A Model-Free Adaptive Cooperative Control Method and System for Grid-Connected Inverters

Abstract

The present invention belongs to the technical field of grid-connected inverter control, and provides a model-free adaptive cooperative control method and system for a grid-connected inverter, including: obtaining the modulation voltage and grid connection point current of the grid-connected inverter; constructing a discrete cooperative control macro variable and a cooperative control differential equation of the grid-connected inverter according to the obtained grid connection point current; constructing a model-free adaptive cooperative control model of the grid-connected inverter according to the modulation voltage, discrete cooperative control macro variable and cooperative control differential equation of the grid-connected inverter; dynamically adjusting the cooperative control convergence factor of the grid-connected inverter according to the constructed model-free adaptive cooperative control model, designing an overshoot suppression strategy for the grid connection point reference current, and completing the control of the grid-connected inverter.

Description

Technical Field

[0001] The invention belongs to the technical field of grid-connected inverter control, and particularly relates to a model-free adaptive cooperative control method and system for a grid-connected inverter. Background Technique

[0002] The statements in this part only provide background technical information related to the invention, and do not necessarily constitute prior art.

[0003] In recent years, with the rapid development of renewable energy represented by wind energy and photovoltaic energy, the installed capacity of distributed generation has been increasing day by day. As an important energy conversion device for renewable energy to access the power grid, the grid-connected inverter is particularly important in distributed generation. However, the grid-connected inverter is easily affected by internal and external parameter changes such as filter parameter mismatch, grid-connected power change, and grid voltage sag, and it is difficult to maintain high-quality grid-connected current, thus affecting the robustness and dynamic response ability of the grid-connected inverter control.

[0004] As understood by the inventor, model-free adaptive control (MFAC) can achieve the control goal only by measuring data using the input / output port (I / O), which is a typical data-driven control method and does not require system model knowledge. Model-free adaptive control uses dynamic linearization technology to establish a data-driven model and introduces a pseudo partial derivative (PPD) to estimate the dynamic change relationship between the input and output of the controlled system. Since the I / O data contains all the information of the controlled system, the traditional unmodeled dynamics will no longer exist in MFAC. At the same time, MFAC is not easily affected by internal and external disturbances of the system and has good robustness.

[0005] Traditional MFAC adopts a control law design method based on a cost function, with the main control goal being that the actual output of the system reaches the expected reference value, without considering the dynamic performance of the controller, and the response speed is poor. In addition, the dynamic linearization model used in MFAC needs to be established on the premise that the system satisfies the Lipschitz hypothesis. When the system reference signal changes greatly at adjacent sampling moments, the Lipschitz condition is no longer satisfied, resulting in the inaccuracy of the dynamic linearization model and easily causing a large overshoot phenomenon. Summary of the Invention

[0006] To solve the above problems, the invention proposes a model-free adaptive cooperative control method and system for a grid-connected inverter, introducing cooperative control theory to improve the dynamic response ability and robustness of traditional model-free adaptive control; suppressing the transient overshoot and oscillation phenomena in traditional model-free adaptive control by designing an overshoot suppression strategy and an adaptive law of the cooperative control convergence factor; significantly improving the current response speed, reducing the power overshoot, and showing good robustness under the condition of filter parameter mismatch.

[0007] According to some embodiments, the first solution of the present invention provides a model-free adaptive cooperative control method for a grid-connected inverter, adopting the following technical solutions:

[0008] A model-free adaptive cooperative control method for a grid-connected inverter, comprising:

[0009] Obtain the modulation voltage and the grid connection point current of the grid-connected inverter;

[0010] Construct a discrete cooperative control macro variable and a cooperative control differential equation of the grid-connected inverter according to the obtained grid connection point current;

[0011] Construct a model-free adaptive cooperative control model of the grid-connected inverter according to the modulation voltage, the discrete cooperative control macro variable and the cooperative control differential equation of the grid-connected inverter;

[0012] According to the constructed model-free adaptive cooperative control model, dynamically adjust the cooperative control convergence factor of the grid-connected inverter, design an overshoot suppression strategy for the grid connection point reference current, and complete the control of the grid-connected inverter.

[0013] As a further technical limitation, the discrete cooperative control macro variable of the grid-connected inverter is related to the grid connection point current and the reference point current of the grid-connected inverter.

[0014] As a further technical limitation, the constructed cooperative control differential equation can make the obtained discrete cooperative control macro variable reach the invariant manifold; before constructing the model-free adaptive cooperative control model of the grid-connected inverter, the forward Euler method is used for the discretization processing of the constructed cooperative control differential equation.

[0015] As a further technical limitation, the constructed model-free adaptive cooperative control model of the grid-connected inverter is the modulation voltage of the grid-connected inverter , that is ; where , is the cooperative control convergence factor, is the estimated value of the pseudo partial derivative, is the grid connection point reference current, is the grid connection point current, is the macro variable adjustment parameter, is the grid connection point current tracking error, is the sampling time, is the cooperative control macro variable.

[0016] As a further technical limitation, an adaptive law that can be dynamically adjusted according to the system error of the grid-connected inverter is designed for the cooperative control convergence factor of the grid-connected inverter to achieve dynamic adjustment of the cooperative control convergence factor of the grid-connected inverter, and a strategy for suppressing overshoot of the grid-connected reference current is designed to suppress the transient overshoot of the grid-connected reference current when the operating conditions change.

[0017] As a further technical limitation, based on the obtained modulation voltage and grid-connected point current of the grid-connected inverter, the current control loop expression of the grid-connected inverter in the two-phase stationary coordinate system is obtained. According to the obtained current control loop expression and the Lipschitz constraint condition, a compact-form dynamic linearization general model of the current control loop with an internal pseudo partial derivative is established, the cost function of the pseudo partial derivative is constructed, the obtained cost function is differentiated, the estimation and reset of the pseudo partial derivative are carried out, and a model-free adaptive control model of the grid-connected inverter is obtained.

[0018] According to some embodiments, the second solution of the present invention provides a model-free adaptive cooperative control system for a grid-connected inverter, and adopts the following technical solution:

[0019] A model-free adaptive cooperative control system for a grid-connected inverter, comprising:

[0020] An acquisition module configured to acquire the modulation voltage and grid-connected point current of the grid-connected inverter;

[0021] A construction module configured to construct a discrete cooperative control macro variable and a cooperative control differential equation of the grid-connected inverter according to the obtained grid-connected point current; and construct a model-free adaptive cooperative control model of the grid-connected inverter according to the modulation voltage, discrete cooperative control macro variable and cooperative control differential equation of the grid-connected inverter;

[0022] A cooperative control module configured to dynamically adjust the cooperative control convergence factor of the grid-connected inverter according to the constructed model-free adaptive cooperative control model, design a strategy for suppressing overshoot of the grid-connected reference current, and complete the control of the grid-connected inverter.

[0023] According to some embodiments, the third solution of the present invention provides a computer-readable storage medium, and adopts the following technical solution:

[0024] A computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, the steps in the model-free adaptive cooperative control method for a grid-connected inverter as described in the first solution of the present invention are implemented.

[0025] According to some embodiments, the fourth solution of the present invention provides an electronic device, and adopts the following technical solution:

[0026] An electronic device includes a memory, a processor, and a program stored in the memory and running on the processor. When the processor executes the program, it implements the steps in the model-free adaptive cooperative control method of the grid-connected inverter as described in the first solution of the present invention.

[0027] According to some embodiments, the fifth solution of the present invention provides a computer program product, adopting the following technical solution:

[0028] A computer program product includes software code, and the program in the software code executes the steps in the model-free adaptive cooperative control method of the grid-connected inverter as described in the first solution of the present invention.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention uses cooperative control theory to replace the control law solution based on the cost function of traditional model-free adaptive control, constructs a macro variable of current error, and uses the fast convergence of differential equations to force the macro variable to converge, improving the response speed and robustness of traditional model-free adaptive control;

[0031] The present invention ensures the rationality of the Lipschitz constraint condition (i.e., the Lipschitz constraint condition) in the dynamic linearization process by designing a model-free adaptive control overshoot suppression strategy, effectively reducing the power and current transient overshoot;

[0032] The present invention adopts a cooperative control convergence factor (i.e., the T-factor adaptive law), enabling the important convergence parameter T of cooperative control to be dynamically adjusted with the system error, achieving a balance between the current response speed and the system power oscillation;

[0033] The present invention only uses input-output I / O data to achieve the control goal, without system modeling, constructs a general data-driven controller, and can be flexibly used in other industrial controls. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings forming a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments and descriptions thereof of this embodiment are used to explain this embodiment and do not constitute an improper limitation to this embodiment.

[0035] Figure 1 It is the control block diagram of the model-free adaptive cooperative control method of the grid-connected inverter in the first embodiment of the present invention;

[0036] Figure 2 It is the structural schematic diagram of the model-free adaptive cooperative control of the grid-connected inverter in the first embodiment of the present invention;

[0037] Figure 3(a) is the power and current waveform diagram of the traditional model-free adaptive control method under the change of reference power in the first embodiment of the present invention;

[0038] Figure 4(b) is the power and current waveform diagram under the change of reference power in the first embodiment of the present invention;

[0039] Figure 4(a) is the current waveform diagram of the traditional model-free adaptive control method under the change of the DC-side inductor of the filter in the first embodiment of the present invention;

[0040] Figure 4(b) is the current waveform diagram under the change of the DC-side inductor of the filter in the first embodiment of the present invention;

[0041] Figure 5 is the structural block diagram of the model-free adaptive cooperative control system of the grid-connected inverter in the second embodiment of the present invention. Specific Embodiments

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0043] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] In the case of no conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0046] Embodiment 1

[0047] Embodiment 1 of the present invention introduces a model-free adaptive cooperative control method for a grid-connected inverter.

[0048] In this embodiment, according to the obtained modulation voltage and grid connection point current of the grid-connected inverter, the current control loop expression of the grid-connected inverter in the two-phase stationary coordinate system is obtained. According to the obtained current control loop expression and the Lipschitz constraint condition, a compact-form dynamic linearization general model of the current control loop with an internal pseudo partial derivative is established, a cost function of the pseudo partial derivative is constructed, the obtained cost function is differentiated, the estimation and reset of the pseudo partial derivative are performed, and a model-free adaptive control model of the grid-connected inverter is obtained; specifically as follows:

[0049] The current control loop of the grid-connected inverter in the two-phase stationary coordinate system is as follows:

[0050] (1)

[0051] Wherein, represents the PWM modulation voltage , represents the grid connection point current , is the system order, is an unknown non-linear function; on the basis that the system is controllable, has continuous partial derivatives and satisfies Lipschitz constraint conditions, a compact form dynamic linearization general model is established, that is:

[0052] (2)

[0053] Wherein, , represents the pseudo partial derivative; the model (2) can be applied to single-input single-output non-linear systems and belongs to a general data-driven model.

[0054] As one or more implementation manners, the cost function of the pseudo partial derivative is:

[0055] (3)

[0056] Wherein, is the estimated value of the pseudo partial derivative, is the weighting factor.

[0057] Derive the obtained pseudo cost function to obtain the estimation algorithm of the pseudo partial derivative , that is:

[0058] (4)

[0059] Wherein, is the step constant, represents the initial value of.

[0060] According to the pseudo partial derivative reset the algorithm, and we can get:

[0061] (5)

[0062] Wherein, is a sufficiently small positive constant.

[0063] In this embodiment, the dynamic response ability and robustness of traditional model-free adaptive control are improved by introducing the cooperative control theory; a model-free adaptive control model of the grid-connected inverter is constructed by designing an overshoot suppression strategy and a cooperative control convergence factor adaptive law (i.e., the T-factor adaptive law) to suppress the transient overshoot and oscillation phenomena in traditional model-free adaptive control; the current response speed is significantly improved, and the power overshoot is reduced.

[0064] Based on the model-free adaptive control model of the grid-connected inverter, the following scheme is added:

[0065] Construct the discrete cooperative control macro variable of the grid-connected inverter, that is

[0066] (6)

[0067] where is a positive constant, represents the grid connection point current and the reference current The error between them is:

[0068] (7)

[0069] Construct a cooperative control differential equation that can make the macro variable reach the invariant manifold , and discretize it using the forward Euler method, that is:

[0070] (8)

[0071] where is the cooperative control convergence factor, and ; is the sampling time; from formula (8), it can be obtained that , and is an exponential sequence. To make converge, the condition needs to be satisfied. Generally, is selected.

[0072] According to formula (2), formula (6) and formula (7), it can be obtained that:

[0073] (9)

[0074] According to formula (8) and formula (9), it can be obtained that:

[0075] (10)

[0076] For the grid connection point reference current , design the following overshoot suppression strategy:

[0077] (11)

[0078] Among them, is a positive constant and needs to satisfy ; when the change between it and its previous moment value exceeds the set value , will be updated to ; this process will be repeated continuously until ; due to being slow time-varying, this strategy can ensure that is maintained within a reasonable range, ensuring the rationality of the Lipschitz assumption, thereby reducing the transient overshoot.

[0079] For the cooperative control convergence factor in formula (10), design the following cooperative control convergence factor adaptive law (i.e., T-factor adaptive law):

[0080] (12)

[0081] Among them, respectively represent the minimum value and the maximum value of the convergence factor ; when the tracking error of the controller is large, T the factor will be increased to suppress oscillations and ensure the stability of the system. On the contrary, when the tracking error of the controller is small, T the factor will be decreased to achieve a faster response speed and adapt to the change of the reference signal; in addition, the parameter is added to adjust the error weight.

[0082] The model-free adaptive cooperative control method adopted in this embodiment is as Figure 1 shown. As shown in Figure 2 the control schematic diagram of the grid-connected inverter operating in the grid-following mode, two controllers in this embodiment are placed in the current inner loop to achieve current tracking in the two-phase stationary coordinate system. It should be noted that according to the instantaneous power calculation method, the change of the reference power is equivalent to the change of the reference current;

[0083] Figures 3(a) and 3(b) respectively show the power and current waveforms of the traditional model-free adaptive control method and the method proposed in this embodiment when the reference power changes from 1 kW to 1.5 kW. It should be noted that the traditional model-free adaptive method here refers to the model-free adaptive control method that obtains the pseudo partial derivative and the control law through the cost function; it can be seen from Figures 3(a) and 3(b) that when the reference power changes, compared with the traditional model-free adaptive control method, the controller proposed in this embodiment can significantly reduce the power and current overshoot, and the response speed is significantly improved;

[0084] Figures 4(a) and 4(b) respectively show the current waveforms of the traditional model-free adaptive control method and the method proposed in this embodiment when the DC-side inductor of the filter changes from 5 mH to 7 mH; it can be seen from Figures 4(a) and 4(b) that when the filter parameters are mismatched, the grid-connected current of the inverter under the traditional model-free adaptive control generates serious distortion, while the grid-connected current of the inverter using the controller proposed in this embodiment has small distortion and fast response speed, indicating the system parameter robustness of the proposed method; from the above analysis, it can be known that the method proposed in this embodiment can improve the response speed and parameter robustness of the traditional model-free adaptive control method, and suppress the dynamic overshoot, with obvious effects.

[0085] In this embodiment, the cooperative control theory is used to replace the control law solution based on the cost function of the traditional model-free adaptive control, construct the macro variable of the current error, and use the fast convergence of the differential equation to force the macro variable to converge, improving the response speed and robustness of the traditional model-free adaptive control; by designing the overshoot suppression strategy of the model-free adaptive control, the rationality of the Lipschitz constraint condition (i.e., the Lipschitz constraint condition) in the dynamic linearization process is ensured, effectively reducing the power and current transient overshoot; by using the cooperative control convergence factor (i.e., the T-factor adaptive law), the important convergence parameter T of the cooperative control can be dynamically adjusted according to the system error, achieving the balance between the current response speed and the system power oscillation; only using the input-output I / O data to achieve the control goal, without system modeling, a general data-driven controller is constructed, which can be flexibly used in other industrial controls.

[0086] Embodiment 2

[0087] Embodiment 2 of the present invention introduces a model-free adaptive cooperative control system for a grid-connected inverter.

[0088] As Figure 5 shown, a model-free adaptive cooperative control system for a grid-connected inverter includes:

[0089] An acquisition module configured to acquire the modulation voltage and the grid connection point current of the grid-connected inverter;

[0090] A construction module configured to construct a discrete cooperative control macro variable and a cooperative control differential equation of the grid-connected inverter according to the obtained grid connection point current; and construct a model-free adaptive cooperative control model of the grid-connected inverter according to the modulation voltage, the discrete cooperative control macro variable and the cooperative control differential equation of the grid-connected inverter;

[0091] A cooperative control module configured to dynamically adjust the cooperative control convergence factor of the grid-connected inverter according to the constructed model-free adaptive cooperative control model, design an overshoot suppression strategy for the grid connection point reference current, and complete the control of the grid-connected inverter.

[0092] The detailed steps are the same as those of the model-free adaptive cooperative control method for grid-connected inverters provided in Embodiment 1, and will not be elaborated here.

[0093] Embodiment 3

[0094] Embodiment 3 of the present invention provides a computer-readable storage medium.

[0095] A computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, it implements the steps in the model-free adaptive cooperative control method for grid-connected inverters as described in Embodiment 1 of the present invention.

[0096] The detailed steps are the same as those of the model-free adaptive cooperative control method for grid-connected inverters provided in Embodiment 1, and will not be elaborated here.

[0097] Embodiment 4

[0098] Embodiment 4 of the present invention provides an electronic device.

[0099] An electronic device, including a memory, a processor, and a program stored on the memory and running on the processor, and when the processor executes the program, it implements the steps in the model-free adaptive cooperative control method for grid-connected inverters as described in Embodiment 1 of the present invention.

[0100] The detailed steps are the same as those of the model-free adaptive cooperative control method for grid-connected inverters provided in Embodiment 1, and will not be elaborated here.

[0101] Embodiment 5

[0102] Embodiment 5 of the present invention provides a computer program product.

[0103] A computer program product, including software code, and the program in the software code executes the steps in the model-free adaptive cooperative control method for grid-connected inverters as described in Embodiment 1 of the present invention.

[0104] The detailed steps are the same as those of the model-free adaptive cooperative control method for grid-connected inverters provided in Embodiment 1, and will not be elaborated here.

[0105] The above are only the preferred embodiments of this embodiment, and are not used to limit this embodiment. For those skilled in the art, this embodiment can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this embodiment shall be included within the protection scope of this embodiment.

Claims

1. A model-free adaptive cooperative control method for grid-connected inverters, characterized in that, include: Obtain the modulation voltage and grid-connected point current of the grid-connected inverter; Constructing discrete cooperative control macro variables and cooperative control differential equations of the grid-connected inverter according to the obtained grid-connected point current; According to the modulation voltage of the grid-connected inverter, the discrete cooperative control macro variables and the cooperative control differential equation, a model-free adaptive cooperative control model of the grid-connected inverter is constructed; According to the constructed model-free adaptive cooperative control model, the cooperative control convergence factor of the grid-connected inverter is dynamically adjusted, and the grid-connected point reference current overshoot suppression strategy is designed to complete the control of the grid-connected inverter; The model-free adaptive cooperative control model of the grid-connected inverter is constructed as follows: the modulation voltage u(k) of the grid-connected inverter is where Δu(k) = u(k) - u(k - 1), T is the cooperative control convergence factor, is the estimated value of the pseudo partial derivative, y * (k + 1) is the grid connection point reference current, y(k) is the grid connection point current, λ is the macro variable adjustment parameter, e(k) is the grid connection point current tracking error, T s is the sampling time, and ψ(k) is the cooperative control macro variable; The cooperative control convergence factor design of the grid-connected inverter can be an adaptive law that can be dynamically adjusted with the grid-connected inverter system error, realize the dynamic adjustment of the cooperative control convergence factor of the grid-connected inverter, design the grid-connected point reference current overshoot suppression strategy, and suppress the transient overshoot of the grid-connected point reference current when the working conditions change; According to the obtained modulation voltage and grid-connected point current of the grid-connected inverter, the current control loop expression of the grid-connected inverter in the two-phase stationary coordinate system is obtained. According to the obtained current control loop expression and Lipschitz constraint, a compact dynamic linearization universal model of the current control loop with built-in pseudo-partial derivatives is established, and a cost function of the pseudo-partial derivatives is constructed. The obtained cost function is differentiated, and the pseudo-partial derivatives are estimated and reset to obtain a model-free adaptive control model of the grid-connected inverter.

2. The model-free adaptive cooperative control method for a grid-connected inverter according to claim 1, wherein The discrete cooperative control macro variables of the grid-connected inverter are related to the grid-connected point current and the reference point current of the grid-connected inverter.

3. A model-free adaptive cooperative control method for a grid-connected inverter as described in claim 1, characterized in that, The constructed cooperative control differential equation can make the obtained discrete cooperative control macro variables reach the invariant manifold; before building the model-free adaptive cooperative control model of the grid-connected inverter, the forward Euler method is used to discretize the constructed cooperative control differential equation.

4. A model-free adaptive cooperative control system for a grid-connected inverter, characterized in that, include: An acquisition module configured to acquire a modulation voltage and a grid-connected point current of a grid-connected inverter; A construction module is configured to construct a discrete cooperative control macro variable and a cooperative control differential equation of the grid-connected inverter according to the obtained grid-connected point current; and to construct a model-free adaptive cooperative control model of the grid-connected inverter according to the modulation voltage, the discrete cooperative control macro variable and the cooperative control differential equation of the grid-connected inverter; A collaborative control module is configured to dynamically adjust the collaborative control convergence factor of the grid-connected inverter according to the constructed model-free adaptive collaborative control model, design a grid-connected point reference current overshoot suppression strategy, and complete the control of the grid-connected inverter; The model-free adaptive cooperative control model of the grid-connected inverter is constructed as follows: the modulation voltage u(k) of the grid-connected inverter is where Δu(k) = u(k) - u(k - 1), T is the cooperative control convergence factor, is the estimated value of the pseudo partial derivative, y * (k + 1) is the grid connection point reference current, y(k) is the grid connection point current, λ is the macro variable adjustment parameter, e(k) is the grid connection point current tracking error, T s is the sampling time, ψ(k) is the cooperative control macro variable; The cooperative control convergence factor design of the grid-connected inverter can be an adaptive law that can be dynamically adjusted with the grid-connected inverter system error, realize the dynamic adjustment of the cooperative control convergence factor of the grid-connected inverter, design the grid-connected point reference current overshoot suppression strategy, and suppress the transient overshoot of the grid-connected point reference current when the working conditions change; Based on the obtained modulation voltage and grid connection point current of the grid-connected inverter, the current control loop expression of the grid-connected inverter in the two-phase stationary coordinate system is obtained. According to the obtained current control loop expression and the Lipschitz constraint conditions, a compact-form dynamic linearization general model of the current control loop with an embedded pseudo partial derivative is established, a cost function of the pseudo partial derivative is constructed, the obtained cost function is differentiated, the estimation and reset of the pseudo partial derivative are carried out, and a model-free adaptive control model of the grid-connected inverter is obtained.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, the steps of the model-free adaptive cooperative control method for the grid-connected inverter described in any one of claims 1-3 are implemented.

6. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, When the processor executes the program, the steps of the model-free adaptive cooperative control method for the grid-connected inverter described in any one of claims 1-3 are implemented.

7. A computer program product, comprising software code, characterized in that, The program in the software code executes the steps of the model-free adaptive cooperative control method for the grid-connected inverter described in any one of claims 1-3.

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