Current decay control in switched reluctance motor

• US RE36,568 E
• Filed: 08/26/1997
• Issued: 02/15/2000
• Est. Priority Date: 12/29/1993
• Status: Expired due to Term

• Current Assignee: Nidec Motor Corporation (Nidec Corporation)
• Original Assignee: Emerson Electric Company
• Inventors: Horst, Gary E.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/920,112
• Time in Patent Office: 903 Days
• Field of Search: 318/254, 318/696, 318/701, 318/702, 318/724, 318/685, 318/138, 318/439
• US Class Current: 318/701
• CPC Class Codes: H02P 25/0925 wherein the converter comprises only one switch per phase

Abstract

A control circuit (10) for controlling the residual or tail current decay in a single phase or polyphase SRM winding when a phase is switched from active to inactive. A Hall-effect type sensor (30) senses rotor position of the SRM. Current flows through a winding (W) of the motor when the motor phase winding is active; and, current flow into the winding decays to zero when the phase becomes inactive. Semiconductor switches (22) direct current flow into the winding when the phase is active and then redirect residual energy in the winding between an energy recovery circuit and an energy dissipation circuit when the phase becomes inactive. A PWM signal generator (44) provides PWM operating signals to the switches to control current flow first into the winding and then between the recovery and dissipation circuits. A control module (42), or microprocessor (52) with a PWM output, is responsive to rotor position information for controlling operation of the PWM signal generator. The signal generator provides PWM signals having one set of signal characteristics when there is current flow to the winding and a different set of characteristics when there is not. This produces alternate intervals of zero voltage and forced commutation residual current decay while the phase is inactive. During the decay interval, both the PWM frequency and pulse duty cycle are variable to produce a current decay scheme which eliminates ringing and motor noise.

Claims

1. A circuit for controlling residual current decay in a single or polyphase SRM comprising:

sensing means for sensing the position of a rotor of the motor;

switch means for directing current flow into a phase winding of the motor when the phase is active and for recovering or dissipating energy in the winding when the phase is inactive, the switch means comprising a first set of switches and a second set of switches, said sets of switches being on respective sides of the phase winding with one set of switches being activated when the phase is active, and deactivated when the phase is inactive;

signal generating means providing an operating signal to the switch means to control current flow and recovery or dissipation, the signal generating means including a PWM signal generator whose output signal pulse width and frequency are a function of the SRM'"'"'s operating characteristics, the second set of switches being modulated by operating signals from the signal generating means whereby operation of the second set of switches is controlled as a function of the signal characteristics of the operating signal;

a capacitor connected in series with the phase winding and charged by the current in the phase winding when the phase becomes inactive thereby to recover a portion of the energy; and

control means responsive to the sensing means for controlling the signal generating means for the signal generating means to provide operating signals having operating characteristics which differ when a phase is active and when it is not, thereby to facilitate energy recovery or dissipation when the phase becomes inactive, the control means effecting both frequency and/or duty cycle of the operating signals to control the rate of decay of the current and consequently motor noise, the control means being responsive to inputs from the sensing means when the phase becomes inactive to reverse the pulse width of the PWM operating signals produced by the signal generating means from those which are produced when the phase is active.

2. The circuit of claim 1 wherein the control means drives the signal generating means to produce an operating signal which provides a soft chopping of the tail current during one portion of a pulse cycle, and a hard chopping the remainder of the cycle.

3. The circuit of claim 2 further including gate means to which the PWM signal is supplied, the gate means deriving control signals for each set of switches from the PWM signals produced by the signal generating means to deactivate the first set of switches when the phase is inactive and to modulate switching of the second set of switches in accordance with the PWM signal characteristics.

4. The circuit of claim 1 wherein the first and second set of switches each comprise a pair of semiconductor switches connected in parallel.

5. The circuit of claim 4 further including power supply means for each set of switches, each power supply means including transformer means for stepping down the line voltage supplied to the SRM, and voltage regulator means for regulating the stepped down voltage.

6. The circuit of claim 1 further including rectification means for full-wave rectifying the phase voltage to the winding.

7. The circuit of claim 1 wherein the sensing means comprises a Hall effect sensor.

8. The circuit of claim 1 wherein the control means includes a microprocessor which receives inputs concerning the SRM'"'"'s operating characteristics and controls the signal characteristics of the operating signal produced by the signal generating means as a function of these inputs.

9. Apparatus for controlling tail current decay in a winding of a single or polyphase SRM, current and voltage being applied to the winding during each interval when the phase is active, the voltage and current being cut-off from the winding when the phase becomes inactive with the energy in the winding being recovered or dissipated under a zero volt condition, the apparatus comprising:

a bus capacitor for storing energy recovered from the winding;

switch means for connecting the phase winding into a circuit including the capacitor when the phase becomes inactive, the switch means including respective first and second sets of switches with one set of switches being connected on one side of the winding and the other set of switches on the other side thereof;

power dissipation means series connected with the winding;

sensing means for sensing the position of a rotor of the motor;

signal generating means providing an operating signal to the switch means to alternately switch the winding into a circuit including the bus capacitor and a circuit including the power dissipation means, the operating signals being used to modulate the state of one of the sets of switches to provide both a hard chopping and a soft chopping of the current; and

,

control means responsive to the sensing means for controlling operation of the signal generating means for the signal generating means to provide operating signals having one set of signal characteristics when a phase is active, and a different set of characteristics when the phase is inactive so to produce the zero voltage, energy recovery and dissipation of the tail current, the control means controlling both the frequency and duty cycle of the operating signals to effect the recovery and dissipation of the tail current and reduce motor noise.

10. The apparatus of claim 9 wherein the control means controls the signal generating means to maintain one of the sets of switches closed during the tail current decay period and switch the other set of switches between their open and closed positions at a rate controlled by the pulse width of the operating signals supplied to this said other set of switches, the tail decay current being soft chopped when the said other set of switches are closed, and hard chopped when the said other set of switches are open.

11. The apparatus of claim 10 wherein the signal generating means includes a PWM signal generator whose output signal pulse width and frequency are a function of the SRM'"'"'s operating characteristics, the control means being responsive to inputs from the sensing means when the phase becomes inactive to reverse the duty cycle of the PWM operating signals produced by the signal generating means from those which are produced when the phase is active.

12. The apparatus of claim 11 further including gate means for each set of switches to which the PWM signals are supplied, the gate means deriving control signals for each respective set of switches from the PWM signals to deactivate the first set of switches when the phase is inactive and to modulate switching of the second set of switches in accordance with the PWM signal characteristics.

13. The apparatus of claim 9 wherein the sensing means comprises a Hall effect sensor.

14. The apparatus of claim 9 wherein the control means includes a microprocessor which receives inputs concerning the SRM'"'"'s operating characteristics and controls the signal characteristics of the operating signal produced by the signal generating means as a function of these inputs, the microprocessor adjusting both the frequency and duty cycle of the PWM signals.

15. A method for controlling tail current decay in a phase winding of a single or polyphase SRM, current and voltage being applied to the phase winding during each interval when the phase is active with the voltage and current being cut-off from the phase winding when the phase becomes inactive, the energy in the phase winding when the phase becomes inactive having to be recovered or dissipated under a zero volt condition, the method comprising:

switching the phase winding into a circuit including a bus capacitor which stores current to recover energy while the phase is inactive, switching the phase winding into the circuit including switching respective first and second sets of switches, one set of switches being connected to one side of the phase winding and the other set of switches being connected on the other side thereof;

alternately switching the winding into an energy dissipation circuit to dissipate a portion of the energy, the winding being switched back and forth between the respective circuits over a plurality of intervals so to decay the current in a controlled manner;

sensing the rotor position of the motor while the phase is inactive;

generating and supplying an operating signal to the switches to effect switching of the phase winding between the bus capacitor circuit and the energy dissipation circuit; and

,

modulating the operation of one of the sets of switches with the operating signals whereby one set of switches remains closed throughout the interval when the phase is inactive and the other set of switches is switched back and forth between open and closed at a modulating frequency determined by the signal characteristics of the operating signal for the tail current to be hard chopped during each interval when both sets of switches are closed, and soft chopped during each interval when the one set of switches is closed and the other set of switches is open thereby to provide a zero volt current decay which is controlled so as to minimize motor noise.

16. The method of claim 15 wherein generating an operating signal includes generating a PWM signal the pulse width and frequency of which are a function of the SRM'"'"'s operating characteristics.

17. The method of claim 16 wherein modulating operation of the one set of switches includes reversing the duty cycle of the PWM operating signals produced by a signal generating means from that which the operating signals have when the phase is active.

18. The method of claim 16 wherein sensing the rotor position includes sensing with a Hall effect sensor.

19. The method of claim 15 further including controlling the signal characteristics of the operating signals with a microprocessor receiving inputs concerning the SRM'"'"'s operating characteristics.

20. A method of decaying the residual current in a winding of a single or polyphase SRM, current being supplied to the winding when the phase is active and the residual current being the current remaining in the winding when the phase become inactive, the method comprising:

switching the winding between a first circuit which is an energy recovery circuit to recover a portion of the energy represented by the residual current and a second circuit which is an energy dissipation circuit which dissipates a portion of the energy represented by the residual current;

controlling the switching of the winding between the energy recovery and energy dissipation circuits in a controlled manner by which the residual current is decayed to zero so as to cause minimal ringing in the motor and thereby reduce motor noise, controlling switching of the winding including switching the winding between the circuits over a plurality of intervals with the winding being switched into one circuit for a portion of each interval and into the other circuit the remainder of the interval, both the duration of each interval and the portion thereof in which the winding is switched into one circuit or the other being variable in a predetermined manner.

21. The method of claim 20 wherein controlling switching of the winding between the respective circuits involves controlling at least one switch used to accomplish switching of the winding with PWM operating signals, the frequency and duty cycle of the PMW signals being variable to vary either the length of each interval during which the winding is connected to both of the respective circuits and the portion of each interval in which the winding is connected in one circuit or the other, the duty cycle of the PWM signals, or both. .Iadd.

22. A circuit for controlling residual current decay in a single or polyphase SRM comprising:

switches for directing current flow into a phase winding of the motor when the phase is active and for recovering or dissipating energy in the winding when the phase is inactive,

a PWM signal generator providing an operating signal to the switches to control current flow and recovery or dissipation of residual current;

a capacitor connected in series with the phase winding and charged be the current in the phase winding when the phase becomes inactive thereby to recover a portion of the energy; and

control means for controlling the signal generated by the PWM signal generator to provide operating signals having operating characteristics which differ when a phase is active and when it is not, thereby to facilitate energy recovery or dissipation when the phase becomes inactive, the control means reversing the pulse width of the operating signals produced by the PWM signal generator when the phase becomes inactive from the pulse width of the operating signals which are produced when the phase is active. .Iaddend..Iadd.23. Apparatus for controlling tail current decay in a winding of a single or polyphase SRM, current and voltage being applied to the winding during each interval when the phase is active, the voltage and current being cut off from the winding when the phase becomes inactive with the energy in the winding being recovered or dissipated under a zero volt condition the apparatus comprising;

a capacitor for storing energy recovered from the winding;

switches for connecting the phase winding into alternate circuit configurations when the phase becomes inactive;

power dissipation means connected with the winding;

a signal generator providing an operating signal to the switches to alternately switch the winding into a circuit including the capacitor and a circuit including the power dissipation means, the operating signals being used to modulate the state of the switches to provide both a hard chopping and a soft chopping of the current; and

control means for controlling operation of the signal generator to provide operating signal having one set of signal characteristics when a phase is active and a different set of characteristics when the phase is inactive so to produce the zero voltage, energy recovery and dissipation of the tail current, the control means controlling both the frequency and duty cycle of the operating signals to effect the recovery and dissipation of the tail current and reduce motor noise. .Iaddend..Iadd.24. A method for controlling tail current decay in a phase winding of a single or polyphase SRM, current and voltage being applied to the phase winding during each interval when the phase is active, with the voltage and current being cut-off from the phase winding when the phase becomes inactive, the energy in the phase winding when the phase becomes inactive having to be recovered or dissipated under a zero volt condition, the method comprising;

switching the phase winding into a recovery circuit including a capacitor to recover energy while the phase is inactive;

alternately switching the winding into an energy dissipation circuit to dissipate a portion of the energy while the phase is inactive the winding being switched back and forth between the energy recovery circuit and the energy dissipation circuit over a plurality of intervals so to decay the current in a controlled manner;

generating and supplying an operating signal to control switching of the phase winding between the energy recovery circuit and the energy dissipation circuit; and

modulating the operation of the switches with the operating signals to provide repeated intervals of zero volt current decay which are controlled so as to minimize motor noise. .Iaddend..Iadd.25. A circuit for controlling residual current decay in a winding of a switched reluctance machine to reduce machine noise, the circuit comprising;

a DC voltage source providing a DC voltage, the DC voltage source defining positive and negative DC rails;

a phase winding, the phase winding having first and second ends;

a switching circuit including a first switching device coupled to the positive DC rail and to the first end of the phase winding and a second switching device coupled to the negative DC rail and to the second end of the phase winding, wherein the first and second switching devices are controlled to;

(i) electrically couple the phase winding across the DC voltage source such that the negative of the DC voltage provided by the DC voltage source is applied across the phase winding, or (ii) electrically isolate at least one end of the chase winding from the DC voltage source such that the volume across the phase winding is approximately zero; and

a control circuit coupled to the switching circuit for controlling the first and second switching devices such that the voltage applied to the phase winding during the interval of residual current decay comprises repeated periods of differing voltage levels having a magnitude that is selected from at least one of the following values;

(i) the negative of the DC voltage provided by the DC voltage source;

or (ii) the voltage established by connecting the phase winding in a closed-loop circuit hit a semiconductor device. .Iaddend..Iadd.26. A method of reducing the amount of noise produced by a switched reluctance machine, the switched reluctance machine having a plurality of phase windings, the method comprising the steps of;

actively energizing a first phase windings such that the current in the first phase winding begins to increase from zero to a peak positive value over a first interval; and

controlling the decay of the current in a second phase winding over the first interval by applying a plurality of periods of differing voltage levels to the second phase winding over the first interval, where the voltage levels have a magnitude selected from the group of;

a negative DC voltage or the voltage resulting from connecting the second phase winding in a closed-loop circuit with a semiconductor device;

wherein the application of the plurality of periods of differing voltage levels applied to the second phase winding is controlled to reduce the amount of noise produced by the machine. .Iaddend..Iadd.27. The method of claim 26 wherein plurality of periods of differing voltage levels applied to the second phase winding includes periods of voltage levels having a negative DC voltage magnitude and period, of voltage levels having a magnitude established by connecting the second phase winding in a closed-loop circuit with a semiconductor device. .Iaddend..Iadd.28. The method of claim 26 wherein;

(i) the switched reluctance machine includes at least one resonant frequency, and (ii) the step of controlling the decay of the current in the second phase winding over the first interval by applying a plurality of periods of differing voltage levels to the second phase winding includes the step of applying the plurality of periods of differing voltages at a frequency that is at least twice the resonant frequency of the machine. .Iaddend..Iadd.29. The method of claim 26 wherein the step of controlling, the decay of the current in the second phase winding over the first interval by applying a plurality of periods of differing voltage levels to the second phase winding includes the step of varying the frequency at which the plurality of periods of differing

23. voltage are applied to the second phase winding. .Iaddend..Iadd.30. The method of claim 26 wherein the step of controlling the decay of the current in the second phase winding over the first interval by applying a plurality of periods of differing voltage levels to the second phase winding includes the step of varying the duty cycle of the plurality of periods of differing voltages applied to the second phase winding. .Iaddend..Iadd.31. The method of claim 26 wherein the step of controlling the decay of the current in the second phase winding over the first interval by applying a plurality of periods of differing voltage levels to the second phase winding includes the steps of:

(i) varying the frequency at which the plurality of periods of differing voltage are applied to the second phase winding, and (ii) varying the duty cycle of the plurality of periods of differing voltage applied to the second phase winding. .Iaddend..Iadd.32. A method of reducing the amount of noise produced by a switched reluctance machine, the switched reluctance machine having at least one phase winding, the method comprising the steps of;

actively energizing a first phase winding over a first interval such that the current in the first phase winding reaches a peak positive value; and

controlling the decay of the current in the first phase winding over a second interval following the first interval by applying a plurality of periods of differing voltage levels to the first phase winding over the second interval, where the periods of differing voltage levels have a magnitude selected from the group of;

(i) a negative DC voltage or (ii) the voltage resulting from connecting the first phase winding in a closed-loop circuit with a semiconductor device;

wherein the application of the plurality of differing voltage levels applied to the phase winding is controlled to reduce the amount of noise produced by the machine. .Iaddend..Iadd.33. The method of claim 32 wherein the plurality of periods of differing voltage levels applied to the first phase winding in the step of controlling the decay of the current in the first phase winding includes periods of voltage levels having both a negative DC voltage magnitude and a voltage magnitude resulting from connecting the first phase winding in a closed-loop circuit with a

24. semiconductor device. .Iaddend..Iadd.34. The method of claim 32 wherein:

(i) the switched reluctance machine includes at least one resonant frequency, and (ii) the step of controlling the decay of the current in the first phase winding over the second interval by applying a plurality of periods of differing voltage levels to the first phase winding includes the step of applying the plurality of periods of differing voltage at a frequency that is at least twice the resonant frequency of the machine. .Iaddend..Iadd.35. The method of claim 32 wherein the step of controlling the decay of the current in the first phase winding over the second interval be applying a plurality of periods of differing voltage levels to the first phase winding includes the step of varying the frequency at which the plurality of periods of differing voltage are applied to the first phase winding. .Iaddend..Iadd.36. The method of claim 32 wherein the step of controlling the decay of the current in the first phase winding over the second interval by applying a plurality of period, of differing voltage levels to the first phase winding includes the step of varying the duty cycle of the plurality of periods of differing voltage applied to the first case winding. .Iaddend..Iadd.37. The method of claim 32 wherein the step of controlling the decay of the current in the first phase winding over the second interval by applying a plurality of periods of differing voltage levels to the first phase winding includes the steps of;

(i) varying the frequency at which the plurality of periods of differing voltage are applied to the first phase winding and (ii) varying the duty cycle of the plurality of periods of differing voltage applied to the first phase winding. .Iaddend..Iadd.38. Apparatus for controlling the decay of current in the phase winding of a switched reluctance machine from a positive value to zero, the apparatus comprising;

a DC voltage source;

a switching device coupled to the voltage source and to the phase winding for controlling the application of voltage to the phase winding;

a control circuit coupled to the switching device, the control circuit adapted to provide a series of pulsed gating signals to the switching device to control the switching device such that the current in the phase winding falls from the positive value to zero in a controlled fashion. .Iaddend..Iadd.39. The apparatus of claim 38 wherein the series of pulsed gating signals provided by the control circuit is such that the voltage applied to the phase winding during the period of current decay repeatedly varies from a negative voltage magnitude to approximately zero volts.

25. Iaddend..Iadd.40. A method of controlling current in a switched reluctance machine, the machine including a rotor, and a phase winding, the method comprising the steps of:

applying electrical power to the phase winding over a first interval of rotor rotation such that the current in the phase winding increases from zero to a positive value; and

controlling the application of electrical power to the phase winding for a period following the first interval such that the current in the phase winding decreases from the positive value to zero through two or more decay intervals, where the slope of the current decay varies over each decay interval. .Iaddend..Iadd.41. The method of claim 40 wherein the step of controlling the application of electric power to the phase winding includes the steps of;

(i) applying a negative voltage to the phase winding over a first decay intervals and (ii) applying a voltage resulting from connecting the phase winding in a closed-loop circuit with a semiconductor device to the phase winding over a second decay interval;

wherein the slope of the current decay over the second decay interval is less than the slope of the current decay over the first decay interval. .Iaddend..Iadd.42. The method of claim 40 wherein the step of controlling the application of electric power to the phase winding includes the step of applying a series of pulse width modulated voltage pulses to the phase winding. .Iaddend.