Small-Signal Analysis and Enhanced Control of Large-Scale PV-Penetrated Power Systems From the Electromechanical Oscillations Point of View

High penetration of photovoltaic (PV) plants in power systems may reduce the damping of electromechanical (EM) oscillatory modes. Implementing auxiliary controllers in the PV plant control system is a well-known technique that can improve the damping of these oscillations. Active power modulation (APM) is an effective auxiliary-control-based method that requires an energy source. Previous works have proposed employing an external energy storage system (ESS) as the energy source of the APM or deloading the PV plant by moving away from its maximum power point (MPP) characteristic. However, installing ESSs is expensive, and distancing from the MPP is not economical. By focusing on the dc-side components of large-scale PV plants, this study proposes an APM method that does not need any ESSs or deloading. Instead, this article first evaluates the available amount of stored energy in the dc-link capacitors of large-scale PV plant inverters and then proposes a novel controller to employ this energy for the APM. Furthermore, impacts of large-scale PV plant penetration levels with and without the proposed controller as well as the PV unit numbers and the power system parameters and operating point on the damping ratio of EM modes and the performance of the proposed controller with various feedback signal types and measurement delays are investigated.