Microgrid cost optimization: a case study on Abu Dhabi

This paper presents a microgrid cost optimization study specifically focused on the United Arab Emirates (UAE) based on the Genetic and Ant-Bee Colony algorithms. The main objective of the paper is to identify size and amount of power supply sources in Microgrids that result in minimum cost. Specific parameters pertaining to the UAE were employed within the new objective function and constraints. Two different scenarios were tested, and their results have been discussed. During this study, it was evident that solar-PV systems were the second most cost-effective way to reduce cost of microgrids preceded by micro-turbines

PokeME: Applying context-driven notifications to increase worker engagement in mobile crowd-sourcing

In mobile crowd-sourcing systems, simply relying on people to opportunistically select and perform tasks typically leads to drawbacks such as low task acceptance/completion rates and undesirable spatial skews. In this paper, we utilize data from TASKer, a campus-based mobile crowd-sourcing platform, to empirically study and discover whether and how various context-aware notification strategies can help overcome such drawbacks. We first study worker interactions, in the absence of any notifications, to discover some spatiooral properties of task acceptance and completion. Based on these insights, we then experimentally demonstrate the effectiveness of two novel, non-personal, context-driven notification strategies, comparing the outcomes to two different baselines (no-notification and random-notification). Finally, using the data from the random-notification mechanism, we derive a classification model, incorporating several novel contextual features, that can predict a worker's responsiveness to notifications with high accuracy. Our work extends the crowd-sourcing literature by emphasizing the power of smart notifications for greater worker engagement

A Review on Multi-Terminal High Voltage Direct Current Networks for Wind Power Integration

With the growing pressure to substitute fossil fuel-based generation, Renewable Energy Sources (RES) have become one of the main solutions from the power sector in the fight against climate change. Offshore wind farms, for example, are an interesting alternative to increase renewable power production, but they represent a challenge when being interconnected to the grid, since new installations are being pushed further off the coast due to noise and visual pollution restrictions. In this context, Multi-Terminal High Voltage Direct Current (MT-HVDC) networks are the most preferred technology for this purpose and for onshore grid reinforcements. They also enable the delivery of power from the shore to offshore Oil and Gas (O&G) production platforms, which can help lower the emissions in the transition away from fossil fuels. In this work, we review relevant aspects of the operation and control of MT-HVDC networks for wind power integration. The review approaches topics such as the main characteristics of MT-HVDC projects under discussion/commissioned around the world, rising challenges in the control and the operation of MT-HVDC networks and the modeling and the control of the Modular Multilevel Converter (MMC) stations. To illustrate the challenges on designing the control system of a MT-HVDC network and to corroborate the technical discussions, a simulation of a three-terminal MT-HVDC network integrating wind power generation and offshore O&G production units to the onshore grid is performed in Matlab's Simscape Electrical toolbox. The results highlight the main differences between two alternatives to design the control system for an MT-HVDC network

Characterisation of gas turbine dynamics during frequency excursions in power networks

Gas turbines inherently depict unique frequency response characteristics compared with other conventional synchronous generation technologies as their active power output is not entirely determined by the governor response during frequency deviations of the power network. Thus, gas turbine dynamics significantly influence on system stability during frequency events in power networks. Power system and power plant operators require improved understanding of the gas turbine characteristics during various frequency events in order to mitigate adverse impact on power system. Therefore a comparative analysis has been performed between combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs) in order to characterise the dynamic behaviour considering different types of frequency events in power networks. Study has shown that CCGTs result in significant frequency variations in power networks in comparison with OCGTs because of the temperature control action performed by the fast acting inlet guide vanes at the combustor. In particular, they are susceptible to lean blowout during large frequency increase events such as short-circuit faults in power networks. Furthermore, a case study was developed based on the New England-39 bus system in order to illustrate the impact of gas turbine dynamics on network frequency during short-circuit events in power networks

Microgrid Stability Definitions, Analysis, and Modeling (Technical Report PES-TR66)

This document defines concepts and identifies relevant issues related to stability in microgrids. It proposes a definition and a classification of microgrid stability, taking into account pertinent microgrid features such as voltage-frequency dependency, unbalancing, low inertia, and generation intermittency. The modeling of microgrid components such as generators, converters, distribution lines, loads, and distributed energy resources for stability analysis is discussed in detail. Analysis techniques and tools relevant to microgrid stability are also reviewed, as well as various examples highlighting some of the stability classes defined in this report

Impact on transient and frequency stability for a power system at very high wind penetration

This paper analyzes the impact on transient and frequency stability for a power system at very high wind penetration (40% wind). Wind penetration is based on the doubly-fed induction generator (DFIG), and a systematic approach has been adopted for wind power integration. A sensitivity analysis has been carried out for each wind integration scenario and for different wind generator loading conditions. A range of fault locations has been selected for stability analysis based on the proximity to synchronous generation and wind farms. The analysis has shown that transient stability performance is subject to fault location in the network, especially when faults are initiated in areas with very high wind penetration. Frequency stability analysis has also shown that areas with lower inertia are more affected by generator outage events than other areas of the interconnected system. The impacts are exacerbated by an increase in wind penetration in the system, and a significant reduction in damping capability has been observed for DFIG-based high wind penetratio

Comparative analysis of dynamic line rating models and feasibility to minimise energy losses in wind rich power networks

Wind power generation has indicated an exponential increase during last two decades and existing transmission network infrastructure is increasingly becoming inadequate to transmit remotely generated wind power to load centres in the network. The dynamic line rating (DLR) is one of the viable solutions to improve the transmission line ampacity during high wind penetration without investing on an additional transmission network. The main objective of this study is to identify the basic differences between two main line rating standards, since transmission network service providers (TNSPs) heavily depend on these two standards when developing their line rating models. Therefore, a parameter level comparison between two line rating models is a timely requirement, in particular for high wind conditions. Study has shown that roughness factor causes a significant difference between both standards. In particular, the IEEE model indicates more conservative approach due to this parameter. In addition, solar heat-gain calculation has also resulted in significant difference in ampacity ratings between two standards. A case study was developed considering a wind rich network and it has shown that by implementing DLR in wind rich regions, it can effectively reduce line overloading incidents and accommodate wind power flows in the network without any curtailment. Moreover, ability of DLR to reduce network energy losses is also demonstrated and emphasised the importance of selecting suitable DLR candidates to minimise energy losses in the network

Capability constraints to mitigate voltage fluctuations from DFIG wind farms when delivering ancillary services to the network

Majority of the wind power resources are typically sited at remote locations in power networks and generated power is transmitted through rural transmission corridors to load centres. With increased penetration level of the wind generation there is an increased requirement to provide ancillary services from distributed wind power resources, hence they are operated under different control strategies to provide ancillary services to the network. The control strategies and capability characteristics will significant impact on voltage fluctuations in distribution networks. This paper presents a comparative analysis between different wind generator control strategies (i.e. power factor control strategy, voltage control strategy and reactive power dispatch strategy) on network voltage fluctuations during variable wind conditions while considering extended reactive power capability (i.e. with both generator and power electronic converter reactive power capabilities) for the doubly-fed induction generator (DFIG). Voltage fluctuations are analysed using real wind data measured at a DFIG based wind farm, and the wind farm model was verified against real measurements. Study has shown that voltage fluctuations are exacerbated when wind generator is at mode transition (i.e. from power optimisation mode to power limitation mode). A sensitivity analysis has shown that voltage fluctuations are exacerbated due to the limitations of the reactive power capability of the DFIG, and the operating point of the DFIG power curve irrespective of the control strategy implemented at the wind generator. Furthermore, a mitigation strategy was developed as an integrated control scheme to the main control scheme in order to reduce voltage fluctuations due to wind power variations. However, effectiveness of the mitigation strategy is greatly affected by the reactive power capability of the DFIG, in particular during high wind turbulences

Investigation of frequency stability during high penetration of CCGTs and variable-speed wind generators in electricity networks

Variable-speed wind generators (VSWGs) are being extensively deployed as the main wind power generation technology around the world. However, when the VSWGs are integrated to gas turbine based (e.g. combined-cycle gas turbines (CCGTs) and open-cycl