AC–DC boost converter based on T-type multi-state switching cell and output voltage balancing

A novel topology of the ac–dc power converter to supply neutral-point-clamped inverters used in ac motor drives and wind offshore power grids is proposed. It is based on the T-type multi-state switching cell, which allows obtaining a five-level voltage waveform downstream of the input filter inductor. The converter presents a high voltage gain due to the transformer secondary windings associated with series-connected diode rectifiers. Prominent main characteristics of this topology include power factor correction, operation of the filter inductor at twice the switching frequency, reduced conduction losses in the semiconductors, and voltage balance across the output capacitors. To verify the operating principle of the converter a design example is described, considering that the converter specifications are: output power of 3 kW; rms input voltage of 110 V; total output voltage of 1 kV, which is equally divided among four capacitors and switching frequency of 20 kHz. Simulation results are shown to validate the theoretical assumptions and verify the behaviour of the rectifier in terms of dynamic response while also supplying unbalanced loads.