Elimination of Harmonics in Photovoltaic Seven-level Inverter with Newton-raphson Optimization

This paper describes a strategy to optimize the switching angle of a modified H-bridge single-phase seven-level inverter for stand-alone photovoltaic (PV) system. The inverter comprises a conventional H- bridge inverter and two bidirectional switches. It can generate seven-level output voltage level, namely +Vdc, +2/3Vdc, +1/3Vdc, 0, -1/3Vdc, -2/3Vdc and -Vdc. Optimized Harmonic Elimination Stepped Waveform (OHESW) technique was employed to improve the output waveform quality. Newton- Raphson method is engaged to solve the transcendental equations from OHESW technique which produces all possible solutions with any random initial guess. Among which sets, the one producing the least output-voltage THD was chosen. Computation resulting from the optimized switching angle was simulated. A small-scale laboratory prototype was built and tested. Its results indicated the proposed method's effectiveness and the application feasibility of the fundamental frequency switching.