Three-phase generator boost circuit

• US 6,020,695 A
• Filed: 07/23/1999
• Issued: 02/01/2000
• Est. Priority Date: 02/19/1999
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: VTC, Inc. (Synaptics Incorporated)
• Inventors: Kelly, David W., Brenden, Jason P., Peterson, Michael J.
• Primary Examiner(s): Masih, Karen
• Application Number:
  US09/360,360
• Time in Patent Office: 193 Days
• Field of Search: 318/254, 318/439, 318/138, 318/49, 318/798, 318/34
• US Class Current: 318/49
• CPC Class Codes: G11B 19/20 Driving; Starting; Stopping; Control thereof

Abstract

A three-phase generator boost circuit for augmenting the back electromotive force produced by a spindle motor of a disk drive is disclosed. First and second nodes provide normal connection to a source of DC voltage for the spindle motor and a second motor connected between the first and second nodes. A commutator is connected to a sequencer to operate the spindle motor. In the event of catastrophic shutdown, two of the lower commutator switches are operated to short circuit the two stator coils having the highest and lowest voltages to store energy in the coils. The commutator switches are then operated to discharge current through the nodes to a storage capacitor for the second motor.

Claims

1. In a circuit for operating a first motor having at least three stator coils connected to a center tap, the circuit including

first and second nodes for connection to a source of DC voltage;

a second motor connected between the first and second nodes and operable by the source of DC voltage;

a commutator comprising;

at least three pairs of switches, each pair comprising an upper switch and a lower switch, each switch including a control element and first and second controlled elements, the first controlled elements of the switches of each pair being connected together and to a respective one of the stator coils, the second controlled element of the switches of each pair being connected a respective one of the first and second nodes; and

a sequencer connected to the control elements of all of the switches, the sequencer being operable in a first mode to selectively operate the switches to provide power from the source of DC voltage to the three stator coils to operate the first motor to rotate a rotor thereof;

a method of operating the sequencer in a second mode to supply power to the second motor from the rotating first motor during an absence of the source of DC voltage at the nodes comprising;

sensing an absence of the source of DC voltage; and

operating the sequencer in response to the absence of the source of DC voltage to selectively operate the switches of the pairs to selectively serially short-circuit two of the stator coils so that back emf from the stator coils while the rotor is rotating is provided to the first and second nodes to supply power to the second motor.

2. The invention of claim 1, including operating the sequencer so that the switches provide power from the source of DC voltage by operating the respective upper switches in sequence so that each upper switch connects the respective stator coil to the first node during an exclusive 120°

rotation of the rotor, and by operating the respective lower switches in sequence so that each lower switch connects the respective stator coil to the second node during an exclusive 120°

rotation of the rotor, the sequence of operation of the lower switches being offset from the sequence of operation of the upper switches by 60°

.

3. The invention of claim 1, wherein the circuit includes a phase detector for detecting a rotational phase of the rotor, and including operating the sequencer in response to absence of the source of DC voltage at the nodes to operate the lower switches so that the two lower switches associated with the stator coils having the highest and lowest voltages connect their respective stator coils to the second node during a first portion of the respective 60°

rotational phase of the rotor, whereby the two stator coils having the highest and lowest voltages are serially short-circuited to the second node during the 60°

rotational phase.

4. The invention of claim 3, wherein the circuit includes a storage device connected between the first and second nodes for storing a charge to operate the second motor, and including operating the sequencer so that none of the switches connect their respective stator coils to either the first or second node during a second portion of the respective 60°

rotational phase, whereby the storage device is charged through inherent diodes of two commutator switches during the second portion of the 60°

rotational phase.

5. The invention of claim 4, including charging the storage device through the inherent diode of the upper switch associated with the coil having the highest voltage and the inherent diode of the lower switch associated with the coil having the lowest voltage.

6. The invention of claim 3, wherein the circuit includes a storage device connected between the first and second nodes for storing a charge to operate the second motor, including operating the sequencer so that the upper switch associated with the stator coil having the highest voltage connects the associated stator coil to the first node and the lower switch associated with the stator coil having the lowest voltage connects the associated stator coil to the second node during a second portion of the respective 60°

rotational phase, whereby the storage device is charged through the connecting upper and lower switches during the second portion of the 60°

rotational phase.

7. The invention of claim 1, wherein the circuit includes a phase detector for detecting a rotational phase of the rotor and a storage device connected between the first and second nodes for storing a charge to operate the second motor,

including operating the sequencer in response to absence of the source of DC voltage at the nodes so that

the lower switch associated with the stator coil having the lowest voltage is operated for an exclusive 120°

rotational period of the rotor that the associated stator coil has the lowest voltage to connect the stator coil having the lowest voltage to the second node for the 120°

period, and

the other lower switches are operated during a first portion of mutually exclusive 60°

rotational phases of the rotor during the 120°

period that the associated coil has the highest voltage to connect the associated stator coil to the second node for the first portion of the respective 60°

phase,

whereby the two stator coils having the highest and lowest voltages are serially short-circuited to the second node during each 60°

rotational phase, and

operating the sequencer so that the upper switch associated with the stator coil having the highest voltage connects the associated stator coil to the first node and the lower switch associated with the stator coil having the lowest voltage connects the associated stator coil to the second node during a second portion of each respective 60°

rotational phase, whereby the storage device is charged through the connecting upper and lower switches during the second portion of each 60°

rotational phase.

8. The invention of claim 1, including operating the sequencer in response to absence of the source of DC voltage at the nodes to operate the lower switches in sequence whereby

a. during a first 60°

rotation of the rotor, the lower switches of the first and second pairs are operated;

b. during a second 60°

rotation of the rotor, the lower switches of the first and third pairs are operated;

c. during a third 60°

rotation of the rotor, the lower switches of the second and third pairs are operated;

d. during a fourth 60°

rotation of the rotor, the lower switches of the first and second pairs are operated;

e. during a fifth 60°

rotation of the rotor, the lower switches of the first and third pairs are operated; and

f. during a sixth 60°

rotation of the rotor, the lower switches of the second and third pairs are operated.

9. A system for supplying power to first and second motors, the first motor having at least three stator coils connected to a center tap, the system comprising:

first and second nodes for connection to a source of DC voltage, the second motor connected between the first and second nodes and operable by the source of DC voltage;

a commutator circuit for operating the first motor, the commutator comprising;

at least three pairs of switches, each switch including a control element and first and second controlled elements, the first controlled elements of the switches of each pair being connected together and to a respective one of the stator coils, the second controlled element of an upper switch of each pair of switches being connected to the first node, and the second controlled element of a lower switch of each pair of switches being connected to the second node; and

a sequencer connected to the control elements of all of the switches,

the sequencer being responsive to the presence of the source of DC voltage at the first and second node to selectively operate the switches to provide power from the source of DC voltage to the three stator coils to operate the first motor to rotate a rotor thereof,

the sequencer being responsive to absence of the source of DC voltage at the nodes to selectively operate the switches of the pairs of switches to selectively short-circuit two of the stator coils so that back emf from the stator coils while the rotor is rotating is provided to the first and second nodes to supply power to the second motor.

10. The system of claim 9, including

a storage capacitor coupled between the first and second nodes for storing voltage to operate the second motor, and

a charge circuit connected to the sequencer to operate the sequencer in a first mode to short circuit two of the stator coils having highest and lowest voltages during a first portion of a 60°

phase of the first motor, and the charge circuit operates the sequencer to a second mode during a second portion of the 60°

phase to charge the capacitor from energy stored in the stator coils that were short circuited in the first mode.

11. The system of claim 10, including a current sensor connected between the storage capacitor and one of the first and second nodes, the charge circuit being responsive to the sensor sensing current below a predetermined threshold when the sequencer is in its second mode to operate the sequencer to its first mode.

12. The system of claim 10, wherein each switch of the commutator has a diode function, the sequencer is operated in its second mode to operate all of the switches so that current from the stator coil having the highest voltage flows through the diode of its associated upper switch to the first node and current flows from the second node to the stator coil having the lowest voltage through the diode of its associated lower switch.

13. The system of claim 12, including a current sensor connected between the storage capacitor and one of the first and second nodes to sense current flowing between the first and second nodes, the charge circuit being responsive to the sensor sensing current below a predetermined threshold when the sequencer is in its second mode to operate the sequencer to its first mode.

14. The system of claim 10, wherein the sequencer is operated in its second mode to operate the switches so that current from the stator coil having the highest voltage flows through the associated upper switch to the first node and current flows from the second node to the stator coil having the lowest voltage through the associated lower switch.

15. A three-phase generator boost circuit for supplying power to a second motor upon catastrophic loss of power to a three phase motor, comprising:

first and second nodes for connection to a DC source, the second motor being connected to the nodes for receiving power from the nodes;

a storage capacitor coupled between the first and second nodes for storing energy for the second motor;

a commutator connected to the nodes for supplying power from a source to stator coils of the three-phase motor, the commutator being operable to supply power from the motor to the nodes during an absence of the DC source and while the motor is rotating, the commutator consisting essentially of;

at least three pairs of semiconductor switches, each switch including a control element and first and second controlled elements, the first controlled elements of the switches of each pair being connected together and to a respective one of the stator coils, the second controlled element of an upper switch of each pair of switches being connected to the first node, and the second controlled element of a lower switch of each pair of switches being connected to the second node; and

a sequencer connected to the control elements of all of the switches, the sequencer being operable to selectively operate the switches to provide power from the source of DC voltage to the three stator coils to operate the first motor to rotate a rotor thereof, and being operable to selectively operate the switches to selectively serially short-circuit two of the stator coils so that back emf from the stator coils while the rotor is rotating is provided to the first and second nodes to supply power to the second motor.

16. The circuit of claim 15, wherein the sequencer is operable to selectively operate a switch of each of two pairs of switches in sequence to provide power from the source of DC voltage to the three stator coils to operate the first motor to rotate its rotor, and being operable to operate the lower switches to selective serially short-circuit two of the stator coils so that back emf from the stator coils while the rotor is rotating is provided to the first and second nodes to supply power to the second motor.

17. The circuit of claim 16, wherein the sequencer is operable to selectively operate the upper switches in sequence to provide power from the source of DC voltage to the three stator coils to operate the first motor to rotate its rotor.

18. The circuit of claim 16, wherein the sequencer operates the switches during successive 60°

phases of the first motor to serially short circuit two of the stator coils through two lower switches during a first mode of each phase and to discharge energy stored in the stator coils to the capacitor during a second mode of the phase.

19. The circuit of claim 18, including

a current sensor coupled between the first and second nodes and responsive to current flowing between the nodes, and

a charge circuit responsive to the sensor sensing current below a predetermined threshold when the sequencer is in its second mode to operate the sequencer to the first mode.

20. For a sequencer that operates a commutator of a three-phase motor in a first mode to provide power from a DC supply connected to a pair of nodes to successive stator coils of the motor to rotate a rotor of the motor, a method of operating the sequencer in a second mode so that back emf from the motor provides power to the pair of nodes, the method comprising:

detecting an absence of DC supply voltage to the nodes; and

operating the commutator in a first manner to selectively serially short-circuit two stator coils during a first portion of successive 60°

phases of the motor while the rotor is rotating; and

operating the commutator in a second manner during the respective 60°

phase so that back emf from the stator coils is provided to the nodes.

21. The method of claim 20, wherein the commutator has at least three pairs of switches, each pair comprising an upper switch and a lower switch, each switch including a control element coupled to the sequencer and first and second controlled elements, the first controlled elements of the switches of each pair being connected together and to a respective one of the stator coils, the second controlled element of the switches of each pair being connected a respective one of the pair of nodes, the step of operating the sequencer in the first manner comprises operating a lower switch of the two pairs associated with the stator coils having the highest and lowest voltages to serially short-circuit the stator coils through one of the nodes.

22. The method of claim 21, wherein each of the switches has an inherent diode function, the step of operating the sequencer in the second manner comprises rendering all of the switches non-conductive and discharging back emf as a current from one of the stator coils that was short-circuited when the sequencer was operated in the first manner through the inherent diode of the respective upper switch to one of the nodes and from the other of the nodes through the inherent diode of the lower switch associated with the other of the stator coils that was short-circuit when the sequencer was operated in the first manner, to thereby charge a storage device connected between the nodes.

23. The method of claim 22, including sensing the current between the nodes during operation of the sequencer in the second manner and operating the sequencer to the first manner if the sensed current is below a threshold.

24. The method of claim 21, wherein the step of operating the sequencer in the second manner comprises operating the upper switch associated with the stator coil having the highest voltage and the lower switch associated with the stator coil having the lowest voltage to discharge back emf as a current from the stator coil having the highest voltage through the respective upper switch to one of the nodes and from the other of the nodes through the lower switch associated with the stator coil having the lowest voltage, to thereby charge a storage device connected between the nodes.

25. The method of claim 24, including sensing the current between the nodes during operation of the sequencer in the second manner and operating the sequencer to the first manner if the sensed current is below a threshold.