EMC optimized BLDC motor control

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Supervisor:
Naszály Gábor
Department of Measurement and Information Systems

In this thesis the driving of an electrically commutated brushless DC motor is described in details. This motor is built in the automatic transmission of vehicles and has the role of driving an electrical oil pump; therefore it has to fulfill all of the requirements of an automotive application. During the development these have to be taken into account, especially the voltage- and temperature range; moreover the EMC properties. The motor power can be several hundred watts, thus the current peaks and thereby the voltage break-ins can cause significant problems in the other units of the vehicle, hence the elimination, or at least reduction of the conducted noise is important. Furthermore the thermal-management of the electrical switching elements is also significant, because on the one hand the high power can cause high dissipation; on the other hand the dissipation is considerably restricted by the high temperature of the oil in the transmission. In addition, the cost factor is another viewpoint, because if the development is successful, it can be in mass production, where literally every cent counts.

The goal of the development is to evolve a new noise cancellation method for DC motors, where advantageous ceramic capacitors are used instead of electrolytic. Moreover I am trying to improve the EMC properties by trying different electronic commutation patterns out. However, changing the commutation pattern can increase the dissipation of the switching elements, not to mention that, how the new noise suppression can affect the price. During my thesis, I investigate the influence of the EMC and dissipation properties on each other, just as on the total cost; and trying to find an optimal solution.

In the course of my job, I approach first on theoretical basis the feasibility of the new method then I simulate them. Thereafter I design and assemble the prototype of the hardware. It is necessary to know the operation of the switching elements to handle the dissipation, thus I deal with it in detail. Finally, I set up a model, wherewith the influence of the commutating patterns and the different settings on the temperature can be observed. Last but not least, I verify my model with tests, draw the conclusions and give further opportunities for improvement.

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