Incorporating ramp problem into the expansion planning of distributed energy resources for improving flexibility of renewable-based distribution network using interval optimization

Substantial increase in variability and uncertainty of net-load due to the higher shares of renewable resources from the generation sector has established the ramp problem in distribution networks. In this situation, maintaining a power balance becomes a challenging practice. To deal with this problem, the fluctuation of the net-load must be controlled during the operation timeslots. However, applying the limitation on the variability of the net-load results in high operational costs in the network. This paper aims to propose a flexibility-oriented approach for expansion planning of distributed energy resources (DERs) in order to reduce operational costs of the system under the situation of realizing control on the net-load’s fluctuations during the operation periods. To accomplish this aim, flexibility constraints are considered into the expansion planning of DERs to put a limit on the maximum hourly up and down ramp rates of the net-load. The proposed expansion planning has been formulated using mixed-integer linear programming to guarantee the optimality of the results. In addition, an interval optimization has been utilized to address uncertainties related to the output power of the clean resources, electricity price, and load consumption due to its computational efficiency. Finally, the effectiveness of the proposed expansion planning approach has been examined using the 33-bus distribution network. The results showed that the flexibility-oriented expansion planning of DERs enriches the flexibility of the distribution network under the condition of applying the limitations on the net-load’s fluctuations. Moreover, it can bring economic profit for the network in comparison with the state in which the expansion planning has been done without considering the flexibility constraints.