Bridge converter circuit

A bridge converter circuit, comprising:

• a first operating voltage terminal for receiving +E volts;
• a second operating voltage terminal for receiving -E volts;
• a reference voltage terminal for receiving a reference potential;
• first and second output terminals for connection to a load therebetween;
• first through fourth banks of switches each having first, second and third terminals, the second terminals of said first and second banks of switches being connected in common to said first output terminal, the second terminals of said third and fourth banks of switches being connected in common to said second output terminal, the first terminals of said first and third banks of switches being connected in common to said first operating voltage terminal, and the first terminals of said second and fourth banks of switches being connected in common to said second operating voltage terminal;
• first and second diode means individually connected between and polarized for both (1) passing current only from said reference voltage terminal to said third terminals of said first and third banks of switches respectively and (2) when forwardbiased clamping their respective third terminal to within one diode voltage drop of said reference potential, thereby protecting their respective bank of switches from overvoltage;
• third and fourth diode means individually connected between and polarized for both (1) passing current only from said third terminals of said second and fourth banks of switches, respectively, to said reference voltage terminal and (2) when forwardbiased clamping their respective third terminal to within one diode voltage drop of said reference potential, thereby protecting their respective bank of switches from overvoltage;
• and
• control means for sequentially operating said converter circuit from one to another of first through fifth combinations of operative states of said first through fourth banks of switches, in a predetermined manner for producing a desired AC voltage across said load, whereby in said first combination said first through fourth banks of switches are operated to connect their respective second and third terminals together, thereby providing bidirectional current flow between said reference voltage terminal and said first and second output terminals, respectively, and applying said reference potential to these output terminals, producing zero volt across said load, in said second combination said first bank of switches is operated for connecting its first, second and third terminals together, and said fourth bank of switches is operated for connecting its second and third terminals together, for applying +E volts to said first output terminal and across said load, in said third combination said first and fourth banks of switching means are operated for connecting their respective first, second and third terminals together, for applying +E volts to said first output terminal, -E volts to said second output terminal, and thereby +2E volts across said load, in said fourth combination said third bank of switches is operated for connecting its second and third terminals together, and said second switching means is operated for connecting its first, second and third terminals together for applying -E volts to said first output terminal and across said load, and in said fifth combination said second and third banks of switches are operated for connecting their respective first, second and third terminals together for applying -E volts to said first output terminal, +E volts to said second output terminal, and thereby -2E volts across said load.

A bridge converter circuit, comprising:

• rectifier means for converting a first AC voltage into first and second DC voltages having levels of +E and -E volts, respectively, relative to a source of reference potential;
• first and second output terminals for applying a second AC voltage across a load connected therebetween;
• first through fourth switching means each having a first terminal, a second terminal and a third terminal, said first and second switching means having their first terminals for receiving +E volts and -E volts, respectively, and their second terminals connected in common to said first output terminal, said third and fourth switching means having their first terminals for receiving +E volts and -E volts, respectively, and their second terminal connected in common to said second output terminal;
• first and second diode means each having an anode electrode connected in common to said source of reference potential, and a cathode electrode connected individually to said third terminal of said first and third switching means, respectively, the combination being operable for providing oppositely directed unidirectional gated current paths between said first output terminal and said source of reference potential, respectively, and
• third and fourth diode means each having a cathode electrode connected in common to said source of reference potential, and an anode electrode connected individually to said third terminal of said second and fourth switching means, respectively, this combination being operable for providing oppositely directed unidirectional gated current paths between said second output terminal and said source of reference potential, respectively, said first through fourth diode means also serving to limit the voltage drop across the first and third terminals, and second and third terminals of said first, third, second, and fourth switching means to E volts, respectively;
• said first through fourth switching means each being operable to a first condition providing a current conduction path only between the second and third terminals, respectively, to a second condition concurrently providing current conduction paths between their first, second, and third terminals, respectively, and to a third condition providing substantial isolation between their said first, second and third terminals, respectively;
• said first through fourth switching means each being concurrently operable to said first condition, for establishing a first configuration of said converter for applying zero volts between said first and second output terminals, and providing bidirectional current flow between each one of said first and second output terminals and said source of reference potential;
• said first through fourth switching means each being concurrently operable to their second, third, first, and first conditions, respectively, for establishing a second configuration of said converter for applying +E volts to said first output terminal and said source of reference potential to said second output terminal;
• said first through fourth switching means being concurrently operable to their second, third, third, and second conditions, respectively, for establishing a third configuration of said converter for applying substantially +E volts to said first output terminal, and -E volts to said second output terminal;
• said first through fourth switching means being concurrently operable to their third, second, first, and third conditions, respectively, for establishing a fourth configuration of said converter for applying -E volts to said first output terminal, and said source of reference potential to said second output terminal;
• said first through fourth switching means being concurrently operable to their third, second, second, and third conditions, respectively, for establishing a fifth configuration of said converter for applying substantially -E volts to said first output terminal, and +E volts to said second output terminal;
• said converter being operable in a predetermined sequence of its first through fifth configurations, for producing said second AC voltage.

A method for converting DC voltages having levels of +E and -E volts relative to a reference potential applied to a reference voltage terminal, into an AC voltage for application across a load connected between first and second output terminals, comprising a predetermined sequence of the combination of the following steps:

• applying said reference potential to said first and second output terminals, while providing bidirectional current flow between said reference voltage terminal, and each one of said first and second output terminals, for producing zero volt across said load;
• applying +E volts to said first output terminal, while providing unidirectional current flow from said second output terminal to said reference voltage terminal, for producing +E volts across said load;
• applying +E volts and -E volts to said first and second output terminals, respectively, for producing +2E volts across said load;
• applying -E volts to said first output terminal, while providing unidirectional current flow from said reference voltage terminal to said second output terminal, for producing -E volts across said load;
• and
• applying -E volts and +E volts to said first and second output terminals, respectively, for producing -2E volts across said load.

A polyphase bridge converter circuit, comprising:

• a first operating voltage terminal for receiving +E volts;
• a second operating voltage terminal for receiving -E volts;
• a reference voltage terminal for connection to a point of reference potential;
• and
• a plurality of phase banks each including:
• an output terminal;
• at least first through fourth switching means each having a main current conduction path, the main current conduction paths of said first through fourth switching means being connected in series in that order from said first to said second operating voltage terminals, the common connection between said second and third switching means being connected to said output terminal, each one of said first through fourth switching means being operable to a first condition for closing or substantially lowering the impedance of its main current conduction path, and to a second condition for opening or substantially increasing the relative impedance of its main current path;
• first unidirectional current means connected between said reference voltage terminal and the common connection between said first and second switching means, and polarized for conducting current from said reference voltage terminal to this common connection;
• and
• second unidirectional current means connected between and polarized for conducting current from the common connection of said third and fourth switching means to said reference voltage terminal;
• the first through fourth switching means of one of said plurality of phase banks being operable over repetitive periods of time through predetermined different combinations of their respective first and second conditions, during each time period, for producing stepwise approximations of desired polyphase related AC output voltages concurrently at the respective output terminals of each phase bank, the number of phase banks being at least equal to the number of phases of AC output voltage desired.

A bridge converter circuit, for converting up to +nE volts into polyphase AC output voltages, where n is an even integer number other than 2 (n=4, 6, 8, 10 . . . ), and E is a constant number, comprising:

• first and second operating voltage terminals for receiving +nE volts and -nE volts, respectively;
• a plurality of phase banks equal in number to at least the number of phases of AC output voltages desired, each including:
• an output terminal;
• a plurality of n/2 first switching means each having a main current conduction path, the main current conduction paths of said switching means being connected in series between said first operating voltage and said output terminals, each one of said switching means being selectively and individually operable to a first condition for opening their main current conduction path, and to a second condition for closing their main current conduction path;
• a plurality of n/2 second switching means each having a main current conduction path, the main current conduction paths of said second switching means being connected in series between said output and second operating voltage terminals, each one of said second switching means being selectively and individually operable to a first condition for opening their main current conduction path, and to a second condition for closing their main current conduction path;
• a plurality of [(n/2)-1] first diodes each having a cathode electrode and an anode electrode;
• a plurality of [(n/2)-1] second diodes each having a cathode electrode and an anode electrode;
• beginning from the uppermost first common connection between the uppermost two of said n/2 first switching means relative to said first terminal, proceeding sequentially downward to the [(n/2)-1] common connection between the lowermost two of said n/2 switching means, each one of said [(n/2)-1] first diodes having their cathode electrodes connected to an individual numerically corresponding one of these [(n/2)-1] common connections, and their anode electrodes individually receiving a different and progressively lower level of DC voltage, respectively;
• beginning from the uppermost first common connection between the uppermost two of said n/2 second switching means relative to said output terminal, proceeding sequentially downward to the [(n/2)-1] common connection between the lowermost two of said n/2 second switching means, each one of said [(n/2)-1] second diodes having their anode electrodes connected to an individual corresponding numerical one of these [(n/2)-1] common connections, and their cathode electrodes to the anode electrodes of the numerically corresponding one of said [(n/2)-1] first diodes, the values of the different levels of DC voltage being chosen for ensuring that the open-circuit voltage breakdown of said plurality of n/2 first and second switching means is not exceeded, provided that said n/2 first switching means are sequentially closed in order from the lowermost one to the uppermost one, and opened in reverse order, and that said n/2 second switching means are sequentially closed in order from the uppermost one to the lowermost one, and opened in reverse order, these switching means being operable to different combinations of their first and second conditions for producing any one of [(n/2)+1] different levels of output voltage at said output terminal.

A method for converting DC voltages having levels of +E and -E volts relative to a reference potential applied to a reference voltage terminal, into an AC voltage for application across a load connected between first and second output terminals, comprising a predetermined sequence of the combination of the following steps:

• applying said reference potential to said first and second output terminals, while providing bidirectional current flow between said reference voltage terminal, and each one of said first and second output terminals, for producing zero volt across said load;
• applying +E volts to said first output terminal, while providing bidirectional current flow from said second output terminal to said reference voltage terminal, for producing +E volts across said load;
• applying +E volts and -E volts to said first and second output terminals, respectively, for producing +2E volts across said load;
• applying -E volts and +E volts to said first output terminal, while providing bidirectional current flow from said reference voltage terminal to said second output terminal, for producing -E volts across said load;
• and
• applying -E volts to said first and second output terminals, respectively, for producing -2E volts across said load.