Prospects for key technologies of new-type urban integrated energy system

1 Introduction

Since the reform and opening up,China’s economy has developed rapidly,and the demand for energy has also increased greatly.In recent years,it has become the world's largest energy consumer [1].Although with the continuous development of science and technology,China’s energy production is gradually increasing,there’s still a gap between supply and demand,needing large amounts of abroad energy import.Moreover,China’s energy consumption structure is extremely unreasonable.Taking several typical areas in China as examples,the proportion of coal consumption in Liaoning Province has reached more than 70%,some provinces with low economic development such as Guangxi,Yunnan and Hebei has reached about 80%,and Guangdong Province has the lowest proportion of 60% [2].It exposes China’s current excessive dependence on traditional energy supply affects China’s environmental protection and sustainable development [3].Improving the development and utilization of renewable energy is an effective way to solve the above problems,but China’s development in this area is just in its infancy.Taking wind power and photovoltaic power generation as an example,due to insufficient system regulation capability,the phenomenon of abandoning is serious [4].

Meanwhile,China has experienced the fastest urbanization process in the world,a large number of people and resources have gathered in cities and urbans.The urbanization rate has increased by 10% in the past ten years,reaching 59.58% in 2018,which is still not so high compared to the urbanization rate of more than 80% in developed countries such as France and Germany,but the rapid expansion of the scale of cities has put great pressure on the urban energy system.The current urban energy system has some common problems with high energy consumption,low integrated energy efficiency,high carbon emission pressure,and insufficient supply and demand interaction [5].The development of urbanization in China is shifting towards the new urbans,which emphasizes not only the improvement of urbanization rate,but also the sustainable development of people-oriented and green ecology.It requires further optimization and development of China’s energy consumption structure [6].

The urbanization of developed countries is relatively mature,and due to the concentration of a large number of people in cities,there is a huge demand for energy,promoting the development and research on urban energy systems.Most of the research conducted in various countries currently focuses on the integrated energy systems and energy internet [7-8].The United States first proposed the concept of energy internet and established the “Future Renewable Electric Energy Delivery and Management System” research institute to conduct research on the application of energy internet in urban energy systems.Germany began researching the core technology of energy internet in 2008,and has established several demonstration areas in the country to conduct experiments in related fields; and Japan mainly focuses on the research of energy network information and energy transfer,taking the “digital grid router” as the main object to conduct experiments in the whole country [9].

In order to meet the new requirements of new urbans for energy systems and improve energy management and optimal control,power systems are gradually shifting to integrated energy systems.The integrated energy system is considered to be the main form of energy for future human society,which combines various energy links such as electricity,gas,heating/cooling and urban infrastructure systems.The energy efficient use and the user multiple energy cascade utilization can be realized through coordinated scheduling of multiple energy sources in the system.When the power system or the rest of the energy system malfunctions,the integrated energy system can also use local energy to achieve uninterrupted energy supply to important users [10]satisfying the energy supply requirements of new urbans.

In summary,the integrated energy system will become one of the important development directions of the new urban energy system in the future,and it is necessary to innovate related technologies such as planning and trading.

2 Characteristics of new urban energy interconnection system

Urban areas have multiple forms of energy access,diverse forms of energy use and complex behavior of energy use [11].According to the difference of geographical locations,resource richness,energy consumption.The new urbans show the characteristics of compact and dense energy-using area,abundant energy equipment,dense and honeycombed areas.Some form multiple energy centers,showing the decentralized and aggregated energy characteristics [12].

The traditional urban energy system has a single form of energy use,and the energy consumption mode is relatively extensive.It is mainly based on electric energy.And it is a radial energy supply mode with a small amount of single energy.The energy facilities are single and the energy transaction is one-way.With the development of cities and urbans,a variety of energy sources are gradually introduced to satisfy the multi-energy demand of cities and urbans,forming a stage of multi-energy forms to supply energy.However,the multi-energy sources mainly provide energy separately and independently,with the lack of coupling [13].In the future,the development direction of new type urban energy system will be transformed into multi-energy coupling and multi-terminal interconnected energy system,which will increase energy coupling and enhance energy efficiency intensively,further developing towards multienergy,multi-layer and multi-ring complex energy system,as shown in Fig.1.

The new type urban energy system is an integrated energy system of “source-network-load-storage” in the interconnection area,which coordinates the various links of production,supply and marketing.The new type urban energy interconnection system is based on the energy hub as a coupling node,with information flow as a medium.Besides,various forms of energy are integrated and connected with each other.It can build an integrated energy system of electrical and thermal energy complementarity horizontally and optimize the “source-network-loadstorage” vertically.It can realize the efficient utilization of clean energy such as distributed photovoltaic and wind power [14],breaking the multi-layer barriers of interaction among energy subsystems such as electric energy,thermal energy and cold energy,and utilizing the interconnection and interdependence of electricity,gas and heat,achieving cleaner and less carbon emissions in the region and realize the energy intensive utilization.

Fig.1 Development direction of urban energy system architecture

The new type urban integrated energy system has the following characteristics:

(1) Clean and low-carbon energy consumption

Due to unreasonable energy structure,increasing energy demand and extensive use of energy,China is unable to save energy and reduce emission [15].The new type urban energy system will connect a large number of new energy sources.By adjusting the energy consumption structure,optimizing the total energy consumption,improving energy efficiency and reducing dependence on fossil energy,the energy transformation will be promoted with the main objective of clean and low-carbon energy consumption.

(2) Intensive utilization of energy resources

Because of the dense population,the high elasticity of energy use form and behavior,and the dense energy resources,the new type urban energy system has created conditions for the rational utilization of energy resources and has adjustable space.Through the coupling interaction of energy and the optimized allocation of various resources,the green and intensive new urban energy internet will be built.Taking the integrated energy development needs of urban and rural areas as the starting point,the comprehensive energy efficiency improvement and local consumption of clean energy will be enhanced to realize the intensive use of new urban energy resources.

(3) Flexible sharing of energy value

The access of new energy,energy storage,electric vehicles and flexible loads has gradually blurred the role of energy producers and consumers,and the market-oriented energy trading mechanism of new urban energy systems has gradually improved.The energy value of new type urban will be shared maximally.On the one hand,the energy supply structure of energy system will be improved,and the efficiency of energy utilization will be increased.On the other hand,the win-win situation of energy value utilization will be realized and the healthy development of energy market will be guided.

(4) Compactness of multi-energy coupling cyberphysical

The new type urban energy system is a system that combines information flow and energy flow closely,and is characterized by the integration of information communication infrastructure and energy and power infrastructure.In the aspect of multi-energy coupling,the new type urban energy system includes a variety of energy access horizontally.By coupling and complementing energy sources such as new energy,oil,coal,electricity,gas,cold and heat,it maximizes the utilization of energy resources and enables the rational utilization of energy resources from high to low grade [16].In the vertical direction,the energy coupling form of the new type urban energy system goes deep into all parts of the “source-network-load-storage”,and there are multi-energy coupling in each part,so that energy resources can be effectively utilized at all stages.At the same time,the development of integrated energy system requires more and more efficient information transmission,which requires the deep integration of information network and energy network to form an intelligent and efficient energy system.

This paper will improve the new urban energy system and build a green,intelligent,efficient and intensive new urban integrated energy system from the aspects of hardware facilities,information support and trading mechanism and from the perspective of building an intelligent energy production and consumption infrastructure,building a multienergy synergistic integrated energy network,fostering a flexible energy trading market model.

3 Key equipment and technology for urban integrated energy system

3.1 Construction of energy connected hub equipment and infrastructures

Under the background of new type urban,the technology of energy interconnection hub is to make full use of the infrastructure of multi-energy conversion,multi-energy open interconnection and energy storage,make full use of the resources endowment of cities and urbans,analyze the characteristics of energy structure of cities and urbans,construct multi-energy complementarity horizontally,optimize the “source-network-load-storage” vertically,improve the way of energy utilization,and maximize energy efficiency utilization.

The new type urban energy system has complex energy coupling in various forms and intensive interaction between “source-network-load” [17].In order to effectively solve the difficulty of multi-energy access,coordinated operation and interactive energy utilization in energy internet,and to provide support for related planning,operation,trading and other technology applications,appropriate infrastructure projects need to be studied respectively.The core technologies of energy interconnection hub include multi-energy conversion infrastructure,energy storage infrastructure and multi-energy coupled infrastructure,which together constitute the infrastructure under the situation of “source-network-load-storage”.

(1) Multi-energy coupled conversion equipment

The multi-energy coupling conversion equipment is mainly used to realize the energy transfer and conversion between various energy networks and realize the efficient utilization and effective control of comprehensive energy.However,with the increasing complexity of new urban energy systems,current energy equipment is difficult to achieve real-time coordinated control of multiple energy systems and energy loads,real-time control of energy storage and conversion,and how to solve the development of open control equipment,how to meet the key technical issues such as the reliability requirements of users’ power supply and hot and cold supply [19],there are a lot of research work to be done.At present,some basic researches have been carried out in the field of multi energy flow system integration.The extensive construction of energy station promotes the deep coupling between various energy systems,which are helpful to realize the efficient and reliable operation of the integrated energy system [20].In the multi energy system,the application of energy router realizes the integrated control of energy internet.Regional building cold,heat and electricity load forecasting device [21],which realizes the regional building cold,heat and electricity load forecasting and comprehensive analysis,lays a good foundation for the efficient use of different energy sources.The integrated energy dynamic monitoring device [22]solves the real-time monitoring problem of different energy sources in the integrated energy system.

At present,the research on multi-energy flow collaborative management is still in its infancy.For multienergy systems,top-down centralized management and control relies heavily on system scheduling and has poor system scalability.It also lacks the corresponding infrastructure to support.Moreover,different types of equipment,different communication protocols and different characteristics of energy output in the energy internet result in the lack of interconnection among key equipment of energy interconnection.Therefore,it is necessary to vigorously build multi-energy conversion infrastructure,develop multi-energy coupling conversion equipment with stronger adaptability and higher stability and achieve efficient management of multi-energy systems.

(2) Energy storage equipment

In the context of new towns,the energy storage infrastructure could act as the energy polymerization device,and cooperate with the multi-energy conversion infrastructure to ensure the sensitive and efficient operation of the system and energy market with rational allocation of production capacity and energy end resources [23].In recent years,energy storage technology has continued to develop,the scale of energy storage has continued to expand,and the impact of energy storage facilities on the entire system has become more prominent.At present,energy storage technology in China has initially had the foundation of industrialization [24],and the energy storage technology represented by electrochemical energy storage has been maturing.Its cost has been further reduced.The mechanical energy storage technology represented by compressed air energy storage has gradually overcome the difficulties in materials and other aspects.The industrialization speed is accelerating.The new energy storage technology represented by lithium air and all solid-state batteries is also developing continuously and has made certain breakthroughs.

At present,energy storage facilities are generally used as backup power sources or used flexibly in the ancillary services market to improve system reliability and economy [24-25].In the future,with the continuous development of new-type urbans,the complex coupling relationship between multi-energy systems means that facilities including electricity,cold,heat,gas storage and some generalized energy storage effects such as natural gas/heat pipes,buildings and electric cars should be vigorously developed.This will further enhance the network ability to absorb and redistribute multi-energy sources,and play an important role in peak load shifting and renewable energy consumption.In order to realize the flexible access of energy storage and support the efficient operation of the energy network,it is necessary to develop an energy storage interconnection device with plug-and-play characteristics to enhance the coordinated operation capability of the energy storage equipment.

(3) Multi-energy open interconnection support infrastructure

Multi-energy open interconnection support infrastructures are mainly used to realize safe and efficient interactive transmission of system energy flow,material flow and information flow,in order to cope with the deep coupling of multi-energy system,the increasing volatility of multienergy load and the large-scale access of distributed new energy.At present,there are some upgrading projects for distribution network [27],which improve the reliability of power supply and the grid-connected ability of renewable energy,and provide grid support for the coupling of various energy systems.In order to monitor the operation status of the system,the related research on the distribution Internet of Things has been carried out.The deep application of the Internet of Things technology in the distribution network can support the demand of the distribution network in lean management and scientific decision-making.Aiming at the wide access of distributed renewable energy,a number of AC/DC hybrid microgrid projects have been constructed,which provide support for the local absorption of various new energy sources [28].

However,at present,the multi-energy open interconnection support infrastructures are mostly concentrated on the grid side.In the future,more compatible support projects need to be constructed,more flexible and adaptable multienergy conversion coordination devices developed to realize the interconnection of multi-energy systems.

3.2 Energy management and control platform

The new-type urbans energy system involves many devices,different management links and massive and complex information data.It needs a technology that can quickly realize the source-network-storage-load information interaction and system management [29].The new-type urbans energy management and control platform takes the needs of integrated energy service providers as the main starting point,using advanced data service technology to provide multi-energy optimization design analysis and control services for integrated energy service providers on the basis of fully considering the characteristics of integrated energy system interconnection and multi-energy coordination in new-type urbans.The energy management platform design framework based on new-type urbans energy interconnection network is shown in the Fig.2.With the multi-energy intelligent interaction device and IEC standard,information flow can be shared and transmitted.With software technology,various key sub-technologies can be integrated into the platform.The main support technology of energy management and control platform is the new-type urbans energy data service technology and integrated energy management and control service technology.

(1) New-type urbans energy data service technology

Due to physical interconnection and multi-energy coordination,the information flows between different energy systems and different system levels of urban integrated energy system are diverse and interact frequently.And they have the characteristics of massive heterogeneity of measurement data [30].In view of its weak information perception breadth,depth,density,serious information barriers and other issues,data service technology takes information security technology as protection,realizes information perception with intelligent acquisition device,and uses extended IEC standards to realize multi-energy device identification and control.It can form a consistent expression of compatible multi-source data such as operational information such as source,network,load,and storage,socio-economic information,and geographic weather information.It is the key foundation for energy management,multi-energy forecasting,transaction evaluation and integrated services of data-driven energy internet.

With the rapid development of information-physical systems,new-type urbans energy data service technology needs to fully study the intelligent collection of multienergy information.So that the physical level perception could be more comprehensive,the measurement performance could be more accurate,and the decisionmaking control could be more intelligent [31].On the basis of considering the independence,integrity and security of massive heterogeneous data,the technology should realize the effective aggregation of multi-source data and explore the internal connection of different data.On the basis of providing complete,accurate and timely information for the system,the technology should consider data transmission security to ensure the interaction between the physical system and energy management and control platform [32].

(2) Integrated energy management and control service technology

Fig.2 Energy management platform framework based on new-type town energy interconnection network

Through on-line monitoring of new energy,energy storage,energy stations and other equipment in urban areas,the new urban energy management and control service technology are based on various information provided by the new urban energy data service technology,energy flow optimization,facility management,and new urban integrated energy systems.Provide joint support and other support,and use IEC standards to build software systems to provide integrated energy service providers with information services such as energy analysis and equipment operation and maintenance.Its main supporting technologies are multi-energy system joint planning technology and multienergy system energy flow optimization technology.

1) Joint planning technology for multi-energy system

Compared with traditional integrated energy system,for new-type urbans integrated energy system,its source and load are strong random,types of them are varied,and behaviors of them are complex.Meanwhile,multi-energy networks are densely coupled and diverse,and multi-user supply and demand bilateral interactions are more frequent [33].For the planning and design of new-type urbans integrated energy system,on the basis of comprehensive consideration of energy interaction characteristics,multi-energy spacetime distribution characteristics,and regional resource endowments,optimizing resource allocation,promoting energy efficiency improvement,and tapping multi-energy synergy potential are the main tasks.In order to provide support for system planning,the joint planning technology for multi-energy systems needs to consider the functional positioning of different types and levels of energy systems,and the energy demand and evolution of urban development to build a centralized/distributed and end-to-end energy internet energy system architecture.According to the newtype urbans geographical features,resource conditions and the original energy grid topology,green intensive planning for multi-energy network is necessary to be carried out.On the basis of considering the uncertainty of urban multienergy load and renewable energy,the multi-objective collaborative planning model of energy station should be established considering multi-energy complementary characteristics.

2) Energy flow optimization technology for multienergy system

The energy sources in new-type urbans integrated energy system show a high degree of integration.With multi-energy complementation and cascade utilization for source-network-load-storage,large-scale renewable energy can be absorbed,multi-energy utilization can be improved,and the degree of dependence of traditional fossil energy can be reduced.Energy flow optimization technology is the key to achieving the goals [34].Firstly,how to reduce the difficulty of multi-energy flow solution based on the accuracy of the system modeling should be considered in order to optimize the operation of New-type urbans energy system [35].Secondly,it is necessary to consider a variety of operation constraints [36]to balance the contradictions between various objectives such as economy,security,and efficiency,so that the system could operate in the optimal state.At the same time,the multi-time scale characteristics and differences of each energy system should be considered.And different scheduling periods should be adopted in multienergy flow optimization dispatch.In addition,considering the difficulty of coordination of energy supply subjects and the strong randomness of demand side,it is necessary to develop the energy flow optimization and management strategy at the annual-season-month-day level based on the analysis of long-term energy use characteristics.

3.3 Energy value sharing technology

Urbans integrated energy system is an energy system that relies on regional management mode innovation and information exchange,coordinates and integrates different forms of urban energy,and achieves coordinated control and planning management of energy.All kinds of energy in the system interact and respond to each other.In the traditional urban integrated energy system,energy sources such as urban power supply companies,gas companies,and heat companies plan,construct,operate,and manage energy production,transmission,and sales independently.The market is relatively closed and lacking effective interaction channels [37-38].

Integrated energy system include robust,flexible and integrated interconnected systems [39].Efficient and flexible integrated energy trading technology is the key to fully tap the flexibility and value of energy,energy storage,load and other aspects of the system,and to improve the operational efficiency and efficiency of the integrated energy system.In 2015,the Power Market Reform Document No.9 “Some Opinions on Further Deepening the Reform of Electric Power System” pointed out that the integrated energy service companies providing hot and cold electricity and individual users with distributed renewable resources are encouraged to participate in market-based transactions as the main body.In the future,in a more pluralistic,flexible,open,competitive and shared market environment,it is particularly important to research and adapt to the multi-functional trading technology.

In the context of global climate change and energy security challenges,China is experiencing the transformation of urban energy consumption structure,and the proportion of green energy consumption represented by photovoltaics is gradually increasing.Under the intermittent and unstable characteristics of renewable energy,the sharing and coordination of green energy among consumers is an important means to promote the transformation of energy consumption.The energy value sharing technology of the urban integrated energy system,through the design of a market-oriented multienergy trading mechanism,supporting the construction and improvement of the infrastructure needed for the energy interconnection market operation,achieving synergy and multi-energy trading of multiple energy sources in the urban energy interconnection system,promoting the flexible local consumption of all types of green energy,improving the user's energy consumption structure and the environmental and social benefits of the energy system,saving the cost of all parties,improving energy flexibility,and promoting energy transformation.The energy value sharing technology mainly relies on the multi-energy transaction sharing technology including a variety of green renewable energy in the urban area.The structural framework is shown in Fig.3.Trading takes place in both centralized and distributed markets.Firstly,the user-side energy management and control terminal and intelligent gateway are used to collect and report a variety of transaction information.Then,based on the multi-energy trading mechanism,the matching between the trading entities is completed.Finally,we use the transaction support platform to promote the landing of multi-functional transactions.

Fig.3 Multi-energy transaction sharing technology framework containing green renewable energy

Under the background of urban integrated energy system,multi-energy trading and sharing technology including many kinds of green renewable resources mainly includes supporting facilities construction,supporting mechanism construction,supporting platform construction and so on.

At present,the number of “prosumers” users with renewable energy,energy storage and load in urban integrated energy systems is increasing.These users enjoy equal status in urban integrated energy systems and rely on high proportion of green renewable energy.At the same time,it plays the role of green energy consumers and providers [40].At the same time,the user-side distributed renewable energy,energy storage,cogeneration and other forms of energy are coupled with each other,and the comprehensive energy resources are increasingly abundant,and the user energy characteristics are increasingly obvious.For the increased demand for comprehensive energy such as electricity,gas,cold and heat,the user-side interaction scene has increased,which puts new demands on the construction of transactions and interactive support facilities.It is necessary to reform the energy consumption system of residents and industrial and commercial users in urban areas,and to build energy management and control terminals and intelligent gateways with the ability of demand response interaction.It can reduce the peak-valley difference of demonstration users and improve the energy utilization and sharing efficiency of end users.

On this basis,for the highly complex user-side electricity price structure and the relatively stable highpermeability green energy price,a multi-energy trading market with multiple green renewable energy sources is established to form a new centralized and distributed multienergy trading model.In order to establish a perfect energy commodity trading mechanism and solve the problems of decentralization of trading subjects,loose and lagged information,serious energy information barrier in energy internet.The urban/local/user multi-tier market structure should be established first,and a centralized/distributed energy multi-level transaction model considering the system operation security constraints should be formed to improve the multi-stakeholder bidding strategy considering uncertainty; Secondly,based on this market model,the multi-energy user response strategy under the interaction of market incentives and user energy behaviors is further established to realize the active participation of users driven by the market [41].It is conducive to flexible local consumption of various types of green energy and improving the structure of users' energy consumption.Provide users with value-added services such as energysaving services and high-reliability power supply,and guide users to participate in green energy sharing transactions,forming an effective support mechanism.

Finally,among various types of prosumers and integrated energy users,a multi-energy transaction management and control platform for community users in the market environment is creating,and promote the demonstration of peer-to-peer energy transaction and electric-heat joint energy trading.Realize the multi-energy sharing transaction mode in urban areas,improve the level of distributed renewable energy consumption,and improve the user energy level and the economic benefits of all parties involved.

4 Conclusions

The integrated energy system is an important development direction of the new urban energy system in the future.This paper introduces the current energy situation in China and analyzes the shortcomings of the energy system in the new development trend of China's urbanization,according to the development direction of global urban energy system,describes the role of integrated energy system in improving energy management and optimization control and introduces the characteristics and advantages of new urban energy system.Its key technologies:the technology of energy interconnection hub,energy management platform and energy value sharing,and its application scenarios in new urbans are described in detail.

Faced with a series of challenges brought about by largescale urbanization,the development of new urban energy systems is the key to solving problems.We hope this paper can provide references for the future research of integrated energy systems for new urbans and promote the continued development of new urban energy systems.

Acknowledgements

This work was supported by National Key R&D Program of China (No.2018YFB0905000),Science and Technology Project of SGCC (SGTJDK00DWJS1800232),National Natural Science Foundation of China (51977141),State Grid Corporation of China project:“Research on Construction Technology of Integrated Energy System for Urban Multifunctional Groups” (SGTJJY00GHJS1900040).

Reference