Benchmarking of Different Orthogonal Signal Generator Configurations for SOGI PLL Applications

Phase locked-loop (PLL) implementation using a second-order generalized integrator orthogonal signal generator (SOGI OSG) is very popular for grid applications involving synchronization and parameter estimation. Depending on the transfer function of the OSG outputs, different configurations of SOGI OSG, namely: standard SOGI (S-SOGI), highpass SOGI (H-SOGI) and lowpass SOGI (L-SOGI) are possible. In this work, these different SOGI OSGs are benchmarked to determine their advantages and disadvantages for PLL implementation. Specifically, the momentary loss of orthogonality at the OSG output during grid disturbances that cause the PLL’s estimated frequency to deviate from its nominal value is evaluated. It is shown that, although the different SOGI-based PLLs share structural similarities, they are indeed distinct in their response to grid disturbances. Experimental results are provided to verify the accuracy of the SOGI OSG benchmark where it is revealed that the S-SOGI PLL, which is the most popular of the SOGI PLLs, may not be suitable for grid applications requiring low-voltage ride-through capability.