Grid-side centralized sampling-based transformer reactive current fast control method and system

Abstract

A fast reactive current control method and system for converters based on centralized sampling on the grid side is proposed. Based on the spectral characteristics of composite harmonics, a clustering method is used to obtain the cluster center harmonic frequency bands of multiple frequency bands. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands. The reduction ratio of the delay time in the repetitive controller is determined based on the frequency of each resonant peak and the fundamental frequency, resulting in an improved fast repetitive controller. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series. The fractional-order delay element is compensated to obtain a compensated fast repetitive controller. The fast repetitive composite controller obtained by connecting the compensated fast repetitive controller in parallel with a PI controller serves as the improved current inner loop. Based on the voltage outer loop and the improved current inner loop, fast reactive current control is achieved, realizing rapid reactive current compensation.

Description

Technical Field

[0001] This invention belongs to the field of reactive power detection technology in power systems. Specifically, it discloses a method and system for rapid control of converter reactive current based on centralized sampling on the grid side. Background Technology

[0002] With the continuous expansion of modern power systems and the widespread application of power electronic equipment, the number of nonlinear loads in the power grid has increased significantly, leading to increasingly serious problems of reactive power fluctuations and harmonic pollution.

[0003] In existing technologies, reactive power detection employs a distributed measurement method, requiring the separate installation of current transformers and voltage sensors in each load branch. This results in high system costs, complex installation and wiring, and difficult maintenance, posing multiple challenges in practical engineering applications. In load-dense areas such as large industrial sites or commercial complexes, a large number of detection devices need to be deployed, causing system hardware costs to increase exponentially. Especially in applications requiring high-precision measurements, the expensive sensor costs significantly extend the project's return on investment period. Complex wiring not only increases construction difficulty but also introduces interference problems during signal transmission. Particularly in the harsh electromagnetic environments of industrial sites, long-distance analog signals are easily interfered with, affecting measurement accuracy. More importantly, in applications with precision loads or sensitive equipment, electromagnetic interference from traditional detection methods may affect the normal operation of the load. This invasive measurement method is severely limited in certain special application scenarios. Moreover, traditional reactive current control methods suffer from slow dynamic response and low control accuracy. These inherent defects make traditional reactive power detection technology unable to meet the requirements of modern smart grids for economy, reliability, and scalability, necessitating the development of new reactive power detection solutions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a fast reactive current control method and system for converters based on centralized sampling on the grid side. It requires only a high-precision detection device at the grid's point of common coupling (PCC) where the converter is connected. The reactive current signal is extracted by real-time acquisition of three-phase voltage and current signals from the grid side, eliminating the need for physical contact with the load, maintaining the integrity of load operation, reducing hardware interference to the load, and significantly reducing hardware costs and installation expenses. Furthermore, the traditional repetitive controller in the converter's current inner loop is rapidly improved by introducing a fractional-order approach to approximate the inherent delay in the repetitive controller, improving compensation accuracy. A PI controller is introduced in parallel with the improved repetitive controller to form a composite control strategy, enabling rapid and effective extraction of the required reactive component. Applying the proposed detection method to an SVG control system achieves rapid compensation of the converter's reactive current, verifying the method's effectiveness.

[0005] The present invention adopts the following technical solution.

[0006] This invention proposes a fast reactive current control method for converters based on centralized sampling on the grid side, comprising: The harmonic detection method based on instantaneous reactive power theory is adopted to detect the harmonics of the current at the common coupling point of the power grid connected to the converter, and to obtain the composite harmonic current superimposed by multiple types of loads. Based on the spectral characteristics of composite harmonics, a clustering method is used to obtain the cluster center harmonic frequency bands of multiple frequency band clusters. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands. Based on the ratio of the reduction of the delay time in the repetitive controller to the resonant peak frequency and the fundamental frequency, an improved fast repetitive controller is obtained. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series, and the fractional-order delay element is compensated to obtain the compensated fast repetitive controller. The fast repetitive controller obtained by connecting the compensated fast repetitive controller in parallel with the PI controller is used as the improved current inner loop; based on the voltage outer loop and the improved current inner loop, the reactive current of the converter is controlled quickly.

[0007] Preferably, multi-scale spectral analysis is performed on the composite harmonics to extract frequency band characteristic parameters from each identified harmonic frequency band, including: center frequency, energy intensity, bandwidth, amplitude time-varying index, phase consistency, and inter-band coupling. Based on the frequency band feature parameter vector, an improved DBSCAN clustering algorithm is used to perform clustering to obtain multiple frequency band clusters; the importance of each frequency band cluster is dynamically evaluated. After sorting the frequency band clusters from highest to lowest importance, the cluster center harmonic frequency bands of the top p frequency band clusters are obtained. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands.

[0008] Preferably, the importance of frequency band clusters is dynamically evaluated as shown in the following formula:

[0009] In the formula, , These are all index variables for frequency band clusters. The number of frequency band clusters, For frequency band clusters The importance of , , They are frequency band clusters Energy intensity, amplitude time-varying index, and phase consistency; For frequency band clusters and The degree of coupling between them , , , All are weighting coefficients, and + + + =1, It is a very small positive number.

[0010] Preferably, the ratio of each resonant peak frequency to the fundamental frequency is calculated, and the greatest common divisor w of all ratios is used as the delay time reduction ratio. Then, the delay time in the inner membrane structure of the improved repetitive controller is... , To improve the delay time in the inner membrane structure of the pre-repetitive controller.

[0011] Preferably, the transfer function of the improved fast repetitive controller As shown in the following formula:

[0012] In the formula, For filters, To shorten the periodic delay stage, For the compensation process, This is the gain coefficient. For compensation filters, For phase compensation stage, These are the interpolation coefficients. This refers to the order of the phase compensation stage.

[0013] Preferably, the delay element Decomposed into integer-order delay elements connected in series and fractional delay , For the closest Positive integers for / w It is a positive fraction, satisfying / w= + ; The fractional delay is approximated by an FIR filter to obtain a parallel connection. +1 integer-order sub-delay stage to compensate for fractional-order delay stages, and +1 sub-delay elements are adjacent in order.

[0014] Preferably, the fractional delay element is denoted as It satisfies the following relationship:

[0015]

[0016] In the formula, , Sub-delay stages The weights and orders, Fractional delay stage order, These are the interpolation coefficients. This represents the upper limit of the interpolation.

[0017] Preferably, the transfer function of the compensated fast repetitive controller is as follows:

[0018] In the formula, This is the transfer function of the compensated fast repetitive controller.

[0019] In another aspect, this invention proposes a fast reactive current control system based on centralized sampling on the power grid side, comprising: The composite harmonic current detection module is used to detect harmonics in the current at the common connection point of the power grid to which the converter is connected, using a harmonic detection method based on instantaneous reactive power theory, to obtain the composite harmonic current superimposed by multiple types of loads. The current inner loop improvement module is used to obtain the cluster center harmonic frequency bands of multiple frequency bands based on the spectral characteristics of composite harmonics using a clustering method. The principle is that each resonant peak covers two adjacent cluster center harmonic frequency bands to determine the resonant peaks. Based on the frequency of each resonant peak and the fundamental frequency, the reduction ratio of the delay time in the repetitive controller is determined to obtain an improved fast repetitive controller. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series. The fractional-order delay element is compensated to obtain a compensated fast repetitive controller. The fast repetitive composite controller obtained by connecting the compensated fast repetitive controller in parallel with a PI controller serves as the improved current inner loop. The reactive current fast control module is used to quickly control the reactive current of the converter based on the voltage outer loop and the improved current inner loop.

[0020] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0021] The present invention is also a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0022] The beneficial effects of this invention are as follows: compared with the prior art, it significantly reduces system cost and installation complexity, requiring only single-point sampling at the grid common coupling point (PCC) without the need to install sensors on each load branch, thus greatly reducing hardware costs and engineering difficulty; it adopts a non-intrusive detection method, avoiding interference with load equipment and ensuring the integrity and safety of load operation; it achieves fast and high-precision reactive power component extraction based on improved instantaneous reactive power theory, eliminating the need for low-pass filters and avoiding phase delay and response lag in traditional detection; and it designs a composite control strategy that matches a fast repetitive controller and a PI controller in parallel, which has both fast dynamic response and high steady-state accuracy, improving the overall compensation performance and control robustness of the SVG system, and is suitable for various complex power grid environments and new energy grid connection scenarios. Attached Figure Description

[0023] Figure 1 This is the flowchart of the fast reactive current control method for converters based on centralized sampling on the power grid side proposed in this invention. Figure 2 This is a diagram of the equivalent circuit model of the SVG proposed in the embodiments of the present invention; Figure 3 This is a block diagram illustrating the implementation of the SVG control system in an embodiment of the present invention. Figure 4 This is a block diagram of the improved fast repeat controller structure in an embodiment of the present invention; Figure 5 This is a block diagram of the PI fast repetitive composite controller in an embodiment of the present invention; Figure 6 This is a waveform diagram of the grid voltage, grid current, and power factor when the SVG is not started in this embodiment of the invention; Figure 7 The waveforms of grid voltage, grid current, and power factor obtained by using the control method proposed in this invention after the SVG is started in this embodiment of the invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0025] Currently, 6-pulse rectifiers are widely used in industrial settings. The characteristic harmonics they generate are mainly non-integer multiples of harmonics such as the 5th (250Hz), 7th (350Hz), 11th (550Hz), and 13th (650Hz), which seriously affect the power quality of the power grid. This invention optimizes traditional methods and proposes a fast reactive current control method for converters based on centralized sampling on the grid side. This method effectively suppresses high-order harmonics such as the 5th, 7th, and 11th harmonics and is adapted to 50Hz fundamental frequency systems. The resonant peak frequency needs to be extended to 6 integer multiples of the fundamental frequency, such as 300Hz and 600Hz, to improve the system's adaptability to harmonics from industrial rectifier loads and to achieve parameter optimization based on actual spectral characteristics.

[0026] like Figure 1 As shown, the method includes the following steps: Step 1: Using the harmonic detection method based on instantaneous reactive power theory, the current at the common coupling point of the power grid connected to the converter is subjected to harmonic detection to obtain the composite harmonic current superimposed by multiple types of loads.

[0027] The proposed centralized sampling scheme based on the power grid side obtains the power grid current signal only through single-point sampling of PCC, without the need for load-side sensors. This sampling method obtains the overall characteristics of the system current, including composite harmonics superimposed by multiple loads, and its harmonic spectrum characteristics are significantly different from those of traditional single-load detection.

[0028] A Static Var Generator (SVG) is a novel static var compensation device with dynamically and continuously bidirectionally adjustable output reactive power. It consists of a voltage source converter, a grid-side filter, and a control unit. The SVG inverts the DC-side voltage into an alternating voltage signal with the same frequency as the grid voltage by controlling the switching of power electronic devices. Ignoring sub-frequency harmonics of the switches, the modulated voltage signal output by the SVG can be equivalent to an alternating voltage source with controllable phase and amplitude, which is connected to the grid via a reactor. In practical systems, the SVG always incurs losses, mainly including copper losses in the series reactor, conduction and switching losses of the VSC switching devices, and dielectric losses in the DC capacitor. These losses are concentrated as the equivalent resistance of the connecting reactor; in this case, the VSC is considered a lossless switching converter. The equivalent circuit of the SVG is as follows: Figure 2 As shown, UL is the voltage across the reactor, and its working principle is as follows:

[0029] In the formula, This is the grid voltage. , These are equivalent resistance and equivalent reactance, respectively. This is the output voltage of the SVG.

[0030] Taking voltage as the reference phase, we get:

[0031] In the formula, SVG output voltage With grid voltage The phase angle between them.

[0032] The active power output by the SVG With reactive power They are respectively:

[0033] because Since the active and reactive power are relatively small, the above formula can be approximated as follows:

[0034] Based on the above derivation, the following conclusion can be drawn: 1) Lagging behind ,Right now When <0, >0 indicates that the SVG absorbs active power from the power source; part of the absorbed electrical energy is used to compensate for the power consumption of the SVG, and the other part is used to charge the DC capacitor and increase the DC voltage. 2) ahead of ,Right now When >0, <0 indicates that the SVG feeds energy back to the power source; the fed-back energy must come from the discharge of the DC capacitor, causing the DC voltage to drop; 3) > hour, >0, SVG emits capacitive reactive power; 4) < hour, <0, SVG absorbs inductive reactive power.

[0035] Traditional reactive power theory Harmonic detection methods first involve measuring the load current. , , The two-phase current is obtained by transforming from a three-phase stationary coordinate system to a two-phase rotating coordinate system. and After transformation, the fundamental current and the rotating phase coordinate system in the load current are relatively stationary; the DC quantity is the fundamental current, and the AC quantity is the harmonic current. Therefore, the transformed load current contains both DC and AC components. and There is also a volume of communication. and ,as follows:

[0036]

[0037] In the formula, This is the angular frequency of the power grid.

[0038] By filtering the transformed load current, the DC component is obtained. After performing an inverse transformation on the DC component, the fundamental current within the load current in the three-phase stationary coordinate system is obtained. , , The composite harmonic current is obtained by subtracting the load current and the fundamental current. , , ,as follows:

[0039]

[0040] This invention significantly reduces system cost and installation complexity, requiring only single-point sampling at the point of common coupling (PCC) of the power grid, eliminating the need to install sensors on each load branch, thus greatly reducing hardware costs and engineering difficulty; it adopts a non-intrusive detection method, avoiding interference with load equipment and ensuring the integrity and safety of load operation; based on improved instantaneous reactive power theory, it achieves fast and high-precision reactive power component extraction without the need for a low-pass filter, avoiding phase delay and response lag in traditional detection.

[0041] Step 2: Based on the spectral characteristics of composite harmonics, a clustering method is used to obtain the cluster center harmonic frequency bands of multiple frequency band clusters. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands.

[0042] Specifically, step 2 includes: Step 2.1: Perform multi-scale spectral analysis on the composite harmonics, extracting frequency band characteristic parameters from each identified harmonic frequency band, including but not limited to: center frequency. Energy intensity ,bandwidth Amplitude time-varying index Phase consistency Inter-band coupling , , These are all index variables for frequency bands.

[0043] Step 2.2: Based on the frequency band feature parameter vector, the improved DBSCAN clustering algorithm is used to perform clustering to obtain multiple frequency band clusters; the importance of each frequency band cluster is dynamically evaluated. The importance of frequency band clusters is dynamically assessed as follows:

[0044] In the formula, , These are all index variables for frequency band clusters. The number of frequency band clusters, For frequency band clusters The importance of , , They are frequency band clusters Energy intensity, amplitude time-varying index, and phase consistency; For frequency band clusters and The degree of coupling between them , , , All are weighting coefficients, and + + + =1, To avoid the denominator being zero, the value is 0.1 in this example, where the value is an extremely small positive number.

[0045] Step 2.3: Sort the frequency band clusters from largest to smallest according to their importance to obtain the cluster center harmonic frequency bands of the top p frequency band clusters. Determine the resonant peaks based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands.

[0046] In this embodiment, an industrial park is connected to the power grid. The resonance peaks determined through the above steps are: the 300Hz (6th harmonic) resonance peak effectively covers the 5th and 7th harmonic frequency bands, the 600Hz (12th harmonic) resonance peak covers the 11th and 13th harmonic frequency bands, and the 900Hz (18th harmonic) resonance peak covers the 17th and 19th harmonic frequency bands; p is set according to the controller performance.

[0047] This invention does not directly set the resonance peak based on existing harmonic research conclusions. Instead, it systematically optimizes the selection based on the spectral characteristics of composite harmonic signals sampled centrally on the power grid side. This avoids the negative impact on compensation accuracy caused by poor matching between the resonance peak distribution and typical harmonic frequency bands.

[0048] Step 3: Based on each resonant peak frequency and the fundamental frequency, determine the reduction ratio of the delay time in the repetitive controller to obtain the improved fast repetitive controller.

[0049] Specifically, the converter's inner current loop includes a repetitive controller; the ratio of each resonant peak frequency to the fundamental frequency is calculated, and the greatest common divisor w of all ratios is used as the delay time reduction ratio. Therefore, the delay time in the inner membrane structure of the improved repetitive controller is... , To improve the delay time in the inner membrane structure of the repetitive controller, the delay time is dynamically adjusted according to the resonant frequency distribution. In this embodiment, the resonant peak frequency is extended to an integer multiple of 6 times the fundamental frequency, i.e., 300Hz, 600Hz, ... Therefore, the delay time in the inner membrane structure of the repetitive controller is shortened to a fraction of its original value. Through this design, the improved repetitive controller can not only provide high gain at the fundamental frequency and its integer multiples, but also achieve precise alignment of multiple non-integer multiples of resonant frequencies. This breaks through the inherent limitation of traditional repetitive controllers that the resonant peak must be an integer multiple of the fundamental frequency, and solves the technical problem of spectral mismatch in multi-frequency resonance scenarios.

[0050] This invention shortens the delay time in the inner membrane structure of a repetitive controller. This is not merely a simple numerical change; it is based on clear technical principles and engineering constraints. Through theoretical analysis and simulation experiments, this invention reveals that shortening the delay time to its original value... This allows the resonant peak frequency to be extended to an integer multiple of six times the fundamental frequency, thus significantly enhancing the suppression capability of higher harmonics such as the 5th, 7th, and 11th harmonics, especially suitable for the harmonic characteristics of 6-pulse rectified loads commonly found in industrial settings. Moreover, this improvement is not simply a reduction in delay time, but a systematic optimization based on the spectral characteristics of the centralized sampling signal at the grid connection point. If the delay were shortened to a fraction of the original value... While it can improve the response speed, the resonant peak distribution does not match the typical harmonic frequency band well, which in turn affects the compensation accuracy.

[0051] In the embodiments, the delay time in the inner membrane structure of the improved repetitive controller targets the integer harmonic characteristics of a single load. In scenarios with centralized sampling on the grid side, it exhibits slow response and poor adaptability when facing complex harmonics. This invention addresses this by shortening the delay time to [a fraction of its original value]. This allows the controller's resonant peaks to be more densely distributed in typical industrial harmonic frequency bands, better matching the system harmonic characteristics under centralized sampling, thereby achieving synergistic optimization of sampling methods and control strategies and improving overall compensation performance.

[0052] This invention couples the techniques of centralized sampling on the power grid side and using spectrum analysis to detect composite harmonics with the technique of adjusting the delay time using the greatest common divisor of the ratios of each resonant peak frequency to the fundamental frequency. This establishes a closed-loop mechanism for spectrum characteristic-driven controller structure reconstruction. That is, the set of resonant peaks obtained from spectrum analysis is directly used as the input condition for delay time calculation. There is a strict causal relationship between the two, enabling the controller structure to be reconstructed in real time in response to changes in the power grid spectrum characteristics. The resonant spectrum of the repeating controller achieves precise spectrum matching with the actual harmonic spectrum of the power grid. Each resonant peak generated by the controller is precisely aligned with the actual harmonic frequency in the power grid that needs to be compensated. And each harmonic frequency in the power grid that needs to be compensated can be precisely covered by a single resonant peak of the controller.

[0053] SVG control system, such as Figure 3 As shown, the phase information of the grid current is extracted, and the grid current is... , , Transforming from a three-phase stationary coordinate system to a two-phase rotating coordinate system generates the reactive power command current for the SVG. The reactive power command current control is input to the controller, and the target value is adjusted by PI. Compared with the actual value of DC voltage The difference between the current on the d-axis and the current on the d-axis The difference between them is used as the active power command current input to the controller, and the controller outputs the d-axis voltage. and q-axis voltage Then the coordinates are transformed , The voltage loop of this invention adopts traditional PI control. The difference between the actual voltage value and the setpoint is used to obtain a current signal, which is then applied to the d-axis component by the PI regulator. This results in the compensation current of the APF containing a certain fundamental active component, allowing the grid to supplement a certain amount of active power to the DC side of the APF, thereby stabilizing the DC side voltage near the setpoint.

[0054] The improved repetitive controller's inner membrane structure is as follows: Figure 4 As shown, where, For the instruction signals that need to be tracked, For output signal, For filters, To shorten the periodic delay stage, For the compensation process, This is the gain coefficient. For compensation filters, As a phase compensation stage, it can effectively control harmonic signals of any integer order. Shortening the delay time in the repetitive control structure enables the SVG system to have good dynamic performance. In centralized sampling mode, the grid current signal contains a composite harmonic spectrum superimposed by multiple loads. In particular, the 6-pulse rectifier load commonly seen in industrial sites will generate significant 5th, 7th, and 11th harmonics. The resonant peaks of traditional integer-cycle delay controllers are only distributed at integer multiples of the fundamental frequency, resulting in limited suppression capability for the above-mentioned characteristic harmonics and slow dynamic response. The improvements made in this invention not only overcome the insufficient adaptability of traditional repetitive controllers in centralized sampling scenarios, but also achieve deep synergy between the sampling strategy and the control structure through frequency domain characteristic reconstruction, forming a high-performance reactive power compensation solution for non-intrusive detection scenarios.

[0055] The transfer function of the improved fast repetitive controller is shown in the following equation:

[0056] In the formula, For filters, To shorten the periodic delay stage, For the compensation process, This is the gain coefficient. For compensation filters, For phase compensation stage, These are the interpolation coefficients. This refers to the order of the phase compensation stage.

[0057] In the embodiment, since the interpolation coefficients in the periodic delay element of the fast repetitive controller are... Reduce to The response time is only 1 / 6 that of a traditional repetitive controller, significantly accelerating the system response speed. However, after reducing the delay time to 1 / 6, the integer implementation of the system sampling frequency and delay element introduces a fractional-order delay problem. / 6 may be a non-integer. In the example, the system sampling frequency is 10kHz and the power grid frequency is 50Hz. / 6 is 33.3. In digital control, Only integers can be used. Choosing 33 or 34 will result in a significant frequency shift, preventing the system from accurately tracking the desired output and affecting harmonic compensation accuracy. Furthermore, the reduced delay time also alters the system's stability margin; therefore, this invention also introduces a phase compensation stage. and filtering stage The system is designed to be stable to avoid the risk of oscillations caused by reduced latency.

[0058] Step 4: Decompose the delay element in the feedback branch of the improved fast repetitive controller into an integer-order delay element and a fractional-order delay element connected in series, and compensate for the fractional-order delay element to obtain the compensated fast repetitive controller. In this process, an FIR filter is used to approximate the fractional delay to obtain multiple integer-order sub-delay elements connected in parallel, which are then used to compensate for the fractional delay elements.

[0059] This invention further introduces fractional-order delay compensation technology, using an FIR filter to approximate the fractional-order delay, thereby ensuring the accuracy of the resonant frequency and avoiding harmonic suppression failure caused by frequency shift. Simultaneously, to match the dynamic characteristics of the fast repetitive controller, this invention performs synergistic optimization of the PI controller parameters, ensuring that the composite control system possesses both fast response and high steady-state accuracy across a wide frequency range through frequency domain analysis and pole placement methods.

[0060] The specific implementation process involves delaying the process. Decomposed into integer-order delay elements connected in series and fractional delay , For the closest Positive integers for / w It is a positive fraction, satisfying / w= + The fractional delay is approximated using an FIR filter to obtain a parallel connection. +1 integer-order sub-delay stages, and The +1 sub-delay stage has adjacent orders, which is used to make it as equivalent as possible to a mathematically existing but practically unrealizable fractional delay. This is more accurate than rounding, thereby improving the accuracy of harmonic compensation.

[0061] Fractional delay element is denoted as It satisfies the following relationship:

[0062]

[0063] In the formula, , Sub-delay stages The weights and orders, Fractional delay stage order, These are the interpolation coefficients. This represents the upper limit of the interpolation.

[0064] like Figure 5As shown, the transfer function of the compensated fast repetitive controller is as follows:

[0065] Step 5: Connect the compensated fast repetitive controller and the PI controller in parallel to obtain the fast repetitive composite controller as the improved current inner loop; based on the voltage outer loop and the improved current inner loop, perform fast control on the reactive current of the converter.

[0066] To further improve the SVG compensation performance, this paper employs a fast repetitive composite controller, consisting of a PI controller and a fast repetitive controller connected in parallel, to construct the current inner loop, such as... Figure 5 As shown, the PI controller uses The input signal is the output signal of the PI controller, and the output signal of the compensated fast repetitive controller is used as... The PI controller, with its proportional-integral characteristic, is responsible for rapidly responding to command errors, leading the dynamic adjustment process of the system, and effectively suppressing transient disturbances such as load changes. The feedforward repetitive controller, based on the internal model principle, provides extremely high open-loop gain for each harmonic frequency in the steady-state phase through a periodic learning mechanism, thereby achieving asymptotic zero-steady-state-error tracking of periodic harmonic signals. The outputs of the two controllers are directly superimposed in the time domain and complement each other in the frequency domain—the PI controller ensures stable control and dynamic performance in the low-frequency range (such as the fundamental frequency), while the fast repetitive controller provides precise suppression in the target harmonic frequency range. This parallel structure fully leverages the advantages of the PI control's speed and the repetitive control's high precision, jointly ensuring that the inner current loop possesses excellent dynamic response and steady-state accuracy over a wide frequency range.

[0067] When the system experiences significant dynamic changes that increase the error, the PI controller plays a dominant role during the delay time of the repetitive controller, keeping the error within a suitable range. After the delay, the repetitive controller begins to function, gradually reducing the error, while the PI controller's effect gradually weakens, and the control system re-enters a steady state. It can be seen that the PI controller is primarily responsible for improving the system's dynamic response performance and enhancing its stability; the repetitive controller is responsible for improving the compensation accuracy when the system is running stably.

[0068] The PI fast repetitive controller has a profound technical connection and system synergy with grid-side centralized sampling. Grid-side centralized sampling acquires the overall system current signal at the point of common coupling, which includes a composite harmonic spectrum formed by the superposition of multiple nonlinear loads. Traditional repetitive controllers based on integer-cycle delays exhibit slow response and limited harmonic suppression accuracy under such multi-source harmonic coupling conditions. This invention shortens the delay time to allow the controller's resonant peaks to be more densely distributed in the frequency domain (e.g., integer multiples of the fundamental frequency), thereby better matching the typical industrial harmonic components such as the 5th, 7th, and 11th orders abundant in the centralized sampling signal. This design not only improves the controller's adaptability to complex harmonic environments but also achieves closed-loop optimization from "single-point sampling" to "fast harmonic tracking": the sampling method determines the controller's frequency response requirements, while the improved control structure fully leverages the effectiveness of the centralized sampling information. These two aspects support each other, jointly constructing a non-intrusive, low-cost, and highly dynamic reactive power compensation system.

[0069] The controlled signal is subjected to space voltage vector pulse width modulation. The three-phase command voltage is transformed into a stationary coordinate system. Then, the region to which it belongs is determined based on the real and imaginary parts of the space command voltage vector. An appropriate combination of values ​​is selected, and the action time of each basic vector is calculated according to the volt-second balance principle. This controls the state of each bridge arm switch of the inverter and outputs the required PWM waveform.

[0070] A three-phase, three-wire, two-level parallel APF model was built using MATLAB / SIMULINK. The model mainly consists of a main circuit and a control circuit. The main circuit includes a parallel APF, with an uncontrolled rectifier bridge as the load. The control circuit includes a centralized sampling and detection circuit for harmonics on the grid side, an outer loop for pi voltage, an inner loop for repetitive pi current, and an SVPWM module. The proposed harmonic detection method was verified through simulation. Figure 6 The above diagram shows the waveforms of grid voltage Vm, grid current, and power factor when the SVG is not started in this embodiment of the invention. The grid voltage amplitude Vm is 300V, the grid current amplitude Im is 200A, and the power factor PF is 0.46. Figure 7 The above diagram shows the waveforms of grid voltage, grid current, and power factor after SVG is started in this embodiment of the invention. The grid voltage amplitude Vm is 300V, the grid current amplitude Im is 100A, and the power factor PF is 0.98.

[0071] In another aspect, this invention proposes a fast reactive current control system based on centralized sampling on the power grid side, comprising: The composite harmonic current detection module is used to detect harmonics in the current at the power grid's point of common coupling using a harmonic detection method based on instantaneous reactive power theory, thereby obtaining composite harmonic currents superimposed by multiple types of loads. The current inner loop improvement module is used to obtain the cluster center harmonic frequency bands of multiple frequency bands based on the spectral characteristics of composite harmonics using a clustering method. The principle is that each resonant peak covers two adjacent cluster center harmonic frequency bands to determine the resonant peaks. Based on the frequency of each resonant peak and the fundamental frequency, the reduction ratio of the delay time in the repetitive controller is determined to obtain an improved fast repetitive controller. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series. The fractional-order delay element is compensated to obtain a compensated fast repetitive controller. The fast repetitive composite controller obtained by connecting the compensated fast repetitive controller in parallel with a PI controller serves as the improved current inner loop. The reactive current fast control module is used to quickly control reactive current based on the voltage outer loop and the improved current inner loop.

[0072] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0073] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0074] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0075] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A fast reactive current control method for a converter based on centralized sampling on the grid side, wherein the converter's inner current loop includes a repetitive controller; characterized in that, include: The harmonic detection method based on instantaneous reactive power theory is adopted to detect the harmonics of the current at the common coupling point of the power grid connected to the converter, and to obtain the composite harmonic current superimposed by multiple types of loads. Based on the spectral characteristics of composite harmonics, a clustering method is used to obtain the cluster center harmonic frequency bands of multiple frequency band clusters. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands. Based on the ratio of the reduction of the delay time in the repetitive controller to the resonant peak frequency and the fundamental frequency, an improved fast repetitive controller is obtained. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series, and the fractional-order delay element is compensated to obtain the compensated fast repetitive controller. The fast repetitive controller obtained by connecting the compensated fast repetitive controller in parallel with the PI controller is used as the improved current inner loop; based on the voltage outer loop and the improved current inner loop, the reactive current of the converter is controlled quickly.

2. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 1, characterized in that, Multi-scale spectral analysis is performed on composite harmonics to extract frequency band characteristic parameters from each identified harmonic frequency band, including: center frequency, energy intensity, bandwidth, amplitude time-varying index, phase consistency, and inter-band coupling. Based on the frequency band feature parameter vector, an improved DBSCAN clustering algorithm is used to perform clustering to obtain multiple frequency band clusters; the importance of each frequency band cluster is dynamically evaluated. After sorting the frequency band clusters from highest to lowest importance, the cluster center harmonic frequency bands of the top p frequency band clusters are obtained. The resonant peaks are determined based on the principle that each resonant peak covers two adjacent cluster center harmonic frequency bands.

3. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 2, characterized in that, The importance of frequency band clusters is dynamically assessed as follows: In the formula, , These are all index variables for frequency band clusters. The number of frequency band clusters, For frequency band clusters The importance of , , They are frequency band clusters Energy intensity, amplitude time-varying index, and phase consistency; For frequency band clusters and The degree of coupling between them , , , All are weighting coefficients, and + + + =1, It is a very small positive number.

4. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 2, characterized in that, Calculate the ratio of each resonant peak frequency to the fundamental frequency. Using the greatest common divisor (w) of all ratios as the delay time reduction ratio, the delay time in the inner membrane structure of the improved repetitive controller is then calculated as follows: , To improve the delay time in the inner membrane structure of the pre-repetitive controller.

5. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 4, characterized in that, Improved transfer function of fast repetitive controller As shown in the following formula: In the formula, For filters, To shorten the periodic delay stage, For the compensation process, This is the gain coefficient. For compensation filters, For phase compensation, These are the interpolation coefficients. This refers to the order of the phase compensation stage.

6. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 5, characterized in that, Delayed process Decomposed into integer-order delay elements connected in series and fractional delay , For the closest Positive integers for / w It is a positive fraction, satisfying / w= + ; The fractional delay is approximated by an FIR filter to obtain a parallel connection. +1 integer-order sub-delay stage to compensate for fractional-order delay stages, and +1 sub-delay elements are adjacent in order.

7. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 6, characterized in that, Fractional delay element is denoted as It satisfies the following relationship: In the formula, , Sub-delay stages The weights and orders, Fractional delay stage order, These are the interpolation coefficients. This represents the upper limit of the interpolation.

8. The fast reactive current control method for converters based on centralized sampling on the grid side according to claim 7, characterized in that, The transfer function of the compensated fast repetitive controller is shown in the following equation: In the formula, This is the transfer function of the compensated fast repetitive controller.

9. A fast reactive current control system for a converter based on centralized sampling on the grid side, used to implement the fast reactive current control method for a converter based on centralized sampling on the grid side as described in any one of claims 1 to 8, characterized in that, include: The composite harmonic current detection module is used to detect harmonics in the current at the common connection point of the power grid to which the converter is connected, using a harmonic detection method based on instantaneous reactive power theory, to obtain the composite harmonic current superimposed by multiple types of loads. The current inner loop improvement module is used to obtain the cluster center harmonic frequency bands of multiple frequency bands based on the spectral characteristics of composite harmonics using a clustering method. The principle is that each resonant peak covers two adjacent cluster center harmonic frequency bands to determine the resonant peaks. Based on the frequency of each resonant peak and the fundamental frequency, the reduction ratio of the delay time in the repetitive controller is determined to obtain an improved fast repetitive controller. The delay element in the feedback branch of the improved fast repetitive controller is decomposed into an integer-order delay element and a fractional-order delay element connected in series. The fractional-order delay element is compensated to obtain a compensated fast repetitive controller. The fast repetitive composite controller obtained by connecting the compensated fast repetitive controller in parallel with a PI controller serves as the improved current inner loop. The reactive current fast control module is used to quickly control the reactive current of the converter based on the voltage outer loop and the improved current inner loop.

10. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-8.

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