Design And Implementation Of Charge And Discharge Device For Electric Tractor

Nowadays,we are realizing the importance of the environment and our country has issued a large number of policies to support the development of the electric vehicle industry.Electric cars are becoming more and more common in life.According to the data released by the China Association of Automobile Manufacturers,in 2018,the sales of new energy vehicles in China reached 1.25 million,including 984000 pure electric vehicles.The energy stored in the battery is the power for electric vehicles,as the market of electric vehicles increases,so does the demand for devices to charge batteries.Most of the charging devices currently on the market use a two-stage topology of an AC/DC circuit plus a DC/DC circuit.This paper will design a device for electric tractors used in specific occasions.Unlike common charging devices,in order to detect the state of leadacid battery used in electric tractors,the device contains a discharging module to discharge lead-acid battery with constant current.Firstly,the paper introduces the device at system level,including the functions of the device and the internal components of the device.Then the design of the control system is discussed due to the functional requirements,for example,the realization of the control system and the resources required by the controller.In the paper,a improved Buck circuit is selected to realize discharging function of the device.Besides,analyze the procedure to calculate the value of components in the circuit.By using state space averaging method,the transfer function of the improved Buck circuit is derived,meanwhile,the control parameters are solved.At last,the electric performance of the discharging module is verified.As for the charging function of the device,a two-stage circuit topology consisting of VIENNA rectifier and phase-shifted full-bridge is selected.Some problems in the phase-shifted full-bridge are discueed.Due to the large output power of the device,an improved phase-shifted full-bridge is adopted.And the parameter of the circuit is analyzed.Then the small signal model of the circuit is derived and the parameters of the double-closed-loop controller are performed.At last,the electric performance of the charging module is verified.Finally,the paper discusses the work process of the device,including charging process,discharging process,fault handling process and emergency protection process.Then the output performance of the device is verified,including the dynamic regulation of charging current and discharging current,the automatic shutdown of the device.