Affected by the negative sequence component and harmonic component of three-phase grid, the conventional three-phase software phase-locked loop (SPLL) circuits were unable to extract the magnitude-phase information of three-phase fundamental positive sequence component accurately, and the dynamic response speed was slow. In order to solve this problem, this paper introduces T/4 time-lapse elimination detection, a novel method of detecting three-phase magnitude-phase based on double d-q synchronous reference frame, functioning in decoupling positive and negative sequences of fundamental wave. When the voltage (or current) fundamental positive and negative sequence components are separated, the positive sequence component as well as the magnitude and phase position of negative sequence component from three-phase fundamental can be detected, so it is effective to restrain the impact on detection precision from negative sequence component. To verify the performance of this novel method, simulation experiments like transient response under normal grid condition, dynamic response under three-phase unbalance with harmonic pollution condition and dynamic response under phase jump condition are carried out. The simulation results verify that the proposed method overcomes the shortcoming of conventional three-phase phase-locked loop and tracks accurately the magnitudes and phases of the foundational positive-sequence voltage under harmonic pollution condition. And the results also verify that the proposed method can suppress odd harmonic propagation and has a higher detecting precision comparing with T/16 time-lapse elimination method. The improved T/4 time-lapse elimination detection can be wildly applied in three-phase power electronic devices.
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