Effect of PLL on Current Distortion of Droop-Controlled Converters in a Control-In-the-Loop Simulation of a Microgrid

A grid-following converter in ac microgrids must include grid synchronization algorithms, such as Phase-Lock Loop (PLL) systems, within its control system, so it is able to properly inject or absorb power. PLL plays an important role to guarantee the stable operation of the converter for distinct grid conditions, and it becomes critical in microgrids with multiple converters, where mutual influence among the control and the interface passive devices of individual converters exists. Moreover, as long as PLLs basically estimate the system phase from voltages on their point of coupling to the grid, the grid synchronization is subjected to errors due to the digital-to-analog conversion and signal processing through conditioning circuits. The paper proposes the discussion on the mutual effects of PLL choice in two grid-following converters in a microgrid and on the impacts of errors introduced by voltage detection of the PLL. Results from real-time simulation through Control-In-the-Loop are presented.