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Peer-reviewed literature
Ultracapacitors: why, how, and where is the technology Andrew Burke;
Abstract This paper covers all the basics of Ultra capacitors from why we need them, their advantages, their working and a detailed comparison of various features of Ultra capacitors with that of batteries. Various concerns like the cost issues and the manufacturing problems of the technologies involved are discussed.The present status and the future scope of the technology is also covered.
Using Ultra capacitors in Photovoltaic Systems. A technical proposal José Antonio Domínguez Vázquez, Fernando Martínez Rodrigo, José Miguel Ruiz and Santiago Lorenzo Matilla
Abstract This paper explores the possibility of using an ultra capacitor as a battery for the photovoltaic systems. The authors model the irradiation by a Gaussian expression. Also discussed is the methods of sizing the PV and the Ultra capacitor system and finally the authors propose five strategies of control for the system
a) System 1: Conventional system: It works at variable power. Starting at a minimum input power, and including a MPP tracking
b) System 2: Using ultra capacitors at variable voltage depending of the ultra capacitors characteristics. Inverter works at constant output power at its maximum efficiency.
c) System 3: Using ultra capacitors at variable voltage. Tracking of the MPP with a DC regulator before the ultra capacitors. Still maximum and minimum working voltages. Inverter works at constant output power at its maximum efficiency.
d) System 4: Same at above but inverter works at two different levels: normal level and upper level for extreme situation (very high input PV power)
e) System 5: Hybrid strategy. We fix a working power. When PV system provides more power, inverter works like a conventional system. When input power is lower, we charge and discharge the ultra capacitors at constant power.
Effective Charging Method for Ultra capacitors Marco S. W. Chan , K. T. Chau , and C. C. Chan
Abstract A charging circuit for Ultra capacitors has been proposed, disadvantages of using common charging methodologies like linear regulators, current transducers and closed loop circuitry for current control have been cited and the use of PWM (pulse width modulation) has been made in the circuit the circuit is basically open loop thereby limiting any stability problems. Theoretical and practical demonstrations of the circuit have been shown and studied.
Abstract This paper proposes a new bidirectional DC/DC converter for supercapacitor applications. The proposed converter has a parallel structure in supercapacitor side (where voltage is low and current is high) and a series structure in the other side. This structure increases efficiency of the converter. For current sharing in the parallel side of the proposed converter, two different methods are recommended and compared in this paper: Current balancing transformer (CBT) and two separate inductors (TSI). Simulation and experimental results show performance of the proposed converter
===Technology Research Of Novel Energy Storage Control For The PV Generation System Jinhui Xue , Zhongdong Yin , Bingbing wu, Ziping wu, Jun li
Abstract Recent years, technologies for new energy have developed rapidly since the energy crisis and the environmental pollution got worse. And the solar energy generation technology tends towards the stage of a large number of applications in engineering from the research stage. This paper designed a grid-connected PV system firstly, then introduced the operation principle of the various parts as well with the control strategy of the power flow. The design of energy storage is of great significance as the output power of PV cells array is greatly affected by the light intensity and the temperature change. Battery is used as the energy storage device normally in the traditional energy storage system. In this paper, it used the Ultracapacitor as the energy storage device after comparing with the battery, and designed the charge-discharge control strategy according to the characteristics of the ultracapacitor. Finally it verified the feasibility of the energy storage control strategy through the simulation models which was built based on the PSCAD/EMTDC platform.
A novel charging control scheme for super capacitor energy storage in photovoltaic generation system Nan Li; Jiancheng Zhang; Yun Zhong;
Abstract A control scheme is described to charge series-connected super capacitors for photovoltaic generation systems. Based on the features of the super capacitors charge, the control scheme consists of three modes, i.e., the constant current charge mode, the constant power charge mode, and the constant voltage charge mode. The shift of three modes can be realized by controlling the duty of IGBT in the Boost-Buck converter system. Meanwhile, the high voltage, which is more suitable for application, can be obtained. Compared with the normal charge method with series-connected current-limiting resistance and the charge method with the constant current charge mode and the constant voltage charge mode, the proposed charging control scheme can shorten the charging time and improve the usage of the electric power generated from the PV arrays. The advantage described above is verified by simulations.
A simplified PV model for low power MPPT controller design Patangia, H.; Gourisetti, S.G.; Siddiqui, A.; Sharma, S.;
Abstract The paper presents a simplified PV model to assist in developing low cost MPPT controller in applications employing mini solar panels. High power drain of the control electronics is prohibitive for such low power application. Theoretical insight assisted by practical test data has been used to develop an equivalent Thevenin's model where the Thevenin's resistance is nonlinear and voltage dependent. The approach has provided a new MPPT criterion in terms of equivalent resistance that is both novel and useful in developing a controller that tracks the maximum power point under dynamic conditions
===Maximum power transfer tracking for a photovoltaic-supercapacitor energy system Kim, Younghyun; Chang, Naehyuck; Wang, Yanzhi; Pedram, Massoud;
Abstract It is important to maintain high efficiency when charging electrical energy storage elements so as to achieve holistic optimization from an energy generation source (e.g., a solar cell array) to an energy storage element (e.g., a supercapacitor bank). Previous maximum power point tracking (MPPT) methods do not consider the fact that efficiency of the charger varies depending on the power output level of the energy generation source and the state of charge of the storage element. This paper is the first paper to optimize the efficiency of a supercapacitor charging process by utilizing the MPPT technique and simultaneously considering the variable charger efficiency. More precisely, previous MPPT methods only maximize the power output of the energy generation source, but they do not guarantee the maximum energy is stored in the energy storage element. Note that the load device takes its energy from the storage element so it is important to maximize energy transfer from the source into the storage element. We present a rigorous framework to determine the optimal capacitance of a supercapacitor and optimal configuration of a solar cell array so as to maximize the efficiency of energy transfer from the solar cells into a bank of supercapacitors. Experimental results show the efficacy of the proposed technique and design optimization framework.
Access point power saving in solar/battery powered IEEE 802.11 ESS mesh networks Yangyang Li; Todd, T.D.; Dongmei Zhao;
Abstract
IEEE 802.11 access point (AP) power saving is an important feature for solar/battery powered ESS mesh networks. In this paper we propose a media access control (MAC) protocol for power-aware multihop infrastructure, based on extensions to IEEE 802.11(e). A power saving mesh AP includes a network allocation map (NAM) in its beacon broadcasts which specifies its temporal operation, and thus coordinates traffic delivery and power saving at both end stations and at the AP. A simple algorithm is proposed for dynamically updating channel activities so that best-effort traffic load changes can be quickly accommodated. Simulation and analytic results are presented for the proposed system which show that the proposed protocol and algorithm can achieve good AP power consumption without any significant end station performance degradation
Real-Time Handoff in Solar/Battery Powered ESS Mesh Networks Fashandi, S.; Todd, T.D.;
Abstract
ESS mesh networks will soon provide extensive coverage deployment for outdoor WLAN hotzones. In these types of networks, solar powered mesh access points (MAPs) and mesh points (MPs) can be used to provide tether-less infrastructure extension in an inexpensive and flexible manner. Unlike conventional WLAN networks, power saving on the access points (APs) is an important feature which can result in significantly reduced solar-powered AP node costs. Unfortunately, when infrastructure nodes conserve power, they become less responsive and this can significantly lengthen the hand off process. In this paper we propose and analyze different algorithms for mitigating these effects, so that real-time handoff can occur as fast as possible. Three different algorithms are proposed for dynamically activating the power saving infrastructure. The proposed algorithms are tested and compared to conventional handoff algorithms via simulation and analysis
The need for access point power saving in solar powered WLAN mesh networks Todd, T.D.; Sayegh, A.A.; Smadi, M.N.; Dongmei Zhao
Abstract
Wireless LAN mesh networks are now being used to deploy Wi-Fi coverage in a wide variety of outdoor applications. In these types of networks, conventional WLAN mesh nodes must be operated using continuous electrical power connections. This requirement may often be very expensive, especially when the network includes expansive outdoor wireless coverage areas. An alternative is to operate some of the WLAN mesh nodes using an energy sustainable source such as solar or wind power. This eliminates the need for a fixed power connection, making the node truly tetherless and allowing more flexibility in node positioning. In this article we first review the background and recent activities in the area of energy sustainable WLAN mesh networks. These types of networks are provisioned geographically, in that the assigned resources are a function of the geographic region where the network is to be deployed. The theory behind this is briefly described using some sample North American locations. We then discuss the current shortcomings of IEEE 802.1 1 when used in these types of networks. IEEE 802.11 requires that the access point be continuously powered, and this requirement is a major barrier to deploying cost-effective sustainable energy networks in certain applications. Recent work is then reviewed that has begun to address the changes that would be required to the standard to better support these types of networks.
Connecting remote sites to the wired backbone by wireless mesh access networks Staub, T.; Anwander, M.; Baumann, K.; Braun, T.; Brogle, M.; Dolfus, K.; Félix, C.; Goode, P.K.;
Abstract
Wireless Mesh Networks (WMNs) operating in the 5 GHz band (IEEE 802.11 a/h) offer a great opportunity to function as wireless access networks. Remote sites that lack direct access to a wired/fibre network may benefit from this technology, as it can be used to bridge possibly large distances. The high gain of directional antennas improves the reception of signals in focused directions and reduces interference from unwanted sources. Therefore, they are the preferred choice for such bridging scenarios. In this paper, we present our experiences with setting up such a Wireless Access Network using directional antennas in the area of Neuchâtel, Switzerland. We describe the necessary equipment and planning steps, highlight common pitfalls and discuss gained insights as well as experimental results. Measured data supports the feasibility of our networking approach, yet reveals the high impact of general challenges that have to be overcome in real-world deployments.
Solar Powered WLAN Mesh Network Provisioning for Temporary Deployments Badawy, G.H.; Sayegh, A.A.; Todd, T.D.
Abstract
WLAN mesh networks are often installed to provide wireless coverage for temporary events. In many of these cases, the WLAN mesh nodes can be operated using an energy sustainable source such as solar power. Node resource assignment consists of provisioning each node with a solar panel and battery combination that is sufficient to prevent node outage for the duration of the deployment. In this paper we consider this resource assignment problem with the objective of minimizing the total battery cost for a given energy source assignment. A methodology and algorithms for determining this resource assignment are first given. We then study the problem in the presence of shortest path and energy aware routing. To evaluate the quality of the resource assignments, we develop a linear programming formulation which gives lower bounds on the network resource assignment. Competitive ratios for different routing algorithms are then used, which demonstrates their effectiveness. We also include the case where some of the deployed nodes are designated in advance as having a continuous power source. Our results show the resource savings which are possible using the design algorithms and the potential resource assignment benefits of energy aware routing.
Energy Aware Provisioning in Solar Powered WLAN Mesh Networks Badawy, G.H.; Sayegh, A.A.; Todd, T.D.
Abstract
WLAN mesh networks are often installed to provide wireless coverage for temporary events. In these types of networks, the WLAN mesh nodes can sometimes be operated using an energy sustainable source such as solar power. Resource provisioning consists of pre-assigning each node with a solar panel and battery combination that is sufficient to prevent node outage for the duration of the deployment. This is done by assuming a temporal load profile for each node, which is then used to perform the assignment using historical solar insolation data for the desired deployment location. Unfortunately, this methodology cannot take into account the state dependencies which occur when the network uses energy aware routing, and therefore the system may be over-provisioned. In this paper we propose a methodology for WLAN mesh node resource assignment that incorporates energy aware routing into the assignment algorithm. The problem consists of determining a network-wide minimum cost resource assignment subject to satisfying the input load profile. A genetic algorithm (GA) has been developed for this purpose. Our results show the large resource savings that energy aware resource assignment can achieve when compared to that done using the conventional methodology. We also study the competitive ratio of both resource assignment schemes and show that for small traffic overloading, energy aware routing performs better than shortest path routing in networks which are provisioned using the proposed methodology.
Abstract
Solar powered WLAN infrastructure is a cost effective option in outdoor deployments where continuous power sources are not practical. In these nodes the cost of the solar panel and battery can be a significant fraction of the total, and therefore reducing access point power consumption is very important. In this type of network, peak bandwidth requirements may not be satisfied by a single access point radio, even though long term average bandwidth requirements may be very low. In this case multiple radio APs or overlapped AP coverage deployment is required to meet this peak demand. When this happens the long term power consumption of the nodes can be reduced by implementing shared dynamic power saving between the WLAN mesh nodes. In this paper we propose and evaluate two algorithms for efficiently activating the solar powered infrastructure when additional bandwidth is needed. The algorithms are designed to be compatible with the existing IEEE 802.11 standard and include conventional load balancing when more than one AP is active in a given coverage area. We demonstrate that the proposed algorithms can significantly reduce the power consumption of the shared solar powered infrastructure.
Energy Management in Solar Powered WLAN Mesh Nodes Using Online Meteorological Data Sayegh, A.A.; Todd, T.D
Abstract
Solar powered WLAN mesh nodes are assigned a solar panel and battery size based on power consumption profiles. If future loading exceeds the design target, then a node may not be able to achieve the outage performance for which it was configured. To prevent this from happening, forced power saving can be used to reduce node power consumption to acceptable levels. However, forced power saving generates a deficit in offered capacity which should be minimized as much as possible. In this paper we first formulate this as a non-linear control problem. An efficient linear programming approximation is then defined and solved based on an offline optimization where future solar insolation is known in advance. This provides a bound on the performance of any real control algorithm. We show that the LP solution is accurate in that it comes very close to achieving a no-control capacity deficit lower bound. A control algorithm is then proposed whose operation uses dynamic access to publicly available on-line meteorological data. The proposed approach uses this on-line data but could also benefit from on-line weather forecasting. Our results show that the proposed algorithm minimizes node outage and performs favorably compared to the offline and no-control lower bounds.
A contribution to the simulation and design optimization of photovoltaic systems M. G. Jaboori, M. M. Saied, and A. A. Hanafy
Abstract
This paper presents guidelines to the proper selection of solar array and battery sizes for use in PV-powered dispersed systems, located far from public power networks. It will also deal with the choice of the key design parameters of separately excited DC motors used for farm irrigation. The selection procedure is based on the accurate system modeling and the annual simulation using actual meteorological (insolation and temperature) and typical load data pertinent to the state of Kuwait. The procedure determines the useful, dumped and commercial energy components, forced upon by system-load interaction. Two systems are investigated, system (1) is an alternating current (AC) residential load of a given annual demand profile on hourly basis, while system (2) represents an imgation setup featuring a DC motor and a battery backup. The results showed that a properly-sized battery interface would enhance the performance of the irrigation system, energywise, by more than 12% compared to the directly coupled case. As for the AC load, there exist optimum battery and PV sizes, where the effective energy is maximum.