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T. W. Nehl

Bio: T. W. Nehl is an academic researcher from Virginia Tech. The author has contributed to research in topics: Finite element method & Electromagnetic coil. The author has an hindex of 16, co-authored 19 publications receiving 800 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a method for calculating the apparent and incremental inductance of rotating machinery is presented. But the method is totally general and utilizes numerical field calculation techniques in obtaining stored energy in the magnetic circuits of such machines.
Abstract: Energy and winding current perturbations form the basis of a method for calculation of the saturated apparent and incremental inductances of rotating machinery as functions of rotor position and machine winding excitation currents. The method is totally general and utilizes numerical field calculation techniques in obtaining stored energy in the magnetic circuits of such machines. Thus, it can be applied to a wide class of machinery with practically any cross-sectional contours and number of windings. It can be used at any given set of excitations (any loads). This method was applied to the calculation of the apparent and incremental inductances of a 15 hp samarium cobalt permanent magnet synchronous machine. The necessary-numerical field soluitions were obtained by finite elements at both rated and no load conditions. The calculated inductances, at various rotor positions, were compared with those obtained during laboratory measurements and the agreement between calculated and measured values was consistently very good. The advantage of this method over the more traditional calculations of only the direct and quadrature axes inductances (or reactances, including transient and subtransient components) is that the entire n > n matrix of incremental inductances that truely govern the dynamic performance of an n winding machine can be determined regardless of the validity of a rotating d-q-o frame of reference.

126 citations

Journal ArticleDOI
TL;DR: In this article, a discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented, which includes modeling of the interaction between these machines and their attached power conditioners.
Abstract: A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The similation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.

110 citations

Journal ArticleDOI
TL;DR: In this article, the three dimensional magnetic vector potential (m.v.p.) variational formulation for magnetostatic field problems with ideal current carrying conductors is given, and an appropriate functional is chosen for this class of problems, which is shown to be stationary whenever the partial differential equations, the Neumann, and the specified Dirichlet boundary conditions are satisfied, within and on the boundary of the volume under investigation, respectively.
Abstract: The three dimensional magnetic vector potential (m.v.p.) variational formulation for magnetostatic field problems, with ideal current carrying conductors is given. An appropriate functional was chosen for this class of problems. Variational techniques were used to prove that the chosen functional is stationary whenever the partial differential equations, the Neumann, and the specified Dirichlet boundary conditions are satisfied, within and on the boundary of the volume under investigation, respectively. The finite element method is used to obtain a numerical approximation of the stationary point of the functional. A three dimensional discretization scheme involving first order tetrahedral elements was used to implement the method. The m. v. p. at each of the four tetrahedral vertices (nodes) has three degrees of freedom (or components) in the x, y and z directions due to the three dimensional nature of the field.

83 citations

Journal ArticleDOI
TL;DR: In this paper, a dynamic model for simulation of the transient interaction between radially oriented permanent magnet-type synchronous machines and their corresponding transistorized current source power conditioners is presented.
Abstract: A dynamic model for simulation of the transient interaction between radially oriented permanent magnet-type synchronous machines and their corresponding transistorized current source power conditioners is presented. Some key machine parameters used in this dynamic model were obtained from finite element field solutions. This dynamic model was used to obtain the transient interaction between a 15-hp samarium cobalt radially oriented permanent magnet electronically operated synchronous machine and its corresponding power conditioner. This machine was constructed for electric vehicle propulsion. Excellent correlation between various digitally simulated and actual test current and voltage waveforms, in various branches of the machine-conditioner network, has been achieved. These results are given. This modeling approach is applied to machines during the design stage, where the finite element modeling is the only way to obtain the necessary machine parameters for dynamic simulation. It is shown how such a combination of the computer-aided design tools can help in prevention of design mis-judgements that can prove costly to remedy once the hardware is in place. This is done through an actual design example of an additional machine being manufactured for electric propulsion applications.

79 citations

Journal ArticleDOI
TL;DR: In this article, a three dimensional finite element formulation and algorithm for the solution of 3D magnetic fields was developed with applications to determination of local flux densities in a 3D field pattern, as well as global energy calculations of an air cored coil.
Abstract: A three dimensional finite element formulation and algorithm for the solution of 3-d magnetic fields was developed. The method is presented here with applications to determination of local flux densities in a 3-d field pattern, as well as global energy calculations of an air cored coil. The results compare well with closed form solution results. Experimental test data of the coil inductance is in agreement with finite element results. The development represents a new technique which is a potentially very powerful tool in many practical applications.

61 citations


Cited by
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Journal ArticleDOI
TL;DR: A phase variable model of the BDCM is developed and used to examine the performance of a BDCm speed servo drive system when fed by hysteresis and pulsewidth-modulated (PWM) current controllers, indicating that the small- and large-signal responses are very similar.
Abstract: For ptI see ibid, vol25, no2, p265-73 (1989) The authors develop a phase variable model of the BDCM (brushless DC motor) and use it to examine the performance of a BDCM speed servo drive system when fed by hysteresis and pulsewidth-modulated (PWM) current controllers Particular attention was paid to the motor large-signal and small-signal dynamics and motor torque pulsations The simulation included the state-space model of the motor and speed controller and real-time model of the inverter switches Every instance of a power device turning on or off was simulated to calculate the current oscillations and resulting torque pulsations The results indicate that the small- and large-signal responses are very similar This result is only true when the timing of the input phase currents with the back EMF (electromotive force) is correct The large-signal and small-signal speed response is the same whether PWM or hysteresis current controllers are used This is because, even though the torque pulsations may be different due to the use of different current controllers, the average value which determines the overall speed response is the same >

672 citations

Journal ArticleDOI
TL;DR: It is illustrated that comparisons between the different motors are difficult by the large number of parameters and the lack of a recommended test scheme, so it is proposed that a standardized drive cycle be used to test and compare motors.
Abstract: This paper presents a critical review of the drivelines in all-electric vehicles (EVs). The motor topologies that are the best candidates to be used in EVs are presented. The advantages and disadvantages of each electric motor type are discussed from a system perspective. A survey of the electric motors used in commercial EVs is presented. The survey shows that car manufacturers are very conservative when it comes to introducing new technologies. Most of the EVs on the market mount a single induction or permanent-magnet (PM) motor with a traditional mechanic driveline with a differential. This paper illustrates that comparisons between the different motors are difficult by the large number of parameters and the lack of a recommended test scheme. The authors propose that a standardized drive cycle be used to test and compare motors.

506 citations

Journal ArticleDOI
TL;DR: In this article, a five-phase brushless permanent magnet motor with concentrated windings has been proposed, where the produced back electromotive force is almost trapezoidal and the motor is supplied with the combined sinusoidal plus third harmonic of currents.
Abstract: A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.

428 citations

Journal ArticleDOI
TL;DR: In this paper, a complete, three phase transformer model for the calculation of electromagnetic transients is presented, which consists of a set of state equations solved with the trapezoidal rule of integration in order to obtain an equivalent Norton circuit at the transformer terminals.
Abstract: A complete, three phase transformer model for the calculation of electromagnetic transients is presented. The model consists of a set of state equations solved with the trapezoidal rule of integration in order to obtain an equivalent Norton circuit at the transformer terminals. Thus the transformer model can be easily interfaced with an electromagnetic transients program. Its main features are: (a) the basic elements for the winding model are the turns; (b) the complete model includes the losses due to eddy currents in the windings and in the iron core; and (c) the solution of the state equations is obtained in decoupled iterations. For validation, the frequency response of the model is compared with tests on several transformers. Applications to the calculation of transients are given for illustration. >

279 citations

Journal ArticleDOI
TL;DR: In this paper, a new type of vector finite-element approximation function is introduced that interpolates not to point values of each component of vector potential, but rather to the tangential projection of the vector potential on each edge of tetrahedral finite elements.
Abstract: Finite‐element vector potential solutions of three‐dimensional magnetic field problems are usually obtained by approximating each component of the vector potential by a separate set of scalar finite‐element approximation functions and by imposing continuity conditions between elements on all three components This procedure is equivalent to imposing continuity of both the normal and the tangential components of the vector potential We show in this paper that this procedure is too restrictive: While continuity of the tangential component of the vector potential is required, continuity of the normal components is not essential in the variational formulation We introduce a new type of vector finite‐element approximation function that has the property that it interpolates not to point values of each component of vector potential, but rather to the tangential projection of the vector potential on each edge of tetrahedral finite elements With the new basis functions, continuity of the normal component of the vector potential is provided only approximately by means of the natural interface conditions inherent in the variational procedure This results in a more efficient procedure for the solution of three‐dimensional magnetostatic field problems than is obtained by enforcing normal component continuity exactly

252 citations