MPPT-considered detailed models of large-scale photovoltaic plants and its application in power system small-signal stability analysis

This paper provides detailed and complete models of the large-scale transmission-connected PV plants which have considered the dynamics of maximum power point tracking (MPPT). These models are based on the WECC's generic PV system models whose circuit and control modes are modified to build our new PV models. In terms of the circuit, the detailed inner-loop current control model is adopted for the inverter's AC-side model. And we also add the models of elements at inverter's DC side, namely, the PV array model for the one-stage PV plant, and the PV array and boost models for the two-stage PV plant. This difference in the circuit introduces the random factors of PV systems (irradiance and temperature), which are the external factors contributing to the fluctuant PV output. In terms of the control modes, we design a similar reactive power control structure. And we also add two active power control modes for the complete PV circuit. They are the constant DC voltage control and MPPT control. These two control modes are used widely and can make the PV plants track the variations of irradiance and temperature in real time to reach their maximum outputs. So, they are the main internal factors contributing to the fluctuant PV outputs. Thus these models can be used to analyze, assess, and control the power system small-signal stability, especially for the case as affected by the fluctuant PV output due to random irradiance and temperature. Finally, we write these models into the modal analysis and transient simulation programs and then verify their correctness. We also show the applications of these models in the analysis and assessment of the power system small-signal stability.