## 3 Simulation Results
### Discussion for Possible Provision of Ancillary Services  
In the literature, it is often mentioned that overvoltages and voltage unbalance are the most common problems in LV grids with areas with high penetration of DERs. Up to this point, the modified three-phase damping control strategy showed superior performance in terms of voltage control, injected power and grid loss reduction, compared to the traditional reactive power voltage control, hard curtailment, and positive-sequence current injection. The presented simulations treat the power quality issues in a steady-state mode via time series simulations. Nevertheless, in [39; 40] the transient behavior of the three-phase damping control strategy is examined under variety of voltage dip types and residual voltages. In [40], a solution for a simultaneous voltage dip and harmonic mitigation are proposed. In [19], the integration of the battery energy storage systems into the three-phase damping control strategy is examined in terms of power quality and grid performance improvement. With this said, it can be concluded that the three-phase damping control strategy has a great potential to provide variety of ancillary services to the DSO. Moreover, further research can be performed into black start capabilities and frequency control so that services to the transmission system operator (TSO) can be provided. The three-phase damping control strategy mitigates the voltage unbalance by acting resistively towards the zero- and negative-sequence voltage components. This behavior results in asymmetrical current injection depending on the rms value and angle of the respective phase voltage but it basically means that the DER will inject larger phase current in the phase with the lower voltage and smaller currents in the phases with the higher voltages. This intuitively means that some oversizing of the power electronic inverter is needed in order to accomplish voltage unbalance mitigation. In [12; 19], very good results are achieved by oversizing the power electronic inverter with 25 to 30%. Nowadays, the inverter costs are much lower compared to 10 or 15 years ago and such an oversizing will not impose a significant capital expenditure to the prosumers, who are interested in providing ancillary services. It is worth mentioning that, in reality, the inverter efficiency will be lower than 100%. This will result in lower energy injection of the presented test cases. It is also interesting to point out that unbalanced grid conditions are examined in the presented results. This implies that, the different \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case** & **Control Strategy** & **Energy** & **Voltage Control** & **Voltage Unbalance** & **Grid Losses** \\ \hline \multirow{2}{*}{C1} & No Control & Excellent & Poor & Poor & Poor \\  & Positive-sequence control & & Poor & Good & Poor & Poor \\  & strategy with variable PF & & & & \\  & Drooped positive-sequence & & & & \\  & control strategy \(g_{d}=0\) & & & & \\  & Drooped three-phase damping & & & & \\  & control strategy with \(g_{d2}=50\) & & & & \\  & Drooped three-phase damping & & & & \\  & control strategy with \(g_{d}=3\) & & & & \\  & control strategy with \(g_{d}=10\) & & & & \\  & Drooped three-phase damping & & & & \\  & control strategy with \(g_{d}=50\) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison table of the performance of the different control strategies. legs of the three-phase voltage sourced inverter will operate at different points of the efficiency curve. Regardless of whether positive-sequence or three-phase damping control strategy is used, this effect will be present. This effect will be more prominent when the three-phase damping control strategy is used, because the exchanged currents will be highly asymmetrical, especially at high values of \(g_{d}\).