Design and comparison of high performance stationary-frame controllers for DVR implementation

The performance of a dynamic voltage restorer (DVR) is determined solely by its controller. The design of high performance control algorithms for DVR control with improved robustness and desirable steady-state and transient characteristics is therefore an important area of study. In this paper, two voltage controllers are proposed in the stationary frame for DVR voltage regulation. A P+resonant controller is first designed to achieve good positive- and negative-sequence fundamental voltage control with the virtue of having high gains around +/- 50 Hz. Stationary-to-synchronous frame transformations carried out in traditional synchronous propotional-integral regulators are no longer required with this method. However, with the purpose of achieving explicit robustness in face of parameter variations, an H infinity controller is also designed. Detailed design procedure is presented to show how an H infinity controller with high gains around +/- 50 Hz can be synthesized through careful selection of its weighting functions. A thorough discussion and performance comparison of these two controllers in both transient and steady-state conditions are also carried out. Finally, both controllers are extensively tested on a laboratory 10-kV medium voltage level DVR system with various voltage sags and loading conditions.