Isolating faults in BLDC motors using discrete square root filtering and Bayes Classification

Brushless DC (BLDC) motors are used extensively in the industry for a wide variety of applications. In the Aerospace industry, they are mainly used as a critical component in the control actuation system in launch vehicles, aircrafts and spacecrafts. A Brushless DC motor is prone to a number of faults that can develop into system failures at a later stage. In particular, overload and overheating can damage the stator coils, thus resulting in lower performance. Open circuit fault, short circuit faults and degradation of the magnets used, etc. are some other common faults that may appear in BLDC motors. Early detection and diagnosis of faults in safety critical systems is essential to have enough time for counter actions such as alternative operation, reconfiguration, maintenance or repair. In this paper, fault detection and isolation in BLDC motors using parameter estimation technique is presented. Discrete Square Root Filtering in Covariance form (DSFC) algorithm is used initially for estimating the physical parameters of the BLDC motor, Viz. resistance, back EMF, etc. The above algorithm has improved numerical properties for implementation in a digital computer. Detection of faults is carried out by comparing the estimated motor parameters with the a priori measured parameter values of the healthy system. Detailed fault diagnosis is subsequently carried out using Bayes Classification. Classification methods represent the diagnosis functional mapping from the symptom space to the space of fault measures. Bayes classifier is a statistical classification technique that is commonly used for fault diagnosis. The approach is based on reasonable assumptions about the statistical distribution of the symptoms that are indicative of the faults. Simulation studies carried out indicates that the developed fault detection and isolation scheme is capable of isolating different types of faults like open circuit, short circuit faults, performance degradation of magnets etc. in BLDC motors.