Showing papers on "Induction motor published in 1997"

Analysis of direct torque control in permanent magnet synchronous motor drives

Abstract: This paper describes an investigation of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) drives. It is mathematically proven that the increase of electromagnetic torque in a permanent magnet motor is proportional to the increase of the angle between the stator and rotor flux linkages, and, therefore, the fast torque response can be obtained by adjusting the rotating speed of the stator flux linkage as fast as possible. It is also shown that the zero voltage vectors should not be used, and stator flux linkage should be kept moving with respect to the rotor flux linkage all the time. The implementation of DTC in the permanent magnet motor is discussed, and it is found that for DTC using available digital signal processors (DSPs), it is advantageous to have a motor with a high ratio of the rated stator flux linkage to stator voltage. The simulation results verify the proposed control and also show that the torque response under DTC is much faster than the one under current control.

An active circuit for cancellation of common-mode voltage generated by a PWM inverter

Abstract: This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage.

A model of large load areas for harmonic studies in distribution networks. Discussion

Abstract: This paper describes on improved model of rotating loads in complex load areas. The first section of the paper concentrates on the theoretical aspects of load modeling in harmonic penetration studies with a particular reference to the rotating part of load. The second section illustrates the results achieved from the experimental surveys conducted both in the laboratory and at a major industrial customer, in order to validate the model porposed in the field The third section describes the calibration stage of the proposed model based on results from a statistical survey conducted at manufacturers on parameter variation vs. frequency with a large sample of both LV and MV induction motors. Finally, some guidelines are also provided for a correct use of the proposed model in system studies concerning harmonic penetration within electric distribution networks.

Design of low-torque-ripple synchronous reluctance motors

Abstract: A design approach oriented to the minimization of torque ripple is presented for synchronous reluctance motors of the transverse-laminated type. First, the possible types of rotors are classified and the more suited rotor structure is evidenced, to be matched to a given stator. Then, the inner rotor design is described, pointing out the low-ripple measures. Lastly, experimental results are given from three different rotors; they confirm the validity of the proposed approach.

Inter-turn stator winding fault diagnosis in three-phase induction motors, by Park's Vector approach

Abstract: The subject of on-line detection and location of inter-turn short circuits in the stator windings of three-phase induction motors is discussed, and a noninvasive approach, based on the computer-aided monitoring of the stator current Park's vector, is introduced. Experimental results, obtained by using a special fault producing test rig, demonstrate the effectiveness of the proposed technique, for detecting inter-turn stator winding faults in operating three-phase induction machines. On-site tests conducted in a power generation plant, using the diagnostic instrumentation system developed, are also reported.

Reduction of common mode currents in PWM inverter motor drives

Abstract: Modern pulsewidth modulation (PWM) inverter motor drives are affected by dangerous common-mode currents due to the high rate of variation of the modulated voltage. An inexpensive alternative to low-pass filters, which are normally used to limit common-mode currents, consists in reducing such currents by using suitable modulation strategies. In this paper, a new approach for designing PWM strategies is presented, which is able to reduce common-mode currents by limiting the amount of variations of the common-mode voltage. The main characteristics of the proposed approach are experimentally evaluated on a standard PWM induction motor drive.

Use of an LC filter to achieve a motor-friendly performance of the PWM voltage source inverter

Abstract: By putting an LC filter between a PWM voltage source inverter and induction motor, standard industrial motors can also be utilized for adjustable speed drive applications. In this paper, the application of an LC filter to medium voltage motors fed by inverters with switching frequencies below 1000 Hz is described. For different filter topologies, rules for the electrical design are discussed as well as solutions for the stability problem. Also discussed are solutions against common mode voltage stress on the motor terminals. An example shows the implication of the filter on the minimum inverter power which has to be installed to feed a given motor.

Characterization of voltage sags in industrial distribution systems

Abstract: This paper describes the various characteristics of voltage sags experienced by customers within industrial distribution systems Special emphasis is paid to the influence of the induction motor load on the characterization of voltage sags During a fault, an induction motor operates as a generator for a short period of time and causes an increase in sag magnitude Its reacceleration after the fault clearance results in an extended post-fault voltage sag The influence of the induction motor on the imbalanced sags caused by single line-to-ground faults (SLGFs) and line-to-line faults (LLFs) has been analyzed in detail For an imbalanced fault, the induction motor current contains only positive- and negative-sequence components Induction motors create a low impedance path for the negative-sequence voltage due to an imbalanced fault This causes a small sustained nonzero voltage with large phase-angle jump in the faulted phase and a voltage drop in the nonfaulted phases with a small phase-angle jump The symmetrical components of the induction motor during the imbalanced sags have been studied The results show that induction motor behavior is determined by positive- and negative-sequence voltages during the imbalanced sag

A direct torque controller for permanent magnet synchronous motor drives

Abstract: This paper describes an investigation of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) drives. The analysis of PMSMs shows that the increase of electromagnetic torque is proportional to the increase of the angle between the stator and rotor flux linkages and therefore fast torque response can be obtained by increasing the rotating speed of the stator flux linkage as fast as possible. The implementation of DTC in PMSM drives is discussed and the switching table specific for an interior PMSM is derived. The proposed control is implemented on a prototype PMSM, which has a standard induction motor stator, and the experimental results show that the torque response is extremely fast. It is also demonstrated that the position sensor is not essential for the inner torque control loop of PMSM drives with DTC.

On the energy optimized control of standard and high-efficiency induction motors in CT and HVAC applications

Abstract: This paper contains an analysis of how the choice of energy optimal control of induction motors is influenced by motor construction, standard versus high-efficiency motor, and by application, constant torque (CT) and heating, ventilation, and air conditioning (HVAC) (interpreted as vector and scalar motor drives). The analysis is made with a 2.2 kW voltage-source-inverter-fed squirrel-cage motor drive as an example throughout the paper, but through statistics on the use of motors and their efficiencies, the conclusions are widened to a broader range (0-50 kW). Energy optimal control strategies are reviewed and cos(/spl thetav/) control, a model-based control, and a search control are implemented in the laboratory in a vector and a scalar motor drive. The convergence speed for the strategies and their ability to reject disturbances are investigated by experiments. It is also shown experimentally that, for both standard and high-efficiency motors, motor energy-efficiency improvement is achievable by energy optimal control below 60% load torque. The energy savings using energy optimal control strategies are measured on a pump system with a certain load cycle. Model-based control is recommended for CT applications and cos(/spl thetav/) control for HVAC applications.

Axial flux machines drives: a new viable solution for electric cars

Abstract: For electric car propulsion systems, the wheel motor is an application that requires the electrical machine has shape flexibility, compactness, robustness, high efficiency, and high torque. Axial flux machines are an interesting solution, where the motor is directly coupled to, or inside, the drive wheels. In this paper, axial flux induction and synchronous machines as wheel motor applications are presented and some considerations for each motor type are drawn by the authors. The structure with two rotors seems to be a very promising solution for both induction and synchronous machines. In the induction motor case, the two rotors can rotate at different speeds, thus the motor can act as a mechanical differential. The axial flux permanent magnet motor with two rotors is very compact and can be integrated inside the wheel.

Voltage control strategy for maximum torque operation of an induction machine in the field-weakening region

Abstract: In this paper, a novel field-weakening scheme for the induction machine is presented. The proposed algorithm, based on the voltage control strategy, ensures the maximum torque operation over the entire field-weakening region without using the machine parameters. Also, by introducing the direct field-oriented (DFO) control, which is insensitive to the variation of machine parameters in the field-weakening region, the drive system can obtain robustness to parameter variations. Moreover, the speed sensorless control can be achieved in the very-high-speed range, where the utilization of the speed sensor is limited. Experimental results for the laboratory induction motor drive system confirm the validity of the proposed control algorithm.

A dual-bridge inverter approach to eliminating common mode voltages and bearing and leakage currents

Abstract: This paper presents a dual-bridge inverter approach to eliminate the motor common-mode voltage and resulting bearing and leakage currents. The novel dual-bridge inverter is controlled to generate balanced excitation of the induction motor under pulsewidth modulation (PWM) inverter operation. Theoretical analysis, simulation results, and experimental results are presented to verify this concept.

Initial rotor angle detection of a nonsalient pole permanent magnet synchronous machine

Abstract: This paper presents a technique that calculates the absolute angular position of a permanent magnet (PM) rotor within a pole pair at standstill. The algorithm works with nonsalient pole motors. By choosing an appropriate voltage pulse width and applying it to each phase winding, the stator currents partially saturate the stator iron, enabling the algorithm to discern between a north pole and a south pole, and subsequently, the absolute position. The scheme is computationally simple and does not rely on the knowledge of any of the motor parameters.

Modeling and simulation of induction machine vector control with rotor resistance identification

Abstract: This paper shows that it is possible to use available commercial software to model and simulate a vector-controlled induction machine system. The components of a typical vector control system are introduced and methods given for incorporating these in the MATLAB/SIMULINK software package. The identification of rotor resistance is important in vector control, if high-performance torque control is needed, and modeling of the extended Kalman filter (EKF) algorithm for parameter identification is discussed. It is certainly advisable, when feasible, to precede implementation of new algorithms, whether for control or identification purposes, with an extensive simulation phase. Additionally, a technique for generating pulse-width modulation (PWM) phase commands to extend machine operation to higher speeds before field weakening occurs is simulated in a vector-controlled induction machine, driven by a PWM inverter. This demonstrates the versatility of the vector-controlled induction machine system model.

A programmable cascaded low-pass filter-based flux synthesis for a stator flux-oriented vector-controlled induction motor drive

Abstract: The concept of a programmable cascaded low-pass filter method of flux vector synthesis has been introduced in the literature. In this paper, the idea is expanded, analyzed, improved, and then applied to a stator flux oriented 100-kW electric vehicle drive. It was verified that the flux estimation works well at zero speed finite torque start-up mode and low- and high-speed field weakening regions, thus completely eliminating the need of a speed sensor.

Induction motors thermal monitoring by means of rotor resistance identification

Abstract: Rotor and stator temperature are of concern in both short-term machine protection and in longer term condition monitoring for large induction machines. Especially, when operating with overload cycles, it is necessary to monitor rotor bars and stator winding temperatures to make sure that the temperature remains below prescribed limits. The purpose of this paper is to present a thermal monitoring technique, for induction motors steady-state operation, based on the rotor resistance identification. Experimental results, for a 4 kW four-pole squirrel cage induction motor, show the industrial viability of the proposed technique.

Passivity-based control of a class of Blondel-Park transformable electric machines

Abstract: Concerns the extension to the general rotating electric machine model of the passivity-based controller method for induction motors. The motor's passivity properties are used at 2 levels. First, we prove that the motor model can be decomposed as the feedback interconnection of two passive subsystems (essentially, the electrical and mechanical dynamics). Then, we design a torque-tracking controller that preserves passivity for the electrical subsystem and leaves the mechanical part as a passive disturbance. This leads to the cascaded controller structure which is typically analyzed involving time-scale separation. Our aim is to characterize a class of machines for which such a passivity-based controller solves the output feedback torque-tracking problem. The class consists of machines whose nonactuated dynamics are damped and whose dynamics can be decoupled. This requires that the air-gap magnetomotive force must be suitably approximated by the first harmonic in its Fourier expansion. These conditions have a clear physical interpretation in terms of the couplings between its dynamics and are satisfied by many machines. The passivity-based controller presented reduces to the well-known indirect vector controller for current-fed induction machines. Our developments constitute an extension to voltage-fed machines of this de facto standard in industrial applications.

Electric motor monitor

Abstract: An ac machine monitor (100), particularly applicable to ac induction motors (102), provides information for ascertaining the health and condition of the motor (102). The monitor (100) is self-contained, having its own internal power source (144), electronics (130), and sensor suite (120-126), and attaches directly to the outer frame (104) of the motor (102). Sensors disposed within the monitor (100) include a motor frame temperature sensor (120), flux sensor (124), vibration sensor (126), and clock. An ambient temperature sensor (122) enables determination of motor frame temperature relative to ambient. Sensor outputs are processed and analyzed by monitor electronics to determine various life history parameters, including motor speed and load, which are stored in electronic memory (142). A communications port (154) enables a peripheral device (362), such as a notebook computer or portable data collector, to communicate with the monitor (100) and download the life history parameters stored in memory (142). Downloaded data can be further analyzed and statistically compared to trend data at a base computer (360) to ascertain the health and condition of the motor (102). The monitor electronics are configured to consume very little power so that the internal power source (144) will continue to power the monitor (100) for several years.

Application of genetic algorithms to motor parameter determination for transient torque calculations

Abstract: This paper applies genetic algorithms to the problem of induction motor parameter determination. Generally available manufacturers' published data like starting torque, breakdown torque, full-load torque, full-load power factor, etc., are used to determine the motor parameters for subsequent use in studying machine transients. Results from several versions of the genetic algorithm are presented, as well as a comparison with the Newton-Raphson method.

Real-time detection of intermittent misfiring in a voltage-fed PWM inverter induction-motor drive

Abstract: This paper develops a real-time condition-monitoring algorithm for pulsewidth modulation (PWM) inverter induction-motor drives. It is designed to detect the intermittent loss of firing pulses of an individual switching device within the inverter. The mathematical model of the induction machine is linearized in the field-torque coordinates, and the misfiring of the inverter is represented by pulse functions, which have effects in both the field and torque directions. Since the fault considered is of an intermittent nature, the time-domain response of the magnetizing and the torque-producing components of the motor stator current is used to form the condition-monitoring signal. The method is adaptive to changes in the operating point during variable-speed operation. Digital simulation and laboratory experiment are utilized to illustrate the method and to evaluate the computational effort required.

High-response flux control of direct-field-oriented induction motor with high efficiency taking core loss into account

Abstract: Stator core loss has significant adverse effects when an induction motor is controlled by the conventional field-oriented method. Therefore, taking core loss into account should make it possible to control the torque very precisely. In this paper, a direct-field-oriented induction motor with a deadbeat rotor flux controller was developed. The method ensures maximum efficiency in the steady state without degradation of the dynamic response. Simulation and experimental results have demonstrated that this method has higher efficiency and good speed response without any degradation in the transient characteristics.

Fuzzy adaptive vector control of induction motor drives

Abstract: This paper deals with the design and experimental realization of a model reference adaptive control (MRAC) system for the speed control of indirect field-oriented (IFO) induction motor drives based on using fuzzy laws for the adaptive process and a neuro-fuzzy procedure to optimize the fuzzy rules. Variation of the rotor time constant is also accounted for by performing a fuzzy fusion of three simple compensation strategies. A performance comparison between the new controller and a conventional MRAC control scheme is carried out by extensive simulations confirming the superiority of the proposed fuzzy adaptive regulator. A prototype based on an induction motor drive has been assembled and used to practically verify the features of the proposed control strategy.

An on-line loss minimization controller for interior permanent magnet motor drives

Abstract: In this paper, an on-line adaptive loss minimization controller (ALMC) for interior permanent magnet motor drives is introduced after the minimum loss operation of these motors is analyzed. The ALMC provides a novel pattern of change in d-axis stator current to achieve a minimum drive input power at any operating condition. The operation of the ALMC results in a smooth and fast loss minimization, thus overcoming the major drawbacks of existing on-line loss minimization control approaches. The proposed ALMC provides more energy savings in comparison with other methods and extends the application of loss minimization control to a class of motor drives requiring efficient and smooth operation in the face of frequent changes in the operating point. The design and DSP implementation of the ALMC applied to an experimental 1 HP rare-earth IPM motor drive are presented. Several experimental results are given to prove the validity of the ALMC.

Method and apparatus for controlling a brushless DC motor that indicates a motor failure

Abstract: A method and apparatus for controlling a brushless DC motor which has a permanent magnet rotor and a 3-phase stator winding for applying a rotating magnetic field to the permanent magnet rotor. A specified reference voltage is compared with the stator winding terminal voltages for each phase. The rotor position is detected from the output of these comparison circuits based on the induced voltages generated in the stator windings which are not conducting when the motor is rotated. The stator windings which conduct current are controlled in response. Furthermore, a specific conduction pattern is supplied to each stator winding when the rotor is stopped, and a reference output determined for the conduction pattern is compared with the output of the comparison circuits when the stator windings are conducting. Abnormalities are detected based on the comparison results of the comparison circuit.

Characteristics of shaft voltage and bearing currents

Abstract: This article reviews investigations into reduced bearing life due to voltage source adjustable speed drive (ASD) AC motor operation. Relevant bearing failure mechanisms and indicators are discussed. dv/dt and electric discharge machining (EDM) contributions are discussed and experimental data presented showing the voltage levels on motor shafts when operating with ASDs. Finally, techniques to reduce shaft voltage are discussed, along with the electrical characteristics and interaction of system components. The example chosen is electrostatic shielded induction motors.

A method for sensorless on-line vibration monitoring of induction machines

Abstract: This paper proposes a method for sensorless on-line vibration monitoring of induction machines based on the relationship between the current harmonics in the machine and their related vibration harmonics. Initially, the vibration monitoring system records two baseline measurements of current and vibration with the machine operating under normal conditions. The baseline data is then evaluated to determine the critical frequencies to monitor on-line. Once these frequencies are determined, the baseline vibration measurement is simply used to scale the current harmonic signal to an estimated vibration level. Based on theoretical analysis, simulation results, and the experimental results shown here, a linear relationship between the current harmonics and vibration level can be assumed. The results of two experiments on a three-phase 230 V, 10 HP induction motor operating under no load are discussed and show the feasibility of this method for sensorless on-line vibration monitoring.

Induction motor drive system for low power applications

Abstract: This paper investigates the utilization of three different configurations of induction motor drives to implement low-cost systems for low-power applications The static power converter side is implemented by a single-phase rectifier cascaded with a four-switch inverter Three different types of induction machines are supplied with the static power converter In the first configuration, a standard three-phase induction machine is employed The second configuration also employs a standard three-phase induction machine, but only two of three windings are used In the third configuration, a standard two-phase induction machine is employed Simulation and experimental results are provided to illustrate the operation of the systems

On dynamic load models for voltage stability studies

Abstract: Appropriate modelling of dynamic loads is of primary importance in voltage stability studies. The paper deals with the modelling of a load consisting of a static load plus an aggregate of induction motors. The behavior of three simplified models for such a load configuration is compared. The three models are (A) a generic nonlinear dynamic model of the first order as proposed by Karlsson and Hill, (B) a static exponential load plus a dynamic first-order model for the induction motors, and (C) a static exponential load plus a dynamic third-order model for the induction motors. A power system with a longitudinal structure is chosen as the case-study. It is shown that for the same perturbation (tripping of one of two high-voltage parallel lines) the simulation results are quite different from each other and, in certain cases, only the third-order dynamic model correctly predicts the voltage collapse phenomena at the load bus. An interpretation of the different behavior of the various models is given.

Air conditioner response to transmission faults

Abstract: This paper describes two multi-phase faults events which occurred during periods of high air conditioning use. There was a significant loss of load in these events which is attributed to air conditioner motor protection. The overall response of the transmission system is simulated using induction motor models based on the characteristics of a typical residential air conditioner compressor motor. The sensitivity of factors such as fault location, fault duration and excitation system performance is also investigated.