Enabling Utility-Scale Solar PV Plants for Electromechanical Oscillation Damping

This paper presents a new control method to enable large-scale solar photovoltaic (PV) plants to damp electromechanical oscillations. The proposed step-down modulation (SDM) control method is based on active power modulation, and it does not require curtailment as in other approaches. After an oscillation event is detected, the PV panel voltage is controlled to transiently deviate the power from its maximum power point (MPP), this power margin is used to modulate active power until the oscillation event is mitigated. Then, the SDM control restores the PV power to its MPP, and it is reset to operate for the next event. The control design, panel voltage strategy, and implementation is tested in a two-area system. A comparison of the SDM control with a curtailment-based PV damping control is also explored in a test case of the 179-bus WECC system with six large-scale PV plants, showing the improved damping capability of the proposed method.