Wide Voltage Output Three Level DC-DC Converter Based On Hybrid Control

With the wide use of new energy power supply systems,electric vehicles as a new energy-saving and environmental friendly means of transport.What's more,the storage battery,as the energy storage unit of the electric vehicle charging system,which characteristic is that with the load increases,the terminal voltage changes widely.Therefore,it is of great significance to study DC-DC converters that can meet the battery output voltage range with constant current and constant voltage switching characteristics.For high voltage and high power applications,an interleaved half-bridge three-level LLC resonant converter is used in this thesis as a power topology.To improve the adaptability of a wide range of output voltages,a hybrid control method combining phase shift(PS)control and frequency conversion(FM)control is used to solve the problem of narrow output voltage range under conventional frequency conversion control.The principle of the half-bridge three-level LLC resonant converter is analyzed,and the fundamental wave equivalent model is established.The best switching point of phase shift control and frequency conversion control are given by the gain curve in the frequency conversion mode and the gain surface under different quality factors in the phase shift mode.To improve the efficiency of the converter and achieve a wide range of output as an indicator,the lagging bridge arm can be selected to achieve the maximum phase shift angle under ZVS conditions.The problem of output current ripple of LLC resonant converter is solved by interleaving parallel connection.Aiming at the problem of two-way parallel non-uniform flow,the influence of three-element parameter deviation on the voltage gain is studied.The adaptive dead-time compensation control strategy is used to improve the converter to obtain the advantage of two-way power sharing.The simulation model is built by software PSIM,the adaptability of voltage wide range output under constant current constant voltage charging mode,and soft switching condition under phase shift light load condition,and dynamic response of load abrupt decrease,and output ripple characteristics and voltage gain effect caused by various parameter deviations are verified.A 15 kW experimental platform with 760V-800 V inputand 300V-750 V output was built.TMS320F2806 was selected as the digital controller chip of the system controller to verify the validity of the wide range voltage output.