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 require detailed application engineering for the particular site to mitigate power factor (PF), line harmonics, torque pulsation, and motor design requirements. In the past decade, manufacturers have started offering voltage-source inverter (VSI) pulsewidth modulated (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 five-level neutral point clamped (NPC) or cascaded H bridge (CHB) topologies, usually limited to 11 kV, but now some manufacturers are utilizing modular multilevel converters (MMCs) for very-high-power applications with voltages above 11 kV. The MMC topology is further explored together with its application to these medium-voltage motors.