## 4 Results and Discussion
### Simulation results
The actuation of the droop controllers on the voltage and frequency in the hybrid distribution network originated a response of the hybrid distribution network in terms of net active power. The active power response obtained from the DC networks provided by each type of resource in each scenario is presented in Figure 20. The active power output in the DC networks before the frequency disturbance is slightly lower than the values presented in Table 3 due to power losses in the cables. Nevertheless, it is possible to observe that the ST is capable of extracting an active power response from the fleet of resources available in the DC networks for all the considered scenarios, in order to provide active power-frequency support to the main power system. Figure 19: ST (droop controller) response to the frequency variations observed in the MV AC network for the net load and net generation scenarios, in terms of voltage and frequency in the hybrid AC/DC network: (**a**)—\(f_{LV}(f_{MV})\) droop; (**b**)— \(V_{LV}(f_{MV})\) droop; (**c**) and (**d**)—\(VDC(f_{MV})\) droop. During under-frequency scenarios, a decrease in power consumption or increase in the generated power (depending on the scenario) takes place. During over-frequency scenarios, an increase in power consumption or decrease in the generated power (depending on the scenario) takes place. The active power response during the under-frequency scenarios is due solely to the reduction of the load power consumption. Controllable PV generation does not provide any contribution for under-frequency scenarios, since it is assumed that it operates at the maximum power point before the frequency disturbance. By contrast, the DC EV chargers are capable of reacting to both over- and under-frequency scenarios occurring in the MV AC network. Non-controllable load also provides active power compensation in both over- and under-frequency scenarios. The chosen droop settings (\(VDC(f_{MV})\) and \(P(VDC)\)) determine that the contribution of controllable units for active power compensation is considerably higher than the contribution of load voltage sensitivity of non-controllable loads. It is worth mentioning that the distinction between the net load and net generation scenarios takes into consideration the net power in the hybrid AC/DC distribution network as a whole, not only in the DC networks. Regarding the AC LV network, the active power adjustment provided by each type of resource is presented in Figure 21. The active power output in the LV AC network before the frequency disturbance is slightly lower than the values presented in Table 3 due to power losses in the cables. Nevertheless, it is possible to observe that the ST is capable of extracting an active power response from the fleet of resources available in the LV AC network for all the considered scenarios, in order to provide active power-frequency support to the main power system. During under-frequency scenarios, a decrease in power consumption takes place, while during over-frequency scenarios, the power consumption increases. The active power response during the under-frequency scenarios is due solely to the reduction of the load power consumption. Controllable PV generation does not provide any contribution for under-frequency scenarios, since it is assumed that it operates at the maximum power point before the frequency disturbance. By contrast, the controllable energy storage and the non-controllable load provide active power compensation in both over- and under-frequency scenarios. The chosen droop settings (\(V_{LV}(f_{MV})\), \(f_{LV}(f_{MV})\) and \(P(f_{LV})\)) determine that the contribution of controllable units for active power compensation is considerably higher than the contribution of  
Figure 20: Active power consumption variation in DC grids due to load voltage sensitivity (dotted area), controllable EV charging (dashed area) and controllable PV generation (white area). Positive values correspond to power consumption. load voltage sensitivity of non-controllable loads.