A Comparison of LMI and GA Based Robust Controller Designs for VSC HVDC

A controller is required for a VSC HVDC (voltage source converter high voltage direct current) terminal that provides good performance across a range of operating conditions. A nominal mixed sensitivity H _infin design is first presented. An LMI based robust H_infin design and two genetic algorithm based direct search methods methods are then applied to optimize the same H_infin norm across an operating range to provide robust performance. It is demonstrated that in this application the controllers designed by direct search using GA give better robust performance than the LMI based method. The principal reason for this is that unlike LMI based methods they do not guarantee quadratic stability across the operating range, even though stability across the operating range is demonstrated