Study of the Interaction Between the AC and DC Side in the Quasi-Z-Source Convertor

Abstract

The impedance source network convertors are very attractive to the dc-ac applications due to its ability to buck and boost the input voltage in the single stage. Many literatures have focused on modelling of the impedance network in the dc side to enhance the system performance. For system design and control optimization, the synthesis and interaction principle between the ac and dc side of the convertors is required. This paper firstly presents the small signal model combining dc and ac side of the bidirectional quasi-Z-source convertor through the circuit-averaging technique. Compared with previous modeling based on the shoot through duty ratio, the modulation ratio is included for the interaction study of ac and dc side. It is founded that oscillation could appear in ac current control loop due to the magnitude margin issue caused by the impedance network. And then instability in the impedance network can be triggered, including the system input current. Based on the mathematical analysis, a design guideline for the ac current controller is proposed. Both the model and controller design guideline are validated by simulation and experimental result.