A global tracking control for speed-sensorless induction motors

The problem of controlling an induction motor without rotor speed measurements is addressed. Arbitrary smooth reference signals for rotor speed and rotor flux modulus are required to be tracked globally (i.e. from any initial condition). A global second-order tracking control is obtained, which is based on a novel rotor speed observer. Simulation results are provided which illustrate the controller performance.     

A nonlinear tracking control for sensorless induction motors

We propose a novel tracking control for induction motors in which only stator currents are used for feedback. Local exponential rotor speed and flux modulus tracking are achieved for any constant reference value and for restricted time-varying reference signals; any known motor parameters values (including constant load torque) and any initial condition, including rotor speed and fluxes, belonging to an explicitly computed domain of attraction are allowed.     

Adaptive control strategy with flux reference optimization for sensorless induction motors

Avoiding mechanical (speed, torque) sensors in electric motor control entails cost reduction and reliability improvement. Furthermore, sensorless controllers (also referred to output-feedback) are useful, even in the presence of mechanical sensors, to implement fault tolerant control strategies. In this paper, we deal with the problem of output-feedback control for induction motors. The solutions proposed so far have been developed based on the assumption that the machine magnetic circuit characteristic is linear. Ignoring magnetic saturation makes it not possible to meet optimal operation conditions in the presence of wide range speed and load torque variations. Presently, an output-feedback control strategy is developed on the basis of a motor model that accounts for magnetic saturation. The control strategy includes an optimal flux reference generator, designed in order to optimize energy consumption, and an output-feedback designed using the backstepping technique to meet tight speed regulation in the presence of wide range changes in speed reference and load torque. The controller sensorless feature is achieved using an adaptive observer providing the controller with online estimates of the mechanical variables. Adaptation is resorted to cope with the system parameter uncertainty. The controller performances are theoretically analyzed and illustrated by simulation.     

感应电机转矩跟踪无源控制及自适应观测器设计

针对感应电机高性能转矩跟踪控制和磁链难以直接测量问题,提出了基于无源性的转矩跟踪和自适应磁链观测器控制方案.首先基于感应电机的无源性特性设计了渐近稳定转矩跟踪控制器,重新配置了系统的平衡点,通过注入阻尼提高系统的收敛速度.然后通过将定子电流和转子磁链作为状态变量构建了自适应磁链观测器,简化了观测器结构,根据Lyapunov稳定性理论设计了自适应控制律,实现转子磁链、转速和定子电阻的在线估计.为减小转速估计误差对观测器的影响,给出了观测器增益矩阵的选择方法.仿真结果表明本文所提出的基于自适应观测器的无源控制方案能够有效提高感应电机的动静态性能.     

An adaptive tracking control from current measurements for induction motors with uncertain load torque and rotor resistance

The problem of controlling sensorless induction motors with uncertain constant load torque and rotor resistance on the basis of stator current measurements only is addressed. A new eighth-order dynamic nonlinear adaptive control algorithm is designed, which relies on a closed loop adaptive observer for the unmeasured state variables (rotor speed and fluxes) and for the uncertain parameters and is not based on non-robust open loop integration of flux dynamics. Local exponential stability of the closed loop tracking and estimation error dynamics is achieved under persistency of excitation conditions which restrict the reference signals and may be interpreted in terms of motor observability and rotor resistance identifiability.     

Partial state feedback control of induction motors with magnetic saturation: elimination of flux measurements

In this paper, we present a singularity-free, rotor position tracking controller for the full order, nonlinear dynamic model of the induction motor that includes the effects of magnetic saturation. Specifically, by utilizing the π-equivalent saturation model, we design an observer/controller strategy that achieves semi-global exponential rotor position tracking and only requires stator current, rotor velocity, and rotor position measurements. Simulation and experimental results are included to demonstrate the efficacy of the proposed algorithm.     

Velocity-sensorless tracking control and identification of switched-reluctance motors

We present a solution to the velocity-sensorless control problem for switched-reluctance motors under parametric uncertainty. Our main results guarantee velocity tracking control for velocity references with constant reference acceleration under the assumption that the load torque, the rotor inertia, the resistance and inductances are unknown. Under a persistency of excitation condition on a function which depends only on reference trajectories, we guarantee uniform global asymptotic stability therefore, we establish conditions for the identification of the physical parameters of the system. Our theoretical findings are supported by simulation results.     

Further results on nonlinear tracking control and parameter estimation for induction motors

The original contribution of this paper, which concerns induction motors with uncertain constant load torque and rotor/stator resistances, is twofold. The first innovative contribution relies on the experimental analysis of the latest theoretically-based sensorless/output feedback solutions to the problem of tracking rotor speed and flux modulus reference signals with the simultaneous estimation of the uncertain parameters. The second novel contribution is constituted by the proof of existence for a new adaptive local flux observer from rotor speed and stator currents/voltages, which, in its full-order or reduced-order-like versions, involves neither over-parameterizations nor non-a priori verifiable first order stator resistance identifiability conditions at steady-state.     

感应电动机直接转矩控制的稳定性分析

稳定性问题的研究在感应电动机直接转矩控制(DTC)中具有重要意义。现有文献主要关注恒转速情形,本文研究更接近实际的情况一一变转速下的DTC稳定性,引入状态反馈机制,首先给出定子磁链控制律存在的充分条件;然后在参考转矩大于或小于负载转矩的情形下,分别给出了转矩控制律存在的充分条件,最后以数值仿真验证了所提控制律的有效性,磁链和转矩相对于参考信号的波动确实是限定在一定容差范围内。     

Discrete time sliding mode control with application to induction motors

This work deals with a sliding mode control scheme for discrete time nonlinear systems. The control law synthesis problem is subdivided into a finite number of subproblems of lower complexity, which can be solved independently. The sliding mode controller is designed to force the system to track a desired reference and to eliminate unwanted disturbances, compensating at the same time matched and unmatched parameter variations. Then, an observer is designed to eliminate the need of the state in the controller implementation. This design technique is illustrated determining a dynamic discrete time controller for induction motors.     

A predictive controller for induction motors using an unknown input observer for online rotor resistance estimation and an update technique for load torque

This paper deals with the design of an output feedback predictive controller for induction motors. The fundamental interest of the proposed controller is the capability of decoupling the mechanical speed and the rotor fluxes, without degradation against the variation of rotor resistance and load torque. Hence, the contribution is to apply two estimation procedures in order to achieve this goal. Namely, an unknown input observer (UIO) is used for the constant time estimation whereas a heuristic solution is exploited for the load torque update. Moreover, rotor flux components are recovered as an unavailable state of the system. Effectiveness of the proposed observers and the performance of the controller are confirmed by simulation results.     

A speed-sensorless indirect field-oriented control for induction motors based on high gain speed estimation

The authors design a new speed sensorless output feedback control for the full-order model of induction motors with unknown constant load torque, which guarantees local asymptotic tracking of smooth speed and rotor flux modulus reference signals and local asymptotic field orientation, on the basis of stator current measurements only. The proposed nonlinear controller exploits the concept of indirect field orientation (no flux estimation is required) in combination with a new high-gain speed estimator based on the torque current tracking error. The estimates of unknown load torque and time-varying rotor speed converge to the corresponding true values under a persistency of excitation condition with a physically meaningful interpretation, basically equivalent to non-null synchronous frequency. Stability analysis of the overall dynamics has been performed exploiting the singular perturbation method. The proposed control algorithm is a “true” industrial sensorless solution since no simplifying assumptions (flux and load torque measurements) are required. Simulation and experimental tests show that the proposed controller is suitable for medium and high performance applications.     

Design and sensitivity analysis of a reduced-order rotor flux optimal observer for induction motor control

This paper aims to give simple and effective design criteria of rotor flux reduced-order observers for motion control systems with induction motors. While the observer is optimized for rotor and stator resistance variations, a sensitivity analysis is carried out in the presence of variations of all the motor parameters by means of either transfer function from true to observed rotor flux or simulation in a MATLAB-SIMULINK environment, assuming the voltages supplying the motor to be different from those supplying the observer. The sensitivity analysis makes it possible to establish design criteria for the observer in question. The behaviour of the proposed reduced order observer is compared with current model and voltage model observers. Experimental results are also given, with the dual aim of confirming the validity of this design method and showing that the observer can be implemented on microprocessor-based devices.     

Hopf bifurcation in indirect field-oriented control of induction motors

The appearance of self-sustained oscillations in high performance AC drives, and in particular, in induction motors whose speed is regulated with the industry standard field-oriented control, is a well-documented but little understood phenomenon. It is well known that the oscillations may be quenched by returning the outer-loop PI speed control, but no precise rules to carry out this task, which may be time consuming, are known. In this paper, we show that these oscillations may arise due to the existence of Hopf bifurcations. Some simple rules for selecting the gains of the PI controller are obtained as a result of our analysis.     

Global observability analysis of sensorless induction motors

The current problems to successfully apply sensorless controllers for induction motors are the existence of operation regimes for which the performance is remarkably deteriorated, due to the difficulties in estimating correctly motor speed and flux, and the lack of a theoretical explanation for this kind of behavior. In this paper a global observability analysis for these machines is carried out. It is first shown that all indistinguishable trajectories of the system, i.e. pairs of state trajectories with the same input/output behavior, can be described by a differential equation on a manifold, named here the indistinguishable dynamics. Studying the stability properties of this latter system it can be shown that the induction motor is not completely observable nor detectable in a local or in a global sense, and for every set of parameters. This implies that it is impossible to construct a state observer for the motor that converges for every trajectory of the system. Moreover, the indistinguishable dynamics provides a systematic method to study, understand and explain particular operation regimes, and this is illustrated by some case studies of practical relevant operating conditions.     

感应电动机定子磁链与转矩的逆解耦及存在性

对于具有多变量、非线性、强耦合特征的异步电动机调速系统,实现定子磁链与电磁转矩的动态解祸控制足提高系统性能的关键.本文从异步电动机的5阶模犁及其固有的电磁特性出发,证明了其系数矩阵的非奇异性,进而结合逆系统理论证明定子磁链与电磁转矩的逆解耦在任何状态下都是存在的.在此基础上设计了一种通过非线性状态反馈的逆解耦控制方案,将复杂系统解耦成电磁转矩与定子磁链的两个独立线性回路,然后利用线性系统理论分别对转矩与磁链调节器进行综合设计.仿真实验结果验证逆解耦的存在性与解耦控制方案的有效性.     

Nonlinear control of induction motors: torque tracking with unknownload disturbance

Ortega and Espinosa (1993) presented a globally stable controller for torque regulation of a complete induction motor model with partial state feedback, i.e., no assumption of flux measurement. The result was established under the assumptions that both the desired and load torques are constant, that the former does not exceed certain bounds which depend on the systems natural damping, and that the motor parameters are known. In the present contributions the authors extend these results in several directions. First, by “adding mechanical damping” to the closed-loop system the authors relax the upper bound condition on the desired torque. Second, the authors use a new controller structure that allows them to treat the case of time-varying desired torque. Finally, a new estimator is proposed to handle time-varying (linearly parameterized) unknown loads     

Transient model of induction machine using rotating magnetic field approach

Most simulation models of electric machines use the coupled circuit approach, where the machine is considered as an electric circuit element with time-varying inductances (abc model) or with constant inductances (dq0 model). On the other hand, the rotating magnetic field approach, which considers the electric machine as two groups of windings producing rotating magnetic fields and can give insight into internal phenomena of the machines, has not yet received much attention in electric machines modeling, especially for machine transient analysis. Based on the rotating magnetic field approach, this paper presents a transient model of the induction machine including main flux saturation effect. Based on the direct computation of the magnetizing fluxes of all machine windings, the model represents instantaneous main flux saturation by simply introducing a main flux saturation factor. No iteration process is involved to incorporate the saturation effects. The model combines the advantages of the dq0 and abc models advantages, such as rapid computation time and nonsymmetrical conditions simulation, respectively. The simulation results and the experimental tests show advantages and verification of the model.     

Nonlinear tracking control for sensorless permanent magnet synchronous motors with uncertainties

The recent advanced solution in Marino, Tomei, and Verrelli (2013) to the tracking control problem for sensorless IMs with parameter uncertainties is translated on the basis of letter swap connections between the models of (nonsalient-pole surface) permanent magnet synchronous motors (PMSMs) and induction ones (IMs). The (stability proof-based) nonlinear adaptive position/speed tracking control for sensorless PMSMs (with simultaneous estimation of uncertain constant load torque and stator resistance), which is accordingly obtained by exploring and decoding the design paths in Marino et al. (2013) and which surprisingly represents a simple generalization of the controller in Tomei and Verrelli (2011), constitutes an innovative solution to the related open problem. Illustrative experimental results are included.     

Finite-time tracking control for robot manipulators with actuator saturation

This paper addresses the finite-time tracking of robot manipulators in the presence of actuator saturation. The commonly-used proportional-derivative (PD) plus dynamics compensation (PD+) scheme is extended by replacing the linear errors in the PD+ scheme with saturated non-smooth but continuous exponential-like ones. Advantages of the proposed controller include semi-global finite-time tracking stability featuring faster transient and high-precision performances and the ability to ensure that actuator constraints are not violated. This is accomplished by selecting control gains a priori, removing the possibility of actuator failure due to excessive torque input levels. Lyapunov's direct method and finite-time stability are employed to prove semi-global finite-time tracking. Simulations performed on a three degree-of-freedom (DOF) manipulator are provided to illustrate the effectiveness and the improved performance of the formulated algorithm.