Showing papers in "IEEE Transactions on Energy Conversion in 1991"

Analysis of a concentrated winding induction machine for adjustable speed drive applications. I. Motor analysis

Abstract: The performance of multiphase machines designed for operation with static power converters is investigated. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Equations which define the transient as well as steady-state behavior, including the computation of all machine inductances, are derived. In deriving these equations the space harmonics are specifically included. Equations for calculation of terminal voltages and electromagnetic torque are modified to account for nonsinusoidal air-gap-flux distributions. A conventional three-phase induction motor including the effect of space harmonics is simulated. >

Identification and control of a DC motor using back-propagation neural networks

Abstract: An artificial-neural-network (ANN)-based high-performance speed-control system for a DC motor is introduced. The rotor speed of the DC motor can be made to follow an arbitrarily selected trajectory. The purpose is to achieve accurate trajectory control of the speed, especially when motor and load parameters are unknown. The unknown nonlinear dynamics of the motor and the load are captured by the ANN. The trained neural-network identifier is combined with a desired reference model to achieve trajectory control of speed. The performances of the identification and control algorithms are evaluated by simulating them on a typical DC motor model. It is shown that a DC motor can be successfully controlled using an ANN. >

Analysis of a concentrated winding induction machine for adjustable speed drive applications. II. Motor design and performance

Abstract: For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating. >

Disturbance observer-based motion control of direct drive motors

Abstract: Simple and high-performance path tracking control and force control based on an acceleration control are proposed. To realize the acceleration control, disturbance feedback is necessary. The disturbance observer whose inputs are a current reference to the power converter and a position signal by simple computation works as if it were a disturbance detector. The control poles of the observer are varied in accordance with the velocity of the motor for precise positioning. The proposed method was applied to the linear synchronous motor, which is used for direct drive linear motor, and was tested. Results are presented. >

Tuning of power system stabilizers using an artificial neural network

Abstract: A new approach using an artificial neural network is proposed to adapt power system stabilizer (PSS) parameters in real time. A pair of online measurements i.e., generator real-power output and power factor which are representative of the generator's operating condition, are chosen as the input signals to the neural net. The outputs of the neural net are the desired PSS parameters. The neural net, once trained by a set of input-output patterns in the training set, can yield proper PSS parameters under any generator loading condition. Digital simulations of a synchronous machine subject to a major disturbance of a three-phase fault under different operating conditions are performed to demonstrate the effectiveness of the proposed neural network. >

A fuzzy logic based stabilizer for a synchronous machine

Abstract: The application of a fuzzy logic controller to improve the stability of electric power systems is presented. The stabilizing signal is computed using the standard fuzzy membership function depending on the speed acceleration state of the generator in the phase plane. The required measurement is the speed deviation over two samples. The effectiveness of the proposed stabilizer is demonstrated by simulation studies for different operating conditions and disturbances. >

Two-axis model development of cage-rotor brushless doubly-fed machines

Abstract: A two-axis model of a cage-rotor brushless doubly-fed machine (BDFM) which is suitable for machine and BDFM drive system dynamics studies is presented. The technique enables the two-axis model to be derived from a detailed model recently developed for investigation of design aspects of the machine. Unlike the conventional approaches to self-cascaded machines analysis, this method permits analysis of the machine characteristics in both dynamic and steady state conditions, and also facilitates machine and drive system design by directly correlating machine performance with machine structure and parameters. The approach allows the machine parameters to be calculated from machine geometry and developed into the model parameters. >

An approach to assess the performance of utility-interactive wind electric conversion systems

Abstract: A probabilistic approach based on the convolution technique is presented to assess the performance of utility-interactive wind electric conversion systems supplying tools. The wind regime is modeled using a Weibull distribution. Expressions are developed to obtain the duration curve for the power injected into the utility grid. The energy injected into the grid and drawn from it to supply the load during the study period can be calculated from this duration curve. The load model employed enables the study period to range from one year to one particular hour-of-day, thus allowing the inclusion of the time-value of energy as appropriate in economic assessments. >

Methodology for on-line incipient fault detection in single-phase squirrel-cage induction motors using artificial neural networks

Abstract: A novel approach for online detection of incipient faults in single-phase squirrel-cage induction motors through the use of artificial neural networks is presented. The online incipient fault detector is composed of two parts: (1) a disturbance and noise filter artificial neural network to filter out the transient measurements while retaining the steady-state measurements, and (2) a high-order incipient fault detection artificial neural network to detect incipient faults in single-phase squirrel-cage induction motors based on data collected from the motor. Simulation results show that neural networks yield satisfactory performance for online detection of incipient faults in single-phase squirrel-cage induction motors. The neural network fault detection methodology presented is not limited to single-phase squirrel-cage motors (used as a prototype), but can also be applied to many other types of rotating machines, with the appropriate modifications. >

Dynamics and stability of wind and diesel turbine generators with superconducting magnetic energy storage unit on an isolated power system

Abstract: Dynamic system analysis is carried out on an isolated electric power system consisting of a diesel generator and a wind-turbine generator. The 150 kW wind turbine is operated in parallel with a diesel generator to serve an average load of 350 kW. A comprehensive digital computer model of the interconnected power system including the diesel and wind-power dynamics with a superconducting magnetic energy storage (SMES) unit is developed. Time-domain solutions are used to study the performance of the power system and control logic. Based on a linear model of the system, it is shown that changes in control-system settings could be made to improve damping and optimization of gain parameters and stability studies are done using the Lyapunov technique and eigenvalue analysis. The effect of introducing the SMES unit for improvement of stability and system dynamic response is studied. >

An adaptive control scheme for speed control of diesel driven power-plants

Abstract: The performance of an incremental Clarke-Gawthrop adaptive control scheme, suitable for a diesel-engine prime mover, is described. The controller uses a predictor that is derived from explicit estimates of the plant deadtime and time constants. Its performance under speed reference changes and load disturbances has been compared to that of a fixed, tuned proportional-integral (PI) controller. The algorithm is found to operate satisfactorily under different values of droop without any additional complexity of computation being incurred. However, the improvement in plant response due to the adaptive algorithm is somewhat reduced at high droops. The effective improvement due to adaptation is also seen to be reduced under 'cold oil' conditions. However, even under such conditions, it is possible to obtain improved response as compared to the PI controller. >

Multivariable generalized predictive control of a boiler system

Abstract: An application of a multiloop generalized predictive control (GPC) scheme to achieve self-tuning control of superheat pressure and steam temperatures in a 200 MW power station drum boiler are presented. Controllers have been designed and evaluated using a detailed nonlinear boiler model which is well established and validated. Results illustrating the performance of the plant with GPC are presented and compared with conventional PI control. The results show that substantial improvements in control can be achieved with the GPC. Steam pressure and temperature variations are greatly reduced, without offsets, and with less controller activity. >

The analysis of a saturated self-excited asynchronous generator

Abstract: The theory of saturated smooth-air-gap machines is applied to the analysis of the transient performance of a self-excited induction generator. Performance equations for this machine are given which utilize the saturated magnetizing inductance L/sub m/= mod psi /sub m/ mod / mod i/sub m/ mod and its derivative dL/sub m//d mod i/sub m/ mod , where psi /sub m/ and i/sub m/ are vectors. The self-excitation process, the switching in of a purely resistive load and of a load with resistors in series with capacitors are studied. Measured results are compared with those computed from the performance equations, and the two are shown to be in good agreement. >

Transient state analysis of a doubly-fed induction generator under three phase short circuit

Abstract: The doubly fed induction generator (DFG) is a variable-speed constant-frequency generator operating in either subsynchronous or supersynchronous mode. The transient behavior of a symmetrically loaded DFG after a three-phase short circuit is presented. Both speed and rotor excitation voltage and frequency remain unchanged during short circuit. The complete mathematical model of the transient state and experimental results are given, along with the transient state equivalent circuit. >

Structural modeling of small and large induction machines using integral manifolds

Abstract: Structural dynamics of small and large induction machines are investigated using integral manifolds and are shown to be markedly different. Whereas the dominant behavior in small machines is characterized by a well-known first-order speed model, the corresponding behavior in large machines is characterized by a novel first-order voltage model. Nonlinear simulations and eigenvalue analyses illustrate the validity of the structural models developed. >

A new sensor for detecting partial discharges in operating turbine generators

Abstract: A partial discharge (PD) sensor has been developed which is able to unequivocally differentiate between PD in the winding and all types of electrical interference. Thus, the sensor will permit an online test for turbine generators, similar to the test now used for hyrogenerators. The sensor requires no high-voltage connection to the winding, and is easily installed in the stator slot, underneath the wedges. Noise is differentiated from PD by the shapes of the electrical pulses from the sensor. The sensor, called the Stator Slot Coupler (SSC), is essentially a directional electromagnetic coupler. Calculations as well as laboratory tests indicate that the couplers can easily survive the electrical, thermal, magnetic, and mechanical stresses in the generator. >

A contribution to the simulation and design optimization of photovoltaic systems

Abstract: Guidelines for the proper selection of solar array and battery sizes for use in photovoltaic-powered dispersed systems located far from public power networks are presented. The choice of key design parameters of separately excited DC motors used for farm irrigation is addressed. The selection procedure is based on accurate system modeling and annual simulation using actual meteorological and typical load data. The procedure determines the useful, dumped, and commercial energy components forced by system-load interaction. Two systems are investigated. System one is an AC residential load of a given annual demand profile on hourly basis, while system two represents an irrigation set-up featuring a DC motor and a battery back-up. The results show that a properly sized battery interface would enhance the performance of the irrigation system by more than 12% compared to the directly coupled case. >

Dynamic simulation of brushless doubly-fed machines

Abstract: Dynamic and steady-state models for the simulation of the performance of experimental brushless doubly-fed machines (BDFM) are presented. The dynamic simulation results are obtained using a two-axis representation which has been developed from a detailed machine design model. In turn, it is shown that several forms of steady-state equivalent circuit can be developed from the two-axis model for different specific modes of operation. Test data in dynamic conditions are compared with the predictions given by the two-axis model. It is concluded that these simplified models will provide adequate representation of full performance for control, stability, and scoping studies. >

Application of superconducting magnetic energy storage unit to improve the damping of synchronous generator

Abstract: A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions. >

Power conditioning systems for superconductive magnetic energy storage

Abstract: Two power conditioning systems for superconductive magnetic energy storage (SMES) are presented. One power conditioning system is based on a hybrid current sourced inverter (CSI), the second is a combination of a DC chopper with a voltage sourced inverter (VSI). Both of these systems have independent control of real and reactive power. These systems have a significant reduction in MVA rating levels as related to the more traditional Graetz bridge. >

Dynamic matrix based control of fossil power plants

Abstract: Theoretical, technical, and practical aspects of the identification and use of dynamic matrices in supervisory control for different types of fossil power plants are discussed. The control structures for once-through and drum boilers are reviewed, and modifications necessary for conversion to matrix base controls are discussed. The control of dynamic, nonlinear models that replicate the response to actual plants is demonstrated. A lecture series and support system of analytical tools for use on personal computers to transfer the technology from its roots in the process industries to fossil power plants are described. >

A thermal cycling type test for generator stator winding insulation

Abstract: A test has been designed and implemented which cycles the temperature between 40 degrees C and 150 degrees C in about 80 min by the use of circulating currents and cooling air. The test has been successfully used to evaluate the relative performance of similar stator bars made by three different manufacturers. The thermal cycling test was able to duplicate the insulation delamination process and presumably those insulation systems which performed well in the thermal cycling test could last longer in service. In addition to being used for pumped-storage generators, the thermal cycling test may be useful to evaluate the insulation system in combustion turbine generators. >

Dynamic response of power conditioning systems for superconductive magnetic energy storage

Abstract: The dynamic response of two power conditioning systems for superconductive magnetic energy storage (SMES) are presented. One power conditioning system is based on a hybrid current sourced inverter (CSI), the second is a combination of a DC chopper with a voltage sourced inverter (VSI). The response of both systems to a load change, a three phase fault, and start-up is presented. >

Optimal design parameters for a PV array coupled to a DC motor via a DC-DC transformer

Abstract: A study is presented of the optimal operating parameters of a system comprising a photovoltaic solar array and a DC electromechanical energy converter (motor) driving a mechanical load. The analysis and design procedure includes the addition of a variable DC-DC matching transformer placed between the array and the motor. It is responsible for adjusting the load curve seen by the array to coincide with its maximum power point. The model takes into consideration the effect of different temperature as well as isolation profiles along the year. The analysis procedure guides the design of DC motors as well as variable DC transformers especially suited to be operated in conjunction with PV arrays. The procedure determines optimal motor constants which lead to an improved overall design in terms of maximizing the total annual gross mechanical energy delivered to a load of a given torque-speed characteristic. >

Analysis of the waveform-detection technique for indirect roto-position sensing of switched reluctance motor drives

Abstract: A sensing technique that monitors rotor-position indirectly by monitoring the phase current waveform is evaluated. Computer simulations showing the effects of back-EMF on phase current rise and fall-times are presented. A control circuit for current-waveform-based rotor-position detection has been implemented using hard-wired digital circuits. Torque-speed and system efficiency characteristics resulting from the application of the method to a 4 kW, four-phase SR motor with IGBT drive are also presented. >

AN improved method of optimization for electrical machines

Abstract: Methods of optimizing the design of electrical machines are discussed. The augmented Lagrangian multiplier method is described, and an algorithm for this method is introduced. The method is compared with the more familiar exterior penalty function method using, as an example, the cost optimization of permanent magnetic variable-speed drive motors. The improved method is shown to be superior, both in its ability to reach an optimum consistently and in the number of required iterations. >

Magnet shaping to reduce induced voltage harmonics in PM machines with surface mounted magnets

Abstract: A simple methodology for reducing induced voltage harmonics in permanent magnet (PM) machines by selecting the appropriate magnet shape and dimensions is presented. The method, which uses a simplified analytical model of the magnetic circuit, is applied to three basic magnet shapes (rectangular, stepped, and trapezoidal), and can be extended to more complex geometries. The results of the analytical models are compared with results obtained from finite element analysis and with test results. >

Synthesis of squirrel cage motors: a key to optimization

Abstract: A method of synthesis, which is a procedure to arrive at a motor of given specifications, is presented. In practice synthesis is followed by an optimization procedure. To illustrate the technique, a motor is synthesized with only one constraint, and more constraints are added, with the conclusion drawn that an optimization procedure is obvious when a synthesis procedure is well defined. It is shown that numerical information may be easily dispensed with and that fuzzy information is essential. The optimization problem is naturally unconstrained without resorting to complex transformation, penalty factors, or approximations by polynomials. It can be easily modified, according to specific needs, by anyone who has a reasonable knowledge of induction machine theory and some common sense; however, no previous experience in design is needed. As for optimization techniques, only the simplest and most obvious one, dichotomy, should be known. An important aspect of the method is that constraints are given in terms of equalities, not of inequalities. >

Multivariable self-tuning power system stabilizer simulation and implementation studies

Abstract: A multi-input multi-output (MIMO) adaptive power system stabilizer which damps dynamic oscillations is presented. The single-input single-output (SISO) pole-shifting adaptive control algorithm is used as the basis. Its extension to the MIMO controller combines and coordinates the stabilizing contributions from both the excitation and governor systems. The advantage of the adaptive feature is that it can track the operating conditions and system structure changes. The proposed stabilizer can be used with hydro and turbogenerators. Computer simulation results show that the adaptive stabilizer improves the damping of power system oscillations. >

A least-squares based model-fitting identification technique for diesel prime-movers with unknown dead-time

Abstract: The recursive least-squares estimation technique is extended for application to systems with small but unknown dead-time delays. This problem is studied with particular reference to when the diesel engine is used as a prime-mover, in which case the dead-time leads to a significant variation in dynamic performance. In practice, least-squares estimators are found to have slow convergence and large output errors, when applied to systems with time-delays. It is shown that by a suitably constrained algorithm, convergence can be quickened and output error can be kept within acceptable limits. Low-order system models with changing dead-time are in general, characterized by modeling errors that are to an extent correlated with the input control signal to the plant. Despite this fact, the developed approach yields very small prediction errors, even when large deterministic disturbances are present. This suggests its possible use in conjunction with adaptive controllers of various types. >