Redesign of Control and Power Electronics for a Test-Bench for Small Internal Combustion Engines

Abstract: This report is about the redesign of control and power electronics for a test-bench for small internal combustion engines.

Since 2008, Luleå Tekniska Universitet is participating in the Shell Eco-Marathon competition, which is a contest in which you should build a car that drives the longest possible distance on the smallest amount of fuel. LTU has entered this competition a number times with a car called Baldos. In order to improve the performance of the motors in the cars that are going to compete they rent a test-bench to be able to test the motors efficiency and improve them. This is expensive so it is desired to have some sort of test-bench at the university. They have tried to build a test-bench but the electronics broke. So the goal is to redesign the electronics in order to have a working test-bench.

First the basic theory behind motor controllers are discussed. After that the theory of DC motors, PWM signals, the H-bridge, switching elements, and the particular problems that we will have to solve like power dissipation, overvoltages, speed control and how to do different measurements. We also introduce a simulation model in Pspice which helped us to predict how the test-bench would work. In addition we explain the relation between the model and the reality. This theoretical explications help us to explain the different decisions that were taken for the final design.

Moreover, we show how our design evolved. We speak about hardware, presenting all elements that we used, their characteristics, and the justification in the cases where it is necessary. Furthermore, we also introduce the software that we have used. We show the basic design and explain the communication between the different elements that we have.

In addition we show different simulations of the model that we made, the characteristics of the DC motor that we used and also a study about the effect of the parasite capacitance in a DC motor.

Finally we show the result in form of the new electronics for the test-bench, share different conclusions, and explaining how the design worked. We also add final impressions and possible improvements.