Voltage look-up table method to control multilevel cascaded transformerless inverters with unequal DC rail voltages

This study presents a new voltage control algorithm for multilevel inverters which are used to connect the distributed generation (DG) sources (like photovoltaic cells) to the network, which is called the voltage look-up table method (VLUTM). This method can build up an almost sinusoidal voltage at the inverter output with the least number of switching in the power circuit, and the best possible harmonic spectrum without the need to any big filtering. On the other hand, in some specific applications where the DG has been set up beside a non-linear load, VLUTM can make a reference voltage based on the reference current to take a desired current form the DG. This way the DG can compensate the major low-order load current harmonics and improve the source side current THD greatly. Decreasing the switching frequency as much as possible, which leads to better efficiency and less EMI problems, the capability of implementation both in single phase and three phase circuitry, and the very simple and desired current control, would be the major benefits of this method. The simulation results taken from Matlab/Simulink and the experimental results on a 1 kVA experimental prototype are presented to evaluate the performance of this method.