Showing papers in "Electric Machines and Power Systems in 1991"
TL;DR: In this article, it was shown that substantial improvements can be made in the design of such motor drives resulting in performance characteristics which match or even exceed that of the induction machine, based on the analysis presented in this paper.
Abstract: Although design of the variable reluctance (switched reluctance( type of synchronous machine has experienced intense activity in recent years, relatively little effort has been expended on improving the torque capability of the synchronous reluctance type of motor drive. Based on the analysis presented in this paper, it appears that substantial improvements can be made in the design of such motor drives resulting in performance characteristics which match or, indeed, perhaps even exceed that of the induction machine.
321 citations
TL;DR: In this article, a variable speed doubly-fed reluctance machine with two sets of sinusoidally distributed windings having pole numbers P1 and P2 is described and the model for the analysis of the machine is presented.
Abstract: The paper describes a new type of variable speed doubly-fed reluctance machine and presents the model for the analysis of the machine. The stator of the machine is equipped with two sets of sinusoidally distributed windings having pole numbers P1 and P2. The rotor consists of simple saliencies of pole number Pr, which is shown to be constrained to particular values by P1 and P2. A d-q-n model and equivalent circuit is developed for this machine. Simulation results using the new model show that this machine can have the advantages of doubly-fed wound-rotor machine while eliminating the complicated wound rotor, brushes and slip rings normally associated with doubly fed machines.
116 citations
TL;DR: In this article, a class of multiphase electric machines with axially laminated anisotropic (ALA) rotors is presented, and the reluctance variation in ALA rotor is computed for a wide range of airgaps and pole pitches.
Abstract: This paper presents a class of multiphase electric machines with axially laminated anisotropic (ALA( passive rotors. Unipolar, two-level bipolar, and sinusoidal current modes are identified. The reluctance variation in ALA rotor is computed for a wide range of airgaps and pole pitches. High ratios of inductances along d and q axes yield high torque densities. Special attention is paid to the sinusoidal current mode through a quantitative comparison with the induction and PM synchronous counterparts with the same stator. It is demonstrated that the ALA rotor sinusoidal current synchronous motor is superior in all respects to the induction motor and almost equals the performance (torque density, efficiency, power factor( the PM synchronous motor.
50 citations
TL;DR: In this paper, the authors use the hybrid method which involves integration of the system equations only once till the controlling u.p is reached to compute the energy margin and then rescheduling is done through an OPF algorithm resulting in a secure but optimal solution.
Abstract: Just as in static security constrained optimization of power systems, there is need to do preventive scheduling if the system state is found to be insecure through dynamic contingency analysis. Current work in this area based on energy functions and sensitivity considerations only computes another feasible and normal operating point either through the controlling u.e.p or the potential energy boundary surface method. In this paper we use the hybrid method which involves integration of the system equations only once till the controlling u.e.p is reached to compute the energy margin. Based on the sensitivity of the energy margin to generation powers, rescheduling is done through an OPF algorithm resulting in a secure but optimal solution. Results on a 3 machine, 9 bus system are very encouraging. This methodology could form a basis for integrating current OPF packages into the DSA package.
35 citations
TL;DR: In this article, a torque vector control (TVC) system was proposed for axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs), which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter.
Abstract: Axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs) have been proved recently capable of higher torque density, higher power factor and efficiency compared to their induction motor counterpart with the same stator. Vector current control systems have been proposed for such drives, based on maximum available torque constant current angle or minimum current for a given torque constant current angle or combined current-voltage control. In an effort to do away with the current controller limitations, especially in the high speed region, the paper proposes a torque vector control (TVC) system which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter. A sliding mode speed controller is added. Extensive digital simulations are presented. They demonstrate the TVC fast response, wide speed range and load rejection performance.
24 citations
TL;DR: A review of the existing techniques for schduling the power generation in an electric power system which consists of various types of generating units is provided in this article. But the focus of this paper is on the economic aspects of power generation scheduling.
Abstract: As the size of an electric power system grows, the economic significance of power generation scheduling becomes more and more apparent. A proper schedule for the generation of electricity will also ensure the reliability of a power system and extend the operational lives of its constituent units. This paper provides a review of the existing techniques for schduling the power generation in an electric power system which consists of various types of generating units. First, power generation scheduling problem will be presented and its economic importance will be discussed. Then, the application of different techniques such as Priority Lists Scheme, Dynamic Programming, Mixed Interger Programming, Benders’ Decomposition and Lagrangian Relaxation in solving this problem will be described. Also, computational advantages and shortcomings of each technique will be discussed. Finally, our experience in advancing the state-of-art, and improving the scheduling process for a large power system will be prese...
19 citations
TL;DR: A piecewise linear model of the magnetic characteristics of a switched-reluctance motor is formulated and the procedure to evaluate the model parameters is illustrated in this article, where the torque position and average torque equations of the motor are calculated and expressed in a normalized form.
Abstract: A novel piecewise linear model of the magnetic characteristics of a switched-reluctance motor is formulated and the procedure to evaluate the model parameters is illustrated. On the basis of the model, the torque-position and average torque equations of the motor are calculated and expressed in a normalized form. A significant figure related to the motor performance is then introduced and discussed. The merit of the model over the existing ones in providing accurate results without complicating the analysis is pointed out.
16 citations
TL;DR: In this article, it was shown that, by adding some components to the classical circuit, eddy currents in windings can be taken into account, which enabled the above circuit to be justified and expressions for the supplementary components values.
Abstract: The precision of the classical equivalent circuit of a transformer is not sufficient for the software simulation of a high frequency power supply to be true. In this paper we show that, by adding some components to the classical circuit, eddy currents in windings can be taken into account. First, this modification was deduced from experimental results. Then, thanks to an homogeneous layer model, an analytical study was carried out. This enabled the above circuit to be justified and expressions to be derived for the supplementary components values. Finally, a more exact geometry was investigated thanks to an electromagnetic software simulation. The corresponding results agree well with analytical and experimental ones.
16 citations
TL;DR: In this article, a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines was presented, which used one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors.
Abstract: The paper presents a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines. The proposed arrangement is adapted to use one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors. Operational and steady-state equivalent circuits for both types are developed and used to predict the dynamic and steadystate behaviours under load conditions. This analysis depends mainly upon the computation of the power angle for a given machine parameters, capacitor ratings, and load conditions at a constant speed. Further, stability limits of both generators are investigated by developing the active-reactive power (P-Q) diagram for each generator. Conditions required to achieve self-excitation are also given. Performances of the two generator types are evaluated theoretically and experimentally.
15 citations
TL;DR: The proposed algorithm is superior to the well-known least error squares technique (LS) used in Ref. 1, when the voltage samples contain bad data or noise in instrumentation and telemetry.
Abstract: This paper presents a new efficient technique for estimating the voltage and frequency of power systems from digitized bus voltage samples. The new algorithm is based on the least absolute value error (LAV) approximation technique. The proposed algorithm is superior to the well-known least error squares technique (LS) used in Ref. 1, when the voltage samples contain bad data or noise in instrumentation and telemetry. The algorithm was tested on off-line simulated data. Results of the comparison between the least error squares technique and the new proposed algorithm are reported in this paper.
11 citations
TL;DR: This paper presents the application of a novel steady-state model of SFCIM to analyse a brushless, variable-speed constant-frequency generating scheme proposed for aircraft applications and the theoretical results obtained are compared with the experimental results.
Abstract: Brushless variable-speed constant-frequency generation finds its place in numerous situations such as aerospace and wind energy applications. In the past, cascade connected induction machines have been considered for aircraft applications due to their reliability compared to existing generating systems. The Single-Frame Cascaded Induction Machine (SFCIM) in variable-speed constant-frequency generating applications is a more favourable solution compared to a two machine system. This paper presents the application of a novel steady-state model of SFCIM to analyse a brushless, variable-speed constant-frequency generating scheme proposed for aircraft applications. The SFCIM considered in this paper consists of two independent stator windings and a rotor with a ‘multicircuit single-layer bar winding’ which is simple and robust. The theoretical results obtained using the new model are compared with the experimental results.
TL;DR: In this article, the steadystate torque and power factor capabilities and the transient performance of a vector ac current-controlled axially laminated anisotropic (ALA) rotor motor drive are investigated.
Abstract: It has been recently demonstrated that axially laminated anisotropic (ALA) rotor reluctance motors have high torque density, power factor and efficiency due to unusually high Ld/Lq ratios. For variable-speed vector-controlled drives no starting cage on the rotor is required. Through digital simulations this paper explores the steady-state torque and power factor capabilities and the transient performance of a vector ac current-controlled ALA-rotor motor drive. Fast torque and speed responses are demonstrated for a two-pole motor up to a speed of 2500 rpm. Good performance down to 0.1 rpm is obtained through an adaptive proportional integral (PI) speed controller.
TL;DR: In this article, a controller for delivering either constant power or maximum power from a wind-turbine-driven grid connected induction generator with double stator windings, one fixed and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described.
Abstract: A controller for delivering either constant power or maximum power from a wind-turbine-driven grid connected induction generator with double stator windings, one fixed and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. The load torque of the generator is controlled by varying the angular displacement between the two stators. The generator can feed power to the grid at variable speed and constant frequency and is termed a Tandem Induction Generator. Dynamic models for the wind energy conversion system are proposed for both controlled and uncontrolled operation to predict changes in shaft speed to shifts in wind speed using data pertaining to a commercial wind turbine. Results based on laboratory tests on a 1hp tandem machine driven by a dc motor demonstrating the feasibility of both controllers are presented. A steady state model of the tandem generator is also proposed and compared to measurements made on the test machine.
TL;DR: In this article, the authors proposed a simple method based on the no-load and short circuit test in order to get the useful machine parameters to adopt in equivalent circuit model for the losses evaluation.
Abstract: At present time, induction motors are widely supplied from several types of solid-state adjustable voltage-frequency controllers with a wide range of operating features. However, in any case, the motor has to be derated for the harmonic effects due to the non-sinusoidal nature of the supply voltage. The authors propose a simple method based on the no-load and short circuit test in order to get the useful machine parameters to adopt in equivalent circuit model for the losses evaluation. Complete experimental results are reported and the comparison between six-step and sinusoidal supplies are summarized.
TL;DR: In this article, a finite element method (FEM) analysis of a commercially available switched reluctance motor (SRM) supplied from its associated power electronic drive is presented, where the instantaneous current and torque waveforms are computed using the results of the FEM analysis with the numerical solution of the nonlinear differential equations describing the drive.
Abstract: This paper presents a finite element method (FEM) analysis of a commercially available switched reluctance motor (SRM) supplied from its associated power electronic drive. The instantaneous current and torque waveforms are computed using the results of the FEM analysis with the numerical solution of the nonlinear differential equations describing the drive. The effects of different machine parameters, speeds, applied voltages and stator winding voltage switching on and off instants are given. Experimental results compare very well with the results calculated by the method of analysis presented in the paper.
TL;DR: In this article, an optimal centralized controller capable of tracking these changes and controlling the nonlinear elements of the power system state vector is proposed, where the primary role played by voltage control and the need to represent the dynamics of the external system are shown from simulation case studies.
Abstract: Power system multiswing transient stability during a disturbance may be substantially improved through proper control of power system bus voltages. These bus voltages are normally nonlinear functions of state variables defined for the generators and their control elements. Postfault changes in the power system may also require a power system operating point different from the prefault value. An optimal centralized controller capable of tracking these changes and controlling the nonlinear elements of the power system state vector is proposed in this paper. The primary role played by voltage control and the need to represent the dynamics of the external system are shown from the results of simulation case studies.
TL;DR: In this paper, the authors presented a solution to an optimal three-phase compensator for power factor correction and load balancing in case where a nonsinusoidal voltage source is feeding a linear unbalanced load.
Abstract: This paper presents a solution to an optimal three-phase compensator for power factor correction and load balancing in case where a nonsinusoidal voltage source is feeding a linear unbalanced load. An objective function which consists of energy loss and compensator cost with load balancing constraints is formulated. A numerical algorithm that converges directly to the global solution to the problem is proposed. Results of special cases found in the literature are derived from simplifications of the general case considered. Simulation results show that optimal compensation found by neglecting harmonic components may lead to severe resonance problems.
TL;DR: In this paper, a model equation for accurate representation of magnetising characteristic of magnetic cores is presented, and a simple procedure is presented for calculation of the coefficients of the model equation.
Abstract: A model equation is presented for accurate representation of magnetising characteristic of magnetic cores. A simple procedure is presented for calculation of the coefficients of the model equation. It has shown that with a little effort, even by using a small electronic hand calculator, magnetising characteristics can be modeled very accurately.
TL;DR: Experimental results show that the single-chip microcomputer Intel 8095-based battery-source Inverter can control a 3 kW synchronous motor drive satisfactorily over a frequency range of 2 to 100Hz.
Abstract: A new PWM algorithm for battery-source three-phase Inverters Is described in this paper. The concept of the algorithm is to determine the pulsewidths by equating the areas of the segments of the sinusoidal reference with the related output pulse areas. The algorithm is particularly suitable to handle a non-constant voltage source with good harmonic suppression. Since the pulsewldths are computable in real time with minimal storage requirement as well as compact hardware and software. It is especially suitable for single-chip microcomputer Implementation. Experimental results show that the single-chip microcomputer Intel 8095-based battery-source Inverter can control a 3 kW synchronous motor drive satisfactorily over a frequency range of 2 to 100Hz.
TL;DR: In this paper, the Hopf Bifurcation theorem is used to determine different stability patterns of a synchronous motor when the system voltage changes and the bifurcations of different equilibrium states are examined.
Abstract: Investigation of synchronous motor stability needs the study of a set of first order nonlinear differential equations. Due to this nonlinearity, the behavior of the synchronous motor during small disturbances is understood by looking at the eigenvalues of the linearised equations. One of the most powerful methods to analyse the dynamics of a nonlinear system is the theory of Hopf Bifurcation which uses the eigenvalues of the linearised system. This paper uses the Hopf Bifurcation theorem to determine different stability patterns of a synchronous motor. As the system voltage changes, the bifurcation of different equilibrium states are examined. A test system is used to simulate the changes taking place in the stationary solution. The properties of the nonlinear periodic solution are also uncovered and the relationship between the two solutions is established.
TL;DR: In this paper, a simple, efficient and reliable method for estimating the state of an integrated multiterminal HVDC/AC power system in the rectangular coordinate form is described.
Abstract: This paper describes a simple, efficient and reliable method for estimating the state of an integrated multiterminal HVDC/AC power system in the rectangular coordinate form. A six variable model is used to represent the converter system. The proposed algorithm performs succesfully in obtaining the state of an AC system with a DC link or a multiterminal DC network. It is possible to implement it for an on-line state estimation. Simulation results of a 30-busbar system are presented for illustration.
TL;DR: In this paper, an analytical solution of the transient current and the torque for the asymmetrical fault condition, and from these, practical equations are developed to determine the peak transient torque and the transient currents.
Abstract: When supply to the induction motor is short circuited the energy stored in machine, causes the machine to behave as a generator. This can result in very large transient negative torque and large transient current, especially in case of asymmetrical fault. This article provides an analytical solution of the transient current and the torque for the asymmetrical fault condition, and from these, practical equations are developed to determine the peak transient torque and the transient current. The analytical solution assumed constant shaft speed. The results obtained compared with the experimental results and with the machine exact deferential equation. It has shown that the results obtained agree well with both the theoretical results obtained from the numerical exact variable speed solution and the experimental results.
TL;DR: In this article, a variable structure speed controller for a non sinusoidal brushless permanent magnets motor drive is presented, where the state point is forced to reach a prescribed surface due to an active change of the control action.
Abstract: This paper describes the application of a variable structure speed controller for a non sinusoidal brushless permanent magnets motor drive. Our trapezoidal brushless motor model changes the working conditions for every phase commutation and moreover it allows to simulate the different structural motor configurations. Controller synthesis is carried out using sliding mode theory with a pole assignment technique. During the sliding motion the state point is forced to reach a prescribed surface due to an active change of the control action. The order of the system is therefore reduced and moreover the dynamic behaviour of the closed-loop system is imposed. Results by digital computer simulation prove parametric variation insensitivity, disturbance rejection, fast transient responses, no overshoot and absence of speed ripples during phase commutations.
TL;DR: A study is reported on to determine the comparative merits of state variable and quasi-ac steady state methods for dynamic performance of the single-phase induction motor.
Abstract: Dynamic performance of the single-phase induction motor is frequently evaluated using quasi-ac steady state methods. State variable methods have also been applied to the problem. This paper reports on a study to determine the comparative merits of each.
TL;DR: In this paper, a new rotor geometry for a high-field high-speed PM synchronous motor is proposed, which employs appropriately located air slots to reduce the armature reaction in conjunction with flux enhancement arrangement without detracting from its mechanical integrity.
Abstract: Although neodymium-iron-boron (Nd-Fe-B) magnets have high-energy product with suitable magnetic and physical properties for applications in electrical machines, the design of permanent magnet (PM) motors is a complicated problem due to their complex geometries and PM material characteristics. This paper initially compares various PM motor geometries and describes their PM material outlay, armature reaction and mechanical integrity. By the employment of appropriately located air slots to reduce the armature reaction in conjunction with flux enhancement arrangement without detracting from its mechanical integrity, a new rotor geometry for a high-field high-speed PM synchronous motor is proposed. Computer-aided electromagnetic calculation and graphical evaluation are employed for the design and optimization of the proposed PM motor. An idea of ‘computer job delegation’ is proposed and implemented within the computer system to provide full utilization of each computer's capabilities as well as parall...
TL;DR: In this article, the authors focus on two major issues which need careful consideration when designing an excitation for variable-reluctance motor (VRM) drives: the modeling of the drive and selecting a topology to toe the drive.
Abstract: This paper focuses on two major issues which need careful consideration when designing an excitation for variable-reluctance motor (VRM( drives. The drive is comprised of a VRM, an inverter and an excitation and control strategy. The controller acts to enforce the excitation. The specific issues addressed here include the modeling of the drive and selecting a topology Toe the drive. These issues were found to be important during the design of an optimal-efficiency excitation for a high-power (60 kW( VRM drive. The drive used for the running example was designed for electric vehicle propulsion using a bifilar wound VRM. The importance of drive modeling is examined through an example. The example uses two magnetic models for the same VRM to generate current waveforms for drive operation at a specific speed. The attributes of the current waveforms are then compared and their influence on excitation design is discussed. The comparison shows that meaningful excitation design requires accurate models o...
TL;DR: In this article, the design, implementation and performance of a multivariable optimal state feedback controller for a Current Source Inverter-fed Induction Motor (CSI-IM) drive using a new reduced order observer to estimate rotor currents have been reported.
Abstract: The design, implementation and performance of a multivariable optimal state feedback controller for a Current Source Inverter-fed Induction Motor (CSI-IM) drive using a new reduced order observer to estimate rotor currents have been reported in this paper. A quadratic performance index together with a set of prescribed closed loop eigenvalues for placement are considered for application to a d-q axes state space linearized model of the drive to derive the control law - for achieving prescribed degree of stability in contrast to an earlier design with only pole-placement. The optimal control law derived is a function of all the states, the inaccessible states like d-q axes rotor currents being estimated by a new observer whose structure is simpler than that of one used in an earlier case. The controller-observer is implemented using an inexpensive microprocessor kit and the experimental results are presented along with the digital simulation results for the controlled drive to show its pe...
TL;DR: In this paper, the Lagrange multiplier functions are used to augment the physical constraints to the cost function of an electric power system to obtain the optimal strategy in terms of power generation and water releases.
Abstract: The solution of an optimization problem using variational means relies on Lagrange multiplier functions, called the adjoint variables to augment the physical constraints to the cost function. The multipliers usually have an economic interpretation, and in the optimal economic operation of an electric power system, one set of multipliers signifies the incremental cost of power delivered at a bus, and the other set relates to the water worth at a given reservoir. The solution of the optimization problem involves iterative techniques to obtain the optimal strategy in terms of power generations and water releases, as well as the adjoint variables. Good initial estimates are of paramount importance to a successful implementation of any iteration scheme specially those that are Newton based. There is an observed pattern of dependence of the adjoint variables and the system state as described by power demands and water availability. Finding such relationships is useful for generation planning activities...
TL;DR: In this paper, the authors presented a comprehensive power system model to study the mid-term dynamic response of isolated power systems to large disturbances such as generating unit outages, where the interaction of the system with its individual components such as prime-mover and generator including their controllers, frequency and voltage dependency of system loads as well as the transmission network is considered.
Abstract: This paper presents a comprehensive power system model to study the mid-term dynamic response of isolated power systems to large disturbances such as generating unit outages. The interaction of the system with its individual components such as prime-mover and generator including their controllers, frequency and voltage dependency of system loads as well as the transmission network is considered in the described model. This model has been applied on the regional power system in Qatar, where a digital package based on the Advanced Continuous Simulation Language (ACSL) is developed to determine the system response during emergency period after generation outages. The simulation results are used to discuss the following problems: – How does the generation outage affect the frequency behaviour and power exchange between different network parts? – How will the voltage level change after such generation deficiency? – Where and when do the system under-frequencies appear, which exceed protection limitati...
TL;DR: In this paper, the speed of an induction motor is controlled using a chopper circuit on the rotor side, where a diode bridge is connected to the diode and the motor equations are analyzed and simulation results are obtained to verify predicted behaviour based on this digital simulation.
Abstract: In this paper, the speed of an induction motor is controlled using a chopper circuit on the rotor side. Analysis of transient, including switching power supply and changing in duty cycle of chopper, and steady-state performance of the chopper-controlled induction motor are predicted-Analysis and simulation consider the induction motor equations from the rotor side where a diode bridge is connected. Experimental results are obtained to verify predicted behaviour based on this digital simulation.