C. Grantham

Online Stator and Rotor Resistance Estimation Scheme Using Artificial Neural Networks for Vector Controlled Speed Sensorless Induction Motor Drive

This paper presents a new method of online estimation for the stator and rotor resistances of the induction motor for speed sensorless indirect vector controlled drives, using artificial neural networks. The error between the rotor flux linkages based on a neural network model and a voltage model is back propagated to adjust the weights of the neural network model for the rotor resistance estimation. For the stator resistance estimation, the error between the measured stator current and the estimated stator current using neural network is back propagated to adjust the weights of the neural network. The rotor speed is synthesized from the induction motor state equations. The performance of the stator and rotor resistance estimators and torque and flux responses of the drive, together with these estimators, are investigated with the help of simulations for variations in the stator and rotor resistances from their nominal values. Both resistances are estimated experimentally, using the proposed neural network in a vector controlled induction motor drive. Data on tracking performances of these estimators are presented. With this speed sensorless approach, the rotor resistance estimation was made insensitive to the stator resistance variations both in simulation and experiment. The accuracy of the estimated speed achieved experimentally, without the speed sensor clearly demonstrates the reliable and high-performance operation of the drive

Terminal voltage control of a wind turbine driven isolated induction generator using stator oriented field control

This paper presents the voltage build up process and terminal voltage control in an isolated wind powered induction generator driven by a variable speed wind turbine using stator flux oriented vector control. Here three-phase induction generator is excited using a PWM inverter/rectifier connected to a single capacitor on the DC side. Wind powered isolated induction generators have an input, wind, which is not controllable, but they can be set to operate within a given variation of speed. Unlike a grid connected induction generator, in an isolated induction generator there should be a control system that keeps the DC bus voltage at a constant value when the speed of the rotor is varied. This paper present the control system to maintain the DC bus voltage at a constant value by varying the flux in the induction generator when the rotor speed is varied. During voltage build up the variation of magnetizing inductance is taken into consideration.

Stator and rotor resistance observers for induction motor drive using fuzzy logic and artificial neural networks

This paper presents a new observer for the rotor resistance of an indirect vector controlled induction motor drive using artificial neural networks supplemented by a fuzzy logic based stator resistance observer. The error between the rotor flux linkages based on a neural network model and a voltage model is back propagated to adjust the weights of the neural network model for the rotor resistance estimation. The error between the measured stator current and its corresponding estimated value is mapped to a change in stator resistance with a proposed fuzzy logic. The stator resistance observed with this approach is used to correct the rotor resistance observer using neural networks. The performance of these observers and torque and flux responses of the drive, together with these estimators, are investigated with the help of simulations. Both modeling and experimental data on tracking performances of these observers are presented. With this approach accurate rotor resistance estimation was achieved and was made insensitive to stator resistance variations both in modeling and experiment.

High-Temperature Superconducting Linear Synchronous Motors Integrated With HTS Magnetic Levitation Components

High-temperature superconductors (HTSs) including HTS bulks and tapes have potential applications in linear motion drive and magnetic levitation/suspension systems generating substantial advantages over conventional ones. When an HTS linear motor is integrated with an HTS magnetic suspension subsystem, it can inherit both merits of HTS linear motion drive and HTS magnetic suspension simultaneously and can be applied into various fields, such as the maglev and electromagnetic aircraft launch systems (EMALSs). Based on different HTS aspects and arrangements, three modes of HTS linear synchronous motor (HTSLSM) integrated with HTS magnetic suspension subsystems have been proposed in this paper. To verify the modes for the design of a practical HTSLSM, the structural features of these systems are described, the magnetization characteristics to obtain HTS bulk magnets, the trapped-field attenuation characteristics of the HTS bulk magnet exposed to external traveling field, and the magnetic field distribution characteristics for different permanent-magnet guideways have been studied with experimental verification. Based on the study, a demonstration prototype of a single-sided HTSLSM integrated with HTS magnetic suspension subsystems has been developed. Its performance and thrust characteristics have been obtained by experimental measurements and compared with theoretical results. With regard to practical applications, two modes of double-sided HTSLSM integrated with HTS magnetic suspension subsystems have been designed for the maglev and EMALS, respectively, and then, the 2-D finite-element-analysis models for the HTSLSMs were built to analyze their performance characteristics. The comprehensive simulations and experimental results constitute a framework for the structural and electromagnetic design of the HTSLSM integrated with HTS magnetic suspension for practical applications.

Simplified flux estimation for control application in induction machines

This paper deals with the problem associated with a pure integrator in the estimation of stator flux linkage in induction machines and proposes a solution. Integration error in a flux estimation system comprises a drift produced by the integrator, somehow related to an initial condition, and the drift produced by an error present in the back electromotive force (EMF) due to measurement offset error in the terminal voltage and/or phase current. The performance of the induction machine control mainly depends on the accuracy of the estimated flux. The proposed method compensates the error produced by the inherent problem in the pure integrator and measurement error. This method can be easily applied in a DSP based induction machine control system to estimate the flux. The execution time required to implement the proposed system is small such that there will not be much software computation burden.

Inverter supplied voltage control system for an isolated induction generator driven by a wind turbine

This paper deals with a technique to control the voltage generated from an isolated three-phase induction generator excited by an inverter and a single DC capacitor for use in a remote area power supply. The speed of the wind turbine that drives the induction generator could be regulated or unregulated. During the voltage build up process there is a variation in the flux linkage of the induction generator. The variation of magnetising inductance is taken into account due to saturation of the core. The terminal voltage of the induction generator is controlled using the vector control technique when the electrical load and rotor speed are varied within a specified range. The output voltage is regulated by varying the flux in the induction generator when the rotor speed is varied. A DC load is connected directly across the DC capacitor and an AC load can be fed by a load side inverter that supplies constant voltage and frequency.

PI and fuzzy estimators for on-line tracking of rotor resistance of indirect vector controlled induction motor drive

This paper presents two methods of estimation of the rotor resistance in the indirect vector controlled induction motor drive. A model reference adaptive scheme is proposed in which the adaptation mechanism is executed using a PI controller and a fuzzy logic. The performance of both estimators and torque and flux responses of the drive are investigated with simulations for variations in the rotor resistance values from their nominal values. When either of the estimators are added to the drive system, the drive system performance does not deteriorate with the variation of the rotor resistance. The two estimation algorithms are designed, one with a PI controller and the other with fuzzy logic. The effectiveness of both algorithms is demonstrated with simulations.

Rotor resistance identification using artificial neural networks for an indirect vector controlled induction motor drive

This paper presents a new method of estimation for the rotor resistance of the induction motor in the indirect vector controlled drive. The back propagation neural network technique is used for the real time adaptive estimation. The error between the desired state variable of an induction motor and the actual state variable of a neural model is back propagated to adjust the weights of the neural model, so that the actual state variable tracks the desired value. The performance of the neural estimator and torque and flux responses of the drive, together with this estimator, are investigated with simulations for variations in the rotor resistance from their nominal values.

A novel method for rapid efficiency measurement of three phase induction motors

This paper describes a novel method for rapid full load efficiency evaluation of three phase induction motors using the synthetic loading technique, without the need to connect a load to the machines drive shaft. The new method uses a digital signal processor (DSP) controlled high switching frequency power electronic inverter to synthetically load the induction machine, while using a new real time data acquisition system to accurately determine and record the machines performance. The method proposed considerably reduces the testing time compared with conventional methods of efficiency measurement and the accuracy of the result is maintained. Moreover the use of the power electronic inverter allows a comprehensive control over all the quantities which determine the rate at which the power is dissipated inside the induction machine. This method can also directly quantify rotational losses of the induction motor under test.

A New Scheme to Direct Torque Control of Interior Permanent Magnet Synchronous Machine Drives for Constant Inverter Switching Frequency and Low Torque Ripple

This paper presents a new direct torque control (DTC) scheme based on space vector modulation (SVM) for interior permanent magnet synchronous machine (IPMSM) drives. The new scheme provides a variable option for the improvement of DTC controlled IPMSM. Closed-loop control of both torque and flux is developed with two proportional-integral (PI) controllers. The stator voltage is generator through SVM unit. The torque and flux ripples are greatly reduced with fixed inverter switching frequency comparing with classical switching-table based DTC scheme. The analysis of the control principle provides a guide to design the controller parameters. Modeling results confirm the effectiveness of the proposed scheme