Reactive power potential of converter-connected renewables using convex power flow optimization

Converter-connected renewable energy sources (RES) in the distribution network alter the power flow in the network. Often, grid reinforcements and additional local reactive power sources are needed to maintain steady state network operation. Converter-connected RES is an accessible local reactive power source for distribution system operators to optimize network operations. However, the non-linearity and non-convexity in the converter equations make their modelling challenging, which further results in the under-utilization of the reactive power capability from these sources. Oftentimes, the converter-connected generator is partially modelled using only apparent power constraints. This paper presents an approach based on Schur's complement and piecewise planar approximation to incorporate the converter equations in a convex power flow optimization routine. The advantages of employing complete converter capabilities for optimal operation of the distribution network are studied via simulations on a real distribution network dataset. A comparison between deploying reactive power according to the minimum grid codes requirement, partial modelling of the converter, and complete converter capabilities is correspondingly presented. Active power losses decrease by 4.1% over 10 month period with high penetration of renewable generation. Furthermore, the voltage profile in the distribution network is improved and the reactive power dependency on the transmission network is reduced.