Design of a small power BLDC motor

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Dr. Vajda István
Department of Electric Power Engineering

Nowadays it is hard to come by a car that lacks power steering, despite the fact that power steering is primarily useful for larger, heavier vehicles like trucks or even earth-moving vehicles. Yet, power steering became a basic function of the “every-day car”, because customers expect a car with it. The Thyssenkrupp Presta Hungary Kft. develops power steering systems for some of the market leading car manufacturers, and at the heart of the aforementioned system is the servo motor. Normally PMSMs are used to fulfil similar functions, however in a number of occasions a special version, the brushless direct current motor (BLDC) is preferred.

During my dissertation project, I had the chance to calculate the electric design of a BLDC motor according to a given specification using the programs available at Thyssenkrupp. The specification data is basically drawn from the specifications of the power steering, which is given by the customer. I began by using Speed (analytical calculating software) to calculate the electric design, which would satisfy the specifications while also possible with current technology. Following this, carrying the result I used Flux 11.1 (finite element simulation software) to once more calculate the parameters of the design, run main simulations about phase currents and torque production, then at last I compared the results from both methods. The construction is successful, if both the analytical approach and the finite element software produce a result that has a tolerance of 10% (difference between the two results).

Hereinafter I made calculations that were not part of my dissertation project, but were useful in producing additional results. Using Flux and Portunus (power electronic simulator) from the same program family I successfully managed co-simulation to gain more accurate simulation result with the FEM method; during a script test I managed to run Speed from Matlab to calculate a specific simulation; furthermore I gained practical experience using Motorcad (a software designed for thermal analysis of electric motors and generators) with which a simulation was completed with a pre-set load cycle in accordance with the performance of the motor.

Overall, although only theoretically, a construction was calculated that would be in line with the current technological requirements, it would also reflect the specifications given by the customer. To make sure the design is accurate, a number of simulation software were used to check and simulate the calculations thus the final construction would be ready for production. Naturally, after production the engine will be thoroughly tested, and upon completion of these test runs could an engine be claimed fit for purpose. However, this is the next phase of production, and the limitations of my dissertation project did not allow me to partake in that.


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