ZCS based soft switched inverter at the output stage of an UPS. An alternative to PWM inverter

The present work proposes the DC link series resonant concept for DC to AC power conversion. The inverter is ZCS-based and operated at 50 kHz and above. A decoupled current control (DCC) strategy of DC link current from the load current is identified. DCC and the elevated switching frequency of the inverter enable the application of the pulse density modulation (PDM) technique to control the current and voltage of the inverter. With a simple control circuitry, the output voltage is maintained to be sinusoidal with total harmonic distortion (THD) less than 3% and with its regulation less than 0.9% for all ranges of loads and types including nonlinear and transient. This paper discusses the operation and control implementation of the proposed inverter. Inverter operation and its control strategy are verified through simulation and the results show that inverter characteristics are attractive for an UPS application with a total digital control.