Abstract
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.
Highlights
Introduction1All-electric ships are the future trend in modern ships owing to their advantages of high fuel efficiency, high power density, and high dynamic response [1,2,3]
Open-end winding motors are used extensively in ship electric propulsion systems, in which medium-voltage high-power inverters are a critical component
Medium-voltage direct current (MVDC) systems offers many advantages over medium-voltage alternating current systems; the former are regarded as the next-generation ship integrated power system (IPS) [1,2]
Summary
All-electric ships are the future trend in modern ships owing to their advantages of high fuel efficiency, high power density, and high dynamic response [1,2,3]. Its DC-link is powered by four separated DC sources to solve the NP voltage balance problem, which is the main drawback of this topology Another solution for open-end winding motor drive is to use multilevel DC-link (MLDCL) inverters [35], which can be regarded as an H-bridge with a multilevel DC-link voltage. It is more complex for higher voltage levels owing to the rapid increase in voltage vectors and redundant switching states [40,41,42,43,44] To alleviate this problem, a hybrid modulation method that combines the three-level SVPWM and PSPWM is proposed in Ref. To solve the capacitor voltage balancing problem of the dual 5L-ANPC inverter, a hybrid modulation method based on PSPWM is proposed, which permits the fundamental frequency switching of series-connected switches and equal frequency switching of other switches. Simulation and experimental results are presented to demonstrate this method
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