Studies And Application Of Space-Time Coordinated Decision-Making Of Bulk Power System Restoration

With the arrival of a new round of energy revolution and the proceeding of "two-replacement",the role of power grid in energy transportation and allocation is highlighted. The safe and stable operation of power grid is of great significance to guarantee the energy supply, maintain social stability and the order of daily life.However, in recent years, the external environment of power grid operation has deteriorated because of the increase of extreme nature disasters. Besides, since the configuration and dynamic characteristics of power grid become more complex with AC/DC interconnection and the integration of large-scale renewable energies, power system security defense will be exposed to new challenges. Against this background, it is particularly necessary to strengthen the power emergency management thereby improve the ability of utilities to deal with large-scale blackout. In order to achieve rapid and secure restoration after a large-scale blackout, studies on the technical issues in power system restoration procedure is required and a scientific and comprehensive restoration plan must be generated.Different from local outages, the large-scale blackout caused by cascading failure is a more extreme scenario with high risk and small probability. In restoration procedure,the usual strategy is to use the internal black-start resources that distributed in different regions and gradually expand the restored range in a "bottom-up" manner. But taking into account the vertical management structure of China's power grid and the lack of black-start resources in some provinces in the north, the restoration would be more efficient if making full use of the ultra-high voltage backbone system and conducting the restoration in a "top-down" manner. "Top-down" restoration has large spatial-temporal span and needs collaboration of multi-level and multi-regional operators,which leads to complex coordination problems. Meanwhile, the operation risk will be higher, more uncertainties will be faced, and restoration decision-making will be more difficult.The dissertation focus on the coordination control and decision-making problems in the process of "top-down" bulk power system restoration (BPSR). The study proceeds both in theoretical level and engineering level based on a comprehensive review of the existing works. First, taking the improvement of restoration efficiency and guarantee of restoration safety as the purpose, a general control framework of BPSR is established. Then, based on this framework, associated control strategies,coordination mechanisms and decision methods are proposed. To generate network and load restoration plans, restoration optimization models and algorithms are designed by using combinatorial optimization theory, graph theory, multi-objective decision theory,etc. Furthermore, based on the theoretical achievements, a software system is developed according to the requirement of realistic engineering demand. Main contributions and innovations of the dissertation are described as follows:1) A space-time coordinated control strategy of BPSR is proposed. Considering the hierarchical characteristic, multi-participation and uncertainty of "top-down" BPSR,a wide-area coordination mechanism and a sequential control approach of BPSR are proposed. The restoration decision-making problem are decomposed both in space dimension and time dimension. By decoupling the restoration control process and triggering the decision process dynamically, multi-level parallel restoration control can be achieved and the uncertain events can be handled effectively. Then, from the decision-making level, the optimization model of each sub-problem is built and associated algorithms are given. By calling and solving the models flexibly in a online environment, specific restoration plans can be generated dynamically and a space-time coordinated restoration control process can be achieved. A case study of Shandong Power System in China verifies the efficacy of the method.2) A hierarchical collaborative optimization method of transmission network restoration is proposed. Based on the proposed space-time coordinated control strategy,in order to obtain the global optimal network restoration plan,a bi-level optimization model of transmission network restoration is built. Different operators' preferences and multiple security constraints are considered in this model. Optimizations of backbone system restoration, local network restoration and generators start-up are handled as a whole. In order to solve the problem rapidly, a mixed solution strategy is proposed. The path search, power flow calculation and voltage optimization are nested into the global search process of upper-level decision variables. Collaborative restoration optimization of both three layers can be achieved with acceptable computation cost. A case study of Shandong Power System in China verifies the efficacy of the method.3) A source-load coordinated restoration optimization method with considering wind farm restoration is proposed. Based on the proposed space-time coordinated control strategy, a source-load coordinated optimization model is built. Optimization of load restoration, wind farm restoration and unit output are considered simultaneously in this model. The objectives are to maximize the amount of load pick-up and minimize the total operation time of each step. Transient frequency security constraint, generator output constraint, system reserve constraint and power flow constraint are considered in this model. By using the lexicographic method and linear approximation method of AC power flows, the model can be converted to a mixed integer linear programming problem, which can dramatically improve the computation efficiency. The case studies of IEEE 118 bus system and Shandong Power System in China verify the efficacy of the method.4) A power system restoration decision-aid and simulation system is developed.The system can provide the functions of full-process restoration decision support,transient and steady state security check, interactive production and management of restoration plan, dispatching order automatic generation and simulation. In an offline environment, it can help the dispatcher produce restoration plans based on the proposed decoupling control strategy and carry out a simulation of the restoration process. In an online environment, it can receive real-time system data from EMS, recognize the blackout scenario automatically, generate and output the restoration plan based on different restoration targets.