A method of controlling an active power filter to prevent resonance

Abstract

The application discloses an active power filter control method for preventing resonance, and relates to the technical field of power quality control.The method injects a harmonic current with a frequency of a pre-judged harmonic frequency into a power supply circuit, compares the change in the grid-side current and the load-side current before and after the injection, obtains a sensitive frequency point, separates the harmonic component corresponding to the sensitive frequency point from the harmonic components corresponding to other frequencies, and respectively generates compensation currents, wherein the harmonic component corresponding to the sensitive frequency point is adjusted through a feedback coefficient, different compensation currents are superimposed to obtain a comprehensive compensation current, the comprehensive compensation current is used to offset the load harmonic current, and the grid-side current is ensured to be undistorted.The technical scheme in the application can realize harmonic impedance adjustment, effectively prevent harmonic amplification, avoid passive element burning or power supply failure, and enhance the safety and reliability of power supply.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power quality control, in particular to a control method of an active power filter for preventing resonance. BACKGROUND

[0002] In a power distribution network, non-linear loads can generate harmonic currents, causing power quality problems such as harmonic amplification of the grid voltage at the point of common coupling, increased line loss, and reactive power compensation capacitors. Using active filters based on power electronic converter technology, the load harmonic current can be offset by generating an equivalent reverse current, thereby ensuring that the grid-side current is distortion-free.

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

[0004] However, when there is a passive filter or a reactive compensation capacitor on the load side, due to the bandwidth limitation of the converter control loop, harmonic or interharmonic amplification may occur between the passive branch and the grid impedance. In severe cases, it can cause passive component burnout or power supply failure. Therefore, a control strategy is needed to prevent resonance in active filters in power supply circuits. SUMMARY

[0005] The purpose of the present application is to provide an active power filter control method that can prevent resonance, 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, which comprises:

[0007] Step 1: Set N predicted harmonic frequencies, determine in turn whether each predicted harmonic frequency belongs to a sensitive frequency point, and record the predicted harmonic frequencies belonging to the sensitive frequency points in a list, specifically including the following steps: Step 1.1: Obtain the original amplitudes 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 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;

[0008] Step 2: Based on the sensitive frequency point list, use the active filter to generate compensation currents corresponding to sensitive frequency points in the grid-side current, compensation currents corresponding to frequencies other than the sensitive frequency points in the load-side current, and compensation currents corresponding to the access point voltage. Superimpose the various compensation currents 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.

[0009] Furthermore, in step 1.2, 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 of the grid side current to and the original amplitude of the load side current , respectively, and the change amplitude of the grid side current after the harmonic current is injected and the load side current variation For comparison, when <1.2* and <1.2* When the current predicted harmonic frequency is determined It is not a sensitive frequency point. ≧1.2* or ≧1.2 When the current predicted harmonic frequency is Belong to the sensitive frequency point, Record in the sensitive frequency point list.

[0011] Further, step 2 specifically comprises: step 2.1, generating a first compensation current based on the harmonic currents corresponding to other frequencies 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 a feedback coefficient of the grid-side current; step 2.3, generating a third compensation current based on the access point voltage and a feedforward coefficient of the access point voltage; and step 2.4, superimposing the first compensation current, the second compensation current and the third compensation current to obtain a comprehensive compensation current, and injecting the comprehensive compensation current at the access point of the active filter to the power supply circuit by using the active filter.

[0012] Further, step 2.1 specifically comprises: sampling the load-side current and filtering and separating the first harmonic component corresponding to other frequencies than the sensitive frequency point, generating a first instruction according to the amplitude and phase information of the first harmonic component, and controlling the converter in the active filter to output a compensation current with the same amplitude and opposite phase as the first harmonic component through the first instruction.

[0013] Further, step 2.2 specifically comprises: sampling the grid-side current and filtering and separating the second harmonic component corresponding to the sensitive frequency point, generating a second instruction according to the amplitude and phase information of the second harmonic component, and controlling the converter to output a current with the same amplitude and opposite phase as the second harmonic component through the second instruction, and multiplying the current by a feedback coefficient to obtain a second compensation current .

[0014] Further, the feedback coefficient is obtained by sequentially passing the grid-side current through THD calculation and proportional integral link.

[0015] Further, step 2.3 specifically comprises: sampling the access point voltage of the active filter, multiplying the access point voltage by a feedforward coefficient to obtain a corresponding compensation value, generating a third instruction based on the compensation value, and controlling the converter to output a third compensation current corresponding to the access point voltage through the third instruction.

[0016] Further, the feedforward coefficient is obtained by sequentially passing the access point voltage through THD calculation and proportional integral link and then taking the reciprocal.

[0017] The application has the following beneficial effects: ​

[0018] The technical solution in the present application injects harmonic current of predicted harmonic frequency into the power supply circuit, and compares the changes in the grid-side current and the load-side current 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. At the same time, the compensation current corresponding to the active filter access point voltage is added, and the compensation current is adjusted using the feedforward coefficient of the access point voltage. The different compensation currents are superimposed, and the load harmonic current is offset 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 failures, improve the power distribution quality of the power grid, and enhance the power supply safety and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The advantages of the above and / or additional aspects of the present application will become apparent and readily understood from 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 one 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 objectives, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features therein can be combined with each other in the absence of conflict.

[0026] In the following description, many specific details are set forth 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 scope of protection 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. The method is used in a power supply circuit from a power grid to a load, wherein an active filter is connected to the power supply circuit. The active power filter control method for preventing resonance includes:

[0028] Step 1: Set N predicted harmonic frequencies, where N is a positive integer, and determine 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 in a list. The specific steps include the following:

[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, and 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. The original amplitude , and the load side current at the current predicted harmonic frequency The original amplitude .

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

[0032] Step 1.2: Use the active filter to inject a harmonic current with a frequency equal to the currently predicted harmonic frequency into the power supply circuit at its access point (i.e., the point where the active filter is connected to the grid). Obtain the amplitude of the grid-side current and the load-side current changes at the predicted harmonic frequency. The amplitude of the harmonic current is 1% to 2% of the rated current amplitude at the active filter access point.

[0033] Use active filters to inject the current predicted harmonic frequency at its access point The harmonic current with an amplitude of 1% to 2% of the rated current amplitude is injected and then the grid side current and the load side current are obtained respectively through the current measuring device, and the grid side current is filtered and separated at the current predicted harmonic frequency. The range of change , and the load side current at the current predicted harmonic frequency The change range .

[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 a 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 a 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 and the original amplitude of the load side current , respectively, and the change amplitude of the grid side current after the harmonic current is injected and the load side current variation For comparison, when <1.2* and <1.2* When the current predicted harmonic frequency is It is not a sensitive frequency point. ≧1.2* or ≧1.2 When the current predicted harmonic frequency is Belong to the sensitive frequency point, the current predicted harmonic frequency 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] Current predicted harmonic frequency After the determination is completed, the active filter stops injecting harmonic current with a frequency of 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 (e.g., 1% to 2% of the rated current) one by one, and detects the grid-side current and the load-side current before and after the output. 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 frequencies other than the sensitive frequency points in the load-side current. The compensation current corresponding to the access point voltage is generated, and the individual compensation currents are superimposed to obtain a comprehensive compensation current. The active filter is used to inject the comprehensive compensation current at the access point. The specific 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] Load side current Sampling is performed and filtering is performed to separate the first harmonic components corresponding to frequencies other than the sensitive frequency point. Based on 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 first instruction controls the converter to output a compensation current with the same amplitude and opposite phase (i.e., 180° phase difference) as the first harmonic component. , that is, to generate a current 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] Grid side current Sampling is performed and filtering is performed to separate the second harmonic component corresponding to the sensitive frequency point. 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. This current is proportional to the feedback coefficient. Multiply to get the second compensation current ; Among them, the feedback coefficient The grid side current After the THD calculation (i.e. total harmonic distortion calculation, used to calculate the current distortion rate of the current signal) and the proportional integral link (i.e. proportional integral compensator, used to calculate the feedback coefficient with the current distortion rate as input), the current signal is converted into a voltage signal. , to adjust the output of the active filter) is obtained, 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 before the active filter, such asFigure 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 feedforward coefficient of the access point voltage;

[0047] Voltage at the active filter access point Sampling, the access point voltage and the feedforward coefficient Multiply to obtain the corresponding compensation value, generate a third instruction to control the output current of the converter based on the compensation value, and control the converter output and the access point voltage through the third instruction The corresponding third compensation current ; Among them, the feedforward coefficient By access point voltage After THD calculation and proportional integral steps, the inverse is obtained, such as Figure 5 shown.

[0048] Step 2.4, the first compensation current , the second compensation current and the third compensation current Superposition is performed to obtain the comprehensive compensation current , using active filters to inject comprehensive compensation current into the power supply circuit at its access point , achieving resonance damping.

[0049] In this embodiment, step 2 is a harmonic filtering mode. In this mode, the active filter generates different control instructions based on different harmonic components and access point voltages, controlling its own converter to output compensation current to the power supply circuit to achieve resonance damping. The harmonic components corresponding to the sensitive frequency point are separated from the harmonic components corresponding to other frequencies, and compensation currents are generated for each of them to adjust the harmonic impedance and prevent harmonic amplification, thereby avoiding burning of passive components or power supply failures.

[0050] It should be noted that each time the active power filter is put into operation, it must first enter the resonant frequency prediction working mode, obtain the sensitive frequency point list, and then switch to the harmonic filtering working mode for continuous operation. When there are major changes in the power supply network structure, operation mode, and user load, such as the reconfiguration of grid nodes, lines, or transformers, switching from normal operation mode to standby or fault operation mode, or the increase or decrease of user load exceeding the preset value, the active power 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, wherein an active filter is connected to the power supply circuit, and the method comprises: Step 1: Set N predicted harmonic frequencies, determine 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 in a list, which specifically includes 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: Use the active filter to inject a harmonic current with a frequency equal to the currently predicted harmonic frequency into the power supply circuit at its access point, and obtain the 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 a 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 a 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 step 1.1 until all predicted harmonic frequencies are traversed; Step 2: Based on the sensitive frequency point list, use the active filter to generate compensation currents corresponding to sensitive frequency points in the grid-side current, compensation currents corresponding to frequencies other than the sensitive frequency points in the load-side current, and compensation currents corresponding to the access point voltage. Superimpose the various compensation currents 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.

2. The active power filter control method for preventing resonance according to claim 1, wherein: In the step 1.2, 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 as claimed in claim 2, wherein: The step 1.3 specifically includes: The original amplitude of the grid side current and the original amplitude of the load side current , respectively, and the change amplitude of the grid side current after the harmonic current is injected and the load side current variation For comparison, when <1.2* and <1.2* When the current predicted harmonic frequency is determined It is not a sensitive frequency point. ≧1.2* or ≧1.2 When the current predicted harmonic frequency is determined Belong to the sensitive frequency point, Record in the sensitive frequency point list.

4. The active power filter control method for preventing resonance according to claim 1, wherein: 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 feedforward 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 according to claim 4, wherein: The step 2.1 specifically includes: Load side current Sampling is performed, and filtering is performed to separate the first harmonic components corresponding to 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 with the same amplitude and opposite phase as the first harmonic component. .

6. The active power filter control method for preventing resonance according to claim 5, wherein: The step 2.2 specifically includes: Grid side current Sampling is performed and filtering is performed to separate the second harmonic component corresponding to the sensitive frequency point. A 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 then compared with the feedback coefficient. Multiply to get the second compensation current .

7. The active power filter control method for preventing resonance according to claim 6, wherein: The feedback coefficient The grid side current It is obtained after THD calculation and proportional integral steps.

8. The active power filter control method for preventing resonance according to claim 6, wherein: The step 2.3 specifically includes: Voltage at the active filter access point Sampling, the access point voltage and the feedforward coefficient Multiply to obtain the corresponding compensation value, generate a third instruction based on the compensation value, and control the converter output and access point voltage through the third instruction The corresponding third compensation current .

9. The active power filter control method for preventing resonance according to claim 8, wherein: The feedforward coefficient By access point voltage It is obtained by taking the inverse after going through THD calculation and proportional integral steps.

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