Impact of non-dispatchable renewables on generator cycling and control via a hierarchical control scheme

Increasing penetration of intermittent non-dispatchable renewable resources to the power grid could result in a less reliable and secure system if the intermittency is ignored. An additional effect of intermittency is the cycling of thermal units as the thermal units are controlled under an economic dispatch controller. This paper proposes an approach to smoothen the intermittency and therefore minimize thermal unit cycling by controlling demand and other customer owned resources. Specifically, a hierarchical optimization and coordination algorithm is proposed that takes advantage of the control capabilities of these resources and optimizes their operation with the ultimate goal to minimize system operating cost and maximized reliability. A byproduct of this optimization is the reduced cycling of dispatchable generating units. Results are demonstrated on a utility scale system with various levels of wind penetration using actual wind generation patterns. It is shown that while the objective of the optimization is the minimization of the overall operating cost of the system, the optimal solution also reduces the number of cycles and the average MW variation per cycle. This minimization of thermal unit wear and tear increases the reliability of the system.