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 (TMDs). Usually, TMDs deploy an IGBT-based two-level voltage source inverter (VSI). Constraints on switching energy losses restrict switching frequency ( $f_{\text {sw}}$ ) 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, the LC filter poses a challenge on the aspect of parameter selection at low $f_{\text {sw}}$ (<1> $f_{\text {sw}}$ and reduction in maximum torque capability of IM constrain the values of filter components. This article deals with the 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 article for low $f_{\text {sw}}$ -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 an LC filter-based IM drive operated in vector control mode. Proposed optimal design and control methodologies are validated through simulations on an 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.