A DC to three-phase boost-buck inverter with stored energy modulation and a tiny DC link capacitor

Three phase voltage source inverters typically feature a significant amount of dc energy storage to maintain a stiff dc bus. In these cases, the dc link capacitor is sized to store enough energy to maintain several tens of cycles of ac output at the rated power. In this paper, we propose to reduce the size of the dc link capacitor dramatically, to store enough energy to provide just one high frequency switching cycle of ac output power. The dc bus is no longer stiff and hence classical sinusoidal pulse width modulation cannot be used. But, the stored energy modulation (SEM) concept that we propose herein synthesizes high quality sinusoidal output voltage waveforms even with such tiny dc link capacitors. In SEM, the switching intervals of the interconnecting switches are carefully determined nonlinear functions of various operating parameters such as reactive component sizing, switching frequency, load levels, etc. This paper presents the analytical and detailed design development of the stored energy modulation approach along with circuit simulation, experimental results and comparative evaluation of a dc to three phase system example.