Modelling of grid-connected single-phase five level neutral point clamped inverter with sliding mode control method

The importance of renewable energy systems that provide clean and sustainable energy is increasing day by day. Photovoltaic systems stand out among renewable energy systems since it is predicted that they will meet a considerable amount of future energy needs. Inverters play an important role in converting the direct current (DC) obtained from the photovoltaic panel into alternating current (AC) and transferring it to the electricity grid. The design of grid-connected inverters is a challenging task both in terms of meeting the required grid standards and the desired control objectives. Therefore, in order to meet control objectives such as fast dynamic response, excellent reference tracking, robustness against parameter variations, easy applicability, low cost, and grid standards such as low total harmonic distortion, low DC transfer to the grid, and low leakage current, this thesis presents the modeling and analysis of a single-phase grid-connected H-bridge neutral point clamped inverter using sliding mode control. The chattering effect, which is the main problem of the sliding mode control method, is reduced by using the boundary layer method. The robustness of the sliding mode control approach against parameter variations is maintained by utilizing a proportional resonant controller while chattering is appropriately controlled. In addition, a transfer function between the measured grid current and the reference grid current was obtained to analyze the effect of the filter parameters on the system. Moreover, the proposed control method naturally dampens the resonance problem in the LCL filter. Finally, a symmetrical LCL filter and a special modulation technique are used to reduce the leakage current. The grid-connected H-bridge neutral point clamped inverter is modeled in MATLAB/Simulink® with the proposed control method, and steady state, transient, robustness to parameter variations, and leakage current analyses are investigated. The results of the simulation demonstrate that the control objectives and grid standards are achieved.