Smart charging for Electric Vehicles (EVs) is gaining traction as a key solution to alleviate grid congestion, delay the need for costly network upgrades, and capitalize on off-peak electricity rates. Governments are now enforcing the inclusion of smart charging capabilities in EV charging stations to facilitate this transition. While much of the current research focuses on managing voltage profiles, there is a growing need to examine harmonic emissions in greater detail. This study presents comprehensive data on harmonic distortion during the smart charging of eight popular EV models. We conducted an experimental analysis, measuring harmonic levels with charging current increments of 1A, ranging from the minimum to the maximum for each vehicle. The analysis compared harmonic emissions from both single and multiple EV charging scenarios against the thresholds for total harmonic distortion (THD) and individual harmonic limits outlined in power quality standards (e.g. IEC). Monte Carlo simulations were employed to further understand the behavior in multi-vehicle scenarios. The results reveal that harmonic distortion increases as the charging current decreases across both single and multiple vehicle charging instances. In case studies where several vehicles charge simultaneously, the findings show that as more EVs charge together, harmonic cancellation effects become more pronounced, leading to a gradual reduction in overall harmonic distortion. However, under worst-case conditions, the aggregate current THD can rise as high as 25%, with half of the tested vehicles surpassing the individual harmonic limits.

This paper presents a new fast-acting backup protection strategy for future hybrid ac-dc distribution networks. By examining the impedance measured by an ac-connected distance protection relay, a unique characteristic is established for faults occurring on the dc-side of an embedded medium-voltage dc (MVDC) link, interconnecting two 33 kV distribution network sections. Based on the identified impedance characteristic, appropriate settings are developed and deployed on a verified software model of a commercially available distance protection relay. To remain stable for ac-side faults, it is found that the tripping logic of the device must be altered to provide correct time grading between standard, ac, protection zones and the fast-acting dc region, which can identify faults on the dc system within 40 ms. An additional confirmatory check is also employed to reduce the likelihood of mal-operation. The proposed solution is trialled on a test system derived from an actual distribution network, which employs distance protection, and is shown to provide stable operation for both standard ac-side faults and dc-side pole-pole-ground and pole-pole events.

The electrification of heat and transport along with significant increases in distributed energy resources pose challenges for distribution network operators (DNOs) as they evolve into distribution system operators (DSOs). Issues may include capacity constraints, voltage excursions, lower supply security and reduced power quality. A method of addressing these matters whilst unlocking capacity is therefore required. This paper will outline the case for the selective interconnection of grid supply points and primary substations via fully controllable power electronic links. This interconnection would form the basis of a `power levelling' network to help alleviate the above concerns as an alternative to a conventional `more copper' reinforcement strategy. Power flows for a conventional network will be benchmarked before assessing the potential capacity release created by delivering energy from multiple substations via controllable interconnection. Medium voltage direct current (MVDC) networks (operating in the range of 5-50 kV) represent a candidate technology for the proposed interconnection. The paper reviews current technology readiness level, international learning and relevant knowledge from other power sectors.

This paper outlines an approach to integrating electric vehicle (EV) charging systems to existing low voltage direct current (LVDC) public electrical transport infrastructure. Existing utility networks face challenges of accommodating a multitude of new connections associated with the adoption of EV charging infrastructure but when present, electrical light rail or tram networks represent a good opportunity to provide fast construction and less disruptive city centre charging implementation. Light rail network operation requires immediate power capacity to be available from any point on the network but if this margin were to be relaxed it opens up opportunities for sharing the available capacity with EV charging systems. This paper presents an electrical capacity assessment based on four separate charging control strategies applied to the public tram system in the City of Edinburgh, Scotland. The results of these studies, earthing and wider system protection requirements are considered and preliminary findings made.

This paper outlines the case for using Medium Voltage Direct Current (MVDC) (5-50 kV) elements in distribution systems as a means to accelerate the deployment of low carbon technologies. The approach uses existing cable and overhead assets, originally designed into the ac system for security purposes. By selective conversion to dc, an inter GSP (grid supply point) balancing network can be created with modifications only required at substations. This approach allows for increased network transfer capability without increasing fault level as would be the case with conventional interconnection. Using data from a real-world Scottish suburban distribution network, the benefits and barriers to such an approach are examined. Power flows for the existing network are benchmarked under various present day and future loading scenarios. Controllable MVDC links are introduced to the network and power flow studies used to assess the value of such an approach to network reinforcement. Cost estimates for such a scheme are projected using data from industrial trials.

This paper looks at the protection implications of introducing fully controllable, embedded, medium voltage dc (MVDC) power electronic links into power distribution networks. Studies have indicated, protection notwithstanding, that embedded MVDC can be used to provide economically attractive, enhanced capacity and control of power flows.