An Optimisation-based Study of Volt-VAr Control from PV Inverters and STATCOMs in LV Unbalanced Networks

Active power export from rooftop PV can lead to increased network voltages. Volt-VAr control (VVC) from an LV STATCOM or PV inverters can absorb reactive power to help reduce this voltage rise, enabling greater active power export from rooftop PV. This paper investigates the impact of active voltage management from these technologies on the amount of active power that can be exported from rooftop PV. Towards this aim, this work adopts state-of-the-art mathematical modelling and optimisation techniques for VVC in unbalanced distribution network. In particular, exact VVC curves are treated directly as a nonlinear function, as opposed to a piecewise linear function that requires binary or integer variables to encode, thanks to a specific feature of the JuMP modelling language. Our modelling is then employed to numerically illustrate, on a real Australian unbalanced LV distribution network, that (i) if inverter VVC is already in place, installing an LV STATCOM provides very little additional voltage management benefits, (ii) in the absence of inverter VVC, Volt-VAr optimisation (VVO) from the LV STATCOM is very effective in maximising active power exports from rooftop PV and (iii) in cases where only a subset of inverters is providing VVC, an LV STATCOM is shown to significantly reduce PV curtailment.