Multilevel inverter, based on multi-stage connection of three-level converters scaled in power of three

A multi-stage inverter using three-state converters is being analyzed for multipurpose applications, such as active power filters, static VAr compensators and machine drives for sinusoidal and trapezoidal current applications. The great advantage of this kind of converter is the minimum harmonic distortion obtained. The drawbacks are the isolated power supplies required for each one of the stages of the multiconverter. In this paper this problem has been overcome by using isolated, bidirectional DC power supplies, which are fed from a common power source. This solution becomes practical because only one converter of the chain, called Master, takes more than 80% of the total active power required by the system. The rest of the converters, called "Slaves", need very low power, and then those DC supplies are small. Another configuration with common DC supply and output transformers is displayed, and simulation results for different applications are shown and compared with similar results obtained with conventional PWM converters. The control of this multi-converter is being implemented using DSP controllers, which give flexibility to the system.