Mitigation of Low-Frequency Inter-Area Oscillation Using Grid-Forming Inverters

Meanwhile, inverter control technologies have also advanced in recent years, one of which is grid-forming (GFM) inverter control. Although there is no universal definition of GFM, it refers to a suite of control strategies that maintain a constant or nearly constant internal voltage phasor in transient and/or sub-transient time frame to allow fast response to grid disturbance, black start, islanding operation, etc.

This paper investigates the potential damping control contribution from GFM inverters. The two-area four-machine system is used for the study. Three different GFM control designs:

droop, virtual synchronous generator (VSG), and dispatchable virtual oscillator (dVOC) are studied. It is concluded that with appropriate parameterization the three control designs have similar performance and can improve the damping ratio of the target oscillation mode. A sensitivity analysis with respect to frequency droop and voltage droop is performed. Larger frequency droop gain can improve the damping control performance for all three GFM control designs, while larger voltage droop gain has negligible impact on the damping control performance for the three GFM control designs. Additionally, the damping control performance of GFM inverters is compared with grid-following (GFL) inverters with a supplemental power oscillation damper (POD). The GFL inverters without a POD have no damping control contribution. With fine-tuned control parameters, the POD on GFL inverters can modulate active power or reactive power to provide similar damping control with GFM inverters.

A similar study is also conducted on the Continental Europe synchronous area system with the replicated December 3rd 2017 event by simulations. Six substation locations are selected with projected IBR plants. An aggregated GFM inverter model with corresponding capacity is used for each plant and is directly connected to each high-voltage bus. The conclusions are similar with those in the previous study on the two-area four-machine system, except that larger voltage droop gain can also improve damping control when the system is marginally small-signal stable.

Moreover, a sensitivity analysis of oscillation damping with respect to number, capacity and location of GFM inverters is conducted. More GFM inverters and larger GFM capacity can both improve damping control performance, while the GFM controllability depends on the substation location.