Double-closed-loop control method, system and equipment for network construction type converter and storage medium

Abstract

The invention relates to the technical field of power electronic control, in particular to a double-closed-loop control method, system and equipment for a network-forming converter and a storage medium, and aims to solve the problems of poor resonance suppression effect, slow dynamic response and weak unbalanced load carrying capacity caused by insufficient damping in the prior art. Firstly, a converter model is established under a synchronous rotating coordinate system, and decoupling is carried out through feedforward; and secondly, the core is that capacitor voltage feedback is introduced to the output of the current controller, a current loop open-loop model is constructed, controller parameters are designed based on root locus analysis, and a current loop pole is configured at an optimal damping point with the damping ratio of 1, so that the resonance of the filter is thoroughly suppressed. And finally, on the basis of the optimized inner ring, voltage ring controller parameters are designed to meet the phase margin requirement. According to the method, the system stability can be effectively enhanced, the voltage response speed and the unbalanced load carrying capacity are greatly improved, and the method is suitable for scenes of new energy grid connection, energy storage, micro-grids and the like.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, and in particular to a dual closed-loop control method, system, device and storage medium for grid-connected converters. Background Technology

[0002] With the increasing penetration rate of renewable energy generation such as wind and solar power, and the widespread application of various power electronic devices in the power system, the modern power grid is transforming towards power electronics. While this transformation brings flexibility and efficiency, it also leads to a continuous decrease in system inertia and a weakening of system strength, which in turn triggers a series of unprecedented stability problems.

[0003] Grid-connected converter technology is considered one of the key means to solve the above problems. Unlike traditional grid-connected converters, grid-connected converters can autonomously establish and maintain the voltage and frequency of the AC grid, providing the necessary inertia and damping support for the system, thereby significantly enhancing the stability of the power system. Therefore, grid-connected converters have extremely important value and broad application prospects in large-scale renewable energy grid-connected power generation, offshore wind power grid connection, energy storage power stations, and independent microgrids.

[0004] Grid-type converters typically employ a dual closed-loop control structure for output voltage and output current. The outer voltage loop controls the amplitude and frequency of the output voltage, while the inner current loop improves the system's dynamic response and controls the output current. Since grid-type converters generally use LC output filters, these filters inherently possess an underdamped resonance peak. In practical control, although the inner current loop can provide some damping to suppress this resonance, its damping effect is limited.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] This invention provides a dual closed-loop control method, system, device, and storage medium for a grid-type converter, which can effectively solve the problems in the background art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A dual closed-loop control method for a grid-type converter includes the following steps:

[0009] A mathematical model of the grid converter is established in a synchronous rotating coordinate system, and cross-coupling terms are eliminated through inductor current and capacitor voltage state feedback.

[0010] A capacitor voltage feedback branch is introduced at the output of the current loop controller to form a new modulation wave signal, and an open-loop transfer function model of the current loop is constructed.

[0011] By using root locus analysis, the parameters of the current loop controller are adjusted so that the current loop poles are located at the unit damping rate and the magnitude of the poles is maximized.

[0012] Based on the frequency characteristics of the open-loop transfer function of the voltage loop and the preset phase margin requirements, the parameters of the outer-loop voltage controller are designed to complete the design of the dual-closed-loop control system.

[0013] Furthermore, establishing the mathematical model of the grid-type converter in the synchronous rotating coordinate system includes the following steps:

[0014] The principal circuit equations are established in the stationary coordinate system abc, and are specifically expressed as follows:

[0015] ;

[0016] in, For the bridge arm output voltage, The voltage across the capacitor. For inductor current, For load current, For filtering inductors, For filtering capacitors, The equivalent resistance for system losses. For the Laplace operator;

[0017] The model is transformed to the αβ coordinate system using a constant amplitude transformation, as shown below:

[0018] ;

[0019] in, For the bridge arm output voltage at , The amount, For the inductor current in , The amount, For capacitor voltage at , The amount, For the load current at , The amount;

[0020] The model is transformed to a synchronously rotating coordinate system (dq axis) using the Park transformation, as shown below:

[0021] ;

[0022] ;

[0023] in, Let be the components of the bridge arm output voltage in terms of d and q. Let be the components of the inductor current in d and q. Let be the components of the capacitor voltage at d and q. Let be the load current components in d and q. Output voltage angular frequency.

[0024] Furthermore, a method for eliminating cross-coupling terms includes the following steps:

[0025] A decoupling term is injected into the modulated wave voltage output by the current controller, as specifically shown below:

[0026] ;

[0027] The reference current is generated by the voltage loop, as shown below:

[0028] ;

[0029] in, For the modulated wave voltage components on the d and q axes, For current controller, The reference current has d-axis and q-axis components.

[0030] Furthermore, after introducing the capacitor voltage feedback branch, the formula for generating the modulated wave voltage command is modified as follows:

[0031] .

[0032] Furthermore, the open-loop transfer function model of the current loop is specifically represented as follows:

[0033] ;

[0034] in, The current controller outputs a modulated wave component. The LC resonant angular frequency, Sampling frequency, is the z-transformation factor.

[0035] Furthermore, the optimal gain is selected through root locus analysis. This results in the current loop pole damping ratio ζ=1 and the pole magnitude reaching its maximum value.

[0036] Furthermore, the open-loop transfer function of the voltage loop is specifically expressed as follows:

[0037] ;

[0038] The equivalent controlled object model of the voltage source is as follows:

[0039] ;

[0040] The voltage loop controller model is as follows:

[0041] ;

[0042] in, For proportional gain, This is the integral gain.

[0043] Furthermore, the parameters of the voltage outer loop controller are designed to meet the following requirements: phase margin ≥ 50°, crossover frequency ≥ 3400 rad / s.

[0044] A grid-type converter system, wherein the controller is configured to execute the aforementioned grid-type converter dual closed-loop control method.

[0045] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the dual closed-loop control method for a grid-type converter.

[0046] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the dual closed-loop control method for a grid-type converter.

[0047] The beneficial effects of this invention are as follows:

[0048] This invention fundamentally eliminates the resonance peak of the LC filter by introducing a capacitor voltage feedback branch at the current loop output and precisely configuring the current loop poles at unit damping rate based on the root locus method, thus providing optimal damping for the system. This enables the system to maintain high stability at all operating points and effectively suppresses output voltage oscillations.

[0049] Because resonance is effectively suppressed, the open-loop frequency response of the voltage loop no longer exhibits abrupt changes in amplitude and phase near the resonant frequency, thus allowing for a significant increase in the voltage loop bandwidth. This greatly accelerates the output voltage response, enabling rapid adjustment to steady state when load changes occur, significantly reducing voltage dips or swells, and effectively avoiding transient power quality problems caused by dynamic processes.

[0050] The present invention can quickly and accurately compensate for the voltage drop generated by unbalanced load current on the output filter. When faced with a three-phase unbalanced load, the control system can effectively suppress the influence of negative sequence components on the output voltage, ensuring that the output voltage remains balanced across the three phases, and significantly improving the power supply quality and reliability of the grid-type converter under complex operating conditions. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 The main circuit and block diagram of the dual closed-loop control method for grid-type converters are shown below.

[0053] Figure 2 A model of a grid-type converter in a synchronous rotating coordinate system;

[0054] Figure 3 The control block diagram of a grid-type converter in a synchronous rotating coordinate system;

[0055] Figure 4 The control block diagram of a grid-type converter in a synchronous rotating coordinate system;

[0056] Figure 5 The block diagram of the d-axis control after decoupling of the grid-type converter;

[0057] Figure 6 The current loop control block diagram for a grid-type converter;

[0058] Figure 7 This is the root locus curve of the current loop;

[0059] Figure 8 This is the frequency response of the voltage loop;

[0060] Figure 9 Simulation results for a capacitorless voltage feedback branch at the output of a traditional current controller;

[0061] Figure 10 The simulation results are for the control method of this invention. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0063] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0064] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0065] This invention discloses a dual closed-loop control method for a grid-type converter, the main circuit and control block diagram of which are shown below. Figure 1 As shown, it includes the following steps:

[0066] A mathematical model of the grid-type converter is established in a synchronous rotating coordinate system, and cross-coupling terms are eliminated through inductor current and capacitor voltage state feedback. A capacitor voltage feedback branch is introduced at the output of the current loop controller to form a new modulation wave signal, and an open-loop transfer function model of the current loop is constructed. The parameters of the current loop controller are adjusted by the root locus analysis method so that the current loop poles are located at unit damping rate and the magnitude of the poles is maximized. Based on the frequency characteristics of the voltage loop open-loop transfer function and the preset phase margin requirements, the parameters of the voltage outer loop controller are designed to complete the design of the dual closed-loop control system.

[0067] A mathematical model of a grid-type converter is established based on output voltage and inductor current feedback in a synchronous rotating coordinate system, including the following steps:

[0068] according to Figure 1 The main circuit shown is represented by the following equations in the stationary coordinate system abc:

[0069] ;

[0070] in, For the bridge arm output voltage, The voltage across the capacitor. For inductor current, For load current, For filtering inductors, For filtering capacitors, The equivalent resistance for system losses. For the Laplace operator;

[0071] The model is transformed to the αβ coordinate system using a constant amplitude transformation, as shown below:

[0072] ;

[0073] in, For the bridge arm output voltage at , The amount, For the inductor current in , The amount, For capacitor voltage at , The amount, For the load current at , The amount;

[0074] The model is transformed to a synchronously rotating coordinate system (dq axis) using the Park transformation, as shown below:

[0075] ;

[0076] ;

[0077] in, Let be the components of the bridge arm output voltage in terms of d and q. Let be the components of the inductor current in d and q. Let be the components of the capacitor voltage at d and q. Let be the load current components in d and q. Output voltage angular frequency.

[0078] The model of the main circuit of the grid converter in the synchronous rotating coordinate system is obtained, such as... Figure 2 As shown. To eliminate cross-coupling terms. The effect of this is to inject a decoupling term into the modulated wave voltage output of the current controller, as specifically shown below:

[0079] ;

[0080] The reference current is generated by the voltage loop, as shown below:

[0081] ;

[0082] in, For the modulated wave voltage components on the d and q axes, For current controller, The reference current has d-axis and q-axis components.

[0083] A capacitor voltage feedback branch is introduced at the output of the current loop. An open-loop transfer function of the current loop is established, and the current loop parameters are designed based on root locus analysis. This achieves a resonant pole with unit damping rate while maximizing the pole magnitude. Specifically, the optimal gain is selected through root locus analysis. This results in the current loop pole damping ratio ζ=1 and the pole magnitude reaching its maximum value.

[0084] like Figure 4 As shown, after introducing the capacitor voltage feedback branch, the formula for generating the modulated wave voltage command is modified as follows:

[0085] .

[0086] The open-loop transfer function model of the current loop is specifically represented as follows:

[0087] ;

[0088] in, The current controller outputs a modulated wave component. The LC resonant angular frequency, Sampling frequency, is the z-transformation factor.

[0089] The current loop control block diagram is obtained, as follows: Figure 6 As shown, the open-loop transfer function of the current loop is as follows:

[0090] ;

[0091] in, This is the gain of the current loop controller.

[0092] With controller gain The change in current loop root trajectory curve is obtained by observing the change in current loop, as shown in the figure. Figure 7 As shown. When The current loop poles have a unit damping ratio, and the magnitudes of the two poles reach their maximum values.

[0093] Furthermore, based on the open-loop transfer function of the voltage loop and the given phase margin requirement, the voltage loop controller parameters are designed; the specific steps are as follows:

[0094] The equivalent controlled object of the voltage source is:

[0095] ;

[0096] in:

[0097] ;

[0098] The open-loop transfer function of the voltage loop is ,in For voltage loop controller, For proportional gain, This is the integral gain.

[0099] The parameters of the voltage outer loop controller are designed to meet the following requirements: phase margin ≥ 50°, crossover frequency ≥ 3400 rad / s. Figure 8 As shown, the crossover frequency is 3430 rad / s and the phase margin is 51°.

[0100] This invention also includes performance verification standards, namely, the output voltage regulation time ≤ 2 ms when the load changes abruptly, and the output voltage THD ≤ 1% under three-phase unbalanced load.

[0101] To verify the superiority of the control method provided in this scheme, simulation analysis was performed in MATLAB / Simulink. The system parameters are shown in Table 1. Figure 9 The figure shows the result obtained by the control method without adding an output voltage feedback branch at the current loop output. Figure 10 The simulation results of this control method show that during a sudden load change of 0.1s, the output voltage fluctuation of this control method is smaller, and it can quickly enter a steady state. Furthermore, when an unbalanced load is applied at 0.2s, the output voltage of this control method is balanced across all three phases, demonstrating a stronger ability to handle unbalanced loads.

[0102] Table 1

[0103]

[0104] The present invention also provides a grid-type converter system, wherein the controller is configured to execute the above-described grid-type converter dual closed-loop control method.

[0105] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the above-described grid-type converter dual closed-loop control method.

[0106] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described dual-closed-loop control method for a grid-type converter, including...

[0107] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0108] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0109] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0110] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0111] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0112] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A dual closed-loop control method for a grid-type converter, characterized in that, Includes the following steps: A mathematical model of the grid converter is established in a synchronous rotating coordinate system, and cross-coupling terms are eliminated through inductor current and capacitor voltage state feedback. A capacitor voltage feedback branch is introduced at the output of the current loop controller to form a new modulation wave signal, and an open-loop transfer function model of the current loop is constructed. By using root locus analysis, the parameters of the current loop controller are adjusted so that the current loop poles are located at the unit damping rate and the magnitude of the poles is maximized. Based on the frequency characteristics of the open-loop transfer function of the voltage loop and the preset phase margin requirements, the parameters of the outer-loop voltage controller are designed to complete the design of the dual-closed-loop control system.

2. The dual closed-loop control method for a grid-type converter according to claim 1, characterized in that, The establishment of the mathematical model of the grid-type converter in the synchronous rotating coordinate system includes the following steps: The principal circuit equations are established in the stationary coordinate system abc, and are specifically expressed as follows: ； in, For the bridge arm output voltage, This is the capacitor voltage. For inductor current, For load current, For filtering inductors, For filtering capacitors, The equivalent resistance for system losses. For the Laplace operator; The model is transformed to the αβ coordinate system using a constant amplitude transformation, as shown below: ； in, For the bridge arm output voltage at , The amount, For the inductor current in , The amount, For capacitor voltage at , The amount, For the load current at , The amount; The model is transformed to a synchronously rotating coordinate system (dq axis) using the Park transformation, as shown below: ； ； in, Let be the components of the bridge arm output voltage in terms of d and q. Let be the components of the inductor current in d and q. Let be the components of the capacitor voltage at d and q. Let be the load current components in d and q. Output voltage angular frequency.

3. The dual closed-loop control method for a grid-type converter according to claim 2, characterized in that, Methods for eliminating cross-coupling terms include the following steps: A decoupling term is injected into the modulated wave voltage output by the current controller, as specifically shown below: ； The reference current is generated by the voltage loop, as shown below: ； in, For the modulated wave voltage components on the d and q axes, For current controller, The reference current has d-axis and q-axis components.

4. The dual closed-loop control method for a grid-type converter according to claim 1, characterized in that, After introducing the capacitor voltage feedback branch, the formula for generating the modulated wave voltage command is modified as follows: 。 5. The dual closed-loop control method for a grid-type converter according to claim 4, characterized in that, The open-loop transfer function model of the current loop is specifically represented as follows: ； in, The current controller outputs a modulated wave component. The LC resonant angular frequency, Sampling frequency, is the z-transformation factor.

6. The dual closed-loop control method for a grid-type converter according to claim 5, characterized in that, Selecting the optimal gain through root locus analysis This results in the current loop pole damping ratio ζ=1 and the pole magnitude reaching its maximum value.

7. The dual closed-loop control method for a grid-type converter according to claim 1, characterized in that, The open-loop transfer function of the voltage loop is specifically expressed as follows: ； The equivalent controlled object model of the voltage source is as follows: ； The voltage loop controller model is as follows: ； in, For proportional gain, This is the integral gain.

8. The dual closed-loop control method for a grid-type converter according to claim 7, characterized in that, The parameters of the voltage outer loop controller are designed to meet the following requirements: phase margin ≥ 50°, crossover frequency ≥ 3400 rad / s.

9. A grid-type converter system, characterized in that, Its controller is configured to perform the dual closed-loop control method for grid-type converters as described in any one of claims 1 to 8.

10. An electronic device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the dual closed-loop control method for a grid-type converter as described in any one of claims 1 to 8.

11. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, implements the steps of the dual closed-loop control method for a grid-type converter as described in any one of claims 1 to 8.

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