Improved DC-link voltage balancing method for cascaded H-bridge rectifier

It is a challenge to balance the DC-link voltages of cascaded H-bridge rectifier (CHBR). We put forward an improved PI-based control method. Firstly, we establish a mathematics model of CHBR and introduce a PI-based DC-voltages balancing method. Then, we adopt the phasorial diagram method to discover and analyze the intrinsic reason that CHBR can not work on no-load condition with this control scheme. Based on the analysis results, measures are taken in control scheme to make the phases of all the cells' AC side voltage equal, which guarantees stability of system when the CHBR works on the no-load condition. The improved method can regulate the cell's voltages well, either the reference voltages are the same or different. Furthermore, it can easily extend to the CHBR with more cells, and is testified by a 4-cell CHBR simulation results. A 2-cell CHBR prototype is built in the laboratory. Accordingly, comparison experiments by the referred control method are done. The experimental results indicate the feasibility of the presented method and good performance on the no-load condition with the improved control scheme.