Discrete-Time Quasi Sliding Mode Control of Single-phase T-type Inverters for Residential PV Applications

This research focuses on improving the performance of single-phase grid-connected DC/AC converters, which is intensively used in PV systems. First, the single-phase T-type topology which offers more voltage level than the conventional H-bridge is used to lower the total harmonic distortion (THD) of the output current. Second, the quasi-sliding mode control in combination with a lump disturbance compensation is used for the current control loop. This approach guarantees that the output current quickly tracks its reference in a few sampling cycles despite the existence of the modeling error. Finally, a DC bus voltage controller with a discrete-time notch filter that exactly extracts the average DC bus voltage from the second harmonic ripple is designed. The proper design of the notch filter plays a key role not only in the improvement of the DC bus voltage control-loop but also in the reduction of the overall THD of the line current. The validity of the proposed solution is verified by numerical simulation using Matlab/Simulink.