On mitigating voltage rise in distribution networks with high solar PV penetration

Abstract

Voltage rise (VR) is the resulting issue of reverse power flow from solar PVs, owing to their high penetration in the distribution network (DN). The main purpose of this thesis is to mitigate VR in such situation. Mitigation methods found in literature are evaluated in chapter 1 from PV-inverter and Distribution Network Operator (DNO)-side. By accurate assessment of the impact of high PV penetration in distribution networks, a risk-free level of PV penetration can be estimated for each customer, to prevent the VR. Accordingly, a comprehensive Index-Based Assessment (IBA) methodology to investigate the impact of high PV penetration in DNs is developed in Chapter 2 which suggests such safe margin and compares it to the Basic Active Power Curtailment (BAPC) method in a modified IEEE 13-bus network. According to the literature review, diverse criteria are considered by hypothetical decision makers, such as cost, required data infrastructure, control complexity and energy losses. A Priority-Based Decision-Making Methodology (PBDMM) is developed to consider these criteria in evaluating state-of-the-art of VR mitigation methods. PBDMM is based on an Analytical Hierarchy Process (AHP), utilizing pair-wise comparisons technique. Consequently, reactive power control (RPC) methods are more robust than other VR mitigating methods. Accordingly, in Chapter 4, major reactive power control methods are elaborated and the results are compared to a base case with no applied VR control strategy and PVs operate at unity power-factor. Finally in chapter 5 a novel index-based single-point-reactive-power-control (SPRPC) methodology is introduced for VR mitigation by absorbing adequate reactive power in a central fashion. The proposed index uses short circuit impedance analysis for best point assessment. SPRPC benefits from "Network effect" and is supported by DNOs, technically and financially, which makes it simple and efficient for VR mitigation. With SPRPC, existing PV inverters do not need to be upgraded and can retain their unity power factor, to avoid conflicting with the grid codes. Comprehensive 24-hour simulation is done on a modified IEEE 69-bus network, emulating a traditional residential grid with high $r/x$ ratio. SPRPC is compared to droop control in terms of efficiency and effectiveness to evaluate its advantages.