Coupled harmonic current filtering method and system for SFC rectifier

Abstract

The invention belongs to the technical field of static frequency converters, and provides a coupled harmonic current filtering method and system for an SFC rectifier, and the method comprises the steps: firstly carrying out the Fourier transform analysis of a current signal and a voltage signal, extracting a coupled harmonic current component in the current signal, and determining the frequency and amplitude of the coupled harmonic current; constructing a correction transfer function according to the extracted coupling harmonic current components; superposing the correction transfer function and a preset basic transfer function to obtain a total transfer function; and finally, according to the obtained total transfer function, changing the equivalent inductance and capacitance values of the filter circuit, and filtering the current of the static frequency converter rectifier. Coupling harmonic current parameters are accurately extracted through a harmonic analysis unit, a constructed correction transfer function can be matched with specific coupling harmonic current in a targeted mode, and the defects that an existing filter is high in universality and poor in pertinence are overcome. The influence of harmonic coupling current is considered, and the filtering effect is improved by correcting the transfer function of the existing filter.

Description

Technical Field

[0001] This invention belongs to the field of static frequency converter technology, and particularly relates to a method and system for filtering coupled harmonic currents in SFC rectifiers. Background Technology

[0002] During operation, static frequency converter (SFC) rectifiers generate coupling current in the circuit due to the switching action of their internal power electronic devices and the electromagnetic and capacitive coupling phenomena between them and the power grid and load.

[0003] In the prior art, in order to filter out the harmonic current generated by the SFC rectifier, a filter is usually configured at the output or input end of the SFC rectifier. The filter is designed based on the preset transfer function G(s), which is derived from the ideal circuit model of the static frequency converter. It only considers the fundamental current and harmonic current generated by the SFC rectifier itself, and does not fully consider the influence of coupling current caused by coupling phenomenon. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method and system for filtering coupled harmonic currents in SFC rectifiers. This invention considers the influence of harmonic coupling currents and improves the filtering effect by modifying the transfer function of existing filters.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for filtering coupled harmonic currents in an SFC rectifier, comprising: Acquire the current and voltage signals of the static frequency converter rectifier; Fourier transform analysis is performed on the current signal and voltage signal to extract the coupled harmonic current component in the current signal and determine the order and amplitude of the coupled harmonic current. Based on the extracted coupled harmonic current components, a modified transfer function is constructed; the modified transfer function is superimposed with the preset basic transfer function to obtain the total transfer function. Based on the obtained total transfer function, the equivalent inductance and capacitance values ​​of the filter circuit are changed to filter the current of the static inverter rectifier.

[0006] Furthermore, the current signal and voltage signal are the current signal and voltage signal at the output terminal and / or input terminal of the rectifier; the acquired current signal and voltage signal are converted into digital signals.

[0007] Furthermore, Fourier transform analysis is performed on the converted digital signal to separate the fundamental component, uncoupled harmonic components, and coupled harmonic components in the current signal, and to determine the order, amplitude, and frequency of the coupled harmonic current. If multiple coupled harmonic currents exist, the target with the highest amplitude and the greatest impact on the power grid is selected for filtering first.

[0008] Furthermore, the basic transfer function for: ; in, , and These are the filter inductance, capacitor, and resistor, respectively.

[0009] Furthermore, the modified transfer function for: ; in, The angular frequency of the coupled harmonic current; This is a correction factor; For the complex variables of the Laplace transform; is the filter damping coefficient for the coupling frequency.

[0010] Furthermore, the correction coefficient for: ; ; in, and These are the ratios of the coupled harmonic currents after filtering to those before filtering; It is the basic transfer function.

[0011] Furthermore, the equivalent inductance, equivalent capacitance, and equivalent resistance of the filter circuit are adjusted according to the total transfer function to filter the current of the static inverter rectifier.

[0012] Furthermore, based on the filtered current signal, Fourier transform analysis is repeated. If the amplitude after filtering is lower than the preset limit, the current total transfer function and filter circuit parameters are maintained; otherwise, the amplitude of the coupled harmonic current is re-determined, and the correction coefficients in the adjustment and correction transfer function are adjusted until the amplitude after filtering is lower than the preset limit.

[0013] Secondly, the present invention also provides a coupled harmonic current filtering system for an SFC rectifier, comprising: The data acquisition module is configured to acquire the current and voltage signals of the static inverter rectifier. The analysis module is configured to perform Fourier transform analysis on the current signal and voltage signal, extract the coupled harmonic current component in the current signal, and determine the order and amplitude of the coupled harmonic current. The correction module is configured to: construct a corrected transfer function based on the extracted coupled harmonic current components; and superimpose the corrected transfer function with the preset basic transfer function to obtain the total transfer function. The filtering module is configured to filter the current of the static inverter rectifier by changing the equivalent inductance and capacitance values ​​of the filtering circuit according to the obtained total transfer function.

[0014] Thirdly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the coupled harmonic current filtering method for an SFC rectifier described in the first aspect.

[0015] Fourthly, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor, wherein the processor executes the program to implement the steps of the coupled harmonic current filtering method for an SFC rectifier described in the first aspect.

[0016] Fifthly, the present invention also provides a computer program product, the computer program product comprising a computer program, which, when executed by a processor, implements the steps of the coupled harmonic current filtering method for an SFC rectifier described in the first aspect.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention first performs Fourier transform analysis on the current and voltage signals to extract the coupled harmonic current components from the current signal, determining the order and amplitude of the coupled harmonic currents. Then, based on the extracted coupled harmonic current components, a modified transfer function is constructed. The modified transfer function is superimposed with a preset basic transfer function to obtain the total transfer function. Finally, based on the obtained total transfer function, the equivalent inductance and capacitance values ​​of the filter circuit are changed to filter the current of the static inverter rectifier. By accurately extracting the coupled harmonic current parameters through the harmonic analysis unit, the constructed modified transfer function can specifically match the coupled harmonic current of a particular order, solving the shortcomings of existing filters that are highly versatile but lack specificity. By considering the influence of harmonic coupled current and modifying the transfer function of existing filters, the filtering effect is improved.

[0018] 2. This invention achieves real-time monitoring and iterative correction of the filtering effect through feedback adjustment. When the load fluctuation of the SFC rectifier or the change of the grid voltage causes the amplitude of the coupled harmonic current to change, the filtering effect can be kept stable by adjusting the correction coefficient. Attached Figure Description

[0019] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0020] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention; Figure 2 This is the sub-process for constructing the modified transfer function in Embodiment 1 of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] Static frequency converter (SFC): An important power conversion device whose main function is to realize the AC-DC conversion of electrical energy. It is widely used in gas turbine power plants, large-scale industrial speed control systems and other scenarios.

[0024] Coupling current: During the operation of an SFC rectifier, the current generated by the switching action of its internal power electronic devices (such as thyristors, IGBTs, etc.) and by electromagnetic coupling and capacitive coupling with the power grid and load.

[0025] LC passive filter: A common type of filter, consisting of an inductor (L) and a capacitor (C), which filters out harmonic currents in the circuit through a specific circuit structure without requiring an external power source.

[0026] Transfer function G(s): In control theory, it is a mathematical model used to describe the relationship between the input and output of a linear time-invariant system. In filtering technology, it is derived based on an ideal circuit model and is used to guide filter design to achieve the filtering of specific harmonics.

[0027] A / D conversion, or analog-to-digital conversion, refers to the process of converting continuously changing analog signals (such as acquired current and voltage analog signals) into discrete digital signals, providing a data foundation for subsequent digital signal processing (such as Fourier transform analysis).

[0028] Fourier transform analysis: a mathematical transformation method that can decompose a signal in the time domain (such as a current signal) into sinusoidal components of different frequencies and amplitudes in the frequency domain. In this invention, it is used to extract the coupled harmonic current components in the current signal and determine their order, amplitude and frequency.

[0029] Fundamental current: refers to the current component with the same frequency as the fundamental frequency of the power grid, and is the main current component for power transmission in the power system.

[0030] Harmonic current: refers to current components whose frequency is an integer multiple (n times, where n is a positive integer greater than 1) of the fundamental frequency of the power grid. It includes uncoupled harmonic current and coupled harmonic current, which can affect the power quality of the power grid and need to be removed by filtering.

[0031] Modified transfer function ΔG(s): In this invention, a transfer function is constructed to compensate for the fact that the basic transfer function does not consider the influence of coupling current. It can be adjusted according to the parameters of the coupling harmonic current (such as amplitude and angular frequency). When superimposed with the basic transfer function, it can improve the filtering effect on the coupling harmonic current.

[0032] Example 1: In power systems, static frequency converters (SFCs) are important power conversion devices widely used in gas turbine power plants, large industrial speed control systems, and other scenarios. Their main function is to convert electrical energy from AC to DC. However, as described in the background section, during operation, SFC rectifiers generate coupling currents in the circuit due to the switching actions of their internal power electronic devices (such as thyristors and IGBTs), as well as electromagnetic and capacitive coupling phenomena with the power grid and load.

[0033] In existing technologies, filters are typically configured at the output or input of SFC rectifiers to filter out harmonic currents generated by the rectifier. Common filters include LC passive filters and active power filters. These filters are designed based on a preset transfer function G(s), which is derived from an ideal circuit model and only considers the fundamental and harmonic currents generated by the SFC rectifier itself, without fully considering the influence of coupling current caused by coupling phenomena.

[0034] To address at least one of the aforementioned problems, this embodiment provides a method for filtering coupled harmonic currents in SFC rectifiers. By considering the influence of harmonic coupling currents, the transfer function of existing filters is modified, thereby improving the filtering effect. Figure 1 As shown, the method includes: S101, Signal Acquisition: The current and voltage signals at the output and / or input terminals of the SFC rectifier are acquired and converted from analog signals to digital signals via A / D conversion.

[0035] Real-time current and voltage signals from the output and / or input terminals of the SFC rectifier are acquired, and the acquired analog signals are converted into digital signals to provide basic data for subsequent coupled harmonic analysis. The signal acquisition must meet the requirement of a sampling frequency of not less than 10kHz to ensure complete capture of high-frequency coupled harmonic current components, and high-precision sensors (current sensor accuracy ≤0.5%, voltage sensor accuracy ≤0.2%) must be used to avoid signal acquisition errors affecting subsequent analysis results.

[0036] S102, Coupled Harmonic Analysis: Perform Fourier transform analysis on the digital signal to extract the coupled harmonic current components from the current signal and determine the order of the coupled harmonic currents. And amplitude.

[0037] Perform Fourier transform analysis on the converted digital signal to separate the fundamental component, uncoupled harmonic components, and coupled harmonic components in the current signal, and determine the order of the coupled harmonic current (denoted as ). Second-rate, (positive integers), amplitude, and frequency ( , (where the frequency is the fundamental frequency of the power grid). If multiple coupled harmonic currents exist, the first one with the highest amplitude and greatest impact on the power grid should be selected first. This approach uses the target filter object as the primary target, avoiding a surge in transfer function complexity caused by multi-target filtering.

[0038] S103, Transfer Function Correction: Based on the results of coupled harmonic analysis, a modified transfer function is constructed, which is then superimposed with the basic transfer function to obtain the overall transfer function.

[0039] S1031, Call the pre-stored basic transfer function The basic transfer function The transfer function for filtering uncoupled harmonic currents in an SFC rectifier, derived based on an ideal circuit model, is expressed as follows: ; in, , and These are the filter inductance, capacitor, and resistor, respectively.

[0040] S1032. Construct the modified transfer function Its expression is: ; in, The angular frequency of the coupled harmonic current; This is a correction factor; For the complex variables of the Laplace transform; The filter damping coefficient for the coupling frequency is determined based on the amplitude of the coupled harmonic current; the larger the amplitude, the larger the correction coefficient.

[0041] S1033, Define the target attenuation rate for filtering. for: ; in, and These represent the ratios of the coupled harmonic currents before and after filtering.

[0042] Based on the fundamental transfer function at the coupling harmonic current angular frequency Determine the correction factor for the amplitude-frequency response at the location. Limit : ; Finally, determine the correction factor. for: .

[0043] S1034, Transfer the basic transfer function With modified transfer function Superimposing these elements yields the overall transfer function: .

[0044] S104, Filtering: Based on the corrected total transfer function, the on and off states of the controllable switching elements are adjusted to change the equivalent inductance and capacitance values ​​of the LC filter circuit, thereby filtering the current of the SFC rectifier and removing [the pollutants]. Secondary coupled harmonic current.

[0045] Based on the filter's total transfer function By adjusting the three equivalent parameters of the filter circuit—equivalent inductance, equivalent capacitance, and equivalent resistance—the current of the SFC rectifier is filtered, with a focus on filtering out [unspecified pollutants]. The adjustment process for the secondary coupled harmonic current must meet the requirement of a dynamic response time of ≤10ms to ensure rapid adjustment when the amplitude of the coupled harmonic current fluctuates, thus maintaining the filtering effect.

[0046] S105, Feedback Adjustment: Perform coupled harmonic analysis on the filtered current to determine... If the amplitude of the secondary coupled harmonic current is lower than the preset limit, and if it does not meet the limit requirement, the transfer function is further modified until the filtering is complete. The amplitude of the secondary coupled harmonic current is lower than the preset value.

[0047] Based on the filtered current signal, repeat the Fourier transform analysis to determine the quality of the filtered signal. If the amplitude of the secondary harmonic current is lower than a preset limit, and the filtered amplitude is lower than the preset limit, maintain the current overall transfer function and filter circuit parameters. If the filtered amplitude is higher than the preset limit, redetermine the amplitude of the secondary harmonic current and return to adjusting the transfer function. Correction coefficients in until after filtering The amplitude of the secondary coupled harmonic current meets the standard.

[0048] This embodiment accurately extracts the coupled harmonic current parameters through a harmonic analysis unit and constructs a modified transfer function. It can specifically match certain coupling harmonic currents, overcoming the shortcomings of existing filters that are broad in scope but weak in specificity. Through feedback adjustment, it achieves real-time monitoring and iterative correction of the filtering effect. When the amplitude of the coupling harmonic current changes due to load fluctuations (±20%) in the SFC rectifier or changes in grid voltage (±10%), the correction coefficient can be adjusted within 10-50ms. To maintain stable filtering performance.

[0049] Example 2: This embodiment provides a coupled harmonic current filtering system for an SFC rectifier, including: The data acquisition module is configured to acquire the current and voltage signals of the static inverter rectifier. The analysis module is configured to perform Fourier transform analysis on the current signal and voltage signal, extract the coupled harmonic current component in the current signal, and determine the order and amplitude of the coupled harmonic current. The correction module is configured to: construct a corrected transfer function based on the extracted coupled harmonic current components; and superimpose the corrected transfer function with the preset basic transfer function to obtain the total transfer function. The filtering module is configured to filter the current of the static inverter rectifier by changing the equivalent inductance and capacitance values ​​of the filtering circuit according to the obtained total transfer function.

[0050] The operating method of the system is the same as the coupled harmonic current filtering method for SFC rectifiers in Embodiment 1, and will not be repeated here.

[0051] Example 3: This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the coupled harmonic current filtering method for an SFC rectifier described in Embodiment 1.

[0052] Example 4: This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the program, it implements the steps of the coupled harmonic current filtering method for SFC rectifiers described in Embodiment 1.

[0053] Example 5: This embodiment provides a computer program product, which includes a computer program. When the computer program is executed by a processor, it implements the steps of the coupled harmonic current filtering method for SFC rectifiers described in Embodiment 1.

[0054] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A method for filtering coupled harmonic currents in an SFC rectifier, characterized in that, include: Acquire the current and voltage signals of the static frequency converter rectifier; Fourier transform analysis is performed on the current signal and voltage signal to extract the coupled harmonic current component in the current signal and determine the order and amplitude of the coupled harmonic current. Based on the extracted coupled harmonic current components, a modified transfer function is constructed; The total transfer function is obtained by superimposing the modified transfer function with the preset basic transfer function; Based on the obtained total transfer function, the equivalent inductance and capacitance values ​​of the filter circuit are changed to filter the current of the static inverter rectifier.

2. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 1, characterized in that, The current and voltage signals are the current and voltage signals at the output and / or input terminals of the rectifier; the acquired current and voltage signals are converted into digital signals.

3. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 2, characterized in that, Fourier transform analysis is performed on the converted digital signal to separate the fundamental component, uncoupled harmonic component and coupled harmonic component in the current signal, and to determine the order, amplitude and frequency of the coupled harmonic current. If multiple coupled harmonic currents exist, the target with the highest amplitude and the greatest impact on the power grid should be selected for filtering first.

4. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 1, characterized in that, The basic transfer function for: ； in, , and These are the filter inductance, capacitor, and resistor, respectively.

5. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 1, characterized in that, The modified transfer function for: ； in, The angular frequency of the coupled harmonic current; This is a correction factor; For the complex variables of the Laplace transform; is the filter damping coefficient for the coupling frequency.

6. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 5, characterized in that, The correction coefficient for: ； ； in, and These are the ratios of the coupled harmonic currents after filtering to those before filtering; It is the basic transfer function.

7. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 1, characterized in that, The equivalent inductance, equivalent capacitance, and equivalent resistance of the filter circuit are adjusted according to the total transfer function to filter the current of the static inverter rectifier.

8. The method for filtering coupled harmonic currents in an SFC rectifier as described in claim 1, characterized in that, Based on the filtered current signal, Fourier transform analysis is repeated. If the amplitude after filtering is lower than the preset limit, the current total transfer function and filter circuit parameters are maintained; otherwise, the amplitude of the coupled harmonic current is re-determined, and the correction coefficients in the correction transfer function are adjusted until the amplitude after filtering is lower than the preset limit.

9. A coupled harmonic current filtering system for an SFC rectifier, characterized in that, include: The data acquisition module is configured to acquire the current and voltage signals of the static inverter rectifier. The analysis module is configured to perform Fourier transform analysis on the current signal and voltage signal, extract the coupled harmonic current component in the current signal, and determine the order and amplitude of the coupled harmonic current. The correction module is configured to construct a corrected transfer function based on the extracted coupled harmonic current components. The total transfer function is obtained by superimposing the modified transfer function with the preset basic transfer function; The filtering module is configured to filter the current of the static inverter rectifier by changing the equivalent inductance and capacitance values ​​of the filtering circuit according to the obtained total transfer function.

10. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the steps of the coupled harmonic current filtering method for an SFC rectifier as described in any one of claims 1-8.

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