A Modified 2-level Three-Phase Inverter Topology with Common Mode Voltage Performance of a 3-level Inverter

An attractive feature of a multilevel inverter is the low common mode voltage (CMV). This means that in a switching cycle the peak to peak (P-to-P)CMV and the value at which transition of CMV happens have lower magnitudes for a multilevel inverter (MLI) compared to a 2-level inverter. This is an important advantage but still does not justify the use of MLIs on account of economic and component count factors. To offset this limitation, this paper proposes a modified 2-level three-phase inverter which exhibits similar reduced CMV performance as does a 3-level inverter. The proposed inverter uses only two extra switches, which makes the total number of switches as 8. The two extra switches allow one of the inverter legs (out of 3) to function as a 3-level inverter leg, while the other 2 legs continue to work as 2-level inverter legs. This results in a unique space vector (SV) diagram with 12 SVs whereas a traditional 2-level inverter has only 8 SVs. It is shown that by appropriately using these 12 SVs a similar CMV performance of a 3-level inverter can be achieved using the proposed topology. Simulation studies are carried out using the PLECS software to validate the various claims.