Research And Design Of Three Level Charging Pile

In recent years,the development of green and light economic at home and abroad has promoted the development of electric vehicles.The charging pile as the power supply of new energy vehicles,its reliability and safety will determine the popularity of new energy vehicles.At the same time,due to frequent failure of charging pile,unstable performance,has been affecting the safety of new energy vehicles and battery life.Therefore,developing a low-harmonic,highefficiency and high-stability charging pile has become a hot topic in the industry and it is of great significance to study it.This dissertation studies the high-power charging pile which is made of VIENNA and three level LLC.This dissertation gives the design program of the three level charging pile,and determines the main power topology of it.Analyzing the working state of the VIENNA rectifier,used the state-space averaging method to calculate the small signal model under different coordinate systems.Current decoupling is realized by current feedforward decoupling,and designed a double loop control system.The equivalent model of LLC is established by FHA,and analyses its DC gain curve and impedance characteristics.In order to solve the problem that the inner tube is more difficult to realize the ZVS than the outer tube,this dissertation analyzes the soft-switching condition,and gives the different calculation methods with minimum and maximum dead-time to ensure the system soft switching conditions.In addition,the double control closed loop of voltage and current is designed to meet the battery's constant voltage and constant current charging requirements.The method to convert the three level SVPWM to two level is analyzed,and studies the problem of the imbalance of neutral point potential in VIENNA.By analyzing the influence of different vectors on the midpoint potential,the modulation strategy of redundant short vector is adopted to solve the problem of capacitance uneven pressure.Aiming at the problem of soft-switch loss and high switching frequency when three level LLC in low-voltage output condition,the strategy of mixed modulation of PFM and PWM is proposed.By adjusting the duty ratio when the freqyency changed,the system can achieve the ZVS of the system in the full output voltage range,to ensure stable and reliable work of the charging pile.The system model of charging pile is established in Matlab/Simulink,which verifies the feasibility of the system.A 15 k W prototype was set up to complete the test of the AC/DC and DC/DC,the measured results verify the consistency with the theoretical analysis.