A method for designing a virtual power system stabilizer to improve stability of a VSG

Abstract

The application provides a virtual power system stabilizer design method for improving VSG stability, and the method comprises the following steps: learning from the design method of a traditional power system stabilizer, adopting a virtual PSS structure in the form of "lead-lag", taking a VSG angular frequency deviation as a period input signal, taking a power deviation as an output signal, introducing the virtual PSS into a power control link of the VSG, and building a VSG grid-connected system structure containing the virtual PSS access according to a rotor motion equation of the VSG and a virtual excitation regulator; according to the VSG grid-connected system structure containing the virtual PSS access, a corresponding Phillips-Heffron model is constructed, a transfer function of the virtual PSS connected to the VSG reactive ring is obtained, so that the defect that the traditional VSG power oscillation risk is large is overcome, the stability of the VSG grid-connected system can be effectively improved, and the robustness and superiority of the VSG control after the virtual PSS is introduced can be ensured to a certain extent.

Description

Technical Field

[0001] This invention belongs to the field of power system stability control technology, specifically relating to a design method for a virtual power system stabilizer to improve VSG stability. Background Technology

[0002] With the formation of the "dual-high" characteristics of high proportion of new energy and high proportion of power electronic equipment, the traditional power system dominated by thermal power generation is gradually transforming into a new type of power system with new energy as the main body. However, under general control methods, new energy units cannot participate in system frequency regulation, resulting in a "low inertia" characteristic of the power system, which leads to prominent stability problems in the "dual-high" power system.

[0003] In existing technologies, the VSG virtual excitation regulator causes the VSG grid-connected system to have negative damping, resulting in poor power system stability. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a design method for a virtual power system stabilizer that improves the stability of the VSG, which can compensate for the disturbance signal of the VSG virtual excitation regulator and make the damping of the VSG grid-connected system positive, thereby improving the stability of the power system and suppressing low-frequency oscillations of the power system.

[0005] To address the above problems, this invention provides a virtual power system stabilizer design method for improving VSG stability, the method comprising the following steps:

[0006] Step 1: Based on the power system stabilizer, using the VSG angular frequency deviation as the input signal and the power deviation as the output signal, the virtual PSS structure is derived;

[0007] Step 2: Introduce the virtual PSS structure into the power control stage of the VSG. Based on the rotor motion equation and virtual excitation regulator equation of the VSG, build a grid-connected VSG system structure with virtual PSS access.

[0008] Step 3: Based on the VSG grid-connected system structure with virtual PSS access, construct the Phillips-Heffron model of the VSG grid-connected system with virtual PSS access, and derive the formula for the VSG electromechanical oscillation circuit based on the Phillips-Heffron model.

[0009] Step 4: Based on the damping torque analysis of the VSG electromechanical oscillation circuit formula, determine the transfer function of the virtual PSS connected to the reactive power link to counteract the inherent negative damping of the VSG virtual excitation regulator, thereby improving the stability of the VSG grid-connected system.

[0010] Optionally, the formula for the virtual PSS structure in step one is as follows:

[0011]

[0012] In the formula, s represents the complex variable used in the Laplace transform, and G VPSS (s) is the transfer function of the virtual PSS, K VPSS T1 is the scaling factor of the virtual PSS; T1-T4 are the time constants of the corresponding lead-lag links.

[0013] The formula for the input and output relationship of the virtual PSS is as follows:

[0014] ΔQ VPSS (s)=G VPSS (s)Δω1

[0015] In the formula, s represents the complex variable used in the Laplace transform, and ΔQ VPSS (s) represents the output power deviation of the VSG, and Δω1 represents the angular frequency deviation of the input VSG.

[0016] Optionally, the VSG rotor motion equations and virtual excitation regulator equations with virtual PSS access in step two are as follows:

[0017]

[0018] In the formula, s is the complex variable used in the Laplace transform, δ1 is the VSG virtual power angle, ω0 is the grid angular frequency reference value, ω1 is the VSG virtual angular frequency, and ω g P is the rated angular frequency of the power grid. VPSS and Q VPSS These represent the active and reactive power outputs of VPSS, respectively. ref Q ref These are the active and reactive power setpoints of the VSG, respectively. P1 and Q1 are the active and reactive power outputs of the VSG, respectively. J and D are... p The inertia coefficient and damping coefficient of the VSG are respectively, K Q V1 is the gain coefficient of the reactive power controller and V2 is the voltage at the VSG port.

[0019] Optionally, the formula for the VSG electromechanical oscillation circuit in step three is as follows:

[0020]

[0021] In the formula, s is the complex variable used in the Laplace transform, Δδ1VSG is the infinitesimal increment of the virtual power angle, and J and D are... p These are the inertia coefficient and damping coefficient of the VSG, respectively; ω0 is the reference value of the grid angular frequency; K1 is the coefficient of the partial derivative of the VSG output active power with respect to the virtual power angle; T1 is the VSG damping torque coefficient; and T2 is the VSG synchronous torque coefficient.

[0022] Optionally, the transfer function formula for the virtual PSS connected after the VSG reactive power loop in step four is as follows:

[0023]

[0024] In the formula, The oscillation mode after VSG is connected to virtual PSS. For virtual PSS in oscillation mode The transfer function under D VPSS The equivalent damping torque provided by the virtual PSS to the VSG electromechanical oscillation circuit. For virtual PSS in oscillation mode The forward transfer function provides damping torque to the VSG electromechanical oscillation circuit.

[0025] Beneficial effects

[0026] The present invention provides a design method for a virtual power system stabilizer to improve VSG stability. Drawing on traditional power system stabilizer design methods, it employs a "lead-lag" virtual PSS structure, using the VSG angular frequency deviation as the input signal and the power deviation as the output signal. The virtual PSS is introduced into the VSG's power control stage, and a VSG grid-connected system structure with virtual PSS access is constructed based on the VSG's rotor motion equation and the virtual excitation regulator equation. A Phillips-Heffron model of the VSG grid-connected system with virtual PSS access is built based on this structure, and the VSG electromechanical oscillation circuit formula is derived from the Phillips-Heffron model. The transfer function of the virtual PSS connected to the reactive power link is determined based on the calculation results of the damping torque analysis method to offset the inherent negative damping of the VSG virtual excitation regulator. This invention overcomes the drawback of traditional VSG power oscillation risk, effectively improves the stability of the VSG grid-connected system, and to a certain extent ensures the robustness and superiority of VSG control after the introduction of virtual PSS.

[0027] 1) This invention addresses the potential negative damping characteristics introduced by the VSG virtual excitation regulator. By drawing on the design methods of traditional power system stabilizers, it adopts a virtual PSS structure in the form of "lead-lag" and uses the VSG angular frequency deviation as its input signal and the power deviation as its output signal, thus proposing a design method for a virtual power system stabilizer to improve the stability of the VSG.

[0028] 2) By constructing a Phillips-Heffron model of a VSG grid-connected system with virtual PSS access, this invention observes that although the reactive power control loop of the VSG can enhance the voltage regulation capability of the system, it also has a negative impact on the electromechanical oscillation loop of the VSG, reducing the stability of the VSG.

[0029] 3) This invention analyzes the VSG using the damping torque method, revealing the composition of the input signal in the electromechanical oscillation circuit of the VSG. Reasonable adjustment of the VSG's inertia coefficient, damping coefficient, and line impedance can provide a certain degree of positive damping for the system, reducing the risk of power oscillation. When the power system is subjected to different disturbances, this invention can enhance the robustness of the VSG, and it also has a certain effectiveness and superiority in improving system stability. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the VSG grid-connected system structure according to an embodiment of the present invention;

[0031] Figure 2 This is a block diagram of the VSG control loop with virtual PSS access according to an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the Phillips-Heffron model of a VSG grid-connected system with virtual PSS access according to an embodiment of the present invention.

[0033] Figure 4 This describes the active power oscillation of the VSG before and after virtual PSS access in an embodiment of the present invention. Detailed Implementation

[0034] See also Figures 1 to 4 As shown in the figure, according to an embodiment of the present invention, a design method for a virtual power system stabilizer to improve VSG stability includes the following steps:

[0035] Step 1: VSG is typically the mainstream control method for providing virtual inertia to new energy power units to improve system frequency regulation, such as... Figure 1 As shown. However, the VSG virtual excitation regulator has negative damping characteristics, resulting in poor stability of the power system with VSG access. Therefore, considering that traditional power system stabilizers generally have a "lead-lag" stage, the virtual PSS of this invention borrows from traditional power system stabilizers and also adopts a "lead-lag" structure to be connected to the power system. The general expression of the virtual PSS structure is:

[0036]

[0037] In the formula, s represents the complex variable used in the Laplace transform, and G VPSS (s) is the transfer function of the virtual PSS, K VPSS T1 represents the scaling factor of the virtual PSS; T1-T4 represent the time constants of the corresponding lead-lag elements. This structure offers advantages such as simplified modeling, ease of analysis, and lack of loss of generality.

[0038] Meanwhile, considering that traditional power system stabilizers typically use the power and frequency of transmission lines as input signals and the excitation voltage as the output signal, but this may affect the reactive power of the synchronous machine, the virtual PSS of this invention uses the VSG angular frequency deviation as its input signal and the power deviation as its output signal. The specific expression is as follows:

[0039] ΔQ VPSS (s)=G VPSS (s)Δω1

[0040] In the formula, s represents the complex variable used in the Laplace transform, and ΔQ VPSS (s) represents the output power deviation of the VSG, and Δω1 represents the angular frequency deviation of the input VSG. The virtual PSS adopts the above input-output relationship to avoid affecting the output reactive power of the VSG.

[0041] Step Two: To effectively improve the stability of the VSG system, the virtual PSS of this invention is introduced into the power control stage of the VSG. Based on the rotor motion equation and virtual excitation regulator equation of the VSG, a grid-connected VSG system structure with virtual PSS access is constructed, as follows: Figure 2 As shown. Figure 2 It can intuitively show the access location of the virtual PSS in the VSG system.

[0042] The VSG rotor motion equations and virtual excitation regulator equations, including virtual PSS access, are as follows:

[0043]

[0044] In the formula, s is the complex variable used in the Laplace transform, δ1 is the VSG virtual power angle, ω0 is the grid angular frequency reference value, ω1 is the VSG virtual angular frequency, and ω g P is the rated angular frequency of the power grid. VPSS and Q VPSS These represent the active and reactive power outputs of VPSS, respectively. ref Q ref These are the active and reactive power setpoints of the VSG, respectively. P1 and Q1 are the active and reactive power outputs of the VSG, respectively. J and D are... p The inertia coefficient and damping coefficient of the VSG are respectively, K Q V1 is the gain coefficient of the reactive power controller and V2 is the voltage at the VSG port.

[0045] Step 3: Based on the VSG grid-connected system architecture considering virtual PSS access, construct the Phillips-Heffron model of the VSG grid-connected system including virtual PSS access, such as... Figure 3As shown, the formula for the VSG electromechanical oscillation circuit is derived from the model. This step can intuitively demonstrate that a small damping torque coefficient of the VSG will have an adverse effect on the stability of the VSG.

[0046] The formula for the VSG electromechanical oscillation circuit is as follows:

[0047]

[0048] In the formula, s is the complex variable used in the Laplace transform, Δδ1VSG is the infinitesimal increment of the virtual power angle, and J and D are... p These are the inertia coefficient and damping coefficient of the VSG, respectively; ω0 is the reference value of the grid angular frequency; K1 is the coefficient of the partial derivative of the VSG output active power with respect to the virtual power angle; T1 is the VSG damping torque coefficient; and T2 is the VSG synchronous torque coefficient.

[0049] Step 4: Based on the derived VSG electromechanical oscillation circuit formula, the damping torque method is used to analyze the VSG stability problem mechanism, determine the transfer function of the virtual PSS connected to the VSG reactive power link, so as to counteract the inherent negative damping of the VSG virtual excitation regulator and achieve the purpose of effectively improving the stability of the VSG grid-connected system.

[0050] The transfer function of the virtual PSS connected after the VSG reactive power loop is:

[0051]

[0052] In the formula, The oscillation mode after VSG is connected to virtual PSS. For virtual PSS in oscillation mode The transfer function under D VPSS The equivalent damping torque provided by the virtual PSS to the VSG electromechanical oscillation circuit. For virtual PSS in oscillation mode The forward transfer function provides damping torque to the VSG electromechanical oscillation circuit.

[0053] The improvement effect of the virtual PSS on VSG stability in this embodiment of the invention is as follows: Figure 4 As shown. Figure 4 Comparison curves of the active power output of VSG when it is connected to the power grid without virtual PSS and with virtual PSS. Figure 4 This design is based on the MATLAB / Simulink simulation platform. In this embodiment, a short-circuit fault occurs at PCC2 at t=1s, causing its voltage to drop to 0.6pu. The output power of VSG before and after using the virtual PSS is observed.

[0054] Depend on Figure 4It can be seen that the active power of the VSG remains stable during normal system operation. After t=1s, the active power output of the VSG without virtual PSS has a large oscillation amplitude, slow convergence, and poor damping characteristics. When connected to the traditional power grid, it is more prone to power instability. In contrast, the active power output of the VSG with virtual PSS converges rapidly after being disturbed, and its oscillation amplitude is much smaller than that of the traditional VSG. This indicates that the virtual PSS can provide positive damping for the system, proving the effectiveness of the virtual PSS in providing stability for the VSG grid-connected system.

[0055] The simulation experiment verified that the virtual power system stabilizer of the present invention can effectively improve the stability of the VSG grid-connected system, and provides certain theoretical support and technical guarantee for the grid-connected operation control of new energy power generation systems using VSG.

[0056] It will be readily understood by those skilled in the art that the aforementioned advantageous methods can be freely combined and superimposed without conflict.

Claims

1. A design method for a virtual power system stabilizer to improve VSG stability, characterized in that, The method includes the following steps: Step 1: Based on the power system stabilizer, using the VSG angular frequency deviation as the input signal and the power deviation as the output signal, the virtual PSS structure is derived; Step 2: Introduce the virtual PSS structure into the power control stage of the VSG. Based on the rotor motion equation and virtual excitation regulator equation of the VSG, build a grid-connected VSG system structure with virtual PSS access. Step 3: Based on the VSG grid-connected system structure with virtual PSS access, construct the Phillips-Heffron model of the VSG grid-connected system with virtual PSS access, and derive the formula for the VSG electromechanical oscillation circuit based on the Phillips-Heffron model. Step 4: Based on the damping torque analysis of the VSG electromechanical oscillation circuit formula, determine the transfer function of the virtual PSS connected to the reactive power link to counteract the inherent negative damping of the VSG virtual excitation regulator, thereby improving the stability of the VSG grid-connected system. The VSG rotor motion equations and virtual excitation regulator equations with virtual PSS access in step two are as follows: ； In the formula, s For the complex variables used in the Laplace transform, For VSG virtual power angle, This is the reference value for the angular frequency of the power grid. For VSG virtual angular frequency, The rated angular frequency of the power grid. and These represent the active and reactive power outputs of the VPSS, respectively. , These are the active power setting value and reactive power setting value for VSG, respectively. , These represent the active and reactive power outputs of the VSG, respectively. J and These are the inertia coefficient and damping coefficient of the VSG, respectively. This represents the gain coefficient of the reactive power controller. VSG port voltage; The formula for the VSG electromechanical oscillation circuit in step three is as follows: ； In the formula, s For the complex variables used in the Laplace transform, The incremental change of the VSG virtual power angle J and These are the inertia coefficient and damping coefficient of the VSG, respectively. This is the reference value for the angular frequency of the power grid. The coefficients of the partial derivative of the active power output of the VSG with respect to the virtual work angle are given. This is the VSG damping torque coefficient. This refers to the VSG synchronous torque coefficient; The transfer function formula for the virtual PSS connected after the VSG reactive power loop in step four is as follows: ； In the formula, The oscillation mode after VSG is connected to virtual PSS. For virtual PSS in oscillation mode The transfer function under, The equivalent damping torque provided by the virtual PSS to the VSG electromechanical oscillation circuit. For virtual PSS in oscillation mode The forward transfer function provides damping torque to the VSG electromechanical oscillation circuit.

2. The virtual power system stabilizer design method for improving VSG stability according to claim 1, characterized in that, The formula for the virtual PSS structure in step one is as follows: ； In the formula, s The complex variable representing the Laplace transform, This is the transfer function for the virtual PSS. The scaling factor for virtual PSS; This represents the time constant of the corresponding lead-lag element; The formula for the input and output relationship of the virtual PSS is as follows: ； In the formula, s The complex variable representing the Laplace transform, For the output power deviation of VSG, The angular frequency deviation of the input VSG.

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