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An Optimized SVPWM Strategy for the Postfault Three-Level NPC Voltage Source Inverters

The three-phase three-level neutral-point-clamp inverters can be reconstructed into eight-switch three-phase inverters (ESTPIs) after a single-phase failure. However, different topologies of the ESTPIs are performed according to the failures in different legs, and accordingly, the ESTPIs are controlled by different kinds of space vector pulsewidth modulation (SVPWM) strategies and control algorithms, which may bring concerns in terms of the computational burden. Meanwhile, the dc-link neutral-point voltage fluctuation of the ESTPIs performs the imbalance three-phase current output and significantly deteriorates the fault-tolerant control performance. To address these problems, an optimized SVPWM strategy is proposed in this article. The three SVPWM algorithms are unified by a coordinate transformation, available for any-phase failure. Moreover, the moving average filter with a proportional controller is used to extract the dc component of the neutral-point voltage, which is regarded as the compensated amount to modify the duty-ratio of the basic voltage vectors. Finally, the current imbalance after single-phase failure is suppressed. The effectiveness of the proposed optimized SVPWM strategy is verified through simulation and experimental tests.