Apparatus for generating three-phase sinusoidal voltages

Claim 2

A three-phase inverter for generating sine-wave voltages at a preselected frequency across a set of three-phase line conductors from a unidirectional voltage source having a center tap coupled to a reference potential comprising: a first inverter connected between the source and the line conductors for producing flattopped output voltage segments alternating between an upper potential above a reference potential and a lower potential below the reference potential at a rate three times the desired frequency and developing three-phase, full-wave, flat-top voltages on the conductors at the desired frequencies, each segment extending over an interval greater than 60 electrical degrees and being terminated by a first commutating voltage on the respective line conductor; a second inverter connected to the source and operating in synchronism with the first inverter for producing at its output signal-phase, flat-top voltages alternating between the upper and lower potential at a rate three times the desired frequency, each half cycle of the singal-phase, flat-top voltage being terminated by a second commutating voltage applied to the output of the second inverter; an inductor having an input tap connected to the output of the second inverter, a low voltage tap connected to the reference potential and a plurality of intermediate voltage taps between the low voltage tap and the input tap, whereby alternating flat-top voltage excitation is applied across the input and low voltage taps, the inductor further having a step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor including a first channel having an input and means for selectively coupling said input to the line conductors in synchronism with the first inverter and a second channel having an input and means for coupling said input to the line conductors in synchronism with the first inverter; means or connecting the low voltage and intermediate taps to the inputs of each of the first and second channels during the period said channels are coupled to a respective line conductor in ascending and descending order in synchronism with the first inverter to approximate on the line conductors, in relation to the reference potential, a balanced and symmetrical voltage; means for momentarily coupling the step-up tap to the inputs of each channel, respectively, at the beginning of the period said channels are coupled to a respective line conductor to supply the first commutating voltage to commutate the first inverter; and means for momentarily coupling a respective one of the line conductors having a flat-top voltage segment thereon to one of the intermediate taps of the inductor at the end of each half cycle of the single-phase, flat-top voltage to generate the second commutating voltage at the input tap of the inductor for commutating the second inverter.

Claim 3

A three-phase inverter for generating sine-wave voltages at a preselected frequency across a set of three-phase line conductors from a unidirectional voltage source having a center tap coupled to a reference potential comprising: a first inverter connected between the source and the line conductors for producing flat-topped output voltage segments alternating between an upper potential above a reference potential and a lower potential below the reference potential at a rate three times the desired frequency and developing three-phase, full-wave, flat-top voltages on the conductors at the desired frequencies, each segment extending over an interval greater than 60 electrical degrees and being terminated by a first commutating voltage on the respective line conductor having the same polarity as said segment relative to the reference potential and having a magnitude greater than said segment; a second inverter connected to the source and operating in synchronism with the first inverter for producing at its output single-phase, flat-top voltages alternating between the upper and lower potential at a rate three times the desired frequency, each half cycle of the single-phase, flat-top voltage being terminated by a second commutating voltage applied to the output of the second inverter having the same polarity as said half cycle of the single-phase voltage relative to the reference potential and having a magnitude greater than said half cycle of the single-phase voltage; an inductor having an input tap connected to the output of the second inverter, a low voltage tap connected to the reference potential and a plurality of intermediate voltage taps between the low voltage tap and the input tap, whereby alternating flat top voltage excitation is applied across the input and low voltage taps, the inductor further having a step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor including a first channel having an input and three bidirectional switches each coupled between the input and a respective one of the line conductors and a second channel hving an input and three bidirectional switches each coupled between said input and a respective one of the line conductors; means for selectively energizing the bidirectional switches in the first and second channels to couple the inputs thereof to the line conductors in synchronism with the first inverter; a first group of bidirectional switch means connected between the low voltage and intermediate taps and the input of the first channel; a second group of bidirectional switch means connected between the low voltage and intermediate taps and the input of the second channel; means for selectively energizing the bidirectional switches in the first and second groups during each period said first and second channels are coupled to a respective line conductor to couple the low voltage and intermediate taps to the inputs of said first and second channels in ascending and descending order in synchronism with the first inverter to approximate on the line conductors, in relation to the reference potential, a balanced and symmetrical voltage; means for momentarily coupling the step-up tap to the inputs of each channel, respectively, at the beginning of the period said channels are coupled to a respective line conductor to supply the first commutating voltage to commutate the first inverter; and means for momentarily energizing a respective one of the bidirectional switches in the first or second channels and one of the bidirectional switches in the first or second group to couple a respective one of the line conductors having a flat top voltage segment thereon with the same polarity as the single-phase voltage to one of the intermediate taps of the inductor at the end of each half cycle of the single-phase, flat-top voltage to generate the second commutating voltage at the input tap of the inductor for commutating the second inverter.

Claim 4

A three-phase inverter for generating sine-wave voltages at a preselected frequency across a set of three-phase line conductors from a unidirectional voltage source having a center tap coupled to a reference potential comprising: a first inverter connected between the source and the line conductors for producing flat-topped output voltage segments alternating between an upper potential above a reference potential and a lower potential below the reference potential at a rate three times the desired frequency and developing three-phase, full-wave, flat-top voltages on the conductors at the desired frequencies, each segment extending over an interval greater than 60 electrical degrees and being terminated by a first commutating voltage on the respective line conductor having the same polarity as said segment relative to the reference potential and having a magnitude greater than said segment; a second inverter connected to the source and operating in synchronism with the first inverter for producing at its output single-phase, flat-top voltages alternating between the upper and lower potential at a rate three times the desired frequency, each half cycle of the single-phase, flat-top voltage being terminated by a second commutating voltage applied to the output of the second inverter having the same polarity as said half cycle of the single-phase voltage relative to the reference potential and having a magnitude greater than said half cycle of the single-phase voltage; an inductor having an input tap connected to the output of the second inverter, a low voltage tap connected to the reference potential and a plurality of intermediate voltage taps between the low voltage tap and the input tap, whereby alternating flat top voltage excitation is applied across the input and low voltage taps, the inductor further having a step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor including a first channel having an input and three bidirectional switches each coupled between the input and a respective one of the line conductors and a second channel hving an input and three bidirectional switches each coupled between said input and a respective one of the line conductors; means for selectively energizing the bidirectional switches in the first and second channels to couple the inputs thereof to the line conductors in synchronism with the first inverter; a first group of bidirectional switch means connected between the low voltage and intermediate taps and the input of the first channel; a second group of bidirectional switch means connected between the low voltage and intermediate taps and the input of the second channel; means for selectively energizing the bidirectional switches in the first and second groups during each period said first and second channels are coupled to a respective line conductor to couple the low voltage and intermediate taps to the inputs of said first and second channels in ascending and descending order in synchronism with the first inverter to approximate on the line conductors, in relation to the reference potential, a balanced and symmetrical voltage; means for momentarily coupling the step-up tap to the inputs of each channel, respectively, at the beginning of the period said channels are coupled to a respective line conductor to supply the first commutating voltage to commutate the first inverter; and means for momentarily energizing a respective one of the bidirectional switches in the first or second channels and one of the bidirectional switches in the first or second group to couple a respective one of the line conductors having a flat top voltage segment thereon with the same polarity as the single-phase voltage to one of the intermediate taps of the inductor at the end of each half cycle of the single-phase, flat-top voltage to generate the second commutating voltage at the input tap of the inductor for commutating the second inverter.