Common-Mode Overvoltage Mitigation in a Medium-Voltage Pump Motor Transformerless Drive in a Mining Plant

The mining process requires different types of pumps to transfer fluids from one point to another. 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 give rise to 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 pulse-width modulated rectifiers are the root causes of this issue. This concern increases when long cables are needed to connect the converter to the motor. This paper presents an application where three-level neutral point clamped transformerless medium-voltage converters are applied to drive motor pumps in a mining plant. The passive filtering techniques used to address the common-mode voltage issues are analyzed through simulations. The proposed solutions are field tested with successful results.