Quantitative analysis method for subsynchronous oscillation stability of wind turbine generator grid-connected system

Abstract

The invention provides a quantitative analysis method for the subsynchronous oscillation stability of a wind turbine generator grid-connected system. The quantitative analysis method comprises the following steps: adding positive and negative sequence voltage disturbance signals to a wind turbine generator grid-connected point; establishing transfer functions of a wind turbine generator phase-locked loop, a current adjusting link and a PWM modulation link; obtaining positive and negative sequence impedance models Zp (s) and Zn (s) of a wind turbine generator, an equivalent impedance model Zg (s) of a power grid and a total impedance model Z (s) of a grid-connected system; determining proper fitting fractal polynomial orders m and n, and fitting the total impedance model Z (s) of the grid-connected system by using the fitting fractal polynomial orders m and n; solving a zero point of the fitting fractal polynomial in a fitting interval according to a fitting result, and determining theoscillation frequency and the damping level of the system according to the solved zero point. According to the invention, the method provided by the invention is provided based on the sequential impedance model in a static coordinate system. The method solves the problem that the traditional Nyquist stability criterion based on a sequential impedance model cannot quantitatively obtain the oscillation frequency and the damping level of the system in the prior art. The problem that the quantitative analysis method based on an aggregation RLC circuit model is narrow in application range is also solved.

Description

Technical field [0001] The invention belongs to the field of sub-synchronous oscillation analysis of new energy power generation grid-connected systems, and specifically relates to a method for quantitative analysis of the sub-synchronous oscillation stability of a wind turbine grid-connected system. Background technique [0002] In recent years, with the intensification of the global energy crisis, new energy power generation technology has received more and more attention. In July 2015, there was a subsynchronous oscillation (SSO) phenomenon in Xinjiang where large-scale direct-drive wind turbines were connected to the weak AC grid. The impedance analysis method has the advantages of clear physical concept and strong scalability, and it has become one of the main methods for studying the SSO problem of wind turbines connected to the grid. The impedance analysis method must first obtain the impedance model of the wind turbine and the power grid, and then use the impedance stabi...

AI Technical Summary

Problems solved by technology

At present, the traditional Nyquist criterion based on impedance characteristics cannot quantitatively analyze the stability of the system, but can only give qualitative stability analysis results, that is, system stability / unstability; the stability quantitative analysis method based on the aggregation RLC circuit method has passed et al. The impedance-based quantitative analysis was realized for the first time in the form of an effective RLC circuit, but this method is only applicable to conditions with small damping, which limits the scope of application of the method.

[0003] In view of the defect that the traditional Nyquist stability criterion based on the sequence impedance model cannot quantify the oscillation frequency and damping level of the system, and the narrow application range of the quantitative analysis method based on the aggregated RLC circuit model, based on the sequence impedance in the static coordinate system model, the present invention proposes a quantitative analysis method that realizes the subsynchronous oscillation stability of the wind turbine grid-connected system under the broadband

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