Capacity release in LV distribution networks with power electronics

Abstract

Connection of low carbon technology to the LV distribution network stresses the network voltage limits. In certain cases this is such that further low carbon technologies such as, distributed generation sources, heat pumps, and electric vehicles, cannot be accommodated without costly network reinforcement. One solution is use power electronics to regulate the voltage and so remove these network voltage constraints. This can defer or even remove the need for network reinforcement and so reduce investment costs for distribution network operators. This thesis examines how these power electronics can be installed into distribution network for the purposes of voltage control and capacity release in constrained networks. The efficacy of five power electronics solutions relative to both reinforcement and de-regulation (or relaxing) of voltage limits is compared in technical and economic aspects. As de-regulation requires knowledge of how the network loads function in response to supply voltage fluctuation an analysis of how de-regulation effects the loads connected to the grid was undertaken. This revealed there is more reliable operation of these loads with voltages well below the present UK limits, however their tolerance of over voltages is shown to be very limited. Following on from this, it was shown that, when coupled to changes to the nominal system voltages, reinforcement could be deferred by de-regulation. Testing and simulation of both motor loads and the magnetics in common power supply units was performed, were a method was outlined for consideration of the losses in a flyback transformer and a boost inductor when subject to supply voltages outside of their tolerance bands. Detailed models of distribution networks are needed to accurately quantify the befits of deregulation and PEDs, so three detailed test networks where assessed in terms of their hosting capacity for low carbon technologies. A load model was presented for load flow studies that enables the model to be used in scenarios where the supply voltages are subject to wide voltage fluctuations. Additionally, the effect of thermally controlled goods was also considered by implementing either constant energy or dynamic thermal model into these goods. Finally to aid in assessment of the huge variance in LV network topology, metrics were developed to indicate the relative constraints a given network will likely face. These where seen in the cases test to be in good agreement with the results of the substantially more time consuming load flow methods.