0278-0046 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIE.2015.2477486, IEEE Transactions on Industrial Electronics IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS Sliding Mode Control for Single-Phase Grid- Connected LCL-Filtered VSI with Double-Band Hysteresis Scheme Hasan Komurcugil, Senior Member, IEEE, Saban Ozdemir, Member, IEEE, Ibrahim Sefa, Member, IEEE, Necmi Altin, Member, IEEE, and Osman Kukrer, Senior Member, IEEE Abstract—This paper presents a sliding mode control (SMC) strategy for single-phase grid-connected LCL-filtered voltage source inverters (VSI) with double-band hysteresis scheme. The proposed SMC is simpler than the existing SMC methods devised for grid-connected VSI since its sliding surface function requires the sensing of capacitor voltage and grid current only. In addition, a double-band hysteresis scheme which ensures the switching of a transistor in the VSI during a half-cycle while it remains either on or off in the other half-cycle of the fundamental period is used to mitigate the switching frequency. Furthermore, the analytical expressions for the instantaneous and average switching frequency are derived. The theoretical considerations and analytical results are verified through computer simulations and experimental results obtained from a 3.3kW system. Simulation and experimental results show that the proposed SMC strategy exhibits an excellent performance in achieving the required control objectives such as fast dynamic response, robustness, sinusoidal grid current with low THD and simplicity in a practical implementation. Index Terms— Grid-connected inverter, single-phase voltage source inverter, sliding mode control, double-band hysteresis scheme. I. INTRODUCTION RID-connected voltage-source inverter (VSI) systems have received a significant attention in recent years due to the growing interest in environmental problems and increased electricity demand [1]. The objective of such system is to deliver power from a renewable energy source (solar and wind) to the utility grid by means of a VSI through a filter. The VSI produces an ac current with a specified frequency at its output which is injected to the grid via a filter. Manuscript received February 3, 2015; revised May 7, 2015 and June 12, 2015; accepted August 9, 2015. Copyright (c) 2015 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org. H. Komurcugil is with the Department of Computer Engineering, Eastern Mediterranean University, Gazimağusa, Mersin 10, Turkey (e-mail: hasan.komurcugil@emu.edu.tr). S. Ozdemir is with the Vocational School of Technical Sciences, Gazi University, 06560 Ankara, Turkey (e-mail: sabanozdemir@gazi.edu.tr). I. Sefa and N. Altin are with the Department of Electrical and Electronic Engineering, Faculty of Engineering, Gazi University, 06560 Ankara, Turkey (e-mail: isefa@gazi.edu.tr; naltin@gazi.edu.tr). O. Kukrer is with the Department of Electrical and Electronic Engineering, Eastern Mediterranean University, Gazimağusa, Mersin 10, Turkey (e-mail: osman.kukrer@emu.edu.tr). Generally, two types of filters (L and LCL) are used to reduce the switching harmonics of the current injected to the grid. The third-order LCL filter is the most widely used topology, due to its advantages such as the ability to operate at lower switching frequency, better attenuation, lower current ripple in the current injected to the grid, and reduced cost and size due to relatively small inductor values [4]. However, the risk of closed-loop instability due to two additional complex- conjugate poles and the necessity of resonant damping are the major disadvantages of LCL filters. Therefore, compared with the L-filter based systems, the design of an appropriate control strategy for an LCL-filter based grid-connected VSI is challenging issue due to the requirements like good quality injected current with low total harmonic distortion (THD), fast dynamic response, and strong stability of the closed-loop system. The damping issue has been tackled either by using passive damping which is realized by inserting a dissipative resistor into the LCL-filter [2], [3] or active damping which is realized by using virtual resistor concept employing an appropriate closed-loop current control method [4]-[6]. Alternatively, the filter-based active damping solution is also proposed [7]. Although the passive damping is simple and has low cost, it causes additional power losses and degrades the harmonic attenuation performance of the LCL filter. On the other hand, the active damping method offers a better attenuation performance without power losses at the expense of increased control complexity. Generally, the control strategies devised for grid-connected VSIs are based on controlling the inverter-side current [8], capacitor current [9], capacitor voltage [10], and grid-current [11]. Although hysteresis current control (HCC) offers strong robustness, fast dynamic response, and simplicity in implementation, it suffers from the variable switching frequency and steady-state error in the grid current [12]. As a remedy to the variable switching frequency problem, an alternative HCC operating with constant switching frequency has been proposed in [13] and [14]. However, these methods have been developed for L-filter based system whose theoretical derivations are not valid for the LCL-filter based systems. Despite the proportional resonant (PR) controllers can achieve zero steady-state error in the grid current, they are sensitive to the frequency variations in the system and their harmonic compensators are limited to a few low-order harmonics [15], [16]. The composite control [17] has also been proposed to achieve the aforementioned requirements. G