Design and Analysis of a 54-Pulse Converter and 7-Level Hybrid Inverter for Medium Voltage Induction Motor Drive

Abstract

Multi-level converter (MLC) and multi-pulse rectification configuration-based system is highly attractive to develop medium-voltage variable frequency drives (MVVFDs), because they supply high-quality power with strong reliability. In this paper, a hybrid symmetric cascaded seven-level inverter is designed by the connections of the one-half bridge and two full H-bridge inverters. Conventional seven-level cascaded H-bridge inverter-based drive employs per phase three-full H-bridges and each power cell requires isolated three DC sources. The present circuit configuration of the 7-level inverter is required less number of semiconductor switches compared to the conventional seven-level cascaded inverter, which indirectly reduces the size of the system due to the reduction of component count like gate driver and control circuit etc. Apart from this, a switching frequency optimal-nearest level control (SFO-NLC) scheme is utilized to generate a low switching frequency gating signal for the 7-level inverter switches. A fifty-four-pulse converter is connected at the grid side of the presented system, which enhance the power quality profile at the grid side and supply the rated power and DC-link voltage at the input terminals of the inverters. Hence, this paper describes the key design concept, developments and operation and control of the power converters to meet the medium-voltage drive applications challenge such as high-power quality, low switching loss and compact size. Furthermore, theoretical, simulation and experimental results using a dSPACE (DS1006) controller-based prototype are included to justify the suitability of the proposed technique.