Multi-mode power converters incorporating balancer circuits and methods of operation thereof

• US 20010001535A1
• Filed: 01/08/2001
• Published: 05/24/2001
• Est. Priority Date: 08/13/1999
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Robert W. Johnson Jr, William J. Raddi
• Inventors: Johnson, Robert W. Jr., Raddi, William J.
• Granted Patent: US 6,314,007 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02J 9/063 Common neutral, e.g. AC input neutral line connected to AC output neutral line and DC middle point
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements

Abstract

A power converter includes first and second voltage busses and a neutral bus. A first switching circuit, e.g., a rectifier circuit, is operative to selectively couple an input node thereof to the first and second voltage busses. A balancer circuit is operative to selectively couple the neutral bus to the first and second voltage busses such that relative magnitudes of respective first and second voltages on the first and second voltage busses are controlled responsive to respective first and second rates at which the balancer circuit couples the first and second voltage busses to the neutral bus. A second switching circuit, e.g., an inverter circuit, is operative to selectively couple the first and second voltage busses to a load connected at an output node thereof. The balancer circuit preferably includes first and second switches operative to selectively couple respective ones of the first and second voltage busses to the neutral bus through an inductance such that the relative magnitudes of the first and second voltages are controlled responsive to respective first and second duty cycles of the first and second switches. The power converter is capable of multiple operating modes and suitable for use in uninterruptible power supplies (UPSs).

Claims

1. A power converter, comprising:

first and second voltage busses;

a neutral bus;

a first switching circuit operative to selectively couple an input node thereof to the first and second voltage busses;

a balancer circuit operative to selectively couple the neutral bus to the first and second voltage busses such that relative magnitudes of respective ones of the first and second voltages on the first and second voltage busses are controlled responsive to respective first and second rates at which the balancer circuit couples the first and second voltage busses to the neutral bus; and

a second switching circuit operative to selectively couple the first and second voltage busses to a load connected at an output node thereof.

2. A converter according to

claim 1

:

wherein the first switching circuit comprises a rectifier circuit operative to produce respective ones of the first and second voltages on respective ones of the first and second voltage busses from an AC input voltage at the input node; and

wherein the second switching circuit comprises an inverter operative to produce an AC output voltage at the output node from the first and second voltages.

3. A converter according to

claim 2

, wherein the balancer circuit comprises first and second switches operative to selectively couple respective ones of the first and second voltage busses to the neutral bus through an inductance such that the relative magnitudes of the first and second voltages are controlled responsive to respective first and second duty cycles of the first and second switches.

4. A converter according to

claim 3

, wherein the first switch is constrained to decouple the first voltage bus from the neutral bus when the second voltage bus is coupled to the neutral bus, and wherein the second switch is constrained to decouple the second voltage bus from the neutral bus when the first voltage bus is coupled to the neutral bus.

5. A converter according to

claim 2

, further comprising:

a first capacitor coupling the first voltage bus to the neutral bus; and

a second capacitor coupling the second voltage bus to the neutral bus,

wherein the first and second capacitors have a per unit capacitance of less than 1.

6. A converter according to

claim 3

, wherein the balancer circuit is operative to switch both of the first and second switches at 50% duty cycles to maintain the first and second voltages at substantially the same magnitude.

7. A converter according to

claim 3

, wherein the balancer circuit is responsive to an AC input voltage applied to the input node of the first switching circuit to vary the respective duty cycles at which the first and second switches operate.

8. A converter according to

claim 7

, wherein the balancer circuit is operative to switch the first switch at a higher duty cycle than the second switch for a first portion of a cycle of the AC input voltage and to switch the second switch at a higher duty cycle than the first switch for a second portion of the cycle of the AC input voltage.

9. A converter according to

claim 3

, wherein the balancer circuit comprises an inductor having a first terminal coupled to the neutral bus, and wherein the first and second switches are operative to selectively couple a second terminal of the inductor to respective ones of the first and second voltage busses.

10. A converter according to

claim 2

, further comprising a battery converter circuit switchably coupled to at least one of the first and second voltage busses.

12. A converter according to

claim 3

, wherein the balancer circuit comprises a transformer including a first winding having a first tap coupled to the first and second switches and a second tap coupled to the neutral bus, and wherein the first and second switches selectively couple the first tap of the transformer to the first and second voltage busses.

13. A converter according to

claim 12

, further comprising first and second diodes, the first diode having a cathode coupled to the first voltage bus, the second diode having a cathode coupled to an anode of the first diode and an anode coupled to the second voltage bus, and wherein the first winding of the transformer has a first end tap coupled to the first and second switches, a second end tap coupled to the anode of the first diode and the cathode of the second diode, and a center tap coupled to the neutral bus.

14. A converter according to

claim 12

, further comprising third and fourth switches, wherein the first winding of the transformer has a first end tap coupled to the first and second switches, a second end tap coupled to the third and fourth switches, and a center tap coupled to the neutral bus, wherein the third switch is operative to couple and decouple the second end tap of the first winding and the first voltage bus, and wherein the fourth switch is operative to couple and decouple the second end tap of the first winding and the second voltage bus.

15. A converter according to

claim 12

, wherein the transformer comprises a second winding inductively coupled to the first winding, and further comprising an AC voltage generating circuit coupled to the second winding of the transformer and operative to apply an AC voltage thereto.

16. A converter according to

claim 15

, wherein the AC voltage generating circuit comprises a battery converter circuit operative to generate an AC voltage on the second winding of the transformer from a DC voltage produced by a battery coupled to the battery converter circuit.

17. A converter according to

claim 15

, wherein the AC voltage generating circuit comprises a combined battery converter/battery charger circuit that is operative to generate an AC voltage on the second winding of the transformer from a DC voltage produced by the battery, and to produce a DC voltage across the battery from an AC voltage induced on the second winding of the transformer.

11. A converter according to claim I 0, wherein the battery converter circuit comprises:

an inductor configured to be connected in series with a battery;

a first switch operative to selectively couple one end of a series combination of a battery and the inductor to one of the first or second voltage busses; and

a second switch operative to selectively couple the one end of the series combination of a battery and an inductor to another end of the series combination of a battery and the inductor.

18. A power converter, comprising:

a rectifier circuit configured to connect to an AC power source and operative to produce first and second DC voltages at first and second voltage busses, respectively, by selectively coupling the first and second voltage busses to the AC power source through a first inductance;

first and second capacitors coupling the first and second voltage busses, respectively, to a neutral bus;

an inverter circuit configured to connect to a load and operative to selectively couple the first and second voltage busses to the load through a second inductance; and

a balancer circuit operative to selectively couple the first and second voltage busses to the neutral bus through a third inductance such that relative magnitudes of the first and second DC voltages are controlled responsive to respective first and second rates at which the balancer circuit couples the first and second voltage busses to the neutral bus.

19. A converter according to

claim 18

, further comprising a switch control circuit, and:

wherein the rectifier circuit comprises;

a first inductor having a first terminal configured to receive an AC input voltage;

a first switch responsive to the switch control circuit to couple and decouple a second terminal of the first inductor and the first voltage bus; and

a second switch responsive to the switch control circuit to couple and decouple the second terminal of the first inductor and the second voltage bus; and

wherein the inverter circuit comprises;

a second inductor having a first terminal configured to connect to a load;

a third switch responsive to the switch control circuit to couple and decouple a second terminal of the second inductor and the first voltage bus; and

a fourth switch responsive to the switch control circuit to couple and decouple the second terminal of the second inductor and the second voltage bus.

20. A converter according to

claim 19

, wherein the switch control circuit is responsive to an AC input voltage applied to the rectifier circuit to control operation of the first, second, third and fourth switches.

21. A converter according to

claim 20

, wherein the switch control circuit is operative to vary respective duty cycles at which the first, second, third and fourth switches are operated responsive to the AC input voltage.

22. A converter according to

claim 20

:

wherein the switch control circuit is operative, when the AC input voltage is at a nominal level, to provide a substantially continuous low impedance connection between the AC power source and the load through the rectifier and inverter circuits;

wherein the switch control circuit is operative, when the AC input voltage is less than the nominal level, to cause the rectifier circuit to boost the magnitudes of the first and second DC voltages while providing respective substantially continuous low impedance connections between the load and respective ones of the first and second voltages busses through the inverter circuit during respective positive and negative half-cycles of the AC input voltage; and

wherein the switch control circuit is operative, when the AC input voltage is greater than the nominal level, to provide respective substantially continuous low-impedance connections between the AC power source and respective ones the first and second voltage busses through the rectifier circuit during respective positive and negative half-cycles of the AC input voltage, while causing the inverter circuit to buck the magnitude of a voltage generated at the load from the first and second DC voltages.

23. A converter according to

claim 22

, wherein the switch control circuit is operative to control the balancer circuit such that the magnitude of the first DC voltage is substantially greater than the magnitude of the second DC voltage during a positive half-cycle of the AC input voltage and such that the magnitude of the second DC voltage is substantially greater than the magnitude of the first DC voltage during a negative half-cycle of the AC input voltage.

24. A converter according to

claim 20

:

wherein the switch control circuit is operative, when the AC input voltage is at a nominal level, to;

switch the first and second switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, while switching the third and fourth switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, during a first positive half-cycle of the AC input voltage; and

switch the first and second switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, while switching the third and fourth switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, during a first negative half-cycle of the AC input voltage;

wherein the switch control circuit is operative, when the AC input voltage is at less than the nominal level, to;

switch the first and second switches at substantially complementary duty cycles sufficiently less than 100% and sufficiently greater than 0%, respectively, to boost the magnitude of the first DC voltage, while switching the third and fourth switches at substantially complementary cycles of approximately 100% and approximately 0%, respectively, during a second positive cycle of the AC input voltage; and

switch the first and second switches at substantially complementary duty cycles sufficiently greater than 0% and sufficiently less than 0%, respectively, to boost the magnitude of the second DC voltage, while switching the third and fourth switches at substantially complementary cycles of approximately 0% and approximately 100%, respectively, during a second negative half-cycle of the AC input voltage; and

wherein the switch control circuit is operative, when the AC input voltage is greater than the nominal level, to;

switch the first and second switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, while switching the third and fourth switches at substantially complementary cycles sufficiently less than 100% and sufficiently greater than 0%, respectively, to buck a voltage applied to the load, during a third positive cycle of the AC input voltage; and

switch the first and second switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, while switching the third and fourth switches at substantially complementary cycles sufficiently greater than 0% and sufficiently less than 100%, respectively, to buck a voltage applied to the load, during a third negative cycle of the AC input voltage.

25. A converter according to

claim 24

:

wherein the balancer circuit comprises;

a third inductor having a first terminal coupled to the neutral bus;

a fifth switch responsive to the switch control circuit to couple and decouple a second terminal of the third inductor and the first voltage bus; and

a sixth switch responsive to the switch control circuit to couple and decouple the second terminal of the third inductor and the second voltage bus; and

wherein the switch control circuit is operative to;

switch the fifth and sixth switches at complementary duty cycles of approximately 0% and approximately 100%, respectively, during the second and third positive half-cycles and to switch the fifth and sixth switches at complementary duty cycles of approximately 100% and approximately 0%, respectively, during the second and third negative half-cycles.

26. A converter according to

claim 19

, wherein the balancer circuit comprises:

a third inductor having a first terminal coupled to the neutral bus;

a fifth switch responsive to the switch control circuit to couple and decouple a second terminal of the third inductor and the first voltage bus; and

a sixth switch responsive to the switch control circuit to couple and decouple the second terminal of the third inductor and the second voltage bus.

27. A converter according to

claim 26

, wherein the switch control circuit is responsive to an AC input voltage applied to the rectifier circuit to control operation of the first, second, third, fourth, fifth and sixth switches.

28. A converter according to

claim 27

, wherein the switch control circuit is operative to vary respective duty cycles at which the first, second, third, fourth, fifth and sixth switches are operated responsive to the AC input voltage.

29. A converter according to

claim 19

, further comprising a battery coupling circuit operative to couple and decouple a battery and the first terminal of the first inductor.

30. A converter according to

claim 19

, further comprising a battery coupling circuit operative to selectively couple a battery to one of the first voltage busses and the neutral bus.

31. A converter according to

claim 26

, wherein the third inductor comprises a first winding of a transformer, the transformer having a second winding inductively coupled to the first winding, and further comprising an AC voltage generating circuit coupled to the second winding of the transformer, configured to connect to a battery, and operative to generate an AC voltage on the second winding of the transformer from a DC voltage produced by the battery.

32. A converter according to

claim 31

:

wherein the balancer circuit is operative to produce a first AC voltage on the first winding of the transformer; and

wherein the AC voltage generating circuit is operative to charge a battery connected thereto from a second AC voltage induced on the second winding of the transformer by the first AC voltage.

33. A method of controlling power transfer between and an AC power source that produces an AC input voltage between a phase bus and a neutral bus, the method comprising the steps of:

selectively coupling first and second voltage busses to the phase bus through a first inductance to produce first and second DC voltages at first and second voltage busses, respectively;

selectively coupling the first and second voltage busses to the load through a second inductance; and

selectively coupling the first and second voltage busses to the neutral bus through a third inductance such that relative magnitudes of the first and second DC voltages are controlled responsive to respective first and second rates at which the first and second voltage busses are coupled to the neutral bus.

34. A method according to

claim 33

:

wherein said step of selectively coupling first and second voltage busses to the phase bus comprises the steps of;

switching a first switch to couple and decouple the phase bus and the first voltage bus through a first inductor; and

switching a second switch to couple and decouple the phase bus and the second voltage bus through the first inductor;

wherein said step of selectively coupling the first and second voltage busses to a load comprises the steps of;

switching a third switch circuit to couple and decouple the first voltage bus and the load through a second inductor; and

switching a fourth switch to couple and decouple the second voltage bus and the load bus through the second inductor.

35. A method according to

claim 34

, wherein said switching steps are performed responsive to the AC input voltage.

36. A method according to

claim 35

, further comprising the step of varying respective duty cycles at which the first, second, third and fourth switches are operated responsive to the AC input voltage.

37. A method according to

claim 35

, comprising the steps of:

providing a substantially continuous low impedance connection between the phase bus and the load through selected combinations of the first, second, third and fourth switches when the AC input voltage is approximately at a nominal level;

switching the first and second switches to boost the magnitudes of the first and second DC voltages while providing respective substantially continuous low impedance connections between the load and respective ones of the first and second voltages busses through respective ones of the third and fourth switches during respective positive and negative half-cycles of the AC input voltage, when the AC input voltage is less than the nominal level; and

providing respective substantially continuous low-impedance connections between the AC power source and respective ones the first and second voltage busses through respective ones of the first and second switches during respective positive and negative half-cycles of the AC input voltage, while bucking a voltage generated at the load from the first and second DC voltages, when the AC input voltage is greater than the nominal level.

38. A method according to

claim 37

, wherein said step of selectively coupling the first and second voltage busses to the neutral bus comprises the step of switching fifth and sixth switches that couple and decouple respective ones of the first and second voltage busses and the neutral bus through a third inductor, such that the magnitude of the first DC voltage is substantially greater than the magnitude of the second DC voltage during a positive half-cycle of the AC input voltage and such that the magnitude of the second DC voltage is substantially greater than the magnitude of the first DC voltage during a negative half-cycle of the AC input voltage.

39. A method according to

claim 35

, comprising the steps of:

when the AC input voltage is at a nominal level;

switching the first and second switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, while switching the third and fourth switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, during a first positive half-cycle of the AC input voltage; and

switching the first and second switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, while switching the third and fourth switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, during a first negative half-cycle of the AC input voltage;

when the AC input voltage is less than the nominal level;

switching the first and second switches at substantially complementary duty cycles sufficiently less than 100% and sufficiently greater than 0%, respectively, to boost the magnitude of the first DC voltage, while switching the third and fourth switches at substantially complementary cycles of approximately 100% and approximately 0%, respectively, during a second positive cycle of the AC input voltage; and

switching the first and second switches at substantially complementary duty cycles sufficiently greater than 0% and sufficiently less than 100%, respectively, to boost the magnitude of the second DC voltage, while switching the third and fourth switches at substantially complementary cycles of approximately 0% and approximately 100%, respectively, during a second negative half-cycle of the AC input voltage; and

when the AC input voltage is greater than the nominal level, to;

switching the first and second switches at substantially complementary duty cycles of approximately 100% and approximately 0%, respectively, while switching the third and fourth switches at substantially complementary cycles sufficiently less than 100% and sufficiently greater than 0%, respectively, to buck a voltage applied to the load, during a third positive cycle of the AC input voltage; and

switching the first and second switches at substantially complementary duty cycles of approximately 0% and approximately 100%, respectively, while switching the third and fourth switches at substantially complementary cycles sufficiently greater than 0% and sufficiently less than 100%, respectively, to buck a voltage applied to the load, during a third negative cycle of the AC input voltage.

40. A method according to

claim 39

, wherein said step of selectively coupling the first and second voltage busses to the neutral bus comprises the steps of:

switching fifth and sixth switches that couple and decouple respective ones of the first and second voltage busses and the neutral bus through a third inductor at complementary duty cycles of approximately 0% and approximately 100%, respectively, during the second and third positive half-cycles; and

switching the fifth and sixth switches at complementary duty cycles of a approximately 100% and approximately 0%, respectively, during the second and third negative half-cycles.

41. A method according to

claim 34

, wherein said step of selectively coupling the first and second voltage busses to the neutral bus comprises the steps of:

switching a fifth switch to couple and decouple the first voltage bus and the neutral bus through a third inductor; and

switching a sixth switch to couple and decouple the second voltage bus and the neutral bus through the third inductor.

42. A method according to

claim 33

, further comprising the step of selectively coupling a battery to at least one of the first inductance, the first voltage bus, or the second voltage bus to enable power transfer between the battery and the first and second voltage busses.