# Towards Flexible Distribution Systems: Future Adaptive Management Schemes
## 3 Future Adaptive Control and Management Methods
### Adaptive PQ Flow Control Window: Stages 1-3  
In order to improve the coordinated provision of flexibility services by flexible active \(P\) and reactive power \(Q\) resources located at different voltage levels, different type of \(PQ\) flow control windows at different levels/connection points (HV/MV, MV/LV, LV customer connection point) could be applied in the future at different evolution stages 1-3. This means, for example, that outer limits of Figure 7\(PQ\) flow control window or reactive power window (RPW) or operating envelope [82] at the HV/MV substation could be more dynamic/adaptive and take the changing needs of DSOs and TSOs into account in real-time. Therefore, more accurate reactive power availability and needs forecasting for control purposes, e.g., \(PQ\) flow control windows between different voltage levels/connection points, will increasingly be needed as more intensive DSO/TSO cooperation is realized during the power system evolution. It should also be taken into account that the \(PQ\) flow  
Figure 6: (**a**) Frequency adaptive DER unit \(PU\)-droop for a BESS during smaller and larger under and over-frequency situations and (**b**) Real-time smooth-frequency adaptive \(PU\)-droop without specific frequency and voltage limits for activation, e.g., for BESS unit [79] (see Tables 3 and 4).  
limits should not unnecessarily restrict the flexibility services provision to upper voltage levels (e.g., from MV network to HV network). On the other hand, dynamic \(PQ\) flow control window HV and MV networks could be used to better support the voltage and angle stability issues (or prevent potential issues and improve power system resiliency) depending on the HV network power flow situation. In addition, the \(PQ\) flow control window (Figure 7) outer limits could be further fine-tuned and adapted based on the changed OLTC value (unlike in Figure 7). Realization of these would also require the development of related market and tariff structures.  
As stated in Table 5, the location of DER units as close as possible to the control point should be prioritized in \(PQ\) flow control participation. At stage 2-3, frequency deviation-dependent operation should be preferred (Table 5), which means that the \(PQ\) flow control functionality would be disabled during larger frequency fluctuations to avoid unwanted effects between other frequency supporting functions.  
In stage 1, adaptive (i) \(PQ\) flow control or RPW limits could be applied between HV (TSO) and MV (DSO) networks so that the seasonal flexibility needs of TSO networks and DSO networks are considered and (ii) customer connection point (household, SME, school, etc., (Figure 3) power factor \(cos(\phi)\) settings e.g., \(cos(\phi)=1\) (winter) and \(cos(\phi)=0.95_{\text{ind}}\) (summer) could be applied at customer connection points. In addition, extended seasonal \(cos(\phi)\) settings at customer connection points could be used, which also take into account local voltage (\(U\)) and/or current (\(I\))/active power \(P\) flows at the connection point. In the next stages, 2-3, more specific, adaptive daily and hourly \(PQ\) flow control windows for different connection points (HV/MV, MV/LV, customer connection point, power-electronic- based normally open points, i.e., soft-open points/SOPs including also potential smart power electronic transformers at HV/MV or MV/LV substations) could be added (Figure 3). These could enable more optimized real-time operation of the TSO and DSO networks by using flexibility services from different types and sizes of resources  
Figure 7: Real-time HV/MV substation \(PQ\) flow-dependent OLTC setting value (kV) with Sundom Smart Grid \(PQ\) flow limits (see Table 5 and Figure 3).  
through flexibility markets and consideration of potential DSO network constraints (e.g., voltage and thermal/current limits).