Showing papers in "IEEE Transactions on Energy Conversion in 1994"
TL;DR: In this article, a theory to predict changes in axial leakage flux resulting from stator winding interturn shorts and an algorithm to locate the position of the faulted coil was developed.
Abstract: One major cause of motor failures is breakdown of the turn insulation leading to puncture of the groundwall. Early detection of interturn shorts during motor operation would eliminate consequential damage to adjacent coils and the stator core reducing repair costs and motor outage time. In addition to the benefits gained from early detection of turn insulation breakdown, significant advantages would accrue by locating the faulted coil within the stator winding. Fault location would not only increase the speed of the repair, but would also permit more optimal scheduling of the repair outage. This work was successful in practically implementing a theory to predict changes in the axial leakage flux resulting from stator winding interturn shorts and in developing an algorithm to locate the position of the faulted coil. An experimental setup consisting of a 200 hp motor loaded by a generator was used to validate this theory. Suitable transducers were developed and installed on this motor. Measurement using this experimental configuration clearly validated the theoretical model. On the basis of this experimental work an instrument to continuously monitor for shorted turns is under development. >
395 citations
TL;DR: In this article, a methodology for calculation of the optimum size of a PV array for a stand-alone hybrid wind/PV power system is developed, where long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used.
Abstract: A methodology for calculation of the optimum size of a PV array for a stand-alone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the probability density functions of the wind speed and the irradiance for each hour of a typical day in a month. The wind speed and irradiance probability density functions and manufacturer's specification on a wind turbine and a PV module were used to calculate the average power generated by the wind turbine and the PV module for each hour of a typical day in a month. The least square method is used to determine the best fit of the PV array and wind turbine to a given load. On the basis of the energy concept an algorithm was developed to find the optimum size of the PV array in the system. >
350 citations
TL;DR: In this article, the rotor design of synchronous reluctance machines can be optimized in terms of a key geometric parameter, i.e., the ratio of the rotor insulation width to the rotor iron width so as to obtain maximum torque production.
Abstract: It is demonstrated that the rotor design of synchronous reluctance machines can be optimized in terms of a key geometric parameter, i.e., the ratio of the rotor insulation width to the rotor iron width so as to obtain maximum torque production. The equation which gives the maximum motor power factor in terms of the saliency ratio has been derived and it is shown that the power factor of 0.8 is a realizable value with the optimal rotor design. An experimental motor has been fabricated and the results of measurements of the motor parameters prove the validity of the rotor design optimization. >
304 citations
TL;DR: Several types of AC bearingless motors have been proposed in this article, which have conventional four-pole stator windings and additional two-pole windings, whose currents produce radial forces acting on the rotor.
Abstract: Several types of AC bearingless motors are proposed. These bearingless motors have conventional four-pole stator windings and additional two-pole windings, whose currents produce radial forces acting on the rotor. General expressions of the machine inductances and radial forces are derived for the cylindrical rotor and salient-pole motors. No-load characteristics of laboratory squirrel-cage induction and reluctance-type synchronous bearingless motors are provided. The test motors were successfully driven by the control circuits. >
184 citations
TL;DR: In this paper, a shunt DC motor driving a centrifugal water pump is supplied from a photovoltaic generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop.
Abstract: A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop. >
115 citations
TL;DR: In this paper, a nonlinear variable structure stabilizer is proposed for a single machine connected to an infinite bus power system and a multimachine system with multimode oscillations, which gives satisfactory dynamic performance and good robustness.
Abstract: A nonlinear variable structure stabilizer is proposed in this paper. Design of this stabilizer involves the nonlinear transformation technique, the variable structure control technique and linear system theory. Performance of the proposed nonlinear variable structure controller in a single machine connected to an infinite bus power system and a multimachine system with multimode oscillations is simulated. The responses of the system with the proposed stabilizer are compared with those obtained with some other kinds of stabilizers when the system is subjected to a variety of disturbances. Simulation results show that the nonlinear variable structure stabilizer gives satisfactory dynamic performance and good robustness. >
114 citations
TL;DR: Novel applications of fuzzy logic for the intelligent control of a slip power recovery system are presented and a direct fuzzy logic controller and an adaptive fuzzy controller, based on model reference adaptive control, are developed and simulated for the doubly-excited induction machine and power converter system.
Abstract: The slip power recovery configuration is an attractive scheme of variable speed drive, with high efficiency and low power converter rating; however, high performance control has been difficult. In this paper, novel applications of fuzzy logic for the intelligent control of a slip power recovery system are presented. A direct fuzzy logic controller and an adaptive fuzzy controller, based on model reference adaptive control, are developed and simulated for the doubly-excited induction machine and power converter system. Compared with field orientation control, the intelligent control of a complex slip power recovery system reduces costs and enhances robust and desired performance. >
102 citations
TL;DR: In this article, a multi-layer neural network (NN) architecture is proposed for the identification and control of DC brushless motors operating in a high performance drives environment, where the motor speed and position are made to follow pre-selected tracks (trajectories) at all times.
Abstract: In this paper, a multi-layer neural network (NN) architecture is proposed for the identification and control of DC brushless motors operating in a high performance drives environment. The NN in the proposed structure performs two functions. The first is to identify the nonlinear system dynamics at all times. Hence, detailed and elaborate models for the DC brushless machines are not needed. Furthermore, unknown nonlinear dynamics that are difficult to model such as load disturbances, system noise and parameter variations can be recognized by the trained neural network. The second function of the NN is to control the motor voltage so that the speed and position are made to follow pre-selected tracks (trajectories) at all times. The control action emulated by the NN is based on the indirect model reference adaptive control. A hardware laboratory setup is utilized to test and evaluate the proposed neural network structure. The paper shows, based on the laboratory test results, that the proposed neural network structure performance was good: the tracking accuracy was very high and the system robustness was quite evident even in the presence of random and severe disturbances. >
94 citations
TL;DR: This paper investigates the robustness of fuzzy logic power system stabilizers using the information of speed and acceleration states of a study unit using nonlinear simulations and shows the feasibility of the proposed fuzzy logic stabilizer.
Abstract: This paper investigates the robustness of fuzzy logic power system stabilizers using the information of speed and acceleration states of a study unit. The input signals are the real power output and/or the speed of the study unit. Nonlinear simulations show the robustness of the fuzzy logic power system stabilizers. Experiments are also performed by using a micro-machine system. The results show the feasibility of the proposed fuzzy logic stabilizer. >
86 citations
TL;DR: In this article, the authors present a utility interactive wind energy conversion scheme with an asynchronous link comprised of a diode bridge rectifier and a line commutated inverter to track and extract maximum power from the wind energy system and transfer this power to the electric utility.
Abstract: The paper presents modelling, simulation and experimental verification of a utility interactive wind energy conversion scheme with an asynchronous link comprised of a diode bridge rectifier and a line commutated inverter. The control objective is to track and extract maximum power from the wind energy system and transfer this power to the electric utility. This is achieved by controlling the firing delay angle of the inverter. Since the diode bridge rectifier has no control on the DC link voltage, a supplementary control loop is used to limit the voltage within a preset voltage threshold. The proposed scheme for regulating the flow of power through the DC link ensures reduced reactive power burden on the self-excitation capacitor banks and better utilisation of available wind energy, while limiting the DC link voltage within a preset voltage threshold. The simulated results are experimentally verified and found to give good power tracking performance. >
81 citations
TL;DR: In this article, a method for the in situ measurement of the parameters of a machine and load combination is given, which uses an output error estimation technique combined with supply voltage perturbations.
Abstract: Simulations of induction motors for power system studies are often hampered by unavailable and/or inaccurate parameter data. A method for the in situ measurement of the parameters of a machine and load combination is given. This uses an output error estimation technique combined with supply voltage perturbations. The technique yields optimum parameter values with minimum disruption to the machine's normal operation. Verifying tests were conducted on individual motors as well as for a group of machines. The results indicate good correlation between estimated values and values obtained from conventional tests. >
TL;DR: In this article, a robust power system stabilizer (PSS) is proposed to improve transient and dynamic stabilities of a turbogenerator connected to an infinite busbar.
Abstract: The H/sup /spl infin// optimal control theory has been used to design a robust power system stabilizer (PSS) to improve transient and dynamic stabilities of a turbogenerator connected to an infinite busbar. It is demonstrated that the effects of disturbances in the machine output can be minimized and sufficient closed-loop stability margins (robustness) can be obtained to tolerate variations in the loop transfer functions, such as those which might arise from unmodeled low-damped high-frequency modes of oscillations. The resulting controller would effectively enhance the synchronizing and damping torques of the machine without the risk of exciting the shaft torsional modes. This is in marked contrast with the unstable performance of linear quadratic (LQ) optimal controllers under similar conditions. The H/sup /spl infin// design methodology also ensures a satisfactory performance of the PSS under a wide range of system operating conditions. >
TL;DR: In this article, a programmable dynamometer is proposed where the user can define the steadystate and inertial torque-speed characteristic of the load, and the user inputs the desired load characteristics by selecting polynomial and inertia coefficients.
Abstract: A programmable dynamometer is proposed where the user can define the steady-state and inertial torque-speed characteristic of the load. Rotating machinery can be tested on this dynamometer to determine their transient and steady-state characteristics with a practical load. The user inputs the desired load characteristics by selecting polynomial and inertia coefficients. The system uses proportional-integral (PI) controllers to control a three-phase induction motor using indirect field orientation. Simulations show that the dynamometer offers excellent tracking of the desired torque-speed characteristic and simplicity of use. >
TL;DR: In this article, the authors present multivariable frequency domain techniques as a tool for controller design and dynamic analysis of an autonomous wind-diesel power system and study how robust model based controllers can be designed for such systems.
Abstract: The aim of this paper is twofold: first to present multivariable frequency domain techniques as a tool for controller design and dynamic analysis of an autonomous wind-diesel power system; and secondly to study how robust model based controllers can be designed for such systems Dynamic system analyses using multivariable frequency domain techniques are verified against detailed nonlinear simulation studies The results are encouraging in the sense that the main conclusions in terms of robust stability and performance agree very well with the simulation results It is also shown that improved performance of the system can be achieved using simple model based controllers >
TL;DR: In this article, a microcomputer based fuzzy logic power system stabilizer is applied to a micro-machine system to investigate its efficiency in real-time control, the stabilizing signal is determined by using measured speed or real power signals at every sampling time to damp the system oscillations.
Abstract: A microcomputer based fuzzy logic power system stabilizer is applied to a micro-machine system to investigate its efficiency in real time control. The stabilizing signal is determined by using measured speed or real power signals at every sampling time to damp the system oscillations. The results show the proposed stabilizer improves the system damping effectively subject to various types of disturbances. >
TL;DR: In this paper, an advanced fuzzy logic control scheme has been proposed for a microcomputer based power system stabilizer to enhance the overall stability of power systems, which utilizes the PID information of the generator speed.
Abstract: An advanced fuzzy logic control scheme has been proposed for a microcomputer based power system stabilizer to enhance the overall stability of power systems. The proposed control scheme utilizes the PID information of the generator speed. The input signal to the stabilizer is the real power output of a study unit. Simulations show the effectiveness of the advanced fuzzy logic control scheme. >
TL;DR: In this paper, an analysis for the calculation of various field harmonics and radial forces in a squirrel cage induction motors is presented, with a view to determine the actual role played by the air-gap harmonic fields on the radial forces.
Abstract: The radial electromagnetic forces in induction motors play an important role in the production of audible noise and vibrations. The magnetic flux pulsations at the iron surfaces produce these radial forces, which act on the stator and rotor structures. An analysis for the calculation of the various field harmonics and radial forces in squirrel cage induction motors is presented in this paper. To verify the validity of the analysis, a squirrel cage induction motor is analyzed. Theoretical and experimental results are presented with a view to determine the actual role played by the air-gap harmonic fields on the radial forces. Also, the effects of loading on the radial forces and the ensuing vibrations are closely examined. >
TL;DR: In this article, an artificial neural network (ANN), trained as an inverse of the controlled plant, was used to function as a power system stabilizer (PSS), which can provide good damping of the power system over a wide operating range.
Abstract: An artificial neural network (ANN), trained as an inverse of the controlled plant, to function as a power system stabilizer (PSS) is presented in this paper. In order to make the proposed ANN PSS work properly, it was trained over the full working range of the generating unit with a large variety of disturbances. Data used to train the ANN PSS consisted of the control input and the synchronous machine response with an adaptive PSS (APSS) controlling the generator. During training, the ANN was required to memorize the reverse input/output mapping of the synchronous machine. After the training, the output of the synchronous machine was applied as the input of the ANN PSS and the output of the ANN PSS was used as the control signal. Simulation results show that the proposed ANN PSS can provide good damping of the power system over a wide operating range and significantly improve the system performance. >
TL;DR: In this article, the authors presented a novel artificial intelligence-based neural network (ANN) pattern classification and online detection scheme for a single machine infinite bus system using specific frequency spectra of the hyperplane discriminant vector of machine rotor angle, speed, accelerating power, instantaneous power, voltage, and current using either a perceptron single layer detection scheme or a two layer feedforward ANN for online classification and detection of fault condition causing first swing transient stability or loss of excitation.
Abstract: The paper presents a novel artificial intelligence-based neural network (ANN) pattern classification and online detection scheme for a single machine infinite bus system. The proposed online relay and dynamic pattern classifier utilizes specific frequency spectra of the hyperplane discriminant vector of machine rotor angle, speed, accelerating power, instantaneous power, voltage, and current using either a perceptron single layer detection scheme or a two layer feedforward ANN for online classification and detection of fault condition causing first swing transient stability or loss of excitation. Other relay binary outputs include fault type and allowable clearing time identification. The detection accuracy is improved by utilizing the cross spectra of discriminant vector input variables correlations. The proposed pattern classification technique can be extended to interconnected multimachine power systems by using relative rotor angles, frequency deviations, tie-line powers, and their cross spectra variables. >
TL;DR: In this article, the effects of interbar currents on the detection of broken rotor bars in a squirrel cage induction motors were investigated, and it was shown theoretically and experimentally that interbar current can reduce any magnetic imbalance brought about by the broken bar.
Abstract: In present monitoring techniques for the detection of broken rotor bars in squirrel cage induction motors, the assumption is made that a broken bar conducts no current. This causes a magnetic imbalance, which can then be detected to indicate a broken bar. In certain motors, however, large currents are still able to flow in the broken bar by means of interbar currents. This paper deals with the effects these currents have on broken bar monitoring. The work shows theoretically and experimentally that interbar currents reduce any magnetic imbalance brought about by the broken bar. >
TL;DR: In this article, the starting process of a large squirrel cage induction motor driving an inertia load through an elastic shaft was studied and it was shown that the torsional torque can be substantially reduced by the proper coordination of the switching operations.
Abstract: The paper presents a comprehensive study of the starting process of a large squirrel cage induction motor driving an inertia load through an elastic shaft. The analysis of the electromagnetic torque of the motor has revealed that there are variable frequency components which interact with the torsional mode of the mechanical system and produce hazardous shaft torque. This torque may exceed the maximum yield of the shaft or it may accumulate and result in a cyclic fatigue fracture. The nature of the problem is explained and the factors which aggravate its impact are discussed. Furthermore, it is shown that the torsional torque can be substantially reduced by the proper coordination of the switching operations. >
TL;DR: In this paper, the relationship between shaft signals and eccentricities of synchronous machines was studied and the magnitude and the thickness of shaft-signal loci reflected steady and dynamic eccentricities.
Abstract: Relationships between shaft signals and eccentricities of salient-pole synchronous machines are studied. The magnitude and the thickness of shaft-signal loci reflect steady and dynamic eccentricities. Harmonic components of shaft signals closely relate to shorted field coils. Threshold records can be used for indications of changes in eccentricities and shorted field coils. Extensive experimental work agrees with the theoretical predictions. >
TL;DR: In this article, an algorithm is proposed to predict the steady state performance of a self-excited induction generator (SEIG) feeding an induction motor (IM) for agricultural pumpsets.
Abstract: The paper assesses the suitability of a self excited induction generator (SEIG) to supply dynamic loads like induction motors. An algorithm is proposed to predict the steady state performance of an SEIG feeding an induction motor (IM). The computed and experimental results are presented for different operating conditions of an SEIG-IM system. A good agreement reached between the predicted and test results validate the effectiveness of the proposed algorithm. Experimentally recorded transients of an SEIG during a series of switching operations are presented to demonstrate the ability of an SEIG to sustain the starting of an IM. By analyzing the performance of a typical 7.5 kW, 3-phase SEIG feeding induction motors of different ratings, useful guidelines are proposed for the design of an SEIG-IM system in autonomous applications like agricultural pumpsets. >
TL;DR: In this paper, a damping scheme using superconducting magnetic energy storage (SMES) unit is proposed to damp subsynchronous resonance (SSR) of the IEEE Second Benchmark Model, system-1 which is a widely employed standard model for computer simulation of power system SSR.
Abstract: A novel damping scheme using superconducting magnetic energy storage (SMES) unit is proposed in this paper to damp subsynchronous resonance (SSR) of the IEEE Second Benchmark Model, system-1 which is a widely employed standard model for computer simulation of power system SSR. The studied system contains a turbine-generator set connected to an infinite bus through two parallel transmission lines, one of which is series-capacitor compensated. In order to stabilize all SSR modes, simultaneous active and reactive power modulation and a proportional-integral-derivative (PID) damping controller designed by modal control theory are proposed for the SMES unit. A frequency domain approach based on eigenvalue analysis and time-domain approach based on nonlinear model simulations are performed to validate the effectiveness of the damping method. It can be concluded from the simulation results that the proposed damping scheme can effectively suppress SSR of the studied system. >
TL;DR: In this article, the results of using a state space model to predict a motor-drive system dynamic performance characteristics under normal operating conditions are presented, and the effects of mutual coupling between motor phases on the analysis results are evaluated.
Abstract: In this first of a set of two companion papers on switched reluctance motor drive systems, the results of using a state space model to predict a motor-drive system dynamic performance characteristics under normal operating conditions are presented. Using this approach, the state space model parameters are determined from series of nonlinear magnetic field solutions, thus accounting for magnetic material nonlinearities and space harmonics due to the motor geometry. The method is applied to a 6/4, 0.15 hp, 5000 r/min switched reluctance motor and resulted in the machine inductances, which compared favorably to measured values. Using these parameters in the state space model, the dynamic performance characteristics of the motor drive system are predicted and verified by comparison to experimental data. In addition, the effects of mutual coupling between motor phases on the analysis results are evaluated. >
TL;DR: In this article, an experimental five phase induction motor and its corresponding power converter and control are designed and fabricated, and some of the design criteria and the experimental results obtained from the tests are presented and discussed.
Abstract: An approach to an analysis of multiphase concentrated winding induction machines specifically designed for operation with static power converters has been presented and simulated by means of a digital computer simulation in previous papers. In order to substantiate the theoretical conclusions regarding the performance of multiphase induction motors, an experimental five phase induction motor and its corresponding power converter and control are designed and fabricated. In this paper some of the design criteria and the experimental results obtained from the tests are presented and discussed. >
TL;DR: In this article, the rotational losses are largely caused by flux that rotates in the plane of the machine laminations, and a test procedure for determining rotational loss in a sample is described.
Abstract: This paper discusses rotational losses and how they are produced in the core materials of induction motors. These losses are largely caused by flux that rotates in the plane of the machine laminations. This suggests that steel specification for applications to rotating machines should be given in terms of rotational loss data as a material characteristic, in much the same fashion as Epstein test results are provided for alternating losses. If a standardized test for rotational losses were to be used, steel producers could rationally investigate the effects of composition and processing variables. This is necessary in order to produce low loss steels for motor applications. Reduction of rotational losses in motor cores could significantly lower AC machine operating costs and contribute to the growing interest and design of high efficiency induction motors. The paper describes a test procedure for determining rotational losses in a sample. It then compares the results with standardized tests from an Epstein test procedure. It is seen that there are significant differences in loss results obtained for the rotational test versus the alternating current test. The authors have investigated a time harmonic finite element formulation utilizing Magnet 2D, a commercially available package. The paper includes a brief analysis of a typical problem using this tool. >
TL;DR: In this article, the authors proposed a nonlinear model of a synchronous generator, its governor and exciter systems, and a superconducting magnetic energy storage (SMES) system connected to the generator terminal.
Abstract: Stabilization of a synchronous generator through control of firing angle of the power converters in superconducting magnetic energy storage (SMES) systems is considered. An optimum strategy of the firing angle control is designed so as to eliminate the transients in minimum time. A nonlinear model of a synchronous generator, its governor and exciter systems, and an SMES system connected to the generator terminal is considered. The optimum firing angle control is derived retaining the nonlinearities of the system dynamics. Digital simulation results indicate that the proposed strategy controls the slowly growing as well as first swing instabilities very effectively. >
TL;DR: In this article, a comparison study of two rotor structures of the DEBRM is presented by finite element analysis by calculating selfand mutual-flux linkage of the dual stator windings as the function of rotor positions.
Abstract: Doubly excited brushless reluctance machine (DEBRM) has gained much attention in the area of variable-speed constant-frequency generating systems and adjustable speed drives. Two types of reluctance rotor structure, axially laminated and simple salient rotors, are suggested in the DEBRM development. Due to the unconventional pole number combination of the stator and rotor, performance evaluation of the DEBRM with different rotor structures is difficult. A comparison study of two rotor structures of the DEBRM is presented in this paper by finite element analysis. It is shown that by calculating selfand mutual-flux linkage of the dual stator windings as the function of rotor positions, performance of the complicated DEBRM can be evaluated conveniently. Various advantages and disadvantages of the DEBRM associated with the two rotor structures are also discussed. >
TL;DR: The design and application of fuzzy control to the problem of automatic voltage regulation of a synchronous generator with use of binary input-output fuzzy associative memories for control is explored.
Abstract: Fuzzy controllers are increasingly being accepted by engineers and scientists alike as a viable alternative for classical controllers. The processes involved in fuzzy controllers closely imitate human control processes. Human responses to stimuli are not governed by transfer functions and neither are those from fuzzy controllers. This study involves the design and application of fuzzy control to the problem of automatic voltage regulation of a synchronous generator. The method explored deals with the use of binary input-output fuzzy associative memories for control. Error and rate of change of voltage are used to maintain a constant output voltage. Software routines were written in the 'C' language and were fast enough for real time computer control. The fuzzy controller was implemented in an IBM compatible personal computer to control an industrial size 5 kVA synchronous machine. >