Protecting the last mile – enabling an LVDC distribution network

Traditional distribution power systems are facing numbers of changes. The major aspects that may influence the shape of the changes include: the connection of small scale renewable and advanced distributed energy resources, the deployment of demand side controls, and the supply of more heat and transport demands. But, because distribution systems have been designed and operated with very limited automation and controllability especially at lower voltages, such changes will grow in impact and extent starting from the tail of the network and working upstream. Consequently the future grid's " last mile " to consumer premises will see significant pressure for the provision of significantly increased power flow capacity and the accommodation of decentralised controls. The last mile network benefits the least from load diversity due to the lower number of consumers that each asset serves, and therefore significantly increased power flow capacity will be required over and above the provision of smart controls. Only then can the anticipated growth in electric vehicle and heat pump deployments, for instance, be accommodated. Further constraints on the choices made in changing the last mile network stem from the scale and intrusive nature of the LV network – options where wholesale changes to cable assets involving significant numbers of disruptive streetworks can be avoided during the transition of the network are very attractive. There is therefore a need for a rethink of the new standard designs to be adopted in last mile network. Furthermore, since most of the decentralised devices generate/consume DC or require a DC intermediate stage, low voltage direct current (LVDC) distribution systems with help of smart controls have the potential to facilitate this transformation. LVDC systems can enable increased penetration of distributed renewables, support better control, accommodate new heat and transport demands, and reduce losses with advantages over the corresponding low voltage alternating current (LVAC) systems. However, integrating LVDC systems within existing power grids will introduce a new complex arrangement of mixed AC and DC systems. In order to increase the feasibility of LVDC networks, and make LVDC distribution systems technically compatible with existing AC systems, this report has investigated the main challenges in doing so. It has also outlined a number of recommendations that can accelerate the implementation of LVDC systems. The report has in particular considered: the potential benefits of LVDC systems for future electricity grids, the possible topologies of LVDC last mile networks, the characteristic behaviour of an …