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[en] With large-scale application of a large number of renewable energy sources, such as wind turbines, photovoltaics, and various power electronic equipment, the power electric system is becoming gradually more power-electronics-based, whose dynamical behavior becomes much complicated, compared to that of traditional power system. The recent developed theory of amplitude–phase motion equation provides a new framework for the general dynamic analysis of such a system. Based on this theory, we study a simple amplitude–phase motion equation, i.e., a single power-electronics device connected to an infinite-large system, but consider its nonlinear effect. With extensive and intensive theoretical analysis and numerical simulation, we find that basically the system shows some similarity with the classical second-order swing equation for a synchronous generator connected to an infinite bus, such as the two types of bifurcation including the saddle-node bifurcation and homoclinic bifurcation, and the dynamical behavior of stable fixed point, stable limit cycle, and their coexistence. In addition, we find that the Hopf bifurcation is possible, but for negative damping only. All these findings are expected to be helpful for further study of power-electronics-based power system, featured with nonlinearity of high-dimensional dynamic systems involved with not only a large timescale but also large space scale.
[en] Highlights: • A self-sustaining water vapor-driven pyroelectric nanogenerator (PNG) is achieved. • The large-area flexible PNG is readily made of commercial available components. • Fast temperature oscillation is achieved by water condensation and evaporation. • The powerful PNG can drive a low-power electronic device to work continuously. Energy harvesting via pyroelectric nanogenerators (PNGs) is emerging as an attractive way to utilize waste heat. However, most of current PNGs need mechanical or electrical alternating devices to achieve the fast temperature oscillation, which is the key for PNGs to work. Herein we report a self-sustaining polymeric PNG driven by water vapor, without any energy-consuming alternating devices. Due to the high latent heat of water vapor, a fast temperature oscillation up to 23 °C/s was achieved by automatic water condensation and evaporation on the surface of the PNG. Thus, the PNG based on commercial polyvinylidene difluoride polymer was able to output an open-circuit voltage of 145 V and a short-circuit current of 0.12 μA/cm2. The peak power density was 1.47 mW/cm3 by volume and 4.12 μW/cm2 by area, which is comparable to previously reported PNGs relying on alternating devices. Our PNG could provide uninterrupted electricity to drive a low-power electronic device (such as a digital watch) to work continuously. The electricity could also be stored in a capacitor for high-power tasks, such as flashing multiple blue LED lights once per minute. The self-sustaining PNG driven by water vapor provides a new strategy for efficiently recovering energy from hot water vapor that are wasted in industry and in our daily life.
[en] Multi-agent system employs the functions of communication, coordination and cooperation among intelligent agents to help people judge and analyze complex phenomena that cannot be directly observed, and it has become an important tool for solving large-scale complex problems. The problem of demand response (DR) in electric power system is difficult to be modeled due to the complicated environment and continuously evolving subjects. Multi-agent system can simulate the operation mechanism of electric power system, thus playing an important role in solving the DR problems. In this study, based on multi-agent simulation, we establish a multi-agent model of residential power market and propose a satisfaction function of residential users about electricity price. We focus on the interaction process among all the agents of power supply side, selling side and demand side and conduct simulation to obtain the selection and decision-making of residential users on different electricity pricing schemes. The results show that multi-agent system is beneficial to analyze, simulate and solve the DR problem in power market. Also, the satisfaction function of residential users on electricity price can support power selling enterprise to better understand the intention of residential users when choosing electricity pricing schemes and participating in DR program.
[en] Highlights: • The first effort to forecast potential sensor applications of TENGs through Tech Mining methods. • Sensor applications of TENGs were identified on 4 levels: usage scenarios, sub-technology, technology and industry. • Researchers should widen interdisciplinary collaboration, pursue connections with industry, and file more patents. The Triboelectric Nanogenerator (TENG), invented in 2012, is an emerging energy harvesting technology that efficiently converts ambient mechanical energy into electricity. Much work has been done to develop this device and improve its performance. However, no systematic report about its applications through large-scale publication and patent data analysis is available. In this study, we use “Tech Mining,” a systematic analytical method based on structured texts applied to publication and patent abstract data, to analyze potential applications of TENGs. A series of applications from product scale to industry scale are identified. The findings show that when used as sensors, TENGs are mostly applicable in automation and energy-intensive industries such as automotive, medical or surgical devices, consumer electronics and household appliances. TENGs in the form of sensors can also be integrated with future-oriented and exponentially growing technologies such as robotics, drones, nanotechnology, and bioinformatics that will create enormous value for future economies. Moreover, applications of TENGs as sensors are also in line with current global trends of science and technology development, including the “Internet of Things,” big data, clean energy, and smart cities. Combined with those technologies and industries, TENGs can help in tackling challenges of global warming, environmental pollution and security systems. We suggest the TENG research community to widen interdisciplinary collaboration, pursue connections with industry, and file more patents as R&D progresses. In addition, research limitations and future development directions of TENG are pointed out.
[en] As Beijing put forward its “one core, two wings” development plan, the development and construction in the Beijing Tongzhou District have turned into a national strategy. However, as a municipal district, energy and CO2 emission data and other statistics are difficult to obtain in Tongzhou and CO2 emissions accounting for a district at this level is rare. This study applies the accounting method of city carbon emissions to the district level. Firstly, we account for the CO2 emissions in the Tongzhou District from 2008 to 2015 according to data availability. Secondly, by using the logarithmic mean Divisa index decomposition approach, the Tongzhou CO2 emissions are decomposed into six main driving factors, including population, per capita GDP, industrial structure, energy intensity, energy consumption structure, and energy-related CO2 emission factors. The result shows that (1) from 2008 to 2015, the CO2 emissions in the Tongzhou District first increased and then decreased and peaked in 2011. (2) Population and per capita GDP both contributed to the change in CO2 emissions in the Tongzhou District during the study period and resulted in 407,200 tons and 346,200 tons increase, respectively. The industrial structure, energy consumption intensity, and energy structure exerted inhibiting effects, offsetting 29,300 tons, 571,500 tons, and 29,300 tons, respectively, and the energy consumption intensity was the most important factor. (3) On this basis, we discuss the annual effects of the driving factors. The results of this study provide great significance and references for research in order to implement the low-carbon development and the “one core, two wings” strategy in the Tongzhou District.
[en] Highlights: • High-density TENG units integrated in the device for water wave energy harvesting. • Air-driven membrane structures for effectively transferring and distributing harvested energy. • Tunable resonate state achieved with a spring-levitated oscillator structure. • Demonstrating excellent output performance and extraordinary scalability. Water wave energy is considered a promising renewable energy source, while currently little has been exploited due to a number of unsolved challenges for present technologies. The triboelectric nanogenerator (TENG), as an emerging energy harvesting technology, shows particular advantages in transforming low frequency mechanical energy into electricity, providing new opportunities for harvesting water wave energy. In this work, an integrated triboelectric nanogenerator array device based on air-driven membrane structures is demonstrated. With novel designs of a spring-levitated oscillator structure and a mechanism to use air pressure to transfer and distribute harvested water wave energy, the device can drive a series of integrated TENG units effectively and simultaneously. While operating at low frequency near the resonant frequency of about 2.9 Hz, the device integrating 38 TENG units shows high output of transferred charges per cycle of 15 μC, short-circuit current of 187 μA and optimized peak power density of 13.23 W m−3. The device can easily integrates large-scale high-density TENG arrays in one package, as can greatly augment the output, providing a promising route to effectively harvest water wave energy for various practical applications.
[en] Highlights: • An all-weather solar cell is created for harvesting energy from sun and rain. • G-CB/PTFE conducting composite is utilized to replace graphene film. • The G-CB/PTFE film has percolating pathways for creating EDL pseudocapacitor. • The launched solar cell extend our knowledge of future all-weather solar cell. Future solar cells may produce electricity in all weathers. We present here a cost-effective and high-efficiency graphene based conducting composite tailored all-weather solar cell that can be actuated with raindrops and sunlight. Due to the formation of π-electron|cation double-layer pseudocapacitance at conducting composite/raindrop interface, the delocalized π-electrons on graphene can migrate along percolating pathways forward at spreading process and backward at shrinking periods, resulting in charging and discharging of the pseudocapacitor. The optimized solar cell yields a photoelectric conversion efficiency of 9.8% under simulated sunlight irradiation (air mass 1.5, 100 mW cm−2) as well as current over several microamps and voltage of hundreds of microvolts under simulated raindrops. This work could extend our knowledge of future all-weather solar cells.
[en] Highlights: • A hard ball is enclosed inside the regular dodecahedron device and the collision of the ball with the multilayer wavy-structured robust WS-TENGs in responding to the kinetic motion of water wave can convert mechanical energy into electricity with excellent performances. Recently, triboelectric nanogenerator (TENG) has been invented as a new energy technology and widely utilized in renewable and sustainable energy harvesting. Here we report a regular dodecahedron device integrated with 12 sets of multilayer wavy-structured robust triboelectric nanogenerators (WS-TENGs) for harvesting water wave energy. Each WS-TENG is composed of a wavy-structured Cu–Kapton–Cu film and two fluorinated ethylene propylene (FEP) thin films sputtered with metal electrodes as a sandwich structure. A hard ball is enclosed inside a polyhedron made by WS-TENGs as the walls; a collision of the ball with the WS-TENG in responding to the kinetic motion of water wave converts mechanical energy into electricity. A high output voltage and current of about 250 V and 150 μA, respectively, are measured by a single unit of WS-TENGs in water. Considering the units can be connected into a net structure, the average output power is expected to be 0.64 MW from 1 km2 surface area in a depth of 5 m. By the virtues of cost effective, low-carbon and environmentally friendly, the development of WS-TENGs can be a significant step towards the large-scale water wave energy harvesting and have great prospects for the blue energy.
[en] Highlights: • We introduce a new analytical model of coupled cascades in flow networks. • We find that increasing coupling enhances the safety of the coupled systems. • However, increasing coupling makes the systems more likely to fail together. In this manuscript, we investigate the abrupt breakdown behavior of coupled distribution grids under load growth. This scenario mimics the ever-increasing customer demand and the foreseen introduction of energy hubs interconnecting the different energy vectors. We extend an analytical model of cascading behavior due to line overloads to the case of interdependent networks and find evidence of first order transitions due to the long-range nature of the flows. Our results indicate that the foreseen increase in the couplings between the grids has two competing effects: on the one hand, it increases the safety region where grids can operate without withstanding systemic failures; on the other hand, it increases the possibility of a joint systems’ failure.
[en] Highlights: • Recent progress in blue energy harvesting with TENG technology is reviewed. • The fundamental physics mechanism of nanogenerators is the Maxwell's displacement current. • The TENG network is proposed for large-scale blue energy harvesting. Widely distributed across the globe, water wave energy is one of the most promising renewable energy sources, while little has been exploited due to various limitations of current technologies mainly relying on electromagnetic generator (EMG), especially its operation in irregular environment and low frequency (the energy for the new era – the era of internet of things.