A multi-pulse AC-DC converter fed space vector modulation (SVM) controlled neutral point clamped (NPC) inverter based vector control induction motor drive (VCIMD) is proposed here for medium power rating applications. To improve the power quality at supply side, a 12-pulse AC-DC converter is used and to meet the IEEE-519 standard, a high-pass filter is also used along with it. A three-level NPC inverter is utilised on the motor side to enhance the required performances of an induction motor drive (IMD). A modified SVM strategy is proposed to balance the capacitor voltages of the NPC inverter and to switch this inverter at very low switching frequency. The neutral point voltage balancing is achieved by the time adjustment between positive and negative small vectors. The model of proposed IMD is developed using the Simulink/MATLAB platform, and simulated response is validated with test results on a developed prototype in the laboratory to demonstrate its usefulness for medium power applications.

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In this article, a new structure is used for induction motor drive (IMD). A-polygon configuration based multi-winding transformer is designed in it to get an eighteen pulse AC-DC converter, which fulfill the DC-supply requirement of a 7-level cascaded H-bridge (CHB) inverter. This 7-level CHB-inverter is utilized at the drive end, to drive an induction motor (IM) and it requires less semiconductors switches and DC-supplies than the existing 7-level CHB-inverter. Therefore, a modified multi-winding transformer is designed to fulfil the need of a 7-level CHB-inverter, which also makes the input current closer to sinusoidal and reduces its THD to an acceptable value. A vector control is used to control an IM, which has good performance than v/f control. A new fundamental frequency switching technique (area equalization modulation strategy) is used in this work, to operate a 7-level CHB-inverter at fundamental frequency switching, which reduces the switching losses and increases efficiency of the system. The comparative study is also given to show the effectiveness of the system. Performance of the system is analyzed in MATLAB/Simulink under various operating conditions of IM. The simulated performances are validated from the experimental results captured from the developed laboratory prototype. INDEX TERMS Multipulse ac-dc converter, multilevel inverter, induction motor drive and power quality.

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