Optimal Power Cost Management Using Stored Energy in Data Centers

Since the electricity bill of a data center constitutes a significant portion of its overall operational costs, reducing this has become important. We investigate cost reduction opportunities that arise by the use of uninterrupted power supply (UPS) units as energy storage devices. This represents a deviation from the usual use of these devices as mere transitional fail-over mechanisms between utility and captive sources such as diesel generators. We consider the problem of opportunistically using these devices to reduce the time average electric utility bill in a data center. Using the technique of Lyapunov optimization, we develop an online control algorithm that can optimally exploit these devices to minimize the time average cost. This algorithm operates without any knowledge of the statistics of the workload or electricity cost processes, making it attractive in the presence of workload and pricing uncertainties. An interesting feature of our algorithm is that its deviation from optimality reduces as the storage capacity is increased. Our work opens up a new area in data center power management.Comment: Full version of Sigmetrics 2011 pape

Competitive Online Peak-Demand Minimization Using Energy Storage

We study the problem of online peak-demand minimization under energy storage constraints. It is motivated by an increasingly popular scenario where large-load customers utilize energy storage to reduce the peak procurement from the grid, which accounts for up to $90\%$ of their electric bills. The problem is uniquely challenging due to (i) the coupling of online decisions across time imposed by the inventory constraints and (ii) the noncumulative nature of the peak procurement. In this paper, we develop an optimal online algorithm for the problem, attaining the best possible competitive ratio (CR) among all deterministic and randomized algorithms. We show that the optimal CR can be computed in polynomial time, by solving a linear number of linear-fractional problems. More importantly, we generalize our approach to develop an \emph{anytime-optimal} online algorithm that achieves the best possible CR at any epoch, given the inputs and online decisions so far. The algorithm retains the optimal worst-case performance and achieves adaptive average-case performance. Simulation results based on real-world traces show that, under typical settings, our algorithms improve peak reduction by over $19\%$ as compared to baseline alternatives

Smart home

Uslijed ubrzanog napretka u bežičnoj komunikaciji i informacijskim tehnologijama, sada je moguće uvesti i implementirati različite razine „pametnosti“ u kuće. Ove pametne kuće su kuće koje mogu da se inteligentno uključe u razne interakcije sa svojim stanovnicima da bi im omogućile udobnost i siguran život. Ovo uključivanje u živote svojih stanara može varirati od jednostavne kontrole ambijentne temperature do ispunjavanja usluga koje su zasnovane na mobilnim agentima. Pametne kuće imaju potencijal da poboljšaju udobnost, pogodnost, sigurnost i zabavu svojim stanovnicima. Povlastice pametne tehnologije u kući mogu biti očigledne za svakoga ukoliko je njihov potencijal upotpunjen. Smatra se kako je potreba za pametnom tehnologijom najočitija za starije ljude i za osobe s invaliditetom, a s obzirom na činjenicu da je do kraja 2013 godine više od polovice Europljana navršilo 65 godina, ova pametna tehnologija ima i veliki tržišni potencijal.Since there has been a rapid advance in wireless communication and information technologies, it is now possible to introduce and implement different smartness into the homes. These smart houses are those that can intelligently engage with their residents thus providing them with comfort and safe living. This engagement in lives of their residents can vary from simple control of temperature do completing services which have been based on mobile agents. Smart homes have the potential to improve comfort, convenience, safety and entertainment to their residents. The benefits of the smart homes can be pretty obvious for everyone if their potential is fulfilled. It's considered that the need for smart technology is most obvious when it comes to elderly and disabled people, and considering the fact that by the end of 2013 there have been over half of Europeans over 65 years old, this smart technology also has a great market potential

Resource Management in Delay Tolerant Networks and Smart Grid

In recent years, significant advances have been achieved in communication networks and electric power systems. Communication networks are developed to provide services within not only well-connected network environments such as wireless local area networks, but also challenged network environments where continuous end-to-end connections can hardly be established between information sources and destinations. Delay tolerant network (DTN) is proposed to achieve this objective by utilizing a store-carry-and-forward routing scheme. However, as the network connections in DTNs are intermittent in nature, the management of network resources such as communication bandwidth and buffer storage becomes a challenging issue. On the other hand, the smart grid is to explore information and communication technologies in electric power grids to achieve electricity delivery in a more efficient and reliable way. A high penetration level of electric vehicles and renewable power generation is expected in the future smart grid. However, the randomness of electric vehicle mobility and the intermittency of renewable power generation bring new challenges to the resources management in the smart grid, such as electric power, energy storage, and communication bandwidth management. This thesis consists of two parts. In part I, we focus on the resource management in DTNs. Specifically, we investigate data dissemination and on-demand data delivery which are two of the major data services in DTNs. Two kinds of mobile nodes are considered for the two types of services which correspond to the pedestrians and high-speed train passengers, respectively. For pedestrian nodes, the roadside wireless local area networks are used as an auxiliary communication infrastructure for data service delivery. We consider a cooperative data dissemination approach with a packet pre-downloading mechanism and propose a double-loop receiver-initiated medium access control scheme to resolve the channel contention among multiple direct/relay links and exploit the predictable traffic characteristics as a result of packet pre-downloading. For high-speed train nodes, we investigate on-demand data service delivery via a cellular/infostation integrated network. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem and an online resource allocation algorithm is proposed. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. In part II, we focus on resource management in the smart grid. We first investigate the optimal energy delivery for plug-in hybrid electric vehicles via vehicle-to-grid systems. A dynamic programming formulation is established by considering the bidirectional energy flow, non-stationary energy demand, battery characteristics, and time-of-use electricity price. We prove the optimality of a state-dependent double-threshold policy based on the stochastic inventory theory. A modified backward iteration algorithm is devised for practical applications, where an exponentially weighted moving average algorithm is used to estimate the statistics of vehicle mobility and energy demand. Then, we propose a decentralized economic dispatch approach for microgrids such that the optimal decision on power generation is made by each distributed generation unit locally via multiagent coordination. To avoid a slow convergence speed of multiagent coordination, we propose a heterogeneous wireless network architecture for microgrids. Two multiagent coordination schemes are proposed for the single-stage and hierarchical operation modes, respectively. The optimal number of activated cellular communication devices is obtained based on the tradeoff between communication and generation costs

Optimal Energy Storage Strategies in Microgrids

Microgrids are small-scale distribution networks that provide a template for large-scale deployment of renewable energy sources, such as wind and solar power, in close proximity to demand. However, the inherent variability and intermittency of these sources can have a significant impact on power generation and scheduling decisions. Distributed energy resources, such as energy storage systems, can be used to decouple the times of energy consumption and generation, thereby enabling microgrid operators to improve scheduling decisions and exploit arbitrage opportunities in energy markets. The integration of renewable energy sources into the nation's power grid, by way of microgrids, holds great promise for sustainable energy production and delivery; however, operators and consumers both lack effective strategies for optimally using stored energy that is generated by renewable energy sources. This dissertation presents a comprehensive stochastic optimization framework to prescribe optimal strategies for effectively managing stored energy in microgrids, subject to the inherent uncertainty of renewable resources, local demand and electricity prices. First, a Markov decision process model is created to characterize and illustrate structural properties of an optimal storage strategy and to assess the economic value of sharing stored energy between heterogeneous, demand-side entities. Second, a multistage stochastic programming (MSP) model is formulated and solved to determine the optimal storage, procurement, selling and energy flow decisions in a microgrid, subject to storage inefficiencies, distribution line losses and line capacity constraints. Additionally, the well-known stochastic dual dynamic programming (SDDP) algorithm is customized and improved to drastically reduce the computation time and significantly improve solution quality when approximately solving this MSP model. Finally, and more generally, a novel nonconvex regularization scheme is developed to improve the computational performance of the SDDP algorithm for solving high-dimensional MSP models. Specifically, it is shown that these nonconvex regularization problems can be reformulated as mixed-integer programming problems with provable convergence guarantees. The benefits of this regularization scheme are illustrated by way of a computational study that reveals significant improvements in the convergence rate and solution quality over the standard SDDP algorithm and other regularization schemes