Parameter identification and adaptive control of an ultrafiltration process in hemodialysis

Develops a simplified time domain process model of ultrafiltration in hemodialysis, i.e., the process of removing excess water from the blood via a tubular filtering membrane. The excess water diffuses into a dialysate whose flow rate is controlled by a variable displacement pump whose displacement angle is governed by a PID controller. The entire process is then represented as a transfer function containing the PID controller parameters. The parameters of the PID controller are adaptively tuned to prescribed 2nd order (critically damped and underdamped) responses based on a least squares estimate of two critical modeling parameters that depend on the filtering membrane characteristics over the course of the dialysis. Simulation studies are performed for the case of magnitude and rate saturation on the pump actuator for a variety of membrane parameters as well as in the presence of blood pressure fluctuations. Results indicate very good performance.