Sweden’s transition toward 100% fossil free electricity generation by 2040 is suggested to be a great factor in the rapid increase in Distributed Energy Resources (DER), particularly Photovoltaic (PV) systems and Electrical Vehicle (EV) chargers, in Low Voltage (LV) distribution networks. While this shift supports environmental goals, it introduces technical challenges, notably in maintaining voltage quality and stability. Overvoltages caused by high PV penetration have become a common issue for Distribution System Operators (DSOs), potentially triggering inverter protection mechanisms, disconnecting customers’ PV installations from the grid, and violating regulatory standards for power quality. Current voltage regulation methods in Sweden rely primarily on On-Load Tap Changing Transformers (OLTCs), which lack the responsiveness needed to manage rapidly fluctuating generation and demand patterns. This creates operational limitations, including delays or denials of new PV connections. To address these challenges, smart inverters capable of reactive (Q) and active (P) power control are being explored as dynamic voltage controllers. This thesis investigates the effectiveness of inverter-based control strategies for mitigating voltage issues in LV grids, based on four criteria and compliance with Swedish regulations. A simulation environment was developed using MATLAB Simulink, including models for typical urban and countryside grid based on typical characteristics from local area grids operated by Vattenfall Eldistribution AB. These models were also adapted for future inverter Hardware-In-The-Loop (HIL) testing in Vattenfall R&D’s Real Time Simulator (RTS) platform. Using the developed simulation environment, three control strategies were evaluated: (1) Q(U) control, (2) P(U) control, and (3) a combined P(U) & constant Q control method. The investigation focused on each controller’s ability to maintain voltages at the customer’s grid connection point within the regulatory bound of (230±10%)V , their responsiveness, and overall stability. Simulation results showed that all strategies maintained voltage within acceptable limits, fulfilling the Swedish Energy Markets Inspectorate (Ei)’s EIFS 2023:3 regulation. The combined P(U) & Q strategy achieved the voltage closest to 230 V, but showed instability due to smaller oscillations, likely caused by time delays and overly aggressive Q-control parameters. The Q(U) strategy demonstrated both high efficiency, including great stability, making it the most balanced option. The P(U) strategy offered the fastest response time but slightly lower voltage reduction effectiveness. In conclusion, while smart inverter-based voltage control can significantly improve LV grid performance under high PV penetration and mitigate overvoltages, none of the strategies alone ensured a voltage level close enough to the nominal 230 V in the long term for all nodes. Therefore, additional gridsupportive technologies are necessary. This work highlights the importance of increasing the complexity of the model, real-time testing with HIL, and advanced control coordination to support the ongoing integration of renewable energy in distribution networks.
Monica Saavedra Granholm (Wed,) studied this question.