Control method and system of hybrid active power filter, and storage medium

Abstract

The invention discloses a control method and system for a hybrid active power filter and a storage medium, and the method comprises the steps: taking an inductance value and a capacitance value of a passive power filter as the input of a particle swarm optimization method, and obtaining an optimized inductance value and an optimized capacitance value; when the harmonic wave frequency filtered by the passive power filter is the same as the harmonic wave frequency filtered by the active power filter, the active power filter is equivalent to a virtual LC filter with the same structure as the passive power filter; otherwise, enabling the active power filter to be equivalent to a virtual resistor; obtaining a harmonic compensation current reference value of the active power filter; and superposing the harmonic compensation current reference value and the reactive compensation current reference value to obtain the total reference current of the active power filter, taking the total reference current as the input of a proportional resonance controller, and performing PWM modulation on the output of the proportional resonance controller. According to the invention, the harmonic current amplification problem of the passive power filter is eliminated, and the stability and compensation performance of a power system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and particularly to a control method, system and storage medium for a hybrid active power filter. Background Art

[0002] In the power system, the hybrid active power filter (HAPF) is widely used in power quality compensation due to its high reliability and flexibility. The traditional HAPF realizes harmonic suppression by connecting an active power filter (APF) and a passive power filter (PPF) in parallel, but there are the following problems:

[0003] 1. Sensor redundancy: The traditional method requires independent measurement of the load current and the PPF current to generate the APF reference current, increasing the hardware cost.

[0004] 2. Current divergence: If the total current (load current + PPF current) is used as the APF reference current, it will cause the divergence of the PPF harmonic current, trigger the overcurrent protection action, and reduce the system reliability.

[0005] 3. Insufficient stability: Existing control strategies mostly aim at single resonance suppression and do not consider the balance between the compensation effect and stability when the APF and PPF operate in coordination.

[0006] Existing solutions (such as TCLC-HAPF, adaptive control strategies) can partially alleviate the problems, but do not fundamentally solve the problems of PPF current amplification and system stability. Therefore, there is an urgent need for a collaborative design method that can eliminate harmonic amplification, reduce sensor dependence and ensure system stability. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a control method, system and storage medium for a hybrid active power filter, which can eliminate the harmonic current amplification problem of the passive power filter and improve the stability and compensation performance of the power system in view of the deficiencies of the prior art.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: A control method for a hybrid active power filter, the hybrid active power filter includes an active power filter and a passive power filter, and the active power filter and the passive power filter are connected in parallel to the power grid; the method includes the following steps:

[0009] Taking the inductance value and capacitance value of the passive power filter as the input of the particle swarm optimization method to obtain the optimized inductance value and capacitance value;

[0010] Determine the harmonic order filtered by the passive power filter according to the optimized inductance value and capacitance value. When the harmonic order filtered by the passive power filter is the same as that filtered by the active power filter, the active power filter is equivalent to a virtual LC filter with the same structure as the passive power filter; otherwise, the active power filter is equivalent to a virtual resistor.

[0011] Extract the harmonic voltage at the common coupling point of the active power filter and the passive power filter to obtain the reference value of the harmonic compensation current of the active power filter.

[0012] Superimpose the reference value of the harmonic compensation current with the reference value of the reactive power compensation current of the active power filter to obtain the total reference current of the active power filter. Use the total reference current as the input of the proportional-resonant controller, and perform PWM modulation on the output of the proportional-resonant controller to obtain the drive signal for the on-off of the switching tubes of the active power filter.

[0013] When optimizing the inductance value and capacitance value, the objective function used is: where min H is the minimum harmonic content of the grid current, I sn and I Loadn are the nth harmonic currents of the grid and the load respectively; the constraint conditions include that the power factor after compensation ≥ 0.97, and the passive power filter is inductive at the harmonic frequency.

[0014] The parameters of the virtual LC filter satisfy: L virtual = 0.98L PPF , C virtual = 0.98C PPF , where L virtual and C virtual represent the virtual inductance and virtual capacitance, and L PPF and C PPF represent the inductance and capacitance of the optimized passive power filter.

[0015] The process of obtaining the reference value of the harmonic compensation current of the active power filter includes: using a notch filter to extract the harmonic voltage V xh at the common coupling point, input the harmonic voltage V xh into the intelligent impedance part G SI to obtain i cx_ref1 , calculate the reference value of the reactive power compensation current i Lxq according to the load condition, and add the two to obtain the reference value of the harmonic compensation current i cx_ref = i cx_ref1 + i Lxq ; icx_ref1 = G SI ·V xh .

[0016] X SI represents the intelligent impedance value, G BPF represents the band-pass filter, Num represents the compensation rate coefficient, L virtual = 0.98L PPF , C virtual = 0.98C PPF , L virtual and C virtual represent the virtual inductor and virtual capacitor;

[0017] When the active power filter is used as a virtual resistor:

[0018]

[0019] When the active power filter is used as a virtual LC filter:

[0020]

[0021] X PPF represents the harmonic reactance of the passive power filter, X s represents the harmonic reactance of the grid inductor, K C represents the compensation rate of the active power filter for harmonics, I cn and I Loadn are respectively the nth harmonic current compensated by the active power filter and the nth harmonic current of the load.

[0022] Where Q Total represents the total reactive power demand, Q PPF represents the reactive power compensated by the passive power filter, V pcc represents the effective value of the line voltage at the point of common coupling.

[0023] The transfer function G i (s) of the proportional resonance controller is: Where K p is the proportional coefficient, K rn is the resonance coefficient of the nth harmonic, ω cn is the bandwidth of the proportional resonance controller, ω0 is the fundamental angular frequency of the grid, and s is the Laplace operator.

[0024] When the grid frequency deviation exceeds the set value, return to re-optimize the inductance value and capacitance value of the passive power filter.

[0025] As an inventive concept, the present invention also provides a control system for a hybrid active power filter, 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.

[0026] As an inventive concept, the present invention also provides a computer-readable storage medium, on which a computer program / instructions are stored; when the computer program / instructions are executed by a processor, the steps of the above method are implemented.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Eliminate harmonic amplification: Simulation and experiments show that the method of the present invention can reduce the PPF current harmonic amplification rate to below 0.17 (0.41 for the traditional method), effectively avoiding the triggering of overcurrent protection.

[0029] 2. Improve compensation performance: When the APF is used as a virtual LC filter, the total harmonic distortion (THD) of the grid current is reduced from 27% to 5.3%, which is better than 10.4% in the virtual resistance mode.

[0030] 3. Enhance reliability: Through PSO optimization (particle swarm optimization) and intelligent impedance control, the system still operates stably when the grid frequency fluctuates by ±0.5 Hz. Description of the Drawings

[0031] Figure 1 It is a circuit structure diagram of the HAPF system, including the connection modes of the APF, PPF and the load.

[0032] Figure 2 It is a comparison of different current detection positions (point A and point B), explaining the mechanism of the divergence of the PPF current caused by the total current detection.

[0033] Figure 3 It is the harmonic equivalent circuit (before and after compensation) under the traditional control strategy.

[0034] Figure 4 It is the transfer function I Ph (s) / I Loadh (s) system block diagram, revealing the existence of right half-plane poles.

[0035] Figure 5 It is the zero-pole distribution diagram of the system based on intelligent impedance control, showing the improvement of system stability.

[0036] Figure 6 It is the PPF parameter optimization flowchart, showing the iterative process of the PSO algorithm.

[0037] Figure 7 It is the current harmonic content after filtering by the PPF designed by PSO, indicating that the grid current harmonics are effectively reduced.

[0038] Figure 8 It is I sn / I LoadnThe amplitude-frequency characteristic curve indicates that the nth harmonic will not be amplified.

[0039] Figure 9 It is the comparison of the harmonic residue rates under different compensation modes, highlighting the advantages of the virtual LC filter.

[0040] Figure 10 It is the overall block diagram of the intelligent impedance control strategy, including the harmonic extraction, impedance generation, and current control modules.

[0041] Figure 11 For i px and i cx The simulation waveforms: (a) under the traditional control strategy; (b) the control strategy proposed in the embodiment of the present invention.

[0042] Figure 12 For v when the APF is used as a virtual resistor x 、i sx 、i cx 、i px 、i Loadx and the experimental waveforms of THD.

[0043] Figure 13 For v when the APF is used as a virtual LC filter x 、i sx 、i cx 、i px 、i Loadx and the experimental waveforms of THD. Specific implementation manners

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below 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 shall fall within the protection scope of the present invention.

[0045] Embodiment 1

[0046] This embodiment provides a collaborative design and harmonic suppression method for a hybrid active power filter based on intelligent impedance, including the following steps:

[0047] 1. Analysis of the PPF harmonic current amplification mechanism: Establish the harmonic equivalent circuit of the HAPF, and reveal the reason for the divergence of the PPF current from the perspectives of the circuit and frequency domain. When compensating with point B (the sum of the load current and the PPF current) as the sampling point of the APF reference current, the APF compensation current will increase the PPF current, and the increased current will be used as the reference value of the APF compensation current, resulting in the divergence of the APF compensation current and the PPF current, and finally causing the PPF overcurrent protection to stop. By analyzing the transfer function and zero-pole diagram of the system, it can be seen that there are right-half plane poles in the system at this time, leading to system instability.

[0048] 2. PPF optimization design: Optimize the PPF parameters according to the load reactive power and the number of filtering times. The optimization goal is to minimize the harmonic content of the grid current. The constraint conditions include avoiding over-compensation of reactive power (limiting the power factor after compensation to 0.97, and calculating the reactive power compensated by the PPF accordingly) and avoiding harmonic amplification of the grid current (ensuring that the PPF is inductive at the harmonic frequency. Considering the grid frequency fluctuation and the uncertainty of component parameters, set the resonance frequency of the PPF to 97% of the rated harmonic frequency). Use the particle swarm optimization (PSO) algorithm to optimize the PPF parameters. The specific steps are as follows:

[0049] 1) Initialize the particle position (X i represents the PPF inductance value, and the capacitance and inductance values are restricted by the boundary conditions) and velocity.

[0050] 2) Calculate the fitness value of the particle according to the fitness function, and select the harmonic content optimization goal as the fitness function.

[0051] 3) Compare the fitness value of each particle with its historical individual optimal value. If it is better, update the individual optimal value.

[0052] 4) Compare the individual fitness value of each particle with the global optimal fitness value. If it is better, update the global optimal value.

[0053] 5) Update the position and velocity of the particle according to the basic principle of the particle swarm.

[0054] 6) Check whether the termination condition is met (reaching the minimum fitness value or the maximum number of iterations). If not, update the inertia weight and return to step 2).

[0055] 3. APF intelligent impedance control strategy:

[0056] 1) Virtual LC filter mode: For the harmonics compensated by PPF (such as the 5th harmonic), the APF is equivalent to a virtual LC filter with the same structure as the PPF. Calculate the compensation rate of the APF for the 5th harmonic current, the residual rate of the 5th harmonic on the grid side, and the harmonic suppression rate at different impedance values. By comparison, it can be seen that when the APF operates as a virtual LC filter, better harmonic suppression effects can be achieved on the grid side. Therefore, in the case of other low-order harmonics not compensated by the PPF, the APF can operate as a resistor; while when compensating for harmonics with the same frequency as the PPF, the APF is more suitable to operate as an LC filter identical to the PPF to enhance the harmonic suppression effect. The specific control process is as follows:

[0057] S1. Extract the harmonic voltage of the point of common coupling (PCC) through a notch filter;

[0058] S2. Obtain the reference value of the APF harmonic compensation current through the intelligent impedance part;

[0059] S3. Add the reference value of the reactive power compensation current to obtain the reference value of the APF compensation current;

[0060] S4. Obtain the gate signal through APF current control and pulse width modulation (PWM).

[0061] 2) Virtual resistor mode: For low-order harmonics (such as the 7th, 11th, and 13th harmonics) without PPF configured, the APF is equivalent to a resistor. Calculate the compensation rate of the APF for the 5th harmonic current, the residual rate of the 5th harmonic on the grid side, and the harmonic suppression rate at different impedance values, and obtain the impedance values required for different load harmonic current compensation rates to suppress the remaining harmonics.

[0062] 4. PPF stability analysis: Based on the proposed intelligent impedance control strategy, establish the harmonic equivalent circuit of the HAPF system, calculate the transfer function of the system and draw the zero-pole diagram. The results show that there are no poles in the right half plane of the system, the PPF current will not diverge, and the system is stable.

[0063] Grid parameters: Line voltage 10 kV, frequency 50 Hz, grid inductance L s = 0.3 mH.

[0064] PPF parameters: After optimization by PSO, the inductance L of the passive filter PPF = 5.28 mH, the capacitance C of the passive filter PPF = 81.7 μF. Use the optimized PPF to filter the grid harmonics, and the results of the harmonic content after filtering are as Figure 7 shown. After compensation by the PPF, the harmonics of the grid current are reduced to about 0.5 times that of the load current harmonics. Figure 8 It is I sn / I LoadnThe amplitude-frequency characteristic curve shows that the nth load harmonic will not be amplified in the power grid, indicating good optimization effect.

[0065] APF control parameters: proportional coefficient K p = 1.2, resonance coefficient K rn = 10, bandwidth ω cn = 15 rad / s. Figure 9 Shows the harmonic residue rate K c on the grid side obtained by using two different schemes of virtual resistance and virtual LC filter under a series of the same load harmonic current compensation rates K h . It is easy to find that when compensating the same-order harmonics as the PPF, the APF operating as an LC filter can obtain lower harmonic residues, and at this time, the optimal effect of simultaneously compensating the grid harmonics by the parallel connection of the APF and the PPF can be achieved; when compensating different-order harmonics from the PPF, the APF can operate in the virtual resistance mode, that is, the intelligent impedance adaptive control technology, Figure 10 which is the overall control block diagram of this technology.

[0066] Figure 10 In it, the PPF is in the state after PSO optimization of parameters and is directly connected in parallel to the power grid as a separate filter. In the APF part, first, the load harmonic current i Lx on the power grid is extracted, and the q-axis component i Lq is obtained through a 3 / 2 transformation. Subsequently, the DC component of i Lq is obtained through a low-pass filter, and finally, the reference reactive power compensation current i Lxq is obtained through a 2 / 3 transformation. At the same time, the harmonic voltage at the coupling point is extracted through a notch filter, and the APF harmonic compensation current reference value i SI is obtained through the intelligent impedance part G cxh_ref . This current is added to the compensation current i cx output by the APF and forms a negative feedback with i Lxq to obtain the final drive current signal, which is modulated by PI to generate a PWM signal and input into the inverter of the APF to complete the task of jointly filtering harmonics with the PPF.

[0067] ● Simulation platform: Build an HAPF model based on MATLAB / Simulink, and the load includes a linear load (RL series) and a nonlinear load (diode rectifier).

[0068] · Experimental results:

[0069] Figure 11 Indicates the APF compensation current i cx and the PPF output current ipx simulation results. Under traditional control, the APF compensation current i cx and the PPF output current i px diverge severely (exceeding 1000 A), while under the proposed method, the APF compensation current i cx and the PPF current i px are stable (not exceeding 500 A), indicating that under the traditional current compensation strategy, the APF compensation current i cx and the PPF output current i px diverge, while the control strategy proposed based on the embodiments of the present invention does not cause the divergence of the two currents;

[0070] Figure 12 represents the experimental waveforms of v x 、i sx 、i cx 、i px 、i Loadx and THD when the APF acts as a virtual resistor. It can be found from the figure that the harmonic THD is 27.1% on the load side. After filtering by the APF and PPF together, it is reduced to 10.4%, having a certain filtering effect. At this time, the voltage waveform is basically sinusoidal, and the current waveform has a certain distortion.

[0071] Figure 13 represents the experimental waveforms of v x 、i sx 、i cx 、i px 、i Loadx and THD when the APF acts as a virtual LC filter. It can be found from the figure that the harmonic THD is 27.1% on the load side. After filtering by the APF and PPF together, it is reduced to 5.3%, having an excellent filtering effect. At this time, both the voltage and current waveforms are basically sinusoidal. Compared with Figure 12 it can be found that when the APF acts as a virtual LC filter, the THD of the grid current is smaller (reduced from 10.4% to 5.3%), and the grid current waveform is closer to sinusoidal, indicating that at the same compensation current, the residual rate of harmonic current is lower and the harmonic compensation effect is better.

[0072] Embodiment 2

[0073] Embodiment 2 of the present invention provides a control 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.

[0074] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk memory.

[0075] In other implementations, the processor may be various types of general-purpose processors such as a central processing unit (CPU) or a digital signal processor (DSP), which is not limited herein.

[0076] Embodiment 3

[0077] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to Embodiment 1 above, on which computer programs / instructions are stored. When the computer programs / instructions are executed by a processor, the steps of the method in Embodiment 1 above are implemented.

[0078] A computer-readable storage medium may be a tangible device that holds and stores instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the above.

[0079] Those skilled in the art should understand that the embodiments of the present application may be provided as a method, a system, or a computer program product. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program code. The solutions in the embodiments of the present application may be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0080] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0081] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operational steps are executed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions for implementing the functions specified in one process or a plurality of processes and / or boxes Figure 1 one process or a plurality of processes and / or boxes Figure 1 steps for implementing the functions specified in one box or a plurality of boxes.

[0082] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to cover the preferred embodiments as well as all changes and modifications falling within the scope of the present application.

[0083] 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 control method for a hybrid active power filter, the hybrid active power filter comprising an active power filter and a passive power filter, the active power filter and the passive power filter being connected in parallel to the power grid; characterized in that, Including the following steps: Taking the inductance value and capacitance value of the passive power filter as the input of the particle swarm optimization method to obtain the optimized inductance value and capacitance value; Determining the harmonic order filtered by the passive power filter according to the optimized inductance value and capacitance value. When the harmonic order filtered by the passive power filter is the same as that filtered by the active power filter, the active power filter is equivalent to a virtual LC filter with the same structure as the passive power filter; Otherwise, the active power filter is equivalent to a virtual resistor; Extracting the harmonic voltage at the common coupling point of the active power filter and the passive power filter to obtain the reference value of the harmonic compensation current of the active power filter; Superimposing the reference value of the harmonic compensation current and the reference value of the reactive power compensation current of the active power filter to obtain the total reference current of the active power filter, taking the total reference current as the input of the proportional resonance controller, and performing PWM modulation on the output of the proportional resonance controller to obtain the driving signal for the on / off of the switching tubes of the active power filter.

2. The control method of the hybrid active power filter according to claim 1, characterized in that, When optimizing the inductance value and capacitance value, the objective function adopted is as follows: where min H is the minimum harmonic content of the grid current, I sn and I Loadn are the nth harmonic currents of the grid and the load respectively; the constraint conditions include that the power factor after compensation is ≥ 0.97, and the passive power filter is inductive at harmonic frequencies.

3. The control method of the hybrid active power filter according to claim 1, characterized in that The parameters of the virtual LC filter satisfy: L virtual = 0.98L PPF , C virtual = 0.98C PPF , where L virtual and C virtual represent the virtual inductor and the virtual capacitor, and L PPF and C PPF represent the inductor and the capacitor of the optimized passive power filter.

4. The control method of the hybrid active power filter according to claim 1, characterized in that, The process of obtaining the harmonic compensation current reference value of the active power filter includes: using a notch filter to extract the harmonic voltage V at the point of common coupling xh , inputting the harmonic voltage V xh into the intelligent impedance part G SI to obtain i cx_ref1 , calculating the reactive power compensation current reference value i according to the load condition Lxq , adding the two to obtain the harmonic compensation current reference value i of the active power filter cx_ref = i cx_ref1 + i Lxq ; icx_ref1 = G SI · V xh .

5. The control method of the hybrid active power filter according to claim 4, wherein X SI represents the intelligent impedance value, G BPF represents the band - pass filter, Num represents the compensation rate coefficient, L virtual = 0.98L PPF , C virtual = 0.98C PPF , L virtual and C virtual represent the virtual inductor and the virtual capacitor; When the active power filter is used as a virtual resistor: When the active power filter is used as a virtual LC filter: X PPF represents the harmonic reactance of the passive power filter, X s represents the harmonic reactance of the grid inductance, K C represents the compensation rate of the active power filter for harmonics, I cn and I Loadn are the nth harmonic current compensated by the active power filter and the nth harmonic current of the load, respectively.

6. The control method of the hybrid active power filter according to claim 4, wherein where Q Total represents the total reactive power demand, and Q PPF represents the reactive power compensated by the passive power filter, and V pcc represents the effective value of the line voltage at the point of common coupling.

7. The control method of the hybrid active power filter according to claim 1, wherein The transfer function G i of the proportional-resonant controller is as follows: where K p is the proportionality coefficient, K rn is the resonant coefficient of the nth harmonic, ω cn is the bandwidth of the proportional-resonant controller, ω0 is the fundamental angular frequency of the power grid, and s is the Laplace operator.

8. The control method of the hybrid active power filter according to claim 1, wherein When the grid frequency deviation exceeds the set value, return to re-optimize the inductance value and capacitance value of the passive power filter.

9. A control system for a hybrid active power filter, comprising a memory, a processor, and a computer program stored on 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.

10. A computer-readable storage medium having a computer program / instructions stored thereon; characterized in that, When the computer program / instructions are executed by the processor, the steps of the method according to any one of claims 1 to 8 are implemented.

Images