A method for controlling a power system, the method comprising: generating, via at least one inverter-based resource of the power system, one or more command signals (450, V CMD) via a regulator of at least one inverter-based resource; dynamically estimating, via the at least one inverter-based resource, a reactive power capability of the at least one inverter-based resource based, at least in part, on a reactive power feedback signal, the one or more command signals (450, V CMD), and upper and lower limits (442, V MAX, 444, V MIN) of the regulator, characterised in that the reactive power capability comprises a reactive power capability upper value (310, Q CapHi) and a reactive power capability lower value (312, Q CapLo), wherein dynamically estimating the reactive power capability of the at least one inverter-based resource comprises: if the one or more command signals equal the upper limit (442, V MAX), then setting the reactive power capability upper value (310, Q CapHi) equal to the reactive power feedback signal and the reactive power capability lower value (312, Q CapLo) equal to a lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource, if the one or more command signals (450, V CMD) equal the lower limit (444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to an upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the reactive power feedback signal, and if the one or more command signals (450, V CMD) do not equal the upper or lower limits (442, V MAX, 444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to the upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource; sending, via the at least one inverter-based resource, the reactive power capability to a system-level controller of the power system; and, controlling the power system based on the reactive power capability. generating, via at least one inverter-based resource of the power system, one or more command signals (450, V CMD) via a regulator of at least one inverter-based resource; dynamically estimating, via the at least one inverter-based resource, a reactive power capability of the at least one inverter-based resource based, at least in part, on a reactive power feedback signal, the one or more command signals (450, V CMD), and upper and lower limits (442, V MAX, 444, V MIN) of the regulator, characterised in that the reactive power capability comprises a reactive power capability upper value (310, Q CapHi) and a reactive power capability lower value (312, Q CapLo), wherein dynamically estimating the reactive power capability of the at least one inverter-based resource comprises: if the one or more command signals equal the upper limit (442, V MAX), then setting the reactive power capability upper value (310, Q CapHi) equal to the reactive power feedback signal and the reactive power capability lower value (312, Q CapLo) equal to a lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource, if the one or more command signals (450, V CMD) equal the lower limit (444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to an upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the reactive power feedback signal, and if the one or more command signals (450, V CMD) do not equal the upper or lower limits (442, V MAX, 444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to the upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource; if the one or more command signals equal the upper limit (442, V MAX), then setting the reactive power capability upper value (310, Q CapHi) equal to the reactive power feedback signal and the reactive power capability lower value (312, Q CapLo) equal to a lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource, if the one or more command signals (450, V CMD) equal the lower limit (444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to an upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the reactive power feedback signal, and if the one or more command signals (450, V CMD) do not equal the upper or lower limits (442, V MAX, 444, V MIN), then setting the reactive power capability upper value (310, Q CapHi) equal to the upper reactive power equipment rating (Q rat) for the at least one inverter-based resource and the reactive power capability lower value (312, Q CapLo) equal to the lower reactive power equipment rating (-Q rat) for the at least one inverter-based resource; sending, via the at least one inverter-based resource, the reactive power capability to a system-level controller of the power system; and, controlling the power system based on the reactive power capability.