Discontinuous Current Mode Control for Minimization of Three-phase Grid-Tied Inverter in Photovoltaic System

Abstract

In this paper, a current control method of discontinuous current mode (DCM) is proposed for a three-phase grid-tied inverter in order to minimize inductors without worsening current total harmonic distortion (THD). In a conventional continuous current mode (CCM) control, current THD increases as an inductor value is reduced, because a zero-clamping phenomenon occurs due to dead-time. In the proposed DCM current control, a zero-current interval is intentionally controlled and a dead-time-induced error voltage is simply compensated with a conventional dead-time compensation. The validation of the control method is confirmed by simulation and a 700W-prototype. As simulation results, compared to the conventional CCM current control, the current THD is reduced by 97.6% with the proposed DCM current control, whereas the inductor volume is reduced by 70%. In the experiments, the current THD is maintained below 5% over load range from 0.3 p.u. to 1.0 p.u. even when the inductance impedance is reduced to 0.5% of the inverter total impedance.