倍压整流型LCC谐振变换器轨迹控制启动策略

Trajectory control based startup strategy for LCC resonant converter with voltage-doubling rectifier

倍压整流型LCC谐振变换器兼顾了串联和并联谐振变换器的优点,具有高电压增益、抗负载短路、兼容变压器寄生参数等能力,已成为医用X光机高压发生器的优选拓扑。然而,倍压整流器中的电容参与谐振,增加了谐振元件数量,导致变换器的动态特性更复杂,进而对建模和控制提出更高的要求。传统的基波近似法和线性控制难以实现精确建模并跟踪控制指标。对此本文采用状态平面分析法,通过分析变换器的工作原理建立各模态归一化状态轨迹方程。在此基础上,提出一种状态轨迹控制启动策略,通过设置谐振电流限幅值,根据输出电压变化规划最优路径,使状态变量在最短时间内跟踪谐振腔最优轨迹,以此计算最佳开关频率。最后,在50 kW/140 kV的样机上验证所提建模方法的准确性和控制策略有效性。实验结果表明,所提方法有效提升了启动速度,实现了不同电压等级之间的快速切换,抑制了谐振腔电流、电压过冲。

The LCC resonant converter integrating voltage-doubling rectifier takes into account the advantages of series and parallel resonant converters.It has become the preferred topology for high-voltage generator for medical X-ray machines,due to the benefits like high voltage gain,anti-load short-circuit,compatibility with transformer parasitic parameters,etc.However,the rectifier capacitors participate in the resonance and increase the number of resonant components,which leads to more complex dynamic characteristics of the converter,which in turn puts forward higher requirements for modeling and control.The conventional fundamental harmonic approximation and linear control are difficult to achieve accurate modeling and track control indicators.To address this,the state plane analysis method was adopted.The normalized state trajectory equation of each mode was established by analyzing the working principle of the converter.On this basis,a state trajectory control strategy of startup was proposed.By setting the limit value of the resonant current and sensing the output voltage,the state variable can track the optimal trajectory of the resonant tank in the shortest time.The optimal switching frequency can then be derived.Finally,the accuracy of the proposed modeling method and the effectiveness of the control strategy were verified on a 50 kW/140 kV prototype.The experimental results show that,compared with the conventional control,the proposed methods effectively improve the startup speed,realize fast switching between different voltage levels,and suppress the resonator current and voltage overshoot.