Phase-locked loop with adaptive signal cancellation for three-phase network side voltage source inverter

Circuits for synchronizing power converters to the three-phase utility voltages are often sensitive to voltage disturbances. Some kind of filtering device is needed. Voltage information is also important for system protection. Both voltage and frequency disturbances could be disadvantageous for the equipment. In this paper an alternative solution for improving the performance of a synchronizing circuit based on a phase-locked loop is proposed. It takes advantage of signal delay cancellation for calculating the symmetrical components of the three-phase voltages, but the delayed signal is estimated by an adaptive method. Other solutions for filtering input voltages are available, but they are mostly frequency dependent. The proposed solution is frequency independent. In addition, inherent signals may be utilized for protection purposes, since both instantaneous frequency and voltage values are estimated. This includes both positive and negative sequence voltages. The design has been simulated, and the simulation results are verified through experimental results.