Verfahren zur Steuerung eines Pulswechselrichters

摘要

1375488 Inverting SIEMENS AG 10 March 1972 [13 March 1971] 11428/72 Heading H2F In a pulse-width modulated inverter, control signals are formed in dependence on the points of intersection of a periodic reference signal r of frequency corresponding to that of the required output with at least two voltage levels a1, a2 adjustable in relation to the required output voltage Ust from the inverter (Fig. 2). As shown, levels a1, a2 are adjusted in such a way that the magnitude of one of said voltage levels a1 (or the difference between two of said levels a2-a1) first increases as the required output voltage Ust is increased and then becomes reduced or maintained constant so as to determine a minimum off period t min . The inverter may be used to control the speed and torque of an asynchronous motor by controlling the triggering times of a bridge of thyristors. By adjusting the magnitude and/or number of voltage level such as a1, a2 the number of on/off periods in each half cycle of the inverter output is determined. The discontinuous laws shown in Fig. 2 may be produced by means of five operational amplifiers (Fig. 3, not shown), resistors and diodes. The periodic reference signal r may have sine, sawtooth, triangular or trapezoidal form.