Transient positive- and negative-sequence estimation based on online elliptical trajectory approximation

As converter based renewable energy systems continue to penetrate the electric power grid, regulatory standards for grid interconnection continue to evolve. One of the most challenging requirements for generative systems is the injection of valuable reactive currents during Low-Voltage Ride-Through (LVRT) events, especially during asymmetric LVRT situations. As state-of-the-art, Phase Looked Loops (PLLs) are used to determine the corresponding amplitudes and phases of positive- and negative-sequence voltages, however, they show an inherent limited dynamic response during LVRT events. Therefore, this paper investigates an estimation algorithm for the positive- and negative-sequence systems that is based on the online elliptical approximation of the voltage space vector trajectory. The algorithm shows fast dynamic performance with regard to grid faults. The real-time capability of the algorithm is shown by implementation on a novel Field Programmable Gate Array (FPGA) based platform. The dynamic performance of the proposed algorithm is shown by direct comparison to common PLL methods.