A Direct-current Island Voltage Stability Control Method Based on Stored Energy Characteristics

Aiming at the issue of voltage instability in high voltage DC weak sending-end systems upon entering the island mode, a voltage stability control method is proposed based on stored energy characteristics. Firstly, a reactive power distribution model of the DC feeder system is established. The relationship between voltage sag and reactive power deficiency after a DC system enters the island mode is analyzed, and the expression for the voltage variation of the converter bus before and after DC island synchronization and desynchronization processes is derived. Subsequently, the dynamic energy function of the DC island system considering the response of the control link is constructed, and the relation between the rectifier current command value and the stored energy is established. On this basis, a current command value adjustment method is put forward, which takes into account the energy stability constraints of the system. The proposed method is capable of reducing the reactive power consumption in the process of DC recovery and achieving the rapid stabilization of voltage fluctuations. Finally, a DC island transmission system model is built on the RT-LAB platform to verify the proposed method. The experimental results demonstrate that the proposed method mitigates the voltage fluctuations after the disconnection of the DC outgoing system to the large capacity grid, and enables rapid recovery of voltage stability after isolated island operation.