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Lyapunov Stability and Performance Analysis of the Fractional Order Sliding Mode Control for a Parallel Connected UPS System under Unbalanced and Nonlinear Load Conditions

Department of Electrical Engineering, Bahria University, Islamabad 44000, Pakistan
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Author to whom correspondence should be addressed.
Energies 2018, 11(12), 3475; https://doi.org/10.3390/en11123475
Received: 11 October 2018 / Revised: 12 November 2018 / Accepted: 13 November 2018 / Published: 13 December 2018
(This article belongs to the Section A: Electrical Engineering)
Parallel-connected uninterruptible power supply (UPS) systems have been used to maintain power supply to the critical load in order to increase power capacity and system reliability. This paper presents a robust and precise voltage control strategy for parallel-connected UPS systems. Each parallel-connected UPS system consists of a three-phase inverter with an output inductor-capacitor (LC) filter directly connected to an AC common bus in order to feed the critical load. Fractional-order sliding mode control (FOSMC) is proposed to maintain the quality of the output voltage despite linear, unbalanced and/or nonlinear load condition. The Riemann-Liouville (RL) fractional derivative is employed in designing the sliding surface. The voltage control strategy effectively eliminates the parametric uncertainties, external disturbances, and reduce the total harmonic distortion (THD) of the output voltage. Furthermore, it also maintains very good voltage regulation such as dynamic response and steady-state error under the nonlinear or unbalanced load conditions. The stability of the proposed controller is proven by applying Lyapunov stability theory. Droop control approach and virtual output impedance (VOI) loop are investigated to guarantee the accurate active and reactive power-sharing for parallel-connected UPS system. Finally, the implementation of the control scheme is carried out by using MATLAB/Simulink real-time environment. View Full-Text
Keywords: distributed generation; uninterruptible power supply; fractional-order sliding mode control; voltage-sourced converter; point of common coupling; virtual impedance loop distributed generation; uninterruptible power supply; fractional-order sliding mode control; voltage-sourced converter; point of common coupling; virtual impedance loop
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MDPI and ACS Style

Ali, M.; Aamir, M.; Khan, H.S.; Waqar, A.; Haroon, F.; Jafri, A.R. Lyapunov Stability and Performance Analysis of the Fractional Order Sliding Mode Control for a Parallel Connected UPS System under Unbalanced and Nonlinear Load Conditions. Energies 2018, 11, 3475. https://doi.org/10.3390/en11123475

AMA Style

Ali M, Aamir M, Khan HS, Waqar A, Haroon F, Jafri AR. Lyapunov Stability and Performance Analysis of the Fractional Order Sliding Mode Control for a Parallel Connected UPS System under Unbalanced and Nonlinear Load Conditions. Energies. 2018; 11(12):3475. https://doi.org/10.3390/en11123475

Chicago/Turabian Style

Ali, Muhammad, Muhammad Aamir, Hussain S. Khan, Asad Waqar, Faheem Haroon, and Atif R. Jafri 2018. "Lyapunov Stability and Performance Analysis of the Fractional Order Sliding Mode Control for a Parallel Connected UPS System under Unbalanced and Nonlinear Load Conditions" Energies 11, no. 12: 3475. https://doi.org/10.3390/en11123475

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