Abstract:

Conventional synchronous generators (SGs) used in fossil fuel plants are being progressively phased out by inverter-based resources (IBRs) such as solar and wind farms mainly due to the decreasing cost of renewable energy resources and climate change concerns. In September 2022, the Australian parliament pledged to cut carbon emissions by 43% by 2030 and to net zero by 2050. This will lead to accelerated deployment of IBRs in the Australian national grid. The vast majority of the currently installed IBRs operate in a grid-following mode, meaning that for their operation, they follow the voltage at their point of connection (PoC) using a phase-locked loop (PLL), while the network voltage/frequency regulation is primarily the responsibility of SGs. A power system consisting of only grid-following inverters (GFLIs) and a decreasing number of SGs poses two main challenges: 1) with the decreasing share of SGs, voltage/frequency control and other services traditionally provided by SGs must be undertaken by alternative sources, and 2) GFLIs face stability risks when operated in weak parts of the grid, due to the unstable operation of their PLL.

The emerging grid-forming inverter (GFMI) technology, however, can enable the Australian grid to absorb an increasing share of renewables with its current infrastructure without the need for billion-dollar investments. GFMIs, as opposed to GFLIs, do not require a PLL for grid synchronisation and may provide voltage/frequency control and system strength services, making them a suitable alternative for replacing the retiring SGs. Currently, the majority of GFMI installations around the world are battery-energy storage system (BESS)-based, meaning that the DC side of the inverter is fed by a battery providing a stiff DC voltage.

To benefit from grid-forming (GFM) control, other inverter-based components, e.g., wind and solar farms, high-voltage DC (HVDC) systems, and STATic COMpensators, may also be retrofitted with grid-forming capability. Although some of the control blocks used for BESS-based GFMI (internal current control loop, point of connection voltage loop, and the primary loop for real and reactive power control) could be similarly adopted for other GFM-IBRs, there are various considerations that are needed to be taken into account to enable GFM capability for non-BESS IBRs. This presentation will shed some light on how various IBRs may be able to provide grid forming capability.