Electric Motor Design and Development Process

How to design an elec­tric motor with high effi­cien­cy and which elec­tric motor design soft­ware is best for this. The pro­ce­dure described here can be applied to both AC motors and DC motors. AC motors include BLDC motors, which are also known as brush­less motors. Axi­al flux motors and induc­tion motors, such as those made by Tes­la, are also designed using this method. The design steps and elec­tro­mag­net­ic cal­cu­la­tions for elec­tric motors are described below.

bldc motor design and development process
elec­tric motor design and devel­op­ment process

1) Define Electric Motor Requirements

The first step to design an elec­tric motor is to write down what the elec­tric motor should do and be able to do. In the indus­try, this is also referred to as defin­ing the require­ments for the elec­tric motor. So how much torque and speed should the elec­tric motor have. What pow­er and effi­cien­cy, how long should the motor be, what diam­e­ter should the motor have. You should start by defin­ing the require­ments for your spe­cif­ic appli­ca­tion, for exam­ple an elec­tric vehi­cle, elec­tric boat or elec­tric air­plane. From this, the require­ments for the elec­tric dri­ve and the bat­tery sys­tem should be derived. From the require­ments for the elec­tric dri­ve, the require­ments for the elec­tric motor and also the invert­er can then be derived. The require­ments should also be pri­or­i­tized so that every­one in the devel­op­ment team knows what is most impor­tant. The pri­or­i­ti­za­tion is impor­tant so that the right type of elec­tric motor can be select­ed later.

electric motor requirements
derive elec­tric motor requirements

2) Create Architecture of Electric Drive System 

An archi­tec­ture of the elec­tric dri­ve sys­tem should also be cre­at­ed, con­sist­ing of the elec­tric motor, an invert­er and, if nec­es­sary, a gear­box. An archi­tec­ture helps to under­stand how the dif­fer­ent com­po­nents inter­act with each oth­er, i.e. mechan­i­cal­ly, elec­tri­cal­ly and ther­mal­ly. The archi­tec­ture helps to under­stand the rela­tion­ships and inter­ac­tion of the elec­tric motor, invert­er and gear­box. With the archi­tec­ture it can be dis­cussed how the dri­ve sys­tem can be opti­mized and where costs can be reduced.

architecture of electric motor drive system
archi­tec­ture of elec­tric motor dri­ve system 

3) Selection of Electric Motor Type and Comparison

In the pre­s­e­lec­tion should be very care­ful­ly con­sid­er what type of elec­tric motor is the best for the spe­cif­ic appli­ca­tion. Each elec­tric motor has its advan­tages and dis­ad­van­tages. With the help of the pre­vi­ous­ly writ­ten require­ments and a pri­or­i­ti­za­tion should be com­pared, which type of elec­tric motor is best suit­ed for the spe­cif­ic appli­ca­tion. It should also be care­ful­ly con­sid­ered in which num­ber of units the elec­tric motor is to be pro­duced lat­er. Because the wind­ing tech­nol­o­gy used is also derived from the num­ber of units. And the wind­ing tech­nol­o­gy has a great influ­ence on the elec­tric motor design.

4) Select a Starting point for Motor Design Calculation

Select the cor­rect start­ing point of the cal­cu­la­tion is not so impor­tant. There are equa­tions for esti­mat­ing the size of the elec­tric motor for a giv­en pow­er. But the eas­i­est way is to sim­ply look at what dimen­sion used oth­er man­u­fac­tur­ers and com­peti­tors who have sim­i­lar require­ments. In most cas­es, the start­ing point for the elec­tric motor design is already giv­en by the require­ments for the motor length and the motor diameter.

5) Analytical Electromagnetic Motor Design Calculation

Ana­lyt­i­cal soft­ware tools are used for the design and cal­cu­la­tion. Input into the soft­ware are the para­me­ters like diam­e­ter, length and volt­age of the elec­tric motor. The motor design soft­ware then cal­cu­lates the torque and speed ana­lyt­i­cal­ly using an equa­tion. This also takes only a few sec­onds until you have a result. You then change the para­me­ters until you get the desired torque. The adjust­ment of the para­me­ters needs a lot of expe­ri­ence because each para­me­ter has a direct influ­ence on dif­fer­ent prop­er­ties of the elec­tric motor. For exam­ple, you can also use opti­miza­tion algo­rithms to help you devel­op a par­tic­u­lar­ly effi­cient elec­tric motor. How­ev­er, the ana­lyt­i­cal cal­cu­la­tion has a big prob­lem and that is the accu­ra­cy of the result of speed, torque and effi­cien­cy. The accu­ra­cy is usu­al­ly between 70 to 80 per­cent. It depends on the com­plex­i­ty of the elec­tric motor and the soft­ware used. How can you now improve the accu­ra­cy or check your result?

ana­lyt­i­cal elec­tric motor design

6) 2D FEM Electric Motor Simulation

The best way to check the ana­lyt­i­cal cal­cu­la­tion is with a 2D FEM sim­u­la­tion. Here, 2D means that the motor is divid­ed into many small pieces in the two dimen­sions X and Y. The small­er these pieces are, the more accu­rate the result will be. The small­er you make these pieces, the more accu­rate the result of the sim­u­la­tion will be, but this will also require more com­put­ing time. The results can then be used to improve the para­me­ters in the ana­lyt­i­cal cal­cu­la­tion. So why should you even take the step back into an ana­lyt­i­cal cal­cu­la­tion again? In a two-dimen­sion­al sim­u­la­tion, only exact­ly one load point is usu­al­ly cal­cu­lat­ed, i.e. the effi­cien­cy at exact­ly one speed/torque point. This usu­al­ly takes sev­er­al min­utes to hours, so it makes more sense to cal­cu­late an effi­cien­cy map ana­lyt­i­cal­ly, with adapt­ed para­me­ters from the 2D simulation.

fem electric motor simulation
2D fem elec­tric motor simulation

7) 3D FEM Electric Motor Simulation

When and why do you also need a 3D sim­u­la­tion? Well, 2D sim­u­la­tion assumes that the struc­ture is repeat­ed in the Z‑direction. But if you look at the elec­tric motor from above, for exam­ple, this is not the case at the top and bot­tom ends of an elec­tric motor. Stray flux­es can occur at the top and bot­tom ends of the motor and one should esti­mate how large their influ­ences are. For very short elec­tric motors, the influ­ence of stray flux­es can be large. There­fore, the results of the 3D sim­u­la­tion should be used again in the 2D sim­u­la­tion. Because the cal­cu­la­tion of an elec­tric motor char­ac­ter­is­tic curve in a 3D sim­u­la­tion would require too much com­put­ing capac­i­ty and time. Anoth­er exam­ple where 3D sim­u­la­tions are need­ed are axi­al flux motors where the elec­tro­mag­net­ic field changes in all 3 dimen­sions. In very long elec­tric motors, bend­ing vibra­tions of the shaft can occur, caus­ing the dis­tance between rotor and sta­tor to change over the length. This dis­tance is also called air gap and its change has of course influ­ence on the torque and its course.

Additional Points for Electric Motor Development

Electric Motor Tests and Measurement

Any­one who sim­u­lates and cal­cu­lates should of course also know how to check the results. Because the dif­fer­ence between the­o­ry and prax­is is big­ger in prax­is than in the­o­ry. Check­ing the results can be divid­ed into 3 steps. Mea­sur­ing the mate­ri­als, for exam­ple the mag­nets and the sheet met­al. The mea­sure­ment of the com­po­nents, for exam­ple the rotor with the mag­nets and the sta­tor with the wind­ings. And final­ly, of course, an active and pas­sive mea­sure­ment of the com­plete elec­tric motor. One should start mea­sur­ing mate­ri­als and com­po­nents as ear­ly as pos­si­ble and incor­po­rate the results into the sim­u­la­tion to improve it.

Mechanical and Thermal Electric Motor Design 

The mechan­i­cal and ther­mal design and sim­u­la­tion of an elec­tric motor is also very impor­tant. Because only with the ther­mal sim­u­la­tion can you find out how long the elec­tric motor can real­ly pro­vide the max­i­mum pow­er. The pro­ce­dure for ther­mal design and cal­cu­la­tion is very sim­i­lar to the elec­tro­mag­net­ic design described above. The results of the elec­tro­mag­net­ic sim­u­la­tion, such as the pow­er loss­es, are incor­po­rat­ed into the ther­mal sim­u­la­tion. A mechan­i­cal sim­u­la­tion is par­tic­u­lar­ly impor­tant if the elec­tric motor gen­er­ates large torques or reach­es high speeds.