Sensor Fault-Tolerant Control of Microgrid Using Robust Sliding-Mode Observer

Ebrahim Shahzad; Adnan Umar Khan; Muhammad Iqbal; Ahmad Saeed; Ghulam Hafeez; Athar Waseem; Fahad R Albogamy; Zahid Ullah

doi:10.3390/s22072524

Sensor Fault-Tolerant Control of Microgrid Using Robust Sliding-Mode Observer

Sensors (Basel). 2022 Mar 25;22(7):2524. doi: 10.3390/s22072524.

Authors

Ebrahim Shahzad¹, Adnan Umar Khan¹, Muhammad Iqbal², Ahmad Saeed¹, Ghulam Hafeez^{3

4}, Athar Waseem¹, Fahad R Albogamy⁵, Zahid Ullah⁶

Affiliations

¹ Department of Electrical Engineering, FET, International Islamic University, Islamabad 44000, Pakistan.
² Research and Innovation Centre of Excellence (KIOS CoE), University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus.
³ Centre of Renewable Energy, Government Advance Technical Training Centre, Peshawar 25100, Pakistan.
⁴ Department of Electrical Engineering, University of Engineering and Technology, Mardan 23200, Pakistan.
⁵ Computer Sciences Program, Turabah University College, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia.
⁶ Department of Electrical Engineering, University of Management and Technology Lahore, Sialkot Campus, Sialkot 51310, Pakistan.

Abstract

This work investigates sensor fault diagnostics and fault-tolerant control for a voltage source converter based microgrid (model) using a sliding-mode observer. It aims to provide a diagnosis of multiple faults (i.e., magnitude, phase, and harmonics) occurring simultaneously or individually in current/potential transformers. A modified algorithm based on convex optimization is used to determine the gains of the sliding-mode observer, which utilizes the feasibility optimization or trace minimization of a Ricatti equation-based modification of H-Infinity (H∞) constrained linear matrix inequalities. The fault and disturbance estimation method is modified and improved with some corrections in previous works. The stability and finite-time reachability of the observers are also presented for the considered faulty and perturbed microgrid system. A proportional-integral (PI) based control is utilized for the conventional regulations required for frequency and voltage sags occurring in a microgrid. However, the same control block features fault-tolerant control (FTC) functionality. It is attained by incorporating a sliding-mode observer to reconstruct the faults of sensors (transformers), which are fed to the control block after correction. Simulation-based analysis is performed by presenting the results of state/output estimation, state/output estimation errors, fault reconstruction, estimated disturbances, and fault-tolerant control performance. Simulations are performed for sinusoidal, constant, linearly increasing, intermittent, sawtooth, and random sort of often occurring sensor faults. However, this paper includes results for the sinusoidal nature voltage/current sensor (transformer) fault and a linearly increasing type of fault, whereas the remaining results are part of the supplementary data file. The comparison analysis is performed in terms of observer gains being estimated by previously used techniques as compared to the proposed modified approach. It also includes the comparison of the voltage-frequency control implemented with and without the incorporation of the used observer based fault estimation and corrections, in the control block. The faults here are considered for voltage/current sensor transformers, but the approach works for a wide range of sensors.

Keywords: H∞; Lyapunov stability; PI control; current/potential transformer; fault diagnosis and estimation; fault-tolerant control; linear matrix inequalities; microgrids; robust control; sliding mode observers.