A specified harmonic compensation method for a hybrid active filter

Abstract

The application discloses a specified harmonic compensation method of a hybrid active filter, which simulates a virtual capacitor for a voltage source inverter in a harmonic domain, and the capacitor value can be adaptively adjusted by a perturbation and observation method, so that the LC filter and the virtual capacitor can generate series resonance at a specified harmonic frequency, and the effect of a multi-tuned filter is achieved, thereby greatly improving the filtering characteristic of the LC single-tuned filter; the control method has the advantages of simple control structure, easy implementation and good filtering effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of harmonic compensation of power quality control, and particularly relates to a specified harmonic compensation method of a hybrid active filter. BACKGROUND

[0002] The continuous growth of power electronic devices such as nonlinear loads and distributed power supplies has brought serious harmonic pollution to power systems. Harmonics can reduce power quality, affect power grid operation reliability, cause line energy loss and endanger equipment safety, etc. The traditional method for governing harmonic pollution in power systems mainly uses passive power filters (PPF). PPF is generally composed of single-tuned or multi-tuned LC filters, which provides a low impedance path for specific harmonic currents to achieve the purpose of harmonic filtering. Although PPF has the advantages of low cost and high efficiency, it also has some inherent disadvantages, such as frequency drift and parameter changes of components, which will cause detuning, and it is easy to cause series / parallel resonance with grid line impedance. Active power filters (APF) can make up for the shortcomings of PPF. Compared with PPF, APF is more flexible and efficient, but pure APF needs a large-capacity voltage source inverter (VSI), which is expensive, and has the disadvantage of low cost performance in high-voltage or high-power applications. Hybrid active filters, as a combination of PPF and APF, not only retain the advantages of APF, but also significantly reduce the cost of pure APF, so they have developed greatly. The control method of hybrid active filter is usually to use the active part to improve the filtering characteristics of passive filter. Since the grid harmonics are mainly odd harmonics, in order to make the hybrid active filter filter the main harmonics efficiently, a simple and stable specified harmonic filtering control method is needed to achieve effective management of grid harmonics. SUMMARY

[0003] In order to solve the problem that the prior art cannot simply and stably compensate for specified harmonics, the present application provides a specified harmonic compensation method of a hybrid active filter, which controls the active part in the hybrid active filter to be equivalent to a virtual capacitor, achieves the effect of a multi-tuned filter, and overcomes the influence of grid frequency drift and L, C parameter errors.

[0004] The technical scheme of the present application is as follows.

[0005] A specified harmonic compensation method of a hybrid active filter, comprising the following steps:

[0006] The voltage across the capacitor C in the LC single-tuned filter of the hybrid active filter is sampled to obtain the capacitor voltage v c; the capacitor voltage v C Harmonic component extraction is performed to obtain the harmonic voltage component v Ch.i , wherein i is in G, and G is a specified harmonic set, and a typical value is G = {5, 7, 11, 13, …};

[0007] According to the obtained harmonic voltage component, the output reference voltage control rate of the voltage source type inverter of the hybrid active filter for i-th harmonic compensation is v h.i = λ i · v Ch.i , wherein v h.i is the i-th component of the output reference voltage of the voltage source type inverter; λ i is a control parameter for actively tuning the i-th harmonic, and the size is adaptively adjusted by the disturbance observation method, and then the output reference voltage of the voltage source type inverter for harmonic compensation is v Harmonic compensation is achieved.

[0008] In the application, the voltage source inverter can be equivalent to a virtual capacitor, and the size is C / λ i , and the purpose is to make the LC single-tuned filter and the virtual capacitor C / λ i produce series resonance at the i-th harmonic frequency, achieve the effect of a multi-tuned filter, and overcome the influence of grid frequency drift and L and C parameter errors.

[0009] As preferred, the expression of λ i is:

[0010] , wherein λ is an initial constant value, and λ is a compensation value; and the compensation value is adaptively adjusted by the disturbance observation method.

[0011] As preferred, the process of the disturbance observation method comprises:

[0012] The power supply current i s is sampled to obtain the power supply current i s ;

[0013] Harmonic component extraction is performed on the power supply current i s to obtain the fundamental current component i sf and the i-th harmonic current component i sh.i ; and then the i-th harmonic current distortion rate THD i is calculated.

[0014] The THD i is subjected to disturbance observation, and λ = λ + Δλ

[0015] , wherein Δλ is a disturbance step;

[0015] The THD i values at adjacent time points are compared, and if THDi (k)<THD i (k-1), then sign = 1, otherwise sign = -1; until THD i is reduced to meet the condition THD i <THD i-max , then sign = 0, λ i is kept unchanged, where THD i-max is the maximum allowable value of the i-th harmonic current distortion of the power grid.

[0016] As a preference, the hybrid active filter is composed of a three-phase voltage source inverter and an LC single-tuned filter in series.

[0017] As a preference, the switching frequency of the three-phase voltage source inverter is set to 10 kHz, L is 3 Mh and C is 90 Uf in the LC single-tuned filter, and the load adopts a three-phase uncontrollable rectifier bridge with a resistance R load, where R is 10 Ω.

[0018] The substantial effects of the present application include:

[0019] I. The active part of the hybrid active filter is controlled equivalently as a virtual capacitor, which is more direct and effective than the existing virtual inductor or virtual resistance control technology, and reduces the calculation amount.

[0020] II. When the virtual capacitor control is performed by the method of the present application, the size of the virtual capacitor can be adaptively adjusted by the perturbation method, which can effectively avoid the adverse effects caused by the parameter drift of the power grid and the parameter error of L and C, and improve the harmonic suppression effect.

[0021] III. The perturbation observation quantity selected by the perturbation method of the method of the present application is the single-harmonic distortion THD i of the grid-side current, when THD i meets the requirement of the power quality index of the power grid, i.e. enters the dead zone, the perturbation ends. The advantage is that the power quality can be accurately controlled, the power quality of the power grid can be monitored, and the capacity of the inverter in the hybrid active filter can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Fig. 1 is a main circuit topology structure diagram of the hybrid active filter in the embodiment of the present application;

[0023] Figure 2 Fig. 2 is a specified harmonic compensation control structure block diagram based on the virtual capacitor in the embodiment of the present application;

[0024] Figure 3 Fig. 3 is a schematic diagram of adaptive adjustment of the virtual capacitor control parameters based on the perturbation observation method in the embodiment of the present application;

[0025] Figure 4FFT analysis diagram of the nonlinear load current waveform and its harmonic content in the embodiment of the present application;

[0026] Figure 5 FFT analysis diagram of the power supply current waveform and its harmonic content after harmonic compensation in the embodiment of the present application. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will combine the embodiments to make a clear and complete description of the technical solutions. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0028] It should be understood that, in various embodiments of the present application, the magnitude of the serial number of each process does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0029] It should be understood that, in the present application, "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0030] It should be understood that, in the present application, "B corresponding to A", "B corresponding to A", "A corresponding to B" or "B corresponding to A" means that B is associated with A, and B can be determined according to A. Determining B according to A does not mean that B is determined only according to A, but also can be determined according to A and / or other information. The matching of A and B is that the similarity of A and B is greater than or equal to a preset threshold.

[0031] The technical solutions of the present application will be described in detail in the following specific embodiments. The embodiments can be combined with each other, and the same or similar concepts or processes can not be described in some embodiments.

[0032] Embodiment:

[0033] A specified harmonic compensation method of a hybrid active filter, comprising the following steps:

[0034] The voltage across the capacitor C in the LC single-tuned filter of the hybrid active filter is sampled to obtain the capacitor voltage v c The harmonic component of the capacitor voltage v C is extracted to obtain the harmonic voltage component vCh.i , where i∈G, and G is a set of specified harmonics, typically G={5,7,11,13…};

[0035] Based on the obtained harmonic voltage components, the output reference voltage control rate of the hybrid active filter voltage source inverter for i-th harmonic compensation is set to v. h.i =λ i ·v Ch.i , where v h.i λ represents the i-th component of the output reference voltage of the voltage source inverter. i For the control parameters of active tuning for the i-th harmonic, whose magnitudes are adaptively adjusted by the disturbance observation method, the output reference voltage for harmonic compensation in the voltage source inverter is: Achieve harmonic compensation.

[0036] like Figure 1 As shown, the hybrid active power filter consists of a three-phase voltage source inverter and an LC single-tuned filter connected in series. Without loss of generality, the following analysis considers only any single-phase circuit among phases a, b, and c. In the harmonic domain, the single-phase mathematical model of the hybrid active power filter can be expressed as:

[0037]

[0038] In the formula, v sh.i v lh.i v Ch.i v h.i These are the i-th harmonic components of the power supply voltage, load terminal voltage, LC filter capacitor voltage, and voltage source inverter output voltage, respectively; i sh i lh i h These are the i-th harmonic components of the power supply current, load current, and voltage source inverter output current, respectively.

[0039] Let v h.i The control law satisfies the following relationship

[0040] v h.i =λ i ·v Ch.i (2)

[0041] In the formula, λ i The control parameters are for compensation of the i-th harmonic. In equation (1), v... Ch.i Substituting the expression into equation (2), we can see that the voltage source inverter can be equivalent to a virtual capacitor with a capacitance value of C / λ. i By choosing an appropriate λ i This allows the inductor L to be in line with the capacitor C / (1+λ). i The impedance is zero at the i-th harmonic frequency, i.e.

[0042]

[0043] From equation (3), we can get Considering the frequency ω i , the drift exists, and the L, C parameters have errors. In order to achieve better filtering effect, the λ i needs to be adaptively adjusted. λ i can be expressed as

[0044]

[0045] In the formula, is the initial constant value, and is the compensation value, which can be obtained by the disturbance observation method.

[0046] As shown in Figure 2 , the specific implementation steps of the specified harmonic compensation control based on virtual capacitance are as follows: first, the capacitor voltage v C is sampled, and the band-pass filter H i (s) is used to extract the i-th harmonic voltage v Ch.i , that is

[0047] v Ch.i = v C H i (s) (5)

[0048] In the formula, the expression of H i (s) is as follows

[0049]

[0050] In the formula, A is the passband bandwidth, and A=20π can be taken.

[0051] Then, according to formula (2) and Figure 2 , the harmonic reference voltage v output by the voltage source inverter can be expressed as the sum of the specified harmonic reference voltage, that is

[0052]

[0053] As shown in Figure 3 , the adaptive adjustment process of λ i by the disturbance observation method is as follows:

[0054] First, the power current i s is sampled, and the band-pass filter H i (s) is used to extract the fundamental current i sf and each harmonic current component i sh.i , and the i-th current distortion rate THD i is calculated, and the calculation formula is as follows

[0055]

[0056] wherein I s , I sh.i are the effective values of i sf and i sh.i , respectively.

[0057] Then, the THD i is disturbed and observed, and let

[0058]

[0059] wherein sign is the disturbance direction identifier, and Δλ is the disturbance step. The THD i values at adjacent time points are compared, if THD i (k) < THD i (k-1), then sign = 1, otherwise sign = -1; if THD i is reduced to satisfy the condition THD i <THD i-max , then sign = 0, and λ i remains unchanged, wherein THD i-max is the maximum allowable value of the i-th harmonic current distortion rate.

[0060] In order to verify the correctness and effectiveness of the specified harmonic compensation strategy of the hybrid active filter based on the virtual capacitance provided by the application, the system is modeled and simulated by using MATLAB / Simulink. The main circuit structure of the model refers to that shown in Figure 1 , the power supply adopts a three-phase power supply with a line voltage of 380V, the inverter switching frequency is set to 10kHz, L in the LC passive filter is 3Mh, C is 90Uf, the load adopts a three-phase uncontrollable rectifier bridge with a resistance Rload, R is 10Ω, and the specified harmonic compensation range is 5, 7, 11 and 13 harmonics.

[0061] In this embodiment, Figure 4 is the nonlinear load current waveform and the FFT analysis of the harmonic content thereof, it can be seen that the waveform distortion of the load current i l is serious, the total harmonic distortion rate is 26.44%, and the harmonic distortion rates of 5, 7, 11 and 13 are 22.51%, 9.90%, 7.59% and 4.23%, respectively.

[0062] Figure 5 is the power supply current waveform and the FFT analysis of the harmonic content thereof after the harmonic compensation, it can be seen that, at this time, the power supply current i sThe waveform approximation of the wave is a sine wave, and the total harmonic distortion rate is 3.60%, wherein the 5th, 7th, 11th and 13th harmonic distortion rates are reduced to 1.52%, 0.82%, 0.96% and 0.79% respectively, and the harmonic compensation effect is very excellent and obvious.

[0063] Through the description of the above embodiments, those skilled in the art can understand that, for the convenience and brevity of description, only the division of the above functional modules is exemplified, and in actual application, the above functions can be completed by different functional modules according to needs, that is, the internal structure of the specific device is divided into different functional modules to complete all or part of the functions described above.

[0064] In the embodiments provided in the present application, it should be understood that the disclosed structures and methods can be implemented in other ways. For example, the above-described embodiments of the structure are only illustrative, for example, the division of the modules or units is only a logical function division, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another structure, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed units can be indirect coupling or communication connection through some interfaces, structures or units, which can be electrical, mechanical or other forms.

[0065] The units described as separate components can or can not be physically separated, and the components shown as units can be one physical unit or multiple physical units, that is, they can be located in one place, or they can be distributed to multiple different places. Part or all of the units can be selected according to actual needs to achieve the purpose of the present embodiment.

[0066] In addition, each functional unit in the embodiments of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The above integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0067] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application essentially or say the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The software product is stored in a storage medium, including a plurality of instructions to make a device (which can be a single-chip microcomputer, a chip, etc.) or a processor execute all or part of the steps of the various embodiments of the method of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0068] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for specified harmonic compensation of a hybrid active filter, characterized by, The method comprises the following steps: The voltage across the capacitor C in the LC single-tuned filter of the hybrid active filter is sampled to obtain a capacitor voltage vc; the harmonic component of the capacitor voltage vc is extracted to obtain a harmonic voltage component , wherein , G is a specified set of harmonics, and a typical value is ; According to the obtained harmonic voltage component, the output reference voltage control rate of the voltage source type inverter of the hybrid active filter for i-th harmonic compensation is , wherein is the i-th component of the output reference voltage of the voltage source type inverter; is a control parameter actively tuned for the i-th harmonic, and the size thereof is adaptively adjusted by the disturbance observation method, and then the output reference voltage of the voltage source type inverter for harmonic compensation is , and harmonic compensation is achieved. The process of the disturbance observation method comprises: The grid-side current is sampled to obtain a power supply current is; The power supply current is is subjected to harmonic component extraction to obtain a fundamental current component isf and an i-th harmonic current component ish.i; and then an i-th harmonic current distortion rate THDi is calculated; The disturbance observation is performed on the THDi index, and let wherein is a disturbance step length; Comparing the THDi values of adjacent time instants, if THDi(k) < THDi(k-1), then , otherwise ; until THDi is reduced to satisfy the condition THDi < THDi-max, where THDi-max is the maximum allowed value of the i-th harmonic current distortion of the electrical network. , remains unchanged.

2. The method of claim 1, wherein the method is a method of specifying harmonic compensation of a hybrid active filter. The The expression is: wherein is an initial constant value, and , is a compensation value; the compensation value is self-adjusted by a perturbation observation method.

3. The method of claim 1, wherein the hybrid active filter is configured to compensate for a specified harmonic. The hybrid active filter is composed of a three-phase voltage source inverter and an LC single-tuned filter in series.

4. The method of claim 3, wherein the method is a method of specifying harmonic compensation of a hybrid active filter, characterized in that, The switching frequency of the three-phase voltage source inverter is set to 10 kHz, L is 3 Mh, C is 90 Uf in the LC single-tuned filter, and the load adopts a three-phase uncontrollable rectifier bridge with a resistance R load, and R is 10 Ω.

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