Experimental investigation of fault-tolerant control strategies for quad-inverter converters

Fault-tolerant control strategies for quad-inverter based multiphase-multilevel converters are proposed and experimentally verified in this paper. Explicitly, the conversion scheme consists of four standard 2-level three-phase voltage source inverters (VSIs), able to supply a dual three-phase induction motor in open-end stator winding configuration (asymmetric six-phase machine), quadrupling the utility power of a single VSI within given voltage and current ratings. The developed modulation scheme has the capability to generate multilevel output voltage waveforms in healthy conditions, equivalent to the one of a 3-level VSI, and to share the total motor power among the four dc sources in each switching cycle. This sharing potentiality is investigated under post-fault operating conditions, when one VSI completely insulated due to a severe failure on it. In such circumstances, the quad-inverter system can perform with reduced power rating by a proper modulation of the remaining three healthy VSIs. The complete multi-phase-multilevel conversion system with the proposed control algorithm under healthy and post-fault operating conditions has been verified by experimental implementation in open-loop control aspect using two dsp TMS320-F2812 processors with two three-phase passive loads in open-end configuration.