The Characteristics and Suppression of Common-Mode Current for Brushless Doubly Fed Generator System

Due to the cancellation of the brush and slip ring, the brushless doubly fed generator (BDFG) is more reliable than the doubly fed induction generator and it has wide prospect in the field of variable speed constant frequency power generation. However, the internal structure of BDFG is complex, which brings difficulties to the analysis of common-mode circuit and the suppression of common-mode current. Based on the structure of BDFG system, the common-mode voltage circuit paths are analyzed. The common-mode equivalent circuit model and the extraction method of equivalent common-mode impedance parameters are presented in this article. The characteristics of each common-mode circuit path are analyzed. The common-mode Path 3 (line-side converter-motor power winding-motor control winding-machine-side converter-line-side converter) is an important factor that affects the common-mode current characteristics of the BDFG system. The relationship between carrier difference and common-mode current characteristics of two pulsewidth modulation converters, in this path, is analyzed emphatically. In order to reduce the common-mode voltage, it is necessary to ensure the carrier synchronization between them. And the control method of carrier synchronization is provided. The experiment is designed based on the experiment platform of the BDFG system. The experimental results verify the correctness of the proposed model and theoretical analysis, as well as the effectiveness of the common-mode current suppression method.