Phase-Locked Loop Enabled Grid Support Strategy Based on Power Conversion System of Energy Storage

In recent years, with the increasing penetration rate of renewable energy in the power grid, the grid faces greater challenges in stable operation. Among these challenges, maintaining stability of voltage and frequency is an important task, requiring a new strategy to better support the grid. However, the support for the power grid provided by traditional grid-following inverters is insufficient. Based on the typical control strategy for grid-following inverters, the characteristics of the phase-locked loop (PLL) are utilized to detect grid voltage and frequency parameter without using external measurement components. By using the reactive power-voltage and active power-frequency relationships in power system, a new grid support strategy is designed. When the grid frequency or voltage deviate from their rated value, the current reference values of inverters could be adjusted by the new strategy to change the output active and reactive power. As a result, the grid could be restored to its normal working conditions. The mathematical model and theoretical calculation of traditional grid-following three-phase inverters and their control strategy are also derived in this paper. All theoretical analyses have been verified by simulation. This new grid support strategy for grid-following three-phase inverters proposed in this paper could improve the design and application of grid support devices.