Research On Cascade-type High-efficiency 6.6kW Electric Vehicle On-board Charger

As an effective way to alleviate the contradiction between energy shortage,environmental pollution and traffic life,electric vehicles which have become an important strategic position in various countries are an important development direction for automobiles.The charging problem has a huge impact on the development of electric vehicles.A key component of the electric vehicle to achieve the charging function is the on-board charger,which is also a research hotspot in recent years.The research goal is to design an efficient on-board charger to meet the charging requirements of vehicle power batteries and to charge batteries safely and quickly.Through a lot of research,it is found that the current main technical solution is a cascading solution.The structure of the front stage and the rear stage is summarized.According to the requirements of the technical indicators,the CCM two-phase interleaved Boost PFC and full-bridge LLC resonant structure are selected as the front and rear stages of the on-board charger.For the pre-stage APFC,the working principle and control process of the circuit are analyzed,the circuit model is established by the state space averaging method,the main transfer function relationship is obtained.The main power device types and parameters of the circuit are designed and the device losses are analyzed.Establishing a simulation model to verify the function of the pre-stage converter,and designing a hardware scheme of control and drive with UCC28070 as the core.The LLC resonant circuit of the rear stage uses a full-bridge structure for both the primary and secondary sides.Using the pulse frequency control method to analyze the circuit modalities of the circuit at different operating frequencies.Using the fundamental wave equivalent analysis method to study the gain characteristics and impedance characteristics of the resonant tank,the gain formula and the inductive capacitive boundary curve equation are obtained.According to the clamped excitation inductance,the LLC is divided into three working states:P,O,and N.The time domain expressions of different states are obtained so that the circuit states under different loads and frequencies can be accurately calculated.The design method of LLC resonant tank in the application of on-board charger is studied,and the magnetic components,capacitors,and semiconductor devices in the main circuit were designed and selected,and related losses were calculated.The simulation model is established to verify the circuit function.The control and drive scheme of the full-bridge LLC circuit are designed based on UCC25600.According to the designed hardware.scheme,a 6.6kW prototype was built and verified through experiments to meet the technical requirements.