Comparative Analysis of Modulation Techniques for Modular Multilevel Converters in Traction Drives

The spreading of electric vehicles led to a renewed interest for innovative traction drives. In this context, an electric traction drive based on a Modular Multilevel Converter and integrating batteries in each module has been recently proposed. This converter concentrates into a single unit, the control of the traction motors, the balancing and energy management of the battery cells and the vehicle recharge functions. By using different modulation techniques it is possible to optimize different aspects like efficiency or THD of output current and voltages. Performance and efficiency in balancing, traction and recharging operations have been analyzed for two modulation techniques: near level modulation and phase disposition PWM. The near level modulation reduces switching losses while the second one better follows voltage references reducing current THD and, consequently, conduction losses. In this paper an innovative modulation technique is proposed and its performance in terms of current THD and global losses are compared with the other two modulation strategies already proposed.