Investigating thermal and life-cycle properties of multi-layer ceramic capacitors

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Supervisor:
Dr. Kovácsházy Tamás
Department of Measurement and Information Systems

This thesis is about investigating thermal and life-cycle properties of multi-layer ceramic capacitors (MLCC), on which I worked at Robert Bosch Ltd., GS-TC Division in Budapest. This division develops control electronics for automatic transmissions, as well as electric oil pumps for gasoline systems. Due to the high temperature of the oil in the transmission, thermal-management and component optimization issues occur. Currently the power line buffering of DC motors is resolved by aluminum electrolytic capacitors because of their high capacitance, although several problems came up with these components, such as life time reduction due to the extreme temperature conditions and the big space they require compared to the MLCCs. On the grounds of these issues a need has conceived, that the electrolytic capacitors should be replaced by ceramic capacitor banks, working in a higher switching frequency, thus producing similar properties. Before applying these changes, further investigations and measurements are required, that will be described in this thesis.

In the course of my task, I am searching for the appropriate capacitors for this application, creating a heat conduction model of these components, then running thermal and life time tests with various electric and temperature properties for validation of the theoretical model. After evaluating the results of the measurements I will be able to create a self-heating and life time model of these MLCCs, as well as to determine a valid rated current for the capacitors, which is unknown at the moment. During the continuous operation life time test, electric parameters, such as capacitance and the equivalent series resistance will be monitored periodically in order to discover the adventitious deratings of the capacitors. By documenting these deratings, a mathematical model can be set up in the function of time and parametric changes.

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