Disturbance observer for multivariate speed-dependent disturbance in DC motors

The disturbance observer (DOB) is a popular tool for disturbance rejection. However, it has not yet been employed in the literature to reject disturbances that are dependent on the output of the plant, though such disturbances are common. Recently, the second author employed the DOB to reject a disturbance that is dependent on the speed of a single motor. This paper extends that work to a system of multiple identical motors in which the disturbance acting on each motor is an output of a multi-input multi-output (MIMO) system with speeds of the motors as the inputs to this MIMO system. In four-wheel steering four-wheel drive (4WS4WD) electric vehicles with DC motors as the driving motors, this MIMO system models the tire-road interaction and dynamic load transfer of the vehicle. This paper develops the conditions under which the conventional DOB can be employed to reject disturbances that are the outputs of MIMO systems. Simulations illustrate the theory.