MIMO disturbance observer for input-output decoupling with application to 4WAS vehicles

A multi input multi output (MIMO) version of the sliding mode disturbance observer (SMDO) scheme for decoupling MIMO nonlinear uncertain systems into single input single output (SISO) systems is presented in this work. The cross-couplings between inputs and outputs, modeling and parameter uncertainties and external disturbances are treated as an extended disturbance to be attenuated by the MIMO disturbance observer. The proposed MIMO disturbance observer has been applied to the four wheel active steering (4WAS) control problem of a road vehicle which has been modeled in CarSim environment. The performances of the MIMO SMDO have also been compared to the performances of the MIMO inverse model based disturbance observer (IMDO) which is a well-known two-degrees-of-freedom disturbance observer architecture in motion control and PID control.