Inverse Park Transformation PLL for VSC-HVDC under Unbalanced Voltage Condition

To realize the fast and accurate extraction of positive-sequence fundamental voltage phase of VSC-HVDC under unbalanced grid. A design scheme of three-phase phase-locked loop (PLL) based on inverse park transform is proposed., that is, the production of quadrature signals is realized by inverse park transform. Theoretically., it is proved that the proposed scheme can effectively carry out signal quadrature processing., and the design method of its key parameters is given. Then., based on the quadrature signal generator., a PLL suitable for VSC-HVDC system under the unbalanced power grid is constructed. The simulation results show that the PLL has good adaptability and can quickly lock the phase.