Enhanced Pulse Width Modulation Methods for 1-ϕ Five-Level Neutral Point Clamped Inverter

This paper proposes enhanced pulse width modulation (PWM) techniques for the single-phase five level neutral point clamped inverter. In comparison with the traditional modulation techniques such as level shifted PWM (LS-PWM) and phase shifted PWM (PS-PWM), the proposed PWM techniques can guarantee enhanced power quality and the power balance between the two-legs of the inverter. With traditional modulation techniques, the losses between both legs of the inverter are not equal due to unequal utilization rate of the switches which reduces the efficiency of the inverter. Further, the unequal power loss distribution will result in unequal junction temperatures of the semiconductor devices which causes the failure of the power devices. Hence the reliability of inverter reduces. To tackle these issues, two enhanced PWM techniques that rely on modified/improved modulating waves and re-arranged triangular waves are introduced in this paper. By using the proposed PWM techniques, the power can be uniformly allocated between the two legs of the inverter. In addition, the switch's utilization rate is the identical with less switching times resulted in reducing the junction temperatures and enhancing the efficiency of the inverter. The proposed modulation techniques are verified through MATLAB simulations and experimentally validated on a 1kVA laboratory prototype of five level inverter.