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 on the stationary frame (with embedded inner current loops) 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 positive- and negative-sequence fundamental frequencies. Complex stationary-to-synchronous frame transformations carried out in traditional synchronous P1 regulators are no longer required with this method. However, with the purpose of achieving explicit robustness in face of parameter variations, an Hinfin controller is also designed. Detailed design procedure is presented to show how an Hinfin controller with high gains around plusmn50 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 is also carried out. Finally, both controllers are extensively tested on a laboratory 10 kV DVR system with various voltage sags and loading conditions. It is shown that both controllers would respond properly for unbalanced voltage sags. With linear loads, both controllers perform well with slight difference during startup transient. The performance of the robust HaD controller becomes more obvious with nonlinear loads due to its better attenuation of the high frequency harmonic distortion