Medium Voltage Drives: Are Isolation Transformers Required?

Traditionally isolation transformers are used on Medium Voltage Drives. Although this provides a means for reducing harmonics, reducing voltage stress on motors or provided a means to achieve a Medium Voltage drive utilizing Low Voltage cells, it increases the size, cost, complexity and losses of the drive system. With the implementation of alternative topologies and new Pulse Width Modulation switching patterns, these goals can be achieved without the use of an isolation transformer. The paper presents the topology and the techniques that can be utilized and proposes an overall ac drive system without the need for the transformer. Experimental results on a 600hp, 4160V drive are also included.