1,721,012 research outputs found
A simple but high-performace IM speed drive
No full textThe paper deals with an induction motor (IM) speed drive having high performance
over a large speed range in the constant torque region. The drive is built up around an outer loop
of speed equipped with an incremental encoder and two inner loops of torque and flux
implemented in a direct torque control (DTC) scheme. The scheme takes advantage of the
available speed to estimate the motor torque and the stator flux magnitude by means of the IM
current model. This allows the full exploitation of the drive capabilities even in the low speed
range. Furthermore, with a suitable representation of the IM current model, the drive can be
operated down up to zero speed. The paper closes by analytically investigating the detuned
behaviour of the scheme due to a rotor time constant mismatch. Experimental results substantiate
the low-speed capabilities of the scheme and the findings on its detuned behaviour
Identificazione parametrica di una macchina sincrona con la tecnica della risposta periodica
No full textConceptual frameworks for dependability and safety of a system
No full textDependability and safety of a system are two topical subjects, which find the proper assessment into the conceptual frameworks of the dependability theory and the functional safety standards. The purpose of this paper is to explicate the two frameworks, showing how one framework supplements the other one. At first the dependability theory is introduced and the related concepts of threatens, attributes and techniques are presented. Regarding the safety, the dependability theory sets the behavioral requirements for a system in case of fault but does not deal with the characteristics of the systems used to achieve the requirements. This gap is filled up by the standards on the functional safety, which are introduced in the second part of the paper together with the concepts of risk, safety function and safety integrity level. Finally, as a case of study, the power converter supplying the air brake system installed aboard trains is analyzed from the dependability and functional safety viewpoint
Steady-state performance degradation of a DTC IM drive under parameter and trasduction errors
No full textWith direct torque control (DTC), the stator flux magnitude and the torque of an induction motor (IM) drive are controlled in a closed-loop way. The actual values of the controlled variables are estimated by processing the inverter dc-link voltage and the stator currents by means of the IM voltage model. Any error in the model parameter (the stator resistance) or in the voltage and current transduction degrades the drive performance. In this paper, a theoretical investigation of the effects of the various errors on a DTC IM drive is carried out. The investigation gives a proof of the drive instability due to some errors and provides, for the other errors, the amount of the deviation produced on the controlled variables in steady state. The theoretical findings are substantiated by experimental and simulation results
Accuracy of the speed estimation in the sensorless induction motor drives based on the MRAS technique
No full textDSP implementation of a Direct Torque Control Induction Motor Drive
No full textThe paper presents a Direct Torque Control (DTC) scheme for an Induction Motor (IM) drive that makes use of only one current sensor inserted in the inverter dc link and of an ad-hoc algorithm to reconstruct the stator currents. DSP implementation of the control system of the novel DTC scheme is illustrated. Experimental traces obtained from the resultant IM drive are shown. They demonstrate that the drive exhibits the excellent performance of a conventional DTC drive although it has the same hardware as a V/f drive
DSP implementation of the control system of a direct torque control induction motor drive with reduced current sensor count
No full textThe paper presents a Direct Torque Control (DTC) scheme for an Induction Motor (IM) drive that makes use of only one current sensor inserted in the inverter dc link and of an ad-hoc algorithm to reconstruct the stator currents. DSP implementation of the control system of the novel DTC scheme is illustrated. Experimental traces obtained from the resultant IM drive are shown. They demonstrate that the drive exhibits the excellent performance of a conventional DTC drive although it has the same hardware as a V/f driv
Band-constrained technique for direct torque control of induction motor
No full textIn this paper, a novel technique for the direct torque control (DTC) of an induction motor is proposed, which overcomes the trouble of high torque ripple afflicting the conventional DTC technique. With the novel technique, the inverter voltage vector selected from the switching table is applied for the time interval needed by the torque to reach the upper (or the lower) limit of the band, where the time interval is calculated from a suitable modeling of the torque dynamics. By this approach, the control system emulates the operation of a torque hysteresis controller of analog type since the application time of the inverter voltage vector is dictated by the allowed torque excursion and not by the sampling period. It is shown by experimental results that the technique yields a considerable reduction of the torque ripple. A further and ultimate reduction is obtained by compensating for the delay inherent in the discrete-time operation of the control system. The outcome is that the torque ripple of the motor is constrained within the hysteresis band of the torque controller, for a band of customary value. An ancillary merit of the technique is the almost full elimination of the average torque error inherent in the conventional technique. If the hysteresis band is shrunk, the torque ripple is bound to swing out the band limits. Under this circumstance, an extension of the technique is developed, which helps keep the torque ripple at minimum. To assess the characteristics of the proposed DTC technique, the following quantities: average torque error, rms value of the torque ripple, and inverter switching frequency are measured for different stator flux angular speeds and hysteresis bands of the torque and flux controllers. As a comparison, the same quantities are given for the conventional DTC techniqu
Analytical formulation of the direct control of induction motor drives
No full textThe direct control of inverter-fed induction motor drives imposes the desired stator flux amplitude and electromagnetic torque into the motor in a closed-loop way without the intermediary of current loops and the employment of a shaft sensor. In this paper a theoretical formulation of the direct control is provided by expressing in an analytical manner the action exerted by the inverter space vectors on the stator flux amplitude and the electromagnetic torque of an induction motor. From the equations describing this action the influence of the operating conditions on the control action are evaluated. Graphical plots concerning a commercial drive help to discuss the results. A review of the induction motor and voltage inverter equations written in terms of space vectors and of the direct control concept open the pape
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