Power supply system with ORing element and control circuit

• US 6,301,133 B1
• Filed: 04/07/1999
• Issued: 10/09/2001
• Est. Priority Date: 04/07/1999
• Status: Expired due to Fees

• Current Assignee: Astec International Limited (Emerson Electric Company)
• Original Assignee: Astec International Limited (Emerson Electric Company)
• Inventors: Wildash, Kevin D., Cuadra, Jason E., Bernat, Mohamed Amin S., Mohan, Krishnamurthi
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/287,865
• Time in Patent Office: 916 Days
• Field of Search: 363/65, 363/69, 363/71, 307/53, 307/58, 307/69, 307/71, 307/82, 307/85-87
• US Class Current: 363/65
• CPC Class Codes: H02J 1/001 Hot plugging or unplugging of load or power modules to or from power distribution networks
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection

Abstract

In a redundant power supply system, N+1 power supply modules are operated in parallel to provide power to a single load which may be connected via a DC bus and may employ a remote voltage sensing circuit. Each power supply module includes an ORing element that isolates a corresponding AC power supply from delivering power to the load in various conditions representing a fault occurring in the system. Each ORing element and power supply module is coupled to a control circuit that drives the operations of the ORing element. The control circuit includes three comparators and associated circuitry each for detecting one of the following conditions of system failure representing by: the presence of reverse current flowing across the ORing element caused by short circuit in the system, a selective overvoltage condition caused by a power supply delivering too much voltage to the load; and a failure in an AC power supply giving rise to an undervoltage condition. An error amplification circuit is responsive to a slow rise starting voltage and prevents overshoot voltages from occurring at the load. A voltage feedback circuit is coupled to the error amplification circuit to prevent false undervoltage conditions and possible overvoltage conditions where a particular power supply module is initialized while other modules are in operation. A warning circuit detects undervoltage and overvoltage conditions in the power supply. The system includes a circuit for overtemperature protection when the ORing element overheats.

Claims

1. A power supply system, comprising:

a load connected to a common bus; and

a plurality of power modules each having an output node, an ORing element operable to selectively couple and decouple said output node to the common bus, and a control circuit for controlling the operation of each ORing element, wherein said control circuit outputs a control signal in response to the occurrence of a predetermined condition, the control signal operating the ORing element to cause the selective coupling and decoupling of the output node from the common bus, and wherein said control circuit is adapted to prevent voltage spikes from occurring at the common bus during the selective coupling and decoupling.

2. The power supply system of claim 1, wherein said ORing element includes a control node and is operable to permit current flow between the common bus and the corresponding output node, wherein said control signal is applied to the control node.

3. The power supply system of claim 2, wherein said control circuit includes a detector for detecting when a rectified voltage falls lower than an undervoltage value, said detector being coupled to the control node and to a source of voltage pulses representing the rectified voltage.

4. The power supply system of claim 3, wherein said detector includes a comparator having a pair of inputs, wherein one of said inputs is connected to the source of voltage pulses and the other of said inputs is connected to a reference voltage representing the undervoltage value, said comparator further having an output connected to the control node for causing the selective coupling and decoupling when said inputs reach a voltage approximately equal to the undervoltage value.

5. The power supply system of claim 4, wherein said detector further includes

a resistor connected in series to a diode,

a pair of voltage dividers coupled respectively to the pair of inputs of said comparator, wherein one of said voltage dividers is arranged to provide the voltage pulses to one of said inputs and to establish a long discharge time constant for the detector, and the other of said voltage dividers is arranged to provide the reference voltage to the other of said inputs and to produce a time constant factor for the detector, wherein said resistor and said diode are disposed between one of said voltage dividers and the module, and

a capacitor arranged in parallel with one of said voltage dividers, said capacitor and said resistor being arranged to provide a fast initialization of the ORing element when the module is initialized with power.

6. The power supply system of claim 2, wherein said control circuit includes a detector for detecting when a short circuit is present in the corresponding module, said detector being coupled to at least the control node.

7. The power supply system of claim 6, in which a reverse current flows through the ORing element when said short circuit occurs, and said detector includes a comparator having a pair of inputs, wherein one of said inputs is coupled to receive the reverse current and the other of said inputs is coupled to receive a reference voltage, said reference voltage corresponding to a threshold current, said comparator further having an output connected to the control node for causing said selective decoupling during an undervoltage condition occurring when said reverse current is approximately equal to the threshold current.

8. The power supply system of claim 7, wherein said detector further includes

a pair of voltage dividers coupled respectively to the pair of inputs of said comparator, wherein one of said voltage dividers is arranged to provide the reference voltage at one of said inputs and the other of said voltage dividers is arranged to provide a voltage representative of the reverse current to the other of said inputs, and

a capacitor coupled to one of said voltage dividers to increase the sensitivity of the detector to instantaneous current flow.

9. The power supply system of claim 8, wherein said capacitor provides a time lag in voltage rise at one of said inputs when said module is initialized with power in a stand-alone mode.

10. The power supply system of claim 8, in which said common bus is connected to a DC bus having a predetermined operating voltage, and wherein one of the voltage dividers includes a resistor for increasing the threshold voltage so that said comparator changes state and turns on the ORing element when the voltage across the ORing element is approximately zero.

11. The power supply system of claim 10, further comprising a resistor connected across the load, wherein said control node is coupled to a voltage source, and said resistor isolates leakage voltage originating at the voltage source from passing to said control circuit when said selective decoupling occurs.

12. The power supply system of claim 6, wherein said detector includes a comparator having a pair of inputs and an output coupled to the control node, wherein one of said inputs is coupled to receive a converter voltage for causing the output of the comparator to change state when said converter voltage increases by approximately one volt and for causing said selective decoupling.

13. The power supply system of claim 2, wherein said common bus operates at a bus voltage, and said control circuit includes a detector for detecting when the bus voltage exceeds an overvoltage value.

14. The power supply system of claim 13, wherein said detector includes a comparator having a pair of inputs, wherein a first of said inputs is connected to receive the bus voltage and the other of said inputs is connected to receive a reference voltage, said reference voltage representing the overvoltage value, said comparator further having an output connected to the control node for causing said selective decoupling when said first of said inputs reaches a voltage approximately equal to said reference voltage.

15. The power supply system of claim 14, wherein said detector further includes a pair of voltage dividers coupled respectively to the pair of inputs of said comparator, wherein one of said voltage dividers is arranged to provide the bus voltage at said first of said inputs, and the other of said voltage dividers is arranged to provide the reference voltage to the other of said inputs.

16. The power supply system of claim 1, wherein said load is connected to a DC bus.

17. The power supply system of claim 1, wherein said common bus is connected to a circuit for sensing voltage at a remote load, said remote sensed voltage being used for eliminating the effects of a voltage drop appearing across the common bus and associated connections.

18. The power supply system of claim 17, wherein said circuit for sensing remote voltage comprises a single op-amp operating as a differential amplifier.

19. The power supply system of claim 17, wherein said control circuit includes a detector for detecting when the remote sensed voltage exceeds an overvoltage value, said detector being coupled to the control node.

20. The power supply system of claim 19, wherein said detector further includes

a comparator having a pair of inputs, and

a pair of voltage dividers coupled respectively to the pair of inputs of said comparator, wherein one of said voltage dividers is arranged to provide a reference voltage at one of said inputs, said reference voltage representing the overvoltage value, and the other of said voltage dividers is arranged to provide the remote sense voltage to the other of said inputs.

21. The power supply system of claim 20, wherein one of said inputs is connected to receive the remote sense voltage and the other of said inputs is connected to receive the reference voltage,

said comparator further having an output connected to the control node for causing the selective decoupling during an overvoltage condition occurring when said inputs reach a voltage approximately equal to the overvoltage value.

22. The power supply system of claim 19, wherein said comparator further includes an output connected to at least the control node for causing the selective decoupling when both inputs reach a voltage approximately equal to the overvoltage value.

23. The power supply system of claim 2, wherein said control circuit includes an error amplifier for preventing a false undervoltage condition arising when the ORing element is uninitialized and when an overvoltage condition occurs on the common bus.

24. The power supply system of claim 23, wherein said error amplifier is operable for preventing the overvoltage condition when the corresponding module is initialized with power while a remaining number of said modules are in operation.

25. The power supply system of claim 24, wherein said error amplifier includes

a comparator having a pair of inputs and an output,

a reference voltage coupled to one of said inputs for providing a slow rise voltage and for preventing a voltage overshoot,

at least two resistors connected in series and disposed between the other of said inputs and the common bus,

a first diode coupled between the resistors and the ORing element, and

a second diode connected both in parallel to and in reverse polarity with the first diode,

wherein one of said resistors and either of the first and second diodes are arranged to provide a voltage feedback loop across the ORing element, wherein the first diode operates to prevent the false undervoltage condition, and wherein the second diode operates to prevent the overvoltage condition.

26. The power supply system of claim 25, wherein the first diode is a Schottky diode.

27. The power supply system of claim 26, wherein the first diode and one of the resistors are connected in series to provide said feedback loop when the false undervoltage occurs, and the second diode is connected in series with one of the resistors to provide the feedback loop when a false overvoltage occurs.

28. The power supply system of claim 2, wherein said control circuit includes a voltage monitoring circuit for monitoring when said module supplies a voltage signal beyond a predetermined range to the common bus, said voltage monitoring circuit being coupled to the ORing element.

29. The power supply system of claim 28, wherein the voltage monitoring circuit includes a circuit for supplying auxiliary power, and a detector having a pair of inputs, one of said inputs being connected to receive the voltage signal and the other of said inputs being connected to said circuit for supplying auxiliary power.

30. The power supply system of claim 29, wherein said detector further includes an output signal for indicating that a predetermined voltage range has been exceeded, and said circuit for supplying auxiliary power includes,

a source for supplying auxiliary power,

a converter circuit coupled to said source,

a voltage divider coupled to the converter circuit for providing the auxiliary power to the other of said inputs, said voltage divider comprising a plurality of resistors, and

a capacitor connected to said voltage divider, wherein said capacitor and one of said resistors provide a time constant that causes said detector to generate the output signal.

31. The power supply system of claim 30, wherein said output signal changes between high and low voltage states, and the other of said resistors is arranged to cause the output signal to change to a low voltage state before the source loses regulation voltage, said low voltage state indicating a power supply failure state.

32. The power supply system of claim 1, wherein each power module further comprises a circuit for detecting if said power module'"'"'s temperature exceeds a predetermined value and for causing the power module to turn off in response thereto.

33. The power supply system of claim 1, wherein said control circuit comprises at least three comparators each having an output coupled to the ORing element, wherein said comparators are arranged so that when any of said outputs generates a control signal the control signal causes said selective coupling and decoupling, and wherein each of said comparators includes a pair of inputs coupled to a respective capacitor for preventing false tripping of any of the comparators due to noise.

34. The power supply system of claim 33, wherein said corresponding module includes

a source of AC power,

a rectifier, and

a converter circuit,

wherein said rectifier comprises a first diode and second diode connected in series across the source, and said converter circuit comprises an inductor and first capacitor connected in series across the second diode and a plurality of resistors connected in series and in parallel between the converter circuit and the ORing element, said common bus being connected to a DC bus, and said ORing element comprising a MOSFET device.

35. A control circuit for detecting a plurality of conditions indicating a failure of a power module in a redundant power supply system having a plurality of such modules, said control circuit being operable to control an ORing element that selectively couples and decouples said module from a power bus, comprising:

a first detector for detecting when a rectified voltage falls lower than an undervoltage value and for generating a first control signal in response thereto;

a second detector for detecting when a short circuit is present in the system and for generating a second control signal in response thereto;

a third detector for detecting one of said conditions occurring when a bus voltage exceeds an overvoltage value and for generating a third control signal in response thereto;

an error amplifier for preventing a false undervoltage or overvoltage condition when the power module initially turns on and for generating a fourth control signal in response thereto; and

a voltage monitoring circuit for detecting when said system supplies a voltage signal beyond a predetermined range and for generating a fifth control signal in response thereto,

wherein each said control signal is separately coupled to the ORing element for causing decoupling of said power module from said bus in response thereto.

36. A method for controlling an ORing element disposed between a power module and a common bus, comprising:

detecting a condition where said module fails to provide power to the common bus;

detecting a condition where a reverse current flows across the ORing element; and

detecting a condition occurring when voltage appearing at the common bus exceeds a predetermined range, causing said ORing element to decouple the power module from the common bus in response to the detection of any said condition.