Optimal Angle Droop for Power Sharing Enhancement With Stability Improvement in Islanded Microgrids

In islanded microgrid, the conventional voltage and frequency droop control is commonly used to share the real and reactive power among parallel inverters in autonomous fashion without communication. However, this is done at the expense of changing the system frequency and voltage. To enhance the power sharing and to restore the frequency and voltage to their nominal values, a secondary loop is added to the droop where in certain cases a communication link is imposed between a centralized controller and each associated droop control. To avoid using complicated multiloop feedbacks, this paper proposes a new angle droop control to share power with improvement in stability and power sharing enhancement. To perfectly control the output voltage of inverters with smaller THD and high bandwidth, a one-loop flatness based control is employed. For stability analysis and droop parameters settings, a model of the power system is developed. The state-space equations are formed with respect to the common reference frame. The resulting system matrix around an operating point is used to derive the eigenvalues to analyze the small-signal stability of the system. The theoretical analysis and the effectiveness of the proposed angle droop have been validated by simulation and experiments.