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This paper proposes a control method for eliminating direct current (DC) flux from the isolation transformer of a customer service device to avoid magnetic saturation. The method is characterised by injecting zero compensation voltage during a designed time. The period during which no compensation voltage is injected is minimised by adjusting the normal compensation time in the initial stage. For a customer service device, such as a dynamic voltage restorer, the reverse turn-off voltage will introduce extra initial flux. The calculation process based on a trigonometric function also takes into account the effects of the initial flux. The experimental results verify the proposed method to prevent DC flux to the isolation transformer.

Sang, Z.-x.; Fang, R.-c.; Du, Z.; Yang, D.-j.; Yan, J., and Lei, H., 2020. The power planning of interacted and interconnected microgrid in pelagic clustering islands based on energy storage vessel transport route. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 172–177. Coconut Creek (Florida), ISSN 0749-0208.There is a lack of effective liaison among pelagic islands; however, an interconnection mode by submarine cables is not feasible or economical. In this paper, we propose to replace some of submarine cables with energy storage vessel (ESV) routes and establish a hybrid power transmission network based integrated energy system of pelagic clustering islands. First, an ESV route was modeled to analyze the transmission efficiency and cost. Then, a hybrid power transmission network planning model of the island integrated energy system was proposed based on multiscene generation and scene clustering. The objective function was the minimum overall cost considering the additional power supply cost under extreme weather scenario. The model was optimized by chaotic gravitational search algorithm. The feasibility and effectiveness of the proposed method are verified through simulation results.

Sang, Z.; Huang, J.; He, J.; Fang, R.; Yan, J., and Lei, H., 2020. The integrated energy system with multiple resources integration in future distribution network of pelagic clustering islands. In: Yang, D.F. and Wang, H. (eds.), Recent Advances in Marine Geology and Environmental Oceanography. Journal of Coastal Research, Special Issue No. 108, pp. 42–47. Coconut Creek (Florida), ISSN 0749-0208.In the overall strategy of national security, the pelagic clustering islands have a special geostrategic significance as an important fulcrum and platform to safeguard national coastal defense and maritime rights and interests. Reliable energy supply is the artery of the development and construction of the pelagic clustering islands. Still, the current research is mostly aimed at the offshore islands, lacking relevant theories and methods for the pelagic clustering islands. Therefore, the current situation of the island grid research, with its limitations and defects when applied to the pelagic clustering islands, are inquired and analyzed in the paper firstly. Furthermore, an integrated energy system (IES) as a future distribution network of pelagic islands is proposed for the purpose of taking full advantage of the abundant renewable energy to optimize the configuration of multiple resources of the islands as a whole. The IES breaks the isolated development pattern of island grid, taking the islands as a whole, interconnected through the originality energy storage vessels (ESVs). Finally, the key technologies required to construct the IES of pelagic islands are summarized, and the design of ESVs as well as the case study are given in order to provide a reference for the development and construction of pelagic clustering islands in China.

The current research on health index for power grid in integrated energy system is mainly focused on single equipment components, which includes the high voltage equipment with high monomer value and a large number of low voltage power distribution equipment, rather than the power system network. Furthermore, those research includes qualitative evaluation and simple calculation model. This paper has carried out the research of distribution network health index theory and its application. The concept and research status of the health index of equipment were summarized. The definition, classification method and model of distribution network health index were proposed.

With the opening of electricity market and the popularization of residential intelligent home, the design and implementation of demand response (DR) projects for large-scale residents to participate in grid interaction will be one of the key points for the operation optimization of electricity retailers. In view of decision-making of the electricity retailer considering residential DR, the characteristics of residential load were analyzed in detail, and then a decision model of the electricity retailer in day-ahead market was established based on potential game, aiming at maximizing its profits with the premise no increasing of the residential electricity cost after DR. Therefore, in order to solve the strategies iterative problems with the large-scale residential players, a distributed parallel iterative algorithm was put forward, which could coordinate strategies updating of residential players via their community agents, and it can protect the residential users’ interests as well as effectively reduce the cost of purchasing electricity and the peak load of the residents.

There are many factors affecting the cost of transformer substation project. The project cost difference is large and the data is discrete. It brings great difficulties to the classification analysis, index preparation and control management of project cost. Based on the project division of transformer substation project, this paper analyzes and identifies the main factors affecting the construction cost of transformer substation project, and uses the Random Forest model to measure 25 of the influencing factors, selects the key influencing factors to provide reference for the cost prediction of transformer substation project.

As the key enablers for future distribution network, the research about fault characteristic on energy router have potential to improve the operational strategies on the interaction and interconnection for micro grid. By studying the operational principles and strategies of fault characteristic of pole-to-ground fault on DC ports of full bridge circuit, the DC output voltage and current of the DC ports based on the resistor-inductor-capacitor (R-L-C) impedance of the full bridge circuit are analyzed, and the formulas on the voltage and current are derived. The influences affected by the variation of energy router operation status are recorded and discussed. Based on the formula derivation, the fault characteristic of the proposed algorithm and control strategies are validated through the numerical simulation in Saber environment.

The short-circuit fault of electric vehicle charging facility based on the DC distribution network and energy router will lead a R-L-C resonant under-damped response. The theoretical deduction on R-L-C resonant under-damped response about fault voltage and current is made to analyze the effects of key influence factors and relevant system parameters. The simulation verified the validity of fault characteristics on resonant under-damped short-circuit current and capacitor voltage, which also indicated the relationship between fault characteristics and basic parameters of energy router employed in electric vehicle charging facility.

As a result of large-scale electric vehicles starting charging at a station, power quality problems, such as voltage sags, will occur in the power grid. Based on this, a custom power device called Dynamic Voltage Restorer (DVR) is proposed to be connected to the electric vehicle charging station to deal with power quality problems. Considering that the filter capacitor can be set at different locations of DVR, i.e. parallel connection at converter side, line side and load side, this paper compares and analyses the mathematical models of three different topologies of DVR, and points out that the disturbance suppression ability of the topology of filter capacitor parallel on load side is relatively strongest, which is more suitable for the application of electric vehicle charging station.

With the progress of automation control technology, residential buildings become more and more intelligent. Home energy management in active distribution power grid connecting renewable energy and electric vehicle has received increasing interest. In this paper, typical structures about the smart home energy management system (SHEMS) is revealed. To reduce the customer electricity bill, an optimal strategy of SHEMS is proposed. The results from simulation show to us that the proposed strategy gives people who live in smart home a more economical and comfortable life.

The multi-level cascade converter is composed of H-bridge module in series. An improved 15-level hybrid cascade converter based on DC energy storage of electric vehicle can be obtained by changing the ratio of DC energy storage to supply voltage from 1:1:1 to 4:2:1 of the traditional cascaded 7-level converter cascaded by three H-bridge modules. In this paper, the modulation strategy of the 15 level hybrid cascade converter is studied, and a new algorithm for the switching angle of the multilevel converter powered by DC energy storage device for electric vehicle is proposed. Based on Saber simulation software, three different modulation strategies, stepped-wave modulation, PWM and partial PWM, are applied to verify and compare. Finally, the simulation results of total harmonic distortion, low-order harmonic component and switching loss of the converter based on the output voltage without any filter are compared, and the related modulation strategies are discussed.

In order to better study the characteristics of energy internet of pelagic island, this paper summarizes the latest research progress of energy internet, divides the research of energy internet into mainland energy internet and island energy internet, and consider that island energy internet should include two core networks of electric energy and thermal energy. Based on the study of the structure and control strategy of core hardware equipment including energy router, energy switch and energy interface, a three-section structure of island energy internet based on these three core hardware devices is proposed to optimize the current research structure of energy internet. With the geographical location, the optimization on generation of wind power, solar power and other renewable energy on resource island is applied with multiple objective particle swarm optimization (MOPSO). The capacity on various sources including battery and fresh water of energy exchange vessel optimized. Finally, the case study about pelagic islands indicated the feasibility of pelagic island energy internet. Finally, the structure of an island energy internet is built.

According to the characteristics and development trend of microgrid, instead of being the pure load, demand-side is treated as a kind of possible power supply (equivalent effect of reduction of the load) which can actively participate in the planning and operation in microgrid. An integrated resources planning model considering direct load control (one of demand responses) in microgrid was proposed. The validity of the proposed model was proved. It can be achieved to minimize the total cost of system planning by using demand response to actively participate in the planning. Depth discussions for the case were done to give comparative analysis of different control strategies, parameters and costs and more planning proposals were given.

The integration of renewable energy resources and storage systems makes power delivery route reconstruction after the N-1 fault taking place more complicated. To solve the calculation problem of smart grid power transfer capability, the time-varying characteristics of renewable energy resources and storage systems were analyzed. Based on this, an N-1 recovery model was proposed on the base of the transfer capability index. Through making the calculation formula of the transfer capability index linear and adopting the artificial intelligence (AI) optimal algorithm based on topology simplification, the operation modes of the power grid, new energy generations and new energy storage systems can be optimized and the maximum power transfer capability of the grid can be achieved.

High penetration of distributed renewable energy is the trend of future power and energy systems. Under the background of retail electricity market reform, retail price mechanism is of great significance to facilitate large-scale integration and consumption of user-side renewable energies. Considering the adoption of renewable energy is essentially the diffusion process of technological innovation, we presented an evaluation method for measuring the diffusion capability of distributed photovoltaic with the retail price mechanism. Firstly, based on the residential double-step tariff structure, the decision models were proposed for energy transactions between retailers and customers using Ramsey pricing theory. Secondly, by introducing the methodology of system dynamics, the market feedback mechanism between the electricity price design and the integration capacity of distributed photovoltaic was analyzed, thus the evolutionary model of distributed photovoltaic dynamic diffusion under the price policy was established. Finally, the criterion of stable diffusion of distributed photovoltaic based on Lyapunov function was developed in this paper.

In order to reduce the investment waste caused by independent planning of wind power, thermal power and power grid in high penetration wind power system, and promote wind power consumption, a new hybrid game planning method for wind fire power grid is proposed. Firstly, combined with renewable energy quota system and green certificate trading mechanism, the game relationship of generation network under high penetration rate is analyzed. Then, a two-stage planning model including master-slave game between network sources and cooperative game of wind power generation is established with grid expansion scheme and wind power capacity as decision variables, and a profit distribution method considering economic and environmental gains of both partners is proposed.

The energy router composed of double active bridge (DAB) can interconnect multiple voltage level AC distribution network through DC lines to form AC/DC hybrid distribution network. The fault types of the system are diverse and the fault characteristics are complex. This paper studies the fault characteristics of the system in detail. The single-phase grounding fault of AC network side and single-phase grounding fault of AC valve side occurred in the system. This paper explored the impact of the AC side of the system after the above failure, and make a detailed comparative analysis. The results show that DAB can isolate the influence of AC side fault, and provide theoretical basis for the selection of grounding mode and the design of protection system for AC/DC hybrid distribution network.

Because of the situations that the interconnection among multi distributed energy system (DES) and interaction among electric, heating and cooling system are not given full consideration, optimal planning of energy internet near user side based on bi-level programming is studied in this paper. First, schematic structure along with mathematic models of each unit is proposed and load characteristic is analyzed. Considering the interconnection of multiple energy as well as multiple distributed system and the combined dispatch of multi energy flow, a bi-level programming model is then presented. The minimum of total annual cost is the objective of upper model whose decision variables are the capacity of each energy unit and minimum annual operating cost is the lower model’s objective whose decision variables are the output of all energy units. Then, the elitist strategy genetic algorithm is employed to solve the upper model, and branch and bound algorithm is applied to optimizing lower model. The simulation results indicate that the proposed planning method of energy internet is effective, multiple energy flow interaction and multiple energy router interconnection are more economic than traditional combined cooling heating and electricity (CCHP) and can alleviate the mismatch of heat-to-electricity ratio between gas turbine and loads, and the multiple energy networks by which DES are interconnected contributes to higher economic benefits than single electric or heating network.

With the gradual emphasis on the development and utilization of islands, the energy supply problem of islands far away from land-based has become increasingly prominent. Based on the traditional single energy acquisition method, this paper establishes an island independent energy cycle system with high reliability power exchange ship as the main part, tidal energy and photovoltaic power generation as the auxiliary. It has opened up an effective way to meet the needs of military life and production on the island.

In order to promote all types of energy utilization, interaction between supply and demand as well as efficient operation, a new generation of energy systems which treats the electricity grid as the core came into being. Unlike traditional power system, the electricity network and gas network in the new generation of energy systems are closely linked through gas-fired units, and influence each other. Therefore, to ensure the safe operation of the future electricity network and natural gas network, the integrated framework for generation, electricity network and gas network expansion planning need to be carried out. Under the premise of meeting the electricity network and gas network safe operation constraints, we propose a multi-stage planning model for the combined generation, electricity network and gas network, in which investment cost and operating cost of the combined system are minimized. Combined generation, electricity network and gas network expansion planning is a large-scale, high-dimensional, non-convex and nonlinear optimization problem, which is difficult to solve. To solve this problem, we propose an incremental piecewise linear method to convert the original model into a large-scale mixed-integer linear optimization problem, allowing the use of sophisticated mathematical optimization method to quickly obtain the optimal solution.

When planning the power grid, it is necessary to obtain the optimal decision scheme according to the market behavior of different stakeholders. In this paper, the virtual game player "nature" is introduced to realize the deep integration of game theory and robust optimization, and a source network load collaborative planning method considering uncertainty and multi-agent game is proposed. Firstly, the planning decision-making models of different stakeholders of DG investment operators, power grid investment operators and power users are constructed respectively; then, the static game behavior between distributed generation (DG) investment operators and power grid investment operators is analyzed according to the transmission relationship of the three; at the same time, robust optimization is used to deal with DG. In this paper, we introduce the virtual game player "nature" to study the dynamic game behavior between the virtual game player and the power grid investment operator. On this basis, the dynamic static joint game planning model is proposed.

This paper takes the AC / DC interconnected system based on DAB energy router as the research object, analyzes the fault characteristics of AC side and DC side in detail, compares and analyzes the influence of DAB energy router on fault characteristics in the system with different grounding methods of DC capacitor midpoint in converter station, and explores the mechanism of interaction between AC and DC sides. The effect of dab on the interaction of AC and DC side faults under different fault types and capacitor neutral grounding modes is analyzed. Finally, the method of post fault system partition and fault analysis is proposed, which lays a theoretical foundation for fault detection and rapid location of AC / DC hybrid distribution system, and provides theoretical support for system equipment selection.

Compared with the direct access to the main power grid and diesel generators, this paper puts forward the scheme of using electric ships to shuttle between islands to transport electric energy, analyzes the limitations and defects of its application in offshore islands; and then puts forward a comprehensive energy supply system of offshore islands. The comprehensive energy supply system can make full use of the rich renewable energy of the islands, and realize the optimal allocation of the overall resources of the islands. At the same time, the energy supply system can break the isolated development pattern of island power grid and connect the island group power exchange ship. This paper analyzes the connotation and characteristics of the system, puts forward the key technology for building the integrated energy supply system of ocean island group, and gives the design and operation analysis example of power exchange ship.

The scenario generation method suitable for solar and wind power obeying any probability distribution and the concept of cluster was brought up to improve the consumption ability of distribution network of medium and high voltage for renewable energy. The planning model of renewable energy access was established based on cluster partition considering the investments and power generation interests of power producers as well as the power match degree within clusters. The Benders decomposition method was employed to solve the planning problem, and the complicated planning problem of renewable energy generation is decomposed into the decomposed investment operation model. Therefore, the access planning of renewable energy taking account of the solar and wind power was realized.

The distribution energy router (DER) is the core of the interacted and interconnected micro grid in future distribution network, which fully meets the needs of the ubiquitous power internet of things (IOT) based future distribution network. The reliability of micro grid which applies the DER is highly related to its cascaded full-bridge converters. With the redundant full-bridge converters and IOT technology, the DER can stand the component failures, hence improve the robustness of the DER as well as the future interacted and interconnected micro grid. For a ubiquitous power IOT technology based DER, this paper proposes a redundancy design for fault tolerant strategy. Several redundancy designs are discussed in detail with operational principles and control strategies. The proposed redundancy design is implemented on the power circuit of one phase for DER consists of a nine-level cascaded full-bridge converter in Saber simulation platform, and the simulation results prove that the redundancy design can minimize the customer’s power interrupt time and the consequent damages to the system.

With the gradual development of bidirectional interacted future distribution network, it is necessary to enter distributed clean power sources with various characteristics, including wind turbine and solar panel. Traditional centralized control has difficulties to fulfill the demands of future distribution networks for safe, stable, and efficient operation. Aiming at the constrained power allocation problem widely studied in smart grid, with the cooperative control algorithm of continuous multi-agent system, this paper proposed a distributed optimization allocation strategy, which is free by the initial state. The proposed distributed algorithm implements parameterization by adding auxiliary variables. In the iterative process, the algorithm only needs to know the state of the distributed power supply of the neighbor, and finally solve the global optimal solution of the system. The simulations prove that the proposed scheme can effectively improve the economic dispatch performance. Furthermore, comparing to the existing algorithm, the proposed algorithm achieves faster optimal solution.

On the basis of analyzing the logical structure of grid information model (GIM), a modeling method of GIM using the set theory is proposed for the substations. By studying the coupling principle of power flow and information flow, the GIM was defined as the interconnection between the set of physical objects and the set of information objects. Then, the GIM was decomposed into the power subsystem and load subsystem, which were described from the aspects of input, output, state changes and network structure. Under the constraints of the existing power grid network, subsystems were connected in accordance with rules from different perspectives to form the complete GIM system.

Dynamic voltage restorers have been examined to compensate voltage sags in distribution networks to avoid production losses, especially in the Premium Power Park(PPP). If the compensation strategy can be optimized to extend the compensation time as long as possible, then the application of DVR in power system can be more popular, and the intelligent level of the power grid can also be effectively improved. As a result, this paper proposed a time-maximized compensation strategy to achieve a maximum compensation time based on the energy-minimized compensation strategy. According to the formula of dc-link discharge, the calculating formula of optimum phase angle jump of load voltage is deduced, and the principle and characteristic of the compensation strategy are analyzed respectively for single-phase and three-phase system. Simulation and experimental results are presented to confirm the effectiveness of the proposed compensation strategy.

As a prospective electric component in the power grid, the reliability of electronic power transformer (EPT) affects the security of the power grid. The fault tolerant strategy about the redundancy control can improve the reliability of EPT, hence secure the power grid. This paper presents the design of fault tolerant strategy on a cascaded multi-level converter (CMLC) based EPT. The operational principle and control scheme for the redundancy control are introduced and analyzed. The proposed fault tolerant strategies are implemented on a single phase nine-level CMLC based EPT in Saber simulation platform. Simulation is illustrated to verify the performance of the proposed fault tolerant design with redundancy control.

Dynamic Voltage Restorer (DVR), as a device of voltage sag compensation, demands fast transient response, and the disturbance of source voltage is a main impact on control performance. The DVR control strategy based on discrete state space will enhance control bandwidth and stability. However, for the discrete space control system, the number of parameters is relatively more which will lead to a complicated design process. To solve this problem, this paper proposed a control parameter design method based on the idea of virtual resistor. Firstly, by means of state feedback control, an adjustable virtual resistor can be series in filter inductor. According to the requirements of steady-state error, phase margin and Routh's criterion in w domain, the variation regions of PI parameters and virtual resistance can be solved by a step-by-step method, and then the appropriate control parameters can be selected. Experimental results from a digital signal processor-based system are included to support theoretical analysis.

In the integrated energy service system, distribution network shall manage to settle its own power balance issue. The market competition that grid corporations open the sale services of electricity to the society and interruptible load is encouraged to participate in ancillary services becomes a development tendency. At this time, a corresponding control strategy was required to instruct interruptible loads scheduling. In this paper, a control strategy using discrete Fourier transform is proposed in combination with the requirements of the electricity market. Under the constraint of the new evaluation criteria, different types of resident interruptible loads were on-demand dispatched in different periods. The root mean square error (RMSE) of the feeder daily forecast could improves the power load control capability of distribution network as well as the quality of power supply.

The development of HVDC technology makes it possible to build a multistage HVDC distribution power system. Firstly, the basic principles and main constraints of voltage level sequence for DC distribution are analyzed in detail. Based on the analysis of the DC distribution capacity of each voltage level, a series of voltage levels of DC distribution network with high voltage, medium voltage, low voltage and ultra-low voltage are proposed, taking the load demand as the basic foundation, considering the manufacturing level of relevant equipment and the need of power grid structure optimization. Finally, the specific voltage level sequence of DC distribution network is proposed.

The DC distribution transformer for electric vehicle charging facility is the key equipment in future active distribution power system, whose reliability relates to robust and reliable operation of distribution power system. With redundancy modules, reliability of the DC distribution transformer is increased as well as the cost. The reliability with different control methods for general DC distribution transformer is analyzed and compared, and an objective function is presented for optimized design. Solutions for minimum value of the function under different circumstances are discussed, and the best scheme for balance between reliability and economy is obtained. Finally, an engineering application is analyzed. Suggested model and number of sub-modules is given, and validity and feasibility of the proposed method is verified.

With the development of DC power transmission technology, it is possible to develop a multilevel urban DC distribution system in integrated energy system. With the basic principle and main constraints of designing for DC distribution voltage level sequence, a sequence of voltage levels of DC distribution power system in different voltage levels is proposed, and the power supply capability, economy evaluation and reliability on voltage level sequence of multilevel DC distribution is discussed in detail through a specific example.

Considering the negative impact of large-scale application of Electric Vehicles (EVs) on power network planning and operation, this paper proposes a coordinated charging strategy for EVs based on valley load tracking, aiming at reducing load fluctuation. By optimizing the charging sequence of EVs, the valley period of the daily load curve tends to be smooth, which plays a better role in filling the valley and reduces the peak-valley difference. Finally, an example is analyzed by Monte Carlo simulation, which proves that the proposed coordinated charging strategy is efficient and practical.

The large investment of electric vehicles and distributed generation has affected the stable operation of distribution network. At the same time, the construction of charging station of electric vehicles not only causes the burden of electric power network, but also the burden of transportation network. How to ensure the stability and economics of distribution network has become an urgent problem. Based on this background, this paper proposes a multi-objective collaborative planning method for distribution network, which considers the charging station of electric vehicle and the distributed generation. In order to find the optimal planning scheme, we use an improved NSGA-II algorithm. Finally, the simulation analysis of the case of IEEE 33-bus shows that the proposed planning method not only ensures the stability and economics of distribution network, but also fully saves the average waiting time of charging users of electric vehicles and improves the traffic satisfaction.

The analysis on fault characteristic of Distribution Electronic Power Transformer (D-EPT) can help design its operation and protection scheme, hence improve the reliability of the D-EPT as well as the distribution power grid. The DC pole-to-pole short-circuit fault at DC-Link is analyzed with R-L-C resonant mode and free-wheeling mode, and the theoretical analysis on the short-circuit voltage and current is based on several influence factors and relevant system parameters, which indicates that the fault characteristics are related to the configuration, operation and system parameters of D-EPT.