Using the Frequency and Pulse Width Modulation Techniques for Regulating the LLC Resonant Converter Output Voltage

This paper analyses the LLC resonant converter below its resonant frequency, because ZVS in MOSFETs and ZCS in output diodes can be achieved in this area and also the converter operates like BOOST converter. Simultaneous switching frequency and pulse width modulation techniques in steadey state are applied for controlling of this converter. In this approach, two control variables are used, which gives designers one more degree of freedom in comparison to the conventional techniques. finally the voltage gain of this converter is defined based on swithing frequency and duty cycle and quality factor. To verify the given analysis the LLC resonant converter has been simulated under the wide output power range of 20-200 W. To regulate the output voltage at 100 V, input voltage has been choosen at 400V and its switching frequency varies in 200-400 kHz and duty cycle in 0.1 0.9. more over experimental results have been presented.