Hengxu Zhang

On transmission expansion planning considering security risk in competitive electricity markets

The traditional transmission planning of merely focusing on one future scenario could not meet the practical demands. New methods and tools for transmission planning are needed in competitive electricity markets. This paper discusses the uncertainties in electricity markets, and then proposes the conception and algorithm of risk factor of transmission planning. A transmission planning model is built based on the risk factor of transmission planning. Using the Monte Carlo simulation method and the genetic algorithm, a planning scheme with the least investment risk in the face of future uncertainties can be obtained. The results of calculation examples demonstrate the feasibility and efficiency of this method.

Trajectory sensitivity-based emergency load shedding optimal algorithm

Huge power transmitted over long distance through some crucial lines increases the probability of a sudden loss of bulk power in the power-receiving system. To prevent such emergency from deteriorating the security of the system, an emergency load shedding model, whose objective is to minimize the total load shedding cost, is built, and then an efficient algorithm is proposed based on trajectory sensitivity. The constraints of the model include transient voltage security, transient frequency security and available load that can be shed. This problem is a large scale, nonlinear programming problem with constraints considering time-varied parameters. The mathematical model is simplified by linearizing the security constraints through trajectory sensitivity, and the consistency of the solution is guaranteed by iterative calculation. The trajectory sensitivity is utilized in guiding the search direction and accelerating the solving process. A provincial power system is used to test the validity of this algorithm.

Optimal transmission planning based on quantitative security risk in uncertain environment

A sound transmission network ensures the secure and economical operation of power system. Several large- scale blackouts in the world have attracted attentions to dynamic and static security of transmission expansion planning. This paper points out that the security risk of transmission system, expressed by quantitative indices, should be considered in the objective function. In order to ensure a flexible transmission system, with probabilistic N-1 safety criteria, this paper builds a transmission planning model considering both static security risk and dynamic security risk. A global optimization framework is developed to resolve the problems caused by the multi-object mathematical model and remarkably reduce the computational burden. Based on EEAC, the proposed method can calculate the stability margin and dynamic risks, identify the grid bottleneck, and can provide guidance to the line expansion. A numerical example is presented to illustrate the validity of the method.