Improving the Fault-Tolerant Operating Range of Automotive 3-Level Inverters by Using Asymmetrical Fundamental Frequency Switching

Fault-tolerant inverters enable reliable drive trains for electric vehicles. Particularly 3-level inverters offer an increased fault-tolerant operability. For certain machine parameters, a reconfiguration process from normal 3-level operation to failure mode is not feasible at higher speeds. To increase the fault-tolerant operating range of the inverter-machine system, an adapted modulation strategy is required. The approach presented in this paper uses transient asymmetric fundamental frequency switching to safely transfer the system from its original operating point to a stable operating point with symmetric modulation. In contrast to ASC operation, the presented method avoids causing an increased transient over-current when a failure occurs.