Improving the Performance of a Cascaded H-Bridge-Based Interline Dynamic Voltage Restorer

An interline dynamic voltage restorer (IDVR) is a new device for sag mitigation which is made of several dynamic voltage restorers (DVRs) with a common dc link, where each DVR is connected in series with a distribution feeder. During the sag period, active power can be transferred from a feeder to another one and voltage sags with long durations can be mitigated. IDVR compensation capacity, however, depends greatly on the load power factor, and a higher load power factor causes lower performance of IDVR. To overcome this limitation, a new idea is presented in this paper which enables reducing the load power factor under sag conditions and, therefore, the compensation capacity is increased. The proposed IDVR employs two cascaded H-bridge multilevel converters to inject ac voltage with lower total harmonic distortion and eliminates the necessity to low-frequency isolation transformers in one side. The validity of the proposed configuration is verified by simulations in the PSCAD/EMTDC environment. Then, experimental results on a scaled-down IDVR are presented to confirm the theoretical and simulation results.