Abstract: This paper proposed a quadrature generator based on the theory of the improved proportional resonance controller. It could solve the problem that the dual second-order generalized integral phase-locked loop cannot be accurately phase-locked under grid fault conditions.The analysis in the frequency domain showed that the double second-order generalized integral phase-locked loop presented a low-pass characteristic, which meant it could suppress the effect on the higher harmonics. But it is hard to eliminate the DC component.He double improved proportional resonant phase-locked loop presented band-pass characteristic, which had a large gain effect on the signal at a specially appointed frequency, effectively suppressed the high-frequency harmonics and the DC component. Therefore, the improved proportional resonant phase-locked loop can collect accurate fundamental positive sequence phase information and promote the power factor of the invert-loop.The experimental result shows that in different situations, such as grid voltage sag, phase mutation, waveform distortion, and DC component, the dual improved proportional resonant phase-locked loop has higher phase-locking accuracy than the dual second-order generalized integral phase-locking loop. Moreover, the dual improved proportional resonant phase-locked loop has better suppression capability for non-basic components, and it could effectively enhance the robustness of the system.

    Key words: phase-locking loop; quadrature generator; dual second-order generalized integral; proportional resonance controller; harmonic