Advanced Voltage Control Strategy for On-Load Tap-Changer Transformers with Distributed Generations

Due to the advantages offered by distributed generation (DG), more and more systems are being connected to local distributed networks to cope with the network constraints and to reduce the losses. However, for conventional feeders which are radial and do not include any DG, the direction of power flow is only from the power grid towards the loads. Therefore the voltages decrease towards the end of the feeder. When DG is connected, the power flow direction can be reversed when the DG output power exceeds the local load. That means the bidirectional power flow can flow, either from the power grid towards loads, or vice versa. Furthermore, the voltage of the DG connection point will be affected and may be out of the statutory limit when a large amount of DG power is produced. Overall, the conventional onload tap-changer (OLTC) voltage control methods may be inappropriate when DG is connected to the networks and new strategies may be required. This paper presents an advanced voltale control strategy for OLTC transformers with DG connection. This OLTC voltage control strategy provides an automatic voltage setting point change for existing OLTC transformers with AVC relays to maintain the feeder voltage and maximize the power from the connected DG according to the direction of the power flow. The proposed OLTC voltage control strategy has been shown to have an improved performance for distributed networks contain DG. This is demonstrated by a selection of simulation studies based on MATLAB SIMULINK.