Three-phase phase-locked loop synchronization algorithms for grid-connected renewable energy systems:A review

The increasing penetration of distributed renewable energy sources (RES) requires appropriate control techniques in order to remain interconnected and contribute in a proper way to the overall grid stability, whenever disturbances occur. In addition, the disconnection of RES due to synchronization problems must be avoided as this may result in penalties and loss of energy generation to RES operators. The control of RES mainly depends on the synchronization algorithm, which should be fast and accurately detect the grid voltage status (e.g., phase, amplitude, and frequency). Typically, phase-locked loop (PLL) synchronization techniques are used for the grid voltage monitoring. The design and performance of PLL directly affect the dynamics of the RES grid side converter (GSC). This paper presents the characteristics, design guidelines and features of advanced state-of-the-art PLL-based synchronization algorithms under normal, abnormal and harmonically-distorted grid conditions. Experimental tests on the selected PLL methods under different grid conditions are presented, followed by a comparative benchmarking and selection guide. Finally, corresponding PLL tuning procedures are discussed.This work was supported by the supported by the Research Promotion Foundation (RPF) of Cyprus under Project KOINA/SOLAR-ERA.NET/1215/06

Dynamics estimation and generalized tuning of stationary frame current controller for grid-tied power converters

The integration of AC-DC power converters to manage the connection of generation to the grid has increased exponentially over the last years. PV or wind generation plants are one of the main applications showing this trend. High power converters are increasingly installed for integrating the renewables in a larger scale. The control design for these converters becomes more challenging due to the reduced control bandwidth and increased complexity in the grid connection filter. A generalized and optimized control tuning approach for converters becomes more favored. This paper proposes an algorithm for estimating the dynamic performance of the stationary frame current controllers, and based on it a generalized and optimized tuning approach is developed. The experience-based specifications of the tuning inputs are not necessary through the tuning approach. Simulation and experimental results in different scenarios are shown to evaluate the proposal.Peer ReviewedPostprint (published version

Performance Analysis of DSOGI PLL under Balanced and Unbalanced Conditions

DPGS (distributed power generation system) gives an efficient and economic way of generating electricity by using renewable energy sources near to the load requirement. And it is the better way for reducing the transmission and distribution losses. But the process of synchronizing the DPGS system with grid is becoming one new challenge. As a consequence, the control of grid-connected power converters, grid synchronization method are very important because in order to implement stable control strategies under generic grid conditions a accurate and fast detecting method of the grid voltage characteristics is required .In actual practice the grid code requirements such as grid stability fault ride through, power quality improvement, power control and grid synchronization etc. should be satisfied by power plant operators. There are so many methods for grid synchronization , has been explained in the literature review to control the parameters like active and reactive power by tracking the phase angle of the supply grid voltage or grid current for proper synchronization of grid and DG system. In this thesis different types of grid synchronization system with DPGS system has been explained and later different types of PLL has been introduced for single phase and 3 phase system. For balanced 3 phase supply for getting better result SRF PLL is advisable, it uses the advanced method of conversion to 2 constant voltages from 2 orthogonal signals known as Park's transform and the Clarke's transform, it will take 3 phase supply as input and gives the 2 orthogonal signals as the output. But whenever the supply voltage is unbalanced the SRF PLL gives the output with the oscillating error means it is going to fail, so in case of the unbalanced supply voltage Decoupled Double Synchronous Reference Frame (DDSRF) PLL is suggested .the DDSRF PLL can detect the sequence components and positive sequence phase angle under unbalancing conditions. For generating the orthogonal signals Second Order Generalized Integrator (SOGI) is the better replacement of Clarke’s transform and it has high capacity of harmonic rejection because it can perform current controller duty and also sequence components also can be detected easily. For grid synchronization another advanced method is Dual Second Order Generalized Integrator - Phase Locked Loop (PLL) has been implemented by using Matlab simulink and LABVIEW under unbalanced conditions like sag and swell

Variable-Frequency Grid-Sequence Detector Based on a Quasi-Ideal Low-Pass Filter Stage and a Phase-Locked Loop

This paper proposes a filtered-sequence phase-locked loop (FSPLL) structure for detection of the positive sequence in three-phase systems. The structure includes the use of the Park transformation and moving average filters (MAF). Performance of the MAF is mathematically analyzed and represented in Bode diagrams. The analysis allows a proper selection of the window width of the optimal filter for its application in the dq transformed variables. The proposed detector structure allows fast detection of the grid voltage positive sequence (within one grid voltage cycle). The MAF eliminates completely any oscillation multiple of the frequency for which it is designed; thus, this algorithm is not affected by the presence of imbalances or harmonics in the electrical grid. Furthermore, the PLL includes a simple-frequency detector that makes frequency adaptive the frequency depending blocks. This guarantees the proper operation of the FSPLL under large frequency changes. The performance of the entire PLL-based detector is verified through simulation and experiment. It shows veryPeer ReviewedPostprint (published version

Quasi Type-1 PLL With Tunable Phase Detector for Unbalanced and Distorted Three-Phase Grid

International audienc

Study of new vector-control algorithms for 3-phase inverters used in renewable agents connected to the low-voltage utility grid with disturbances

[ESP] La demanda de energía eléctrica se ha ido incrementando a través de los años debido al desarrollo que han tenido el sector industrial y de transporte, sumándose además el aumento de la población mundial y el desarrollo de nuevas tecnologías que requieren mayor cantidad de energía. Por ello, y con el propósito de generar la energía eléctrica necesaria para suplir a estos sectores, el consumo de combustible ha presentado un aumento significativo. Así, la energía consumida en el año 2010 fue de unos 153,000 TWh y se prevé que para el año 2020 esta cifra ascienda a 184,000 TWh, siendo la mayor parte de esta energía proveniente de combustibles fósiles, aunque el futuro de esta tendencia es incierto. Además, la población mundial se está concienciando cada vez más de los efectos negativos medioambientales que está provocando el llamado “efecto invernadero” y, como consecuencia, se están creando una serie de políticas energéticas con el fin de reducir la generación de gases y partículas contaminantes. Una alternativa para reducir la dependencia de los combustibles fósiles y, a la vez, reducir las emisiones de los gases tóxicos causantes del efecto invernadero, es el uso de fuentes de energías renovables como la solar fotovoltaica y la eólica, así como el uso de pilas de combustibles para almacenamiento de energía, todas ellas a instalar en el mix energético. En este sentido, los nuevos agentes renovables que se conecten a la red eléctrica trifásica de baja tensión deben controlarse adecuadamente y cumpliendo con las legislaciones energéticas vigentes. En este sentido, deben diseñarse nuevas y sofisticadas estrategias de control con el propósito de controlar adecuadamente las corrientes de línea de los inversores de conexión a red utilizados en los agentes renovables cuando existan perturbaciones en la red eléctrica de baja tensión, tales como las variaciones de su frecuencia nominal, los desequilibrios en las tensiones trifásicas y la presencia de contaminación armónica de baja frecuencia. Por todo lo anteriormente mencionado, esta tesis está enfocada en el estudio de varios algoritmos de control y sincronización utilizados en inversores en fuente de tensión (VSI) para conexión a red que operan como los acondicionadores de potencia para los sistemas renovables. Los estudios realizados se aplican a un sistema fotovoltaico, pero pueden extenderse a cualquier tipo de agente renovable utilizado en un sistema de Generación Distribuida. [ENG] Throughout decades, the electric power demand has been rising due to the growth of the industrial sector and transportation, and the development of new technologies that require more energy together with the increase of the global population have led to a higher fuel demand needed for the electric energy generation. The global energy consumption in 2010 was 153,000 TWh and it is expected an increment to 184,600 TWh by 2020, the majority provided by fossil fuels, although the future of these trend is uncertain. Besides, greenhouse effect is causing environmental changes that concern mankind and the creation of new energetic policies is a fact. An alternative for reducing the fossil fuel dependence and the reduction of the greenhouse gas emission is the use of clean and infinite renewable energy sources such as photovoltaic, wind, as well as fuel cells for energy storage, which have been installed in the energetic mix. In this context, new renewable agents are connected to the 3-phase utility grid and must be properly controlled according to power electrical legislations. For this, new and sophisticated control algorithms are to be designed in order to control properly the line currents of the grid-connected inverter when variations of the nominal frequency, voltage unbalances and low-order harmonics are present in the 3-phase utility grid voltage. This thesis is focused in the study of several control and synchronization algorithms used in grid-connected Voltage Source Inverters (VSI) working as the power conditioner circuits for renewable energy systems. The study of these algorithms is carried out using a grid-connected photovoltaic system, but they can be extended to any renewable agent in any distributed generation system.Universidad Politécnica de Cartagen

Grid sequence detector based on a stationary reference frame

This paper proposes a new three-phase positive sequence detector. The scheme is based on a stationary reference frame and a Moving Average Filter (MAF) that guarantees the complete cancellation of harmonics and grid imbalances. The performance of the MAF is mathematically analyzed and a proper selection of the optimal filter’s window width is realized. The proposed detector operates in open loop and there is no PI controller to be tuned. Thus, the dynamic response and simplicity is improved compared to other solutions. Performance of the proposed detector is verified through simulation and experiment. It shows very good performance under extreme grid voltage conditions, allowing fast detection of the grid voltage positive sequence (within one grid voltage cycle).Postprint (published version

Direct Instantaneous Power Control of Three-level Grid-connected

Power electronic grid-connected inverters are widely applied as grid interface in renewable energy sources. This paper presents direct instantaneous power control of a three-phase three-level Neutral Point Clamped (NPC) grid-connected inverter in photovoltaic generation systems. The system consists of a PV array, DC/DC converter, three-level NPC LC filter and the grid. In order to achieve maximum power point  tracking (MPPT), an adaptive perturb and observe MPPT is used. For balancing the neutral point (NP) voltage, the control scheme through proportional integral (PI) control according to  the direction of the NP current based on redundant vector selection is used. Direct instantaneous power control is developed in a rotating synchronous dq reference frame with space vector modulation with improved operation performance study of the positive sequence detector (PSD) plus a synchronous a synchronous reference frame phase-locked loop (PLL) as the synchronization method. The performance of the proposed method is investigated by a grid-connected photovoltaic system with a nominal power of 12kW. The feasibility of the proposed method is verified through experimental results, showing good steady-state and dynamic performance

Voltage feed-forward performance in stationary reference frame controllers for wind power applications

In order to improve the connected current and the response speed of the controller, stationary reference frame control strategy with proportional resonant (P-R) controller due to its high dynamic and good harmonic compensation performance characteristics was already used in many different DG applications. This paper introduced an additional stationary reference frame control strategies with voltage feed-forward method. By using this method, both the quality of grid connected current and the dynamic performance are improved, which also validated by experiments.Postprint (published version