宽电压范围LLC变换器混合控制的研究

Research on Hybrid Control of LLC Converter with Wide Voltage Range

针对电动汽车充电机宽输出电压范围和转换效率之间的矛盾,探讨了一种LLC变换器的混合控制方案。在高输出电压段采用调频控制,在中输出电压段LLC工作于谐振模式,采用调节母线电压实现充电电压的控制,在低输出电压段采用同时调节频率和移相角的混合控制策略,以达到在宽电压输出范围内均获得较高转换效率的目的。分析了在低输出电压段变频移相混合控制下的连续和断续工作模式,通过时域分析法推导了电压和电流的表达式,求出了保证开关管ZVS开通的条件。同时控制频率和移相角变量,可显著减小超谐振频率段的开关频率和关断损耗,在保证调压能力的基础上,提高变换器的效率。在7.5 kW LLC变换器试验样机上,验证了该混合控制策略的有效性。

In order to resolve the contradiction between the wide output voltage range and conversion efficiency of electric vehicle chargers,a hybrid control scheme of LLC converter is discussed.In the high output voltage section,frequency modulation control is used.In the middle output voltage section LLC works in resonance mode and the bus voltage is adjusted to regulate output voltage.In the low output voltage section,a hybrid control strategy that adjusts frequency and phase shift angle simultaneously is used and a high conversion efficiency is achieved over a wide voltage output range.The paper analyzes the continuous and discontinuous working mode under the hybrid control of variable frequency and phase shift angle in the low output voltage section.The expressions of voltage and current are deduced by the time domain analysis method,and the conditions to ensure the ZVS of the primary switches are obtained.Controlling the two variables of frequency and phase shift angle at the same time can significantly reduce the switching frequency and turn-off loss when above-resonance mode is applied.Efficiency of the converter can be improved on the basis of ensuring the voltage regulation capability.The effectiveness of the proposed hybrid control strategy is verified on a 7.5 kW LLC converter experimental prototype.