Grid connected inverter’s control strategy needs to detect the positive- and negative-sequence component of voltages and currents under unbalanced voltage condition in the power system. This paper studies a kind of resonant controller called the reduced order resonance (ROR) regulator, which is reduced from the traditional second order generalized integrator (SOGI). The regulator is able to achieve floating control of alternating voltage’s positive- or negative-component independently at a given frequency. A new positive- and negative-sequence component detecting method is proposed. Integral factor is added in the regulator and the angular frequency is obtained by phase locked loop’s feedback. Simulation and experiment results show the proposed method can achieve zero error tracking of grid voltage’s positive- and negative- component in stationary reference frame quickly, and has fast dynamic response and a certain degree of harmonic suppression ability.