For grid-tied inverters, rapid and accurate obtainment of real-time grid phase is the basic and important function for stable operation. Among existing grid synchronization schemes, open-loop synchronization (OLS) met...
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Currently,a grid-connected inverter is required to inject a dual-sequence current during asymmetric grid sags,which means both positive and negative sequence phases should be *** paper proposes an open-loop phase sync...
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Currently,a grid-connected inverter is required to inject a dual-sequence current during asymmetric grid sags,which means both positive and negative sequence phases should be *** paper proposes an open-loop phase synchronization(OLS)method of positive and negative sequences for an asymmetric grid based on the moving average filter(MAF),which does not need to separate the positive and negative sequence fundamental components of grid *** a benefit,there is no double-frequency oscillation in the estimated phases at offnominal frequencies since the positive and negative sequence phases are obtained *** proposed method not only has the inherent advantages of OLS,but also further improves the dynamic response since the window length of MAF is only 1/6 of the fundamental *** effectiveness of the proposed OLS is verified by experimental results.
synchronization is a crucial process in the operation of grid-connected distributed energy sources. synchronization techniques are classified in closed-loop (CLS) and open-loop synchronization (OLS) techniques. Unlike...
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synchronization is a crucial process in the operation of grid-connected distributed energy sources. synchronization techniques are classified in closed-loop (CLS) and open-loop synchronization (OLS) techniques. Unlike the CLS technique, OLS techniques are recent and less known. This paper discusses a comparative analysis of the three prominent state-of-the-art OLS techniques. Accordingly, a benchmark model is proposed to systematically evaluate the performance of the OLS techniques under grid voltage disturbances such as harmonic distortions, voltage unbalance, DC offset, and low voltage ride through operation. Given the hardware resource utilization, the computational complexity and the execution time are also presented to judge the efficacy of the proposed model. Thus, engineers/or researchers can better understand the choice of hardware resources and the preferred dynamic performance of a synchronization scheme applied to control and protect a grid-tied power converter. Simulation and experimental results are presented and discussed to demonstrate the purpose of the proposed model.
open-loop synchronization techniques OLSs can be classified into True (TOLS) and Pseudo or Quasi-OLSs (POLS/QOLS). The TOLS means a system that has no feedback in its structures which results in unconditional stabilit...
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ISBN:
(纸本)9781665435543
open-loop synchronization techniques OLSs can be classified into True (TOLS) and Pseudo or Quasi-OLSs (POLS/QOLS). The TOLS means a system that has no feedback in its structures which results in unconditional stability. Roughly speaking the advanced TOLSs suffers from two main drawbakcks:1) compromising performances under off-nominal frequencies in faulty conditions, 2) inefficiency under large frequency drifts and high computation time. To tackle the problem of frequency adaptivity, the POLS uses a frequency estimator. This technique works efficiently under large frequency drifts even in faulty conditions and benefits from low computation time. However, one of the main challenges in OLS techniques is how to improve dynamic performance without compromising the ability to reject disturbances. In this paper, an enhancement is made to the standard POLS to tackle this problem. The use of a cascade positive fundamental components estimator (PFCE) will allow us to enhance the response time while keeping the phase and magnitude error at their lowest. The mathematical model is presented then simulated. The simulation results validate this proposal.
This paper presents a novel method for synchronizing an islanded system to the main grid without feedback control. The idea is based on the understanding that the main concern in synchronization is the switching trans...
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This paper presents a novel method for synchronizing an islanded system to the main grid without feedback control. The idea is based on the understanding that the main concern in synchronization is the switching transients. Therefore, we propose to use preinsertion impedance to reduce the transients. In addition, the impedance is selected such that the transients are acceptable as long as both parties operate in pre-established operating conditions. As a result, feedback control to adjust generator voltage and frequency and the associated communication link are avoided. The proposed approach could result in significant cost savings for islanded systems located in remote areas. In addition, the extra effort required for generator adjustments, especially for multiple units, can be eliminated. Technical considerations and design method for the selection of the impedance size are presented. Simulation studies are conducted to evaluate the performance of the method. The results prove that the transients can be effectively reduced and open-loop synchronization is indeed achievable.
In a TDMA Satcom system, network synchronization methods for highly mobile Satcom stations produce serious timing error. In order to solve this problem, an open-loop network synchronization method based on Kalman filt...
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In a TDMA Satcom system, network synchronization methods for highly mobile Satcom stations produce serious timing error. In order to solve this problem, an open-loop network synchronization method based on Kalman filtering estimation principle is proposed. While maintaining the advantages of traditional open-loop network synchronization methods, such as simple implementation, the new method will greatly improve timing accuracy.
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