MagNet

Accurately modeling the skewed rotor of an Induction Motor

MOTORS & GENERATORS WITH MAGNET

Induction motors are one of MagNet's specialties.The induction motor analysed here is a typical three-phase motor,but MagNet modeling improvements have made it easy to include features that were previously ignored.The rotors of induction motors often have skewed slots to minimize torque ripple;this is now easily created and accurately modeled.

The stator windings in this model are realistic involute shapes,created with the multi-segment sweep option,which has powerful automatic blend calculations making the creation of these and other complex coil shapes easy.Accurately modeled coils means that end effects can be studied.

The periodic boundary condition allows the modeler to take advantage of symmetries;in this case,only a 60-degree section is modeled,reducing the problem size by a factor of 6.

Methods and Results

STATOR INVOLUTE WINDINGS

A picture of half of one of the stator involute windings is shown on the left.Once this segment is created in MagNet,multiple instances of it can be imported with transformations applied in order to create the full set of stator windings.Possible transformations that can be applied to objects in Infolytica's 金宝博滚球专家software packages are scale,rotation,mirror and shift.Any number or combination of these transformations can be applied in our 金宝博滚球专家software.

EASY DESIGN OF INVOLUTE WINDINGS

To facilitate the design of 3D devices in our 金宝博滚球专家software,a feature,multi segment sweeps,was added allowing for the easy design of complex paths such as the involute shown above.The image on the the left is a snapshot of the dialog box associated with the involute winding.

CUTAWAY VIEW OF THE INDUCTION MOTOR

An exploded view of the induction motor is shown here;parts of the motor are removed in order to see the windings and skewed rotor better.

MAGNETIC FLUX DENSITY

This is an arrow and shaded plot display of the magnetic flux density.The rotor is not displayed in this field view,as only a slice through it is shown.Note the effect of the field on the stator due to the skewed rotor.

MESH GENERATED IN MAGNET

This is an arrow and shaded plot display of the magnetic flux density.The rotor is not displayed in this field view,as only a slice through it is shown.Note the effect of the field on the stator due to the skewed rotor.

Creating a VHDL-AMS model of a claw-pole alternator

MOTORS & GENERATORS WITH MAGNET

A VHDL-AMS model of a claw-pole alternator is created using the System Model Generator.VHDL-AMS is a format which can be read by many circuit and system simulators,including SystemVision from Mentor Graphics.The System Model Generator creates a Response Surface Model (RSM) of the claw-pole by driving MagNet to execute a number of static solves at different phase currents and rotor positions.This RSM is embedded in the VHDL-AMS file to create a component which is functionally equivalent to the original MagNet model,but which can be evaluated extremely quickly in a transient circuit simulation.

Methods and Results

SYSTEMVISION CIRCUIT

The claw-pole component is shown here in the SystemVision circuit.In SystemVision it is a simple matter to create this component from the VHDL-AMS file.The pins are automatically labeled from information in the file,and the model parameters,such as the number of turns in the windings,can be modified in a properties dialog.

CAPTURING NONLINEARITIES IN THE RSM

The current shown here compares well with that simulation,in particular,note that the third harmonic content is clearly evident,showing that the RSM is capturing one of the essential properties of these machines: nonlinearities.

DIODE SWITCHING BEHAVIOUR

The diode currents shown here also compare well with the full transient solution.The diode switching behavior can be difficult to simulate,the fact the two simulations give identical results is as much a verification of the transient solution as of the system simulator.

PHASE VOLTAGES

The phase voltages are shown here.They are much smoother than their counterparts from the MagNet transient simulation,since the circuit simulator can afford to take much smaller time steps.Simulating this transient takes a few seconds in SystemVision,compared to many hours for the MagNet transient simulation.

BATTERY RIPPLE VOLTAGE

One of the benefits of the VHDL-AMS model is the ease with which different operating conditions can be simulated.Shown here is the battery ripple voltage at 1500 rpm and 3000 rpm.In both cases the resistive load has been adjusted such that the battery itself has approximately zero current through it.

DIODE BRIDGE BEHAVIOUR

At a lower speed (1500 rpm) the delta-connected diode bridge exhibits the behavior shown here.This result is obtained by simply editing the speed parameter in the claw-pole's property dialog.Another version of the claw-pole VHDL-AMS model has a separate mechanical terminal which allows an engine to drive the alternator at dynamically changing speeds.

3-phase Transformer

TRANSFORMERS WITH MAGNET

The model presented here is the simulated results of the ohmic losses and flux density of a 3 phase transformer with a three limbed paramagnetic core ( μ_p≈8.0412×〖10〗^(-3) N⁄A^2 ).The symmetry in the z-axis has been used to minimize the problem size and accelerate solution time.The coils are made of three concentric layers of different thickness.

Methods and Results

MESH

The initial 3D mesh contained 325,207 tetrahedra and 58,831 nodes for the Time-Harmonic 3D solver with second order Newton polynomials.The mesh is slightly modified during the simulation,因此,建立非均匀四面体。A comparison between the initial and the final 3D mesh can be seen.

MAGNETIC FIELD

To the left is a cut section of the B-field magnitude on the XZ plane at the middle of the coils,at 0° and 90°.The B field density stays below 0.26 Tesla.

CURRENT DENSITY ON MAIN COILS

This animation shows that the current density J on the surface of the main coils reaches 2.045 A/m2,each coil having a phase shift of 60°.

JXB LORENTZ FORCE

The force resulting from the interaction of the magnetic field and the current density is shown here to reach a peak of 329.5 kN.

IMPEDANCE OF EACH WINDING

The impedance of each winding can easily be calculated using the results from the 3D Time-Harmonic solver.Using the complex current and voltage of the windings provided by MagNet,either in separate magnitude and phase or in real and complex components.

TIME AVERAGE OHMIC LOSS

The picture shows the time average ohmic loss along z-axis oriented red arrow.The main winding has the highest ohmic power loss around 51 kW,the middle winding has approximate 31 kW ohmic power loss and the external winding has a 11 kW time average ohmic power loss.This graph was made using the Field Line Graph functionality of MagNet.The values given are time-averaged.