Feedforward Enhanced Robust Grid-Connected Control Method for Energy Storage Converters under Wide Grid Impedance

Abstract

This application relates to a feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance conditions, belonging to the field of power electronic control technology. This method transforms the current loop PI parameter design problem into optimizing the feasible stability region of the current loop controller. With the goal of maximizing the common adaptability of the stability region under different grid impedance conditions, it calculates the optimal feedforward coefficients and further calculates a set of current loop PI parameters that can cover wide grid impedance variations and possess high stability. Ultimately, it achieves feedforward-enhanced robust grid-connected control of energy storage converters under wide grid impedance conditions, fundamentally overcoming the blindness and inefficiency of traditional empirical parameter tuning, and significantly improving parameter design efficiency, overall system stability, and grid adaptability.

Description

Technical Field

[0001] This application relates to the field of power electronic control technology, and in particular to a feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance. Background Technology

[0002] New energy sources such as wind and solar power exhibit significant intermittency and volatility, necessitating the configuration of energy storage batteries to ensure stable grid operation. The energy storage converter, serving as the interface between the energy storage battery and the grid, primarily functions to convert direct current (DC) into alternating current (AC) synchronized with the grid. However, the high-speed switching of the power switching devices within the energy storage converter introduces a significant amount of high-order harmonics near the switching frequency into the output generator-side current. Therefore, an LCL filter is typically connected between the energy storage converter and the grid, utilizing its excellent high-frequency attenuation characteristics to meet grid-connected power quality requirements. The energy storage converter, LCL filter, grid impedance, and grid together constitute the grid-connected system. The LCL filter includes a generator-side filter inductor connected to the energy storage converter, a grid-side filter inductor connected to the grid, and a filter capacitor between the connection point between the generator-side and grid-side filter inductors and ground. This grid-connected system typically employs a grid-following control strategy, achieving synchronization with the grid through a phase-locked loop (PLL) controller and regulating the active and reactive power injected into the grid through a closed-loop current loop controller.

[0003] LCL filters generate high-gain resonance peaks at their resonant frequencies, which can easily lead to oscillations and instability in grid-connected systems. Existing technologies primarily suppress resonance in two ways: First, passive damping, which involves adding physical damping resistors to the LCL filter to suppress resonance by consuming resonant energy. However, this results in continuous power loss and is economically unsustainable in medium-to-high power scenarios. Second, active damping, which introduces capacitor voltage feedforward into the current loop controller of the energy storage converter. Specifically, the error between the machine-side current flowing through the machine-side filter inductor and its command value is input to the current loop PI regulator to obtain the machine-side current feedback. Simultaneously, the capacitor voltage is multiplied by a feedforward coefficient to obtain the capacitor voltage feedforward. The current feedback and voltage feedforward are then superimposed to output a modulation signal used to control the output of the energy storage converter. This feedforward channel introduces an equivalent negative impedance into the control loop, thereby suppressing the LCL filter's own resonance peak at the source, achieving lossless active damping, and improving the stability of the grid-connected system. The selection of the feedforward coefficient typically relies on engineering experience or trial-and-error methods.

[0004] However, existing voltage feedforward-based technical solutions still have significant drawbacks: current research has failed to systematically analyze the impact of feedforward coefficients on the stability boundary of current loop PI parameters, and has not fully considered the stability coupling problem caused by the interaction between grid impedance and energy storage converter. The selection of feedforward coefficients and the tuning of current loop PI parameters are often handled separately, lacking a unified collaborative design criterion. While the efficiency is low, it is even more difficult to ensure that the current loop PI regulator maintains sufficient stability margin when the grid impedance varies over a wide range, resulting in a high risk of instability in the grid-connected system under the condition of wide range of grid impedance variations. Summary of the Invention

[0005] In view of this, it is necessary to provide a feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance conditions, in order to solve the technical problems of low efficiency and high instability risk in the existing technology under wide grid impedance variation conditions.

[0006] To address the aforementioned issues, in a first aspect, this application provides a feedforward-enhanced robust grid-connected control method for an energy storage converter under wide grid impedance, applied to a grid-connected system. The grid-connected system includes an energy storage converter, an LCL filter, a grid impedance, and a grid connected in sequence. The current loop controller of the energy storage converter adopts a control strategy combining capacitor voltage feedforward and machine-side current feedback. The capacitor voltage feedforward is adjusted by a feedforward coefficient, and the machine-side current feedback is adjusted by current loop PI parameters.

[0007] The method includes:

[0008] Obtain the open-loop transfer function of the current loop controller in the grid-connected system. The open-loop transfer function is related to the feedforward coefficient, the current loop PI parameter, and the grid impedance.

[0009] Under different feedforward coefficients and different grid impedances, the current loop PI parameters are calculated when the open-loop transfer function satisfies the preset stability margin. The feasible stability region of the current loop PI parameters under different feedforward coefficients and different grid impedances is obtained. The optimal feedforward coefficient is determined with the goal of maximizing the area of ​​the feasible stability region under different grid impedances.

[0010] The feedforward coefficient in the open-loop transfer function is fixed to the optimal feedforward coefficient. Under different grid impedance conditions, the current loop PI parameter when the open-loop transfer function satisfies the preset stability margin is calculated. Several feasible stability regions of the current loop PI parameter under different grid impedances are obtained. The intersection of the several feasible stability regions is calculated, and the target current loop PI parameter is selected from the intersection.

[0011] The energy storage converter is controlled based on a current loop controller configured with the optimal feedforward coefficient and the target current loop PI parameters.

[0012] In one implementation, obtaining the open-loop transfer function of the current loop controller in the grid-connected system includes:

[0013] Small-signal modeling is performed on the current loop controller, the LCL filter, the grid impedance, and the delay term to obtain a small-signal model;

[0014] Based on the small-signal model, the equivalent impedance transfer function from the output voltage of the current loop PI regulator of the current loop controller to the machine-side current and the complex frequency domain model of the current loop PI regulator are determined.

[0015] Multiplying the equivalent impedance transfer function by the complex frequency domain model of the current loop PI regulator yields the open-loop transfer function of the current loop controller in the grid-connected system.

[0016] In one implementation, the open-loop transfer function is:

[0017] ;

[0018] In the formula, Let k represent the open-loop transfer function. pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, and the complex frequency is represented by s. F represents the delay term. v L represents the feedforward coefficient. if C represents the value of the machine-side filter inductance. f L represents the value of the filter capacitor. gf L represents the value of the grid-side filter inductance. g This indicates the power grid impedance value.

[0019] In one implementation, the delay term employs a control delay comprising one beat and a modulation delay approximately half a beat, and the complex frequency domain model of the delay term is:

[0020] ;

[0021] In the formula, G d (s) represents the delay term, T s s represents the sampling period, and s represents the complex frequency.

[0022] In one implementation, the stability margin includes magnitude margin and phase margin.

[0023] In one implementation, calculating the current loop PI parameters when the gain margin and phase margin of the open-loop transfer function satisfy preset constraints includes:

[0024] Traverse the cutoff frequencies and calculate the current loop PI parameters when the amplitude of the open-loop transfer function at the cutoff frequency is 1 and the phase margin is a preset phase threshold, thus obtaining the first stable boundary of the current loop PI parameters.

[0025] By iterating through the phase crossover frequencies, the current loop PI parameters are calculated when the phase of the open-loop transfer function at the phase crossover frequency is -180° and the magnitude margin is a preset magnitude threshold. The second stable boundary of the current loop PI parameters is obtained, and the first stable boundary and the second stable boundary enclose the feasible stable region.

[0026] In one implementation, the optimal feedforward coefficient is determined with the goal of maximizing the feasible stability region area under different grid impedances. This includes determining the optimal feedforward coefficient with the goal of maximizing the comprehensive fitness index composed of the minimum, average and standard deviation weights of the feasible stability region area under different grid impedances.

[0027] In one embodiment, the calculation formula for the current loop controller is:

[0028] ;

[0029] In the formula, u d U represents the direct-axis component of the modulated signal. q i represents the cross-axis component of the modulated signal. fd i represents the direct-axis component of the machine-side current. fq i represents the quadrature-axis component of the machine-side current. dref The command value i represents the direct-axis component of the machine-side current. qref The command value, k, represents the quadrature-axis component of the machine-side current. pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, the complex frequency is represented by ω0, and the rated angular frequency of the power grid is represented by L. if Indicates the machine-side filter inductance, u cd U represents the direct-axis component of the capacitor voltage. cq F represents the quadrature-axis component of the capacitor voltage. v This represents the feedforward coefficient.

[0030] Secondly, this application also provides an electronic device, including a memory and a processor;

[0031] The memory is used to store programs;

[0032] The processor, coupled to the memory, is used to execute the program stored in the memory to implement the steps of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance described above.

[0033] Thirdly, this application also provides a computer-readable storage medium storing a program or instructions that, when executed by a processor, implement the steps of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance described above.

[0034] The beneficial effects of this application are as follows: The feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance provided in this application establishes an open-loop transfer function of the current loop controller that includes feedforward coefficients, current loop PI parameters, and grid impedance. It systematically analyzes the dynamic coupling mechanism of these three components and their synergistic impact on system stability margin, overcoming the limitation of separate design of feedforward coefficients and current loop PI parameters in traditional designs. Based on this, the design problem of current loop PI parameters is transformed into optimizing the feasible stability region of the current loop controller. With the goal of maximizing the common adaptability of the stability region under different grid impedance conditions, the optimal feedforward coefficients are calculated, and further, a set of current loop PI parameters that can cover wide grid impedance variations and has high stability is calculated. Ultimately, feedforward-enhanced robust grid-connected control of energy storage converters under wide grid impedance is achieved, fundamentally overcoming the blindness and inefficiency of traditional empirical parameter tuning, and significantly improving parameter design efficiency, overall system stability, and grid adaptability. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the grid-connected system provided in an embodiment of this application;

[0036] Figure 2 A schematic flowchart illustrating the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance provided in this application embodiment;

[0037] Figure 3 This is a flowchart illustrating step S201 in an embodiment of this application;

[0038] Figure 4 This is a schematic diagram of the structure of the small signal model provided in the embodiments of this application;

[0039] Figure 5 A schematic diagram of the Bode plot of the open-loop transfer function provided in the embodiments of this application;

[0040] Figure 6 This is a flowchart illustrating step S202 in an embodiment of this application;

[0041] Figure 7 A schematic diagram of the feasible stability region of the current loop PI parameters under weak power grid and different feedforward coefficients provided in the embodiments of this application;

[0042] Figure 8A schematic diagram of the feasible stability region of the current loop PI parameters under strong power grid and different feedforward coefficients provided in the embodiments of this application;

[0043] Figure 9 This is a schematic diagram of the feasible stability region of the current loop PI parameters under different short-circuit ratios provided in the embodiments of this application;

[0044] Figure 10 A schematic diagram of the steady-state waveforms of capacitor voltage, grid-side current, and generator-side current under strong power grid conditions provided for embodiments of this application;

[0045] Figure 11 A schematic diagram of the steady-state waveforms of capacitor voltage, grid-side current, and generator-side current under weak grid conditions provided in the embodiments of this application;

[0046] Figure 12 This is a schematic diagram of the structure of the electronic device provided in the embodiments of this application;

[0047] Reference numerals in the attached diagram: 1. Energy storage converter; 2. LCL filter; 3. Power grid; 4. Phase-locked loop controller; 5. Current loop controller; 6. Space vector modulation module. Detailed Implementation

[0048] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0049] It should be understood that the illustrative drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may be implemented out of order, and steps without logical contextual relationships may be reversed or performed simultaneously. Furthermore, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, or in one or more hardware modules or integrated circuits, or in different network and / or processor grid-connected systems and / or microcontroller grid-connected systems.

[0050] The terms "first," "second," etc., used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a technical feature specified with "first" or "second" may explicitly or implicitly include at least one of those features. "And / or" describes the relationship between related objects, indicating that three relationships may exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone.

[0051] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0052] This application provides a feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance, which will be described below.

[0053] To facilitate understanding of the proposed solution, the grid-connected system for which the energy storage converter is applied will be described in detail first.

[0054] like Figure 1 As shown, the equivalent circuit model of the grid-connected system includes an energy storage converter 1, an LCL filter 2, and a grid impedance L connected in sequence. g And grid 3. Among them, energy storage converter 1 uses DC bus voltage V dc As input, the switching devices (such as IGBTs) of its bridge arms are controlled by PWM modulation signals, and the outputs are the three-phase side voltage vector V and the three-phase side current vector I. f The LCL filter 2 is connected between the energy storage converter 1 and the power grid 3 to filter out the switching harmonics of the energy storage converter 1. Its structure includes: a machine-side filter inductor L connected to the energy storage converter 1. if 1. Grid-side filter inductor L connected to power grid 3 gf and the filter inductor L connected to the machine side if With the grid-side filter inductor L gf The filter capacitor C between the connection point and ground f Filter capacitor C f The three-phase capacitor voltage vector at both ends is U c The current flows through the grid-side filter inductor L gf The vector of the three-phase grid-side inductor current is I. g Grid impedance L g Including transformer impedance L T and line impedance L lGrid-side filter inductor L gf With grid impedance L g The connection point is the grid connection point, and the three-phase grid voltage vector of grid 3 is E. g .

[0055] like Figure 1 As shown, in the above equivalent circuit model, due to the discretized operation and nonlinear characteristics of the switching devices of the energy storage converter 1, its output three-phase side voltage vector V and three-phase side current vector I... f In addition to the required fundamental component, the system also contains high-frequency harmonics. These harmonics will excite the LCL filter 2 to resonate at its resonant frequency, generating a high-gain resonant peak (primarily manifested as the oscillation of the three-phase capacitor voltage vector Uc), affecting the stability of the grid-connected system.

[0056] like Figure 1 As shown, to suppress the resonance peak of LCL filter 2, this application adopts a grid-following control strategy with capacitor voltage feedforward. Specifically, the control system of energy storage converter 1 includes a phase-locked loop controller 4, a current loop controller 5, and a space vector modulation module 6. The inputs of the control system include the three-camera side current vector I... f and three-phase capacitor voltage vector U c It is necessary to first perform a Park transformation to convert it into the direct-axis component i of the machine-side current in a synchronous rotating coordinate system. fd and cross-axis component i fq and the direct-axis component u of the capacitor voltage cd and cross-axis component u cq Then it can be used by subsequent modules.

[0057] Among them, the three-camera side current vector I f (including i) fa i fb and i fc The direct-axis component i converted to machine-side current fd and cross-axis component i fq The Parker transformation formula is:

[0058] ;

[0059] In the formula, i fd i represents the direct-axis component of the machine-side current. fq i represents the quadrature-axis component of the machine-side current. fa i fb and i fc Represents the three-phase camera-side current vector I f The phase components, ω represents the angular frequency of the previous cycle of the power grid.

[0060] The three-phase capacitor voltage vector U c (including u)ca u cb and u cc Converted to the direct-axis component u of the capacitor voltage cd and cross-axis component u cq The Parker transformation formula is:

[0061] ;

[0062] In the formula, u cd U represents the direct-axis component of the capacitor voltage. cq The quadrature-axis component of the capacitor voltage, u ca u cb and u cc Represents the three-phase capacitor voltage vector U c The phase components in the diagram, where ω represents the angular frequency of the previous cycle of the power grid.

[0063] like Figure 1 As shown, the phase-locked loop controller 4 is based on the quadrature-axis component u of the capacitor voltage. cq Tracking the real-time phase angle θ of the power grid pll The corresponding calculation formula is:

[0064] ;

[0065] In the formula, ω pll The real-time angular frequency of the power grid is represented by ω0, and the rated angular frequency of the power grid is represented by u. cq k represents the cross-axis component of the capacitor voltage vector. ppll k represents the proportional gain of the PI controller in a phase-locked loop (PLL) controller. ipll θ represents the integral coefficient of the PI controller in the phase-locked loop controller. pll denoted by s, which represents the real-time phase angle of the power grid.

[0066] like Figure 1 As shown, the current loop controller 5 is based on the machine-side current (i fd and i fq ) and its instruction value (i dref and i qref The error is used to perform machine-side current feedback, based on the capacitor voltage (u). cd and u cq ) and feedforward coefficient F v Perform capacitor voltage feedforward, and based on capacitor voltage (u) cd and u cq Cross-decoupling is performed to output the direct-axis component u of the modulated signal. d and cross-axis component u q The corresponding calculation formula is:

[0067] ;

[0068] In the formula, u d U represents the direct-axis component of the modulated signal. q i represents the cross-axis component of the modulated signal. fd The direct-axis component of the generator-side current (used to control the active power injected into the grid), i fq The quadrature-axis component of the generator-side current (used to control reactive power injected into the grid), i dref The command value representing the direct-axis component of the machine-side current (determined by an externally given active power command), i qref The command value representing the quadrature-axis component of the generator-side current (determined by an externally given reactive power command), k pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, the complex frequency is represented by ω0, and the rated angular frequency of the power grid is represented by L. if Indicates the machine-side filter inductance, u cd U represents the direct-axis component of the capacitor voltage. cq F represents the quadrature-axis component of the capacitor voltage. v This represents the feedforward coefficient.

[0069] like Figure 1 As shown, the space vector modulation module 6 first utilizes the real-time phase angle θ of the power grid output by the phase-locked loop controller 4. pll The direct-axis component u of the modulation signal output by the current loop controller 5 d and cross-axis component u q The inverse Parker transform is converted into a three-phase modulation signal synchronized with the power grid 3, and then the SVPWM algorithm generates six PWM modulation signals to control the switching devices inside the energy storage converter 1.

[0070] like Figure 1 As shown, the capacitor voltage U is collected in real time. c Multiply it by the feedforward coefficient F v Then, the signal is directly injected into the modulation signal of the current loop controller 5. This feedforward channel introduces an equivalent negative impedance in the control loop, thereby suppressing the resonance peak of the LCL filter 2 itself from the source and improving the stability of the grid-connected system.

[0071] Existing technologies in selecting feedforward coefficients F v At that time, the feedforward coefficient F was not systematically analyzed. v For the current loop PI parameters (the proportional coefficient k of the current loop PI regulator) pc and integral coefficient k ic The influence of the stability boundary was not fully considered, nor was the grid impedance L adequately taken into account. g Stability coupling problem caused by interaction between the energy storage converter and the feedforward coefficient F v Selection of current loop PI parameters (k)pc and k ic The setting of the current loop PI regulator is often handled piecemeal, relying mainly on engineering experience or cumbersome trial-and-error methods, lacking a unified collaborative design criterion. This results in low efficiency and makes it even more difficult to ensure that the current loop PI regulator operates within the grid impedance L. g Maintaining sufficient stability margin over a wide range of variations results in a grid-connected system with a grid impedance L g There is a high risk of instability under a wide range of varying operating conditions.

[0072] Therefore, this application provides a feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance, such as... Figure 2 As shown, the feedforward-enhanced robust grid-connected control method for energy storage converters under wide grid impedance includes:

[0073] S201. Obtain the open-loop transfer function of the current loop controller in the grid-connected system. The open-loop transfer function is related to the feedforward coefficient, the current loop PI parameter, and the grid impedance.

[0074] In some embodiments, such as Figure 3 As shown, step S201 includes:

[0075] S2011. Perform small-signal modeling on the current loop controller, delay term, LCL filter and grid impedance in the grid-connected system to obtain the small-signal model;

[0076] Specifically, the small-signal model is as follows: Figure 4 As shown, Figure 4 In the middle, the current loop controller 5 includes a current loop PI regulator, G c (s) is the complex frequency domain model of the current loop PI regulator. In the formula, k pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, and the complex frequency is represented by G. d (s) represents the delay term, which includes one beat (i.e., The control delay and the approximate half-beat (the average delay caused by PWM updates during modulation, typically half a sampling period, i.e.) Modulation delay of ) In the formula, T s The sampling period is represented by s, and the complex frequency is represented by F. v L is the feedforward coefficient. if C is the value of the machine-side filter inductance. f L is the value of the filter capacitor. gf L is the value of the grid-side filter inductance. g Let i be the power grid impedance value. ref The command value i is the direct-axis component of the machine-side current. dref(or the command value i of the quadrature axis component of the machine-side current) qref ), i f i is the direct-axis component of the machine-side current fd (or the quadrature-axis component i of the machine-side current) fq ), u c u is the direct-axis component of the capacitor voltage. cd (or the quadrature-axis component u of the capacitor voltage) cq ), i g This represents the direct-axis component (or quadrature-axis component) of the grid-side inductor current. Since the small-signal model of the direct-axis component is consistent with that of the quadrature-axis component, it can be represented by only one small-signal model.

[0077] S2012. Based on the small-signal model, determine the equivalent impedance transfer function from the output voltage of the current loop PI regulator of the current loop controller to the machine-side current and the complex frequency domain model of the current loop PI regulator.

[0078] Specifically, such as Figure 4 As shown, the transfer function of the small-signal model is simplified, and the result from the current loop PI regulator G is derived. c (s) output voltage to machine-side current i f Between these, there is a capacitor voltage feedforward channel and a delay term G. d (s), LCL filter and mains impedance L g Equivalent impedance transfer function Z o (s) is:

[0079] ;

[0080] In the formula, Z o (s) represents the equivalent impedance transfer function, s represents the complex frequency, and F v L represents the feedforward coefficient. if C represents the value of the machine-side filter inductance. f L represents the value of the filter capacitor. gf L represents the value of the grid-side filter inductance. g T represents the power grid impedance value. s Indicates the sampling period.

[0081] S2013. Multiply the equivalent impedance transfer function by the complex frequency domain model of the current loop PI regulator to obtain the open-loop transfer function of the current loop controller in the grid-connected system.

[0082] Specifically, the equivalent impedance transfer function Z o (s) multiplied by the complex frequency domain model G of the current loop PI regulator c (s), obtaining the open-loop transfer function T of the current loop controller when the feedback point of the current loop controller (the point where the error signal of the machine-side current and the command value of the machine-side current is generated) is disconnected.c (s) is:

[0083] ;

[0084] In the formula, Let G represent the open-loop transfer function. c (s) represents the complex frequency domain model of the current loop PI regulator, k pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, and the complex frequency is represented by G. d (s) represents the delay term, T s F represents the sampling period. v L represents the feedforward coefficient. if C represents the value of the machine-side filter inductance. f L represents the value of the filter capacitor. gf L represents the value of the grid-side filter inductance. g This indicates the power grid impedance value.

[0085] Correspondingly, the open-loop transfer function T c (s) amplitude-frequency response |T c (s)| and phase frequency characteristic ∠T c (s) is:

[0086] ;

[0087] ;

[0088] In the formula, The frequency is represented by j, the imaginary unit is represented by k. pc k represents the proportional gain of the current loop PI regulator. ic T represents the integral coefficient of the current loop PI regulator. s F represents the sampling period. v L represents the feedforward coefficient. if C represents the value of the machine-side filter inductance. f L represents the value of the filter capacitor. gf L represents the value of the grid-side filter inductance. g This indicates the power grid impedance value.

[0089] For example, with a rated power Taking a 125kW energy storage converter as an example, let's illustrate this in detail. Given L... if 140 μH, C f 32μF, L gf The system sampling frequency is 5μH. With a switching frequency of 16kHz and a DC bus voltage V dc It is 750V, and the mains voltage is E.g Valid value 230V, mains frequency The frequency is 50Hz, based on the above parameters, and the mains impedance L is fixed. g and current loop PI parameters (k pc and k ic Plotting different feedforward coefficients F v Bode plot of the above open-loop transfer function under the given conditions, as follows: Figure 5 As shown, Figure 5 The upper half is the amplitude-frequency response |T c The lower half of the curve (s) represents the phase frequency response ∠T. c (s) curve, with different colored curves corresponding to different feedforward coefficients F. v We mainly observe the green, blue, and red curves, and the feedforward coefficients F corresponding to the green, blue, and red curves. v (Values ​​range from 0 to 1) and increase sequentially.

[0090] When analyzing the stability of the current loop controller, if the height of the resonant peak exceeds 0 dB (i.e., the gain is greater than 1), then near the resonant frequency, the open-loop gain will be greater than 1 and the phase may be close to -180°. The current loop controller will face the risk of instability (oscillation). As the innermost loop, the instability of the current loop controller will directly lead to the instability of the entire grid-connected system. This application employs two key stability margin parameters (gain margin and phase margin) to evaluate the stability of the grid-connected system. Gain margin (GM) measures how much gain margin the current loop controller has from its critical gain (0 dB) at the phase critical point. A larger GM indicates a higher tolerance for gain variations in the current loop controller, resulting in better system stability. Insufficient GM indicates that the current loop controller's resonant peak is too high, and even small parameter changes or disturbances may cause the closed-loop poles to cross the imaginary axis, leading to instability. Phase margin (PM) measures how much phase margin the current loop controller has from its oscillation (-180° phase) at the amplitude critical point. A larger PM indicates better damping and smaller overshoot in the current loop controller, resulting in stronger grid-connected system stability. Insufficient PM indicates that the current loop controller has insufficient phase margin at the cutoff frequency. Excessive phase lag in the vicinity can easily cause oscillations or even divergence in the dynamic response, leading to instability.

[0091] Depend on Figure 5 It can be seen that as the feedforward coefficient F v The increase (corresponding to) Figure 5 The curve changes from green to blue to red. This indicates an increase in the resonant frequency, a decrease in the resonant peak amplitude, and a decrease in the phase crossover frequency of the current loop controller. (The frequency at which the phase-frequency response curve crosses the -180° line), gain margin (at the phase crossing frequency). At this point, the difference in amplitude-frequency response is less than 0 dB. This improves the efficiency of the grid-connected system, thereby effectively reducing the risk of grid instability caused by the resonance peak crossing the 0 dB line.

[0092] However, with the feedforward coefficient F v The increase of the open-loop cutoff frequency (The frequency at which the amplitude-frequency response curve crosses the 0 dB line directly reflects the response speed of the current loop controller, and the cutoff frequency.) The higher the frequency, the faster the current loop controller response, and the greater the closed-loop control bandwidth (cutoff frequency). The bandwidth (positively correlated with the closed-loop control bandwidth, which can be used as an approximate indicator of the dynamic response speed of the current loop controller) is also significantly broadened, resulting in a higher cutoff frequency. This results in a larger phase lag introduced by the delay term (a negative phase angle indicates lag), which in turn directly reduces the phase margin of the current loop controller (at the cutoff frequency). At this point, the phase difference value at a phase frequency response distance of -180° is... ).

[0093] Therefore, the feedforward coefficient F v While suppressing the resonance peak of the current loop controller (improving the gain margin GM), it also reduces the phase margin PM and the feedforward coefficient F. v When selecting a current loop controller, it is necessary to weigh the amplitude margin GM and the phase margin PM to improve the stability of the grid-connected system.

[0094] S202. Under different feedforward coefficients and different grid impedances, calculate the current loop PI parameters when the open-loop transfer function satisfies the preset stability margin, obtain the feasible stability region of the current loop PI parameters under different feedforward coefficients and different grid impedances, and determine the optimal feedforward coefficient with the goal of maximizing the area of ​​the feasible stability region under different grid impedances.

[0095] In some embodiments, such as Figure 6 As shown, step S202 calculates the current loop PI parameters when the open-loop transfer function satisfies the preset stability margin, including:

[0096] S2021. Traverse the cutoff frequencies and calculate the current loop PI parameters when the amplitude of the open-loop transfer function at the cutoff frequency is 1 and the phase margin is a preset phase threshold. This yields the first stable boundary of the current loop PI parameters.

[0097] Specifically, traversing the cutoff frequency Calculate the current loop PI parameters that simultaneously satisfy the following equations:

[0098] ;

[0099] In the formula, This represents the cutoff frequency, and j represents the imaginary unit. Indicates at the cutoff frequency The open-loop transfer function at that point. This indicates the open-loop transfer function at the cutoff frequency. The amplitude at that point, This indicates the open-loop transfer function at the cutoff frequency. Phase at that point, Indicates phase margin, This indicates the preset phase threshold.

[0100] S2022. Traverse the phase crossover frequency and calculate the current loop PI parameters when the phase of the open-loop transfer function at the phase crossover frequency is -180° and the gain margin is a preset gain threshold. Obtain the second stable boundary of the current loop PI parameters. The first stable boundary and the second stable boundary enclose the feasible stable region.

[0101] It should be noted that the embodiments of this application do not limit the order of steps S2021 and S2022.

[0102] Specifically, traversing the phase crossing frequency Calculate the current loop PI parameters that simultaneously satisfy the following equations:

[0103] ;

[0104] In the formula, This represents the phase crossover frequency, and j represents the imaginary unit. Indicates the phase crossing frequency The open-loop transfer function at that point. This indicates the open-loop transfer function at the phase crossover frequency. The amplitude at that point, This indicates the open-loop transfer function at the phase crossover frequency. Phase at that point, Indicates the gain margin. This indicates the preset amplitude threshold.

[0105] In some embodiments, determining the optimal feedforward coefficients in S202 with the objective of maximizing the feasible stability region area under different grid impedances includes: determining the optimal feedforward coefficients with the objective of maximizing a comprehensive fitness index composed of the minimum, average, and standard deviation weights of the feasible stability region area under different grid impedances, wherein the comprehensive fitness index... Used to quantify the overall stability domain performance under a single feedforward coefficient, for a given feedforward coefficient Let the area of ​​its feasible stability region under N typical power grid short-circuit ratios be . ( ), comprehensive fitness index for:

[0106] ;

[0107] In the formula, This represents the overall fitness index. Indicates the first The area of ​​a feasible stability region This represents the average area of ​​the feasible stability region. The standard deviation of the feasible stability region area. , and This indicates the preset weighting coefficients.

[0108] In other embodiments, to establish analytical models under different grid strengths, the grid impedance L is calculated using the short-circuit ratio (SCR). g Under the assumption that the power grid is predominantly inductive, the grid short-circuit ratio (SCR) is defined as the ratio of the short-circuit capacity at the grid connection point to the rated power of the energy storage converter.

[0109] ;

[0110] In the formula, Indicates the short-circuit ratio of the power grid. Indicates the short-circuit capacity of the power grid. Indicates the rated power of the energy storage converter. Indicates the effective value of the grid voltage. Indicates the power grid frequency. This indicates the power grid impedance.

[0111] Therefore, the grid impedance can be calculated using the following formula:

[0112] ;

[0113] In the formula, Indicates the power grid impedance. Indicates the effective value of the grid voltage. Indicates the short-circuit ratio of the power grid. Indicates the power grid frequency. This indicates the rated power of the energy storage converter.

[0114] For example, amplitude threshold =6dB, phase threshold =30°, effective value of grid voltage Grid frequency sampling frequency Rated power of energy storage converter Machine-side filter inductor Filter capacitor Grid-side filter inductor .

[0115] In the impedance of a weak power grid, i.e., a large power grid In this scenario, the short-circuit ratio (SCR) is selected as 4, and the feedforward coefficient is... The feasible stability region of the current loop PI parameters at 0.1, 0.6, and 0.9 is as follows: Figure 7 As shown, the feedforward coefficients can be observed. When the value is small, the amplitude margin GM becomes the main limiting factor because the resonance peak cannot be well suppressed, resulting in a small stability region area. This leads to a small feedforward coefficient. When the value is large, the phase margin PM becomes the main limiting factor due to its impact on the control bandwidth, which also reduces the area of ​​the stable region; therefore, the extreme feedforward coefficients... The selection of each factor will affect the stability region of the current loop PI parameters; the feedforward coefficient in the middle is the most important factor. This allows for a larger stability region.

[0116] Impedance of a strong power grid, i.e., a small power grid In this scenario, the short-circuit ratio (SCR) is selected as 400, and the feedforward coefficient is... The stability boundaries of the PI parameters of the current loop controller at 0.1, 0.6, and 0.9 are as follows: Figure 8 As shown, it can be observed that the feedforward coefficient under a strong network... The smaller the impact on the stability boundary, the smaller the feedforward coefficient. The larger the stability domain range, the smaller the overall range of selectable current loop PI parameters.

[0117] Therefore, considering the parameter design under grid adaptability, a moderate feedforward coefficient is needed. This is a better choice, as it maximizes the parameter stability region of the current controller. In this example, a feedforward coefficient is selected. It is 0.6.

[0118] S203. Fix the feedforward coefficients in the open-loop transfer function to the optimal feedforward coefficients. Under different grid impedance conditions, calculate the current loop PI parameters when the open-loop transfer function satisfies the preset stability margin. Obtain several feasible stability regions of the current loop PI parameters under different grid impedances. Calculate the intersection of several feasible stability regions and select the target current loop PI parameters from the intersection.

[0119] For example, selecting the optimal feedforward coefficient The value is 0.6. Then, the stability domains of the current loop PI parameters are obtained for short-circuit ratios (SCR) of 4, 40, and 400, respectively. Figure 9 As shown, the intersection represents the stable current loop PI parameters that adapt to a wide short-circuit ratio range. Any set of target current loop PI parameters can be selected from these parameters.

[0120] S204. The energy storage converter is controlled based on a current loop controller configured with optimal feedforward coefficients and target current loop PI parameters.

[0121] The optimal feedforward coefficient and target current loop PI parameters obtained by the method of this application can ensure that the energy storage converter operates stably within a wide short-circuit ratio range.

[0122] To verify the effectiveness of the method proposed in this application, a verification experiment was also conducted, selecting the power grid impedance. The grid short-circuit ratio (SCR) is 400, i.e., a strong grid. The feedforward coefficient F is designed according to the method described in this application. v and current loop PI parameters (k pc and k ic ), to obtain the steady-state waveforms of capacitor voltage, grid-side current, and generator-side current of the energy storage converter grid-connected system under strong grid conditions, such as Figure 10 As shown, from Figure 10 It can be seen that during steady-state operation, the capacitor voltage, grid-side current, and generator-side current show almost no distortion or oscillation, exhibiting a good sine wave pattern; the selected grid impedance... The grid short-circuit ratio (SCR) is 1.3, indicating a weak grid. Based on the method described in this application, the feedforward coefficient F is designed. v and current loop PI parameters (k pc and k ic ), to obtain the steady-state waveforms of capacitor voltage, grid-side current, and generator-side current of the energy storage converter grid-connected system under weak grid conditions, such as Figure 11 As shown, from Figure 11 It can be seen that during steady-state operation, the capacitor voltage, grid-side current, and generator-side current show almost no distortion or oscillation, exhibiting a good sine wave, which verifies the effectiveness of the proposed method in enhancing stability over a wide short-circuit ratio range.

[0123] Compared with existing technologies, this application establishes an open-loop transfer function for the current loop controller that includes feedforward coefficients, current loop PI parameters, and grid impedance. It systematically analyzes the dynamic coupling mechanism of these three components and their synergistic impact on system stability margin, overcoming the limitation of separate design of feedforward coefficients and current loop PI parameters in traditional designs. Based on this, the current loop PI parameter design problem is transformed into optimizing the feasible stability region of the current loop controller. With the goal of maximizing the common adaptability of the stability region under different grid impedance conditions, the optimal feedforward coefficients are calculated, and further, a set of current loop PI parameters that can cover wide grid impedance variations and possess high stability is calculated. Ultimately, a feedforward-enhanced robust grid-connected control of the energy storage converter under wide grid impedance conditions is achieved, fundamentally overcoming the blindness and inefficiency of traditional empirical parameter tuning, and significantly improving parameter design efficiency, overall system stability, and grid adaptability.

[0124] like Figure 12 As shown, this application also provides an electronic device. This electronic device includes at least a processor 121 and a memory 122.

[0125] Processor 121 may include one or more processing cores, such as a quad-core processor, an octa-core processor, etc. Processor 121 may be implemented using at least one hardware form selected from DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). Processor 121 may also include a main processor and a coprocessor. The main processor, also known as a CPU (Central Processing Unit), is used to process data in the wake-up state; the coprocessor is a low-power processor used to process data in the standby state. In some embodiments, processor 121 may integrate a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the screen. In some embodiments, processor 121 may also include an AI (Artificial Intelligence) processor, which is used to handle computational operations related to machine learning.

[0126] The memory 122 may include one or more computer-readable storage media, which may be non-transitory. The memory 122 may also include high-speed random access memory and non-volatile memory, such as one or more disk storage devices or flash memory devices. In some embodiments, the non-transitory computer-readable storage media in the memory 122 is used to store at least one instruction, which is executed by the processor 121 to implement the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance provided in the method embodiments of this application.

[0127] In some embodiments, the electronic device may also optionally include a peripheral device interface and at least one peripheral device. The processor 121, memory 122, and peripheral device interface can be connected via a bus or signal line. Each peripheral device can be connected to the peripheral device interface via a bus, signal line, or circuit board. Indicatively, peripheral devices include, but are not limited to, radio frequency circuits, touch displays, audio circuits, and power supplies.

[0128] Of course, electronic devices may also include fewer or more components, and this embodiment does not limit this.

[0129] Accordingly, this application also provides a computer-readable storage medium for storing computer-readable programs or instructions. When the programs or instructions are executed by a processor, they can implement the steps or functions of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance provided in the above-described method embodiments.

[0130] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0131] The above provides a detailed description of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0132] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A feedforward-enhanced robust grid-connected control method for an energy storage converter under wide grid impedance, characterized in that, Applied to a grid-connected system, the grid-connected system includes an energy storage converter, an LCL filter, a grid impedance, and a grid connected in sequence. The current loop controller of the energy storage converter adopts a control strategy that combines capacitor voltage feedforward and machine-side current feedback. The capacitor voltage feedforward is adjusted by the feedforward coefficient, and the machine-side current feedback is adjusted by the current loop PI parameter. The method includes: Obtain the open-loop transfer function of the current loop controller in the grid-connected system. The open-loop transfer function is related to the feedforward coefficient, the current loop PI parameter, and the grid impedance. Under different feedforward coefficients and different grid impedances, the current loop PI parameters are calculated when the open-loop transfer function satisfies the preset stability margin. The feasible stability region of the current loop PI parameters under different feedforward coefficients and different grid impedances is obtained. The optimal feedforward coefficient is determined with the goal of maximizing the area of ​​the feasible stability region under different grid impedances. The feedforward coefficient in the open-loop transfer function is fixed to the optimal feedforward coefficient. Under different grid impedance conditions, the current loop PI parameter when the open-loop transfer function satisfies the preset stability margin is calculated. Several feasible stability regions of the current loop PI parameter under different grid impedances are obtained. The intersection of the several feasible stability regions is calculated, and the target current loop PI parameter is selected from the intersection. The energy storage converter is controlled based on a current loop controller configured with the optimal feedforward coefficient and the target current loop PI parameters.

2. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 1, characterized in that, Obtaining the open-loop transfer function of the current loop controller in the grid-connected system includes: Small-signal modeling is performed on the current loop controller, the LCL filter, the grid impedance, and the delay term to obtain a small-signal model; Based on the small-signal model, the equivalent impedance transfer function from the output voltage of the current loop PI regulator of the current loop controller to the machine-side current and the complex frequency domain model of the current loop PI regulator are determined. Multiplying the equivalent impedance transfer function by the complex frequency domain model of the current loop PI regulator yields the open-loop transfer function of the current loop controller in the grid-connected system.

3. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 2, characterized in that, The open-loop transfer function is: ； In the formula, Let k represent the open-loop transfer function. pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, and the complex frequency is represented by s. F represents the delay term. v L represents the feedforward coefficient. if C represents the value of the machine-side filter inductance. f L represents the value of the filter capacitor. gf L represents the value of the grid-side filter inductance. g This indicates the power grid impedance value.

4. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 2, characterized in that, The delay term employs a control delay of one beat and a modulation delay of approximately half a beat. The complex frequency domain model of the delay term is as follows: ； In the formula, G d (s) represents the delay term, T s s represents the sampling period, and s represents the complex frequency.

5. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 1, characterized in that, The stability margin includes magnitude margin and phase margin.

6. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 5, characterized in that, Calculating the current loop PI parameters when the open-loop transfer function satisfies a preset stability margin includes: Traverse the cutoff frequencies and calculate the current loop PI parameters when the amplitude of the open-loop transfer function at the cutoff frequency is 1 and the phase margin is a preset phase threshold, thus obtaining the first stable boundary of the current loop PI parameters. By iterating through the phase crossover frequencies, the current loop PI parameters are calculated when the phase of the open-loop transfer function at the phase crossover frequency is -180° and the magnitude margin is a preset magnitude threshold. The second stable boundary of the current loop PI parameters is obtained, and the first stable boundary and the second stable boundary enclose the feasible stable region.

7. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 1, characterized in that, To maximize the feasible stability region area under different grid impedances, the optimal feedforward coefficients are determined, including: to maximize the comprehensive fitness index composed of the minimum, average and standard deviation of the feasible stability region area under different grid impedances.

8. The feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in claim 1, characterized in that, The calculation formula for the current loop controller is as follows: ； In the formula, u d U represents the direct-axis component of the modulated signal. q i represents the cross-axis component of the modulated signal. fd i represents the direct-axis component of the machine-side current. fq i represents the quadrature-axis component of the machine-side current. dref The command value i represents the direct-axis component of the machine-side current. qref The command value, k, represents the quadrature-axis component of the machine-side current. pc k represents the proportional gain of the current loop PI regulator. ic The integral coefficient of the current loop PI regulator is represented by s, the complex frequency is represented by ω0, and the rated angular frequency of the power grid is represented by L. if Indicates the machine-side filter inductance, u cd U represents the direct-axis component of the capacitor voltage. cq F represents the quadrature-axis component of the capacitor voltage. v This represents the feedforward coefficient.

9. An electronic device, characterized in that, Including memory and processor; The memory is used to store programs; The processor, coupled to the memory, is used to execute the program stored in the memory to implement the steps of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, The readable storage medium stores a program or instructions that, when executed by a processor, implement the steps of the feedforward enhanced robust grid-connected control method for energy storage converters under wide grid impedance as described in any one of claims 1 to 8.

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