A novel adaptive controller for one-stage PV power plants considering PLL dynamic performance

The ongoing transition from power systems dominated by synchronous machines to systems based on renewable energy sources (RES) is pushing a change from conventional robust power systems towards weak low-inertia systems. Stability problems can manifest in several ways in these systems. Problems such as small-signal, voltage, and converter-driven instability are more likely to arise in weak networks. Recent experience has shown that the phase-lock-loop (PLL) control loop is among the key instability drivers in RES power plants. Moreover, the dynamic performance of RES and their interaction with the grid during faults strongly depend on system strength at the connection point and the control strategy implemented. In this context, this paper contributes by proposing a novel adaptive controller that considers the dynamic performance of the PLL and the level of network strength, along with a methodology for systematically tuning its control parameters. The controller is specially designed for photovoltaic (PV) power plants to ensure that these units can successfully ride through grid faults even when connected to weak networks. The stability of the system under all operating conditions is achieved by considering the level of network strength endogenously in the tuning process. The proposed Control and methodology are validated through transient simulations using the 9-bus IEEE test system.