Abstract-- In order to meet standard specifications in terms of power quality and safety for grid-connected systems the phase angle, the amplitude and the frequency of the grid voltage are a critical piece of information. Phase locked loop (PLL) algorithms are very important for grid synchronization and monitoring in most of the grid-connected power converters system. This paper presents a performance comparison of single-phase synchronization techniques: Synchronous Reference Frame-Phase Locked Loop (SRF-PLL), Enhanced Phase-Locked-Loop (EPLL), Quadrature-Phase Locked Loop (QPLL) and Second-Order Generalized Integrator - Phase Locked Loop (SOGI-PLL). I. INTRODUCTION In case of photovoltaic systems, an accurate and fast detection of the phase angle, amplitude and frequency of the utility voltage is required by grid-connected converters in order to guarantee the correct generation of the current reference signal and to meet the demands regarding the operation boundaries with respect to voltage amplitude and frequency values required by standards [1]. The new issued grid codes put more stringent demands regarding the capability of the PV systems to track the grid-voltage variations of amplitude and frequency and to reject harmonic distortions [2-4]. Deviation from these limits represents abnormal conditions and may require disconnection of the PV system from the grid. Additionally, the detection of the grid phase angle can be used also for anti-islanding detection algorithms. Numerous methods for synchronization and grid-voltage monitoring have been presented in the technical literature about DPGS (Distributed Power Generation System) [5- 20]. The main difference among different PLL methods is the configuration of the phase detector (PD). The PD structure of the SRF-PLL creates an orthogonal component of the grid voltage in order to create a virtual two-phase system. The EPLL and the QPLL present a band-pass adaptive filter (BPAF) to estimate the phase error at the fundamental frequency. The SOGI-PLL is based on frequency adaptive quadrature-signals generation by means of the Second-Order Generalized Integrator- Quadrature Signal Generator (SOGI-QSG) filter. In this paper the performance of above synchronization techniques has been reported in case of distorted utility conditions. In Section II the standards requirements for grid-connected PV-Systems are discussed. In Section III four single-phase synchronization techniques: SRF-PLL, EPLL, QPLL, SOGI-PLL are described. Performances in case of voltage sags, frequency variations and harmonic distortions are verified and compared in Section IV. Fig.1. PV system II. PV-SYSTEM REQUIREMENTS FOR MONITORING AND SYNCHRONIZATION The purpose of the power electronics in PV systems is to convert the dc current from the PV panels into ac current with the highest possible efficiency and the lowest cost. The basic structure of a PV system is shown in Fig. 1. The standard IEC 61727 allows a limit of 5% for the current Total Harmonic Distortion factor (THD) with individual limits of 4% for each odd harmonic from the 3rd to the 9th and 2% for the harmonics from the 11th to the 15th. Besides it requires high power factor (>0.9). These requirements rely not only on the tracking capability of the current controller but also on the harmonic filtering capability of the synchronization method. Moreover, according to IEC 61727, it is defined the continuous operation area between 0.85 and 1.10 pu for the voltage amplitude and ± 1 Hz around the nominal frequency [2-4]. Abnormal conditions can arise from the utility grid which requires a response from the grid-connected PV system. Also in this case an accurate and fast grid voltage monitoring is necessary in order to comply with these requirements. Additionally, the detection of the grid phase angle can be used also for anti-islanding detection algorithms, in particular the amplitude of the grid voltage is used in over/under voltage protection and the estimated frequency is required for over/under frequency protection. The tracking techniques have to provide: - robustness with respect to noise, stationary and transient disturbances; Monitoring and Synchronization Techniques for Single-Phase PV Systems A. Nagliero, R. A. Mastromauro, M. Liserre, A. Dell’Aquila Dept of Electrotechnical and Electronic Engineering Polytechnic of Bari Via E.Orabona 4 70125-Bari, Italy nagliero@deemail.poliba.it, mastromauro@deemail.poliba.it, liserre@poliba.it, dellaqui@poliba.it 978-1-4244-7919-1/10/$25.00 ©2010 IEEE SPEEDAM 2010 International Symposium on Power Electronics, Electrical Drives, Automation and Motion 1404