Method of and apparatus for generating three-phase sinusoidal voltages

Claim 2

A three-phase inverter effective to generate substantially sine-wave voltages across a set of three-phase line conductors from a unidirectional voltage source having a center tap, the three-phase inverter comprising in combination: a first inverter connected between the source and the conductors and effective, by controlled rectifier action, to produce three-phase flat-top full-wave voltages on the respective line conductors in relation to the center tap, each conduction period being terminated by a commutating voltage on the respective line conductor sufficient to reverse bias the corresponding controlled rectifier; a second inverter connected to said source and operable to produce singlephase, flat-top voltage at a predetermined frequency; an inductor having a plurality of taps connected between said second inverter and the center tap, whereby alternating tap-flat voltage excitation appears thereacross at said predetermined frequency, said inductor further having at least one step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor having two channels and means to connect the same to the three three-phase line conductors, respectively; means effective during the period each channel of the voltage distributor is connected to a line conductor to connect said first mentioned taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductors to approximate on each conductor, in relation to the center tap, a balanced and symmetrical voltage; and means effective at the beginning of each of said periods momentarily to apply voltage from the last mentioned tap to the respective line conductor so as to commutate the first inverter in slaved relation to the operation of said last means.

Claim 11

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage having a center tap, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors providing an output alternating in polarity above and below said center tap at three times the frequency F1 and effective to produce three-phase, full-wave voltages on said line conductors in relation to said center tap at said frequency F1; a single-phase inverter connected to said source and operating in synchronism with said first inverter at three times said frequency F1; an inductor having a plurality of taps connected between said single-phase inverter and said center tap, whereby an alternating flat-top voltage appears thereacross having a repetition rate three times the frequency of said frequency F1; a voltage distributor having two channels and Means to connect the same to the three three-phase line conductors, respectively, when said first inverter is not applying voltages thereto; and means effective during the period each channel of the voltage distributor is connected to a line conductor to connect said taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductor to simulate a true sinusoidal voltage between each pair of respective line conductors.

Claim 12

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage having a center tap, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors providing an output alternating in polarity above and below said center tap at three times the frequency F1 and effective to produce three-phase, full-wave voltages on said line conductors in relation to said center tap at said frequency F1; a single-phase inverter connected to said source and operating in synchronism with said first inverter at three times said frequency F1; an inductor having a plurality of taps connected between said single-phase inverter and said center tap, whereby an alternating flat-top voltage appears thereacross having a repetition rate three times the frequency of said frequency F1; a voltage distributor having two channels and Means to connect the same to the three three-phase line conductors, respectively, when said first inverter is not applying voltages thereto; and means effective during the period each channel of the voltage distributor is connected to a line conductor to connect said taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductor to simulate a true sinusoidal voltage between each pair of respective line conductors.

Claim 13

A three-phase inverter effective to generate substantially sine-wave voltages across a set of three-phase line conductors from a unidirectional voltage source having a center tap, the inverter comprising in combination: a first inverter connected between the source and the conductors and effective, by controlled rectifier action, to produce three-phase flat-top full-wave voltages on the respective line conductors in relation to the center tap, each conduction period being terminated by a commutating voltage on the respective line conductor sufficient to reverse bias the corresponding controlled rectifier; a second inverter connected to said source and operable to produce single-phase, flat-top voltage at a predetermined frequency; an inductor having a plurality of taps connected between said second inverter and the center tap, whereby alternating flat-top voltage excitation appears thereacross at said predetermined frequency, said inductor further having at least one step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor having two channels and means to connect the same to the three three-phase line conductors, respectively; means effective during the period each channel of the voltage distributor is connected to a line conductor to connect said first mentioned taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductors and simulate a true sinusoidal voltage across each pair of respective line conductors; and means effective at the beginning of each of said periods to momentarily apply voltage from the last mentioned tap to the respective line conductor so as to commutate the first mentioned inverter in sequence with the operation of the last means.

Claim 14

A three-phase inverter effective to generate substantially sine-wave voltages across a set of three-phase line conductors from a unidirectional voltage source having a center tap, the inverter comprising in combination: a first inverter connected between the source and the conductors and effective, by controlled rectifier action, to produce three-phase flat-top full-wave voltages on the respective line conductors in relation to the center tap, each conduction period being terminated by a commutating voltage on the respective line conductor sufficient to reverse bias the corresponding controlled rectifier; a second inverter connected to said source and operable to produce single-phase, flat-top voltage at a predetermined frequency; an inductor having a plurality of taps connected between said second inverter and the center tap, whereby alternating flat-top voltage excitation appears thereacross at said predetermined frequency, said inductor further having at least one step-up tap in voltage multiplying position in relation to the flat-top voltage; a voltage distributor having two channels and means to connect the same to the three three-phase line conductors, respectively; means effective during the period each channel of the voltage distributor is connected to a line conductor to connect said first mentioned taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductors and simulate a true sinusoidal voltage across each pair of respective line conductors; and means effective at the beginning of each of said periods to momentarily apply voltage from the last mentioned tap to the respective line conductor so as to commutate the first mentioned inverter in sequence with the operation of the last means.

Claim 15

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms having a given frequency by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms having the given frequency, the apparatus comprising: center voltage generating means for alternately producing upper and lower center voltage segments at three times the given frequency, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generating means including voltage level developing means and voltage level synthesizing means, the voltage level developing means including transformer means for alternately producing an upper set of step voltage levels ranging between the neutral potential and the upper potential and a lower set of step voltage levels ranging between the neutral potential and the lower potential at three times the given frequency, the voltage level synthesizing means including a plurality of step level selector switches each associated with a different one of the step voltage levels in each of the upper and lower sets for alternately providing simultaneous upper left and right voltage segments and simultaneous lower left and right voltage segments at three times the given frequency, the upper left and right voltage segments ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps, thE lower left and right voltage segments descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps, the discrete voltage steps having predetermined magnitudes of predetermined durations; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper and lower left and right voltage segments to the phase lines to define corresponding upper and lower left and right waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 16

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms having a given frequency by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms having the given frequency, the apparatus comprising: center voltage generating means for alternately producing upper and lower center voltage segments at three times the given frequency, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generating means including voltage level developing means and voltage level synthesizing means, the voltage level developing means including transformer means for alternately producing an upper set of step voltage levels ranging between the neutral potential and the upper potential and a lower set of step voltage levels ranging between the neutral potential and the lower potential at three times the given frequency, the voltage level synthesizing means including a plurality of step level selector switches each associated with a different one of the step voltage levels in each of the upper and lower sets for alternately providing simultaneous upper left and right voltage segments and simultaneous lower left and right voltage segments at three times the given frequency, the upper left and right voltage segments ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps, thE lower left and right voltage segments descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps, the discrete voltage steps having predetermined magnitudes of predetermined durations; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper and lower left and right voltage segments to the phase lines to define corresponding upper and lower left and right waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 17

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms having a given frequency by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms having the given frequency, the apparatus comprising: center voltage generating means connected to the neutral point for providing upper and lower center voltage portions each exceeding one-sixth of a cycle, the upper and lower center voltage portions being substantially constant respectively at an upper potential above the neutral and at a lower potential below the neutral; left/right voltage generating means including voltage level developing means and voltage level synthesizing means, the voltage level developing means including transformer means for alternately providing upper and lower sets of step voltage levels at three times the given frequency, the upper set of step voltage levels ranging between the neutral potential and the upper potential and the lower set of step voltage levels ranging between the neutral potential and the lower potential, the voltage level synthesizing means including voltage level selecting means and voltage level commutating means, the voltage level selecting means including first and second banks of unicontrol step level selector switches arranged in corresponding ones of first and second sets of subbanks, the step level selector switches in each of the subbanks of the first and second banks each associated with a different nonadjacent one of the step levels in each of the upper and lower sets of step voltage levels, the voltage level commutating means including first and second groups of bicontrol voltage level commutator switches, the bicontrol voltage level commutator switches in each of the first and second groups respectively connected in series between a common output and the unicontrol step voltage level selector switches in a different associated one of the subbanks in the first and second banks, the corresponding ones of the first and second banks of step level selector switches and the first and second groups of voltage level commutator switches connecting successive ones of the upper and lower sets of step levels during successive ones of left and right step periods to alternately define a different one of upper left and right voltage portions and a different one of lower left and right voltage portions, the upper left and right voltage portions ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps, the lower left and right voltage portions descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps, the discrete voltage steps having predetermined magnitudes and predetermined durations, the bicontrol voltage level commutator switches in each of the first and second groUps commutating the unicontrol step voltage level selector switches in the corresponding ones of the first and second banks; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage portions to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper and lower left and right voltage portions to the phase lines to define corresponding upper and lower left and right waveform portions in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 18

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms having a given frequency by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms having the given frequency, the apparatus comprising: center voltage generating means connected to the neutral point for providing upper and lower center voltage portions each exceeding one-sixth of a cycle, the upper and lower center voltage portions being substantially constant respectively at an upper potential above the neutral and at a lower potential below the neutral; left/right voltage generating means including voltage level developing means and voltage level synthesizing means, the voltage level developing means including transformer means for alternately providing upper and lower sets of step voltage levels at three times the given frequency, the upper set of step voltage levels ranging between the neutral potential and the upper potential and the lower set of step voltage levels ranging between the neutral potential and the lower potential, the voltage level synthesizing means including voltage level selecting means and voltage level commutating means, the voltage level selecting means including first and second banks of unicontrol step level selector switches arranged in corresponding ones of first and second sets of subbanks, the step level selector switches in each of the subbanks of the first and second banks each associated with a different nonadjacent one of the step levels in each of the upper and lower sets of step voltage levels, the voltage level commutating means including first and second groups of bicontrol voltage level commutator switches, the bicontrol voltage level commutator switches in each of the first and second groups respectively connected in series between a common output and the unicontrol step voltage level selector switches in a different associated one of the subbanks in the first and second banks, the corresponding ones of the first and second banks of step level selector switches and the first and second groups of voltage level commutator switches connecting successive ones of the upper and lower sets of step levels during successive ones of left and right step periods to alternately define a different one of upper left and right voltage portions and a different one of lower left and right voltage portions, the upper left and right voltage portions ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps, the lower left and right voltage portions descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps, the discrete voltage steps having predetermined magnitudes and predetermined durations, the bicontrol voltage level commutator switches in each of the first and second groUps commutating the unicontrol step voltage level selector switches in the corresponding ones of the first and second banks; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage portions to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper and lower left and right voltage portions to the phase lines to define corresponding upper and lower left and right waveform portions in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 19

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage having a center tap, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors and effective to produce three-phase, full-wave voltages on the respective line conductors in relation to the center tap at said frequency F1; a single-phase, full-wave inverter connected to said source and operating at three times said frequency F1; inductor means having two series of taps connected between said single-phase, full-wave inverter and said center tap, whereby alternating excitation voltage appears thereacross at three times said frequency F1; and a voltage distributor effective to connect said inductor taps to said three-phase line conductors, respectively, when said first inverter is not applying voltage thereto, said voltage distributor providing connections between only one of said line conductors and only one of said series of inductor taps during each half-cycle of said alternating excitation voltage, said voltage distributor further having at least one pair of main switch elements connected between said one line conductor and said one series of taps, a pair of buses connected to each pair of said main switch elements, and secondary switch elements effective, sequentially, to connect taps of said one series of said transformer taps to said main switch elements through said buses, said main switch elements having current interrupting capability to terminate the circulating current between any two of said taps in sequential order so as to produce corresponding stepped sequentially rising or falling voltages on said conductors to simulate across the respective line conductors a substantially sinusoidal voltage.

Claim 20

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage having a center tap, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors and effective to produce three-phase, full-wave voltages on the respective line conductors in relation to the center tap at said frequency F1; a single-phase, full-wave inverter connected to said source and operating at three times said frequency F1; inductor means having two series of taps connected between said single-phase, full-wave inverter and said center tap, whereby alternating excitation voltage appears thereacross at three times said frequency F1; and a voltage distributor effective to connect said inductor taps to said three-phase line conductors, respectively, when said first inverter is not applying voltage thereto, said voltage distributor providing connections between only one of said line conductors and only one of said series of inductor taps during each half-cycle of said alternating excitation voltage, said voltage distributor further having at least one pair of main switch elements connected between said one line conductor and said one series of taps, a pair of buses connected to each pair of said main switch elements, and secondary switch elements effective, sequentially, to connect taps of said one series of said transformer taps to said main switch elements through said buses, said main switch elements having current interrupting capability to terminate the circulating current between any two of said taps in sequential order so as to produce corresponding stepped sequentially rising or falling voltages on said conductors to simulate across the respective line conductors a substantially sinusoidal voltage.

Claim 25

A three-phase inverter for providing a substantially sinusoidal output at a preselected frequency F1 from a source of unidirectional voltage, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors and effective to produce three-phase, full-wave voltages on the respective line conductors at said frequency F1; a single-phase, full-wave inverter connected to said source and operating at three times said frequency F1; an inductor having a plurality of taps connected across the output of said single-phase, full-wave inverter, whereby an alternating excitation voltage appears thereacross having a repetition rate three times said frequency F1; a voltage distributor effective to connect said inductor taps to said three-phase line conductors, respectively, when said first inverter is not applying voltage thereto; and means effective as a control of said distributor to sequentially connect said taps in ascending or descending order so as to produce corresponding stepped sequentially rising or falling voltages to simulate across respective pairs of line conductors substantially sinusoidal voltages.

Claim 26

A three-phase inverter for providing a substantially sinusoidal output at a preselected frequency F1 from a source of unidirectional voltage, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors and effective to produce three-phase, full-wave voltages on the respective line conductors at said frequency F1; a single-phase, full-wave inverter connected to said source and operating at three times said frequency F1; an inductor having a plurality of taps connected across the output of said single-phase, full-wave inverter, whereby an alternating excitation voltage appears thereacross having a repetition rate three times said frequency F1; a voltage distributor effective to connect said inductor taps to said three-phase line conductors, respectively, when said first inverter is not applying voltage thereto; and means effective as a control of said distributor to sequentially connect said taps in ascending or descending order so as to produce corresponding stepped sequentially rising or falling voltages to simulate across respective pairs of line conductors substantially sinusoidal voltages.

Claim 27

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors providing an output alternating in polarity at three times said frequency F1 and effective to produce three-phase, full-wave voltages on said line conductors at said frequency F1; a single-phase inverter connected to said source and providing an alternating output in synchronism with said first inverter at three times said frequency F1; means including a plurality of output taps connected across the output of said single-phase inverter, whereby a plurality of flat-top voltage levels appear thereacross having a repetition rate three times the frequency of said frequency F1; a voltage distributor and means to connect the same to the three three-phase line conductors, respectively, when said first inverter is not applying voltage thereto; and means effective during the period said voltage distributor is connected to a line conductor to connect said taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductor to simulate a true sinusoidal voltage between each pair of respective line conductors.

Claim 28

A three-phase inverter for generating voltage at a preselected frequency F1 from a source of unidirectional voltage, comprising in combination: a set of three-phase line conductors; a first inverter connected between said source and said conductors providing an output alternating in polarity at three times said frequency F1 and effective to produce three-phase, full-wave voltages on said line conductors at said frequency F1; a single-phase inverter connected to said source and providing an alternating output in synchronism with said first inverter at three times said frequency F1; means including a plurality of output taps connected across the output of said single-phase inverter, whereby a plurality of flat-top voltage levels appear thereacross having a repetition rate three times the frequency of said frequency F1; a voltage distributor and means to connect the same to the three three-phase line conductors, respectively, when said first inverter is not applying voltage thereto; and means effective during the period said voltage distributor is connected to a line conductor to connect said taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductor to simulate a true sinusoidal voltage between each pair of respective line conductors.

Claim 29

A three-phase inverter for generating substantially sinusoidal voltages at a preselected frequency on a set of three-phase line conductors from a unidirectional voltage source, comprising a first inverter connected between said source and said conductors, producing a substantially flat-topped output alternating in polarity at a rate three times said frequency, and developing three-phase full-wave voltages on said conductors at said frequency; a second, single-phase inverter connected with said source and providing an alternating output in synchronization with said first inverter at a rate three times said frequency and developing ascending and descending waveform portions; and a voltage distributor connected with said second inverteR to apply said ascending and descending waveform portions to said conductors, respectively, to synthesize voltages between respective pairs of line conductors in substantial approximation to sinusoidal voltages at said frequency by combining respective ascending, descending, and flat-topped wave portions.

Claim 30

A three-phase inverter for generating substantially sinusoidal voltages at a preselected frequency on a set of three-phase line conductors from a unidirectional voltage source, comprising a first inverter connected between said source and said conductors, producing a substantially flat-topped output alternating in polarity at a rate three times said frequency, and developing three-phase full-wave voltages on said conductors at said frequency; a second, single-phase inverter connected with said source and providing an alternating output in synchronization with said first inverter at a rate three times said frequency and developing ascending and descending waveform portions; and a voltage distributor connected with said second inverteR to apply said ascending and descending waveform portions to said conductors, respectively, to synthesize voltages between respective pairs of line conductors in substantial approximation to sinusoidal voltages at said frequency by combining respective ascending, descending, and flat-topped wave portions.

Claim 33

In a three-phase electrical system including three separate phase lines ad a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms, the apparatus comprising: center voltage generating means connected to the neutral point for alternately providing upper and lower center voltage segments each extending over approximately a 60 electrical degree interval, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generating means connected to the neutral point for alternately providing simultaneous upper left and right voltage segments and simultaneous lower left and right voltage segments each extending over approximately a 60 electrical degree interval, the upper left and right voltage segments ascending and descending respectively in a series of discrete voltage steps between the neutral potential and the upper potential, the lower left and right voltage segments descending and ascending respectively in a series of discrete voltage steps between the neutral potential and the lower potential; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper left and right voltage segmen ts and the lower left and right voltage segments to the phase lines to define corresponding upper left and right waveform portions and lower left and right waveform portions in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 34

In a three-phase electrical system including three separate phase lines ad a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms, the apparatus comprising: center voltage generating means connected to the neutral point for alternately providing upper and lower center voltage segments each extending over approximately a 60 electrical degree interval, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generating means connected to the neutral point for alternately providing simultaneous upper left and right voltage segments and simultaneous lower left and right voltage segments each extending over approximately a 60 electrical degree interval, the upper left and right voltage segments ascending and descending respectively in a series of discrete voltage steps between the neutral potential and the upper potential, the lower left and right voltage segments descending and ascending respectively in a series of discrete voltage steps between the neutral potential and the lower potential; center voltage distributing means connected between the center voltage generating means and the phase lines for applying the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means connected between the left/right voltage generating means and the phase lines for applying the upper left and right voltage segmen ts and the lower left and right voltage segments to the phase lines to define corresponding upper left and right waveform portions and lower left and right waveform portions in each cycle of each of the line-to-neutral voltage waveforms; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 35

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms, the apparatus comprising: center voltage generating means for providing upper and lower center voltage segments each extending over approximately a 60 electrical degree interval, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generatIng means including voltage level developing means and voltage level synthesizing means, the voltage level developing means establishing upper and lower sets of step voltage levels and upper and lower commutator voltage levels, the upper set of step levels ranging between the neutral potential and the upper potential and the lower set of step levels ranging between the neutral potential and the lower potential, the upper commutator level residing above the upper potential and the lower commutator level residing below the lower potential, the voltage level synthesizing means connected with the voltage level developing means for producing upper and lower left and right voltage segments each extending approximately a 60 electrical degree interval and for producing upper and lower commutator voltage pulses, the upper left and right voltage segments ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps having magnitudes determined by the upper set of step levels, the lower left and right voltage segments descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps having magnitudes determined by the lower set of step levels, the upper and lower commutator voltage pulses having magnitudes determined by the upper and lower commutator levels; center voltage distributing means including first and second groups of unicontrol center voltage phase selector switches each connected between the center voltage generating means and a different one of the phase lines, the center voltage phase selector switches in each of the first and second groups applying a different one of the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means including first and second groups of unicontrol left/right phase selector switches each connected between the left/right voltage generating means and a different one of the phase lines, the left/right phase selector switches in each of the first and second groups applying a different one of the upper left and right voltage segments and a different one of the lower left and right voltage segments to the phase lines to define corresponding upper and lower left and right waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms, the left/right phase selector switches in each of the first and second groups further applying a different one of the upper and lower commutator voltage pulses to the phase lines to commutate the center voltage phase selector switches in a diferent one of the first and second groups through forced commutation, the center voltage phase selector switches in each of the first and second groups further applying a different one of the upper and lower center voltage segments to the phase lines to commutate the left/right phase selector switches in a different one of the first and second groups through forced commutation; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 36

In a three-phase electrical system including three separate phase lines and a neutral point having a neutral potential, apparatus for producing balanced three-phase sinusoidal line-to-line voltage waveforms by constructing balanced three-phase cyclical and symmetrical line-to-neutral voltage waveforms, the apparatus comprising: center voltage generating means for providing upper and lower center voltage segments each extending over approximately a 60 electrical degree interval, the upper and lower center voltage segments substantially constant respectively at an upper potential above the neutral potential and at a lower potential below the neutral potential; left/right voltage generatIng means including voltage level developing means and voltage level synthesizing means, the voltage level developing means establishing upper and lower sets of step voltage levels and upper and lower commutator voltage levels, the upper set of step levels ranging between the neutral potential and the upper potential and the lower set of step levels ranging between the neutral potential and the lower potential, the upper commutator level residing above the upper potential and the lower commutator level residing below the lower potential, the voltage level synthesizing means connected with the voltage level developing means for producing upper and lower left and right voltage segments each extending approximately a 60 electrical degree interval and for producing upper and lower commutator voltage pulses, the upper left and right voltage segments ascending and descending respectively between the neutral potential and the upper potential in a series of discrete voltage steps having magnitudes determined by the upper set of step levels, the lower left and right voltage segments descending and ascending respectively between the neutral potential and the lower potential in a series of discrete voltage steps having magnitudes determined by the lower set of step levels, the upper and lower commutator voltage pulses having magnitudes determined by the upper and lower commutator levels; center voltage distributing means including first and second groups of unicontrol center voltage phase selector switches each connected between the center voltage generating means and a different one of the phase lines, the center voltage phase selector switches in each of the first and second groups applying a different one of the upper and lower center voltage segments to the phase lines to define corresponding upper and lower center waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms; and left/right voltage distributing means including first and second groups of unicontrol left/right phase selector switches each connected between the left/right voltage generating means and a different one of the phase lines, the left/right phase selector switches in each of the first and second groups applying a different one of the upper left and right voltage segments and a different one of the lower left and right voltage segments to the phase lines to define corresponding upper and lower left and right waveform portions respectively in each cycle of each of the line-to-neutral voltage waveforms, the left/right phase selector switches in each of the first and second groups further applying a different one of the upper and lower commutator voltage pulses to the phase lines to commutate the center voltage phase selector switches in a diferent one of the first and second groups through forced commutation, the center voltage phase selector switches in each of the first and second groups further applying a different one of the upper and lower center voltage segments to the phase lines to commutate the left/right phase selector switches in a different one of the first and second groups through forced commutation; whereby the three-phase line-to-line voltage waveforms are approximately sinusoidal.

Claim 37

A three-phase inverter effective to generate substantially sine-wave voltages on a set of three-phase line conductors from a unidirectional voltage source, the three-phase inverter comprising in combination: a first inverter connected between the source and the conductors effective, by controlled rectifier action, to produce three-phase flat-top voltages on the line conductors; a second inverter connected to said source and operable to produce a single-phase, flat-top output voltage at a predetermined frequency; an inductor having a plurality of taps connected across said second inverter output, whereby alternating flat-top voltage excitation appears thereacross at said predetermined frequency; a voltage distributor and means to connect the same to the three three-phase lIne conductors, respectively; and means effective during the period said voltage distributor is connected to a line conductor to connect said inductor taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductors, whereby the combined flat-top and ascending-descending voltage waveforms developed on said conductors provide high fundamental, low harmonic approximately sinusoidal three-phase voltages on said conductors.

Claim 38

A three-phase inverter effective to generate substantially sine-wave voltages on a set of three-phase line conductors from a unidirectional voltage source, the three-phase inverter comprising in combination: a first inverter connected between the source and the conductors effective, by controlled rectifier action, to produce three-phase flat-top voltages on the line conductors; a second inverter connected to said source and operable to produce a single-phase, flat-top output voltage at a predetermined frequency; an inductor having a plurality of taps connected across said second inverter output, whereby alternating flat-top voltage excitation appears thereacross at said predetermined frequency; a voltage distributor and means to connect the same to the three three-phase lIne conductors, respectively; and means effective during the period said voltage distributor is connected to a line conductor to connect said inductor taps sequentially to the same in ascending or descending order so as to produce the corresponding stepped sequentially rising or falling voltages on said conductors, whereby the combined flat-top and ascending-descending voltage waveforms developed on said conductors provide high fundamental, low harmonic approximately sinusoidal three-phase voltages on said conductors.