A system for improving plug-and-play performance of grid-forming converters in a direct current microgrid

Abstract

The application belongs to the technical field of direct-current micro-grid control, and specifically discloses a system for improving plug-and-play performance of network-constructed converters in a direct-current micro-grid; the system adds an additional controller Q on the basis of the original PI double closed-loop controller of each network-constructed DC-DC buck converter in the direct-current micro-grid, and establishes a state space model of a multi-converter interconnection control system containing the additional controller. The system stability condition is decomposed through Lyapunov stability theory, and the gain parameters of the Lyapunov matrix and the additional controller Q are designed to ensure the overall stability of the system. Meanwhile, the gain of the additional controller Q is optimized to improve the response performance of the distributed power supply and limit the amplitude of the control signal. The application also discloses a corresponding control system, a computing unit and a computer readable storage medium.

Description

[0001] This application is a divisional application of application number 202510533666.1, filed on April 27, 2025, entitled "A Method and System for Improving the Plug-and-Play Performance of Grid-Type Converters in DC Microgrids," and the applicant is North China University of Technology. Technical Field

[0002] This invention belongs to the field of DC microgrid control technology, and specifically discloses a system for improving the plug-and-play performance of grid-type converters in DC microgrids. Background Technology

[0003] With the widespread application of DC power generation and consumption equipment such as photovoltaic power generation, energy storage, and DC charging, DC microgrids, compared to AC microgrids, are a more efficient form of DC power generation and consumption operation and management due to their higher conversion efficiency, simpler control methods, and lack of reactive power distribution issues. However, in DC microgrids, due to system expansion, equipment failures, and other reasons, distributed generation equipment may be connected to or disconnected from the DC microgrid, causing significant changes in the system structure. This leads to problems such as the original control strategies of the DC-DC buck converters of each generation device becoming inapplicable, reduced overall system stability or stability margin, and decreased overall system control performance. Therefore, it is difficult to achieve plug-and-play operation of DC-DC buck converters in DC microgrids.

[0004] To achieve plug-and-play control of distributed power source buck converters in DC microgrids, there are currently different control design methods, mainly distributed device control design methods based on passive characteristics and controller design methods based on robustness theory.

[0005] a) The dissipative theory-based design method is a distributed controller design approach. It allows for independent design of control strategies for each buck converter. When the control characteristics of each buck converter remain passive, the overall system stability can still be guaranteed when multiple buck converters are connected to a microgrid. The advantage of this method is that it allows for independent design of control strategies for each distributed power converter, independent of line and other distributed power source parameters. However, its disadvantages include a relatively conservative design, lower overall system control performance, and the need for direct redesign or modification of buck converter control, which may be difficult to implement for some existing equipment.

[0006] (b) The robustness-based design method utilizes Lyapunov stability and robust control theory. Considering uncertainties such as the connection and disconnection of distributed power sources, it designs system stability constraints for all possible scenarios and solves the Buck converter controller using the Lyapunov linear matrix inequality. This allows the DC microgrid to maintain system stability and effective operation even after some distributed devices are connected or disconnected, achieving plug-and-play capability for the Buck converter. The advantage of this method is its high robustness to system uncertainties; the disadvantages are that it requires consideration of various uncertainties caused by system changes, potentially leading to a more complex design. Furthermore, the need to satisfy stability requirements under various uncertainties can result in a conservative system design, or even unsolvable controller parameters. Additionally, this method still requires redesigning and modifying the controller, making it difficult to apply to existing equipment.

[0007] Therefore, the main problems of the current plug-and-play controller design method for DC microgrid network-based converters are summarized as follows: 1. The two existing controller design methods based on passive characteristics and robust stability are relatively conservative, resulting in insufficient converter control performance, and may even lead to an unsolvable controller design problem. 2. Current methods all require redesigning the equipment control strategy, which is difficult to apply to existing Buck converters if the manufacturer does not grant the controller modification permissions. Summary of the Invention

[0008] To address the aforementioned issues, this invention discloses a method and system for improving the plug-and-play performance of grid-type converters in DC microgrids. The method, without altering the original control strategy of the buck converter, designs additional control algorithms based on the existing controller of the buck converter to improve the overall control performance of the microgrid. This ensures that the microgrid remains stable even after some distributed power sources are connected or disconnected, thereby achieving plug-and-play capability for buck converters in DC microgrids.

[0009] The objective of this invention is achieved through the following technical solution.

[0010] A method for improving the plug-and-play performance of grid-type converters in DC microgrids includes the following steps: (1) An additional controller Q is added to the original PI dual closed-loop controller of each grid-type DC-DC buck converter in the DC microgrid; (2) Establish a state-space model of the multi-converter interconnected control system including the additional controller Q. The model describes the dynamic characteristics of the system by decomposing it into local terms and interconnected coupling terms. (3) Based on Lyapunov stability theory, the system stability conditions are decomposed into local term stability conditions and interconnected coupling term stability conditions, and the overall system stability is ensured by designing the Lyapunov matrix and the gain parameters of the additional controller Q. (4) Optimize the gain of the additional controller Q to improve the response performance of the distributed power supply while meeting the stability constraints, and limit the amplitude of the control signal to avoid exceeding the device capacity limit.

[0011] Furthermore, in the above-mentioned method for improving the plug-and-play performance of grid-type converters in DC microgrids, the output signal of the additional controller Q is superimposed with the output signal of the original PI controller to form a total control signal.

[0012] Furthermore, in the aforementioned method for improving the plug-and-play performance of grid-type converters in DC microgrids, the stability condition of the interconnection coupling term is achieved by constructing a Laplace matrix that satisfies semi-negative definiteness.

[0013] Furthermore, in the aforementioned method for improving the plug-and-play performance of grid-type converters in DC microgrids, the optimization objective of the additional controller Q is to minimize the real part of the system poles, and the optimal gain value is solved using a numerical optimization toolkit.

[0014] This invention also discloses a control system for improving the plug-and-play performance of grid-type converters in DC microgrids, characterized in that it includes: (1) Multiple network-type DC-DC buck converters: Each converter is equipped with a PI dual closed-loop controller; (2) Additional controller module: connected in parallel with the PI controller of each converter, used to generate compensation control signals; (3) Modeling module: used to construct the state-space model of a multi-converter interconnected control system including additional controllers; (4) Stability analysis module: Verify system stability and design gain parameters based on Lyapunov theory; (5) Optimization module: used to optimize the gain value of the additional controller under the condition of satisfying stability constraints.

[0015] Furthermore, in the above system, the (2) additional controller module adopts a distributed design and does not rely on other converter parameters or line parameters.

[0016] Furthermore, in the above system, the optimization module (5) ensures that the control signal does not exceed the device capacity limit by limiting the gain amplitude.

[0017] Furthermore, the aforementioned system supports plug-and-play distributed power sources and automatically maintains stable operation of the microgrid after power is connected or disconnected.

[0018] This invention discloses a computing unit for performing the above-described method, comprising: Modeling unit: Used to construct the state-space model of the multi-converter interconnected control system; b. Stability determination unit: Based on Lyapunov stability theory, decompose stability conditions and design matrix parameters; c. Optimization Unit: Solve for the optimal gain value of the additional controller Q using a numerical optimization toolkit; d Control signal generation unit: Outputs the optimized gain value to the additional controller module.

[0019] The present invention also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described method for improving the plug-and-play performance of grid-type converters in DC microgrids.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a control method and system for improving the plug-and-play performance of grid-type converters in DC microgrids.

[0021] Based on Lyapunov stability analysis, this invention enables distributed converter design without requiring inter-node line parameters or other converter parameters.

[0022] This invention can ensure the stability of DC microgrids and improve the plug-and-play performance and control response performance of devices when distributed devices are connected and disconnected, without modifying the existing control strategy of the buck converter. Attached Figure Description

[0023] Figure 1 A schematic diagram of a multi-bus DC microgrid structure containing multiple distributed micro-sources; Figure 2 A schematic diagram illustrating the principle of plug-and-play control performance improvement for DC microgrid buck converters based on an additional controller. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] Example 1 This embodiment discloses a method for improving the plug-and-play performance of grid-type converters in DC microgrids, including the following steps: (1) An additional controller Q is added to the original PI dual closed-loop controller of each grid-type DC-DC buck converter in the DC microgrid; (2) Establish a state-space model of the multi-converter interconnected control system including the additional controller Q. The model describes the dynamic characteristics of the system by decomposing it into local terms and interconnected coupling terms. (3) Based on Lyapunov stability theory, the system stability conditions are decomposed into local term stability conditions and interconnected coupling term stability conditions, and the overall system stability is ensured by designing the Lyapunov matrix and the gain parameters of the additional controller Q. (4) Optimize the gain of the additional controller Q to improve the response performance of the distributed power supply while meeting the stability constraints, and limit the amplitude of the control signal to avoid exceeding the device capacity limit.

[0026] The output signal of the additional controller Q is superimposed on the output signal of the original PI controller to form the total control signal.

[0027] The stability condition of the interconnection coupling term is achieved by constructing a semi-negative definite Laplace matrix for the Lypunove stability criterion matrix of the system.

[0028] The optimization objective of the additional controller Q is to minimize the real part of the system poles, and the optimal gain value is solved using a numerical optimization toolkit.

[0029] like Figure 1 This is a schematic diagram of the multi-bus DC microgrid structure containing multiple distributed micro-sources according to the present invention. Figure 2 This demonstrates the principle behind the plug-and-play performance improvement of DC microgrid buck converters, such as... Figure 2 As shown, based on the PI dual closed-loop controller of each buck converter in the microgrid, an additional controller Q is designed. The additional controller Q outputs an additional control signal u. Q This enables plug-and-play functionality for each converter in the microgrid, improving the response capability of each converter while ensuring the stability of the microgrid.

[0030] Example 2 This embodiment discloses a distributed design method for the additional controller Q of a DC microgrid buck converter: 1) Establish the state-space model of the DC-DC buck converter interconnection system of the DC microgrid and the PI controller of the buck converter itself: 1.1) State-space model of an interconnected DC microgrid system with a DC-DC buck converter: (1a) Let the above expression be denoted as (1b) In the formula, the converter m state variables , V Cm , i Lm For converter m LC filter capacitor voltage and inductor current L m , C m , R Lm , R mn These are, respectively, the LC filter inductor, the filter capacitor, the inductor parasitic resistance, and the busbar. mn Interconnection line resistance R mn .

[0031]

[0032] Converter total control signal u m = u km + u Qm , u km The original PI controller output control signal, u Qm This is a compensation control signal for the additional controller. d m For load current disturbance i load,m , P load,m For a constant power load, after linearization at the operating voltage point .

[0033] 1.2) State-space model of dual closed-loop PI controller: (2a) Right now (2b) In the formula: the input signal of the PI dual closed-loop controller is the converter output feedback. y m The PI controller outputs the control signal as follows: u km , k p1 , k i1 For the proportional and integral gain of the voltage loop PI controller, kp2 , k i2 For the proportional and integral gain of the current loop PI controller.

[0034]

[0035] 1.3) Substituting equation (2b) into equation (1b) yields the state space of the interconnected system with a PI controller: (3) In the formula

[0036] 1.4) Performance Enhancement: The additional controller Q is a constant gain vector, i.e. Q m =[ q 1, q 2, q 3, q 4] (4) Q m The controller's output signal is

[0037] 1.5) Establish an additional controller that includes performance enhancements. Q The state-space model of a multi-converter interconnected control system will Q Substitute the control output signal into the controlled object, the first m The state space of the converter control system is: (6.1) In the formula

[0038] Let equation (6.1) be denoted as (6.2) In the formula 1.6) Includes the original PI controller and Q The overall state-space model of the multi-converter interconnected control system is as follows: (7.1) The global state-space model above is denoted as (7.2) In the formula

[0039] 2) In the system state-space equation (7.2) Ag Diagonal block matrix A gmm Decomposed into: local items +Coupling terms

[0040] (8) 3) The overall Lyapunov stability condition of the system (7.2) is: (9.1) In the formula: . Then there is (9.2) The entire system matrix A g It can be decomposed into a diagonal matrix according to equation (8). A diag and coupling matrix A coup : Substituting into equation (9.1), the system stability condition can be transformed into: (10a) Can be converted (10b) Finally, the stability inequality (10b) for the overall control system can be decomposed into: Stability condition for diagonal terms: (11a) Stability condition for interconnect coupling terms: (11b) When both of the above conditions (11a) and (11b) are met, equation (9.1) can be guaranteed to be met, and the overall microgrid system will be stable.

[0041] 4) Design matrix P The stability condition (11b) for the interconnect coupling terms is a semi-negative definite matrix: The stability condition (11b) for interconnection coupling terms expands to: (12) Let the system's Lypunov matrix P m , P n , P k The following conditions must be met: (12) Then the stability inequality of the coupling terms of the entire system in equation (11b) is: (13) The above matrix is ​​a symmetric matrix, with the sum of its rows and columns both being 0, negative values ​​on the diagonal, and all other elements being >= 0. Therefore, the Lypunnov stability test matrix for the above coupling terms is a Laplace matrix. L , is a semi-negative definite matrix.

[0042] 5) Then design each Q This can be achieved by making the matrix on the left side of equation (11a) negative definite or semi-negative definite: (14) That is, only needs to satisfy (15) In the formula:

[0043] Meets the requirements of constant power load range P load =[0, P load,max Within this range, the following LMI matrix can be negative definite: (16) 6) Simultaneously, to improve the system's distributed power source response capability, while ensuring overall system stability, the poles λ of each distributed power source should be shifted as far to the left as possible: Ultimately, for m =1,2,..., N , Q m The optimization objective is: (16) matrix P The equality and LMI inequality constraints are as follows: (17.1) (17.2) Furthermore, to avoid excessive control signal amplitude exceeding equipment capacity limits, restrictions are imposed. Q Gain magnitude: (17.3) Finally, numerical optimization toolkits such as Yalmip are used to numerically optimize equation (16). Based on satisfying equations (17.1), (17.2), and (17.3), the converters that minimize equation (16) are found. Q value.

[0044] Example 3 This embodiment discloses a control system for improving the plug-and-play performance of grid-type converters in DC microgrids, characterized in that it includes: (1) Multiple network-type DC-DC buck converters: Each converter is equipped with a PI dual closed-loop controller; (2) Additional controller module: connected in parallel with the PI controller of each converter, used to generate compensation control signals; (3) Modeling module: used to construct the state-space model of a multi-converter interconnected control system including additional controllers; (4) Stability analysis module: Verify system stability and design gain parameters based on Lyapunov theory; (5) Optimization module: used to optimize the gain value of the additional controller under the condition of satisfying stability constraints.

[0045] The additional controller module (2) adopts a distributed design and does not rely on other converter parameters or line parameters.

[0046] The optimization module (5) ensures that the control signal does not exceed the device capacity limit by limiting the gain amplitude.

[0047] The system supports plug-and-play distributed power sources and automatically maintains stable operation of the microgrid after power is connected or disconnected.

[0048] Example 4 This embodiment discloses a computing unit for executing the method described in embodiment 1 or 2, including: Modeling unit: Used to construct the state-space model of the multi-converter interconnected control system; b. Stability determination unit: Based on Lyapunov stability theory, decompose stability conditions and design matrix parameters; c. Optimization Unit: Solve for the optimal gain value of the additional controller Q using a numerical optimization toolkit; d Control signal generation unit: Outputs the optimized gain value to the additional controller module.

[0049] As can be seen from the above embodiments, this invention, based on Lyapunov stability analysis, realizes a distributed design of the distributed converter without relying on other converter parameters or line parameters. Without modifying the existing control strategy of the Buck converter, it ensures the stability of the DC microgrid after distributed devices are connected or disconnected, improving the plug-and-play performance and control response performance of the devices. Simultaneously, by limiting the gain amplitude, it avoids the problem of control signals exceeding the device capacity limit.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of the present invention, or equivalent structural or procedural transformations made using the content of the present invention specification, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of protection of the present invention patent.

Claims

1. A system for improving the plug-and-play performance of grid-type converters in DC microgrids, characterized in that, include: (1) Multiple grid-type DC-DC buck converters: Based on the PI dual closed-loop controller of each grid-type DC-DC buck converter in the DC microgrid, an additional controller Q is added; the additional controller Q is connected in parallel with the PI controller of each converter to generate compensation control signals; (2) Modeling module: Establish a state-space model of the multi-converter interconnected control system containing the additional controller Q. The model describes the dynamic characteristics of the system by decomposing it into local terms and interconnected coupling terms. 1) Establish the state-space model of the DC-DC buck converter interconnection system of the DC microgrid and the PI dual closed-loop controller of the buck converter itself: 1.1) State-space model of an interconnected DC microgrid system with a DC-DC buck converter: (1a) Let the above expression be denoted as (1b) In the formula, the converter m State variables are , V Cm , i Lm For converter m LC filter capacitor voltage and inductor current L m , C m , R Lm , R mn These are the LC filter inductor, filter capacitor, inductor parasitic resistance, and the line resistance connecting bus m and n, respectively. ； Converter total control signal u m = u km + u Qm ; u km This is the output control signal of the PI dual closed-loop controller; u Qm For compensation control signals of the additional controller; d m For load current disturbance i load,m ; P load,m For a constant power load, after linearization at the operating voltage point ; 1.2) State-space model of dual closed-loop PI controller: (2a) Right now (2b) In the formula: the input signal of the PI dual closed-loop controller is the converter output feedback. y m The PI dual closed-loop controller outputs the control signal as follows: u km , k p1 , k i1 For the proportional and integral gain of the voltage loop PI controller, k p2 , k i2 For the proportional and integral gain of the current loop PI controller; ； 1.3) Substituting equation (2b) into equation (1b) yields the state space of the interconnected system with a PI controller: (3) In the formula, ； 1.4) Performance Enhancement: The additional controller Q is a constant gain vector, i.e. Q m =[ q 1, q 2, q 3, q 4] (4) The output signal of the additional controller Q is ； 1.5) Establish a system that includes additional controllers Q The state-space model of a multi-converter interconnected control system will include an additional controller. Q Substituting the output signal into the controlled object, we obtain the first... m State-space model of converter control system; (3) Stability analysis module: Based on Lyapunov stability theory, the system stability conditions are decomposed into local term stability conditions and interconnected coupling term stability conditions. The overall system stability is ensured by designing the Lyapunov matrix and the gain parameters of the additional controller Q. (4) Optimization module: Optimize the gain of the additional controller Q to improve the response performance of the distributed power supply while meeting stability constraints, and limit the amplitude of the control signal to avoid exceeding the device capacity limit.

2. The system according to claim 1, characterized in that, The stability condition of the interconnection coupling term is achieved by constructing a Laplace matrix that satisfies semi-negative definiteness.

3. The system according to claim 1, characterized in that, The optimization objective of the additional controller Q is to minimize the real part of the system poles, and the optimal gain value is solved using a numerical optimization toolkit.

4. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the system according to any one of claims 1-3.

Images