CN115940675A - Model-free prediction current control method and system for rectifier - Google Patents
Model-free prediction current control method and system for rectifier Download PDFInfo
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Abstract
The invention discloses a model-free prediction current control method and system for a rectifier, wherein the method comprises the following steps: constructing a PWM rectifier mathematical model, and carrying out discretization processing on the mathematical model to obtain a current predicted value expression at the next moment; expanding the disturbance T into an independent state variable, designing a state equation of a nonlinear extended observer, discretizing the state equation, and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain; and calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage, and generating PWM (pulse-width modulation) pulse for controlling a rectifier switching tube. When a mathematical model of the rectifier is established, the disturbance part of the system is independent; and then, a disturbance part is observed in the current control by utilizing a nonlinear extended observer, so that circuit model parameters of a rectifier are prevented from being introduced in the predictive control, and the robustness of the predictive control is improved.
Description
Technical Field
The invention relates to the technical field of power electronic control, in particular to a model-free prediction current control method and system for a rectifier.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The rectifier has the characteristics of bidirectional energy flow, unit power factor and the like, and the application range is wide. The prediction current control is used as a nonlinear control means, has the characteristics of good dynamic performance, good control effect and the like, and is very suitable for rectifier nonlinear systems. However, in practical application, the rectifier has a parameter mismatch problem, and the conventional predictive control relies on an accurate mathematical model of the system, so that when the system parameters do not match with the actual parameters, the control performance and effect of the algorithm are greatly limited.
The prior art discloses a model-free predictive current control method based on an extended state observer, which realizes current control without any motor parameter 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 for control, and cannot observe unknown disturbances of the system, which affects the control accuracy of the system.
Disclosure of Invention
In order to solve the problems, the invention provides a model-free prediction current control method and system of a rectifier based on a nonlinear extended observer.
In some embodiments, the following technical scheme is adopted:
a method of model-free predictive current control for a rectifier, comprising:
constructing a PWM rectifier mathematical model, wherein an unknown part of a system is represented by disturbance T in the mathematical model;
discretizing the mathematical model to obtain a current predicted value expression at the next moment;
expanding the disturbance T into independent state variables, designing a state equation of a nonlinear extended observer, discretizing the state equation, and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain;
and calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage, and generating PWM (pulse-width modulation) pulse for controlling a rectifier switching tube.
In other embodiments, the following technical solutions are adopted:
a rectifier model-free predictive current control system, comprising:
the model building module is used for building a PWM rectifier mathematical model, and the unknown part of the system is represented by disturbance T in the mathematical model;
the model processing module is used for carrying out discretization processing on the mathematical model to obtain a current predicted value expression at the next moment;
the disturbance observation module is used for expanding the disturbance T into independent state variables, designing a state equation of the nonlinear extended observer, discretizing the state equation and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain;
and the switching tube control module is used for calculating to obtain the rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage and generating PWM (pulse-width modulation) pulse for controlling the rectifier switching tube.
In other embodiments, the following technical solutions are adopted:
a terminal device comprising a processor and a memory, the processor being configured to implement instructions; the memory is configured to store a plurality of instructions adapted to be loaded by the processor and to perform the rectifier model-free predictive current control method described above.
In other embodiments, the following technical solutions are adopted:
a computer readable storage medium having stored therein a plurality of instructions adapted to be loaded by a processor of a terminal device and to execute the above-described method of model-free predictive current control of a rectifier.
Compared with the prior art, the invention has the beneficial effects that:
(1) When a mathematical model of the rectifier is established, the disturbance part of the system is independent; and then, a disturbance part is observed in the current control by utilizing a nonlinear extended observer, so that circuit model parameters of a rectifier are prevented from being introduced in the predictive control, and the robustness of the predictive control is improved.
(2) The invention utilizes the nonlinear extended observer to observe the disturbance part in the current control, and compared with a linear observer, the static error of the current observation value of the system is greatly reduced.
Additional 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.
Drawings
FIG. 1 is a diagram of a rectifier topology in an embodiment of the present invention;
FIG. 2 is a control structure diagram of the nonlinear extended observer in the discrete domain in the embodiment of the present invention;
FIG. 3 is a schematic diagram of a model-free current predictive control process for a rectifier in an embodiment of the invention;
FIG. 4 (a) is a schematic diagram of a simulated waveform of the output voltage at the DC side in the embodiment of the present invention;
fig. 4 (b) is a schematic diagram of a simulation waveform of a grid-connected three-phase current in the embodiment of the present invention;
fig. 4 (c) is a schematic diagram comparing observation errors of a grid-connected current d-axis under a linear observer and a nonlinear observer.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example one
In conjunction with fig. 1, a t-rectifier system includes: three-phase AC power supply, L-type filter, T-type three-level rectifier topology, and two DC-side capacitors C 1 ,C 2 d.C. load R load . The three-phase alternating current power supply enters a rectifier topology after being filtered, and is rectified by the rectifier to obtain direct current voltage with a set size, and the direct current voltage is supplied to a direct current load.
The rectifier system topology of the embodiment is suitable for structures such as flying capacitor type, I type, T type and mixed type. The hardware system also comprises a sampling conditioning circuit, a control circuit, a driving circuit, a protection circuit and the like. The signal of the rectifier is connected with the control circuit through the sampling conditioning circuit, and the control circuit is communicated with the protection circuit to realize overcurrent and overvoltage protection. Meanwhile, the control circuit is communicated with the driving circuit, and the PWM signals are used for switching on and switching off the controllable device through the driving circuit.
Based on the above topology structure, in one or more embodiments, a method for controlling a rectifier model-free prediction current is disclosed, which, with reference to fig. 3, specifically includes the following steps:
(1) Constructing a mathematical model of the PWM rectifier, and representing an unknown part of the system by using disturbance T in the mathematical model;
specifically, a mathematical model of a three-level PWM rectifier is defined as follows:
wherein i is a three-phase current signal at the network side, and u is a three-phase voltage signal of the rectifier; α is the input gain, which in this example is-90; t is the system disturbance and T is the rectifier sampling time.
(2) Discretizing the mathematical model to obtain a current predicted value expression at the next moment;
in this embodiment, the discretized mathematical model is:
i(k+1)＝[T(k)+αu(k)]t+i(k)；
where t is the sampling time of the rectifier system, and t =10 in this embodiment -4 s; i (k + 1) is a current predicted value, and i (k) is a current measured value at the current moment; t (k) is system disturbance at the current moment, u (k) is a rectifier voltage signal at the current moment, alpha is input gain, and T is rectifier sampling time.
(3) In order to improve the performance of the system under the uncertain condition, expanding the disturbance T into an independent state variable and designing a state equation of a nonlinear expansion observer, discretizing the state equation, and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain;
in this embodiment, for a three-phase rectifier system:
the state equation for expanding the disturbance acting on the system into independent state variables and designing the nonlinear extended observer in current control is as follows:
where u is the rectifier voltage signal, α is the input gain, β is the gain, e i For current observation error, i 1 Is the actual value of the three-phase current of the rectifier in the dq coordinate system, z 1 As current i in dq coordinate system 1
Observed value of 2 As observed values of the disturbance T (i.e. values measured by a non-linear extended observer), z 1 、z 2 Are each z 1 And z 2 Derivative of (c), fal (e) i A, δ) is a nonlinear error function:
With reference to fig. 2, discretizing the state equation obtains:
wherein the content of the first and second substances,
is the current observation value at the next moment>
For real-time observation of the current, e i (k) And observing errors in real time for the current. />
For perturbing the observation value>
And (d) the disturbance observed value at the next moment, and u (k) is a real-time measured value of the transformation voltage.
The fal function affects the steady-state and dynamic performances of the observer, and in the embodiment, delta =0.1 in the fal function; a =0.1.
Transforming the discrete state equation to a discrete domain:
wherein e is i (z) is a current observation error in the z-domain,
Is the observed value of the current in the z domain, i (z) is the actual current value in the z domain, and->
And the observed value of the disturbance in the z domain is u (z), and the voltage value of the rectifier in the z domain is u (z).
The observed perturbation value T is obtained in the discrete domain.
The embodiment observes the disturbance part of the system through the nonlinear extended observer, has higher observation precision compared with a linear extended observer, and has lower requirements on a system mathematical model compared with a traditional prediction control method such as model prediction control and the like.
(4) And calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage, and generating PWM (pulse width modulation) pulse for controlling a rectifier switching tube.
Specifically, a rectifier voltage expression is deduced based on a discretized rectifier mathematical model:
order: i (k + 1) = i * (k)
Finally, the following is obtained:
wherein i * (k) And (3) giving a current reference for the PI voltage outer ring, calculating a real-time disturbance value T (k) by a nonlinear extended observer, and taking i (k) as a real-time measurement value.
And (4) outputting the deduced u (k) to a post-stage modulation link to generate a PWM pulse signal for controlling the on-off of a rectifier switching tube so as to realize current control.
The method is suitable for SVPWM and dual-vector model prediction of two-stage and three-stage modulation modes, has strong universality for the modulation link of the later stage, can be widely applied to different occasions such as low and medium voltage, is not limited in sampling frequency, and has strong practicability.
In order to verify the effect of the method of the embodiment, the embodiment performs simulation verification in a T-type three-level rectifier platform of Simulink; fig. 4 (a) - (b) show the simulation waveform of the output voltage on the dc side and the simulation waveform of the three-phase current of the grid-connected when the desired voltage is 350V for connecting the load to the three-level rectifier; as can be seen from the simulation result, the output of the rectifier is controlled to be about 350V, the distortion of grid-connected current is small, and the working state of the rectifier is good. Fig. 4 (c) shows a comparison diagram of the grid-connected current d-axis observation error under the linear observer and the nonlinear observer, and it can be seen that the static error of the system current observation value is very small when the nonlinear observer is used compared with the linear observer.
According to the simulation result, the model-free prediction current control method provided by the embodiment does not need system circuit parameters (such as inductance parameters and inductance resistance parameters) and is small in observation error, dependence degree of prediction control on the system parameters can be effectively reduced, and performance of the rectifier is improved.
Example two
In one or more embodiments, a rectifier model-free predictive current control system is disclosed, comprising:
the model building module is used for building a PWM rectifier mathematical model, and the unknown part of the system is represented by disturbance T in the mathematical model;
the model processing module is used for carrying out discretization processing on the mathematical model to obtain a current predicted value expression at the next moment;
the disturbance observation module is used for expanding the disturbance T into independent state variables, designing a state equation of the nonlinear extended observer, discretizing the state equation and converting the discretized state equation into a discrete domain; obtaining an observed value of disturbance T in a discrete domain;
and the switching tube control module is used for calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage and generating PWM (pulse width modulation) pulse for controlling the switching tube of the rectifier.
It should be noted that, the specific implementation of each module described above has been described in detail in the first embodiment, and is not described in detail here.
EXAMPLE III
In one or more implementations, a terminal device is disclosed that includes a server including a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing a rectifier model-free predictive current control method of example one when executing the program. For brevity, no further description is provided herein.
It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general purpose processors, digital signal processors DSP, application specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, and so on. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory may include both read-only memory and random access memory, and may provide instructions and data to the processor, and a portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information.
In implementation, the steps of the above method may be performed by integrated logic circuits of hardware in a processor or instructions in the form of software.
Example four
In one or more implementations, a computer-readable storage medium having stored therein a plurality of instructions adapted to be loaded by a processor of a terminal device and to perform the method of model-free predictive current control for a rectifier of example one is disclosed.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive changes in the technical solutions of the present invention.
Claims (10)
1. A model-free predictive current control method for a rectifier is characterized by comprising the following steps:
constructing a PWM rectifier mathematical model, wherein an unknown part of a system is represented by disturbance T in the mathematical model;
discretizing the mathematical model to obtain a current predicted value expression at the next moment;
expanding the disturbance T into an independent state variable, designing a state equation of a nonlinear extended observer, discretizing the state equation, and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain;
and calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage, and generating PWM (pulse width modulation) pulse for controlling a rectifier switching tube.
2. The model-free predictive current control method for the rectifier according to claim 1, wherein a mathematical model of the PWM rectifier is constructed, specifically:
wherein i is a three-phase current signal at the network side, u is a rectifier voltage signal, alpha is an input gain, T is system disturbance, and T is rectifier sampling time.
3. The model-free predictive current control method for the rectifier according to claim 1, wherein discretizing the mathematical model to obtain a predicted current value expression at the next moment, specifically:
i(k+1)＝[T(k)+αu(k)]t+i(k)
wherein i (k + 1) is a current predicted value, and i (k) is a current measured value at the current moment; t (k) is system disturbance at the current moment, u (k) is a rectifier voltage signal at the current moment, alpha is input gain, and T is rectifier sampling time.
4. The model-free predictive current control method of a rectifier according to claim 1, wherein the disturbance T is expanded into independent state variables and the state equation of the nonlinear extended observer is designed, specifically:
where u is the rectifier voltage signal, α is the input gain, β is the gain, e i For current observation error, i 1 Is the actual value of the three-phase current of the rectifier in the dq coordinate system, z 1 As current i in dq coordinate system 1 An observed value of z 2 In order to perturb the observed value of T,
are each z 1 And z 2 Gamma is the nonlinear error function gain;
fal(e i a, δ) is a nonlinear error function:
a and δ are both constants.
5. The model-free predictive current control method for the rectifier according to claim 1, wherein the state equation is discretized, and the discretized state equation is converted into a discrete domain, specifically:
wherein e is i (z) is a current observation error in the z domain,
Is the observed value of the current in the z domain, i (z) is the actual current value in the z domain, and->
Is a disturbance observed value in a z domain,u (z) is the rectifier voltage value in the z domain.
6. The model-free predictive current control method for a rectifier of claim 5 wherein the observations of the disturbance T and the current observations are solved in a discrete domain.
7. The model-free predictive current control method for the rectifier according to claim 1, wherein the rectifier voltage is calculated based on an observed value of disturbance T, specifically:
where u (k) is the rectifier voltage, T (k) is the observed value of the disturbance T, i * (k) And giving a current reference for the PI voltage outer loop, wherein i (k) is a real-time measurement value, alpha is an input gain, and t is the sampling time of the rectifier.
8. A model-free predictive current control system for a rectifier, comprising:
the model building module is used for building a PWM rectifier mathematical model, and the unknown part of the system is represented by disturbance T in the mathematical model;
the model processing module is used for carrying out discretization processing on the mathematical model to obtain a current predicted value expression at the next moment;
the disturbance observation module is used for expanding the disturbance T into independent state variables, designing a state equation of the nonlinear extended observer, discretizing the state equation and converting the discretized state equation into a discrete domain; obtaining an observed value of the disturbance T in a discrete domain;
and the switching tube control module is used for calculating to obtain rectifier voltage based on the observed value of the disturbance T, modulating the rectifier voltage and generating PWM (pulse width modulation) pulse for controlling the switching tube of the rectifier.
9. A terminal device comprising a processor and a memory, the processor being configured to implement instructions; the memory is configured to store a plurality of instructions, wherein the instructions are adapted to be loaded by the processor and to perform the method for model-free predictive current control of a rectifier of any of claims 1-7.
10. A computer readable storage medium having stored therein a plurality of instructions, wherein the instructions are adapted to be loaded by a processor of a terminal device and to perform the method of model-free predictive current control of a rectifier of any of claims 1-7.
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| CN116505780A (en) * | 2023-06-28 | 2023-07-28 | 哈尔滨理工大学 | Current-free sensor model prediction method and device for double-active-bridge converter |
| CN116505780B (en) * | 2023-06-28 | 2023-09-12 | 哈尔滨理工大学 | Current-free sensor model prediction method and device for double-active-bridge converter |
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