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This project proposes an improved phase disposition pulse width modulation for a modular multilevel inverter which is used for a photovoltaic grid connection. Here modular multilevel inverter is used as an interface between photovoltaic panel and grid. Modular multilevel inverters has been increased in the recent years due to its advantages such as better harmonic profile, reduced EMI, staircase waveform. This phase disposition pulse width modulation is based on selective virtual loop mapping method to achieve capacitor voltage balance in lower and upper arms of MMI. The concept of virtual submodule is established first, by changing the mapping routines between virtual submodules and real sub modules, the capacitor voltages of the upper/lower arms capacitors can be well balanced. This method does not require sorting of voltages from highest to lowest, it just picks the MIN and MAX capacitor voltages of sub modules. The percentage THD values of the multilevel inverter are analyzed by using PI control scheme and Fuzzy Logic Control scheme. Simulation has been carried out using MATLAB/SIMULINK. |
