THE MODIFIED SVC CONTROL DEVICES TO BALANCE 3-PHASE CURRENTS AT AC VOLTAGE UNBALANCE

摘要

PURPOSE: A modified svc control devices to balance 3-phase currents at AC voltage unbalance is provided to reduce harmonic instability due to a rush current which is generated in a single phase fault or transition state by adding an auxiliary signal to a PLL(Phase-Locked Loop). CONSTITUTION: An SVC comprises a thyristor device and inductance. A voltage sensor measures three phase voltage of a system. A mean value operator calculates the mean value of measured three phase voltage. A first comparator(50) compares the mean value with a reference voltage to calculate an error. A PI controller amplifies and corrects the error. A PLL generates 6 switching signal at each phase. A current sensor(95) measures the three-phase current of the system. A switch modulation controller calculates an error corresponding to the instability of the three-phase current.