Droop control is widely used in parallel operation of inverters in microgrid. This control method will lead to frequency deviation. Although frequency deviation can be reduced by decreasing the droop coefficient

the control performance will be affected. This paper proposes a new control method by combining the droop control

virtual impedance and power coordinate transformation. Coordinate transformation is carried out for the active power P and reactive power Q by virtual impedance

by which general active Pd and general reactive power Qd are obtained. Droop characteristic between Pd and frequency f is proved while controlling Qd by adjusting the virtual impedance. By choosing the ratio between virtual resistance and virtual reactance according to the power factor of load

Pd will approach zero and thus the steady-state frequency deviation will be made to approach zero. The P and Q sharing is adjusted by choosing proper droop coefficients and the impedance amplitude inversely in inverse proportion to inverters' rated capacity. The proposed method can achieve near zero steady state frequency deviation and proportional sharing of active power and reactive power. Simulation by MATLAB has confirmed the effectiveness of the proposed control method.