平面变压器寄生参数对LLC谐振变换器性能的影响分析及优化设计验证

Analysis and optimization design of parasitic parameters of planar transformer for LLC resonant converter

平面变压器由于其散热性能好、电流密度大、功率密度高等优点已经取代了传统绕线式变压器,但是其固有高寄生电容会导致LLC谐振变换器的零电压开关(ZVS)失效。针对该问题,在考虑寄生参数的情况下,对变换器进行模态分析和数学推导,详细分析了变压器寄生电容导致谐振电流产生畸变的过程,并解释了其导致软开关失效的原因。基于此通过磁集成技术降低变压器绕组间的寄生电容,并且设计了一种交替绕组结构降低变压器绕组内的寄生电容,将平面变压器的寄生电容最小化。最后搭建180 W半桥LLC平台,将优化后的样机与传统样机进行对比实验验证。实验结果表明,经过结构优化后,平面变压器的寄生电容得到了降低,解决了由于寄生参数导致的LLC谐振变换器软开关失效问题。

Planar transformer has replaced the traditional winding transformer due to its good heat dissipation performance,high current density and high power density,but its inherent high parasitic capacitance may lead to zero-voltage switching(ZVS)failure.To solve this problem,in this paper,the modal analysis and mathematical formula derivation of the converter are carried out considering the parasitic parameters.The resonant current distortion caused by the transformer parasitic capacitance and the loss of the soft switch are analyzed in detail.Then,the parasitic capacitance between transformer windings is reduced by magnetic integration,and an alternating winding structure is designed to reduce the parasitic capacitance in the transformer winding,so as to minimize the total parasitic capacitance.Finally,a 180 W half-bridge LLC platform is built,and the optimized prototype is compared with the traditional one for experimental verification.The experimental results show that the parasitic capacitance of the planar transformer is reduced after structural optimization,and the problem of soft switching loss of LLC resonant converter caused by parasitic parameters is solved.