Research On Interleaved LLC Resonant Converter Technology

As energy problem becomes increasingly nervous, the efficiency of DC/DC converter has become an important index in measuring switching power supply quality. Compared with traditional PWM converter, resonant converter have many advantages, such as high frequency, small switching losses, low EMI noise and small size in many DC/DC converter topologies. Especially, LLC resonant converter may realize the zero voltage switching-on (ZVS) of switch, zero current switching-off (ZCS) of vice-side rectifier diodes, convenient for integrated magnetic and can also confront wide variations of input voltage and output load through varies little operating frequency. Due to these desirable advantages, LLC-SCR has been received extensive attention and applied in many applications. However LLC converter vice edge rectifier network does not contain the inductance, which cause the secondary side current discontinuous resulting in the large peak current for higher power rating. The ratio of the output current root-mean-square value and average value is 0.48. So when the output power increased, serious thermal phenomenon of output filters capacitance could be caused. That will shorten the life of power supply.In this paper, a simple indirect parallel LLC-SRC topology is proposed based on the literatures. The two way LLC driving pulse crisscross 90°, which could effectively reduce output current ripple, the number of output filter capacitance and the size of converter. Besides, it can increase the output power rating of the converter.The two converter realize interleaved paralleling through two capacitors in series to branch the input voltage. The paralleling topology share output filter capacitors, and only needs the voltage control loop to steady the output voltage. Also the current control loop is not necessary. After the control pulse frequency is split, the driving signal which crisscrosses 90°is obtained. The indirect parallel topology realizes load current sharing automatically with simple structure.This article analyzed the working principle in detailed. Using first harmonic approximation (FHA) method, the voltage gain characteristic, impedance characteristic, no-load characteristic and the constraints of zero voltage switching were analyzed. On the basis of the principle analysis, the main circuit and control circuit of system were designed by MathCAD. Then the system design was certificated by PSIM software. And a 24 V/14 A prototype was built. The experimental results showed that the indirect parallel topology realized load current sharing automatically, all switchs realized zero voltage switching-on in all the load ranges, switch noise was decreased obviously. And efficiency test curve showed that the half-load efficiency of converter was 95.3%.