# Influence of Load Dynamics on Converter-Dominated Isolated Power Systems
## 5 Control Strategies for the Mitigation of the Impacts Induced by Induction Motor Loads
### Combined Use of the Proposed Control Strategies  
In Sections 5.1 and 5.2, two distinct solutions were presented, which have proven to, individually, be effective with respect to the provision of improved reacceleration  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**IM Load (\%)**} & \multirow{2}{*}{**IM Load**} & \multicolumn{3}{c}{**\(S_{\text{BESS }}\) (MVA)**} \\ \cline{3-5}  & & **Base Case** & **Strategy 1** & **Strategy 2** \\ \hline
11\% & L5 & 18 & 12 & 12 \\
15.5\% & L3 & 28 & 12 & 12 \\
21\% & L4 + L5 & 28 & 12 & 12 \\
26.5\% & L3 + L5 & 38 & 12 & 12 \\
27\% & L1 & 25 & 12 & 12 \\
36.5\% & L3 + L4 + L5 & 46 & 17 & 16 \\
36.5\% & L2 & – & 63 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Grid-forming BESS power converter sizing vs. IM load percentage.  
Figure 32: Small (**left**) and large (**right**) industrial motors’ speeds and terminal voltages.  
of IM loads following a network fault. However, as previously mentioned, the results of Sections 5.1 and 5.2 were obtained considering the operational scenario presented in Section 4.2.1 (which comprises 26.5% of IM loads).  
Hence, in extreme operating conditions with large shares of IM loads, it may be interesting to simultaneously implement and adopt the two considered solutions. For this purpose, in this section, the same operational scenario was considered (Table 1); however, this time, 42.5% of IM load was integrated (\(L_{1}\) and \(L_{3}\) were modeled as IM loads--see Table 2). Thus, three distinct test cases were compared: (Case 1) the FRT strategy presented in Figure 15 was implemented in the grid-following units, 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. (same parametrization as Section 5.1.2), with the VSM reference voltage being fixed to \(V_{ref}\) = 0.98 p.u.; (Case 2) the implemented FRT strategy in the grid-following units corresponds to the strategy presented in Section 2.2, where the voltage magnitude control strategy presented in Figure 27 was implemented in the BESS (\(V_{1}\) = 0.5 p.u., \(V_{2}\) = 0.8 p.u., \(V_{3}\) = 1 p.u., \(V_{4}\) = 1.03 p.u., \(V_{1}^{\prime}\) = 0.98 p.u., \(V_{2}^{\prime}\) = 1.1 p.u. and a \(V_{ref}\) limitation ramp of \(-0.1\) p.u. (\(V\))/s--same parametrization as Section 5.2.2); (Case 3) both proposed strategies were considered, using the parametrization of Case 1 and Case 2.  
The results are presented in Figures 33-36, with it being observed that only in Case 3 is the full recovery of all IM loads assured. Moreover, it is also verified that the BESS pre-fault frequency and voltage regime is achieved approximately 2 s after the fault clearance. In Figure 35, it is observed that the combination of the two presented control strategies induced a post-fault voltage increase, within the admissible range, that positively contributed to the reacceleration of all the IM loads.  
In summary, the results demonstrate that the individual contributions of the proposed control solutions presented in Section 5.1 (Case 1) and Section 5.2 (Case 2) were not capable of ensuring the re-excitation of the IM loads in operational scenarios with very large shares of IM loads (despite being effective in operational scenarios with moderate shares of IM loads). In this sense, it was concluded that by combining the control effort provided by the two control strategies, it was possible to successfully re-excite all the IM loads in the moments subsequent to the fault clearance.