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Nonlinear Time-Transient in Switched Reluctance Motors (T.E.A.M. Problem 24)

Motors and Generators with MagNet

This is a test rig of configuration similar to that of a switched reluctance machine. It is made of solid medium-carbon steel and mounted in a nonmagnetic cage which can rotate about a stainless steel shaft. This example shows a nonlinear transient problem, which was solved by MagNet's Transient 3D solver.

Each stator pole has a 350-turn coil around it, and the rotor is fixed at 22 degrees relative to the stator. A step voltage of 23.1 V is applied to the series connected coils. A search coil is wound around a rotor pole to measure the total magnetic flux, and a Hall probe measures the y-component of the magnetic flux density at a specified position in the air gap between rotor and stator. Finally, a piezoelectric transducer measures the torque on the rotor.

Using MagNet's Transient 3D solver, the current, torque, rotor pole flux and the air gap point flux density are calculated. The simulation results agree well with the measured data published in the problem definition.

The following is based on the Testing Electromagnetic Analysis Methods (T.E.A.M.) problem #24: Nonlinear Time-Transient Rotational Test Rig. The benchmark can be found on the International Compumag Society's website.

Switched Reluctance Motor Rotational Test Rig

METHODS and RESULTS

MATERIAL MODELING: B-H CURVE

Material properties are critical to accurate calculations. The T.E.A.M. problem specifies the material B-H curve, but there are not enough data points in the critical region at the "knee" of the B-H curve. By adding one more data point to the material curve, good agreement with experiment was obtained. The graph at right shows where the extra point was added in relation to the original published data.

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MagNet's COIL CURRENTS

The graphs illustrate the result of MagNet simulation for the test rig switched reluctance machine.

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COMPARING MEASURED vs SIMULATED COIL CURRENTS

Comparison of the coil currents between the published T.E.A.M. data and the results obtained from MagNet.The steady state current agrees exactly, since this depends only on the DC resistance of the coils, which is specified. The error in the transient current can be attributed to both experimental error and material modeling error (due to insufficient material data).

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MagNet's TORQUE RESULTS

Result of Torque from MagNet for the test rig switched reluctance machine.

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COMPARING MEASURED vs SIMULATED TORQUE

Comparison of the torque values between the published T.E.A.M. data and the MagNet results. Since the Magnet uses the half model, the result is the half of the total torque. Torque is one of the more difficult quantities to compute accurately, but these results show that MagNet's torque calculation is accurate.

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MagNet's ROTOR FLUX RESULTS

This graphs plots the result of the rotor flux as simulated in MagNet for the test rig switched reluctance machine.

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COMPARING MEASURED vs SIMULATED ROTOR FLUX

The comparison of the total flux through the rotor pole, measured with the open circuited sense coil, is shown in this graph.

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MagNet's FLUX DENSITY RESULT

This graphs plots the result of the flux density as simulated in MagNet for the test rig switched reluctance machine.

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COMPARING MEASURED vs SIMULATED FLUX DENSITY

The flux density values obtained from MagNet are compared with the published T.E.A.M. data. The experimental data was obtained using a Hall probe in the air gap. In MagNet, the field sampler tool allows quick and easy plotting of any field over either space or time, and of course it is even possible to probe inside components, something a Hall sensor cannot do.

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