Network configuration type converter transient synchronous stability improvement and analysis method considering virtual impedance effect
Patent Information
- Application Number
- CN202311316313.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-10
- Publication Date
- 2026-10-30
- Estimated Expiration
- 2043-10-10
AI Technical Summary
但当电网发生故障时，虚拟同步机控制的构网型变流器会出现暂态同步失稳问题，威胁电网安全可靠运行
[0035]本发明针对现有构网型变流器在暂态同步稳定性方面存在的问题，设计了全新的无功功率环改进控制方法，克服了在采用相同能量函数构建方法的情况下，计及虚拟阻抗的构网型变流器系统阻尼符号无法确定的情况，实现了计及虚拟阻抗作用的构网型变流器暂态同步稳定性的提升，从而有效提高了构网型变流器运行的稳定性。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of transient stability control and analysis of grid-type converters, specifically to a method for improving and analyzing transient synchronous stability of grid-type converters that takes into account the effect of virtual impedance. Background Technology
[0002] New energy power generation systems are connected to the grid via converters. Their advantage lies in complete controllability; power conversion and transmission can be achieved through different control methods depending on the characteristics of the renewable energy source and the strength of the grid. For grid-connected converters, methods such as droop control or virtual synchronous machine control can be used to provide relatively stable voltage and frequency.
[0003] Virtual synchronous machine (VSM) control, by simulating the external characteristics of synchronous generators, can provide inertial support for the power grid and has become a research hotspot in recent years. However, when a grid fault occurs, the grid-type converter controlled by VSM may experience transient synchronization instability, threatening the safe and reliable operation of the power grid. Moreover, considering the effect of virtual impedance, the change in the energy function of the grid-type converter causes the system damping to no longer maintain a non-negative state. Therefore, when using the same energy function construction method, a new and improved control method is needed.
[0004] Therefore, how to improve the control method to effectively enhance the transient synchronization stability of grid-type converters and ensure that the system damping corresponding to the energy function constructed after the improved control is non-negative is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0005] To address the problems of transient synchronization stability in existing grid-type converters, this invention proposes a method for improving and analyzing transient synchronization stability of grid-type converters that takes into account the effect of virtual impedance. The aim is to improve the transient stability of grid-type converters after a fault and construct a non-negative energy function for system damping, thereby improving the operational stability of grid-type converters.
[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:
[0007] The present invention provides a method for improving and analyzing transient synchronous stability of a grid-type converter that takes into account the effect of virtual impedance. The method includes the following steps:
[0008] S1: Taking into account virtual impedance to eliminate the equivalent resistance of the large power grid, achieving power decoupling, and thus constructing the grid-type converter energy function considering the effect of virtual impedance:
[0009] The grid-type converter uses virtual synchronous machine control, and thus the active power P and reactive power Q of the grid-type converter can be obtained using equation (1):
[0010]
[0011] In equation (1), E' represents the virtual voltage output by the grid-connected converter; U g Represents the grid voltage; δ' is the virtual phase angle difference between the grid-connected converter and the grid; B t G represents the equivalent conductance of the large power grid after adding virtual impedance; tv B represents the virtual equivalent conductance formed by the ratio of the virtual resistance to the square of the equivalent impedance of the main power grid after adding the virtual impedance. tv The virtual equivalent susceptance is formed by the ratio of the virtual reactance to the square of the equivalent impedance of the large power grid after adding the virtual impedance.
[0012] The simplified third-order dynamic model is constructed using equation (2):
[0013]
[0014] In equation (2), and Let δ', representing the first and second derivatives of the virtual phase angle difference δ' between the grid-connected converter and the grid with respect to time, respectively; ω0 and ω g ω' represents the reference angular velocity and the main grid angular velocity, respectively; J is the virtual angular velocity of the grid-type converter; P0 and Q0 are the reference active power and reference reactive power, respectively; E0 is the rated output voltage of the grid-type converter. Let D be the time derivative of the virtual voltage E' output by the grid-connected converter; D, D p and D q These are the equivalent damping coefficient, active power loop droop coefficient, and reactive power loop droop coefficient, respectively; K q It is the voltage loop integral constant;
[0015] Using equation (3), we construct the energy function V0(δ′,ω′,E′) that takes into account the effect of virtual impedance:
[0016]
[0017] In equation (3), α is a constant;
[0018] Using equation (4), we obtain the total differential of the energy function V0(δ′,ω′,E′) with respect to the three state variables δ′, ω′, and E′.
[0019]
[0020] In equation (4), V0(δ′,ω′,E′) is simplified to V0, then and Let V0 represent the differential of V0 with respect to δ', the differential of V0 with respect to ω', and the differential of V0 with respect to E', respectively.
[0021] S2: Improve the reactive power loop of the grid-type converter to enhance its transient synchronization stability.
[0022] Using equation (5), a simplified third-order dynamic model is constructed by adding a compensation term to the reactive power loop in equation (2):
[0023]
[0024] In equation (5), and δ″ represents the first and second derivatives of the virtual phase angle difference δ″ between the grid-type converter and the grid after the improvement of the reactive power loop, respectively; ω″ is the virtual angular velocity of the grid-type converter after the improvement of the reactive power loop. To improve the time derivative of the virtual voltage E″ of the grid-type converter output after the reactive power loop;
[0025] S3: Constructing an energy function to perform transient stability analysis on the grid-type converter with improved reactive power loop:
[0026] The energy function V(δ″,ω″,E″) after the improvement of the reactive power loop is constructed using equation (6):
[0027]
[0028] Simplify V(δ″,ω″,E″) to V, and then use equation (7) to obtain the differential of V with respect to δ″. The differential of V with respect to ω″ and the differential of V with respect to E″
[0029]
[0030] Using equation (8), we obtain the total differential of the energy function V(δ″,ω″,E″) with respect to the three state variables δ″, ω″, and E″. Used to characterize the stability of grid-type converters after improving the reactive power loop:
[0031]
[0032] The present invention provides an electronic device, including a memory and a processor, wherein the memory is used to store a program that supports the processor in executing the transient synchronization stability improvement and analysis method of the grid-type converter, and the processor is configured to execute the program stored in the memory.
[0033] The present invention discloses a computer-readable storage medium on which a computer program is stored, wherein the computer program, when executed by a processor, performs the steps of the transient synchronization stability improvement and analysis method for the grid-type converter.
[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0035] This invention addresses the problem of transient synchronization stability in existing grid-type converters by designing a novel improved reactive power loop control method. This method overcomes the situation where the damping sign of a grid-type converter system considering virtual impedance cannot be determined when using the same energy function construction method. It improves the transient synchronization stability of the grid-type converter considering the effect of virtual impedance, thereby effectively enhancing the operational stability of the grid-type converter. Attached Figure Description
[0036] Figure 1 A schematic diagram of a grid-connected converter that incorporates a virtual impedance strategy according to this invention.
[0037] Figure 2 The control block diagram of the grid-type converter with virtual impedance virtual synchronous machine control introduced in this invention;
[0038] Figure 3 This is a diagram showing the potential energy distribution of the unimproved reactive power loop when the kinetic energy is 0, according to the present invention.
[0039] Figure 4 This is a system potential energy distribution diagram of the improved reactive power loop of the present invention when the kinetic energy is 0;
[0040] Figure 5 The figure shows the simulation results of the inverter output voltage change before and after the fault when the reactive power loop is not improved in this invention.
[0041] Figure 6 The figure shows the simulation results of the inverter output power change before and after the fault when the reactive power loop is not improved in this invention.
[0042] Figure 7 This is a dynamic response diagram of the active power sharing ratio of a ring flexible interconnected microgrid group under light load access according to the present invention.
[0043] Figure 8 This is a dynamic response diagram of the active power sharing ratio of a ring-shaped flexible interconnected microgrid group under heavy load access according to the present invention. Detailed Implementation
[0044] In this embodiment, a method for improving and analyzing the transient synchronous stability of a grid-type converter that takes into account the effect of virtual impedance is characterized by including the following steps:
[0045] S1: Taking into account virtual impedance to eliminate the equivalent resistance of the large power grid, achieving power decoupling, and thus constructing the grid-type converter energy function considering the effect of virtual impedance:
[0046] In this embodiment, the grid-connected schematic diagram of the grid-connected converter considering the virtual impedance strategy is shown below. Figure 1 As shown, the grid-type converter uses virtual synchronous machine control. Equation (9) is the equivalent impedance of the power grid after the virtual impedance is added to the grid-type converter:
[0047]
[0048] In equation (9), r v For the added virtual resistance, x v For the added virtual reactance; R g and X g These are the equivalent resistance and equivalent reactance of the power grid before the addition of the virtual impedance, R. t and X t These are the equivalent resistance and equivalent reactance of the power grid after adding virtual impedance, respectively.
[0049] The control block diagram of a grid-type converter with virtual impedance-based virtual synchronous machine control is shown below. Figure 2 As shown, the active power P and reactive power Q of the grid-type converter controlled by the virtual synchronous machine are obtained using equation (10):
[0050]
[0051] In equation (10), E' represents the virtual voltage of the grid-type converter output; U g Represents the grid voltage; δ' is the virtual phase angle difference between the grid-connected converter and the grid; B t This represents the equivalent conductance of the large power grid after adding virtual impedance, i.e. G tv B represents the virtual equivalent conductance formed by the ratio of the virtual resistance to the square of the equivalent impedance of the main power grid after adding the virtual impedance. tv The virtual equivalent susceptance is formed by the ratio of the virtual reactance to the square of the equivalent impedance of the large power grid after adding the virtual impedance.
[0052] Equation (11) is a simplified third-order dynamic model:
[0053]
[0054] In equation (11), and Let δ', representing the first and second derivatives of the virtual phase angle difference δ' between the grid-connected converter and the grid with respect to time, respectively; ω0 and ω gω' represents the reference angular velocity and the main grid angular velocity, respectively; J represents the virtual angular velocity of the grid-type converter; P0 and Q0 represent the reference active power and reference reactive power, respectively; E0 represents the rated output voltage of the grid-type converter. Let D be the time derivative of the virtual voltage E' at the output of the grid-connected converter; D, D p and D q These are the equivalent damping coefficient, active power loop droop coefficient, and reactive power loop droop coefficient, respectively; K q is the voltage loop integral constant.
[0055] Using equation (12), we construct the energy function V0(δ′,ω′,E′) that takes into account the effect of virtual impedance:
[0056]
[0057] In equation (12), α is a constant.
[0058] Using equation (13), we obtain the total differential of the energy function V0(δ′,ω′,E′) with respect to the three state variables δ′, ω′, and E′.
[0059]
[0060] In equation (13), V0(δ′,ω′,E′) is simplified to V0. and Let V0 represent the differentials of V0 with respect to δ', V0 with respect to ω', and V0 with respect to E', respectively. Clearly, the sign of the global damping of the system cannot be determined. Therefore, it is necessary to propose an improved control method to maintain non-negative damping of the system while using the same energy function construction method. The potential energy distribution diagram of the unimproved reactive power loop when the kinetic energy is 0, i.e., ω = ω0, is shown below. Figure 3 As shown.
[0061] S2: Improve the reactive power loop of the grid-type converter to enhance its transient synchronization stability.
[0062] Based on the part in equation (13) where the sign cannot be determined, a compensation term needs to be added to change the system damping. However, the construction of the energy function is often quite complex. In this embodiment, a method of adding a compensation term to the reactive power loop and then improving the energy function is adopted. A simplified third-order dynamic model after adding a compensation term to the reactive power loop in equation (11) is constructed using equation (14):
[0063]
[0064] In equation (14), and δ″ represents the first and second derivatives of the virtual phase angle difference δ″ between the grid-type converter and the grid after the improved reactive power loop, respectively; ω″ is the virtual angular velocity of the grid-type converter after the improved reactive power loop. To improve the time derivative of the virtual voltage E″ of the reactive power loop back-grid converter.
[0065] S3: Constructing an energy function to perform transient stability analysis on the grid-type converter with improved reactive power loop:
[0066] The energy function V(δ″,ω″,E″) after the improvement of the reactive power loop is constructed using equation (15):
[0067]
[0068] Simplify V(δ″,ω″,E″) to V, and use equation (16) to obtain the differential of V with respect to δ″. The differential of V with respect to ω″ and the differential of V with respect to E″
[0069]
[0070] Using equation (17), the total differential V(δ″,ω″,E″) with respect to the three state variables δ″, ω″, and E″ is obtained, which is used to characterize the stability of the grid-type converter after the improvement of the reactive power loop:
[0071]
[0072] Clearly, the global damping of the system is non-negative, and the grid-type converter with the improved reactive power loop is an energy-dissipating system. This indicates that during short-circuit fault recovery, if the system state is within the attraction domain, the transient synchronous stability of the system can be guaranteed. The potential energy distribution diagram of the system with the improved reactive power loop when the kinetic energy is 0 is shown below. Figure 4 As shown, the system has a stable equilibrium point and an unstable equilibrium point. The system can only be stable at the stable equilibrium point.
[0073] In this embodiment, an electronic device includes a memory and a processor. The memory stores a program that supports the processor in executing the above-described method, and the processor is configured to execute the program stored in the memory.
[0074] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the above method.
[0075] To verify the effectiveness of the hierarchical control method proposed in this invention, a system as described above was built in Matlab / Simulink. Figure 1 The simulation model shown employs a virtual synchronous machine control for the grid-type converter and considers the power decoupling effect of virtual impedance. A three-phase short-circuit fault is assumed to occur in the power grid at t=5s, causing the grid voltage to drop to 0.55pu, and the fault lasts for 0.5s. The transient synchronous stability of the system is compared and analyzed under the conditions of no improvement to the reactive power loop and improved reactive power loop.
[0076] Operating Condition 1: No improvement to the reactive power loop;
[0077] Before the fault occurred, the inverter output voltage was constant, and the system was operating normally. At t=5s, the fault occurred, the grid voltage dropped, causing a sharp drop in the inverter output voltage. At this time, the active power output decreased, and the reactive power output increased. The fault was cleared at t=5.5s, but the inverter voltage, output active power, and output reactive power all entered an oscillating state and could not return to the pre-fault levels. The simulation results of the inverter output voltage changes before and after the fault without improving the reactive power loop are as follows: Figure 5 As shown, the simulation results of the inverter output power change before and after the fault without improving the reactive power loop are as follows: Figure 6 As shown.
[0078] Operating Condition 2: Improved reactive power loop;
[0079] Before the fault occurred, the inverter output voltage was constant, and the system was operating normally. At t=5s, the fault occurred, the grid voltage dropped, causing a sharp drop in the inverter output voltage. At this time, the active power output decreased, and the reactive power output increased. However, due to the improvement of the reactive power loop, the fluctuations in active and reactive power were smaller than in condition 1, and the stability of the inverter during the fault duration was improved. At t=5.5s, the fault was cleared, but the inverter voltage, output active power, and output reactive power all returned to their pre-fault levels. The simulation results of the inverter output voltage changes before and after the fault with the improved reactive power loop are as follows: Figure 7 As shown, the simulation results of the inverter output power change before and after the fault in the improved reactive power loop are as follows: Figure 8 As shown.
[0080] Simulation results show that the proposed transient synchronization stability enhancement control method for grid-type converters, which takes into account the effect of virtual impedance, can effectively improve the transient synchronization stability of the grid-type converter when activated, thereby significantly enhancing the operational stability of the grid-type converter. The effectiveness of the proposed method has been well demonstrated.
Claims
1. A method for improving and analyzing transient synchronous stability of a grid-type converter, taking into account the effect of virtual impedance, characterized in that, Includes the following steps: S1: Taking into account virtual impedance to eliminate the equivalent resistance of the large power grid, achieving power decoupling, and thus constructing the grid-type converter energy function considering the effect of virtual impedance: The grid-type converter uses virtual synchronous machine control, and thus the active power P and reactive power Q of the grid-type converter can be obtained using equation (1): In equation (1), E' represents the virtual voltage output by the grid-connected converter; U g Represents the grid voltage; δ' is the virtual phase angle difference between the grid-connected converter and the grid; B t G represents the equivalent conductance of the large power grid after adding virtual impedance; tv B represents the virtual equivalent conductance formed by the ratio of the virtual resistance to the square of the equivalent impedance of the main power grid after adding the virtual impedance. tv The virtual equivalent susceptance is formed by the ratio of the virtual reactance to the square of the equivalent impedance of the large power grid after adding the virtual impedance. The simplified third-order dynamic model is constructed using equation (2): In equation (2), and Let δ', representing the first and second derivatives of the virtual phase angle difference δ' between the grid-connected converter and the grid with respect to time, respectively; ω0 and ω g ω' represents the reference angular velocity and the main grid angular velocity, respectively; J is the virtual angular velocity of the grid-type converter; P0 and Q0 are the reference active power and reference reactive power, respectively; E0 is the rated output voltage of the grid-type converter. Let D be the time derivative of the virtual voltage E' output by the grid-connected converter; D, D p and D q These are the equivalent damping coefficient, active power loop droop coefficient, and reactive power loop droop coefficient, respectively; K q It is the voltage loop integral constant; Using equation (3), we construct the energy function V0(δ′,ω′,E′) that takes into account the effect of virtual impedance: In equation (3), α is a constant; Using equation (4), we obtain the total differential of the energy function V0(δ′,ω′,E′) with respect to the three state variables δ′, ω′, and E′. In equation (4), V0(δ′,ω′,E′) is simplified to V0, then and Let V0 represent the differential of V0 with respect to δ', the differential of V0 with respect to ω', and the differential of V0 with respect to E', respectively. S2: Improve the reactive power loop of the grid-type converter to enhance its transient synchronization stability. Using equation (5), a simplified third-order dynamic model is constructed by adding a compensation term to the reactive power loop in equation (2): In equation (5), and δ” represents the first and second derivatives of the virtual phase angle difference δ” between the grid-type converter and the grid after the improvement of the reactive power loop, respectively; ω” is the virtual angular velocity of the grid-type converter after the improvement of the reactive power loop; To improve the time derivative of the virtual voltage E” of the grid-type converter output after the reactive power loop; S3: Constructing an energy function to perform transient stability analysis on the grid-type converter with improved reactive power loop: The energy function V(δ″,ω″,E″) after the improvement of the reactive power loop is constructed using equation (6): Simplify V(δ″,ω″,E″) to V, and then use equation (7) to obtain the differential of V with respect to δ″. The differential of V with respect to ω” The differential of V with respect to E Using equation (8), we obtain the total differential of the energy function V(δ″,ω″,E″) with respect to the three state variables δ″, ω″, and E″. Used to characterize the stability of grid-type converters after improving the reactive power loop:
2. An electronic device, comprising a memory and a processor, characterized in that, The memory is used to store programs that support the processor in executing the transient synchronization stability improvement and analysis method for the grid-type converter as described in claim 1, and the processor is configured to execute the programs stored in the memory.
3. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is run by the processor, it executes the steps of the transient synchronization stability improvement and analysis method for the grid-type converter as described in claim 1.