ANSYS Motor-CAD: Demagnetization Modelling and Analysis of an IPM Motor

Hello everyone, David Giglio here with Ozen Engineering. In this video, I will discuss how to use ANSYS MotorCAD to model and analyze the demagnetization of permanent magnets and the effect this has on the back EMF and torque performance of an IPM motor.

Go to file for this example, open template, choose the E8 automotive application template.

Then go to input data, settings, calculation, and set the magnet mesh length to 0.5 and set the air gap internal points and air gap surface points to 720. In the materials tab, go to magnet, change the type to N38UH, which has a remnant flux density reference value of 1.26 Tesla at a reference temperature of 20 degrees Celsius.

In the materials database tab, we can select materials using the model, and we will see all the material names for the material in the model. Select the magnet name, and we will see the display of the demagnetizing curves for this material.

We see in the dashed line that Maxwell defines the linear region as the point which separates the linear region from the nonlinear region, and this point is defined as the deviation from the linear region by 10% or more.

So, as we move away from the linear region and as this slope, this linear slope, deviates by 10%, we enter the nonlinear region. Let's discuss some characteristics of the linear region.

The linear region is carefully set up to ensure that the x and y coordinates are below 50 and z units are in µregel for each front and back mirror normal.

The standard virtual normal curve can be scaled down to zero, and if the VICO-aligned curves are coming from the same point at some point in the current, the Nmul curves and as we set the similarly, the red curves are called the normal curves and are defined by this equation here.

As the intrinsic curve is defined here. And the leftmost curve is the curve of the lowest temperature. As temperature increases, these curves, similar curves, they scale down. So, let's look at the linear region operation. Let's say we start at point A.

We have a remnant flux density at this temperature. And we move from point A to point B. We see that the flux density decreases. So, the magnets demagnetize. And if we increase the temperature, we go to point C. The magnets demagnetize further.

However, since we're in the linear region, we can reverse the operating points. Reverse the operation of the motor. Go back the same path. And we can return to the original operating point. And the demagnetization is fully reversed.

However, if we operate at any point on any non-linear part of the curve. For example, we go to point A, point F. We're in the linear region. But then we increase the temperature. We go to point E. And then we cool the magnet to the point C. And then we go to point E.

The magnet flux density will not return to point F. Even if we cool it back to the temperature of 20 degrees. It will be at a lower point. Such as G, for example. And if we reduce H to zero. It will return in this path here. Known as a recorrelation. So, at H zero.

The point is not on the original point A. The remnant flux density will be lower. And similarly, let's say we are at point D. On this 180 degree Celsius curve. We can increase H. Be at point C. We can remove H to zero. We will go back to point D. And we can increase H. And we can remove H to zero.

We can go back to point D. The demagnetization is reversed. So, go to point C. The magnet is demagnetized. But we can reverse the operation. And go to point D. However, if we go from point D to point E. We enter the nonlinear region. And then we remove H. Reduce it to zero.

We return on this recoil path. And we end up with a remnant flux density that is less. As long as we operate always operate in the linear region. We can go from different curves. Right? Different temperatures. 20 degrees. We can go to 160. 180. Right? And we can go back. We cool the magnets.

We go back to the original operating point. Whenever we go to any nonlinear region on any curve. And we cannot go back in reverse to the same path. Right? We will return to H zero at a different point. And here. So, BR is temperature dependent. It is expressed in terms of a reference.

Remnant flux density. Multiply the value. The expression within the parentheses. And alpha is negative. So, as temperature increases. This value expressed within the parentheses. Is less than one. And a value less than one. Multiply the reference value. Will give a smaller. Value for BR. Okay?

And the normal curve. Is expressed as. B equals the reference. The remnant flux density. Plus mu H. Where mu can be expanded. And multiply across H to. So, we have these two terms. Mu naught H. Plus mu naught chi H. And the intrinsic curve is defined as. J equals the remnant flux density.

Plus mu naught chi H. The nonlinearity of the curves. Are embedded in this chi term. Okay. So, let's go back to motorcat. Now go to calculation. We set the current to 480 amps. Set the phase advance angle. Electrical angle to 45 degrees. The highest short circuit transient.

Usually occurs if the short circuit. Arises at peak torque. And basic speed. Set the magnet temperature to 160 degrees. For this example. And set the armature winding temperature. To 165 degrees. The armature winding temperature. Should be higher than the magnet temperature.

Since the armature windings. Are the main sources of heat. In the motor. And drives the temperature rise. In the machine. And then on the performance test. We check the sudden short circuit box. The short circuit will be applied to all phases. And we are doing this test.

To calculate the operating point for the current. In. Under the short circuit conditions. Now we. Select solve electric model. And in a few seconds. We get the solution. And we go to graphs. We go to dq axis current versus time. And we see that the. We looking at the peak. Negative peak.

And we see that. The. Negative peak. Of the. D axis current. Okay. Here is 11. Negative 1100. So we go to. Calculations. We set this to. 1100. And set the phase to 9 degrees. To get the negative value. Right. And then we uncheck. Sudden short circuit. And now we select. The magnetization.

And now we run. The magnetization test. And in a few seconds. We get the result. The magnetization test. And in a few seconds. We get the result. The magnetization test. And in a few seconds. We get the result. And then we can analyze. The results. On the table here. Out the data. And. Here.

Shows the. Reference. Magnet. Magnetic. On flux density. Value. 1. 26. Tesla. At temperature. 160 degrees. At. What. I want. So. 1. 26. Tesla. Is at 20 degrees. And at 160 degrees. Temperature. Of the magnet. The remnant. Flux density. Is 1. 0. For eight. The knee point.

Is 0. 2645. At this. 160 degrees. Celsius curve. And. The magnet. The magnetization. Ratio. Is. 0. 9488. Which. Means. Among. All. The magnets. Right. The total volume. Of the magnets. 94. Point. 8. 8%. Has. Been. Demagnetized. Not. Considering. The amount. The extent. Has. Been. Demagnetized. By.

Any. Amount. By. Any. Extent. Yes. So. 94.8%. Has. Been. Demagnetized. So. In. Terms. Of. Individual. Magnets. One. Of. The. Magnets. In. The. Lower. Level. Of. Magnets. Okay. Again. Now. Remember. This. Is. Not. The. Extent. Not. How. Strongly. They. Have. The. Magnet. Is. Just. Yes. Or. No. Has.

The. Magnet. Be. Demagnetized. By. The. Extent. Of. The. Permanent. Demagnetization. Right. Permanent. Magnetic. Flux. Loss. Permanent. Magnetic. Flux. Density. Loss. Right. So. At. At. 160. Degrees. Right. The. Remnant. Flux. Density. Is. 1. 0. 0. Five. And. So. If. The. Magnetization. Is.

Permanent. Is. 100. Fulfillment. Of. Permanent. Magnetic. Flux. Density. Right. There. Are. Some. In. The. Western. Question. Right. Of. The. Magnetization. magnets have not operated in the nonlinear region.

Okay, that's there for reference, but these magnets have operated in the nonlinear region, and we see that the L2 magnets, magnets closer to the windings over here, closer to the air gap, have been permanently demagnetized, and it shows the B field within the magnet pointing in the opposite direction intended for it.

Opposite direction, the magnets were designed to operate in, okay?

And we see that the magnetic flux density is non-uniform, and the magnets, L1 magnets, further away from the air gap, further away from the windings, the windings which are producing the opposing field, producing the demagnetizing field, right?

It does not affect the L1 magnets as much as the L2 magnets. We see that the L1 magnets still have its magnetization pointing outwards, and the magnetic flux density within these magnets are very uniform, except in the sides, there's slight variation.

Let's now go to the calculation tab and model the demagnetization effects on back EMF and torque. So on the performance test, select torque, we may leave demagnetization checked or unchecked. If we leave it checked, we will have the demagnetization results available in the output.

In the output data tab, if we uncheck this, these results will no longer be available. However, this is not necessary to analyze the demagnetization effects on the torque and back EMF, right? So let's choose, go to input data, settings, graphs.

We choose data points and lines to have this on the plots. In calculation, we will choose custom, waveform, and the drive type appears when we select this.

And then whatever waveform we have here, we need to clear all points, load the waveform you want to choose for this analysis, short circuit, demagnetization effects on the back EMF. And our waveform shown here that we're using for this example, the first two cycles are zero current.

And then the third cycle, there's a short circuit, no light short circuit, which will be multiplying, scaling the value we have here for the peak current, 1100 amps for this short circuit operating point. And at the end of the third cycle, the two remaining cycles have zero current.

So this is the waveform we have. We just now need to run, solve the emagnetic model. We have the results now, the model's solved in, one minute and 10 seconds, which is actually quick.

So to see the results, we go to graphs, terminal voltages, and we can see, we can zoom in, let's see before the short circuit, the voltage is about 244 volts. And then we can go to, after the short circuit, we see the voltage reduced to 195 volts approximately.

This is a 20% reduction in the terminal voltage due to the demagnetization effects on the back EMF. Okay, now we can go to calculation. We can go to, again, drive. We can clear these points, go to load the waveform. Now we're gonna see the effects on the torque.

So go to your waveform you wanna use for this analysis. Here we have it from the tutorial folder.

And now in this case, we have normal operation for two cycles, and then a short circuit occurs, a scaled, normalized short circuit waveform, which will multiply again the peak current, 1100 amps, and we have phase of energy zero degrees. Now we solved electric magnetic model, and let's, just, wait.

It should take perhaps a little more than a minute. So I'll pause here until we get the results. Torque, the emagnetic model solved in just over a minute. And we'll go to now, go to graphs. We can see the torque curves.

We go to, before the short circuit occurred, the peak torque is about 283 newton meters. And after the short circuit, the, short circuit, we can see the peak torque. Peak torque is about 262 newton meters. This is about a 7.42% decrease in the torque due to the magnetization.

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