Online reduction of fifth and seventh harmonics in single phase quasi square wave inverters

Inverters form a major part of power electronic industry. The AC output of inverter is mainly controlled by pulse width modulation (PWM) technique. The PWM approaches are accompanied by harmonics due to the switched nature of power electronic devices. There are many ways to eliminate the harmonics such as selective harmonic elimination. Selective harmonic elimination is associated with tremendous task of numerical computations in offline. The tremendous task of computing is reduced by implementing an online approach of harmonic reduction using an active filter(compensating inverter). The proposed work is implemented on a single phase quasi-square wave inverter which is considered as an abundant harmonic source. A neutral point clamped three level leg is used as main inverter as well as active filter(compensating inverter). The online computation of phase voltage harmonics is carried out on a low cost PIC 18F4550 controller. The control pulses of the active filter are generated from the phase voltage harmonics. The main inverter is connected in series with active filter(compensating inverter) in the proposed topology. Theoretical analysis of this proposed strategy is presented in this paper with simulation and experimental results. The added advantage of the proposed method is the reduction of harmonics with reduced number of devices.