## 2 Implementation of VI-Based Inverters
### Synchrotron
Although it is a reduced-order model from seventh-order model, second- to third-order systems balance complexity and accuracy for the representation of dynamic characteristics of the SM. The parameter tuning is crucial for stability and performance. Hence, a method to directly compute controller parameter in the synchronverter by using a damping correction loop replaces the iterative method based on small-signal analysis to simplify the tuning process while achieving the desired transient and steady-state performance [69]. [PERSON] designed a synchronverter that improves the damping of inter-area oscillation and the transient stability of a power system based on IEEE benchmark two-area network. Inter-area oscillation is caused by disturbances within interconnected generators through weak transmission lines. The transient stability of a power system is guaranteed by synchronverter, which ensures synchronism even though there is a major disturbance [70]. As presented in Table 5, the synchronverter exhibits merits and demerits that will have to be increasingly addressed in the future by researchers. Table 6 shows the current development of synchronverter in the application of RES, ESS and power system. \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Type of Application** & **Ref.** & **Type of Synchronverter** & **Highlights of Control Strategy** \\ \hline \multirow{8}{*}{General} & [66] & Hot seamless transfer & Additional seamless transfer branch to enable single-phase synchronverter acts as an uninterrupted power source \\ \cline{2-5}  & [62] & Self-synchronized synchronverter & Modification on synchronverter which does not require PLL to synchronize itself to the grid. Instead of PLL, virtual impedance is utilized. \\ \cline{2-5}  & [71] & Self-synchronized synchronverter with enhanced dynamics and current limitation & The droop ratio is decoupled from the damping coefficient and a PR current inner loop is added. \\ \cline{2-5}  & [64] & Bounded frequency and voltage & Integration of bounded frequency and voltage to ensure synchronverter always operates in a stable region. \\ \cline{2-5}  & [72] & Modified self-synchronized synchronverter & A filter has been used in filter-based current feeding loops to eliminate the power ripples. \\ \hline \multirow{8}{*}{Solar PV} & [65] & Grid-connected PV inverters without PLL & Self-synchronizing inverter without the need of PLL is able to interface the solar PV system to the utility grid. \\ \cline{2-5}  & [67] & Bounded droop control & It provides the synchronverter with power limitation and more flexible design process. \\ \cline{2-5}  & [16] & Grid integration of PV system using synchronverter & Interface solar photovoltaic module was connected as DC source to the inverter. The inverter was connected to the grid without any transformer. \\ \hline \multirow{2}{*}{HVDC} & [73] & Synchronverter-based emulation and control of HVDC & Control strategy for HVDC based on synchronverter \\ \cline{2-5}  & [74] & Flexible droop characteristics & The controller has flexibility since it avoids the constraint between the damping and droop characteristics in power regulating loop. \\ \hline \multirow{2}{*}{Wind Farm} & [17] & Self-synchronization of wind farm in MMC-based HVDC & Synchronverter is implemented on the wind energy conversion system converter to synchronize them to the Modular MMC-based HVDC system. \\ \hline \multirow{2}{*}{ESS} & [75] & Grid-connected ESS using synchronverters & Lithium-ion batteries as ESS is connected to the power grid via synchronverters. It improves the stability of the grid and supplies power during high demand. \\ \hline \multirow{2}{*}{Power system} & [70] & Synchronverter for damping inter-area oscillations in two-area power systems & Synchronverter is utilized to improve the damping of inter-area oscillations and transient stability of a power system. \\ \cline{2-5}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Current synchronverter merits and demerits.