Repetitive control for a dynamic voltage restorer for power-quality improvement

This paper presents a control system based on a repetitive controller to compensate key power-quality disturbances, namely voltage sags, harmonic voltages and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a specified bandwidth. The control structure contains a feed-forward term to improve the transient response and a feedback term to ensure zero error in steady-state. PSCAD/EMTDC has been used to carry out all modelling aspects of the repetitive controller and test system. Simulation results show that the control approach performs effectively and yields excellent voltage regulation. Further work is required towards a digital implementation of the controller.