High-power machine drive, using nonredundant 27-level inverters and active front end rectifiers

A nonredundant 27-level inverter using "H" converters is being analyzed for high power machine drive applications. The main advantage of this kind of converter is the minimum harmonic distortion obtained at the machine side. The drawbacks are the large number of isolated dc power supplies required for each one of the three stages of the multistage converter. In this paper this problem has been overcome in two ways: 1) by using independent windings for each phase of the motor and 2) by using independent input transformers. Special configurations and combinations of diode rectifiers and active front end rectifiers for one of the stages of the drive are used to eliminate input harmonics. The topology can also keep high power factor at the input terminals. Simulation results are shown and some experiments with small three-stage prototype are displayed. The control of this multiconverter is being implemented using DSP controllers, which give flexibility to the system.