Equivalent ramp rate function for thermal power systems

The equivalent modeling method is extensively used in the area of power system optimization. The thermal power system can be simplified into an equivalent thermal unit in the studies where the performance of individual units is not the focus. Conventionally, the equivalent ramp rate for the equivalent thermal unit is the summation of each unit's ramp rate. However, the equivalent ramp rate relies heavily on the operating points of each thermal unit. In this paper, a concept termed the equivalent ramp rate function (ERRF) for thermal power systems is proposed. Given the principle of dispatch such as cost minimization, the impact of each thermal unit's operating point is accurately considered in ERRF. An algorithm is proposed to numerically build the ERRF. The case study based on the IEEE 30-bus system indicates that the proposed ERRF can reflect more realistically the system-wide ramping capability. For example, the ERRF can be utilized as an “offline” evaluation tool to assess the potential wind curtailment due to lack of ramping flexibility. The impact of different cost functions on the shapes of ERRF is also presented.