Patent ID: 8144490
Filing Date: 2012-03-27
Classification: H02M,Y10S

Abstract:
1. A method of operating a three level converter comprising: when a DC link voltage of the three level converter is lower than one-half of a rated DC link voltage of the converter, controlling the output voltage of the converter by, for each leg of the converter, alternately connecting an output terminal of the leg to the positive terminal or the negative terminal of the DC link; and when the DC link voltage is at least one-half of the rated DC link voltage, controlling the output voltage of the converter by, for each leg, selectively connecting the output terminal of the converter to the positive terminal, the negative terminal, or a mid-point of the DC link; wherein controlling the output voltage of the converter when the DC link voltage is lower than one-half the rated DC link voltage further comprises maintaining outer switching devices of the three level converter in an ON state while alternately switching inner switching devices of the three level converter to ON and OFF states.