Patent ID: 6944037
Filing Date: 2005-09-13
Classification: H02M

Abstract:
1. A method for generating an AC output voltage in a frequency range from a DC input voltage, comprising: pulse-width modulating the DC input voltage at a higher switching frequency than a frequency of the AC output voltage to produce a first pulse train and a second pulse train, wherein the first and second pulse trains are modulated to correspond to one half-cycle of the AC output voltage to be generated, and wherein pulses of the first pulse train are shifted with respect to pulses of the second pulse train, the pulses of the first pulse train occurring during gaps between pulses of the second pulse train; applying the first pulse train and the second pulse train to a primary winding of a transformer to output from a secondary winding of the transformer a third pulse train having pulses of opposite polarities; rectifying the pulses of the third pulse train output from the secondary winding of the transformer to generate fourth pulse train having pulses of one polarity and corresponding to successive half-cycles of the AC output voltage to be generated; and periodically reversing the polarity of a plurality of successive pulses of the fourth pulse train at twice the frequency of the AC output voltage to be generated, wherein by periodically reversing the fourth pulse train obtained after rectification, an output pulse train is obtained which is a pulse-width modulated representation of the AC output voltage with respect to the amplitude, frequency and polarity, wherein the rectifying the pulses of the third pulse train and the periodically reversing of the polarity of the plurality of successive pulses of the fourth pulse train are performed by a rectifying switch having a bridge structure, each bridge arm of said bridge structure having two back-to-back series-connected diodes, and each diode being bridged by a switching transistor, wherein one of the switching transistors and an other of the switching transistors in each bridge arm are alternately driven at twice the frequency of the AC output voltage, one of the diodes and an other of the diodes of each bridge arm alternately forming an active arm of the bridge, thereby obtaining the output pulse train which is the pulse-width modulated representation of the AC output voltage with respect to amplitude, frequency and polarity.