# Influence of Load Dynamics on Converter-Dominated Isolated Power Systems
## 5 Control Strategies for the Mitigation of the Impacts Induced by Induction Motor Loads
### Fault Ride Through Strategy for Grid-Following Units
#### 5.1.1 Simulation Results and Discussion  
In order to demonstrate the performance of the proposed control solution with respect to the ability to provide improved conditions for post-fault IM load reacceleration, three distinct conditions are compared in this subsection: (Case 1) Voltage/active and reactive current dynamic control imposed by the system operator of Madeira Island [26; 34]. In this case, priority is given to the active current injection during the short-circuit event, whose contribution should be, at least, equal to the pre-fault active current injection. Simultaneously, the reactive current should be injected proportionally to the terminal voltage of the generation unit (a voltage dead-band of 0.1 p.u. and a voltage/reactive current control gain equal to \(-2.5\) were considered). (Case 2) Voltage/reactive current dynamic control, similar to the requirement imposed by the Spanish insular grid code [35; 36]. In this case, priority is given to the reactive current injection, being proportional to the terminal voltage of the generation unit (a voltage dead-band of 0.1 p.u. and a voltage/reactive current control gain equal to \(-2.5\) were considered). (Case 3) The voltage/reactive current strategy presented in Figure 15, where \(V_{1}=0.5\) p.u., \(V_{2}=0.9\) p.u., \(V_{3}=0.9\) p.u. and \(V_{4}=1.06\) p.u. As it can be observed in Figure 16, only in Case 3, where the proposed strategy is adopted, is it possible to assure a successful recovery of all IM loads and hence the stabilization of the grid frequency and network voltage when the 12 MVA BESS power converter capacity is assumed. In addition, the control strategy employed in Case 3 successfully reduces the BESS reactive power contribution following the fault clearance compared to the other cases, as it can be observed from the results presented in Figure 17 (note that the use of the hysteresis-type solution led to a reactive current injection stabilization different from the pre-fault state). It is also observed that the BESS pre-fault active power regime is achieved approximately 1.5 s after the fault clearance. In Figure 18, the CI-RES active and reactive current outputs (only the WFI response is presented since all CI-RES generators present a similar dynamic behavior) are depicted, being notable that, only in Case 3, a  
Figure 15: Proposed reactive current/voltage strategy for converter-based generators operating as grid-following units. relevant post-fault reactive current injection after the fault clearance is observed, which is a result of the proposed voltage/reactive current hysteresis-type characteristic. Finally, from Figure 19, it is evidenced that the IM load (L3 is presented as an illustrative example) only recovers after the network short-circuit clearance in Case 3. It is also demonstrated that the prolonged CI-RES reactive current injection contributes to increase the IM load terminal voltage in the moments subsequent to the fault clearance, due to a faster re-excitation, thus contributing to a faster IM load reacceleration. Figure 16: BESS power converter synthetic frequency and terminal voltage for different reactive current-voltage injection profiles. Figure 17: BESS power converter active and reactive power outputs for different reactive current-voltage injection profiles. Figure 18: WF1 active and reactive current outputs following different reactive current-voltage injection profiles. In conclusion, the obtained results demonstrate that the complete recovery of all IM loads is only accomplished in Case 3. This is due to the contribution provided by the prolonged reactive current injection from the CI-RES to the grid (as can be observed in Figure 18), which is not observed for Cases 1 and 2. Thus, in Cases 1 and 2, without the prolonged contribution of the CI-RES, the BESS power converter is not able to provide the necessary reactive current amount required for the successful re-excitation of the IM loads following the fault clearance.