Being adaptive to the higher penetration of distributed energy sources in future distribution network, active distribution network(ADN)has become a new development trend with the characteristics of flexible network topology and strict demand for control and communication. Coordinate optimization system can realize the complementary utilization of multi-type controllable resources in active distribution network. In this paper, typical control structure and control modes of active distribution network coordinate control system in recent years are summarized, and the advantages and constraints of different structures are analyzed. System architecture and functions of the ADN coordinate optimization system are discussed based on the national 863 program “Key technologies and demonstration of ADN with renewable energy source” demonstration project located in Guiyang. The multidimensional and hierarchical optimization control structure of the demonstration project are highlighted together with the characteristic of source-load interaction. It is expected to provide some help for the follow-up coordinate control system research and active distribution network management.

In order to enhance the effect and performance of the active distribution network(AND)control, based on ADN Feeder Control Error theory, a distributed model predictive control method for ADN area coordinate control is proposed. Firstly, an autonomous area control model containing intermittent energy resources, load and storage units within the area are established to consider the short-term trend of power output and other forecasting information. Then distributed control method is proposed to solve the coupling issues of optimization targets among different areas, and realize the coordinate control among different areas. Online rolling optimization and real-time measurement feedback are used to achieve the overall optimal control with future forecasts, therefore the global optimization of the whole feeder is assured. Calculation simulation and comparison of the proposed control method with the traditional PI control verify the effectiveness of the proposed method.

Firstly, the characteristics of active distribution network(ADN), control resources and process control under various operating conditions are analyzed in this paper. In order to implement ADN process control in a variety of operating state, an active distribution network management system(ADMS)based on SCADA platform technology is designed. ADMS includes comprehensive operation and decision-making system, distribution automation system, active load management system, etc. Through information exchange, assist control and unified operation management of subsystems, the global optimization operation and regional coordinated operation control under grid connected status, fault location and fast recovery power supply operation control under fault status and the isolated network operation control of ADN under off-network status can be carried out in ADMS, and the loads under various operating conditions can be actively controlled and managed to meet the ADN operational requirements. ADMS operates reliablely in the experiment platform, and provides the reference for further study of ADMS.

The active management and control of active distribution network(ADN)involves the interactive participation of numerous users and various systems, which needs an unified common information model to maintain semantic uniformity of information and promote information integration from the metadata level. Considering the interaction difficulty among distribution automation subsystems caused by different information models, based on the ontology theory, a depth-limited mapping algorithm is proposed to efficiently achieve the automatic matching and mapping of heterogeneous information models. Meanwhile, a multi-level model verification tool is developed based on information schema, ontology model and topology rules to test the message format, information model and model quality of exchanged information, and filter out abnormal information. Tested by a study case with distributed generation, the proposed mapping algorithm and verification tool is verified effective, and can help maintain the consistency of interacted information and promote information integration of ADN.

The current characteristics at fault occurrence time in active distribution networks are studied, based on the principle of polarity check of current transformer, a fault location algorithm for active distribution network based on polarity check is proposed in view of network topology parameter of the distributed feeder automation. This algorithm checks the isonym end of topology polarity and wiring polarity in distribution network topology in the network topology and isonym end of polarity check, generates fault location topology coefficient matrix, and locates fault according to the current waveform of fault occurrence time and fault location topology coefficient matrix. An intelligent distribution terminal with intelligent distributed feeder automation based on the fault location algorithm is developed and is simulated and verified by RTDS, the results show that the fault location algorithm based on polarity check in active distribution network system can accurately and effectively carry out fault location without relying on voltage transformer.

With the high penetration of distributed generators(DGs), the radial structure of conventional distribution system will change to multi-terminal type. Influenced by the short-circuit current injected from distributed generators, fault location scheme for distribution network based on over current protection may be invalid. The fault current characteristics for active distribution network is investigated, and the relationship between the differences of current phase and fault location is found, a novel distributed feeder automation(FA)fault location method of active distribution network is presented. With this method, each terminal excutes distribued calculation according to the fault over-current and current phase of the terminal itself and neighboring terminal to achieve fault location. This method is applicable for complex active distribution network with multi-source, multi-branch and multi-contact, and it can locate the fault exactly since it does not depend on voltage and each terminal uses distributed decision. Finally, the feasibility and effectiveness of the proposed method is verified by DIgSILENT simulation analysis and engineering example.

To solve the problem of rising peak-valley load difference, the paper proposes an optimized flexible load control algorithm for air-conditioned room, electric water heater, and electric vehicle respectively from the view of customers. Based on time-of-use price, the algorithm completes the dual-objective optimization control considering constraints of economic benefits and user comfort, and can be realized through intelligent user terminals. In the algorithm, traditional load models for air-conditioner room and water-heater are improved, the multivariable thermodynamic process is separated into several independent univariate sub-processes, the model parameters are obtained by parametric regression from history data, therefore, random parameters are reduced in the algorithm. Optimized control considering two main kinds of electric vehicles, grid to vehicle(G2V)and vehicle to grid(V2G)by the algorithm are also studied; particle swarm optimization(PSO)algorithm is used to solve the optimal results. Finally, simulation result on MATLAB shows the advantage of the algorithm at economic benefits, user experience, and load shifting effect.

“Vehicle-network” interaction and benefit dispersion are not fully considered in the process of optimal allocation of battery swapping station(BSS). Aiming at this issue, a cooperative game based optimal capacity configuration model of BSS for electric vehicles(EVs)is proposed in this paper. Firstly, an operation sequence simulation model of BSS considering both charging and discharging process is proposed. Based on this, taking the maximized total net profit of alliance between BSS and distribution company(DISCO)as the objective, the safe operation of distribution network and the battery swapping needs of EV users as constraints, a cooperative game based optimal capacity configuration model of BSS is built. One profit distribution mechanism, equal modified disruption propensity(MDP)is introduced to distribute the profit of alliance reasonably in the model which decides the optimal numbers of batteries and chargers initially purchased and the optimal charging-discharging power of BSS in each time. Matlab toolbox YALMIP is employed to solve the proposed model which is a typical mixed integer nonlinear optimization problem. Finally, the feasibility and effectiveness of the proposed method are verified by an actual distribution network.

Water and gas resources are rich in the southwest of China, but it is difficult to connect distributed renewable resources, such as small hydropower(SHP)and combined cooling heating and power(CCHP), to the distribution network. To meet this challenge, the mathematical models and operation characteristics of SHP and CCHP are well studied, and a coordinated control and optimization approach for SHP and CCHP integrated into distribution network is proposed. In grid-connected mode, dispatched power is allocated between SHP and CCHP based on the equal increamental principle. In isolated mode, with the advantage of faster response speed, CCHP is used to assist SHP for primary frequency regulation when load fluactuation occurs. With overall considerations of cooling, heating and power load demand, not only the consumptive ability for distributed energy resources(DER)and overall operation economy is improved, but also it can provide support to distribution network with SHP or CCHP when abnormal condition or maintenance plan is encountered, and hence the reliability of power supply is improved.

In order to improve the peak-load regulation capability of distributed combined cooling heating and power(CCHP)system and adapt to the active control and management of active distribution network, a high efficient distributed CCHP system for active distribution network is presented. The system can run at a coordinated mode, in which the heat and power are decoupled and concerted, and the system can adjust the peak of power grid and reduce abandoned wind, water and light. Meanwhile, the system can deeply recycle the waste heat of the flue gas of the engine and greatly increase the energy efficiency. The flow chart and the operation mode of the system are described in detail, then the energy efficiency and the economy are evaluated. Simulation calculation is done in a specific case to analyze the operation characteristics of the system according to the heating, cooling and power load. Results show that the energy-conservation ratio of heating of the system is 13.4% and the annual energy-saving ratio is 6.6%. According to the current energy prices, the economy of the system is not much different from the conventional CCHP system. The influence of tariff on the economy of the system is relatively large. The thermoelectric ratio is normaly 1.5 to 2 times of the conventional CCHP system, at most 2 times bigger, which can alleviate the intergration pressure of power grid.

Combined cooling, heating and power(CCHP)system provides a good solution to save energy and reduce emission, owing to its high energy conversion efficiency. However, it is restricted by the fixed heat-electricity ratio, which means that it needs to be in good coordination with grid and supplementary combustion equipments to achieve the effect. To make CCHP multi-energy complementary system to achieve economic, energy saving, environmental protection effect, this paper proposes an optimal control strategy which considers both supply side and demand side. The method calculates the change of user load after flexible load participating in the demand response through the calculation of system fuzzy electricity price. Then, on this basis, the multi-energy complementary objective function is proposed to schedule the multi-energy output. The results of an example analysis show that CCHP optimization strategy can help to save economic costs, reduce greenhouse gas emissions and save primary energy consumption.

Depending on the time scale and the function, a three-layer hierarchical coordinated control framework of microgird is presented. The framework is applied to a typical micro-grid, which involves both the internal combustion engine CCHP system with the synchronous generator and other inverter distributed generation(DG)systems. For the typical micro-grid, specific coordinated control strategies are proposed. An additional controller based on status-followed control is utilized in the switching controller to ensure the smooth transition of the battery’s output power during the control mode switching. The simulation results of the micro-grid under different operating modes and mode switching processes show the effectiveness of the proposed coordinated control strategies. Furthermore, the effects of the CCHP system in the micro-grid coordinated control are also analyzed.