TWM581333U - Controller for direct-current brushless motor - Google Patents

Abstract

A controller for a brushless DC motor. The controller is connected to a commutation circuit. The commutation circuit includes three voltage dividers and three comparators. Each voltage divider includes a first resistor and a second resistor connected in series. The first resistor is connected to the corresponding terminal voltage of the three-phase coil of the DC brushless motor; each comparator includes a positive input terminal and a negative input terminal, and the positive input terminal of each comparator is connected to the first resistor of the corresponding voltage divider and The second resistor is connected to a node, and the negative input terminal of each comparator is connected to the node of an adjacent voltage divider. The controller includes: a three-bias resistor, which connects a bias source to each voltage divider. A control circuit that detects the back-EMF signals of the coils of each phase and controls the voltage source to provide an offset voltage to the node of the corresponding voltage divider.

Description

Controller of DC Brushless Motor

This creation is related to the brushless motor control technology; in particular, it refers to a controller of a DC brushless motor, which can improve the problem of phase lag when using a DC brushless motor commutation circuit.

The sensorless drive technologies currently used in commutation circuits of brushless motors include the back-EMF zero-crossing estimation method and the terminal voltage comparison estimation method.

Among them, the back-EMF zero-crossing point estimation method is to compare the terminal voltage of the phase coil with non-conducting phase and the virtual neutral voltage to obtain the back-EMF zero-crossing point; Therefore, when driving various types of motors with different parameters, it is more difficult to control and there are some defects.

In addition, the terminal voltage comparison estimation method is to compare the terminal voltage of the three-phase coil and the back-EMF change to obtain the commutation signal of the three-phase coil. For example, China's patent No. I290415 "Non-phase of three-phase brushless DC motor Sensor commutation circuit and three-phase commutation signal detection method "is to use the terminal voltage comparison estimation method to obtain a pulse signal with a phase of 30 degrees behind the zero-crossing point of the back-EMF, as a detection of the actual rotation of the brushless motor Commutation signal. The drive technology using the terminal voltage comparison estimation method does not require the relevant characteristic parameters of the motor, so it can be widely used in various types of motors with different driving parameters. However, most of the commutation point back-EMF of the terminal voltage comparison estimation method described above need to be filtered , And it is easy to cause the commutation time delay (lag), and generate a surge current, which will affect the electromagnetic compatibility (EMC) and motor output efficiency. Therefore, how to improve the phase lag problem when applying the motor control technology of the terminal voltage comparison estimation method is one of the research directions of new people.

In view of this, the purpose of this creation is to provide a controller of a brushless DC motor and a control method thereof, which can effectively improve the problem of phase lag and achieve the purpose of phase synchronization.

In order to achieve the above purpose, the present invention provides a controller of a brushless DC motor for connection to a commutation circuit. The commutation circuit includes a three-component voltage divider and three comparators, each of which includes A first resistor and a second resistor in series, one end of each of the first resistors is respectively connected to a corresponding terminal voltage of a three-phase coil of the DC brushless motor; each of the comparators includes a positive input terminal and a negative input terminal, And the positive input terminal of each comparator is connected to a node corresponding to the first resistor and the second resistor of the voltage divider, and the negative input terminal of each comparator is connected to an adjacent one The node of the voltage divider is connected, and the controller includes: a three-bias resistor having an input terminal and an output terminal, each of the input terminals is connected to a voltage source, and each of the output terminals is respectively connected to each of the voltage dividers; A control circuit is electrically connected to the three-phase coil to detect the back-EMF signal of each phase coil, and controls the voltage source to supply power according to the detection result, so as to provide an offset voltage through a corresponding bias resistor. to It should be of the node of the voltage divider.

The effect of this creation is that by detecting the back-EMF signals of the coils of each phase, the offset voltage is provided to the node of the corresponding voltage divider at an appropriate timing to effectively compensate the problems of backward or delayed commutation, and even reach Effect of forced advance commutation and phase advance control.

In order to explain this creation more clearly, an example is described in detail below with reference to the drawings. Please refer to FIG. 1 and FIG. 2, the three-phase coils U, V, W, the commutation circuit 10 and the controller 20 of the DC brushless motor applied in the embodiment of the present invention. In this embodiment, the three-phase coils U, V, and W are described by using the Y connection method as an example. In other embodiments, the three-phase coils using the Δ connection method may also be used.

The operation phase sequence of the three-phase coils U, V, and W of the brushless DC motor is usually controlled by a driver. For example, the driver may be, but is not limited to, using multiple MOSFETs or multiple IGBTs. And other switching elements, and in one embodiment, six MOSFETs can be used to divide into three upper arm switches and three lower arm switches, and control the on and off of these upper arm switches and lower arm switches in order to drive Each phase coil U, V, W is driven by a DC brushless motor.

The commutation circuit 10 basically includes a three-component voltage divider 12 and three comparators U1A, U1B, U1C. Each of the voltage divider 12 includes a first resistor R1, R3, R5 and a second resistor connected in series. Resistors R2, R4, R6, one end of each of the first resistors R1, R3, R5 is connected to the corresponding terminal voltages M1, M2, M3 of the three-phase coils U, V, W of the DC brushless motor, and each of the first The connection between the resistors R1, R3, R5 and each of the second resistors R2, R4, R6 is regarded as a node N1, N2, N3; each of the comparators U1A, U1B, U1C includes a positive input terminal and a negative input terminal, The positive inputs of each comparator U1A, U1B, U1C are connected to nodes N1, N2, N3 corresponding to voltage divider 12, and the negative input is connected to nodes N1, N2, N3 of an adjacent voltage divider 12. . Furthermore, in this embodiment, the node N1 of the first component voltage comparator is connected to the negative input terminal of the first comparator U1A and the positive input terminal of the second comparator U1B; The node N2 of the second comparator U1B is connected to the negative input terminal of the third comparator U1C; the node N3 of the third voltage comparator is connected to the negative input terminal of the third comparator U1C and the first The positive input of each comparator U1A is connected. In one embodiment, the voltage divider 12 may further be provided with filter capacitors C1, C2, and C3 to form an RC filter.

Through the design of the commutation circuit 10 described above, each of the comparators U1A, U1B, and U1C can obtain the back-EMF signals VM1, VM2, and VM3 of the three-phase coils after divided by two adjacent phase coils and pass through the comparator U1A , U1B, U1C comparison operation to estimate the corresponding commutation logic signal. For example, please cooperate with Figure 2, Figure 3, and Table 1 below. In one embodiment, you can control the upper arm switches Q1, Q3, Q5 and The lower arm switches Q2, Q4, and Q6 are switched on and off to control the excitation timing and commutation sequence of the three-phase coils U, V, and W; and the back-EMF signals VM1, VM2, and VM3 of each phase coil pass through the comparator U1A After comparing the calculations of U1B and U1C, the logical signals HC, HB, and HA with an electrical angle of 30 degrees behind the back EMF zero crossing can be obtained. The phase difference between the logical signals HC, HB, and HA is 60 degrees. HC, HB, HA and the commutation signals sensed by the Hall sensor are also 30 degrees behind the phase difference, so they can be used as commutation signals and can be divided into six conduction phase sequence angle intervals, which are 0 to 60 degrees, 60 to 120 degrees, 120 to 180 degrees, 180 to 240 degrees, 240 to 300 degrees, 300 to 360 degrees, A phase sequence corresponding Hall state S1 ~ S6. Table I Hall state S1 HALL STATE: Bin = 110: 6 VM1 ＞ VM2, HC = 1 VM2 ＞ VM3, HB = 1 VM3 ＜ VM1, HA = 0 Hall state S2 HALL STATE: Bin = 100: 4 VM1 ＞ VM2, HC = 1 VM2 ＜ VM3, HB = 0 VM3 ＜ VM1, HA = 0 Hall state S3 HALL STATE: Bin = 101: 5 VM1 ＞ VM2, HC = 1 VM2 ＜ VM3, HB = 0 VM3 ＞ VM1, HA = 1 Hall state S4 HALL STATE: Bin = 001: 1 VM1 ＜ VM2, HC = 0 VM2 ＜ VM3, HB = 0 VM3 ＞ VM1, HA = 1 Hall state S5 HALL STATE: Bin = 011: 3 VM1 ＜ VM2, HC = 0 VM2 ＞ VM3, HB = 1 VM3 ＞ VM1, HA = 1 Hall state S6 HALL STATE: Bin = 010: 2 VM1 ＜ VM2, HC = 0 VM2 ＞ VM3, HB = 1 VM3 ＜ VM1, HA = 0

However, in actual situations, when sampling the back-EMF signal, it is usually accompanied by noise, which easily leads to the misjudgment of the commutation signal. The back-EMF passes through the components such as the voltage divider and comparator, and the calculation time of the components such as the comparator. The impact will cause the commutation time to be delayed and lagging behind, resulting in a time gap between the estimated commutation signal and the actual commutation demand point, so that during commutation, a surge current will easily occur, except that it may cause jitter during motor operation In addition to low motor output efficiency, it will also affect electromagnetic compatibility.

Therefore, please refer to FIG. 2 again. The controller 20 provided in this work includes three bias resistors R7, R8, R9 and a control circuit 22. Each of the bias resistors R7, R8, R9 has an input terminal and An output terminal is connected to a voltage source V1, V2, V3, and each output terminal is connected to nodes N1, N2, N3 of the voltage divider 12. The control circuit 22 is electrically connected to the three-phase coils U, V, and W. The control circuit 22 can detect the back-EMF signals of the phase coils U, V, and W, and control the supply of the voltage sources V1, V2, and V3 according to the detection results. The electric energy is supplied to the nodes N1, N2, N3 of the corresponding voltage divider 12 by providing offset voltages through the corresponding bias resistors R7, R8, R9.

The control method of the DC brushless motor to which the above-mentioned controller is applied is to first supply power to the DC brushless motor so that the DC brushless motor operates to generate a back-EMF signal. For example, in one embodiment, one of the phase coils may be excited first, and then the next phase coil may be sequentially excited to achieve a brushless motor startup operation procedure. Then, the control circuit 22 detects the back-EMF signals of the phase coils, and the commutation order (sequence) of the phase coils U, V, and W can be determined based on this, so that the control circuit 22 can detect or Predict the control logic sequence of the phase sequence when the motor is running, and provide the offset voltage to the nodes N1, N2, N3 corresponding to the voltage divider 12 according to the detection result to provide the offset voltage to the nodes N1, N2, N3 to change The back-EMF signals VM1, VM2, VM3 on nodes N1, N2, N3, so that the comparators U1A, U1B, U1C can compare the back-EMF signals VM1, VM2, VM3 in advance to output the commutation logic signal in advance, and can achieve the mandatory The effects of early phase commutation, phase lag, and even phase advance control.

For example, with reference to FIGS. 2 to 4, in one embodiment, the control circuit 22 can detect or predict the phase control logic sequence when the motor is running. After the logic sequence control of the motor operation is completed in the previous phase sequence, a positive offset voltage is provided in a timely manner to the node of the voltage divider corresponding to the phase coil of the next phase sequence, for example, in the interval 120˚ ~ 240 In the middle, after the completion of the last phase sequence 60˚ to 120˚ logic signal control, the control circuit 22 will output the power in time to control the voltage source V2 to output a positive offset voltage to the phase coil via the offset resistor R8. The node N2 of the voltage divider 12 corresponding to V, thereby referring to FIG. 4, the back-EMF signal VM2 corresponding to the node N2 will rise by a predetermined value between the interval 120˚ to 240˚. Therefore, when the comparator U1B compares the back-EMF signal VM1 of the node N1 with the back-EMF signal VM2 of the node N2 in the interval 120˚ to 180˚, the logic signal HC can be switched in advance to achieve the effect of early commutation. When the comparator U1C compares the back-EMF signal VM2 of node N2 with the back-EMF signal VM3 of node N3 in the interval 180HB to 240˚, the logic signal HB can be switched in advance to achieve the effect of early commutation.

In addition, in the interval 240˚ ~ 360˚, after completing the previous phase sequence 180˚ to 240˚ logic signal control, the control circuit 22 will output the control voltage source V1 at an appropriate time to output a power via the offset resistor R7. The positive offset voltage reaches the node N1 of the voltage divider 12 corresponding to the phase coil U. Therefore, referring to FIG. 4, the back-EMF signal VM1 corresponding to the node N1 will rise between the range 240˚ to 360˚. A predetermined value. Therefore, when the comparator U1A compares the back-EMF signal VM3 of the node N3 with the back-EMF signal VM1 of the node N1 in the interval 240˚ to 300˚, the logic signal HA can be switched in advance to achieve the effect of early commutation. When the comparator U1B compares the back-EMF signal VM1 of the node N1 with the back-EMF signal VM2 of the node N2 in the interval 300˚ to 360˚, the logic signal HC can be switched in advance to achieve the effect of early commutation.

In addition, in the interval 0˚ ~ 60˚, after completing the previous phase sequence 300˚ to 360˚ logic signal control, at this time the control circuit 22 will control the voltage source V3 to output power in time to output a voltage via the offset resistor R9. The positive offset voltage reaches the node N3 of the voltage divider 12 corresponding to the phase coil V. Therefore, referring to FIG. 4, the back-EMF signal VM3 corresponding to the node N3 will rise between the interval 0˚ to 120˚. A predetermined value. Therefore, when the comparator U1C compares the back-EMF signal VM3 of the node N3 with the back-EMF signal VM2 of the node N2 in the interval 0˚ to 60˚, the logic signal HB can be switched in advance to achieve the effect of early commutation. When the comparator U1A compares the back-EMF signal VM3 of the node N3 with the back-EMF signal VM1 of the node N1 in the interval 60˚ to 120˚, the logic signal HA can be converted in advance to achieve the effect of early commutation.

As a result, the logic signals HC, HB, and HA obtained in Figure 4 will be ahead of the logic signals HC, HB, and HA shown in Figure 3. For example, the phase advances to the point indicated by the vertical dashed line and the arrow in Figure 4, and improvement can be achieved. Phase lag problem and the effect of early commutation.

In addition, the value of the provided offset voltage can be controlled by the control circuit 22 based on the measured slope of the back-EMF signal, the magnitude of the voltage value, the magnitude of the phase current, or the level of the motor speed. For example, if you want to perform phase advance control, you can increase the value of the offset voltage provided.

In addition, in an embodiment, the manner in which the control circuit 22 determines which node N1, N2, N3 offset voltage is to be provided may be: when the back-EMF signal of one of the phase coils is measured to rise to a predetermined threshold value , Providing a positive offset voltage to the node of the voltage divider corresponding to the phase coil of the next phase sequence. For example, please cooperate with Figures 3 and 4 to provide a positive value when the back-EMF signal VM3 rises to a predetermined threshold or exceeds a predetermined threshold in the interval 60˚ ~ 120˚. The offset voltage is applied to the node N2 of the voltage divider 12 corresponding to the phase coil V of the next phase sequence, so as to raise the level of the back electromotive force signal VM2 of the node N2. When the back-EMF signal VM2 rises to a predetermined threshold or exceeds the predetermined threshold in the interval 180˚ ~ 240 或, a positive offset voltage is provided to the corresponding phase coil U of the next phase sequence Node N1 of voltage divider 12 to raise the level of back electromotive force signal VM1 at node N1; when in the range 300˚ ~ 360˚, when the measured back electromotive force signal VM1 rises to a predetermined threshold or exceeds a predetermined threshold At this time, a positive offset voltage is provided to the node N3 of the voltage divider 12 corresponding to the phase coil W of the next phase sequence, so as to raise the level of the back electromotive force signal VM3 of the node N3. In this way, it can also achieve the effect of improving the backward phase or changing the phase in advance.

It is also mentioned that the length of the aforementioned offset offset voltage interval is not limited to 120 degrees. In one embodiment, the control circuit 22 can detect or predict the phase control logic sequence when the motor is running, and can borrow This predicts the occurrence time or position of the next commutation point, and is close to the commutation point or a short interval near the commutation point, such as but not limited to within 2 degrees, 5 degrees, 10 degrees, 15 degrees, Or another interval, an offset voltage is provided to the node of the corresponding voltage divider, and the offset voltage is removed after the commutation is completed. For example, when the commutation point is approached, a positive offset voltage in the form of a pulse wave (pulse) can be provided, so that the corresponding logic signal is converted in advance, and the effect of early commutation can be achieved.

In addition, in an embodiment, the control circuit of the controller may output offset voltages through the bias resistors in a predetermined sequence according to a preset program, for example, according to the bias resistor R7 → the bias resistor R8 → the bias voltage. The resistor R9 outputs the offset voltage in order. When using this controller, the user must connect the output of the bias resistor to the node of the corresponding voltage divider according to the commutation order of the phase coils. For example, when the preset program is based on the bias resistor When R7 → bias resistor R8 → bias resistor R9 sequentially output the offset voltage, the commutation sequence of the three-phase coil of the applied DC brushless motor is phase coil U → phase coil V → phase coil W , The user must first connect the output terminal of the bias resistor R7 to the node N1 of the voltage divider corresponding to the phase coil U, and connect the output terminal of the bias resistor R8 to the node of the voltage divider corresponding to the phase coil V N2, the output terminal of the bias resistor R9 is connected to the node N3 of the voltage divider corresponding to the phase coil W. In this way, the controller can provide the offset voltage to the voltage divider corresponding to each phase coil in the predetermined sequence.

Through the design of the above-mentioned controller and control method, by detecting the back-EMF signals of the coils of each phase, and providing the offset voltage to the nodes of the corresponding voltage divider at an appropriate timing, it can effectively compensate for the backward or delayed commutation. Problems, or to achieve the effect of forced advance commutation and phase advance control. Please refer to Figures 5 to 7 for the waveforms of the line voltage and phase current at different timebases. On the left side of the imaginary line L is the waveform of the line voltage and phase current before the offset voltage is compensated. The left side of L is the line voltage and phase current waveform after offset voltage compensation. It can be seen from the figure that after the offset voltage is compensated, the waveform of the line voltage obviously becomes evenly symmetric, and the surge of the phase current is also effectively reduced.

In addition, in an embodiment, the manner in which the control circuit 22 determines which node N1, N2, N3 offset voltage is to be provided may be: when the control circuit 22 detects that the back-EMF signal of one phase coil starts to rise, A negative offset voltage is provided to the node of the voltage divider corresponding to the phase coil of the previous phase sequence. For example, as shown in Figures 8 to 9, when in the interval 60˚ ~ 180˚, after completing the previous phase sequence 0˚ ~ 60˚ logic signal control, or when the back-EMF signal VM3 is detected or predicted, it starts. When rising or rising to a predetermined threshold, the control circuit 22 can timely control the voltage source V1 to provide a negative offset voltage to the node N1 of the voltage divider 12 corresponding to the phase coil U of the previous phase sequence, so that The back-EMF signal VM1 of node N1 is at a lower level, so that the comparator U1A compares the back-EMF signal VM3 of node N3 with the back-EMF signal VM1 of node N1 in the interval 60˚ ~ 120˚, so that the logic signal HA can be switched in advance To achieve the effect of early commutation. In the interval 1201 ~ 180˚, when the comparator U1B compares the back-EMF signal VM1 of node N1 with the back-EMF signal VM3 of node N2, the logic signal HC can be switched in advance to achieve the effect of early commutation.

In addition, when in the interval 180˚ ~ 300˚, after completing the previous phase sequence 120˚ ~ 180˚ logic signal control, or when it is measured that the back-EMF signal VM2 starts to rise or rises to a predetermined threshold, the control circuit 22 The voltage source V3 can be controlled in time to provide a negative offset voltage to the node N3 of the voltage divider 12 corresponding to the phase coil V of the previous phase sequence, so that the back-EMF signal VM3 of the node N3 drops to a level, thereby When the comparator U1C compares the back-EMF signal VM2 of node N2 with the back-EMF signal VM3 of node N3 in the interval 180˚ ~ 240˚, the logic signal HB can be switched in advance to achieve the effect of early commutation. In the interval 2401 ~ 300˚, when the comparator U1A compares the back-EMF signal VM3 of node N3 with the back-EMF signal VM1 of node N1, the logic signal HA can be converted in advance to achieve the effect of early commutation.

In addition, when in the interval 300 区间 ~ 60˚, after completing the previous phase sequence 240˚ ~ 300˚ logic signal control, or when it is detected that the back-EMF signal VM1 starts to rise or rises to a predetermined threshold, the control circuit 22 The voltage source V2 can be timely controlled to provide a negative offset voltage to the node N2 of the voltage divider 12 corresponding to the phase coil W of the previous phase sequence, so as to lower the level of the back-EMF signal VM2 of the node N2, thereby When the comparator U1B compares the back-EMF signal VM1 of node N1 with the back-EMF signal VM2 of node N2 in the interval 300˚ ~ 360˚, the logic signal HC can be switched in advance to achieve the effect of early commutation. In the interval 3601 ~ 60˚, when the comparator U1C compares the back-EMF signal VM3 of node N3 with the back-EMF signal VM1 of node N1, the logic signal HB can be switched in advance to achieve the effect of early commutation.

In this way, the phase of the logic signals HC, HB, and HA can also be advanced, and the problems of backward or delayed commutation can be effectively compensated, or the effects of forced early commutation and phase advance control can be achieved.

In addition, please cooperate with FIG. 10. In an embodiment, the controller further includes a compensation potential adjustment circuit. The compensation potential adjustment circuit includes three resistors R13, R14, and R15 connected in parallel, and each of the resistors R13, R14. One end of R15 is connected to the voltages M1, M2, and M3 of the three-phase coil, and the other end is connected to a neutral point, such as a virtual neutral point N4, or it can be directly connected to the actual neutral point. N, the control circuit 22 is connected to the neutral point N4 or N, and the control circuit 22 adjusts the value of the output offset voltage correspondingly based on the average voltage value of the neutral point N4 (or the neutral point N). According to the different speed or load of the brushless motor, the offset voltage to be compensated can be adaptively adjusted to obtain better phase advance compensation or phase backward compensation effect.

In addition, in an embodiment, the control circuit may also measure the back-EMF signal at the terminal voltage as a node to determine how much offset voltage is provided to which voltage divider. In addition, in an embodiment, the voltage source may be provided by a controller, or the controller may control one or more external voltage sources to output electric energy. The above description is only the preferred and feasible embodiment of this creation. For example, the equivalent changes of applying the description of this creation and the scope of patent application should be included in the scope of patent of this creation.

[This creation]

10‧‧‧ Commutation Circuit

12‧‧‧ Voltage Divider

20‧‧‧ Controller

22‧‧‧Control circuit

C1, C2, C3‧‧‧Filter capacitors

HC, HB, HA‧‧‧Logic signals

M1, M2, M3 ‧‧‧ terminal voltage

N1, N2, N3‧‧‧nodes

N, N4 ‧‧‧ neutral point

R1, R3, R5‧‧‧first resistor

R2, R4, R6‧‧‧Second resistor

R7, R8, R9‧‧‧ bias resistor

R10-R16‧‧‧Resistor

C4‧‧‧Capacitor

U1A, U1B, U1C‧‧‧ Comparator

VM1, VM2, VM3 ‧‧‧ Back-EMF signals

V1, V2, V3‧‧‧ voltage source

FIG. 1 is a schematic diagram of a controller, a three-phase coil of a DC brushless motor, and a commutation circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram of the controller and the commutation circuit of the above embodiment. Figures 3 and 4 are timing diagrams of back-EMF signals and logic signals. Figures 5 to 7 are waveform diagrams of line voltage and phase current, revealing waveform differences before and after offset voltage compensation. Figures 8 and 9 are timing diagrams of back-EMF signals and logic signals. FIG. 10 is a schematic circuit diagram showing that the neutral point average voltage is used to provide a compensation reference potential to the control circuit.

Claims (11)

A controller for a brushless DC motor is used to connect a commutation circuit. The commutation circuit includes a three-component voltage divider and three comparators. Each voltage divider includes a first resistor and a first resistor connected in series. Two resistors, one end of each of the first resistors is respectively connected to the corresponding terminal voltage of the three-phase coil of the DC brushless motor; each of the comparators includes a positive input terminal and a negative input terminal, and each of the comparator's positive input terminals A node connected to the first resistor and the second resistor corresponding to the voltage divider, and the negative input terminal of each comparator is connected to the node of an adjacent voltage divider. The control The device includes: a three-bias resistor having an input terminal and an output terminal, each of the input terminals is connected to a voltage source, and each of the output terminals is respectively connected to the node of each of the voltage dividers; a control circuit, and The three-phase coils are electrically connected to detect the back-EMF signals of the coils of each phase, and control the voltage source to supply power according to the detection results, so as to provide an offset voltage to the corresponding branch via a corresponding bias resistor. Press Node. The controller of the DC brushless motor as described in claim 1, wherein the control circuit detects the control logic sequence of the phase sequence when the DC brushless motor is running to predict the next commutation point and approach the commutation. At that point, the offset voltage is provided to the node corresponding to the voltage divider. The controller of the brushless DC motor according to claim 2, wherein the offset voltage is in the form of a pulse, and the offset voltage is removed after the commutation is completed. The controller of the brushless DC motor according to claim 1, wherein the control circuit outputs the offset voltage via each of the bias resistors according to a predetermined sequence. The controller of the brushless DC motor according to claim 1, wherein when the control circuit detects that the back-EMF signal of one of the phase coils starts to decrease, it provides a positive offset voltage to the phase of the previous phase sequence. The node of the voltage divider corresponding to the coil. The controller of the brushless DC motor according to claim 5, wherein the control circuit controls the output offset voltage value according to the measured falling slope of the back-EMF signal, the magnitude of the voltage value, or the magnitude of the current value. The controller of the brushless DC motor according to claim 1, wherein when the control circuit detects that the back-EMF signal of one of the phase coils starts to rise, a negative offset voltage is provided to the phase coil of the previous phase sequence The corresponding node of the voltage divider. The controller of the brushless DC motor according to claim 7, wherein the control circuit controls the output offset voltage value according to the measured rising slope, voltage value or current value of the back-EMF signal. The controller of the brushless DC motor according to claim 1, wherein the control circuit determines the commutation order of the phase coils according to the back electromotive force signals of the phase coils, and when one of the phase coils' back electromotive forces is measured When the signal rises to a predetermined threshold, a positive offset voltage is provided to the node of the voltage divider corresponding to the phase coil of the next phase sequence. The controller of the brushless DC motor according to claim 1, wherein the control circuit determines the commutation order of the phase coils according to the back electromotive force signals of the phase coils, and when one of the phase coils' back electromotive forces is measured When the signal rises to a predetermined threshold, a negative offset voltage is provided to the node of the voltage divider corresponding to the phase coil of the previous phase sequence. The controller of the brushless DC motor according to claim 1, comprising a compensation potential adjustment circuit. The compensation potential adjustment circuit includes three resistors connected in parallel, and one end of the resistors is connected to each of the three ends of the three-phase coil. Voltage, the other end is connected to a neutral point; the control circuit is electrically connected to the neutral point and correspondingly adjusts the value of the offset voltage output based on the average voltage value of the neutral point.