Maximize Power Efficiency Research Articles

Robust Data-driven Estimation of Wave Excitation Force for Wave Energy Converters

This paper proposes a data-driven technique to estimate the wave excitation force (WEF) which is an essential signal for wave forecasting and implementing power efficiency maximization control of Wave Energy Converters (WECs). A Bayesian probabilistic model of a WEC hydrodynamic system is described to generate robust WEF estimates. Specifically, the WEF uncertainty can be estimated based on observations through Gaussian Process (GP) modeling. It is shown that this modern way of incorporating the first principle modelling into a probabilistic framework has stronger robustness properties than the alternative of calculating estimates of a parametric function representation. Unlike the sample-based non-linear Kalman Filter, the means and covariances of the joint probabilities can be directly computed based on analytic moment matching that allow for reliable state-dependent uncertainty propagation. The results presented demonstrate the accuracy and robustness of the proposed data-driven wave excitation force estimator.

Deployment Strategies of Multiple Aerial BSs for User Coverage and Power Efficiency Maximization

Unmanned aerial vehicle-based aerial base stations (BSs) can provide rapid communication services to ground users and are thus promising for future communication systems. In this paper, we consider a scenario where no functional terrestrial BSs are available and the aim is deploying multiple aerial BSs to cover a maximum number of users within a certain target area. To this end, we first propose a naive successive deployment method, which converts the non-convex constraints in the involved optimization into a combination of linear constraints through geometrical relaxation. Then, we investigate a deployment method based on $K$ -means clustering. The method divides the target area into $K$ convex subareas, where within each subarea, a mixed integer non-linear problem is solved. An iterative power efficient technique is further proposed to improve coverage probability with reduced power. Finally, we propose a robust technique for compensating the loss of coverage probability in the existence of inaccurate user location information. Our simulation results show that the proposed techniques achieve an up to 30% higher coverage probability when users are not distributed uniformly. In addition, the proposed simultaneous deployment techniques, especially the one using iterative algorithm, improve power-efficiency by up to 15% compared with the benchmark circle packing theory.

On-line Optimization of Power Efficiency in 3D Multicore Processors

This paper considers the problem of maximizing power efficiency in multi-core processors by dynamic voltage frequency scaling. We formulate the problem in an on-line setting and apply to it a gradient-based stochastic approximation algorithm. We use a cycle-level, full-system simulation platform capable of realistic modeling of state-of-the-art microarchitectures executing industry-standard benchmarks (Splash 2). The optimization algorithm computes the gradients by the Infinitesimal Perturbation Analysis (IPA) sample-based sensitivity analysis technique. Despite the fact that the system’s characteristics vary widely with time and hence the optimum point varies as well, the simulation experiments exhibit a tracking of the optimal values. To our knowledge this is the first application of IPA to co-optimizing throughput performance and power in computer processors.

SDM for Power-Efficient Undersea Transmission

We discuss space division multiplexing as a means of increasing link capacity for power limited transmission in undersea communication. Theoretical study of erbium-doped fiber amplifiers-based space division multiplexing (SDM) transmission shows the existence of optimal values of spectral efficiency, signal-to-noise ratio, and span length that maximize power efficiency. We experimentally confirm the existence of an optimal spectral efficiency and demonstrate power efficient SDM transmission using 12-core multicore fiber. Modulation format, amplifier, and link design are discussed in connection to SDM power efficient transmission.

Quantum Bee Colony Optimization and Non-dominated Sorting Quantum Bee Colony Optimization Based Multi-relay Selection Scheme

In cooperative multi-relay networks, the relay nodes which are selected are very important to the system performance. How to choose the best cooperative relay nodes is an optimization problem. In this paper, multi-relay selection schemes which consider either single objective or multi-objective are proposed based on evolutionary algorithms. Firstly, the single objective optimization problems of multi-relay selection considering signal to noise ratio (SNR) or power efficiency maximization are solved based on the quantum bee colony optimization (QBCO). Then the multi-objective optimization problems of multi-relay selection considering SNR maximization and power consumption minimization (two contradictive objectives) or SNR maximization and power efficiency maximization (also two contradictive objectives) are solved based on non-dominated sorting quantum bee colony optimization (NSQBCO), which can obtain the Pareto front solutions considering two contradictive objectives simultaneously. Simulation results show that QBCO based multi-relay selection schemes have the ability to search global optimal solution compared with other multi-relay selection schemes in literature, while NSQBCO based multi-relay selection schemes can obtain the same Pareto front solutions as exhaustive search when the number of relays is not very large. When the number of relays is very large, exhaustive search cannot be used due to complexity but NSQBCO based multi-relay selection schemes can still be used to solve the problems. All simulation results demonstrate the effectiveness of the proposed schemes.

A Unit Commitment Algorithm and a Compact MILP Model for Short-Term Hydro-Power Generation Scheduling

This paper presents a unit commitment algorithm that defines each unit discharge given the water head, the total plant downstream flow, the variable discharge upper limit, the unit efficiency curves, and the restricted operating zones in order to maximize power efficiency. This algorithm is part of the preprocessing phase that is intended to approximate a hydro-power production function that represents individualized unit decisions. A compact mixed-integer linear programming formulation, with fewer integer variables, based on an equivalent unit model and a piecewise linear generation function, is proposed. The unit commitment is integrated without increasing the model size and complexity due to the preprocessing phase. Moreover, the optimal aggregate decision is automatically converted to unit decisions by the proposed algorithm. The coordination with mid/long-term planning is performed by taking into account the power demand allocated to the hydro-power plants. Numerical tests on Brazilian hydro-power plants demonstrate that the proposed formulation has lower computational cost than unit individualized models considering a given accuracy level for the generation function approximation.

Automated SOFC Design Exploration

We present automated computer aided engineering (CAE) to maximize power efficiency and minimize temperature variations in fuel cell stack design. Validated cell models are applied to preliminary 3-D stack simulations, where proprietary optimization algorithms quickly obtain better multi-parameter designs. Each simulation conserves flow, energy, species, and charge transport using segregated solvers with a high degree of linearization and efficient sparse matrix solvers. Automated workflows and state-of-the-art search algorithms allow for fast design space exploration of fuel cell dimensions, properties and operating conditions. Efficiency relates electric power output to reactant enthalpy loss and air-compression work input. To minimize temperature variation, while maintaining high efficiency for fixed fuel flowrate of 7.35E-7 kg/s, an optimal air flowrate of 2E-4 kg/s is preferred for square cells of 36 cm2 active area and 5.25 mm height. Wide serpentine channels with cathode supported membrane-electrode-assemblies (MEA) minimize pressure drop and diffusion length scales. Serpentine channels entering and leaving in opposite corners of the cell are found preferable for minimizing temperature variations.

Power efficiency, phase noise, and DC offset in constant envelope OFDM transceivers

AbstractThis paper considers constant envelope orthogonal frequency‐division multiplexing (CE‐OFDM) that is an attractive candidate for the future Long Term Evolution over satellite and device‐to‐device communications in merging public safety and commercial networks. The constant envelope modulation allows power amplifier (PA) to operate near saturation levels thus maximizing power efficiency. Because the phase noise transforms just into an additive noise term after the phase detector, the CE‐OFDM has significant advantage compared with phase noise sensitive OFDM. The transceiver power efficiency is evaluated by measuring the bit error rate as a function of average PA input signal‐to‐noise ratio so that the effects of the PA nonlinearities are taken into account in the performance evaluation. Our simulation results show that with a typical nonlinear satellite amplifier, the CE‐OFDM has up to 6.0dB gain compared with the OFDM. This is beneficial especially in a channel having high attenuation. The consistent gains for the ideally linearized amplifier and common terrestrial three‐way Doherty amplifiers are 2.2 and 2.5dB, respectively. The enhanced PA efficiency enables battery to be smaller or last longer in mobiles devices. For CE‐OFDM implementation, a simple transmitter and receiver structure with novel direct current offset removal is presented by keeping in mind that the key factor for the rapid uptake of the future fifth generation systems is the maximization of technology commonalities with existing systems. Copyright © 2016 John Wiley & Sons, Ltd.

A Design of a Wireless Power Receiving Unit With a High-Efficiency 6.78-MHz Active Rectifier Using Shared DLLs for Magnetic-Resonant A4 WP Applications

This paper presents a full-CMOS wireless power receiving unit (WPRU) with a high-efficiency 6.78-MHz active rectifier and a dc–dc converter for magnetic-resonant alliance for wireless power (A4WP) applications. The proposed high-efficiency active rectifier with delay-locked loop (DLL) is a highly efficient receiver circuit intended for use in resonant wireless charging applications with a resonant frequency of 6.78 MHz. Each MOSFET of the proposed rectifier is turned on and off based on the ac input voltage. The delay between the ac input current and the ac input voltage due to the delays of internal blocks such as voltage limiter, level shifter, gate driver, and comparator will cause the reverse leakage current, degrading the power efficiency. Thus, the proposed active rectifier adopts the DLL to compensate for the delay caused by internal blocks, which leads to the removal of reverse leakage current and the power efficiency maximization. Moreover, to maximize power efficiency, negative impedance circuit (NIC) is also adopted to minimize switching loss. In the case of dc–dc converter, phase-locked loop is adopted for the constant switching frequency in process, voltage, and temperature (PVT) variation to solve the efficiency reduction problem, especially by heat. This chip is implemented using 0.18 μm BCD technology with an active area of 3.5 mm × 3.5 mm. When the magnitude of the ac input voltage is 8.95 V, the maximum efficiencies of the proposed active rectifier and dc–dc converter are 91.5% and 92.7%, respectively. The range of ac input voltage is 3–20 V, and the efficiency of the WPRU is about 80.86%.

An optimal power control algorithm for STDMA MAC protocols in multihop wireless networks

Multihop spatial time division multiple access (STDMA) medium access control (MAC) protocols constitute an important building block of wireless networks. There are not many practical power control algorithms that can optimally tradeoff power consumption against transmission rates with a reasonable computational complexity. In this paper, we introduce an energy-efficient distributed power control algorithm for STDMA MAC protocols. The motivation for this study is two fold, namely, maximizing the spatial reuse of the system resources and maximizing power efficiency. We develop a mathematical formulation for maximizing spatial reuse and power efficiency under discrete SINR and rate constrains. After proving that power is a convex function of data rates in our problem, we demonstrate that our problem in simultaneous transmission environments can be reduced to a linear programming (LP) problem. Then, we solve this LP problem using dynamic programming (DP). Finally, based on our proposed solution, we propose a low complexity optimal power control (OPC) algorithm which can be generically embedded within any existing STDMA MAC protocol. Through analytical and experimental studies, we show that our power control algorithm cannot only significantly improve the throughput, power consumption, and delay performance of STDMA MAC protocols compared to their baseline alternatives, but also outperform existing STDMA algorithms.

Battery Optimization of Android Phones by Sensing the Phone Using Hidden Markov Model

This paper presents a novel framework that includes an inhomogeneous (time-variant) Hidden Markov Model(HMM) and learning from data concepts. The framework either recognizes or estimates user contextual inferences called ’user states’ within the concept of Human Activity Recognition (HAR) for future context-aware applications. Context-aware applications require continuous data acquisition and interpretation from one or more sensor reading(s). Therefore, device battery lifetimes need to be extended due to the fact that constantly running built-in sensors deplete device batteries rapidly. In this sense, a framework is constructed to fulfill requirements needed by applications and to prolong device battery lifetimes. The ultimate goal of this paper is to present an accurate user state representation model, and to maximize power efficiency while the model operates. Most importantly, this research intends to create and clarify a generic framework to guide the development of future context-aware applications. Moreover, topics such as user profile adaptability and variant sensory sampling operations are examined. The proposed framework is validated by simulations and implemented in a HAR-based application by the smart phone accelerometer.

Power Control for Efficient Operation of a PEM Fuel Cell System by Nonlinear Model Predictive Control

Efficiency of polymer electrolyte membrane (PEM) fuel cells depends directly on anode and cathode gas pressures, and stack temperature. For an efficient chemical reaction and a safe operation for both stationary and dynamic loads all values must fall within specific ranges. This paper deals with realtime nonlinear model predictive control (NMPC) of electrical power for a PEM fuel cell system. The NMPC is split into three nonlinear optimization problems to calculate the optimal stack current and the supply of anode and cathode with hydrogen and oxygen. For real-time application the predictive control algorithm is matched to the sampling time of the system. This NMPC handles all kinds of dynamic load changes, while maximizing power efficiency without a steady state error. Modeling of relevant anode and cathode site fuel cell peripherals is shown. Experimental results on a test bench with a 4.4kW PEM fuel cell are presented.

Power Efficiency Maximization of an RF Energy Harvester by Fine-tuning an L-matching Network and the Load

L-matching networks have been proposed for boosting the power efficiency of radiofrequency (RF) energy harvesters. This paper shows that power efficiency is maximized by fine-tuning the components of the L-matching network and the load. Simulations at 868MHz with commercial components and a Rogers substrate resulted in maximum power efficiencies of 10.9%, 30.7%, and 55.2% for input powers of -30 dBm, -20 dBm, and -10 dBm, respectively. Experimental results showed efficiencies of 31.8% and 52.0% at -20 dBm and -10 dBm, respectively, close to the simulation results, but at a frequency of 814MHz.

Design for minimum energy in interstellar communication

Radio communication over interstellar distances is studied, accounting for noise, dispersion, scattering and motion. Large transmitted powers suggest maximizing power efficiency (ratio of information rate to average signal power) as opposed to restricting bandwidth. The fundamental limit to reliable communication is determined, and is not affected by carrier frequency, dispersion, scattering, or motion. The available efficiency is limited by noise alone, and the available information rate is limited by noise and available average power. A set of five design principles (well within our own technological capability) can asymptotically approach the fundamental limit; no other civilization can achieve greater efficiency. Bandwidth can be expanded in a way that avoids invoking impairment by dispersion or scattering. The resulting power-efficient signals have characteristics very different from current SETI targets, with wide bandwidth relative to the information rate and a sparse distribution of energy in both time and frequency. Information-free beacons achieving the lowest average power consistent with a given receiver observation time are studied. They need not have wide bandwidth, but do distribute energy more sparsely in time as average power is reduced. The discovery of both beacons and information-bearing signals is analyzed, and most closely resembles approaches that have been employed in optical SETI. No processing is needed to account for impairments other than noise. A direct statistical tradeoff between a larger number of observations and a lower average power (including due to lower information rate) is established. The "false alarms" in current searches are characteristic signatures of these signals. Joint searches for beacons and information-bearing signals require straightforward modifications to current SETI pattern recognition approaches.

Adaptive and Energy Efficient Context Representation Framework in Mobile Sensing

This paper presents a novel framework that includes an inhomogeneous (time-variant) Hidden Markov Model (HMM) and learning from data concepts. The framework either recognizes or estimates user contextual inferences called ‘user states’ within the concept of Human Activity Recognition (HAR) for future context-aware applications. Context-aware applications require continuous data acquisition and interpretation from one or more sensor reading(s). Therefore, device battery lifetimes need to be extended due to the fact that constantly running built-in sensors deplete device batteries rapidly. In this sense, a framework is constructed to fulfill requirements needed by applications and to prolong device battery lifetimes. The ultimate goal of this paper is to present an accurate user state representation model, and to maximize power efficiency while the model operates. Most importantly, this research intends to create and clarify a generic framework to guide the development of future context-aware applications. Moreover, topics such as user profile adaptability and variant sensory sampling operations are examined. The proposed framework is validated by simulations and implemented in a HAR-based application by the smartphone accelerometer. According to the results, the proposed framework shows an increase in power efficiency of 60% for an accuracy range from 75% up to 96%, depending on user profiles.

Circuit-level Design of a Power Supply Unit with Extra Low-noise Output for Portable Integrated SoCs

Switch-mode voltage regulators are considered as the dominant choice for low-power integrated power supplies. Employing the advantages of a switch-mode voltage regulator in 0.18µm CMOS technology, a power supply has been designed for a complete System-on-Chip (SoC). While offering enough drive capability for the entire system, the supply provides an extra highly-regulated output for noisesensitive analog blocks. At first, a front-end buck regulator converts the time-variant unregulated input voltage to an initially-regulated general voltage. To further regulate this voltage for noise-sensitive blocks, a new continuous-time buffered voltage source has been added to the circuit. To maximize power efficiency and to benefit from an initiallyregulated input, this source is connected to the front-end switch-mode regulator output. For proper operation, the minimum input voltage to the supply is 1.3V. With this minimum input voltage, the 1.1V switching regulator sources up to 1A output current. The continuous-time 0.9V- buffered source provides up to 100mA for noise-sensitive units. It converts the 1.1V regulated voltage to a 0.9V smooth output.

Experimental Study of A Frequency-Adjustable Piezoelectric Bimorph Energy Harvester

Piezoelectric energy harvesters are ideal for capturing energy from mechanical vibrations in ambient environments. The operating and source frequencies must match for the energy harvester to produce useful power. In this article, a new, broadband piezoelectric energy harvester that is implemented as a series of connected vibrating piezoelectric bimorph beams is designed and tested. The experimental results show that the operating frequency can be adjusted by changing the stiffness of a connecting spring and/or a small mass mounted on the bimorph. The results provide a foundation for the design of frequency-self tuning piezoelectric energy harvesters capable of maximizing power efficiency.

High Efficiency 500W RF Generator

In the previous literature about RF generator, Efficiency of output of RF generator can reach 60-70 percent. In this paper, a new 500W RF generator with high efficiency and high stability is designed and fabricated for plasma applications. The efficiency of a power amplifier in the RF generator is improved by using Class-E amplifier. The Class-E power amplifiers described here is based on a load network synthesized to have a transient response which maximizes power efficiency even if the active device switching times are substantial fractions of the AC cycle. For that circuit, the author measures 73 percent efficiency of output of RF generator at 13.56MHZ and 478W output from DE375 MOSFET. The main reasons of power dissipation mainly are analyzed, and some measures are taken to improve them by the optimization principles and experimental results and the efficiency of the power output can reach above 70 percent.

Stepped-plate transducer as an energy transmitter

Power transmission through acoustic energy may be useful in such cases as supplying power to wireless small sensors. In the case, the radiation and reception power efficiency is important. Even in ultrasonic frequency bands, the power efficiency of most acoustic radiators in air is not high enough. The stepped-plate ultrasonic transducers, introduced by Gallego-Juarez etal. [Ultrasonics 16, 267–271(1978)], may be a good candidate for the radiator for this purpose because it can effectively generate highly directive, large-amplitude, ultrasonic sounds in air. The transducer consists of langevin transducer that causes wave generation, mechanical amplifier, and stepped radiation plate. Although it is reported to achieve 80% of power efficiency, it is not reported how to achieve maximum power efficiency. For design of large-amplitude, high-efficiency stepped-plate transducer, the design of not only individual parts but also system integration of entire transducer is important. In this research, we developed an analytical model for the whole transducer by combining continuum models of each parts and found proper design parameters for the radiation power and the power transmitting efficiencies. Then, we seek the optimal design for maximizing power efficiency through parametric analyses, and the results are confirmed through finite element method analysis. [Work supported by ETRI (South Korea).]

Optimal Power Control for Multi-User Relay Networks over Fading Channels

In energy-constrained wireless networks such as sensor networks, it is important to maximize power efficiency by minimizing power consumption for a given quality of service such as the data rate; it is equally important to evenly or fairly distribute power consumption to all nodes to maximize the network life. In this paper, we develop optimal power control methods to balance the tradeoff between energy efficiency and fairness for wireless cooperative networks where several relays assist the communication of multiple source-destination pairs. Our optimal power control policy is derived in a quasi-closed form by solving a convex optimization problem with a properly chosen cost-function. We further develop novel stochastic optimization algorithms to dynamically learn the statistics of the wireless channels on-the-fly to approach the optimal power control policy. Moreover, our power control algorithm can be implemented distributedly at relays requiring each relay to know its local channel state information. Simulation results demonstrate the merits of our power control methods.