Study Of High Efficient And Fast Response Electric Drive System Control Strategy For Electric Vehicles

With the advantages of no pollution emissions and low noise, electric vehicles, which integrate in lots of high-tech, are creating a revolution in the world auto industry. So far, inadequate driving range is still the main fencing to hinder the development of electric vehicle. In order to solve this problem, we should first develop high-energy density batteries; second, we must greatly limits its operation losses to improve the efficiency of the electric drive system, thus effectively use of limited energy. The second issue can be solved from the following two aspects: First, advanced variable frequency variable speed and its optimization control technologies should be used to realize the energy supply by need, that is, to meet requirements for electric vehicles running speed, driver force and the steady and dynamic properties of the premise to minimize electric drive system input energy; second, efficiently feed the energy transformed from the mechanical energy back to inverter's DC bus and stored in on-board energy source when the motor runs in a regenerative braking state.Induction motor(IM) with advantages of small size, light weight, low cost, maintenance-free, is widely used in the electric vehicle electric drive systems. Till now, the improvement of IM system efficiency is at the expense of lowering its dynamic response. So it can only use in the system with slow dynamic response, such as water pumps, etc. As to electric vehicles and Robot systems, which require rapid response to the demands of the occasion, a new high-performance variable frequency drive system control strategy is needed. Aimed to the above issue, optimization theory, motor control techniques and vehicle theory are adopted in this paper to the further study of high efficient and fast response electric drive system control strategy for electric vehicles. It is obvious that, the study will not only have theoretical and academic value to the development of motor control theory and many other related branches, but also have great practical significance in the development of China's intellectual property rights of advanced technology for electric vehicles and the industrialization of the electric vehicles.This paper first discusses the key technologies in electric vehicle electric drive system: induction motor efficiency optimization, fast dynamic response and regenerative braking control techniques and the corresponding development, then indicates main topic of the research and the arrangement of chapters.Combined electric vehicles drive equations with the typical driving cycle analysis, the loads and operation region characteristics of induction motor are discussed. Then, the power flow and losses in electric drive system are analyzed. At the end the paper briefly present the DSP TMS320LF2407A based vector control experimental system, which is to validate the algorithm.Considering that electric vehicle induction motor has a small magnetic inductance which increases iron loss, thus should not be neglected. Based on the physical model of induction motor in three-phase stationary coordinates, the dynamic mathematical model of induction motor including iron loss in synchronous rotating coordinate system is established. The corresponding equivalent circuit diagram and the simulation model using S-Function are also presented. Upon analysis, the stator d, q-axis current can both affect the rotor flux establishment and torque output of the field oriented vector control with the presence of iron loss, even in the steady state, they are no longer decoupling. Rotor flux and torque control variable changes from the stator current d, q-axis components to magnetizing current d, q-axis component. According to the relationship between them, the dynamic and steady two compensation solutions are proposed through controlling the stator current to meet the required magnetizing current to achieve motor rotor flux and torque output decoupling control. Comparison simulation results show that dynamic compensation strategy overcomes the influence that the field-oriented and output torque is not accurate in the classical vector control due to neglect of iron loss, and gets a satisfactory performance; Steady-state compensation solution has not as good performance as the dynamic one before the establishment of magnetic field, while after that it still can achieve a similar performance with dynamic compensation strategy and more easily realize.Induction motor has notorious poor efficiency under light load, which declines the performance. Aimed to this problem, its efficiency optimization control strategy is studied. First, the paper analyze the principle of the induction motor control system efficiency optimization control and propose an induction motor full speed range efficiency optimization strategy based on the loss model. Simulation and the experimental results show the validity of control strategies. Then, the paper explore related issues in the implementation of efficiency optimization control: (1) magnetic flux limit of efficiency optimization within the whole operation region; (2) using parameter sensitivity analysis method to discuss the influence of motor's parameters change to the efficiency optimization control precision, and explores the feasibility of further improving the efficiency by utilizing the law the parameters changes; (3) dynamic performance and the efficiency during the activation of efficiency optimization. Finally a comprehensive analysis of the efficiency optimization control based on search and minimum stator current and loss model respectively is presented to discuss the distinction and links among them, and found that each algorithm has its own characters. Among them, loss model based on method can reach global optimum without any additional hardware. It has a fast optimization speed and a fairly stable torque and speed in the optimization process.Quick torque response in wide speed range is required by electric vehicle electric drive system. First, combined induction motor output torque and rotor flux expression, the infection of dynamic response speed caused by efficiency optimization strategy is discussed. Then, considering the electric vehicles still need to have a fast dynamic response to the characteristics of overtaking acceleration in the highway, a fast torque response control strategy suitable above base frequency is proposed, which distribute magnetizing current and torque current according to the voltage constraint offset in the dynamic process, guaranteeing that the value of the output torque in each time approximates the maximum. The strategy breaks through the limitation of maximum torque control strategy, which based on the steady state analysis when solving fast torque output problem in dynamic process. Simulation and the experimental results show that the proposed control strategy can provide greater dynamic torque output, reducing the infection of electric vehicle's dynamic response speed caused by efficiency optimization strategy.To efficiently recycle regeneration energy is the main problem of electric vehicles in low intensity brake process. The paper first analyze the principle, braking patterns, braking System basic requirements and impact factors of the electric vehicles regenerative braking feedback. For that typical urban cycle brakes frequently, electric vehicles often have light braking condition and only energy of driving wheel can be fed to the DC bus, an efficient regenerative braking control strategy for electric vehicle which combine the induction motor regenerative braking efficiency optimization control and improved braking force distribution strategy is proposed. Assign the braking force to the driving wheel as much as possible under the condition that the vehicle has good stability during the braking process; guarantee the braking intensity on the premise to make use of the electrical regenerative braking, then use optimization control to reduce the electric drive system operating loss during the braking process. The electric vehicle simulation software ADVISOR is adopted in the simulation. The simulation results show that whether to activate the regenerative braking energy has great impact on electric vehicle energy efficiency. And with improved braking force distribution strategy and braking region efficiency optimization control, regenerative braking energy recycle rate has been greatly increased. Finally, the simulation results show that using efficiency optimization and efficient regenerative braking can get a good continued driving distance and energy efficiency, which offers a sound solution for the rational use of electric vehicles with limited energy.