Pulse Energy Modulation in a Three-Switch Buck-Boost Inverter for Distributed Generation Systems

Single-phase grid-connected inverters play an important role in small distributed generation (DG) systems. This paper illustrates the circuit configuration and operation principle of a novel single-phase, single-stage, three-switch, fly-back, buck-boost inverter. The equivalent circuits associated with the four operation modes are established for the charging and discharging process. The inverter can operate in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). Most importantly, a new pulse generation method called pulse energy modulation (PEM) is proposed and applied to the three-switch buck-boost inverter in this paper. PEM signals for controlling the power switches are generated by meeting the output energy demand in each switching period with the stored energy in the coupled fly-back inductors. The duty ratio of PEM is thus determined by the energy demand and dc input voltage. The efficiency of the inverter used PEM is analyzed. A 400W experimental prototype is built in the laboratory to verify the operation of the proposed pulse energy modulation method. The inverter controller employs DSP dsPIC33FJ64MC506 for controlling, detecting and protecting functions. Experimental results have shown that PEM provides a new modulation mechanism for controlling the three-switch buck-boost inverter to inject a sinusoidal current into the grid under a wide range of operating conditions.