Investigation of Inter-Line Dynamic Voltage Restorer with virtual impedance injection

The Inter-Line Dynamic Voltage Restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for voltage sag that appears in its feeder (voltage control mode), the other inverters pump the required power into the dc bus (power control mode). Each inverter will have both voltage and power controllers; only one controller is in use during the abnormal conditions according to its feeder state. The voltage controller uses one of the dynamic voltage restoration techniques. In this paper, the in-phase technique is applied and two types of loads are considered (constant impedance and three phase induction motor). Since the voltage restoration process may need real power injection into the distribution system. The power controller injects this power via voltage injection; this voltage injection is simulated by voltage drop across series virtual impedance. A new scheme is proposed to select the impedance value. The impedance value is selected such that the power consumed by this impedance represents the required power to be transferred without perturbing the load voltage. The performance of this system is also studied during voltage swell. Simulation results substantiate the proposed concept.