Control Method of Displacement Overvoltage Suppression Switching to Ground Fault Arc-suppression for Flexible Power Source

Abstract

Flexible power source has the functions of neutral point displacement overvoltage suppression and ground fault arc-suppression, which are essential for safe and stable operation of distribution networks. However, when the displacement overvoltage suppression is switched online to fault arc-suppression, the flexible power source has the problem of output overcurrent. Aiming at the overcurrent problem at the moment of switching, a control method of amplitude difference over-limit active blocking is proposed to realize the reliable switching of the flexible power source operation mode. First, the operation mechanism of flexible power source is introduced, and a closed-loop control method is proposed which shares the current inner control loop. Then, the equivalent circuit models are established in two operation modes, and the principle of overcurrent during the switching process is analyzed. The switching state is determined by whether the quantity of voltage sudden change exceeds the limit in the displacement overvoltage suppression mode. And then the AC output is blocked until the upper arc-suppression command is received, and the flexible power source switches to the ground fault arc-suppression mode. The simulation analyzes the rationality of the two operation modes and their switching control methods. Finally, a prototype is developed and applied in a 66 kV power grid of China, and the field test results verify the reliability and advancement of the proposed method.