Enhanced fault ride-through of power converters using hybrid grid synchronization

Inaccurate phase-angle jump estimation of the grid voltage during faults is one of the major causes for poor fault ride-through performance of converters. To overcome this issue and make the converter’s current controller robust, this paper proposes a hybrid grid synchronization transition technique. In this concept, a synchronous reference frame based phase-locked loop (SRFPLL) grid synchronization method is used during normal grid operation and switched to an arctangent based phase-angle estimation during grid faults. Simultaneously frequency estimation is switched to the arctangent derived frequency. A common transition method, which depends on the phase-angle error between the two phase estimation techniques, is proposed to ensure a smooth transition between the hybrid phase-angle and frequencies. The transition technique is implemented using the current control of a three-phase voltage source converter in the synchronous reference frame. The performance of the converter during both symmetrical and asymmetrical grid faults along with the fault ride-through strategies is tested using real-time experiments. It is observed that the transition based hybrid grid synchronization technique reduces the loss of synchronism duration. Additionally, it offers a more robust converter current control performance compared to the SRFPLL technique over a wide range of voltage sags and phase-angle jumps.