Calculation Of Power System Transmission Capability Considering Unit Commitment And Economic Dispatch

In the perfect power market, all the Generation Companies sell their outputs to the Grid Company, and all the Distribution Companies purchase their energy requirement from the Grid Company. In the generation-sided power market, the Grid Company makes economic decisions on the trade planning through the datum of load forecasting and Generation Companies' bids. At the same time, the Grid Company purchases the Generation Companies' outputs at the price of system marginal price. According to the result of trade planning, the Generation Companies arrange their generators to provide power to the grid. In the process of making decisions on the trade planning, the economy of the grid is considered chiefly, so the Grid Company is charged with assuring the secure and reliable operation of the grid. Confirming the power system transmission capability has good effect on restricting the actions of the trade and assuring the security of the grid.In the power market, the power system transmission capability is the basic data to both sides of the power trade. It is referred to the capability of transmitting power from one area to another area through all the transmission lines in given system operational environment. For making good use of existing transmission system and increasing the stability margin of the system, the method of calculating the power system transmission capability should simulate the operation of the system and calculate the maximal power system transmission capability.Power system is a complicated nonlinear dynamic system. Along with the increasing of power exchange amount between the two areas, the typical problems of nonlinear dynamic system, such as Hopf bifurcation and saddle-node bifurcation may appear, so the security of the system may be destroyed. How to calculate the power system transmission capability in complicated voltage stability constraint conditions exactly becomes a desirable study problem in the power system nowadays.Now the main methods of calculating the power system transmission capability are continuation power flow calculating method (CPF method) and optimal power flow calculating method (OPF method). The calculating problem of the power system transmission capability in constraint conditions of steady-state voltage stability is discussed in this paper. For the disadvantage differing from the practical operation that the increasing direction of the outputs of generators is confirmed through preestablished method, this paper presented a new calculating method. The fashion of generation dispatching considering grid economy is obtained from the result of unit commitment and economic dispatch of short-term trade planning in power market. Then the power system transmission capability is calculated in given fashion of generation dispatching using CPF program. If the increasing requirement of the load can't be met using the fashion of generation dispatching considering grid economy, a new fashion of generation dispatching which can increase the power system transmission capability is produced using OPF program. So the power system transmission capability is improved, and the requirement of load change is met furthest.