An energy optimized control scheme for a transformerless DVR

The dynamic voltage restorer (DVR) is considered as the most effective and economic solution for voltage disturbances. This paper presents an energy optimized control scheme for a transformerless DVR. The DVR structure is based on a cascaded H-bridge multilevel inverter topology to eliminate the need of insertion transformers. The proposed control algorithm maintains a balanced load-side voltage even during the compensation of unbalanced disturbances with a minimum active power injection. Moreover, the proposed scheme maximizes the ride-though capability of the DVR during voltage sags. This feature is verified by using capacitors instead of dc sources as energy storage elements for the DVR. Furthermore, the proposed minimum energy scheme prevents the rise in the dc-side voltage of the inverter when compensating voltage swells. The performance of the proposed DVR system is evaluated for compensating different types of voltage disturbances. The results validate the robustness and the accuracy of the proposed system.

► This paper presents an energy optimized scheme for a transformerless DVR.
► The proposed compensation scheme controls the phase angle of the load-side voltage.
► Depending on the supply voltage phasor, the DVR can operate with either zero or minimum active power.
► One advantage of the proposed method is the maximization of the ride-through capability of the DVR.
► Fast response and accurate compensation even during the transition periods are revealed.