Research on optimal reclosing time of AC/DC hybrid system based on dynamic energy

Abstract

A method to calculate the optimal reclosing time of AC/DC hybrid system based on dynamic energy is proposed. First, in the whole fault process starting from fault initiation to accelerated tripping of circuit breakers after reclosing, the dynamic energy function that characterizes the stability degree of system is built. On this basis, the variation rate of dynamic energy is defined as the energy accumulation speed, which quantitatively characterizes the accumulation or consumption of dynamic energy in the fault duration. And detailed expressions of energy accumulation speed when single-phase fault and three-phase fault occur in the system are derived respectively. Then, with the accumulated dynamic energy of system being the minimum as the objective, the optimal reclosing time is searched, and the pattern in which the trajectory of operating points passes new equilibrium point when the system is reclosed at the optimal reclosing time is revealed. Finally, hardware-in-the-loop tests are conducted in RT-LAB for simulation verification. Simulation results demonstrate that, as reclosing time varies, total accumulated dynamic energy of system has multiple minimum points. Selecting the reclosing time calculated according to the method can improve stability of system.