Brushless pulsed D.C. motor

• US 5,068,582 A
• Filed: 05/29/1990
• Issued: 11/26/1991
• Est. Priority Date: 05/29/1990
• Status: Expired due to Term

• Current Assignee: A. O. Smith Corporation
• Original Assignee: A. O. Smith Corporation
• Inventors: Scott, Kenneth C.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/529,920
• Time in Patent Office: 546 Days
• Field of Search: 318/138, 318/254, 318/439
• US Class Current: 318/400.35
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 6/21 Open loop start

Abstract

A commutated brushless dc motor includes a detector which senses the zero crossings of the unenergized winding. A timing system includes a reference capacitor coupled to the detection unit and charged to a voltage proportional to zero crossing time. The voltage is compared to a capacitor charged from a constant current source. At a percentage level of the reference capacitor, a commutating pulse is applied to a winding commutating circuit. The incoming pulses drive a counter and actuates a programmed decoder which generates output signals for commutation of the windings and selection of the next unenergized winding. The detector is selectively connected to sense the induced voltage in the unenergized winding. To start the motor, a separate charging circuit creates initial pulses to energize the windings and accelerate the motor. At a given speed, the zero crossing circuit is enabled. An integrated circuit system has the zero crossing signals applied to a resettable counter which counts at a fixed rate between zero crossings. The count is latched and is proportional to the time between zero crossings. The counter signal and the latched signal are compared to generate the commutating pulse.

Claims

1. A commutated brushless dc motor comprising a stator with a plurality of circumferentially spaced stator windings, a rotor coupled to said stator and rotatably mounted to rotate relative to said stator winding as the result of energization of said windings, a dc power supply to establish pulsed energization of said windings in sequence with at least one winding de-energized, an alternating current induced signal being induced in said de-energized winding and having periodic zero crossings, a timing device coupled to the stator to monitor the time between the zero crossings of said induced signal and generating an electrical zero crossing signal proportional to such time, a signal latch unit coupled to said timing device and storing the zero crossing signal as a latched signal, a reset unit connected to said timing device to initiate a new timing cycle to generate a next zero crossing signal, and a comparator connected to said timing device and said latch unit and responsive to a proportion of the latched signal to generate said pulsed energization of said windings in a continuous repetitive sequence.

2. In the brushless motor of claim 1 wherein said induced signal has an alternating period of 360°

and said stator includes three windings, each winding being commutated "on " to initiate pulsed energization at 30°

in the induced signal and the respective related rotor rotation and commuted "off" at 150°

to terminate said pulsed energization such that the three windings are sequentially pulsed energized for successive periods of 120°

in each 360°

rotation of said rotor.

3. In the motor of claim 1 wherein said timing device is a timing capacitor and a constant current charging circuit actuated by successive zero crossing signals and thereby establishing a timing capacitor charge equal to the period between zero crossings.

4. The motor of claim 3 wherein said timing device includes a reference capacitor coupled to said timing capacitor and set to a reference voltage equal to the voltage of the timing capacitor at each zero crossing, said comparator being connected to said timing capacitor and to said reference capacitor and creating a switching signal in response to a charge in said timing capacitor equal to a percentage level of the reference voltage on the reference capacitor.

5. The motor of claim 4 including a zero crossing detector having detection switch means to sequentially monitor the zero crossing of the stator windings, power switch means connected to sequentially connect said stator windings to power, a programmed decoder connected to said comparator and decoding the switching signals and generating power output signals to said power switch means for commutation of the stator windings and control signals to said detection switch means of the zero crossing detector to select the unenergized winding for monitoring the next zero crossing.

6. The motor of claim 5 wherein said comparator includes a first input connected to said timing capacitor and a second input, a voltage dividing network connected to said reference capacitor and having a reference output line connected to said second input, said comparator responding to a voltage on the timing capacitor equal to the reference voltage on said reference output line to generate said switching signal, a monostable circuit connected to said comparator to generate a sharp pulse signal.

7. A brushless dc motor having a rotor and a stator with at least three equicircumferentially spaced windings connected in a wye configuration in with a common center line and connected to a switched dc power supply and having separate switch units for selectively energizing said windings and thereby causing rotation of said rotor, said rotation of said rotor inducing an induced electrical signal in said windings, comprising a sensor coupled to said windings and responsive to a zero crossing of the induced electrical signal in said windings, a signal generator creating a control signal having a characteristic varying from a reference level proportionately with time, said signal generator including a reset unit for resetting said generator to said reference level, a control reference unit connected to said signal generator and set to correspond to said control signal and having an output corresponding to a selected percentage of the control signal, a trigger signal source connected to the output of said control reference unit and to said signal generator operable to establish a switching signals with said signal generator at a signal output equal to said selected percentage of said control signal, and said sensor being connected to said signal generator and operable to reset said signal generator at each of said zero crossings and thereby repetitively establish said control signal proportional to the period between successive zero crossing, and a circuit for connecting of said trigger signal source to said separate switch units and thereby establish sequential actuation of said separate switch units and pulsed energization of said windings.

8. The motor of claim 7 wherein said signal generator includes a power supply, a timing capacitor connected to said power supply and charged at a constant rate with time to establish said control signal, said sensor includes a zero crossing detector connected to said windings for generating a zero crossing signal at each zero crossing of said windings, said reset unit including a reset switch connecting said timing capacitor to said reference level at each zero crossing, a reference capacitor, a switch connecting said reference capacitor to said timing capacitor and setting said reference capacitor to a reference voltage, a proportional signal decoder coupled to said reference capacitor and establishing a control reference signal proportional to a fixed percentage of said reference voltage, said trigger signal source coupled to said proportional signal decoder and to said timing capacitor and generating a switching signal when said control signal of said timing capacitor corresponds to said reference signal.

9. The motor of claim 8 including a sequence controller for establishing sequential and cyclical energizing of said windings and for sequential and cyclical sensing the induced signal in said windings.

10. The motor of claim 7 including a counter having a reset element for setting the counter to a reference count and counting at a fixed rate from said reference count, said sensor connected to said windings and establishing a reset signal at each zero crossing of said induced signals in said windings, said sensor being connected to said reset element to reset said counter to the reference count at each zero crossing, a latch count unit connected to said counter and set to one half the count in the counter at each reset of the counter, a comparator to compare the count in said counter and in said latch count unit and operable to generate a trigger signal when the count in said counter equals the count in said latch count unit whereby said windings are sequentially energized for fixed periods related to the periods between said zero crossings and establishing a smooth continuous rotation of said rotor.

11. A controlled power supply for energizing a brushless dc motor having a rotor with circumferentially spaced magnetic poles and a stator with circumferentially spaced windings, comprising a switching device connected to said windings and having a plurality of input controls for sequentially energizing said windings and establishing an interacting magnetic field sequentially stepped about said rotor and thereby establishing rotation of said rotor, at least one of said windings being de-energized and having an induced signal induced therein as a result of the rotation of said rotor, said induced signal varying in a periodic manner with spaced zero crossings in accordance with the rotation of said rotor, a detector coupled to said windings and sequentially operably coupled to the de-energized windings to sense the induced signal in successive windings and thereby the position of the rotor relative to the stator, a timing device connected to said detector and generating a control signal directly proportionally to the period between said zero crossings, a signal dividing unit connected to said timing device and generating a fixed percentage signal for each successive control signal, a comparator connected to the signal dividing unit and to the timing device and generating a trigger signal with said control signal being equal to said fixed percentage signal, and a controller connecting said comparator to said input controls to actuate the switching device to sequentially energize the windings in response to the sequence of said trigger signals.

12. A brushless dc motor having a permanent magnet rotor and a stator with a plurality of equicircumferentially spaced windings having one inner end of the windings connected to a common line and each of the outer ends of the winding connected to a dc power supply, said windings being sequentially energized with dc power positively supplied to one of said windings and returned to said supply through a second of said windings, and said positive power being sequentially applied to said windings in one direction for forward rotation of said motor and in a reverse direction for reverse rotation of said motor, said rotor inducing an alternating sinusoidal induced voltage in the unenergized winding to be next energized, said induced voltage having two zero crossings in each voltage cycle, the improvement in a control for switching of said power supply to said windings, comprising a zero crossing detecting network connected to said windings for detecting the zero crossing of each induced voltage in said unenergized winding, a voltage reference line, said detecting network including a resistive coupling network including a separate first voltage resistor dividing branch connected to the end of each winding and to said voltage reference line and including a second voltage resistor dividing branch connected to said common line connection and said voltage reference line, a gate unit connected to each of said resistor dividing branches, said gate unit having a common output line, a first comparator amplifier having first input connected to said common output line and having a second input connected via the second voltage resistor dividing branch to said common line connection, an inverted amplifier to invert the output signal of said first comparator amplifier, a second comparator amplifier having a first input connected to said voltage reference line and having a second input, first and second transfer switches connecting said first comparator amplifier and said inverter amplifier to said second input of said second comparator amplifier, three detection switches connected one each to each of the first voltage resistor dividing branches, first and second transfer switches, a programmer coupled to sequentially actuate said three detection switches in sequence to sequentially couple the output of the windings to said first comparator amplifier and to alternately actuate said first and second transfer switches for alternately actuating such first and second transfer switches to establish a positive input signal to said second comparator amplifier and thereby generate a pulse output signal at each zero crossing of the unenergized winding and establishing a series of pulse signals precisely identifying the zero crossing points in the sinusoidal induced voltage in the unenergized winding and thereby the position of said rotor relative to said stator windings, a measurement and timing circuit including a timing device to create a time signal proportional to the period between successive zero crossing in said unenergized windings, a storage device to store the time signal and including a proportional output element to establish a reference signal equal to a percentage of said time signal which equals to the period between the last zero crossing and the next winding energization, a trigger comparator connected to said timing device and to said storage device and establishing a switching signal to said programmer in response to the input of said time signal and said reference signal.

13. The motor of claim 12 wherein said measurement and timing circuit includes a reference capacitor and a timing capacitor, a constant current source, said timing capacitor being connected to said constant current source for charging said timing capacitor at a preselected constant rate, a first gated switch connected to said timing capacitor to discharge said timing capacitor, a second gated switch connected to said reference capacitor and to said timing capacitor to set said reference capacitor at the charge level of said timing capacitor, said first and second gated switches having inputs connected to the output of said zero crossing detecting network and having said second gate switch actuated for a momentary period prior to actuation of the first gated switch to thereby set the reference capacitor to the charge set on the timing capacitor and to immediately thereafter discharge the timing capacitor, a reference voltage dividing network coupled to said reference capacitor and establishing a proportional reference voltage signal equal to the voltage created in said timing capacitor in a selected rotation of said rotor, said trigger comparator having a first input connected to said reference voltage dividing network and a second input connected to said timing capacitor, said trigger comparator establishing an output when the output of said timing capacitor equals the proportional signal from said reference voltage dividing network.

14. The motor of claim 13 wherein said measurement and timing circuit includes a starting circuit for generating a fixed series of pulses independent of said pulse output signal at each zero crossing to initiate operation of said motor to establish operative zero crossing signal pulses, comprising a start voltage dividing network connected to said power supply, a start comparator having a first input connected to said start voltage dividing network and to said timing capacitor, the output of the start comparator developing a train of pulses for controlling the starting of said motor, an OR gate connected to said start comparator and to said trigger comparator and thereby establishing a train of pulses when generated from either of said start comparator or said trigger comparator, said starting circuit being established whereby said timing capacitor is reset by said zero crossing signal pulse prior to the level on said timing capacitor rising to the level for actuating said start comparator.

15. The motor of claim 13 wherein said programmer includes a recycling counter to establish a series of pulse signals with one pulse for each zero crossing of said induced voltage during each revolution of said motor and to repetitively count said pulses in sequential count cycles, said programmer including a decoder to decode the pulse position in each said count cycle and establish sequential actuation of the switches of said zero crossing detecting network to sequentially activate the unenergized winding, said decoder including switch output lines coupled to actuate said detection switches and said first and second transfer switches to selectively supply the power to said windings in sequence.

16. The motor of claim 15 wherein said power supply includes positive power switches, one for each of said windings and connected between said power source and the end of said corresponding winding, return switches connected between said positive power switches and said power supply to form a return path for the power through one and a second winding, said decoder actuating one of said positive power switches and one of said return switches to establish the flow through said windings.