A three phase reference current generator for power electronic converters under distorted utility conditions

This paper presents an improved three phase PLL technique to generate the reference signals for power electronic converters in a grid connected system. The synchronization scheme employed for phase information should provide a high degree of immunity to power system disturbances because its sensitivity affects the reference signal generated. The SRF PLL works well under balanced and undistorted conditions however the reference signal generated using SRF PLL is distorted under phase unbalancing and harmonics conditions. The performance of the SRF PLL can be improved by reducing the bandwidth but this increases the locking time. To overcome the above limitation an improved three phase PLL based on a linear phase finite impulse response (FIR) filter has been developed. The addition of FIR to the system eliminates the ripples due to the distortions in the utility. The improved PLL technique is simulated in MATLAB and results for abnormal grid conditions such as unbalance, harmonics, phase jump and dc offset are presented to demonstrate its phase-tracking ability.