For a DC distributed power system, system stability can be predicted by dividing it into source and load subsystems, and then applying the Nyquist criterion to the impedance interaction between the source and load model. However, the generalized Nyquist criterion is extremely complicated and cannot directly reveal effective control strategies to reduce interaction problems of cascade three-phase AC systems. Specifically, as a current force rectifier, this characteristic makes it difficult to judge the stability of a cascade three-phase Vienna AC system. To deal with the aforementioned problems, a simplified small signal stability criterion is presented for an AC distributed power system. Based on the criterion, the small signal model and impedance based on the reduced order model in the d-q domain are studied theoretically. For the instability issue, an impedance regulator design method is presented. The correctness of the simplified stability criterion and the effectiveness of the proposed impedance regulator method are validated by extensive simulation and experiment.

This study presents two neutral‐point balance control methods for a hybrid VIENNA rectifier, which is composed of a parallel system of a single‐switch three‐phase Boost rectifier and a VIENNA rectifier. Each rectifier in this topology processes part of the output power, therefore, a highly efficient and reliable performance is achieved in this rectifier system. However, the unbalance voltage of two DC‐link capacitors in the VIENNA‐type three level rectifier is also reflected in this hybrid rectifier. The fluctuation reason in neutral‐point has been analysed using a mathematical model, meanwhile, the two methods with a hybrid algorithm and a simplified method based on zero‐sequence component injection are proposed to control neutral‐point fluctuation in this hybrid rectifier system. Furthermore, the performance comparison between these two methods is provided. The effectiveness of the two control methods has been verified using experimental results.