A new virtual-flux-vector based droop control strategy for parallel connected inverters in microgrids

Voltage and frequency droop method is commonly used in microgrids to achieve proper autonomous power sharing without rely on intercommunication systems. This paper proposes a new control strategy for parallel connected inverters in microgrid applications by drooping the flux instead of the inverter output voltage. Firstly, the relation between the inverter flux and the active and reactive power is mathematically obtained. Secondly, a novel flux droop method is then developed in order to regulate the active and reactive powers by drooping the flux amplitude and the phase angle, respectively. In addition, a small- signal model is developed in order to design the main control parameters and study the system dynamics and stability. The proposed control scheme includes a direct flux control (DFC) algorithm, which avoids the use of PI controllers and PWM modulators. Furthermore, in order to reduce the flux ripple, a model predictive control (MPC) scheme is integrated into the DFC. The obtained results shows that the proposed flux droop strategy can achieve active and reactive power sharing with much lower frequency deviation and better transient performance than the conventional droop method, thus which make it very attractive, highlighting the potential use in microgrid applications.