The chronic renal disease as the frequent secondary disease of the diabetes is quite often among elderly people. This illness is lethal and cannot be cured; however the life of those patients who have this illness can be elongated by dialysis therapy. This therapy requires a dialysis machine which cleans the blood of the patient with dialysate fluid through the dialyzer. This fluid is prepared by the hemodialysis machine using the following components: cleaned and filtered water and salt solutions. Besides the salt concentration the fluid flow and the temperature are also important parameters of the dialysate fluid.
My thesis is about the examination of the control loops of the hemodialysis machine; its task is to prepare the dialysate fluid. Besides the examination of the operation of these control loops, my task was to understand the hardware and the software structure of the machine, identify each relevant plant, and plan the optimal controllers for them. I also had to test the robust performance of the implemented controllers.
During the first semester of the thesis, I could understand the structure of the machine and the parameters of the flow control plant had been identified and two types of controllers were implemented, and tested on the dialysis machine.
In the second semester I implemented an adaptive controller that decreased the fluctuation of the flow pumps. After that, I created a cascade temperature controller that was able to control the temperature of the dialyzer despite of the large delay time and the external noises, and a conductivity controller that was capable of mixing two different dissolved salts into the dialyzing fluid with the appropriate mixing ratio.
At the end of my thesis I analyzed the implemented control loops for robust stability and robust performance.