  Regarding the variability of renewable energy sources (RESs), especially in
the operation time periods, their high penetration faces the net load pattern
of the power system with a major ramp rate challenge. Although employing a
market-based mechanism by the independent system operator (ISO) can address
this challenge, it may not be possible to handle this challenge in all
networks. In such networks, the required flexibility can be supplied by
decreasing the ramp rate of the purchased power of distribution companies
(Discos) from the market since their net load has an important impact on the
system's netload. Therefore, a flexibility-constrained operation problem for
the distribution networks with distributed energy resources (DERs) and
microgrids (MGs) is proposed in this paper to decrease the ramp-rate of the
Disco's purchased power from the market. This problem is formulated using a
bi-level two-stage stochastic model where the problem of the Disco and the MGs
are modeled as the upper-level and lower-level problems, respectively. The
proposed model is applied to the IEEE 33-bus standard test network with three
MGs. The results show the effectiveness of the proposed model to decrease the
ramp-rate of the Disco's purchased power from the market.
