Experiment on Three-Phase Inverter with Output LC-filter under Unbalanced load Conditions using Robust Control

This thesis presents a robust control technique for three-phase LC-filtered inverter under unbalanced load conditions. Under unbalanced load cases, the output voltage becomes unbalanced due to the presence of negative sequence voltage. To obtain a well-balanced three-phase voltage, the negative sequence must be eliminated. Therefore, a paralleled voltage control is proposed in this paper for positive and negative sequence. Positive sequence control is designed to regulate the output voltage using a given reference and negative sequence control is employed to compensate the unbalanced voltage. The control law of this method utilizes integral control to provide offset-free output and state feedback control to bring stability to the system. In addition, the uncertainty model is considered in this thesis so that the overall stability and robustness of the system can be improved. This method is employed using dq-synchronous frame with sampling frequency of 10kHz. The efficacy of this control method is verified using simulation results and experiments on a three-phase inverter prototype using TMS320F28335 DSP control board.