TWI691160B - Controller and control method of DC brushless motor - Google Patents

Abstract

A controller and control method 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 first resistor connected in series. Two resistors, each 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 corresponding voltage divider The first resistor and the second resistor are 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: three bias resistors, respectively connected to a bias voltage source A node of each voltage divider; a control circuit that detects the back electromotive force signal of each phase coil, and controls the voltage source to provide an offset voltage to the node of the corresponding voltage divider.

Description

Controller and control method of DC brushless motor

The invention relates to the brushless motor control technology; in particular, it refers to a controller and control method of a DC brushless motor, which can improve the problem of phase lag when using a DC brushless motor commutation circuit.

The sensorless drive technology currently applied to the commutation circuit of the brushless motor includes 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 obtain the zero-crossing point of the back-EMF by measuring the terminal voltage of the phase coil of the non-conducting phase and the virtual neutral voltage. However, predicting the correct commutation point is related to the characteristics of the motor. Therefore, when driving various types of motors with different parameters, it is more difficult to control and lacks.

In addition, the terminal voltage comparison estimation method is to obtain the commutation signal of the three-phase coil by measuring the terminal voltage of the three-phase coil and the change of the back electromotive force, for example, China Patent No. I290415 "No Sensor commutation circuit and three-phase commutation signal detection method", that is, using the terminal voltage comparison estimation method to obtain a pulse signal at a phase of 30 degrees behind the zero-crossing point of the back electromotive force 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 drive parameters. However, the back electromotive force of the commutation point of the foregoing terminal voltage comparison estimation method mostly needs to be filtered. , And it is easy to cause the commutation time delay (lagging), and generate a surge current, which in turn affects electromagnetic compatibility (EMC) and motor output efficiency. Therefore, how to change It is one of the research and development directions of the inventors to make good use of the phase lag problem when applying the motor control technology of the terminal voltage comparison estimation method.

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

In order to achieve the above object, the present invention provides a controller for a brushless DC motor, which is connected to a commutation circuit. The commutation circuit includes a three-component voltage divider and three comparators. Each of the voltage dividers includes: A first resistor and a second resistor connected in series, one end of each first resistor is 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 the positive input terminal of each comparator is connected to a node connecting the first resistor and the second resistor of the corresponding voltage divider, and the negative input terminal of each comparator is connected to the adjacent one The node connection of the voltage divider, the controller includes: three bias resistors, having an input terminal and an output terminal, each input terminal is connected to a voltage source, and each output terminal is respectively connected to each voltage divider; A control circuit electrically connected to the three-phase coils for detecting the back electromotive force signal of each phase coil, and controlling the voltage source to supply electric energy according to the detection result, so as to provide an offset voltage through a corresponding one of the bias resistors To the node corresponding to the voltage divider.

In order to achieve the above object, the present invention provides a control method of a DC brushless motor. The DC brushless motor is connected to a commutation circuit. The commutation circuit includes a three-component voltage divider and three comparators, each of the voltage dividers It includes a first resistor and a second resistor connected in series, one end of each first resistor is 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 And each of the comparator's The positive input terminal is connected to a node connecting the first resistor and the second resistor of the corresponding voltage divider, and the negative input terminal of each comparator is connected to the node of an adjacent one of the voltage divider The control method includes the following steps: supplying power to the DC brushless motor to operate the DC brushless motor; detecting the back electromotive force signal of each phase coil, and providing an offset voltage to the corresponding sub-point according to the detection result On the node of the compressor.

The effect of the present invention is that by detecting the back electromotive force signal of each phase coil, the offset voltage is provided to the node of the corresponding voltage divider at an appropriate timing point, so as to effectively compensate the problem of lagging or delay in commutation, and even achieve The effect of forced early commutation and phase advance control.

〔this invention〕

10: commutation circuit

12: Voltage divider

20: Controller

22: control circuit

C1, C2, C3: filter capacitor

HC, HB, HA: logical signal

M1, M2, M3: terminal voltage

N1, N2, N3: Node

N, N4: Neutral point

R1, R3, R5: the first resistance

R2, R4, R6: second resistance

R7, R8, R9: bias resistor

R10-R16: resistance

C4: capacitance

U1A, U1B, U1C: comparator

VM1, VM2, VM3: Back EMF signal

V1, V2, V3: voltage source

FIG. 1 is a schematic diagram of a controller, a three-phase coil of a brushless DC motor, and a commutation circuit according to an embodiment of the invention.

2 is a circuit diagram of the controller and the commutation circuit of the above embodiment.

Fig. 3 and Fig. 4 are timing diagrams of back EMF signals and logic signals.

5 to 7 are waveform diagrams of line voltage and phase current, revealing the difference in waveform before and after the offset voltage is compensated.

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.

In order to explain the present invention more clearly, an embodiment will be described in detail with reference to the drawings. Please refer to FIG. 1 and FIG. 2 for a brushless DC applied in an embodiment of the present invention The three-phase coils U, V, W of the motor, the commutation circuit 10 and the controller 20. In this embodiment, the three-phase coils U, V, W are Y-connected as an example, and in other embodiments, a delta-connected three-phase coil may also be used.

The operation phase sequence of the three-phase coils U, V, W of the DC brushless motor is usually controlled by a driver. For example, the driver may be, but not limited to, using multiple MOSFETs or multiple IGBTs Such as switching elements, and in one embodiment, six MOSFETs can be used to divide into three upper arm switches and three lower arm switches, and by controlling the on and off of these upper arm switches and lower arm switches, they are driven in sequence 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 voltage divider 12 includes a first resistor R1, R3, R5 and a second Resistors R2, R4, R6, one end of each of the first resistors R1, R3, R5 is respectively 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 input terminal of each comparator U1A, U1B, U1C is connected to the corresponding node N1, N2, N3 of the voltage divider 12, and the negative input terminal is connected to the adjacent node N1, N2, N3 of the voltage divider 12 . Furthermore, in this embodiment, the node N1 of the first voltage divider is connected to the negative input terminal of the first comparator U1A and the positive input terminal of the second comparator U1B; the second component voltage divider Is connected to the negative input of the second comparator U1B and the positive input of the third comparator U1C; the node N3 of the third voltage divider is connected to the negative input of the third comparator U1C and the first The positive input of the comparator U1A is connected. In an embodiment, the voltage divider 12 may be further provided with a filter capacitor C1, C2, C3, which may constitute an RC filter.

Through the design of the above-mentioned commutation circuit 10, each of the comparators U1A, U1B, U1C can obtain the back-EMF signals VM1, VM2, VM3 after the voltage division of two or two adjacent phase coils in the three-phase coil, and pass through the comparator U1A , U1B, U1C comparison operation to estimate the corresponding commutation logic signal, for example: please match Figure 2, Figure 3 and Table 1 below, in one embodiment, you can control the upper arm switches Q1, Q3, Q5 and The on and off states of the lower arm switches Q2, Q4, Q6 are switched to control the excitation timing and commutation sequence of the three-phase coils U, V, W; and the back-EMF signals VM1, VM2, VM3 of each phase coil pass through the comparator U1A , U1B, U1C After comparison operation, the logical signals HC, HB, HA that are 30 degrees behind the back electromotive force zero crossing can be obtained, and the phase difference between the logical signals HC, HB, HA is 60 degrees, due to the logical signal HC, HB, HA and the commutation signal sensed by the Hall sensor are also behind by a phase difference of 30 degrees. Therefore, it can be used as a commutation signal and can be divided into six conduction phase sequence angle intervals, respectively 0 degrees to 60 degrees, 60 degrees to 120 degrees, 120 degrees to 180 degrees, 180 degrees to 240 degrees, 240 degrees to 300 degrees, 300 degrees to 360 degrees, each phase sequence corresponds to a Hall state S1~S6.

However, in the actual situation, when sampling the back-EMF signal, it is usually accompanied by noise, which is likely to cause misjudgment of the commutation signal. After the back-EMF passes through the voltage divider, the comparator and other components, and the calculation time of the comparator and other components, etc. The impact will cause the commutation time to be delayed and lagging, resulting in a time difference between the estimated commutation signal and the actual commutation demand point, so that during commutation, a surge current will easily occur, except for the possibility of causing jitter when the motor is running In addition to the low output efficiency of the motor, it will also affect the electromagnetic compatibility.

Therefore, please refer to FIG. 2 again, the controller 20 provided by the present invention includes three bias resistors R7, R8, R9 and a control circuit 22, and each bias resistor R7, R8, R9 has an input terminal and An output terminal, each input terminal is connected to a voltage source V1, V2, V3, and each output terminal is connected to each node N1, N2, N3 of the voltage divider 12. The control circuit 22 is electrically connected to the three-phase coils U, V, W. The control circuit 22 can detect the back electromotive force signals of the phase coils U, V, W, and control the supply of the voltage sources V1, V2, V3 according to the detection results. The electrical energy is used to provide an offset voltage to the nodes N1, N2, and N3 of the corresponding voltage divider 12 through the corresponding bias resistors R7, R8, and R9.

The control method of the DC brushless motor to which the above controller is applied is that the DC brushless motor is firstly supplied with power so that the DC brushless motor operates to generate a counter electromotive force signal. For example, in one embodiment, one of the phase coils can be excited first, and then the next phase coil can be sequentially excited to achieve the brushless motor start-up operation procedure. Then, the control circuit 22 detects the back electromotive force signal of each of the phase coils, and the commutation order (sequence) of the phase coils U, V, W can be determined according to this, by which the control circuit 22 can detect or The control logic sequence that predicts the phase sequence when the motor is running, and provides the offset voltage to the nodes N1, N2, N3 of the corresponding voltage divider 12 according to the detection result to provide the offset voltage to the nodes N1, N2, N3 to change Back-EMF signals VM1, VM2, VM3 on nodes N1, N2, N3, so that comparators U1A, U1B, U1C can The back-EMF signals VM1, VM2, VM3 are compared in advance to output the commutation logic signals early, and the effects of forced early commutation, phase not lagging, and even phase leading control can be achieved.

For example, please refer to FIGS. 2 to 4. In one embodiment, the control circuit 22 can detect or predict the control logic sequence of the phase sequence when the motor is running. After the logical sequence control of the motor operation is completed in the previous phase sequence, a positive offset voltage is provided 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 logic signal control of the last phase sequence 60° to 120° is completed, the control circuit 22 will control the voltage source V2 to output electric energy in time to output a positive offset voltage to the phase coil through 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 in the interval of 120° to 240°. Therefore, when the comparator U1B compares the back-EMF signal VM1 of the node N1 and the back-EMF signal VM2 of the node N2 in the interval of 120° to 180°, the logic signal HC can be converted in advance to achieve the effect of early commutation. In addition, when the comparator U1C compares the back-EMF signal VM2 of the node N2 and the back-EMF signal VM3 of the node N3 in the interval 180° to 240°, the logic signal HB can be converted in advance to achieve the effect of early commutation.

In addition, when the logic signal control of the previous phase sequence 180° to 240° is completed in the interval 240°~360°, the control circuit 22 will output the control voltage source V1 at the appropriate time to output a power through 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 240° and 360°. A predetermined value. In this way, 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 converted in advance to achieve the effect of early commutation. When the comparator U1B compares the back-EMF signal VM1 of the node N1 and the back-EMF signal VM2 of the node N2 in the interval of 300° to 360°, the logic signal HC can be converted in advance to achieve the effect of early commutation.

In addition, when the logic signal control of the last phase sequence 300° to 360° is completed in the interval of 0° to 60°, the control circuit 22 will control the voltage source V3 to output power in time to output a voltage through the offset resistor R9. The positive offset voltage is applied to 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 0° and 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 converted in advance to achieve the effect of early commutation. In addition, 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 of 60° to 120°, the logic signal HA can be converted in advance to achieve the effect of early commutation.

In this way, the logical signals HC, HB, HA obtained in FIG. 4 will lead the logical signals HC, HB, HA shown in FIG. 3, for example, the phase is advanced to the point indicated by the vertical dotted line and arrow in FIG. 4, and the 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 according to the measured falling slope of the back-EMF signal, the magnitude of the voltage value, the magnitude of the phase current value, or the level of the motor speed. For example, if phase advance control is to be performed, the offset voltage value provided can be increased.

In addition, in one embodiment, the way for the control circuit 22 to determine which node N1, N2, N3 offset voltage to provide may also be: when the back-EMF signal of one of the phase coils is measured to rise to a predetermined threshold , Providing a positive offset voltage to the node of the voltage divider corresponding to the phase coil of the next phase sequence. For example, as shown in Figures 3 and 4, when the measured back-EMF signal VM3 rises to or exceeds a predetermined threshold in the interval 60° to 120°, a positive value is provided The offset voltage is given to the node N2 of the voltage divider 12 corresponding to the phase coil V of the next phase sequence, so that the back-EMF signal VM2 of the node N2 rises. When the measured back-EMF signal VM2 rises to a predetermined threshold in the interval 180°~240° or exceeds When the threshold is set, a positive offset voltage is provided to the node N1 of the voltage divider 12 corresponding to the phase coil U of the next phase sequence, so that the level of the back-EMF signal VM1 at the node N1 rises; Between 300° and 360°, when the measured back-EMF signal VM1 rises to a predetermined threshold or exceeds a predetermined threshold, a positive offset voltage is provided to the partial voltage corresponding to the phase coil W of the next phase sequence The node N3 of the device 12 causes the level of the back-EMF signal VM3 of the node N3 to rise. In this way, the effect of improving the phase lag or commutation in advance can also be achieved.

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

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

Through the design of the above controller and control method, by detecting the back electromotive force signal of each phase coil, and providing the offset voltage to the corresponding voltage divider node at the appropriate time point, it can effectively compensate the lag or delay of commutation Problems, or to achieve the effect of forced early commutation, phase advance control. Please refer to Figures 5 to 7 for waveforms of line voltage and phase current at different timebases. On the left side of imaginary line L is the waveform of line voltage and phase current before offset voltage compensation. On the imaginary line The right 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 becomes obviously symmetrical, and the surge of the phase current also effectively decreases.

In addition, in one embodiment, the way for the control circuit 22 to determine which node N1, N2, N3 offset voltage to provide may also be: when the control circuit 22 measures that the back-EMF signal of one of the coils 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 the logic signal control of the last phase sequence 0° to 60° is completed in the interval of 60° to 180°, or when the detected or predicted back-EMF signal VM3 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 level of the back-EMF signal VM1 at the node N1 drops, and thus, when the comparator U1A compares the back-EMF signal VM3 of the node N3 with the back-EMF signal VM1 of the node N1 at a range of 60° to 120°, the logic signal HA can be converted in advance , To achieve the effect of early commutation. In addition, when the comparator U1B compares the back-EMF signal VM1 of the node N1 with the back-EMF signal VM3 of the node N2 in the interval of 120°-180°, the logic signal HC can be converted in advance to achieve the effect of early commutation.

In addition, when the logic signal control of the last phase sequence 120°~180° is completed in the interval 180°~300°, or when the measured back electromotive force 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 level of the back-EMF signal VM3 at the node N3 decreases. 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 converted in advance to achieve the effect of early commutation. In addition, 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°-300°, the logic signal HA can be switched in advance to achieve the effect of early commutation.

In addition, when in the interval 300°~60°, after the completion of the previous phase sequence 240°~300° logic signal control, or when the measured back-EMF signal VM1 starts to rise or rises to a predetermined threshold, the control circuit 22 The voltage source V2 can be controlled in time 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 that the level of the back-EMF signal VM2 at the node N2 decreases. 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 of 300° to 360°, the logic signal HC can be converted in advance to achieve the effect of early commutation. In addition, when the comparator U1C compares the back-EMF signal VM3 of the node N3 with the back-EMF signal VM1 of the node N1 in the interval 360°~60°, the logic signal HB can be converted in advance to achieve the effect of early commutation.

In this way, the phases of the logic signals HC, HB, and HA can be advanced, which can effectively compensate the problem of backward or delayed commutation, or can achieve the effect of forced early commutation and phase advance control.

In addition, please refer to FIG. 10, in one embodiment, the controller further includes a compensation potential adjustment circuit, the compensation potential adjustment circuit includes three parallel resistors R13, R14, R15, each of the resistors R13, R14 , One end of R15 is connected to each of the three-phase coil Terminal voltages M1, M2, M3, the other end is connected to a neutral point, for example to a virtual neutral point N4, or it can also be directly connected to the actual neutral point N, the control circuit 22 is connected to the neutral point N4 Or N, the control circuit 22 adjusts the value of the output offset voltage based on the average voltage value of the neutral point N4 (or neutral point N), so that the speed of the brushless motor or the load Differently, the offset voltage to be compensated is adjusted adaptively to obtain better phase lead compensation or phase lag compensation.

In addition, in an embodiment, the control circuit may also measure the back electromotive force signal at the terminal voltage to determine how much offset voltage is provided to the node of which voltage divider. In addition, in an embodiment, the voltage source may be provided by a controller, or the controller controls one or more external voltage sources to output electrical energy. The above is only the preferred and feasible embodiments of the present invention, and any equivalent changes in applying the description of the present invention and the scope of patent application should be included in the patent scope of the present invention.

12: Voltage divider

22: control circuit

C1, C2, C3: filter capacitor

HC, HB, HA: logical signal

M1, M2, M3: terminal voltage

N1, N2, N3: Node

R1, R3, R5: the first resistance

R2, R4, R6: second resistance

R7, R8, R9: bias resistor

U1A, U1B, U1C: comparator

VM1, VM2, VM3: Back EMF signal

V1, V2, V3: voltage source

Claims (16)

A controller for a DC brushless motor is used to connect a commutation circuit. The commutation circuit includes a three-component voltage divider and three comparators. Each of the voltage dividers includes a first resistor and a first resistor connected in series. Two resistors, one end of each first resistor is 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 positive input terminal of the comparator A node connected to the first resistor and the second resistor of the corresponding voltage divider, the negative input terminal of each comparator is connected to the node of the adjacent voltage divider, the control The device includes: three bias resistors, having an input terminal and an output terminal, each input terminal is connected to a voltage source, and each output terminal is respectively connected to the node of each voltage divider; a control circuit, and The three-phase coils are electrically connected to detect the back-EMF signal of each phase coil, and control the voltage source to supply electrical energy according to the detection result, so as to provide an offset voltage to the corresponding sub-point through a corresponding one of the bias resistors On the node of the compressor. The controller of the brushless DC motor according to claim 1, wherein the control circuit detects the control logic sequence of the phase sequence when the brushless DC motor is running to predict the next commutation point and approach the commutation At this 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 pulses, and after the commutation is completed, the offset voltage is removed. The controller of the brushless DC motor according to claim 1, wherein the control circuit outputs the offset voltage through 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 electromotive force signal of one of the phase coils begins to decrease, a positive offset voltage is provided 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, voltage value or current value of the back-EMF signal. The controller of the brushless DC motor according to claim 1, wherein when the control circuit detects that the back electromotive force signal of one of the phase coils starts to rise, it provides a negative offset voltage to the phase coil of the previous phase sequence The node corresponding to 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 coil 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 the back electromotive force of one of the phase coils 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 includes a compensation potential adjustment circuit including three parallel resistors, and one ends of the resistors are respectively connected to the ends of the three-phase coil The other end of the voltage is connected to a neutral point; the control circuit is electrically connected to the neutral point and adjusts the value of the output offset voltage based on the average voltage value of the neutral point. A control method for a DC brushless motor. The DC brushless motor is connected to a commutation circuit. The commutation circuit includes a three-component voltage regulator and three comparators. Each of the voltage dividers includes a first resistor connected in series and A second resistor, one end of each first resistor is 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 the positive of each comparator The input terminal is connected to a node connecting the first resistor and the second resistor of the corresponding voltage divider, and the negative input terminal of each comparator is connected to the node of an adjacent one of the voltage divider, The control method includes the following steps: supplying power to the DC brushless motor to operate the DC brushless motor; detecting the back electromotive force signal of each phase coil, and providing an offset voltage to the corresponding divided voltage according to the detection result On that node of the device. The control method according to claim 12, wherein the commutation order of the phase coils is determined according to the back electromotive force signals of the phase coils, and when one of the phase coil back electromotive force signals is measured, it rises to a predetermined valve Value, provide a positive offset voltage to the node of the voltage divider corresponding to the phase coil of the next phase sequence. The control method according to claim 12, wherein the commutation order of the phase coils is determined according to the back electromotive force signals of the phase coils, and when one of the phase coil back electromotive force signals is measured, it rises to a predetermined valve Value, it provides a negative offset voltage to the node of the voltage divider corresponding to the phase coil of the previous phase sequence. The control method described in claim 12 includes the following steps: according to the control logic sequence of the phase sequence of the brushless DC motor during operation, to predict the next commutation point, and provide the deviation when approaching the commutation point Move the voltage to the node corresponding to the voltage divider. The control method according to claim 15, wherein the offset voltage is in the form of a pulse, and after the commutation is completed, the offset voltage is removed.

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