Speed Control of Three-Phase Induction Motor Employing a Modular Multilevel Inverter Under Normal and Fault Tolerant Conditions

Incapability under faulty conditions is one of the most important problems of induction motor drives which are controlled by multilevel inverters. This paper investigates a modular multilevel inverter which is employed as an induction motor drive with capability of operation under normal and faulty conditions. For this aim, different switching scenarios have been defined for each switch under faulty conditions. In this method, when one of the switches is faulted, the switching scenario is altered and the motor operates in its normal mode although a percent of output power is lost. One of the most important factors in multilevel inverter design is the number of the power electronic elements which directly influences the cost of the system. From this view point, the presented multilevel inverter structure employs fewer number of power electronic elements in comparison with other conventional multilevel inverter topologies. The other advantage of the presented topology is its capability to cascade different units which can be used for high power motor applications. To illustrate the efficiency of the proposed system, a closed loop indirect field oriented control method has been applied to the suggested topology. Different scenarios including normal and abnormal conditions have been applied to the system. To verify the valid operation of the presented system, a 15 kW three phase induction motor is selected and simulated using MATLAB/Simulink software. According to the analysis and simulation results, the presented system shows a good performance under various conditions. In addition, good voltage balancing and low total harmonic distortion are the main features of the proposed system. © 2018, The Korean Institute of Electrical and Electronic Material Engineers.