| Those loss of the vehicle braking energy accounts for approximately 10–30%of the total energy consumption in urban driving conditions,and braking energy recovery devices can convert part of the vehicle kinetic energy into mechanical energy or electrochemical energy for recovery and storage.To date,most studies have focused on converting the kinetic energy of vehicle braking into electrochemical energy,storing part of the braking energy through motor/generator-batteries.The motor regenerative braking technology is capable of transferring energy from mechanical energy to electrochemical energy and vice versa.Under braking conditions,the reminder can be recovered and used in theory during braking except the energy consumed by air resistance,road resistance,and other mechanical friction,but in fact,not all braking energy can be recovered.The motor regenerative braking system only recovers the braking energy on the driving wheel.Moreover,it should be noted that there was efficiency loss in the energy conversion process.Especially when the braking time is short,the energy storage speed is restricted by the chemical reaction speed of the battery electrode“active substance”,to lower the energy recovery efficiency.Furthermore,the energy conversion amount is limited by the rated capacity of the electric drive device.Aiming at the characteristics of existing motor regenerative braking technology,ultracapacitors could achieve high efficiency and superior power control in a short time,especially suitable for unpredictable urban conditions.However,this paper introduces a flywheel hybrid power system from another perspective to capture/release high power.For the several typical energy storage devices,flywheel energy storage possesses the characteristics of high instantaneous power and fast response,making it one of the energy storage technologies with a promising future.Therefore,a new approach of storing a vehicle’s kinetic energy by flywheel,the electromagnetic coupling braking energy recovery system(EC-BERS),was proposed,which provides a new technical scheme for the dynamic coupling of flywheel and powertrain system.It can transfer most of the kinetic energy in the deceleration process into the flywheel’s kinetic energy directly,making it possible to capture more power than rated power.At the same time,the battery processes less energy,which is beneficial to prolonging the battery life.Surrounding this new structure scheme,this paper carries out mathematical modeling,case study and experimental research,and mainly does the following research work:(1)The total energy consumed by the driving wheels under various driving conditions of the vehicle is derived theoretically,and the calculation formula of battery participation in the braking energy recovery process is given.Based on the analysis of the wheel-wheel energy recovery/release process of the existing battery energy recovery technology,further problems to be solved by this technology are proposed in terms of the conversion efficiency of multiple energy forms and the capacity limit of the electric drive system.According to the topology structure scheme,the wheel-to-wheel energy conversion efficiency of the new dynamic coupling system and the electric hybrid power system has been compared and analyzed,and the superiority of the new topology structure in power transmission characteristics is demonstrated theoretically.The power flow in the process of energy recovery and release has been analyzed based on considering the iron loss of the outer rotor,the copper loss and stray loss of the inner rotor winding,and the loss of the inverter,which lays a foundation for the modeling and simulation of the subsequent system.A two-stage flywheel energy storage device has been designed,which increases the specific energy of the energy storage device by 5.80 times and improves the energy density of the flywheel.The influence of different flywheel materials on the energy density of the energy storage device is discussed.The mass of the flywheel energy storage device using E-glass/epoxy and AS4 carbon/epoxy is more suitable for the vehicle application of flywheel energy storage,which is of great significance for the research on the dynamic coupling technology of the transmission system.(2)According to the established topology of the new dynamic coupling system,the mathematical models of the key components of the system in the three-phase static coordinate system,the two-phase static coordinate system and the two-phase rotation coordinate system are derived in combination with the analysis results of the power flow characteristics of the system,and the simulation test bench is established to verify the accuracy of the established model.The inherent characteristics and dynamic characteristics of the electromagnetic coupler have been analyzed by the established system model,which laid a foundation for the subsequent research on the power characteristics and energy characteristics of the electromagnetic coupling braking energy recovery system.(3)Based on Kirchhoff’s voltage law,the mathematical model of the three-phase bridge VSR topology in the two-phase rotating coordinate system has been established.The generation process of SVPWM of three-phase bridge VSR is analyzed theoretically,and the input voltage,the sector number of the voltage vector,the action time of each sector boundary vector,the action time of each phase switching function and PWM signal are obtained under the coordinate system,which provides a theoretical basis for realizing the recovery of the system’s differential power.The feedforward decoupling control strategy of i_d and i_q is introduced,and the voltage vector(u*_d,_u*_q)of the AC side of the three-phase VSR is obtained by PI operator.The effect of the initial capacitor voltage on the amount of energy recovered is analyzed,and the results show that the energy recovered by the system increased significantly with the increase of the initial capacitor voltage.(4)Based on the established electromagnetic coupling braking energy recovery system model,the power characteristics and energy characteristics of the system under continuous deceleration-cruising condition and deceleration-cruising-acceleration condition have been analyzed.The mathematical model of regenerative braking energy recovery system is established.The power characteristics and battery involvement of the two braking energy recovery systems have been compared under the same deceleration cruise condition.Compared with the regenerative braking energy recovery system of the motor,the simulation results show that the new dynamic coupling system can give full play to the maximum torque under different speed ranges,the maximum power transferred by the mechanical port is not limited by the rated power of the electromagnetic coupler,and the battery power contribution in the energy transfer process is much less than that of the battery power contribution in the electric drive system,which is conducive to extending the battery life.(5)The research and development of the new dynamic coupling system is completed.Through the system function test platform,it is verified whether the electromagnetic coupling braking energy recovery system can solve the conversion of various energy forms and the capacity limit of the electric drive system.The test results show that vehicles equipped EC-BERS can store kinetic energy in the form of both mechanical and electrochemical energy when decelerating.The power transferred by the mechanical port of the electromagnetic coupler during deceleration-cruise is not limited by its rated power,and the battery participation is 0.51 and 0.53under low-speed and high-speed operating conditions,respectively. |
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