Evolution of Very High Power (>15 MW) Medium Voltage Drives

Very high power adjustable speed motor applications above 15 MW historically used Load Commutated Inverter drives coupled to designed for purpose synchronous motors. These systems required detailed application engineering for the particular site to mitigate potential power factor, line harmonics, torque pulsation, and motor design requirements. In the past decade manufacturers have started offering Voltage Source Inverter PWM drives at these power levels, up to 13.8 kV motor voltage for both induction and synchronous motors, which have fewer application complications. These large drives were initially based on either 5-level Neutral Point Clamped or Cascaded H Bridge topologies, usually limited to 11 kV, but now some manufacturers are utilizing Modular Multilevel Converters for the very high power, applications with voltages above 11 kV. The Modular Multilevel Converter topology will be further explored together with its application to these medium voltage motors.