Pulse energy modulation of a single-stage three switch buck-boost inverter
University of New Brunswick
This Ph.D. thesis focuses on a single-phase, single-stage, dc-ac power inverter for small distributed generation (DG) systems. Different topologies of single-phase inverters are reviewed and discussed. A low-cost single-stage inverter topology for DG systems is investigated. The proposed topology is featured with a buck-boost configuration in order to step-up or step-down the input dc voltage. The operation of this inverter is structured to deliver its output power to the grid in a single stage circuitry. The single stage topology has several advantages, such as high efficiency, low cost and compact size. Methodologies of inverter system modeling and design are discussed. Performances of the proposed inverter topology are investigated in simulation and laboratory experimentation. The modulation strategy used to control the power switches is an important part of the inverter operation. In this thesis, a new energy based modulation strategy is proposed and implemented. Pulse Energy Modulation (PEM) is proposed as a new approach to generate inverter switching pulses based on the desired output energy within an output pulse. The energy demand is calculated from the output voltage and reference current, while the modulation index of the inverter is calculated based on the instantaneous energy demand. Detailed analyses of the inverter under discontinuous and continuous inductor current conduction modes are discussed. Simulation and experimental results show that PEM provides sinusoidal output current and robust control under large variations in the input de voltage and output ac current.