A simple and accurate approach to solve the power flow for balanced islanded microgrids

Power flow studies are very important in the planning or expansion of power system. With the integration of distributed generation (DG), micro-grids are becoming attractive. So, it is important to study the power flow of micro-grids. In grid connected mode, the power flow of the system can be solved in a conventional manner. In islanded mode, the conventional method (like Gauss Seidel) cannot be applied to solve power flow analysis. Hence some modifications are required to implement the conventional Gauss Seidel method to islanded micro-grids. This paper proposes a Modified Gauss Seidel (MGS) method, which is an extension of the conventional Gauss Seidel (GS) method. The proposed method is simple, easy to implement and accurate in solving the power flow analysis for islanded microgrids. The MGS algorithm is implemented on a 6 bus test system. The results are compared against the simulations results obtained from PSCAD/EMTDC which proves the accuracy of the proposed MGS algorithm

A novel approach to solve power flow for islanded microgrids using modified Newton Raphson with droop control of DG

The study of power flow analysis for microgrids has gained importance where several methods have been proposed to solve these problems. However, these schemes are complic ated and not easy to implement due to the absence of a slack bus as well as the dependence of the power on frequency as a result of the droop characteristics. This paper proposes simple and e ffec- tive modifications to the conventional method (Newton Raphs on) to compute the power flow for microgrids. The presented metho d provides a simple, easy to implement, and accurate approach to solve the power flow equations for microgrids. The propose d method is applied to two test systems: a 6-bus system and a 38- bus system. The results are compared against simulation result s from PSCAD/EMTDC which validate the effectiveness of the develo ped method. The proposed technique can be easily integrated in current commercially available power system software and c an be applied for power system studies method is applied to two test systems: a 6-bus system and a 38-bus system. The results are compared against simulation results from PSCAD/EMTDC which validate the effectiveness of the developed method. The proposed technique can be easily integrated in current commercially available power system software and can be applied for power system studies

Linking Proteomic and Transcriptional Data through the Interactome and Epigenome Reveals a Map of Oncogene-induced Signaling

Cellular signal transduction generally involves cascades of post-translational protein modifications that rapidly catalyze changes in protein-DNA interactions and gene expression. High-throughput measurements are improving our ability to study each of these stages individually, but do not capture the connections between them. Here we present an approach for building a network of physical links among these data that can be used to prioritize targets for pharmacological intervention. Our method recovers the critical missing links between proteomic and transcriptional data by relating changes in chromatin accessibility to changes in expression and then uses these links to connect proteomic and transcriptome data. We applied our approach to integrate epigenomic, phosphoproteomic and transcriptome changes induced by the variant III mutation of the epidermal growth factor receptor (EGFRvIII) in a cell line model of glioblastoma multiforme (GBM). To test the relevance of the network, we used small molecules to target highly connected nodes implicated by the network model that were not detected by the experimental data in isolation and we found that a large fraction of these agents alter cell viability. Among these are two compounds, ICG-001, targeting CREB binding protein (CREBBP), and PKF118–310, targeting β-catenin (CTNNB1), which have not been tested previously for effectiveness against GBM. At the level of transcriptional regulation, we used chromatin immunoprecipitation sequencing (ChIP-Seq) to experimentally determine the genome-wide binding locations of p300, a transcriptional co-regulator highly connected in the network. Analysis of p300 target genes suggested its role in tumorigenesis. We propose that this general method, in which experimental measurements are used as constraints for building regulatory networks from the interactome while taking into account noise and missing data, should be applicable to a wide range of high-throughput datasets.National Science Foundation (U.S.) (DB1-0821391)National Institutes of Health (U.S.) (Grant U54-CA112967)National Institutes of Health (U.S.) (Grant R01-GM089903)National Institutes of Health (U.S.) (P30-ES002109

Grid code violation during fault triggered islanding of hybrid micro-grid

The major advantage of a micro-grid is its ability to run in both grid connected and islanded mode of operation providing higher flexibility and reliability. With increasing popularity of micro-grids and their existence becoming more and more prominent in existing power systems, more stringent adherence to frequency and voltage standards are being requested by Distribution Network Operators (DNO's) in order to maintain proper functionality of the grid. In case of any violations to the aforementioned standards, the distributed generation will have to be disconnected to ensure system security. Fault triggered islanding causes large excursions in system voltage and frequency which may lead to disconnection of DG's thereby threatening the grid integrity and strength. In this paper a review of IEEE standards and North American Electric Reliability Corporation suggested standards is presented. The use of dynamic voltage restorer as series compensation to ensure successful islanding without violating the standards is proposed. A comprehensive analysis is conducted by time domain simulations using Matlab/Simulink software

Performance of the OVP/UVP and OFP/UFP method with voltage and frequency dependent loads

In previous literature, constant RLC loads were assumed to impose, on the islanding detection method, the hardest detectable case. For this reason, distributed-generation (DG) islanding studies are usually analyzed and performed by using constant RLC loads. In this paper, different types of loads are taken into account by modeling the load's voltage and frequency dependence. The performance of the over/undervoltage and over/underfrequency protection (OVP/UVP and OFP/UFP) method is examined for the different load models and the results are compared with the constant RLC load case. The analysis is conducted on a constant power-controlled DG designed to operate at unity power factor. A generalized formula, for calculating the nondetection zone of the OVP/UVP and OFP/UFP method, is derived in terms of the load's voltage and frequency dependence parameters. The analysis is further extended on a constant current-controlled DG interface

Scheduled Perturbation To Reduce Nondetection Zone For Low Gain Sandia Frequency Shift Method

It is known that the choice of gain (K) in the Sandia frequency shift (SFS) scheme has direct impacts on the stability of a system with grid-connected distributed generations (DGs). In this paper, a scheduled perturbation technique is proposed to reduce the stability impact of K. In the proposed technique, chopping fraction (cf) is used to compensate for reduction in the value of K, where higher cf values are used to achieve zero nondetection zone (NDZ) under low gain SFS. It is shown by analysis that theoretical reduction of NDZ can be always achieved for a nonzero value of cf. Simulations for single- and multi-DGs systems are performed to verify the analytical analysis. It is shown that an appropriate design of scheduled signal duty cycle (d) is of critical importance to realize the proposed reduction in NDZ. While close synchronization of perturbation signals for multi-DG system is required, a delay of 0.33 s is shown to be tolerated for a two-DG system. Synchronization can be achieved either through locally synchronized timers or by limited communication among DGs. The proposed technique provides an attractive option for systems with high DG penetration by reducing the negative impact of K on stability

A Transient Stiffness Measure for Islanding Detection of Multi-DG Systems

Islanding detection is important to ensure the reliability and safety of distributed generation (DG). In this paper, a new active islanding detection method (IDM) is proposed, and it depends on individually estimating an overall transient stiffness measure for any multi-DG system to establish a clear separation between prior- and post-islanding stiffness. For the multi-DG system to avoid spectrum overlapping, each of its DGs is required to perturb at distinct frequencies. By using this concept of perturbation separation, the proposed technique can be applied to multi-DG systems without requiring any communication among the DGs. Simulation results show that the proposed technique is scalable and robust against different loading conditions and variations of grid stiffness levels as well as with respect to the number of connected DGs and different types of DG controllers. It is also shown that the proposed technique can successfully distinguish islanding conditions from other disturbances that may occur in power system networks

Micro-grid operation of inverter based distributed generation with voltage and frequency dependent loads

Distribution systems are experiencing increasing penetration of distributed generation (DG). One attractive option is to use the available DG capacity during utility outages by forming planned micro-grids. Load sharing among different DG, during micro-grid operation, could be accomplished by equipping each DG with a P-f and Q-V droop characteristic. In this paper, we analyze the impact of the loads' voltage and frequency dependence on the micro-grid's frequency and voltage deviation during a planned islanding condition. The system was modeled and analyzed using PSCAD/EMTDC. The simulation results and mathematical analysis show that the load's voltage and frequency dependence is an important factor when choosing the DG droop characteristic. The results also show that some loading conditions could lead to an unstable micro-grid operation.Masdar Institute of Science and Technolog

Development Of Dynamic Estimators For Islanding Detection Of Inverter-Based Dg

In this paper, a new islanding detection method (IDM) is proposed to dynamically estimate islanding occurrence. The proposed dynamic estimators estimate amplitudes and phase angles of the current injected by the grid at the point of common coupling with the distributed generation (DG) in addition to the DG\u27s bus voltage. A distributed two-level algorithm is proposed to detect an islanding condition for single and multi-DG configurations. Analytical design and transient analysis are carried out for the islanding detection problem to determine the nondetection zone (NDZ) of the proposed islanding detection algorithm. A local low-frequency meshed communication network is sufficient to achieve distributed islanding detection capability for a general multi-DG network with negligible NDZ. It is shown through simulations that the proposed IDM can successfully distinguish an islanding condition from other disturbances that may occur in power system networks

A Transient Stiffness Measure For Islanding Detection Of Multi-Dg Systems

Islanding detection is important to ensure the reliability and safety of distributed generation (DG). In this paper, a new active islanding detection method (IDM) is proposed, and it depends on individually estimating an overall transient stiffness measure for any multi-DG system to establish a clear separation between prior- and post-islanding stiffness. For the multi-DG system to avoid spectrum overlapping, each of its DGs is required to perturb at distinct frequencies. By using this concept of perturbation separation, the proposed technique can be applied to multi-DG systems without requiring any communication among the DGs. Simulation results show that the proposed technique is scalable and robust against different loading conditions and variations of grid stiffness levels as well as with respect to the number of connected DGs and different types of DG controllers. It is also shown that the proposed technique can successfully distinguish islanding conditions from other disturbances that may occur in power system networks