Relay Based Auto Tuner for Calibration of SCR Pump Controller Parameters in Diesel After Treatment Systems

In this paper, the application of relay-based auto tuning method for calibration of PID parameters of SCR (Selective Catalytic Reduction) pump pressure controller in a diesel engine is described. SCR pump, which is defined as the plant of the system in this study, provides urea for pressure line in the SCR urea dosing system. The pump is actuated by a BLDC (brushless DC) motor and the motor adjusts the pump frequency. As a result, the speed of the motor is controlled by PWM signal which is determined by PID controller. Auto tuner was designed to bypass the actual SCR pump controller with relay signal which introduces an oscillation to the system. Based on the relay and plant output signals, system identification is finalized as a first order system with dead time. Once the model is identified, different tuning algorithms such as Ziegler-Nichols, Tyreus Luyben, Ciancone-Marlin and Internal Mode Control become available for comparison. The best algorithm, based on comparison results, can be selected by users. In this study, Ziegler- Nichols method is chosen based on the system performance.