Small-signal analysis of a fast central control for large scale PV power plants

Large scale Photovoltaic (PV) power plants are expected to comply with future grid code requirements that will demand a faster dynamic response. Such scenario will impact the operation of the Power Plant Controller (PPC), resulting in a reduction of response time that might bring potential interactions with the PV inverters and the AC network. This paper analyses the dynamic response and interactions within a large scale PV power plant. A small-signal model of the PV power plant is implemented including the PV inverter control, the AC collection grid and the PPC. Also, this model includes the dynamics associated to the delays of PPC measurements, communications, inverters and the Maximum Power Point Tracking. A case study based on a 4-inverter PV power plant is considered in the paper. Then, the stability and oscillation modes are analysed for different delay times and PPC parameters. A PPC design is approached implementing an H2-based parametric design on the corresponding PI controllers and the minimum response time is assessed. Moreover, in order to deal with large systems and facilitate the PPC design, a simplified model is proposed based on the relevant dynamics from the complete small-signal model.