Active power filter control method for preventing resonance

Abstract

The invention discloses an active power filter control method for preventing resonance, and relates to the technical field of electric energy quality control, and the method comprises the steps: obtaining a sensitive frequency point through a mode of injecting a harmonic current with the frequency being a pre-judged harmonic frequency into a power supply circuit, and comparing the changes of a power grid side current and a load side current before and after injection; according to the method, harmonic components corresponding to sensitive frequency points are separated from harmonic components corresponding to other frequencies, compensation currents are generated respectively, the harmonic components corresponding to the sensitive frequency points are adjusted through feedback coefficients, and then different compensation currents are superposed to obtain a comprehensive compensation current. The load harmonic current is offset by using the comprehensive compensation current, so that the current on the power grid side is ensured to be distortionless; according to the technical scheme, harmonic impedance adjustment can be achieved, harmonic amplification is effectively prevented, passive element burning or power supply faults are avoided, and power supply safety and reliability are enhanced.

Description

Technical Field

[0001] The present application relates to the technical field of power quality control, and in particular to an active power filter control method for preventing resonance from occurring. Background Art

[0002] In the distribution network, nonlinear loads will generate harmonic currents, causing power quality problems such as the grid voltage at the common connection point, harmonic amplification in the grid reactive compensation capacitor, and increased line losses. Using active filters based on power electronic conversion technology, the load harmonic current can be offset by generating a reverse current equal to the harmonic component in the load current, thereby ensuring that the grid side current is distortion-free.

[0003] The conventional control method of active filters is to detect the load current, separate the amplitude and phase information of each harmonic component, process it as the output current instruction of its own converter, and implement output current instruction tracking through closed-loop control.

[0004] However, when there is a passive filter or reactive compensation capacitor on the load side, due to the limitation of the converter control loop bandwidth, it is possible to generate harmonic or interharmonic amplification between the passive branch and the grid impedance. In severe cases, it may cause passive components to burn out or power supply failure. Therefore, it is necessary to provide a control strategy for preventing resonance from occurring in active filters in power supply circuits. Summary of the invention

[0005] The purpose of the present application is to provide an active power filter control method that can prevent resonance from occurring, adjust the harmonic impedance at the access point of the active filter, prevent harmonic amplification, and thus produce a resonance damping effect.

[0006] The technical solution of the present application is to provide an active power filter control method for preventing resonance, the method comprising:

[0007] Step 1, set N predicted harmonic frequencies, judge whether each predicted harmonic frequency belongs to a sensitive frequency point in turn, and record the predicted harmonic frequencies belonging to the sensitive frequency points into a list, which specifically includes the following steps: Step 1.1, obtain the original amplitude of the grid-side current and the load-side current at the current predicted harmonic frequency; Step 1.2, use the active filter to inject a harmonic current with a frequency of the current predicted harmonic frequency into the power supply circuit at its access point, and obtain the change amplitude of the grid-side current and the load-side current at the predicted harmonic frequency; Step 1.3, when the change amplitude of the grid-side current is small, When the change amplitude of the grid-side current is greater than or equal to the predetermined multiple of its original amplitude and the change amplitude of the load-side current is less than the predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency does not belong to the sensitive frequency point; when the change amplitude of the grid-side current is greater than or equal to the predetermined multiple of its original amplitude or the change amplitude of the load-side current is greater than or equal to the predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency belongs to the sensitive frequency point, and the predicted harmonic frequency is recorded in the sensitive frequency point list; step 1.4, stop injecting harmonic current, update the predicted harmonic frequency, and return to execute step 1.1 until all predicted harmonic frequencies are traversed;

[0008] Step 2: Based on the list of sensitive frequency points, an active filter is used to generate compensation currents corresponding to sensitive frequency points in the grid-side current, compensation currents corresponding to other frequencies other than the sensitive frequency points in the load-side current, and compensation currents corresponding to the access point voltage. Each compensation current is superimposed to obtain a comprehensive compensation current, and an active filter is used to inject the comprehensive compensation current into the power supply circuit at its access point.

[0009] Furthermore, in step 2.1, the amplitude of the harmonic current is 1% to 2% of the amplitude of the rated current at the access point of the active filter.

[0010] Furthermore, step 1.3 specifically includes: changing the original amplitude i of the grid-side current to SE1 and the original amplitude of the load side current i LE1 , respectively, and the change amplitude i of the grid-side current after the harmonic current is injected SE2 and the load side current variation i LE2 For comparison, when i SE2 <1.2*i SE1 And i LE2 <1.2*i LE1 When the current predicted harmonic frequency f is determined E It is not a sensitive frequency point. SE2 ≥1.2*i SE1 or LE2 ≥1.2i LE1 When the current predicted harmonic frequency f is determined E It is a sensitive frequency point, and fE is recorded in the sensitive frequency point list.

[0011] Furthermore, step 2 specifically includes: step 2.1, generating a first compensation current based on harmonic currents corresponding to other frequencies other than the sensitive frequency point in the load side current; step 2.2, generating a second compensation current based on the harmonic currents corresponding to the sensitive frequency points in the grid side current and the feedback coefficient of the grid side current; step 2.3, generating a third compensation current based on the access point voltage and the feedforward coefficient of the access point voltage; step 2.4, superimposing the first compensation current, the second compensation current and the third compensation current to obtain a comprehensive compensation current, and using the active filter to inject the comprehensive compensation current into the power supply circuit at its access point.

[0012] Furthermore, step 2.1 specifically includes: L Sampling is performed, and filtering is performed to separate the first harmonic components corresponding to the frequencies other than the sensitive frequency point, and a first instruction is generated according to the amplitude and phase information of the first harmonic component. The first instruction is used to control the converter in the active filter to output a compensation current i having the same amplitude and opposite phase as the first harmonic component. Cr1 .

[0013] Furthermore, step 2.2 specifically includes: S The second harmonic component corresponding to the sensitive frequency point is sampled and filtered to separate it. The second instruction is generated according to the amplitude and phase information of the second harmonic component. The second instruction is used to control the converter to output a current with the same amplitude and opposite phase as the second harmonic component. The current is compared with the feedback coefficient k. IS Multiply to get the second compensation current i Cr2 .

[0014] Furthermore, the feedback coefficient k IS The grid-side current i S It is obtained after THD calculation and proportional integral steps.

[0015] Furthermore, step 2.3 specifically includes: adjusting the voltage u at the access point of the active filter S Sampling, the access point voltage u S and the feedforward coefficient k US The corresponding compensation value is obtained by multiplication, and a third instruction is generated based on the compensation value. The third instruction is used to control the output of the converter and the access point voltage u S The corresponding third compensation current i Cr3 .

[0016] Furthermore, the feedforward coefficient k US The voltage u at the access point S It is obtained by taking the inverse after THD calculation and proportional integral steps.

[0017] The beneficial effects of this application are:

[0018] The technical solution in the present application injects harmonic current of predicted harmonic frequency into the power supply circuit, and compares the way in which the grid-side current and the load-side current change before and after the injection, separates the harmonic components corresponding to the sensitive frequency point from the harmonic components corresponding to other frequencies, generates compensation currents respectively, and uses the feedback coefficient of the grid-side current to adjust the compensation current corresponding to the sensitive frequency point, and at the same time adds the compensation current corresponding to the access point voltage of the active filter, and uses the feedforward coefficient of the access point voltage to adjust its compensation current, superimposes different compensation currents, and offsets the load harmonic current by the superimposed comprehensive compensation current; the technical solution in the present application accurately compensates for harmonic currents of different frequencies by component compensation, realizes harmonic impedance adjustment, can effectively prevent harmonic amplification, reduce the impact of harmonics on the power supply system, avoid burning of passive components or power supply failure, improves the power distribution quality of the power grid, and enhances the safety and reliability of power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The advantages of the above and / or additional aspects of the present application will become apparent and easily understood in the description of the embodiments in conjunction with the following drawings, in which:

[0020] Figure 1 is a schematic flow chart of a resonant frequency prediction working mode according to an embodiment of the present application;

[0021] Figure 2 is a schematic flow chart of a compensation current generation process in a harmonic filtering working mode according to an embodiment of the present application;

[0022] Figure 3 is a schematic diagram of a power supply circuit structure and a current sampling position of an active filter according to an embodiment of the present application;

[0023] Figure 4 is a schematic flow chart of a feedback coefficient generation process according to an embodiment of the present application;

[0024] Figure 5 is a schematic flow chart of a feedforward coefficient generation process according to an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0026] In the following description, many specific details are elaborated to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present application is not limited to the specific embodiments disclosed below.

[0027] like Figures 1 to 3 As shown, this embodiment provides an active power filter control method for preventing resonance from occurring. The method is used for a power supply circuit from a power grid to a load, and an active filter is connected to the power supply circuit. The active power filter control method for preventing resonance from occurring includes:

[0028] Step 1, setting N predicted harmonic frequencies, where N is a positive integer, judging in turn whether each predicted harmonic frequency belongs to a sensitive frequency point, and recording the predicted harmonic frequencies belonging to the sensitive frequency points into a list, specifically comprising the following steps:

[0029] Step 1.1, obtaining the original amplitudes of the grid-side current and the load-side current at the current predicted harmonic frequency;

[0030] The active filter is set in the power supply circuit between the grid and the load, obtains the grid-side current and the load-side current through the current measuring device, and filters and separates the grid-side current at the current predicted harmonic frequency f E The original amplitude i SE1 , and the load-side current at the current predicted harmonic frequency f E The original amplitude i LE1 .

[0031] In this embodiment, the current measuring device may be a current transformer, a Hall current sensor or the like.

[0032] Step 1.2, using the active filter to inject a harmonic current having a frequency of the current predicted harmonic frequency into the power supply circuit at its access point (i.e., the point where the active filter is connected to the power grid), and obtain the change amplitude of the grid-side current and the load-side current at the predicted harmonic frequency, wherein the amplitude of the harmonic current is 1% to 2% of the rated current amplitude at the active filter access point;

[0033] The active filter is used to inject a harmonic current with a frequency of the current predicted harmonic frequency fE and an amplitude of 1% to 2% of the rated current amplitude at its access point. After injection, the grid-side current and the load-side current are obtained through the current measuring device, and the grid-side current is filtered and separated at the current predicted harmonic frequency fE. E The change in i SE2 , and the load-side current at the current predicted harmonic frequency f E The change in i LE2 .

[0034] Step 1.3, when the change amplitude of the grid-side current is less than a predetermined multiple of its original amplitude and the change amplitude of the load-side current is less than a predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency does not belong to the sensitive frequency point; when the change amplitude of the grid-side current is greater than or equal to a predetermined multiple of its original amplitude or the change amplitude of the load-side current is greater than or equal to a predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency belongs to the sensitive frequency point, and the predicted harmonic frequency is recorded in the sensitive frequency point list;

[0035] The original amplitude of the grid-side current i SE1 and the original amplitude of the load side current i LE1 , respectively, and the change amplitude i of the grid-side current after the harmonic current is injected SE2 and the load side current variation i LE2 For comparison, when i SE2 <1.2*i SE1 And i LE2 <1.2*i LE1 When the current predicted harmonic frequency f is determined E It is not a sensitive frequency point. SE2 ≥1.2*i SE1 or LE2 ≥1.2i LE1 When the current predicted harmonic frequency f is determined E Belong to the sensitive frequency point, the current predicted harmonic frequency f E Record in the sensitive frequency point list.

[0036] Step 1.4, the active filter stops injecting harmonic current, updates the predicted harmonic frequency, and returns to step 1.1 until all predicted harmonic frequencies are traversed;

[0037] After the current predicted harmonic frequency fE is determined, the active filter stops injecting harmonic current with the current predicted harmonic frequency into the power supply circuit, updates to the next predicted harmonic frequency, and executes step 1 for the next predicted harmonic frequency until all predicted harmonic frequencies are traversed.

[0038] In this embodiment, step 1 is a resonant frequency prediction working mode. In this mode, the active filter injects harmonic currents of the predicted harmonic frequency in small amplitudes (such as 1% to 2% of the rated current) one by one, detects the grid-side current and the load-side current before and after the output, and if it is found that the component at the frequency point is significantly increased after the injection, the frequency point is used as a sensitive frequency point.

[0039] Step 2: Based on the sensitive frequency point list, an active filter is used to generate compensation currents corresponding to sensitive frequency points in the grid-side current and compensation currents corresponding to other frequencies other than the sensitive frequency points in the load-side current, and compensation currents corresponding to the access point voltage are generated. The compensation currents are superimposed to obtain a comprehensive compensation current, and the active filter is used to inject the comprehensive compensation current at the access point. Specifically, the steps include:

[0040] Step 2.1, generating a first compensation current based on harmonic currents corresponding to frequencies other than the sensitive frequency point in the load side current;

[0041] The load side current i L Sampling is performed, and filtering is performed to separate the first harmonic components corresponding to the frequencies other than the sensitive frequency point. According to the amplitude and phase information of the first harmonic component, a first instruction for controlling the output current of the converter in the active filter is generated. The converter is controlled by the first instruction to output a compensation current i having the same amplitude and opposite phase (i.e., 180° phase difference) as the first harmonic component. Cr1 , that is, a harmonic current is generated that is equal to and opposite to the first harmonic component.

[0042] In this embodiment, a bandpass filter for filtering out harmonic currents corresponding to sensitive frequency points can be provided in the front stage of the active filter. After sampling the load side current, the harmonic currents corresponding to the sensitive frequency points are filtered out by the bandpass filter to obtain harmonic components corresponding to other frequencies.

[0043] Step 2.2, generating a second compensation current based on the harmonic current corresponding to the sensitive frequency point in the grid-side current and the feedback coefficient of the grid-side current;

[0044] The grid-side current i S Sampling is performed, and the second harmonic component corresponding to the sensitive frequency point is separated by filtering. According to the amplitude and phase information of the second harmonic component, a second instruction for controlling the output current of the converter is generated. The converter is controlled by the second instruction to output a current with the same amplitude and opposite phase as the second harmonic component. The current is proportional to the feedback coefficient k. IS Multiply to get the second compensation current i Cr2 ; Among them, the feedback coefficient k IS The grid-side current i S After THD calculation (i.e. total harmonic distortion calculation, used to calculate the current distortion rate of the current signal) and proportional integral link (i.e. proportional integral compensator, used to calculate the feedback coefficient k with the current distortion rate as input), IS , to adjust the output of the active filter) and then obtain, such as Figure 4 shown.

[0045] In this embodiment, a bandpass filter that only allows harmonic currents corresponding to sensitive frequency points to pass can be set in the front stage of the active filter, such as Figure 2 As shown, after sampling the load side current, the harmonic currents corresponding to other frequencies are filtered out by such a bandpass filter to obtain the harmonic components corresponding to the current sensitive frequency point.

[0046] Step 2.3, generating a third compensation current based on the access point voltage and a feed-forward coefficient of the access point voltage;

[0047] The voltage u at the active filter access point S Sampling, the access point voltage u S and the feedforward coefficient k US The corresponding compensation value is obtained by multiplication, and a third instruction for controlling the output current of the converter is generated based on the compensation value. The third instruction is used to control the output current of the converter and the access point voltage u S The corresponding third compensation current i Cr3 ; Among them, the feedforward coefficient k US The voltage u at the access point S After THD calculation and proportional integration, the inverse is obtained, such as Figure 5 shown.

[0048] Step 2.4: Set the first compensation current i Cr1 , the second compensation current i Cr2 and the third compensation current i Cr3 The comprehensive compensation current i is obtained by superposition Cr , using active filter to inject comprehensive compensation current i into the power supply circuit at its access point Cr , to achieve resonance damping.

[0049] In this embodiment, step 2 is a harmonic filtering working mode. In this mode, the active filter generates different control instructions according to different harmonic components and access point voltages, controls its own converter to output compensation current to the power supply circuit, and realizes resonance damping; wherein, the harmonic components corresponding to the sensitive frequency point are separated from the harmonic components corresponding to other frequencies, and compensation currents are generated respectively to adjust the harmonic impedance and prevent harmonic amplification, thereby avoiding burning of passive components or power supply failure.

[0050] It should be noted that each time the active filter is put into operation, it needs to enter the resonant frequency prediction working mode first, obtain the sensitive frequency point list, and then switch to the harmonic filtering working mode for continuous operation. When the power supply network structure, operation mode and user load undergo major changes, such as the reconfiguration of the nodes, lines or transformers of the power grid, switching from the normal operation mode to the standby or fault operation mode, and the increase or decrease of the user's load exceeding the preset value, the active filter should be shut down and restarted to update the system sensitive frequency point list information.

[0051] The steps in this application can be adjusted in order, combined, and deleted according to actual needs.

[0052] The units in the device of the present application can be combined, divided and deleted according to actual needs.

[0053] Although the present application is disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and are not intended to limit the application of the present application. The scope of protection of the present application is defined by the appended claims and may include various modifications, alterations and equivalents made to the invention without departing from the scope and spirit of the present application.

Claims

1. A method for controlling an active power filter to prevent resonance, characterized in that: The method is used for a power supply circuit from a power grid to a load, an active filter is connected to the power supply circuit, and the method comprises: Step 1, setting N predicted harmonic frequencies, judging in turn whether each predicted harmonic frequency belongs to a sensitive frequency point, and recording the predicted harmonic frequencies belonging to the sensitive frequency points into a list, specifically comprising the following steps: Step 1.1, obtaining the original amplitudes of the grid-side current and the load-side current at the current predicted harmonic frequency; Step 1.2, using an active filter to inject a harmonic current having a frequency of the current predicted harmonic frequency into the power supply circuit at its access point, and obtaining a variation amplitude of the grid-side current and the load-side current at the predicted harmonic frequency; Step 1.3, when the change amplitude of the grid-side current is less than a predetermined multiple of its original amplitude and the change amplitude of the load-side current is less than a predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency does not belong to the sensitive frequency point; when the change amplitude of the grid-side current is greater than or equal to a predetermined multiple of its original amplitude or the change amplitude of the load-side current is greater than or equal to a predetermined multiple of its original amplitude, it is determined that the current predicted harmonic frequency belongs to the sensitive frequency point, and the predicted harmonic frequency is recorded in the sensitive frequency point list; Step 1.4, stop injecting harmonic current, update the predicted harmonic frequency, and return to execute step 1.1 until all predicted harmonic frequencies are traversed; Step 2: Based on the list of sensitive frequency points, an active filter is used to generate compensation currents corresponding to sensitive frequency points in the grid-side current, compensation currents corresponding to other frequencies other than the sensitive frequency points in the load-side current, and compensation currents corresponding to the access point voltage. Each compensation current is superimposed to obtain a comprehensive compensation current, and an active filter is used to inject the comprehensive compensation current into the power supply circuit at its access point.

2. The active power filter control method for preventing resonance from occurring according to claim 1, characterized in that: In the step 2.1, the amplitude of the harmonic current is 1% to 2% of the amplitude of the rated current at the access point of the active filter.

3. The active power filter control method for preventing resonance from occurring as claimed in claim 2, characterized in that: The step 1.3 specifically includes: The original amplitude of the grid-side current i SE1 and the original amplitude of the load side current i LE1 , respectively, and the change amplitude i of the grid-side current after the harmonic current is injected SE2 and the load side current variation i LE2 For comparison, when i SE2 <1.2*i SE1 And i LE2 <1.2*i LE1 When the current predicted harmonic frequency f is determined E It is not a sensitive frequency point. SE2 ≧1.2*i SE1 or LE2 ≧1.2i LE1 When the current predicted harmonic frequency f is determined E It is a sensitive frequency point. E Record in the sensitive frequency point list.

4. The active power filter control method for preventing resonance from occurring according to claim 1, characterized in that: The step 2 specifically includes: Step 2.1, generating a first compensation current based on harmonic currents corresponding to frequencies other than the sensitive frequency point in the load side current; Step 2.2, generating a second compensation current based on the harmonic current corresponding to the sensitive frequency point in the grid-side current and the feedback coefficient of the grid-side current; Step 2.3, generating a third compensation current based on the access point voltage and a feed-forward coefficient of the access point voltage; Step 2.4: superimpose the first compensation current, the second compensation current and the third compensation current to obtain a comprehensive compensation current, and use the active filter to inject the comprehensive compensation current into the power supply circuit at its access point.

5. The active power filter control method for preventing resonance as claimed in claim 4, characterized in that: The step 2.1 specifically includes: The load side current i L Sampling is performed, and filtering is performed to separate the first harmonic components corresponding to the frequencies other than the sensitive frequency point, and a first instruction is generated according to the amplitude and phase information of the first harmonic component. The first instruction is used to control the converter in the active filter to output a compensation current i having the same amplitude and opposite phase as the first harmonic component. Cr1 .

6. The active power filter control method for preventing resonance as claimed in claim 5, characterized in that: The step 2.2 specifically includes: The grid-side current i S The second harmonic component corresponding to the sensitive frequency point is sampled and filtered to separate it. The second instruction is generated according to the amplitude and phase information of the second harmonic component. The second instruction is used to control the converter to output a current with the same amplitude and opposite phase as the second harmonic component. The current is compared with the feedback coefficient k. IS Multiply to get the second compensation current i Cr2 .

7. The active power filter control method for preventing resonance as claimed in claim 6, characterized in that: The feedback coefficient k IS The grid-side current i S It is obtained after THD calculation and proportional integral steps.

8. The active power filter control method for preventing resonance as claimed in claim 6, characterized in that: The step 2.3 specifically includes: The voltage u at the active filter access point S Sampling, the access point voltage u S and the feedforward coefficient k US The corresponding compensation value is obtained by multiplication, and a third instruction is generated based on the compensation value. The third instruction is used to control the output of the converter and the access point voltage u S The corresponding third compensation current i Cr3 .

9. The active power filter control method for preventing resonance as claimed in claim 8, characterized in that: The feedforward coefficient k US The voltage u at the access point S It is obtained by taking the inverse after THD calculation and proportional integral steps.

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