Enhancing Photovoltaic Hosting Capacity in Distribution Grid via Grid Reconfigurations, PV Droops and Battery Inverter Control

The EU 2030 climate and energy framework has set a mandatory goal to achieve a renewable energy share in the final energy demand of 32% by 2030. Moreover, in the final National Energy and Climate Plan (NECP) Luxembourg has defined its renewable generation share goal at 25% by 2030. Between 2018 and 2019, three times more photovoltaic (PV) panels were installed than in the previous years. To achieve the NECP target and to ensure further smooth integration of PV systems, the PV hosting capacity (HC) of the grid should be enhanced.
This thesis discusses the common issues and current developments of HC enhancement and presents three HC enhancement techniques: grid reconfiguration and grid-code modification, extended current droop control and transformer loading control.
First, the thesis analyzes the potential of grid reconfiguration in HC enhancement. For the analysis the grid configurations are divided into meshed and radial subsets. The grid reconfiguration analysis and HC calculation are done using pandapower and NetworkX library. The cross-influence and the location of DG are considered while determining the HC of the grid. The analysis shows that proper grid configuration selection is important as it can substantially increase the HC and decrease the average loading in the lines.
Second, the impact of extended current droops on HC enhancement is investigated. In the designed extended current droops (Id(V ), Iq(V )), extra reactive power reserve is made available by changing the droop gain of the reactive current droop when the overvoltage is not cleared by the existing reactive power reserve. The simulations proved that the extended current droops are a viable grid reinforcement strategy which can not only regulate the voltage at the point of common coupling (PCC), but also relax the transformer loading and improve overall voltage and frequency stability. Additionally, oversizing of the inverter increases the reactive power reserve, which in turn lowers the voltage profile and decreases the amount of curtailed active power.
Finally, two novel communication-less transformer overloading protection strategies based on a battery energy storage (BES): transformer protection droops (TPD) and direct loading control (DLC), are designed and compared. Both strategies force the PV inverters to curtail their active power output without relying on communication. The strategies have been tested on detailed models, where the total installed PV power varies between 0.9 to 2 times the transformer rating. The static and dynamic performance of the DLC is superior to the TPD control strategy. DLC is a robust control strategy. It can reduce the transformer loading by 41%, compared to the grid configuration without BES and bring the system to the steady-state within 700ms in the worst-case scenario. It also ensures to keep the system voltages within safe operational limits. It can be used as a backup active power curtailment solution in the cases of communication failure in centralized control.