Abstract

The impact of large-scale wind power integration on the stable operation of power system has attracted great attention. This paper presents a method to analyze the influence of doubly-fed induction generation (DFIG) on the power system transient stability by using transient energy function. The transient energy function of the system with DFIG is constructed based on the rotor equation of the system by introducing the equivalent parallel grounded admittance model of DFIG and the critical energy of the system is given. Furtherly, the effect of DFIG on the system transient stability margin is analyzed. In addition, combined the influence of DFIG on the change of system state variables with the energy accumulation process during the fault, the influence mechanism and quantitative analysis of the DFIG on the system critical clearing time and transient power angle variation of synchronous machines are realized. In the simulation analysis, two different LVRT schemes of DFIG are compared, and the simulation results verify the correctness of the proposed method.

Abstract

Building Integrated photovoltaic (BIPV) is an important application scenario of thin film solar cells. As an effective means to improve the efficiency of thin film solar cells, the design of micro-lens structure should match its application scenario to maximize power generation efficiency. In this paper, an optimal design method for the structure of micro-lens used in BIPV is proposed. BIPV lighting roof application scenario is taken as an example. The light trapping performance of different micro-lens structures, under solar illumination during the summer solstice, is analyzed through using Tracepro software. The results show that the V-groove micro-lens has the best light trapping performance when the vertex angle is 110° and the groove depth is 300μm. Compared with non-micro-lens scenario, the irradiance flux on the incident surface of the amorphous silicon can be increased by 16.28%.

Abstract

China’s strict coal-to-gas policy in the recent years has brought unexpected natural gas demand into the domestic market, leading to additional uncertainty and pressure, and further increased China’s import dependency rate. The current situation urges China to establish valid storage system for natural gas, which have been proved to be a preferred method in circumstances with high uncertainties. In this paper, we implement a model based on welfare economics to show the optimal gas storage capacity and its monthly scheme. The result indicates the basic optimal natural gas storage size to be 11.91 billion cubic meters. Under normal conditions, the storage shall reach its peak near November, then begin to release through the next April, and switch back to injection progress to prepare for the upcoming winter.

Abstract

Hydrogen-based energy systems are a viable solution to perform long-term storage of excess intermittent renewable energy. However, such systems are rarely considered in energy system optimization. Moreover, whenever these technologies are considered, the model parameters are considered known and fixed, which can result in suboptimal designs, sensitive to uncertainty. To evaluate the inclusion of a hydrogen-based system in a global energy system and to address the uncertainty on its techno-economic performance, we performed an optimization under uncertainty of a solar-powered, grid-connected household, supported by batteries and hydrogen storage. This paper illustrates the effect of the hydrogen-based energy system on the uncertainty of the predicted levelized cost of electricity. The inclusion of the hydrogen system decreases the standard deviation of the levelized cost of electricity by 4.3 €/MWh (13%) at the expense of an increase in mean levelized cost of electricity by 100 €/MWh (28%). Consequently, despite the gain in robustness, including a hydrogen-based storage system in the considered urban area is not beneficial overall. Future works will focus on including remote areas, to fully exploit the gain in robustness induced by hydrogen-based storage systems.

Abstract

A dual-motor coupling propulsion system with multi-speed transmission offers the possibility of comprehensive improvement of the vehicle, with an increased difficulty and time cost of design though. This paper takes an electric city bus as research object to design a matching dual-motor propulsion system with two-speed transmission. For convenience and rapidity, a bi-level programming method for parameter matching and energy management of the propulsion system is established. The inner level seeks for the optimal control rules concluding gearshift schedule and torque-allocation proportion for instantaneous minimum power loss, while the outer level leverages the particle swarm optimization algorithm (PSO) to seek the optimal propulsion system parameters within reasonable limits. The objective function of the whole loop takes into account the whole power loss of the entire C-WTVC condition. It indicates that the proposed design and energy management strategy provide a significant improvement of the powertrain efficiency and great reduction of the design cost.

Abstract

Thermoelectric generators (TEGs) have been widely used to recover high temperature waste gas in recent years. The TEG performance relates directly to the hot side temperature of thermoelectric modules (TEMs) which is highly affected by the layouts of modules. By the numerical results, it is found that the structure of TEMs uniformly distributed on the four sides of the heat exchanger can reach the smallest temperature difference at the air temperature of 500K and air velocity of 2.4m/s. Also, the TEMs distributed on the one side of the heat exchanger can achieve the highest output power of 11.36W whereas the highest efficiency is reached for the structure of TEMs uniformly distributed on the four sides of the heat exchanger. It can be concluded that the higher coverage ratio of TEMs on the surfaces of heat exchanger is, the higher conversion efficiency may bring. The findings of this work may provide a new method to improve the performance of TEG.

Abstract

Hydrate formation and blockage are commonly encountered in gas and oil transportation pipelines, causing significant equipment damages and financial loss. The development and utilization of environmentally friendly and low dosage kinetic hydrate inhibitors (KHIs) could help remit hydrate formation and protect the pipelines. Safranine O is considered a promising candidate with huge potential. Safranine O is soluble in water and self-assembles into macromolecules with antifreeze protein properties. In this work, it was found that 0.1 wt% safranine O could completely inhibit the formation of methane hydrate at a subcooling of 7.7 °C. Upon a higher dosage of 1 wt%, the inhibition subcooling could be further extended to 8.59 °C. In the both CIR and SGR, the inhibitory effect of 0.5% mass fraction safranine O was better than 0.5% mass fraction PVCap. This will effectively limit the formation of hydrate at a wide temperature and pressure range. The results could provide a brand new KHI with promising applications in the prevention of hydrate blockage in gas pipelines.

Abstract

The design and optimization of heat exchange equipment for effective and efficient performance are imperative and need a thermodynamic analysis. In this study, the effects of mass flux, vapour quality, inclination angle, and flow pattern were investigated on the local entropy generation during the condensation of HFC 134a in an inclined smooth tube. Results showed that the effect of inclination on entropy generation was insignificant for high mass fluxes cum high quality and for Re ≥ 1.75×105 . For high mass fluxes, entropy generation decreased with quality but was unpredictable for low mass fluxes. 66.7% of the data for the gravity-independent flow and 87.5% of the data for gravity-dependent flow were found to have local minimum entropy generation number during upward and downward flows respectively.

Abstract

To improve the cold-starting performance of a polymer electrolyte fuel cell (PEFC), we devised a microporous layer (MPL) with a planar wettability distribution. Hydrophilic and hydrophobic strips in the MPL were arrayed in alternating rows in the in-plane direction. Due to the exclusion of liquid water from the hydrophobic regions, the water moved towards the hydrophilic areas and was absorbed. Since frozen water near the interface between the MPL and catalyst layer (CL) was thought to inhibit the continuation of power generation, minimizing the amount of water on the CL was important. We extended the continuous operating temperature range to encompass lower temperatures and improved the operating time of the PEFC at subfreezing temperatures.

Abstract

How to enhance the ability of distribution systems to cope with the volatility of renewable energy sources and load, i.e. flexibility, has become a crucial issue for power system operation. In this paper, a two-stage robust model is proposed, which considers the volatility and uncertainty of renewable distributed generators and makes full use of dynamic reconfiguration to enhance the flexibility of distribution systems. Furthermore, several flexibility indexes are proposed to quantitatively evaluate the flexibility from the perspective of whole horizon and each period. Finally, the IEEE-33 system is used to test the validity of the proposed method.