State estimation of an electronic throttle body

Electronic throttle body (ETB) is a device used in cars to regulate air inflow into the motor´s combustion system. Its good behavior is crucial for the superimposed engine speed control system. However, electronic throttle body is a highly nonlinear process, and its only measurable state is the throttle valve position measured by a cheap potentiometer of low resolution, resulting in significant quantization noise. In order to apply an advanced control strategy, all states should be usually available and the measurement noise should be reduced. With these two goals in mind we have implemented an extended Kalman filter (EKF), as a common solution for state estimation of nonlinear systems, and an unscented Kalman filter (UKF), which is a preferable solution when the process nonlinearities are very strong. Both filters are based on discrete time piece-wise affine process model which uses new friction model. By experimental tests on a real ETB it is shown that UKF gives better estimates of its state variables.