CN116470577A - Model-free prediction-based three-phase grid-connected inverter control method - Google Patents

Model-free prediction-based three-phase grid-connected inverter control method Download PDF

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Publication number
CN116470577A
CN116470577A CN202310446614.1A CN202310446614A CN116470577A CN 116470577 A CN116470577 A CN 116470577A CN 202310446614 A CN202310446614 A CN 202310446614A CN 116470577 A CN116470577 A CN 116470577A
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model
phase
value
coordinate system
free prediction
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Inventor
李昱
治文辉
高建波
王启武
李庆卓
贾中青
翟瑞占
刘道杰
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Laser Institute of Shandong Academy of Science
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Laser Institute of Shandong Academy of Science
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0025—Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Inverter Devices (AREA)

Abstract

The embodiment of the application provides a three-phase grid-connected inverter control method based on model-free prediction, which is used for solving the technical problems of low control bandwidth and large steady-state error of the existing inverter control strategy. The method comprises the following steps: and measuring three-phase current, carrying out coordinate transformation on the obtained measured value, predicting an observed value of the current at the next moment in a model-free prediction module, comparing the current value predicted by the model-free prediction module with a reference value, sending the error into a proportional-integral controller for decoupling and feedforward compensation, calculating SPWM reference voltage, and applying the SPWM reference voltage to an inverter to realize control.

Description

Model-free prediction-based three-phase grid-connected inverter control method
Technical Field
The application relates to the technical field of converter control, in particular to a three-phase grid-connected inverter control method based on model-free prediction.
Background
In recent years, new energy industries are being developed greatly in various countries in the world, and the energy supply mode is changed to a green, environment-friendly and low-carbon energy supply mode. Currently, power systems are evolving from mechatronic devices to power electronic devices. Under the background, a power electronic converter control strategy with small steady-state error, quick response and strong anti-interference capability is particularly important. Taking a classical three-phase inverter as an example, a PI (proportional-integral) control technology is generally adopted for a linear control strategy. The current reference value and the current feedback value are compared, the difference value is sent to the PI controller, and finally the switching tube is controlled by using the pulse width modulation technology, so that the output voltage of the inverter is increased or decreased, and the expected control effect is finally achieved.
Because links such as analog-to-digital conversion, calculation time and pulse width modulation exist, a digital control system inevitably introduces time delay when in application. The time delay reduces the system control bandwidth and increases the steady state error. And in practical applications, the steady state error of the system may further increase due to unknown disturbances and model uncertainties.
Disclosure of Invention
The embodiment of the application provides a three-phase grid-connected inverter control method based on model-free prediction, which is used for solving the technical problems of low control bandwidth and large steady-state error of the existing inverter control strategy.
In one aspect, an embodiment of the present application provides a method for controlling a three-phase grid-connected inverter based on model-free prediction, where the method includes:
step S1: on the side of the power gridIs of the three-phase current I a 、I b 、I c Converting the three-phase static coordinate system into a two-phase static coordinate system based on the following formula;
wherein I is α 、I β The current value of the three-phase current in an alpha-beta coordinate system is given;
step S2: converting the two-phase stationary coordinate system into a two-phase rotating coordinate system based on the following formula;
where θ=ωt, ω is grid angular frequency, I d 、I q The current value of the three-phase current in a d-q coordinate system is obtained;
step S3: and constructing a model-free prediction module and predicting a current value at the next moment, wherein a mathematical model of the power grid side of the model-free prediction module is as follows:
wherein V is d And V q E is the output voltage value of the three-phase grid-connected inverter on the d axis and the q axis d And E is q The value of the power grid voltage on the d axis and the q axis is respectively, R is parasitic resistance, and L is an inductance filter;
step S4: transforming the mathematical model of the model-free prediction module on the power grid side to obtain the following model:
i is as follows d And F d The linear extended state observer for the state variables further constructs a new model,
wherein the method comprises the steps ofRespectively I in (4) d 、F d Estimate of beta 1d And beta 2d For error feedback gain of observer, +.>
Step S5: the model (5) is rewritten in matrix form as:
wherein the method comprises the steps ofC＝(10)，/>y is the output of the observer, +.>Is the observed value of y, and the characteristic equation of the extended state observer can be expressed as:
|sI-(A-DC)|＝s 2 +β 1d s+β 2d (7)
wherein I is an identity matrix, s is the root of a characteristic equation;
step S6: make the root of the characteristic equation fall at-omega 0 Where beta is obtained 1d And beta 2d Is that
β 1d ＝2ω 0 (8)
β 2d ＝ω 0 2 (9)
By para-omega 0 The configuration is carried out such that,discretizing the model (5) into:
step S7: z obtained by prediction 1d The difference value between the reference value at the moment of k+1 and the reference value at the moment of k+1 is sent to a PI controller, and the output of the controller is obtained after output decoupling and feedforward compensation
Step S8: to be calculatedAnd the output voltage of the inverter is controlled by the SPWM modulator.
The three-phase grid-connected inverter control method based on model-free prediction is an improvement on a classical three-phase inverter control strategy in terms of time delay. The predictive control model is combined with the extended state observer to obtain a model-free predictive model, and is used to improve the classical three-phase inverter control strategy. And comparing the reference value at the next time with the grid-connected current value at the next time predicted by the model-free prediction module, and sending the difference value of the reference value to the controller to form a closed-loop negative feedback loop. Because the grid-connected current value at the next moment predicted by the model-free prediction module is not affected by any time delay, the time delay generated by the system in links such as analog-to-digital conversion, calculation time, pulse width modulation and the like is compensated. When the model-free prediction module is designed, all uncertain parts of the system are estimated by using the extended state observer and are integrated into the model-free prediction module, so that the anti-interference capability of the system is enhanced. Therefore, the embodiment of the application is superior to the classical three-phase grid-connected inverter control strategy in the aspects of dynamic response, current ripple, tracking error, robustness and the like.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute an undue limitation to the application. In the drawings:
fig. 1 is a control block diagram of a three-phase grid-connected inverter based on model-free prediction according to an embodiment of the present application.
Detailed Description
For the purposes, technical solutions and advantages of the present application, the technical solutions of the present application will be clearly and completely described below with reference to specific embodiments of the present application and corresponding drawings. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.
In recent years, new energy industries are being developed greatly in various countries in the world, and the energy supply mode is changed to a green, environment-friendly and low-carbon energy supply mode. Currently, power systems are evolving from mechatronic devices to power electronic devices. Under the background, a power electronic converter control strategy with small steady-state error, quick response and strong anti-interference capability is particularly important. Taking a classical three-phase inverter as an example, a PI (proportional-integral) control technology is generally adopted for a linear control strategy. The current reference value and the current feedback value are compared, the difference value is sent to the PI controller, and finally the switching tube is controlled by using the pulse width modulation technology, so that the output voltage of the inverter is increased or decreased, and the expected control effect is finally achieved.
Because links such as analog-to-digital conversion, calculation time and pulse width modulation exist, a digital control system inevitably introduces time delay when in application. The time delay reduces the system control bandwidth and increases the steady state error. And in practical applications, the steady state error of the system may further increase due to unknown disturbances and model uncertainties.
Aiming at the problem of time delay of a control system in practical application, the application provides an improved control strategy of a three-phase grid-connected inverter based on model-free prediction. The prediction control model is combined with the extended state observer to form a model-free prediction module, so that an output feedback value at the next moment is predicted. And at the next moment, comparing the feedback value of the next moment predicted by the model-free prediction module with the reference value of the next moment, and feeding back the difference value to the controller. The feedback value of the next moment predicted by the model-free prediction module is not affected by the time delay, so that the time delay of the system due to links such as analog-to-digital conversion, calculation time, pulse width modulation and the like is compensated.
The embodiment of the application provides a three-phase grid-connected inverter control method based on model-free prediction, and the technical scheme provided by the embodiment of the application is described in detail through the attached drawings.
Fig. 1 is a system block diagram of an embodiment of the present application. As shown in fig. 1, the method mainly comprises the following processes:
step S1: three-phase current I at power grid side a 、I b 、I c Converting the three-phase static coordinate system into a two-phase static coordinate system based on the following formula;
wherein I is α 、I β The current value of the three-phase current in an alpha-beta coordinate system is given;
step S2: converting the two-phase stationary coordinate system into a two-phase rotating coordinate system based on the following formula;
where θ=ωt, ω is grid angular frequency, I d 、I q The current value of the three-phase current in a d-q coordinate system is obtained;
step S3: and constructing a model-free prediction module and predicting a current value at the next moment, wherein a mathematical model of the power grid side of the model-free prediction module is as follows:
wherein V is d And V q E is the output voltage value of the three-phase grid-connected inverter on the d axis and the q axis d And E is q The value of the power grid voltage on the d axis and the q axis is respectively, R is parasitic resistance, and L is an inductance filter;
step S4: transforming the mathematical model of the model-free prediction module on the power grid side to obtain the following model:
i is as follows d And F d The linear extended state observer for the state variables further constructs a new model,
wherein the method comprises the steps ofRespectively I in (4) d 、F d Estimate of beta 1d And beta 2d For error feedback gain of observer, +.>
Step S5: the model (5) is rewritten in matrix form as:
wherein the method comprises the steps ofC＝(1 0)，/>y is the output of the observer, +.>Is the observed value of y, and the characteristic equation of the extended state observer can be expressed as:
|sI-(A-DC)|＝s 2 +β 1d s+β 2d (7)
wherein I is an identity matrix, s is the root of a characteristic equation;
step S6: root of the characteristic equation is made to be zero to fall at-omega 0 Where beta is obtained 1d And beta 2d Is that
β 1d ＝2ω 0 (8)
β 2d ＝ω 0 2 (9)
By para-omega 0 Configuring, discretizing the model (5) into:
step S7: z obtained by prediction 1d (k+1) and the difference value of the reference value at the moment of k+1 are sent into a PI controller to obtain
Step S8: to be calculatedAnd the output voltage of the inverter is controlled by the SPWM modulator.
The three-phase grid-connected inverter control method based on model-free prediction is an improvement on a classical three-phase inverter control strategy in terms of time delay. The predictive control model is combined with the extended state observer to obtain a model-free predictive model, and is used to improve the classical three-phase inverter control strategy. And comparing the reference value at the next time with the grid-connected current value at the next time predicted by the model-free prediction module, and sending the difference value of the reference value to the controller to form a closed-loop negative feedback loop. Because the grid-connected current value at the next moment predicted by the model-free prediction module is not affected by any time delay, the time delay generated by the system in links such as analog-to-digital conversion, calculation time, pulse width modulation and the like is compensated. When the model-free prediction module is designed, all uncertain parts of the system are estimated by using the extended state observer and are integrated into the model-free prediction module, so that the anti-interference capability of the system is enhanced. Therefore, the embodiment of the application is superior to the classical three-phase grid-connected inverter control strategy in the aspects of dynamic response, current ripple, tracking error, robustness and the like.
All embodiments in the application are described in a progressive manner, and identical and similar parts of all embodiments are mutually referred, so that each embodiment mainly describes differences from other embodiments. In particular, for the device embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and reference is made to the description of the method embodiments in part.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises the element.
The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. which are within the spirit and principles of the present application are intended to be included within the scope of the claims of the present application.

Claims (1)

1. The method for controlling the three-phase grid-connected inverter based on model-free prediction is characterized by comprising the following steps of:
step S1: three-phase current I at power grid side a 、I b 、I c Converting the three-phase static coordinate system into a two-phase static coordinate system based on the following formula;
wherein I is α 、I β The current value of the three-phase current in an alpha-beta coordinate system is given;
step S2: converting the two-phase stationary coordinate system into a two-phase rotating coordinate system based on the following formula;
where θ=ωt, ω is grid angular frequency, I d 、I q The current value of the three-phase current in a d-q coordinate system is obtained;
step S3: and constructing a model-free prediction module and predicting a current value at the next moment, wherein a mathematical model of the power grid side of the model-free prediction module is as follows:
wherein V is d And V q E is the output voltage value of the three-phase grid-connected inverter on the d axis and the q axis d And E is q The values of the grid voltage on the d axis and the q axis are respectively, R is parasitic resistance, LIs an inductive filter;
step S4: transforming the mathematical model of the model-free prediction module on the power grid side to obtain the following model:
i is as follows d And F d The linear extended state observer for the state variables further constructs a new model,
wherein the method comprises the steps ofRespectively I in (4) d 、F d Estimate of beta 1d And beta 2d For error feedback gain of observer, +.>
Step S5: the model (5) is rewritten in matrix form as:
wherein the method comprises the steps ofC＝(1 0)，/>y is the output of the observer, +.>Is the observed value of y, and the characteristic equation of the extended state observer can be expressed as：
|sI-(A-DC)|＝s 2 +β 1d s+β 2d (7)
Wherein I is an identity matrix, s is the root of a characteristic equation;
step S6: make the root of the characteristic equation fall at-omega 0 Where beta is obtained 1d And beta 2d Is that
β 1d ＝2ω 0 (8)
β 2d ＝ω 0 2 (9)
By para-omega 0 Configuring, discretizing the model (5) into:
step S7: z obtained by prediction 1d (k+1) and the difference value of the reference value at the moment of k+1 are sent into a PI controller to obtain
Step S8: to be calculatedAnd the output voltage of the inverter is controlled by the SPWM modulator.
CN202310446614.1A 2023-04-20 2023-04-20 Model-free prediction-based three-phase grid-connected inverter control method Pending CN116470577A (en)

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