Modular active power filter parallel system

Abstract

The invention discloses a modular active power filter parallel system, which is characterized in that a plurality of modular active power filters are connected in parallel, all the parallel active power filters are provided with a common sampling current sensor on a power grid side, and the parallel system is not provided with a central controller. Distributed control can eliminate a central controller and problems introduced by the central controller. The modular APF shares the current according to the capacity proportion, so that the current and thermal stress are reasonably distributed. The APF module can be freely connected or disconnected without interfering with any other APF module. The system is high in redundancy, good in reliability, good in expansibility and convenient to maintain.

Description

A modular active power filter parallel system Technical Field

[0001] This invention relates to a power filter, and more particularly to a modular active power filter parallel system. Background Technology

[0002] Currently, the increasing use of various nonlinear loads exacerbates power quality (PQ) problems, especially for islanded microgrids. Active power filters (APFs) are a mature harmonic compensation solution. However, in high-power applications, a single APF, due to its limited rated power, is insufficient to meet power filtering requirements. Existing solutions mainly fall into two categories. One is to increase the rated power of a single APF, such as through parallel IGBTs and hybrid APFs. However, these solutions are neither scalable nor conducive to maintenance or production. Therefore, another capacity expansion method—parallel operation—has emerged. This compensation method is more flexible. For example, the capacity can be changed by altering the number of APFs.

[0003] Figure 1 is a schematic diagram of an active power filter in the prior art.

[0004] Deficiencies of existing technology:

[0005] There are various parallel APF schemes, which can be divided into two categories: centralized control and distributed control. Distributed control schemes were proposed earlier, but they cannot simultaneously achieve scalability and current sharing capabilities. To enhance the scalability of APF groups, researchers turned to centralized control. In centralized control, the APFs are controlled by a central controller, and any communication failure or failure of a single APF will cause the entire system to crash. This is an inherent drawback of the central controller, and the only way to solve this problem is to remove the central controller.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a modular active power filter parallel system to solve the above-mentioned technical problems existing in the prior art.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] The modular active power filter parallel system of the present invention employs multiple modular active power filters connected in parallel. All parallel active power filters are provided with a common sampling current sensor on the grid side. The parallel system does not have a central controller.

[0010] Compared with existing technologies, the modular active power filter parallel system provided by this invention has high redundancy, good reliability, good scalability, and convenient maintenance. Attached Figure Description

[0011] Figure 1 is a schematic diagram of an active power filter in the prior art;

[0012] Figure 2 is a schematic diagram of the modular active power filter parallel system and control principle provided in an embodiment of the present invention;

[0013] Figure 3 is a control block diagram of a single active power filter system according to an embodiment of the present invention.

[0014] Figure 4 is a control block diagram of multiple active power filter systems according to an embodiment of the present invention.

[0015] Figure 5 is a schematic diagram of the simulation results of a single APF in an embodiment of the present invention.

[0016] Figure 6 is a schematic diagram of the simulation results of three APFs in an embodiment of the present invention;

[0017] Figure 7 is a schematic diagram of the Fourier decomposition of load current, APF current and grid current in an embodiment of the present invention;

[0018] Figure 8 is a schematic diagram of the transient operating waveform after one APF trips according to an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them, and do not constitute a limitation on the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0020] First, the following explanations are provided for the terms that may be used in this article:

[0021] The terms “including,” “contains,” “comprising,” “having,” or other similar semantic descriptions shall be interpreted as non-exclusive inclusion.

[0022] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0023] The contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments used in the embodiments of this invention are not specified, they are all conventional products that can be purchased commercially.

[0024] The modular active power filter parallel system of the present invention employs multiple modular active power filters connected in parallel. All parallel active power filters are provided with a common sampling current sensor on the grid side. The parallel system does not have a central controller.

[0025] The output current of each modular active power filter ( It is controlled to the following value:

[0026]

[0027] in, It is the grid current ( The harmonic components in the signal are filtered. Filtering is performed to obtain the data. It is a positive real number, that is It was magnified The output is then multiplied by the active power filter. Size and Proportional.

[0028] When only one modular active power filter is operating in the parallel system, the harmonic components of the grid current are calculated as follows:

[0029]

[0030] in This represents the harmonic components in the load current.

[0031] The larger the value, the smaller the harmonic components of the grid current; when When it is greater than 100, Less than 1% This means that load harmonics are effectively filtered out.

[0032] When multiple modular active power filters are in operation, the parallel system of multiple modular active power filters is equivalent to a single modular active power filter. Its control gain is the sum of the control gains of all active power filters, which means that the parallel system has enhanced harmonic filtering capability.

[0033] In summary, the modular active power filter parallel system of this invention has two main advantages: 1) distributed control (eliminating the problems introduced by a central controller); 2) modular APFs, where each APF shares the current proportionally to its capacity, thus rationally distributing current and thermal stress. APF modules can be freely connected or disconnected without interfering with any other APF modules. When one APF stops working, the remaining APFs will assume its workload, maintaining normal system operation. Users can determine the number of APFs in the parallel system based on the required total capacity. Maintenance only requires replacing a portion of the APFs without disabling harmonic compensation. In conclusion, the modular APF parallel system offers high redundancy, good reliability, good scalability, and convenient maintenance.

[0034] To more clearly demonstrate the technical solution and its effects provided by the present invention, the embodiments of the present invention will be described in detail below with reference to specific examples.

[0035] Example 1

[0036] 1. The connection diagram of the modular active power filter parallel system of the present invention is shown in Figure 2.

[0037] All active power filters sample grid-side current, therefore only one current sensor is needed, making this solution more cost-effective compared to a single current sensor for each power filter. The output current of the active power filter ( It is controlled to the following value:

[0038]

[0039] in It is the grid current ( The harmonic components in the signal can be filtered. Filter the data to obtain the desired information. It is a positive real number. That is... It was magnified The output is then multiplied by the active power filter. Size and Proportional.

[0040] In practical applications, we expect the output current of a single active power filter in a parallel group to be proportional to its own capacity, thus ensuring that all active power filters in the parallel group age at the same rate. Based on the above analysis, this can be achieved by adjusting the control gain of the active power filters. This is achieved by setting it to be proportional to its own capacity. In other words, the proposed control algorithm is implemented in each active power filter in the parallel group of active power filters, and... Proportional to capacity, the system automatically distributes current proportionally among active power filters. This process requires no communication or central controller. Furthermore, this parallel active power filter system supports hot-swapping. Replacing a faulty active power filter does not require interrupting the operation of other active power filters.

[0041] When only one active power filter is working in the parallel system, the system control block diagram is shown in Figure 3.

[0042] The harmonic components of the grid current can be calculated as follows:

[0043]

[0044] in This represents the harmonic components in the load current. It is evident that... The larger the value, the smaller the harmonic components of the grid current. When When it is greater than 100, Less than 1% This means that load harmonics are effectively filtered out.

[0045] Similarly, when multiple active power filters are connected in parallel to the system, the system control block diagram is shown on the left side of Figure 4, where each square represents an active power filter. Combining multiple branches can be equivalent to the diagram on the right side of Figure 4. That is, a system of multiple active power filters in parallel can be equivalent to a single active power filter, and its control gain is the sum of the control gains of all active power filters. In other words, the parallel system has a stronger ability to filter harmonics.

[0046] 2. Detection and experimental verification

[0047] To verify the effectiveness of the APF parallel control scheme, relevant simulations were performed. The control gain was set to 100 kVA, which can be set by the user. The grid voltage was 50Hz / 380V, and the grid impedance was simulated using a 0.96mH inductor. The nonlinear load was a 9kW constant power load with a diode rectifier at the front end.

[0048] 3. Steady-state performance verification

[0049] When there is only one APF in the parallel group, its capacity is assumed to be 10kVA, therefore its The value was set to 1000. Figure 5 shows the steady-state simulation results. It can be seen that the harmonics in the load current (total harmonic distortion (THD) of 39.3%) are well compensated by the APF, and the final THD of the grid current is 4.1%. This proves that the proposed control scheme can work well even under single APF system, weak grid and constant power load.

[0050] When the three APFs are operating in parallel, their capacities are assumed to be 2kVA, 4kVA, and 6kVA, respectively. Therefore, their... The values ​​were set to 200, 400, and 600 respectively. Figure 6 shows the steady-state simulation results. The grid current was well compensated by the three APFs, with a THD of 3.4%. Figure 7 shows the Fourier decomposition of the current in Figure 6. As can be seen from the figure, the output current ratio of the three APFs with the same resonant frequency is 1:2:3, which is the same as their capacity ratio, thus achieving a good current sharing effect.

[0051] 4. Transient performance verification

[0052] Under the parallel operation condition of three APFs shown in Figure 6, APF2 (4kVA capacity) trips due to an internal fault. Its transient waveform is shown in Figure 8. After APF2 trips, the output currents of APF1 and APF3 gradually increase. After approximately 0.04s, the output currents of APF1 and APF3 fully cover the remaining harmonic load of APF2. This demonstrates that the proposed parallel APF scheme supports hot-swapping. Adding or removing one APF in the system does not affect the operation of the other APFs or their harmonic compensation performance.

[0053] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A modular active power filter parallel system, characterized in that, Multiple modular active power filters are connected in parallel, and all the parallel active power filters are equipped with a common sampling current sensor on the grid side. There is no central controller in this parallel system.

2. The modular active power filter parallel system according to claim 1, characterized in that, The output current of each modular active power filter ( It is controlled to the following value: ;in, It is the grid current ( The harmonic components in the signal are filtered. Filtering is performed to obtain the data. It is a positive real number, that is It was magnified The output is then multiplied by the active power filter. Size and Proportional.

3. The modular active power filter parallel system according to claim 2, characterized in that, When only one modular active power filter is operating in the parallel system, the harmonic components of the grid current are calculated as follows: ;in This represents the harmonic components in the load current. The larger the value, the smaller the harmonic components of the grid current; when When it is greater than 100, Less than 1% This means that load harmonics are effectively filtered out.

4. The modular active power filter parallel system according to claim 3, characterized in that, When multiple modular active power filters are in operation, the parallel system of multiple modular active power filters is equivalent to a single modular active power filter. Its control gain is the sum of the control gains of all active power filters, which means that the parallel system has enhanced harmonic filtering capability.

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