A new force-commutated current source inverter

Current source inverters (CSI's) were a common drive topology in the early days of electronic machine drives because of their effective use of the thyristor. The CSI's popularity was reduced over time with the introduction of fully controlled semiconductor switches, such as the MOSFET or IGBT, which provided greater possibilities for machine control and performance via the modern voltage source inverter. Today, CSI's are typically limited to the very large power applications where the thyristor is still the most economic choice for the switch device. Unfortunately, an inverter which uses strictly thyristors is unable to take advantage of the modern modulation and control techniques, while an inverter which uses fully controlled switches, such as the gate turn-off thyristor (GTO), can implement these techniques; however, the inverter becomes very expensive to build due to the controlled switch's high cost.; This research proposes a solution to this dilemma by introducing a new CSI switch pole topology which consists of two thyristors, two diodes and one fully-controlled switch. This topology provides the control performance of a CSI formed with six fully controlled switches along with a potentially lower cost, since the number of expensive controlled switches are cut in half. A novel resonant commutation assist circuit is proposed to reduce the thyristor commutation time. This circuit is analyzed and a complete design procedure is presented. Issues regarding the control and operation of the new topology are examined. The operation of the proposed topology is demonstrated through a combination of simulation and experimental tests. The development of a high power test facility needed for testing under target application power levels is also described.