Open-end winding motors are used extensively in ship electric propulsion systems, in which medium-voltage high-power inverters are a critical component. To increase the system voltage and power density, a dual five-level active neutral-point clamped (ANPC) inverter is proposed herein to drive medium-voltage open-end winding motors for ship electric propulsion. Each phase of this inverter comprises two five-level ANPC bridges and all the phases are powered by a common direct-current link. A hybrid modulation method is proposed to control this inverter. The series-connected switches in all the five-level ANPC bridges are operated at the fundamental frequency, and the other switches are controlled with a phase-shifted pulse-width modulation (PWM), which can achieve a natural balance between the neutral-point voltage and flying capacitor voltages in a carrier period. A closed-loop capacitor voltage balancing method based on adjusting the duty ratios of the PWM signals is proposed. The neutral-point voltage and flying capacitor voltages can be controlled independently and balanced without affecting the output phase voltage. Simulation and experimental results are presented to demonstrate the validity of this method.

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The brushless doubly-fed induction generator (BDFIG) provides an interesting alternative to the commonly applied conventional doubly-fed induction generator in wind turbines. In this paper, a novel voltage control strategy of stand-alone operation BDFIG for variable speed constant frequency wind energy conversion systems was presented. Based on the model of the generator, the power winding stator voltage and flux for stand-alone operation BDFIG are only determined by the equivalent PW stator magnetizing current which are independent of load, but PW stator terminal output power is only determined by load. An indirect PW stator flux orientated vector control scheme is employed to control the BDFIG by regulating the amplitude and frequency of the control winding stator current appropriately, and this results in constant generator terminal voltage and frequency for variations in both load and wind speed. In addition, simulation results prove the feasibility and validity of the proposed scheme, and excellent steady and dynamic state performance is achieved.

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