Research On 15kW Full-bridge LLC Resonant Converter And Hybrid Control

The rapid development of the automobile industry has intensified the energy crisis.The emergence of electric vehicles has alleviated the situation,and high-power fast charging systems have become an important research direction.High-power fast charging system which is built by integrated module is an ideal solution in the industry.Generally,15kW,20kW and 30kW basic modules are used for system integration.The performance of the basic module will directly affect the performance of the entire fast charging system.The thesis has studied the structure,control and efficiency affected by parameters of the 15kW basic module.The 15kW basic module topology adopts a full-bridge LLC resonant circuit,and the core of the soft switch is a resonant network.Resonant network is mainly composed of a magnetizing inductance L_m,a resonant inductor L_r and a resonant capacitor C_r.The switching tube ZVS and the secondary rectifying diode ZCS are realized by the resonance of the resonant network,and the switching loss of the power tube is reduced.The thesis analyzes the working principle of full-bridge LLC resonance in different frequency intervals,establishes mathematical modeling of LLC resonant network,and analyzes the relationship between voltage gain and series equivalent impedance of resonant network.The relationship between the resonant frequency and the voltage gain of the converter is analyzed by MATLAB simulation.It is found that the impedance characteristics of the resonant network are the key to decide whether the circuit realizes soft switching.The thesis has completed the parameters of the magnetic components such as transformers and resonant networks and device selection.To solve voltage gain distortion of full-bridge LLC circuit in the light-loaded circuit.The thesis adopts a hybrid control mode that is,the circuit selects the phase-shifted full-bridge(PSFB)operating mode at light load,and selects LLC resonance at rated power and heavy load.Traditional PID control has some disadvantages that slow dynamic response,especially in light load.The fuzzy external PID controller with better dynamic performance is used in the voltage outer loop,The main circuit soft switch is implemented as a hybrid fuzzy controller that can smoothly transition between full-bridge LLC and PSFB.Therefore,the thesis proposes a hybrid fuzzy control strategy for full-bridge LLC circuits,that is,the voltage outer loop adopts a fuzzy PID controller with better dynamic performance,and according to the specific conditions of the load,the main circuit working mode smoothly transitions between the LLC mode and the PSFB mode.The hybrid fuzzy control strategy whitch complishs soft switching is a controller with excellent dynamic and static performance over the full load range.The design of transformer and resonant network parameters is simulated by Saber simulation software.The waveforms of voltage and current at key points are analyzed.It is verified that the LLC resonant network and transformer parameters can realize ZV-ZCS performance.Complete the schematic diagram of the main circuit,drive circuit,sampling and protection circuit and PCB drawing work,and set up the experimental prototype for experimental verification.The comparison between the experimental waveform and the simulated waveform proves that the fuzzy hybrid full-bridge LLC circuit proposed in this paper can realize ZV-ZCS performance in full load,reduce the switching loss of power tube,improve power supply efficiency and improve EMI characteristics.