With wide application of inverters in modern industry, common-mode voltage (CMV) problems invoked severe negative effects. Hardware and software solutions have been proposed to reduce the CMV. Compared with hardware CMV mitigation solutions, software strategies based on pulse-width modulation (PWM) modifications have aroused widespread attention for their cost-effective and control flexible advantages. Up to date, various reduced CMV PWM (RCMV-PWM) strategies have been reported, such as active zero state PWM, remote state PWM, near state PWM, phase-shifted carrier PWM, carrier peak position modulation and so on. For convenience of understanding and utilising the existed RCMV-PWM strategies, this study conducts a review on this topic. According to the principle of CMV reduction algorithms, the study divides the reported RCMV-PWM strategies into three different categories. It also presents comparisons of CMV reduction techniques and output performances (like CMV value, output ripple and linearity range) between different strategies. Meanwhile, CMV suppression principles, problems in implementation and improvements of each technique are described in detail. Moreover, the inherent characteristics and development tendencies of the RCMV-PWM techniques are discussed so as to offer reference for further research.

LLC resonant converters, generally adopting frequency modulation control, can hardly achieve high efficiency under both heavy and light load conditions. Especially under light load conditions, the high-switching frequency seriously degrades converter's efficiency. This study propose a new pulse-width modulation (PWM) control strategy for LLC resonant converters under light load applications on the premise of no change in the main circuit structure. The voltage gain of the converter is regulated by varying duty ratio instead of increasing switching frequency and therefore zero-current switching for rectifier diodes can be realised under light load conditions. With the proposed PWM control strategy, the gain is not affected by the load variations and an optimal design of the magnetic components is possible, therefore the efficiency is further improved by reducing both the switching losses and the losses in magnetic components. Experimental results demonstrate the effectiveness of the proposed PWM strategy by increasing the efficiency of LCC resonant converter, especially under light load conditions.

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