Improving inverter efficiency at low power by reducing switching frequency

The inverter is a major component of a renewable energy system and its performance affects the overall performance of the system. For typical household applications in remote areas, often there is need to operate at low power conditions where inverter efficiency can drop dramatically. Efficient operation at low power is important especially for stand-alone applications in developing countries where system cost must be kept low. In this paper, we investigated the impact of switching frequency upon switching loss for a single-phase Sinusoidal Pulse Width Modulation (SPWM) inverter. Results show that reducing the switching frequency reduces switching loss at low power levels thus improving inverter efficiency. This may result in a reduced PV module size requirement and thus lower system cost. In addition, efficient low power inverters would allow the continued operation of essential lighting when the battery bank is nearly discharged. A mathematical model is given to calculate the major loss components (i.e. switching loss, conduction loss) in the system. The inverter is operated in the range of 200W rated power to 9W (4.5 % of the rated power) along with the change in frequency from 20 kHz to 200 Hz.