Cascade Control vs Full-State Feedback

Cascade control systems find a wide range of applications and acceptance in the industry. They, however, are not as featured in the academy. Taking the case of a DC motor position control, this paper points out the advantages and limitations of the cascade control system. The current, speed and position controllers are tuned following the Root Locus and the Magnitude and Symmetric Optimum criteria. These last two methods are commonly found in German literature but not in America. The methods and the adjustment procedure for the nested loops are explained. Up next, the importance of a feedforward compensator, in order to mitigate the natural delay in the system time response due to the nested structure, is proved. Finally, the cascade control system is compared to state-space feedback control, highlighting limitations of a full state feedback design in terms of disturbance rejection, adjustability of control parameters and implementation challenges.