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This study presents a topology for cascaded multilevel inverter (MLI). Each module is made up of Hand halfbridges, two isolated equal dc sources and a bidirectional auxiliary circuit. One leg of the H-bridge and the half-bridge are cut and the corresponding terminals are connected to the both ends of an equal split dc source. The free ends of the halfbridge are connected together to form a common output node of the inverter. The auxiliary circuit is inserted between the midpoint of the split dc sources and this very output node. The output point of the uncut leg of the H-bridge forms the remaining output node. With this circuit arrangement, proper control of the switches in the bridges and the auxiliary circuit, in each cascaded cell, can produce nine output voltage levels. A comparison is made between the proposed inverter, classical CHB and some of the recent developed MLI topologies with respect to specified figure of merits, as well as the per unit power losses. For two cascaded modules, simulation and experimental verifications are carried out on the proposed inverter topology for an R-L load; adequate results are presented.

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Sensor-less based direct vector control techniques are widely used for three-phase induction motor drive. Whereas in case of multiple motor control, it becomes intensively complicated and found very few research articles support to industrial applications. A straight forward direct vector control with sensor-less operation for parallel connected two similar rated induction motors driven by single three-phase inverter is proposed and verified numerically by simulation software test under balanced and unbalanced conditions. The proposed control algorithm adapts the nature observer to estimate the rotor speed, rotor flux and load torque of both motors. Simulation results along with theoretical background provided in this article confirm the feasibility of operation of the ac motors and proves reliability for industrial applications. Padmanaban Sanjeevikumar (M'12, SM'15) received B.E., M.Tech. (with distinction), and Ph.D degree in electrical engineering