A reliable, interface-friendly medium voltage drive based on the robust IGCT and DTC technologies

The use of a voltage source power converter topology for medium voltage drive products allows to realize a utility interface compatible with IEEE 519-1992 by means of a series 12-pulse (or optionally a 24-pulse) diode rectifier without any harmonic filters or power factor correction equipment. On the motor side, the three-level voltage source inverter, also known as the neutral-point clamped (NPC) inverter, is the preferred type. In combination with the newest snubberless IGCT (integrated gate-commutated thyristor) technology, it is possible to build MV inverters without series connection up to 4 kV line-to-line voltage and higher. This results in a highly efficient and reliable MV power converter system with a minimum parts count. By using an LC-filter between the inverter and motor terminals, feeding of standard motors without derating becomes possible. With the use of direct torque control (DTC), as developed for low voltage drives, the MV drives applications benefit from the synergies with low voltage drives. Specific add-ons for the NPC inverter and the lossless resonance control of the LC-filter are needed. The DTC and the IGCT have been in commercial operation for several years, showing their expected very high levels of reliability and robustness. Both technologies reach today's known limits of physics, either in silicon or in torque control dynamics.