Increasing the capacity of the Low Voltage Distribution Networks using All-SiC AC-AC Converters

Abstract

Towards 2020, future energy scenarios predict an excessive penetration of distributed generation (DG) in low voltage (LV) networks as well as a significant uptake of electric vehicles (EVs) and electro-heating. The Distribution Network Operators (DNOs) in UK will face significant challenges towards this de-carbonised electricity generation and consumption shift. The deployment of these so-called low carbon technologies (LCTs) will impact the performance of the distribution network in such way where solutions will be needed to maintain capacity, reliability and the availability of the electricity supply to customers. The practise to put more copper on the ground – reinforcement - in order to facilitate these changes is found to be expensive and disruptive to the public and business. An innovative solution proposed in this thesis is to increase the voltage along the distribution feeders and step it back down at a customer’s premises. Results show that a significant increase at the hosting capacity of the existing network can be achieved and power quality problems such as overvoltage caused by DG can be avoided. The voltage step-down device, which is termed a voltage control unit (VCU), is to be located in the meter-box of each house. This location raises challenges round the temperature rise in the box caused by VCU losses, and the subsequent effect on the electricity meter and cut-out fuse. It also imposes constraints on the size and weight of the VCU so that a very high efficiency design is required, with high power density and small mass. The optimum VCU design was found to be a power electronic AC Chopper using new Silicon Carbide (SiC) MOSFETs and diodes. The technology was demonstrated by designing, constructing and testing two interleaved, parallel operation, 1 kW AC Chopper modules. Results from the prototype were compared against Spice simulation results and theory and confirmed that the target efficiency of 99% was achieved.