CN114884406A

CN114884406A - Motor system and motor driving method

Info

Publication number: CN114884406A
Application number: CN202110164348.4A
Authority: CN
Inventors: 李文定
Original assignee: Sentelic Corp
Current assignee: Sentelic Corp
Priority date: 2021-02-05
Filing date: 2021-02-05
Publication date: 2022-08-09

Abstract

The present disclosure relates to a motor system and a motor driving method for detecting a back electromotive force without affecting stability of a motor device. The motor driving method comprises the following steps: detecting a detection voltage value between a first switch and a second switch in a driving circuit, wherein the driving circuit is electrically connected to a power supply and the motor device and is used for controlling the first switch and the second switch according to a switching frequency so as to provide a driving current to the motor device; judging the driving current according to the detection voltage value; when the driving current is smaller than a preset value, the first switch and the second switch are turned off for a detection period, wherein the time length of the detection period is a fixed value; detecting a back electromotive force of the motor device during the detection to calculate a return-to-zero time of the back electromotive force; and adjusting the switching frequency according to the zeroing time.

Description

Motor system and motor driving method

Technical Field

The present disclosure relates to a motor system and a motor driving method, and more particularly, to a technique for calculating a rotor position by determining a back electromotive force.

Background

With the development of technology, the operating frequency of various electronic devices increases, but the increase of the operating frequency causes the internal temperature of the electronic device to increase relatively when the electronic device is operated, so that the fan is essential to maintain the operation of the electronic device in order to prevent the high temperature from affecting the operation of the electronic device and even damaging the electronic device.

When the fan system is in operation, the operation state needs to be determined according to the position of the rotor of the motor. Although a position sensor may be disposed in the fan system to detect the rotor of the motor, this requires higher cost and larger installation space. Therefore, a driving method suitable for application to a Sensorless (Sensorless) fan system is required.

Disclosure of Invention

The present disclosure relates to a motor driving method, comprising the following steps: detecting a detection voltage value between a first switch and a second switch in a driving circuit, wherein the driving circuit is electrically connected to a power supply and the motor device and is used for controlling the first switch and the second switch according to a switching frequency so as to provide a driving current to the motor device; judging the driving current according to the detection voltage value; when the driving current is smaller than a preset value, the first switch and the second switch are turned off for a detection period, wherein the time length of the detection period is a fixed value; detecting a back electromotive force of the motor device during the detection to calculate a return-to-zero time of the back electromotive force; and adjusting the switching frequency according to the zeroing time.

In one embodiment, the motor driving method further includes: detecting the back electromotive force of the motor device during the detection period to obtain a plurality of detected electromotive force values; and calculating the return-to-zero time of the back electromotive force based on the detected electromotive force values.

In one embodiment, the drive current passes through zero during sensing.

In one embodiment, a method of calculating a return-to-zero time of a back electromotive force includes: obtaining a variation characteristic line according to the detected electromotive force values; and calculating the zero-returning time of the back electromotive force according to a slope of the change characteristic line.

In one embodiment, the driving circuit includes a plurality of bridge arm units, and the first switch and the second switch are located in the same one of the bridge arm units.

In one embodiment, the first switch and the second switch are turned off when the detection voltage value between the first switch and the second switch is detected.

In one embodiment, the switching frequency is the frequency of the pwm signal, and the time duration of the detection period is an integer multiple of the period of the pwm signal.

In one embodiment, the time length of the detection period is a fixed number of periods of the pwm signal.

In one embodiment, the current phase and the voltage phase of the motor device vary according to the switching frequency.

In one embodiment, the motor apparatus is a three-phase motor having three input nodes, and the detection node between the first switch and the second switch is connected to one of the input nodes.

The present disclosure also relates to a motor system including a drive circuit, a motor device, and a control circuit. The driving circuit is electrically connected to the power supply and at least comprises a first switch and a second switch. The driving circuit is used for generating a driving current. The motor device is electrically connected to the driving circuit and used for receiving the driving current. The control circuit is electrically connected to the driving circuit and used for detecting the detection voltage value between the first switch and the second switch. When the control circuit judges that the driving current value is smaller than the preset value according to the detection voltage value, the control circuit switches off the first switch and the second switch for a detection period so as to detect the back electromotive force of the motor device and calculate the return-to-zero time of the back electromotive force.

In one embodiment, the control circuit is used for obtaining a plurality of detected electromotive force values when detecting the back electromotive force of the motor device during the detection period, and calculating the return-to-zero time of the back electromotive force according to the detected electromotive force values.

In one embodiment, the drive current passes through zero during sensing.

In one embodiment, the control circuit is further configured to obtain a variation characteristic line according to the detected electromotive force values, and the control circuit calculates the return-to-zero time of the back electromotive force according to a slope of the variation characteristic line.

In one embodiment, the driving circuit includes a plurality of bridge arm units, the first switch and the second switch are located in the same one of the bridge arm units, and the control circuit controls the first switch and the second switch according to the switching frequency.

In one embodiment, the control circuit maintains the first switch and the second switch in an off state when detecting a detection voltage value between the first switch and the second switch.

In one embodiment, the control circuit adjusts the switching frequency according to the return-to-zero time of the back electromotive force.

The present disclosure detects the back electromotive force for a fixed time (i.e., a detection period) using a period of the zero-crossing point of the driving current, and then presumes the zero-return time of the back electromotive force zero-crossing point. Therefore, the problems of instability or abnormity of the motor system caused by overlong detection time can be avoided.

Drawings

FIG. 1 is a schematic view of a motor system according to some embodiments of the present disclosure;

FIG. 2A is a schematic diagram of various signal waveforms in accordance with some embodiments of the present disclosure;

FIG. 2B is a partial schematic diagram of signal waveforms in accordance with some embodiments of the present disclosure;

FIG. 3 is a flow chart of a motor driving method according to some embodiments of the present disclosure.

[ notation ] to show

100 motor system

110 drive circuit

120 motor device

130 control circuit

B1-B3 bridge arm unit

N1-N3 detection node

NU input node

NV input node

NW input node

Vb supply power

Q1 first switch

Q2 second switch

Vp drive voltage

Ip drive current

Ve back electromotive force

Td detection period

d1 first distance

d2 second distance

A, detecting electromotive force value

B, detecting the electromotive force value

S301-S307

Detailed Description

In the following description, for purposes of explanation, numerous implementation details are set forth in order to provide a thorough understanding of the various embodiments of the present invention. It should be understood, however, that these implementation details are not to be interpreted as limiting the invention. That is, in some embodiments of the invention, such implementation details are not necessary. In addition, for the sake of simplicity, some conventional structures and elements are shown in the drawings in a simple schematic manner.

When an element is referred to as being "connected" or "coupled," it can be referred to as being "electrically connected" or "electrically coupled. "connected" or "coupled" may also be used to indicate that two or more elements are in mutual engagement or interaction. Moreover, although terms such as "first," "second," …, etc., may be used herein to describe various elements, these terms are used merely to distinguish one element or operation from another element or operation described in similar technical terms. Unless the context clearly dictates otherwise, the terms do not specifically refer or imply an order or sequence nor are they intended to limit the invention.

Fig. 1 is a schematic diagram of a motor system 100 according to some embodiments of the present disclosure. The motor system 100 includes a driving circuit 110, a motor device 120, and a control circuit 130. The driving circuit 110 is electrically connected to the power supply Vb and the motor device 120, and includes a plurality of switching elements. In an embodiment, the driving circuit 110 controls the switching elements to be turned on and off according to the control signals UH, UL, WH, WL, VH, and VL, respectively, to output the driving current.

The motor device 120 is electrically connected to the output end of the driving circuit 110 to receive the driving current. In one embodiment, the motor device 120 is used to rotate the blades (not shown) of the fan 100. In some embodiments, the motor device 120 is a three-phase motor having three input nodes NU, NV, NW. In some embodiments, the motor system 100 is applied to a fan system. That is, the motor device 120 is used to rotate the fan blades, but the disclosure is not limited thereto, and the disclosure can also be applied to other types of devices.

The driving circuit 110 includes three bridge arm units B1-B3. Each of the bridge arm cells B1 through B3 includes a first switch Q1 and a second switch Q2, which are electrically connected to different input nodes NU, NV, NW, respectively. The first switch Q1 and the second switch Q2 of each of the arm units B1 to B3 are turned on or off according to the control signals UH, UL, WH, WL, VH, and VL to supply three-phase driving currents to the motor device 120. Since the operation of the three-phase motor is understood by those skilled in the art, it is not described herein.

The control circuit 130 is electrically connected to any of the bridge arm units B1-B3 in the driving circuit 110, and is configured to provide the control signals UH, UL, WH, WL, VH, and VL, and further configured to detect a detection voltage value of a detection node between the first switch Q1 and the second switch Q2. As shown in fig. 1, the control circuit 130 can be connected to any one of the detection nodes N1, N2, N3. In one embodiment, the control circuit 130 generates the control signals UH, UL, WH, WL, VH, VL according to the rotation speed signal. The rotation speed signal is a pulse width modulation signal, and the frequency of the pulse width modulation signal corresponds to the control signals UH, UL, WH, WL, VH, and VLM for controlling the switching frequency of the first switch Q1 and the second switch Q2.

The control circuit 130 can determine the current information of the driving current, such as the current magnitude and the current direction, according to the detected voltage value. When the control circuit 130 determines that the driving current is smaller than the predetermined value, the control circuit 130 ensures that the first switch Q1 and the second switch Q2 connected thereto are maintained in the off state for a fixed time. For convenience of explanation, this time will be referred to as "detection period" herein. During the detection period, the control circuit 130 detects the magnitude and trend of the back electromotive force (back EMF) of the motor device 120, and calculates the time for the back EMF to return to zero.

In one embodiment, the aforementioned "predetermined value" is a value close to zero. In other words, the control circuit 130 detects the back electromotive force during the zero-crossing of the drive current. The control circuit 130 may then begin timing the "detection period" when the drive current approaches zero. In other embodiments, the control circuit 130 may also start timing the "detection period" (i.e., the time point when the driving current is zero is the starting point of the detection period) when determining that the driving current is zero.

Specifically, during the detection period, the control circuit 130 will detect the back electromotive force of the motor device 120 at different time points to obtain a plurality of detected electromotive force values. Based on these detected electromotive forces, the variation trend of the back electromotive force can be deduced to estimate the return-to-zero time of the back electromotive force.

In other embodiments, the control circuit 130 stores a parametric model of the motor device 120, so that the control circuit 130 can only detect the back electromotive force once during the detection period, and can calculate the return-to-zero time of the back electromotive force. In addition, the control circuit 130 may adjust the rotation speed or the driving voltage of the driving motor 120 through the detected back electromotive force without using a parametric model, so as to calculate the return-to-zero time of the back electromotive force.

Fig. 2A is a signal waveform diagram including a drive voltage Vp, a drive current Ip, and a back electromotive force Ve of a motor device according to some embodiments of the present disclosure. In fig. 2A, the horizontal axis represents time, and the vertical axis represents the variation trend of current, voltage, and electromotive force. As shown in the figure, the control circuit 130 detects the back electromotive force Ve of the motor device 120 during the zero-crossing point of the driving current Ip (i.e., the detection period Td) to obtain at least two detected electromotive force values. These detected electromotive force values may form a variation characteristic line. The time when the change characteristic line meets the zero point can be estimated from the slope of the change characteristic line or the coordinates of the detected electromotive force value A, B in accordance with a trigonometric function.

Fig. 2B is a partially enlarged view of fig. 2A. As shown, the control circuit 130 detects the back electromotive force Ve of the motor device 120 to obtain two detected electromotive force values A, B. Since the curve of the driving current Ip is close to the curve of the back electromotive force Ve, when the driving current Ip approaches zero (i.e., the detection period Td), the back electromotive force Ve will also be near the zero point. Accordingly, the variation characteristic line L formed by connecting these detected electromotive force values A, B can be regarded as a curve equivalent to the back electromotive force Ve. The control circuit 130 can obtain the first distance d1 (in fig. 2B, the driving current Ip corresponding to the detected electromotive force value a is zero, so the first distance d1 is the coordinate value of the detected electromotive force value a) according to the detected electromotive force value a and the value of the driving current Ip at the same time. Then, the second distance d2 can be calculated by the first distance d1 and the slope of the variation characteristic line. The second distance d2 is the time difference between "the time when the back electromotive force Ve returns to zero" and "the time when the detected electromotive force value a is detected".

The control circuit 130 is used for calculating the rotor position of the motor device 120 according to the zeroing time of the back electromotive force Ve and the rotation speed signal. The control circuit 130 can determine whether the operation status of the motor system 100 is expected. Since those skilled in the art can understand the method for calculating the rotor position according to the back electromotive force, it is not described herein.

Specifically, in order to operate the motor 120 with a desired efficiency and avoid excessive energy consumption, the phases of the driving voltage Vp and the driving current Ip of the motor 120 should correspond to each other (e.g., the phases of the signal waveforms coincide). Therefore, in one embodiment, after the control circuit 130 calculates the return-to-zero time of the back electromotive force and calculates the rotor position, the control circuit 130 adjusts the frequency of the rotation speed signal (i.e., changes the switching frequency of the control signals UH, UL, WH, WL, VH, VL) to change the voltage phase of the driving voltage Vp and the current phase of the driving current Ip so that the two phases can be close to each other.

In some embodiments, when the control circuit 130 detects the voltage value detected between the first switch Q1 and the second switch Q2, the control circuit 130 keeps the first switch Q1 and the second switch Q2 in an off state, so as to avoid the occurrence of an abnormality in the arm cells B1 to B3 due to a short circuit. In other words, the time when the control circuit 130 detects the detected voltage value is at the time when the first switch Q1 and the second switch Q2 are both turned off.

The present disclosure detects the back electromotive force for a fixed time (i.e., a detection period) using a period during which the driving current crosses zero (or approaches zero). The zero-returning time of the zero-crossing point is estimated through a plurality of detected electromotive force values of the back electromotive force in the detection period, so that the problems of instability or abnormality of the motor system 100 caused by overlong detection time can be avoided.

In some embodiments, the control signals UH, UL, WH, WL, VH, VL are generated according to the rotation speed signal, and are also a pulse width modulation signal. The duration of the detection period is a fixed number of periods (e.g., an integer multiple of the period) of the pwm signal. For example, the time length of the detection period may be 2-5 periods of the PWM signal. In one embodiment, the time length of the detection period may be 3 periods of the pwm signal. The time length of the detection period is a fixed value, but is not limited to the length of 2-5 cycles. The implementation can be adjusted according to the requirements.

Fig. 3 is a flowchart of a motor driving method according to some embodiments of the disclosure. In step S301, the control circuit 130 outputs control signals UH, UL, WH, WL, VH, and VL to the drive circuit 110 based on the rotation speed signal, and causes the drive circuit 110 to output a drive current to the motor device 120. The motor 120 operates according to the driving current and drives the fan blades.

In step S302, when the motor device 120 is running, the control circuit 130 detects the states of the first switch Q1 and the second switch Q2 of one of the bridge arm units B1-B3. When the first switch Q1 and the second switch Q2 are both turned off, the control circuit 130 detects the detected voltage value between the first switch Q1 and the second switch Q2. In one embodiment, the control circuit 130 will periodically repeat step S302 to record a plurality of detected voltage values.

In step S303, the control circuit 130 determines the current information (e.g., current magnitude, current flow direction) of the driving current according to the detected voltage value. In one embodiment, the control circuit 130 detects the driving current outputted by the driving circuit 110 when the first switch Q1 and the second switch Q2 are both off, and records the driving current as a current curve (the driving current Ip shown in fig. 2A).

In step S304, the control circuit 130 continuously determines whether the driving current is smaller than a predetermined value (e.g., zero). If the driving current is not less than the predetermined value, step S303 is continued. In some embodiments, the drive current will pass through zero during the detection period.

In step S305, when the driving current is smaller than the predetermined value, the control circuit 130 controls/changes the control signals UH, UL, WH, WL, VH, and VL to maintain the first switch and the second switch in the off state for a fixed detection period.

In step S306, the control circuit 130 detects the back electromotive force of the motor device 120 during the detection period to obtain a plurality of detected electromotive force values, and calculates the return-to-zero time of the back electromotive force. In one embodiment, the control circuit 130 uses a variation characteristic line formed by a plurality of detected electromotive force values as a variation trend of the back electromotive force, and calculates the time to zero according to the slope thereof.

In step S307, the control circuit 130 determines the rotor position of the motor device 120 based on the calculated return-to-zero time. Then, the rotational speed signal or the control signal is adjusted according to the rotor position. The switching frequency of the control signals UH, UL, WH, WL, VH, VL will change accordingly, so that the current phase and the voltage phase of the motor device 120 can be close to each other to improve the operation efficiency.

In one embodiment, the motor system 100 performs the motor driving method in each cycle, so that the motor system 100 has good performance. The number of times the control circuit 130 detects the back electromotive force can be arbitrarily adjusted by a user, but the detection period Td is a fixed value. Since the zero time is calculated according to the variation characteristic lines of the detected electromotive forces, the control circuit 130 does not need to actually detect the time point at which the back electromotive force is zero. Accordingly, the abnormal operation caused by the long closing time of the first switch Q1 and the second switch Q2 can be avoided.

Various elements, method steps or technical features of the foregoing embodiments may be combined with each other without limiting the order of description or presentation in the drawings in the present disclosure.

Although the present disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure, and therefore, the scope of the disclosure should be determined by that defined in the appended claims.

Claims

1. A motor driving method, comprising:

detecting a detection voltage value between a first switch and a second switch in a driving circuit, wherein the driving circuit is electrically connected to a power supply and a motor device and is used for controlling the first switch and the second switch according to a switching frequency so as to provide a driving current to the motor device;

judging the driving current according to the detection voltage value;

when the driving current is smaller than a preset value, turning off the first switch and the second switch for a detection period, wherein the time length of the detection period is a fixed value;

detecting a back electromotive force of the motor device during the detection period to calculate a zeroing time of the back electromotive force; and

and adjusting the switching frequency according to the zeroing time.

2. The motor driving method according to claim 1, further comprising:

detecting the back electromotive force of the motor device during the detection period to obtain a plurality of detected electromotive force values; and

calculating the zeroing time of the back electromotive force according to the plurality of detected electromotive force values.

3. The motor driving method according to claim 2, wherein the driving current passes through a zero point during the detection.

4. The motor driving method as claimed in claim 3, wherein the method of calculating the return-to-zero time of the back electromotive force comprises:

obtaining a variation characteristic line according to the plurality of detected electromotive force values; and

calculating the zeroing time of the back electromotive force according to a slope of the change characteristic line.

5. The motor driving method according to claim 1, wherein the driving circuit comprises a plurality of bridge arm units, and the first switch and the second switch are located in the same one of the plurality of bridge arm units.

6. The motor driving method as claimed in claim 5, wherein the first switch and the second switch are turned off when the detected voltage value between the first switch and the second switch is detected.

7. The method as claimed in claim 1, wherein the switching frequency is a frequency of a PWM signal, and a time duration of the detection period is an integer multiple of a period of the PWM signal.

8. The method as claimed in claim 7, wherein the time length of the detection period is a fixed number of periods of the PWM signal.

9. The motor driving method as claimed in claim 1, wherein a current phase and a voltage phase of the motor device are varied according to the switching frequency.

10. The motor driving method as claimed in claim 1, wherein the motor device is a three-phase motor having three input nodes, and a detection node between the first switch and the second switch is connected to one of the three input nodes.

11. A motor system, comprising:

the driving circuit is electrically connected with a power supply and at least comprises a first switch and a second switch, wherein the driving circuit is used for generating a driving current;

a motor device electrically connected to the driving circuit for receiving the driving current; and

and the control circuit is electrically connected with the driving circuit and used for detecting a detection voltage value between the first switch and the second switch, wherein when the control circuit judges that the driving current value is smaller than a preset value according to the detection voltage value, the control circuit turns off the first switch and the second switch for a detection period so as to detect a reverse electromotive force of the motor device and calculate a zeroing time of the reverse electromotive force.

12. The motor system of claim 11, wherein the control circuit is configured to obtain a plurality of detected electromotive force values when detecting the back electromotive force of the motor device during the detection period, and calculate the zeroing time of the back electromotive force according to the detected electromotive force values.

13. The motor system of claim 12, wherein the drive current passes through zero during the sensing.

14. The motor system of claim 13, wherein the control circuit is further configured to obtain a variation curve according to the detected electromotive forces, and the control circuit calculates the zeroing time of the back electromotive force according to a slope of the variation curve.

15. The motor system of claim 11, wherein the driving circuit comprises a plurality of bridge arm units, the first switch and the second switch are located in a same one of the plurality of bridge arm units, and the control circuit controls the first switch and the second switch according to a switching frequency.

16. The motor system of claim 15, wherein the control circuit maintains the first switch and the second switch in an off state when detecting the detected voltage value between the first switch and the second switch.

17. The motor system of claim 15, wherein the switching frequency is a frequency of a pwm signal, and a time duration of the detection period is an integer multiple of a period of the pwm signal.

18. The motor system of claim 17, wherein the length of time of the detection period is a fixed number of periods of the pwm signal.

19. The motor system of claim 15, wherein the control circuit adjusts the switching frequency based on the zeroing time of the back emf.

20. The motor system of claim 19, wherein a current phase and a voltage phase of the motor device vary according to the switching frequency.