A real-time emulation of a modular multilevel converter with integrated energy storage devices has been carried out. The real-time model is detailed and implemented using MicroLabBox/dSPACE. The system is tested and compared to an experimental prototype of the converter. The main advantage of the proposed real-time system is that it gives higher fidelity for further investigations, specifically in electric vehicle applications where it can be integrated into a real-time emulated electric vehicle. The model can be extended to a higher number of levels as it has no constraints on the number of switches or batteries/cells. Also, it can be integrated in a power hardware in the loop system to decrease the testing time of a product. This is a novel proposal of a real-time emulation of the converter in an electric vehicle application using MicroLabBox/dSPACE.
Low carbon liquid fuels are needed for maritime shipping and long-haul trucking which are difficult to decarbonize by use of battery energy storage or hydrogen. Thermochemical conversion of biomass to liquid fuel (BTL) is a promising option to produce carbon-neutral liquid fuel. However, no commercial BTL plants are yet operating and one of the main reasons is the cost of produced fuel. Here we propose two processes in order to improve the economic appeal of BTL process for producing methanol. These processes employ natural gas as a swing fuel and utilize the synergy between natural gas reforming and biomass gasification. Through this integration, we can use the synergistic effects of adding H2-rich syngas (H2/CO mixture) from natural gas to carbon-rich syngas from biomass to produce the right H2/CO ratio for methanol synthesis while maintaining a high carbon utilization. The biomass syngas generation step in both designs is the same and utilize the illustrative example of an entrained flow gasifier (EFG) with subsequent cleaning of the generated syngas to remove H2S, dust, soot, etc. The differentiating feature of these processes is the syngas generation step from natural gas. In the first design, an autothermal reformer (ATR) is used to generate syngas, while the O2 required for both biomass gasification and natural gas reforming is provided by a solid oxide electrolysis cell (SOEC). The H2 stream from the SOEC is used to adjust the stoichiometry of the methanol synthesis reactor. In the second design, natural gas is sent to a gas-heated-reformer (GHR) followed by an ATR. The heat required in the GHR is provided by the exhaust stream from the ATR, which is the best method to utilize the high temperature exergy of the exhaust stream. The reformed gas has high hydrogen content, but not enough to have the correct stoichiometric number prior to the methanol synthesis. Therefore, a fraction of the reformed gas is sent to a water gas shift (WGS) reactor followed by a CO2 capture unit. The produced stream is used to adjust the stoichiometric number prior to the methanol synthesis reactor. The flexibility and economics of the two processes are compared to a stand-alone BTL process. While the produced methanol includes some fossil carbon, the synergy of this integration and added flexibility would increase the economic viability of deployment of biomass-based fuel production.
Gas-liquid thermoacoustic engine, using gas as working fluid and liquid as phase-matching element, can operate at a lower heat source temperature than the gas-only thermoacoustic engine, which is attractive for low-grade heat recovery. Rayleigh-Taylor instability, which is induced when a low-density fluid accelerates a high-density fluid, can occur in gas-liquid thermoacoustic engine. In this work, cylindrical or spherical floats with different dimensions were employed to suppress the Rayleigh-Taylor instability in a gas-liquid standing-wave thermoacoustic engine. Comparison between the onset and damping temperature differences obtained from the conditions with or without float was conducted to analyze the effects of instability on the onset and damping processes. The experimental results show that the dimension of float has marked effects on the onset and damping temperature differences, and there exists an optimal dimension for both cylindrical and spherical floats to achieve the lowest onset and damping temperature differences. After installing the float, the maximum decreases in the onset and damping temperature differences are 19.0% and 21.8%, respectively. This work demonstrates that the suppression of Rayleigh- Taylor instability by the suitably sized float can reduce the onset and damping temperature differences of a gas-liquid standing-wave thermoacoustic engine for low-grade heat recovery.
A personalized stationery air treatment unit is proposed in this work to provide acceptable breathable air quality and adequate thermal comfort in in poorly ventilated spaces. The system consists of a coaxial personalized ventilation system integrated with an antibacterial filter and a metal organic framework-coated thermoelectric cooling unit. Validated mathematical models were developed to minimize the system size while maintaining thermally comfortable conditions. The system was simulated to determine its operative conditions and its required energy consumption. The supplied air conditions at the user’s breathing zone were met by the system ensuring acceptable air quality and thermal comfort levels. The system needed a total of 60 g of Nb-OFFIVE-1-Ni adsorbent with 130 W of electrical energy to properly operate the cooling unit and the fans.
This paper proposes an intelligent battery health-aware energy management strategy (EMS) for the hybrid electric bus (HEB) with a deep reinforcement learning (DRL) method. Firstly, an EMS based on twin delayed deep deterministic policy gradient (TD3) algorithm considering battery health is innovatively designed to minimize the total operating cost of the HEB. Secondly, the superiority of the proposed EMS over the state-of-the-art deep deterministic policy gradient (DDPG) based strategy is validated. Simulation results show that the proposed EMS accelerates the convergence by 24.00% and reduces the total operating cost by 9.58% compared with the EMS based on DDPG.
In order to cope with the environmental problems of climate deterioration, reduce carbon emissions and develop environmentally friendly energy sources without delay. The global energy system is undergoing tremendous changes, accelerating the transformation of the energy structure, and promoting the development of the energy structure to a low-carbon or even carbon-free direction. Renewable energy has received attention due to its clean and green characteristics. Wind power generation, as an important way to develop renewable energy, faces grid security challenges due to the volatility and uncontrollability of wind speed. In this paper, a systematic prediction method is proposed for wind speed: the wind speed sequence is decomposed by the variational modal decomposition method according to the principle of envelope entropy, and the extreme learning machine network optimized by the bat algorithm is used to predict the data after decomposing. Besides, error sequence correction method based on kernel density estimation is proposed to predict residual. The availability of the model proposed in this paper is proved by experiments, and a good prediction effect is obtained. In order to heighten the utilization of wind energy, the wind power dispatching of relevant departments provides a reference method.
Quaternary chalcopyrite semiconductors, Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe), have attracted increasing attention for photovoltaics (PV) application in recent years. However, due to the cell architecture borrowed from CuInxGa(1-x)Se2 (CIGS) devices, the open-circuit voltage is the limiting factor preventing further increases in solar cell efficiency. In the present study, band edge energies of Cu2ZnSnS4 and Cu2ZnSnSe4 were analysed electrochemically in order to show band energy alignments of CZTS and CZTSe. The electrochemical steady-state potential windows were also investigated; this provides vital information for various applications of both materials. The valence band energy offset between CZTS and CZTSe was found to be 0.5 eV. Compared with the flat band potential of CdS (-0.8 V vs Ag/AgCl), the open circuit potential in the dark between CZTS and CdS is therefore 0.4 V and 0.9 V for CZTSe. Moreover, from chronoamperometric measurements using an electrochemical field-effect transistor, the conductivity of CZTSe is found to be three orders higher than CZTS, which proves that CZTSe is significantly better for charge transfer.
In low permeability reservoirs, poor water injection development effect, high water injection pressure, formation energy can not be effectively supplemented and other problems often lead to unsatisfactory development effect, so it is a big problem to change the development mode to improve oil recovery. The injection of carbon dioxide into the reservoir and geological storage of the injected CO2 can greatly reduce the viscosity of crude oil, improve the fluidity of the oil, and reduce the oil seepage resistance, thus improving the development effect and enhancing the oil recovery. Yesanbo oilfield is located in the south of Dagang oilfield, which is a typical low permeability reservoir. Considering the dual advantages of carbon dioxide geological storage and enhanced oil recovery, this paper chooses this area for reservoir numerical simulation study. Based on the mechanism model, the number of injection Wells, injection velocity, Ratio of vertical to horizontal permeability (Kv/Kh), The influence of critical water saturation value on carbon capture ， utilization and storage (CCUS) scheme operation. The results show that a horizontal well with two straight gas injection Wells is the best. The higher the gas injection rate, the greater the carbon storage and cumulative oil production. When Kv/Kh value increases, the carbon storage decreases, and the cumulative oil production increases. Critical water saturation value increases cumulative oil production and carbon storage decreases. The CCUS scheme constructed in Yesanpu oilfield has dual functions of oil displacement and carbon sequestration, which significantly improves oil recovery and deposits a considerable amount of carbon dioxide into the reservoir. This study provides a scientific basis for the operation of CCUS in the oilfield.
The growing energy demand, depleting fossil fuel reserves, and global warming concerns call for a further increase in biomass energy utilization. At present, biomass is mostly used in small-scale applications where the production of electricity is technically and economically disadvantageous. On the other hand, district or communityscale CHP applications with higher efficiencies and lower specific investment costs are a better alternative. Biomass combined heat and power (BCHP) systems can reduce GHG emissions and also have the potential for higher overall energy efficiencies than conventional home heating methods. In this research, an organic Rankine cycle (ORC)-based BCHP for community-scale applications is investigated concerning technical and economic aspects. MDM (Octamethyltrisiloxane) is selected as the ORC working fluid, taking into account the cycle efficiency and system design. The heat of biomass combustion in the boiler is used to vaporize the organic working fluid in the evaporator. The working fluid vapor drives the turbine that spins an alternator. A mathematical model for the community-scale ORC BCHP system is developed to predict its operational performance. Various costs for the BCHP plant are analyzed and the cost of electricity (COE) is calculated. The community-scale or district BCHP plant generates 520.9 kWe electricity with the electrical efficiency reaching 17.24 % at a turbine inlet temperature of 250 °C, and provides hot water with a heating load of 2365.7kWth at a temperature of 79.2 °C. The COE of the BCHP plant is 98.2 $/MWh when not including CO2 credit.
A solar-based vapour absorption machine (VAM) chiller-based district cooling system (DCS) has been designed and its financials have been worked out in the context of a high-rise 80 apartment tower. Comparisons have been made with a vapour compression refrigeration (VCR) based DCS, and with the existing system of 3 unitary split air conditioning units per apartment. The solar VAM DCS carbon footprint is 75% and 78 % smaller than VCR DCS and unitary system. While the capital cost is 58 % larger than VCR DCS, the operating costs are 63 % lower. The VAM-based DCS, though practically complex, has the potential for substantial carbon savings which is needed to slow down carbon emissions.