Current THD reduction for grid-connected inverter operating in discontinuous current mode

This paper proposes a Discontinuous current mode (DCM) feedback current control for the grid-connected inverter in order to achieve the low THD of the grid current at wide load range. In the DCM operation, the nonlinearity between the duty ratio and the current occurs in the current command response, whereas another nonlinearity between the disturbance voltage and the current occurs in the disturbance response. Therefore, the nonlinearity in the current command response is compensated by utilizing the duty ratio at the previous calculation period, whereas the nonlinearity in the disturbance response is utilized in order to reduce the effect of the disturbance and improve the grid current THD at light load. As a result, the grid current THD of the proposed DCM feedback current control is reduced by 89.0% at light load of 0.1 p.u. compared to the conventional Continuous current mode (CCM) feedback current control. Furthermore, the smooth current regulation is confirmed even when the load step change occurs from 1.0 p.u. to 0.1 p.u.