Assessment and control of voltage in active distribution networks

Abstract

As the economy grows, power demand increases accordingly. However, meeting this demand through traditional generation methods is becoming increasingly impractical due to high capital costs, significant transmission expenses and losses, declining fossil fuel reserves, and growing environmental concerns. Renewable-Based Distributed Generation (RBDG) is emerging as the optimal solution. Historically, conventional energy sources accounted for 76% of global power generation, while renewable energy contributed 24%. By 2050, projections indicate a dramatic shift, with RBDGs expected to supply 85% of global power, leaving conventional sources at just 15%. Additionally, the rise of Electric Vehicles (EVs) is driving the expansion of charging infrastructure within distribution networks, boosted by advances in battery energy storage systems. Previously, RBDGs operated at a unity power factor without the capability to control active or reactive power, limiting their ability to manage network voltage profiles. While reinforcing the network with reactive power-compensating devices is a straightforward solution, it is costly. On-Load Tap Changers (OLTC) offer another option, but their limited range and slow response time, along with their inability to handle bidirectional power flow, reduce their effectiveness in active distribution networks. With advancements in power electronic inverter technology, RBDGs can now regulate both active and reactive power, helping maintain network voltage profiles. Active Power Curtailment (APC) and Reactive Power Compensation (RPC) are common strategies for RBDG inverters to manage voltage issues. However, arbitrarily selecting RBDGs for voltage control is not economically optimal. Thus, evaluating the impact of RBDGs on bus voltage is crucial for developing fast and dynamic voltage control strategies. These strategies are classified into centralized and decentralized control. Decentralized control is preferred over centralized control due to better economic efficiency. In decentralized voltage control, coordination with devices like OLTCs, voltage regulators, and reactive power compensators is necessary. Therefore, a hierarchical voltage control approach is adopted and implemented in multiple stages. In the primary stage, optimal settings for voltage-controlling devices are planned based on the stochastic nature of loads and generation. Subsequently, decentralized control using DGs is carried out. The increasing integration of RBDGs affects the network’s voltage profile and reduces its Hosting Capacity (HC) due to their stochastic characteristics. Battery Energy Storage Systems (BESS) help mitigate these effects through their charging and discharging capabilities. Distribution networks typically include small (residential), medium (community), and large-scale BESS. Larger BESS offer a higher benefit-cost ratio for enhancing the network’s HC. However, optimizing the placement of large BESS is challenging due to varying impacts of power fluctuations from RBDGs depending on their size and location. The Sobol sensitivity index is used to identify the most influential RBDGs in the network. Installing BESS with the most dominant RBDG helps improve HC. By optimally managing the BESS charging and discharging profiles and tuning voltage control parameters, the network’s HC is further enhanced.