Discrete-Time Sliding Mode Control of Grid-Connected T-type Converter Applied to PV Systems

Abstract

The use of renewable energy such as photovoltaic (PV) in residential applications has been increasing dramatically in recent years. In such applications, single-phase DC/AC converters that transform the direct current to alternating current are normally used as an interface between clean energy and the grid. In order to connect to the grid, several strict requirements of the grid code must be fulfilled. In this research, various solutions are proposed to enhance the performance of the single-phase DC/AC converters in grid-connected mode. First, the single-phase T-type topology which offers more voltage level than the conventional H-bridge topology is used to lower the total harmonic distortion (THD) of the output current as well as to reduce the cost of the boost reactor. Second, the quasi-sliding mode control in combination with a lump disturbance compensation is employed for the current control loop. This approach guarantees that the output current can quickly track 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 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 injected current. The validity of the proposed solution is verified by numerical simulation using Matlab/Simulink.