Showing papers in "IEEE Transactions on Energy Conversion in 1993"

Branch-and-bound scheduling for thermal generating units

Abstract: A branch-and-bound method for scheduling thermal generating units is presented. The decision variables are the start and stop times and the generation levels of the units. A simple rule is defined to compute the lower bound of each candidate schedule for interim computation usage, and the branching process takes place on the subschedule with the lowest lower bound. The heap data storage structure and space saving encoded data representations for partially fulfilled unit commitment schedules are utilized to facilitate the branch-and-bound procedure. By successive branching and bounding, the unit commitment schedule with the minimum cost can be obtained. Two examples, a 10 unit, 24 h and a 20 unit, 36 h case, are shown to illustrate the effectiveness of the proposed algorithm. >

Battery energy storage for frequency regulation in an island power system

Abstract: Large battery energy storage (BES) facilities may provide significant dynamic operation benefits for electric utilities. One area in which a BES facility could be useful is the frequency regulation requirement. This feature is significantly important for island power systems. The purpose of this paper is to quantify the effects of a 30 MW battery on the frequency regulation in the Israeli isolated power system. The study was performed on a single area model representing the whole power system and containing a first order transfer function that represented the BES performance. >

Control by variable rotor speed of a fixed-pitch wind turbine operating in a wide speed range

Abstract: Variable rotor speed control of a fixed-pitch wind turbine is investigated on a system consisting of a wind turbine which can operate in a wide speed range, from 0 to 38 RPM. It produces any desired output from the rated (20 kW) to no-load, providing there is enough wind. A special technique is used to determine the operating point of the wind turbine by using the measured rotor speed and power. A difficult problem with this type of wind turbine control is to make the upper speed limit reasonably high to capture as much energy as possible but still low enough to avoid power peaks. >

Capacitance requirements of self-excited induction generators

Abstract: A simple method for computing the minimum value of capacitance, C min. required for initiating voltage build-up in a three-phase self-excited induction generator (SEIG) is presented. Based on the steady-state equivalent circuit model, a consideration of the circuit conductances yields a sixth-degree polynomial in the per-unit frequency. The polynomial can be solved for real roots, which enables the value of C/sub min/ to be calculated. Critical values of load impedance and speed, below which the machine fails to self-excite irrespective of the capacitance used, are found to exist. Closed form solutions for C/sub min/ are derived for no-load and inductive loads. Using the same numerical approach, an interative procedure is developed for predicting the capacitance required for maintaining the terminal voltage at a preset value when the generator is supplying load. Experimental results obtained on a 2 kW induction machine confirm the feasibility and accuracy of the proposed methods. >

An artificial neural network based adaptive power system stabilizer

Abstract: An artificial neural network (ANN)-based power system stabilizer (PSS) and its application to power systems are presented. The ANN-based PSS combines the advantages of self-optimizing pole shifting adaptive control strategy and the quick response of ANN to introduce a new generation PSS. A popular type of ANN, the multilayer perceptron with error backpropagation training method, is used in this PSS. The ANN was trained by the training data group generated by the adaptive power system stabilizer (APSS). During the training, the ANN was required to memorize and simulate the control strategy of APSS until the differences were within the specified criteria. Results show that the proposed ANN-based PSS can provide good damping of the power system over a wide operating range and significantly improve the dynamic performance of the system. >

Modeling of emergency diesel generators in an 800 megawatt nuclear power plant

Abstract: Computer models have been developed of emergency diesel generators and their associated emergency core cooling system induction motors during sequencing and results compared with field tests. Models required to perform studies of emergency diesel generators in a nuclear plant are presented. Field measurements indicating different response of two seemingly identical generator excitation systems are discussed. Results of 480 volt AC contactor dropout testing are provided for determining voltage limits in the 480 volt system during motor starting transients. >

Analysis and average-value modeling of line-commutated converter-synchronous machine systems

Abstract: Analytical relationships are established which can be used to predict the steady-state characteristics of line-commutated AC-DC-converter-synchronous machine systems. In particular, basic relationships are established in which the average DC voltage and the average electromagnetic torque are related to the converter firing delay angle. It is shown that these average-value relationships predict the steady-state performance with significantly higher accuracy than the classical converter average-value equations in which the d-axis subtransient reactance is used as the commutating reactance. >

An adaptive power system stabilizer based on the self-optimizing pole shifting control strategy

Abstract: An adaptive power system stabilizer (APSS) employing a new self-optimizing pole shifting control strategy and its application to a power system are described in this paper. Based on an identified model of the system, the control is computed by an algorithm which shifts the closed-loop poles of the system to some optimal locations inside the unit circle in the z-domain to minimize a given performance criterion. With the self-optimization property, outside intervention in the controller design procedure is minimized, thus simplifying the tuning procedure during commissioning. Also, a new method of calculating the variable forgetting factor in real-time parameter identification is discussed. Studies show that the proposed APSS can provide good damping of the power system over a wide operating range and significantly improve the dynamic performance of the system. >

A novel self-induced self-regulated single phase induction generator. I. Basic system and theory

Abstract: This paper describes a newly developed single phase capacitor self excited induction generator with self regulating features, suitable for oil engine driven portable gen-sets for autonomous/standby power generation. The system is also suitable for microhydel and wind energy systems. The generator has two specially designed stator windings in quadrature, connected externally to a shunt and a series capacitor respectively. It employs a standard die-cast squirrel cage rotor. Special features, advantages and theoretical concepts of the system are highlighted. >

An on-line method to detect incipient failure of turn insulation in random-wound motors

Abstract: Induction motors used in various mining industry applications fail frequently because they are subjected to severe operating conditions. Periodic test procedures are inappropriate for many installations and the cramped and hazardous mining environment makes unscheduled motor replacements difficult and time-consuming to perform. An online detector of insulation degradation is proposed and demonstrated analytically and experimentally. This detector, termed the effective negative-sequence impedance, is computed from the voltage and current phasors at the motor terminals. It can be used frequently, even continuously, and does not interfere with normal motor operation. With this detector, motor replacements can be scheduled, thereby reducing production downtime associated with emergency maintenance actions. >

A trajectory sensitivity method for the identification of nonlinear excitation system models

Abstract: A sensitivity method for identifying parameters of nonlinear synchronous generator models is proposed and applied to the identification of the parameters of IEEE type ST3 and DC1 models. The method generates the sensitivities directly from the nonlinear model and does not require linearization. The use of singular values and singular vectors to detect the identifiability of parameters is discussed. The identification of the parameters requires, in general, very few iterations. The presence of noise in data reduces the identifiability of the parameters. However, reasonable approximations can be obtained if the parameters to be identified are chosen carefully. >

Pipe crawling inspection robots: an overview

Abstract: Pipe crawling inspection robots (PCIRs) are playing an important and expanding role in remote testing and inspection of 4 in. to 8 ft. diameter pipes. PCIRs provide the power, process and pulp industries with an economical and time-saving approach to inspection of insulated, buried or inaccessible pipes. Three locomotive mechanisms of PCIRs, commonly-employed nondestructive testing (NDT) sensors and techniques, as well as field deployments are discussed in this paper. >

Performance of single phase induction generators

Abstract: The paper describes the performance of an isolated self-excited single phase induction generator when the excitation capacitor is connected to one winding and the load is connected to the other. Depending upon the equivalent circuit, nonlinear simultaneous equations of the magnetisation reactance and operation frequency, have been used for computer simulation of the two cases. Newton Rhapson numerical methods have been found suitable for the solution of the equations. Computer results have been supported by laboratory tests. The models have been used to study the effect of machine parameters on the general performance of the machine. >

A step towards improvements in the characteristics of self excited induction generator

Abstract: Improvements of voltage regulation characteristics of self-excited induction generators (SEIGs) are investigated. Typical results of the sensitivity studies performed are presented and conclusions are drawn to suggest guidelines for design of such generators. >

Aspects of design optimisation for switched reluctance motors

Abstract: Existing papers about suitable switched reluctance motor (SRM) airgap dimensions, which give optimum performance for doubly-salient structure motors, are reviewed and their deficiencies are mentioned. The recommendations of these papers cover a wide range of t/ lambda (tooth width/tooth pitch), which can optimise the performance of the SRM. Although some parts of these results are supported by the present work, some other parts may not be correct. A developed software package has been applied to the design of a single-tooth peg stator pole SRM. It is concluded that the optimum ratio of t/ lambda is between 0.33 and 0.40. Using the design constraints considered, the optimum split ratios (defined as the ratio of rotor diameter to stator outer core diameter) are estimated at between 0.57 and 0.63. The ratio between the back of core width and half of tooth width in the motor is estimated and it is found that the best range of this ratio is from 1.1 to 1.3. >

A technique for the steady-state analysis of a self-excited induction generator with variable speed

Abstract: A method to analyze the steady-state open loop behaviour of a self-excited induction generator with an unregulated prime mover is presented. The proposed method needs little mathematical effort and does not require an assumption about the generator speed. The proposed approach based on nodal analysis allows one to use arbitrary functions for the torque-speed characteristic of the prime mover and for the saturation of the magnetizing inductance without complicating the solution process. It always leads to a single equation for the frequency. An example is presented demonstrating the advantages of the proposed method. The analytical results are verified by measurements. >

Determination of the parameters representing the cross-magnetizing effect in saturated synchronous machines

Abstract: This paper introduces the concept of the cross-magnetizing phenomenon in saturated synchronous machines (the magnetic coupling between the direct and quadrature-axis). The parameters which represent this cross-magnetizing effect are defined and techniques for determining these parameters are proposed. In these techniques, there is no need for an auxiliary winding in the q-axis of the machine and, thus, they can be applied to conventional synchronous machines. Experimental results which verify the accuracy of these techniques are presented. >

Optimization of load shedding system

Abstract: An optimization algorithm is presented for an underfrequency load shedding system which is composed of several stages that are tripped at preset frequencies. The optimization of this system is considered with respect to a cost function that includes a dynamic part, which is the integral of the deviation from nominal frequency, and a static part which is the total load shedding. The optimization is constrained by the requirement of minimum allowed frequency and limitation on the total load of the shedding system. A projected gradient method is used for the solution, and analytic expressions for the partial derivatives are used to simplify the computation. Results of applying the optimization to a model of the Israeli power system are given together with a study of the cost parameters. >

Determination of the model parameters of machines from the reactance operators x/sub d/(p), x/sub q/(p) (evaluation of standstill frequency response test)

Abstract: A method is presented for determining the characteristic quantities and model parameters from the given frequency responses x/sub d/(js), x/sub q/(js). The curves of values measured on a large turbogenerator at standstill are used as an example. The characteristic values and model parameters are determined for various models (with four, three, and two rotor circuits in each axis) and are compared with the results of short-circuit tests and with advanced calculations. >

Laboratory implementation of a neural network trajectory controller for a DC motor

Abstract: The laboratory implementation of a neural network controller for high performance DC drives is described. The objective is to control the rotor speed and/or position to follow an arbitrarily selected trajectory at all times. The control strategy is based on indirect model reference adaptive control (MRAC). The motor characteristics are explicitly identified through a multilayer perceptron type neural network. The output of the trained neural network is used to drive the motor in order to achieve a desired time trajectory of the controlled variable. The neural network controller is assembled in a commercially available PC-based real-time control system shell, using software subroutines. An H-bridge, DC/DC voltage converter is interfaced with the computer to generate the specified terminal voltage sequences for driving the motor. All software and hardware components are off the shelf. The versatility of the motor/controller arrangement is displayed through real-time plots of the controlled states. >

Starting characteristics of direct current motors powered by solar cells

Abstract: The authors deal with the calculation of the starting to rated current ratio and starting to rated torque ratio of the permanent magnet, separately, series and shunt excited motors when powered by solar cells for the two cases where the system includes a maximum-power-point-tracker (MPPT), and without an MPPT. Comparing these two cases, one gets a torque magnification of about three for the permanent magnet motor and about seven for other motor types at rated design insolation. The calculation of the torques may assist the photovoltaic system designer to determine the advantage of including an MPPT in the system as far as the starting characteristics of the DC motors are concerned. >

Modelling of alternating-current machines having multiple rotor circuits

Abstract: The modeling of a synchronous or an asynchronous machine forms the basis of simulation investigations made with high-powered computers Many phenomena and processes require corresponding refinement of the models used, and an increase in input in the form of fictive rotor circuits A method is presented which has been tested out over a relatively long period of time The general equations contain none of the usual approximations, and can be programmed quite readily Numerical examples are given as an aid in applying the procedures >

Application of fuzzy logic in the speed control of AC servo system and an intelligent inverter

Abstract: A fuzzy logic controller for use in the fully digital speed control of AC servomotor systems is presented. An intelligent inverter is also proposed to reduce the switching loss and the current harmonics in induction motors. A 16 bit single-chip microprocessor is used to reduce the number of circuit components for cost reduction and reliability enhancement. In order to facilitate the instantaneous control of motor torque, indirect field orientation is adopted along with a current-regulated pulse-width-modulation voltage-source inverter. A computer simulation for assessing the feasibility of the system proposed is described. Circuit design and software development are then undertaken. Simulation results are verified experimentally. >

Tidal energy: promising projects: La Rance, a successful industrial-scale experiment

Abstract: In some few special areas of the world, the range of the variation of the sea level due to the tide can be impressive. For centuries man has been harnessing this energy with the operation of tidal mills. At present, the design of tidal power does not present new scientific issues. Nevertheless, additional research and development should be carried out in three fields: interface of the tidal power station output with National Grids and above all a sound assessment of its economic interest; design and implementation of work according to the site; and environmental effects. On November 26, 1966, the La Rance tidal power station was inaugurated after 25 years of design in various fields, and 25 years afterwards it is still the only industrial prototype of a large size tidal power station. Currently several important schemes are also under study throughout the world. >

Optimal capacity of the battery energy storage system in a power system

Abstract: This paper investigates the optimal capacity of a battery energy storage system in a power system. The Taiwan Power Company System is used as an example system to test this algorithm. Results show that the maximum economic benefit of battery energy storage in a power system can be achieved by this algorithm. >

A novel self-exited self-regulated single phase induction generator. II. Experimental investigation

Abstract: Part I of this paper presents the basic system, theoretical modelling and typical test results of a novel self-excited self regulated induction generator. In this part, the results of a detailed experimental investigation are presented to assess its suitability for practical applications. The steady state performance of the self-excited single phase induction generator, maintaining the terminal voltage within a close range is investigated under realistic loading conditions in the laboratory. Detailed experimental results are presented and discussed. Necessary tests to obtain machine parameters for theoretical modelling are also developed and relevant results of the prototype presented. The effects of series and shunt capacitors, prime mover speed, load and load power factor are investigated. It has been shown to exhibit a better voltage waveform as compared to commercially available sets. The experimental results confirm that this new generating system can be favourably employed for use as a small portable generator driven by nearly constant speed prime movers such as oil engines or hydro turbines. >

Application of simultaneous active and reactive power modulation of superconducting magnetic energy storage unit to damp turbine-generator subsynchronous oscillations

Abstract: An active and reactive power (P-Q) simultaneous control scheme, which is based on a superconducting magnetic energy storage (SMES) unit, is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is used to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions. >

Analysis and average-value modeling of dual line-commutated converter-6-phase synchronous machine systems

Abstract: Analytical relationships are established which can be used to predict the average value characteristics of a dual line-commutated power converter/6-phase synchronous machine system. In particular, basic relationships are established in which the average DC power converter voltages and the average q- and d-axis stator currents are related to the power converter firing delay angles. These relationships should be useful in the design and average value simulation of dual line-commutated power converter/6-phase synchronous machine systems. >

A probabilistic method for the evaluation of the performance and the reliability of wind-diesel energy systems

Abstract: A probabilistic method for the evaluation of the performance and the reliability of wind-diesel energy systems with constrained wind generation is presented. The method computes the expected annual wind and diesel energy production as well as the system loss of load probability and expected unserved energy by processing the statistics of the wind speed and the system load demand. The performance of the method is demonstrated with computational results. >

An approach to assess the performance of utility-interactive photovoltaic systems

Abstract: A probabilistic approach based on the convolution technique for assessing the performance of utility-interactive photovoltaic systems supplying loads is presented. Analytical 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. >