Analysis and Control of Three-Phase Interleaved SCC-LLC Resonant Converter Load Sharing Considering Component Tolerance

The conduction loss becomes extremely large if applied LLC converter in high power electrical vehicle (EV) applications. Interleaving technique can help reduce the conduction loss and expand load capacity for LLC converter. However, component tolerance on resonant tanks causes load sharing problem, leading to severe performance degrading. To solve the problem, Switch-controlled Capacitor (SCC) circuit is added into resonant tanks to offset the component tolerance through reducing equivalent resonant capacitance. The load sharing characteristic of a three-phase LLC converter with and without SCC circuit is analyzed. The proposed control strategy reduces the SCC MOSFET voltage stress. Thus, lower voltage rating MOSFET which usually features of lower turn-on resistance can be used. Phase shedding technique is also performed to improve the light load efficiency. A prototype of a 250V - 430V input, 14V/260A output three-phase SCC-LLC prototype has been built and tested. Experimental results demonstrate the effectiveness of the SCC circuit and the proposed control strategy. Good current sharing performance among three phases is obtained. In addition, a peak efficiency of 96.7% and a full load efficiency of 95.8% are achieved at 380V input.