Motor system and operating method thereof

Abstract

A motor system and an operation method thereof are provided. The motor system comprises a brushless direct current motor, a driving circuit, a voltage division circuit, a change-over switch and an analog-to-digital converter. The brushless DC motor includes first to third coils, and the drive circuit includes first to third sets of switches. Each commutation has a set of switches to output a pulse width modulation drive voltage to the connected coil, another set of switches to couple the connected coil to ground, and a last set of switches to float the connected coil. The number of the voltage division circuits is three, and each voltage division circuit comprises a first resistor, a second resistor and a bypass diode. The first resistor includes a first terminal coupled to the coil. The second resistor comprises a first end coupled to the first resistor and a second end coupled to the change-over switch, so that the second end receives the control voltage or is grounded. The bypass diode is connected in parallel with the first resistor. The analog-to-digital converter receives the back electromotive force signal after voltage division from the second end of the first resistor to judge a back electromotive force zero crossing point so as to carry out commutation.

Description

Technical Field

[0001] The present invention relates to an electronic device, and in particular to a motor system and an operating method thereof. Background Art

[0002] Brushless direct current (BLDC) motors are widely used in robotics, computer equipment, medical equipment, automotive drives, pumps, and household appliances. Compared with traditional brushed motors, BLDC motors can improve efficiency, require less maintenance (no carbon brush and commutation plate wear problems), and can achieve a flat torque curve in all rated speed ranges.

[0003] Common BLDC motors provide three-phase configurations. Since the rotor of a BLDC motor rotates under the influence of the magnetic field of the stator coil, the position of the rotor must be tracked to effectively drive the rotor. The motor system can track the rotor position based on the zero-crossing point of the back EMF of the BLDC motor. However, in the related art, it is impossible to accurately detect the zero-crossing point of the back EMF when the back EMF voltage is close to zero. Summary of the invention

[0004] The embodiment provides a motor system, including a brushless DC motor, a drive circuit, a voltage divider circuit, a switch and an analog-to-digital converter. The brushless DC motor includes a first coil, a second coil and a third coil, and the first coil, the second coil and the third coil are coupled to each other at a neutral point. The drive circuit includes a first set of switches coupled to the first coil, a second set of switches coupled to the second coil, and a third set of switches coupled to the third coil. Each set of switches includes a semiconductor switch of an upper arm and a lower arm, and the semiconductor switch can be a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) for example, and each semiconductor switch has a parasitic diode or a flywheel diode in parallel. Each phase change has a set of switches to output a pulse width modulated drive voltage to the connected coil, another set of switches is used to couple the connected coil to the ground terminal, and the last set of switches is used to float the connected coil. There are three sets of voltage divider circuits, and each set of voltage divider circuits includes a first resistor, a second resistor and a bypass diode. The first resistor includes a first end and a second end, and the first end is coupled to the coil. The second resistor includes a first end coupled to the second end of the first resistor, and a second end coupled to the switch for selectively receiving a control voltage or a ground voltage. The bypass diode includes a first end (cathode) coupled to the first end of the first resistor, and a second end (anode) coupled to the second end of the first resistor. The three groups of voltage divider circuits can share a group of switches or a dedicated switch can be set for each voltage divider circuit. The analog-to-digital converter is coupled to the voltage divider circuit to receive a back electromotive force signal from the second end of the first resistor, to make the second end of the second resistor receive a control voltage or a ground voltage according to the pulse width modulation duty cycle, and to determine the back electromotive force zero crossing point according to the back electromotive force signal.

[0005] The embodiment also provides an operating method of a motor system, wherein the motor system includes a brushless DC motor, a drive circuit, a voltage divider circuit, a switching switch and an analog-to-digital converter, wherein the brushless DC motor includes a first coil, a second coil and a third coil, wherein the first coil, the second coil and the third coil are coupled to each other at a neutral point, wherein the drive circuit includes a first group of switches coupled to the first coil, a second group of switches coupled to the second coil, and a third group of switches coupled to the third coil, wherein each time a phase is changed, a group of switches outputs a pulse width modulated drive voltage to the connected coil, another group of switches is used to couple the connected coil to the ground terminal, and the last group of switches is used to float the connected coil. There are three groups of voltage divider circuits, each group of voltage divider circuits includes a first resistor, a second resistor and a bypass diode. The first resistor includes a first end coupled to the coil and a second end. The second resistor includes a first end coupled to the second end of the first resistor and a second end coupled to the switching switch for optionally receiving a control voltage or a ground voltage. The bypass diode includes a first end coupled to the first end of the first resistor and a second end coupled to the second end of the first resistor. The analog-to-digital converter is coupled to the voltage divider circuit. The method includes that in each switch switching state, the analog-to-digital converter receives a back electromotive force signal from the second end of the first resistor connected to the voltage divider circuit coupled to the secondary floating coil, the switching switch makes the second end of the second resistor receive the control voltage or the ground voltage according to the pulse width modulation duty cycle, and the analog-to-digital converter determines the back electromotive force zero crossing point based on the back electromotive force signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a motor system according to an embodiment of the present invention.

[0007] Figure 2 yes Figure 1 Flow chart of the operating method of the motor system.

[0008] Figure 3 show Figure 1 Schematic diagram of a motor system detecting a back-EMF zero-crossing point when the back-EMF signal is at a logic low level.

[0009] Figure 4 show Figure 1 Schematic diagram of a motor system detecting a back-EMF zero-crossing point when the back-EMF signal is at a logic high level.

[0010] Figure 5 show Figure 1 Waveform diagram of the back-EMF signal of the motor system.

[0011] Figure 6 is a schematic diagram of another motor system in an embodiment of the present invention.

[0012] Figure 7is a schematic diagram of another motor system in an embodiment of the present invention.

[0013] Figure 8 show Figure 1 Waveform diagram of the motor system.

[0014] The reference numerals are described as follows:

[0015] 1, 6, 7: Motor system

[0016] 10: Control circuit

[0017] 12: Driving circuit

[0018] 121: The first set of switches

[0019] 122: The second set of switches

[0020] 123: The third switch

[0021] 14: Brushless DC motor

[0022] 16, 16-1, 16-2, 66, 76: voltage divider circuit

[0023] 17,204: Power supply end

[0024] 18:Analog-to-digital converter

[0025] 19: Ground terminal

[0026] 20: Switching circuit

[0027] 200: Operation method

[0028] 202: switch control circuit

[0029] 60: Pull-up circuit

[0030] S202 to S208: Steps

[0031] D1 to D6: parasitic diodes

[0032] Db, Db1: first bypass diode

[0033] Db2: Second bypass diode

[0034] eu, ev and ew: back electromotive force

[0035] eun, evn and ewn: coil voltage

[0036] Ewn: Coil voltage after resistor voltage division

[0037] Ewn_H0, Ewn_L0: Back EMF zero-crossing level

[0038] GND: Ground voltage

[0039] I1, I2: current

[0040] Lu: First coil

[0041] Lv: Second coil

[0042] Lw: The third coil

[0043] N: Neutral point

[0044] Nv, Nu, Nw: nodes

[0045] R1: The first resistor

[0046] R2: Second resistor

[0047] S1 to S6: Control signal

[0048] SH1 and SH2, SL1 to SL3: Sampling

[0049] Ssw: switching signal

[0050] Su, Sv and Sw: driving signals

[0051] SW: Switch

[0052] t, t1 to t6: time

[0053] T1, T3, T5: upper arm switch

[0054] T2, T4, T6: Lower arm switch

[0055] V, VH, VL, VDC: voltage

[0056] VCC: Control voltage

[0057] VQ, VD: critical voltage DETAILED DESCRIPTION

[0058] Figure 1 1 is a schematic diagram of a motor system 1 according to an embodiment of the present invention. The motor system 1 may include a control circuit 10, a drive circuit 12, a brushless direct current (BLDC) motor 14, a voltage divider circuit 16, 16-1 and 16-2, an analog-to-digital converter (ADC) 18, and a switch circuit 20. The control circuit 10 may be coupled to the drive circuit 12, the drive circuit 12 may be coupled to the BLDC motor 14, the BLDC motor 14 may be coupled to the voltage divider circuit 16, 16-1 and 16-2, and the voltage divider circuit 16 may be coupled to the ADC 18 and the switch circuit 20.

[0059] The brushless DC motor 14 may include a rotor and a stator and may be operated by powering on three phases (U phase, V phase and W phase). The rotor may be equipped with a permanent magnet and may rotate or translate with an air gap between it and the stator. The stator may include a yoke, a coil Lu, a coil Lv and a coil Lw. The yoke may be cylindrical and may be arranged in a manner surrounding the rotor. The coil Lu, the coil Lv and the coil Lw may be distributed on the yoke, and the coil Lu, the coil Lv and the coil Lw may be coupled to each other at a neutral point N. In detail, the coil Lu may include a first end; and a second end, coupled to the neutral point N. Similarly, the coil Lv may include a first end; and a second end, coupled to the neutral point N. The coil Lw may include a first end; and a second end, coupled to the neutral point N.

[0060] The voltage divider circuit 16 can be coupled to the first end of the coil Lw. Figure 1 The embodiment only shows that the voltage divider circuit 16 is coupled to the analog-to-digital converter 18, but the present invention is not limited thereto. In some embodiments, the three voltage divider circuits 16, 16-1 and 16-2 of the motor system 1 can be respectively coupled to the first end of the coil Lw, the first end of the coil Lv and the first end of the coil Lu. In addition, the three voltage divider circuits 16, 16-1 and 16-2 can also be coupled to the analog-to-digital converter 18, and each is coupled to a corresponding switching switch. In other embodiments, the motor system 1 may also include a multiplexer, and the first end of the coil Lu, the first end of the coil Lv and the first end of the coil Lw can be coupled to the voltage divider circuit 16 via the multiplexer.

[0061] The drive circuit 12 can alternately excite two of the coils Lu, Lv and Lw in a predetermined order to form a rotating magnetic field, thereby driving the rotor to rotate. When the rotor rotates, the coils Lu, Lv and Lw can generate back electromotive forces (back EMF) eu, ev and ew respectively. Switching the direction of the current in the windings in a predetermined order to maintain a constant magnetic field direction and keep the rotor rotating or translating smoothly is called commutation. The analog-to-digital converter 18 can detect the back EMF zero crossing of the back EMF eu, ev or ew, and the control circuit 10 can determine the time point of commutation based on the back EMF zero crossing. The motor system 1 can accurately detect the back EMF zero crossing without using a sensor or a neutral point.

[0062] The driving circuit 12 may include a first set of switches 121 coupled to the coil Lu, a second set of switches 122 coupled to the coil Lv, and a third set of switches 123 coupled to the coil Lw. In detail, the first set of switches 121 may include an upper arm switch T1 and a lower arm switch T2, the second set of switches 122 may include an upper arm switch T3 and a lower arm switch T4, and the third set of switches 123 may include an upper arm switch T5 and a lower arm switch T6. The switches T1 to T6 may be N-type bipolar junction transistors (BJT). In some embodiments, the switches T1 to T6 may also be P-type transistors or other types of N-type transistors, such as N-type metal oxide semiconductor field-effect transistors (MOSFET). The upper arm switch T1 may include a control terminal coupled to the control circuit 10, a first terminal coupled to the power supply terminal 17, and a second terminal. The lower arm switch T2 may include a control terminal coupled to the control circuit 10; a first terminal coupled to the second terminal of the upper arm switch T1; and a second terminal coupled to the ground terminal 19. The upper arm switch T3 may include a control terminal coupled to the control circuit 10; a first terminal coupled to the power supply terminal 17; and a second terminal. The lower arm switch T4 may include a control terminal coupled to the control circuit 10; a first terminal coupled to the second terminal of the upper arm switch T3; and a second terminal coupled to the ground terminal 19. The upper arm switch T5 may include a control terminal coupled to the control circuit 10; a first terminal coupled to the power supply terminal 17; and a second terminal. The lower arm switch T6 may include a control terminal coupled to the control circuit 10; a first terminal coupled to the second terminal of the upper arm switch T5; and a second terminal coupled to the ground terminal 19. The power supply terminal 17 may provide a DC voltage VDC, such as 24V, and the ground terminal 19 may provide a ground voltage GND, such as 0V. The switches T1 to T6 may have body diodes D1 to D6 , respectively.

[0063] The control circuit 10 may include a microcontroller, a microprocessor, a field programmable gate array (FPGA) or other types of control circuits. The control circuit 10 may generate control signals S1 to S6 to control switches T1 to T6 respectively, thereby generating drive voltages Su, Sv and Sw, and further controlling the excitation of coils Lu, Lv and Lw respectively. When the motor system 1 is operating, the drive circuit 12 may excite two of coils Lu, Lv and Lw and the remaining one of the floating coils Lu, Lv and Lw to drive the rotor to rotate. For example, the control circuit 10 can generate a pulse width modulation (PWM) control signal S1 and a logic low control signal S2 to enable the first set of switches 121 to output a PWM drive voltage Su to the coil Lu and generate a logic low control signal S3 and a logic high control signal S4 to enable the second set of switches 122 to couple the coil Lv to the ground terminal 19 to excite the coil Lu and the coil Lv, and generate a logic low control signal S5 and a logic low control signal S6 to enable the third set of switches 123 to float the coil Lw.

[0064] Since the coil Lw is floating, the voltage ewn at the second end of the coil Lw (node ​​Nw) is not affected by the driving voltage Sw and directly reflects the change of the back electromotive force ew. However, since the neutral point signal is affected by the different switching states of the driving voltage Su in PWM ON and PWMOFF, the back electromotive force signal Ewn will also have two intervals: PWM on time (ON time) and PWM off time (OFF time). When the back electromotive force signal Ewn is in the PWM off time, the back electromotive force signal Ewn has a logic low level, and the voltage ewn at the node Nw can be expressed by the following formula (1):

[0065] ewn=1.5ew formula (1)

[0066] When the back electromotive force signal Ewn is at the PWM on time, the back electromotive force signal Ewn has a logic high level, and the voltage ewn of the node Nw can be expressed by the following formula (2):

[0067] ewn=0.5VDC+1.5ew formula (2)

[0068] According to formulas (1) and (2), the voltage ewn can be used to detect the back electromotive force zero crossing point. According to formula (1), when the back electromotive force signal Ewn is at the PWM off time and the back electromotive force zero crossing point (ew = 0V) occurs, the voltage ewn is 0V. According to formula (2), when the back electromotive force signal Ewn is at the PWM on time and the back electromotive force zero crossing point (ew = 0V) occurs, the voltage ewn is VDC / 2.

[0069] However, because the anode voltage of the parasitic diode D6 is equal to the ground voltage GND (0V), during the PWM cut-off time interval, if the voltage ewn of the node Nw is less than the voltage drop of the critical voltage of the parasitic diode D6 (e.g., 0.7V), the parasitic diode D6 will be turned on, and the voltage ewn of the node Nw will be clamped at -0.7V. This clamped voltage is then divided by the voltage divider circuit 16 to attenuate the back electromotive force voltage to a smaller value before being input to the ADC. Since the back electromotive force Ewn signal is small, it is easy to be interfered by circuit noise and misjudge the zero crossing point. For example, during the PWM cut-off time of the back electromotive force signal Ewn, the voltage ewn may be less than -0.7V, so the parasitic diode D6 will clamp the voltage ewn at the critical voltage of the parasitic diode (-0.7V), causing the subsequent circuit to be unable to determine whether the back electromotive force zero crossing is about to occur. After the back electromotive force ew is greater than -0.7V, if the sampling point of the voltage ewn is close to or exceeds the back electromotive force zero-crossing point, the subsequent circuit cannot accurately detect the back electromotive force zero-crossing point based on the voltage ewn.

[0070] The voltage divider circuit 16 may be further connected to a switch circuit 20. The switch circuit 20 may include a switch SW and a switch control circuit 202. The switch SW includes a control terminal coupled to the switch control circuit 202; a first terminal optionally coupled to the power supply terminal 204 or the ground terminal 19; and a second terminal coupled to the second terminal of the second resistor R2. The switch control circuit 202 may be coupled to the control circuit 10.

[0071] The voltage divider circuit 16 and the switch circuit 20 can adjust the voltage level of the back electromotive force signal Ewn at the PWM cut-off time to reduce or eliminate the influence of the parasitic diode D6, so that the back electromotive force signal Ewn can instantly reflect the actual back electromotive force ew change to accurately detect the back electromotive force zero crossing point. The voltage divider circuit 16 may include a first resistor R1, a second resistor R2 and a first bypass diode Db. The first resistor R1 includes a first end coupled to the coil Lw, and a second end. The second resistor R2 includes a first end coupled to the second end of the first resistor R1, and a second end for optionally receiving a control voltage VCC (e.g., 3.3V) or a ground voltage GND of the switch circuit 20. The first bypass diode Db includes a first end coupled to the first end of the first resistor R1, and a second end coupled to the second end of the first resistor R1. The first end of the first bypass diode Db is a cathode, and the second end of the first bypass diode Db is an anode. The critical voltage VD of the first bypass diode Db may be greater than the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6 of the third group of switches 123. For example, the critical voltage VD of the first bypass diode Db may be 1V, and the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6 may be 0.7V. The analog-to-digital converter 18 may be coupled to the second end of the first resistor R1, and may receive the back electromotive force signal Ewn from the second end of the first resistor R1 to determine the back electromotive force zero crossing point, and then perform a commutation operation. Specifically, once the back electromotive force zero crossing point is detected, the analog-to-digital converter 18 may transmit a notification message to the control circuit 10 to notify the control circuit 10 to perform a commutation operation. In some embodiments, the analog-to-digital converter 18 may also transmit the back electromotive force signal Ewn to the control circuit 10, and the control circuit 10 may determine the commutation timing based on the back electromotive force signal Ewn. In addition, the control circuit 10 may determine the pulse width modulation duty cycle, and then transmit the switch signal SW to the switch control circuit 202 based on the pulse width modulation duty cycle.

[0072] When the back electromotive force signal Ewn is at the PWM off time, the voltage at the second end of the second resistor R2 can be set to a high voltage (such as the control voltage VCC) to set the first bypass diode Db to a forward bias. Therefore, the back electromotive force signal Ewn can be expressed by the following formula (3):

[0073] Ewn=1.5ew+VD formula (3)

[0074] During the PWM on-time of the back electromotive force signal Ewn, the voltage at the second end of the second resistor R2 can be set to a low voltage (such as the ground voltage GND) to set the first bypass diode Db to a reverse bias voltage. Therefore, the back electromotive force signal Ewn can be expressed by the following formula (4):

[0075] Ewn= (0.5VDC+1.5ew) *R2 / (R1+R2) Formula (4)

[0076] The control circuit 10 can make the second end of the second resistor R2 receive the control voltage VCC or the ground voltage GND according to the pulse width modulation duty cycle. In detail, the control circuit 10 can transmit the switch signal Ssw to the switch control circuit 202 according to the pulse width modulation duty cycle, and the switch control circuit 202 can determine the switch state of Ssw according to the switch signal Ssw. In some embodiments, the switch control circuit 202 can set the switch signal Ssw to a logic high level when the back electromotive force signal Ewn is on during the PWM conduction time to couple the first end of the switch SW to the ground terminal 19, and set the switch signal Ssw to a logic low level when the back electromotive force signal Ewn is off during the PWM to couple the first end of the switch SW to the control voltage VCC, such as Figure 2 The operation method 200 is shown. The circuit configuration and operation of the voltage divider circuits 16-1 and 16-2 may be similar to the voltage divider circuit 16, and the description thereof may refer to the previous paragraphs, which will not be repeated here.

[0077] Figure 2 2 is a flow chart of the operation method 200 of the motor system 1. The operation method 200 includes steps S202 to S208, wherein steps S202 to S206 are used to set the voltage of the second end of the second resistor R2 according to the pulse width modulation drive signal, and step S208 is used to determine the back electromotive force zero crossing point. Any reasonable step change, sequence or adjustment falls within the scope of the present disclosure. Steps S202 to S208 are explained as follows:

[0078] Step S202: The analog-to-digital converter 18 receives the back electromotive force signal Ewn from the second end of the first resistor R1, and the control circuit 10 generates a PWM signal to determine whether the three sets of switches of the switch circuit 20 are turned on or off. The PWM on or off is reflected in whether the back electromotive force signal Ewn is a high level voltage or a low level voltage. If it is a high level voltage, continue to step S206; if it is a low level voltage, continue to step S204;

[0079] Step S204: The second end of the second resistor R2 receives the control voltage VCC;

[0080] Step S206: The second end of the second resistor R2 receives the ground voltage GND;

[0081] Step S208: The analog-to-digital converter 18 determines the back-electromotive force zero-crossing point according to the back-electromotive force signal Ewn.

[0082] The following combination Figures 3 to 5 The method of operation 200 is explained. Figure 5The waveform diagram of the back electromotive force signal Ewn of the motor system 1 is shown, wherein the horizontal axis is time t, the vertical axis is voltage V, the back electromotive force zero-crossing level Ewn_H0 is the zero-crossing level of the PWM on-time, and the back electromotive force zero-crossing level Ewn_L0 is the zero-crossing level of the PWM off-time. When the voltage of the back electromotive force signal Ewn is equal to the back electromotive force zero-crossing level Ewn_H0 or Ewn_L0, the analog-to-digital converter 18 determines that the back electromotive force zero-crossing is detected. In some embodiments, the back electromotive force zero-crossing level Ewn_H0 may be equal to 0.5VDC*R2 / (R1+R2), and the back electromotive force zero-crossing level Ewn_L0 may be equal to (VD). Figure 3 A schematic diagram showing the motor system 1 detecting a back-electromotive force zero-crossing point when the back-electromotive force signal Ewn is at a logic low level. Figure 4 A schematic diagram showing the motor system 1 detecting a back-electromotive force zero-crossing point when the back-electromotive force signal Ewn is at a logic high level.

[0083] First reference Figure 5 At time t1, the control circuit 10 determines that the back electromotive force signal Ewn is at a logic high level (step S202), and thus sets the switch signal Ssw to couple the first end of the switch SW to the ground terminal 19 to output the ground voltage GND to the second end of the second resistor R2, forming Figure 4 The circuit is configured (step S206), the back electromotive force signal Ewn is received from the second end of the first resistor R1 to obtain a high level sample sH1, and the back electromotive force zero point is determined according to the high level sample sH1 (S208). Figure 4 , the upper arm switch T1 and the lower arm switch T4 are turned on, and the current I2 flows from the power supply terminal 17 through the coil Lu and the coil Lv to the ground terminal 19, so that the back electromotive force signal Ew is at a logic high level. When the second end of the second resistor R2 receives the ground voltage GND, the first resistor R1 and the second resistor R2 form a voltage divider, and the first bypass diode Db is reverse biased and does not conduct, so the back electromotive force signal Ewn is the divided voltage of the voltage ewn. Figure 5 Since the high level sample sH1 is less than the back electromotive force zero crossing level Ewn_H0, the analog-to-digital converter 18 determines that the back electromotive force zero crossing is not detected.

[0084] At time t2, the control circuit 10 determines that the back electromotive force signal Ewn is at a logic low level (step S202), and thus sets the switch signal Ssw to couple the first end of the switch SW to the power supply terminal 17 to output the control voltage VCC to the second end of the second resistor R2, forming Figure 3 The circuit configuration (step S204) receives the back electromotive force signal Ewn from the second end of the first resistor R1 to obtain a low level sample sL1, and determines the back electromotive force zero point according to the low level sample sL1 (S208). Figure 3, the upper arm switch T1 is turned off and the lower arm switch T4 is turned on, and the current I1 flows from the parasitic diode D2 through the coil Lu and the coil Lv to the ground terminal 19, so that the back electromotive force signal Ew is at a logic low level. When the second end of the second resistor R2 receives the control voltage VCC, the first bypass diode Db is forward biased and turned on, and the first bypass diode Db forms a bypass of the resistor R1, so the voltage level of the back electromotive force signal Ewn is shifted up, and without the voltage division of the resistor R1, the back electromotive force signal Ewn can be prevented from being attenuated by the voltage divider circuit 16. Figure 5 Since the low level sampling sL1 is less than the back electromotive force zero crossing level Ewn_L0, the analog-to-digital converter 18 determines that the back electromotive force zero crossing is not detected.

[0085] At time t3, the switch circuit 20 determines that the back electromotive force signal Ewn is a logic low level through the control circuit 10 (step S202), so the switch signal Ssw is set to couple the first end of the switch SW to the power supply terminal 17 to output the control voltage VCC to the second end of the second resistor R2 (step S204), receive the back electromotive force signal Ewn from the second end of the first resistor R1 to obtain a low level sample sL2, and determine the back electromotive force zero point according to the low level sample sL2 (S208). Since the low level sample sL2 is equal to the back electromotive force zero crossing level Ewn_L0, the analog-to-digital converter 18 determines that the back electromotive force zero crossing has been detected.

[0086] At time t4, the switch circuit 20 determines that the back electromotive force signal Ewn is a logic high level through the control circuit 10 (step S202), so the switch signal Ssw is set to couple the first end of the switch SW to the ground terminal 19 to output the ground voltage GND to the second end of the second resistor R2 (step S206), receive the back electromotive force signal Ewn from the second end of the first resistor R1 to obtain a high level sample sH2, and determine the back electromotive force zero point according to the high level sample sH2 (S208). Since the high level sample sH2 is close to the back electromotive force zero-crossing level Ewn_H0, the analog-to-digital converter 18 determines again that the back electromotive force zero-crossing point has been detected, and notifies the control circuit 10 that the back electromotive force zero-crossing point has been detected.

[0087] At time t5, the switch circuit 20 determines the back electromotive force signal Ewn as a logic low level through the control circuit 10 (step S202), and thus sets the switch signal Ssw to couple the first end of the switch SW to the power supply terminal 17 to output the control voltage VCC to the second end of the second resistor R2 (step S204), receives the back electromotive force signal Ewn from the second end of the first resistor R1 to obtain a low level sample sL3, and determines the back electromotive force zero point according to the low level sample sL3 (S208). Since the low level sample sL3 is greater than the back electromotive force zero-crossing level Ewn_L0, the analog-to-digital converter 18 determines again that the back electromotive force zero-crossing point has been detected, and notifies the control circuit 10 that the back electromotive force zero-crossing point has been detected.

[0088] The control circuit 10 can perform commutation after a delay of 30 electrical degrees after the back electromotive force is detected to cross the zero point.

[0089] Although Figures 1 to 5 The embodiment only shows the detection of the back EMF zero-crossing point of the back EMF ew, the present invention is not limited to this, and those skilled in the art may also apply the present invention to the detection of the back EMF zero-crossing point of the back EMF eu and ev. In addition, although the embodiment discloses the detection of the back EMF zero-crossing point based on the high-level sampling and low-level sampling of the back EMF signal Ewn, the present invention is not limited to this, and those skilled in the art may also detect the back EMF zero-crossing point based only on the high-level sampling or low-level sampling of the back EMF signal Ewn. In some embodiments, when the duty cycle of the back EMF signal Ewn exceeds 50%, the motor system 1 may detect the back EMF zero-crossing point based only on the high-level sampling of the back EMF signal Ewn; when the duty cycle of the back EMF signal Ewn is less than 50%, the motor system 1 may detect the back EMF zero-crossing point based only on the low-level sampling of the back EMF signal Ewn, thereby increasing the sampling accuracy. During each PWM on and off period, the detection of the back EMF zero-crossing point is not limited to once.

[0090] Figures 1 to 5 The embodiment uses a bypass diode to prevent the back EMF signal Ewn from being attenuated by the voltage divider circuit 16 during the cut-off time of PWM, thereby reducing the back EMF signal Ewn, and to increase the DC level of the signal, so that the back EMF signal Ewn can instantly reflect the actual back EMF ew change, thereby accurately detecting the back EMF zero crossing point.

[0091] Figure 6 is a schematic diagram of another motor system 6 in an embodiment of the present invention. The difference between the motor system 6 and the motor system 1 is that the first bypass diode Db1 and the second bypass diode Db2 in the voltage divider circuit 66 are used to replace the first bypass diode Db in the voltage divider circuit 16. The following is an explanation of the difference between the motor system 6 and the motor system 1. The explanation of other components in the motor system 6 can be referred to the previous paragraphs and will not be repeated here.

[0092] The first bypass diode Db1 includes a first end coupled to the first end of the first resistor R1, and a second end. The second bypass diode Db2 includes a first end coupled to the second end of the first bypass diode Db, and a second end coupled to the second end of the first resistor R1. The critical voltage of the first bypass diode Db1 and the critical voltage of the second bypass diode Db2 may be greater than, equal to, or less than the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6. The cross voltage between the second end of the second bypass diode Db2 and the first end of the first bypass diode Db1 may be greater than the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6. For example, the critical voltage of the first bypass diode Db1 may be 0.6V, the critical voltage of the second bypass diode Db2 may be 0.6V, the cross voltage between the second end of the second bypass diode Db2 and the first end of the first bypass diode Db1 may be 1.2V, and the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6 may be 0.7V.

[0093] Since the voltage across the second end of the second bypass diode Db2 and the first end of the first bypass diode Db1 is greater than the critical voltage VQ of the parasitic diode D6 of the lower arm switch T6, the voltage divider circuit 66 can use a bypass diode with a smaller critical voltage to increase the Ewn voltage level at the cut-off time of PWM, thereby compensating for the effect of the parasitic diode D6 clamping the Ewn voltage at a negative potential, so that the back electromotive force signal Ewn can instantly reflect the actual change of the back electromotive force ew, thereby accurately detecting the zero crossing point of the back electromotive force.

[0094] Although the voltage divider circuit 66 only uses two stacked bypass diodes, those skilled in the art can apply the spirit of the present invention to configure other numbers of stacked bypass diodes in the voltage divider circuit 66 to meet actual needs.

[0095] Figure 7 is a schematic diagram of another motor system 7 in an embodiment of the present invention. The difference between the motor system 7 and the motor system 1 is that the pull-up circuit 60 in the voltage divider circuit 76 is used to replace the switch SW in the voltage divider circuit 16. The following is an explanation of the difference between the motor system 7 and the motor system 1. The explanation of other components in the motor system 7 can be referred to the previous paragraphs and will not be repeated here.

[0096] The pull-up circuit 60 is coupled to the analog-to-digital converter 18 and the second end of the second resistor R2. The analog-to-digital converter 18 is used to control the pull-up circuit 60 to output the control voltage VCC to the second end of the second resistor R2 when the back electromotive force signal Ewn is at a logic low level; and can control the pull-up circuit 60 to output the ground voltage GND to the second end of the second resistor R2 when the back electromotive force signal Ewn is at a logic high level.

[0097] The pull-up circuit 60 may include a microprocessor or a transistor. In some embodiments, the pull-up circuit 60 may include a microprocessor coupled to the second end of the second resistor R2 and the analog-to-digital converter 18, for receiving the switch signal Ssw to output the control voltage VCC or the ground voltage GND to the second end of the second resistor R2. The pull-up circuit 60 may be integrated with the control circuit 10 into a single chip. In other embodiments, the pull-up circuit 60 may include a pull-up transistor and a pull-down resistor, the pull-down resistor including a first end coupled to the second end of the second resistor R2; and a second end coupled to the ground terminal 19. The pull-up transistor includes a control end coupled to the control circuit 10 for receiving the switch signal Ssw; a first end coupled to the control voltage VCC; and a second end coupled to the second end of the second resistor R2. When the back electromotive force signal Ewn is at a logic high level, the control circuit 10 can output a logic low level in the switch signal Ssw so that the second end of the second resistor R2 receives the ground voltage GND; when the back electromotive force signal Ewn is at a logic low level, the analog-to-digital converter 18 can output a logic high level in the switch signal Ssw so that the second end of the second resistor R2 receives the control voltage VCC.

[0098] The voltage divider circuit 76 can use a bypass diode to increase the Ewn voltage level at the PWM cut-off time to compensate for the effect of the parasitic diode D6 clamping the Ewn voltage at the negative potential diode, so that the back electromotive force signal Ewn can instantly reflect the actual back electromotive force ew change, thereby accurately detecting the back electromotive force zero crossing point.

[0099] Figure 8 The waveform diagram of the back electromotive force signal Ewn of the motor system 1 is shown, wherein the horizontal axis is time t and the vertical axis is voltage. The back electromotive force signal Ewn may include PWM pulses, oscillating between the voltage VDC and 0V. In some embodiments, the voltage VDC is equal to the external input drive power voltage.

[0100] At time t1, the motor system 1 undergoes commutation. During the PWM off period, the switch circuit 20 outputs a logic low-level switch signal Ssw, so that the second end of the second resistor R2 still receives the control voltage VCC. The voltage of the back-electromotive force signal Ewn generates a voltage higher than VD due to the coil inductance current freewheeling effect. Since it is a predictable state, it can be eliminated by a logic program. At time t2, the back-electromotive force signal Ewn drops to near zero, indicating that the phase coil inductance has been discharged to zero. Thereafter, during the PWM off period, because the ewn back-electromotive force signal is clamped by the D6 diode, and the critical voltage VQ of D6 is close to the VD voltage, the Ewn voltage is maintained near 0V during the PWM off period.

[0101] At time t3, the low level voltage of the back electromotive force signal Ewn increases and the D6 diode is turned off, and Ewn can receive the unattenuated ewn back electromotive force signal. Between time t3 and time t4, the low level of the back electromotive force signal Ewn gradually increases from 0V. At time t4, the low level of the back electromotive force signal Ewn reaches (VD), so the motor system 1 detects the back electromotive force zero crossing point.

[0102] The motor system and operation method in the embodiment of the present invention adjusts its voltage level at the PWM cut-off time so that the diode can detect the signal change of the back-electromotive force signal ewn below the zero level, so that the back-electromotive force signal Ewn instantly reflects the actual back-electromotive force ew change to accurately detect the back-electromotive force zero crossing point.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A motor system, characterized in that: include: A brushless DC motor comprises a first coil, a second coil and a third coil, wherein the first coil, the second coil and the third coil are coupled to each other at a neutral point; The driving circuit includes: A first set of switches, coupled to the first coil, for outputting a pulse width modulation driving signal to the first coil; A second set of switches is coupled to the second coil and is used to couple the second coil to the ground; and A third set of switches is coupled to the third coil and used to float the third coil; The voltage divider circuit comprises: A first resistor including a first end coupled to the third coil, and a second end; A second resistor including a first end coupled to the second end of the first resistor, and a second end for selectively receiving a control voltage or a ground voltage; and A first bypass diode includes a first end coupled to the first end of the first resistor and a second end coupled to the second end of the first resistor; and The analog-to-digital converter is coupled to the voltage divider circuit, and is used to receive a back electromotive force signal from the second end of the first resistor, enable the second end of the second resistor to receive the control voltage or the ground voltage according to the back electromotive force signal, and determine the back electromotive force zero crossing point according to the back electromotive force signal.

2. The motor system according to claim 1, characterized in that: The voltage divider circuit is coupled to a switch circuit, and the switch circuit includes: switch control circuit; and Switches, including: A control terminal coupled to the switch control circuit; A first terminal, optionally coupled to a power supply terminal or the ground terminal; and The second end is coupled to the second end of the second resistor.

3. The motor system according to claim 2, characterized in that: The motor system also includes: The control circuit is coupled to the analog-to-digital converter and the switch control circuit, and is used for coupling the first end of the switch to the power supply end to output the control voltage to the second end of the second resistor when the back electromotive force signal is at a logic low level.

4. The motor system according to claim 2, characterized in that: The motor system also includes: The control circuit is coupled to the analog-to-digital converter and the switch control circuit, and is used for coupling the first end of the switch to the ground end to output the ground voltage to the second end of the second resistor when the back electromotive force signal is at a logic high level.

5. The motor system according to claim 1, characterized in that: The voltage divider circuit further includes a pull-up circuit coupled to the analog-to-digital converter and the second end of the second resistor.

6. The motor system according to claim 5, characterized in that: The analog-to-digital converter is used for controlling the pull-up circuit to output the control voltage to the second end of the second resistor when the back electromotive force signal is at a logic low level.

7. The motor system according to claim 5, characterized in that The analog-to-digital converter is used for controlling the pull-up circuit to output the ground voltage to the second end of the second resistor when the back electromotive force signal is at a logic high level.

8. The motor system according to claim 1, characterized in that: The critical voltage of the first bypass diode is greater than the critical voltage of the parasitic diode of the lower arm switch of the third set of switches; The first end of the first bypass diode is a cathode; and The second end of the first bypass diode is an anode.

9. The motor system according to claim 1, characterized in that: The voltage divider circuit also includes a second bypass diode, including a first end coupled to the second end of the first bypass diode, and a second end coupled to the second end of the first resistor, and a voltage across the second end of the second bypass diode to the first end of the first bypass diode is greater than a critical voltage of a parasitic diode of a lower arm switch of the third set of switches.

10. An operating method of a motor system, the motor system comprising a brushless DC motor, a drive circuit, a voltage divider circuit and an analog-to-digital converter, the brushless DC motor comprising a first coil, a second coil and a third coil, the first coil, the second coil and the third coil being coupled to each other at a neutral point, the drive circuit comprising a first set of switches coupled to the first coil for outputting a pulse width modulation drive signal to the first coil, a second set of switches coupled to the second coil for coupling the second coil to a ground terminal, and a third set of switches coupled to the The third coil is used to float the third coil. The voltage divider circuit includes a first resistor, a second resistor and a bypass diode. The first resistor includes a first end coupled to the third coil and a second end. The second resistor includes a first end coupled to the second end of the first resistor and a second end for selectively receiving a control voltage or a ground voltage. The bypass diode includes a first end coupled to the first end of the first resistor and a second end coupled to the second end of the first resistor. The analog-to-digital converter is coupled to the voltage divider circuit, characterized in that: The method includes: The analog-to-digital converter receives a back electromotive force signal from the second end of the first resistor; The analog-to-digital converter enables the second end of the second resistor to receive the control voltage or the ground voltage according to the back electromotive force signal; and The analog-to-digital converter determines a back electromotive force zero-crossing point according to the back electromotive force signal.

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