电动汽车非接触充电器中移相变频控制策略的研究

与传统接触式充电相比,非接触充电为电动汽车充电提供了更加安全方便的充电方式。但非接触充电中的磁耦合变压器工作于松耦合状态,存在较大的漏感,为了确保传输功率和降低功率器件的定额,通常要在原边或/和副边采用补偿网络,这使得系统成为高阶系统,控制难度加大。传统的控制方式有恒频PWM控制和变频PFM控制。恒频PWM易丢失软开关条件,影响变换效率。变频控制在宽负载范围、变参数条件下也存在一些不足。提出频率跟踪和移相策略相结合的控制方案,使用频率跟踪来保证系统工作在最佳频率,使用移相控制获得稳定的输出电压,对该方案进行了仿真分析,并设计了一台1kW基于数字控制全桥非接触电动汽车充电器样机,实验结果验证了所提出控制策略的可行性与正确性。

A Novel Combined Frequency Tracking and Phase Shift Control Strategy for Contactless Electric Vehicle Battery Charger

In contactless electric vehicle battery charger,loosely coupled inductive charging technology offers a safe and convenient means to accomplish charging process.However,the mutual coupling within such charging systems is generally weak.To deliver the required power and ensure equipment sizes remain manageable,it is necessary to operate at high frequency.Moreover, resonant circuits are normally employed in the primary and/or secondary networks to further boost the power transfer capability,while minimizing the required VA ratings of the power supply.This makes the contactless battery charger becomes a high order system, adding the difficulties of effective control.Generally,both fixed-frequency phase shift control and variable-frequency control can be used.The former is relatively simpler,but increases the required VA rating and is only suitable for transformer with small variation of air gap.Variable-frequency controllers ideally operate at the zero phase angle point of the load impedance in order to minimize the VA rating of the supply.However,the ideal control point is difficult to determine for more than one zero phase angle condition probably existing in the frequency spectrum.If a variable-frequency controller can not deal with uncertainty in the bifurcation region, the operational frequency of the power supply will either drift away from the desired operating position or move unstably. Consequently,the power transfer capability will drop significantly.In order to solve these problems,a novel combined frequency tracking and phase shift control strategy was proposed,which used a frequency tracking method to insure the system working under an appropriate frequency and obtaining the stable output voltage using phase shift control.Finally,a 1kW digitally controlled full bridge contactless battery charger prototype was built.Experimental results showed that the novel control strategy can realize good frequency tracking and stable output.