An Enhanced Joint Indicator for Starter Failure Diagnostics in Auxiliary Power Unit

Degradation of the starter can lead to the failure of starting Auxiliary Power Units (APU) and the consequent safety hazards. To improve performance monitoring and malfunction prediction of APUs, in this paper, two indicators are developed based on the physics-based model of the APU starting process. The indicators quantify the health level of the starter and provide diagnostic information with no need for past measurements from the system. The health indicators are proposed to identify the degradation of the starter at both the system level and component level. An enhanced joint indicator is then developed to aggregate the two individual indicators to detect the starter failure within a two-dimensional feature space. Receiver operating characteristic (ROC) curves are adopted to evaluate the diagnostic performance of the three indicators and the optimal thresholds are determined based on the trade-off between the diagnostic reliability and the operating cost reduction. The enhanced joint indicator exhibits superior diagnostic performance and offers a significant improvement in overall maintenance costs.