A method and system for model-free predictive current control of a rectifier

Abstract

The application discloses a kind of rectifier model-free predictive current control method and system, method includes: constructing PWM rectifier mathematical model, mathematical model is discretized processing, obtains the current predictive value expression of next time;Disturbance T is expanded into independent state variable and the state equation of nonlinear extended observer is designed, the state equation is discretized, and the state equation after discretization is converted to discrete domain;Obtained in discrete domain the observation value of disturbance T;Based on the observation value of disturbance T, the rectifier voltage is calculated, the rectifier voltage is modulated, generates PWM pulse, for the control of rectifier switch tube.The application establishes rectifier mathematical model, and the disturbance part of system is independent;Then, the disturbance part is observed in current control using nonlinear extended observer, which avoids introducing the circuit model parameters of rectifier in predictive control, and increases the robustness of predictive control.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, and in particular to a model-free predictive current control method and system for rectifiers. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Rectifiers feature bidirectional energy flow and unity power factor, making them widely applicable. Predictive current control, as a nonlinear control method, offers excellent dynamic performance and control effectiveness, making it highly suitable for nonlinear systems like rectifiers. However, in practical applications, rectifiers can suffer from parameter mismatch issues. Traditional predictive control relies on precise mathematical models of the system; when system parameters do not match actual parameters, the algorithm's control performance and effectiveness are severely limited.

[0004] Existing technology discloses a model-free predictive current control method based on an extended state observer, which achieves current control without any motor parameters and greatly improves the robustness of model predictive control (MPC) to corresponding control parameters. However, this control method is based on a linear extended state observer, which cannot observe unknown disturbances in the system, affecting the control accuracy of the system. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a model-free predictive current control method and system for rectifiers based on a nonlinear extended observer. When establishing the mathematical model of the rectifier, the disturbance part of the system is isolated, and the nonlinear extended observer is used to observe the disturbance part in current control. Predictive current control is achieved by discretizing the nonlinear extended observer.

[0006] In some implementations, the following technical solutions are adopted:

[0007] A model-free predictive current control method for a rectifier includes:

[0008] A mathematical model of a PWM rectifier is constructed, in which the unknown part of the system is represented by a disturbance T.

[0009] The mathematical model is discretized to obtain the expression for the predicted current value at the next time step;

[0010] The perturbation T is expanded into an independent state variable, and the state equation of the nonlinear extended observer is designed. The state equation is discretized and transformed into a discrete domain. The observed value of the perturbation T is obtained in the discrete domain.

[0011] The rectifier voltage is calculated based on the observed value of the disturbance T. The rectifier voltage is then modulated to generate PWM pulses, which are used to control the rectifier switching transistors.

[0012] In other embodiments, the following technical solutions are adopted:

[0013] A rectifier model-free predictive current control system includes:

[0014] The model building module is used to build a mathematical model of a PWM rectifier, in which the unknown parts of the system are represented by a disturbance T.

[0015] The model processing module is used to discretize the mathematical model to obtain the current prediction value expression for the next time step.

[0016] The disturbance observation module is used to expand the disturbance T into independent state variables and design the state equation of the nonlinear extended observer. The state equation is discretized and transformed into a discrete domain. The observed value of the disturbance T is obtained in the discrete domain.

[0017] The switching transistor control module is used to calculate the rectifier voltage based on the observed value of the disturbance T, modulate the rectifier voltage to generate PWM pulses, and use them to control the rectifier switching transistors.

[0018] In other embodiments, the following technical solutions are adopted:

[0019] A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded by the processor and executed by the above-described rectifier model-free predictive current control method.

[0020] In other embodiments, the following technical solutions are adopted:

[0021] A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of an end device of the above-described rectifier model-free predictive current control method.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) When establishing the mathematical model of the rectifier, the disturbance part of the system is isolated; then, the nonlinear extended observer is used to observe the disturbance part in the current control, which avoids introducing the circuit model parameters of the rectifier in the predictive control and increases the robustness of the predictive control.

[0024] (2) The present invention utilizes a nonlinear extended observer to observe the disturbance part in current control, which greatly reduces the static error of the system current observation value compared with the linear observer.

[0025] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] Figure 1 This is a diagram of the rectifier topology in an embodiment of the present invention;

[0027] Figure 2 This is a control structure diagram of the nonlinear extended observer in the discrete domain in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the rectifier model-free current prediction control process in an embodiment of the present invention;

[0029] Figure 4(a) is a schematic diagram of the simulated DC-side output voltage waveform in an embodiment of the present invention;

[0030] Figure 4(b) is a schematic diagram of the simulated three-phase current waveform in the embodiment of the present invention;

[0031] Figure 4(c) is a schematic diagram comparing the observation errors of the grid-connected current d-axis under linear and nonlinear observers. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, 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.

[0034] Example 1

[0035] Combination Figure 1 The T-type rectifier system includes: a three-phase AC power supply, an L-type filter, a T-type three-level rectifier topology, two DC-side capacitors C1 and C2, and a DC load R. load The three-phase AC power supply is filtered and then enters the rectifier topology. After rectification, a DC voltage of a set value is obtained and supplied to the DC load.

[0036] The rectifier system topology in this embodiment is applicable to flying capacitor, I-type, T-type, and hybrid structures. The hardware system also includes a sampling and conditioning circuit, a control circuit, a drive circuit, and a protection circuit. The rectifier signal is connected to the control circuit via the sampling and conditioning circuit, and the control circuit communicates with the protection circuit to achieve overcurrent and overvoltage protection. Simultaneously, the control circuit communicates with the drive circuit, and the PWM signal is used by the drive circuit to turn the controllable devices on and off.

[0037] Based on the above topology, in one or more embodiments, a rectifier model-free predictive current control method is disclosed, combined with... Figure 3 Specifically, it includes the following process:

[0038] (1) Construct a mathematical model of the PWM rectifier, and represent the unknown part of the system with the disturbance T in the mathematical model;

[0039] Specifically, the mathematical model of a three-level PWM rectifier is defined as follows:

[0040]

[0041] Where i is the grid-side three-phase current signal, u is the rectifier three-phase voltage signal; α is the input gain, which is -90 in this embodiment; T is the system disturbance, and t is the rectifier sampling time.

[0042] (2) Discretize the mathematical model to obtain the expression for the predicted current value at the next moment;

[0043] In this embodiment, the discretized mathematical model becomes:

[0044] i(k+1)=[T(k)+αu(k)]t+i(k);

[0045] Where t is the sampling time of the rectifier system, and in this embodiment t = 10. -4 s; i(k+1) is the predicted current value, i(k) is the measured current value at the current moment; T(k) is the system disturbance at the current moment, u(k) is the rectifier voltage signal at the current moment, α is the input gain, and t is the rectifier sampling time.

[0046] (3) In order to improve the performance of the system under uncertain conditions, the disturbance T is expanded into an independent state variable and the state equation of the nonlinear extended observer is designed. The state equation is discretized and transformed into the discrete domain. The observed value of the disturbance T is obtained in the discrete domain.

[0047] In this embodiment, for a three-phase rectifier system:

[0048]

[0049] In current control, the disturbance acting on the system is expanded into an independent state variable, and the state equation of the nonlinear extended observer is designed as follows:

[0050]

[0051] Where u is the rectifier voltage signal, α is the input gain, β is the gain, and e is the input voltage signal. i To represent the current observation error, i1 is the actual value of the three-phase current of the rectifier in the dq coordinate system, and z1 is the current i1 in the dq coordinate system.

[0052] ...the observed value of z1, z2 is the observed value of perturbation T (i.e., the value measured by the nonlinear extended observer), z1 and z2 are the derivatives of z1 and z2 respectively, fal(e i (a, δ) is a nonlinear error function:

[0053] Both a and δ are constants.

[0054] Combination Figure 2 Discretizing the above state equations, we obtain:

[0055]

[0056] in, The current observation value at the next moment. e is the real-time observed value of the current. i (k) represents the real-time current observation error. For perturbation of observations, is the observed value of the disturbance at the next moment, and u(k) is the real-time measured value of the transformed voltage.

[0057] The fal function affects the steady-state and dynamic performance of the observer. In this embodiment, δ = 0.1 and a = 0.1 in the fal function.

[0058] Transform the discrete state equations to the discrete domain:

[0059]

[0060] Among them, e i (z) represents the current observation error in the z-domain. Let i(z) be the observed current value in the z-domain, and i(z) be the actual current value in the z-domain. Let u(z) be the disturbance observation value in the z-domain, and u(z) be the rectifier voltage value in the z-domain.

[0061] The observed perturbation value T can be obtained in the discrete domain.

[0062] This embodiment observes the disturbance part of the system using a nonlinear extended observer, which has higher observation accuracy than a linear extended observer. At the same time, compared with traditional predictive control methods such as model predictive control, the method in this embodiment has lower requirements for the mathematical model of the system.

[0063] (4) The rectifier voltage is calculated based on the observed value of the disturbance T. The rectifier voltage is modulated to generate PWM pulses, which are used to control the rectifier switching transistors.

[0064] Specifically, based on the discretized mathematical model of the rectifier, the rectifier voltage expression is derived:

[0065]

[0066] Let: i(k+1)=i * (k)

[0067] The final result is:

[0068]

[0069] Among them, i * (k) is the reference current given to the outer loop of the PI voltage, the real-time disturbance value T(k) is calculated by the nonlinear extended observer, and i(k) is the real-time measured value.

[0070] The derived u(k) is output to the subsequent modulation stage to generate a PWM pulse signal, which is used to control the switching of the rectifier transistor to achieve current control.

[0071] The method described in this embodiment is applicable to modulation methods such as SVPWM, two-stage and three-stage dual-vector model prediction, and has strong universality for subsequent modulation stages. It can be widely used in different occasions such as low and medium voltage, and the sampling frequency is not limited, making it highly practical.

[0072] To verify the effectiveness of the method in this embodiment, simulation verification was performed on the Simulink T-type three-level rectifier platform. Figures 4(a)-(b) show the simulated waveforms of the DC-side output voltage and the grid-connected three-phase current when the three-level rectifier is connected to a load and the desired voltage is 350V. The simulation results show that the rectifier output is controlled at around 350V, the grid-connected current distortion is small, and the rectifier is working well. Figure 4(c) shows a schematic diagram comparing the d-axis observation error of the grid-connected current under linear and nonlinear observers. It can be seen that the static error of the system current observation value is extremely small when using the nonlinear observer compared to the linear observer.

[0073] The simulation results above show that the model-free predictive current control method proposed in this embodiment does not require system circuit parameters (such as inductance parameters and inductance resistance parameters), and has small observation errors. It can effectively reduce the dependence of predictive control on system parameters and improve the performance of the rectifier.

[0074] Example 2

[0075] In one or more embodiments, a rectifier model-free predictive current control system is disclosed, comprising:

[0076] The model building module is used to build a mathematical model of a PWM rectifier, in which the unknown parts of the system are represented by a disturbance T.

[0077] The model processing module is used to discretize the mathematical model to obtain the current prediction value expression for the next time step.

[0078] The disturbance observation module is used to expand the disturbance T into independent state variables and design the state equation of the nonlinear extended observer. The state equation is discretized and transformed into a discrete domain. The observed value of the disturbance T is obtained in the discrete domain.

[0079] The switching transistor control module is used to calculate the rectifier voltage based on the observed value of the disturbance T, modulate the rectifier voltage to generate PWM pulses, and use them to control the rectifier switching transistors.

[0080] It should be noted that the specific implementation methods of the above modules have been described in detail in Implementation Example 1, and will not be repeated here.

[0081] Example 3

[0082] In one or more embodiments, a terminal device is disclosed, including a server. The server includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the rectifier model-free predictive current control method of Embodiment 1. For simplicity, further details are omitted here.

[0083] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0084] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0085] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0086] Example 4

[0087] In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and executed by the rectifier model-free predictive current control method of Embodiment 1.

[0088] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A model-free predictive current control method for a rectifier, characterized in that, include: A mathematical model of a PWM rectifier is constructed, in which the unknown part of the system is represented by a disturbance T. The mathematical model of the PWM rectifier is constructed as follows: in, This is the three-phase current signal on the grid side. This is the rectifier voltage signal. Let T be the input gain, and T be the system disturbance. t The rectifier sampling time; The mathematical model is discretized to obtain the expression for the predicted current value at the next time step; The perturbation T is expanded into independent state variables, and the state equation of a nonlinear extended observer is designed. This state equation is then discretized, and the discretized state equation is transformed into a discrete domain. The perturbation is obtained in the discrete domain. T Observed values; The perturbation T is expanded into independent state variables, and the state equation of the nonlinear extended observer is designed as follows: in, This is the rectifier voltage signal. For input gain, For gain, e i For current observation error, i 1 represents the three-phase current of the rectifier. dq The actual value in the coordinate system z 1 is dq Current in coordinate system i The observed value of 1, z 2 represents disturbance T The observed values, , They are respectively z 1 and z The derivative of 2, The gain is a nonlinear error function. For nonlinear error functions: ； and All are constants; The state equation is discretized, and the discretized state equation is transformed into a discrete domain, specifically as follows: in, For the current observation error in the z-domain, For current observations in the z-domain, The actual current value in the z-domain, For the perturbation observations in the z-domain, The rectifier voltage value in the z-domain; Based on disturbance T The rectifier voltage is calculated from the observed values, and the rectifier voltage is modulated to generate PWM pulses, which are used to control the rectifier switching transistors.

2. The rectifier model-free predictive current control method as described in claim 1, characterized in that, The mathematical model is discretized to obtain the expression for the predicted current value at the next time step, specifically: in, This is the predicted current value. This is the current measurement value at the current moment; For the system disturbance at the current moment, This represents the rectifier voltage signal at the current moment. For input gain, t This is the rectifier sampling time.

3. The rectifier model-free predictive current control method as described in claim 1, characterized in that, The perturbation is obtained by solving in the discrete domain. T The observed values ​​and current observation values.

4. The rectifier model-free predictive current control method as described in claim 1, characterized in that, Based on disturbance T The rectifier voltage is calculated from the observed values, specifically: in, This is the rectifier voltage. For disturbance T The observed values, Provide a current reference for the outer loop of the PI voltage. For real-time measurements, For input gain, t This is the rectifier sampling time.

5. A control system for the rectifier model-free predictive current control method as described in any one of claims 1-4, characterized in that, include: The model building module is used to build a mathematical model of a PWM rectifier, in which the unknown parts of the system are represented by a disturbance T. The model processing module is used to discretize the mathematical model to obtain the current prediction value expression for the next time step. The disturbance observation module is used to expand the disturbance T into independent state variables and design the state equation of the nonlinear extended observer. The state equation is discretized, and then transformed into a discrete domain. The disturbance is obtained in the discrete domain. T Observed values; Switching transistor control module, used for disturbance-based control T The rectifier voltage is calculated from the observed values, and the rectifier voltage is modulated to generate PWM pulses, which are used to control the rectifier switching transistors.

6. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed by the rectifier model-free predictive current control method according to any one of claims 1-4.

7. A computer-readable storage medium storing a plurality of instructions, characterized in that, The instructions are adapted to be loaded by the processor of the terminal device and executed by the rectifier model-free predictive current control method according to any one of claims 1-4.

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