METHOD FOR STARTING A SENSORLESS SINGLE-PHASE ELECTRIC MOTOR AND SENSORLESS SINGLE-PHASE ELECTRIC MOTOR

Abstract

A method for starting a sensorless single-phase electric motor. The electric motor includes a permanent magnetic motor rotor, an electromagnetic motor stator having a stator coil, a power electronics which energizes the stator coil, a current sensor which measures a current flowing in the stator coil, and a control electronics which controls the power electronics. The control electronics is connected with the current sensor. The method includes energizing the stator coil with an alternating drive voltage, monitoring a drive current which is generated in the stator coil by the alternating drive voltage, and commutating the alternating drive voltage whenever the drive current reaches a predefined positive current threshold value or a predefined negative current threshold value.

Claims

1-6. (canceled)

7. A method for starting a sensorless single-phase electric motor, the electric motor comprising: a permanent magnetic motor rotor; an electromagnetic motor stator comprising a stator coil; a power electronics which is configured to energize the stator coil; a current sensor which is configured to measure a current flowing in the stator coil; and a control electronics which is configured to control the power electronics, the control electronics being connected with the current sensor, the method comprising: energizing the stator coil with an alternating drive voltage; monitoring a drive current which is generated in the stator coil by the alternating drive voltage; and commutating the alternating drive voltage whenever the drive current reaches a predefined positive current threshold value or a predefined negative current threshold value.

8. The method as recited in claim 7, wherein, the alternating drive voltage is generated based on a pulse-width-modulated drive signal, and a duty cycle of the pulse-width modulated drive signal is continuously increased up to a predefined set duty cycle during a ramp phase.

9. The method as recited in claim 7, further comprising: detecting an initial rotor orientation by: energizing the stator coil with a positive detection voltage pulse which has a positive electrical polarity; energizing the stator coil with a negative detection voltage pulse which has a negative electrical polarity; measuring a positive detection current pulse which is generated in the stator coil by the positive detection voltage pulse; measuring a negative detection current pulse which is generated in the stator coil by the negative detection voltage pulse; determining a first detection parameter by evaluating the positive detection current pulse; determining a second detection parameter by evaluating the negative detection current pulse; and determining a magnetic orientation of the permanent magnetic motor rotor when resting by comparing the first detection parameter with the second detection parameter.

10. The method as recited in claim 9, further comprising: providing the alternating drive voltage with an initial electrical polarity which is defined based on the magnetic orientation which is determined of the permanent magnetic motor rotor when resting.

11. The method as recited in claim 9, further comprising: energizing the stator coil with at least three positive detection voltage pulses and with at least three negative detection voltage pulses; measuring each of the at least three positive detection current pulses and each of the at least three negative detection current pulses; determining the first detection parameter by adding up maximum absolute values of each of the at least three positive detection current pulses; and determining the second detection parameter by adding up maximum absolute values of each of the at least three negative detection current pulses.

12. The method as recited in claim 11, further comprising: providing the alternating drive voltage with an initial electrical polarity which is defined based on the magnetic orientation which is determined of the permanent magnetic motor rotor when resting.

13. A sensorless single-phase electric motor comprising: a permanent magnetic motor rotor; an electromagnetic motor stator comprising a stator coil; a power electronics which is configured to energize the stator coil; a current sensor which is configured to measure a current flowing in the stator coil; and a control electronics which is connected with the current sensor, the control electronics being configured to control the power electronics and to perform the method as recited in claim 7.

Description

[0041] An embodiment of the invention is described with reference to the enclosed drawings, wherein

[0042] FIG. 1 shows a schematic illustration of a sensorless single-phase electric motor according to the invention, wherein a motor rotor is oriented in a first rest position,

[0043] FIG. 2 shows a temporal course of a) a feed voltage b) a feed current and c) a first detection parameter and second detection parameter during an initial rotor orientation detection procedure, and

[0044] FIG. 3 shows a temporal course of a) the feed voltage and b) the feed current during a rotor acceleration procedure.

[0045] FIG. 1 shows a sensorless single-phase electric motor 10 comprising an electromagnetic motor stator 12 with a ferromagnetic stator body 14 and a single stator coil 16. The stator body is designed as a so-called laminated stator body, i.e. the stator body 14 is made of a stack of ferromagnetic metal sheets. The stator body 14 is provided substantially U-shaped, wherein a first pole leg 18 defines a first stator pole and an opposite second pole leg 20 defines a second stator pole. The stator coil 16 is arranged satellite-like at a bridge portion 22 mechanically and magnetically connecting the two pole legs 18,20.

[0046] The electric motor 10 also comprises a rotatable permanent-magnetic motor rotor 24. The motor is diametrically magnetized thereby defining a magnetic north pole N and a magnetic south pole S.

[0047] The electric motor 10 also comprises a power electronics 26 and control electronics 28. The power electronics 26 is electrically connected with the stator coil 16 via a stator connection line 30 for energizing the stator coil 16 with a defined effective feed voltage V. The power electronics 26 is controlled by the control electronics 28 via a pulse-width-modulated drive signal PWM, wherein an effective amplitude of the feed voltage V is controlled via the duty cycle D—i.e. the on-time ratio—of the drive signal PWM. The control electronics 28 is also configured to control an electrical polarity of the feed voltage V.

[0048] If the stator coil 16 is not energized, the motor rotor 24 moves into one of two static rest positions RP1,RP2 with opposite magnetic orientations of the motor rotor 24. The two rest positions RP1,RP2 of the motor rotor 24 are schematically illustrated in FIG. 1 by arrows representing the orientation of the magnetic north pole N for the first rest position RP1 and the second rest position RP2, respectively. As visible in FIG. 1, the north pole N of the motor rotor 24 points toward the first pole leg 18 in the first rest position RP1 and points toward the second pole leg 20 in the second rest position RP2.

[0049] If the stator coil 16 is energized with a positive feed voltage V, a positive electromagnetic field is generated, wherein the first pole leg 18 provides a magnetic north pole and the second pole leg 20 provides a magnetic south pole. If the stator coil 16 is energized with a negative feed voltage V, a negative electromagnetic field is generated, wherein the first pole leg 18 provides a magnetic south pole and the second pole leg 20 provides a magnetic north pole.

[0050] The positive electromagnetic field accelerates the motor rotor 24 toward a first drive position DPI in which the north pole N of the motor rotor 24 points toward the second pole leg 20. The negative electromagnetic field accelerates the motor rotor 24 toward a second drive position DP2 in which the north pole N of the motor rotor 24 points toward the first pole leg 18. The two drive positions DP1,DP2 are schematically illustrated in FIG. 1 by arrows representing the orientation of the magnetic north pole N for the first drive position DP1 and the second drive position DP2 of the motor rotor 24, respectively.

[0051] The electric motor 10 also comprises a current sensor 32 being arranged in the stator connection line 30 to measure an electric feed current I flowing through the stator connection line 30 and, as a result, flowing through the stator coil 16. The current sensor 32 is connected with the control electronics 28 in that way that the present feed current I can be evaluated by the control electronics 28.

[0052] The motor electronics 28 is configured to execute an initial rotor orientation detection procedure. In the rotor orientation detection procedure, the power electronics 26 is controlled by the control electronics 28 to alternately energize the stator coil 16 with three positive detection voltage pulses Vp and with three negative detection voltage pulses Vn as schematically illustrated in FIG. 2a. Each positive detection voltage pulse Vp is provided with a positive electrical polarity and generates a positive electromagnetic detection field. Each negative detection voltage pulse Vn is provided with a negative electrical polarity and generates an opposite negative electromagnetic detection field.

[0053] The resulting feed current I is monitored by the control electronics 28 via the current sensor 32. As schematically illustrated in FIG. 2b, the three positive detection voltage pulses Vp generate three positive detection current pulses Ip, and the three negative detection voltage pulses Vn generate three negative detection current pulses In. Each positive detection current pulse Ip has a maximum absolute value of about I1, and each negative detection current pulse In has a maximum absolute value of about I2 being greater than I1.

[0054] The control electronics 28 determines a first detection parameter P1 by evaluating all positive detection current pulses Ip, in particular by adding up maximum absolute values of the three positive detection current pulses Ip. The control electronics 28 determines a second detection parameter P2 by evaluating all negative detection current pulses Ip, in particular by adding up maximum absolute values of the three negative detection current pulses In.

[0055] The control electronics 28 compares the determined first detection parameter P1 and second detection parameter P2 to determine the present magnetic orientation of the resting motor rotor 24, i.e. the present static rotor rest position.

[0056] If the motor rotor 24 is oriented in the first rest position RP1—i.e. the magnetic rotor north pole N is located adjacent to the first pole leg 18—the generated positive electromagnetic field is weakened and the generated negative electromagnetic field is enhanced by the permanent-magnetic field of the motor rotor 24. If the motor rotor 24 is oriented in the second rest position RP2—i.e. the magnetic rotor north pole N is located adjacent to the second pole leg 20—the generated positive electromagnetic field is enhanced and the generated negative electromagnetic field is weakened by the permanent-magnetic field of the motor rotor 24. Therefore, if the motor rotor 24 is oriented in the first rest position RP1, the determined second detection parameter P2 is higher than the determined first detection parameter P1, and if the motor rotor 24 is oriented in the second rest position RP2, the determined first detection parameter P1 is higher than the determined second detection parameter P2.

[0057] As schematically illustrated in FIG. 2c, the determined second detection parameter P2 is significantly higher compared to the determined first detection parameter P1. Therefore, in the described case, the resting motor rotor 24 is oriented in the first rest position RP1 as illustrated in FIG. 1.

[0058] The control electronics 28 is configured to subsequently execute an acceleration procedure to accelerate the resting motor rotor 24. In the acceleration procedure, the control electronics 28 controls the power electronics 26 to energize the stator coil 16 with an alternating drive voltage Vd, wherein the initial electrical polarity of the drive voltage is defined based on the determined magnetic orientation of the resting motor rotor 24.

[0059] If the resting motor rotor 24 is oriented in the first rest position RP1, the drive voltage Vd is provided with a positive initial electrical polarity so that a positive electromagnetic field is generated initially which accelerates the resting motor rotor 24 out of the first rest position RP1 toward the first drive position DP1. If the resting motor rotor 24 is oriented in the second rest position RP2, the drive voltage Vd is provided with a negative initial electrical polarity so that a negative electromagnetic field is generated initially which accelerates the resting motor rotor 24 out of the second rest position RP2 toward the second drive position DP2. As visible in FIG. 3a, in the present case, the drive voltage Vd is provided with a positive initial electrical polarity because the resting motor rotor 24 is oriented in the first rest position RP1.

[0060] The control electronics 28 is configured to continuously monitor—via the current sensor 32—a drive current Id generated in the stator coil 16 by the alternating drive voltage Vd. As visible in FIG. 3, the control electronics 28 is configured to commutate the drive voltage Vd each time when the measured drive current Id reaches a predetermined positive current threshold value Itp or a predetermined negative current threshold value Itn. Because the effective value of the drive current Id depends on the present rotational position of the motor rotor 24, the described commutation scheme provides an indirectly rotor-position-controlled commutation of the drive voltage Vd.

[0061] As visible in FIG. 3a, the control electronics 28 is also configured to continuously increase the duty cycle D of the pulse-width-modulated drive signal PWM up to a predefined set duty cycle Ds during an initial ramp phase R to thereby continuously increase the effective amplitude of the drive voltage Vd up to a predefined set effective voltage amplitude Vs. Because of the current-threshold-controlled commutation of the drive voltage Vd, this also provides a continuously increasing alternation frequency of the drive voltage Vd.

REFERENCE LIST

[0062] 10 sensorless single-phase electric motor

[0063] 12 motor stator

[0064] 14 stator body

[0065] 16 stator coil

[0066] 18 first pole leg

[0067] 20 second pole leg

[0068] 22 bridge portion

[0069] 24 motor rotor

[0070] 26 power electronics

[0071] 28 control electronics

[0072] 30 stator connection line

[0073] 32 current sensor

[0074] D duty cycle

[0075] DP1 first drive position

[0076] DP2 second drive position

[0077] Ds set duty cycle

[0078] I feed current

[0079] In negative detection current pulses

[0080] Ip positive detection current pulses

[0081] Itn negative current threshold value

[0082] Itp positive current threshold value

[0083] N magnetic north pole

[0084] P1 first detection parameter

[0085] P2 second detection parameter

[0086] PWM pulse-width-modulated drive signal

[0087] R ramp phase

[0088] RP1 first rest position

[0089] RP2 second rest position

[0090] S magnetic south pole

[0091] t time

[0092] V effective feed voltage

[0093] Vd alternating drive voltage

[0094] Vn negative detection voltage pulses

[0095] Vp positive detection voltage pulses

[0096] Vs set effective drive voltage amplitude