A grid-connected converter harmonic and negative sequence current compound control method and system based on adaptive decoupling

Abstract

The application discloses a grid-connected converter harmonic and negative sequence current compound control method and system based on adaptive decoupling, and a self-adaptive decoupling controller is connected in series at the input end of a forward path of a resonant controller; the transfer function thereof is equal to the closed-loop transfer function of a fundamental closed-loop control system which is only composed of a PI controller and a full-state feedback controller. When a step occurs in a grid-connected current reference instruction, the controller pre-processes an error signal, so that the resonant controller is not excited in a dynamic process, and the dynamic response of the system is determined by the PI controller and the full-state feedback controller, thus realizing complete decoupling of the fundamental control and harmonic / negative sequence suppression in the dynamic response; in a steady state, the resonant controller still exists in a disturbance closed-loop transfer function, and the non-static suppression capability of specific harmonic and negative sequence components is reserved. The application significantly reduces the steady-state harmonic distortion rate of the grid-connected current, and guarantees excellent performance of high-bandwidth and no overshoot in the dynamic process.

Description

Technical Field

[0001] This invention relates to the field of control of grid-connected converters for power electronic devices, and more particularly to an adaptive decoupling control method for output current when the grid voltage contains harmonics and negative sequence components. Background Technology

[0002] With the large-scale application of power electronic equipment in the power grid, the problem of voltage distortion at the point of common coupling has become increasingly prominent, resulting in a large number of harmonics and negative sequence components in the output current of grid-connected converters, which seriously threatens the power quality and equipment safety of the power grid.

[0003] To suppress grid-connected current harmonics under grid voltage distortion conditions, a resonant controller is typically connected in parallel with an outer-loop PI (Proportional-Integral) controller to form a PIR (Proportional-Integral-Resonant) controller. The resonant controller utilizes its characteristic of generating infinite open-loop gain at a specific frequency to effectively suppress harmonic disturbances at that frequency, significantly reducing the total harmonic distortion rate of the grid-connected current in steady state.

[0004] However, traditional PIR controllers have inherent dynamic performance defects. The introduction of a resonant controller results in a pair of low-damping-ratio conjugate complex dominant poles in the closed-loop system. Simultaneously, the parallel connection of the PI controller and the resonant controller in the control loop leads to mutual coupling in their dynamic responses. When the grid-connected current reference command undergoes a step change, the system output exhibits significant overshoot and sustained oscillations, posing a potential threat to the safe and stable operation of the converter and sensitive loads. These problems are inherent defects of traditional PIR controllers and are difficult to solve through controller parameter optimization.

[0005] To address the aforementioned issues, some existing solutions propose temporarily shutting down the resonant controller during dynamic processes to prevent oscillations. However, determining when to turn it on is constrained by various factors, making its engineering implementation complex. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method that can decouple the dynamic response of the PI controller and the resonant controller from the control structure level, so that the system can maintain steady-state harmonic suppression capability while having high bandwidth and no overshoot dynamic response performance.

[0007] To solve the above technical problems, the present invention adopts the following technical solution:

[0008] First, this invention proposes a composite control method for harmonics and negative sequence current in grid-connected converters based on adaptive decoupling, specifically including the following steps:

[0009] A dual-closed-loop fundamental wave control system for a grid-connected converter is constructed to generate fundamental wave modulation components. The outer loop uses a proportional-integral controller, and the inner loop uses a full-state feedback controller. The closed-loop poles of the fourth-order augmented system model are placed on the positive real axis inside the unit circle in the discrete domain, and the parameters of the inner loop state feedback coefficient matrix and the outer loop proportional-integral controller are tuned accordingly.

[0010] Based on the fundamental wave control system, one or more resonant controllers G are connected in parallel. R (z), generating harmonics and negative sequence compensation modulation components; the resonant frequency of the resonant controller is set according to the positive and negative sequence attributes of the harmonics to be suppressed in the ABC coordinate system, mapped to the equivalent frequency in the dq coordinate system.

[0011] Based on the positive-sequence current reference value determined by the fundamental wave control system, a dual second-order generalized integrator phase-locked loop is used to extract the positive-sequence voltage component and the negative-sequence voltage component of the grid voltage. A negative-sequence current reference value is generated based on the negative-sequence voltage component, and the magnitude of the negative-sequence current reference value has a preset quantitative relationship with the negative-sequence voltage component. The negative-sequence current reference value is superimposed with the positive-sequence current reference value to obtain the total grid-connected current reference value, and the total grid-connected current reference value is used as the current input of the resonant controller and the adaptive decoupling controller.

[0012] An adaptive decoupling controller T(z) is connected in series at the input of the forward path of the resonant controller. Its transfer function is adaptively adjusted according to the current operating conditions of the converter and the changes in the filter parameters to achieve dynamic decoupling between fundamental wave control and harmonic / negative sequence control.

[0013] The fundamental modulation component output by the dual closed-loop fundamental control system is superimposed with the harmonic and negative sequence compensation modulation components output by all resonant controllers to generate the final bridge arm modulation signal.

[0014] Furthermore, the resonant controller G R The specific expression for (z) is:

[0015]

[0016] Where, k R ω is the proportionality constant, n1 and n2 are undetermined zeros, and ω r T is the resonant angular frequency. s Let z be the sampling period, and z be the discrete-domain operator.

[0017] Furthermore, the step of generating the negative sequence current reference value includes:

[0018] The amplitudes of the positive-sequence and negative-sequence currents are dynamically allocated based on the negative-sequence voltage imbalance at the grid connection point. The negative-sequence current reference value i - refCalculate using the following formula:

[0019] ,

[0020] Among them, I max U is the maximum output current of the converter, F is the preset unbalance weighting coefficient, and U is the maximum output current of the converter. - For the negative sequence voltage amplitude, U + This represents the positive sequence voltage amplitude.

[0021] Furthermore, the transfer function of the adaptive decoupling controller T(z) is set to be the closed-loop transfer function G of the fundamental wave control system consisting only of the proportional-integral controller and the full-state feedback controller under the current operating condition. c (z), the specific expression is:

[0022] ,

[0023] Among them, G PI P(z) is the transfer function of the proportional-integral controller, and P(z) is the transfer function of the equivalent controlled object in the inner loop after the introduction of state feedback. This transfer function is adaptively corrected by the real-time identification results of grid harmonics and filter parameters.

[0024] Furthermore, the adaptive adjustment of the parameters of the adaptive decoupling controller T(z) is based on the following: the harmonic order distribution of the grid voltage at the common coupling point, the online identification values ​​of the machine-side inductance and grid-side inductance of the LCL filter, and the filter capacitor; when the changes of the above parameters exceed the preset threshold, the rolling optimization update of the parameters is triggered.

[0025] Furthermore, by introducing an adaptive decoupling controller T(z), the system's improved closed-loop transfer function G... Rce (z) satisfies:

[0026]

[0027] When T(z) = G c When (z), G Rce (z) and the closed-loop transfer function G of the fundamental system without any resonant controller. c (z) are strictly equal, so that the conjugate complex poles introduced by the resonant controller in the closed-loop transfer function are precisely canceled by the corresponding zeros introduced by the adaptive decoupling controller, and the dynamic response mode of the resonant controller does not appear in the closed-loop characteristics from the system reference input to the output.

[0028] Furthermore, in steady state, the resonant controller remains fully present in the disturbance closed-loop transfer function, and its infinite gain characteristic at the resonant frequency is fully preserved, which is used to suppress the influence of grid voltage disturbances and negative sequence components at the corresponding frequencies on the grid-connected current without steady-state error.

[0029] Furthermore, the parameters of the resonant controller are optimized based on system stability, specifically including:

[0030] In the equivalent disturbance open-loop circuit that ignores the influence of the proportional-integral controller and other parallel resonant controllers, the first zero point n1 of the resonant controller is configured to cancel the real pole with the minimum damping and the maximum magnitude in the inner loop transfer function of the controlled object, so as to reduce the system order.

[0031] The second zero point n2 of the resonant controller is positioned inside the discrete domain unit circle, close to the resonant open-loop conjugate pole, thus pulling the root locus branch back into the unit circle.

[0032] Based on the corrected root locus diagram, the proportional gain of the resonant controller is selected according to the stability margin requirements to ensure that the system has sufficient gain margin and phase margin under all operating conditions.

[0033] Secondly, this invention also proposes a composite control system for harmonics and negative sequence current of a grid-connected converter based on adaptive decoupling. The system is deployed in a grid-connected converter connected between the power grid and the load, and is used to ensure the dynamic response speed of the grid current and the accuracy of steady-state harmonic suppression. The system includes:

[0034] The fundamental wave control module, which includes an outer loop proportional-integral controller and an inner loop full-state feedback controller, is used to generate the fundamental wave modulation component.

[0035] The harmonic and negative sequence suppression module contains one or more parallel resonant controllers for generating harmonic and negative sequence compensation modulation components;

[0036] An adaptive decoupling control module is deployed at the input of the resonant controller. Its transfer function is adaptively adjusted according to the output of the parameter online identification module to achieve dynamic decoupling between fundamental wave control and harmonic / negative sequence control.

[0037] The online parameter identification module estimates the changes in filter parameters and grid harmonic frequencies online based on real-time sampling data of grid voltage and current.

[0038] The synthesis module is used to superimpose the output of the fundamental wave control module with the outputs of all harmonic and negative sequence suppression modules to generate the final bridge arm modulation signal.

[0039] Furthermore, the present invention also proposes an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the steps of the method proposed in the present invention.

[0040] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0041] This invention connects an adaptive decoupling controller in series at the forward input of the resonant controller. Its transfer function is equal to the closed-loop transfer function of the fundamental closed-loop control system, which consists only of a PI controller and a full-state feedback controller. When the grid-connected current reference command experiences a step change, this controller preprocesses the error signal, ensuring that the resonant controller is not excited during dynamic processes. The system's dynamic response is entirely determined by the PI controller and the full-state feedback controller, achieving complete decoupling of fundamental control and harmonic / negative sequence suppression in the dynamic response. In steady state, the resonant controller remains fully present in the disturbance closed-loop transfer function, retaining its ability to suppress specific harmonics and negative sequence components without steady-state error. Therefore, this invention significantly reduces the steady-state harmonic distortion rate of the grid-connected current while ensuring excellent performance with high bandwidth and no overshoot during dynamic processes. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a system control block diagram using a traditional PIR controller.

[0044] Figure 2 This is a system control block diagram that incorporates the adaptive decoupling controller T(z) proposed in this invention.

[0045] Figure 3 This refers to the step response waveform of the output current when the grid voltage is distorted after adopting the strategy proposed in this invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0047] Example 1: This example proposes a composite control method for harmonics and negative sequence current of a grid-connected converter based on adaptive decoupling. The parameters of the grid-connected converter used in this invention are as follows: DC bus voltage 750V, filter capacitor 30μF.

[0048] The filter inductors are 0.02mH and 0.1mH, and the switching frequency and sampling frequency are both 50kHz. The system control block diagram incorporating the adaptive decoupling controller T(z) proposed in this invention is shown below. Figure 2 As shown. Specifically, it includes the following steps:

[0049] S1. Construct and tune a fundamental-wave dual-closed-loop control system with high bandwidth and no overshoot characteristics. The specific steps are as follows:

[0050] (1) First, establish an accurate mathematical model of the converter under grid-connected mode. Considering the symmetry of the d-axis and q-axis components of the three-phase system in the dq rotating coordinate system, a unified model is established in the complex domain to simplify the design. The voltage u of the three-phase grid (A, B, and C) is collected. g and grid-connected current i g The dq-axis components are obtained after Clark and Park transforms. Consider the inherent sampling period T of the digital control. s The computational delay is calculated, and a fourth-order augmented discrete state-space model is established as follows:

[0051] ,

[0052] Where, x d (k) = [i f (k) u f (k) i g (k) u o (k)] T i f (k) represents the machine-side filter inductance L at time k. f The current, u f (k) represents the filter capacitor C at time k. f voltage, i g (k) represents the grid-side filter inductance L at time k. g The current, u o (k) represents the bridge arm output voltage at time k. M, H, and G are the system matrix, input matrix, and disturbance matrix in the third-order discrete-domain state-space model without considering the one-time calculation delay, respectively. C c To calculate the grid-connected current i from the state vector g The output matrix of (k); A d B d D d and C d These are the augmented system matrix, augmented input matrix, augmented disturbance matrix, and augmented output matrix of the energy storage converter in the discrete domain, respectively.

[0053] (2) To achieve arbitrary configuration of the inner loop dynamic performance, a full-state feedback controller is introduced, and its control law is:

[0054]

[0055] Among them, u PI The control quantity output by the outer loop proportional-integral controller is used to form the modulation signal reference value of the bridge arm output voltage; the state feedback coefficient matrix K f= [K if K uf K ig K uo ], K if K uf K ig and K uo The state variables i are respectively f u f i g and u o The corresponding feedback coefficient.

[0056] To ensure zero steady-state error tracking of the step reference signal, a proportional-integral controller is introduced in the outer loop:

[0057]

[0058] Among them, G PI (z) is the transfer function of the proportional-integral controller, k P and k I These are the proportional and integral coefficients of the PI controller in the discrete domain, respectively, m=1−k I / k P Let z be the undetermined zero of the PI controller, and z be the discrete-domain operator. To achieve high bandwidth, the closed-loop transfer function G needs to be configured. c The poles of (z). To achieve overshoot-free operation and simplify the design, a zero-pole cancellation strategy is adopted: let the zero m of the PI controller be parallel to a pole p of the desired closed-loop transfer function. obj5 Cancel.

[0059] To obtain the desired dynamic response, based on the requirement of "high bandwidth and no overshoot nominal dynamic performance," the four outer-loop poles are positioned on the positive real axis within the unit circle of the discrete z-plane. Specifically, all desired closed-loop poles are made to be positive real poles with identical values ​​to simplify the analysis and ensure no overshoot. Let p be the standard pole in the continuous domain. std = −2π / T s T s Representing the sampling period, in actual configuration, the pole coefficient h = 0.4, then:

[0060]

[0061] Using MATLAB's `place` function, based on the pole vector p = [0.081, 0.081, 0.081, 0.081] and the system matrix (A... d B d ), find the state feedback coefficient matrix K f .

[0062] Based on the steady-state requirement that the DC gain of the closed-loop transfer function is 1, the proportional coefficient k of the PI controller can be solved. p :

[0063]

[0064] Among them, P oN (1) Let P be the molecule of the controlled object P(z). oN (z) is the value at z=1. At this point, all parameters of the fundamental-wave dual-loop control system have been tuned.

[0065] S2. Design the parameters of the resonant controller. The specific steps are as follows: like Figure 1 As shown, the traditional PIR controller uses the grid-connected current reference value. i gref With grid-connected current feedback value i g The deviation between the two values ​​is used as the control input, and this deviation signal is simultaneously fed into the proportional-integral controller. G PI ( z and resonant controller G R ( z The two control outputs, when superimposed, act on the equivalent controlled object in the inner loop after the introduction of state feedback. P ( z ), grid voltage disturbance u g Then through the disturbance channel Q ( z Affecting grid-connected current i g This structure can use the high gain of the resonant controller at the target frequency to suppress steady-state harmonics and negative sequence current components. However, the conjugate complex poles introduced by the resonant controller will participate in the dynamic response from the reference input to the grid current, causing the dynamic processes of the proportional-integral controller and the resonant controller to be coupled with each other, which can easily lead to overshoot or oscillation when the grid current reference value changes.

[0066] To suppress grid-connected current harmonics and negative sequence components caused by grid voltage distortion and asymmetrical faults, one or more resonant controllers G are connected in parallel to the fundamental wave control system. R (z) forms a PIR controller. This embodiment takes the suppression of the 5th negative sequence, 7th positive sequence, 11th negative sequence, and 13th positive sequence harmonics as an example, and designs two resonant controllers G. R6 (z) and G R12 (z). Parameter design follows these steps to ensure system stability:

[0067] (1) Configuration of zero point n1

[0068] Analyzing the inner-loop transfer function P(z) after introducing state feedback, it contains a real pole far from the origin with a large magnitude, which dominates the decay rate of the system's transient response. To reduce the system order and improve the response speed, the first zero n1 of the resonant controller is configured to cancel out this pole.

[0069] (2) Configuration of zero point n2

[0070] After n1 is canceled out, plot the equivalent open-loop transfer function Q of the perturbation. Ro The root locus of (z) is plotted. The root locus begins at a pair of conjugate open-loop poles on the unit circle. Without adding zeros, as k... R If the number of poles increases, the root locus will immediately leave the unit circle, causing the system to become unstable. To solve this problem, the second zero, n2, is positioned inside the unit circle on the positive real axis near the conjugate pole to attract root locus branches and pull them back into the unit circle. In this embodiment, n2 = 0.9 is chosen.

[0071] (3) The proportional coefficient k of the resonant controller R Selection

[0072] After determining the zeros n1 and n2, the corrected root locus diagram is plotted. Considering both the system's stability margin and harmonic suppression capability, k is selected. R The value of is chosen such that the closed-loop poles are located inside the unit circle and have an appropriate damping ratio. In this embodiment, k is chosen. R6 =1.8, k R12 =0.9.

[0073] S3. Construct and configure the adaptive decoupling controller T(z).

[0074] (1) Determine the transfer function of the adaptive decoupling controller T(z).

[0075] In one or more resonant controllers G R An adaptive decoupling controller T(z) is connected in series at the forward path input of (z). The core feature of this controller is that its transfer function is set to be the closed-loop transfer function G consisting only of the fundamental dual-loop control system (i.e., PI controller + state feedback) under the current operating condition. c (z):

[0076] ,

[0077] Among them, G PI (z) is the transfer function of the proportional-integral controller, and P(z) is the inner loop transfer function after introducing state feedback.

[0078] (2) Mechanism of complete decoupling of dynamic response

[0079] As shown in the formula above, since T(z) = G c The introduction of (z) improves the closed-loop transfer function G. Rce (z) and the closed-loop transfer function G of the fundamental system without any resonant controller. c (z) are strictly equal. This means that, at reference input i gref To output i g On the transmission path, the resonant controller G R (z) All conjugate complex poles introduced are canceled, and the dynamic response of the proportional-integral and resonant controllers is completely decoupled.

[0080] In the dynamic process, due to

[0081] ,

[0082] This means that when the grid-connected current reference command changes abruptly, the input error signal of the resonant controller remains zero, and the resonant controller is not excited throughout the entire dynamic process. The dynamic response of the system is entirely determined by the fundamental frequency controller, thus achieving complete decoupling of fundamental frequency control and harmonic / negative sequence suppression in terms of dynamic response.

[0083] (3) Retention of steady-state harmonic / negative sequence suppression capability

[0084] Although the resonant controller is decoupled during dynamic processes, its functionality is fully preserved in steady state. Consider the disturbance input u. g To output i g The disturbance closed-loop transfer function Q Rce (z):

[0085] ,

[0086] The denominator of this transfer function still includes the resonant controller G. R (z), when the frequency of the disturbance signal equals the resonant frequency, makes Q Rce (z)=0. Therefore, specific harmonics and negative sequence disturbances in the grid voltage are still suppressed by the resonant controller with infinite gain in steady state without steady-state error, ensuring low THD of the grid-connected current.

[0087] (4) Implementation of the adaptive mechanism

[0088] The system includes an online parameter identification module for adaptive adjustment of T(z). This module performs the following operations:

[0089] ① Filter parameter identification: Using the voltage and current sensors of the converter itself, the key parameters of the LCL filter are identified online through a recursive algorithm during non-characteristic moments of grid-connected operation: machine-side inductance, grid-side inductance, and filter capacitor.

[0090] ② Power grid harmonic frequency tracking: Using a phase-locked loop structure based on dual second-order generalized integrators, the fundamental frequency of the power grid voltage and the frequencies of each major harmonic are extracted in real time and used to update the resonant angular frequency of the resonant controller.

[0091] ③ Parameter Rolling Optimization: Set thresholds (e.g., inductance change exceeding 5%, capacitance change exceeding 10%, or mains frequency deviation exceeding 0.2Hz). When the change in the online identification result exceeds the preset threshold, the controller parameters are triggered for rolling optimization and update.

[0092] S5, Modular Integration and Workflow of Control Systems

[0093] The entire control system is implemented in the DSP through modular programming, and includes five core functional modules. Its workflow is as follows:

[0094] (1) Initialization: After the DSP is powered on, the main program is executed to initialize all peripherals and load the default control parameters (including K). f , k p , m, etc., and G R (the coefficient of z) enables interruption.

[0095] (2) Interrupt service routine: in each sampling period T s During the interrupt, the following subtasks are executed sequentially:

[0096] ① Online parameter identification module: Reads ADC sampling data u g and i g Call the algorithm to update L f , L g C f Estimate the values ​​of parameters such as [parameter name]. If the change exceeds the threshold, set the parameter update flag.

[0097] ② Adaptive decoupling control module: Detects parameter update flag; if set, recalculates K based on the newly identified parameters. f , k p , m and other parameters, update T(z) and G R The coefficients of (z) are then removed, and the flags are cleared.

[0098] ③ Fundamental wave control module: Calculates the deviation based on the grid-connected current reference value and feedback value; the PI controller calculates the fundamental wave modulation voltage component based on the deviation.

[0099] ④ Harmonic and Negative Sequence Suppression Module: After processing the deviation signal between the reference current and the feedback current through T(z), it is input to the parallel resonant controller G. R6 (z), G R12 In (z), the harmonic compensation modulation voltage component is calculated.

[0100] ⑤ Synthesis Module: The fundamental modulation component and all harmonic compensation components are vector-superimposed to obtain the final bridge arm output voltage command.

[0101] Through the above steps, this specific implementation method fully realizes the "composite control method for harmonics and negative sequence current of grid-connected converter based on adaptive decoupling". While ensuring the system's high bandwidth and overshoot-free dynamic performance, it achieves excellent steady-state harmonic and negative sequence current suppression effects and has adaptive capability to parameter changes.

[0102] like Figure 3 As shown, under conditions of grid voltage distortion, after adopting the adaptive decoupling composite control method proposed in this invention, when the grid current reference value undergoes a step change, the output grid current can quickly track the reference value without significant overshoot or oscillation during the dynamic process. After entering steady state, the parallel resonant controller still maintains its suppression effect at the target harmonic and negative sequence frequencies, thereby reducing the harmonic distortion and negative sequence components of the output current. These results demonstrate that this invention, by introducing an adaptive decoupling controller into the forward path of the resonant controller, effectively reduces the harmonic distortion and negative sequence components of the output current. T ( z While maintaining steady-state harmonic and negative sequence suppression capabilities, it avoids the dynamic response coupling between the proportional-integral element and the resonant element in traditional PIR controllers.

[0103] Example 2: This example proposes a composite control system for harmonics and negative sequence current of a grid-connected converter based on adaptive decoupling. The system is deployed in a grid-connected converter, which is connected between the power grid and the load. It is used to ensure the dynamic response speed of the grid current and the accuracy of steady-state harmonic suppression. Specifically, it includes:

[0104] The fundamental wave control module, which includes an outer loop proportional-integral controller and an inner loop full-state feedback controller, is used to generate the fundamental wave modulation component.

[0105] The harmonic and negative sequence suppression module contains one or more parallel resonant controllers for generating harmonic and negative sequence compensation modulation components;

[0106] An adaptive decoupling control module is deployed at the input of the resonant controller. Its transfer function is adaptively adjusted according to the output of the parameter online identification module to achieve dynamic decoupling between fundamental wave control and harmonic / negative sequence control.

[0107] The online parameter identification module estimates the changes in filter parameters and grid harmonic frequencies online based on real-time sampling data of grid voltage and current.

[0108] The synthesis module is used to superimpose the output of the fundamental wave control module with the outputs of all harmonic and negative sequence suppression modules to generate the final bridge arm modulation signal.

[0109] Example 3: Further, in one embodiment of the present invention, an electronic device is also proposed, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the various steps of the method described in the present invention, which will not be described in detail here.

[0110] It should be noted that the processing flow of the computer-readable storage medium or electronic device mentioned in the above embodiments corresponds to the specific steps of the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0111] The program code used to implement the methods of this application may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the functions / operations specified in the flowcharts and / or block diagrams are implemented. The program code may be executed entirely on a machine, partially on a machine, as a standalone software package partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0112] In the context of this application, a computer-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A computer-readable medium can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite control method for harmonics and negative sequence current in a grid-connected converter based on adaptive decoupling, characterized in that, include: A dual-closed-loop fundamental wave control system for a grid-connected converter is constructed to generate fundamental wave modulation components. The outer loop uses a proportional-integral controller, and the inner loop uses a full-state feedback controller. The closed-loop poles of the fourth-order augmented system model are placed on the positive real axis inside the unit circle in the discrete domain, and the parameters of the inner loop state feedback coefficient matrix and the outer loop proportional-integral controller are tuned accordingly. Based on the fundamental wave control system, one or more resonant controllers G are connected in parallel. R (z), generating harmonics and negative sequence compensation modulation components; the resonant frequency of the resonant controller is set according to the positive and negative sequence attributes of the harmonics to be suppressed in the ABC coordinate system, mapped to the equivalent frequency in the dq coordinate system. Based on the positive-sequence current reference value determined by the fundamental wave control system, a dual second-order generalized integrator phase-locked loop is used to extract the positive-sequence voltage component and the negative-sequence voltage component of the grid voltage. A negative-sequence current reference value is generated based on the negative-sequence voltage component, and the magnitude of the negative-sequence current reference value has a preset quantitative relationship with the negative-sequence voltage component. The negative-sequence current reference value is superimposed with the positive-sequence current reference value to obtain the total grid-connected current reference value, and the total grid-connected current reference value is used as the current input of the resonant controller and the adaptive decoupling controller. An adaptive decoupling controller T(z) is connected in series at the input of the forward path of the resonant controller. Its transfer function is adaptively adjusted according to the current operating conditions of the converter and the changes in the filter parameters to achieve dynamic decoupling between fundamental wave control and harmonic / negative sequence control. The fundamental modulation component output by the dual closed-loop fundamental control system is superimposed with the harmonic and negative sequence compensation modulation components output by all resonant controllers to generate the final bridge arm modulation signal.

2. The method according to claim 1, characterized in that, Resonant controller G R The specific expression for (z) is: ， Where, k R ω is the proportionality constant, n1 and n2 are undetermined zeros, and ω r T is the resonant angular frequency. s Let z be the sampling period, and z be the discrete-domain operator.

3. The method according to claim 1, characterized in that, The step of generating the negative sequence current reference value includes: The amplitudes of the positive-sequence and negative-sequence currents are dynamically allocated based on the negative-sequence voltage imbalance at the grid connection point. The negative-sequence current reference value i - ref Calculate using the following formula: ， Among them, I max U is the maximum output current of the converter, F is the preset unbalance weighting coefficient, and U is the maximum output current of the converter. - For the negative sequence voltage amplitude, U + This represents the positive sequence voltage amplitude.

4. The method according to claim 1, characterized in that, The transfer function of the adaptive decoupling controller T(z) is set to the closed-loop transfer function G of the fundamental wave control system consisting only of the proportional-integral controller and the full-state feedback controller under the current operating condition. c (z), the specific expression is: ， Among them, G PI P(z) is the transfer function of the proportional-integral controller, and P(z) is the transfer function of the equivalent controlled object in the inner loop after the introduction of state feedback. This transfer function is adaptively corrected by the real-time identification results of grid harmonics and filter parameters.

5. The method according to claim 4, characterized in that, The adaptive adjustment of parameters of the adaptive decoupling controller T(z) is based on the following: the harmonic order distribution of the grid voltage at the common coupling point, the online identification values ​​of the machine-side inductance and grid-side inductance of the LCL filter, and the filter capacitor; when the changes of the above parameters exceed the preset threshold, the rolling optimization update of the parameters is triggered.

6. The method according to claim 1, characterized in that, After introducing an adaptive decoupling controller T(z), the system's improved closed-loop transfer function G Rce (z) satisfies: ， When T(z) = G c When (z), G Rce (z) and the closed-loop transfer function G of the fundamental system without any resonant controller. c (z) are strictly equal, so that the conjugate complex poles introduced by the resonant controller in the closed-loop transfer function are precisely canceled by the corresponding zeros introduced by the adaptive decoupling controller, and the dynamic response mode of the resonant controller does not appear in the closed-loop characteristics from the system reference input to the output.

7. The method according to claim 6, characterized in that, In steady state, the resonant controller remains fully present in the disturbance closed-loop transfer function, and its infinite gain characteristic at the resonant frequency is fully preserved, which is used to suppress the influence of grid voltage disturbances and negative sequence components at the corresponding frequencies on the grid-connected current without steady-state error.

8. The method according to claim 1, characterized in that, The parameters of the resonant controller are optimized based on system stability, specifically including: In the equivalent disturbance open-loop circuit that ignores the influence of the proportional-integral controller and other parallel resonant controllers, the first zero point n1 of the resonant controller is configured to cancel the real pole with the minimum damping and the maximum magnitude in the inner loop transfer function of the controlled object, so as to reduce the system order. The second zero point n2 of the resonant controller is positioned inside the discrete domain unit circle, close to the resonant open-loop conjugate pole, thus pulling the root locus branch back into the unit circle. Based on the corrected root locus diagram, the proportional gain of the resonant controller is selected according to the stability margin requirements to ensure that the system has sufficient gain margin and phase margin under all operating conditions.

9. A composite control system for harmonics and negative sequence current of a grid-connected converter based on adaptive decoupling, the system being deployed in a grid-connected converter connected between the power grid and the load, used to ensure the dynamic response speed of the grid current and the steady-state harmonic suppression accuracy, characterized in that... include: The fundamental wave control module, which includes an outer loop proportional-integral controller and an inner loop full-state feedback controller, is used to generate the fundamental wave modulation component. The harmonic and negative sequence suppression module contains one or more parallel resonant controllers for generating harmonic and negative sequence compensation modulation components; An adaptive decoupling control module is deployed at the input of the resonant controller. Its transfer function is adaptively adjusted according to the output of the parameter online identification module to achieve dynamic decoupling between fundamental wave control and harmonic / negative sequence control. The online parameter identification module estimates the changes in filter parameters and grid harmonic frequencies online based on real-time sampling data of grid voltage and current. The synthesis module is used to superimpose the output of the fundamental wave control module with the outputs of all harmonic and negative sequence suppression modules to generate the final bridge arm modulation signal.

10. An electronic device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the computer program is executed by the processor, it implements the method described in any one of claims 1-8.

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