Motor controller

Abstract

A motor controller comprises a switching circuit, a driver circuit, and a pulse-width modulation circuit. The switching circuit is coupled to a three-phase motor to drive the three-phase motor. The driver circuit generates a plurality of control signals to control the switching circuit. The pulse-width modulation circuit receives a first pulse-width modulation signal and generates a second pulse-width modulation signal to the driver circuit, wherein the first pulse-width modulation signal has a first duty cycle and the second pulse-width modulation signal has a second duty cycle. When the motor controller activates a floating phase to detect a back electromotive force of the floating phase, the motor controller sets the second duty cycle to be greater than or equal to a minimum value.

Description

Technical Field

[0001] The present invention relates to a motor controller, and more particularly to a motor controller applicable to a sensorless three-phase motor. Background Art

[0002] Traditionally, three-phase motors can be driven in two ways. One uses Hall sensors to switch phases and drive the motor. The other is to drive the motor without Hall sensors. Because Hall sensors are susceptible to environmental influences, resulting in reduced sensing accuracy, and adding Hall sensors increases system size and cost, sensorless drive methods have been proposed to address these issues.

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

[0004] In view of the aforementioned problems, an object of the present invention is to provide a motor controller that can easily detect a 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 has a switching circuit, a driving circuit, and a pulse width modulation circuit. The switching circuit has 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. In addition, 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. In other words, the first coil, the second coil, and the third coil are arranged in a Y-shaped manner. The driving 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 for controlling the conduction 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 a first pulse width modulation signal to generate a second pulse width modulation signal to the driving circuit, wherein the first pulse width modulation signal has a first duty cycle and the second pulse width modulation signal has a second duty cycle.

[0006] The driver 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 switch circuit, respectively, to conduct two of the first coil, the second coil, and the third coil. When the driver circuit generates the first voltage vector to the switch circuit, the driver circuit conducts the first and fourth transistors, and disables the second, third, fifth, and sixth transistors, to sequentially conduct the first and second coils. In this case, a floating phase is formed in the third coil. When the driver circuit generates the second voltage vector to the switch circuit, the driver circuit conducts the first and sixth transistors, and disables the second, third, fourth, and fifth transistors, to sequentially conduct the first and third coils. In this case, a floating phase is formed in the second coil. When the driver circuit generates the third voltage vector to the switch circuit, the driver circuit turns on the third and sixth transistors, and turns off the first, second, fourth, and fifth transistors, to sequentially conduct the second and third coils. A floating phase is now formed in the first coil. When the driver circuit generates the fourth voltage vector to the switch circuit, the driver circuit turns on the second and third transistors, and turns off the first, fourth, fifth, and sixth transistors, to sequentially conduct the second and first coils. A floating phase is now formed in the third coil. When the driver circuit generates the fifth voltage vector to the switch circuit, the driver circuit turns on the second and fifth transistors, and turns off the first, third, fourth, and sixth transistors, to sequentially conduct the third and first coils. A floating phase is now formed in the second coil. When the driver circuit generates the sixth voltage vector to the switching circuit, the driver circuit turns on the fourth and fifth transistors and turns off the first, second, third, and sixth transistors, sequentially turning on the third and second coils. At this point, a floating phase is formed in the first coil. Therefore, when the driver circuit switches phases according to the order of the first, second, third, fourth, fifth, and sixth voltage vectors, the three-phase motor can be driven to rotate forward one revolution. When the driver circuit switches phases according to the order of the fourth, fifth, sixth, first, second, and third voltage vectors, the three-phase motor can be driven to rotate counterclockwise one revolution.

[0007] When the motor controller activates the floating phase to detect the back EMF of the floating phase, it limits the second duty cycle so that it is greater than or equal to a minimum value to prevent the on-time interval of the second PWM signal from being too short. Therefore, when the motor controller detects the back EMF of the floating phase during the on-time interval, detection is facilitated and the detection success rate is increased. Depending on the application, the minimum value can be set to 10%, 20%, or another appropriate value. When the motor controller is not operating in a floating phase mode, the motor controller keeps the second duty cycle relative to the first duty cycle, thereby adjusting the speed of the three-phase motor. When the motor controller detects a back EMF during a detection time interval, the motor controller determines whether to limit the second duty cycle based on the magnitude of the second duty cycle. For example, if the second duty cycle is less than a predetermined value, the motor controller limits the second duty cycle to the predetermined value. When the motor controller operates in a non-detection time interval, the motor controller causes the second working cycle to change along with the first working cycle, thereby performing a function of adjusting a rotation speed of the three-phase motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a timing diagram of a conventional sensorless driving method.

[0009] Figure 2 FIG. 1 is a schematic diagram of a motor controller according to an embodiment of the present invention.

[0010] Figure 3 FIG. 1 is a timing diagram of an embodiment of the present invention.

[0011] Explanation of the accompanying symbols: 10-motor controller; VCC-endpoint; GND-endpoint; 100-switching circuit; 110-driving 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 endpoint; V-second endpoint; W-third endpoint; 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 pin voltage; Su-first drive signal; Sv second drive signal; Sw third drive signal; Td-detection time interval. DETAILED DESCRIPTION

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

[0013] Figure 2 The figure shows 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. 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 drive signal Su, a second drive signal Sv, and a third drive signal Sw to drive the three-phase motor M. The first transistor 101 is coupled to a terminal VCC and the 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 the 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 the 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 third transistor 103 can each be a P-type metal oxide semiconductor transistor. The second transistor 102, the fourth transistor 104, and the sixth transistor 106 can each be an N-type metal oxide semiconductor transistor.

[0014] One end of the first coil L1 is coupled to the first terminal U. One end of the second coil L2 is coupled to the second terminal V. One end of the third coil L3 is coupled to the third terminal W. Furthermore, the other end of the first coil L1 is coupled to the other end of the second coil L2 and the other end of the third coil L3. In other words, the first coil L1, the second coil L2, and the third coil L3 are arranged in a Y-shape. The driving 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 driving circuit 110. The first pulse width modulation signal CMD has a first duty cycle, and the second pulse width modulation signal Vp has a second duty cycle.

[0015] The driver 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 switch circuit 100, respectively, to conduct two of the first coil L1, the second coil L2, and the third coil L3. When the driver circuit 110 generates the first voltage vector to the switch circuit 100, the driver circuit 110 turns on the first transistor 101 and the fourth transistor 104, and turns off the second transistor 102, the third transistor 103, the fifth transistor 105, and the sixth transistor 106, to sequentially conduct the first coil L1 and the second coil L2. A floating phase is then formed in the third coil L3. When the driver circuit 110 generates the second voltage vector to the switch circuit 100, the driver circuit 110 turns on the first transistor 101 and the sixth transistor 106, and turns off the second transistor 102, the third transistor 103, the fourth transistor 104, and the fifth transistor 105, to sequentially conduct the first coil L1 and the third coil L3. At this time, a floating phase is formed in the second coil L2. When the driver circuit 110 generates a third voltage vector to the switch circuit 100, the driver circuit 110 turns on the third transistor 103 and the sixth transistor 106, and turns off the first transistor 101, the second transistor 102, the fourth transistor 104, and the fifth transistor 105, 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 driver circuit 110 generates a fourth voltage vector to the switch circuit 100, the driver circuit 110 turns on the second transistor 102 and the third transistor 103, and turns off the first transistor 101, the fourth transistor 104, the fifth transistor 105, and the sixth transistor 106, 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 driver circuit 110 generates a fifth voltage vector to the switching circuit 100, the driver 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, to sequentially conduct the third coil L3 and the first coil L1. A floating phase is now formed in the second coil L2. When the driver circuit 110 generates a sixth voltage vector to the switching circuit 100, the driver 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, to sequentially conduct the third coil L3 and the second coil L2. A floating phase is now formed in the first coil L1. Therefore, when the driver 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, the three-phase motor M can be driven to rotate forward one revolution.When the driving circuit 110 switches the phases according to the sequence of the fourth voltage vector, the fifth voltage vector, the sixth voltage vector, the first voltage vector, the second voltage vector, and the third voltage vector, the three-phase motor M can be driven to rotate reversely for one revolution.

[0016] Figure 3 This is a timing diagram for one embodiment of the present invention. The waveforms of the first drive signal Su, the second drive signal Sv, and the third drive signal Sw all resemble an M-shaped waveform, but their phase angles differ by 120 degrees. The second drive signal Sv lags the first drive signal Su by a phase angle of 120 degrees. The third drive signal Sw lags the second drive signal Sv by a phase angle of 120 degrees. When the first drive signal Su is subtracted from the second drive signal Sv, a waveform similar to a sine wave is obtained. In other words, the current waveforms flowing through the first coil L1 and the second coil L2 will also resemble this sine wave.

[0017] Specifically, when the motor controller 10 starts a floating phase to detect a back electromotive force of the floating phase, the motor controller 10 limits the second duty cycle of the second pulse width modulation signal Vp so that the second duty cycle is greater than or equal to a minimum value to avoid a conduction time interval of the second pulse width modulation signal Vp being too small. Therefore, when the motor controller 10 detects the back electromotive force of the floating phase during the conduction time interval, the detection can be made easier and the success rate of the detection can be improved. Depending on different applications, the minimum value can be set to 10%, 20%, or other appropriate values. When the motor controller 10 is not operating in a floating phase mode, the motor controller 10 makes the second duty cycle of the second pulse width modulation signal Vp related to the first duty cycle of the first pulse width modulation signal CMD, thereby performing the function of adjusting the speed of the three-phase motor M. As Figure 3 As shown, when the motor controller 10 detects a back EMF during a detection time interval Td, the motor controller 10 determines whether to limit the second duty cycle based on the size of the second duty cycle. For example, when the second duty cycle is less than a predetermined value, the motor controller 10 limits the second duty cycle to the predetermined value. When the motor controller 10 operates during a non-detection time interval, the motor controller 10 causes the second duty cycle to vary with the first duty cycle, thereby adjusting the rotational speed of the three-phase motor M.

[0018] While the present invention has been described with reference to preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and similar arrangements that are apparent to those skilled in the art. Therefore, the scope of the claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

[0019] The above descriptions are merely preferred embodiments of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should fall within the scope of the present invention.

Claims

1. A motor controller for driving a three-phase motor having a first coil, a second coil, and a third coil, wherein: The motor controller includes: a switching circuit coupled to the three-phase motor, wherein the switching circuit includes a first terminal, a second terminal, and a third terminal, wherein the first terminal, the second terminal, and the third terminal respectively provide a first driving signal, a second driving signal, and a third driving signal to drive the three-phase motor; a driving circuit for generating a plurality of control signals to control the switch circuit; as well as A pulse width modulation circuit is used to receive a first pulse width modulation signal to generate a second pulse width modulation signal to the driving circuit, wherein the first pulse width modulation signal has a first duty cycle and the second pulse width modulation signal has a second duty cycle. When the motor controller activates a floating phase to detect a back electromotive force of the floating phase, the motor controller causes the second duty cycle to be greater than or equal to a minimum value. When the motor controller is not operating in a floating phase mode, the motor controller causes the second duty cycle to be related to the first duty cycle.

2. The motor controller according to claim 1, wherein: The motor controller detects the back electromotive force of the floating phase during an on-time interval of the second PWM signal.

3. The motor controller according to claim 1, wherein: The minimum value is set to 10%.

4. The motor controller according to claim 1, wherein: A waveform of the first driving signal is similar to an M-shaped waveform, a waveform of the second driving signal is similar to the M-shaped waveform, and a waveform of the third driving signal is similar to the M-shaped waveform.

5. The motor controller according to claim 1, wherein: One end of the first coil is coupled to the first end, one end of the second coil is coupled to the second end, and one end of the third coil is coupled to the third end.

6. The motor controller according to claim 1, wherein: The switching circuit further comprises: a first transistor coupled to a fourth terminal and the first terminal; a second transistor coupled to a fifth terminal and the first terminal; a third transistor coupled to the fourth terminal and the second terminal; a fourth transistor coupled to the fifth terminal and the second terminal; a fifth transistor 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. 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; a driving circuit for generating a plurality of control signals to control the switch circuit; and A pulse width modulation circuit is used to receive a first pulse width modulation signal to generate a second pulse width modulation signal to the driving circuit, wherein the first pulse width modulation signal has a first duty cycle and the second pulse width modulation signal has a second duty cycle. When the motor controller detects a back electromotive force during a detection time interval, the motor controller determines whether to limit the second duty cycle based on the size of the second duty cycle.

8. The motor controller according to claim 7, wherein: When the second duty cycle is less than a predetermined value, the motor controller limits the second duty cycle to be equal to the predetermined value.

9. The motor controller according to claim 7, wherein: When the motor controller operates in a non-detection time interval, the motor controller causes the second duty cycle to change along with the first duty cycle.

10. The motor controller according to claim 7, wherein: When the motor controller operates in a non-detection time interval, the motor controller performs a function of adjusting a rotation speed of the three-phase motor.

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