Fault-tolerant speed measurement for the control of a DC-motor

This paper describes a control system that has been designed to handle sensor faults and therefore could be considered as fault-tolerant control one. The fault tolerant controller is based on the output of the speed sensor and two speed observers. The first one is a suboptimal Kalman filter based on the state model of the machine. The second one is based on the estimation of the frequency of one “rotor slot harmonic” present in the DC current signal which contains speed information. The two observers guarantee the best dynamic and steady state performances required by the application and also improve the reliability in the event of sensor loss or sensor recovery. The fault tolerant controller reorganization is based on a control decision block which depends on the steady state and dynamic performances of the two observers. The results of the control system show the effectiveness of this approach in the event of speed sensor loss and recovery.