Investigation of inverter-based voltage control methods to mitigate grid effects of photovoltaic sources

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Supervisor:
Dr. Hartmann Bálint
Department of Electric Power Engineering

In the next few years it is expected that the photovoltaic (PV) capacity will significantly grow owing to the decreasing PV module prices. According to the Energy Technology Perspectives (ETP) forecast, the levelized cost of energy (LCOE) of the residential PV systems will be 50 percent lower in 2035 than in 2015, which can be the basis of the large scale deployment of the PV systems in Hungary as well. The negative effects of active power injection of PV systems mainly occur in the low-voltage distribution networks. The most important negative impact is the voltage rise which is caused by the reverse power flow of PV generation. The voltage rise is considered the principal limiting factor of integrating PV systems into the electrical power system. The mitigation of voltage rise can be feasible via different strategies. Network reinforcement, on-load tap-changer transformer, energy storage, active power curtailment or reactive power control can all effectively reduce the voltage rise caused by the PVs. However, voltage control through reactive power injection from PV is one of the easiest to implement, and one of the most economical solution. In this paper, we investigated two different reactive power control methods which are suitable to the variable output of PV systems:

1. cosφ(P)

2. Q(U)

Although, Hungarian grid codes do not involve regulations which can mitigate the expected negative effects of the PV generation. The purpose of this paper is to investigate how PV systems should take part in the voltage regulation with the use of reactive power control methods. In order to achieve this, a low voltage distribution grid model is created which is representative for the Hungarian situation and based on real grid parameters. This model is suitable for investigating the negative impacts of the active power injection of PV systems. For that purpose, scripts were written and steady-state simulations were executed with the use of Digsilent Programming Language. The results show that the network hosting capacity is largely limited if the PV systems do not take part in the voltage control due to the significant voltage rise. The hosting capacity can be considerably increased with the use of reactive power control methods. Neverthless, the results also showed, that the parameterization of the afermentioned methods has a huge impact to the simulation results.

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