Study On Control Strategy And Hil Experiment For Distributed Driving Electric Vehicle

Due to oil shortage and increasingly deteriorating environment, it is a consensus among people to strive to develop new energy vehicle represented by electric vehicle, which is also an effective approach to solving environment problem and realizing sustainable development. Distributed driving is a comparatively novel electric vehicle structure. In comparison with traditional centralized driving, it is characterized by more flexible structural arrangement, larger passenger compartment, higher transmission efficiency and more flexible control system. Distributed driving electric vehicle can take control of the driving state of different wheels and reach the control effect that is unrealizable for centralized driving control, thus promoting the dynamic property, economical efficiency and safety of vehicle. This thesis carries out study on the control strategies of distributed driving electric vehicle including driving energy conservation, electromechanical braking system and anti-lock brake system, and establishes the hardware-in-the-loop test and simulation platform to verify the developed control strategies.Firstly, the author analyzes the structure and working principle of permanent magnet synchronous motor drive system, elaborates space voltage vector control method and establishes the mathematical model of motor drive system by taking interior permanent magnet synchronous motor. Based on the motor drive system model, the motor drive system hardware-in-the-loop subsystem is established on NI PXIe platform and meanwhile the vehicle dynamic model subsystem based on Car Sim RT platform and mechanical braking semi-physical subsystem is also set up, composing a full distributed driving electric vehicle hardware-in-the-loop test platform. These subsystems can work in coordination with each other on the constructed hardware-in-the-loop test platform. The comparison between the experimental data of established hardware-in-the-loop platform and experimental data of motor test-bed shows that the hardware-in-the-loop platform can report the practical work state of motor drive system and the whole vehicle accurately, verifying that the hardware-in-the-loop platform can meet the real-time request of motor simulation and possesses favorable accuracy.Secondly, the hierarchical control framework that applies to the distributed driving system is designed, which includes kinetic control layer(upper layer) and executive layer(lower layer) and can decouple the kinetic control of distributed driving vehicles and the optimize control of motor drive system, and allow them to avoid conflicts. This framework is featured by definite control concept, strong expansibility and universality. The driving energy-saving control strategy is designed based on hierarchical control framework, which is classified into upper torque distribution optimal control strategy and lower motor efficiency optimal control strategy. The electric efficiency optimum adopts feedforward control and feedback control and analyzes its principle and structure. The combination of feedforward and feedback control can speed up the torque response speed of motor. The designed driving energy-saving control strategy is tested on the hardware-in-the-loop platform and the result verifies the effect of new control strategy in torque response speed acceleration and energy saving.Thirdly, the author explores the electromechanical braking system of electric vehicle. Through analyzing braking condition and restricted factors of braking energy regeneration effect of electric vehicle, an improved I-curve distribution control strategy is proposed and a new braking system control mechanism is designed for implementing this strategy. This strategy can reach the ideal braking distribution and realize the maximization of braking energy regeneration without altering traditional mechanical braking system, which can reduce the cost of electromechanical braking system. The control strategy is put into the upper control strategy of hierarchical control for verification on the hardware-in-the-loop test platform. Through comparing the experimental result with that of traditional electric car, it can conclude that the proposed improved I-curve distribution control strategy can achieve ideal brake force distribution and obviously improve the recovery of regenerative braking.Finally, this thesis studies the anti-lock brake system of distributed driving electric vehicle. The control idea that realizes ABS control through adjusting regenerative braking torque is determined based on its features and relevant control strategy is designed as well. The control strategy is added with fractional order PID control algorithm, and fuzzy control algorithm is adopted to conduct online self-tuning of control parameters of the algorithm so as to improve control quality. Likewise, ABS control strategy is verified on the established hardware-in-the-loop test platform and the experiment is carried out on various road conditions. The result shows that the proposed ABS control strategy can complete anti-lock braking control on different road conditions. The comparison between test result and integer order PID control proves the advantages of relevant fractional order PID control algorithm.