ANALYSIS, HARDWARE IMPROVEMENT AND OPERATION OF A MULTILEVEL CHB INVERTER

With the electrification of many sectors it became important to investigate in high fault tolerance and reliability. In the case of electric drives different studies proved that the best choice for safety-critical operation is the 9-phase permanent magnet synchronous motor: different connection topologies are possible to drive the machine, but the best configuration is that with a separated 9-phase system, driven by nine 5-level Cascaded H-Bridge inverters (5LCHBI), each one connected to one motor phase. In a Cascaded H-Bridge inverter multiple H-Bridges with independent DC sources are connected in series. A single module can produce three different voltage levels as output and the total output voltage of the inverter is the sum of the output voltage produced by each single cell. Hence by connecting two modules in series it will be possible to obtain an output with five voltage levels. In this thesis the theory behind inverters and multicarrier PWM schemes for CHB inverters is studied. Since some PCB modules had already been designed and manufactured, the control signals for the switches of the inverter are generated with a microcontroller and then a test bench for a small electric drive is assembled in the laboratory, with the purpose of driving an electric machine. Finally a model of the inverter is assembled in LTspice, this analysis on component-level aims at reproducing the behavior of the inverter during switching operations and to help having future hardware improvements. This master's thesis continues the development of a multilevel inverter for a 9-phase electric drive and it does so by studying the theory of the inverter and PWM modulation schemes, investigating on the functionalities of a microcontroller and on how to instruct it to output PWM signals and drive a multiphase machine, discussing the results of analysis at component-level by creating a model to analyze switching operations of the inverter. The results of this work could be a starting point for future research on this topic.