Fault tolerant control of electronically coupled distributed energy resources in microgrid systems

This paper proposes a sensor fault tolerant control (FTC) strategy for electronically-coupled distributed energy resource (DER) units in grid-connected microgrid systems. First, a fault dependent dynamical model of the DER unit incorporating sensor faults is proposed. The FTC strategy is then developed using a sliding mode observer (SMO) which has an inherent robustness property. The rational for using a SMO is the need to detect and reconstruct any fault that may occur in output measurements of the system as a result of sensor failure. The fault signals are reconstructed by using a robust approach that encompasses uncertainties in the system, such as frequency variation. This paper also represents the cyber attack as an unknown sensor fault, and consequently the DER current sensor measurements manipulated by a data integrity attack can be detected and reconstructed. The reconstructed fault signals are then used to modify the faulty sensor measurements, which are fed to the voltage source converter (VSC) controller. This ensures accurate generation of pulse width modulation (PWM) signals and consequently accurate tracking of real and reactive power references. Different case studies are tested on a detailed nonlinear model of the DER system. The impact of faults on the DER performance and the effectiveness of the proposed FTC scheme are evaluated through extensive simulation studies. Experimental verification of the method is provided to further validate the proposed approach.