Abstract: Discontinuous conduction mode (DCM) for inverters requires a small size of inductor and can realize soft switching for switches. Therefore, DCM can effectively improve the efficiency and power density for inverters. However, the current stress under DCM is relatively high. Targeting this issue, T-type three-level circuit was used to construct the LCL-filtered grid-connected inverter in this paper. And the inverter-side inductor worked under mixed conduction mode (MCM) combined by DCM when the load current was small and trapezium conduction mode (TPCM) when it was high, so as to realize the soft switching and reduce the current stress. Both DCM and TPCM could realize the fixed switching frequency, but it was difficult to design the controller based on the conventional state average model. Therefore, a charge quantity model which takes the charge quantity output from the bridge as the control variable was proposed in this paper. This model was a linear two-order model, which greatly simplified the design of controller. Based on the proposed model, a direct charge control (DCC) method with fixed switching frequency was proposed. Finally, the good performance of the proposed model and control method was verified by the simulations and experiments.