Interaction Behavior and Stability Analysis of Low-Voltage Multi-Terminal DC System

The stability problem of low-voltage multi-terminal DC (MTDC) system has drawn lots of interest. This paper focuses on oscillation instability phenomenon of low-voltage MTDC system and analyses the interaction behavior between each voltage-source converter (VSC) and DC network oscillation modal. The typical structure and control strategy of low-voltage MTDC system under master-slave control is first described and its equivalent circuit is established. Then the interaction behavior analytical model is proposed and the source-network and network-load interaction characteristics are studied. Furthermore, a system stability analysis method is built based on the modularized modelling which can solve the problem of how to deal with the complexity of high-order low-voltage MTDC system. The transfer function of the whole system is conveniently established revealing the mechanism of system instability. The proposed method can provide effective stability assessment for low-voltage MTDC system. Finally, the results are verified using electromagnetic transient simulation and validated experimentally using a low-voltage three-terminal DC system test platform with AC 0.4kV/DC 800V. This research can be flexibly promoted to high-order systems for controller design and performance optimization.