Halvledare för höga strömmar i fordon
Examensarbete för masterexamen
Mechanical relays are more and more being replaced with semiconductor technology. In this thesis it is investigated if and how the larger loads could be controlled by transistors. The main part of this work aims to create and verify a solution that can control the starter motor, as well as protect it in case of any failure. The different malfunctions that the solution protects against is high current, too high peak current, low current, maximum crank time and minimum cool off time. The timers also protect indirectly against overheating of the starter engine. The transistors used are BTS555, from Infineon. Typical rated current of the transistor is 158 A and it has integrated functions such as temperature protection, short circuit protection and current sensing. The functions was tested and evaluated. The temperature protection and current sensor was found to satisfy the specification. The short circuit protection did not protect against all kinds of short circuit failures thus an external over current protection has been added. To control the starter motor, twelve transistors were connected in parallel, to allow for a total of initial start current 2 000 A and a continuous maximum current of 1 150 A. A series of tests were performed on the transistors, the external protections and the starter motor, until everything worked together as planned. The control circuits is designed with simple gate logic in combination with other active and passive components. The transistors are the largest expense. The used solution has an estimated price of 400 SEK, assembling excluded. The assembling is estimated to take one hour. Conclusions made from measurements and tests shows that it is possible to control the starter motor by using semiconductor technology. Since the solenoid in the current starter relay will not be excluded, the solution might be hard to motivate in an economic aspect. The advantages with a semiconductor solution are the protective functions and that the starter motor will be disconnected from the batteries when not being used. To control the smaller loads, such as the preheater, the semi conductor relay is a competitive alternative since the mechanical relay and the fuse can be replaced.
Elkraftteknik , Electric power engineering