Method and apparatus for starting a sensorless polyphase DC motor in dual-coil mode and switching to single coil mode at speed

• US 5,455,885 A
• Filed: 02/13/1995
• Issued: 10/03/1995
• Est. Priority Date: 06/30/1993
• Status: Expired due to Term

• Current Assignee: SGS-Thomson Microelectronics (STMicroelectronics NV)
• Original Assignee: SGS-Thomson Microelectronics (STMicroelectronics NV)
• Inventors: Cameron, Scott W.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Masih, Karen
• Application Number:
  US08/387,386
• Time in Patent Office: 232 Days
• Field of Search: 318/771, 318/778, 318/779, 318/780, 388/834, 388/808
• US Class Current: 388/834
• CPC Class Codes: H02P 6/085 in a bridge configuration
• CPC Class Codes: H02P 6/21 Open loop start

Abstract

A method and apparatus for operating a polyphase dc motor selectively in dual-coil or uni-coil commutation modes. The motor has a plurality of "Y" connected driving coils connected together at a center tap. Each driving coil has an input node at an end opposite the center tap, and is driven by a switch pair. Each switch pair is arranged for connection in series across a power supply voltage, and has a node between each switch connected to a respective one of the coil input nodes. An additional pair of switches are provided for connection in series across the power supply with a connection node between each switch connected to the center tap. A circuit is provided to operate the switches to cause a driving current to be passed between sequentially selected pairs of the driving coils for an initial start-up time. Also, a circuit to operate the switches after the initial start-up time is provided to cause a driving current to be passed between sequentially selected only single ones of the driving coils and the center tap current input node. The apparatus also has a circuit for detecting a zero crossing of a bemf signal of a floating one of the driving coils and a delay circuit for establishing a delay between a zero crossing and a commutation of driving signals to the coils. A circuit operates the delay circuit to provide a first predetermined delay in dual-coil mode and a second predetermined delay in uni-coil mode.

Claims

1. A method for operating a polyphase dc motor of the type having a plurality of driving coils connected together at a center tap current input node, having a pair of switches arranged for connection in series across the power supply voltage and having a connection node between each switch connected to the center tap, each driving coil having a coil current input node at an end opposite said center tap connection, and a plurality of pairs of switches for connection, each pair being arranged for connection in series across a power supply voltage, each pair having a connection node between each switch of each pair, connected to a respective one of said coil current input nodes comprising;

commutating said plurality of pairs of switches to operate in a dual coil mode during a start-up time; and

after the start-up time, selectively commutating said plurality of pairs of switches to operate in a uni-coil mode.

2. The method of claim 1 wherein each of said switches is a MOSFET.

3. The method of claim 1 wherein said polyphase dc motor is a three-phase dc motor.

4. The method of claim 1 wherein said plurality of driving coils comprise a wye connected set of driving coils.

5. The method of claim 1 wherein said motor has a two pole rotor.

6. A method for operating a polyphase dc motor of the type having a plurality of driving coils connected together at a center tap current input node, having a pair of switches arranged for connection in series across the power supply voltage and having a connection node between each switch connected to the center tap, each driving coil having a coil current input node at an end opposite said center tap connection, and a plurality of pairs of switches for connection, each pair being arranged for connection in series across a power supply voltage, each pair having a connection node between each switch of each pair, connected to a respective one of said coil current input nodes comprising;

operating said switches during an initial start-up time to cause a driving current to be passed between sequentially selected pairs of said driving coils in accordance with the following table;

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA 1A uB 1B uC 1C uC.sub.tap 1C.sub.tap __________________________________________________________________________Phase A-B C ON OFF OFF ON OFF OFF OFF OFF Phase A-C B ON OFF OFF OFF OFF ON OFF OFF 2 Phase B-C A OFF OFF ON OFF OFF ON OFF OFF 3 Phase B-A C OFF ON ON OFF OFF OFF OFF OFF 4 Phase C-A B OFF ON OFF OFF ON OFF OFF OFF 5 Phase C-B A OFF OFF OFF ON ON OFF OFF OFF 6 __________________________________________________________________________

and after start-up, between only single ones of said driving coils and the center tap according to the following table;

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA 1A uB 1B uC 1C uC.sub.tap 1C.sub.tap __________________________________________________________________________Phase A-C.sub.tap B&

C ON OFF OFF OFF OFF OFF OFF ON A+ Phase C.sub.tap -C A&

B OFF OFF OFF OFF OFF ON ON OFF C- Phase B-C.sub.tap A&

C OFF OFF ON OFF OFF OFF OFF ON B+ Phase C.sub.tap -A B&

C OFF ON OFF OFF OFF OFF ON OFF A- Phase C-C.sub.tap A&

B OFF OFF OFF OFF ON OFF OFF ON C+ Phase C.sub.tap -B A&

C OFF OFF OFF ON OFF OFF ON OFF B- __________________________________________________________________________

in which;

the center tap is denoted C_tap ;

each coil is denoted respectively A, B, and C;

each high side switch is denoted respectively uA, uB, uC, uC_tap ;

each low side switch is denoted respectively 1A, 1B, 1C, 1C_tap ;

each phase is denoted (+) if current flows into the designated coil to the center tap and (-) if current flows out of the designated coil from the center tap;

and an open switch is denoted OFF, and a closed switch is denoted "ON".

7. A method for operating a polyphase dc motor of the type having a plurality of driving coils connected together at a center tap current input node, each driving coil having a coil current input node at an end opposite said center tap connection, and a plurality of pairs of switches for connection, each pair being arranged for connection in series across a power supply voltage, each pair having a connection node between each switch of each pair, connected to a respective one of said coil current input nodes comprising;

providing an additional pair of switches arranged for connection in series across the power supply voltage and having a connection node between each switch connected to the center tap;

operating said switches to cause a driving current to be passed between sequentially selected pairs of said driving coils for an initial start-up time;

after the initial start-up time, operating said switches to cause a driving current to be passed between sequentially selected only single ones of said driving coils and said center tap current input node; and

establishing a predetermined first delay between a zero crossing of a bemf signal of a floating coil and a commutation of driving signals to said coils on the dual-coil mode and establishing a second predetermined delay in uni-coil mode.

8. The apparatus of claim 7 wherein said second predetermined delay is essentially zero.

9. Apparatus for operating a polyphase dc motor of the type having a plurality of driving coils connected together at a center tap, each driving coil having a coil current input node at an end opposite said center tap, and a plurality of switch pairs, each switch pair arranged for connection in series across a power supply voltage, each switch pair having a node between each switch connected to a respective one of said coil current input nodes comprising:

an additional pair of switches arranged for connection in series across the power supply voltage and having a connection node between each switch connected to the center tap;

a sequencing circuit for individually operating said switches during said start-up to cause a driving current to be passed between sequentially selected pairs of said driving coils in accordance with the following table;

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA 1A uB 1B uC 1C uC.sub.tap 1C.sub.tap __________________________________________________________________________Phase A-B C ON OFF OFF ON OFF OFF OFF OFF Phase A-C B ON OFF OFF OFF OFF ON OFF OFF 2 Phase B-C A OFF OFF ON OFF OFF ON OFF OFF 3 Phase B-A C OFF ON ON OFF OFF OFF OFF OFF 4 Phase C-A B OFF ON OFF OFF ON OFF OFF OFF 5 Phase C-B A OFF OFF OFF ON ON OFF OFF OFF 6 __________________________________________________________________________

and after start-up, between only single ones of said driving coils and the center tap according to the following table;

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA 1A uB 1B uC 1C uC.sub.tap 1C.sub.tap __________________________________________________________________________Phase A-C.sub.tap B&

C ON OFF OFF OFF OFF OFF OFF ON A+ Phase C.sub.tap -C A&

B OFF OFF OFF OFF OFF ON ON OFF C- Phase B-C.sub.tap A&

C OFF OFF ON OFF OFF OFF OFF ON B+ Phase C.sub.tap -A B&

C OFF ON OFF OFF OFF OFF ON OFF A- Phase C-C.sub.tap A&

B OFF OFF OFF OFF ON OFF OFF ON C+ Phase C.sub.tap -B A&

C OFF OFF OFF ON OFF OFF ON OFF B- __________________________________________________________________________

in which;

the center tap is denoted C_tap ;

each coil is denoted respectively A, B, and C;

each high side switch is denoted respectively uA, uB, uC, uC_tap ;

each low side switch is denoted respectively 1A, 1B, 1C, 1C_tap ;

each phase is denoted (+) if current flows into the designated coil to the center tap and (-) if current flows out of the designated coil from the center tap;

and an open switch is denoted OFF, and a closed switch is denoted "ON".

10. Apparatus for operating a three-phase polyphase dc motor of the type having a plurality of wye connected driving coils connected together at a center tap, each driving coil having a coil current input node at an end opposite said center tap, and a four pairs of transistor switches for connection in series across a power supply voltage, each pair of transistor switches having a node respectively connected to a respective one of said coil current input nodes and said center tap, comprising:

a switch commutating circuit to operate said switches in a dual-coil mode;

a switch commutating to operate said switches in a uni-coil mode; and

.

a circuit to selectively connect one of said switch operating circuits to change between dual-coil mode and uni-coil mode.

11. The apparatus of claim 10 wherein each of said transistors switches is a MOSFET.

12. The apparatus of claim 10 wherein said motor is a sensorless three-phase dc motor.

13. The apparatus of claim 10 wherein said motor has a two pole rotor.

14. The apparatus of claim 10 further comprising a sequencing circuit for individually operating said switches during said start-up to cause a driving current to be passed between sequentially selected pairs of said driving coils and said center tap current input node in accordance with the following table:

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA lA uB lB uC lC uC.sub.tap lC.sub.tap __________________________________________________________________________Phase A-B C ON OFF OFF ON OFF OFF OFF OFF Phase A-C B ON OFF OFF OFF OFF ON OFF OFF 2 Phase B-C A OFF OFF ON OFF OFF ON OFF OFF 3 Phase B-A C OFF ON ON OFF OFF OFF OFF OFF 4 Phase C-A B OFF ON OFF OFF ON OFF OFF OFF 5 Phase C-B A OFF OFF OFF ON ON OFF OFF OFF 6 __________________________________________________________________________

and after startup, between only single ones of said driving coils and the center tap according to the following table;

space="preserve" listing-type="tabular">__________________________________________________________________________Current flows Floating from-to Coils uA lA uB lB uC lC uC.sub.tap lC.sub.tap __________________________________________________________________________Phase A-C.sub.tap B&

C ON OFF OFF OFF OFF OFF OFF ON A+ Phase C.sub.tap -C A&

B OFF OFF OFF OFF OFF ON ON OFF C- Phase B-C.sub.tap A&

C OFF OFF ON OFF OFF OFF OFF ON B+ Phase C.sub.tap -A B&

C OFF ON OFF OFF OFF OFF ON OFF A- Phase C-C.sub.tap A&

B OFF OFF OFF OFF ON OFF OFF ON C+ Phase C.sub.tap -B A&

C OFF OFF OFF ON OFF OFF ON OFF B- __________________________________________________________________________

in which;

the center tap is denoted C_tap ;

each coil is denoted respectively A, B, and C;

each high side switch is denoted respectively uA, uB, uC, UC_tap ;

each low side switch is denoted respectively 1A, 1B, 1C, 1C_tap ;

each phase is denoted (+) if current flows into the designated coil to the center tap and (-) if current flows out of the designated coil from the center tap;

and an open switch is denoted OFF, and a closed switch is denoted "ON".

15. The apparatus of claim 10 further comprising a circuit to select said circuit to operate said switches in a dual-coil mode for an initial start-up time and to select said a circuit to operate said switches after the initial start-up time in a uni-coil mode.

16. The apparatus of claim 10 further comprising a circuit for detecting a zero crossing of a bemf signal of a floating one of the driving coils;

a delay circuit for establishing a delay between a zero crossing and a commutation of driving signals to said coils;

and a circuit for operating said delay circuit to provide a first predetermined delay in dual-coil mode and a second predetermined delay in uni-coil mode.

17. The apparatus of claim 16 wherein said second predetermined delay is essentially zero.