• Energy Research
• 2016-2025close
• Tsinghua University close

Abstract China has the advantage of learning from the mistakes made by nations that have developed their nuclear power energy system in the last century. Such mistakes encompass the lack of sustainable development of the nuclear energy and poor planning in the back-end of the nuclear fuel cycle. The present paper studies the evolution of a double strata cycle with fast reactor gradually replacing the LWR. It starts from 2035 and covers the historical development of nuclear energy in China to the year 2100. The paper studies the ADS impact on the NFC and estimates the number and the deploying schedule of the ADS reactors to limit the accumulation of minor actinides. The other aspects considered here are natural uranium resources, fuel utilization efficiency, proliferation and diversion risks, spent fuel production and overall materials flow. Additionally, perturbation calculations were performed to evaluate the impact of the uncertainty on key parameters. The results are discussed in view of the Chinese nuclear fuel cycle plan and their policy implications are thoroughly evaluated.

High voltage direct current (HVDC) technology is the ideal solution for long distance bulk power transmission. However, different from AC systems, differential protection of HVDC lines still faces a lot of challenges. We claim that from the perspective of state estimation, the essence of differential protection is to estimate state variables using measured data, of which the validity indicates whether there is a fault. Therefore, the performance of the differential protection is highly related to the model accuracy. Using a detailed distributed parameter line model, this paper developed a novel differential protection method for HVDC lines based on traveling waves with high reliability. The optimal differential point is also discussed to enhance protection rapidity. Experiments demonstrate that the proposed protection could soon detect internal faults with high fault resistance while maintaining reliability when external faults occur.

Given the increased percentage of wind power in power systems, chance-constrained optimal power flow (CC-OPF) calculation, as a means to take wind power uncertainty into account with a guaranteed security level, is being promoted. Compared to the local CC-OPF within a regional grid, the global CC-OPF of a multi-regional interconnected grid is able to coordinate across different regions and therefore improve the economic efficiency when integrating high percentage of wind power generation. In this global problem, however, multiple regional independent system operators (ISOs) participate in the decision-making process, raising the need for distributed but coordinated approaches. Most notably, due to regulation restrictions, commercial interest, and data security, regional ISOs may refuse to share confidential information with others, including generation cost, load data, system topologies, and line parameters. But this information is needed to build and solve the global CC-OPF spanning multiple areas. To tackle these issues, this paper proposes a distributed CC-OPF method with confidentiality preservation, which enables regional ISOs to determine the optimal dispatchable generations within their regions without disclosing confidential data. This method does not require parameter tunings and will not suffer from convergence challenges. Results from IEEE test cases show that this method is highly accurate.

Abstract In the study, a three-dimensional CFD simulating model coupling with reasonable turbulent model and reduced chemical kinetic mechanism was established and validated. The auto-ignition development and knocking characteristics of a downsized spark-ignition (SI) gasoline rotary engine (RE) under different boosted conditions were numerically investigated. Results showed that as inlet pressure increased from 1.12 bar to 1.16 bar, the knocking intensity (KI) of the RE was enhanced gradually, and the knocking onset was advanced. However, with the further augment of inlet pressure, the KI did not further increase due to the larger heat dissipation loss caused by high turbulent kinetic energy in the long and narrow combustion chamber of the RE. This indicated that the structure of the downsized SI RE had a certain ability of knocking suppression when inlet pressure was sufficiently boosted. The KI of the RE was more serious in the trailing part of the combustion chamber as compared to other positions due to the unidirectional flow field, especially on both sides near the end cover in the trailing part of the combustion chamber. Therefore, it was concluded that strengthening the cooling of both sides near the end cover in the trailing part of the combustion chamber may be an effective way to reduce the KI of a downsized boosted SI RE. In addition, the KI is closely related to auto-ignition development processes, e.g. end-gas auto-ignition modes. Under the mass fraction of unburned mixtures at the moment of end-gas auto-ignition, the local KI caused directly by single hot-spot auto-ignition was higher than that caused by multiple hot-spots auto-ignitions, and the local KI caused by homogeneous auto-ignition was higher than that caused by multiple hot-spots auto-ignitions.

The power system ranks the first among the greatest engineering achievements in the 20th century. With “strong electric power” as the carrier, the power system constitutes the great aorta of modern society for energy transmission; while with “weak electric power” as the carrier, the information network constitutes the nervous system of modern society. Both of them penetrate into all aspects of human society (e.g., science, production, life, international relations), and then promote the modern civilization to achieve rapid development. In terms of science, the power system has promoted the developments of materials, physics, chemistry, automation, information, medicine, and so on. This way, the system of modern science and technology is constituted. In terms of production, the second industrial revolution marked by the wide application of “strong electric power” is also called the electric power technology revolution. It has promoted another major leap in the productivity of human society after the steam revolution. The third industrial revolution marked by the widespread application of “weak electricity” is also known as the information technology revolution, which promotes the continuous evolution of industrial civilization to a much higher level. And the fourth industrial revolution, which is centered on the energy revolution, will meet the needs of human beings at a higher level and get rid of the constraints of the environment on human activities. In terms of life, electric power has become the most indispensable part of human life, ranging from material life to spiritual life, from behavioral habits to thinking ways, and from personal life to social life. In terms of international relations, the development of the power system is conducive to the fundamental solution of energy and environmental problems, thus the international political and economic competition around energy and environment has turned to the competition centered on clean power systems to some extent. As the basic platform for energy production and supply, the development of the future power system must follow the general orientation of the energy revolution. The basic form, management mechanism and technical characteristics of the power system will also undergo tremendous changes as follows: (1) The proportion of renewable energy in the power system will be increased continuously, and the power system will be tightly coupled with gas system and thermal system to form an electricity-centric energy internet. (2) The development mode of building “higher, farther and larger” power grid will turn to the co-development mode of large power grid and small power grid, and the trend of power electronation of power system will be strengthened gradually. (3) Market competition will penetrate into the weak monopolies of the power system. Each subject can play a full game in each link, so as to obtain the optimal allocation of funds, technology and human resources. (4) Digitalization and intellectualization will be the most important technical characteristics of the future power system, which will achieve leapfrog development in observability, controllability and intellectualization.

Abstract Thermal runaway and its propagation are bottlenecks for the safe operation of lithium-ion battery systems. This study investigates the influence of characteristic thermophysical parameters during battery thermal runaway, such as the self-heating temperature (T1), triggering temperature (T2), mass loss, and critical heat transfer power (Pc), on the failure propagation behavior in a battery system. A parametric study is conducted based on a failure propagation model. This model not only captures the behavior of thermal failure, but also accounts for the changes in the thermophysical parameters before and after thermal runaway. The results of the modeling analysis demonstrate that increasing T1 and T2 can both delay the thermal runaway propagation. The delay achieved by increasing T2 is greater than that observed by increasing T1. The peak heat transfer power Pc plays a critical role in delaying the thermal runaway propagation. When the peak heat transfer power level is greater than Pc, thermal runaway propagation mainly results from heat transfer, whereas when the peak heat transfer power level is less than Pc, thermal runaway propagation mainly arises from self-heating. This study reveals the dynamic mechanism of thermal runaway propagation within a battery module, thus providing guidance for the safety design of battery systems.