Apparatus for controlling pulse width modulation of inverter circuits

Claim 2

In power inverter apparatus for converting DC voltage from a DC voltage source into an AC output voltage for application to an electrical load, the combination of, at leasT first and second single pole power stages, each comprised of conduction controlled switching devices operatively connected between said DC voltage source and said electrical load to develop first and second output pole voltages respectively in response to conduction control signals to form said AC output voltage, first circuit means for generating said conduction control signals to control said output pole voltages between an unmodulated, or a full output pole voltage condition, and a modulated, or reduced output pole voltage condition, second circuit means for developing a reference square wave of a frequency which is three times the fundamental frequency of said AC output voltage, said reference square wave being in identical phase relationship with each of said unmodulated pole voltages such that the leading edge of said unmodulated output pole voltages coincide with a leading edge of said reference square wave, third circuit means for integrating said reference square wave to develop a constant amplitude sawtooth voltage having quarter wave symmetry, positive and negative polarity segments symmetrically disposed about a zero voltage level and a frequency which is three times the fundamental frequency of said AC output voltage, fourth circuit means for generating at least first and second AC square waves, said square waves corresponding in frequency and phase displacement to the unmodulated output pole voltages of said first and second single pole power stages respectively, said first circuit means comparing sawtooth voltage to each of said AC square waves and transmitting conduction control signals to said first and second power stages when the respective AC square waves intersect said sawtooth voltage, the amplitude of said AC square waves determining the modulation angle of the respective conduction controlled power switching devices.

Claim 3

In power inverter apparatus as claimed in claim 1 further including feedback circuit means coupled between the outputs of said single pole power stages and said third circuit means to adjust the amplitude of said AC square wave voltage to compensate for DC content in the respective output pole voltages.

Claim 4

In power inverter apparatus as claimed in claim 1 including means for limiting the amplitude of the square wave reference voltage to a value less than the amplitude of said sawtooth voltage waveform.

Claim 5

In power inverter apparatus as claimed in claim 1 wherein the magnitude of the pulse shape voltage output of said fourth circuit means is a function of the respective pole voltages.

Claim 6

In a multiphase power inverter apparatus for supplying an AC output voltage to an electrical load from a source of direct current, the combination of, n single pole power stages wherein n is an integer and a multiple of 3, said single pole power stages comprised of conduction controlled power switching devices operatively connected between said source of direct current and said electrical load for developing said AC output in response to conduction controlled signals, n comparator circuit means wherein each comparator circuit means has a first and second input and an output, the output of each comparator circuit means being operatively coupled to one of said single pole power stages, said comparator circuit means generating said conduction control signals to control the modulation angle of said conduction controlled power switching devices as a means for pulse width modulating the pole voltage outputs of the respective single pole power stages between an unmodulated output pole voltage corresponding to full voltage and a modulated output pole voltage corresponding to voltage less than full voltage, first circuit means for developing n pulse shape outputs corresponding to the unmodulated output pole voltage of the respective single pole power stages, second circuit means operatively connected to the output of said first circuit means and responding to said pulse shape output voltages to Develop a reference square wave having a frequency which is three times the fundamental frequency of said AC output voltage, said reference square wave being in identical phase relationship with each of said n pulse shape outputs such that the leading edge of each of said pulse shape outputs coincides with a leading edge of said reference square wave, third circuit means for integrating said reference square wave to develop an output sawtooth voltage of constant magnitude and quarter wave symmetry at a frequency which is three times the fundamental frequency of said AC output voltage, said sawtooth voltage having positive and negative polarity segments symmetrically disposed about a zero voltage level, fourth circuit means responding to the n pulse shape outputs of said first circuit means by developing n pulse shape outputs corresponding in frequency and phase displacement to the respective unmodulated pole voltage outputs and exhibiting positive and negative polarity segments, said sawtooth voltage being supplied to the first input of each of said n comparator circuit means and the n pulse shape outputs of said fourth circuit means being supplied to the second inputs of the respective comparator circuit means, said comparator circuit means generating conduction controlled signals for the respective single pole power stages when the pulse shape inputs of the respective comparator circuit means intersect said sawtooth reference voltage, the amplitude of said pulse shape inputs determining the modulation angle of the conduction controlled power switching devices of the respective single pole power stages.

Claim 7

In a multiphase power inverter apparatus for supplying an AC output voltage to an electrical load from a source of direct current, the combination of, n single pole power stages wherein n is an integer and a multiple of 3, said single pole power stages comprised of conduction controlled power switching devices operatively connected between said source of direct current and said electrical load for developing said AC output in response to conduction controlled signals, n comparator circuit means wherein each comparator circuit means has a first and second input and an output, the output of each comparator circuit means being operatively coupled to one of said single pole power stages, said comparator circuit means generating said conduction control signals to control the modulation angle of said conduction controlled power switching devices as a means for pulse width modulating the pole voltage outputs of the respective single pole power stages between an unmodulated output pole voltage corresponding to full voltage and a modulated output pole voltage corresponding to voltage less than full voltage, first circuit means for developing n pulse shape outputs corresponding to the unmodulated output pole voltage of the respective single pole power stages, second circuit means operatively connected to the output of said first circuit means and responding to said pulse shape output voltages to Develop a reference square wave having a frequency which is three times the fundamental frequency of said AC output voltage, said reference square wave being in identical phase relationship with each of said n pulse shape outputs such that the leading edge of each of said pulse shape outputs coincides with a leading edge of said reference square wave, third circuit means for integrating said reference square wave to develop an output sawtooth voltage of constant magnitude and quarter wave symmetry at a frequency which is three times the fundamental frequency of said AC output voltage, said sawtooth voltage having positive and negative polarity segments symmetrically disposed about a zero voltage level, fourth circuit means responding to the n pulse shape outputs of said first circuit means by developing n pulse shape outputs corresponding in frequency and phase displacement to the respective unmodulated pole voltage outputs and exhibiting positive and negative polarity segments, said sawtooth voltage being supplied to the first input of each of said n comparator circuit means and the n pulse shape outputs of said fourth circuit means being supplied to the second inputs of the respective comparator circuit means, said comparator circuit means generating conduction controlled signals for the respective single pole power stages when the pulse shape inputs of the respective comparator circuit means intersect said sawtooth reference voltage, the amplitude of said pulse shape inputs determining the modulation angle of the conduction controlled power switching devices of the respective single pole power stages.

Claim 8

In apparatus as claimed in claim 5 including means for limiting the magnitude of the pulse shape output voltage of said fourth circuit means to a voltage less than the peak value of the said sawtooth voltage.

Claim 9

In apparatus as claimed in claim 5 wherein the magnitude of the pulse shape output of said fourth circuit means is a function of the respective output pole voltages.

Claim 10

In apparatus as claimed in claim 5 including transformer circuit means for coupling the outputs of the single pole power stages.