Monitoring and fault-tolerant control of distributed power generation: Application to solid oxide fuel cells

This paper presents a hierarchical structure for fault detection and fault-tolerant control of distributed energy resources (DERs). The structure consists of distributed monitoring and control systems that perform local fault diagnosis and control system reconfiguration, together with a supervisor that communicates with the local controllers and provides high-level oversight and contingency measures in the event that local fault recovery is not possible. To realize this structure, an observer-based output feedback controller is initially designed for each DER to regulate its output in the absence of faults. The design accounts explicitly for practical implementation issues such as measurement sampling and plant-model mismatch. Fault detection is performed by comparing the output of the observer with that of the DER, and using the discrepancy as a residual. An explicit characterization of the minimum allowable sampling rate that guarantees both closed-loop stability and residual convergence in the absence of faults is obtained and used as the basis for deriving (1) a time-varying threshold on the residual which can be used to detect faults for a given sampling period, and (2) controller reconfiguration laws that determine the feasible fall-back control configurations that preserve stability. Finally, the design and implementation of the fault detection and fault-tolerant control architecture are demonstrated using a simulated model of a solid oxide fuel cell plant.