Retrofit of fixed speed induction motors with medium voltage drive converters using NPC three-level inverter high-voltage IGBT based topology

This paper presents a solution to allow simple and risk-free retrofit of existing fixed speed induction motors with medium voltage adjustable speed drives to achieve attractive energy savings. The presented medium voltage adjustable speed drive consists of a twelve-pulse diode rectifier and a three-level neutral point clamped inverter using high-voltage IGBTs. Innovative features of the drive include series-connection of high-voltage IGBTs. The motor control is based on field-oriented vector control and an optimized PWM modulator, so that switching losses and current harmonics are minimized. An EMC-sinusoidal output filter is available to retrofit existing fixed speed motors with adjustable speed drive converter without incurring overvoltage stress on the winding insulation system, changes on the motors, the mechanical couplings, or the motor feeder cables, excitation of motor critical speed, or reduction in shaft power. Experimental and field results are also presented to confirm the proposed topology and related energy savings.