Investigation Of Pulse-Width Modulation And Predictive Control Algorithms For Eight-Switch Three-Phase Inverters

The three-level neutral-point-clamped (NPC) inverter has been widely applied in various areas since being proposed in 1981. However, the failure of power semiconductor devices in a leg will seriously threaten the safety operation of the three-level NPC inverter. To solve this problem, the three-level NPC inverter can be translated into single-leg fault-tolerant topologies. Based on that, the three-level NPC inverter can be translated into the eight-switch three-phase inverter (ESTPI) after the failure of a leg. In this dissertation, the various space vector pulse-width modulation (SVPWM) algorithms for ESTPI, the methods to enhance the DC-link voltage utilization ratio of the ESTPI and the model predictive control algorithm with the DC-link voltage fluctuation suppression for ESTPI-fed asynchronous motor drive systems are investigated.Firstly, the three different topologies of ESTPIs and the basic principle of theirs SVPWM algorithms are introduced and the mathematical model of the ESTPI are also investigated. To reveal the relationship among the SVPWM algorithm based on all basic voltage vectors named SVPWM-1 and the SVPWM algorithm based six small vectors and the zero vector named SVPWM-2 of three different ESTPIs, the comparison investigation of these six SVPWM algorithms are carried out. To enhance the DC-link voltage utilization ratio of the ESTPI, the SVPWM over-modulation algorithms for ESTPI are investigated and a superposition-principle-based SVPWM-2 over-modulation algorithm is proposed. The validity of the theoretical analysis is verified by simulation and hardware-in-the-loop (HIL) experimental results.Secondly, the basic principle of the carrier-based pulse-width modulation (CBPWM) algorithm for ESTPI is introduced. Based on the regular sampling method, the equivalent CBPWM algorithms of SVPWM-1 and SVPWM-2 in the linear region are derived, respectively, and the comparison of these two CBPWM algorithms are also carried out. On the basis of that, the relationship between of SVPWM-1 and SVPWM-2 is revealed. To enhance the voltage utilization ratio of the ESTPI by using the CBPWM algorithm, on the basis of the regular sampling method, the equivalent CBPWM algorithm of the superposition-principle-based SVPWM-2 over-modulation algorithm is derived. Moreover, the change rules of modulating functions of the equivalent CBPWM algorithms are summarized with the change of the modulation index. The validity of the theoretical analysis is verified by simulation and HIL experimental results.Finally, to achieve the high-performance control of ESTPI-fed asynchronous motor drive systems with DC-link voltage fluctuation suppression, a six small vectors and the zero vector based finite-control-set model predictive torque control algorithm is proposed. The validity of the theoretical analysis is verified by simulation and HIL experimental results.