Energy internet is a networked cyber-physical system including the production, transmission, consumption, storage and transformation devices of various primary and secondary energy sources and corresponding information, communication, control and protection devices. In the energy internet, the power grid is the core. In this paper, the key facilities in energy internet and their future development are reviewed from the following 4 aspects: energy production, transmission, conversion and storage. 4 energy carriers are investigated, i.e., power, natural gas, heating, and transportation. The distinct characteristics and technical requirements of these energy networks are analyzed. The energy router concept in electrical systems and the interfaces between electricity and other energy carriers are introduced. Besides, hybrid energy storage technologies and their development tendency under multiple energy carriers are predicted. In order to better coordinate the application of these key equipment in energy internet, the supporting technologies in the energy internet are expounded from two aspects of planning and operation. Finally, some thoughts on the development of energy internet are given.

Large-scale energy storage is known as an effective way to shift on-peak electricity loads to off-peak periods, and utilize wind, solar, and other types of new energy sources which are volatile and intermittent. Basic principles of compressed air energy storage (CAES) are firstly introduced,and technical advantages of non-afterburning compressed air energy storage (NF-CAES) based on compression heat recovery is expounded, including characteristics of supplying cold, heat, and electricity simultaneously,and key technologies of CAES are discussed.The state of art of CAES at home and abroad is analyzed. Finally, the potential application prospects of CAES in future power grid and micro-energy grid are discussed.

After a decade of rapid development, renewable energy has become one of the important energy supply forms in China. Under the new round electricity system reform in China, establishing a strategic price subsidy mechanism and market trading mechanisms for renewable energy is a key solution to accommodating and developing the renewable energy. Compared with the market mechanisms of renewable energy in other countries, the research of renewable energy trading in electricity market is far away from mature in China. The current situation of the mechanism and price policies of renewable energy in China is outlined and analyzed in this paper. The mechanism of renewable energy participating the electricity markets in foreign countries are summarized and analyzed. The state-of-art researches on how to trade the renewable energy in the electricity markets are reviewed. Finally, the paper prospects the potential research fields of renewable energy trading in the electricity market and discusses its future development in China.

Market mechanism on demand side response plays an important role on the new round of electricity reform in China. In order to develop the pathway of market mechanism which is suitable for demand side response in China, the differences between demand side management(DSM) and demand side response(DR) are analyzed. Then, several interactive modes, such as price-based DR, incentive-based DR and value-added services-based DR, are discussed. The multi-dimensional fuzzy description method is put forward to describe the multiple attributes of various DRs. Moreover, by introducing foreign electricity market experiences, the problems and opportunities of electricity market in China are analyzed. Several development proposals are also put forward in this paper.

The techonology of power electronics has widely used in power generation, power transmission and power utilization of modern power system. At the same time, power system is expanding and integrating new energies sources such as wind power, photoelectric power, hydroelectric power, etc., in a large scale. As a result, the randomness of power system becomes increasingly evident. Under the new background, new models of the power system are necessary for its research. The new background of power system is summarized as power electronics, randomness and smart grid in this paper. It is pointed that the new needs for power system modeling may include accurency, wide-area and variation. Then the new trends of power system modeling are foreseen, i.e. equivalent modeling, on-line distributed modeling and hybrid time and frequency domain modeling.

This paper presents a new decision support platform for intermittent generation integration analysis and planning. The platform has many analysis functions which are organized into 5 categories with 21 top level functions and 68 lower level ones.It is capable to perform many power system analysis required for intermittent power connection including generation expansion planning, coordinated generation and network planning, plan assessment, on-line monitoring and parameter identification of intermittent generation farms, whole process simulation, etc. It provides an effective platforom for tackling difficult challenges in power system planning and simulation analysis caused by the integration of large scale intermittent power sources, such as wind and PV powers. Finally the platform has been successfully used and demonstrated in planning 2020 Northwest China power grid. The results show its potentials in practical engingering applications.

The power grid security early warning technology is important to ensure the security and stability of the power grid. Firstly, the development situation of analytical power grid security early warning technologies is introduced, and some engineering problems are discussed briefly. Secondly, the framework of the power grid intelligent security early pre-warning technology based on big simulation data is proposed, and the feasibility and advantages of hybrid model-driven and data-driven method are dicussed. At last, the tentative application in Guangdong Power Grid has a good effect.

As more distributed new energy being accessed to power grid, it has a great influence on the harmonic studies of power system. It is urgent to solve the harmonic issues of distributed new energy connected to the grid and detect the harmonics and inter-harmonics accurately, figure out the distribution property of the harmonics, identify the harmonic sources and assess the harmonic responsibilities, as well as to reveal the mechanism of harmonic propagation and resonance and analyze the harmonic instability. Therefore, the harmonic hot issues of distributed generation connected to grid are described on aspects of harmonic measurement, harmonic identification, harmonic responsibility assessment, harmonic resonance and harmonic instability, which contribute theory reference to the studies on harmonic issues of distributed generation accessed to grid.

DC distribution network has been gained increasingly interests due to its flexible control, excellent power quality, and capability to integrate distributed generators and DC loads. However, the fault characteristics of DC networks are different in nature as compared with AC power networks. The protection technology of an AC network is hard to be directly applied into the DC distribution network. Besides, the over-current capability of DC converters is weak and the restoration control is relatively complicated, which presents higher requirements for fast and accurate fault identification, location and isolation. Therefore, the protection technology becomes one of key technologies for developing DC distribution network. In this paper, the topology of DC distribution network is discussed by analyzing the fault occurrence, identification, location and isolation. The fault identification and location are considered as the key issues in DC distribution network protection. On the basis of this, the main points and difficulties of the protection technology are analyzed. The state of the art of fault identification and location in DC distribution network is evaluated and the technology perspective is investigated as well.

The large-scale application of silicon rubber (SR) line insulators in China has improved the outdoor insulation level in power systems significantly. China has become the first country in which the organic outdoor insulation dominates UHV AC and DC transmission systems. The organic outdoor insulation is the hot spot in the field of research and application of outdoor insulation in power systems, and SR composite insulator is the representative. In this paper, the operational problems of composite line insulators are classified and analyzed. And the market share and competitiveness of composite insulators are compared with those of porcelain and glass insulators. The obvious advantages, prospect of development and existing problems of the application of composite insulators in substations and converter stations are discussed. Some other problems and opportunities in the development of organic outdoor insulation are analyzed.

Transmission lines intricately distribute in the Pearl River Delta region and other major cities in high density, which on the one hand influence the environmental landscape, on the other hand compress the human living space. Facing the contradiction between power and environment, how to achieve the harmonious development of power grid and environment is one of the key problems to be solved for future power grid. The concept of constructing the integrated energy underground passage is proposed in this paper. Applying the large-capacity transmission cable and pipeline transmission technology, all the transmission lines will be transferred underground to achieve three-dimensional use of land resources, resolve the outstanding contradiction between power and environment. The underground pipe network construction process in developed areas should be comprehensively optimized, considering the energy transmission passages, construction of information delivery passages and rail transport corridors, to achieve the widely shared underground corridors. Current technical development situation of large capacity DC cables, and AC and DC transmission pipelines is also analyzed.

Roof insulators of high-speed electric multiple units (EMUS) are important mechanical supporting component for high voltage equipment, which in addition isolates the catenary from the train’s roof in electric, the flashover of roof insulators may lead to interruption of power supply or even outage. However, due to the specificity and severity of operation environment for high-speed railway in China, accidents caused by the flashover of insulators often occurred, which seriously affect the safe operation of high-speed railway. Through deep research on revelant scientific problems, accidents of trains result from insulator flashover have been greatly reduced, but these kinds of problem haven’t been solved fundamentally. In this paper, research progresses of roof insulators used for high-speed EMUS are reviewed from the follwing aspects: structure and material property, pollution flashover characteristics, sand dust flashover characteristics under strong wind, insulation online monitoring, methods for accelerated aging test and aging test platform. In the end, this paper forcasts future research key points.

Facing severe challenges from climate change, environment and energy in the 21^st century, power systems have been udergoing certain new developing trends.The developing trends of power systems are discussed and summarized in this paper as follows: more incorporation of renewable energy, more adoption of distributed power systems based on micro-grids, more DC type of transmission and distribution, and becoming more electronic.Then the challenges to power electonics, which is the core technology for electric power conversion and control, under such developing trends are analyzed.Some of these challenges can be solved by the research and development efforts within power electronics area, while the others can only be addressed and coped with through close collaboration between power electronics and the related areas.

Under the background of energy saving and environmental protection, electric vehicle technologies are being developed fast and become a research hot topic around the world. The types of electric vehicles and current industry situation are reviewed in this paper with a focus on their driving motor types, specially permanent magnet (PM) traction motors. The key technologies adopted in PM motors and the development trend of traction motors are discussed. Finally, the influence of electric vehicles on power grid during charging and discharging is summarized, and the development trend of electric vehicle industry is predicted.

Silicon carbide (SiC) power devices have the advantages of high voltage, high temperature and high frequency, which show great potential to be used in future power grid. Several major breakthroughs in R&D and industrialization of SiC material and devices obtained resently are introduced. With 6 inch 4H-SiC wafer and its extensional products are avaliable and getting more mature, SiC power devices with higher voltage, larger conduct current and more efficiency will be developed. The perspectives of applications of SiC power electronic devices in power grid are proposed. Full SiC power devices have shown great advantanges and market perspect of distributed energy converter, solid-state transformer and solid-state breaker.

Along with the rapid increase of peneration level of grid connected photovoltaic (PV) generation systems, higher requirements of the optimized design and control performance of the grid connected PV systems both at user and grid sides are brought forward. The technology development status of grid-connected PV systems is given, and topological development of grid connected PV inverters is described and sorted into three types: isolated or non-isolated inverter, single-stage or two-stage inverter, and two-level or multi-level inverter. The future challenges and prospects are given on the coordinative control between static var compensator and grid connected PV inverter, the virtual synchronous generator control among grid connected PV inverters, and the technology of global synchronous pulse width modulation.