Читать книгу Mathematical Programming for Power Systems Operation - Alejandro Garcés Ruiz - Страница 14

The economic dispatch problem may include hydroelectric power plants; said plants, generate two fundamental changes into the model. On the one hand, the model becomes dynamic since current operational decisions affect the future operation of the system. On the other hand, the problem becomes stochastic, because the inflows are usually random variables, especially in long-term models. The later aspect is usually solved by an accurate forecasting of the loads and the inflows; hence, it is possible to formulate a deterministic problem, called hydrothermal dispatch or hydrothermal coordination. The basic model has the following structure, namely:

(1.2)

Where i represents thermal units and j enumerates hydroelectric units; t represents the time, thus, pit is the power generated by the thermal unit i at time t. The values of ajt, vjt, pjt, qjt and sjt are respectively, the inflow, volume, power, outflow, and spillage of the hydroelectric unit j at time t. Figure 1.2, which is self-explanatory, shows these variables.

Figure 1.2 Schematic representation of the variables associated to a hydroelectric generation unit.

In this model, g represents the relation between generated power, outflow, and water volume stored in the dam. Although the planning horizon may be of short-term (1 day to 1 week), medium-term (1 month), or long-term (1 or more years), we are interested only in the short-term model. As aforementioned, the problem may be stochastic since power demands dt and inflows ajt are all random variables. However, a determinist model is suitable to understand the problem and its practical implementation. The situation becomes even more problematic when introducing other renewable energies, such as wind generation and photovoltaic solar generation. Chapter 9 presents the hydrothermal dispatch problem.