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.
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.
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.
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?
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.
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.