Nyhetsflöde

Dear students,

Below is important information about the study visit to ABB Corporate Research, ABB LV Motors and ABB Machines.

Who can attend: The bus takes 49 passengers. The registered students are listed here. If your name is marked in yellow, you can only attend if students higher up on the list don't show up. 

Date: Wednesday Nov. 16th.

Time and place: The bus leaves from Lindstedtsvägen 3 at 7.50 SHARP. Be there on time or you will not participate. 

Lunch: ABB Corporate Research serves a salad lunch to each participant.

Best,

Oskar

Dear students,

Eq. (1) in Project 3's project description contains a typo. The correct expression should be:

$$T_e\!=\!\frac{3p}{4}\left(\psi_di_q-\psi_qi_d\right).$$

Here is the project description without the typo.

Sincerely,

Oskar

Dear students,

Petter Eklund provided the following neat tips regarding how the code for Project 1 can be made faster:

In Geometry.m: 

Change line 7 to:
mi_probdef(SlipFreq,'meters','planar',1e-8,ActiveL,30,1);

The last parameter (=1) causes the solver to use Newton-Raphson which will render the solving times considerably shorter.

Thanks Petter!

Best,

Oskar

Dear students,

After yesterday's two lectures, the complete course content has been covered. To really grasp the more advanced aspects covered in Chapter 8 (the interaction between eddy-current and hysteresis losses and Tellinens's hysteresis model) you absolutely have to spend some time with the text in your study chamber.

Further, Claes pointed out an error on one of the lecture slides (the missing \(j\)). Here is the corrected slide (the error is not present in the course book).

Looking forward to discuss with you during the coming project tutorial sessions.

Sincerely,

Oskar

Dear students,

Some input regarding Project 1 following the discussions during today's project work:

• When computing the rated torque using FEMM and comparing with the motor rate plate data, it is reasonable to assumed that the rotor bars are not at room temperature; 100 degC is more close to reality.
• Remember also to take the short-circuit ring into account when setting the conductivity for the rotor bars (as outlined in the course book).
• The air-gap length is close to \(\delta\!\approx\!0.3\) mm (rather than 0.4 mm I saw that some used in their code).

Best,

Oskar

Dear students,

Here is a photo of the motor template for the motor used in Project 1 and 2.

Best,

Oskar

Dear students,

After today's lecture, Chapter 5 and Chapter 6 have now been covered in complete. On the two coming lectures, I plan to cover Chapter 7 (first lecture on Tuesday Sept. 27th) and Chapter 8 (second lecture on Tuesday Sept. 27th). 

Best,

Oskar

Dear students,

Today, I covered Section 6.1 to Section 6.7.2 in the course book. During next lecture, I aim to cover Chapter 6 in complete and conclude with the remaining FEM theory in Chapter 5.

Best,

Oskar

Dear students,

In Project 1, assignment 2.1 b), you may learn more by plotting the radial flux density from FEMM using a material in the rotor and stator laminations with very high relative permeability (e.g., \(\mu_r\!=\!10000\)). In this way, the impact of magnetic saturation will be removed and the agreement with the theory developed in Chapter 1 will be better. In summary, for assignment 2.1 b), it is ok to use a "linear steel" when comparing with theory.

Best,

Oskar

Dear students,

For Project 1, I have received some questions about how to add a contour in the whole air gap in order to plot, e.g., the air-gap flux density. It can be done in several ways but this is how I implemented it in Matlab:

%Clear all selected contours (if any)
mo_clearcontour;
%Define a contour in the middle of the air gap
mo_addcontour(0,-RotorRad-AirGapHeight/2);
mo_addcontour(0,RotorRad+AirGapHeight/2);
mo_bendcontour(180,5);
mo_addcontour(0,RotorRad+AirGapHeight/2);
mo_addcontour(0,-RotorRad-AirGapHeight/2);
mo_bendcontour(180,5);

Best,

Oskar

Dear students,

On today's lecture, I covered Chapter 2 in complete and Sections 3.1-3.4.2 in Chapter 3. On Thursday's lecture, I plan to cover the remaining parts of Chapter 3 and Sections 5.3-5.4 of Chapter 5. If time allows, I will continue with the first parts of Chapter 4.

As a preparation for Friday's project work, please install FEMM on your laptop and make sure that you can run the Matlab files belonging to Project 1. Most likely, you need to change the path where the FEMM files are located. Hence, you need to edit the 'addpath' command (on line 8 in RunMe.m) to point at the correct location (i.e,. where femm42\mfiles are located on your computer).

Best,

Oskar

Dear students,

After yesterday's lecture, we have now covered Chapter 1-3 in complete and Chapter 5 except for the parts presenting the details of the finite element method. On the next lecture, I aim at covering Chapter 4 in complete.

An interesting question (question 2 below) arose that I, on the lecture, wasn't able to provide a good enough answer to. The question(s) went along these lines:

The force (due to the magnetic field only) is given by Lorenz force law, i.e., \(\mathbf{F}\!=\!q\left(\mathbf{v}\times\mathbf{B}\right)\Rightarrow d\mathbf{F}\!=\!\mathbf{J}\times\mathbf{B} dV\).

Question 1: Why does \(\Rightarrow\) hold here; i.e., can you illustrate how the force on a travelling charge \(q\) travelling with the speed \(\mathbf{v}\) is related to the current density \(\mathbf{J}\)?

Question 2: \(\mathbf{J}\) is identically zero in the air gap. Then, \(d\mathbf{F}\) is also zero. Hence, computing the torque by integrating along the air gap would yield zero torque. Why is this not the case?

"Answer": In this document (proper reference on first page, relevant parts in yellow) it is shown why \(\Rightarrow\) holds. Further, the force on a conductor carrying a current and subjected to an external magnetic field is calculated both by integrating the total force in the region where \(\mathbf{J}\!\neq\!0\) (i.e., inside the conductor) as well as using Maxwell's stress tensor outside the conductor (where \(\mathbf{J}\!=\!0\)). The result of the two calculations are identical and while this only is a verification by example, it represents a good argument why Maxwell's stress tensor can be applied to calculate torque of electric machinery by integrating in the air gap.

Best,

Oskar

Dear students,

On the first lecture, I covered Chapter 1, pp. 1-12. On the next lecture, I aim at covering Chapter 1 in complete as well as Section 5.1 and Section 5.3 to Section 5.5 in Chapter 5. I recommend you to read ahead in advance.

Best,

Oskar

Dear students,

The course's project assignments are included in the course material available at STEX but you can also get them here. The deadlines for the project hand ins are:

• Project 1 and Project 2: Friday, Sept. 30th.
• Additional two projects (most students do Project 3 and Project 4): Friday, Oct. 14th.

Note that for PhD students following the course, all five projects have to be handed in though no strict deadlines are given. If you belong to this category, I strongly recommend you to follow the deadlines above anyway (at least for Project 1-4).

Best,

Oskar 

Dear students,

For some of of the projects, you need some additional files. They can be downloaded here:

Project 1

Project 3

Project 4

Best,

Oskar

Dear students,

Soon, you are welcome to the course 'EJ2222 - Design of electrical machines'; looking forward to meet you all. As a preparation, you can now buy the course material at STEX (Osquldas väg 10).

To further prepare, make sure to have FEMM (Windows only) and Matlab installed on your laptop (if you have one). The freeware FEM solver FEMM can be downloaded at http://www.femm.info/wiki/HomePage

Best regards,

Oskar Wallmark (course responsible)