A New Strategy for Control of Cascaded H-bridge Rectifiers with Uneqaul Loads

In this paper, a new control strategy is applied to a cascaded H-bridge (CHB) rectifier in order to regulate dc bus voltages and to balance them, even if the attached loads consume various amounts of power. The input current is also programmed to be sinusoidal and in-phase with the input voltage. With the maximum switching frequency of 1 kHz, the switching loss is kept low while the current distortion is below 5%. Additionally, no filter is employed at the dc side of the converter to smooth dc voltage waveforms. The proposed CHB rectifier connects directly to 6.6 kV ac system and eliminates the need to bulky step-down transformers. This converter can feed different dc and ac loads, at the same time. Simulation results are carried out for an 11- level, 6.6 kV, 2 MW CHB rectifier and presented in this paper.

Keywords:

active rectifier , cascaded multilevel converter , power factor correction (PFC) , voltage balancing , medium voltage and high power converters