Steve Pekarek

An efficient and accurate model for the simulation and analysis of synchronous machine/converter systems

A new synchronous machine model is presented which is readily implemented in either circuit-based or differential-equation-based simulation programs. This model is well suited for the simulation and analysis of synchronous machine-power converter systems. It is based upon standard representations and no approximations are made in its derivation. However, the numerical implementation is shown to be significantly more efficient. An example is provided which demonstrates a 1700% increase in simulation speed with no observable loss in accuracy. The model includes provisions for an arbitrary number of damper or rotor windings and may be easily modified to represent synchronous or induction machines with an arbitrary number of stator phases.

A model-in-the-loop interface to emulate source dynamics in a zonal DC distribution system

A model-in-the-loop capability (MIL) has been developed to emulate the dynamics of alternative power sources in a hardware-based dc zonal electrical distribution system. Using this tool, models of the power sources are simulated in real-time and interfaced with hardware components at the voltage and current levels of the power system. Coupling between simulation and hardware is established through a dc/dc power converter using model/wall-clock time synchronization. The MIL capability is illustrated in the emulation of a synchronous machine/converter power source. Results of time-domain and frequency-domain studies are provided to validate the approach.

A field reconstruction method for optimal excitation of permanent magnet synchronous machines

Vibration caused by torque ripple and radial force harmonics is a concern in many applications of permanent magnet synchronous machines (PMSMs). Alternative methods of machine design and/or stator excitation to minimize torque ripple have received considerable attention in recent years. Comparatively, methods to minimize radial force harmonics have received less attention. In this paper, a field reconstruction (FR) method is derived that provides a designer with the capability to rapidly determine the radial and tangential components of force under arbitrary stator excitation. Using the field reconstruction method, stator current waveforms that minimize the ripple of both torque and radial force are derived subject to the constraint of maintaining a satisfactory level of torque density.

Investigation of Force Generation in a Permanent Magnet Synchronous Machine

Traditional analysis of permanent magnet synchronous machines has focused upon establishing a relationship between the quadrature and direct axis stator current (or voltage) and the electromagnetic force created to establish rotation (torque). In this paper, an alternative analysis of electromagnetic force production is considered. Specifically, the influences of - and -axis stator current on both the radial and tangential components of the airgap flux densities are first evaluated. Using a Maxwell stress tensor approach, the fields are then used to evaluate both the radial and tangential component of force density created in the airgap of the machine. From this perspective several interesting observations are made. First, it is shown that the -axis current has zero influence on the average tangential force (torque), as predicted using traditional analysis, but it has a significant influence on the average radial component of force. Second, it is shown that the -axis current contributes to both the average radial and average tangential components of force. Interestingly, it is also shown that under standard operating conditions, the average radial force far exceeds that of the average tangential component of force. Therefore, one can conclude that the magnetic fields established create a significant component of force in a direction that cannot produce torque.

Applications of power electronics-based systems in vehicular technology: state-of-the-art and future trends

Power electronics-based systems and components have been increasingly used in land, air, and sea vehicles over the past decade. This has turned the vehicular products into a primary market for power electronics applications. Moreover, the existing trend in more electrification of the vehicles represents an even bigger potential for an increase in the existing demand. Although the primary incentive for introduction of multiconverter systems into vehicular technologies was to enhance fuel economy and environmental issues associated with vehicles; today, improvement of fault tolerance, cost, and compactness have boost the motivation for development of the more electric vehicles. The use of numerous converters has an impending impact on the overall system. The multiconverter system is highly prone to interaction within and between subsystems, varied source and load profiles, reduced power quality, degraded static and dynamic behavior of the system, and in some cases effect system stability. Traditionally, converters have been designed and analyzed on standalone basis using conservative approaches. However, in the context of multiconverter systems such approaches can lead to devastating consequences in terms of irreparable collapse of the entire system. Thus, it is inevitable to set new approaches that address issues of system dynamic and large signal perturbations. Existing work to address these issues is reviewed in this paper. In addition, a testbed is presented to provide a resource for the community to test design scenarios.

Multilayer control of an induction motor drive:A strategic step for automotive applications

Fault tolerance is a critical attribute in automotive electrical and propulsion systems. In this paper, a control scheme is presented that allows an induction motor drive system to operate in the event of multiple sensor failures. Automatic diagnosis of sensor fault and recovery is performed and used to reconfigure the drive system controls to achieve the best performance in lieu of component degradation. This approach couples a new digital delta-hysteresis regulation scheme with a model reference adaptive system scheme in order to provide fault tolerance for both phase-current and rotor position (speed) sensors. Simulation and experimental results are provided to show the effectiveness of the proposed scheme

An accurate method of neglecting dynamic saliency of synchronous machines in power electronic based systems

In this paper, motivations for neglecting dynamic saliency in detailed models of power electronic-based systems are presented. A new method of neglecting dynamic saliency is introduced in which approximate operational impedances are derived from original dynamic salient models. New machine parameters are obtained by fitting to the approximate impedance curves, yielding model parameters in which dynamic saliency is eliminated. An example synchronous machine/converter system is provided that demonstrates the accuracy and increased simulation efficiency resulting from this technique. Therein, errors resulting from neglecting dynamic saliency are reduced from greater than 25% using traditional approximations to less than 0.6%. In addition, simulations using the new approximate model are greater than 48% faster than simulations based upon the original dynamic salient model.

Analysis and Validation of a Population-Based Design of a Wound-Rotor Synchronous Machine

In recent research, a new magnetic equivalent circuit model and solution technique were developed to enable rapid calculation of the performance of wound-rotor synchronous machines. Herein, the development of a population-based design tool that utilizes the MEC is first described. The design tool is then applied to perform multiobjective optimization of a 2-kW portable power generator. Validation has been achieved through construction of a machine that was selected from the Pareto-optimal front (POF) of mass versus loss. Comparisons are made between designed and measured torque (instantaneous and average), open-circuit voltage, efficiency, and q- and d-axis flux linkages. This comparison is done in light of observations that the anhysteretic BH curve for the steel material obtained prior to and subsequent to machine construction have significant differences. Despite the variance, the measured and expected performances match reasonably well. Finally, an analysis of the machines on the POF is used to shed light on several interesting trends in design variables.

On the use of singular perturbations to neglect the dynamic saliency of synchronous machines

A common approximation used in the analysis of power systems is the neglect of the dynamic saliency in synchronous machines. In this paper, it is shown that eliminating the error associated with neglecting dynamic saliency can be accomplished with the addition of singular perturbation(s) into the machine model. By considering the elimination of error in such a way, singular-perturbationbased model-order-reduction techniques are used to derive detailed-and reduced-order models of synchronous machines in which dynamic saliency is eliminated with zero error and no added numerical cost.

An efficient and accurate method of representing magnetic saturation in physical-variable models of synchronous machines

When analyzing machine/converter systems it is convenient to represent the stator variables in physical (abc) form. It has been shown that a physical-variable voltage-behind-reactance form of the synchronous machine model can be derived which is numerically more efficient than existing physical-variable models. In this research, a new voltage-behind-reactance model is derived which incorporates the effects of magnetic saturation. This model is shown to have the same numerical efficiency of the unsaturated model and is readily implemented in either circuit-based or differential-equation based simulation languages. An example system is provided which demonstrates the accuracy and efficiency of this model for a wide-range in operating conditions.