I'm developing full bridge based LLC. I haven't seen any development with full bridge and mostly work with only half bridge. I'm using resonant converter controller IC by modifiying 2 gate pulses to 4 pulses. What could be the possible challenges with this design?
Basically, full bridge inverter brings can operate well with higher input current as compared to half bridge. In my view, there is not so many different things here between them. However, you should note:
(1) voltage gain is different in two cases
(2) the driver circuit is obviously changed
Possibly the electric noise will be of higher frequencies. The solution is to add low-pass filters on all wires and use a thin metal encapsulation of the converter (and eventually use shielded motor cables and connect the motor metal housing as well). That should keep the radio noise in.
One issue in a full-bridge LLC relates to holding the input voltage bus constant enough not to effect the resonant waveforms. When designing a half-bridge LLC, the resonant capacitor can be split between the upper and lower rails. When splitting the resonant capacitor between the upper and lower rails, the resonant capacitor also contributes stability to the input bus. If the resonant capacitor is single-ended, the waveforms will be the same only in the case of an infinitely stiff input bus. So just make sure that the input bus has adequate capacitance (both high and low-frequency). Otherwise, the resonant waveforms could be effected and be distorted from sinusoidal waveforms, sometimes having slightly different waveforms between the two half-cycles.
Another issue relates to not being able to use voltage clamping as a simple means to limit current. In a half-bridge configuration, the addition of diodes to the half-bridge capacitor tie point will limit the voltage excursion on the resonant capacitance and can be used as a very simple and inexpensive means to limit the maximum current that can flow in the resonant tank. This technique cannot be used for a full-bridge.
Generally speaking, half-bridge LLCs are much more forgiving circuits than full-bridge LLCs, so one should typically only go to a full-bridge configuration at very high power levels.
The main issues to be considered are the assigned and selected parameters. As the voltage gain should be known, and it is a function of frequency ratio, load values, and inductance ratio. Once all these parameters been carefully selected. You need to consider the approach of generation your pulse (controller algorithm) , by using fixed frequency with duty cycle variation, or fixed duty cycle with varying switching frequency.
Based on my simple experience in this topic, the variable frequency control is the most efficient one. Besides, try to use higher frequency to minimize losses, and noise interfacing.