Single-phase power inverters with buck-boost and power decoupling capabilities
University of New Brunswick
This Ph.D. thesis focuses on the active power decoupling techniques to eliminate the inherent double-line frequency power mismatch between the DC side and the AC side in single-phase inverter systems. Three new single-phase inverter topologies with active power decoupling control are proposed on three streams of single-phase inverter systems: single-phase differential inverters, single-phase bridge inverters, and two-stage single-phase bridge inverters. The salient features of the proposed topologies are: 1) the large electrolytic capacitors in the order of mF have been replaced by small film capacitors of around 100uF; 2) the absence/mitigation of second-order ripple power enables higher efficiency of photovoltaic (PV) panel; 3) the boost/buck-boost capabilities increase DC voltage utilization; and 4) the small number of power electronic devices compared with the existing inverters that have both voltage boosting and active power decoupling capabilities. Pulse energy modulation (PEM) and hybrid modulation are proposed and applied to the differential inverters and bridge inverters, enabling the inverters to operate under both discontinuous conduction mode (DCM) and continuous conduction mode (CCM), and switch between DCM and CCM seamlessly. The inverters have zero-current switching under DCM when the instantaneous power is low, and small ripple current under CCM when the instantaneous power is high. Small-signal modeling analyses are conducted to show the characteristics of the proposed inverter topologies and modulation techniques. Simulation and experimental results are presented to demonstrate and verify the success of power decoupling with substantial mitigation of second-order ripple power, and the feasibility of inverters with PEM and hybrid modulation working under both DCM and CCM.