A Stability Judgment Method for APF Parallel System Based on Global Admittance Analysis

Abstract

The invention discloses a global admittance analysis based stability determination method of an APF parallel operation system. The method comprises the following steps of (1) building a current loop and a harmonic control loop admittance model; (2) building a full admittance form equivalent circuit according to the admittance model; (3) obtaining a full admittance expression of the parallel operation system according to a voltage expression of a PCC of a power grid; and (4) drawing an Nyquist curve of full admittance, wherein the stability criteria is as follows: the parallel operation system is stable when positive through frequency and negative through frequency of a negative real axis of an s plane are equal, otherwise the parallel operation system is out of stable. The equivalent form of the above criteria is as follows: all real parts Rd of full admittance gains corresponding to all resonant points of the parallel operation system are larger than 0. According to the stability determination method proposed by the invention, the stability condition of the parallel operation system can be effectively obtained by analyzing frequency-domain characteristic of full admittance, the stability determination method can be used for analyzing the APF parallel operation system under a complicated coupling condition, the fundamental factor affecting the stability of the parallel operation system can be obtained, and the stability determination method has high feasibility and practical value.

Description

technical field [0001] The invention belongs to the field of power systems, in particular to a method for judging the stability of an APF parallel system based on global admittance analysis. Background technique [0002] With the gradual increase of power equipment invested in various industries, the harmonic content in the power grid is gradually increasing, such as low-voltage large-capacity rectifiers for electrolysis in the chemical caustic soda industry. Therefore, the demand for modular multi-machine parallel active filtering with large capacity, high precision and high reliability is increasing, and it has gradually become a research hotspot. The stability analysis of the modular multi-machine parallel system is the focus of research in this field. It is related to the safe and reliable operation of the whole system. It is necessary to establish a mathematical model for the parallel system, and then analyze and study the coupling between the electrical quantities in e...

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Problems solved by technology

The limitation of this method is that the stability of the entire parallel system (that is, the stability of the voltage at the PCC of the power grid and the output current of all parts) is directly determined by the stability of the total output current of the parallel unit, but it fails to reflect the stability of the total output current of the parallel system. The essential reason for the stability of each part; the impedance ratio is the ratio of the two transfer functions, and the equivalent total impedance of the parallel unit is obtained by paralleling the impedance of multiple parallel units. When the impedance transfer function of the parallel unit is complex or the number of parallel units is large And when the impedance is asymmetrical, its frequency domain characteristics are not easy to obtain, so it is difficult to qualitatively analyze the stability of the coupling loop

The limitation of this method is that the coupling gain is the ratio of two sets of transfer functions (admittance ratio), and its form is often very complicated in a multi-machine parallel system, and it is difficult to analyze its frequency domain characteristics to obtain stability judgments

In addition, the output current stability of the parallel unit is directly analyzed as the response stability of the entire parallel system, and the essential reason for determining the response stability of the entire parallel system cannot be given.

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