Mitigation of voltage sag for DVR to comply with voltage security protocol via elliptical trajectory compensation

In this paper, a flexible power dispatch strategy based on the elliptical trajectory is proposed to maximize the operating region for dynamic voltage restorer (DVR) during voltage sags. This control scheme introduces two individual parameters to accomplish continuous power delivery within the voltage security boundaries required by the loads. These two key parameters are presented in the exact mathematical equations of instantaneous power dispatch, which allows the individual control of active power and reactive power of DVR. Under the provisions of the given control strategy, the load voltage regulation and flexible power dispatch are combined together by the voltage sag compensation of the elliptical trajectory. Thus, the voltage source converters output current can be limited within the maximum rated value. A smooth transition can be achieved as well during changes in the operation scheme when fulfilling the presented power delivery. Eight scenarios of different active and reactive power delivery are presented to validate the feasibility of the proposed strategy. Finally, laboratory results are used to reveal the effectiveness of the given control schemes.