Thomas W. Nehl

Inverter EMI modeling and simulation methodologies

A numerical prediction of electromagnetic interference (EMI) allows evaluation of EMI performances at the design stage and before prototyping. It can also help reduce the post-prototype electromagnetic compatibility cost by minimizing late redesign and modifications of a drive implementation. This paper describes two simulation approaches with time- and frequency-domain simulations and verifies them with experimental results. Both time- and frequency-domain simulation approaches are found effective as long as the noise source and propagation path are properly modeled. The three-dimensional (3-D) finite-element-analysis (FEA)-based parasitic parameter extraction tool-Ansoft Spicelink has been used substantially. To gain additional degree of confidence, the results obtained from FEA are verified with closed-form solutions and actual measurements.

Electric machinery parameters and torques by current and energy perturbations from field computations. I. Theory and formulation

In this first of a two-part article, the well-established energy/current (E/C) perturbation method of computation of machine winding inductances is reviewed. The methods efficacy in machine performance calculations is delineated and verified in a companion paper by comparison to experimental results. The critical role that winding inductance parameters have in modeling and simulation of the nonsinusoidal steady state time-domain (forced response) performance of electric machinery is demonstrated using state models in both the winding flux linkage and current-based frames of reference. The computed machine performance characteristics include profiles of winding inductances, induced terminal voltage waveforms, and instantaneous torque profiles that contain all the ripples due to the significant space harmonics in a machine. The method and associated formulations and techniques are shown to be very effective in both 2D-FE and 3D-FE electric machinery field solutions involving substantial degrees of saturation and complexity of construction. The machines analyzed in the comparison paper include a 15-HP permanent magnet brushless DC motor, a 1.2-HP three-phase induction motor, and a 14.3 kVA three-phase modified Lundell alternator possessing very complex magnetic circuit geometries. The well-posedness of the method held true for all these cases, as well as many other case-studies briefly reviewed here.

Analytical modeling of eddy-current losses caused by pulse-width-modulation switching in permanent-magnet brushless direct-current motors

An analytical approach is developed to predict the inverter high frequency pulse width modulation (PWM) switching caused eddy-current losses in a permanent magnet brushless dc motor. The model uses polar coordinates to take curvature effects into account, and is also capable of including the space harmonic effect of the stator magnetic field and the stator lamination effect on the losses. The model was applied to an existing motor design and was verified with the finite element method. Good agreement was achieved between the two approaches. Hence, the model is expected to be very helpful in predicting PWM switching losses in permanent magnet machine design.

Transient finite element modeling of solenoid actuators: the coupled power electronics, mechanical, and magnetic field problem

A transient 2-D finite element model for fast-acting pulse-width-modulated (PWM) solenoid actuators is presented. The unique feature of this model is that it couples the electrical, mechanical, and magnetic systems of these devices. Transient calculations taking into account the nonlinearity of the magnetic materials, eddy currents, and motion are compared with dynamic test results for a ball-type solenoid. Flexibility of the software allows one to apply it to any type of PWM solenoid actuator and any desired excitation profile. >

Nonlinear two-dimensional finite element modeling of permanent magnet eddy current couplings and brakes

A two-dimensional finite element model is developed to model the electromagnetic behavior of permanent magnet type eddy current couplers under constant speed operation. The model accounts for the nonlinearity of the steel flux paths and is verified using test measurements from a prototype eddy current coupler. The proposed solution differs from conventional magnetostatic finite element models in that an unknown current-density distribution must be determined through an iterative process. The model is used to study the influence of certain design parameters on the torque-speed characteristics of such devices. >

ANTIC85: a general purpose finite element package for computer aided design and analysis of electromagnetic devices

A description is given of ANTIC85, a powerful and user-friendly finite-element-based magnetic field analysis package. This program is used for the design and analysis of electromechanical devices for automotive applications. It is applicable to general two-dimensional and axisymmetric three-dimensional static and transient nonlinear magnetic field problems. The unique feature of this package is its ability to solve the coupled power-electronic, mechanical, and magnetic field problem for solenoid actuators. The theoretical basis and structure of this package are presented. Applications to a four-pole 3 kW permanent-magnet starter motor and a variable-reluctance-type speed sensor are shown. >

Three-phase inverter differential mode EMI modeling and prediction in frequency domain

This paper describes a frequency domain approach to the prediction of differential mode (DM) conducted electromagnetic interference (EMI) for a three-phase inverter at the early design stage. The approach is able to calculate the DM conducted EMI with more accurate noise source and parasitic path identification. The DM noise sources are identified as three device switching current and their frequency domain expressions are derived according to inverter operating principle. The parasitic components are identified using FEM analysis. The calculated DM EMI result is compared with experimental data and it can predict the high frequency resonant peak precisely. It is indicated that the frequency domain analysis with accurate noise source and parasitic modeling is an effective tool for DM EMI prediction for three-phase inverter circuit.

EMI characterization and simulation with parasitic models for a low-voltage high current AC motor drive

In this paper, a 12-V 1-kW permanent-magnet ac motor drive is tested extensively at a wide frequency range, and the frequency spectra are partitioned for identification of noise sources and their propagation paths. Switching characterization of the power MOSFET and its body diode reverse-recovery characterization are evaluated for circuit modeling. The parasitic components and common mode path are identified and measured with the time-domain reflectometry (TDR) method. The inverter circuit model is then constructed with major parasitic inductance and capacitance in device modules, passive components, leads, and interconnects. To verify the validity of the inverter model, a comparative study is performed with computer simulations and hardware experiments. The fundamental mechanisms by which the electromagnetic interference (EMI) noises are excited and propagated are analyzed, and the significant roles of parasitic elements coupling with device switching dynamics in EMI generation are examined. The results indicate that the identification of parasitic inductance through TDR measurement helps verify the voltage spike during turn-off, or vice versa. The conducted EMI noise caused by parasitic components of bus capacitor, dc bus, and devices is proven to be identifiable with the characterization and simulation techniques used in this paper.

An integrated relative velocity sensor for real-time damping applications

Semi-active suspension systems using real time damping (RTD) provide significant improvement in vehicle ride and handling without the high cost of fully active suspensions. RTD systems require a variable rate damper (shock absorber), a relative velocity sensor (RVS), and a controller. To reduce the cost of such systems, a method for integrating a moving magnet relative velocity sensor directly into the shock absorber is presented. This integrated relative velocity sensor (IRVS) uses existing hydraulic and mechanical components as part of its magnetic circuit to reduce part count and cost. Sensitivity to key design parameters is analyzed using a finite element model. The IRVS is self energizing, requires no signal processing electronics, and can be integrated into standard shock absorber configurations. Prototype sensors were tested on a vehicle and provided excellent performance under all testing conditions.

Adaptive refinement of first order tetrahedral meshes for magnetostatics using local Delaunay subdivisions

A mesh refinement algorithm for arbitrary tetrahedral meshes has been developed. The algorithm is suitable for use in a variety of adaptive mesh refinement schemes and has the following features: (1) it can be applied to both optimal (Delaunay) and nonoptimal meshes, (2) new nodes are inserted using a perturbed edge bisection to prevent crossing edges, and (3) the Delaunay criterion is applied locally over each tetrahedron selected for refinement. The advantage of the local Delaunay subdivision is that it decouples the subdivision process, which reduces computation time. The method has been successfully applied to several magnetostatic problems modeled using first-order tetrahedra, and has produced refined meshes of over 215000 elements. >