Harmonic treatment method, device and equipment of voltage detection type active power filter

Abstract

The application provides a harmonic treatment method, device and equipment of a voltage detection type active power filter, and relates to the technical field of harmonic treatment. The method comprises the following steps: obtaining three-phase network side alternating current voltages of a public connection point of a power distribution network to be treated; transforming the three-phase network side alternating current voltages to a two-phase stationary coordinate system to obtain two-phase voltage signals, and performing differential operation on the two-phase voltage signals and a delay signal with a preset proportional fundamental wave period to obtain an increment signal; wherein the preset proportional fundamental wave period is 1 / 6 of a fundamental wave period; performing improved sliding discrete Fourier transform on the increment signal to obtain extraction signals of each preset odd harmonic, and determining a total harmonic extraction signal according to the extraction signals; generating a harmonic compensation voltage instruction according to the total harmonic extraction signal, and completing harmonic treatment according to the harmonic compensation voltage instruction. The application can improve the harmonic extraction speed.

Description

Technical Field

[0001] This invention relates to the field of harmonic mitigation technology, and in particular to a harmonic mitigation method, apparatus, and equipment for a voltage-sensing active power filter. Background Technology

[0002] With the large-scale integration of industrial power electronic equipment into the power distribution network, frequency converters and rectifiers continuously introduce harmonics into the grid, causing problems such as voltage distortion at the point of common coupling and degraded power quality. Active power filters are the mainstream devices for mitigating grid harmonics. Based on the type of sampling signal, they can be divided into current-sensing and voltage-sensing types. Among them, voltage-sensing active power filters rely on grid-side voltage sampling to suppress harmonics, giving them unique advantages in voltage distortion mitigation scenarios.

[0003] Harmonic extraction algorithms are the core of voltage-sensing active power filter control systems, and the output accuracy and response speed of the algorithm directly determine the harmonic compensation performance. Existing harmonic extraction algorithms for voltage-sensing active power filters generally employ Discrete Fourier Transform (DFT) and conventional sliding DFT to separate harmonic components. These algorithms rely on continuously acquiring sampling data within a complete fundamental frequency cycle for computation.

[0004] However, a data window with a complete fundamental period introduces a significant inherent time delay, resulting in slow harmonic extraction. When load switching or operating condition disturbances cause sudden changes in grid harmonics, the algorithm struggles to quickly track the dynamic changes in harmonics, leading to delayed harmonic compensation command output and ultimately poor harmonic mitigation performance. Summary of the Invention

[0005] This invention provides a harmonic mitigation method, apparatus, and device for a voltage-sensing active power filter, to solve the problem that existing harmonic mitigation methods are slow in extracting harmonics, thus affecting the harmonic mitigation effect.

[0006] In a first aspect, embodiments of the present invention provide a harmonic mitigation method for a voltage-sensing active power filter, comprising: Obtain the three-phase AC voltage at the point of common coupling of the distribution network to be treated; The three-phase grid-side AC voltage is transformed to a two-phase stationary coordinate system to obtain a two-phase voltage signal. The two-phase voltage signal and the delayed signal with a preset ratio of the fundamental frequency period are then used to perform differential operations to obtain an incremental signal. The preset ratio of the fundamental frequency period is 1 / 6 of the fundamental frequency period. An improved sliding discrete Fourier transform is performed on the incremental signal to obtain the extraction signals of each preset odd harmonic, and the total harmonic extraction signal is determined based on the extraction signals. The total harmonics extraction signal is used to generate a harmonic compensation voltage command, and the harmonic mitigation is performed according to the harmonic compensation voltage command.

[0007] In one possible implementation, the step of performing an improved sliding discrete Fourier transform on the incremental signal to obtain the extracted signals of each preset odd harmonic includes: The amplitude and phase angle adjustment factor is determined based on the total number of sampling points within one cycle of the fundamental wave and the order of the target harmonic to be extracted. For each preset odd harmonic, the corresponding rotation factor is determined based on the total number of sampling points in one cycle of the fundamental wave and the preset odd harmonic number. The incremental signal, the amplitude and phase angle adjustment factor and the rotation factor corresponding to the preset odd harmonic are multiplied together to calculate the product result. The preset odd harmonic extraction signal is obtained by updating and iterating based on the product result and the harmonic iteration component of the previous time step.

[0008] In one possible implementation, determining the amplitude and phase adjustment factor based on the total number of sampling points within one cycle of the fundamental wave and the target harmonic order to be extracted includes: Based on the total number of sampling points in one cycle of the fundamental wave and the number of the target harmonic to be extracted, construct the complex exponential reference term corresponding to the target harmonic; Construct an expression for the window zeros, take the first derivative with respect to the complex variable, and assign the complex variable to the complex exponent corresponding to the target harmonic frequency, and solve to obtain the derivative value; The amplitude and phase angle adjustment factor is calculated based on the complex exponential reference term and the derivative value.

[0009] In one possible implementation, before performing differential operations on the two-phase voltage signals and the delayed signal with a preset proportional fundamental period to obtain the incremental signal, the method further includes: The two-phase voltage signals are delayed by a preset ratio of the fundamental frequency period to obtain the delayed signal; The step of performing differential operations based on the two-phase voltage signals and a delayed signal with a preset proportional fundamental period to obtain an incremental signal includes: The incremental signal is calculated by subtracting the two-phase voltage signal and the delayed signal.

[0010] In one possible implementation, determining the total harmonic extraction signal based on the extracted signal includes: Extract the real and imaginary parts of the extracted signal corresponding to each preset odd harmonic, and calculate the instantaneous amplitude and phase of each preset odd harmonic based on the real and imaginary parts; For each preset odd harmonic, the voltage signal of each preset odd instantaneous harmonic is reconstructed to the three-phase stationary coordinate system by inverse Clarke transformation based on the amplitude and phase. The total harmonic extraction signal is obtained by superimposing the preset odd-order instantaneous harmonic voltage signals respectively.

[0011] In one possible implementation, transforming the three-phase grid-side AC voltage to a two-phase stationary coordinate system to obtain a two-phase voltage signal includes: The three-phase grid-side AC voltage is converted to a two-phase stationary coordinate system using the Clarke transform to obtain the voltage signal in the two-phase stationary coordinate system. Discretize the voltage signal in the two-phase stationary coordinate system to obtain the two-phase voltage sampling components; The two-phase voltage sample components are stored in a sliding data window queue to obtain the two-phase voltage signal.

[0012] In one possible implementation, the harmonic mitigation based on the harmonic compensation voltage command includes: Based on the harmonic compensation voltage command and the fundamental voltage command, the total voltage reference command is obtained; The total voltage reference command is sequentially input into the voltage outer loop and the current inner loop for closed-loop regulation to obtain the modulation reference signal; Space vector pulse width modulation is performed based on the modulation reference signal to generate a drive control signal; The driving control signal generates a corresponding compensation voltage, and harmonic mitigation is performed based on the corresponding compensation voltage.

[0013] In one possible implementation, generating the harmonic compensation voltage command based on the total harmonic extraction signal includes: The total harmonic distortion (THD) extraction signal is input into the feedback gain unit with a preset proportional control gain coefficient, and the THD extraction signal is multiplied by the preset proportional control gain coefficient to obtain the product result. The product result is then determined as the harmonic compensation voltage command.

[0014] Secondly, embodiments of the present invention provide a harmonic mitigation device for a voltage-sensing active power filter, comprising: Harmonic extraction and instruction generation module, voltage and current dual closed-loop control module for active power filter, DC side voltage control module and SVPWM modulation module; The harmonic extraction and command generation module is used to acquire the three-phase AC voltage at the point of common coupling of the distribution network to be treated, transform the three-phase AC voltage to a two-phase stationary coordinate system to obtain a two-phase voltage signal, and perform differential operation on the two-phase voltage signal and a delayed signal with a preset proportional fundamental period to obtain an incremental signal; wherein the preset proportional fundamental period is 1 / 6 of a fundamental period; perform an improved sliding discrete Fourier transform on the incremental signal to obtain the extraction signals of each preset odd harmonic, and determine the total harmonic extraction signal based on the extraction signals; generate a harmonic compensation voltage command based on the total harmonic extraction signal, and complete harmonic treatment based on the harmonic compensation voltage command; The voltage and current dual closed-loop control module of the active power filter is used to receive the harmonic compensation voltage command and the fundamental voltage reference command, superimpose them to obtain the total voltage reference command, introduce the inverter side voltage and inverter side current feedback signals, and output the modulation reference signal through closed-loop adjustment calculation of voltage outer loop and current inner loop. The DC-side voltage control module is used to acquire the actual DC-side voltage of the active power filter, calculate the difference between the actual DC-side voltage and the DC-side voltage reference to obtain a voltage error signal, output the active power compensation reference value through the P regulator, and then input it into the droop control module. Combined with the inverter-side voltage and inverter-side current sampling signals, it outputs the fundamental voltage reference command and the synchronization phase. The SVPWM modulation module is used to receive the modulation reference signal, perform space vector pulse width modulation operation, and generate drive control signals for the power switching transistors of the main power circuit.

[0015] Thirdly, embodiments of the present invention provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0016] This invention provides a harmonic mitigation method, apparatus, and device for a voltage-sensing active power filter. First, the three-phase grid-side voltage signal is transformed into two-phase voltages through coordinate transformation, simplifying harmonic complex calculations. Differential calculations are performed using a 1 / 6 preset ratio of the fundamental period, significantly shortening data processing time compared to a full fundamental period data window and compressing the inherent latency of the algorithm. Simultaneously, differential calculations suppress steady-state fundamental components, retaining only the incremental signal of dynamically changing voltages, reducing invalid calculations caused by steady-state components and suppressing interference from irrelevant frequency components. Then, an improved sliding discrete Fourier transform is performed based on the incremental signal, eliminating the need to process constant fundamental components and reducing iterative computation. The combination of differential preprocessing and the improved sliding discrete Fourier transform enhances harmonic separation selectivity, ensures accurate harmonic extraction, and effectively improves harmonic tracking response capability. Finally, harmonic compensation voltage commands are generated based on the total harmonic extraction signal to achieve harmonic mitigation. Attached Figure Description

[0017] Figure 1 This is an application scenario diagram of the harmonic mitigation method for voltage-sensing active power filters provided in this embodiment of the invention; Figure 2a This is the overall system control block diagram of the voltage-sensing active power filter provided in the embodiments of the present invention; Figure 2b This is the equivalent control topology diagram of the voltage-sensing active power filter provided in the embodiments of the present invention; Figure 3 This is a flowchart illustrating the implementation of the harmonic mitigation method for a voltage-sensing active power filter provided in this embodiment of the invention. Figure 4 This is a schematic diagram of the harmonic extraction algorithm structure of SOHSDFT provided in an embodiment of the present invention; Figure 5 This is a waveform diagram of the steady-state compensation result verified by the experimental platform provided in the embodiments of the present invention; Figure 6 This is a waveform diagram of the dynamic response results verified by the experimental platform provided in this embodiment of the invention; Figure 7 This is a schematic diagram of the harmonic mitigation device for a voltage-sensing active power filter provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0018] In recent years, with the development of power electronics technology, new power generation and transmission technologies that use power electronic devices as important carriers, such as new energy power generation, flexible power transmission, and microgrids, have received attention. While these emerging technologies improve energy efficiency and alleviate the energy crisis, they also bring about a series of power quality deterioration problems, such as system harmonics and voltage distortion. Poor power quality can lead to a series of economic and social problems, including energy waste, reduced equipment lifespan, and threats to the normal operation of critical equipment.

[0019] Traditional parallel active power filters, as an effective means of power quality management, often employ current-sensing control strategies, requiring real-time detection of harmonic source currents. However, in many practical engineering projects and complex power grid nodes, load current is often difficult to obtain directly; moreover, traditional current-controlled devices are prone to harmonic amplification when faced with grid background harmonic voltage distortion, limiting their compensation performance. To address these issues, voltage-sensing active power filters (VDAPFs) have gradually become an important development direction in this field due to their characteristics of not requiring load-side current detection and actively absorbing grid harmonics by using equivalent virtual harmonic conductance. Furthermore, to achieve better high-frequency switching subharmonic attenuation, the main power circuit of a VDAPF typically uses an LCL filter instead of a traditional L-type inductor.

[0020] However, the steady-state compensation accuracy and system stability of VDAPFs using LCL filters are highly dependent on the real-time performance and accuracy of grid-side harmonic voltage extraction. Traditional harmonic extraction algorithms (such as instantaneous reactive power theory based on low-pass filters and conventional discrete Fourier transform) generally suffer from drawbacks such as hysteresis in dynamic response, high computational load, and susceptibility to interference from non-characteristic frequency band signals. Designing a harmonic detection and extraction algorithm that balances high steady-state accuracy with extremely fast dynamic response, and then, after acquiring accurate specific harmonic voltage signals, calculating compensation commands using a rigorous harmonic control law and outputting accurate positive-level space vector pulse width modulation (SVPWM) drive signals, is a crucial technical challenge that urgently needs to be addressed to further improve the dynamic response performance and control robustness of VDAPFs.

[0021] Several studies have presented solutions for selective harmonic control of active power filters. X. Yuan et al. proposed a generalized integral control algorithm, namely a proportional resonant controller. However, when dealing with multi-band harmonics, the controlled frequency bands are prone to mutual interference, and for voltage-sensing active power filter architectures containing LCL filters, the system is highly susceptible to changes in the parameters of the controlled object and the grid impedance, resulting in poor robustness. C. Lascu et al. further proposed a vector resonant regulator to improve the frequency selectivity and dynamic performance of the proportional resonant controller; however, this algorithm is easily affected by the parameters of the controlled object, and its effectiveness is generally limited. P. Mattavelli et al. proposed a harmonic control algorithm based on the Discrete Fourier Transform (DFT), which has excellent harmonic frequency selectivity and good dynamic performance, but its control structure relies on a fixed full-cycle data window, resulting in large computational delays and significant hysteresis in the system's dynamic response. In VDAPF closed-loop control requiring extremely fast response, if the compensation command is calculated by substituting the extracted results into the control expression, the delay of the traditional extraction algorithm will cause a phase shift in the output command.

[0022] To address the numerous shortcomings of existing technologies, this invention proposes a harmonic mitigation method for voltage-sensing active power filters. Based on differential preprocessing with a 1 / 6 fundamental period reduced data window and an improved sliding discrete Fourier transform algorithm, this method significantly reduces algorithm computation delay and improves dynamic response speed while ensuring steady-state accuracy of harmonic extraction. Furthermore, it corrects singular value errors caused by window reduction using L'Hopital's rule, thus completely resolving the technical contradiction of traditional algorithms where speed and accuracy cannot be simultaneously achieved, making it suitable for complex dynamic harmonic mitigation scenarios in power grids.

[0023] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] Figure 1 This diagram illustrates an application scenario of the harmonic mitigation method for a voltage-sensing active power filter provided in an embodiment of the present invention. (Example:) Figure 1 As shown, the active power filter 102 is connected in parallel to the common coupling point PCC between the three-phase AC power grid 101 and the harmonic source 103. The active power filter centrally manages the harmonic voltage generated on the power grid side, effectively acting as a virtual harmonic conductance to actively absorb specific harmonics from the power grid, thereby improving the PCC voltage. The active power filter includes a main power circuit and its control section. The main power circuit consists of a DC-side capacitor... C dc Six power switching transistors ( S 1~ S 6) A three-phase voltage-source inverter consisting of its anti-parallel diodes, and an LCL filter on the output side (composed of the inverter-side inductor). L 1. Grid-side inductorL 2. Filter capacitor C f and its damping resistor R d Composition) For ease of description, the PCC grid-side voltage is labeled as... u pcc The DC-side voltage of the active power filter is marked as V dc The inverter output voltage is marked as u o The output current is marked as i o .

[0025] like Figure 2a This is the overall system control block diagram of a voltage-sensing active power filter. The active power filter control section is divided into four main parts: a grid-side harmonic extraction and command generation loop 201, a voltage and current dual closed-loop control inner loop 202, a DC-side voltage control loop 203, and an SVPWM modulation loop 204. The grid-side harmonic extraction and command generation loop 201 generates harmonic compensation commands. V href DC-side voltage control loop 203, combined with droop control, generates fundamental voltage reference commands. V ref The two instructions are superimposed and sent to the inner loop 202 of the voltage and current dual closed-loop control for closed-loop tracking control; finally, the positive level high-frequency switching signal of the main power circuit switching transistor is generated through the SVPWM modulation stage 204.

[0026] Specifically, in the grid-side harmonic extraction and command generation loop 201, a voltage sensor is used to sample the PCC point voltage in real time. u pcc The signal is input to the improved Sliding Discrete Fourier Transform (SOHSDFT) module. Internally, the module employs a 1 / 6-period sliding data window mechanism to precisely eliminate the fundamental component and rapidly extract the preset odd-order harmonic characteristic voltages. V pcch Subsequently, according to the control law, it passes through the proportional gain module. K (correspond KV pcch = V href ), to obtain the final harmonic compensation voltage command for the active power filter. V href .

[0027] See appendix Figure 2aThe DC-side voltage control loop 203 in the middle uses a voltage sensor to sample the actual DC-side voltage. V dc Compared with the preset DC-side voltage reference V dcref The voltage error signal is obtained by taking the difference; this error signal is then processed by a P regulator (the gain is denoted as P). K v Output active power compensation reference value P ref This data is then input to the droop control module. The droop control module combines the sampled inverter-side voltage with... u o and inverter-side current i 0, Output fundamental voltage reference command V ref and synchronization phase ωt .

[0028] Fundamental voltage reference command V ref Harmonic compensation voltage command V href By superimposing these parameters, the total voltage reference command for the inner loop 202 of the dual closed-loop control of the active power filter is obtained. V * ref .

[0029] Voltage and current dual closed-loop control inner loop 202 introduces inverter-side voltage. u o and inverter-side current i 1. Feedback is provided. The inner and outer loop regulators (including the outer voltage loop PI controller, the quasi-resonant controller QR, and the inner current loop PI controller) respond to the total voltage reference command. V * ref The system performs fast, zero-steady-state-error tracking closed-loop control. Its output modulation signal is sent to the SVPWM modulation stage 204 to generate precise positive-level drive pulses to control the output of the three-phase inverter, thereby achieving rapid dynamic suppression and compensation of specific harmonics under complex power grid conditions.

[0030] Furthermore, to characterize the aforementioned control connections, an equivalent control topology diagram of the voltage-sensing active power filter was constructed, see [reference needed]. Figure 2b Common coupling point voltage V pcc (s) The preset odd harmonics are extracted by the SOHSDFT module and then proportionally gained. K Forming harmonic compensation voltage command V href Harmonic compensation voltage command V href With fundamental voltage reference commandV ref After converging at the outer voltage loop reference input, the system enters a dual-loop voltage and current control. Furthermore, from an equivalent control perspective, the dual-loop voltage and current control includes the outer voltage loop controller. G u ( s and current inner loop controller G i ( s The modulation stage employs an equivalent gain. K pwm Characterization; the main power circuit includes the inverter-side inductor. L 1 and its equivalent series resistance R 1. Filter capacitor C f and damping resistor R d , grid-side inductor L 2 and its equivalent series resistance R 2, of which i o (s) represents the output current. V pcc (s) represents the voltage at the point of common coupling. For the first... k The pre-defined odd harmonics, the point of common coupling voltage is selected by the corresponding SOHSDFT harmonic selection circuit G. SOHSDFTk ( s and proportional gain K The corresponding harmonic compensation component is generated and connected to the voltage outer loop reference input terminal, thereby forming a harmonic feedback control branch that is connected to the dual closed-loop control terminal through the harmonic extraction and gain circuit from the voltage detection terminal at the common connection point.

[0031] Based on the above overall system architecture and control logic, this invention constructs a complete harmonic mitigation implementation process, see [link to relevant documentation]. Figure 3 The diagram illustrates the implementation flowchart of the harmonic mitigation method for a voltage-sensing active power filter provided in this embodiment of the invention, detailed below: Step 301: Obtain the three-phase AC voltage at the point of common connection of the distribution network to be treated.

[0032] In some embodiments, the point of common coupling (PCC) is the node where a nonlinear load in a distribution network connects to the power grid. It is the main location where harmonics are generated and observed, and an active power filter collects voltage at this location for harmonic detection. The three-phase grid-side AC voltage is the three-phase power frequency AC voltage at the PCC, which includes the fundamental voltage and the 6k±1st order characteristic harmonic, where k is a positive integer (e.g., 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th, etc.).

[0033] In this embodiment, voltage is directly sampled at the harmonic generation node to achieve voltage detection-type harmonic extraction, eliminating the need to sample load current and simplifying sensor configuration.

[0034] Step 302: Transform the three-phase grid-side AC voltage to a two-phase stationary coordinate system to obtain a two-phase voltage signal, and perform differential operation on the two-phase voltage signal and the delayed signal with a preset proportional fundamental period to obtain an incremental signal; wherein, the preset proportional fundamental period is 1 / 6 of the fundamental period.

[0035] In some embodiments, the two-phase stationary coordinate system is a two-phase orthogonal stationary coordinate system obtained by Clarke transform, eliminating three-phase coupling and facilitating harmonic analysis calculations. The two-phase voltage signal is the α- and β-axis discrete voltage signal obtained by Clarke transforming, discretely sampling, and storing the three-phase voltage in a sliding window. The preset proportional fundamental period is 1 / 6 of the duration of a complete fundamental period of the power grid, which reduces the core parameters of the sliding data window in this scheme and adapts to the 6k±1 harmonic. The delayed signal is the hysteresis signal obtained by delaying the two-phase voltage signal by 1 / 6 of the fundamental period. The incremental signal is the differential signal obtained by subtracting the delayed signal from the current two-phase voltage signal.

[0036] In this embodiment, differential operation naturally suppresses the steady-state fundamental component, filters out the fundamental, retains 6k±1 characteristic harmonics, and eliminates invalid operations caused by the fundamental. A 1 / 6 fundamental period is used as the differential time delay to match the characteristic harmonic frequency characteristics of the power grid. This achieves a smaller data sliding window, shortening signal processing time and improving the dynamic response speed of harmonics. This invention utilizes a 1 / 6 fundamental period-minimized sliding data window mechanism for dynamic updates, compressing the dynamic response time of harmonic extraction to 3.3ms, significantly shortening the system's tracking time for step disturbances and significantly improving the transient response speed of closed-loop control.

[0037] Step 303: Perform an improved sliding discrete Fourier transform on the incremental signal to obtain the extraction signals of each preset odd harmonic, and determine the total harmonic extraction signal based on the extraction signals.

[0038] In some embodiments, the improved sliding discrete Fourier transform is an iterative discrete Fourier algorithm based on narrowing the data window and introducing amplitude and phase angle adjustment factors. The preset odd harmonics are the 6k±1th characteristic harmonics of the power grid. The harmonic extraction signal is the complex component of the single harmonic separated by the improved sliding discrete Fourier transform. The total harmonic extraction signal is the composite harmonic voltage signal obtained by restoring each harmonic component to three phases through inverse Clarke transform and then superimposing them.

[0039] In this embodiment, an improved sliding discrete Fourier transform is performed based on the incremental signal. Compared with the traditional integer-period improved sliding discrete Fourier transform, the window is smaller and the harmonic extraction convergence speed is faster. By introducing an amplitude and phase angle adjustment factor, the harmonic amplitude and phase distortion caused by shrinking the data window is overcome, ensuring that the harmonic extraction has no steady-state error, zero attenuation, and zero phase shift. Each characteristic harmonic is separated separately and then reconstructed and superimposed to obtain the total harmonic signal, realizing selective harmonic extraction, which is convenient for precise harmonic control.

[0040] Step 304: Generate a harmonic compensation voltage command based on the total harmonic extraction signal, and complete harmonic mitigation based on the harmonic compensation voltage command.

[0041] In some embodiments, the harmonic compensation voltage command is the target compensation voltage reference value that the active power filter needs to output.

[0042] In this embodiment, the extracted grid harmonic signal is converted into a voltage compensation command that can be executed by the active power filter; the active power filter is driven to output a reverse compensation voltage to cancel the harmonic voltage at the distribution network point of common coupling, suppress voltage distortion, and achieve harmonic mitigation.

[0043] This invention provides a harmonic mitigation method for a voltage-sensing active power filter. First, the three-phase grid-side voltage signal is transformed into two-phase voltages through coordinate transformation, simplifying harmonic complex calculations. Differential calculations are performed using a 1 / 6 preset ratio of the fundamental period, significantly shortening data processing time compared to a full fundamental period data window and compressing the inherent latency of the algorithm. Simultaneously, differential calculations suppress steady-state fundamental components, retaining only the incremental signal of dynamically changing voltages, reducing invalid calculations caused by steady-state components and suppressing interference from irrelevant frequency components. Then, an improved sliding discrete Fourier transform is performed based on the incremental signal, eliminating the need to process constant fundamental components and reducing iterative computation. The combination of differential preprocessing and the improved sliding discrete Fourier transform enhances harmonic separation selectivity, ensures accurate harmonic extraction, and effectively improves harmonic tracking response capability. Finally, harmonic compensation voltage commands are generated based on the total harmonic extraction signal to achieve harmonic mitigation.

[0044] To further refine the iterative principle and correction mechanism of the core algorithm of this invention, the specific implementation steps of the improved sliding discrete Fourier transform are described in detail below.

[0045] In one possible implementation, an improved sliding discrete Fourier transform is performed on the incremental signal to obtain the extracted signals of each preset odd harmonic, including: The amplitude and phase angle adjustment factor is determined based on the total number of sampling points within one cycle of the fundamental wave and the order of the target harmonic to be extracted. For each preset odd harmonic, the corresponding rotation factor is determined based on the total number of sampling points in one cycle of the fundamental wave and the preset odd harmonic number. The incremental signal, the amplitude and phase angle adjustment factor and the rotation factor corresponding to the preset odd harmonic are multiplied to obtain the product result. The preset odd harmonic extraction signal is obtained by updating and iterating based on the product result and the harmonic iteration components of the previous time step.

[0046] In some embodiments, the total number of sampling points within one cycle of the fundamental frequency is the total number of sampling points of the analog-to-digital converter within a complete cycle of the power grid fundamental frequency, determined by both the sampling frequency and the power grid fundamental frequency, and is a fundamental parameter of the discrete algorithm. The target harmonic order to be extracted is the 6k±1th characteristic odd harmonic to be separated and extracted. The amplitude and phase angle adjustment factor is the core correction coefficient; due to the use of a 1 / 6 shrinking sliding data window, the filter zero point falls at the harmonic operating point, generating a 0 / 0 type singular point. This complex correction factor is derived through L'Hopital's rule and is used to compensate for the harmonic amplitude attenuation and phase shift caused by the shrinking window. The preset rotation factor corresponding to the odd harmonic is the standard complex exponential rotation factor of the discrete Fourier transform, which is used to shift the signal spectrum, convert the target harmonic into a DC component, and achieve harmonic separation. The harmonic iteration component of the previous moment is the sliding discrete Fourier transform iteration storage term. The improved sliding discrete Fourier transform relies on the recursive calculation of historical iteration values, eliminating the need to repeatedly perform complete summation and reducing the computational load. The extracted signal of the preset odd harmonic is the complex form harmonic component corresponding to the single target harmonic, which includes real-time amplitude and phase information (complex signal in αβ coordinate system).

[0047] In this embodiment, an improved iterative computation process for the sliding discrete Fourier transform is implemented: a corresponding rotation factor is configured for each target odd harmonic to achieve harmonic frequency selection and separation; an amplitude and phase angle adjustment factor is introduced to correct the amplitude and phase distortion caused by shrinking the sliding data window; and harmonic components are solved in real time according to an iterative recursive method. Based on differential preprocessing of incremental signals, it can quickly and successively selectively extract each characteristic odd harmonic, accelerating harmonic tracking speed; it can also correct the computational distortion caused by shrinking the window, ensuring harmonic extraction accuracy, and taking into account both the dynamic response speed and steady-state extraction accuracy of harmonic detection, providing reliable harmonic information for accurate harmonic compensation of active power filters. The harmonic extraction algorithm of this invention can effectively improve the dynamic response speed, steady-state compensation accuracy, and control robustness of active power filters. It has excellent selectivity for preset odd harmonic frequencies. By accurately locking the characteristic ripple of 300Hz and integer multiples thereof, it completely eliminates the cumbersome design of digital low-pass filters and avoids the mutual influence between controlled harmonic components. It has high steady-state accuracy and strong robustness. This algorithm is directly designed for voltage-sensing active power filter architectures that include LCL filters. It can extract and compensate for harmonics without steady-state error, effectively overcoming the system's sensitivity to changes in grid impedance and filter parameters.

[0048] The core innovation of the above-mentioned improved algorithm lies in the accurate solution of the amplitude and phase adjustment factor. The specific steps for solving the amplitude and phase adjustment factor are as follows.

[0049] In one possible implementation, the amplitude and phase adjustment factor is determined based on the total number of sampling points within one cycle of the fundamental wave and the target harmonic order to be extracted, including: Based on the total number of sampling points in one cycle of the fundamental wave and the order of the target harmonic to be extracted, construct the complex exponential benchmark term corresponding to the target harmonic; Construct an expression for the window zeros, take the first derivative with respect to the complex variable, and assign the complex variable to the complex exponent corresponding to the target harmonic frequency, and solve to obtain the derivative value; The amplitude and phase angle adjustment factor is calculated based on the complex exponential benchmark term and derivative value.

[0050] In some embodiments, the complex exponential reference term is the complex exponential signal term corresponding to the target harmonic frequency, serving as the standard reference complex number for the target harmonic in the discrete frequency domain and a reference for amplitude and phase correction. The window zero-point construction expression is the zero-point expression of the comb filter transfer function established in the Z-domain by shrinking the sliding data window by 1 / 6 of the fundamental period; this zero point falls precisely at the target harmonic frequency, forming a 0 / 0 type indeterminate singularity, which would fail to be calculated directly. The complex variable is the complex variable z in the Z-transform, a complex frequency domain variable of the discrete system. Taking the first derivative involves differentiating the zero-point expression with respect to the complex variable, a necessary mathematical operation for solving the 0 / 0 limit using L'Hopital's rule. The complex exponent corresponding to the target harmonic frequency is the complex value corresponding to the sinusoidal steady-state operating frequency of the target subharmonic in the discrete Z-domain.

[0051] In the specific implementation process, iterative calculations are performed on the incremental signal using the improved sliding discrete Fourier transform algorithm to extract the first... h 1, h 2, ..., h m Second-rate( h To preset the odd harmonic order, , k Complex eigencomponents of the αβ axis of the harmonics (non-negative integers) X h ( n This process is in discrete... Z Domain utilization Construct a zero-point reshaping generator with comb filtering characteristics. In the target... h Second harmonic frequency There is Therefore, together with the poles of the corresponding digital oscillator, a 0 / 0 type indeterminate form is formed, and the amplitude and phase adjustment factor can be obtained using L'Hôpital's rule. For the 0 / 0 type singular value at the target frequency, a dynamic amplitude and phase adjustment factor obtained according to L'Hôpital's rule for complex functions is introduced. λ Steady-state corrections are performed, among which, The corrected discrete iterative relationship is shown in the following equation: In the formula, V pcc_αβ( n )express αβ shaft voltage signal, For the corresponding number h The rotation factor corresponding to the pre-set odd harmonics. The harmonic iteration component of the previous time step. This is a delayed signal with a delay of 1 / 6 of a fundamental frequency period.

[0052] In this embodiment, the complete solution process for the amplitude and phase angle adjustment factor is implemented. Addressing the challenge of 0 / 0 type singular values ​​appearing at the target harmonic frequency due to narrowing the sliding data window, the mathematical principle of L'Hôpital's rule is used. The expression for the zero point of the window is differentiated and substituted into the target harmonic frequency to solve for the limit. The amplitude and phase angle adjustment factor is then calculated using the complex exponential reference term. This adjustment factor is used to correct the harmonic amplitude attenuation and phase shift caused by narrowing the data window, overcoming the technical contradiction between "shortening the window to improve response speed" and "decreasing harmonic extraction accuracy." This ensures that the improved sliding discrete Fourier transform can accurately extract each characteristic odd harmonic, maintaining steady-state extraction accuracy while accelerating the dynamic response of harmonic detection. This invention's improved sliding discrete Fourier transform harmonic extraction algorithm, based on the idea of ​​the sliding discrete Fourier transform, constructs a system for extracting typical odd harmonics in the power grid. αβ A dynamic tracking model in a stationary coordinate system. This is achieved by introducing a differential update mechanism with a reduced sliding data window in a discrete coordinate system. Z The pole-zero distribution of the transfer function is reshaped within the domain, and a rotation factor corresponding to the preset odd harmonics is introduced into the control calculation loop for complex multiplication and cumulative iteration. Combined with L'Hopital's rule for complex functions, singular values ​​are corrected, completely eliminating the need for cumbersome digital low-pass filter design, thus achieving optimal ultra-fast dynamic response (algorithm response time up to 3.3ms) and extremely strong anti-interference capability of the control system. A cleverly utilized 1 / 6 reduction in the sliding data window... αβ In a stationary coordinate system, the window length, combined with the frequency shift characteristics of the rotation factor, precisely constructs the reshaped zero point of the comb filter. Without the need for additional complex low-pass filter design, the L'Hopital's rule correction factor naturally achieves effective suppression of high-frequency ripple and extremely fast, zero-steady-state-error extraction (zero attenuation and zero phase shift) of specific odd harmonics, greatly simplifying the parameter tuning process of the controller.

[0053] The high-precision input of the aforementioned algorithm relies on a stable differential preprocessing signal. To clarify the complete generation logic of the incremental signal, the specific implementation methods of differential delay and difference preprocessing are explained in detail below.

[0054] In one possible implementation, before performing differential operations on the two-phase voltage signals and a delayed signal with a preset proportional fundamental period to obtain the incremental signal, the method further includes: The two-phase voltage signals are delayed by a preset ratio of the fundamental frequency period to obtain the delayed signal; The incremental signal is obtained by performing differential operations on the two-phase voltage signal and the delayed signal with a preset ratio of the fundamental period, including: The incremental signal is calculated by subtracting the two-phase voltage signal and the delayed signal.

[0055] In the specific implementation process, a reduced sliding data window mechanism optimized for preset odd harmonics is introduced. The latest data window at the current moment is used... αβ The αβ axis voltage sample value is differentially analyzed with historical sampling points (delayed by N / 6 beats) moved out of the sliding data window queue. N / 6 corresponds to one-sixth of the fundamental period of the power grid (approximately 3.33 ms). This window length, combined with the subsequent rotation factor frequency shift characteristics, precisely constitutes an efficient separation interval for the typical odd-order harmonic characteristic period of the power grid. The dynamic incremental signal Δ of the αβ axis voltage is extracted through differential analysis. V pcc_αβ(n) = V pcc_αβ(n) - V pcc_αβ(n-N / 6) This incremental signal serves as the unified computational input for each specific odd harmonic extraction unit.

[0056] In this embodiment, the timing logic for differential preprocessing is implemented as follows: first, the two-phase voltage signals are delayed by 1 / 6 of the fundamental period to obtain a delayed signal; then, the incremental signal is obtained by subtracting the two-phase voltage signals from the delayed signal. This differential preprocessing effectively suppresses steady-state fundamental components, eliminates fundamental information that does not participate in harmonic mitigation, and reduces the computational load of subsequent improved sliding discrete Fourier transforms. Simultaneously, the differential structure adapts to the 6k±1 order power grid characteristic harmonics, fully preserving the odd-order harmonic components to be extracted; and it effectively reduces the effective data window of the algorithm, shortens the harmonic detection convergence time, and improves the harmonic extraction response speed, providing a high-quality input signal for fast and accurate harmonic separation operations in the backend.

[0057] After the accurate extraction of single harmonics is completed, the complex harmonic components in the two-phase coordinate system need to be reconstructed back to the three-phase coordinate system to synthesize the complete three-phase total harmonic signal, which is adapted to the inverter output architecture of the three-phase active power filter. The specific reconstruction and synthesis process is as follows.

[0058] In one possible implementation, determining the total harmonic extraction signal based on the extracted signal includes: Extract the real and imaginary parts of the extracted signal corresponding to each preset odd harmonic, and calculate the instantaneous amplitude and phase of each preset odd harmonic based on the real and imaginary parts; For each preset odd harmonic, the voltage signal of each preset odd instantaneous harmonic is reconstructed to the three-phase stationary coordinate system by inverse Clarke transformation based on the amplitude and phase. The total harmonic extraction signal is obtained by superimposing the preset odd-order instantaneous harmonic voltage signals.

[0059] In some embodiments, the real and imaginary parts are two orthogonal components of the complex harmonic components. The instantaneous amplitude and phase of the preset odd harmonic are obtained by solving the complex real and imaginary parts, representing the amplitude and phase of the harmonic voltage at the current moment. The inverse Clarke transform is the inverse transform of the Clarke transform; it realizes the reverse mapping of the signal from the two-phase αβ stationary coordinate system to the three-phase abc stationary coordinate system. Each preset odd instantaneous harmonic voltage signal is obtained by inverse coordinate transformation of a single harmonic, resulting in the three-phase voltage waveform of that harmonic in the abc three-phase coordinate system.

[0060] In practical implementation, the harmonic extraction algorithm based on SOHSDFT provided by this invention is composed of the first... h 1, h 2, ..., h m ( h 1~ h m (A positive odd number, representing the preset odd harmonic order to be compensated) This consists of an extraction unit for the preset odd harmonic order and a signal summation function. Each preset odd harmonic extraction unit has a consistent control structure. h The extraction unit for the first-order odd harmonic consists of a sliding data window delay section, a difference operation section, a rotation factor complex multiplication section, a singular value correction factor multiplication section, and an accumulation iteration section; the discreteness of the extraction unit... αβ The shaft voltage signal input is simultaneously connected to the input of the sliding data window delay section and the positive input of the differential operation section; the old sampling point signal shifted out by the sliding data window delay section of each preset odd harmonic extraction unit serves as the negative input of the differential operation section; the incremental signal obtained from the differential operation is corrected by the rotation factor complex multiplication, dynamic amplitude and phase angle adjustment factor, and accumulated iterative solution, and then outputs the corresponding instantaneous harmonic characteristic signal; the signal output of each preset odd harmonic extraction unit ( V pcch_h1 , V pcch_h2 ,..., V pcch_hmThe summation is used as the input to the signal summation function, and the output of the signal summation function is used as the total harmonic extraction signal in the active power filter voltage compensation command calculation stage. V pcch .

[0061] Each preset odd harmonic αβ Complex eigencomponents X h ( n The real and imaginary parts are extracted separately, and the instantaneous amplitude and phase are calculated. Then, the inverse Clarke transform is used to reconstruct the three-phase stationary coordinate system to obtain the preset odd-order instantaneous harmonic voltage signals. V pcch_h1 , V pcch_h2 ,..., V pcch_hm ).

[0062] The preset odd-order instantaneous harmonic voltage signals are summed to obtain the total harmonic extraction signal of the preset harmonic voltages on the active power filter grid side. V pcch ,Right now V pcch = V pcch_h1 + V pcch_h2 +...+ V pcch_hm .like Figure 4 As shown.

[0063] In this embodiment, the reconstruction and synthesis of harmonic components from a two-phase stationary coordinate system to a three-phase stationary coordinate system are realized. First, the amplitude and phase of the complex extracted signals of each harmonic are analyzed. Then, each odd harmonic is reconstructed into a three-phase instantaneous harmonic voltage signal through an inverse Clarke transform. Finally, the total harmonic extraction signal is obtained by superposition. On the one hand, the harmonic components separated in the αβ coordinate system are restored to three-phase signals, adapting to the control output architecture of a three-phase active power filter. On the other hand, the method of independent reconstruction and superposition of single harmonics accurately preserves the amplitude and phase characteristics of each characteristic harmonic, avoiding phase distortion during harmonic superposition. This ensures that the final total harmonic extraction signal accurately reflects the harmonic distortion at the point of common coupling of the power grid, guaranteeing the accuracy and reliability of the subsequently generated compensation voltage command.

[0064] All the above signal processing and harmonic extraction algorithms are based on digital discrete signals. However, the original power grid analog voltage signal needs to undergo standardized preprocessing such as coordinate transformation and sampling buffering before it can be used for algorithm operation. The specific signal preprocessing process is as follows.

[0065] In one possible implementation, the three-phase grid-side AC voltage is transformed to a two-phase stationary coordinate system to obtain a two-phase voltage signal, including: The three-phase grid-side AC voltage is converted to a two-phase stationary coordinate system using the Clarke transformation to obtain the voltage signal in the two-phase stationary coordinate system. Discretize the voltage signal in the two-phase stationary coordinate system to obtain the two-phase voltage sampling components; The two-phase voltage sample components are stored in a sliding data window queue to obtain the two-phase voltage signal.

[0066] In some embodiments, the Clarke transform is a linear orthogonal coordinate transformation from a three-phase stationary abc coordinate system to a two-phase stationary αβ coordinate system, decoupling the three-phase voltages and converting them into two orthogonal voltages, facilitating complex domain harmonic algorithm computation. The voltage signal in the two-phase stationary coordinate system is a continuous-time domain orthogonal analog voltage signal along the α and β axes. The two-phase voltage sample components are the digital voltage values ​​of the α and β channels at discrete times after sampling. The sliding data window queue is a first-in, first-out (FIFO) data buffer queue in memory, continuously storing the latest sampled values ​​and discarding the oldest sampled values, forming a sliding window, which is the data carrier for the sliding discrete Fourier algorithm.

[0067] In the specific implementation process, a voltage sensor is used to detect the three-phase grid-side AC voltage at the common coupling point of the active power filter in real time, and the Clarke transform is used to convert the voltage signal in the three-phase stationary coordinate system to a two-phase stationary coordinate system. αβ Discretization sampling is performed in the coordinate system to obtain the current time. αβ The axis voltage is sampled, and the sampled value is stored in the sliding data window queue; assuming the total number of discrete sampling points within the fundamental period of the power grid is... N .

[0068] In this embodiment, the conversion process from three-phase voltage to two-phase discrete-time voltage signals is implemented. First, the three-phase voltage coupling is decoupled using the Clarke transform, reducing the computational complexity of subsequent algorithms. Then, discrete sampling is used to digitize the analog signal. Finally, a sliding data window queue is used to buffer the sampled data, constructing a time-series signal that can be accessed in real time. This provides a standardized two-phase discrete voltage input for subsequent delay differential preprocessing and improved sliding discrete Fourier transform.

[0069] After obtaining accurate harmonic compensation voltage commands and fundamental grid-connected voltage commands, harmonic mitigation is finally achieved through power modulation and inverter output. The specific driving and compensation implementation process is as follows.

[0070] In one possible implementation, harmonic mitigation is performed based on a harmonic compensation voltage command, including: Based on the harmonic compensation voltage command and the fundamental voltage command, the total voltage reference command is obtained; The total voltage reference command is sequentially input into the voltage outer loop and the current inner loop for closed-loop regulation to obtain the modulation reference signal; Space vector pulse width modulation is performed based on the modulation reference signal to generate a drive control signal; The corresponding compensation voltage is generated by driving the control signal, and harmonic mitigation is completed based on the corresponding compensation voltage.

[0071] In some embodiments, the fundamental voltage command is the power frequency fundamental voltage reference command required for the grid-connected operation of the active power filter; the voltage-type active power filter cannot only output harmonic voltage, but needs to superimpose the fundamental component to maintain DC-side voltage stability and achieve reliable grid connection. The total voltage reference command is the complete three-phase voltage setpoint value sent to the inner loop of the voltage-current dual closed-loop control. The modulation reference signal is the two-phase stationary coordinate system voltage vector command (modulation wave reference vector) sent to the SVPWM modulation module, and is the output signal of the inner loop of the voltage-current dual closed-loop control. Space vector pulse width modulation is the digital modulation algorithm of the three-phase two-level voltage-type inverter, which is deployed inside the SVPWM modulation module in this invention. The drive control signal is the pulse modulation signal output by the digital controller, used to drive the inverter power switching devices. The corresponding compensation voltage is the AC voltage output by the power main circuit (three-phase inverter) of the active power filter according to the drive signal modulation, which includes the fundamental voltage component and the harmonic compensation component. Harmonic mitigation involves injecting compensation voltage into the distribution network's point of common coupling to offset the harmonic voltages present in the grid, suppress voltage distortion, and improve power quality.

[0072] In the specific implementation process, space vector pulse width modulation is performed to generate a positive level high-frequency drive signal for the main power circuit switching transistor, which controls the three-phase inverter to output the corresponding compensation voltage through the LCL filter in order to dynamically offset the harmonic voltage distortion on the grid side.

[0073] In this embodiment, a power conversion link from voltage command to actual harmonic compensation is implemented. The harmonic compensation voltage command is combined with the fundamental voltage command to generate a drive control signal, which controls the active power filter inverter to output the corresponding compensation voltage. On the one hand, the introduction of the fundamental voltage command ensures the stable grid-connected operation of the active power filter and maintains the normal operating state of the device; on the other hand, the output compensation voltage is modulated according to the drive signal to cancel the grid harmonic voltage at the point of common coupling, giving full play to the role of the front-end harmonic detection algorithm, and ultimately achieving harmonic suppression in the distribution network.

[0074] The accurately extracted total harmonic signal needs to be converted into a compensation command through a standardized control strategy, and then physical harmonic compensation is achieved through a modulation drive stage. The specific implementation methods of command generation and power output are as follows.

[0075] In one possible implementation, generating a harmonic compensation voltage command based on the total harmonic extraction signal includes: The total harmonic distortion (THD) extraction signal is input into the feedback gain unit with the preset proportional control gain coefficient, and the THD extraction signal is multiplied by the preset proportional control gain coefficient to obtain the product result. The product result is then determined as the harmonic compensation voltage command.

[0076] In some embodiments, the feedback gain unit is a proportional amplifier module (proportional gain K), which is a digital multiplier in digital control and belongs to a sub-unit within the harmonic extraction and command generation module. The preset proportional control gain coefficient is a proportional adjustment coefficient, a real gain; it is pre-tuned according to the active power filter capacity and grid operating conditions. It is used to adjust the compensation intensity, and the gain magnitude determines the strength of harmonic compensation by the active power filter. The harmonic compensation voltage command is the harmonic compensation voltage command that the active power filter inverter needs to output; the waveform of this command is opposite to the grid harmonic voltage and is used to cancel harmonic distortion at the point of common coupling.

[0077] In the specific implementation process, the total harmonics (THM) signal is extracted. V pcch Introducing a voltage compensation command calculation step and setting the proportional control gain coefficient. K Based on a specific harmonic control expression KV pcch = V href To obtain the target output harmonic voltage command of the active power filter. V href .

[0078] In this embodiment, the conversion from the total harmonic distortion (THD) extraction signal to the harmonic compensation voltage command is realized. The THD extraction signal, representing grid distortion, is multiplied by a preset proportional control gain coefficient to obtain the harmonic compensation voltage command. Employing a proportional control method, the structure is simple and easy to implement in engineering, allowing for flexible adjustment of the harmonic compensation level and significantly simplifying the tuning workload of the active power filter control parameters. It also establishes a signal bridge between the harmonic detection stage and the power inverter output stage, providing an accurate reference command for the subsequent output of the active power filter's reverse compensation voltage to suppress grid harmonic voltage distortion.

[0079] To fully verify the feasibility, accuracy, and dynamic performance of the proposed algorithm and governance method, a hardware-in-the-loop experimental verification platform was built. The harmonic extraction and control algorithm based on SOHSDFT provided by this invention was deployed on the controller for experimental verification. The experiment focused on the PCC voltage distortion condition and simultaneously tested 5... th 7 th ,11 th ,13 th The main odd harmonics were compensated and controlled; the experimental results are shown in the appendix. Figure 5 and attached Figure 6 In the picture u pccThis represents the PCC voltage waveform. i ga This represents the current waveform on the grid side of phase A. 200V / div means each division on the vertical axis corresponds to 200V, 20A / div means each division on the vertical axis corresponds to 20A, and 20ms / div means each division on the horizontal axis corresponds to 20ms.

[0080] Appendix Figure 5 It is a steady-state experimental waveform. Figure 5 The horizontal axis represents time. Figure 5 The upper half of the waveform, showing the red, green, and blue lines, represents the voltage waveform at point PCC. Figure 5 The vertical axis of the upper half represents the PCC voltage. Figure 5 The lower half of the green waveform is the A-phase grid-side current waveform. Figure 5 The lower half of the graph represents the current on the vertical axis. The experimental waveform shows that specific odd-order harmonic voltages on the grid side are effectively absorbed and compensated by the VDAPF, significantly reducing the harmonic distortion rate of the voltage at the PCC point and restoring it to a highly sinusoidal waveform. (Appendix) Figure 6 The horizontal axis represents time, and the vertical axis represents the voltage at point PCC. (Appendix) Figure 6 This is the dynamic response waveform of an active filter when a sudden load is applied at time t1, and the harmonic source and background harmonics change. As can be seen from the figure, thanks to… N With its narrowing window mechanism and zero-point reshaping characteristics, the system can accurately track abrupt harmonic changes and reach a new steady state within approximately 3.3 ms. This verifies the correctness and reliability of the ultra-fast harmonic extraction and compensation control algorithm provided in this invention, offering excellent reference value for power quality management engineering applications in complex power grid environments.

[0081] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0082] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0083] Figure 7 A schematic diagram of the harmonic mitigation device for a voltage-sensing active power filter provided in an embodiment of the present invention is shown. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are described in detail below: like Figure 7 As shown, the harmonic mitigation device 7 of the voltage-sensing active power filter includes: Harmonic extraction and instruction generation module 71, voltage and current dual closed-loop control module 72 of active power filter, DC side voltage control module 73 and SVPWM modulation module 74; The harmonic extraction and command generation module 71 is used to acquire the three-phase AC voltage at the point of common coupling of the distribution network to be treated, transform the three-phase AC voltage to a two-phase stationary coordinate system to obtain two-phase voltage signals, and perform differential operations on the two-phase voltage signals and a delayed signal with a preset proportional fundamental period to obtain incremental signals; wherein the preset proportional fundamental period is 1 / 6 of the fundamental period; perform an improved sliding discrete Fourier transform on the incremental signals to obtain the extraction signals of each preset odd harmonic, and determine the total harmonic extraction signal based on the extraction signals; generate a harmonic compensation voltage command based on the total harmonic extraction signal, and complete the harmonic treatment based on the harmonic compensation voltage command; The voltage and current dual closed-loop control module 72 of the active power filter is used to receive the harmonic compensation voltage command and the fundamental voltage reference command, and superimpose them to obtain the total voltage reference command. It introduces the inverter side voltage and inverter side current feedback signals, and outputs the modulation reference signal through closed-loop adjustment calculation of voltage outer loop and current inner loop. The DC-side voltage control module 73 is used to acquire the actual DC-side voltage of the active power filter, calculate the difference between the actual DC-side voltage and the DC-side voltage reference to obtain the voltage error signal, output the active power compensation reference value through the P regulator, and then input it into the droop control module. Combined with the inverter-side voltage and inverter-side current sampling signals, it outputs the fundamental voltage reference command and the synchronization phase. The SVPWM modulation module 74 is used to receive the modulation reference signal, perform space vector pulse width modulation calculation, and generate drive control signals for the power switching transistors of the main power circuit.

[0084] Figure 8 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Figure 8 As shown, the electronic device 8 of this embodiment includes a processor 80 and a memory 81. The memory 81 stores a computer program 82. When the processor 80 executes the computer program 82, it implements the steps in the various method embodiments described above. Alternatively, when the processor 80 executes the computer program 82, it implements the functions of each module / unit in the various device embodiments described above.

[0085] For example, computer program 82 may be divided into one or more modules / units, which are stored in memory 81 and executed by processor 80 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 82 in electronic device 8.

[0086] Electronic device 8 may include, but is not limited to, processor 80 and memory 81. Those skilled in the art will understand that... Figure 8This is merely an example of electronic device 8 and does not constitute a limitation on electronic device 8. It may include more or fewer components than shown, or combine certain components, or different components. For example, electronic device 8 may also include input / output devices, network access devices, buses, etc.

[0087] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0088] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0089] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A harmonic mitigation method for a voltage-sensing active power filter, characterized in that, include: Obtain the three-phase AC voltage at the point of common coupling of the distribution network to be treated; The three-phase grid-side AC voltage is transformed to a two-phase stationary coordinate system to obtain a two-phase voltage signal. The two-phase voltage signal and the delayed signal with a preset ratio of the fundamental frequency period are then used to perform differential operations to obtain an incremental signal. The preset ratio of the fundamental frequency period is 1 / 6 of the fundamental frequency period. An improved sliding discrete Fourier transform is performed on the incremental signal to obtain the extraction signals of each preset odd harmonic, and the total harmonic extraction signal is determined based on the extraction signals. The total harmonics extraction signal is used to generate a harmonic compensation voltage command, and the harmonic mitigation is performed according to the harmonic compensation voltage command.

2. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, The step of performing an improved sliding discrete Fourier transform based on the incremental signal to obtain the extracted signals of each preset odd harmonic includes: The amplitude and phase angle adjustment factor is determined based on the total number of sampling points within one cycle of the fundamental wave and the order of the target harmonic to be extracted. For each preset odd harmonic, the corresponding rotation factor is determined based on the total number of sampling points in one cycle of the fundamental wave and the preset odd harmonic number. The incremental signal, the amplitude and phase angle adjustment factor and the rotation factor corresponding to the preset odd harmonic are multiplied together to calculate the product result. The preset odd harmonic extraction signal is obtained by updating and iterating based on the product result and the harmonic iteration component of the previous time step.

3. The harmonic mitigation method for a voltage-sensing active power filter according to claim 2, characterized in that, The determination of the amplitude and phase adjustment factor based on the total number of sampling points within one cycle of the fundamental wave and the target harmonic order to be extracted includes: Based on the total number of sampling points in one cycle of the fundamental wave and the number of the target harmonic to be extracted, construct the complex exponential reference term corresponding to the target harmonic; Construct an expression for the window zeros, take the first derivative with respect to the complex variable, and assign the complex variable to the complex exponent corresponding to the target harmonic frequency, and solve to obtain the derivative value; The amplitude and phase angle adjustment factor is calculated based on the complex exponential reference term and the derivative value.

4. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, Before performing differential calculations based on the two-phase voltage signals and the delayed signal with a preset proportional fundamental period to obtain the incremental signal, the method further includes: The two-phase voltage signals are delayed by a preset ratio of the fundamental frequency period to obtain the delayed signal; The step of performing differential operations based on the two-phase voltage signals and a delayed signal with a preset proportional fundamental period to obtain an incremental signal includes: The incremental signal is calculated by subtracting the two-phase voltage signal and the delayed signal.

5. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, The step of determining the total harmonic extraction signal based on the extracted signal includes: Extract the real and imaginary parts of the extracted signal corresponding to each preset odd harmonic, and calculate the instantaneous amplitude and phase of each preset odd harmonic based on the real and imaginary parts; For each preset odd harmonic, the voltage signal of each preset odd instantaneous harmonic is reconstructed to the three-phase stationary coordinate system by inverse Clarke transformation based on the amplitude and phase. The total harmonic extraction signal is obtained by superimposing the preset odd-order instantaneous harmonic voltage signals respectively.

6. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, The process of transforming the three-phase grid-side AC voltage to a two-phase stationary coordinate system to obtain a two-phase voltage signal includes: The three-phase grid-side AC voltage is converted to a two-phase stationary coordinate system using the Clarke transform to obtain the voltage signal in the two-phase stationary coordinate system. Discretize the voltage signal in the two-phase stationary coordinate system to obtain the two-phase voltage sampling components; The two-phase voltage sample components are stored in a sliding data window queue to obtain the two-phase voltage signal.

7. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, The process of harmonic mitigation based on the harmonic compensation voltage command includes: Based on the harmonic compensation voltage command and the fundamental voltage command, the total voltage reference command is obtained; The total voltage reference command is sequentially input into the voltage outer loop and the current inner loop for closed-loop regulation to obtain the modulation reference signal; Space vector pulse width modulation is performed based on the modulation reference signal to generate a drive control signal; The driving control signal generates a corresponding compensation voltage, and harmonic mitigation is performed based on the corresponding compensation voltage.

8. The harmonic mitigation method for a voltage-sensing active power filter according to claim 1, characterized in that, The step of generating a harmonic compensation voltage command based on the total harmonic extraction signal includes: The total harmonic distortion (THD) extraction signal is input into the feedback gain unit of the preset proportional control gain coefficient, and the THD extraction signal is multiplied by the preset proportional control gain coefficient to obtain the product result. The product result is then determined as the harmonic compensation voltage command.

9. A harmonic mitigation device for a voltage-sensing active power filter, characterized in that, include: Harmonic extraction and instruction generation module, voltage and current dual closed-loop control module for active power filter, DC side voltage control module and SVPWM modulation module; The harmonic extraction and command generation module is used to acquire the three-phase AC voltage at the point of common coupling of the distribution network to be treated, transform the three-phase AC voltage to a two-phase stationary coordinate system to obtain a two-phase voltage signal, and perform differential operation on the two-phase voltage signal and a delayed signal with a preset proportional fundamental period to obtain an incremental signal; wherein the preset proportional fundamental period is 1 / 6 of a fundamental period; perform an improved sliding discrete Fourier transform on the incremental signal to obtain the extraction signals of each preset odd harmonic, and determine the total harmonic extraction signal based on the extraction signals; generate a harmonic compensation voltage command based on the total harmonic extraction signal, and complete harmonic treatment based on the harmonic compensation voltage command; The voltage and current dual closed-loop control module of the active power filter is used to receive the harmonic compensation voltage command and the fundamental voltage reference command, superimpose them to obtain the total voltage reference command, introduce the inverter side voltage and inverter side current feedback signals, and output the modulation reference signal through closed-loop adjustment calculation of voltage outer loop and current inner loop. The DC-side voltage control module is used to acquire the actual DC-side voltage of the active power filter, calculate the difference between the actual DC-side voltage and the DC-side voltage reference to obtain a voltage error signal, output the active power compensation reference value through the P regulator, and then input it into the droop control module. Combined with the inverter-side voltage and inverter-side current sampling signals, it outputs the fundamental voltage reference command and the synchronization phase. The SVPWM modulation module is used to receive the modulation reference signal, perform space vector pulse width modulation operation, and generate drive control signals for the power switching transistors of the main power circuit.

10. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 8.

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