scholarly journals A Protection Method Based on Feature Cosine and Differential Scheme for Microgrid

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Lai Lei ◽  
Cong Wang ◽  
Jie Gao ◽  
Jinjin Zhao ◽  
Xiaowei Wang
Keyword(s):  
Time Domain ◽  
High Accuracy ◽  
Current Level ◽  
Fault Current ◽  
Time Domain Simulation ◽  
Overcurrent Protection ◽  
Protection Method ◽  
Islanded Mode ◽  
Differential Scheme ◽  
The Difference

The fault current level of microgrid is different between islanded mode and grid connected mode. This situation degrades the performance of traditional overcurrent protection schemes. Hence, this paper proposes a protection method based on feature cosine and differential scheme. Firstly, feature cosine is proposed; it employs ellipse equation and minimum least squares to quantify the united behavior about voltage and current. Secondly, fault current direction and feature cosine are analyzed when fault occurs at different locations of a typical microgrid, and then the difference of feature cosine between faulty and healthy section locations is obtained. Thirdly, based on feature cosine and differential scheme, the differential direction is defined and utilized to detect faulty section location. Lastly, various time domain simulation case studies, including different microgrid operation modes, grounding resistances, faulty types, faulty section locations, and noise influence, are conducted and demonstrate that the proposed protection has high accuracy.

scholarly journals Optimization-Based Formulations for Short-Circuit Studies with Inverter-Interfaced Generation in PowerModelsProtection.jl

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2160
Author(s):  
Arthur K. Barnes ◽  
Jose E. Tabarez ◽  
Adam Mate ◽  
Russell W. Bent
Keyword(s):  
Optimization Problem ◽  
Short Circuit ◽  
Problem Formulation ◽  
Power Delivery ◽  
Fault Current ◽  
Protective Device ◽  
Protective Relaying ◽  
Overcurrent Protection ◽  
Short Circuits ◽  
Optimization Problem Formulation

Protecting inverter-interfaced microgrids is challenging as conventional time-overcurrent protection becomes unusable due to the lack of fault current. There is a great need for novel protective relaying methods that enable the application of protection coordination on microgrids, thereby allowing for microgrids with larger areas and numbers of loads while not compromising reliable power delivery. Tools for modeling and analyzing such microgrids under fault conditions are necessary in order to help design such protective relaying and operate microgrids in a configuration that can be protected, though there is currently a lack of tools applicable to inverter-interfaced microgrids. This paper introduces the concept of applying an optimization problem formulation to the topic of inverter-interfaced microgrid fault modeling, and discusses how it can be employed both for simulating short-circuits and as a set of constraints for optimal microgrid operation to ensure protective device coordination.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

Study of HVDC System and Subsynchronous Oscillation

2015 ◽  
Vol 1092-1093 ◽  
pp. 356-361
Author(s):  
Peng Fei Zhang ◽  
Lian Guang Liu
Keyword(s):  
Power Plant ◽  
Time Domain ◽  
Simulation Method ◽  
Time Domain Simulation ◽  
Stable Convergence ◽  
Turbine Generator ◽  
Plant Model ◽  
Subsynchronous Oscillation ◽  
Hvdc System ◽  
Simulation Results

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

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