An Online Compensation Method of DC Drift for Three‐Phase Current Reconstruction with DC‐Link Resistance

Abstract

In a three-phase power convertor system, phase current reconstruction technique using a DC-link resistance can reduce the cost and weight of the diving system. The three-phase current without DC offset in normal condition is introduced in this paper firstly. Based on this premise, the DC-link current offset is considered and the logical relationship between threephase voltage, three-phase current, and DC offset are analyzed and depicted. The DC offset introduced during the sampling processes a distortion into phase current, which is composed of fundamental and harmonic frequency based on FFT analysis. The fundamental component of the distortion shares the same phase angle with counterpart voltage, which distorts power factor and amplitude of three-phase currents. The harmonic components of the distortion can be transformed into 6th harmonic components in synchronous dq axes and undermine the performance of the controlling system. After that, a practical method is proposed to solve this problem, namely sampling the DC offset signal during the period of the zero voltage vectors. An analogy sample circuit is designed and tested. This method can avoid the DC offset from the source. Finally, its effectiveness is verified via simulation and experiment.