Design of MRAS based control systems for load sharing of two DC motors with a common stiff shaft

In this paper, the behavior of a stiff shaft in a drive system consisting of two DC motors driving a common load is investigated. The expectation is to get both motor armature currents to match, indicating successful load sharing. The new idea of using Model Reference Adaptive Systems (MRAS) approach has been applied to design a control system such that two motors are identical in speed-torque characteristics. The design can be achieved in such a way that the two motors can contribute the same amount to the total load in the case that the DC motors are identical, or contribute partly to the total load and proportionally to their nominal torques in the case that the two motors are not identical. Both simulation and experimental results confirm the precise and robust performance and the ease of tuning and implementation, featured by the proposed control structure. The slave motor current strictly follows the master motor current with a maximum error between them is always smaller than 5%.