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The magnetic equivalent circuit (MEC) technique is a powerful analysis and design tool that combines relative accuracy with moderate computational effort. In this paper, a nodal-based MEC formulation and a mesh-based MEC formulation of a magnetic system are compared. The Newton-Raphson algorithm is used to solve the algebraic system, and to draw conclusions about the computational efficiency of the two formulations under linear and nonlinear operation. Although the two formulations exhibit similar performance under linear operating conditions, the performance of the mesh-based model is significantly better than that of the nodal-based model under nonlinear operation. Index Terms--Magnetic equivalent circuit (MEC), permeance, reluctance.

Traditional analysis and design of induction machines have been largely based upon lumped-parameter models. An alternative tool used for field-based evaluations of an induction machine is the finite-element method. Although useful, its computational complexity limits its use as a design tool. In this paper, a field reconstruction (FR) method for induction machine simulation is introduced. The FR method utilizes a small number of finite-element evaluations to establish basis functions of normal and tangential flux densities. The basis functions are then used to estimate the magnetic field under arbitrary stator excitation. Using such a tool, evaluation of fields and forces produced by a machine under alternative excitation strategies can be explored efficiently. Moreover, alternative field-based derivation of stator/rotor excitation control can be explored. Index Terms--Field reconstruction (FR), finite element (FE), induction machine, Maxwell stress tensor, torque and radial force.

lOver the past several years, there has been renewed interest in modeling electrical machines using phase (abc) variables. This paper considers modeling induction machines using phase variables in a voltage-behind-reactance (VBR) formulation. Specifically, three VBR models are proposed wherein the rotor electrical subsystem is modeled using flux linkages as state variables expressed in the qd reference frame. The stator electrical dynamics are represented in abc phase coordinates that enable direct interface of the machine model to an external network. Such a direct interface is advantageous when the machine is fed from a power electronic converter and/or when the modeling is carried out using circuit-based simulators. Computer studies of an induction machine demonstrate that the proposed VBR models achieve a 740% improvement in computational efficiency as compared with the traditional coupled-circuit phase-domain model. Index Terms--Coupled-circuit (CC) model, dynamic simulation, induction machine, qd model, voltage-behind-reactance (VBR) model.

A method of representing the effects of magnetic saturation in a coupled-circuit model of a claw-pole alternator is presented. In the approach considered, the airgap flux density produced by each winding is expressed as a function of magnetic operating point. A challenge in the implementation is that the air-gap flux densities consist of several significant harmonics, each of which changes at a distinct rate as iron saturates. Despite this complication, it is shown that relatively simple measurements can be used to determine model parameters. The model is implemented in the analysis of several alternator/rectifier systems using a commercial state-model-based circuit analysis program. Comparisons with experimental results over a wide range of speeds and operating conditions demonstrate its accuracy in predicting both the steady state and transient behavior of the systems. Index Terms--Electromagnetic torque, rectifiers, state model, synchronous machines.

A Hall-effect-sensor-based position observer that is suitable for mitigation of torque ripple in permanent-magnet synchronous machines is derived. The observer includes an initial commissioning routine to compensate for the offset in the placement of Hall sensors, which is shown to be necessary for effective control of torque harmonics. Using the position observer in lieu of a high-precision encoder, the overall cost of control-based torque-ripple mitigation is reduced significantly. In addition to the observer, an enhancement is made to a recently developed torque-ripple mitigation algorithm. Specifically, the algorithm is modified to compensate for sensor delay. Proposed methods have been validated in simulation and hardware. Index Terms--Permanent-magnet machines, position measurement, torque control, torque measurement.

The analytical derivation of the average-value models (AVMs) for synchronous-machine-fed rectifier systems depends on many factors and is challenging in general. Various models presented in the literature rely on a single operating mode and a dc filter configuration. A recently proposed parametric approach utilizes a detailed simulation as a basis to establish an AVM that uses a proper full-order qd generator model. This paper presents a procedure to extract the appropriate nonlinear algebraic functions to represent the rectifier averaged behavior. In contrast to existing methods, the proposed procedure does not require significant analytical derivations and/or computational resources and results in a highly accurate dynamic AVM. The proposed methodology is validated with the results of detailed simulation and hardware experiment, and is shown to be very accurate in predicting the large-signal time-domain transients as well as the small-signal frequency-domain characteristics. Index Terms--Average-value model, impedance characterization, line-commutated rectifier, synchronous machine.

One of the primary design requirements of automotive generation systems is maximizing power density subject to the constraint of minimizing the overall system cost. However, with the progress made in the reduction of automotive drive train noise, the torque ripple of the generator has been found to be a dominant noise source under idle conditions at high electrical loads. Thus, an added design constraint is the minimization of the torque ripple produced by the machine. In order to evaluate alternative machine designs (and select an optimal), numerical tools are typically applied. In this research, a focus is placed on the creation of numerical tools that can be used to effectively search for an optimal design. A primary tool is an evolutionary algorithm (EA) that has been integrated within a customized magnetic equivalent circuit (MEC) model of the machine. The selection of an EA that is most likely to converge to an optimal solution in the least amount of time is described along with its use in selecting an optimal rotor-pole geometry. Index Terms--Alternator, evolutionary algorithm (EA), generator, magnetic circuits, optimization.

A new average-value model of a rectifier circuit in a synchronous-machine-fed rectifier system is set forth. In the proposed approach, a proper state model of the synchronous machine in the qd-rotor reference frame is used, whereas the rectifier/dc-link dynamics are represented using a suitable proper transfer function and a set of nonlinear algebraic functions that are obtained from the detailed model using numerical averaging. The new model is compared to a detailed simulation as well as to measured data and is shown to be very accurate in predicting the large-signal time-domain transients as well as small-signal frequency-domain characteristics. Index Terms--Average-value model (AVM), impedance characterization, line-commutated rectifier, synchronous machine.

A new power electronics laboratory has been constructed at the University of Missouri--Rolla. Key components of the laboratory are a set of custom-designed hardware and software tools. The novel hardware tools include five mobile power electronics testbeds that each contain the semiconductor devices, gate-drive boards, voltage and current sensors, and computer interface connections required to study a wide range of circuit topologies and control techniques. Novel software tools include a set of virtual instruments used for control, data capture, and data analysis. A description of these tools, along with their use in power electronics courses, laboratory exercises, and student research projects, is presented. Index Terms--Distal control, laboratories, motor drives, operational amplifiers, power electronics.

A novel multirate method of simulating power-electronic-based systems containing a wide range of time scales is presented. In this method, any suitable integration algorithm, with fixed or variable time-step, can be applied to the fast and/or slow subsystems. The subsystems exchange coupling variables at a communication interval that can be fixed or varied dynamically depending upon the state of the system variables. The proposed multirate method is applied to two example power systems that include power-electronic subsystems. Increases in simulation speed of 183-281% over established single-rate integration algorithms are demonstrated. Index Terms--Computer simulation, multirate algorithms, numerical integration, power system modeling.

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 a singular perturbation(s) into the machine model. By considering the elimination of error in such a way, singular-perturbation-based model-order-reduction techniques are used to derive detailed- and reduced-order models of synchronous machines where dynamic saliency is eliminated with zero error and no added numerical cost. Index Terms--Singularly perturbed systems, synchronous machine, transient analysis.

A lumped-parameter coupled-circuit model of a claw-pole alternator is derived. To derive the model, analytical techniques are used to define a three-dimensional (3-D) Fourier-series representation of the airgap flux density. Included in the series expansion are the harmonics introduced by rotor saliency, concentrated stator windings, and stator slots. From the airgap flux density waveform, relatively simple closed-form expressions for the stator and rotor self- and mutual-inductances are obtained. The coupled-circuit model is implemented in the simulation of an alternator/rectifier system using a commercial state-model-based circuit analysis program. Comparisons with experimental results demonstrate the accuracy of the model in predicting both the steady-state and transient behavior of the machine. Index Terms--Fourier series, power conversion harmonics, synchronous machines, torque measurement.

The derivation of accurate dynamic average-value models for synchronous machine--rectifier systems is challenging, A recently proposed parametric approach uses a computer-aided procedure for constructing the required averaged models, wherein the key nonlinear functions are extracted from a detailed (valve-by-valve) simulation. This letter shows that by using a judicious selection of parametric functions, a model obtained at a fixed generator speed is also valid for variable speeds. This is an important feature that makes this approach applicable to systems where electromechanical dynamics and variable speed operation is required. Index Terms--Average-value model, electromechanical interactions, line-commutated rectifier, synchronous machine.