A combined MV and LV network voltage regulation strategy for the reduction of voltage unbalance

Voltage regulation is a crucial practice in distribution networks to ensure that the steady state voltage levels at customer connection points are within prescribed limits. In addition to ensuring required voltage levels, within a range of power quality problems, voltage unbalance is an important factor that determines the quality of supply. With regard to voltage regulation, one of the common methods employed by distribution network service providers is volt/var control. This method regulates the voltage of a network by controlling the voltage at the zone substation and by the injection or absorption of reactive power at different locations in the network. Typically, volt/var control is employed in medium voltage networks only, which overlooks the growth of distributed generation in low voltage networks. The increasing penetration of distributed generation may change the paradigm of voltage regulation to the extent that traditional volt/var control may not be effective. However, the effects of this increasing penetration can be countered by exploiting the versatility of distributed generation devices. This paper proposes a holistic volt/var control approach which takes into account voltage regulation in both medium and low voltage networks and voltage unbalance reduction in a low voltage network. The proposed control method utilises an on load tap changer and a fixed capacitor bank in the medium voltage network and also photovoltaic inverters in the low voltage network. The proposed control is tested on a modified IEEE 13 node test feeder over a 24-hour period over which the load varies. The results demonstrated that the proposed control method is able to perform voltage regulation and voltage unbalance reduction concurrently.