A Multilevel Inverter with Increased Linear Modulation Range For Electric Transportation Applications

This paper presents a hybrid multilevel inverter topology, combining a two-level inverter with a capacitor-fed H-bridge circuit in each phase. The proposed converter has an extended linear modulation range compared to conventional multilevel converters. In the extended linear modulation range, an additional pole voltage level in each phase, increasing the number of levels from four to five, is achieved by adding the CHB capacitor voltage to the DC link voltage V _dc +V _dc /3). In the extended linear modulation range, space vector PWM control is possible with the increased pole voltage levels, resulting in the absence of low-order harmonics in phase voltages. Compared to conventional schemes, this feature is very useful in Electric vehicle (EV) applications where the drive is operating in the flux weakening region, where in the present case, we can get maximum phase peak fundamental amplitude in sinusoidal operation compared to six-step mode operation in conventional schemes. The H bridges’ capacitor voltages can be controlled using space vector redundancies. It is required to tightly regulate the capacitor voltages to one-third of the DC link voltage to maintain proper voltage levels in the output phase voltages. Maintaining the required capacitor voltages involves applying space vector redundancies, which charge or discharge the capacitors as needed. Experimental results for both steady-state and transient conditions are presented to validate the effectiveness of the proposed inverter topology.