A Truly NTD-Based PLL: Simple Approach of Double-Frequency Oscillation Rejection

Nonfrequency-dependent transport delay phase-locked loop (NTD-PLL) comprised of an additional transport-delay (TD) unit in the Park transformation matrix (TM), supposedly to improve the offset and double-frequency oscillatory errors (DFOEs) during the frequency deviations. This modification in the Park TM, however, does not eliminate the DFOEs from all the estimation parameters of the utility grid. It is shown in this letter that the issue can be completely alleviated from all the estimation parameters of the grid just by adding another TD unit in the Park TM of NTD-PLL. The effectiveness of the suggested approach is verified through numerical and experimental results.