| 摘要 |
The invention relates to voltage conversion devices, whether for inversion (constant voltage to alternating voltage), or conversion (alternating voltage to constant voltage). It includes a pulse-width-modulator and a threephase, three-legged bridge, each leg of the bridge having a pair of complementary switches (S1/S1*, S2/S2*, S3/S3*). One of the switches S1, S2 or S3 (S1*, S2* or S3*) conducts in those time intervals where the associated reference voltage UA UB or Uc has a higher (smaller) amplitude than the other two reference voltages. According to the present invention, (a) three reference voltages are supplied, (b) the maximum of these voltages is detected, (c) the maximum is subtracted from the peak value of a triangle wave used for forming the PWM signal, and (d) the difference is added to each of the reference voltages to form augmented reference voltages supplying a PWM, which in turn supplies PWM signals to a three-phase semiconductor bridge. The result is that when one of the three reference voltages is greater than the other two, a switch of one of the three complementary pairs of such switches in the bridge conducts, while in each of the other two complementary pairs, both switches open and close in response to the PWM signal such that only two currents are independently controlled by each of the two complementary pairs which are allowed to open and close, and the third current, associated with the complementing pair which is not allowed to switch, is controlled by the other two. Keeping one switch in each leg closed for one-third of the period of the reference voltage allows control of all three load currents to be dictated by the switching in only two legs.
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