Studies On Transfer Capability Calculation And Available Transfer Capability Decision-making Under Static Constraints

As the transmission carrier of power electricity, transfer capability of power grid influences power generation and consummation level straightly, and it is an important index in power system operation all the while. When it serves as the carrier of power market, it also embodies the allowable dimension of commodity flow, thus represents different market signals. With the increase of power market competition degree, especially when various trading modes (pool, bilateral) coexist, the new concepts like existing transmission commitments, total transfer capability, available transfer capability (ATC) and its margin emergence. Transfer capability calculation and ATC decision-making has special meanings in keeping the security operation of power system, managing the transmission congestion, and in leading market tradings, which has become a very important studying and practice subject needing solved urgently.After reviewing the transfer capability study history, on the lay of power system operation dispatching, this paper studies transfer capability calculation method and ATC decision-making mechanism under static constraints roundly and deeply from more general view. The concept of transfer capability and the intension of ATC under power market are raveled more and the transfer capability integrated estimation system is formed preliminarily.Firstly, in transfer capability calculation study, aiming at different requirements, various calculation methods adapting different situations are improved and put forward, which have achieve well effects in actual engineering calculation. The main work and contribution are as follows: (1) On the basis of power specialty analysis of transmission components, the power circle is educed, and the carrying capabilities of transmission components are modified supposing constant voltage magnitude accordingly. So the rash advance of direct calculation method based on DC sensitivities is amended. The concision and fast speed of the method is preserved and the precision is improved, and also it achieves well effect in actual large power grid application. (2) Aiming at the influence brought by reactive power and voltage level, this paper takes various static constraints into account based on AC power flow, and amend the RPF based direct method in its step size and constraints disposing, also in the computation efficiency, which makes the practicality of direct calculation methods strides forward one step and accords with the fact more. (3) The generalized transfer capability linear programming model and corresponding algorithm are put forward based on DC power flow. The computation under arbitrary appointed source points set, sink points set and constraints can be carried out conveniencely using the proposed model, which embodies its generalization. For the model solution, the infeasible primal-dual path-following interior point method is put forward, in which the scale factor, barrier factor, the step size and sparseness rule are disposed effectively, thus the method achieves well effect in convenience, problem scale, solution speed, and robustness. (4) The optimal power flow (OPF) based method under AC power flow is studied. Aiming at current research, combining the optimization method in mathematics with transfer capability physical essence, a new transfer capability solution method with real power optimization and reactive power optimization solved alternately is put forward. It is found that under normal conditions, transfer capability depends on the change of voltage phase mainly, and the minimization of power loss is in conformity with the maximization of transfer capability. On the basis of this idea, the calculation can be divided into two sub-problems. One is the prediction of incremental transfer capability, which can be calculated by means of simplified linear non-loss equivalent circuit and solved through linear programming model and algorithm. The other, along with unceasing variation of transfer capability, a nonlinear reactive power optimization sub-problem with minimized power loss under certain real power operating mode is to be built to correct the influence of reactive power on transfer capability. The nonlinear optimization model is solved through the non-linear programming path-following interior point method. The rules of effective step size control and convergence criterion are given based on fore-mentioned theory analysis. The proposed method realizes the combination of physical rule reflected in transfer capability with optimization method in mathematics, adapts the operating rule of power system, simplifies the solution model, and makes the concept clearer. Examples demonstrate the new method can achieve similar calculation precision with method based on full OPF model, and its processing speed is faster. So, it is suitable for large scale power system transfer capability calculation. (5) On the basis of the above research, the phase shifter is introduced as example. The transfer capability calculation considering FACTS devices is solved through additional injected power and the optimization method based on DC power flow is expanded effectively.Next, on the basis of transfer capability calculation method research, taking the inherent uncertain factors in power system into account, transfer capability probabilistic simulation is carried out, which establishes the foundation for ATC decision-making research. The concrete work and contribution are as follows: (1) the stochastic outage of generation and transmission units and the fluctuation of buses load are expressed in probabilistic form. The non-sequential Monte-Carlo simulation technique and transfer capability solution methods are combined to fulfill the transfer capability probabilistic simulation idea. (2) During the simulation, for certain system state constituted by each unit state, a quick topology analysis method whose core is Gauss elimination and whose processing manner is similar as linear equation group solution is adopted, so as to analyze and obtain network configuration for each simulation. (3) For certain system state, the correction of infeasible state and transfer capability solution of feasible state are realized using the same optimization model, which embodies the reality of probabilistic simulation and makes the results accord with the truth. (4) The arbitrary event during the simulation is analyzed at large, and the probability density and cumulative probability distribution results are credible. Examples demonstrate the probabilistic simulation method is in conformity with the truth in computation condition selection and the probabilistic expression of uncertainties, and it is flexible in algorithm processing. The generalized transfer capability margin can be definitely quantified in probabilistic form and the analytic risk indices are also given, which provide scientific foundation for ATC decision-making under the power market.Thirdly, on the basis of the above research, the transfer capability homogeneousness concept is put forward. The relationship between power system existing operating mode (or dispatching) and ATC is taken as the key, and the ATC optimal decision-making under power market is thoroughly studied. The concrete work and main contribution are as follows: (1) The index indicating transfer capability homogeneousness is defined, and the new terms like homogeneous grid, grid according with economic flow are put forward. These new concepts describe the degree in which transfer capability is utilized, and they provide the standard for ideal grid whose transfer capability and power generation dispatching economy are in phase. So, new idea is introduced in transfer capability analysis. (2) The multi-objective function with generation cost and transfer capability homogeneousness weighted is constructed. The relationship between system existing generation dispatching and transfer capability is revealed through comparative analysis between security economic dispatch and security homogeneous dispatch, and the variation rule analysis between generation cost and transfer capability homogeneousness with the change of weighting coefficient. (3) Example analyses demonstrate that the difference between specific power system with ideal instance can be identified effectively using the above concepts and method. When the difference is great, for definite load requirement, different generation dispatching modes determine different ATC value and generation costs at the same time. So, it is advised that the determination of dispatching mode should be considered unified and coordinated with transfer capability and its distribution in actual power system operating. (4) The above idea is deepen through introduction of economic mechanism under probabilistic conditions and a new method for ATC probabilistic optimal decision-making considering system existing dispatching is put forward. The relations among existing power generation dispatch, load curtailment and ATC are quantified economically with the objective of maximizing composite benefits. The non-sequential Monte-Carlo simulation is used to solve the probabilistic problems and the ATC probability distribution is obtained through the simulation, on the basis of which a decision-making model considering tradeoff between benefit and risk is established. Then a sequential search algorithm combining interpolation technique is used to determine the optimal ATC. The optimal ATC decision-making method under probabilistic environment is evolved.Lastly, aiming at the current status of transfer capability analysis software development in China, the acquired studying production in the paper is combined with actual power grid practice, and the power grid transfer capability integrated estimation system is studied and developed independently. Transfer capability calculation and ATC decision-making are integrated in the system. It pays attention to not only the engineering practicability but also theory prospect. The successful application in actual power grid exhibits its well performance, and the analyses results provide constructive references for the establishment of power system operating mode. The integrated estimation system is a useful analysis tool for transfer capability analysis, which accords with the characteristic of power market and has broad application and generalization value.