An Interleaved Secondary-Side Modulated LLC Resonant Converter for Wide Output Range Applications

In this paper, an LLC type converter with two interleaved pulsewidth modulation (PWM) rectifiers is proposed. Compared with the conventional LLC converter, it achieves a wide voltage regulation range independent of load. In the proposed structure, each secondary-side PWM rectifier can operate individually. With the interleaving technique and shared primary-side switching network, the circuit secondary-side current stress is halved and the primary-side current stress is largely reduced. Besides, the filter capacitor requirement is reduced. Therefore, the proposed structure is a good option for medium/high power wide output range applications. The symmetrical LLC resonant tanks always operate at the resonant frequency, which marks the optimal operation point of the LLC resonant tank. Therefore, the conduction loss is effectively mitigated. In the proposed converter, zero-voltage turning-on (ZVS) of the primary-side MOSFETs can be ensured and is independent of the load. Moreover, the turning-off currents of the primary-side MOSFETs are small and are also load independent. This brings the benefits of minimized circulating current and negligible turning-off loss and no MOSFET turning-off voltage spike. The secondary-side auxiliary MOSFETs turn-on with ZVS and rectifying diodes turn-off with limited di/dt. Topological analysis and experimental results of a 1.3 kW/100 kHz prototype generating 230-440 V output from 390-V input are presented. The prototype demonstrates 97.31% peak efficiency and good performance over a wide output range.