# Research Needs for Realization of Zero-Carbon Power Grids with Selected Case Studies
## 3 Selected Case Studies and Numerical Results
### Network Reconfiguration and Distributed Generation
#### 3.2.2 Real-Time DG Control in Coordination with Scheduled SW Operations  
Existing DG control relies on feedback loops. Uncertainties in the estimates of DG and load modeling parameters should be considered. Otherwise, the DG-mediated control of grid frequency and voltages can be ineffective; stable and reliable grid operation is compromised. Figure 9 shows a new strategy for real-time FR of a reconfigurable MG; the feedforward control of SG and IG power outputs is coordinated with SW on-off operations to reduce frequency deviations attributable to NR-aided load restoration [64]. The feedforward frequency controllers (FFCs) were developed with the aid of an analytical dynamic model of the reconfigurable MG, as discussed in Section 3.2.1. The FFCs were then integrated with the PFC and SPC feedback loops (Figure 10) to ensure power sharing among the DGs and a supply-and-demand balance in the steady state, respectively. Figure 11 shows the results of small-signal analytical and simulation case studies. The proposed control strategy was more effective and robust than the conventional feedback-only strategies;  
Figure 7: The (**a**) conventional and (**b**) new methods for NR modeling.  
Figure 11: (**a**) Bode plots of the \(\Delta f\)(s)/\(\Delta P_{L}\)(s) values for the new FR strategy (Case 1) and conventional FR strategies (Cases 2–4); (**b**) Bode plots of \(\Delta f\)(s)/\(\Delta P_{L}\)(s) values with the errors in DG parameter estimates; and (**c**) comparisons of \(f\), \(1\,\mathbf{V}\,|\,\Sigma_{g}\,P_{Mg}\), and \(\Sigma_{i}\,P_{IGi}\) (from top to bottom) during NR-aided load restoration.  
Figure 10: A small-signal model of an islanded reconfigurable MG with supplementary FFCs showing the feedback loops for the inertia response emulation and primary and secondary frequency control.  
Similarly, Figure 12a shows a new strategy for the real-time voltage regulation (VR) of a reconfigurable MG [65]. Optimal feedforward control of the terminal voltages of SGs and IGs is coordinated with SW operations to pre-emptively mitigate transient voltage deviations caused by NR. The dynamic responses of bus voltages to NR are estimated using an analytical model of a reconfigurable network, discussed in Section 3.2.1. The responses are integrated to afford robust optimization of the feedforward voltage controllers (FVCs) that minimize terminal voltage deviations. Uncertainties in the estimates of DG modeling parameters and load demands are considered during optimization, further improving the robustness of FVC operation. The FVCs are incorporated in parallel with the existing feedback control loops, as are the FFCs (Figures 9 and 10); steady-state deviations in DG terminal voltages are eliminated. Figure 12b shows the results of a case study, verifying that the new VR strategy (i.e., Cases 1 and 2 in Table 9) was better than the conventional PI- and robust controller-based strategies (i.e., Cases 3 and 4 in Table 9). Table 10 lists the corresponding numerical results.