System Identification Based Adaptive Droop Control Strategy for Predominantly Resistive Microgrids

The conventional droop control schemes have been developed assuming predominantly inductive power lines, however in distribution grids with both resistive and inductive power lines, the appropriate reactive power sharing becomes a challenge. The use of large droop coefficients can improve the reactive power sharing, however, this approach deteriorates the system damping. This paper establishes a mathematical relation between the inverter droop coefficients and the damping coefficient of the inverter active power output. Based on this relationship, an adaptive droop coefficient power-sharing strategy is proposed that is applicable to grids with predominantly resistive lines. The proposed adaptive control continuously estimates the damping ratio of the inverter's active power response and using the derived relationship, it adjusts the droop coefficients. The damping ratio is estimated by perturbing the reactive power droop coefficient and analysis of the active power response of the inverter with Matrix-Pencil algorithm. The reactive power droop coefficient is updated until the inverter response exhibits critically damped behavior. Damping-coefficient based adaptive droop control brings two main advantages: (i) minimizing active and reactive power coupling effect that improves reactive power sharing (ii) preserving microgrid stability through adaptive adjustment of power droop coefficients that ensures the required level of system damping, hence enabling inverters to act as stability reservoirs.