Driving AC motors through long distances with DC transmission: Experimental results

Driving induction motors with PWM inverters through long distances result in several undesired high frequency phenomena, such as transient overvoltages at the motor terminals, common-mode currents flowing through the system and the presence of a cable charging current, among others. Instead of filters, which represent the traditional method for the mitigation of these problems, in a previous work the authors proposed an alternative solution, where the rectifier and inverter bridges are separated and connected by the long cable, being the latter located right besides the motor. This alternative configuration, based on DC transmission, aside from solving the aforementioned problems, provides the additional benefits of reducing the voltage drop in the cable and providing copper economy for the power transmission. In this context, in the present work a prototype of a long cable motor drive system was built in both configurations (conventional and with DC transmission). Several results involving the transient overvoltages, cable charging and common-mode currents were obtained from each system and compared, in order to demonstrate the effectiveness of the proposed drive system topology in reducing these undesirable phenomena.