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A magnitude-phase detection method for grid-connected PCC of distributed generation systems based on sequence decoupling

It is a precondition of riding through the grid faults for distributed generation systems that the magnitude/phase information of voltages or currents at the grid-connected point of common coupling (PCC) must be acquired precisely, so that the control subsystem of the distribution systems could tackle the faults. However, the conventional three-phase software phase-locked loop (SPLL), which adopted PI control method and is widely used for the magnitude-phase detection, had a low speed of dynamic response affected by negative-sequence and harmonic components, so that it could not exactly acquire the magnitude/phase information of fundamental positive-sequence component. This paper proposes a novel three-phase magnitude-phase detection method based on double dq synchronous reference frame. The proposed method can decouple the positive dq and negative dq sequences and detect the magnitudes/ phases of fundamental positive-sequence component and negative-sequence component of three-phase voltages or currents. The simulation results verify that the proposed method overcomes the shortcoming of conventional three-phase SPLL and tracks accurately the magnitude/phase of the fundamental positive-sequence voltage under bad harmonic condition. The proposed method can suppress odd harmonic propagation and has a higher detecting precision. Thus, it can be widely used in the three-phase power electronics equipment.