A Digital PLL Scheme for Three-Phase System Using Modified Synchronous Reference Frame

This paper proposes a novel phase-locked loop (PLL) control strategy to synthesize unit vector using the modified synchronous reference frame (MSRF) instead of the traditional synchronous reference frame. The unit vector is used for vector rotation or inverse rotation in vector-controlled three-phase grid-connected converting equipment. The developed MSRF-PLL is fast in transient response compared to standard PLL technique. The performance is robust against disturbances on the grid, voltage wave with harmonic distortion, and noise. The proposed algorithm has been analyzed in detail and was fully implemented digitally using digital signal processor TMS320F2812. The experimental evaluation of the MSRF-PLL in a shunt active power filter confirms its fast dynamic response, noise immunity, and applicability.