Trajectory control based startup strategy for LCC resonant converter with voltage-doubling rectifier
The LCC resonant converter integrating voltage-doubling rectifier takes into account the advan-tages of series and parallel resonant converters. It has become the preferred topology for high-voltage gen-erator 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 conven-tional control,the proposed methods effectively improve the startup speed,realize fast switching between different voltage levels,and suppress the resonator current and voltage overshoot.
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