Single-phase five-level inverter with less number of power elements for grid connection

Recently, the emergence of single phase multilevel inverter has been increased due to its advantages over traditional one. This paper proposes a single-phase five level pulse width modulation (PWM) inverter for grid connection employing PI controller to perform unity power factor. Two triangular carrier signals identical to each other with an offset equivalent to the amplitude of the reference signal were used to generate PWM signals for the switches. The proposed inverter has the advantage of less number of components. Operational principles with switching functions are analyzed. A digital proportional integral current control algorithm is implemented in FPGA XC3S400 to control the injected current into the grid to be almost sinusoidal. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. Some switches operate at fundamental frequency and others operate at switching frequency. The proposed inverter has been compared with the conventional single-phase five-level PWM inverter. The effectiveness of the proposed inverter and its control technique has been verified theoretically, using PSIM simulation program, and experimentally, using laboratory prototype system.