Method for enhancing operation stability of weak power grid of network-forming converter based on additional stabilizer design

Abstract

The invention discloses an additional stabilizer design-based weak power grid operation stability enhancement method for a network construction type converter, and belongs to the technical field of stability analysis and control of a new energy power system. The method comprises the following steps: constructing a network construction type converter overall control structure of a network construction type converter grid-connected system by adopting a virtual synchronous control method, and constructing an optimization strategy of an additional stabilizer of the network construction type converter overall control structure, and the stability control voltage output of the power system is completed through the overall control structure of the network-forming converter added with the optimization strategy. According to the method provided by the invention, the problem of low-frequency oscillation under a weak power grid condition can be effectively suppressed on the premise of not changing a main body control framework of the network construction type converter. The design method not only improves the overall stability and dynamic performance of the grid-connected system of the network-forming converter, but also can provide theoretical basis and engineering reference for control parameter optimization and system stability design under the weak network condition.

Description

Technical Field

[0001] This invention belongs to the field of stability analysis and control technology of new energy power systems, and more specifically, relates to a method for enhancing the stability of grid-type converters operating in weak power grids based on the design of additional stabilizers. Background Technology

[0002] To alleviate the resource and environmental pressures caused by fossil fuel consumption and reduce greenhouse gas emissions, the traditional power system, dominated by thermal and hydropower, is gradually transforming into a new power system led by new energy sources such as wind and solar power. This transformation not only changes the primary energy structure of the power system but also significantly impacts the functional positioning of power sources, network topology, and operational characteristics. With a large number of new energy installations connected to the grid, the new power system exhibits the "dual high" characteristics of "high proportion of new energy access" and "high proportion of power electronics," posing new challenges to the system in terms of power source grid construction capabilities, power balance regulation, and operational stability.

[0003] Unlike traditional synchronous motor systems centered on thermal power units, new energy sources such as wind and solar power typically connect to the power grid via power electronic interfaces, with voltage source converters being a typical example. Based on their synchronization method with the grid, voltage source converters are mainly divided into grid-connected converters and grid-connected converters. Existing research indicates that grid-connected converters may experience dynamic instability under strong grid conditions. To address this issue, existing research has largely focused on analyzing their instability mechanisms and proposing corresponding suppression strategies to eliminate oscillating instability under strong grid conditions. However, research on the instability mechanisms and suppression measures of grid-connected converters under weak grid conditions remains relatively scarce. Some literature points out that considering the power imbalance across the DC voltage terminals reduces their stability under weak grid conditions.

[0004] Currently, the main methods for suppressing oscillation instability in power electronic power systems fall into the following three categories: (1) The method based on control parameter adjustment improves the dynamic response and stability of the converter by optimizing the controller parameter settings. This method is simple in structure and easy to implement, and does not require changes to the system hardware configuration. However, for complex power systems with strong nonlinearity and strong coupling characteristics, it is difficult to guarantee the global optimality and coordination consistency of parameter tuning. (2) Hardware-based improvement methods enhance system stability by optimizing system topology or configuring additional hardware components. While this method can improve dynamic characteristics to some extent, it is usually costly, has limited applicability, and is not widely applicable in engineering. (3) Based on the method of control strategy improvement, the original control strategy of the system is changed by configuring additional stabilizers or improving the structure of the control loop, thereby improving the stability of the system under small disturbances. The most commonly used method is to learn from the analysis method of complex torque, optimize the damping characteristics of the system, and effectively suppress oscillation instability. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method for enhancing the stability of grid-connected converters operating in weak grid conditions based on an additional stabilizer design. This method aims to solve the problem of oscillation and instability in grid-connected converters under weak grid conditions. The invention employs an additional stabilizer to improve the system control strategy and suppress this instability. Its purpose is to increase the critical short-circuit ratio of grid-connected converters operating under weak grid conditions, maintain the safe and stable operation of the grid-connected converter system, and provide a reference for the optimized design of equipment.

[0006] To achieve the above objectives, this invention provides a method for enhancing the stability of grid-connected converters operating in weak power grids based on an additional stabilizer design, which mainly includes the following steps: A virtual synchronous control method is used to construct the overall control structure of the grid-connected converter in a grid-connected system. An optimization strategy for an additional stabilizer is constructed to build the overall control structure of the grid-type converter. This optimization strategy is used to achieve power system stability control voltage output through the overall control structure of the grid-type converter. The additional stabilizer is introduced at the output phase angle of the virtual synchronization control loop, and its transfer function is:

[0007] in, T ω The time constant of the filtering stage. K e This is the proportional coefficient of the filtering stage. m Let the order of the phase compensation circuit be denoted as . α、T These are the parameters for the phase compensation stage. K 1. K 2 represents the isolation coefficient for the isolation process.

[0008] Furthermore, the order of the additional stabilizer phase compensation stage... m It depends on the lag phase value obtained from the Bode plot of the closed-loop transfer function. θ h .

[0009]

[0010] The symbol [ ] represents rounding up, which means increasing a value to the nearest integer larger than it.

[0011] Additional stabilizer phase compensation parameters α、T。

[0012]

[0013] Additional stabilizer filter element time constant T ω and proportionality coefficient K e 。T ω This is the time constant of the filtering stage. T ω The design must ensure that signals with a certain oscillation frequency can pass through the filtering stage. Therefore, the cutoff frequency is 1 / T ω The bandwidth should be less than the bandwidth required to satisfy the system's time scale, ensuring that all compatible oscillation frequencies can pass through the filtering stage. To select suitable parameters, the oscillation suppression effect will be iteratively compared until the final proportional coefficient is determined. K e .

[0014] Additional stabilizer isolation coefficient K 1. K 2. To ensure the stabilizer has a good damping effect, the selection is usually based on a comprehensive consideration of the values ​​of various parameters of the actual system.

[0015] The present invention also provides an electronic device, comprising: a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the above-described method.

[0016] The present invention also provides a computer-readable storage medium storing computer instructions for causing a processor to perform the above-described method.

[0017] The present invention also provides a computer program product, including a computer program or instructions that, when executed by a processor, implement the above-described method.

[0018] Overall, compared with the prior art, the improved control strategy proposed by this invention has a more significant effect on oscillation suppression. This invention proposes a method to improve the stability of grid-type converters operating in weak power grids based on the design of additional stabilizers. By adjusting the control strategy of the additional stabilizers, the dynamic stability performance of grid-type converters under weak power grid conditions is improved, providing a feasible technical path for the safe and stable operation of new power systems. Attached Figure Description

[0019] Figure 1 A schematic diagram of the overall structure of an additional stabilizer in a grid-connected system for a grid-connected converter.

[0020] Figure 2 This is a schematic diagram of the design method for an additional stabilizer to suppress instability in weak power grids for grid-type converters proposed in this invention.

[0021] Figure 3 Bode plot comparison of port closed-loop transfer function of grid-connected converter system under weak grid conditions with and without additional stabilizer.

[0022] Figure 4 A comparison of the changes in characteristic roots of a grid-connected converter system before and after configuring an additional stabilizer.

[0023] Figure 5 The active power dynamic response waveform diagram after configuring an additional stabilizer for a grid-connected system of a grid-connected converter. Detailed Implementation

[0024] To make the objectives, core technical solutions, and advantages of this invention clearer, the invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments described below are only used to illustrate the technical principles and implementation methods of this invention, and are not intended to limit its scope of protection. Furthermore, the various technical features involved in different embodiments of this invention can be arbitrarily combined and extended in application, provided there is no logical conflict.

[0025] To address the issue of dynamic instability that grid-connected converters are prone to in weak grid environments, this invention proposes a method for enhancing the stability of grid-connected converters in weak grid conditions, based on an additional stabilizer. This includes: A virtual synchronous control method is used to construct the overall control structure of the grid-connected converter in a grid-connected system. An optimization strategy for an additional stabilizer is constructed to build the overall control structure of the grid-type converter. This optimization strategy is used to achieve power system stability control voltage output through the overall control structure of the grid-type converter. The additional stabilizer is introduced at the output phase angle of the virtual synchronization control loop, and its transfer function is:

[0026] in, T ω The time constant of the filtering stage. K e This is the proportional coefficient of the filtering stage. m Let the order of the phase compensation circuit be denoted as . α、T These are the parameters for the phase compensation stage.K 1. K 2 represents the isolation coefficient of the isolation circuit. This scheme suppresses system oscillations and improves phase margin by configuring filtering, phase compensation, and signal isolation circuits in the converter control structure. Simultaneously, based on grid characteristics and converter dynamic response features, the parameters of the additional stabilizer are optimized, significantly improving the critical short-circuit ratio and dynamic stability margin of the system under weak grid conditions, providing technical support and design basis for safe and reliable grid-connected operation.

[0027] In the specific implementation of this invention, the effectiveness of the designed additional stabilizer was verified through simulation by establishing a dynamic model of the grid-connected system of the grid-connected converter under weak grid conditions. The instability of the grid-connected converter in weak grid conditions mainly stems from the strong coupling effect between the DC voltage control link and the synchronization link. Therefore, as... Figure 1 As shown, this invention takes a fourth-order grid-connected converter system containing the two key control loops mentioned above as the research object. The additional stabilizer outputs the phase angle signal from the synchronization element. δ GFM As input, the effective signal is extracted by the filtering module, and then processed step by step by the phase compensation module and the isolation module before being applied to the DC voltage reference command. U dcref This achieves steady-state regulation and oscillation suppression of the overall dynamic characteristics of the system. The specific implementation process is as follows: Figure 2 As shown.

[0028] By comparing the changes in the Bode plots of the closed-loop transfer functions at the input and output ports, the distribution of eigenvalues, and the time-domain response characteristics of active power in a grid-connected system with a grid-connected converter before and after configuring the additional stabilizer, the effectiveness of the additional stabilizer in improving system dynamic performance and suppressing instability in weak grid conditions can be verified. The analysis results show that after configuring the additional stabilizer, the oscillation instability phenomenon of the grid-connected converter under weak grid conditions is significantly alleviated, and the system can maintain a safe and stable operating state. Figure 3 The analysis results show that when the system is in a weak grid instability state, the Bode plot of the closed-loop transfer function at the frequency corresponding to the instability characteristic root exhibits a negative phase characteristic, indicating insufficient phase margin and significant phase lag. After configuring the additional stabilizer, the phase curve of the system within the same frequency range shifts upward to the positive phase range, showing that the additional stabilizer effectively provides phase compensation, improves the system's phase margin and damping characteristics, and enables the grid-connected system to maintain stable operation under weak grid conditions. Figure 4As shown, without an additional stabilizer, the grid-connected converter system exhibits a pair of positive characteristic roots located in the right half of the complex plane, indicating an unstable state characterized by weak grid oscillations and instability. However, when an additional stabilizer is installed, these characteristic roots shift to the left half of the imaginary axis and transform into negative characteristic roots, indicating a redistribution of system poles, improved dynamic characteristics, and thus stable operation. Figure 5 It can be seen that at 1 second, the grid-connected system under this weak grid condition was subjected to a small disturbance. At this time, the active power of the grid-connected system without an additional stabilizer exhibited oscillation and instability. However, after the additional stabilizer was installed, the originally oscillating active power waveform quickly decayed and returned to stability. Overall, the introduction of the designed additional stabilizer can significantly improve the dynamic performance of the grid-connected system of the grid-connected converter under weak grid conditions, effectively suppress the oscillation and instability of the system, and improve its critical stability level under low short-circuit ratio conditions.

[0029] In summary, this invention addresses the instability issues that easily occur in grid-connected converter systems operating in weak grid conditions by proposing a suppression and compensation method based on an additional stabilizer. This method can effectively compensate for the system phase by adjusting the distribution of system eigenvalues ​​when grid strength decreases, transforming the originally divergent oscillating dynamic response into a gradual decay process, thereby achieving steady-state recovery and dynamic stability. After adopting this method, the critical short-circuit ratio of the grid-connected converter under weak grid conditions is improved, and the system stability margin is significantly enhanced, providing a powerful technical framework for the safe and reliable operation of grid-connected systems in complex grid environments.

Claims

1. A method for enhancing the stability of a grid-connected converter operating in weak power grids based on an additional stabilizer design, characterized in that, Includes the following steps: A virtual synchronous control method is used to construct the overall control structure of the grid-connected converter in a grid-connected system. An optimization strategy for an additional stabilizer is constructed to build the overall control structure of the grid-type converter. This optimization strategy is used to achieve power system stability control voltage output through the overall control structure of the grid-type converter. The additional stabilizer is introduced at the output phase angle of the virtual synchronization control loop, and its transfer function is: in, T ω The time constant of the filtering stage. K e This is the proportional coefficient of the filtering stage. m Let the order of the phase compensation circuit be denoted as . α、 T These are the parameters for the phase compensation stage. K 1. K 2 represents the isolation coefficient for the isolation process.

2. The method for enhancing the stability of a grid-type converter operating in a weak power grid as described in claim 1, characterized in that, The overall control structure of the grid-connected converter system is constructed using a virtual synchronous control method. This structure includes: the deviation between the DC voltage and its command value is used to output the active power command value through DC voltage control, and the deviation between the active power and its command value is used to output the phase angle through virtual synchronous control.

3. The method for enhancing the stability of a grid-type converter operating in a weak power grid as described in claim 1, characterized in that, The symbol [ ] represents rounding up. θ h The magnitude of the phase jump in the Bode plot of the closed-loop transfer function corresponds to the lag phase value. ω d The imaginary part frequency value of the dominant instability eigenvalue.

4. The method for enhancing the stability of a grid-type converter operating in a weak power grid as described in claim 1, characterized in that, The time constant of the filtering stage T ω Filtering stage proportional coefficient K e Isolation coefficient of isolation process K 1. K 2. The oscillation suppression effect was obtained through repeated iterations and comparisons.

5. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1 to 4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 4.

7. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by a processor, they implement the steps of the method as described in any one of claims 1 to 4.

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