# Optimization of Active Distribution Network Operation with SOP Considering Reverse Power Flow
## 6 Conclusions  
This paper investigates the challenges posed by the increasing penetration of distributed generation (DG) in distribution networks, particularly concerning the management of reverse power flow. In Section 2, an analysis is conducted on three factors affecting reverse power flow in distribution networks: the parameters of the on-load tap changer (OLTC), the reactive power compensation capacity installed on both sides of the OLTC, and the electrical distance from the DG to the OLTC. The following conclusions are drawn:  
1. When transmitting reverse power flow, the OLTC, designed as a step-down transformer, is utilized as a step-up transformer. Consequently, even when the tap ratio of the OLTC reaches its limit, the ideal reverse power flow transmitted is only about 80% of its rated capacity. The specific impact of the OLTC tap ratio on the capacity for reverse power flow transmission is detailed in Equations (23) and (24) and Figure 6.
2. The reactive power compensation capacity on both sides of the OLTC also influences the transmission of reverse power flow. Without additional reactive power compensation, insufficient reactive power capacity on the low-voltage side of the OLTC restricts the transmission of reverse power flow to approximately 30% of the rated capacity. However, by adding extra reactive power compensation on the low-voltage side, the capacity for reverse power flow transmission can be increased to about 80% of the OLTC's rated capacity, albeit at the cost of additional installation, which raises the operational expenses of the distribution network. 3. The electrical distance from the DG to the OLTC further limits the capacity for reverse power flow transmission, which can drop to around 30% of the OLTC's capacity under the most adverse operating conditions. Section 3 synthesizes the analysis of these three influencing factors and concludes that the impact of the OLTC tap ratio on reverse power flow transmission capacity is contradictory to the effect of the electrical distance from the DG to the OLTC. To address this, a parameter, \(b_{t}\) is introduced to describe the voltage on the low-voltage side of the OLTC. This, combined with the aforementioned factors, leads to a precise method for calculating the capacity for reverse power flow transmission in distribution networks, as outlined in Table 1.  
Section 4 establishes a joint operational optimization model for multiple distribution networks that includes an SOP to enhance the reverse power flow transmission capability of individual distribution networks. In the case studies presented in Section 5, the operational results of the distribution networks are analyzed under independent operation, dual network operation, and triple network operation, leading to the following conclusions:  
When the distribution network operates independently, the capacity for reverse power flow is relatively poor, leading to significant curtailment of wind and solar energy when distributed generation (DG) output is high. However, interconnecting multiple distribution networks through the SOP can facilitate the sharing of reverse power flow capabilities among different networks, thereby reducing the curtailment of wind and solar energy and enhancing overall operational efficiency. Nonetheless, this approach requires further refinement, as joint operation largely depends on the operational conditions of the various distribution networks. If multiple distribution networks simultaneously need to export reverse power flow, the effectiveness of this method will be constrained. Additionally, the high costs associated with the SOP significantly limit the output capacity for reverse power flow. Future research should consider the integration of energy storage systems (ESS) to form an E-SOP, which would allow for the storage of electricity during peak DG output periods and enable export during times when the joint system has surplus capacity for reverse power flow. This will be a focal point for the next phase of research.