Indirect torque control of switched reluctance motors using iterative learning control

This paper proposes the use of iterative learning control (ILC) in designing a torque controller for switched reluctance motors (SRMs). The demanded motor torque is first distributed among the phases using a torque-sharing function. Following that, the phase torque references are converted to phase current references by a torque-to-current converter and the inner current control loop tracks the phase current references. SRM torque is a highly nonlinear and coupled function of rotor position and phase current. Hence, the phase current references for a given demanded torque can not be obtained analytically. Assumption of linear magnetization characteristics results in an invertible torque function. However, the nominal phase current references obtained using this torque function will lead to some torque error as motor enters into magnetic saturation. For a constant demanded torque, the error in the phase current references will be periodic with rotor position. Hence, we propose to use ILC to add a compensation current to the nominal phase current references so that torque error is eliminated. Similarly, current tracking for the nonlinear and time-varying system is achieved by combining a simple P-type feedback controller with an ILC controller. The proposed scheme uses ILC to augment conventional feedback techniques and hence, has better dynamic performance than a scheme using only ILC. Experimental results of the proposed scheme for an 8/6 pole, 1-hp SRM show very good average as well as instantaneous torque control.     

An MRAC-based nonlinear speed control of an interior PM synchronous motor with improved maximum torque operation

A model reference adaptive control (MRAC)-based nonlinear speed control strategy of an interior permanent magnet (IPM) synchronous motor with an improved maximum torque operation is presented. In most servo systems, the controller is designed under the assumption that the electrical dynamics are neglected by the field-oriented control. This requires a high-performance inner-loop current control strategy. However, the separate designs for a high-performance current regulator and a robust speed controller need considerable effort. To overcome this limitation, an MRAC-based nonlinear speed control strategy for the IPM synchronous motor is presented, considering the whole nonlinear dynamics. Nonlinear speed control is achieved by an input–output linearization scheme. This scheme, however, gives an unsatisfactory performance under the mismatch of the system parameters and load conditions. For the robust output response, the controller parameters are estimated by an MRAC technique in which the disturbance torque and flux linkage are estimated. The adaptation laws are derived from Lyapunov stability theory. In view of the drive efficiency, the motor has to provide the maximum torque for a given input. To drive the IPM synchronous motor under improved maximum torque operation, the estimated flux linkage is employed for the generation of the d-axis current command. The robustness and output performance of the proposed control scheme are verified through simulation results.     

Motor control and torque coordination of an electric vehicle actuated by two in-wheel motors

In this research, an electric vehicle actuated by two in-wheel DC motors is developed. By properly coordinating the motor torques, both drive-by-wire and electrical steering can be achieved. Two critical issues respectively related to the design of motor controllers and the coordination of the two motor torques under control saturation are investigated in this study. Firstly, as for the in-wheel motors that are used for driving and steering simultaneously, their operation covers a wider dynamic range that forward acceleration (deceleration), and reverse acceleration (deceleration) may occur alternately. To perform driving and steering smoothly and efficiently, each motor should be switched to an appropriate mode to generate the torque demanded. Secondly, during the high-speed maneuvering, the high back-emf voltage in the motor coil substantially reduces the motor’s torque generating capability. Since the electrical steering depends on the differential torque of two wheels, when electrical steering is demanded in this case, torque/current saturation may occur in either one of the motors and the electrical steering performance could be seriously degraded. To address these issues, controllers of two levels are proposed. For the low-level controller (the motor controller), it operates the motor automatically in an appropriate mode for performance and efficiency consideration. An input transformation is introduced to cancel the nonlinearity in current dynamics so as to control the motor torque easily and precisely regardless of mode switching. For the high-level controller (the torque coordination controller), besides generating reference commands to the low-level controllers, during control saturation it can also properly re-distributes control signals to maintain consistent steering performance and provides compensation for integrator windup. The control system is implemented and the performance is experimentally and numerically validated.     

A torque controller suitable for electric vehicles

A torque controller suitable for electric vehicles is studied. The controller ensures that an induction motor generates motor torque efficiently, stably and accurately. The torque control system feeds back an assumed motor torque calculated using the secondary magnetic flux and the torque current detected from current sensors of the primary currents. The motor torque is controlled by using the torque current reference determined from the generated secondary magnetic flux and the magnetizing current reference. The magnetizing current reference is determined on the basis of the torque current reference so that motor torque generation efficiency is always optimal. The magnetizing current regulator is operated according to the magnetizing current reference. This ensures the motor generates the motor torque stably even in transient states. Fundamental performance characteristics, such as response, accuracy and efficiency of the motor torque are verified by simulation and experiments. The torque controller is judged suitable for the drive system of electric vehicles     

Torque Feedforward Control Technique for Permanent-Magnet Synchronous Motors

This paper proposes a torque control method for interior permanent-magnet (IPM) motors operating in a wide speed range requiring high torque/power accuracy and a fast dynamic response. Using the fact that the motor parameters are nonlinear and significantly vary with direct and quadrature current operating points, a new optimal operating plane is generated. This operating plane combines the maximum torque per ampere (MTPA) curve, current limit circle, and maximum torque per volt (MTPV) curve, voltage limitations, and torque calculation under the nonlinear parameter variations. As a result, new feedforward tables are generated, which make full use of measured motor parameters. The new torque and flux regulators built around the feedforward tables provide a fast dynamic response and accurate steady-state torque/power production. The proposed controller was implemented and successfully tested on a 105-kW IPM motor electric drive used in a fuel-cell vehicle program.      

High-performance speed servo system considering Voltage saturation of a vector-controlled induction motor

Generally, a speed servo system of a vector-controlled induction motor has limitations of motor voltage and current. When the speed servo system has a large torque reference, the output of its PI controller is often saturated. In this case, the conventional servo system stops the integral calculation of its PI controller. However, this system often has a large overshoot and/or an oscillated response caused by both a windup phenomenon and phase error on the vector control condition. This paper proposes a new speed servo system considering voltage saturation for the vector-controlled induction motor. The proposed control method compensates the phase error on vector control condition quickly, and always keeps the vector control condition. The experimental results show that the proposed system well regulates the motor speed and the secondary magnetic flux for a large torque reference without a windup phenomenon.     

High-Speed Control of IPMSM Drives Using Improved Fuzzy Logic Algorithms

This paper presents an improved fuzzy logic controller (FLC) for an interior permanent magnet synchronous motor (IPMSM) for high-performance industrial drive applications. In the proposed control scheme for high-speed operations above the rated speed, the operating limits of IPMSM are expanded by incorporating the maximum torque per ampere operation in constant torque region and the flux-weakening operation in constant power region. The power ratings of the motor and the inverter are considered in developing the control algorithm. A new and simple FLC is utilized as a speed controller. The FLC is developed to have less computational burden, which makes it suitable for real-time implementation, particularly at high-speed operating conditions. The complete drive is implemented in real-time using digital signal processor (DSP) controller board DS 1102 on a laboratory 1-hp IPM motor. The efficiency of the proposed control scheme is evaluated through both experimental and computer simulation results. The proposed controller is found to be robust for high-speed applications     

Design of a fault-tolerant IPM motor for electric power steering

This paper deals with the design of an interior permanent magnet (IPM) motor for power steering. Such an application requires an imperative fault-tolerant capability that is obtained by means of a redundant solution with two motors on the same shaft. A ball-screw system converts the rotating movement into the linear movement of the steering rack. In addition, the IPM motor has to exhibit very low braking torque after a short-circuit fault. Useful relationships between the maximum braking torque and the motor parameters are found and used in the design of the motor.     

A novel bearingless interior permanent magnet slice motor driven blood pump

A 2-pole bearingless interior permanent magnet (IPM) motor with slice rotor configuration is presented in this paper. A novel IPM rotor is designed considering direct and indirect operational specifications such as force constant, torque constant, axial/radial stiffness and cogging torque. Cogging torque and its resulting vibrations affect motor and levitation operation significantly. Hence, various rotor configurations are simulated using the finite element method to develop a topology that minimizes these phenomena. The final topology is tested for closed-loop levitation and speed control. The motor is also tested for its intended application as a blood pump. A mock circulatory loop is developed to measure the performance of the pump. The simulation results, experimental control system performance and pump performance results are shown and explained in the paper.     

Speed control system design and experimentation for interior PMSM drives

This paper presents a robust speed-control strategy using a Takagi–Sugeno fuzzy model for interior permanent magnet synchronous motor (IPMSM) drives. The sufficient conditions of linear matrix inequalities, which can guarantee the existence of the fuzzy controller gains, are derived from a common quadratic Lyapunov function. Moreover, the maximum torque per ampere control is incorporated to improve the torque production in the constant torque region and the efficiency of the IPMSM drive. The global stability of an observer-based control system is analytically proven. Simulations and experiments are conducted to demonstrate the feasibility of the proposed approach through a prototype IPMSM drive system. Consequently, the proposed fuzzy control methodology can achieve less steady-state error and less sensitivity than the conventional feedback linearisation control method under motor parameter variations and external disturbances.     

Modeling and control strategies for a variable reluctancedirect-drive motor

A high-performance ripple-free dynamic torque controller for a variable-reluctance (VR) motor intended for trajectory tracking in robotic applications is designed. A modeling approach that simplifies the design of the controller is investigated. Model structure and parameter estimation techniques are presented. Different approaches to the overall torque controller design problem are discussed, and the solution adopted is illustrated. A cascade controller structure consisting of a feedforward nonlinear torque compensator, cascaded to a nonlinear flux or current closed-loop controller is considered, and optimization techniques are used for its design. Although developed for a specific commercial motor, the proposed modeling and optimization strategies can be used for other VR motors with magnetically decoupled phases, both rotating and linear. Laboratory experiments for model validation and preliminary simulation results of the overall torque control system are presented     

Nonlinear adaptive control of direct-drive brushless DC motors andapplications to robotic manipulators

Robust adaptive nonlinear control of brushless DC (BLDC) motors is considered. A controller is designed for the plant that is robust to parametric and dynamic uncertainties in the entire electromechanical system. These uncertainties are shown to be bounded by polynomials in the states. In addition, the controller can reject any bounded unmeasurable disturbances entering the system. A model for the motor incorporating magnetic saturation is used to design voltage-level control inputs for the motor. The design methodology is based on our earlier work on adaptive control of nonlinear systems. The overall stability of the system is shown using Lyapunov techniques. The tracking error is shown to be globally uniformly bounded. The design procedure is shown to be also applicable to multilink manipulators actuated by BLDC motors. The performance of the controller is verified through simulations and comparisons with a proportional-integral-derivative-type controller are made     

Automatic flux-weakening control of permanent magnet synchronousmotors using a reduced-order controller

This study presents a novel means of designing a simple and effective position and velocity controller for permanent magnet synchronous motors (PMSM). In contrast to the conventional two-loop control methods with full-state feedback, the proposed controller does not need current information of the motor for feedback purposes. However, under normal operation the steady-state d-axis current can still be controlled to zero to minimize power dissipation. In addition, implementing a simple overmodulation strategy allows the controller to automatically generate a flux-weakening control to expand the range of operating speed when voltage saturation occurs. In addition to not depending on system parameters used by the controller, the automatically generated demagnetizing current is also optimal in the sense of minimum power dissipation that differs from the maximum output torque design or the constant power design of the general flux-weakening control methods. Simulation and experimental results show that the controller can achieve an effective speed and position control with near-minimum power dissipation, even when voltage saturation occurs     

A new torque and flux control method for switched reluctance motordrives

Switched reluctance (SR) motors have an intrinsic simplicity and low cost that make them well suited to many applications. However the motor's doubly salient structure and highly nonuniform torque and magnetization characteristics lead to the inability to excite the motor using conventional AC motor waveforms, or apply established AC motor rotating field theory to the motor. Furthermore, high torque ripple is inherent in the motor unless a torque ripple reduction strategy is employed. Thus, control of the motor is difficult and complex compared to other machines. Previous methods of control have fallen into two main categories: those which use a simplified linear model and those which account for the motor saturation. The simplified linear model schemes have the advantage of simplicity and tractability but are inaccurate in most practical SR drives, whereas the nonlinear schemes have the problem of high complexity and computational expensiveness which makes real-time implementation difficult. To overcome these problems, in this paper, a novel control method for the SR motor is derived from analysis of the nonuniform torque characteristics of the motor. The control method applies the philosophy of direct torque control (DTC). Unlike previous direct torque control schemes for the SR motor drive, the new method does not involve short flux patterns, a change of the motor winding configuration, or the use of a bipolar current drive. Thus, the scheme can be conveniently implemented on any normal type of SR motor drive. In addition, the scheme overcomes the problems associated with torque ripple control in the SR motor by regulating the torque output of the motor within a hysteresis band. Furthermore, the scheme is very simple and can be implemented in real-time with low cost microprocessor hardware     

基于模型预测控制的电动汽车轮毂电机转矩控制研究

分布式驱动电动汽车（Distributed Drive Electric Vehicles,DDEV）采用内嵌式轮毂电机,使各车轮独立可控,具有调节形式多样化等突出优点.合理的轮毂电机转矩分配是保证DDEV稳定性的关键.本文为提高DDEV稳定性,分析了轮毂电机转矩分配与稳定性的关系,提出一种基于模型预测控制器的DDEV轮毂电机转矩分配控制系统.所提出的控制系统由上层控制器和下层控制器两个主要部分组成.上层控制器设计了基于拉盖尔函数的模型预测控制器,综合分析保证DDEV稳定性所需的轮毂电机转矩约束条件,实现轮毂电机最优转矩分配,提高DDEV稳定性.下层控制器对四个轮毂电机进行实时控制,执行上层控制器设计的最优转矩分配方案.最后在搭建的Matlab/Simulink环境下进行仿真验证.     

Dynamic response of a hydraulic servo-valve torque motor with magnetic fluids

As magnetic fluids (MF) show higher saturation magnetization and larger viscosity when exposed to a magnetic field, large damping forces or resistance will be exerted on the armature of a hydraulic servo-valve torque motor by magnetic fluids if they are filled into the working gaps of the motor. This paper focuses on the application of magnetic fluids in a hydraulic servo-valve torque motor, especially the influence of magnetic fluids on the dynamic response of the motor. After introducing the working principle of the torque motor with magnetic fluids, the dynamic mathematical models of the torque motor and magnetic fluids are presented. The torque working on the armature introduced by magnetic fluids is analyzed. In order to study the influence of magnetic fluids, dynamic response of the torque motor is simulated and tested when magnetic fluids are applied or not in the motor. Simulation and experimental results show an obvious influence of magnetic fluids on the dynamic response of the hydraulic servo-valve torque motor.     

A sensorless optimal control system for an automotive electric power assist steering system

This paper considers the analysis and design of a double-pinion-type electric power assist steering (EPAS) control system. A simplified model of the augmented steering assembly-electric motor system is developed using Lagrangian dynamics, and an optimal controller structure for the model is proposed. Three main advances to the state of the art are presented in this paper. First, a state-space design model is used rather than an input-output model. A state-space formulation for a system model that incorporates motor electrical dynamics is obtained with the assist motor angular position as the output. Second, linear quadratic regulator (LQR) and Kalman filter techniques are employed to arrive at an optimal controller for the EPAS system. The selection of weighting coefficients for the LQR cost function is discussed. Finally, the authors present a control strategy that eliminates the steering column torque sensor, a critical component in existing EPAS controller designs. The proposed control strategy presents an opportunity to improve EPAS system performance and also reduce system cost and complexity.     

Nonlinear control of a series DC motor: theory and experiment

The control problem for a series DC motor is considered. Based on a nonlinear mathematical model of a series-connected DC motor, it is shown that the combination of a nonlinear transformation and state feedback (feedback linearization) reduces the nonlinear control design to a linear control design. To demonstrate its effectiveness, an experimental study of this controller is presented. These experimental results are also compared with a simulation of the closed-loop system. Finally, it is shown that a nonlinear observer (with linear error dynamics) for speed and load torque can be constructed based only on measurements of the motor current. Experimental results of this speed and load-torque estimator are also presented     

New self-tuning fuzzy PI control of a novel doubly salient permanent-magnet motor drive

In a doubly salient permanent-magnet (DSPM) motor drive, it is difficult to get satisfied control characteristics by using a normal linear proportional plus integral (PI) controller due to the high nonlinearity between speed and current or torque. Hence, a new self-tuning fuzzy PI controller with conditional integral, which is performed by a single-chip N87C196KD, is proposed. The initial parameters of the controller are optimized by using genetic arithmetic. Simulation and experiments on the newly proposed 8/6-pole DSPM machine have shown that the proposed new self-tuning fuzzy PI controller offers better adaptability than the normal linear PI control and that the developed motor drive offers better steady-state and dynamic performances.     

基于反推的永磁同步电动机伺服系统的位置跟踪控制

永磁同步电动机工作性能优越，在当前交流伺服系统的驱动控制当中起着越来越重要的作用。为了实现永磁同步电动机的精确位置跟踪，把一种新颖非线性控制方法Backstepping应用于永磁同步电动机伺服系统控制器的设计。Backstepping控制器的设计以保证系统的全局一致渐近稳定为原则，因此该控制器不但可以保证系统的全局一致渐近稳定，而且系统具有快速跟踪，定位精确的特点。系统的设计能够有效降低转矩变化对位置跟踪性能的影响。最后通过Matlab仿真验证了系统设计的有效性和可行性。