A Study on Robust Control of Three Phase AC/DC Converter under Unbalanced Grid Voltage

This thesis presents “a robust control technique for three-phase AC/DC converter under unbalanced grid conditions”. The control method consists of inner-loop robust grid-current control and outer-loop proportional integral control for constant voltage (CV) control. A dual-current control for the inner-loop positive and negative sequence is employed to eliminate the unbalanced current caused by the grid so that a constant voltage can be provided to DC loads. The inner-loop robust controllers utilize state feedback with integral action in the dq​​​​ synchronous frame. A linear matrix inequality-based optimization scheme is used to determine stabilizing gains of the controllers to maximize the convergence rate to steady state in the presence of uncertainties. The uncertainties of the system are described as the potential variation range of the inductance and resistance in the L-filter.