Robust control design for the voltage tracking loop of a DVR

The Dynamic Voltage Restorer (DVR) is a solution for protection of sensitive loads from voltage sags and swells. Its basic function is to inject voltages in the grid line in order to mitigate voltage sags and/or swells. Typically the controller structure for a DVR is composed by an inner current loop and an outer voltage loop. Usually a proportional or proportional integral controller is used for the current loop and a resonant controller is used for the voltage loop. This paper presents the design of a robust controller for the voltage tracking loop of a DVR that guaranties the robust stability against load parameters variation, and assures the tracking of a sinusoidal voltage waveform and the rejection of the non linear load current influence with a pre specified error. The voltage controller design is based on H8 parameter specification approach. All the performance and robustness requirements are specified and analyzed based on the frequency response plot of closed loop transfer function. The proposed controller performance is validated by using PSIM software simulation and by experiments carried out on a DVR.