Medium Voltage Induction Motor Drive feed by Multi Pulse Converter and Asymmetric Multi Level Inverter with On-Line Angle Selection based Modulation

Low switching frequency operation is mandatory in high-level multi-level inverter to enhance the switch utilization as well as to gain excellent efficiency profile of converter with low power losses. Apart from this, variable speed drive required voltage level and frequency variation when the drive operates below the base speed. Hence, a new fundamental frequency switching technique with an online angle calculation-based modulation technique is presented for a nine-level (1:1:2) asymmetric reduced switch cascaded H-bridge multi-level inverter (ARSCHB-MLI), where this technique is known as the area equalization modulation strategy (AEMS). Power converters in the high power range are often used, increasing the power-quality issues in the system. To overcome the issues at the drive end of the system, the induction motor is powered by a nine-level inverter, which is designed with a ten-switches and three-voltage DC sources per phase. For better power quality performance, online angles are calculated at different values of modulation index, which changes the width of steps voltage levels as speed variation of the drive. This strategy ensures that the quality of inverter output is acceptable as per standard regardless of the drive's operating frequency. Multi-pulse converter technique is adopted at the grid end to sustain the power quality as per the IEEE 519 standard. This paper serves as a guideline of how one can design, operates and control of the power converter for medium voltage drive system.

I. Introduction

In the recent years, the power converters (multi pulse AC-DC and multilevel DC-AC) family for medium voltage drives have been attracting attention of power electronics engineers. Because, the most of the bigger industries like gas, oil, and cement industry have been paying attention to driving variable speed high power compressors, and conveyers by the medium voltage drive, where medium voltage induction motors (MVIM) ranging from 3.3kV to I3.8kV have emerged as an economically viable technology in these applications. Behind this economical technology, the power converters have played a key role to make it successful [I]. In the medium voltage adjustable speed drive application, power converters create many issues like power quality, high power losses, complex control system, large number of components (semiconductor switch, gate driver), size and costs. As a result, most recent research has been focused on enhancing the performance and efficiency of power converter topologies that are already in use. Following this advancement, research in this field is being expedited in order to improve the performance of the medium voltage drive system in terms of improving power quality profile, lowering power losses, and reducing system size.