Cascaded energy storage converter inertia damping optimization method suitable for multi-power-grid condition

Abstract

The invention relates to a converter grid-connected control technology, and aims to provide a cascade energy storage converter inertia damping optimization method suitable for a multi-power-grid condition. Comprising the main steps of grid-connected system modeling, inertial parameter optimization, damping parameter optimization and parameter design under the multi-power-grid condition. The inertia and damping parameters are optimized through the transfer characteristic and the step response characteristic, the dynamic response performance and the system stability of the cascade energy storage converter can be effectively improved, and the voltage source supporting reliability of the converter is ensured; by establishing an optimization parameter library and an optimization parameter curve covering various power grid strengths, the configuration and debugging process of the system is simplified, the complexity and time demand of parameter setting are reduced, and the adaptability of the system under different power grid operation conditions is effectively enhanced.

Description

Technical Field

[0001] The invention relates to the field of converter grid-connected control, and in particular to an inertial damping optimization method for a cascaded energy storage converter adaptable to multiple power grid conditions. Background Art

[0002] With the transformation of energy structure, new energy power generation such as wind power and solar energy has developed rapidly. However, due to the inherent intermittent and volatile nature of new energy power generation, the stability of the power grid faces unprecedented challenges. In order to meet these challenges, large-capacity energy storage technology has become an important means to ensure the stability of the power grid. Among them, cascade energy storage technology has gradually become the mainstream choice for large-capacity energy storage applications due to its advantages in single-machine large capacity and medium and high voltage direct connection. Cascade energy storage converters actively provide voltage support for the power grid by adopting voltage source control, which is a potential solution to improve the stability of the power grid in the future.

[0003] Short Circuit Ratio (SCR) is an important technical indicator in the new energy grid-connected system, which is used to describe the ratio of the current to the rated current when the system is short-circuited. Specifically defined as the ratio of the short-circuit current to the rated current when a short circuit occurs in the system on the new energy power supply side. This indicator reflects the response ability of the new energy power supply to the short-circuit current of the power grid and the ability of the power supply to withstand a short circuit. In the design and operation of the grid-connected system, it is of great significance to accurately understand and master the short-circuit ratio. The physical meaning of the short-circuit ratio is to measure the current capacity that the system can withstand and the range of stable operating conditions. Therefore, it can be used to predict and analyze the performance of the power grid under different short-circuit conditions, and provide theoretical support for subsequent equipment selection and system optimization design.

[0004] The multiple grid conditions described in the present invention refer to the actual scenario where the grid system operates under different short-circuit ratio conditions. In order to ensure that the cascaded energy storage converter can adapt to the short-circuit ratio changes of the grid system and maintain continuous and stable operation, the cascaded energy storage converter needs to have the ability to follow and adjust the operating parameters.

[0005] The commonly used voltage source control is the virtual synchronous machine (VSG) control strategy, which supports and stabilizes the power grid by simulating the inertia and damping characteristics of traditional synchronous machines; however, this type of technology still has shortcomings when facing practical applications under multiple power grid conditions. Because the existing inertia and damping parameter design methods often fail to fully consider the specific operating conditions of the power grid and the stability margin of the converter. When facing fluctuations under different power grid conditions, the adaptability of the existing methods is limited, which may lead to a decrease in system stability. In addition, the existing design methods fail to fully optimize the dynamic response characteristics of the cascade energy storage converter, resulting in the converter being difficult to achieve the best effect in terms of response speed and accuracy, and its dynamic performance still has a lot of room for improvement. Although many research institutions have paid enough attention to the above problems, there are no public reports of effective solutions.

[0006] Therefore, it is necessary to propose a new solution to optimize and adjust the inertia and damping parameters of the voltage source cascade energy storage converter so that the cascade energy storage converter can more stably support the grid operation under multiple grid conditions. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide an inertial damping optimization method for a cascaded energy storage converter that is adaptable to multiple power grid conditions.

[0008] In order to solve the above technical problems, the solution of the present invention is:

[0009] A method for optimizing inertial damping of a cascaded energy storage converter adapted to multiple power grid conditions is provided, comprising the following steps:

[0010] (1) Grid-connected system modeling

[0011] The grid-connected converter system model is established based on Kirchhoff's law and small signal, and the grid-connected system transfer function is derived as a system model for analyzing transfer characteristics and step response.

[0012] (2) Inertia parameter optimization

[0013] Draw a root locus diagram of the grid-connected system using the transfer function, draw an equal damping line in it, and record the inertia coefficient corresponding to the intersection of the root locus and the equal damping line; then draw a Bode diagram based on the inertia coefficient and the system model in step (1), and confirm the most preferred inertia coefficient based on the phase margin requirement of the grid-connected system;

[0014] (3) Damping parameter optimization

[0015] Combine the system model and the optimal inertia coefficient to draw the step response curve under different damping coefficients; by analyzing each step response curve and combining the dynamic characteristics requirements of the converter, obtain the maximum damping coefficient of the grid-connected system when meeting the response time and overshoot requirements, and use it as the optimal damping coefficient;

[0016] (4) Parameter design under multiple power grid conditions

[0017] The short circuit ratio adjustment step is set, and multiple short circuit ratio conditions that gradually increase to the maximum short circuit ratio are determined; then, under each short circuit ratio condition, the operation contents of steps (1) to (3) are repeatedly performed to obtain the most preferred inertia coefficient and the best damping coefficient under different grid strength conditions, and a control parameter library is constructed; on this basis, linear interpolation fitting is performed to obtain the inertia coefficient optimization parameter curve and the damping optimization parameter curve under different short circuit ratio conditions.

[0018] The present invention further provides an inertia damping optimization control method for a cascaded energy storage converter that is adaptable to multiple power grid conditions. On the basis of the aforementioned method, the cascaded energy storage converter is further controlled by using optimized control parameters; specifically, the method comprises: during the converter grid-connected process, selecting a corresponding inertia coefficient optimization parameter curve and a damping optimization parameter curve according to the real-time SCR value of the system power grid; and then using the control parameters corresponding to each curve to control the operation of the cascaded energy storage converter, so that the grid-connected system can maintain stability and good dynamic response under various power grid conditions.

[0019] The present invention also provides a high-voltage direct-mounted cascade energy storage system capable of realizing inertial damping optimization control, wherein the cascade energy storage system has a three-phase star structure, each phase of which is composed of a filter reactor L f and N energy storage modules connected in series; the structures of the energy storage modules are the same, and all include an H-bridge, a filter circuit, and a series battery cluster as an energy storage power source arranged in sequence; the controller module of the energy storage system includes a processor and a computer-readable storage medium, and a computer program is stored on the computer-readable storage medium; when the computer program is executed by the processor, the optimization method or control method as described above can be implemented.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention optimizes inertia and damping parameters through transfer characteristics and step response characteristics, which can effectively improve the dynamic response performance and system stability of the cascaded energy storage converter and ensure the reliability of the converter voltage source support.

[0022] (2) The present invention simplifies the system configuration and debugging process by establishing an optimization parameter library and optimization parameter curve covering various power grid strengths, reduces the complexity and time requirement of parameter setting, and effectively enhances the adaptability of the system under different power grid operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the main circuit topology diagram of the cascaded energy storage converter grid-connected system.

[0024] Figure 2 It is a flowchart of inertial damping parameter optimization process.

[0025] Figure 3 It is a power step response waveform diagram of the method of the present invention under different power grid conditions. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described clearly and completely in conjunction with the accompanying drawings and embodiments. It should be understood that the described embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Any modification, equivalent replacement made to the present invention under the inspiration of the present invention, or a product similar to the present invention obtained by combining the present invention with other technical features, all fall within the protection scope of the present invention.

[0027] Part I Implementation of the Invention

[0028] 1. First, the main circuit of the cascaded energy storage converter grid-connected system of the present invention is as follows: Figure 1 As shown in the figure, the cascade energy storage converter adopts a three-phase star-type cascade H-bridge structure and has the ability to directly connect to high voltage. This structure has the ability to directly connect to high voltage, which helps to achieve high efficiency and flexibility, making it suitable for large-capacity applications.

[0029] Specifically, each phase is composed of a filter inductor and N energy storage modules in series. The energy storage modules have the same structure, including an H bridge, a filter circuit, and a series battery cluster as an energy storage power source arranged in sequence.

[0030] 2. If Figure 2 As shown, the inertial damping optimization method of the cascaded energy storage converter adapted to multiple power grid conditions of the present invention comprises the following steps:

[0031] (1) Grid-connected system modeling

[0032] The grid-connected converter system model is established based on Kirchhoff's law and small signal, and the grid-connected system transfer function is derived as a system model for analyzing transfer characteristics and step response.

[0033] The parameters used in system modeling include grid parameters, converter parameters and control parameters; among them, grid parameters include short-circuit ratio, grid voltage and grid angular frequency; converter parameters include rated power and rated output voltage; control parameters include inertia coefficient and damping coefficient.

[0034] The transfer function is specifically shown as follows:

[0035]

[0036] Where G(s) is the transfer function; V0 is the rated output voltage of the converter; V g is the grid voltage; SCR is the short-circuit ratio; P0 is the rated power of the converter; J is the inertia coefficient; ω0 is the grid voltage angular frequency; s is the Laplace operator; and D is the damping coefficient.

[0037] (2) Inertia parameter optimization

[0038] Use the transfer function to draw the root locus diagram of the grid-connected system, draw the equal damping line in it, and record the inertia coefficient corresponding to the intersection of the root locus and the equal damping line; then draw the Bode diagram based on the inertia coefficient and the system model, and confirm the optimal inertia coefficient based on the phase margin requirement of the grid-connected system; specifically include:

[0039] First, set the initial damping coefficient D1, and use the transfer function constructed in step (1) to draw the root locus diagram; draw equal damping lines with specific damping ratios in the root locus diagram, and record the inertia coefficient corresponding to the intersection of the root locus and the equal damping line, which is recorded as J1; then, draw the Bode diagram based on the inertia coefficient J1 and the system model, and check whether J1 meets the phase margin condition based on the phase margin requirement of the grid-connected system; if the phase margin meets the requirement, confirm that J1 is the most preferred inertia coefficient Jx; if the phase margin does not meet the requirement, gradually reduce the value of the inertia coefficient by 5% until it meets the requirement, and use the inertia coefficient J2 at this time as the most preferred inertia coefficient Jx.

[0040] (3) Damping parameter optimization

[0041] First, set the damping adjustment step length D0, and gradually increase the damping coefficient from the minimum damping coefficient D1 to the maximum damping coefficient D2; combine the system model constructed in step (1) and the optimal inertia coefficient Jx in step (2), and draw the step response curve under each damping parameter. Then, by analyzing each step response curve and combining the dynamic characteristics requirements of the system, obtain the maximum damping coefficient of the grid-connected system when meeting the response time and overshoot requirements, and use it as the optimal damping coefficient Dx.

[0042] (4) Parameter design under multiple power grid conditions

[0043] The grid conditions can be divided into three levels according to the short circuit ratio (SCR): strong grid (SCR>3), weak grid (3≥SCR>1.5) and very weak grid (1.5≥SCR). In order to adapt to different grid strengths, the parameters are designed by the following method:

[0044] First, set the short-circuit ratio adjustment step length S0 so that SCR gradually increases from 1 to the maximum short-circuit ratio SCR max , determine multiple short-circuit ratio conditions; then, under each short-circuit ratio condition, repeat the operations of steps (1) to (3) to obtain the optimal inertia coefficient and the optimal damping coefficient under different grid strength conditions, and build a control parameter library; on this basis, perform linear interpolation fitting to obtain the inertia coefficient optimization parameter curve and the damping optimization parameter curve under different short-circuit ratio conditions.

[0045] 3. After obtaining the above-mentioned inertia coefficient optimization parameter curve and damping optimization parameter curve, they can be further used to realize the inertia damping optimization control method of the cascade energy storage converter that adapts to multiple power grid conditions. Specifically, based on the previous optimization method, the optimized control parameters are further used to control the cascade energy storage converter; including:

[0046] During the inverter grid-connected process, the corresponding inertia coefficient optimization parameter curve and damping optimization parameter curve are selected according to the real-time SCR value of the system power grid; then the control parameters corresponding to each curve are used to control the operation of the cascade energy storage inverter, so that the grid-connected system can maintain stability and good dynamic response under various power grid conditions.

[0047] The present invention adopts a virtual synchronous machine control strategy as a voltage source type control. By simulating the inertia and damping characteristics of traditional synchronous machines, the virtual synchronous machine control strategy can significantly improve the dynamic response capability and stability of the grid-connected system, effectively support the frequency and voltage regulation of the grid, and especially adapt to the operation requirements under different grid strengths.

[0048] 4. In the high-voltage direct-mounted cascade energy storage system of the present invention, its controller module includes a processor and a computer-readable storage medium, and a computer program is stored on the computer-readable storage medium; when the computer program is executed by the processor, it can implement the optimization method or control method as described above.

[0049] Part II: A specific application example

[0050] In this example, the circuit topology and control model of the converter grid-connected system are constructed in the PLECS simulation software to verify the specific feasibility and corresponding technical effects of the present invention.

[0051] Figure 1The main circuit topology diagram of the grid-connected system of the cascaded energy storage inverter implemented in the present invention adopts a three-phase star-type cascaded H-bridge structure. In this example, each phase is composed of a filter inductor and 40 energy storage modules in series. The structure of each energy storage module is the same, including an H-bridge, a filter circuit, and a series battery cluster (composed of 300 cells in series, each cell has a rated voltage of 3.2V and a rated capacity of 280Ah) arranged in sequence as an energy storage power source. The operating conditions are set as follows: grid voltage 20.2kV, grid frequency 50Hz, and the rated power of the cascaded energy storage inverter is 10MVA.

[0052] In this example, the control parameter design conditions are set as follows: the system phase margin condition is that the phase margin is not less than 20 degrees, the damping adjustment step D0 is 1, the initial damping coefficient D1 is 1, the maximum damping coefficient D2 is 200, the response time requirement is not more than 500ms, the overshoot requirement is not higher than 5%, the short-circuit ratio adjustment step S0 is 0.25, and the maximum short-circuit ratio SCRmax is 4.

[0053] Figure 2 It is a flowchart of the inertial damping parameter optimization process of the present invention, and its specific implementation steps are as follows:

[0054] (1) Grid-connected system modeling

[0055] According to the set grid parameters and cascade energy storage converter parameters, the overall transfer function model of the grid-connected system is established as a system model for analyzing transfer characteristics and step response;

[0056] Derived by Kirchhoff's law and small signal modeling method, the transfer function G(s) of the grid-connected system is obtained as follows:

[0057]

[0058] Where G(s) is the transfer function; V0 is the rated output voltage of the converter; V g is the grid voltage; SCR is the short-circuit ratio; P0 is the rated power of the converter; J is the inertia coefficient; ω0 is the grid voltage angular frequency; s is the Laplace operator; and D is the damping coefficient.

[0059] (2) Inertia parameter optimization

[0060] Using the transfer function and the initial damping coefficient D1, plot the root locus and Bode plots.

[0061] First, the inertia coefficient J1 when the damping ratio is 0.707 is determined through the root locus diagram, and then the inertia coefficient is optimized in combination with the phase margin requirement. If J1 meets the condition that the phase margin is not less than 20 degrees, the inertia coefficient Jx = J1 is preferred; if not, the inertia coefficient is gradually reduced by 5% until the requirement is met, and the inertia coefficient at this time is recorded as J2, and Jx = J2.

[0062] (3) Damping parameter optimization

[0063] Combined with the optimal inertia coefficient Jx, by setting the damping adjustment step D0 = 1, the damping coefficient D is gradually increased from 0 to the maximum damping coefficient D2 = 200; based on the system model and combined with the optimal inertia coefficient, the step response curves under each damping parameter are drawn respectively. Combined with the dynamic characteristics requirements of the grid-connected system, by analyzing each step response curve, the maximum damping coefficient that meets the converter response time and overshoot requirements is obtained, and it is used as the optimal damping coefficient Dx.

[0064] (4) Parameter design under multiple power grid conditions

[0065] With S0 as the step length, gradually increase SCR from 1 to the maximum short-circuit ratio SCR max Under each SCR condition, the above optimization steps are repeated to build the inertia and damping control parameter library under different grid strength conditions, and the optimized parameter curve is obtained through linear interpolation fitting.

[0066] (5) Control under multiple power grid conditions

[0067] According to the SCR value of the current system power grid, the corresponding inertia coefficient optimization parameter curve and damping optimization parameter curve are selected; then the control parameters corresponding to each curve are used in the virtual synchronous machine control strategy as a voltage source type control to ensure the stability and dynamic response of the converter under various power grid conditions.

[0068] Figure 3 The power step response waveforms of the method of the present invention under different grid strength conditions are shown. The results show that the system can achieve stable operation under different grid operating conditions (SCR = 1.3 and 3.3) and has good dynamic response.

Claims

1. A method for optimizing inertial damping of a cascaded energy storage converter adapted to multiple power grid conditions, characterized in that: The following steps are involved: (1) Grid-connected system modeling The grid-connected converter system model is established based on Kirchhoff's law and small signal, and the grid-connected system transfer function is derived as a system model for analyzing transfer characteristics and step response. (2) Inertia parameter optimization Draw a root locus diagram of the grid-connected system using the transfer function, draw an equal damping line in it, and record the inertia coefficient corresponding to the intersection of the root locus and the equal damping line; then draw a Bode diagram based on the inertia coefficient and the system model in step (1), and confirm the most preferred inertia coefficient based on the phase margin requirement of the grid-connected system; (3) Damping parameter optimization Combine the system model and the optimal inertia coefficient to draw the step response curve under different damping coefficients; by analyzing each step response curve and combining the dynamic characteristics requirements of the converter, obtain the maximum damping coefficient of the grid-connected system when meeting the response time and overshoot requirements, and use it as the optimal damping coefficient; (4) Parameter design under multiple power grid conditions The short circuit ratio adjustment step is set, and multiple short circuit ratio conditions that gradually increase to the maximum short circuit ratio are determined; then, under each short circuit ratio condition, the operation contents of steps (1) to (3) are repeatedly performed to obtain the most preferred inertia coefficient and the best damping coefficient under different grid strength conditions, and a control parameter library is constructed; on this basis, linear interpolation fitting is performed to obtain the inertia coefficient optimization parameter curve and the damping optimization parameter curve under different short circuit ratio conditions.

2. The method according to claim 1, characterized in that In the step (1), the parameters used in system modeling include grid parameters, converter parameters and control parameters; wherein the grid parameters include short-circuit ratio, grid voltage and grid angular frequency; the converter parameters include rated power and rated output voltage; and the control parameters include inertia coefficient and damping coefficient.

3. The method according to claim 1, characterized in that The transfer function described in step (1) is specifically as follows: Where G(s) is the transfer function; V0 is the rated output voltage of the converter; V g is the grid voltage; SCR is the short-circuit ratio; P0 is the rated power of the converter; J is the inertia coefficient; ω0 is the grid voltage angular frequency; s is the Laplace operator; and D is the damping coefficient.

4. The method according to claim 1, characterized in that The step (2) specifically comprises: First, set the initial damping coefficient D1, and use the transfer function of the grid-connected system to draw the root locus diagram; draw equal damping lines with specific damping ratios in the root locus diagram, and record the inertia coefficient corresponding to the intersection of the root locus and the equal damping line, which is recorded as J1; Then, a Bode diagram is drawn based on the inertia coefficient J1 and the system model, and according to the phase margin requirements of the grid-connected system, it is checked whether J1 meets the phase margin conditions; if the phase margin meets the requirements, J1 is confirmed as the most preferred inertia coefficient; if the phase margin does not meet the requirements, the value of the inertia coefficient is gradually reduced by 5% until it meets the requirements, and the inertia coefficient J2 at this time is taken as the most preferred inertia coefficient.

5. The method according to claim 1, characterized in that When drawing the step response curve in step (3), first set the damping adjustment step length, and gradually increase the damping coefficient from the minimum damping coefficient to the maximum damping coefficient; Based on the system model and the optimal inertia coefficient, the step response curves under each damping parameter are drawn respectively.

6. The method according to claim 1, characterized in that The cascade energy storage converter adopts a star-type cascade H-bridge structure and has the capability of high voltage direct connection.

7. A cascade energy storage converter inertial damping optimization control method adapted to multiple power grid conditions, characterized in that: Based on the method described in any one of claims 1 to 6, the cascaded energy storage converter is further controlled by using the optimized control parameters; specifically comprising: During the inverter grid-connected process, the corresponding inertia coefficient optimization parameter curve and damping optimization parameter curve are selected according to the real-time SCR value of the system power grid; then the control parameters corresponding to each curve are used to control the operation of the cascade energy storage inverter, so that the grid-connected system can maintain stability and good dynamic response under various power grid conditions.

8. The method according to claim 7, characterized in that The control method adopts the virtual synchronous machine control strategy as voltage source type control, which has the ability to simulate the inertia and damping characteristics of traditional synchronous machines.

9. A high-voltage direct-mounted cascade energy storage system capable of achieving inertial damping optimization control, characterized in that: The cascade energy storage system has a three-phase star structure, each phase consists of a filter reactor L f and N energy storage modules connected in series; each energy storage module has the same structure, including an H-bridge, a filter circuit, and a series battery cluster as an energy storage power source arranged in sequence; The controller module of the energy storage system includes a processor and a computer-readable storage medium, on which a computer program is stored; when the computer program is executed by the processor, it can implement the optimization method or control method as described in any one of claims 1 to 8.

Images