Oscillated Power Compensation of a Three-phase Grid-connected Inverter Using Robust Control

A robust control strategy is proposed for a three-phase grid-connected inverter under unbalanced grid voltage conditions in this thesis. This scheme consists of dual-current controllers for positive and negative sequence components to achieve one of three control objectives: i) supplying balanced three-phase current, ii) supplying constant active power, and iii) supplying constant reactive power to the grid without offset error for given reference values using the same controller gains. Each of the controllers utilizes state feedback with integral action in the dq-rotational frame and uses Sinusoidal pulse width modulation (SPWM). A Linear Matrix Inequality-based optimization scheme is used to determine stabilising gains of the controllers to minimize the time to steady state in the occurrence of uncertainties. The uncertainties of the system are described as the potential variation range of the inductance and resistance in the L-filter. The efficacy of the proposed method is verified through simulation.