Haoran Ji

Coordinated Control Method of Voltage and Reactive Power for Active Distribution Networks Based on Soft Open Point

The increasing penetration of distributed generators (DGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). The conventional voltage regulation devices limited by the physical constraints are difficult to meet the requirement of real-time voltage and VAR control (VVC) with high precision when DGs fluctuate frequently. However, soft open point (SOP), a flexible power electronic device, can be used as the continuous reactive power source to realize the fast voltage regulation. Considering the cooperation of SOP and multiple regulation devices, this paper proposes a coordinated VVC method based on SOP for ADNs. First, a time-series model of coordinated VVC is developed to minimize operation costs and eliminate voltage violations of ADNs. Then, by applying the linearization and conic relaxation, the original nonconvex mixed-integer nonlinear optimization model is converted into a mixed-integer second-order cone programming model which can be efficiently solved to meet the requirement of voltage regulation rapidity. Case studies are carried out on the IEEE 33-node system and IEEE 123-node system to illustrate the effectiveness of the proposed method.

Optimal operation of soft open points in active distribution networks under three-phase unbalanced conditions

The asymmetric integration of distributed generators (DGs) exacerbates the three-phase unbalanced condition in distribution systems. The serious unbalanced operation causes inefficient utilization of network assets and security risks in the system. Soft open point (SOP) is a flexible power electronic device which can achieve accurate active and reactive power flow control to balance the power flow among phases. This paper proposes an SOPs-based operation strategy for unbalanced active distribution networks. By regulating the operation of SOPs, the strategy can reduce power losses and simultaneously mitigate the three-phase unbalance of the upper-level grid. Semidefinite programming (SDP) relaxation is advocated to convert the original non-convex, nonlinear optimization model into an SDP formulation, which can be efficiently solved to meet the requirement of rapid adjustment. Case studies are conducted on the modified IEEE 33-node and IEEE 123-node distribution system to verify the effectiveness and efficiency of the proposed strategy.

A hybrid optimization algorithm for distribution network coordinated operation with SNOP based on simulated annealing and conic programming

Soft normally open point (SNOP) is a novel power electronic device installed in place of normally-open point. The application of SNOP will greatly promote the flexibility and controllability of distribution network. Considering the high investment of SNOP, both tie switch and SNOP should be taken into account in the coordinated operation problem of distribution network. Firstly, the optimization model for distribution network coordinated operation with SNOP and tie switch is proposed. Then, combining the simulated annealing method with conic programming, this paper proposes a hybrid optimization algorithm, involving simulated annealing method to obtain the switch states and conic programming to optimize the transmitted power of SNOP. This hybrid algorithm can solve the above large-scale mixed-integer nonlinear problem accurately and rapidly, while satisfying the demand of distribution network coordinated operation. Finally, the IEEE 69-node system is used to demonstrate the effectiveness of the proposed hybrid algorithm.

A fast modeling method of distribution system reconfiguration based on mixed-integer second-order cone programming

Network reconfiguration is a primary means of changing the operation mode of the distribution system with distributed generation. A model for the distribution system reconfiguration problem based on mixed-integer second-order cone programming is presented in this paper. Firstly, the network reconfiguration model is built to minimize the active power losses of distribution system with distributed generation. Then, some equivalent conversion and relaxation are presented to cast the initial mixed-integer nonlinear model above into a mixed-integer second-order cone model, which can be reliably and efficiently solved to global optimality by using the available commercial software. Finally, case studies on IEEE 33-node test feeder are conducted and the results demonstrate the validity as well as effectiveness of the proposed model.

An equivalent A-Stable dynamic simulation algorithm of active distribution networks based on the implicit projective method

The dynamic characteristics of active distribution networks (ADNs) need to be concerned if a large number of distributed generators are connected. A highly efficient and reliable simulation algorithm with good numerical stability is therefore essential for the stability analysis of ADNs. This paper proposes a novel dynamic simulation algorithm of ADNs based on the implicit projective method, which is a second order integration algorithm. The proposed method is an equivalent A-Stable method and the calculation efficiency is increased significantly compared with the traditional integration algorithms. It is especially suitable for the dynamic simulation and stability analysis of the ADNs with a large number of DGs. Case studies based on the IEEE 123-node test feeder show the feasibility and effectiveness of the proposed method, which is verified through the comparison with the commercial simulation tool DIgSI-LENT/PowerFactory and the traditional trapezoidal method.

A projective based dynamic simulation algorithm of active distribution networks

The dynamic characteristics of active distribution networks (ADNs) need to be concerned if a large number of distributed generators are connected. A highly efficient and reliable dynamic simulation algorithm is therefore essential for the stability analysis of ADNs. This paper proposes a novel dynamic simulation algorithm of ADNs based on the projective integration method, which is a second-order explicit integration algorithm. The proposed method greatly improves the numerical stability of the traditional explicit algorithms and increases the efficiency significantly at the same time. It is especially suitable for the dynamic simulation and stability analysis of the ADNs with a large number of DGs. Case studies based on the IEEE 123-node test feeder show the effectiveness and efficiency of the proposed method, which is verified through the comparison with the commercial simulation tool DIgSILENT/PowerFactory.