Economic dispatch of wind-thermal power system with MW and ramp rate dependent generator costs

Making use of the steam heat storage in thermal generators enables them to operate in a “fast mode” to ramp up or down faster than regular, so as to better catch up with the fluctuations of wind power to improve system wind utilization. In such fast mode, generators have MW-dependent ramp rates and, distinguished from regular units, MW and ramp rate dependent coal consumption costs. Existing economic dispatch models usually use MW-dependent generator cost functions and constant ramp rate limits, and are thus not applicable to systems containing fast mode generators. This paper presents a new formulation of dynamic economic dispatch for wind-thermal power systems, to take into account ramping capabilities and costs of generators in their fast mode. In our model, the objective is to minimize a two-variable quadratic generator cost function depending on both output levels and ramp rates, and generator ramp rate limits are MW-dependent piece-wise linear functions. The formulation can be solved by using existing quadratic programming methods. In numerical examples implemented by using CPLEX, our model is demonstrated on the IEEE 30-bus system containing two 600MW thermal units with real data. Results show that by using our model, unit ramping capabilities are better utilized in system dispatch to substantially save curtailed wind energy, and total generator costs are reduced.