Transformerless pulse width modulated inverter for providing three phase voltage for a three wire load

Claim 2

An inverter for converting a direct current voltage to threephase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the voltage difference between two modulated voltages includes a pulse of width M during the first 30* of a quarteR cycle of one phase of the polyphase voltage, a pulse of width N minus M during the second 30*, and a pulse of width N during the third 30*, the pulse of width M approximating the area in the first 30* of one phase of the polyphase voltage and the pulse of width N approximating the area in the third 30*, the pulses in the following quarter cycle occurring in a reverse sequence to the pulses in the preceeding quarter cycle and the pulses in the following half cycle occurring in the same sequence as the preceeding half cycle but being of opposite polarity.

Claim 3

An inverter of the kind described in claim 1 in which the pulse in the second 30* of each quarter cycle is replaced by two pulses of widths one-half of the difference of N-M spaced a distance M during the second 30* of each quarter cycle, and the converting means includes means for providing three-phase sinusoidal voltages for use with a three-wire load.

Claim 4

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the converting means is a filter which filters out harmonic frequency components in the modulated voltages to provide the sinusoidal voltages.

Claim 5

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the converting means is a filter which filters out harmonic frequency components in the modulated voltages to provide the sinusoidal voltages.

Claim 6

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and means to vary the direct current voltage to change the amplitude of the sinusoidal voltages.

Claim 7

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and means to vary the direct current voltage to change the amplitude of the sinusoidal voltages.

Claim 8

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and control means for maintaining the sinusoidal voltages at a constant amplitude connected to the pulse train means and to the converting means, the control means having means for comparing the sinusoidal voltages to a reference voltage and means for controlling the width of pulses of width M and N.

Claim 9

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and control means for maintaining the sinusoidal voltages at a constant amplitude connected to the pulse train means and to the converting means, the control means having means for comparing the sinusoidal voltages to a reference voltage and means for controlling the width of pulses of width M and N.

Claim 10

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for convertiNg the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and in which the modulating means includes a plurality of switching means connected to the logic circuit and receiving the direct current voltage and controlled by the pulse control signal for modulating the direct current voltage for providing the modulated voltages.

Claim 11

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for convertiNg the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and in which the modulating means includes a plurality of switching means connected to the logic circuit and receiving the direct current voltage and controlled by the pulse control signal for modulating the direct current voltage for providing the modulated voltages.

Claim 12

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and in which the source of timing pulses has means for changing the repetition rate of the timing pulses to change the frequency of the sinusoidal voltages.

Claim 13

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and in which the source of timing pulses has means for changing the repetition rate of the timing pulses to change the frequency of the sinusoidal voltages.

Claim 14

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and means to vary the direct current voltage to change the amplitude of the sinusoidal voltages, and in which the source of timing pulses is connected to the pulse generator and has means for changing the repetition rate of the timing pulses to change the frequency of the sinusoidal voltages.

Claim 15

An inverter for converting a direct current voltage to three-phase sinusoidal voltages comprising means for providing two pulse trains, one pulse train having pulses of width M and the other pulse train having pulses of width N, means receiving a direct current voltage and responsive to the pulse trains for modulating the direct current voltage to provide three modulated voltages having 120* phase difference with each other, converting means connected to the modulating means for converting the voltage differences between the three modulated voltages to provide the three-phase sinusoidal voltages, and in which the pulse train means includes a source of timing pulses, and a pulse generator connected to the timing pulse source and providing the pulse trains in response to the timing pulses; and the modulating means includes a logic circuit connected to the timing pulse source and to the pulse generator and providing a pulse control signal, in response to the pulse trains and to the timing pulses, for each phase of the three-phase sinusoidal voltages for modulating a direct current voltage, and means to vary the direct current voltage to change the amplitude of the sinusoidal voltages, and in which the source of timing pulses is connected to the pulse generator and has means for changing the repetition rate of the timing pulses to change the frequency of the sinusoidal voltages.