Solving Duty-ratio Limitation for Four-phase Input-Parallel Output-Series DC-DC Converter with Asymmetrical PWM Scheme

The literature has conducted many studies on the input-parallel output-series (IPOS) converter. To increase the voltage gain, by synthesizing two single IPOS converters, a four-phase input-parallel output-series (4P- IPOS) converter was introduced recently. However, the duty ratio must be greater than 0.5 (i.e., D > 0.5) for the converter to work correctly, so it suffers from duty-ratio limitation. Moreover, there was no study on using a bipolar DC grid or a dual-output configuration. This paper proposed an asymmetrical PWM scheme, which easily implements to solve the duty-ratio limitation of the 4P-IPOS converter. Additionally, the use of a dual-output connection is studied. As a result, the converter not only can work with D < 0.5 and maintains the high voltage gain (i.e., $\left. {\frac{{{V_o}}}{{{V_{{\text{in }}}}}} = \frac{4}{{1 - D}}} \right)$, but also achieve outputs voltage balancing (i.e., Vo1= Vo2) as well as currents balancing (i.e., IL1= IL2, IL3= IL4). An 800-W prototype converter is used in simulation and experimentation to validate the suggested PWM technique.