CN-121984019-A - Low-frequency oscillation suppression method and system for grid-structured converter under weak current grid

CN121984019ACN 121984019 ACN121984019 ACN 121984019ACN-121984019-A

Abstract

The invention provides a method and a system for suppressing low-frequency oscillation of a grid-built converter under a weak current grid, wherein the method is based on a grid short-circuit ratio obtained by adopting a preset double-mode identification strategy, the control parameters of the grid-built converter are adaptively adjusted through a preset parameter mapping relation, stability sufficiency check is carried out on the adjusted control parameters, after the check is passed, the adjusted control parameters are applied to a virtual synchronous machine control algorithm to execute grid-connected control, the low-frequency oscillation characteristic is extracted from a monitored grid-connected point frequency signal, an enhancement suppression mechanism is triggered after the low-frequency oscillation characteristic exceeds a threshold value, real-time sensing of the grid strength, adaptive adjustment of multi-parameter cooperation, active monitoring, rapid suppression of low-frequency oscillation, continuous self-learning optimization and stability sufficiency check are realized, and the problem of low-frequency oscillation of the grid-built converter under the weak current grid is effectively solved.

Inventors

SUN JIXIN
Fuck movie
PENG CHEN
Bian Bajiba
Qiong Zhuoma
Zhao Puchuan
FENG YINYIN
ZHANG XIONGXIONG
Tan hisayoshi
ZHOU HUI
ZHAO WENTAO
CHEN SILIN
LI CHAOBING
GAO YUAN
ZENG YI
XU JIANGBO
XU YANZHAO
WU JINGMING

Assignees

国网西藏电力有限公司电力科学研究院
西藏中试电力科学技术服务有限责任公司
国网西藏电力有限公司

Dates

Publication Date: 20260505
Application Date: 20251231

Claims (10)

1. The method for suppressing the low-frequency oscillation of the grid-structured converter under the weak current grid is characterized by comprising the following steps of: based on a power grid short-circuit ratio obtained by adopting a preset double-mode identification strategy, the control parameters of the grid-constructed converter are cooperatively and adaptively adjusted through a preset parameter mapping relation, wherein the control parameters comprise a virtual inertia coefficient, a virtual damping coefficient and a virtual impedance parameter; Performing stability sufficiency check on the adjusted control parameters, and applying the adjusted control parameters to a virtual synchronous machine control algorithm after the check is passed so as to execute grid-connected control; and extracting low-frequency oscillation characteristics from the monitored grid-connected point frequency signals, and triggering an enhancement suppression mechanism after the low-frequency oscillation characteristics exceed a preset threshold value.
2. The method of claim 1, wherein the obtaining of the grid short circuit ratio comprises: After the power grid is started or changed, injecting a small-amplitude power disturbance signal into the power grid by adopting the active disturbance in a preset dual-mode identification strategy, extracting a voltage response component at the disturbance frequency, and calculating the power grid short-circuit ratio according to the power voltage sensitivity, or, And during steady-state operation of the power grid, acquiring a power sequence and a voltage sequence during steady-state operation by adopting a passive observation method in a preset dual-mode identification strategy, and constructing a linear regression model to solve the power-voltage sensitivity so as to calculate the power grid short-circuit ratio.
3. The method of claim 1, wherein the collaborative adaptive adjustment of control parameters of the grid-connected converter through a preset parameter mapping relationship comprises: The virtual inertia coefficient is adaptively adjusted through a piecewise linear mapping function based on the power grid short-circuit ratio, and the virtual inertia coefficient is adjusted to be larger under the condition that the power grid short-circuit ratio is weaker; Calculating basic damping and additional damping through a double-layer framework mapping function based on a power grid short-circuit ratio to obtain a total virtual damping coefficient, wherein the double-layer framework comprises a basic damping layer and an additional damping layer as adjusted virtual damping coefficients, the basic damping layer calculates to obtain the basic damping according to a target damping ratio, the adjusted virtual inertia coefficient and virtual stiffness, and the additional damping layer calculates to obtain the additional damping according to a nonlinear function of frequency deviation, so that the adjusted additional damping gradually approaches 0 when the frequency deviation is smaller, and the adjusted additional damping rapidly increases when the frequency deviation is increased; And adjusting fundamental virtual impedance and harmonic impedance parameters of the virtual impedance based on a preset impedance mapping relation according to the grid short-circuit ratio.
4. A method according to claim 3, wherein the total virtual damping coefficient is obtained by the following calculation: Wherein, the As a result of the overall virtual damping coefficient, As a result of the basic damping, In order to provide additional damping, the damping, As the gain factor of the gain factor, Is a non-linear index of the non-linear index, In order to achieve the target damping ratio, As the absolute value of the frequency deviation, For the virtual stiffness to be a function of the stiffness, Is virtual inertia.
5. A method according to claim 3, wherein said adjusting fundamental virtual impedance and harmonic impedance parameters of virtual impedance based on a preset impedance mapping according to a grid short ratio comprises: And adjusting the resistance-reactance ratio of the fundamental wave virtual impedance according to the power grid short-circuit ratio, wherein the weaker the power grid short-circuit ratio is, the larger the resistance-inductance ratio of the fundamental wave virtual impedance is, and setting the amplitude of the specific subharmonic virtual impedance as a preset multiple of the amplitude of the fundamental wave virtual impedance.
6. The method of claim 1, wherein the stability adequacy check comprises at least one or more of the following, and wherein the check is passed if all check conditions are simultaneously satisfied: Verifying that the system damping ratio corresponding to the adjusted control parameter is larger than a minimum stable damping ratio threshold; based on a pre-constructed system state space model, verifying that a positive definite matrix meets Lyapunov stability conditions; Verifying that the maximum amplitude of the loop gain of the power-frequency outer loop in the frequency band of 0.2-3Hz is less than 1 based on a pre-constructed loop transfer function, which is the power-frequency outer loop open loop gain from frequency deviation to electromagnetic power.
7. The method of claim 1, wherein the low frequency oscillation characteristic comprises oscillation amplitude, oscillation decay time and oscillation energy, wherein the triggering condition of the enhanced damping mechanism is any one of an overrun oscillation amplitude, an overlong oscillation decay time or an overrun oscillation energy, and wherein the enhanced damping mechanism is configured to calculate an additional damping increment according to the oscillation amplitude through a nonlinear function and to superimpose the additional damping increment on a current virtual damping coefficient.
8. A low-frequency oscillation suppression system for a grid-structured converter under a weak current grid, comprising: The mapping module is used for cooperatively and adaptively adjusting control parameters of the grid-structured converter through a preset parameter mapping relation based on the power grid short-circuit ratio obtained by adopting a preset double-mode identification strategy, wherein the control parameters comprise a virtual inertia coefficient, a virtual damping coefficient and a virtual impedance parameter; The checking module is used for checking the stability sufficiency of the adjusted control parameters, and applying the adjusted control parameters to a virtual synchronous machine control algorithm after the checking is passed so as to execute grid-connected control; The monitoring module is used for extracting low-frequency oscillation characteristics from the monitored grid-connected point frequency signals and triggering an enhancement suppression mechanism after the low-frequency oscillation characteristics exceed a preset threshold value.
9. The electronic equipment is characterized by comprising at least one processor and a memory, wherein the memory and the processor are connected through a bus; the memory is used for storing one or more programs; a method of suppressing low frequency oscillations of a low current grid-connected converter according to any of claims 1 to 7 when the one or more programs are executed by the at least one processor.
10. A readable storage medium having stored thereon an execution program which, when executed, implements the weak-current-network-under-grid converter low-frequency oscillation suppression method according to any one of claims 1 to 7.

Description

Low-frequency oscillation suppression method and system for grid-structured converter under weak current grid Technical Field The invention relates to the field of control of power electronic converters, in particular to a method and a system for suppressing low-frequency oscillation of a grid-built converter under a weak current grid. Background Along with the continuous improvement of permeability of new energy sources such as wind power, photovoltaic and the like in a power grid, a large amount of distributed energy sources are connected with a grid through a power electronic converter. A Grid-formed (Grid-formed) converter is controlled by a virtual synchronous machine (VSG), and can actively support the frequency and voltage of a power Grid, so that the Grid-formed (Grid-formed) converter becomes an important technical route for new energy Grid connection. In remote areas where the power grid infrastructure is weak or offshore wind farms, the power grid Short Circuit Ratio (SCR) is below 2.5, belonging to a weak power grid environment. Under the condition of weak current network, the dynamic interaction between the grid-structured converter and the power network can cause the problem of low-frequency power oscillation. The low frequency oscillation is represented by continuous periodic fluctuation of the system frequency and active power in the low frequency band, and when severe, the system is unstable. The physical mechanism of the low-frequency oscillation is that the equivalent impedance of a weak current network is large, the power-frequency coupling generated by the control of a virtual synchronous machine of a network-structured converter and the impedance of a power network form a negative damping effect, and when the system damping is insufficient, the small disturbance can cause continuous oscillation. The oscillation frequency is mainly determined by virtual inertia and virtual stiffness, and the oscillation damping speed is determined by the damping ratio of the system. The prior art mainly has the following defects: First, the fixed parameter design cannot adapt to dynamic changes in grid strength. Conventional VSG control employs constant virtual inertia and damping coefficients that fail to maintain an optimal damping ratio as grid strength changes. The dynamic response is influenced by excessive damping when the power grid is strong, and the oscillation is caused by insufficient damping when the power grid is weak. Lack of real-time sensing capability of grid strength is a fundamental problem. Second, single parameter tuning is difficult to effectively suppress low frequency oscillations. The partial method only adjusts virtual inertia or virtual damping, and multi-parameter collaborative optimization is not realized. Increasing inertia alone can reduce the oscillation frequency but increase the adjustment time, increasing damping alone can accelerate the damping but affect the power response, the damping effect is limited, the oscillation amplitude is reduced by usually less than 50%, and the damping time is still longer. Third, there is a lack of real-time oscillation monitoring and active response mechanisms. The existing method generally relies on offline analysis or passive waiting for natural damping of oscillation, and cannot be rapidly involved in the early stage of oscillation. When unexpected abnormal oscillations occur, the fixed parameters do not provide adequate damping capacity, missing the optimal damping opportunity. Fourth, control strategy curing is not adaptively optimized. The parameter mapping relation is set based on experience or simulation, and cannot be optimized according to actual operation data in a self-learning mode. The parameters are required to be reset under different equipment and different working conditions, the adaptability is poor, and the engineering application is difficult. Fifth, a stability sufficiency criterion is lacking. The lack of a quantitative checking mechanism for system stability after parameter adjustment may lead to new oscillation or instability risks caused by control parameter out-of-range. Therefore, a method capable of sensing the power grid strength in real time, performing multi-parameter collaborative self-adaptive adjustment, actively monitoring, rapidly suppressing low-frequency oscillation, performing continuous self-learning optimization and checking stability sufficiency is urgently needed, and the problem of low-frequency oscillation of the grid-built converter under the weak current grid is effectively solved. Disclosure of Invention The invention provides a method and a system for suppressing low-frequency oscillation of a grid-structured converter under a weak current network, which are used for solving the problems that the fixed parameter design in the prior art cannot adapt to dynamic change of power grid strength, single parameter adjustment is difficult to effectively suppress low-frequency oscillation and the