| 摘要 |
The invention relates to a method and apparatus for controlling an inverted rectifier having a constant DC supply voltage and adjustable frequency and amplitude of the fundamental oscillation of the output voltage. The rectifier is for an AC motor and the phase voltage is at least partly formed by width-modulated pulses and the voltage-time area of the pulse series is increased to eliminate an inadequate pulse spacing. Switching elements in the rectifier require a certain switching time and care must thus be taken to ensure that certain minimum pulse widths or pulse spacings must be observed to avoid short circuiting in the rectifier. Also to be avoided is pulse bridging which leads to a sudden increase in the voltage-time area and thus to a leap in the amplitude of the fundamental oscillation of the output voltage. The effects of this, e.g. in the magnetization of a connected motor, are undesirable. In accordance with the invention the increase in the voltage-time area is partially compensated by a reduction in the widths of at least some of the remaining pulses. Every time the voltage-time area is suddenly increased, the width of other impulses is reduced by way of compensation. The entire voltage-time area is therefore not suddenly increased, so that a substantially continuous voltage control can be achieved. If the remaining pulses have a smaller width after the compensation, the spacing therebetween is increased and the following switching-over becomes delayed. In a preferred embodiment each phase voltage consists of six sections of which the third and fourth are unmodulated, the second and fifth are occupied by wider impulses, and the first and sixth are occupied by narrower impulses, and switching-over to unmodulated operation takes place in the second and fifth or first and sixth sections and the reduction in impulse widths takes place in the respective remaining sections. This form of phase voltage gives a linked voltage that has extremely few higher harmonics. This switching-over produces between the normal operation and the maximum voltage, at which the entire half-wave consists of a through-going voltage block, at least one intermediate stage in which regulation is possible without the impulse spacings becoming too small.
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