Unstable Output Power Research Articles

Structural and photoelectrochemical characterization of heterostructured carbon sheet/Ag2MoO4-SnS/Pt photocapacitor

Photocapacitors can harvest solar energy and store it in the form of electrical energy and are expected to solve the problem of unstable power output of solar cells under fluctuating sunlight. In the present study, a novel heterostructured carbon sheet/Ag2MoO4-SnS/Pt photocapacitor was developed. In this photocapacitor, SnS nanoparticles act as capacitive platform via redox pseudocapacitance, whereas Ag2MoO4 molecules act as the active core of the photocapacitor. The crystalline structure and the surface morphology of Ag2MoO4-SnS film on carbon sheet was examined by powder X-ray diffraction method (XRD) and Scanning Electron Microscopy (SEM), respectively. The XRD pattern indicates that Ag2MoO4 film on carbon sheet is in β phase with respect to Ag2MoO4. The SEM images reveal Ag2MoO4 film on carbon sheet composing of cubic structures, and SnS film on carbon sheet/Ag2MoO4 composing of spherical nanoparticles. The carbon sheet/Ag2MoO4-SnS/Pt heterostructured photocapacitor, when subjected to visible light illumination, showed a specific capacitance of 340 F/g with an open circuit potential of 1.25 V vs. Ag/AgCl electrode. The high capacitance obtained with this novel device may be attributed to the large specific area and high conductivity of the Ag2MoO4-SnS film. This research study has opened a new avenue for an effective heterostructured photocapacitor.

Using a Machine Learning Algorithm Integrated with Data De-Noising Techniques to Optimize the Multipoint Sensor Network.

In this paper, for an intensity wavelength division multiplexing (IWDM)-based multipoint fiber Bragg grating (FBG) sensor network, an effective strain sensing signal measurement method, called a long short-term memory (LSTM) machine learning algorithm, integrated with data de-noising techniques is proposed. These are considered extremely accurate for the prediction of very complex problems. Four ports of an optical coupler with distinct output power ratios of 70%, 60%, 40%, and 30% have been used in the proposed distributed IWDM-based FBG sensor network to connect a number of FBG sensors for strain sensing. In an IWDM-based FBG sensor network, distinct power ratios of coupler ports can contain distinct powers or intensities. However, unstable output power in the sensor system due to random noise, harsh environments, aging of the equipment, or other environmental factors can introduce fluctuations and noise to the spectra of the FBGs, which makes it hard to distinguish the sensing signals of FBGs from the noise signals. As a result, noise reduction and signal processing methods play a significant role in enhancing the capability of strain sensing. Thus, to reduce the noise, to improve the signal-to-noise ratio, and to accurately measure the sensing signal of FBGs, we proposed a long short-term memory (LSTM) deep learning algorithm integrated with discrete waveform transform (DWT) data smoother (de-noising) techniques. The DWT data de-noising methods are important techniques for analyzing and de-noising the sensor signals, and it further improves the strain sensing signal measurement accuracy of the LSTM model. Thus, after de-noising the sensor data, these data are fed into the LSTM model to measure the sensing signal of each FBG. The experimental results prove that the integration of LSTM with the DWT data de-noising technique achieved better sensing signal measurement accuracy, even in noisy data or environments. Therefore, the proposed IWDM-based FBG sensor network can accurately sense the signal of strain, even in bad or noisy environments; can increase the number of FBG sensors multiplexed in the sensor system; and can enhance the capacity of the sensor system.

A Fractional-Order Wireless Power Transfer System Insensitive to Resonant Frequency

Since electric power was first transferred wirelessly by Tesla over a hundred years ago, wireless power transfer (WPT) systems have always been composed of integer-order components, such as inductors and capacitors. Recent studies have shown that efficient WPT can be achieved in the range of tens of centimeters or even meters by using magnetic-coupling of two or more integer-order resonant circuits. However, their transfer efficiency and output power are highly sensitive to the resonant frequency. Unfortunately, the resonant frequency is easily disturbed by metal or nonresistive load and so on in real-world application, which will unavoidably lead to transfer efficiency reduction and unstable output power in these integer-order circuits. Therefore, this article proposes and experimentally demonstrates a fractional-order WPT system containing a fractional-order capacitor, in which the transfer efficiency and output power are inherently stable and insensitive to the resonant frequency. The results show that the efficiency and output power only change within 1% when the receiver resonant frequency is detuned by ±5%. In contrast, the WPT systems that are sensitive to the resonant frequency suffer from fall in the efficiency of around 30%, and a largely unstable output power. The available experiments verify the effectiveness of the proposed system.

Self-powered ultra-flexible electronics via nano-grating-patterned organic photovoltaics.

Next-generation biomedical devices1-9 will need to be self-powered and conformable to human skin or other tissue. Such devices would enable the accurate and continuous detection of physiological signals without the need for an external power supply or bulky connecting wires. Self-powering functionality could be provided by flexible photovoltaics that can adhere to moveable and complex three-dimensional biological tissues1-4 and skin5-9. Ultra-flexible organic power sources10-13 that can be wrapped around an object have proven mechanical and thermal stability in long-term operation13, making them potentially useful in human-compatible electronics. However, the integration of these power sources with functional electric devices including sensors has not yet been demonstrated because of their unstable output power under mechanical deformation and angular change. Also, it will be necessary to minimize high-temperature and energy-intensive processes10,12 when fabricating an integrated power source and sensor, because such processes can damage the active material of the functional device and deform the few-micrometre-thick polymeric substrates. Here we realize self-powered ultra-flexible electronic devices that can measure biometric signals with very high signal-to-noise ratios when applied to skin or other tissue. We integrated organic electrochemical transistors used as sensors with organic photovoltaic power sources on a one-micrometre-thick ultra-flexible substrate. A high-throughput room-temperature moulding process was used to form nano-grating morphologies (with a periodicity of 760 nanometres) on the charge transporting layers. This substantially increased the efficiency of the organophotovoltaics, giving a high power-conversion efficiency that reached 10.5 per cent and resulted in a high power-per-weight value of 11.46 watts per gram. The organic electrochemical transistors exhibited a transconductance of 0.8 millisiemens and fast responsivity above one kilohertz under physiological conditions, which resulted in a maximum signal-to-noise ratio of 40.02 decibels for cardiac signal detection. Our findings offer a general platform for next-generation self-powered electronics.

Numerical analysis of a tidal current generator with dual flapping wings

Flapping wings, inspired by the mechanism of birds and fish, can act as generators to harvest energy from tidal currents. The hydraulic system is simplified as a spring-damper system to establish the coupling equations relating to the wing motion and the hydrodynamic forces. To provide guidance for design of a fully flow-induced flapping wings energy harvesting system, the behaviors of both system response and energy extraction performance are analyzed using two-dimensional numerical approach. Depending on the rotary actuator radius R, and the volume ratio β between the cylinder and rotary actuator, three distinguishable behaviors are observed in the system response and energy extraction performance. At larger R and smaller β, the dual wings tend to undergo a damped reduction flapping motion because the pitching motion consumes a significant amount of energy. Both decreasing R and increasing β can reduce the energy consumption of the pitching motion, and thus allow the dual wings to achieve a sustainable flapping motion. Although an irregular response can achieve a self-sustained flapping motion, it is unfavorable owing to its unstable power output. The regular response essential for stable energy harvesting is realized over a range of coupling parameters. The energy extraction performance of the system is closely associated with β but also slightly depends on R.

Core Abilities Evaluation Index System Exploration and Empirical Study on Distributed PV-Generation Projects

In line with the constraints of environmental problems and economic development, large-scale renewable-generation projects have been planned and constructed in recent years. In order to achieve sustainable power development and improve the power supply structure, China’s government has focused on distributed photovoltaic (PV) generation projects due to their advantages of clean emission and local consumption. However, their unstable output power still brings a series of problems concerning reliability, investment income, and available substitution proportion to traditional power, and so on. Therefore, it is imperative to understand the competitive development abilities of distributed PV generation projects and measure them effectively. First, through various investigation methods such as literature reviews, feasibility report analysis and expert interviews, the factors that influence the core abilities of distributed PV-generation projects were explored based on the micro-grid structure. Then, with the indexed exploration results, the factors were classified into 6 dimensions, i.e., investment and earning ability, production and operation ability, power-grid coordination ability, energy-conservation and emission-reduction ability, sustainable development ability, and society-serving ability. Meanwhile, an evaluation index system for core abilities of distributed PV-generation project was constructed using all quantitative indicators. Third, for examining the availability of the evaluation index system, combination weighting and techniques for order preference by similarity to an ideal solution (TOPSIS) methods were adopted to assess the practical distributed PV-generation projects. The case study results showed that installed capacity, local economy development, and grid-connected power quantity will influence the core abilities of distributed PV-generation project, obviously. The conclusions of the evaluation analysis on core abilities can provide useful references to operate and manage distributed PV-generation projects and promote their sustainable and health advantages. The proposed evaluation index system can also be used to assess power-generation projects in other types of energy, such as wind power and hydropower.

Improving Electricity Consumption Estimation for Electric Vehicles Based on Sparse GPS Observations

Improving the estimation accuracy for the energy consumption of electric vehicles (EVs) would greatly contribute to alleviating the range anxiety of drivers and serve as a critical basis for the planning, operation, and management of charging infrastructures. To address the challenges in energy consumption estimation encountered due to sparse Global Positioning System (GPS) observations, an estimation model is proposed that considers both the kinetic characteristics from sparse GPS observations and the unique attributes of EVs: (1) work opposing the rolling resistance; (2) aerodynamic friction losses; (3) energy consumption/generation depending on the grade of the route; (4) auxiliary load consumption; and (5) additional energy losses arising from the unstable power output of the electric motor. Two quantities, the average energy consumption per kilometer and the energy consumption for an entire trip, were focused on and compared for model fitness, parameter, and effectiveness, and the latter showed a higher fitness. Based on sparse GPS observations of 68 EVs in Aichi Prefecture, Japan, the traditional linear regression approach and a multilevel mixed-effects linear regression approach were used for model calibration. The proposed model showed a high accuracy and demonstrated a great potential for application in using sparse GPS observations to predict the energy consumption of EVs.

Graphical Analysis of a DC-DC Converter Effect on a Fuel Cell: D-transformation

In practical cases, the use of a renewable energy device with a DC-DC converter is preferred to a single device alone for the purpose of compensating unstable output power and intrinsic limitations of the device. However there has not been fundamental understanding how to transform the device internal properties not only the output current and voltage. Therefore, a fundamental understanding of the DC-DC converter is urgently required. In this study, we investigate the fundamental role of a DC-DC converter when connected with renewable devices. We use a graphical and mathematical method for qualitative and quantitative analysis. The analysis is model-based and done for boost, buck and buck-boost converters, respectively. We find that the essential role of the DC-DC converter is to transform the fundamental electrical properties of a device to suitable properties for the load.

Fault current limiter‐battery energy storage system for the doubly‐fed induction generator: analysis and experimental verification

Weak low voltage ride-through (LVRT) ability and unstable output power are two major problems faced by the doubly-fed induction generator (DFIG). To solve these two problems simultaneously, a commercially available fault current limiter-battery energy storage system (FCL–BESS), which is suitable to be applied in a microgrid, is proposed in this study. During normal operation, the FCL–BESS stabilises the output power of DFIG by compensating the fluctuating component of DFIG output power with energy buffering capability provided by the battery energy storage system (BESS). On occurrence of a grid fault, the FCL–BESS enhances the LVRT ability of DFIG by inserting the fault current limiting inductor into the stator, which weakens the rotor back electromagnetic force voltage and limits the rotor overcurrent. The FCL–BESS also stabilises the DC-link voltage by the BESS, which further strengthens the controllability of grid-side converter and rotor-side converter. Moreover, the FCL–BESS is able to help grid voltage recover fast and smoothly by providing power support to the grid. Experiments under different conditions have been carried out with a 2 kW prototype to evaluate the performance of the proposed FCL–BESS. Experimental results show that the FCL–BESS have much better performance than using single fault current limiter or BESS and can solve the two problems faced by the DFIG simultaneously and effectively.

Operation strategy for a lab-scale grid-connected photovoltaic generation system integrated with battery energy storage

The operation strategy for a lab-scale grid-connected photovoltaic generation system integrated with battery energy storage is proposed in this paper. The photovoltaic generation system is composed of a full-bridge inverter, a DC–DC boost converter, an isolated bidirectional DC–DC converter, a solar cell array and a battery set. Since the battery set acts as an energy buffer to adjust the power generation of the solar cell array, the negative impact on power quality caused by the intermittent and unstable output power from a solar cell array is alleviated, so the penetration rate of the grid-connected photovoltaic generation system is increased. A lab-scale prototype is developed to verify the performance of the system. The experimental results show that it achieves the expected performance.

Nowcasting of Spatial Average Irradiance in Several km Radius Area using All-sky Image

Because of the unstable power output characteristics of a photovoltaic power generation system (PVS), the on-line monitoring or nowcasting of the aggregated PVS power output is important for the stable operation of electric power system. In this paper, we propose a nowcasting method of the spatial average irradiance in the area of several km radius using the all-sky image and the observed irradiance both at single point. First, the proposed method classifies the sky condition based on the color information of the all-sky image. If the sky is classified as the uniform condition (very fine or very cloudy), the spatial average irradiance is estimated as the same with the single point observed irradiance. If not, the spatial average irradiance is estimated by using a neural network (NN) model utilizing the color information as the inputs. As a result of a demonstrative study for several months, the Root Mean Square Error (RMSE) of the NN model-based estimation for the periods of the non-uniform sky condition is 103.8W/m2 (15.2%). Because the performance of the sky condition classification is high, RMSE for the periods of the uniform sky condition is 41.8W/m2 (8.7%), resulting in RMSE of 77.4W/m2 (13.5%) for the entire periods.

Power and temperature control of fluctuating biomass gas fueled solid oxide fuel cell and micro gas turbine hybrid system

This paper addresses how the power and temperature are controlled in a biomass gas fueled solid oxide fuel cell (SOFC) and micro gas turbine (MGT) hybrid system. A SOFC and MGT dynamic model are developed and used to simulate the hybrid system performance operating on biomass gas. The transient behavior of both the SOFC and MGT are discussed in detail. An unstable power output is observed when the system is fed biomass gas. This instability is due to the fluctuation of gas composition in the fuel. A specially designed fuel controller succeeded not only in allowing the hybrid system to follow a step change of power demand from 32 to 35 kW, but also stably maintained the system power output at 35 kW. In addition to power control, fuel cell temperature is controlled by introduction and use of a bypass valve around the recuperator. By releasing excess heat to the exhaust, the bypass valve provided the control means to avoid the self-exciting behavior of system temperature and stabilized the temperature of SOFC at 850 °C.

Double-clad 10-W Yb3+-doped fiber master oscillator power fiber amplifier for He3+ optical pumping.

We describe an all-fiber ytterbium-doped laser followed by a double-stage ytterbium-doped double-clad fiber amplifier of 10-W output power for helium pumping. Different cavity designs are investigated with the goal of achieving high-power multimode emission at 1083 nm, wavelength tunability over the helium absorption bands, and linewidth envelope control over the range 1-3 GHz. We point out the domains with unstable output power and discuss their origin.