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A Novel Thyristor-Based CSI Topology With Multilevel Current Waveform for Improved Drive Performance

Load-commutated inverters (LCIs), combined with wound-field synchronous machines (WFSMs), can be an excellent solution for high power drives, but their present technology suffers from important drawbacks related to low power factor, large torque pulsations, and poor starting performance. This paper presents a new LCI design intended to overcome the mentioned limitations. An SCR-based forced-commutation circuit is added to the common inverter topology to obtain a five-level waveform for the stator current. This leads to significantly reduced current harmonics and torque pulsations, in addition to bringing benefits in terms of lower additional losses. As a further advantage, the proposed design allows for a significant power factor enhancement. Finally, it enables the WFSM to be started with a much smoother torque compared to the traditional pulsed operating mode of conventional LCI drives. Simulation studies are conducted on a high-power drive scheme to show the aforementioned improvements. Also, a reduced-scale laboratory prototype of a WFSM drive system is tested to verify the feasibility of the proposed converter.