# 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  
Recently, insular network operators developed new grid codes which provide specific FRT capabilities to the grid-following CI-RES, namely, involving voltage-sensitive active and/or reactive current injections [34; 35]. However, in this paper, it is demonstrated that these voltage/current requirements should be adapted in order to facilitate the accommodation of 100% CI-RES generation penetration levels in networks with high shares of IM loads. Hence, a novel voltage/reactive current strategy for the grid-following CI-RES is proposed. From Figure 11 (base case), it is verified that after the fault clearance, the network voltage returns almost instantaneously to a value close to its nominal value. However, from Figures 9 and 10, a large reactive power injection from the BESS power converter is observed for about 2-3 s after the voltage recovery, which is due to the IM reactive power consumption in the moments subsequent to the fault clearance. This post-fault behavior evidences the need for large amounts of reactive power support in the moments subsequent to the fault clearance. In the proposed solution, CI-RES interfaces are intended to contribute to the provision of the reactive current in the reacceleration phase of IM loads.  
Aiming to better exploit the available resources in this period, the proposed control strategy consists of a voltage/reactive current hysteresis-type characteristic, instead of the well-known voltage/reactive current droop control, as depicted in Figure 15. As it can be observed in the proposed solution, for voltage dips lower than \(V_{2}\), the reactive current injection will be defined by the blue curve, injecting 1 p.u. of reactive current when the CI-RES terminal voltage reaches \(V_{1}\). This trajectory depicted in blue corresponds to the CI-RES terminal voltage decrease following a network fault. When the CI-RES terminal voltage increases and reaches \(V_{1}\), the voltage/reactive current characteristic switches to the green curve, returning to the blue curve when the CI-RES terminal voltage reaches \(V_{4}\). The use of this hysteresis-type voltage/reactive current injection curve might lead tosituations in which the post-fault reactive power injection is different from the pre-fault one. Such situation can be easily overpassed by a manual intervention of the system operator to reset the reactive power setpoint of the units or by a local reset action at the CI-RES interface a few seconds following post-fault voltage stabilization. It is also important to notice that for CI-RES terminal voltage values lower than \(V_{2}\), priority will be given to the reactive current injection; otherwise, priority will be given to the active current injection. The goal of prioritizing the active current injection for \(V>V_{2}\) is intended to improve the system stability when the voltage reaches values closer to the nominal one, where active power consumption will also increase. However, this prolonged reactive current injection in the correspondent period (\(V>V_{2}\)) will only be achieved for cases where the CI-RES is not operated at its maximum active power capacity before fault occurrence, being limited as a function of the active current setpoint (\(I_{p}\)) and of the converter nominal current (\(I_{n}\)). Therefore, for these operational scenarios, exploiting the solution in the BESS power converter is also necessary to facilitate IM load recovery.