Abstract

This study focuses on the special requirement of synchronization of firing pulses for a power converter operating with a weak AC system. The challenge for the synchronization technique is in providing a fast dynamic response while maintaining a high accuracy of equi-distant pulse generation during steady state operation and maintaining stability within a range of system frequency and phase deviations. The phase locked loop (PLL) technique plays an important role in providing a reference signal synchronized with the AC system. With the development of new PLL techniques, it is possible to improve the dynamic response, robustness, harmonic rejection and stability of the converter system. These new techniques consist of an enhanced PLL and 3-phase PLL based on the DQZ method. A variety of these new synchronization techniques are investigated and compared with a conventional PLL in this thesis. The test system used is a 12-pulse HVDC converter operating with a weak AC system that is modeled with the EMTP RV simulation program