Control and Operation of Power Distribution System for Optimal Accommodation of PV Generation

Abstract

The renewable policies in various countries are driving significant growth of grid connected renewable generation sources such as the Photovoltaics (PVs). Typically a PV generation is integrated into power systems at the low and the medium voltage distribution level. The uptake of an intermittent power from the PVs is challenging the power system operation and control. The network voltage control is one of the major challenges during the operation of the distribution connected PVs. The active power injection from a PV plant causes variable voltage rise. This forces the existing voltage control devices such as on-load tap-changer (OLTC) and voltage regulator (VR) to operate continuously. The consequence is the reduction of the operating life of the voltage control mechanism. Also, the conventional non-coordinated reactive power control results in the operation of the VR at its control limit (VR runaway condition). This research focuses on the distribution voltage control in the presence of PV generation and helps to establish detailed insights into the various associated challenges. Firstly, the typical grid integrated PV topologies are discussed. The existing power system operational practices are presented and their limitations are identified. A voltage control methodology to tackle challenges such as over-voltage, excessive tap counts and VR runaway is presented. These challenges are alleviated through the coordinated reactive power control. The reactive power coordination is achieved through the deterministic distribution optimal power flow solved through the interior point technique. The irradiance and the load forecasting errors are another set of challenges from the distribution network operators’ perspective. The stochastic optimal voltage control strategy is proposed to tackle the element of randomness associated with the forecast errors. The stochastic operational risks such as an over- voltage and a VR runaway are defined through a chance constrained optimization problem. The simulation study is performed using a realistic 95-bus UK generic distribution network model and a practically measured irradiance to demonstrate the effectiveness of the proposed control strategies. The thesis makes an effort to offer an insight into the operational challenges and propose strategies to achieve a seamless integration of the PVs into the power systems.