. The method for harmonic suppression of a hybrid active power filter system according to claim 1, characterized in that: Also includes: The impedance mode of the active power filter is switched according to the harmonic characteristics of the load. The specific implementation process includes: For certain harmonics that have been compensated by the passive power filter, the active power filter is equivalent to an LC filter; For other subharmonics that are not compensated by the passive power filter, the active power filter is equivalent to a virtual resistor.

4. The method for harmonic suppression of a hybrid active power filter system according to claim 3, characterized in that: When the active power filter is equivalent to an LC filter, L v =0.98L PPF , C v =0.98C PPF ; L v , C v are the inductance and capacitance of the active power filter respectively; L PPF , C PPF They are the optimal value of the capacitor and the optimal value of the inductor of the passive power filter respectively.

5. The method for harmonic suppression of a hybrid active power filter system according to claim 1, characterized in that: The discrete transfer function G of the repetitive controller is RC (z) is expressed as: Where N is the number of sampling times, Q(z) is the auxiliary compensator, K rc For repetitive control of adjustable gain, z m is a phase lead compensator, S(z) is a second-order Butterworth low-pass filter, and z is the complex variable of z-transform in discrete domain.

6. The method for harmonic suppression of a hybrid active power filter system according to claim 1, characterized in that: The additional damping controller controls the load harmonic current I Loadh A process comprising the following steps is performed: The current of the active power filter is transformed into the dq coordinate system, and the DC component is extracted using an average low-pass filter; By transferring the function G dq_damp (s) Compensate the high-frequency oscillation component in the dq coordinate system to generate a damping signal Δi dq_damp ; The damping signal Δi dq_damp After inverse transformation to the abc coordinate system, the output of the additional damping controller is obtained.

7. The method for harmonic suppression of a hybrid active power filter system according to claim 6, characterized in that: R v , C v are virtual resistance and virtual capacitance respectively; s is the Laplace operator.

8. The method for harmonic suppression of a hybrid active power filter system according to claim 1, characterized in that: For any phase of the injection-type adaptive impedance unit, it includes a first branch and a second branch in parallel, the first branch includes a first inductor and a switch tube module connected in series with the first inductor, and the switch tube module includes two switch tubes in parallel; the second branch includes a first capacitor; the output ends of the first branch and the second branch are both connected to the second capacitor through the second inductor.

9. A hybrid active power filter system harmonic suppression system, comprising a memory, a processor and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 8.

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