Comparison of Three Single-Phase PLL Algorithms for UPS Applications
TL;DR: The developed models proved to accurately represent the PLLs under real test conditions and are presented, providing a refined method for performance evaluation and comparison.
Abstract: In this paper, the performance assessment of three software single-phase phase-locked loop (PLL) algorithms is carried out by means of dynamic analysis and experimental results. Several line disturbances such as phase-angle jump, voltage sag, frequency step, and harmonics are generated by a DSP together with a D/A converter and applied to each PLL. The actual minus the estimated phase-angle values are displayed, providing a refined method for performance evaluation and comparison. Guidelines for parameters adjustments are also presented. In addition, practical implementation issues such as computational delay effects, ride-through, and computational load are addressed. The developed models proved to accurately represent the PLLs under real test conditions.
Citations
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TL;DR: In this paper, a detailed analysis of the main operation modes and control structures for power converters belonging to micro-grids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations.
Abstract: The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.
2,621 citations
Cites background from "Comparison of Three Single-Phase PL..."
...In spite of the good behavior of the SRF-PLL under balanced grid conditions, its performance is deteriorated when the threephase input signal becomes unbalanced or distorted [27], [28]....
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TL;DR: A new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies is presented.
Abstract: This paper presents a new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for single- and three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.
950 citations
TL;DR: In this paper, a self-synchronized synchronverter is proposed to improve the performance of grid-connected inverters by removing the dedicated synchronization unit, which can automatically synchronize itself with the grid before connection and track the grid frequency after connection.
Abstract: A synchronverter is an inverter that mimics synchronous generators, which offers a mechanism for power systems to control grid-connected renewable energy and facilitates smart grid integration. Similar to other grid-connected inverters, it needs a dedicated synchronization unit, e.g., a phase-locked loop (PLL), to provide the phase, frequency, and amplitude of the grid voltage as references. In this paper, a radical step is taken to improve the synchronverter as a self-synchronized synchronverter by removing the dedicated synchronization unit. It can automatically synchronize itself with the grid before connection and track the grid frequency after connection. This considerably improves the performance, reduces the complexity, and computational burden of the controller. All the functions of the original synchronverter, such as frequency and voltage regulation, real power, and reactive power control, are maintained. Both simulation and experimental results are presented to validate the control strategy. Experimental results have shown that the proposed control strategy can improve the performance of frequency tracking by more than 65%, the performance of real power control by 83%, and the performance of reactive power control by about 70%.
793 citations
TL;DR: An intelligent load-shedding algorithm for intentional islanding and an algorithm of synchronization for grid reconnection to implement grid-connected and intentional-islanding operations of distributed power generation are proposed.
Abstract: Intentional islanding describes the condition in which a microgrid or a portion of the power grid, which consists of a load and a distributed generation (DG) system, is isolated from the remainder of the utility system. In this situation, it is important for the microgrid to continue to provide adequate power to the load. Under normal operation, each DG inverter system in the microgrid usually works in constant current control mode in order to provide a preset power to the main grid. When the microgrid is cut off from the main grid, each DG inverter system must detect this islanding situation and must switch to a voltage control mode. In this mode, the microgrid will provide a constant voltage to the local load. This paper describes a control strategy that is used to implement grid-connected and intentional-islanding operations of distributed power generation. This paper proposes an intelligent load-shedding algorithm for intentional islanding and an algorithm of synchronization for grid reconnection.
581 citations
Cites background from "Comparison of Three Single-Phase PL..."
...A PI regulator can be used to control this variable, and the output of this regulator is the grid frequency [28]....
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TL;DR: The paper presents two systematic methods to design the control parameters of a typical MAF-based PLL: one for the case of using a proportional-integral (PI) type loop filter (LF) in the PLL, and the other for the cases of using an proportional-Integral-derivative (PID) type LF.
Abstract: The phase-locked loops (PLLs) are probably the most widely used synchronization technique in grid-connected applications. The main challenge that is associated with the PLLs is how to precisely and fast estimate the phase and frequency, when the grid voltage is unbalanced and/or distorted. To overcome this challenge, incorporating moving average filter(s) (MAF) into the PLL structure has been proposed in some recent literature. An MAF is a linear-phase finite-impulse-response filter, which can act as an ideal low-pass filter, if certain conditions hold. The main aim of this paper is to present the control design guidelines for a typical MAF-based PLL. The paper starts with the general description of MAFs. The main challenge associated with using the MAFs is then explained, and its possible solutions are discussed. The paper then proceeds with a brief overview of the different MAF-based PLLs. In each case, the PLL block diagram description is shown, the advantages and limitations are briefly discussed, and the tuning approach (if available) is evaluated. The paper then presents two systematic methods to design the control parameters of a typical MAF-based PLL: one for the case of using a proportional-integral (PI) type loop filter (LF) in the PLL, and the other for the case of using a proportional-integral-derivative (PID) type LF. Finally, the paper compares the performance of a well-tuned MAF-based PLL when using the PI-type LF with the results of using the PID-type LF, which provides useful insights into their capabilities and limitations.
441 citations
Cites background from "Comparison of Three Single-Phase PL..."
...They typically consist of three basic parts: a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO) [12]....
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References
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Book•
01 Oct 1999
TL;DR: This is the first book to offer in-depth analysis of voltage sags and interruptions and to show how to apply mathematical techniques for practical solutions to these disturbances.
Abstract: "Power quality problems have increasingly become a substantial concern over the last decade, but surprisingly few analytical techniques have been developed to overcome these disturbances in system-equipment interactions. Now in this comprehensive book, power engineers and students can find the theoretical background necessary for understanding how to analyze, predict, and mitigate the two most severe power disturbances: voltage sags and interruptions.This is the first book to offer in-depth analysis of voltage sags and interruptions and to show how to apply mathematical techniques for practical solutions to these disturbances. From UNDERSTANDING AND SOLVING POWER QUALITY PROBLEMS you will gain important insights intoVarious types of power quality phenomena and power quality standardsCurrent methods for power system reliability evaluationOrigins of voltage sags and interruptionsEssential analysis of voltage sags for characterization and prediction of equipment behavior and stochastic predictionMitigation methods against voltage sags and interruptions"Sponsored by:IEEE Power Electronics Society, IEEE Industry Applications Society, IEEE Power Engineering Society.
2,052 citations
"Comparison of Three Single-Phase PL..." refers background in this paper
...These disturbances and their effects on industrial power equipment are currently subjects of research [12]–[15]....
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...However, when grid faults occur, equipment become exposed to phase-angle jumps and voltage sags [15]....
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TL;DR: In this article, a phase-locked loop (PLL) system under distorted utility conditions is presented and a control model of the PLL system is developed and recommendations are made on tuning of this model specially for operation under common utility distortions such as line notching, voltage unbalance/loss, and frequency variations.
Abstract: Operation of a phase locked loop (PLL) system under distorted utility conditions is presented. A control model of the PLL system is developed and recommendations are made on tuning of this model specially for operation under common utility distortions such as line notching, voltage unbalance/loss, and frequency variations. The PLL is completely implemented in software without any filters. All analytical results are experimentally verified.
1,061 citations
TL;DR: In this article, an enhanced phase-locked loop (EPLL) based synchronization method is proposed for distributed generation units, e.g., wind generation systems, which utilize power electronic converters as an integral part of their systems.
Abstract: This paper presents a new synchronization method which employs an enhanced phase-locked loop (EPLL) system. The operational concept of the EPLL is novel and based on a nonlinear dynamical system. As compared with the existing synchronization methods, the introduced EPLL-based synchronization method provides higher degree of immunity and insensitivity to noise, harmonics and other types of pollutions that exist in the signal used as the basis of synchronization. The salient feature of the EPLL-based synchronization method over conventional synchronization methods is its frequency adaptivity which permits satisfactory operation when the centre frequency of the base signal varies. The proposed EPLL-based method of synchronization is also capable of coping with the unbalanced system scenarios. Structural simplicity of the EPLL-based method greatly simplifies its implementation in digital software and/or hardware environments as an integral part of a digital control platform for power electronic converters. The primary application of the proposed synchronization method is for the distributed generation units, e.g., wind generation systems, which utilize power electronic converters as an integral part of their systems.
565 citations
"Comparison of Three Single-Phase PL..." refers background or methods in this paper
...The models could only predict the averaged evolution of the estimated frequencies of the parkPLL and EPLL....
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...To estimate the phase-angle, open-loop and closed-loop methods are available [8], [10]....
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...The second is based on the inverse Park transformation (parkPLL) [5], [6], and the later is based on an adaptive phase detection scheme, originally called enhanced PLL (EPLL) [8], [9]....
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...Hence, neglecting the PD dynamics and taking phase φ as input, for small phase differences φ̂ − φ, the EPLL closed-loop transfer function can be approximated by φ̂(s) φ(s) ∼= kv skp + ki s2 + skvkp + kvki (23) where kv = V/2 is the static PD gain....
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...5 displays the block diagram of the EPLL [8], [9]....
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30 Sep 2001
TL;DR: In this paper, a detailed analysis of phase-locked loop structures for utility connected systems is presented, and a single-phase PLL structure derived from the three-phase topology is discussed and its behavior under distorted utility conditions is analyzed.
Abstract: This paper presents a detailed analysis of PLL structures for utility connected systems. The three-phase PLL (phase-locked loop) structure capable of fast tracking the utility voltage vector is studied. A single-phase PLL structure, derived from the three-phase PLL topology, is discussed and its behavior under distorted utility conditions is analyzed. Additionally, the conventional zero-crossing PLL is studied and an alternative implementation for this PLL is proposed in order to improve its dynamic behavior. Simulation and experimental results from a DSP-based system are included to support the theoretical analysis.
374 citations
16 Jun 2005
TL;DR: Simulation and experimental results are used to evaluate the behavior of the synchronization methods under different kind of grid disturbances such as voltage dips, harmonics and notches.
Abstract: Nowadays, it is a general trend to increase the electricity production using distributed power generation systems (DPGS) based on renewable energy resources such as wind, sun or hydrogen. Jf these systems are not properly controlled, their connection to the utility network can generate problems on the grid side. Therefore, considerations about power generation, safe running and grid synchronization must be done before connecting these systems to the utility network. This paper is mainly dealing with the grid synchronization issues of distributed systems. An overview of the synchronization methods as well as their major characteristics is given. New solutions to optimize the synchronization methods when running on distorted grid conditions are discussed. Simulation and experimental results are used to evaluate the behavior of the synchronization methods under different kind of grid disturbances such as voltage dips, harmonics and notches.
358 citations
"Comparison of Three Single-Phase PL..." refers methods in this paper
...To estimate the phase-angle, open-loop and closed-loop methods are available [8], [10]....
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