A Variable Frequency Constant Current Control for LCC Resonant Capacitor Charging Power Supply Based on State Plane Analysis

Capacitor charging power supply is an essential part of the pulsed plasma thruster (PPT), which performance determines the thrust precision, the maximum repetition frequency of pulse discharge, and the overall efficiency of the PPT system. In order to meet the requirements of charging speed and charging linearity of the capacitor charging power supply, this paper investigates the LCC resonant converter working in discontinuous current mode 2 (DCM2). A steady-state model is built by state plane analysis and the analytical expression for average output current and equivalent voltage gain, resonant capacitance ratio, and switching frequency is derived. Then, a critical discontinuous constant current control charging strategy is proposed. As the charging voltage rises, the switching frequency is constantly adjusted to track the critical discontinuous switching frequency, which increases the effective width ratio of output current and thus improves the output capacity of current. At the same time, the output current closed- loop control based on PI algorithm is introduced to realize constant current output and ensure the charging linearity. Finally, simulation results based on PLECS confirm the accuracy of the theoretical analysis and the feasibility of the proposed strategy.