Common-mode overvoltage mitigation in a medium voltage pump motor transformerless drive in a mining plant

Mining process requires several types of mining pumps to transfer a fluid from one point to another in the process. In the majority of applications, those pumps are driven by variable speed motor drives in order to improve the energy efficiency of the overall system. Large pumps, ranging from hundreds of kW to a few MW, usually demand medium voltage converters. Transformerless converters reduce the footprint required for the installation, but produce additional concerns related to the common-mode voltages applied to the system and motor. The absence of an isolation transformer along with the use of PWM rectifiers are the root causes of this issue. This concern increase when long cables are needed to connect the converter to the motor. This paper presents an application where 3L NPC transformerless medium voltage converters were applied to drive motor pumps in a mining plant. The passive filter techniques used to address the common-mode voltage issue were analyzed through simulations and compared with the field results.