Abstract
Three-phase unbalanced conditions in distribution networks are conventionally caused by load imbalance, asymmetrical fault conditions of transformers and impedances of three phases. The uneven integration of single-phase distributed generation (DG) worsens the imbalance situation. These unbalanced conditions result in financial losses, inefficient utilisation of assets and security risks to the network infrastructure. In this study, a phase-changing soft open point (PC-SOP) is proposed as a new way of connecting soft open points (SOPs) to balance the power flows among three phases by controlling active power and reactive power. Then an operational strategy based on PC-SOPs is presented for three-phase four-wire unbalanced systems. By optimising the regulation of SOPs, optimal energy storage systems dispatch and DG curtailment, the proposed strategy can reduce power losses and three-phase imbalance. Second-order cone programming (SOCP) relaxation is utilised to convert the original non-convex and non-linear model into an SOCP model which can be solved efficiently by commercial solvers. Case studies are conducted on a modified IEEE 34-node three-phase four-wire system and the IEEE 123-node test feeder to verify the effectiveness, efficiency and scalability of the proposed PC-SOP concept and its operational strategy.
Highlights
1.1 Three-phase imbalance in distribution networksThree-phase imbalance commonly happens in around 70% of the UK's low voltage (LV) power distribution networks [1, 2]
Single-phase optimal power flow (OPF): In [52], the authors formulate the singlephase OPF in the distribution networks as a mixed-integer second-order cone program (MISOCP), for which the global optimal solution up to the desired accuracy can be found by using available commercial solvers
The paper is organised as follows: Section 2 is the unbalanced three-phase optimal operation problem formulation, in three-phase four-wire distribution systems; Section 3 presents the case study with four different cases for comparison and result analysis; Section 4 summarises the conclusion of the paper
Summary
Three-phase imbalance commonly happens in around 70% of the UK's low voltage (LV) power distribution networks [1, 2]. Unbalanced three-phase voltages are observed more frequently because of increasing single-phase DER installations and uncertainties of renewable power generation outputs [8, 9] and charging/ discharging of batteries and electric vehicles. The time variances of load and DG make the imbalance changing between phases. To improve the switching performance, new types of switches with power-electronic devices, such as soft open points (SOPs), designed and installed to replace these traditional tie switches with much shorter response time (20 ms) [18], provide an alternative novel solution to flexible distribution networks. We have chosen to focus on the SOP-enabled network reconfiguration for alleviating three-phase imbalance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
