Improved hybrid fixed-frequency modulation strategy for series resonant converters for wide range applications

In recent years, resonant converters have been widely used in the fields of electric vehicles and renewable energy systems due to their excellent characteristics in terms of high energy density, high energy efficiency, wide output range, and wide ZVS range. Conventional resonant converters generally adopt pulse frequency modulation (PFM) in a wide range of output applications. This means the frequency varies over a wide range, which results in problems such as high switch loss, large noise, and high EMI. To solve this problem, this paper proposes a hybrid fixed-frequency modulation strategy applied to a wide range of outputs based on the series resonant converter, where asymmetrical voltage-cancellation control (AVC control) and its improved strategy (IAVC control) are applied in the normalized gain ranges of [0.5, 1] and [0, 0.5]. The proposed modulation strategy achieves lower switching loss, higher efficiency, and better ZVS characteristics in wide voltage output and load ranges. Under the same output voltage and power, to realize ZVS, the proposed hybrid modulation has a smaller switching frequency and resonant current, which improves efficiency and reduce losses, especially in the case of low voltage gain and light load conditions. Finally, experimental data obtained from an 80 V input and a 800 W power max prototype circuit are included to verify the proposed hybrid modulation strategy.