Minimum power operation of cascade inverter based dynamic voltage restorer for power quality improvement

This thesis introduces an enhanced implementation of a dynamic voltage restorer (DVR) based on a Voltage Sourced Converter (VSC) topology, for power quality improvement in a power network. Building on earlier research that has shown that sag compensation ability is greatly enhanced by permitting energy storage on the dc side of the VSC, a new control method is introduced which mitigates sag with minimum real power injection. This technique requires a much smaller energy reservoir on the dc side. It also permits the energy reservoir to be a capacitor instead of higher capacity reservoir such as a battery. A modular H-bridge multilevel cascade converter topology is used which has the benefits of one-phase compensation as well as transformerless operation.; The thesis also introduces a modified new topology and the corresponding control system where the capacitor energy storage can be even further reduced by active modulation of the power factor during a sag. The thesis also demonstrates that the auxiliary function of harmonic compensation can be easily integrated into the control of the DVR.; The operational limits and the component selection of the circuit parameters is conducted from simplified analytical formulation of the circuit equations.; Extensive analysis of the dynamic performance is conducted using electromagnetic transients simulation on the PSCAD/EMTDC program.; Finally, all key conclusions are supported by small scale physical implementation in the laboratory.