Average Power Demand Research Articles

Bandwidth-Based Control Strategy for a Series HEV With Light Energy Storage System

The twin goals of maximizing fuel economy (FE) and improving consumer acceptance by reducing the cost of the energy storage system (ESS) in a series hybrid electric vehicle (SHEV) powertrain is addressed here by using energy storage as a means for filtering drive-cycle power demands on the engine, rather than an energy source for supplying an all-electric drive mode. The concept is intended to minimize, if not eliminate, the battery in the SHEV without resorting to full-range proportional control of the engine and generator. An initial optimization study reported for a mid-size SHEV showed that a 4.5-kWh lithium-ion battery pack was still required. In this paper, a sports-car-class SHEV was studied, where the challenge is to reduce the size of the ESS even more because the available space allocation is only one fourth that of the mid-size vehicle. In this paper, a controller is developed, which allows a hybridized SHEV to be realized with a light ESS. The controller includes a duty-cycling feature that manages the engine performance in multiple efficient regions and a bandwidth-limited (BWL) proportional controller feature that limits low-bandwidth battery current. The performance of the controller has been validated for a SHEV powertrain model with an 80- $\text{V}_{\mathrm{dc}}$ 1.125-kWh battery, plus an 80- $\text{V}_{\mathrm{dc}}$ 46.4-F ultracapacitor module using a customized Autonomie vehicle model. The results show that the combined FE of the new design is increased by 13%, compared with the corresponding FE in the equivalent conventional vehicle. Additional FE improvement is possible by reducing the engine size further to reflect the average power demand imposed by real drive cycles.

Using Power Demand and Residual Load Imbalance in the Load Balancing to Save Energy of Parallel Systems

Power consumption of the High Performance Computing (HPC) systems is an increasing concern as large-scale systems grow in size and, consequently, consume more energy. In response to this challenge, we have develop and evaluate new energy-aware load balancers to reduce the average power demand and save energy of parallel systems when scientific applications with imbalanced load are executed. Our load balancers combine dynamic load balancing with DVFS techniques in order to reduce the clock frequency of underloaded computing cores which experience some residual imbalance even after tasks are remapped. The results show that our load balancers present power reductions of 7.5% in average with the fine-grained variant that performs per-core DVFS, and of 18.75% with the coarse-grained variant that performs per-chip DVFS over real applications.

Cogeneration topology for wind energy conversion system using doubly‐fed induction generator

A novel wind energy conversion system (WECS) with cogeneration topology is presented in this study. In the proposed scheme, doubly-fed induction generator (DFIG) is used as the major source for power generation in grid-isolated mode. The wind turbine operated DFIG is integrated with a permanent magnet ac generator and a solar photovoltaic (PV) module to supplement the both rotor power requirement of DFIG and part of the average load power demand. The performance of a grid-isolated WECS, over wide speed range can be significantly improved through the sequential extraction of wind power along with an augmented solar PV source. The proposed scheme is economically viable with feasible unit cost of generated power. The control scheme has been simulated and experimentally validated with a practical 2.5 kW DFIG using dSPACE DS1104 module, which produced satisfactory results.

Enhanced Transmit Antenna Selection Scheme for Secure Throughput Maximization Without CSI at the Transmitter

This paper addresses the establishment of secure communication links between Alice and Bob in the presence of an eavesdropper (Eve). The proposed scenario assumes: 1) MIMOME wiretap channel; 2) transmit antenna selection at the Alice; 3) no channel state information at the transmitter; 4) fixed Wyner codes; and 5) guarantee of secure throughput by both quality of service and secrecy outage constraints. We propose a simple protocol to enhance security via transmit antenna selection, and then assess its performance in a closed form by means of secrecy outage and successful transmission probabilities. We assume these probabilities are our constraints and then maximize the secure throughput, establishing a security-reliability tradeoff for the proposed scenario. Our numerical results illustrate the effect of this tradeoff on the secure throughput as well as on the number of antennas at Alice, Bob, and Eve. Interestingly, a small sacrifice in reliability allows secrecy enhancement in terms of secure bps/Hz. We apply this idea in our smart grid application (where Alice represents a smart meter and Bob an aggregator) to exemplify that, although Eve may acquire some samples of the average power demand of a household, it is not enough to properly reconstruct such curve.

Maximizing the link throughput between smart meters and aggregators as secondary users under power and outage constraints

This paper assesses the communication link from smart meters to aggregators as (unlicensed) secondary users that transmit their data over the (licensed) primary uplink channel. The proposed scenario assumes: (i) meters’ and aggregators’ positions are fixed so highly directional antennas are employed, (ii) secondary users transmit with limited power in relation to the primary, (iii) meters’ transmissions are coordinated to avoid packet collisions, and (iv) the secondary links’ robustness is guaranteed by an outage constraint. Under these assumptions, the interference caused by secondary users in both primary (base-stations) and other secondary users can be neglected. As unlicensed users, however, meter–aggregator links do experience interference from the mobile users of the primary network, whose positions and traffic activity are unknown. To cope with this uncertainty, we model the mobile users spatial distribution as a Poisson point process. We then derive a closed-form solution for the maximum achievable throughput with respect to a reference secondary link subject to transmit power and outage constraints. Our numerical results illustrate the effects of such constraints on the optimal throughput, evincing that more frequent outage events improve the system performance in the scenario under study. We also show that relatively high outage probabilities have little effect on the reconstruction of the average power demand curve that is transmitted from the smart meter to the aggregator.

Performance Analysis of Hybrid DSTATCOMwith Different Type of Loads

This paper describes the performance of hybrid DSTATCOM (Distribution Static Compensator) on different loads.Hybrid DSTATCOM based on super capacitor and batteries, which improve the power quality problem like voltage Sags/Swells; harmonics and power factor must be corrected.DSTATCOM is a custom power device that is used to regulate the power quality problem. Super capacitor are used to meet the instantaneous power demand since they can store and quickly release significant amount of energy, while the batteries are used to meet the average power demand. The simulations were performed using MATLAB Simulation(R2014a).

Exploring Fuel-Saving Potential of Long-Haul Truck Hybridization

Comparisons are reported on the simulated fuel economy for parallel, series, and dual-mode hybrid electric long-haul trucks, in addition to a conventional powertrain configuration, powered by a commercial 2010-compliant 15-L diesel engine over a freeway-dominated heavy-duty truck driving cycle. The driving cycle was obtained by measurement during normal driving conditions. The results indicated that both parallel and dual-mode hybrid powertrains were capable of improving fuel economy by 7% to 8%. However, there was no significant fuel economy benefit for the series hybrid truck because of internal inefficiencies in energy exchange. When reduced aerodynamic drag and tire rolling resistance were combined with hybridization, there was a synergistic fuel economy benefit for appropriate hybrids that increased the fuel economy benefit to more than 15%. Long-haul hybrid trucks with reduced aerodynamic drag and rolling resistance offered lower peak engine loads, better kinetic energy recovery, and reduced average engine power demand. Thus, it is expected that hybridization with load reduction technologies offers important potential fuel energy savings for future long-haul trucks.

Performance/energy trade‐off in scientific computing: the case of ARM big.LITTLE and Intel Sandy Bridge

Power consumption is one of the main challenges to achieve Exascale performance. Current research trends aim at overcoming power consumption constraints using low-power processors. Although new processors feature sensors that enable precise power measurements, they provide different interfaces to collect data, making it difficult to correlate performance with energy consumption. To overcome this issue, the authors developed a platform-independent tool that collects power and energy data from homogeneous and heterogeneous systems. Using this tool, they provide a detailed comparison between a low-power processor (ARM big.LITTLE) and a high performance processor (Intel Sandy Bridge-EP) using all applications from the NAS parallel benchmarks and a real-world soil irrigation simulator. The results show that the average power demand of Intel Sandy Bridge-EP is within 12.6× to 152.4× higher than ARM big.LITTLE, whereas its average energy consumption is within 1.6× to 7.1× superior. Overall, ARM big.LITTLE presented a better performance/energy trade-off when it takes <9.2× the execution time of Intel Sandy Bridge-EP to solve the same problem.

Control of grid converters for PV array excited wind-driven induction generators with unbalanced and nonlinear loads

In this paper, a new control algorithm for grid connected inverter fed by Photovoltaic array (PV) excited wind-driven induction generator (IG) for unbalanced nonlinear load at point of common coupling (PCC) is proposed. The proposed composite power controller comprises of multi control loops such as power, voltage and current loops. The power control loop generates positive sequence reference current based on the availability of PV power and the average power demand of the load and negative sequence reference currents to compensate the oscillating power component that appears due to the unbalanced nonlinear load at the PCC and further, drop due to non-fundamental power component is compensated by addition of virtual non-linear impedance to the current control loop. The voltage control loop generates the reactive current reference to compensate the drop due to nonlinear magnetizing reactance of IG to eliminate the machine de-rating effect. The current control loop regulates the average and suppresses the oscillating power in dual decoupled double synchronous reference frame to generate modulating signal to the PV sourced inverter. Exhaustive simulations are carried out for the proposed scheme for varying irradiations, wind speed and load variations at the PCC in MATLAB and compared with direct power control scheme.

Ether-Bond-Containing Ionic Liquids as Supercapacitor Electrolytes.

Electrochemical capacitors (ECs) are electrical energy storage devices that have the potential to be very useful in a wide range of applications, especially where there is a large disparity between peak and average power demands. The use of ionic liquids (ILs) as electrolytes in ECs can increase the energy density of devices; however, the viscosity and conductivity of ILs adversely influence the power density of the device. We present experimental results where several ILs containing different cations have been employed as the electrolyte in cells containing mesoporous carbon electrodes. Specifically, the behavior of ILs containing an ether bond in an alkyl side chain are compared with those of a similar structure and size but containing purely alkyl side chains. Using electrochemical impedance spectroscopy and constant current cycling, we show that the presence of the ether bond can dramatically increase the specific capacitance and reduce device resistance. These results have the important implication that such ILs can be used to tailor the physical properties and electrochemical performance of IL-based electrolytes.

A mixed-integer optimization model for electricity infrastructure development

We formulate a mixed-integer program that can be used to analyze the decision between centralized and decentralized technologies for new energy infrastructure development. The formulation minimizes the cost of meeting both average and peak power demand in each specified demand node. We demonstrate our methodology with a case study of Rwanda, accounting for existing generation and transmission infrastructure. Thirteen ongoing or proposed projects are considered as potential new centralized generation facilities and the decentralized technology is modeled after a small (\(\sim \)50 W) solar home system. The case study is repeated using population data at four different resolutions while varying demand levels and decentralized technology cost. A tipping point effect is observed, where the optimal infrastructure tips from being primarily centralized to primarily decentralized under certain combinations of the demand and cost parameters. These tipping points are largely consistent across the four data resolutions. Finding a solution within 1 % of optimal was often found to be computationally expensive in formulations with greater than approximately 200 nodes and 800 edges. However, formulations using less dense population data are shown to accurately identify the same tipping points while requiring fewer computational resources. Examples of the minimum cost electricity infrastructure in Rwanda are also shown for several specific combinations of parameters.

Research on energy management of dual energy storage system based on the simulation of urban driving schedules

Due to increasing concerns on environmental pollution and depleting fossil fuels, electric vehicles have recently been gaining increasing worldwide interest as a promising potential long-term solution to sustainable personal mobility. However, an energy storage system composed of battery and ultra capacitor can display a preferable performance for vehicle propulsion. As the ultra capacitor can fulfill the transient power demand fluctuations, the battery can be downsized to fit the average power demand without facing peak loads. Besides, braking energy can be recovered by the ultra capacitor. This study focuses on a vehicular system powered by two energy storage devices: battery and ultra capacitor. However, energy management strategy is necessary to split the power demand of a vehicle in a suitable way in order to maximize the performance while promoting the fuel economy and endurance of dual energy storage system components. In this paper, a dual energy storage system composed of ultra capacitor and the battery is introduced, the desire discharge current of the vehicular system under urban driving schedules is analyzed, and the working conditions of vehicular system are divided into four modes according to the state of energy storage system, a new hysteresis current control strategy is proposed for the developed vehicular system. The mathematical and electrical models of the vehicular system are developed in detail and simulated using MATLAB and Simulink environments.

Sizing Stack and Battery of a Fuel Cell Hybrid Distribution Truck

An existing fuel cell hybrid distribution truck, built for demonstration purposes, is used as a case study to investigate the effect of stack (kW) and battery (kW, kWh) sizes on the hydrogen consumption of the vehicle. Three driving cycles, the NEDC for Low Power vehicles, CSC and JE05 cycle, define the driving requirements for the vehicle. The Equivalent Consumption Minimization Strategy (ECMS) is used for determining the control setpoint for the fuel cell and battery system. It closely approximates the global minimum in fuel consumption, set by Dynamic Programming (DP). Using DP the sizing problem can be solved but ECMS can also be implemented real-time. For the considered vehicle and hardware, all three driving cycles result in optimal sizes for the fuel cell stack of approximately three times the average drive power demand. This demonstrates that sizing the fuel cell stack the average or maximum power demand is not necessarily optimal with respect to a minimum fuel consumption. The battery is sized to deliver the difference between specified stack power and the peak power in the total power demand. The sizing of the battery is dominated by its power handling capabilities. Therefore, a higher maximum C-rate leads to a lower battery weight which in turn leads to a lower hydrogen consumption. The energy storage capacity of the battery only becomes an issue for C-rates over 30. Compared to a Range Extender (RE) configuration, where the stack size is comparable to the average power demand and the stack is operated on a constant power level, optimal stack and battery sizes with ECMS as EnergyManagement Strategy significantly reduce the fuel consumption. Compared to a RE strategy, ECMS makes much better use of the combined power available from the fuel cell stack and the battery, resulting in a lower fuel consumption but also enabling a lower battery weight which consequently leads to improved payload capabilities.

The wind/hydrogen demonstration system at Utsira in Norway: Evaluation of system performance using operational data and updated hydrogen energy system modeling tools

An autonomous wind/hydrogen energy demonstration system located at the island of Utsira in Norway was officially launched by Norsk Hydro (now StatoilHydro) and Enercon in July 2004. The main components in the system installed are a wind turbine (600 kW), water electrolyzer (10 Nm 3/h), hydrogen gas storage (2400 Nm 3, 200 bar), hydrogen engine (55 kW), and a PEM fuel cell (10 kW). The system gives 2–3 days of full energy autonomy for 10 households on the island, and is the first of its kind in the world. A significant amount of operational experience and data has been collected over the past 4 years. The main objective with this study was to evaluate the operation of the Utsira plant using a set of updated hydrogen energy system modeling tools (HYDROGEMS). Operational data (10-min data) was used to calibrate the model parameters and fine-tune the set-up of a system simulation. The hourly operation of the plant was simulated for a representative month (March 2007), using only measured wind speed (m/s) and average power demand (kW) as the input variables, and the results compared well to measured data. The operation for a specific year (2005) was also simulated, and the performance of several alternative system designs was evaluated. A thorough discussion on issues related to the design and operation of wind/hydrogen energy systems is also provided, including specific recommendations for improvements to the Utsira plant. This paper shows how important it is to improve the hydrogen system efficiency in order to achieve a fully (100%) autonomous wind/hydrogen power system.

Thermoelectric Energy Harvesting for Wireless Sensor Systems in Aircraft

The use of structural health monitoring in the aerospace industry has many benefits including improved safety, reduced maintenance and extended aircraft lifecycles. A major focus of current research in this area is the development of wireless sensor 'nodes‘ which rely on batteries as a power source, severely limiting the product lifespan. This paper presents the results of work carried out to examine the feasibility of replacing or supplementing existing battery power supplies using thermoelectric energy conversion from ambient temperature differences in aircraft. An average power demand of 1mW over a typical sensor duty cycle is identified for current wireless sensor hardware. Temperature differentials between the wing fuel tanks and external air are determined and a theoretical model for thermoelectric energy harvesting potential is developed. Results indicate that average power outputs sufficient for the intended application of 6.6-22mW could be achieved during flight, based on a commercially available thermoelectric module of 30×30×4.1mm. An experimental investigation of the performance of this module when subjected to appropriate temperature conditions, using a Ranque-Hilshe vortex tube to generate easily controlled temperatures to -25°C is described. Excellent consistency is demonstrated between theoretical predictions and experimental results, confirming the accuracy of the theoretical model.

Hydrogen production characteristics of a bioethanol solar reforming system with solar insolation fluctuations

Abstract The development of a bioethanol steam reforming system (FBSR) is considered as a means of distributing energy using PEM fuel cells. Small-scale solar collectors (collection areas on the order of several m 2 ) are installed in a house as a method for applying the FBSR. However, the temperature distribution of a reforming catalyst fluctuates under conditions of unstable solar insolation. Therefore, heat transfer analysis applied in reforming the catalyst layer of the reactor and the temperature distribution and transient response characteristics of the gas composition of the process were investigated. As a case study, meteorological data for representative days in March and August in Sapporo, Japan were recorded, and the hydrogen production speed, power generation output and amount of electricity purchased were analyzed. The results showed that although fluctuations in solar insolation affected the efficiency of the FBSR, the average efficiency of each representative day exceeded 40%. By installing two solar collectors, each with a collection area of 1 m 2 , 21–25% of the average power demand of an individual house can be supplied.

A wavelet-fuzzy logic based energy management strategy for a fuel cell/battery/ultra-capacitor hybrid vehicular power system

Abstract Due to increasing concerns on environmental pollution and depleting fossil fuels, fuel cell (FC) vehicle technology has received considerable attention as an alternative to the conventional vehicular systems. However, a FC system combined with an energy storage system (ESS) can display a preferable performance for vehicle propulsion. As the additional ESS can fulfill the transient power demand fluctuations, the fuel cell can be downsized to fit the average power demand without facing peak loads. Besides, braking energy can be recovered by the ESS. This study focuses on a vehicular system powered by a fuel cell and equipped with two secondary energy storage devices: battery and ultra-capacitor (UC). However, an advanced energy management strategy is quite necessary to split the power demand of a vehicle in a suitable way for the on-board power sources in order to maximize the performance while promoting the fuel economy and endurance of hybrid system components. In this study, a wavelet and fuzzy logic based energy management strategy is proposed for the developed hybrid vehicular system. Wavelet transform has great capability for analyzing signals consisting of instantaneous changes like a hybrid electric vehicle (HEV) power demand. Besides, fuzzy logic has a quite suitable structure for the control of hybrid systems. The mathematical and electrical models of the hybrid vehicular system are developed in detail and simulated using MATLAB®, Simulink® and SimPowerSystems® environments.

Energy Management Fuzzy Logic Supervisory for Electric Vehicle Power Supplies System

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper introduces an energy management strategy based on fuzzy logic supervisory for road electric vehicle, combining a fuel cell power source and two energy storage devices, i.e., batteries and ultracapacitors. The control strategy is designed to achieve the high-efficiency operation region of the individual power source and to regulate current and voltage at peak and average power demand, without compromising the performance and efficiency of the overall system. A multiple-input power electronic converter makes the interface among generator, energy storage devices, and the voltage dc-link bus. Classical regulators implement the control loops of each input of the converter. The supervisory system coordinates the power flows among the power sources and the load. The paper is mainly focused on the fuzzy logic supervisory for energy management of a specific power electronic converter control algorithm. Nevertheless, the proposed system can be easily adapted to other converters arrangements or to distributed generation applications. Simulation and experimental results on a 3-kW prototype prove that the fuzzy logic is a suitable energy management control strategy. </para>

Energy Saving Lighting Control Systems for Open-Plan Offices: A Field Study

We conducted a field study in a deep-plan office building equipped with suspended direct-indirect luminaires located centrally in cubicle workstations. In order to reduce lighting energy use, the luminaires employed integral occupancy sensors and light sensors (daylight harvesting), as well as individual dimming control accessed through occupants' computer screens. Data were collected from 86 workstations over a year to examine the energy savings and power reduction attributable to the controls, and how the controls were used. An awareness campaign that used e-mail reminders to encourage the occupants to use the individual control feature of the lighting system was also conducted. Results indicate that the lighting system generated substantial energy savings and peak power reductions compared to a conventional fluorescent lighting system installed on a neighboring floor. The installed lighting power was 42 percent lower than that of the conventional system. The three controls combined saved 42 to 47 percent in lighting energy use compared to the same lights used at full power during work-hours; this translated into overall savings of 67 to 69 percent compared to the conventional lighting system. If the three lighting controls systems had been installed separately, occupancy sensors would have saved, on average, 35 percent if used alone, light sensors (daylight harvesting) 20 percent, and individual dimming 11 percent. The light sensor savings were, as expected, higher in perimeter workstations, and would have matched the performance of the occupancy sensors with some modifications to the control parameters. The average daily peak power demand for lighting was also reduced by a similar amount, which resulted in an average effective lighting power density of only 3 W/m2. Although not detailed in this paper, surveys indicated that the studied lighting system was also associated with higher occupant satisfaction. This was likely due to the individual dimming control, although use of this control beyond an initial preferred setting was rare.

Design and power management of a solar‐powered “Cool Robot” for polar instrument networks

AbstractThe Cool Robot is a four‐wheel‐drive, solar‐powered, autonomous robot designed to support summertime science campaigns in Antarctica and Greenland over distances exceeding 500 km. This paper provides an overview of key features of the robot, including design for good mobility, high efficiency, and long‐term deployment under solar power in harsh polar environments. The Cool Robot's solar panel box, comprising panels on four sides and a top panel, encounters insolation variations with a bandwidth of up to 1 Hz due to sastrugi. The paper details a unique photovoltaic control algorithm to accommodate these variations. We deployed the robot at Summit Camp, Greenland to validate its mobility and power budget and to assess the photovoltaic control system. The 61 kg robot drove continuously at 0.78 m/s on soft snow, its 160 W average power demand met by solar power alone under clear skies above 16° sun elevation. The power‐control system reliably matched input with demand as insolation varied during testing. A simple GPS waypoint‐following algorithm provides low‐bandwidth path planning and course correction and demonstrated reliable autonomous navigation during testing over periods of 5–8 h. Field data validate the Cool Robot design models and indicate that it will exceed its design goal of carrying a 15 kg payload 500 km across Antarctica in 2 weeks. A brief description of instrument payloads and scientific studies aided by networks of such autonomous solar robots is provided. © 2007 Wiley Periodicals, Inc.