Zhou Sizhan

Unified stability criterion of bidirectional power flow cascade system

The stability issues of cascade system have been studied for many years. Some classic criterions in the form of Zo/Zi like Middlebrook criterion has been proposed and the validity have been proved in the case like voltage source with a current sink. But they meet the challenge in some application, especially in the case of current source with voltage sink. In this paper, the stability issues of a bidirectional energy storage system have been discussed. System level small signal models are established to derive the transfer function in each mode. A unified stability criterion is summarized after the discussion of different modes. It can be seen that the stability only depends on the terminal characteristics design.

Improved DC-link voltage control of PMSG WECS based on feedback linearization under grid faults

This paper proposes a DC-link voltage control method for the permanent magnet synchronous generator (PMSG) wind power system with a full-rated back-to-back converter, to improve the dc-link voltage dynamic response under normal operation and grid faults conditions. The dc-link voltage is controlled by the motor-side converter, while the grid-side converter is responsible for the maximum power point tracking. Considering the system nonlinear characteristic, a dc-link voltage controller is designed based on the feedback linearization theory. With this control scheme, the dc-link voltage responses much faster than other control structures. It can suppress the dc-link voltage fluctuation with the wind speed varying and prevent the voltage from rising too high under grid faults. The validity of the control algorithm has been verified by simulation with Matlab/Simulink, and the results show a better dc-link dynamic response with the proposed control scheme.