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The amplitude, frequency and phase angle of the grid voltage are essential three components to ensure synchronization for grid interactive inverters. Synchronous reference frame-phase locked loop (SRF-PLL) is widely used to obtain these components. Although the SRF-PLL shows a perfect performance under ideal grid conditions, its performance deteriorates under unbalanced and distorted grid conditions. Therefore, researchers have been working to provide more advanced PLL methods. A dual third order generalized integrator PLL (DTOGI-PLL) and quasi-type-1 PLL (QT1-PLL) are two PLL methods that have come to the fore in grid synchronization recently. As with any method, these PLL methods have both advantages and disadvantages. The aim of this study is to integrate the advantages of the two methods, and to develop a new PLL method with better performance than these two methods. It means that the proposed PLL has the adaptive filtering capability of the DTOGI-PLL and fast transient response of the QT1-PLL. The effectiveness of the proposed PLL is confirmed by experimental results. The experimental results demonstrate that the proposed PLL is a more effective method than the DTOGI-PLL and QT1-PLL under adverse grid conditions.

In this study, an advanced phase-locked-loop (PLL), which has a simple structure and a low computational burden is proposed. The proposed PLL also improves the dynamic performance and the filtering capability of the conventional three-phase enhanced-PLL (3pEPLL) significantly. The conventional 3pEPLL operates three individual EPLL blocks for each phase voltage and a fourth EPLL for estimation of the magnitude, frequency, and phase angle, which considerably increases the structural complexity and computational burden. However, the proposed PLL called enhanced-3pEPLL (E2PLL) employs only two single-phase EPLL modules in its pre-filtering stage. A moving-average-filter (MAF) is also supplemented on the error signal path of these EPLL modules, which allows smoother estimation of the magnitude, frequency, and phase angle, and improves the filtering capability of the EPLLs. Unlike the conventional 3pEPLL, the proposed E2PLL employs a quasi-type-1 PLL (QT1-PLL) to estimate the magnitude, frequency, and phase information of the fundamental grid voltage. The structure of QT1-PLL is similar to a type-1 PLL, which offers a low transient response time. The small-signal model of the proposed PLL is derived for stability analysis and parameter design procedure. The effectiveness of the E2PLL is verified owing to experimental results and comparison with the conventional 3pEPLL and QT1-PLL.

In grid interactive power converter applications, phase locked loop (PLL) algorithms are very important to realize grid synchronization. The performance of PLL should not be affected by adverse conditions such as voltage unbalance, harmonics, frequency and phase changes. Otherwise, synchronization errors occur between the grid interactive inverter and the grid. In this paper, two different PLL algorithms are simulated by modeling under MATLAB/Simulink. The performances of the PLLs are comparatively presented under four different grid conditions such as balanced, unbalanced, harmonics and variable frequency. In this study, synchronous reference frame-PLL (SRF-PLL) and decoupled double synchronous reference frame-PLL (DDSRF-PLL) which are mostly used, state-of-arts and effective PLL algorithms are analyzed by modeling in grid synchronization applications. It has also been demonstrated the positive and negative aspects of the PLLs based on the obtained results.

Recently, several approaches with the ability to reject the DC-offset in phase locked loop (PLL) methods have been developed. These approaches include different filtering structures which can be classified into two categories: prefiltering before the PLL input and in-loop filtering in the PLL control loop. As highlighted in the literature, the DC-offset rejection methods based on in-loop filtering have received less attention due to their slow dynamic performance. Therefore, this paper proposes an alternative DC-offset rejection technique as in-loop filtering of the PLL. The effectiveness of the proposed PLL is confirmed by simulation and experimental results.

In recent years, to fast and accurately extract the grid voltage information, using cascaded delayed signal cancellation (CDSC) operators in the prefiltering stage of phase locked loops (PLLs) has become highly popular. Non-adaptive CDSC (NCDSC) operators do not cause the stability problems unlike adaptive CDSC operators. So, researchers use the NCDSC operators intensely. Nonetheless, the NCDSC operators have two main drawbacks: (1) the dynamic responses of NCDSC-PLLs are not fast enough, similar to adaptive CDSC operators-based PLLs; and (2) the imbalance rejection capability of the NCDSC-PLLs dramatically deteriorates in case of large frequency variations. In this paper, to overcome these problems, two enhanced NCDSC-PLLs, which are called the ENCDSC-PLL1, and ENCDSC-PLL2, are suggested. The parameter design procedures of suggested PLLs are given by means of their small- signal models. Since the proposed ENCDSC-PLLs are the nonminimum-phase systems, their stability analyses are evaluated by Nyquist diagram. The feasibility and effectiveness of the proposed ENCDSC-PLLs are validated by experimental results.

In grid interactive power converter applications, phase locked loop (PLL) methods are very important to realize grid synchronization. The performance of PLL which is used should be affected by adverse conditions such as voltage unbalance, harmonics, frequency and phase changes. Furthermore, in these adverse conditions, the phase angle of grid voltages and positive sequence component of grid voltages in fundamental grid frequency are needed to determine quickly and accurately. Otherwise, synchronization errors occur between the grid interactive inverter and the grid.In this paper, different PLL methods are simulated under MATLAB/Simulink. The performances of the PLL methods are comparatively presented under three different conditions such as unbalanced, harmonics and variable frequency grid. It has also put forward the positive and negative aspects of the PLL methods based on the obtained results., Şebeke etkileşimli güç dönüştürücü uygulamalarında, şebeke senkronizasyonunun gerçekleştirilebilmesi için faz kilitleme döngüsü (PLL) yöntemleri oldukça önemlidir. Kullanılan PLL’nin performansı; gerilim dengesizliği, harmonikler, frekans ve faz değişimi vb. olumsuz durumlardan etkilenmemelidir. Üstelik bu olumsuz durumlarda, şebeke faz açısının ve temel şebeke frekansındaki pozitif sıralı bileşen geriliminin hızlı ve doğru bir şekilde belirlenmesi gerekir. Aksi durumda, şebeke etkileşimli dönüştürücü ile şebeke arasında senkronizasyon hataları meydana gelmektedir.Bu makalede, farklı PLL yöntemlerinin MATLAB/Simulink’te benzetimi yapılmıştır. Dengesiz, harmonikli ve değişken frekanslı şebeke durumu gibi üç farklı şebeke koşulu altında PLL yöntemlerinin performansları karşılaştırmalı olarak sunulmuştur. Ayrıca, elde edilen sonuçlara dayanarak PLL yöntemlerinin artı ve eksi yönleri ortaya konulmuştur.

Recently, various phase locked loop (PLL) methods have been improved for a reliable and robust synchronization under non-ideal grid conditions. One of the PLLs is a hybrid PLL (HPLL) which is an improved structure of the quasi-type-1 PLL (QT1-PLL) method. In this paper, an enhanced HPLL that offers both fast transient response and increased disturbance rejection capability for dominant harmonics is proposed. The proposed PLL includes adaptive all-pass-filters (APFs) in pre-filtering stage to eliminate fundamental frequency negative sequence (FFNS) component. Thus, window-width of the moving average filter (MAF) is reduced by three times compared with the HPLL by means of removing the FFNS component. So, the proposed PLL, which is called fast-hybrid PLL (FH-PLL), considerably ensures a fast transient response. Also, in case of grid faults (for example, type-B, type-C, type-D, and etc.), at the same time frequency change occurs, the FH-PLL completely blocks the FFNS component by means of using adaptive DAPF. In this study, it is experimentally implemented HPLL, QT1-PLL, and the proposed FH-PLL methods. The effectiveness of the FH-PLL is verified owing to experimental results and comparison with the QT1-PLL and HPLL.

Electrical energy's transfer, obtained from the wind energy systems, directly to the grid or load is not possible in terms of efficiency and usability. For these reasons, grid interactive inverters are largely used for wind energy systems. In this study, three phase grid interactive Voltage Source Inverter (VSI) controlled by Space Vector Pulse Width Modulation (SVPWM) has been performed. The current controller model, Proportional-Integral (PI) controller regulated the injected grid current, has been implemented as the grid interactive VSI control model. In order to operate between inverter and grid synchronously, the phase angle of grid voltage is detected by using Phase Locked Loop (PLL) in dq-synchronous reference frame. This system has been simulated under MATLAB/SIMULINK. Simulation results illustrate that inverter output voltages are in same phase and frequency with grid voltages.

Space Vector Pulse Width Modulation (SVPWM) technique is extensively used to control the three-phase voltage source inverter (VSI) of wind energy systems. The main advantages of SVPWM method are fixed switching frequency, low harmonic content and higher DC bus utilization. In terms of the use of the DC bus voltage compared to conventional PWM method provides 15.15% more efficient usage. This paper focuses on SVPWM controlled three-phase VSI simulated under MATLAB/SIMULINK.