Future vehicle driven by electricity and Control-research on four-wheel-motored "UOT electric march II"

The electric vehicle (EV) is the most exciting object to apply "advanced motion control" technique. As an EV is driven by electric motors, it has the following three remarkable advantages: 1) motor torque generation is fast and accurate; 2) motors can be installed in two or four wheels; and 3) motor torque can be known precisely. These advantages enable us to easily realize: 1) high performance antilock braking system and traction control system with minor feedback control at each wheel; 2) chassis motion control like direct yaw control; and 3) estimation of road surface condition. "UOT Electric March II" is our novel experimental EV with four in-wheel motors. This EV is made for intensive study of advanced motion control of an EV.     

Motion control in an electric vehicle with four independentlydriven in-wheel motors

We study methods of motion control for an electric vehicle (EV) with four independently driven in-wheel motors. First, we propose and simulate a novel robust dynamic yaw-moment control (DYC). DYC is a vehicle attitude control method that generates yaw from torque differences between the right and left wheels. The results of simulations, however, identify a problem with instability on slippery, low μ roads. To solve this problem, a new skid detection method is proposed that will be a part of traction control system (TCS) for each drive wheel. The experimental results show that this method can detect a skidding wheel, without any information on chassis velocity. Therefore, this method will be of great help during cornering or braking in a TCS. These methods will be integrated and tested in our new experimental EV     

Modular integrated longitudinal and lateral vehicle stability control for electric vehicles

In this paper, the problem of integrated longitudinal and lateral vehicle stability control is addressed using a modular optimal control structure. The optimization process of the high level model predictive control (MPC) controller determines required longitudinal force and yaw moment adjustments to minimize the error between vehicle longitudinal and lateral vehicle stability dynamic states with respect to the target courses. The low level controller is designed to optimally regulate torque at each wheel based on the control inputs of the high level controller, and distribute required torque between the wheels via actuation system. The actuation system that is utilized to implement the proposed control structure functions based on all-wheel drive technology that can provide active control of both traction and yaw moment control with differential torque. The multi-layered structure of the control system allows modularity in design. The performance of the control structure is investigated by conducting experimental tests. The experimental tests have been performed on an electric Chevrolet Equinox vehicle equipped with four independent motors. The results show that the integration of the vehicle longitudinal and lateral dynamics preserves vehicle stability in a planar motion and improves the vehicle dynamic response, especially in challenging driving maneuvers.     

Lateral stabilization of a four wheel independent drive electric vehicle on slippery roads

In this paper, a new controller is proposed for lateral stabilization of four wheel independent drive electric vehicles without mechanical differential. The proposed controller has three levels including high, medium and low control levels. Desired vehicle dynamics such as reference longitudinal speed and reference yaw rate are determined by higher level of controller. Moreover, using a neural network observer and a fuzzy logic controller, a novel reference longitudinal speed generator system is presented. This system guarantees the vehicle’s stable motion on the slippery roads. In this paper, a new sliding mode controller is proposed and its stability is proved by Lyapunov stability theorem. This sliding mode control structure is faster, more accurate, more robust, and with smaller chattering than classic sliding mode controller. Based on the proposed sliding mode controller, the medium control level is designed to determine the desired traction force and yaw moment. Therefore, suitable wheel forces are calculated. Finally, the effectiveness of the introduced controller is investigated through conducted simulations in CARSIM and MATLAB software environments.     

A five-leg inverter for driving a traction motor and a compressor motor

This paper presents an integrated inverter for speed control of a traction motor and a compressor motor to reduce the compressor drive cost in electric vehicle/hybrid electric vehicle applications. The inverter comprises five phase-legs; three of which are for control of a three-phase traction motor and the remaining two for a two-phase compressor motor with three terminals. The common terminal of the two-phase motor is tied to the neutral point of the three-phase traction motor to eliminate the requirement of a third phase leg. Further component reduction is made possible by sharing the switching devices, dc bus filter capacitors, gate drive power supplies, and control circuit. Simulation and experimental results are included to verify that speed control of the two motors is independent from each other.     

Design of a VDC System for All-Wheel Independent Drive Vehicles

It is shown that the vehicle dynamic control (VDC) system can improve the vehicle handling and active safety of driver and passengers considerably. The control of vehicle yaw moment through differential braking, based on the vehicle dynamic state feedbacks, is a traditional way of VDC. In this study, a new VDC system for a four motorized-wheels electric vehicle has been developed, for which the traction of each wheel can be controlled individually. Using this feature, the new VDC system provides the desired tractive force of vehicle and the desired external yaw moment through the integrated control of wheel motors. The structure of the control system is a multilayer type, which has been developed by using independent controllers, designed in accordance with the appropriate theories.     

Vehicle motion control with subsystem prioritization

This paper presents a new approach for integrated vehicle motion control, coordinating multiple vehicle subsystems of a passenger car including friction brake system, near-wheel drive electric motors, wheel steer actuators, camber angle actuators, dynamic tire pressure system and actuators generating additional normal forces. The proposed algorithms are based on restriction weights into the cost function of optimization-based control allocation. Hardware-in-the-loop investigation using a test rig with hardware components of friction brake system and dynamic tire pressure system showed that the proposed approach allows to achieve lower energy consumption and energy losses without significant impairment of motion stability and vehicle handling as compared to conventional control allocation.     

四轮驱动四轮转向的汽车电子差速转向控制

通过汽车转向时稳定性分析阐明了四轮转向的优点。而鉴于轮毂电机在电动汽车上应用的诸多优点,及其功率受结构体积的限制,轮毂电机的应用将使汽车由性能更好的四轮驱动替代两轮驱动,它不但充分利用了地面对车轮的附着力和驱动力,而且结合用直线步进电机控制转向力的汽车转向系统,能更容易地实现全面改善转向性能的四轮转向系统。由于四轮驱动...     

A fault-tolerant control architecture for induction motor drives in automotive applications

This paper describes a fault-tolerant control system for a high-performance induction motor drive that propels an electrical vehicle (EV) or hybrid electric vehicle (HEV). In the proposed control scheme, the developed system takes into account the controller transition smoothness in the event of sensor failure. Moreover, due to the EV or HEV requirements for sensorless operations, a practical sensorless control scheme is developed and used within the proposed fault-tolerant control system. This requires the presence of an adaptive flux observer. The speed estimator is based on the approximation of the magnetic characteristic slope of the induction motor to the mutual inductance value. Simulation results, in terms of speed and torque responses, show the effectiveness of the proposed approach.     

Evaluation of soft switching for EV and HEV motor drives

Soft switching has the potential of reducing switch stresses and of lowering the switching losses as compared to hard switching. To understand the effectiveness of the soft-switching technique, when applied to electric vehicle (EV) and hybrid electric vehicle (HEV) systems, it may be necessary to first evaluate their system requirements and performance. This evaluation process would require knowledge of the vehicle dynamics. The vehicle load requires a special torque-speed profile from the drivetrain for minimum power ratings to meet the vehicle's operational constraints, such as initial acceleration and gradability. The selection of motor and its control for EV and HEV applications are dictated mainly by this special torque-speed requirement. As a consequence, this requirement will have a strong influence on the converter operation. This paper makes an attempt to evaluate EV and HEV running in both standard Federal Test Procedure 1975 city driving and highway driving cycles. A simplified analysis is carried out for several of the most commonly used electric motors operating on the optimal torque-speed profile. Special attention is given to the converter conduction and switching losses, by analyzing the switching losses, and by assuming that an ideal soft-switching scheme will have zero switching losses, one can evaluate the improvement in the system efficiency if a soft-switching control is used. The relative significance of soft switching for EV and HEV systems is then established     

Iterative learning control of antilock braking of electric and hybrid vehicles

Hybrid electric vehicles (HEVs) use multiple sources of power for propulsion which provides great ease and flexibility to achieve advanced controllability and additional driving performance. In this paper, the electric motor in HEV and electric vehicle (EV) propulsion systems is used to achieve antilock braking performance without a conventional antilock braking system (ABS). The paper illustrates that the antilock braking of HEV can be easily achieved using iterative learning control for various road conditions. A vehicle model, a slip ratio model, and a vehicle speed observer were developed to control the antilock performance of HEV during braking. Through iterative learning process, the motor torque is optimized to keep the tire slip ratio corresponding to the peak traction coefficient during braking. Simulations were performed on a compact size vehicle to validate the proposed control method. The control algorithm proposed in this paper may also be used for the ABS control of conventional vehicles.     

A Novel Traction Control for EV Based on Maximum Transmissible Torque Estimation

Controlling an immeasurable state with an indirect control input is a difficult problem faced in traction control of vehicles. Research on motion control of electric vehicles (EVs) has progressed considerably, but traction control has not been so sophisticated and practical because of this difficulty. Therefore, this paper takes advantage of the features of driving motors to estimate the maximum transmissible torque output in real time based on a purely kinematic relationship. An innovative controller that follows the estimated value directly and constrains the torque reference for slip prevention is then proposed. By analysis and comparison with prior control methods, the resulting control design approach is shown to be more effective and more practical, both in simulation and on an experimental EV.      

A new strategy for traction control in turning via engine modeling

The driving stability is affected by driven wheel slip, which can be controlled by the driven wheel torque. In a vehicle powered by an internal combustion engine, the torque can be controlled by an engine management system. The sliding mode algorithm is the mechanism behind the design of the traction control system (TCS). The longitudinal slip is controlled by the position of the throttle valve. The vehicle model used has seven degrees of freedom and a two-state engine model, i.e., the mass of air in the intake manifold and the engine speed. Time-delay transport is considered in the engine model used. A nonlinear tire model for combined slip is used for tire force computation. Due to the nonlinear dynamic of the tire, vehicle, and engine, the control method of sliding mode is used for its robustness. A controller is designed based on the dynamic surface control, for which two first-order surfaces are defined. The effectiveness of the controller is demonstrated with simulation results for different maneuvers. Results show that for different road conditions, the acceleration performance, directional stability, and steerability of a vehicle equipped with TCS is improved. The reason is that the slip is controlled by keeping it in a desired range     

Computer-aided design and analysis of direct-driven wheel motordrive

This paper presents the computer-aided design (CAD) and performance analysis of a novel direct-driven wheel brushless DC motor drive for electric vehicles (EVs). The proposed motor is a permanent magnet square-wave motor, whose rotor with rare earth magnets forms the exterior of the motor, which can be fitted with a wheel tire to realize the direct drive for each wheel of an EV. The interior stator with its windings is rigidly mounted onto the suspension and frame structure of the vehicle. In order to achieve the direct drive without any mechanical transmission for EVs, the wheel motor has been designed as a low-speed high-torque motor. The design and optimization of the motor geometry was achieved with the aid of finite-element electromagnetic field analysis. Simulation studies on the transient performance of the motor drive were also carried out. This involved the creation of the motor transient model and formulation of a motor control strategy to ensure the wheel motor drive runs efficiently in the entire permitted speed and load range. The application of CAD techniques in the design of this very unconventional drive is described in this paper     

A novel driver assist stability system for all-wheel-drive electric vehicles

A novel driver-assist stability system for all-wheel-drive electric vehicles is introduced. The system helps drivers maintain control in the event of a driving emergency, including heavy braking or obstacle avoidance. The system comprises a fuzzy logic system that independently controls wheel torque to prevent vehicle spin. Another fuzzy wheel slip controller is used to enhance vehicle stability and safety. A neural network is trained to generate the required reference for yaw rate. Vehicle true speed is estimated by a sensor data fusion method. The intrinsic robustness of fuzzy controllers allows the system to operate in different road conditions successfully. Moreover, the ease of implementing fuzzy controllers gives a potential for vehicle stability enhancement.     

Doppler-Based Ground Speed Sensor Fusion and Slip Control for a Wheeled Rover

High-speed unmanned ground vehicles evolving on natural terrains can exhibit a significant slip and skid. An estimation of both friction and traction forces can allow to achieve a better control. In order to implement a control architecture based on the vehicle dynamic model and the wheel–soil interaction model, the knowledge of the wheels slip rate is required. The wheel angular velocities can be precisely measured. But the true measurement of the ground speed of the vehicle is much more challenging. A low-cost Doppler radar is used, in conjunction with an accelerometer, to obtain the ground speed. Thus, the knowledge of the slip rate allows us to setup an in situ procedure for the estimation of soil parameters that is based on the measurement of the motors torques. A wheel slippage controller has also been implemented, which is a first step toward high-level dynamic control.      

Design of an Optimal Fuzzy Controller for Antilock Braking Systems

Antilock braking systems (ABSs) have been developed to improve vehicle control during sudden braking, especially on slippery road surfaces. The objective of such control is to increase wheel traction force in the desired direction while maintaining adequate vehicle stability and steerability and reducing the vehicle stopping distance. In this paper, an optimized fuzzy controller is proposed for ABSs. The objective function is defined to maintain the wheel slip to a desired level so that maximum wheel traction force and maximum vehicle deceleration are obtained. All the components of a fuzzy system are optimized using genetic algorithms. The error-based global optimization approach is used for fast convergence near the optimum point. Simulation results show fast convergence and good performance of the controller for different road conditions     

A Loss-Minimization DTC Scheme for EV Induction Motors

This paper proposes a strategy to minimize the losses of an induction motor propelling an electric vehicle (EV). The proposed control strategy, which is based on a direct flux and torque control scheme, utilizes the stator flux as a control variable, and the flux level is selected in accordance with the torque demand of the EV to achieve the efficiency-optimized drive performance. Moreover, among EV's motor electric propulsion features, the energy efficiency is a basic characteristic that is influenced by vehicle dynamics and system architecture. For this reason, the EV dynamics are taken into account. Simulation tests have been carried out on a 1.1-kW EV induction motor drive to evaluate the consistency and the performance of the proposed control approach     

Adhesion control in railroad traction

This article presents a new approach to adhesion control for railroad traction. Based on a combined torque and speed observation the controller detects the actual adhesion utilization at the wheel and applies an adequate torque limitation. Hence the traction unit optimally takes use of the available adhesion. No measurement of the absolute train velocity is needed. The effectiveness of the proposed method has been investigated by railroad tests with a subway electric traction unit. The results and their good conformity with computer simulation are presented in detail.