Showing papers on "Induction motor published in 1995"

Space vector modulated three-phase to three-phase matrix converter with input power factor correction

Abstract: Analysis, design, and implementation of the space vector modulated three-phase to three-phase matrix converter with input power factor correction are presented. The majority of published research results on the matrix converter control are given an overview, and the one which employs simultaneous output-voltage and input-current space vector modulation, is systematically reviewed. The modulation algorithm is theoretically derived from the desired average transfer functions, using the indirect transfer function approach. The algorithm is verified through implementation of a 2 kVA experimental matrix converter driving a standard induction motor as a load. The switching frequency is 20 kHz. The modulator is implemented with a digital signal processor. The resultant output voltages and input currents are sinusoidal, practically without low-frequency harmonics. The input power factor is above 0.99 in the whole operating range.

Model-based current control of AC machines using the internal model control method

Abstract: In the present paper, the internal model control (IMC) method is introduced and applied to AC machine current control. A permanent magnet synchronous machine is used as an example. It is shown that the IMC design is straightforward and the resulting controller is simple to implement. The controller parameters are expressed in the machine parameters and the desired closed-loop rise time. The extra cost of implementation compared to PI control is negligible. It is further shown that IMC is able to outperform PI control with as well as without decoupling with respect to dq variable interaction in the presence of parameter deviations.

Standard load models for power flow and dynamic performance simulation

Abstract: The authors recommend standard load models for power flow and dynamic simulation programs. The goal of this paper is to promote better load modeling and advanced load modeling, and to facilitate data exchange among users of various production-grade simulation programs. Flexibility of modeling is an important consideration. For transient stability, longer-term dynamics, and small-disturbance stability programs, the authors recommend the structure of multiple load types connected to a load bus. Load types are static including discharge lighting, induction motors, synchronous motors, and transformer saturation. For each load type, multiple models may be connected to the bus. For longer-term dynamics programs, a model for LTC transformers is also recommended.

Finite element analysis of electrical machines

Abstract: Preface. 1. Introduction to Finite Elements. 2. Nonlinear Problems. 3. Permanent Magnets. 4. Eddy Current Analysis. 5. Computation of Losses, Resistance and Inductance. 6. Calculation of Force and Torque. 7. Synchronous Machines in the Steady State. 8. The Induction Motor in Steady State. 9. Time Domain Modeling of Induction Machines. 10. Air-Gap Elements for Electrical Machines. 11. Axiperiodic Solutions.

Effect of PWM inverters on AC motor bearing currents and shaft voltages

Abstract: This paper investigates AC induction motor shaft voltage problems, current flow through motor bearings and electric discharge current problems within bearings when operated under both pure sinewave and pulse width modulated (PWM) inverter sources. Experience suggests that PWM voltage sources with steep wavefronts especially increase the magnitude of the above electrical problems, leading to motor bearing material erosion and early mechanical failure. Previous literature suggests that shaft voltage-bearing current problems under 60 Hz sinewave operation are predominantly electromagnetically induced. It is proposed that under PWM operation these same problems are now predominantly an electrostatic phenomenon. A system model to describe this phenomenon is characterized and developed. Construction and test of a new electrostatic shielded induction motor (ESIM) verifies this model and is also a possible solution to the bearing current problem under PWM operation. >

Transient analysis of cage induction machines under stator, rotor bar and end ring faults

Abstract: An analysis method is developed for modeling of multi phase cage induction motors with asymmetry in the stator, arising due to an interturn fault resulting in a disconnection of one or more coils making up a portion of a stator phase winding and any distribution and number of rotor bar and end-ring failures. The approach, based on the winding functions, makes no assumption as to the necessity for sinusoidal MMF and therefore include all the space harmonics in the machine. Simulation and experimental results confirm the validity of the proposed method. >

Analysis of airgap flux, current and vibration signals as a function of the combination of static and dynamic airgap eccentricity in 3-phase induction motors

Abstract: This paper provides new information for the online diagnosis of airgap eccentricity in 3-phase induction motors. A new theoretical analysis of the interaction between harmonic field components due to static and dynamic rotor eccentricity which previous research has not considered is put forward, The resultant nonsupply-frequency current components produced in the supply current which are highlighted by the analysis are found to exist experimentally and indeed shown to be a function of the combined effect of both dynamic and static eccentricity. Further vibration analysis is put forward to identify which particular form of rotor eccentricity is dominant; hence illustrating how faults can be identified in a motor using condition monitoring techniques.

Fuzzy logic based on-line efficiency optimization control of an indirect vector-controlled induction motor drive

Abstract: Improvement of adjustable speed drive system efficiency is important not only from the viewpoints of energy saving and cooling system operation, but also from the broad perspective of environmental pollution. The paper describes a fuzzy logic based on-line efficiency optimization control of a drive that uses an indirect vector controlled induction motor speed control system in the inner loop. At steady-state light-load condition, a fuzzy controller adaptively decrements the excitation current on the basis of measured input power such that, for a given load torque and speed, the drive settles down to the minimum input power, i.e., operates at maximum efficiency. The low-frequency pulsating torque due to decrementation of rotor flux is compensated in a feedforward manner. If the load torque or speed command changes, the efficiency search algorithm is abandoned and the rated flux is established to get the best transient response. The drive system with the proposed efficiency optimization controller has been simulated with lossy models of the converter and machine, and its performance has been thoroughly investigated. An experimental drive system with the proposed controller implemented on a TMS320C25 digital signal processor, has been tested in the laboratory to validate the theoretical development. >

Improvements in EMC performance of inverter-fed motor drives

Abstract: An experimental investigation of conducted radio-noise emission from a conventional pulse width modulated (PWM) inverter of medium power feeding an induction motor is described. It is determined that the inverter system generates considerable impulse currents through the power leads feeding the system resulting in serious conducted electromagnetic interference (EMI) problems and significant voltage waveform distortion in the power system. The dominant emission sources in the system are identified. A proposed model of the drive system for the purpose of evaluation of EMI are developed. Several low-cost strategies for improvement in EMC performance of the PWM inverter are then proposed. Experimental results demonstrate that disturbance from the modified system can be dramatically reduced, and that the EMC performance of the system has come very close to meeting the IEC CISPR and FCC limits on conducted emissions for digital devices.

Monitoring of defects in induction motors through air-gap torque observation

Abstract: This paper suggests a method to monitor defects such as cracked rotor bars and the shorted stator coils in induction motors. Air-gap torque can be calculated while the motor is running. No special down time for measurement is required. Data of the air-gap torque for a motor should be periodically kept for comparison purposes. Since more data than just a line current are taken, this method offers other potential possibilities that cannot be handled by examining only a line current. The theoretical foundation for this proposed method is presented. Experiments conducted on a 5-hp motor show the validity and potential of this approach. Further studies are planned to extend the proposed method in detail and to monitor defects developed in other types of rotating machines. >

Improved direct torque and flux vector control of PWM inverter-fed induction motor drives

Abstract: In this paper, a direct torque and stator flux vector control system is presented. The principle of this method was proposed by Takahashi and Noguchi in 1985. In contrast to the field oriented control, no coordinate transformation and current control loop is required. In practical application, however, problems occur with starting and operation in the zero speed region. This paper shows how, by introducing an additional carrier signal to the torque controller input, a robust start and improved operation in the low speed region can be achieved. The simulation and experimental results which illustrate the performances of the proposed system are presented. Also, nomograms for controller design are given. >

Instantaneous stator power as a medium for the signature analysis of induction motors

Abstract: Preventive maintenance of electric drive systems with induction motors involves continuous monitoring of operation, to detect electrical and mechanical conditions that may lead to a failure. Intensive research efforts have, for some time, been focused on motor current signature analysis (MCSA). MCSA techniques utilize results of spectral analysis of the stator current of an induction motor to diagnose abnormal conditions both in the motor and driven system. Reliable interpretation of the current spectra is difficult, as distortions of the current waveform caused by abnormalities in the drive system are usually minute. In this paper, an alternate medium for motor signature analysis, namely the instantaneous stator power, is proposed. It is shown, both by computer simulations and laboratory experiments, that the instantaneous power carries more information than the current itself, since not only the current magnitude but also the phase shift between the current and voltage waveforms are affected by irregularities in the motor or other parts of the drive system. Utilization of the instantaneous stator power as a medium for signature analysis opens new possibilities in the automated diagnosis of induction motor drives.

Thermal Modelling of Small Cage Induction Motors

Abstract: The loadability of electric machines is above all determined by temperature limits. In this work, thermal network models, suitable for totally enclosed fan cooled (TEFC) induction motors, are used to predict the machine temperatures. Two specific models are suggested: one with 107 nodes, which primarily is intended as a design tool, and one with 7 nodes, for increased simplicity. The steady-state solution method is valid in a broad speed-range and for variable load. Time-dependent solutions are obtained as a function of four input variables: frequency, stator voltage, torque and ambient temperature.

A multilevel voltage-source converter system with balanced DC voltages

Abstract: In this paper, a multilevel voltage-source converter system is proposed for high-voltage, high-power applications such as back-to-back interconnection of power systems, large induction motor drives, and electrical traction drives. Multilevel voltage-source converters have a voltage unbalance problem in the DC capacitors. The problem may be solved by use of additional voltage regulators or separate DC sources. However, these solutions are found not to be practicable for most applications. The proposed converter system can solve the voltage unbalance problem of the conventional multilevel voltage-source converters, without using any additional voltage balance circuits or separate voltage sources. The mechanism of the voltage unbalance problem is analyzed theoretically in this paper. The voltage unbalance problem of multilevel converters in the DC capacitors has been solved by the proposed internal connections of the AC/DC and DC/AC converters. The validity of the new converter system is demonstrated by simulation and experiment. >

A new optimized space vector modulation strategy for a component minimized voltage source inverter

Abstract: This paper presents a new space vector modulation strategy suitable for a low cost PWM-VSI inverter employing only four switches, four diodes and a split capacitor bank in the DC-link. The work is motivated by the need of an efficient and flexible modulation method, which is optimized with respect to minimum machine torque ripple. The modulation strategy is named Space Vector Modulation for Four Switch Inverter (SVMFSI) and is realized by planning the switching patterns between four active voltage vectors on the basis of a desired flux trajectory for the stator flux vector in the AC-machine (variable speed induction motor drive). The strategy is implemented in a single 8-bit microcontroller as a double sided modulation strategy. Simulations of the motor torque ripple are performed at a switching frequency of 4 kHz and indicate a torque ripple of 14% at nominal load. Finally, selected results are verified experimentally on a 1.5 kVA prototype B4 inverter. The test results indicate high quality output voltage spectra with no low-order voltage harmonics and a harmonic loss factor (HLF) of 1.12% at unity modulation index. >

Selection of capacitors for the self regulated short shunt self excited induction generator

Abstract: The self regulating feature of a self-excited induction generator (SEIG) by connecting additional capacitors is examined. A system consisting of both shunt and series capacitors has been analyzed. A methodology has been explained to choose an appropriate set of values of these capacitors for desired voltage regulation. Performance of short and long shunt configurations has been compared which shows the superiority of the short shunt connection. The results of a detailed investigation on a conventional 3.7 kW induction motor operated as a SEIG are presented to illustrate the effectiveness of the proposed method. Close agreement between predicted and test results has been observed, thereby establishing the validity of the analysis carried out and the criterion adopted. >

Switched reluctance generators for wind energy applications

Abstract: The switched reluctance machine has very good characteristics in term of efficiency, control simplicity and robustness. The rotor is made of solid iron with no electrical excitation and this results in considerable robustness and reliability. The machine is cost competitive with the cage induction motor, has superior efficiency to it and its power converter is cheaper and fundamentally more reliable. Even with these advantages, its use as a generator has not been properly investigated. This paper describes the use of a 7.5 kW switched reluctance machine working as a generator and discusses the control systems and the application of this sort of generator connected in a variable speed wind turbine system. >

Rotor cage fault diagnosis in three-phase induction motors, by Park's vector approach

Abstract: The subject of on-line detection of rotor cage faults in three-phase induction motors is discussed, and a noninvasive approach, based on computer-aided monitoring of the stator current Park's vector, is introduced, Both simulation and laboratory test results demonstrate the effectiveness of the proposed technique, for detecting broken rotor bars or end-rings in operating three-phase induction machines. On-site tests conducted in a power plant, using the diagnostic instrumentation system developed, are also reported.

Design of a traveling wave type ultrasonic motor

Abstract: The purpose of the present paper is to establish a method of design for a traveling wave type ultrasonic motor. This method is based on two models for the ultrasonic motor. A two-dimensional elastic contact model is used for estimating the friction drive between the rotor and vibrator of the motor. Moreover, an electrical equivalent circuit is used to estimate the interaction between the electrical and mechanical parts of the vibrator. The proposed method is applied to the design of a prototype motor. To determine applicability of the method, the load characteristics of the prototype motor are measured. The measured characteristics agree with the required ones which are specified in advance. As a result, the validity of the proposed method is experimentally confirmed. >

The effect of long motor leads on PWM inverter fed AC motor drive systems

Abstract: Advances in power electronic technology have improved the performance and output waveforms of PWM voltage source inverters and have made them the popular choice for many general purpose variable speed induction motor drives in energy saving applications. Switching frequencies of 10 to 20 kHz with 0.1 /spl mu/s rise times are common with the current insulated gate bipolar transistor (IGBT) technology. In many industrial applications the PWM inverter and the motor must be at separate locations, thus requiring long motor leads. This paper examines the effect of long motor leads on high frequency PWM inverter fed AC motor drives. Cable transmission theory and cable capacitance analysis are presented and voltage reflections are investigated. A flexible computer model is developed and the analysis is confirmed by simulations and verified by experimental results from case studies. >

Semiconductor power losses in AC inverters

Abstract: The AC induction motor is the workhorse of modern industry. Worldwide about 50 million motors are installed every year which are greater than 1/2 hp. Three-phase induction motors are very simple and inexpensive to build. An AC motor may be used for variable speed applications with the addition of an AC inverter. An accurate model of semiconductor power losses is necessary to design a reliable invertor system using a minimum amount of silicon. Equations for the average and RMS transistor and diode currents are derived based on a quantitative analysis of the current waveforms. Conduction losses in the semiconductor devices are then approximated using a piecewise linear approximation of the device's on-voltage characteristics. Measurements of switching energy versus current are used to obtain a curve of losses versus current. Integration of these losses over a full sine wave period is used to obtain a closed form expression for switching losses as a function of sine wave current. Total losses, conduction losses and switching losses are compared to thermal measurements. The model is further tested by comparing predicted and actual losses at different PWM frequencies.

A current-source inverter fed induction motor drive system with reduced losses

Abstract: Standard low- and medium-power induction motor drives are based on the pulse width modulation (PWM) voltage-source inverter (VSI) fed from a diode rectifier. The dual topology, based on the current-source inverter/rectifier structure is used in medium- and high-power applications. This paper analyzes the existing motor drives based on current-source topologies and proposes a control strategy that addresses some of the drawbacks of this approach compared to the voltage-source approach. The proposed strategy features the following: (1) an online operated PWM CSI, using instantaneous output capacitor voltage control based on space-vector modulation; and (2) an additional inverter modulation index control loop, ensuring constant inverter modulation index and minimum DC-link current operation. The resulting additional advantages include the following: (1) fixed and reduced motor voltage distortion; (2) minimized DC-bus inductor losses; (3) minimized switch conduction losses; and (4) elimination of motor circuit resonances. Experimental results based on a DSP implementation are given.

Variable-frequency synchronous motor drives for electric vehicles

Abstract: The performance capability envelope of a variable-frequency, permanent-magnet synchronous motor drive with field weakening is dependent upon the product of maximum current and direct-axis inductance. To obtain a performance characteristic suitable for a typical electric vehicle drive, in which short-term increase of current is applied, it is necessary to design an optimum value of direct-axis inductance. The paper presents an analysis of a hybrid motor design which uses a two-part rotor construction comprising a surface-magnet part and an axially laminated reluctance part. This arrangement combines the properties of all other types of synchronous motor and offers a greater choice of design variables. It is shown that the desired form of performance may be achieved when the high-inductance axis of the reluctance part is arranged to lead the magnet axis by 90/spl deg/ (elec.).

Torque capability and control of a saturated induction motor over a wide range of flux weakening

Abstract: The first part of this paper covers an investigation of the maximum torque which an induction motor with saturated air gap inductance can generate over its permitted speed range, when voltage as well as current are limited. From the investigation, three regions of operating speed are identified, based on limiting quantities which determine the maximum obtainable torque. In each of these regions a different control strategy must be applied. When maximum torque is not required, efficiency can be optimized but this strategy should not be applied at low torque levels when good dynamic performance is required. The second part illustrates how a modified rotor flux oriented control strategy is applied to achieve full utilization of the torque capability over the whole speed range. Several measures for improving dynamic and transient behavior of the drive in the flux weakening region are suggested. Performance of the new control strategy is verified by experiments. >

High performance control of a three-level IGBT inverter fed AC drive

Abstract: Three-level PWM inverters have been increasingly employed in industry and traction applications where high power and efficiency energy conversions are required. This paper presents a high performance control of a cage induction motor drive fed by a 100 hp three-level IGBT inverter operating at a low switching frequency. A practical mathematical model of the drive control system is established to aid in the control design to improve the system stability, dynamic performance and robustness over a wide speed range. The modeling and the simulation in Matlab/Simulink facilitate the self-tuning of the regulators in the multi-loop systems. The field oriented control and three-level space-vector modulation together with the drive protection and diagnostics are implemented in software based on a DSP TMS320C31. Experimental results based on the IGBT inverter prototype are given to verify the design and performance. Test results in motor common-mode voltage reduction and inverter neutral-point potential control are also briefly presented.

Analysis and comparison of PM synchronous motor and induction motor type magnetic bearings

Abstract: In this paper, a general solution of radial position control applicable to PM synchronous type and induction type rotating motors is presented. The rotor of the permanent magnet motor is assumed to have sinusoidally distributed magnetic poles along the axial surface, while the rotor of the induction type motor is assumed to have uniform magnetic property. The inner wall of the stator is also assumed to have a current sheet, which can produce an arbitrary current distribution. The same number of magnetic poles gives the rotating torque to the rotor, while plus/minus two poles of the motoring control produces a pure radial force to the rotor. By controlling the magnitude and phase of the plus/minus two-pole current distribution relative to the motoring magnetic pole, the radial force can be controlled in the radial coordinate. This general solution is experimentally confirmed by using a simple experimental setup. >

A systematic approach to selecting flux references for torque maximization in induction motors

Abstract: This paper addresses the problem of optimal selection of the flux reference in induction machines. The results are based on a standard differential equation model of the induction machine and give the value of the flux reference which maximizes the torque at constant speed subject to voltage and current limits. Both the motor and generator modes are considered. The formulas are useful for the real-time programming of digital controllers designed to achieve maximum performance of AC drives at high speeds. Experimental results are given to validate the analysis and demonstrate the usefulness of the optimal flux reference in high-performance servo applications.

Precision torque control in inverter-fed induction machines using fuzzy logic

Abstract: In direct torque control of induction machines, none of the switching states is able to generate the exact voltage vector to produce the desired changes in torque and flux in most of the switching instances. This causes a high ripple in torque. This ripple can be reduced by applying a selected inverter switching state for a portion of switching period (defined as duty ratio /spl delta/) and the zero switching state for the rest of the period. The duty ratio during each switching state is a nonlinear function of torque error, flux error and flux position therefore fuzzy logic control is used to determine the duty ratio during each switching state. The simulation results indicate the ripple is reduced to less than 1/3 of the conventional DTC using the duty ratio control. Under duty ratio control the torque depends upon the changes in torque and flux during the zero switching state. These changes are minimized by using the stator flux optimization. >

Exponentially convergent rotor resistance estimation for induction motors

Abstract: A new estimation algorithm is presented which provides exponential estimation of rotor resistance for induction motor drives in physical operating conditions. The exponential convergence is not influenced by the value assumed by rotor speed, including zero speed. The algorithm also provides flux estimates and may be viewed as an adaptive observer. Experimental results show good performance with a sampling time of 0.8 ms which makes the algorithm implementable on-line by available digital signal processors. >