Applying Two Equidistant Samples-based-PLL on Unbalanced Three-Phase
Signals with DC Offsets
Abstract
Delayed signal cancellation (DSC) is a popular method to separate the
fundamental frequency positive- and negative-sequence components from
unbalanced three-phase signals. Conventional DSC can separate the
sequence components using a quarter-cycle delay. Fast DSC tools can
achieve the same with less than a quarter-cycle delay. However, neither
conventional nor fast DSC can handle DC offset without requiring
additional delayed signals. This letter addresses this issue by
proposing a modified DSC to estimate the sequence components with DC
offset rejection and having arbitrarily fast convergence speed, i.e.,
low memory requirement. Two equidistant delayed samples of the measured
grid voltages/currents are required to implement the proposed technique
and can easily be applied in a phase-locked loop (PLL). Comparative
experimental results demonstrate the suitability of the proposed
approach over other DSC methods.