Transient response comparison of virtual oscillator controlled and droop controlled three-phase inverters under load changes

This study compares two inverter control methods, virtual oscillator control (VOC) and droop control, in terms of time responses of a three-phase single-inverter system under a load step change. The analytical comparison is aided by small-signal modelling. Two small-signal VOC models are derived from the average VOC dynamics by approximating average power differently; two small-signal droop control models using distinct filters are also assessed. By letting the two controllers have similar droop characteristics in steady state, participation analyses are performed to predict transient responses of the systems. The analyses are verified by simulations and experiments. This study presents a meticulous comparison between VOC and droop control in a three-phase system. It is demonstrated that two types of linearized models produce similar transient responses in the output voltage and current amplitudes. VOC has a faster transient response in instantaneous frequency while the droop controller can have a transient response as fast as the VOC in the terminal voltage amplitude. This reveals that the VOC and droop controller can be designed to yield similar responses under a load disturbance. Comparing them in a stand-alone system aids in understanding the control loop as a step towards understanding transient behavior in multiple source systems.