This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown.

Direct torque control of PWM inverter-fed AC motors - a survey

An induction motor is the most frequently used electric machine in high-performance drive applications. Control schemes of such drives require an exact knowledge of at least some of the induction motor parameters. Any mismatch between the parameter values used within the controller and actual parameter values in the motor leads to a deterioration in the drive performance. Numerous methods for induction machine on-line and off-line parameter estimation have been developed exclusively for application in high-performance drives. This paper aims at providing a review of the major techniques used for the induction motor parameter estimation. The paper is illustrated throughout with experimental and simulation examples related to various parameter estimation techniques.

A review of RFO induction motor parameter estimation techniques

This paper investigates problems associated with the implementation of a direct torque control (DTC) strategy for an interior permanent-magnet synchronous motor drive. The DTC technique is increasingly drawing attention because of elimination of current controllers and, hence, their inherent delays, and elimination of the rotor position sensor. The latter advantage perhaps is the main impetus for considering this new approach of torque control. Problems associated with this controller, namely, the offset in the current measurements, the stator resistance variation, and the requirement of initial rotor position are addressed in this paper. Ways of mitigating of these problems are also investigated in this paper. These are evaluated with modeling and experimental studies, results of which are also presented.

Problems associated with the direct torque control of an interior permanent-magnet synchronous motor drive and their remedies

A standard design procedure for a single-sided and longitudinal flux-based linear switched reluctance machine is developed in this paper. The proposed design procedure utilizes the rotating switched reluctance machine design by converting the specifications of the linear machine into the equivalent rotary machine. The machine design is carried out in the rotary domain, which is then transformed back into the linear domain. Such a procedure brings to bear the knowledge base and familiarity of the rotary machine designers to design a linear machine effectively. This paper contains the illustration of the proposed design procedure for a 4.8-m-long prototype. An analysis procedure is developed with a magnetic model and results from it are verified with finite-element analysis prior to construction of the prototype. Extensive experimental correlation in the form of inductance versus position versus current and propulsion force versus position versus current to validate the analysis and design procedure is given in the paper.

Design of a linear switched reluctance machine

Linear switched reluctance motor (LSRM) drives are investigated and proved in this study as an alternative actuator for vertical linear transportation applications such as a linear elevator. A one-tenth-scaled prototype elevator that is focused on a home elevator with LSRMs is designed, and extensive experimental correlation is presented for the first time in this paper. The proposed LSRM has twin stators and a set of translator poles without yoke placed between the two stators. The features of the LSRM and the prototype elevator are described. Furthermore, a control strategy for the prototype elevator is introduced consisting of four control loops, viz., (1) current, (2) force, (3) velocity, and (4) position feedback control loops. Force control of the experimental prototype elevator employs the proposed force distribution function. A trapezoidal velocity profile is introduced to control vertical travel position smoothly during ascent, descent, and stop of the elevator. Conventional proportional-integral controller is used for the current and velocity control loops and their designs are described. The proposed control strategy is dynamically simulated and experimentally correlated. The analytical and experimental results of this paper prove that LSRMs are one of the strong candidates for linear elevator propulsion drives.

Ropeless Elevator With Linear Switched Reluctance Motor Drive Actuation Systems

The converter topology with a minimum number of power devices and control implementations to facilitate the pulsation-free force control of the linear switched reluctance machines are investigated for the first time in this paper. The minimization of the devices offers cost reduction, compact packaging, and enhanced overall reliability. With that in view, a topology with 3N/sub sc/+3 devices is chosen where N/sub sc/ is the number of sectors in the linear machine. The propulsion force with conventional control of single-phase excitation has high-commutation torque pulsation and it is overcome with a multiphase excitation strategy, proposed in this paper. Further, the proposed control strategy reduces the normal force pulsation. A systematic step-by-step design procedure of the switching strategy for the converter known as unipolar switching strategy, proportional plus integral current controller, and gating control strategy of a long linear switched reluctance machine is presented. Experimental correlation of the proposed converter arrangement and control strategy is presented with a 4.8 m-long linear switched reluctance machine in achieving the stated objectives.

A linear switched reluctance motor: converter and control

Direct torque control (DTC) has drawn the attention of the motor drives designers because its implementation requires no position sensor. Crucial to the success of this scheme is the estimation of electromagnetic torque and stator flux linkages using the measured stator voltages and currents. The estimation is dependent only on one machine parameter, stator resistance. The variation of the stator resistance, which is usually in the range of 0.75-1.7 times its nominal value, deteriorates the performance of the drive by introducing errors in the estimated flux linkage's magnitude and its position and hence in the electromagnetic torque. Resistance change also skews the torque linearity thus making the motor drive a less than ideal torque amplifier. Parameter compensation using stator current phasor error has been proposed in literature. To obtain the stator current phasor error, the stator current reference is required which is not usually available in direct torque control schemes. An analytical derivation of the stator current phasor reference is derived systematically from the reference electromagnetic torque and flux linkages. The error between the stator current phasor reference and its measured value is a measure of the stator resistance variation from its set value. For the first time, it is demonstrated in this paper that the DTC motor drive system can become unstable when the set value of the stator resistance in the controller is higher than the stator resistance in the machine. Hence parameter adaptation is not only important for torque linearity but also for stability of the system is shown in this paper.

Adaptive stator resistance compensator for high performance direct torque controlled induction motor drives

A frictionless linear switched reluctance propulsion system generates both a propulsive force for moving a load linearly, and a normal force for lifting the load. The normal force acts in a direction substantially perpendicular to a direction of the propulsive force.

Byeong-Seok Lee

Papers

Design of a linear switched reluctance machine

A linear switched reluctance motor: converter and control

Adaptive stator resistance compensator for high performance direct torque controlled induction motor drives

Transportation system with linear switched reluctance actuator for propulsion and levitation