Nonlinear supersets to droop control

Abstract

This paper offers a suite of extensions to Virtual Oscillator Control - a time-domain control method for islanded inverters whereby they are controlled to emulate the dynamics of weakly nonlinear limit-cycle oscillators. First, we develop a coordinate transformation to derive the PWM switching signals from the oscillator dynamic states in a manner that allows the inverter terminal-voltage amplitude and frequency to be traded off against a parametric linear combination of average active and reactive power. Additionally, we compare the time-domain performance of VOC to droop control for parallel connected inverters in two cases: synchronization from a cold start and inverter addition. Finally, with a view towards developing output filter-design strategies as well as outlining strategies for grid-connected operations, we derive a sufficient condition for a Virtual-Oscillator-controlled inverter to be entrained to a stiff voltage source.