In this paper, a method is proposed, for the first time, to increase the linear modulation range till full base speed irrespective of load power factor for a multilevel inverter fed induction motor (IM) drive. A 5-level inverter with a single DC source is used for the proposed scheme. Using this method, linear PWM operation of the inverter can be achieved till peak phase fundamental voltage of 0.637Vdc without exceeding machine phase voltage rating. This method eliminates all the lower order harmonics from machine phase voltage till the full speed range of operation. The proposed 5-level inverter scheme is realized by cascading a 2-Level inverter with a capacitor fed H-Bridge, feeding Open-End Induction Motor (OEIM) drive from one end and a capacitor fed 2-Level inverter from the other end. The proposed scheme uses Space Vector (SV) redundancy to balance all the capacitors during its operation. Operation of the proposed drive is analyzed extensively for normal 5- Level operation as well as during the extended modulation range. Experimental results for steady state and transient state operation are presented to validate the proposed scheme.

This article proposes a novel nine-level multilevel inverter topology with an instantaneous voltage balancing scheme of stacked dc-link capacitors for an induction motor (IM) drive application. Three neutral points (NPs, terminal joints of four series-connected capacitors) across a single dc-link are balanced instantaneously (within a sampling interval) by ensuring zero current at the NPs. The proper selection of pole voltage from the redundancies provides zero current at any NP during the pulsewidth modulation operation under a steady-state and transient operation. A five-level stacked inverter and three cascaded hybrid-bridge (CHB) inverter cells are used in each phase. Along with the balancing of dc-link capacitors, CHB capacitors’ voltage balancing is also achieved using the pole voltage redundancies at all modulation indexes for all power factor and load. It is also possible to increase more number of levels using more low-voltage switches, and a generalized form of the topology is presented. The concept is validated using a laboratory-developed nine-level inverter with a three-phase IM load, operated under “V/f” control. The detailed experimental results for the steady and transient condition, simulation studies for switching loss, and harmonic content in the phase voltage are also presented.