Design Of On-Vehicle Inverter Power Supply

With the diversification of car functions and configurations,more and more electronic devices are assembled into cars,such as car DVDs,car refrigerators,mobile TVs,etc.These electrical devices require AC220V.The on-vehicle inverter power supply can boost and invert the battery 24V DC to obtain 220V AC power,which can be used by various electrical equipment.Therefore,it is being used more and more.Two-stage structure of vehicle-mounted inverters is studied in this thesis.The first stage is an input-parallel output-series full-bridge LLC resonant converter,and the second stage is a single-phase full-bridge inverter.Firstly,in order to meet the requirement of wide range input voltage,the control strategy of LLC resonant converter combining variable frequency and phase shift is analyzed.The fundamental harmonic approximation method is used to establish the equivalent model of the LLC resonant converter in the variable frequency mode,and its voltage gain characteristics in variable frequency mode are analyzed.The time domain analysis method is used to model the equivalent of the LLC resonant converter in the phase shift mode,and its voltage gain characteristics in the phase shift mode are analyzed.The transformer and resonance parameters of the LLC resonant converter are designed based on theoretical analysis and simulation analysis.Secondly,the inverter output filter parameters are designed according to the inductor current ripple and the capacitor reactive loss limit.Double closed loop control strategy is used for single phase inverters,and the inductor current inner loop and the output voltage outer loop are designed by engineering design method.The principle of secondary ripple generation of DC bus voltage is analyzed.The harmonic effect of bus voltage ripple on output voltage is suppressed by introducing bus voltage feedforward.Thirdly,the soft start strategy of two-stage circuit is considered.A high-frequency phase shift plus frequency reduction start mode is applied to pre-stage LLC converter,and an open loop plus closed loop start mode is applied to the inverter,which can realize the smooth establishment of the output voltage.Finally,a 3kW two-stage circuit test prototype with input DC 18-36V,output AC 220V was built to verify the theoretical analysis.Experimental results show that the designed circuit can be smoothly started and stable in a wide input range.