Speed -Sensorless Estimation And Position Control Of Induction Motors For Motion Control Applications

Thesis (Ph.D.) University of Alaska Fairbanks, 2006High performance sensorless position control of induction motors (IMs) calls for estimation and control schemes which offer solutions to parameter uncertainties as well as to difficulties involved with accurate flux and velocity estimation at very low and zero speed. In this thesis, novel control and estimation methods have been developed to address these challenges. The proposed estimation algorithms are designed to minimize estimation error in both transient and steady-state over a wide velocity range, including very low and persistent zero speed operation. To this aim, initially single Extended Kalman Filter (EKF) algorithms are designed to estimate the flux, load torque, and velocity, as well as the rotor, Rr' or stator, Rs resistances. The temperature and frequency related variations of these parameters are well-known challenges in the estimation and control of IMs, and are subject to ongoing research. To further improve estimation and control performance in this thesis, a novel EKF approach is also developed which can achieve the simultaneous estimation of R r' and Rs for the first time in the sensorless IM control literature. The so-called Switching and Braided EKF algorithms are tested through experiments conducted under challenging parameter variations over a wide speed range, including under persistent operation at zero speed. Finally, in this thesis, a sensorless position control method is also designed using a new sliding mode controller (SMC) with reduced chattering. The results obtained with the proposed control and estimation schemes appear to be very compatible and many times superior to existing literature results for sensorless control of IMs in the very low and zero speed range. The developed estimation and control schemes could also be used with a variety of the sensorless speed and position control applications, which are challenged by a high number of parameter uncertainties

Data-driven online temperature compensation for robust field-oriented torque-controlled induction machines

Squirrel-cage induction machines (IMs) with indirect field-oriented control are widely used in industry and are frequently chosen for their accurate and dynamic torque control. During operation, however, temperature rises leading to changes in machine parameters. The rotor resistance, in particular, alters, affecting the accuracy of the torque control. The authors investigated the effect of a rotor resistance parameter mismatch in the control algorithm on the angular rotor flux misalignment and the subsequent deviation of stator currents and motor torque from their setpoints. Hence, an online, data-driven torque compensation to eliminate the temperature effect is proposed to enable robust torque-controlled IMs. A model-based analysis and experimental mapping of the temperature effect on motor torque is presented. A temperature-torque lookup-table is subsequently implemented within the control algorithm demonstrating the ability to reduce the detrimental effect of temperature on torque control. Experimental results on a 5.5 kW squirrel-cage induction motor show that the proposed data-driven online temperature compensation method is able to reduce torque mismatch when compared to having no temperature compensation. Up to 17% torque mismatch is reduced at nominal torque and even up to 23% at torque setpoints that are lower than 20% of the nominal torque. A limited torque error of <1% remains in a broad operating range

Modelling and detection of faults in axial-flux permanent magnet machines

The development of various topologies and configurations of axial-flux permanent magnet machine has spurred its use for electromechanical energy conversion in several applications. As it becomes increasingly deployed, effective condition monitoring built on reliable and accurate fault detection techniques is needed to ensure its engineering integrity. Unlike induction machine which has been rigorously investigated for faults, axial-flux permanent magnet machine has not. Thus in this thesis, axial-flux permanent magnet machine is investigated under faulty conditions. Common faults associated with it namely; static eccentricity and interturn short circuit are modelled, and detection techniques are established. The modelling forms a basis for; developing a platform for precise fault replication on a developed experimental test-rig, predicting and analysing fault signatures using both finite element analysis and experimental analysis. In the detection, the motor current signature analysis, vibration analysis and electrical impedance spectroscopy are applied. Attention is paid to fault-feature extraction and fault discrimination. Using both frequency and time-frequency techniques, features are tracked in the line current under steady-state and transient conditions respectively. Results obtained provide rich information on the pattern of fault harmonics. Parametric spectral estimation is also explored as an alternative to the Fourier transform in the steady-state analysis of faulty conditions. It is found to be as effective as the Fourier transform and more amenable to short signal-measurement duration. Vibration analysis is applied in the detection of eccentricities; its efficacy in fault detection is hinged on proper determination of vibratory frequencies and quantification of corresponding tones. This is achieved using analytical formulations and signal processing techniques. Furthermore, the developed fault model is used to assess the influence of cogging torque minimization techniques and rotor topologies in axial-flux permanent magnet machine on current signal in the presence of static eccentricity. The double-sided topology is found to be tolerant to the presence of static eccentricity unlike the single-sided topology due to the opposing effect of the resulting asymmetrical properties of the airgap. The cogging torque minimization techniques do not impair on the established fault detection technique in the single-sided topology. By applying electrical broadband impedance spectroscopy, interturn faults are diagnosed; a high frequency winding model is developed to analyse the impedance-frequency response obtained

Adaptivni estimator brzine za bezsenzorsko vektorsko upravljanje asinkronim motorom zasnovan na umjetnoj neuronskoj mreži

This paper presents an adaptive speed observer for an induction motor using an artificial neural network with a direct field-oriented control drive. The speed and rotor flux are estimated with the only assumption that from stator voltages and currents are measurable. The estimation algorithm uses a state observer combined with an intelligent adaptive mechanism based on a recurrent neural network (RNN) to estimate rotor speed. The stator and rotor resistances are estimated by a simple Proportional-Integrator (PI) controller, which reduces sensitivity to variations, due essentially to the influence of temperature. The proposed sensorless control scheme is tested for various operating conditions of the induction motor drive. Experimental results demonstrate a good robustness against load torque disturbances, the estimated fluxes and rotor speed converge to their true values, which guarantees that a precise trajectory tracking with the prescribed dynamics.Ovaj članak opisuje adaptivni estimator brzine temeljen na umjetnoj neuronskoj mreži, koji se primijenjuje na asinkroni motor pogonjen izravnim vektorskim upravljanjem. Brzina i magnetski tok rotora estimiraju se uz pretpostavku dostupnosti mjerenja napona i struja statora. Algoritam koristi estimator stanja u kombinaciji s inteligentnim adaptivnim mehanizmom temeljenim na povratnoj neuronskoj mreži (RNN) kako bi se estimirala brzina rotora. Otpori statora i rotora estimiraju se jednostavnim Proporcionalno-Integralnim (PI) regulatorom, čime se smanjuje osjetljivost na varijacije uzrokovane utjecajem temperature. Predložena bezsenzorska upravljačka shema testirana je za različite radne uvjete asinkronog motora. Eksperimentalni rezultati pokazuju visoki stupanj robusnosti s obzirom na poremećaj momenta tereta, a estimirani tokovi i brzina rotora konvergiraju prema stvarnim vrijednostima što garantira precizno praćenje trajektorija uz zahtijevanu dinamiku

A Comparative Analysis of Field Oriented Control and Direct Torque Control of Induction Motor Drive

Electric Motor Drive System is employed in the various industrial applications such as pumping, air blowing, cooling and compression refrigeration. The motor drive speed control can be achieved by variety of techniques, but an emerging one is Variable Frequency Drive System (VFDS). The motor driven equipment on a typical industrial site accounts for approximately two thirds of the electricity consumption. Now-a-days induction motor is the main work-horse of the industries. So controlling of performance of induction motor is most precisely required in many high performance applications. Scalar control method gives good steady state response but poor dynamic response. While vector control method gives good steady state as well as dynamic response. But it is complicated in structure so to overcome this difficulty, direct torque control introduced. This paper discusses the comparative analysis of Field Oriented Control (FOC) and Direct Torque Control (DTC) methods of Polyphase Induction Motor (PIM) according to their working principle, structure complexity, performance, merits and demerits

Performance Comparison of Different Speed Estimation Techniques in Sensorless Vector Controlled Induction Motor Drives

Field-oriented control and direct torque control are fast becoming necessities of modern industrial setups for induction motor drive control. Induction motors are considered as the beginning part to create any electrical drive system to be subsequently utilized for several industrial requirements. So now a day due to its high application the need to control the performance of the induction motor is gaining importance. In modern control system, IM is analyzed by different mathematical models mainly depending on its applications. Vector control method is suitably applied to induction machine in 3-phase symmetrical or in 2-phase unsymmetrical version. For vector control IM is realized as DC motor having its characteristics. This dissertation work is aimed to give a detailed idea about the speed control and variations in an induction motor through vector control technique thereby showing its advantage over the conventional scalar method of speed control. It also focusses on the speed estimation techniques for sensorless closed loop speed control of an IM relying on the direct field-oriented control technique. The study is completed through simulations with use of MATLAB/Simulink block sets allowing overall representation of the whole control system arrangement of the Induction motor. The performance of different sensorless schemes and comparison between them on several parameters like at low speed, high speed etc. is also provided emphasizing its advantages and disadvantages. The analysis has been carried out on the results obtained by simulations, where secondary effects introduced by the hardware implementations have not been considered. The simulations and the evaluations of different control techniques are executed using parameters of a 50 HP, 60 Hz induction motor which is fed by an inverter

Experimental results of vector control for an asynchronous machine

The aim of this article is contributeto the advanced vector control strategy of asynchronous machines. Analyzes of experimental of indirect field-oriented control are presented. In this context, we propose vector control algorithms to provide solutions to the disadvantages of field-oriented control FOC.The results obtained from various methods of determining the parameters for asynchronous machine are compared. We calculate the various parameters and then we present the technical characteristics of each element of the asynchronous machine; finally, we implement the vector control used asbasis of comparison between the simulation under Matlab/Simulink software and experiments. The simulation and experimental tests show that the proposed controller is suitable for medium and high-performance applications

Differential-Algebraic Approach to Speed and Parameter Estimation of the Induction Motor

This thesis considers a differential-algebraic approach to estimating the speed and rotor time constant of an induction motor using only the measured terminal voltages and currents. It is shown that the induction motor speed satisfies both a second-order and a third-order polynomial equation whose coefficients depend the stator voltages, stator currents, and their derivatives. Further, it is shown that as long as the stator electrical frequency is nonzero, the speed is uniquely determined by these polynomials. The speed so determined is then used to stabilize a dynamic (Luenberger type) observer to obtain a smoothed speed estimate. With full knowledge of the machine parameters and filtering of the sensor noise, simulations and experiments indicate that this estimator has the potential to provide low speed (including zero speed) control of an induction motor under full load. A differential-algebraic approach is also used to obtain an estimate of the rotor time constant of an induction motor, again using only the measured stator voltages and currents. Experimental results are presented to demonstrate the practical use of the identification method

Accurate Induction Machines Efficiency Mapping Computed by Standard Test Parameters

The extensive electrification process that is taking hold in several applications makes increasingly necessary the virtualization of electric components for energetic and performance assessments during the system design stage. For this purpose, this paper proposes a straightforward methodology for computing the efficiency maps of induction machines operated in wide torque-speed ranges. The modeling approach is based on the induction machine equivalent circuit defined in the rotor dq coordinates. The procedure allows computing a set of efficiency maps at different machine temperatures and supply voltage levels, both for motor and generator operation modes. The equivalent circuit parameters at different frequencies and voltages are determined by means of the well-known no-load and locked-rotor tests, thus including in the modelling the machine nonlinearities, skin effect and the iron losses. The proposed methodology has been validated on a 10 kW, 4-pole induction machine. The comparison between computed and experimental efficiency maps for different operating conditions, confirm the validity of the proposed methodology