Motor drive device, drive assembly and electric tool

Abstract

The present disclosure relates to a motor drive device, a drive assembly and an electric tool, the device comprising a three-phase motor, a three-phase full-bridge inverter, a voltage detection module, a drive module and a control module, the drive module outputs a drive signal and a detection signal alternately in the Kth control cycle when the rotation speed of the three-phase motor is less than a preset rotation speed; the voltage detection module detects the first voltage of the third bridge arm when the drive signal is applied and the second voltage of the third bridge arm when the detection signal is applied; the control module is used to output a commutation signal after a delay when the first voltage and the second voltage are equal, so that the drive module adjusts the drive signal and the detection signal for commutation, and outputs the adjusted drive signal and the adjusted detection signal in the K+1th control cycle. The motor drive device of the embodiment of the present disclosure can realize torque retention when the three-phase motor is at a low speed, and detect the commutation point in real time for accurate commutation, thereby realizing precise control of the three-phase motor.

Description

Technical Field

[0001] The present disclosure relates to the field of motor control technology, and in particular to a motor drive device, a drive assembly and an electric tool. Background Art

[0002] The current position sensorless control lacks in-depth research on maintaining torque at low speed and heavy load. The use of grabbing the non-conducting opposite potential zero crossing cannot solve the problem of maintaining torque at low speed and heavy load, cannot achieve accurate phase change, and cannot achieve accurate control of low speed and heavy load electrodes. There are technical difficulties in solving the technical problems in situations where low speed and heavy load are required, such as electric drills and electric picks. Summary of the invention

[0003] In view of this, the present disclosure proposes a motor driving device, which includes a three-phase motor, a three-phase full-bridge inverter, a voltage detection module, a driving module and a control module.

[0004] The three-phase full-bridge inverter comprises a first bridge arm, a second bridge arm and a third bridge arm, each bridge arm comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm of each bridge arm are provided with transistors, and the three-phase full-bridge inverter is used to drive the three-phase motor;

[0005] The driving module is connected to each transistor of the three-phase full-bridge inverter, and is used to alternately output a driving signal and a detection signal in the Kth control cycle when the speed of the three-phase motor is less than a preset speed, wherein the driving signal is used to drive the upper bridge arm of the first bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, the lower bridge arm of the second bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect, and the detection signal is used to drive the upper bridge arm of the second bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, the lower bridge arm of the first bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect, wherein K is an integer;

[0006] The voltage detection module is connected between the upper bridge arm and the lower bridge arm of each bridge arm of the three-phase full-bridge inverter, and is used to detect the first voltage of the third bridge arm when the driving signal acts and the second voltage of the third bridge arm when the detection signal acts;

[0007] The control module is connected to the voltage detection module and the driving module, and is used to output a switching signal after a preset delay when the first voltage and the second voltage are equal, so that the driving module adjusts the driving signal and the detection signal for switching, and outputs the adjusted driving signal and the adjusted detection signal in the K+1th control cycle.

[0008] In a possible implementation, the voltage detection module includes a first voltage detection unit, a second voltage detection unit, and a third voltage detection unit, which are respectively connected between the upper bridge arm and the lower bridge arm of each phase of the three-phase full-bridge inverter, wherein each voltage detection unit includes a first detection resistor and a second detection resistor,

[0009] The first end of the first detection resistor is connected between the upper bridge arm and the lower bridge arm of the corresponding phase, and the second end of the first detection resistor is connected to the first end of the second detection resistor, for outputting a detection voltage;

[0010] A second terminal of the second detection resistor is grounded.

[0011] In a possible implementation, the control module is used to: when the first voltage and the second voltage are equal, determine that the angle rotated by the rotor of the three-phase motor is 30°, and determine the preset time length to be the time length of the delay of 30°.

[0012] In a possible implementation manner, the driving module is further configured to: when controlling the corresponding half-bridge switch in a PWM manner, control a duty cycle of the PWM to be less than or equal to 40%.

[0013] In a possible implementation, the three-phase full-bridge inverter includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a sixth transistor, wherein the first transistor and the fourth transistor constitute a first bridge arm, and the fourth transistor is a lower bridge arm, the second transistor and the fifth transistor constitute a second bridge arm, and the fifth transistor is a lower bridge arm, the third transistor and the sixth transistor constitute a third bridge arm, and the sixth transistor is a lower bridge arm, wherein the first ends of the windings of the three-phase motor are connected, and the second ends of the windings are respectively connected between the first transistor and the fourth transistor, between the second transistor and the fifth transistor, and between the third transistor and the sixth transistor.

[0014] In a possible implementation, the three-phase full-bridge inverter further includes a plurality of first input resistors, a plurality of second input resistors, and a plurality of input capacitors, and the stator of the three-phase motor includes a first winding, a second winding, and a third winding, wherein the gate of each transistor of the three-phase full-bridge inverter is electrically connected to the second end of the first input resistor, the first end of the second input resistor, and the first end of the input capacitor, the source of each transistor of the three-phase full-bridge inverter is electrically connected to the second end of the input capacitor and the second end of the second input resistor, and the first end of the first input resistor is used to input the drive signal or the detection signal,

[0015] The drain of the first transistor, the drain of the second transistor, and the drain of the third transistor are electrically connected, and the source of the fourth transistor, the source of the fifth transistor, and the source of the sixth transistor are electrically connected.

[0016] The source of the first transistor is electrically connected to the drain of the fourth transistor and the first end of the first winding, the source of the second transistor is electrically connected to the drain of the fifth transistor and the first end of the second winding, and the source of the third transistor is electrically connected to the drain of the sixth transistor and the first end of the third winding.

[0017] The second end of the first winding, the second end of the second winding, and the second end of the third winding are grounded.

[0018] In a possible implementation manner, the motor is a three-phase brushless DC motor.

[0019] According to another aspect of the present disclosure, a drive assembly is provided, and the motor drive device of the drive assembly is provided.

[0020] According to another aspect of the present disclosure, an electric tool is provided. The electric tool includes the drive assembly.

[0021] In the disclosed embodiment, when the speed of the three-phase motor is lower than the preset speed and is in the low-speed heavy-load mode, the driving module alternately outputs a driving signal and a detection signal in the Kth control cycle, so as to use the driving signal to drive the upper bridge arm of the first bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the second bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the detection signal to drive the upper bridge arm of the second bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the first bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the voltage ... The detection module detects the first voltage of the third bridge arm when the drive signal is applied and the second voltage of the third bridge arm when the detection signal is applied, and uses the control module to output a commutation signal after a preset delay when the first voltage and the second voltage are equal, so that the drive module adjusts the drive signal and the detection signal for commutation, and outputs the adjusted drive signal and the adjusted detection signal in the K+1th control cycle. The motor drive device of the embodiment of the present disclosure can achieve torque maintenance when the three-phase motor is at low speed, and detect the commutation point in real time for accurate commutation, thereby realizing precise control of the three-phase motor.

[0022] Further features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0024] Figure 1 A schematic diagram of a motor driving device according to an embodiment of the present disclosure is shown.

[0025] Figure 2 A schematic diagram of a motor driving device according to an embodiment of the present disclosure is shown.

[0026] Figure 3a A schematic diagram showing a magnetization curve of a stator core of a three-phase motor according to an embodiment of the present disclosure is shown. Figure 3b A schematic diagram showing a magnetization curve BH and a magnetic permeability curve μ-H of a ferromagnetic material used in a three-phase motor according to an embodiment of the present disclosure is shown.

[0027] Figure 4 A schematic diagram showing the relationship between the electronic inductance of a three-phase motor and the change in the angle between the magnetic potential generated by the armature winding and the permanent magnet magnetic potential according to an embodiment of the present disclosure is shown.

[0028] Figure 5a A schematic diagram of an equivalent circuit of a motor according to an embodiment of the present disclosure is shown.

[0029] Figure 5b A schematic diagram of an equivalent circuit of a motor according to an embodiment of the present disclosure is shown.

[0030] Figure 6a and Figure 6b A schematic diagram of a circuit for detecting motor running timing and pulse timing according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0031] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0032] In the description of the present disclosure, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present disclosure.

[0033] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present disclosure, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] In the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0035] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0036] In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present disclosure can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present disclosure.

[0037] See also Figure 1 , Figure 1 A schematic diagram of a motor driving device according to an embodiment of the present disclosure is shown.

[0038] like Figure 1 As shown, the device includes a three-phase motor 10, a three-phase full-bridge inverter 20, a voltage detection module 30, a drive module 40 and a control module 50.

[0039] The three-phase full-bridge inverter 20 includes a first bridge arm, a second bridge arm and a third bridge arm, each bridge arm includes an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm of each bridge arm are provided with transistors. The three-phase full-bridge inverter 20 is used to drive the three-phase motor 10;

[0040] The driving module 40 is connected to each transistor of the three-phase full-bridge inverter 20, and is used to alternately output a driving signal and a detection signal in the Kth control cycle when the speed of the three-phase motor 10 is less than a preset speed. The driving signal is used to drive the upper bridge arm of the first bridge arm in the three-phase motor 10 to switch in a pulse width modulation PWM mode, the lower bridge arm of the second bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect. The detection signal is used to drive the upper bridge arm of the second bridge arm in the three-phase motor 10 to switch in a pulse width modulation PWM mode, the lower bridge arm of the first bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect, wherein K is an integer;

[0041] The voltage detection module 30 is connected between the upper bridge arm and the lower bridge arm of each bridge arm of the three-phase full-bridge inverter 20, and is used to detect the first voltage of the third bridge arm when the driving signal acts and the second voltage of the third bridge arm when the detection signal acts;

[0042] The control module 50 is connected to the voltage detection module 30 and the driving module 40, and is used to output a switching signal after a preset delay when the first voltage and the second voltage are equal, so that the driving module 40 adjusts the driving signal and the detection signal for switching, and outputs the adjusted driving signal and the adjusted detection signal in the K+1th control cycle.

[0043] In the disclosed embodiment, when the speed of the three-phase motor is lower than the preset speed and is in the low-speed heavy-load mode, the driving module alternately outputs a driving signal and a detection signal in the Kth control cycle, so as to use the driving signal to drive the upper bridge arm of the first bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the second bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the detection signal to drive the upper bridge arm of the second bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the first bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the voltage ... The detection module detects the first voltage of the third bridge arm when the drive signal is applied and the second voltage of the third bridge arm when the detection signal is applied, and uses the control module to output a commutation signal after a preset delay when the first voltage and the second voltage are equal, so that the drive module adjusts the drive signal and the detection signal for commutation, and outputs the adjusted drive signal and the adjusted detection signal in the K+1th control cycle. The motor drive device of the embodiment of the present disclosure can achieve torque maintenance when the three-phase motor is at low speed, and detect the commutation point in real time for accurate commutation, thereby realizing precise control of the three-phase motor.

[0044] It should be noted that each module and unit of the embodiment of the present disclosure may be implemented by a hardware circuit, or by using a general hardware circuit in combination with relevant existing logic.

[0045] First, possible implementations of the three-phase full-bridge inverter 20 are exemplarily introduced. It should be noted that the present disclosure does not limit possible implementations of the three-phase full-bridge inverter 20. In other implementations, the three-phase full-bridge inverter 20 may also have other implementations.

[0046] The following is an exemplary introduction to possible implementations of each module.

[0047] See also Figure 2 , Figure 2 A schematic diagram of a motor driving device according to an embodiment of the present disclosure is shown.

[0048] like Figure 2 As shown, the three-phase full-bridge inverter 20 may include a first transistor Q1, a second transistor Q2, a third transistor Q3, a fourth transistor Q4, a fifth transistor Q5, and a sixth transistor Q6, wherein the first transistor Q1 and the fourth transistor Q4 constitute a first bridge arm, and the fourth transistor Q4 is a lower bridge arm, the second transistor Q2 and the fifth transistor Q5 constitute a second bridge arm, and the fifth transistor Q5 is a lower bridge arm, the third transistor Q3 and the sixth transistor Q6 constitute a third bridge arm, and the sixth transistor Q6 is a lower bridge arm, wherein one end of each winding of the three-phase motor 10 is electrically connected, and the other end of each winding is electrically connected between the first transistor Q1 and the fourth transistor Q4, between the second transistor Q2 and the fifth transistor Q5, and between the third transistor Q3 and the sixth transistor Q6.

[0049] In a possible implementation, the first transistor Q1, the second transistor Q2, the third transistor Q3, the fourth transistor Q4, the fifth transistor Q5, and the sixth transistor Q6 may be metal-oxide-semiconductor field-effect transistors (MOSFET) and insulated gate bipolar transistors (IGBT), wherein the transistors may be implemented based on silicon carbide SiC and gallium nitride GaN to improve performance.

[0050] In the disclosed embodiment, one control cycle corresponds to one commutation.

[0051] In one possible implementation, Figure 2As shown, the three-phase full-bridge inverter 20 may further include multiple first input resistors, multiple second input resistors, and multiple input capacitors to filter the input signal. The stator of the three-phase motor 10 includes a first winding A, a second winding B, and a third winding C. The gates of the transistors of the three-phase full-bridge inverter 20 are electrically connected to the second end of the first input resistor, the first end of the second input resistor, and the first end of the input capacitor. The sources of the transistors of the three-phase full-bridge inverter 20 are electrically connected to the second end of the input capacitor and the second end of the second input resistor. The first end of the first input resistor is used to input a control signal.

[0052] The drain of the first transistor Q1, the drain of the second transistor Q2, and the drain of the third transistor Q3 are electrically connected, and the source of the fourth transistor Q4, the source of the fifth transistor Q5, and the source of the sixth transistor Q6 are electrically connected.

[0053] The source of the first transistor Q1 is electrically connected to the drain of the fourth transistor Q4 and the first end of the first winding, the source of the second transistor Q2 is electrically connected to the drain of the fifth transistor Q5 and the first end of the second winding, and the source of the third transistor Q3 is electrically connected to the drain of the sixth transistor Q6 and the first end of the third winding.

[0054] A second end of the first winding A, a second end of the second winding B, and a second end of the third winding C are grounded.

[0055] In one example, if Figure 2 As shown, the first input resistor may include a first resistor R1, a third resistor R3, a fifth resistor R5, a seventh resistor R7, a ninth resistor R9, and an eleventh resistor R11; the second input resistor may include a second resistor R2, a fourth resistor R4, a sixth resistor R6, an eighth resistor R8, a tenth resistor R10, and a twelfth resistor R12; and the input capacitor may include a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, and a sixth capacitor C6.

[0056] In one example, the three-phase full-bridge inverter 20 may further include a plurality of freewheeling diodes disposed between the source and the drain of each transistor, for providing a freewheeling path when the transistor is turned off to prevent the transistor from being damaged.

[0057] In a possible implementation, the three-phase motor 10 may be a three-phase brushless DC motor.

[0058] In one example, the embodiment of the present disclosure realizes the Y connection (or star connection) of the three-phase motor 10 by electrically connecting one end of each winding of the stator, and the other end of each winding is electrically connected between the first transistor Q1 and the fourth transistor Q4, between the second transistor Q2 and the fifth transistor Q5, and between the third transistor Q3 and the sixth transistor Q6.

[0059] In one example, if Figure 2 As shown, the three-phase motor 10 may include a first winding A, a second winding B and a third winding C (corresponding to phase A, phase B, phase C, and corresponding to the first bridge arm, the second bridge arm, and the third bridge arm, respectively), one end of the first winding A is electrically connected between the first transistor Q1 and the fourth transistor Q4, one end of the second winding B is electrically connected between the second transistor Q2 and the fifth transistor Q5, and one end of the third winding C is electrically connected between the third transistor Q3 and the sixth transistor Q6.

[0060] In a possible implementation, Figure 2 As shown, the voltage detection module 30 includes a first voltage detection unit 310, a second voltage detection unit 320 and a third voltage detection unit 330, which are respectively connected between the upper bridge arm and the lower bridge arm of each phase of the three-phase full-bridge inverter 20, wherein each voltage detection unit includes a first detection resistor Re1 and a second detection resistor Re2,

[0061] The first end of the first detection resistor Re1 is connected between the upper bridge arm and the lower bridge arm of the corresponding phase, and the second end of the first detection resistor Re1 is connected to the first end of the second detection resistor Re2 for outputting the detection voltage Vde;

[0062] A second end of the second detection resistor Re2 is grounded.

[0063] In a possible implementation, the control module 50 is used to: when the first voltage and the second voltage are equal, determine that the angle rotated by the rotor of the three-phase motor 10 is 30°, and determine the preset time length to be the time length of the delay of 30°.

[0064] The embodiment of the present disclosure does not limit the specific duration of the 30° delay, and those skilled in the art can set it according to needs and actual conditions.

[0065] In a possible implementation manner, the driving module 40 is further configured to: when controlling the corresponding half-bridge switch in a PWM manner, control a duty cycle of the PWM to be less than or equal to 40%.

[0066] In a possible implementation, the driving module 40 of the embodiment of the present disclosure may be implemented by a dedicated motor driving chip, or may be constructed by discrete components, which is not limited by the embodiment of the present disclosure.

[0067] The control module 50 of the disclosed embodiment may include a processing component, wherein the processing component includes but is not limited to a separate processor, or a discrete component, or a combination of a processor and a discrete component. The processor may include a controller having an execution instruction function in an electronic device, and the processor may be implemented in any appropriate manner, for example, by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors or other electronic components. Inside the processor, the executable instructions may be executed by hardware circuits such as logic gates, switches, application-specific integrated circuits (ASICs), programmable logic controllers, and embedded microcontrollers.

[0068] The embodiment of the present disclosure does not limit the specific implementation of the control module 50 .

[0069] The following is an exemplary introduction to the principle of determining the commutation point under low speed and heavy load to achieve motor drive control in the embodiment of the present disclosure.

[0070] See also Figure 3a and Figure 3b , Figure 3a A schematic diagram showing a magnetization curve of a stator core of a three-phase motor according to an embodiment of the present disclosure is shown. Figure 3b A schematic diagram showing a magnetization curve BH and a magnetic permeability curve μ-H of a ferromagnetic material used in a three-phase motor according to an embodiment of the present disclosure is shown.

[0071] In one example, in order to maximize the use of core materials, the no-load operating point of the motor is selected where the rising slope of the magnetization curve is small, such as Figure 3b Point A in .

[0072] The rated operating point of the motor core is not at its maximum magnetic permeability, but on the right side of the maximum magnetic permeability, such as Figure 3b As shown in point A. When current is passed through the stator armature winding, the armature reaction caused by the armature magnetic potential will cause the operating point to shift, resulting in a change in magnetic permeability.

[0073] In one example, the inductance of the motor stator armature winding can be obtained by Equation 1:

[0074]

[0075] Further, we can get formula 2:

[0076]

[0077] According to Ampere's circuit theorem, Formula 2 can be transformed into Formula 3:

[0078]

[0079] Among them, ψ S Represents the stator armature flux, N S represents the number of turns of the stator armature winding, S represents the cross-sectional area of ​​the magnetic circuit, i S represents the stator armature winding current, L is the magnetic path length, R mψ It represents the magnetic resistance of the main magnetic circuit of the motor, which is mainly composed of two parts: the iron core magnetic resistance and the air gap magnetic resistance. B represents the magnetic induction intensity.

[0080] The magnetic resistance of the motor main magnetic circuit can be obtained by formula 4:

[0081]

[0082] Among them, R Fe Represents the core magnetic resistance, R σ Represents the air gap reluctance, L Fe Indicates the core magnetic path length, μ Fe Indicates the core magnetic permeability, L σ Indicates the air gap magnetic path length, μ σ Represents the air gap permeability.

[0083] In one example, for a selected motor, the number of turns of the stator armature winding is N S is a constant, and for surface mounted brushless DC motors, the air gap length L σ is certain, the air gap permeability μ σ unchanged, then the air gap magnetic resistance R σ is constant; for the core reluctance with a longer magnetic circuit, the magnetic potential generated by the armature winding will cause the magnetic field intensity H to change, resulting in different magnetic permeabilities μ for the magnetization and demagnetization effects. Fe .

[0084] In one example, when the absolute value of the angle between the magnetic potential generated by the armature winding and the permanent magnet magnetic potential is less than 90°, the component of the armature magnetic potential on the d-axis is positive, which will lead to a magnetization effect. Figure 3b It can be seen that the magnetic permeability of the core will become smaller, thereby reducing the stator inductance; when the absolute value of the angle between the magnetic potential generated by the armature winding and the permanent magnet magnetic potential is greater than 90°, such as Figure 3b As shown, the component of the armature magnetic potential on the d-axis is negative, which will cause a demagnetization effect, the magnetic permeability of the core will increase, and thus the stator inductance will increase.

[0085] See also Figure 4 , Figure 4 A schematic diagram showing the relationship between the electronic inductance of a three-phase motor and the change in the angle between the magnetic potential generated by the armature winding and the permanent magnet magnetic potential according to an embodiment of the present disclosure is shown.

[0086] Figure 4 The middle ordinate represents the change of stator inductance with the change of the angle of the rotor relative to the stator. When the angle of the rotor relative to the stator is less than 90°, the stator inductance is greater than the original inductance, that is, the stator inductance is more than 100% of the original inductance.

[0087] In one example, if Figure 4 As shown, the smaller the angle between the armature magnetic potential and the permanent magnet magnetic potential, the greater the magnetization effect and the smaller the corresponding stator winding inductance.

[0088] In one example, the motor phase voltage of a brushless DC motor may be as shown in Equation 5:

[0089]

[0090] Among them, u a,b,c represents phase voltage, R represents phase resistance, L S represents the stator phase inductance, i a,b,c Represents the phase current, e a, b ,c Indicates opposite electric potential.

[0091] In one example, when the motor is at rest or at a very low speed, the back EMF e a, b ,c Very small, can be ignored; the phase resistance of the motor is usually very small, and the phase containing resistance can also be ignored. In this case, the above formula 5 can be simplified to:

[0092]

[0093] From formula 6, we can see that when the motor speed is very low, the phase voltage is approximately proportional to the stator phase inductance. When the speed is very high, the voltage sampled is considered to be the back-EMF phase voltage caused by the speed and the voltage drop on the inductance and resistance is ignored. At low speed, it is just the opposite, because the speed is very low, the back-EMF is related to the speed e=C e φn, where C is a constant, φ is the magnetic flux of the permanent magnet and can also be considered constant. Therefore, the back electromotive force of the motor is directly positively correlated with the speed. For this reason, when the motor starts, the current is large, the speed is too low and the back electromotive force is too small. The voltage on the voltage basically acts on the inductance and resistance of the motor, so the starting current is large.

[0094] From the above analysis, we can see that the stator inductance of the brushless DC motor is not always constant. The stator inductance will increase with the continuous increase of the stator current (such as Figure 3a As shown in Figure 2, when the stator current reaches a certain value, the stator inductance will reach saturation; at the same time, the rotor permanent magnet also has a great influence on the stator inductance, such as Figure 4 shown.

[0095] The motor drive device proposed in the embodiment of the present disclosure can solve the problem that the sampling value is inaccurate due to the small back electromotive force at low speed, which affects the normal operation of the motor.

[0096] See also Figure 5a , Figure 5a A schematic diagram of an equivalent circuit of a motor according to an embodiment of the present disclosure is shown.

[0097] In one example, assuming that the normal drive is that the upper bridge of phase A of the motor (the upper bridge arm of the first bridge arm) is energized, and the lower bridge of phase B (the lower bridge arm of the second bridge arm) is energized for analysis, when the motor drive device of the embodiment of the present disclosure is used to drive the motor, the back electromotive force of the non-conducting phase C (the third bridge arm) is collected. At this time, the motor equivalent circuit is as follows Figure 5a shown.

[0098] In one example, under the condition of relatively low speed, the actual adjusted output PWM duty cycle is relatively small (the maximum output driving duty cycle of the embodiment of the present disclosure is 40%), and within the same PWM output cycle, a pulse used for detection, i.e., a detection signal, is inserted. The stator flux direction at the time of inserting the pulse sampling and outputting the pulse differs by 180°.

[0099] See also Figure 5b , Figure 5b A schematic diagram of an equivalent circuit of a motor according to an embodiment of the present disclosure is shown.

[0100] In one example, if the drive signal adopts the A up (upper bridge arm of the first bridge arm) B down (lower bridge arm of the second bridge arm) conduction mode, when the drive signal is injected into the three-phase full-bridge inverter 20, the motor equivalent circuit is as follows: Figure 5b shown.

[0101] Among them, RA, RB, and RC represent the equivalent resistances of phases A, B, and C respectively.

[0102] The actual motor operation is analyzed below.

[0103] See also Figure 6a and Figure 6b , Figure 6a and Figure 6b A schematic diagram of a circuit for detecting motor running timing and pulse timing according to an embodiment of the present disclosure is shown.

[0104] exist Figure 6a and Figure 6b In the figure, “×” indicates current inflow, “·” indicates current outflow, and X, Y, and Z represent three orthogonal directions.

[0105] Figure 6a and Figure 6b The 120° conduction mode is adopted (only two phases are energized at the same time), where: Figure 6a For the driving pulse moment, assuming that the motor runs clockwise, the next correct conduction moment is A up and C down (according to the control principle of brushless DC motor, the angle between the stator flux and the rotor flux is essentially changing from 120° to 60°. After 60°, the phase must be changed to continue to maintain the angle of 120°, and the average torque is 90°, and the force is maximum). At this time, the non-conducting phase C (the third bridge arm) changes from a voltage close to the power supply voltage to the ground (generally 0V), that is, the C phase is a falling edge at this time.

[0106] In one example, if Figure 6a As shown, the A phase flux F a Direction and permanent magnet flux F r The angle is 150°, and as the rotor rotates clockwise, the angle gradually decreases; the B phase flux F b Direction and permanent magnet flux F r The included angle is 90°, and as the rotor rotates clockwise, the included angle gradually decreases.

[0107] In an example, assume that the stator inductance of the motor reaches saturation after the current is passed for a long enough time. At this time, the stator inductance itself is L S ,like Figure 6a As shown, when the rotor is in a horizontal position, the inductance value of the permanent magnet on the stator phase A is L r cos(30°)(L r is the equivalent inductance generated by the stator phase when the angle between the permanent magnet and the stator is 0°. Since the flux linkage F of phase A is a Direction and permanent magnet flux F r The angle is greater than 90°, Figure 4 It can be seen that this is demagnetization. From the above analysis, it can be seen that the inductance increases at this time, that is, the actual inductance value of phase A at this time is L A =L S +L r cos(30°), and as the angle gradually decreases, the inductance of phase A gradually increases; by the same token, it can be concluded that the inductance value of phase B at this time is L S .

[0108] In one example, Formula 7 can be obtained according to Formula 6:

[0109]

[0110] In one example, when the detection signal is injected, the actual magnetic circuit direction is as follows: Figure 6b As shown, according to the above, the inductance value of phase A is L A =L S +L r cos(30°), at this time the inductance value of phase B is L S Assuming a clockwise rotation angle of θ (between 0 and 60°), the reverse potential of C under the action of the driving signal is:

[0111]

[0112] In one, under the action of the detection signal, the back electromotive force of C is:

[0113]

[0114] According to formula 8, we can get:

[0115]

[0116] According to formula 9, we can get:

[0117]

[0118] Therefore, it can be seen that at the falling edge of the non-conducting phase, the back electromotive force of the non-conducting phase C under the driving pulse and the detection pulse is greater than half of the power supply voltage. Subtracting formula 9 from formula 8, we can get:

[0119]

[0120] By commonizing the numerator of the above formula and rearranging it, we can get:

[0121] e C -e C '=(sin(60°-θ)-sinθ)(L S +L r (sin(60°-θ)+sinθ))·VCC Formula 12

[0122] In an example, since the angle is between 0 and 60 degrees (one commutation cycle), and the sine function is monotonically increasing in the range of 0 to 60 degrees, it can be known that:

[0123] When θ<30°, formula 12 is greater than 0, that is, the reverse potential of C under the driving pulse is greater than the reverse potential of C under the detection pulse;

[0124] When θ=30°, formula 12 is 0, that is, the reverse potential of C under the driving pulse is equal to the reverse potential of C under the detection pulse;

[0125] When θ>30°, formula 12 is less than 0, that is, at this time, the reverse potential of C under the driving pulse is less than the reverse potential of C under the detection pulse.

[0126] According to the above analysis, when it is detected that the non-conducting opposite potential C under the driving pulse and the detection pulse is equal, the rotor rotates 30°. At this time, the actual commutation point can be calculated based on the delay time, and accurate commutation can be achieved.

[0127] In the disclosed embodiment, when the speed of the three-phase motor is lower than the preset speed and is in the low-speed heavy-load mode, the driving module alternately outputs a driving signal and a detection signal in the Kth control cycle, so as to use the driving signal to drive the upper bridge arm of the first bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the second bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the detection signal to drive the upper bridge arm of the second bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, turn on the lower bridge arm of the first bridge arm, and disconnect the upper bridge arm and the lower bridge arm of the third bridge arm, and use the voltage ... The detection module detects the first voltage of the third bridge arm when the drive signal is applied and the second voltage of the third bridge arm when the detection signal is applied, and uses the control module to output a commutation signal after a preset delay when the first voltage and the second voltage are equal, so that the drive module adjusts the drive signal and the detection signal for commutation, and outputs the adjusted drive signal and the adjusted detection signal in the K+1th control cycle. The motor drive device of the embodiment of the present disclosure can achieve torque maintenance when the three-phase motor is at low speed, and detect the commutation point in real time for accurate commutation, thereby realizing precise control of the three-phase motor.

[0128] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A motor drive device, characterized in that: The device includes a three-phase motor, a three-phase full-bridge inverter, a voltage detection module, a drive module and a control module. The three-phase full-bridge inverter comprises a first bridge arm, a second bridge arm and a third bridge arm, each bridge arm comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm of each bridge arm are provided with transistors, and the three-phase full-bridge inverter is used to drive the three-phase motor; The driving module is connected to each transistor of the three-phase full-bridge inverter, and is used to alternately output a driving signal and a detection signal in the Kth control cycle when the speed of the three-phase motor is less than a preset speed. The driving signal is used to drive the upper bridge arm of the first bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, the lower bridge arm of the second bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect. The detection signal is used to drive the upper bridge arm of the second bridge arm in the three-phase motor to switch in a pulse width modulation PWM mode, the lower bridge arm of the first bridge arm to turn on, and the upper bridge arm and the lower bridge arm of the third bridge arm to disconnect, wherein K is an integer, and one control cycle corresponds to one commutation; The voltage detection module is connected between the upper bridge arm and the lower bridge arm of each bridge arm of the three-phase full-bridge inverter, and is used to detect the first voltage of the third bridge arm when the driving signal acts and the second voltage of the third bridge arm when the detection signal acts; The control module is connected to the voltage detection module and the driving module, and is used to output a commutation signal after a preset delay when the first voltage and the second voltage are equal, so that the driving module adjusts the driving signal and the detection signal for commutation, and outputs the adjusted driving signal and the adjusted detection signal in the K+1th control cycle, The driving module is also used to: when controlling the corresponding half-bridge switch in a PWM manner, control the PWM duty cycle to be less than or equal to 40%, The motor is a three-phase brushless DC motor.

2. The device according to claim 1, characterized in that The voltage detection module includes a first voltage detection unit, a second voltage detection unit and a third voltage detection unit, which are respectively connected between the upper bridge arm and the lower bridge arm of each phase of the three-phase full-bridge inverter, wherein each voltage detection unit includes a first detection resistor and a second detection resistor, The first end of the first detection resistor is connected between the upper bridge arm and the lower bridge arm of the corresponding phase, and the second end of the first detection resistor is connected to the first end of the second detection resistor, for outputting a detection voltage; A second terminal of the second detection resistor is grounded.

3. The device according to claim 1, characterized in that The control module is used to: when the first voltage and the second voltage are equal, determine that the angle rotated by the rotor of the three-phase motor is 30°, and determine that the preset time length is the time length of the delay of 30°.

4. The device according to claim 1, characterized in that The three-phase full-bridge inverter includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a sixth transistor. The first transistor and the fourth transistor constitute a first bridge arm, and the fourth transistor is a lower bridge arm. The second transistor and the fifth transistor constitute a second bridge arm, and the fifth transistor is a lower bridge arm. The third transistor and the sixth transistor constitute a third bridge arm, and the sixth transistor is a lower bridge arm. The first ends of the windings of the three-phase motor are connected, and the second ends of the windings are respectively connected between the first transistor and the fourth transistor, between the second transistor and the fifth transistor, and between the third transistor and the sixth transistor.

5. The device according to claim 4, characterized in that The three-phase full-bridge inverter further includes a plurality of first input resistors, a plurality of second input resistors, and a plurality of input capacitors. The stator of the three-phase motor includes a first winding, a second winding, and a third winding. The gate of each transistor of the three-phase full-bridge inverter is electrically connected to the second end of the first input resistor, the first end of the second input resistor, and the first end of the input capacitor. The source of each transistor of the three-phase full-bridge inverter is electrically connected to the second end of the input capacitor and the second end of the second input resistor. The first end of the first input resistor is used to input the drive signal or the detection signal. The drain of the first transistor, the drain of the second transistor, and the drain of the third transistor are electrically connected, and the source of the fourth transistor, the source of the fifth transistor, and the source of the sixth transistor are electrically connected. The source of the first transistor is electrically connected to the drain of the fourth transistor and the first end of the first winding, the source of the second transistor is electrically connected to the drain of the fifth transistor and the first end of the second winding, and the source of the third transistor is electrically connected to the drain of the sixth transistor and the first end of the third winding. The second end of the first winding, the second end of the second winding, and the second end of the third winding are grounded.

6. A drive assembly, characterized in that: The drive assembly comprises a motor drive device as described in any one of claims 1-5.

7. An electric tool, characterized in that: The electric tool comprises the drive assembly according to claim 6.

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