Method and apparatus for operating an inverter consisting of two sub-inverters

Claim 3

The method accordint to claim 1 and further including the step of controlling the number of reversals such that the time spacing between two reversals does not fall below a lower limit determined essentially by the recovery time of the controlled rectifiers of the sub-inverters.

Claim 4

The method according to claim 1 and further including the step of subdividing reversal portion of the control angle into n+1 sections of equal size by n reversals of the two sub-inverters.

Claim 5

The method accordint to claim 3 and further including the step of controlling the number of reversals so that the time spacing between two reversals does not fall below a lower limit Δt min determined essentially by the recovery time of the controlled rectifiers of the sub-inverters.

Claim 6

The method according to claim 3 and further including the step of changing the number of sections as a function of the change in control angle.

Claim 7

The method according to claim 5 wherein said step of changing the number of sections is always carried to result in an increase or decrease of one.

Claim 8

The method according to claim 5 wherein the step of changing the number of sections in the increasing direction is carried out when the time spacing Δτ between two reversals becomes equal to a predetermined upper limit Δτ max .

Claim 9

The method accordint to claim 7 wherein said upper limit Δτ max is equal to twich the lower limit Δτ max .

Claim 10

In an inverter consisting of two sub-inverters whose inputs are connected to a DC voltage and whose outputs are connected with each other through a choke having a center tap such that the AC output voltages of the sub-inverters shifted relative to each other by an adjustable control angle are combined using the choke to form a resultant voltage at the center tap, apparatus for reversing, within the range of the control angle, the two AC output voltages at least once and simultaneously in opposite directions comprising: a. a frequency generator furnishing first and second modified triangular voltages having the same frequency and amplitude but phase shifted relative to each other by one-half their period; b. first and second comparator means each made up of a plurality of comparators having as first inputs said two modified triangular voltages respectively; c. means for providing as further inputs to both said first and second comparator means a plurality of voltages, the difference in voltages between each two voltages being equal, said means comprising a voltage divider provided with a common control voltage used for determining the control angle; d. first and second modulation means having the outputs of said respective first and second comparator means as inputs and providing outputs to control the sub-inverters in the range of the control angle such that a reversal takes place each time a comparator in one of said comparator means switches over.

Claim 11

In an inverter consisting of two sub-inverters whose inputs are connected to a DC voltage and whose outputs are connected with each other through a choke having a center tap such that the AC output voltages of the sub-inverters shifted relative to each other by an adjustable control angle are combined using the choke to form a resultant voltage at the center tap, apparatus for reversing, within the range of the control angle, the two AC output voltages at least once and simultaneously in opposite directions comprising: a. a frequency generator furnishing first and second modified triangular voltages having the same frequency and amplitude but phase shifted relative to each other by one-half their period; b. first and second comparator means each made up of a plurality of comparators having as first inputs said two modified triangular voltages respectively; c. means for providing as further inputs to both said first and second comparator means a plurality of voltages, the difference in voltages between each two voltages being equal, said means comprising a voltage divider provided with a common control voltage used for determining the control angle; d. first and second modulation means having the outputs of said respective first and second comparator means as inputs and providing outputs to control the sub-inverters in the range of the control angle such that a reversal takes place each time a comparator in one of said comparator means switches over.

Claim 12

Apparatus according to claim 9 wherein said frequency generating means comprises: a. an oscillator having a triangular voltage output; and b. summing means having as inputs the outputs of said oscillator and a fixed DC voltage, said summing means adding said fixed DC voltage to the triangular voltage output of said oscillator to form said first and second triangular voltage waveforms.

Claim 13

Apparatus according to claim 10 wherein three identical inverters each comprising two sub-inverters are used to provide a three-phase output and further including: a. first and second ring counters having an outout of said frequency generating means as inputs; b. first, second and third phase signal means having the outputs of said ring counter and the outputs of said modulation means as inputs said phase signal means providing phase signal outputs for switching the three pairs of sub-inverters.

Claim 14

Apparatus according to claim 10 and further including means coupled to said voltage divider for adjusting the ratio of said voltage divider.

Claim 15

Apparatus according to claim 12 wherein said means comprise a plurality of switches each responsive to a separate control signal input and a forward-backward counter providing as outputs the control signal inputs to said group of switches.

Claim 16

Apparatus according to claim 13 and further including means for providing forward and backward inputs to said counter, said means comprising first and second monostable multi-vibrators having a delay time equal to a minimum time Δ t min which time between two reversals cannot drop below and logic means to combine the outputs of said two monostables to provide a backward count input to said counter, if the time between two reversals drops below said time Δ t min .

Claim 17

Apparatus according to claim 14 and further including means to provide a forward count input to said forward-backward counter, said means comprising: a. third and fourth monostable multi-vibrators having a delay time equal to twice the minimum time Δ t min said delay time being the maximum time desired between two reversals; and b. means combining the outputs of said third and fourth monostables to provide a forward count input to increase the count of said forward-backward counter if the time between the reversal exceeds the time twice Δ t min .

Claim 18

Apparatus according to claim 15 wherein said voltage divider comprises a series circuit of equal resistances coupled between said control voltage and ground, with taps for partial voltages being taken off after every second resistor starting with resistor coupled to said control voltage.

Claim 19

Apparatus according to claim 16 wherein at the tap between each two resistors in said voltage divider one of said plurality of switches is coupled with the other side of all switches coupled to ground.