Tracking Performance of Electric Power Steering System Based on the Mixed H_2/H_∞ Strategy

The tracking performance of motor current is an important factor that affects the assistance torque of electric power steering （EPS） system. Bad tracking performance will cause assistant torque delay, and make road feeling bad, and is influenced by the input steering torque and system measuring noise. However the existing methods have some shortages on system＇s robust dynamic performance and robust stability. The mixed H2/H∞ strategy for recirculating ball-type EPS system in a pure electric bus is proposed, and vehicle dynamic model of the system is established. Due to the existence of system model uncertainty, disturbance signals, sensor noises and the demand of system dynamic performance, the indexes of robust performance and road feeling for drivers are defined as the appraisal control objectives. The H∞ method is introduced to design the H∞ controller, and the H2 method is applied to optimize the H∞ controller, thus the mixed H2/H∞ controller is designed. The response of EPS system to the motor current command with amplitude of 20 A, the road disturbance with amplitude of 500 N and the sensor random noise with the amplitude of 1 A is simulated. The simulation results show that the recirculating ball-type EPS system with the mixed H2/H∞ controller can attenuate the random noises and disturbances and track the boost curve well, so the mixed H2/H∞ controller can improve the system＇s robust performance and dynamic performance. For the purpose of verifying the performance of the designed control strategy, the motor current tracking performance ground tests are conducted with step response input of the steering wheel, double-lane steering test and lemniscate steering test, respectively. The tests show that the mixed H2/H∞ controller for the recirculating ball-type EPS system of pure electric bus is feasible. The designed controller can solve the robust performance and robust stability of the system, thus improve the tracking performance of the EPS system and provide satisfied road feeling for the drivers.

Controller Design for Electric Power Steering System Using T-S Fuzzy Model Approach

Pressure ripples in electric power steering （EPS） systems can be caused by the phase lag between the driver s steering torque and steer angle, the nonlinear frictions, and the disturbances from road and sensor noise especially during high-frequency maneuvers. This paper investigates the use of the robust fuzzy control method for actively reducing pressure ripples for EPS systems. Remarkable progress on steering maneuverability is achieved. The EPS dynamics is described with an eight-order nonlinear state-space model and approximated by a Takagi-Sugeno （T-S） fuzzy model with time-varying delays and external disturbances. A stabilization approach is then presented for nonlinear time-delay systems through fuzzy state feedback controller in parallel distributed compensation （PDC） structure. The closed-loop stability conditions of EPS system with the fuzzy controller are parameterized in terms of the linear matrix inequality （LMI） problem. Simulations and experiments using the proposed robust fuzzy controller and traditional PID controller have been carried out for EPS systems. Both the simulation and experiment results show that the proposed fuzzy controller can reduce the torque ripples and allow us to have a good steering feeling and stable driving.

Model development and parameter investigation of a column-type electric power steering system

In this paper, the performance of a column-type electric power steering （EPS） system and vehicle has been studied and a detailed mathematical model for the system has been established. Based on the mathematic model of the optimization design for steering feel, the parameters of the EPS system and vehicle on steering performance have been investigated. Moreover, the effects of the parameters on system stability have been analyzed and compared by the method of absolute sensitivity and the results are given in the end.

H∞ control of novel active steering integrated with electric power steering function

Based on the traditional active steering system, a novel active steering system integrated with electric power steering function was introduced, which can achieve the functions of both active steering and electric power steering. In view of the interference from road random signal and sensor noise in the novel active steering system, the H∞ control model of the novel active steering system was built. With satisfying steering feel, good robust performance and steering stability being the control objectives, the H∞ controller for the novel active front steering (AFS) system was designed. The simulation results show that the novel AFS system with H∞ control strategy can attenuate the road interference quickly, and there is no resonance peak in the bode diagram. It can make the driver obtain more useful information in the low frequency range, and attenuate the road interference better in the high frequency range, thus the driver can get more satisfying road feeling. Therefore, the designed H∞ controller can synthesize the advantages of both robust performance and robust stability, and has certain contribution to the design of novel AFS system.

Integration optimization of novel electric power steering system based on quality engineering theory

The dynamic model of a novel electric power steering (EPS) system integrated with active front steering function (the novel EPS system) is built.The concepts and quantitative expressions of the steering road feel,steering sensibility,and steering operation stability are introduced.Based on quality engineering theory,the optimization algorithm is proposed by integrating the Monte Carlo descriptive sampling,elitist non-dominated sorting genetic algorithm (NSGA-Ⅱ) and 6-sigma design method.With the steering road feel and the steering portability as optimization targets,the system parameters are optimized by the proposed optimization algorithm.The simulation results show that the system optimized based on quality engineering theory can improve the steering road feel,guarantee steering stability and steering portability and thus provide a theoretical basis for the design and optimization of the novel electric power steering system.

Precise Compound Control of Loading Force for Electric Load Simulator of Electric Power Steering Test Bench

Electric load simulator(ELS) systems are employed for electric power steering(EPS) test benches to load rack force by precise control. Precise ELS control is strongly influenced by nonlinear factors. When the steering motor rapidly rotates, extra force is directly superimposed on the original static loading error, which becomes one of the main sources of the final error. It is key to achieve ELS precise loading control for the entire EPS test bench. Therefore, a three-part compound control algorithm is proposed to improve the loading accuracy. First, a fuzzy proportional–integral plus feedforward controller with force feedback is presented. Second, a friction compensation algorithm is established to reduce the influence of friction. Then, the relationships between each quantity and the extra force are analyzed when the steering motor rapidly rotates, and a net torque feedforward compensation algorithm is proposed to eliminate the extra force. The compound control algorithm was verified through simulations and experiments. The results show that the tracking performance of the compound control algorithm satisfies the demands of engineering practice, and the extra force in the ELS system can be suppressed by the net torque corresponding to the actuator’s acceleration.

Study on Characteristic of Electric Power Assist Steering System

A pinion-type electric power steering (EPS) equipped on a sedan is reached in this paper. A three-freedom dynamic model of this system is created. The variables affecting assist character is analyzed. The formulas of simpled steering resistance force and the relationship between assist gain and vehicle speed are presented for the first time. Assist character is found based on the parameters of a sedan at last. This assist character is fit for the control rule of the EPS system through analyzing this character. The assist character figure offers reference for system design and control. Furthermore, this research method has generality for assist character of different kinds of vehicles.

Performance optimization of electric power steering based on multi-objective genetic algorithm

The vehicle model of the recirculating ball-type electric power steering (EPS) system for the pure electric bus was built. According to the features of constrained optimization for multi-variable function, a multi-objective genetic algorithm (GA) was designed. Based on the model of system, the quantitative formula of the road feel, sensitivity, and operation stability of the steering were induced. Considering the road feel and sensitivity of steering as optimization objectives, and the operation stability of steering as constraint, the multi-objective GA was proposed and the system parameters were optimized. The simulation results show that the system optimized by multi-objective genetic algorithm has better road feel, steering sensibility and steering stability. The energy of steering road feel after optimization is 1.44 times larger than the one before optimization, and the energy of portability after optimization is 0.4 times larger than the one before optimization. The ground test was conducted in order to verify the feasibility of simulation results, and it is shown that the pure electric bus equipped with the recirculating ball-type EPS system can provide better road feel and better steering portability for the drivers, thus the optimization methods can provide a theoretical basis for the design and optimization of the recirculating ball-type EPS system.

Electrical power assisted steering for EVs and HEVs

Electrical power assisted steering (EPAS) is one of the key components, especially for electrical vehicle. It has attracted much attention for their advantages with respect to improved fuel economy and has been widely adopted as automotive power-steering equipment in recent years. EPS (electrical power steering) controllers contain MCU (microprocessor control unit) to implement the complex control algorithms. EPS control strategy development is the core technology of the whole system. To achieve the better performance of driving, both mechanical structures and electrical structures are totally designed as a whole. Model-based development is recommended to software design. There are several trends about EPS’ future, such as high power EPS development, high voltage EPS development and steering-by-wire technology.

基于功能安全的汽车EPS系统安全冗余研究

电动助力转向(electric power steering,EPS)系统是车辆常用的转向执行器,其失效将严重影响驾乘人员的安全。为提高EPS系统的安全性与可靠性,基于功能安全标准建立EPS系统安全冗余机制:基于ISO26262对EPS系统进行研究,通过相关项定义、危害分析与风险评估(HARA),得到系统的功能安全目标与需求,并对其进行分配;设计EPS系统架构、容错机制,以提高系统的安全性;最后,对所设计的安全冗余机制进行台架试验。结果表明,在单侧桥驱芯片故障、单侧电机位置传感器故障、双侧电机位置传感器故障等故障注入的情况下,系统能够实现预期响应,满足功能安全目标,验证了所设计安全冗余机制的有效性。

大齿条力冗余R-EPS转向器开发及验证

为了满足前轴载荷较大乘用车电动助力转向产品的需要,对大齿条力冗余R-EPS转向系统进行开发,全新设计了齿条、滚珠丝杠及皮带传动等机构,制定了R-EPS电控系统冗余方案,设计了电控系统失效时的容错机制,通过转向手力调校和匹配,转向手力和转向跟随性均满足车辆使用需求,产品经台架试验和整车道路试验验证了产品性能优良、安全可靠。

基于Simscape的APA-EPS系统建模及人机共驾转向控制策略研究

人机共驾是智能车辆实现高度自动驾驶之前的过渡阶段,由于驾驶员与驾驶辅助系统同时在环,存在驾驶权分配的问题,智能车辆的转向系统必须实时敏捷地执行驾驶员和驾驶辅助系统的转向控制指令。本文针对搭载于某智能MPV的平行轴式电动助力转向系统(APA-EPS)研究人机共驾转向控制策略。首先对APA-EPS系统进行Simscape建模,并通过台架试验验证了模型的准确度。随后基于模糊PID控制算法和模糊滑模控制算法分别设计了人驾和机驾模式下的控制策略。在驾驶员主导驾驶车辆时,根据距离影响度函数和角度影响度函数确定转向控制权重;在驾驶辅助系统主导驾驶车辆时,采用滑动时间窗口监测驾驶员的接管请求。仿真试验结果表明,人驾和机驾的控制策略均具有较好的转角跟随效果,人机共驾时转向控制权能够及时进行切换,且APA-EPS的转向盘转角响应迅速。

抑制汽车EPS-PMSM谐波电流的可变阶跃函数补偿方法

针对三相逆变器死区时间与导通压降引起汽车电动助力转向永磁同步电机低转速下的谐波电流,提出了对α及β轴电压进行可变阶跃函数补偿的方法。为降低补偿电压摄动,保证谐波电流的抑制效果,通过电流平均法获得准确的三相电流极性。为提高输出波形质量,消除电机低速轻载工况下零电流钳位现象,提出利用可变梯形函数进行α轴及β轴电压补偿。对未补偿、传统平均电压补偿和可变阶跃函数补偿下的EPS-PMSM谐波电流进行数值仿真评估。结果表明:在电机低速轻载工况下,相较传统平均电压补偿法,可变阶跃函数补偿法将电流总谐波失真率再降低约23.42%,并消除了零电流钳位现象。

轮毂电机电动汽车EPS系统控制策略研究

为降低轮毂电机电动汽车非簧载质量增加对整车操纵稳定性的影响,以某轮毂电机电动汽车电动助力转向系统(Electric Power Steering,EPS)为研究对象,对其参数匹配和控制策略进行研究。设计了目标车型的直线型助力特性曲线,在助力控制的基础上加入阻尼、回正控制,采用PID控制算法对助力电流进行调节。基于ADAMS/Car搭建轮毂电机电动汽车整车动力学模型,通过MATLAB/Simulink搭建EPS控制模型,实现联合仿真。对操纵稳定性进行了转向盘角阶跃和转向盘角脉冲仿真试验,加入EPS控制后,整车横摆角速度、侧向加速度、质心侧偏角值均有所降低。结果表明:研究的EPS控制策略提高了轮毂电机电动汽车的操纵稳定性,具有较好的控制效果。

基于模糊神经控制的EPS系统设计

为提高自动驾驶过程中汽车转向的轻便性和鲁棒性,建立了自动驾驶汽车的EPS系统模型,提出了基于径向基神经网络的辅助特性曲线模块和模糊神经网络PID控制算法,并运用Matlab/Simulink和Carsim建立整车联合仿真.结果表明:基于径向基神经网络的辅助特性曲线平滑度更高,为后续整车仿真精确性提供了良好的基础,且基于模糊神经网络PID的EPS系统比常规神经网络PID控制系统更优,对自动驾驶汽车的EPS系统设计具有重要意义.

含特殊转向工况的汽车EPS电动机控制策略

电动助力转向(EPS)电动机的控制是EPS系统设计的关键之一。建立了汽车三自由度转向模型和EPS系统动力学模型,设计了EPS助力特性和包含回正过程补偿、紧急避让过程补偿、满载大角度转弯补偿等特殊转向工况的电动机控制策略,利用Matlab/Simulink进行了仿真,与不包含特殊工况补偿的情况进行了性能比较及分析。仿真结果表明,含特殊转向工况的汽车EPS电动机控制策略具有更好的操纵性能和安全性能。这对指导EPS电动机控制策略的开发、功能的增强和优化以及转向操纵安全的提高都具有重要的工程应用意义。

基于遗传算法的EPS系统参数优化

根据纯电动大客车电动助力转向(EPS)系统工作的具体要求,开发了适合纯电动大客车EPS系统使用的循环球式电动助力转向器,建立了纯电动大客车循环球式EPS系统动力学模型及整车二自由度转向模型。在此基础上提出了系统转向路感、转向灵敏度以及转向操稳性的概念,并根据多元函数有约束优化问题的特点应用遗传算法对系统参数进行了优化设计。仿真结果表明:基于遗传算法优化的系统参数提高了系统的转向路感和转向操稳性。

电动汽车EPS曲线型助力特性的设计及试验

为了研究助力特性对汽车的操纵稳定性和转向路感的影响,建立电动助力转向(EPS)系统动力学模型和汽车三自由度转向模型,设计转向盘力矩函数和车速感应函数,确定曲线型助力特性曲线的参数和形式。基于某微型轿车设计实车试验系统,进行原地转向试验、双纽线试验和蛇形试验。试验结果表明:曲线型助力特性可以在转向轻便性和路感之间达到一个较理想的平衡点;原地转向试验的转向轻便性峰值和标准差分别提高48.11%和49.65%,双纽线试验的转向轻便性峰值和标准差分别提高60.03%和57.84%,蛇形试验的转向轻便性峰值和标准差分别提高41.94%和41.36%;EPS控制有效提高了汽车的转向轻便性,降低了驾驶员的疲劳强度。

自适应模糊神经网络在EPS中的应用

文章介绍了汽车电动助力转向系统(EPS)的组成及工作原理;为解决汽车EPS系统非线性问题,将模糊逻辑与神经网络相结合,采用了基于T-S(Takagi-Sugeno)模型的自适应神经网络模糊推理系统(ANFIS)控制策略;仿真试验验证了系统模型和控制理论的有效性和正确性。

低附着路面条件的EPS控制策略

低附着路面上,车辆自回正力矩显著降低,传统电动助力转向控制策略不能很好地克服这一不利影响,导致车辆回正性能降低,路感丧失甚至带来驾驶员对车辆的误操纵,或导致车辆不能及时回正;在建立基于整车动力学的电动助力转向系统模型的基础上,经电动机电流和转矩传感器测得转矩值,拟合得到当前路面条件下的自回正力矩,同时通过转向盘转角信息计算理想路面条件下的名义自回正力矩,结合路面估计算法,将被识别的路面附着系数等级分为高、中、低,设计基于路面附着系数的助力电流控制策略和基于时变滑模变结构控制的回正控制策略,仿真结果表明可有效改善车辆在低附着路面上的操纵路感和回正性能。建立基于LabVIEW PXI的电动助力转向(Electric power steering,EPS)硬件在环试验平台,并对控制策略进行试验验证,试验结果和仿真结果基本一致。