978-1-5386-4699-1/18/$31.00 ©2018 IEEE A New Slip Surface Sliding Mode Controller to Implement MPPT Method in Photovoltaic System Amir Shahdadi Faculty of Electrical and Computer Engineering University of Sistan and Baluchestan amir.shahdadi@pgs.usb.ac.ir Ahmad Khajeh Faculty of Electrical and Computer Engineering University of Sistan and Baluchestan akhajeh@ece.usb.ac.ir S. Masoud Barakati Faculty of Electrical and Computer Engineering University of Sistan and Baluchestan smbaraka@ece.usb.ac.ir Abstract— Maximum power point tracking (MPPT) has important role in a photovoltaic system (PV) control. The nonlinear nature of photovoltaic systems has led researchers to use nonlinear controllers to attain maximum power from PV. A DC-DC converter is utilized to implement MPPT in addition to regulate the output voltage. In this paper, a sliding mode control is proposed based on a new slip surface on a single-ended primary-inductor converter (SEPIC) which is used as the DC-DC converter. To examine the system performance, three different modes of operation are analyzed. Simulation results verify the effectiveness of the proposed system under different transients. Keywords— photovoltaic standalone systems, sliding mode control, SEPIC converter, slip surface. I. INTRODUCTION Penetration of photovoltaic systems has been increased in power grids in recent years. To increase the efficiency of the photovoltaic systems, an optimal control called maximum power point tracking (MPPT) is often used [1]. The MPPT can be implemented in PV systems in three different methods: on- line, off-line, and hybrid [2, 3]. Off-line methods are known as the cheapest and simplest methods. However, disadvantage of this method is due to the fact that it does not have enough precision performance because it uses off-line sampling of PV parameters, results in approximated values of the coefficients to track the MPPT [4-6]. In order to achieve sufficient accuracy, it is necessary to sample the parameters on-line. The only disadvantage of on-line methods is low speed compared to off-line methods. The hybrid method, as the name implies, is a combination of off-line and on-line methods [7, 8]. Therefore, both advantages in hybrid techniques, the fast speed of off-line methods and the accuracy of online methods can be achieved in the hybrid method. According to the above, it can be guessed that the cost of these methods will be higher. Recent studies focus more on online methods, including two commonly used methods: Perturbation and observation (P&O) algorithm [9, 10] and incremental conductance (INC) algorithm [11, 12]. A photovoltaic system is inherently a nonlinear system and the switching of power electronics converter is essentially nonlinear [13]. Many MPPT methods are based on linearization of the system around the point of operation to obtain controller coefficients. Therefore, the controller does not warranty the accurate operation of the system in all areas. Accordingly, using of nonlinear controllers will be more favorable. There some published works in the literature that show the application of nonlinear control for MPPT. In [15] used a controller based on energy-sampled data model of the PV system for MPPT, an adaptive controller has been proposed for MPPT in [16] and sliding mode controller applied to track maximum power in [17]. In this paper, to achieve the MPPT the sliding mode controller using a single-ended primary-inductor converter (SEPIC) will be studied in order to adjust the voltage of the PV panel. The SEPIC converter offers a better performance in comparison with conventional buck-boost converter. In the sliding mode controller a new slip surface is proposed, which increases the speed and accuracy of the system, as well as the system's resistance. The rest of the paper is organized as follows. Sliding mode control and sliding surfaces are discussed in section 2. In section 3, modeling and sliding mode control of the SEPIC converter connected to the PV system is presented. The simulation results are provided in section 4. Finally, section 5 concludes the paper. II. SLIDING MODE CONTROL A. Selecting the slip surface The slip surface is known as one of the basic concepts in controlling sliding mode. S in sliding mode control is usually introduced as a slip surface. The slip surface establishes a relationship between system dynamics based on control objectives. Achieving of the slip surface by using the switch operation and the stability of the system dynamics on it is one of the main conditions for achieving control objectives [19, 20]. In fact, in order to use a sliding mode controller in converters based on switching, the system should control the relationship between the slip surface changes and the state of the switching. The switching states should be selected so that the system dynamics will always remain on the slip surface (S=0 or availability condition). In addition, the switching signal should be in the open range of zero and one when the dynamics are on the slip surface (control equivalent condition) [5]. 2018 9th Annual Power Electronics, Drives Systems and Technologies Conference (PEDSTC) 212