GB1413145A - Inverters - Google Patents

Abstract

1413145 Inverting DEUTSCHE AUTOMOBIL GmbH 24 Aug 1972 [27 Aug 1971] 39544/72 Heading H2F In a method of controlling an inverter having a plurality of controlled rectifiers (e.g. thyristors) each device is arranged to be pulsed during only part of its conductive period, the pulsing frequency being varied in dependence on the fundamental output frequency and the voltage time integral of the pulses over the pulsing period being maintained constant i.e. the output voltage being effectively proportional to frequency, the proportionality being adjustable by a further control signal. Fig. 1 (not shown) relates to a three-phase bridge of six thyristors with in verse diodes, each thyristor being capable of being turned on and off by unspecified means. Fig. 2 shows the control circuit for the inverter, the fundamental frequency being determined by the frequency of pulses a which are fed to a divider 1 which provides pulses b, c at half and quarter frequency, the latter being passed to a counter 2 to provide six control signals each displaced by 60 degrees to control a gate 6 which distributes turn-on and turn-off pulses to the thyristors of the inverter 7. Pulses at input frequency a, half frequency b or quarter frequency c are selected by gate 3 and fed to a shaper 4 so as to provide pulses g the duration of which is a function of the further control signal supplied at l. The pulses g are monitored in a comparator 5 which provides a signal i so as to determine which frequency will be passed by the gate 3. Comparator 5 determines whether the duration of pulse g is greater than or less than a fixed duration which is a function of the duration of oscillation phenomena in the commutating circuit. When low frequency pulses a are supplied, the inverter 7 produces a low frequency three-phase output for an asynchronous motor, the average value of the output being generally low but controllable by the signal at l. Fig. 4 (not shown) relates to operation when high frequency pulses are supplied at a, gate 3 being arranged to select quarter frequency pulses, each thyristor being pulsed on and off only once at the mid-point of its conductive period. Reference has been directed by the Comptroller to Specification 1,362,849.