Grid Impact Assessment of Unbalanced Penetration of Distributed Generation, Electrified Mobility & Heating in the Near and Far Future

Abstract

The EU strives to lower greenhouse gas emissions. To reach this goal, many energy intensive processes in the residential sector such as heating and transportation will be electrified using heat pumps and electric vehicles (EVs) respectively. Simultaneously, a transition of electricity generation to sustainable sources will take place, necessitating an increased adoption of rooftop photovoltaic (PV) systems.

The adoption of PV systems, heat pumps and EVs, also known as low carbon technologies (LCTs), can increase three-phase unbalance in low voltage (LV) distribution networks as many of these components will be connected to a single phase of the three-phase network. Threephase unbalance is undesirable in a three-phase system, as it causes among others, energy losses and a suboptimal use of network capacity.

The aim of this thesis is to evaluate the impact of different combinations and penetration levels of LCTs on three-phase unbalance in different real LV distribution networks through simulations and how unbalance is affected by LCT location, season and LCT control schemes.

Simulations were performed on six different grids, varying in level of urbanization and loading, with increasing levels of LCT penetration (0%, 50%, 80%, 100%). In these simulations, LCTs were integrated in varying combinations (PV & EV, PV & HP and PV & EV & HP). For every simulation, the maximum and mean voltage unbalance factor (VUF) was determined. Seasonal effects and the effect of an LCT control scheme were also evaluated.

Simulations showed that the voltage unbalance factor exceeded the legal limit of 3% for two of the six grids for high levels of LCT penetration when all LCTs are integrated. Combining all three LCTs resulted in the highest unbalance levels. Varying the locations of the LCTs resulted in significant differences in unbalance levels. Comparing a winter week with a summer week, the overall unbalance is similar, however, the contribution of the PV systems to the unbalance is increased, while the contribution of EV chargers and heat pumps is decreased.
The effect of the LCT control scheme was limited.

As the integration of LCTs will increase considerably in the near future, three-phase unbalance levels exceeding the limit of 3% will occur more often. To prevent unbalance levels from structurally exceeding the legal limit of 3%, more effective control schemes should be designed and implemented.