A Three-Phase Three-Level NPC Inverter Based Grid-Connected Photovoltaic System With Active Power Filtering Serkan Sezen Edremit Vocational School Balıkesir University Balıkesir, Turkey serkansezen@balikesir.edu.tr Ahmet Aktas Dep. of Energy Systems Eng. Kocaeli University Kocaeli, Turkey ahmet_aktas_1987@hotmail.com Mehmet Ucar Dep. of Elect.-Electron. Eng. Duzce University Duzce, Turkey mehmetucar@duzce.edu.tr Engin Ozdemir Dep. of Energy Systems Eng. Kocaeli University Kocaeli, Turkey eozdemir@kocaeli.edu.tr Abstract—This paper presents a three-phase three-level neutral point clamped (NPC) inverter based single-stage grid- connected photovoltaic (PV) system with shunt active power filter (APF) functionality. The proposed system can perform both the maximum real power injection with the perturb and observe (P&O) maximum power point tracking (MPPT) algorithm from the PV panels into the grid and active power filtering to compensate the load current harmonics. Thus, the PV system operates more efficiently compared to the conventional PV systems and can be useful for power system applications. Control of the proposed system is based on synchronous reference frame control algorithm and hysteresis band current control technique. The effectiveness of the proposed system is demonstrated with Matlab/Simulink simulations and validated through dSPACE DS1103 real-time control platform based laboratory experimental results. Keywords—photovoltaic system; active power filter; grid connected; multilevel inverter; maximum power point tracking. I. INTRODUCTION Photovoltaic (PV) systems are becoming increasingly popular as a renewable source. The PV systems can be grouped into stand-alone systems and grid-connected systems [1]-[3]. Grid-connected PV systems are having more interest recently because they do not need physical storage systems (batteries) and so the investment cost is reduced. In grid-connected PV systems, maximum power point tacking (MPPT) techniques are used to deliver maximum power into the grid [4]. Because of having low implementation complexity Perturb&Observe method is widely used in PV systems [5]. Single-stage and two-stage grid-connected systems are commonly used topologies in PV applications [6], [7]. Two-stage system, has some disadvantages what are less efficient, being larger and more costly disadvantage. Therefore single-stage structure is widely used today due to small size, low cost, high efficiency and high reliability. Higher power equipments require higher voltages, which limit the maximum DC voltage level. Therefore a new family of multilevel inverters has emerged as the solution for solar applications, as the PV array is directly connected to each level of the DC link. NPC topology is popular since it has the advantages such as: DC-link capacitors are common to three phases, switching frequency can be low and reactive current and negative phase sequence current can be controlled [8]. Another benefit of using 3L NPC topology is the lower current THD; that reduces the filtering effort (less copper needed, lower losses in the filter) [9]. Also, the increasing use of power electronic devices and non-linear loads is known to cause serious problems in electric power systems. Therefore, the PV system combined with the function of a shunt active power filter (APF) can be useful for the application in the power distribution system [10]-[17]. The active filtering capability does not require modifications to the power stage. Also, single-phase or three-phase multilevel inverters for PV system grid integration have been suggested in order to improve the performance of the PV system [18]-[21]. In this study, the operation of a three-level neutral point clamped (NPC) inverter for the PV system including the function of APF, is investigated. The general diagram of grid connected PV system with APF function proposed in this work is shown in Fig. 1. The synchronous reference frame (dq) control strategy has been used for PV system active power injection and APF harmonic currents filtering. Hysteresis control technique has been applied for the switching pattern generation. The perturb and observe (P&O) MPPT technique is used and integrated with the dc- link controller. The feasibility of the proposed system is verified through Matlab/Simulink simulations and an experimental prototype with a dSPACE DS1103 real-time control board. 3-level NPC inverter Cdc2 Cdc1 vdc D PV Panels Lf Lf Lf + - Grid Non-linear Load Fig. 1. General diagram of grid-connected PV system with APF function. 16th International Power Electronics and Motion Control Conference and Exposition Antalya, Turkey 21-24 Sept 2014 PEMC 2014 1572