Combined with the actual problems of the medium-voltage (MV) AC distribution network in Songshan Lake area of Dongguan, the technical scheme of an MVAC distribution network project for demonstration with HVDC-flexible interconnection is studied. The main wiring mode, connection transformer configuration and grounding mode are demonstrated. The modular multi-level converter and power electronic DC transformer in the system are preliminarily designed, and the technical requirements for key equipment are determined. The system overcurrent and overvoltage characteristics are analyzed by simulation, thus overcurrent tolerance and insulation coordination requirements being put forward. The overall control architecture and protection configuration of the system are designed, and the control and protection strategy of the system is defined. The new main connection topology proposed in this article is used in a practical demonstration project. The scheme of high-ripple design for compact equipment is adopted and the AC fault coordination response strategy is proposed. All those new technologies are demonstrated and verified with simulation, which provide reference for follow-up related research and engineering practice.

Objectives To address the operational security issues in the new-type distribution network caused by the high-penetration integration of renewable energy, this paper proposes a coordinated optimization method for intelligent soft open points and multiple types of shared energy storage, by integrating these flexible devices while considering the risk of flexibility deficiency. Methods Firstly, the flexible regulation mechanism of flexible resources, including intelligent soft open points and multiple types of shared energy storage, is elaborated, and a flexibility deficiency risk indicator based on conditional value at risk is constructed. Secondly, considering flexibility, safety, and economy, a coordinated optimization model for intelligent soft open points and multiple types of shared energy storage in the new-type distribution network is established. Finally, the proposed method is tested on an improved IEEE 33-bus system to verify its effectiveness. Results The proposed coordinated optimization method for intelligent soft open points and multiple types of shared energy storage, considering flexibility deficiency risk, can fully cope with the volatility of renewable energy output and the randomness of load demand, effectively reduce active power loss of the new-type distribution network, and enhance its flexibility, safety, and economy. Conclusions The proposed flexibility optimization model provides significant practical reference value for flexible scheduling of new-type distribution systems.

Soft open point （SOP） can provide real-time power flow control, fast fault self-healing and feeder load balancing, and has been widely used in distribution networks. However, grid voltage dips （GVD） are typical large disturbance conditions, and the stable operation mechanism of distribution network SOP under these conditions cannot be analyzed through small signal methods. Therefore, the mixed potential theory （MPT） is used to study the stability of SOP under GVD conditions, and the parameter optimization strategies and virtual capacitor control strategies are proposed. Firstly, a nonlinear average model of SOP is established. On this basis, the large signal stability criterion （LSSC） for SOP under GVD conditions is derived using MPT. In addition, in order to enhance the stability of the SOP system, parameter optimization strategies and control strategies for constructing virtual capacitors are proposed based on LSSC. Finally, the effectiveness of the above method is verified through MATLAB/Simulink time-domain simulation, namely: 1） based on LSSC, the stability of SOP under GVD can be effectively analyzed; 2） the system prameter optimization strategy based on LSSC and the construction of virtual capacitor control strategy can effectively improve the stable operation ability of the system under large disturbance conditions.

Large scale integration of intermittent distributed generation (DG) challenges the reliable and secure operation of distribution systems. Therefore, this paper proposes a two-stage robust scheduling method for flexible interconnected distribution systems considering energy storage and dynamic reconfiguration. Firstly, a two-stage robust scheduling model for flexible interconnected distribution systems is established, considering flexible distribution switches (FDSs), energy storage and dynamic reconfiguration. In the first stage, the network topologies and energy storage outputs are globally optimized considering their temporal correlation and day-ahead forecasting uncertainties of the DG outputs. In the second stage, the FDS power in each time slot is dispatched according to the decisions of the first stage and ultra-short-term DG forecast. Then, an improved column and constraint generation algorithm is adopted to solve the robust model, where an alternating direction process is used to accelerate the sub-problem. Finally, the effectiveness of the proposed robust scheduling model and algorithm is verified using the 33-node and 69-node distribution systems with promising results.

A large proportion of distributed generation and electric vehicles are connected to distribution station areas. This results in several problems, such as insufficient hosting capacity, unbalanced load rates, and out-of-limit voltage. The flexible interconnection of the station areas is an effective solution to these problems. This paper proposes a master-slave game planning model for the flexible interconnection of distribution station areas, considering economic and power supply capacities. The proposed model considers economic decision-making as the main player and power supply capacity decision-making as the subordinate player, jointly participating in the planning decision-making process. First, a power flow model of the substation area is established using a DC bus-segmented chain flexible interconnection structure. Subsequently, a planning model based on a master-slave game is established. The interconnection schemes and installed capacity of the interconnected devices are used as the main player strategy, the minimum annual comprehensive cost is the payment. The load apparent power of the substation areas is used as the subordinate player strategy, and the maximum power-supply capacity under N-0 security constraints is the payment. The power-flow constraints of the substation areas operation are considered in the model. The particle swarm optimization algorithm is used to solve this problem. Finally, an IEEE-33 node distribution network connected to a high proportion of photovoltaic power generation in the substation area is analyzed. The results show that the proposed model can balance the operational economy and power supply capacity of the system.

The increasing penetration of uncontrollable distributed generators (NDGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). Soft open point (SOP) can realize accurate power flow control and continuous voltage regulation. Centralized control strategies of SOP are difficult to meet the requirement of fast voltage and reactive power control because of the heavily computational and communicational burdens. Local voltage control based on the real-time measurements has a fast response to the frequent distributed generators (DGs) fluctuations. In this paper, an optimization method of local control strategy of SOP based on kriging metamodel is proposed. Taking minimum network losses as the objective function, the metamodel for local control of SOP is constructed based on the kriging methods. Then, the operation strategies of SOP are developed by calculating the optimal weighted vector based on real-time measurements. The proposed local voltage control strategies of SOP based on only local measurements can quickly response to the frequent DGs fluctuations and lighten the computation burdens with large networks. Case studies under different scenarios on the IEEE 33-node system are conducted to verify the effectiveness of the proposed method, and the results show that the proposed method can effectively solve the problems of voltage deviation and voltage fluctuation caused by high penetration of DGs.