# Solutions to Increase PV Hosting Capacity and Provision of Services from Flexible Energy Resources
## 3 Simulation Results and New Frequency Adaptive _Pu_-Droop
### Frequency Adaptive PU-Droops for PVs and BESSs During Larger Under- and Over-Frequency Situations  
Based on the simulations results of Section 3.1. it can be concluded that  
* Use of _PU_-blocking is needed from system-wide perspective in order to enable feasible operation of PV 2 (without BESS 3) in Cases 2a and 2b during 50.07 Hz over-frequency situation. * With BESS 3 in Case 5b during 49.8 Hz under-frequency situation however, PV 2 output needs to be curtailed more with _PU_-blocking due to BESS 3 unit's more rapid and extensive participation in system frequency support. * Therefore, use of _PU_-blocking is not recommended from PV curtailment viewpoint when there are both PV and BESS at the same network connection point. On the other hand, simultaneous BESS frequency support with _PU_-blocking logic is higher. * One potential option to avoid PV 2 curtailment could be disabling _Pf_-control of BESS 3 during under-frequency events. On the other hand, that is not optimal from whole-system perspective especially if frequency deviation is large and frequency support is needed. By considering above conclusions there is a need for development of _PU_-droops in order to avoid the mentioned shortcomings and challenges. Therefore, in this section 'frequency adaptive _PU_-droops' are proposed. The idea, settings, and PSCAD implementation of the frequency adaptive _PU_-droop are presented in Figure 7. For example with PV 2 and BESS 3 the adaption of frequency adaptive _PU_-droops would mean that when frequency is e.g., \(\geq\) 0.2-0.5 Hz and between over-voltage limits 1.05-1.15 pu or under-voltage limits 0.85-0.95 pu then active _PU_-droops would be changed from _PU_-droop 1 (Figure 2) to _PU_-droop 2 or 3 (Figure 7). Standard EN 50160 [45] defines that LV network supply voltage variations under normal operation should not exceed \(\pm\) 10% of nominal voltage \(U_{\text{n}}\) (99% of the 10-min mean RMS value over one week) and none of the 10-min mean RMS values shall exceed \(\pm\) 15% of \(U_{\text{n}}\). When comparing these frequency  
Figure 7: Frequency adaptive _PU_-droops’ (**a**) idea and settings for PVs and BESSs during larger under and over-frequency situations and (**b**) PSCAD implementation of the PV and BESS droops 2.  
adaptive _PU_-droop settings (Figure 7) to standard EN 50160 [45] requirements regarding supply voltage variation in LV network, it can be stated that standard requirements are respected. Frequency adaptive _PU_-droops should be used without _PU_-blocking in cases with PV + BESS at the same connection point in order to enable PV or BESS unit participation in frequency control markets as well as to maximize smaller LV network connected demand (loads) participation in frequency control. In Tables 7 and 8, active and reactive power of PV 2 and BESS 3 (Figure 1) as well as PV 2/BESS 3 connection point voltage (U_PV_2, Figure 1) values during larger under-frequencies (49.4 Hz) in Cases 7a and 7b are presented. In both cases OLTC set value is 20.0 kV. Case 7a is similar to 2b and Case 7b is same as 5a (Table 2). The under-frequencies (49.4 Hz) however, are larger (Table 3) and both Cases 7a and 7b are done without _PU_-blocking in PV 2/BESS 3 due to their 'frequency adaptive _PU_-droops' (Figure 7). From Tables 7 and 8 it can be seen that during larger under-frequencies (49.4 Hz) in Case 7a with only PVs (no BESS6), the frequency adaptive _PU_-droop enables larger PV 2 output and power system frequency support also during simultaneous demand response at \(t\) = 95 s (see Case 7a \(\Delta P_{\text{TOTAL}\_758}\) and \(\Delta P_{\text{TOTAL}\_958}\) values in Table 9 when compared to Case 7b with PVs and BESSs during 49.4 Hz under-frequency events the combined frequency support of PV 2 and BESS 3 is increased (see Case 7b \(\Delta P_{\text{TOTAL}\_758}\) and \(\Delta P_{\text{TOTAL}\_958}\) values in Table 9 when compared to Case 5a) and their total effect due to 'frequency adaptive _PU_-droops' is much better from the whole system point of view.