High-Frequency Characteristics Analysis of Transformer-Based Voltage Multiplier in Lightweight Process of Unidirectional High Step-up Converters for Offshore Wind Farms

To realize the lightweight of unidirectional high step-up converters for offshore wind farms, it is necessary to increase the switching frequency. However, there is a gap in the analysis of the switching frequency effect, the frequency characteristics of the converter are not clear enough to provide theoretical guidance for the high-frequency design. To address this problem, the effect of switching frequency on the voltage conversion ratio (VCR) and maximum output power (MOP) of the widely used transformer-based voltage multiplier (TBVM) in unidirectional high step-up converters is discussed in this article. More accurate mathematical models for two types of TBVMs, pulsewidth modulation TBVM (PTBVM) and resonant TBVM (RTBVM) are established. The effect of frequency on VCR, MOP, stresses together with losses is analyzed in detail accordingly. Theoretical analysis and comparison show that, in PTBVM, the increase in switching frequency decreases MOP and enlarges the VCR sensitivity to the load, and power switches suffer from large current stresses due to circulating power. In contrast, RTBVM is more suitable for high-frequency applications for the following advantages: duty cycle independent characteristics, higher maximum output power, higher efficiency, and load-insensitive VCR. Finally, experiments at 100 kHz switching frequency verified the theoretical analysis.