Abstract: In back-to-back cascaded converter systems, the output impedance of front sub-converter will interact with the input impedance of the rear sub-converter. If the system parameters are not designed properly, it will worsen system stability. In this paper, the concept of impedance-coordination control is proposed. Low-frequency impedances of the front and rear sub-converters in the cascade system are modified to be resistive so that the low-frequency phase shift is zero, which may improve the stability of back-to-back cascaded converter system. Based on the cascaded topology of dual H-bridge DC/DC converters and three-phase two-level inverters, this paper compares the proposed control with conventional control strategies. The impedance-based stability evaluations show that, in low frequency range, the proposed control can promote both the front source converter and rear load converter to present resistive impedance towards dc link, then phase shift of the impedance interaction can be greatly reduced, which contributes to a better stability. Simulation and experiment verify the effectiveness of the proposed control strategy.

Key words: back-to-back converter, impedance behaviors, stability, impedance-coordination control