A novel DC-to-AC controlled multi-level inverter

Ac-to-dc converters are widely used for ac-to-dc conversion, speed control of dc motors etc. This paper presents a novel transformer based dc-to-ac multi-level converter topology where instead of pulse-width modulation, tap changing is done to shape the output voltage sinusoidal. The load is connected at the secondary side of the isolating and tap changing transformer. During each half cycle, a controller circuit is used to switch different switching devices connected to the tap changing transformer, systematically. The controller circuit receives command signal in form of voltage or current and supplies the required switching signals to the relevant switching devices and ultimately controls the magnitude of output voltage and the overall performance of the multi-level inverter. A MATLAB based model is developed for nine level output voltage. THD of the output voltage is reduced drastically with the proposed circuit. Moreover due to nine levels of inverter, the requirements of filters also reduced.