Performance Improvement of Dynamic Voltage Restorer using Proportional - Resonant Controller

The paper presents the design and analysis of proportional resonant controller as a solution to the inherent drawbacks of proportional integral controller while operating with a sinusoidal reference. PI controller offers maximum gain for frequencies close to d. c. and hence work well for control algorithms in synchronous reference frame. In applications like Dynamic voltage restorer where unbalance voltage is controlled and hence control algorithm in stationary reference frame is used, PI controller leads to significant steady state error. Since the error feeding the PI-controller is a continuously varying quantity, I-controller cannot reduce the steady state error effectively. Hence only way to reduce the steady state error is by increasing the P-controller constant. But the analysis shows that there is a limitation in giving higher value of gain for the PI-controller, as it magnifies the resonant frequency components. The paper studies the need for high performance control algorithm using proportional resonant controller in reducing the drawbacks of PI controller. Detailed analysis and design of controller constants is presented in the paper. Finally the proposed controller is tested in a 10kVA DVR system with various sags and load conditions.