Decoupled droop control techniques for inverters in low-voltage AC microgrids

This paper discusses the droop control method for inverters participating in low voltage microgrids and its application as a primary control layer which can be actuated from a secondary control layer to dispatch active and reactive power. To that end, an independent and decoupled relationship between frequency and active power; and voltage and reactive power is desirable. When the classic droop control method is applied to inverters connected to the microgrid through RL type impedance, this decoupled actuation is lost. Different variants of decoupled techniques are presented and analyzed from the point of view of static and dynamic behavior. The analysis is supported on a linear dynamic phasor model of the droop controlled inverter, and verified by simulations of behavior in an isolated microgrid and in grid tied mode using a detailed SIMULINK/SimPowerSystems model of the inverter and its internal control. Among the diverse techniques, the recently proposed droop control method with dynamic decoupling is signaled as advantageous, not only in terms of decoupled actuation but also in flexibility in adjustment of static and dynamic response.