Quantitative Analysis Method for Subsynchronous Oscillation Stability of Wind Turbine Grid-connected System

Abstract

The present invention proposes a quantitative analysis method for subsynchronous oscillation stability of a wind turbine grid-connected system, including the following steps: adding positive and negative sequence voltage disturbance signals to the wind turbine grid-connected point; establishing a wind turbine phase-locked loop, a current regulation link and PWM modulation Link transfer function; get wind turbine positive and negative sequence impedance model Z p (s), Z n (s), grid equivalent impedance model Z g (s) and the grid-connected system total impedance model Z(s); determine the appropriate fitting fractional polynomial order m, n, and use it to fit the grid-connected system total impedance model Z(s); according to the fitting result Calculate the zero point of the fitting fractional polynomial within the fitting interval, and determine the system oscillation frequency and damping level according to the calculated zero point. The method of the present invention is based on the sequence impedance model in the static coordinate system, which solves the defect that the traditional Nyquist stability criterion based on the sequence impedance model cannot be quantified to obtain the system oscillation frequency and damping level, and the quantitative analysis method based on the aggregation RLC circuit model problems with a narrow scope of application.

Description

technical field [0001] The invention belongs to the field of new energy power generation grid-connected sub-synchronous oscillation analysis, and in particular relates to a method for quantitative analysis of 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, the subsynchronous oscillation (SSO) phenomenon of large-scale direct-drive wind turbines connected to the weak AC power grid appeared in Xinjiang region of my country. Impedance analysis method has become one of the main methods to study the SSO problem of wind turbines connected to the grid due to its advantages of clear physical concept and strong expansibility. Using the impedance analysis method, the impedance model of the wind turbine and the power grid must be obtained first, and then the stabili...

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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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