Guanyu Song

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.

An interactive operation strategy for microgrid cooperated with distribution system based on demand response

Microgrid is an autonomous system which can achieve self-control, self-protection and self-management. It will not only comprehensively exploit the advantages of renewable energy sources (RES) in environment protection and energy conservation, but also overcome its intermittency and volatility, reduce the impact to distribution system when the distributed energy resources (DERs) are connected to the distribution network as microgrids. Deployment of microgrids can facilitate efficient demand side management and integration of RESs at the distribution level. This paper proposed an interactive operation strategy for microgrid cooperated with distribution system based on demand response. In the present paper, a day-ahead operation optimization model of microgrid on account of electricity purchasing cost, electricity selling benefits, generation cost of distributed generations (DGs) is proposed. And then an interaction model in which the microgrid responds to the interaction demand through adjusting the scheduling plan aiming at dealing with the excessive peak load of distribution system is presented. We analyzed the relationship between interaction capacity and interaction cost via sensitivity analysis and finally achieved the interaction between the microgrid and the distribution system. The simulation results in a microgrid, which has a wind turbine (WT), photovoltaic (PV) system, energy storage system (ESS) and loads, demonstrate the effectiveness of the proposed method.

Matrix exponential based electromagnetic transients simulation algorithm with Krylov subspace approximation and accurate dense output

The ever-increasing scale of system interconnection and diverse dynamic time constants of power equipment pose challenges to power system electromagnetic transients simulation algorithm. In this paper, an advanced numerical integration method based on matrix exponential operator is proposed. Krylov subspace approximation is utilized to effectively reduce the problem dimension, and an accurate dense output formula is established to enable the method adopting larger simulation step size and revealing higher frequency dynamic details simultaneously. Accuracy, numerical stability and computation efficiency is demonstrated through numerical case studies.

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.

EMTP-type realization of model reduction algorithms for transient simulation of distribution networks

Model reduction is a popular trend in large-scale system simulations. It is also an effective way to improve the efficiency of distribution system simulations. In this paper, the realization of state-space-based model reduction methods in EMTP-type programs is presented. The state-space model of linear time-invariant distribution network is reduced and simulated with the detailed nodal model in EMTP-type programs. The combined state-space nodal analysis algorithm is adopted as the interface between the state-space models and the nodal models. Simulations are performed to show the feasibility and validity of the proposed method, and the improvement in efficiency with the application of model reduction.

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.

Adaptive DAE solving algorithm for power system transient simulation via matrix exponential operator

The ever-increasing scale of system interconnection and diverse dynamic time constants of power equipment pose challenges to power system transient simulation algorithms. In this paper, an adaptive numerical integration method for DAE systems based on matrix exponential operator is presented. Krylov subspace technique is utilized to effectively reduce the problem dimension. A novel step adaption scheme is established to enable the method adjusting the computation step size according to error budget while maintaining the output step size unchanged. Acceleration is accomplished without perceived degradation in the simulation results. Numerical performance and computation efficiency is demonstrated through numerical case studies.

A fast optimization method for the distribution system with energy storage based on conic programming

Application of energy storage system (ESS) has been a chance and challenge to distribution system operation and integration of renewable energy sources (RESs). A conic programming (CP) based method is proposed for the optimization of distribution system with ESS in this paper. Firstly, the operation optimization model considering the state of charge (SOC) of ESS is built to minimize the active power losses of distribution system with distributed generation (DG). Equivalent CP model is conversed based on the initial model as format required, which can be solved by some mature optimization tools. Finally, case studies show the feasibility as well as effectiveness of the proposed method.

Dynamic time-domain simulation and analysis of medium-low voltage microgrid

Considering different application scenarios and questions to be solved, electromagnetic transient simulation and transient stability simulation are rarely performed simultaneously for the calculation of traditional bulk power system, which are quite different from element modeling to simulation algorithm. But its not true for the analysis and calculation of microgrid and active distribution system. Its a common question for the user to choose a proper simulation tool. Meanwhile, the two simulation results should be consistent with each other intrinsically due to the same physical system. In this paper, the difference and consistency of the two type simulations is set forth in detail. They are applied to a typical microgrid test case respectively using DIgSILENT and Matlab/SimPowerSystems, and detailed comparisons are provided to verify their consistency and difference. Its helpful to understand the various transient processes and make a more reasonable choice for the related research. At the same time, the application guidance for the two type simulations is drawn.