Four Quadrant Medium Voltage Drives

Medium voltage drives require regenerative capability for applications like lifts, conveyors with overhauling loads and other applications that require torque control or fast deceleration. One method to provide regeneration at low cost and low complexity in medium voltage drives is with the use of six-step control method. While the control of front-end semiconductor devices is simple, the resulting input currents have much higher distortion during regeneration as compared with the currents during motoring. During the last decade, the cascaded H-bridge (CHB) inverter has become the topology of choice for medium voltage (MV) motor drive applications. In this paper a CHB topology with low inverter count of nine is considered with six-step control. A new method to control the front-end devices of the individual inverters is proposed. Implementation of the method with a multi-pulse transformer is described. This method is shown, through simulations and circuit measurements, to improve the input current distortion of the input currents during regeneration while meeting the limits recommended in the IEEE-519 Standard.