Low Switching Frequency PWM Fed Medium Voltage High Power Traction Motor Drive with Optimized LC Filter

Abstract

Induction motor (IM) drives, rated above 750 kW, are utilized for railway traction applications. These drives are popularly known as traction motor drives (TMD). Usually, TMDs deploy IGBT based two-level voltage source inverter (VSI). Constraints on switching energy losses restrict switching frequency (fsw) below 1 kHz. Consequently, motor line current quality deteriorates significantly. LC filter, connected at the output of VSI, provides a possibility of improving total harmonic distortion (THD) in motor line current. However, LC filter poses a challenge on the aspect of parameter selection at low fsw (< 1 kHz). A narrow band gap between rated fundamental frequency & fsw and reduction in maximum torque capability of IM constrain the values of filter components. This paper deals with optimized design, analysis, and control methodology of LC filter based high-power TMDs. A technique for determining the optimized filter parameters is proposed in this paper for low fsw fed IM drive. Small signal model analyses of standard and LC filter based IM drives are performed considering the inverter delay. A suitable active damping coefficient is proposed for LC filter based IM drive operated in vector control mode. Proposed optimal design and control methodologies are validated through simulations on a 850 kW, 2.2 kV, 65 Hz IM drive. Analytical and simulation findings are reinforced through experimental measurements on a 3.7 kW, 400 V, 50 Hz IM drive. © 2015 IEEE.