This letter proposes a method for fast and accurate estimation of three-phase grid frequency under unbalanced and distorted conditions. It includes a recursive discrete Fourier transform-based ...frequency adaptive bandpass filter for α - β signals generated by the Clarke transform and a two-point-based algorithm for frequency estimation. The proposed method is relatively simple to implement and can eliminate adverse influences created by the imbalances, dc offset and both odd and even harmonics. It can also provide fast estimation with a response time of almost one fundamental cycle under grid disturbances. Moreover, it can present improved performance when compared to several methods reported in the technical literature. The advantages of the proposed method are confirmed by both simulated and real-time experimental results.
All-pass filter (APF) passes all frequency components of a signal without altering their amplitude, but changes their phase. This feature has made the APF a versatile building block in different ...signal processing applications. The focus of this article is on APF-based phase-locked loops (PLLs), where the APF is required for creating a 90° phase shift at the fundamental frequency. Such a phase shift is needed for generating a fictitious orthogonal signal in single-phase applications and rejecting the grid voltage imbalance in three-phase systems. To the best of authors' knowledge, none of the APF-based PLLs have an accurate model yet. This gap in knowledge makes the analysis of these synchronization systems and identifying their advantages/disadvantages compared to state-of-the-art structures complicated. The main objective of this article is to bridge this knowledge gap.
A Study on Three-Phase FLLs Golestan, Saeed; Guerrero, Josep M.; Vasquez, Juan C. ...
IEEE transactions on power electronics,
2019-Jan., 2019-1-00, 20190101, Volume:
34, Issue:
1
Journal Article
Peer reviewed
Open access
Contrary to the phase-locked loop (PLL), which has almost reached a mature stage of development in power and energy applications (particularly in three-phase systems), the frequency-locked loop (FLL) ...is not a mature technique yet. This is probably because of the implementation of FLLs in the stationary reference frame, which makes their modeling, tuning, and performance enhancement more complicated than PLLs. The aim of this paper is conducting a research on three-phase FLLs. Providing a review of recent advances, introducing the concept of inloop filters for designing more advanced FLLs, demonstrating the FLL modeling and tuning in the presence of an inloop filter, analyzing the advantages and disadvantages of using an inloop filter in the FLL structure, and establishing a connection between FLLs and PLLs are the main parts of this research.
The wetting/antiwetting behavior of liquid droplets on a solid surface is not an apparent or simple contact between two phases, but among three phases. Inspired by the antiwetting behavior of oil ...droplets on fish scales in water, a superoleophobic and low‐adhesive interface is created on a solid substrate with micro/nanohierarchical structures, using oil/water/solid three‐phase systems.
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In this paper, a voltage modulated direct power control for three-phase pulsewidth modulated rectifier is proposed. With the suggested method, the differential equations describing the rectifier ...dynamics are changing from a linear time-varying system into a linear time-invariant one. In this way, conventional feedback and feedforward controllers are applicable for the independent control of active and reactive powers. The proposed method has guaranteed that the closed system is globally exponentially stable. A feedback linearization method is also employed for generating the active power reference of inner loops. Finally, some experimental tests are conducted to verify its effectiveness.
In recent years, a large number of three-phase phase-locked loops (PLLs) have been developed. One of the most popular ones is the complex coefficient filter-based PLL (CCF-PLL), which benefits from a ...sequence selective filtering ability. This feature enables the CCF-PLL to selectively reject/extract disturbances before the PLL control loop while maintaining an acceptable dynamic behavior. The aim of this letter is presenting a simple yet effective approach to enhance the standard CCF-PLL performance without requiring any additional computational load.
This paper proposes a new power flow (PF) formulation for electrical distribution systems using the current injection method and applying the Laurent series expansion. Two solution algorithms are ...proposed: a Newton-like iterative procedure and a fixed-point iteration based on the successive approximation method (SAM). The convergence analysis of the SAM is proven via the Banach fixed-point theorem, ensuring numerical stability, the uniqueness of the solution, and independence on the initializing point. Numerical results are obtained for both proposed algorithms and compared to well-known PF formulations considering their rate of convergence, computational time, and numerical stability. Tests are performed for different branch R/X ratios, loading conditions, and initialization points in balanced and unbalanced networks with radial and weakly-meshed topologies. Results show that the SAM is computationally more efficient than the compared PFs, being more than ten times faster than the backward–forward sweep algorithm.
•Two novel efficient power flow algorithms for distribution systems.•Linearization using Laurent series expansion.•Convergence and stability analysis using Banach fixed-point theorem.•Proposed algorithms are at least three times faster than the backward–forward sweep.
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•A simple molecular simulation protocal for computing IFT in 3-phase systems is given.•Oil molecules are observed in the interfacial region of aqueous + vapor phase.•The presence of ...oil reduces IFT of H2O+gas phase in H2O + CH4 + oil 3-phase systems.•Spreading coefficients ofH2O + CH4 + oil 3-phase systems are calculated.•IFTs from simulation are in good agreement with those from DGT.
A straightforward molecular simulation protocol has been proposed to study the interfacial properties of the three-phase fluid systems. With this protocol, the interfctcial tension (IFT) can be calculated based on the pressure tensor of the entire simulation box of the two-phase systems split from the three-phase system without calculating the debatable pressure tensor profile. Water + methane + oil (decane, hexadecane, and toluene) three-phase systems was studied at different temperatures (323–423 K) and pressures (up to around 20 MPa). Reasonable agreement was found among the results obtained from molecular simulation, density gradient theory with the cubic-plus-association equation of state, and available experimental data in the literature. The IFT of the aqueous phase + vapor phase in the three-phase systems is smaller than the IFT in water + methane two-phase systems. Importantly, the reduction of IFT of aqueous phase + vapor phase in the three-phase systems containing decane or hexadecane is moderate while that in the three-phase systems containing toluene is significant, which can be explained by the stronger enrichment of toluene in the interfacial region in contrast to that of decane or hexadecane. Meanwhile, methane accumulates in the interfacial region of the aqueous phase + decane/hexadecane-rich phase in the three-phase systems, which causes the reduction of IFT with pressure while the opposite pressure effect was reported in the water + decane/hexadecane two-phase systems. The interfacial properties of the oil-rich phase + vapor phase in the three-phase systems are hardly affected by water due to the small amount of dissolved water. Furthermore, the calculated spreading coefficient of different types of oil in contact with water + methane under three-phase conditions follows this order: toluene > decane > hexadecane.
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With the increased prevalence of power converters in power systems, especially three-phase voltage source converters (VSCs), the stability analysis of power electronics-based power systems has ...received much attention recently. To this end, different impedance models, such as the dq -domain, sequence-domain, and phasor-domain impedance models among others, have been developed for three-phase VSCs in recent years. A common trend in all these impedance models, which have no noticeable practical advantage compared to each other, is considering a standard synchronous reference frame phase-locked loop (SRF-PLL) for the synchronization of the VSC with the power grid. The standard SRF-PLL, however, has a limited filtering ability and, therefore, may not be very practical in most applications. To deal with this shortcoming of the SRF-PLL, a great number of advanced three-phase PLLs have been proposed in the literature. These advanced PLLs may have different feedback/feedforward loops and filters in their structures, which make including their dynamics in the available impedance models complicated. Bridging this gap in research is the objective of this article. To this end, it is demonstrated that advanced three-phase PLLs have an alternative representation, which can be easily obtained and included in the available dq -frame impedance model. Several case studies are presented to verify this idea.
In three-phase power and energy applications, the synchronous reference frame phase-locked loop (SRF-PLL) is a popular tool for synchronization purposes. The SRF-PLL can be easily and effectively ...customized for different scenarios by changing its loop filter. Recently, some supposedly different PLLs using the steady-state linear Kalman filter have been developed. The main aim of this letter is to analyze these PLLs. It is demonstrated that they are actually equivalent to some well-known SRF-PLL structures and, therefore, provide no advantage compared to them.
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