motor controller

Abstract

A motor controller has a switching circuit and a drive circuit. The switching circuit is coupled to a three-phase motor to drive the three-phase motor. The drive circuit generates a plurality of control signals to control the switching circuit. The motor controller utilizes a first pulse width modulation waveform and a second pulse width modulation waveform to drive the three-phase motor, wherein the first pulse width modulation waveform and the second pulse width modulation waveform have different frequencies. The motor controller utilizes the second pulse width modulation waveform to detect a commutation point, wherein the frequency of the first pulse width modulation waveform is greater than the frequency of the second pulse width modulation waveform.

Description

Technical Field

[0001] This invention relates to a motor controller, and more particularly to a motor controller applicable to sensorless three-phase motors. Background Technology

[0002] Traditionally, three-phase motors can be driven in two ways. One is by using Hall sensors to switch phases and thus drive the motor. The other is to drive the motor without Hall sensors. Because Hall sensors are easily affected by external environmental factors, leading to decreased sensing accuracy, and because installing Hall sensors increases system size and cost, sensorless driving methods have been proposed to solve these problems.

[0003] Figure 1 This is a timing diagram for an existing sensorless drive method. The pulse width modulation (PWM) signal Vpw has a duty cycle. Generally, the motor controller controls the motor speed by adjusting the duty cycle. In a sensorless drive method, the motor controller detects the back electromotive force (EMF) of the floating phase by comparing the floating phase pin voltage Vf with a reference voltage Vr, and then switches the phase. The motor controller can use the on-time interval of the PWM signal Vpw to detect the commutation point. Since the floating phase pin voltage Vf varies with the PWM signal Vpw, the timing of the PWM signal Vpw must be carefully considered to detect the correct commutation point. Figure 1 As shown, the motor controller detects the commutation point before the falling edge of the pulse width modulation signal Vpw. This is because after the rising edge of the pulse width modulation signal Vpw, the floating phase voltage Vf becomes unstable due to switching noise. Therefore, detecting the commutation point before the falling edge of the pulse width modulation signal Vpw ensures that the floating phase voltage Vf is in a most stable state. However, when the motor controller uses the on-time interval of the pulse width modulation signal Vpw to detect the commutation point, if the on-time interval is too short, the floating phase voltage Vf will not have enough time to stabilize, making it difficult to detect the back electromotive force of the floating phase. Summary of the Invention

[0004] In view of the aforementioned problems, the object of the present invention is to provide a motor controller that is easy to detect the back electromotive force of a floating phase.

[0005] According to the present invention, a motor controller is provided. The motor controller is used to drive a three-phase motor, wherein the three-phase motor has a first coil, a second coil, and a third coil. The motor controller includes a switching circuit, a driving circuit, and a pulse width modulation circuit. The switching circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a first terminal, a second terminal, and a third terminal, wherein the switching circuit is coupled to the three-phase motor to drive the three-phase motor. One terminal of the first coil is coupled to the first terminal. One terminal of the second coil is coupled to the second terminal. One terminal of the third coil is coupled to the third terminal. Furthermore, the other terminal of the first coil is coupled to the other terminal of the second coil and the other terminal of the third coil. That is, the first coil, the second coil, and the third coil are arranged in a Y-shape. The drive circuit generates a first control signal, a second control signal, a third control signal, a fourth control signal, a fifth control signal, and a sixth control signal to control the conduction status of the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, and the sixth transistor, respectively. The pulse width modulation circuit receives the first pulse width modulation signal and generates a second pulse width modulation signal to the drive circuit. The motor controller adjusts the speed of the three-phase motor according to the first pulse width modulation signal.

[0006] The driving circuit can generate a first voltage vector, a second voltage vector, a third voltage vector, a fourth voltage vector, a fifth voltage vector, and a sixth voltage vector to the switching circuit to turn on two of the first coil, the second coil, and the third coil. When the driving circuit generates the first voltage vector to the switching circuit, the driving circuit turns on the first transistor and the fourth transistor, and turns off the second transistor, the third transistor, the fifth transistor, and the sixth transistor, to sequentially turn on the first coil and the second coil. At this time, a floating phase is formed in the third coil. When the driving circuit generates the second voltage vector to the switching circuit, the driving circuit turns on the first transistor and the sixth transistor, and turns off the second transistor, the third transistor, the fourth transistor, and the fifth transistor, to sequentially turn on the first coil and the third coil. At this time, a floating phase is formed in the second coil. When the driving circuit generates the third voltage vector to the switching circuit, the driving circuit turns on the third and sixth transistors, and turns off the first, second, fourth, and fifth transistors, to sequentially turn on the second and third coils. At this time, a floating phase is formed in the first coil. When the driving circuit generates the fourth voltage vector to the switching circuit, the driving circuit turns on the second and third transistors, and turns off the first, fourth, fifth, and sixth transistors, to sequentially turn on the second and first coils. At this time, a floating phase is formed in the third coil. When the driving circuit generates the fifth voltage vector to the switching circuit, the driving circuit turns on the second and fifth transistors, and turns off the first, third, fourth, and sixth transistors, to sequentially turn on the third and first coils. At this time, a floating phase is formed in the second coil. When the drive circuit generates the sixth voltage vector to the switching circuit, the drive circuit will turn on the fourth and fifth transistors, and will not turn on the first, second, third, and sixth transistors, thereby sequentially turning on the third and second coils. At this time, the floating phase is formed in the first coil. Therefore, when the drive circuit switches phases according to the order of the first, second, third, fourth, fifth, and sixth voltage vectors, it can drive the three-phase motor to rotate one revolution forward. When the drive circuit switches phases according to the order of the sixth, fifth, fourth, third, second, and first voltage vectors, it can drive the three-phase motor to rotate one revolution reverse.

[0007] To reduce current ripple in the three-phase motor, the motor controller can use a high-frequency pulse-width modulation (PWM) waveform to drive the three-phase motor. When the motor controller activates a floating phase to detect a commutation point, it can switch to a low-frequency PWM waveform to drive the three-phase motor and use a conduction time interval of the low-frequency PWM waveform to detect the back electromotive force of the floating phase. That is, when the motor controller uses the conduction time interval to detect the commutation point, it avoids the conduction time interval being too short, thus making detection easier. According to an embodiment of the present invention, the motor controller uses a first PWM waveform and a second PWM waveform to drive the three-phase motor, wherein the first PWM waveform and the second PWM waveform have different frequencies. The motor controller uses the second PWM waveform to detect a commutation point during a detection time interval, wherein the frequency of the first PWM waveform is greater than the frequency of the second PWM waveform. The motor controller uses the first pulse-width modulation (PWM) waveform to drive the three-phase motor during a time interval outside the detection time interval. The designer can design a PWM signal that includes both the first and second PWM waveforms, wherein the PWM signal can be coupled to the drive circuit to adjust the speed of the three-phase motor. Furthermore, the motor controller can determine whether to switch phases by detecting the back electromotive force (EMF) of a floating phase. The motor controller can use a conduction time interval of the second PWM waveform to detect the back EMF of the floating phase. Attached Figure Description

[0008] Figure 1 This is a timing diagram for an existing sensorless driving method.

[0009] Figure 2 This is a schematic diagram of a motor controller according to an embodiment of the present invention.

[0010] Figure 3 This is a timing diagram of an embodiment of the present invention.

[0011] Figure labeling: 10 - Motor controller; VCC - Terminal; GND - Terminal; 100 - Switching circuit; 110 - Drive circuit; 120 - Pulse width modulation circuit; CMD - First pulse width modulation signal; Vp - Second pulse width modulation signal; 101 - First transistor; 102 - Second transistor; 103 - Third transistor; 104 - Fourth transistor; 105 - Fifth transistor; 106 - Sixth transistor; U - First terminal; V - Second terminal; W - Third terminal; C1 - First control signal; C2 - Second control signal; C3 - Third control signal; C4 - Fourth control signal; C5 - Fifth control signal; C6 - Sixth control signal; L1 - First coil; L2 - Second coil; L3 - Third coil; M - Three-phase motor; Vpw - Pulse width modulation signal; Vr - Reference voltage; Vf - Floating phase voltage; Su - First drive signal; Sv - Second drive signal; Sw - Third drive signal; Td - Detection time interval. Detailed Implementation

[0012] The objects, features, and advantages of the invention will become more apparent from the following description. Preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0013] Figure 2 This is a schematic diagram of a motor controller 10 according to an embodiment of the present invention. The motor controller 10 is used to drive a three-phase motor M, wherein the three-phase motor M has a first coil L1, a second coil L2, and a third coil L3. The motor controller 10 includes a switching circuit 100, a driving circuit 110, and a pulse width modulation circuit 120. The switching circuit 100 includes a first transistor 101, a second transistor 102, a third transistor 103, a fourth transistor 104, a fifth transistor 105, a sixth transistor 106, a first terminal U, a second terminal V, and a third terminal W, wherein the switching circuit 100 is coupled to the three-phase motor M to drive the three-phase motor M. The first terminal U, the second terminal V, and the third terminal W respectively provide a first driving signal Su, a second driving signal Sv, and a third driving signal Sw to drive the three-phase motor M. The first transistor 101 is coupled to a terminal VCC and a first terminal U, while the second transistor 102 is coupled to the first terminal U and a terminal GND. The third transistor 103 is coupled to terminal VCC and the second terminal V, while the fourth transistor 104 is coupled to the second terminal V and the terminal GND. The fifth transistor 105 is coupled to terminal VCC and the third terminal W, while the sixth transistor 106 is coupled to the third terminal W and the terminal GND. The first transistor 101, the third transistor 103, and the fifth transistor 105 can each be a P-type metal-oxide-semiconductor (MOSFET). The second transistor 102, the fourth transistor 104, and the sixth transistor 106 can each be an N-type MOSFET.

[0014] One end of the first coil L1 is coupled to the first end U. One end of the second coil L2 is coupled to the second end V. One end of the third coil L3 is coupled to the third end W. Furthermore, the other end of the first coil L1 is coupled to the other ends of the second coil L2 and the third coil L3. That is, the first coil L1, the second coil L2, and the third coil L3 are arranged in a Y-shape. The drive circuit 110 generates a first control signal C1, a second control signal C2, a third control signal C3, a fourth control signal C4, a fifth control signal C5, and a sixth control signal C6 to control the conduction of the first transistor 101, the second transistor 102, the third transistor 103, the fourth transistor 104, the fifth transistor 105, and the sixth transistor 106, respectively. The pulse width modulation circuit 120 receives a first pulse width modulation signal CMD and generates a second pulse width modulation signal Vp to the drive circuit 110. The motor controller 10 adjusts the speed of the three-phase motor M according to the first pulse width modulation signal CMD.

[0015] The driving circuit 110 can generate a first voltage vector, a second voltage vector, a third voltage vector, a fourth voltage vector, a fifth voltage vector, and a sixth voltage vector to the switching circuit 100 to turn on two of the first coil L1, the second coil L2, and the third coil L3. When the driving circuit 110 generates the first voltage vector to the switching circuit 100, the driving circuit 110 turns on the first transistor 101 and the fourth transistor 104, and does not turn on the second transistor 102, the third transistor 103, the fifth transistor 105, and the sixth transistor 106, to sequentially turn on the first coil L1 and the second coil L2. At this time, a floating phase is formed in the third coil L3. When the driving circuit 110 generates the second voltage vector to the switching circuit 100, the driving circuit 110 turns on the first transistor 101 and the sixth transistor 106, and does not turn on the second transistor 102, the third transistor 103, the fourth transistor 104, and the fifth transistor 105, to sequentially turn on the first coil L1 and the third coil L3. At this time, a floating phase is formed in the second coil L2. When the driving circuit 110 generates a third voltage vector to the switching circuit 100, the driving circuit 110 will turn on the third transistor 103 and the sixth transistor 106, and will not turn on the first transistor 101, the second transistor 102, the fourth transistor 104, and the fifth transistor 105, so as to sequentially turn on the second coil L2 and the third coil L3. At this time, a floating phase is formed in the first coil L1. When the driving circuit 110 generates a fourth voltage vector to the switching circuit 100, the driving circuit 110 will turn on the second transistor 102 and the third transistor 103, and will not turn on the first transistor 101, the fourth transistor 104, the fifth transistor 105, and the sixth transistor 106, so as to sequentially turn on the second coil L2 and the first coil L1. At this time, a floating phase is formed in the third coil L3. When the drive circuit 110 generates a fifth voltage vector to the switching circuit 100, the drive circuit 110 turns on the second transistor 102 and the fifth transistor 105, and turns off the first transistor 101, the third transistor 103, the fourth transistor 104, and the sixth transistor 106, so as to sequentially turn on the third coil L3 and the first coil L1. At this time, a floating phase is formed in the second coil L2. When the drive circuit 110 generates a sixth voltage vector to the switching circuit 100, the drive circuit 110 turns on the fourth transistor 104 and the fifth transistor 105, and turns off the first transistor 101, the second transistor 102, the third transistor 103, and the sixth transistor 106, so as to sequentially turn on the third coil L3 and the second coil L2. At this time, a floating phase is formed in the first coil L1. Therefore, when the drive circuit 110 switches phases according to the order of the first voltage vector, the second voltage vector, the third voltage vector, the fourth voltage vector, the fifth voltage vector, and the sixth voltage vector, it can drive the three-phase motor M to rotate one revolution forward.When the drive circuit 110 switches phases according to the order of the sixth voltage vector, the fifth voltage vector, the fourth voltage vector, the third voltage vector, the second voltage vector, and the first voltage vector, it can drive the three-phase motor M to reverse one revolution.

[0016] Figure 3 This is a timing diagram according to an embodiment of the present invention. The waveforms of the first driving signal Su, the second driving signal Sv, and the third driving signal Sw are all similar to an M-shaped waveform, but their phase angles differ by 120 degrees from each other. The second driving signal Sv lags the first driving signal Su by a phase angle of -120 degrees. The third driving signal Sw lags the second driving signal Sv by a phase angle of -120 degrees. For example, when the first driving signal Su is subtracted from the second driving signal Sv, a waveform similar to a sine wave is obtained. Therefore, the current waveform flowing through the first coil L1 and the second coil L2 will also be similar to this sine wave.

[0017] To reduce current ripple in the three-phase motor M, the motor controller 10 can use a high-frequency pulse-width modulation (PWM) waveform to drive the three-phase motor M. When the motor controller 10 activates a floating phase to detect a commutation point, it can switch to a low-frequency PWM waveform to drive the three-phase motor M and use a conduction time interval of the low-frequency PWM waveform to detect the back electromotive force of the floating phase. In other words, when the motor controller 10 uses the conduction time interval to detect the commutation point, it avoids the conduction time interval being too short, thus making detection easier. Figure 3 As shown, when the motor controller 10 detects back electromotive force within a detection time interval Td, it can avoid the conduction time interval being too short, thus improving the detection success rate. According to an embodiment of the present invention, the motor controller 10 uses a first pulse width modulation (PWM) waveform and a second PWM waveform to drive a three-phase motor M, wherein the first PWM waveform and the second PWM waveform have different frequencies. The motor controller 10 uses the second PWM waveform to detect the commutation point within the detection time interval Td, wherein the frequency of the first PWM waveform is greater than the frequency of the second PWM waveform. The motor controller 10 uses the first PWM waveform to drive the three-phase motor M during time intervals outside the detection time interval Td. The designer can design a PWM signal that has both a first PWM waveform and a second PWM waveform, wherein the PWM signal can be coupled to the drive circuit 110 to adjust the speed of the three-phase motor M. Furthermore, the motor controller 10 can determine whether to switch phases by detecting the back electromotive force of the floating phase. The motor controller 10 can use a conduction time interval of the second pulse width modulation waveform to detect the back electromotive force of the floating phase.

[0018] Specifically, the second pulse width modulation signal Vp can be a multi-frequency signal. When the motor controller 10 operates in a non-floating phase mode, the second pulse width modulation signal Vp can have a first frequency and a first pulse width modulation waveform to reduce the current ripple of the three-phase motor M. When the motor controller 10 operates in a floating phase mode, the second pulse width modulation signal Vp can have a second frequency and a second pulse width modulation waveform to improve the success rate of commutation point detection, wherein the first frequency is greater than the second frequency. The motor controller 10 can determine whether to switch phases by detecting the back electromotive force of the floating phase. When the motor controller 10 uses the on-time interval of the second pulse width modulation signal Vp to detect the commutation point, it can avoid the on-time interval being too small, thus making detection easier.

[0019] While the invention has been described by way of example with reference to preferred embodiments, it should be understood that the invention is not limited to the embodiments disclosed herein. Rather, the invention is intended to cover various modifications and similar configurations that will be apparent to those skilled in the art. Therefore, the scope of the claim should be interpreted in the broadest sense to include all such modifications and similar configurations.

[0020] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A motor controller for driving a three-phase motor, characterized in that, The motor controller includes: A switching circuit, coupled to the three-phase motor to drive the three-phase motor; and A drive circuit is used to generate multiple control signals to control the switching circuit. The motor controller uses a first pulse width modulation waveform and a second pulse width modulation waveform to drive the three-phase motor. The first pulse width modulation waveform and the second pulse width modulation waveform have different frequencies. The motor controller uses the second pulse width modulation waveform to detect a commutation point during a detection time interval. The motor controller uses the first pulse width modulation waveform to drive the three-phase motor during a time interval outside the detection time interval.

2. The motor controller as described in claim 1, characterized in that, The motor controller further includes a pulse width modulation signal having the first pulse width modulation waveform and the second pulse width modulation waveform, which is coupled to the drive circuit to adjust a speed of the three-phase motor.

3. The motor controller as described in claim 1, characterized in that, The motor controller uses the second pulse width modulation waveform to detect a back electromotive force of a floating phase.

4. The motor controller as described in claim 1, characterized in that, A frequency of the first pulse width modulation waveform is greater than a frequency of the second pulse width modulation waveform.

5. The motor controller as described in claim 1, characterized in that, The switching circuit includes a first terminal, a second terminal, and a third terminal, which respectively provide a first drive signal, a second drive signal, and a third drive signal to drive the three-phase motor.

6. The motor controller as described in claim 5, characterized in that, The switching circuit further includes: A first transistor is coupled to a fourth terminal and the first terminal; A second transistor is coupled to a fifth terminal and the first terminal; A third transistor is coupled to the fourth terminal and the second terminal; A fourth transistor is coupled to the fifth terminal and the second terminal; A fifth transistor is coupled to the fourth terminal and the third terminal; as well as A sixth transistor is coupled to the fifth terminal and the third terminal.

7. The motor controller as described in claim 5, characterized in that, The waveform of the first driving signal is similar to an M-shaped waveform, the waveform of the second driving signal is similar to the M-shaped waveform, and the waveform of the third driving signal is similar to the M-shaped waveform.

8. A motor controller for driving a three-phase motor, characterized in that, The motor controller includes: A switching circuit is coupled to the three-phase motor to drive the three-phase motor; A drive circuit for generating multiple control signals to control the switching circuit; and A pulse width modulation circuit is provided to receive a first pulse width modulation signal to generate a second pulse width modulation signal to the drive circuit. The second pulse width modulation signal is a multi-frequency signal. When the motor controller operates in a non-floating phase mode, the second pulse width modulation signal has a first frequency and a first pulse width modulation waveform. When the motor controller operates in a floating phase mode, the second pulse width modulation signal has a second frequency and a second pulse width modulation waveform.

9. The motor controller according to claim 8, characterized in that, The motor controller determines whether to switch phases by detecting the back electromotive force of a floating phase.

10. The motor controller as described in claim 8, characterized in that, The motor controller uses a conduction time interval of the second pulse width modulation signal to detect a commutation point.

11. The motor controller as described in claim 8, characterized in that, The first frequency is greater than the second frequency.

12. The motor controller as described in claim 8, characterized in that, The switching circuit includes a first terminal, a second terminal, and a third terminal, which respectively provide a first drive signal, a second drive signal, and a third drive signal to drive the three-phase motor.

13. The motor controller as described in claim 12, characterized in that, The switching circuit further includes: A first transistor is coupled to a fourth terminal and the first terminal; A second transistor is coupled to a fifth terminal and the first terminal; A third transistor is coupled to the fourth terminal and the second terminal; A fourth transistor is coupled to the fifth terminal and the second terminal; A fifth transistor is coupled to the fourth terminal and the third terminal; as well as A sixth transistor is coupled to the fifth terminal and the third terminal.

14. The motor controller as described in claim 12, characterized in that, The waveform of the first driving signal is similar to an M-shaped waveform, the waveform of the second driving signal is similar to the M-shaped waveform, and the waveform of the third driving signal is similar to the M-shaped waveform.

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