Fast DC component suppression method for phase locked loop

The reasons of measured grid voltage signals including dc components in the grid-tied applications could be the original input signal with dc component, the zero drift of detecting elements and converters, or the grid system fault. When the measured grid voltage has the undesired dc component, the low frequency oscillation would appear in the traditional phase locked loop (PLL) and in consequence induce the inaccuracy of calculated phase angle and amplitude. A traditional method to eliminate the DC component in the measured AC signal is to convert the AC signals to DQ components in the synchronous reference frame and then assume a low-pass filter with the low cut off frequency to filter out the low order harmonics added in the converted dc signals, which however would unavoidably prolong the system response time and is unsatisfied in those applications need fast reaction function. This paper proposes a fast dc component suppression method for the phase locked loop, which can fast filter out the dc component appeared in the sampled AC signal. Moreover, the proposed PLL can keep the fast and accurate calculation of fundamental voltage amplitude and phase angle even though the harmonic distortion occurs. Simulation and experimental results verified the effectiveness of the proposed method.