Pulse-width-modulation method for providing extended linearity, reduced commutation losses and increase in inverter/converter output voltage

摘要

The invention relates to voltage conversion devices, whether for inversion or conversion includes a pulse-width-modulator 3 and a three-phase, three-legged bridge, each leg 56,58,60 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 itervals 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 UA, UB, UC are supplied, (b) the maximum of these voltages is detected, (c) the maximum is subtracted from the peak value UTP of a triangle wave used for forming the PWM signal, and (d) the difference is added to each of the reference voltages UA,UB,UC to form augmented reference voltages UA min ,UB min ,UC min supplying a PWM. 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, 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. IMAGE IMAGE