Power tool and control method thereof

Abstract

The application discloses an electric tool and a control method thereof. The electric tool comprises a motor, a torque detection module, a rotating speed detection module and a controller. The motor has a multi-phase stator winding. Each phase winding of the motor can be conducted in a first conduction mode and a second conduction mode within a certain phase belt. The torque detection module is used for detecting the output torque of the motor. The rotating speed detection module is used for detecting the rotating speed of the motor. The controller is electrically connected with the torque detection module, the rotating speed detection module and the motor. The controller is configured to acquire the output torque and the rotating speed of the motor. In a first working stage, the electric angle of the motor conducted in the second conduction mode is adjusted to maintain the rotating speed of the motor in a substantially stable state. In a second working stage, the stator winding is controlled to be conducted in the first preset electric angle in the second conduction mode. The electric tool can consider the rotating speed and the output torque of the motor under different working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electric power tools, in particular to an electric power tool and a control method thereof. BACKGROUND

[0002] Different types of electric power tools need to have different output performances in the process of tool starting or normal working for different use conditions, for example, only the cutting speed needs to be concerned when cutting thin wood board with an electric saw, and the output torque needs to be concerned when cutting steel plate. Therefore, the tool needs to consider both the rotating speed and the output torque in different working stages or different conditions. SUMMARY

[0003] In order to solve the problems in the prior art, the purpose of the present application is to provide an electric power tool which can effectively consider both the rotating speed and the output torque of a motor.

[0004] The present application adopts the following technical solutions:

[0005] An electric power tool comprises: a motor having multi-phase stator windings, each phase winding of the motor can be conducted and worked in a first conduction mode and a second conduction mode within a selected phase band; a torque detection module for detecting the output torque of the motor; a rotating speed detection module for detecting the rotating speed of the motor; a controller electrically connected with at least the torque detection module, the rotating speed detection module and the motor; the controller is configured to: acquire the output torque and the rotating speed of the motor; in a first working stage, adjust the electric angle at which the motor is conducted and worked in the second conduction mode, so as to maintain the rotating speed of the motor in a substantially stable state; in a second working stage, control the stator windings to be conducted in the first preset electric angle in the second conduction mode.

[0006] Further, the controller is configured to: control the stator windings to be conducted in the second preset electric angle in the first conduction mode in both the first working stage and the second working stage.

[0007] Further, the controller is configured to: in the first working stage, when the electric angle at which the motor is conducted and worked in the second conduction mode reaches a preset angle threshold, control the stator windings to be conducted in the third preset electric angle in the second conduction mode.

[0008] Further, it further comprises: a current detection module for detecting the working current of the motor; the controller is configured to: acquire the working current of the motor and calculate the change slope of the working current; in the first working stage, when the working current of the motor reaches a current threshold under the first change slope, control the stator windings to be conducted in the first preset electric angle so that the motor enters the second working stage.

[0009] Further, the output current of the motor has the first change slope in the first working stage, and has a second change slope in the second working stage; the first change slope is greater than the second change slope.

[0010] Further, when the working current of the motor reaches a current threshold under the first change slope in the first working stage, the electric angle at which the stator winding is turned on in the second turning-on mode is the maximum electric angle that can be reached in the second turning-on mode.

[0011] Further, the first preset electric angle is less than or equal to the maximum electric angle at which the stator winding is turned on in the second turning-on mode in the first working stage.

[0012] Further, the first turning-on mode includes turning on any two phase windings of the motor, and the second turning-on mode includes turning on three phase windings of the motor.

[0013] A control method of an electric tool, the electric tool comprising: a motor having a plurality of phase stator windings, each phase winding of the motor being capable of being turned on in a first turning-on mode and a second turning-on mode in a selected phase band; a torque detection module for detecting an output torque of the motor; a rotating speed detection module for detecting a rotating speed of the motor; and a controller electrically connected with at least the torque detection module, the rotating speed detection module and the motor; the control method comprising: obtaining the output torque and the rotating speed of the motor; in a first working stage, adjusting an electric angle at which the motor is turned on in the second turning-on mode, so as to maintain the rotating speed of the motor in a substantially stable state; and in a second working stage, controlling the stator winding to be turned on in the second turning-on mode at a first preset electric angle.

[0014] Further, the method further comprises: controlling the stator winding to be turned on in the first turning-on mode at a second preset electric angle in the first working stage and the second working stage.

[0015] The present application has the advantages of providing an electric tool capable of considering the rotating speed and the output torque of the motor under different working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structural schematic diagram of an electric tool provided by an embodiment of the present application;

[0017] Figure 2 is a circuit block diagram of an electric tool provided by an embodiment of the present application;

[0018] Figure 3is a schematic diagram of magnetic potential change in the motor when two of the three conductive modes are provided by the embodiment of the present application;

[0019] Figure 4 is a schematic diagram of magnetic potential change in the motor when three of the three conductive modes are provided by the embodiment of the present application;

[0020] Figure 5 is a schematic diagram of a certain phase in-band winding conductive mode provided by the embodiment of the present application;

[0021] Figure 6 is a schematic diagram of magnetic potential synthesis provided by the embodiment of the present application;

[0022] Figure 7 is a schematic diagram of a certain phase in-band winding conductive mode provided by the embodiment of the present application;

[0023] Figure 8a and Figure 8b is a schematic diagram of motor power and flux weakening capability comparison provided by the embodiment of the present application;

[0024] Figure 9 is a circuit block diagram of an electric tool provided by the embodiment of the present application;

[0025] Figure 10 and Figure 11 is a schematic diagram of electromagnetic torque provided by the embodiment of the present application;

[0026] Figure 12 is a schematic diagram of output performance of tools in different stages provided by the embodiment of the present application;

[0027] Figure 13 is a circuit block diagram of an electric tool provided by the embodiment of the present application;

[0028] Figure 14 is a schematic diagram of output performance of tools in different stages provided by the embodiment of the present application. DETAILED DESCRIPTION

[0029] The present application will be described in detail below with reference to the drawings and specific embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, and not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, not all the structures.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0031] The electric power tool to which the technical solution of the present application is applied includes any electric power tool that can adopt a brushless and non-inductive electric control mode, such as a sander, an electric drill, an electric circular saw, a reciprocating saw, a miter saw, and the like. Other types of electric power tools that can adopt the essential content of the technical solution disclosed below can also fall within the protection scope of the present application.

[0032] In the embodiments of the present application, reference is made to Figure 1 Taking a sander as an example, the electric power tool 100 at least includes a casing 10, a motor 11 (not shown) in the casing, a bottom plate 12, a transmission mechanism (not shown), a holding portion 13, and a battery pack 14. Figure 1 The motor is built in the casing 10. In an embodiment, the casing 10 includes a left casing and a right casing, which are assembled by being closed from left and right directions to the middle and fastened by screws. In an embodiment, the motor shaft of the motor is parallel to the bottom plate 12 and is built in the front end of the tool 100. The motor 11 drives the transmission mechanism to make the fixed sanding paper on the bottom plate 12 perform sanding work. The transmission mechanism at least serves to connect the motor shaft and an output shaft and can be two-stage transmission gears. The casing 10 is formed with the holding portion 13 for the user to hold according to ergonomics. The tool 100 further includes an electronic film switch for controlling the on-off switch. The battery pack 14 is inserted at the rear end of the tool, and the longest side of the battery pack 14 is parallel to the bottom plate plane, so that the overall volume of the tool is small.

[0033] Referring to the circuit block diagram of the electric power tool shown in

[0034] The driving system of the motor 11 at least includes a driving circuit 20, a power module 21, a rotor position detection module 22, an electric parameter detection module 23, and a controller 24.

[0034] Figure 2

[0035] In one embodiment, the motor 11 is a brushless direct current motor (BLDC). In one embodiment, the motor 11 is a sensorless BLDC. In one embodiment, the motor 11 is a sensored BLDC. In this application, the brushless direct current motor can be an inner rotor motor or an outer rotor motor. The motor 11 includes at least three phase stator windings A, B, C, which can be connected in star or delta configuration. In motor speed control, for a BLDC with Hall sensors or other hardware devices to detect rotor position, the sensor can be used to detect the rotor position directly, and the motor speed can be adjusted according to the rotor position. However, for a sensorless BLDC, since there is no sensor in the motor to detect the rotor position, the rotor position can be detected by detecting the back electromotive force of the winding or other ways. However, the sensorless BLDC cannot accurately obtain the rotor position when starting or low-speed load, which can cause unstable output torque. For the speed control of the sensorless BLDC, the field weakening or voltage regulation method is generally used. The cost of the voltage regulation method is relatively high, and the traditional field weakening method can greatly reduce the power of the motor. In this application, the stator magnetic potential is adjusted to control the speed, which can solve the above problems. Of course, the stator magnetic potential can also be adjusted to adjust the motor speed in the sensored BLDC.

[0036] In one embodiment, the power supply can be selected as an alternating current power supply, so that the power supply module 21 can be connected to a 120V or 220V alternating current power supply. In one embodiment, the power supply can be selected as a battery pack, which can be composed of a group of battery units. For example, the battery units can be connected in series to form a single power supply branch to form a 1P battery pack. The output voltage of the battery pack is changed by a specific power control module, such as a DC-DC module, to output a suitable power supply voltage for the drive circuit 20, the motor 11, etc. to supply power. Those skilled in the art can understand that the DC-DC module is a mature circuit structure, which can be selected according to the specific parameters of the power tool.

[0037] The rotor position detection module 22 is used to identify the rotor position. In one embodiment, the rotor position detection module 22 can include a Hall sensor for detecting the rotor position. In one embodiment, the rotor position detection module 22 can estimate the rotor position based on the floating phase voltage or phase current of the motor. In this application, the rotor position detection module can also include any other method or hardware device capable of detecting the rotor position.

[0038] The electrical parameter detection module 23 can detect the electrical parameters of the motor 11 in real time during operation, such as the speed of the motor. Optionally, the electrical parameter detection module 23 can also detect the output torque of the motor, or detect the power efficiency of the motor based on the speed and torque.

[0039] The drive circuit 20 is electrically connected to the stator windings A, B, and C of the motor 11, and is used to transfer current from the power module 21 to the stator windings A, B, and C to drive the motor 10 to rotate. In one embodiment, the drive circuit 20 includes multiple switching elements Q1, Q2, Q3, Q4, Q5, and Q6. The gate of each switching element is electrically connected to the controller 23 to receive control signals from the controller 23. The drain or source of each switching element is connected to the stator windings A, B, and C of the motor 10. Switching elements Q1-Q6 receive control signals from the controller 23 and change their respective conduction states, thereby changing the current applied by the power module 21 to the stator windings A, B, and C of the motor 11. In one embodiment, the drive circuit 20 may be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g., FETs, BJTs, IGBTs, etc.). It is understood that the aforementioned switching elements may also be any other type of solid-state switch, such as an insulated-gate bipolar transistor (IGBT), a bipolar junction transistor (BJT), etc.

[0040] To enable the motor 11 to rotate, the drive circuit 20 has multiple drive states. The controller 24 can output corresponding PWM drive signals based on the rotor's position information to control the switching elements in the drive circuit 20, causing the drive circuit to switch its conduction state, thereby changing the conducting phase of the motor stator winding and the magnitude and direction of the current in the conducting winding. It should be noted that different conducting phases of the stator winding and changes in the magnitude and direction of the current in the winding will lead to changes in the magnitude and direction of the stator magnetomotive force.

[0041] like Figure 3 This diagram illustrates the change in magnetomotive force (MOF) during the commutation process (two-phase conduction, i.e., two-by-two conduction) in the three-phase windings of a three-phase non-inductive BLDC motor. The MOF includes the rotor magnetomotive force of the motor. Stator magnetomotive force of stator winding The motor performs one commutation for every 60 electrical degrees the rotor rotates, meaning each phase winding occupies a 60° phase band. The rotor's position information corresponds to six different phase bands, and the PWM drive signal output by the controller 24 can correspond to six different signal combinations. In one embodiment, signal 0 represents the winding's off state, and signal 1 represents the winding's on state. Furthermore, Figure 3 The dashed lines represent the Hall scale formed when the Hall positions of the three-phase windings are parallel to the rotor direction. Under this Hall scale, the Hall positions of the stator windings can be determined as the rotor position changes. Specifically, the Hall positions of the three-phase windings, the combination of PWM signals output by the controller, and the corresponding conduction states of the stator windings are shown in Table 1:

[0042] Table 1

[0043]

[0044]

[0045] The 0 under the Hall position column in Table 1 indicates that the Hall position of the corresponding winding falls in the S level of the rotor, and the 1 under the Hall position column indicates that the Hall position of the corresponding winding falls in the N level of the rotor. The 0 under the PWM signal combination column in Table 1 indicates that the lower tube of the corresponding winding is turned on, the 1 under the PWM signal combination column indicates that the upper tube of the corresponding winding is turned on, and the X under the PWM signal combination column indicates that neither the upper tube nor the lower tube of the corresponding winding is turned on.

[0046] It can be seen that, in the 360° electrical angle interval, the direction of the rotor magnetic potential Figure 3 changes constantly in the process of the rotation of the rotor, and the size of the rotor magnetic potential is constant; the stator magnetic potential is synthesized by the magnetic potentials of the two-phase stator windings that are turned on, the direction of the stator magnetic potential changes with the commutation of the stator windings, and the size of the stator magnetic potential is also related to the turn-on direction and the turn-on current of the phase windings. For example, when the PWM signal output by the controller in Table 1 is (1, 0, X), the rotor rotates in the 30°-90° phase zone, the A and B windings are turned on in the A+B- mode, the rotor magnetic potential is in the direction parallel to the rotor, the stator magnetic potential Figure 3 is synthesized by the magnetic potentials of the A and B phase windings, that is the rotor commutes once every 60 electrical angles, and the commutation process of the rotor according to the driving signal shown in Table 1 corresponds to the commutation process indicated by the arrow in Table 2, and the corresponding rotor magnetic potential and stator magnetic potential also change as shown in Table 2. Table 3 shows the change process of the magnetic potential when the three-phase windings of the three-phase non-inductive BLDC are all turned on, that is, the three-phase windings are all turned on. Table 4 is the correspondence between the Hall position, the PWM signal and the turn-on state of the motor stator winding in the mode in which the three-phase windings are all turned on: Figure 3 Figure 3

[0047] As shown in Table 4, the 0 under the Hall position column indicates that the Hall position of the corresponding winding falls in the S level of the rotor, and the 1 under the Hall position column indicates that the Hall position of the corresponding winding falls in the N level of the rotor. The 0 under the PWM signal combination column in Table 4 indicates that the lower tube of the corresponding winding is turned on, the 1 under the PWM signal combination column indicates that the upper tube of the corresponding winding is turned on, and the X under the PWM signal combination column indicates that neither the upper tube nor the lower tube of the corresponding winding is turned on. Figure 4 Table 4

[0048]

[0049] Hall position PWM signal combination Stator winding conduction state (0，1，0) (1，0，0) A+B-C- (0，1，1) (1，1，0) A+B+C- (0，0，1) (0，1，0) B+C-A- (1，0，1) (0，1，1) B+C+A- (1，0，0) (0，0，1) C+A-B- (1，1，0) (1，0，1) C+A+B-

[0050] It can be seen that, in the 360° electrical angle interval, the direction of the rotor magnetic potential Figure 4 changes constantly in the process of the rotation of the rotor, and the size of the rotor magnetic potential is constant; the stator magnetic potential is synthesized by the magnetic potentials of the three-phase stator windings that are turned on, the direction of the stator magnetic potential changes with the commutation of the stator windings, and the size of the stator magnetic potential is also related to the turn-on direction and the turn-on current of the three-phase windings. For example, when the PWM signal output by the controller in Table 3 is (1, 1, 1), the rotor rotates in the 0°-120° phase zone, the A, B and C windings are turned on in the A+B+C- mode, the rotor magnetic potential is in the direction parallel to the rotor, the stator magnetic potential Figure 4 ​​​​The PWM signal outputted by the controller is (1, 0, 0), the rotor rotates in the phase zone of 30°-90°, the A, B, C windings are conducted in the mode of A+B-C-, the rotor magnetic potential In the direction parallel to the rotor, the stator magnetic potential The magnetic potential synthesized by the A, B, C phase windings is The rotor commutates once every 60 electrical degrees, the commutation process of the rotor according to the driving signal shown in Table 2 corresponds Figure 4 The commutation process indicated by the arrow, the corresponding rotor magnetic potential and stator magnetic potential also change as shown in Figure 4 .

[0051] The magnetic potential synthesized by the A, B, C phase windings is Figure 3 and Figure 4 It can be seen from the comparison that the conduction mode of the motor stator winding affects the size of the stator magnetic potential, the stator magnetic potential when the three-phase windings are all conducted under unit current is greater than the stator magnetic potential when the windings are conducted in pairs. Therefore, in order to obtain a larger stator magnetic potential in the selected phase zone, the controller 24 can change the PWM signal to control the stator winding to work in the combined conduction mode of two-by-two conduction and three-in-one conduction. Specifically, as shown in Figure 5 , in the phase zone of 60°, the stator winding of the motor can be controlled to conduct in the three-in-one conduction mode for an electrical angle of β°, and in the two-by-two conduction mode for an electrical angle of 60-β°, and β is defined as the expansion angle. In an embodiment, the two-by-two conduction process in the selected phase zone can be continuous or intermittent. The selected phase zone can be any selected phase zone, and the size of the selected phase zone is not limited in the embodiment of the application.

[0052] In an embodiment, the stator magnetic potential and the rotor magnetic potential can obtain the synthesized magnetic potential of the motor according to a certain synthesis mode. For example, as shown in Figure 6 , the first direction of the position of the rotor is defined as the direct axis, and the second direction perpendicular to the direct axis is defined as the quadrature axis. The components of the stator magnetic potential on the direct axis and the quadrature axis are and After being synthesized with the rotor magnetic potential, the first synthesized magnetic potential in the direct axis direction and the second synthesized magnetic potential in the quadrature axis direction can be formed. It should be noted that Figure 6 the size of the angle θ between the rotor magnetic potential and the stator magnetic potential can represent the current excitation capability of the motor. For example, when the angle θ between the rotor magnetic potential and the stator magnetic potential is obtuse, the motor has a weak magnetic capability, and when the angle θ is acute, the motor has a strong magnetic capability. In an embodiment, the angle θ is obtuse.

[0053] In the present application, the first synthesized magnetic potential is the synthesis of and , as long as the synthesized magnetic potential is greater than the original A smaller magnitude indicates an enhanced field-weakening capability of the motor; therefore, the magnitude of the first resultant magnetomotive force characterizes the motor's field-weakening capability, and the motor speed can be adjusted by adjusting the first resultant magnetomotive force. The second resultant magnetomotive force is the component of the stator magnetomotive force on the quadrature axis. Based on the angle θ between the stator magnetomotive force and the quadrature axis shown in Figure 6, due to the electromagnetic torque of the motor... Where K is a fixed value, W represents the magnetic residual energy, and Thus electromagnetic torque That is, the electromagnetic torque is related to the stator magnetomotive force component along the quadrature axis; therefore, the magnitude of the second resultant magnetomotive force characterizes the motor's work capacity. By adjusting the magnitude of the second resultant magnetomotive force, the electromagnetic torque can be adjusted, thereby affecting the motor's work capacity. It should be noted that... Figure 6 As shown in the decomposition diagram of the composite magnetomotive force, the second composite magnetomotive force can be adjusted to reach the expected value while keeping the first composite magnetomotive force constant. In other words, this application can ensure the motor's work capacity, i.e., its output efficiency, while increasing the motor speed.

[0054] In this application, the motor output efficiency is the efficiency of the motor power output, which represents the motor's work capacity.

[0055] Similarly, by Figure 6 It can be seen that there is a corresponding relationship between the rotor position and the rotor magnetomotive force. When the rotor position is determined, the combined magnetomotive force of the two can be adjusted by adjusting the stator magnetomotive force, thereby controlling the electrical parameters output by the motor.

[0056] In one embodiment, such as Figure 7 As shown, to obtain a higher magnetic weakening capability, a leading conduction angle α can be set. That is to say, whether in the two-to-two conduction mode or the three-to-three conduction mode, the winding has a leading conduction angle α.

[0057] Referring to Figure 8, which compares the field weakening capability and work capacity of the motor, the horizontal axis represents the expansion angle. Figure 8a The vertical axis represents the motor's work capacity. Figure 8b The vertical axis represents the excitation capability of the motor, which includes strong magnetic capability and weak magnetic capability. Figure 8a Line 1 represents the motor's work capacity when there is no lead angle and the windings are conducting in pairs, i.e., the motor's work capacity when the lead angle is 0 and the extension angle is also 0; Line 2 represents the motor's work capacity when there is no lead angle and the windings are conducting in pairs or in three-three combinations, i.e., the motor's work capacity when the lead angle is 0 and the extension angle is not 0; Line 3 represents the motor's work capacity when there is a lead angle and the windings are conducting in pairs or in three-three combinations, i.e., the motor's work capacity when the lead angle is not 0 and the extension angle is not 0. Figure 8bLine 1 represents the excitation capability of the motor when there is no advance angle and the windings are two-by-two conduction, i.e., the advance angle is 0 and the extension angle is also 0; line 2 represents the excitation capability of the motor when there is no advance angle and the windings are two-by-two conduction and three-by-three conduction combination, i.e., the advance angle is 0 and the extension angle is not 0; line 3 represents the excitation capability of the motor when there is an advance angle and the windings are two-by-two conduction and three-by-three conduction combination, i.e., the advance angle is not 0 and the extension angle is also not 0. Among them, when the excitation is positive, it represents the strong magnetic capability, and when the excitation is negative, it represents the weak magnetic capability. It can be seen from Figure 8a that setting a certain extension angle can increase the doing function of the motor. Preferably, the range of the extension angle β is 0-π / 3. Setting the extension angle α on the basis of the extension angle will reduce the doing function of the motor to a certain extent, but even at π / 3, the difference between line 1 and line 3 is less than 0.2, that is, increasing the advance angle has little effect on the doing function of the motor to a certain extent. It can be seen from Figure 8b that setting the extension angle β can increase the weak magnetic capability of the motor, and increasing the advance angle α on this basis will greatly improve the weak magnetic capability of the motor. As can be seen from the above, the appropriate extension angle can balance the weak magnetic capability and the doing function of the motor, and can improve the motor speed on the premise of ensuring the doing function.

[0058] In a specific implementation, the controller 24 can obtain rotor position information, because the rotor position is different, the conduction mode of the stator winding is also different, and the stator magnetic potential is different under different conduction modes of the winding. Therefore, the controller 24 can control the change of the conduction state of the winding according to the rotor position information, and then adjust the stator magnetic potential, and then determine the synthesized magnetic potential of the motor according to the rotor magnetic potential and the adjusted stator magnetic potential, and the electrical parameters output by the motor under the synthesized magnetic potential are within the preset parameter range. That is, by adjusting the synthesized magnetic potential of the motor, the motor can meet certain rotation characteristics. In an embodiment, the electrical parameter of the motor can be the motor speed, or the output power efficiency determined based on the speed and torque. The above process can be understood as follows: the controller can adjust the conduction mode of the electronic winding according to the rotor position information, so that the motor speed can reach a certain speed or the motor speed can be improved to a certain range, while ensuring that the motor has good output power efficiency. Among them, the conduction mode of the winding includes two-by-two conduction and / or three-by-three conduction and / or combination of two-by-two conduction and three-by-three conduction, and the extension angle and / or the advance angle under different conduction modes.

[0059] It can be seen from Figure 3 and Figure 4It can be seen that the stator magnetic potential in the three-phase motor with any two-phase stator winding conducting is less than the stator magnetic potential in the three-phase motor with all three-phase windings conducting. Therefore, when the rotor is in the first preset position, the controller 24 can increase the stator magnetic potential by controlling the motor to connect to the power module in a manner that all three-phase stator windings are conducting. When the rotor is in the second preset position, the controller 24 can reduce the stator magnetic potential by controlling the motor to connect to the power module in a manner that any two-phase stator windings are conducting. The increase in the stator magnetic potential can be to keep the current direction of the stator magnetic potential unchanged and increase the size of the stator magnetic potential, or to change the direction of the stator magnetic potential while increasing its size. The reduction of the stator magnetic potential can be to keep the current direction of the stator magnetic potential unchanged, reduce the stator magnetic potential to zero or to a certain value, or to change the direction of the stator magnetic potential while reducing the stator magnetic potential to zero or to a certain value.

[0060] In one embodiment, when the rotor is in the first preset position, the controller can control the stator windings to switch from the two-by-two conducting mode to the three-by-three conducting mode, and when the rotor is in the second preset position, the controller can control the stator windings to switch from the three-by-three conducting mode to the two-by-two conducting mode. It can be understood that in the selected phase band, the two-by-two conducting mode or the three-by-three conducting mode can be switched multiple times, so the above-mentioned first preset position and second preset position are not a fixed rotor position, but a position of the rotor when the motor's resultant magnetic potential changes to cause the electrical parameters to exceed the preset range during the rotation of the rotor. In a specific implementation, the controller identifies the current rotor position through the rotor position detection module 22 and determines whether the current position is the first preset position or the second preset position.

[0061] That is, in the selected phase band, adjusting the number of conducting stator windings by detecting the rotor position information can adjust the stator magnetic potential, thereby affecting the resultant magnetic potential, i.e., the first resultant magnetic potential and the second resultant magnetic potential, to achieve the premise of less affecting the motor's doing function, and to improve the motor speed.

[0062] As can be seen from the above embodiment, the conducting mode of the three-phase non-inductive BLDC stator windings in the selected phase band can be switched according to the rotor position information, for example, between the first conducting mode of two-phase windings conducting and the second conducting mode of all three-phase windings conducting. In this embodiment, it is defined that the two-phase stator windings conduct a first electrical angle in the first conducting mode, i.e., the two-by-two conducting mode, and the three-phase stator windings conduct a second electrical angle in the second conducting mode, i.e., the three-by-three conducting mode. The motor has a first electromagnetic torque when conducting the first electrical angle in the first conducting mode, and has a second electromagnetic torque when conducting the second electrical angle in the second conducting mode. The electromagnetic torque is also the output torque of the motor, which can represent the doing function of the motor.

[0063] Since the motor itself has a reluctance torque that affects the motor's ability to do work, the reluctance torque and the electromagnetic torque under different conduction modes jointly constitute the total torque of the motor, and the total torque can accurately reflect the motor's ability to do work. It can be understood that the greater the total torque of the motor under unit current, the more power-saving the tool is, so under the premise of ensuring the motor's ability to do work and improving the motor's speed, the energy consumption can be further reduced.

[0064] Referring to Figure 9 The circuit block diagram of the electric tool shown in FIG. 4 further comprises a torque detection module 25 for detecting the output torque of the motor under different conduction modes of the stator winding. For example, the first electromagnetic torque of the motor when the motor is conducted for the first electric angle under the first conduction mode and the second electromagnetic torque of the motor when the motor is conducted for the second electric angle under the second conduction mode can be detected. It can be understood that the torque detection module 25 can also detect the reluctance torque of the motor, wherein the reluctance torque is caused by the difference in magnetic resistance of the direct axis and the cross axis of the rotor in the motor.

[0065] Referring to Figure 10 and Figure 11 The electromagnetic torque schematic diagram shown in FIG. 5, the horizontal axis represents the angle of rotation of the rotor, and the vertical axis represents the size of the torque. Line 1 is the total torque of the motor under the first conduction mode, line 2 is the total torque of the motor under the second conduction mode, line 3 is the first electromagnetic torque of the motor under the first conduction mode, line 4 is the second electromagnetic torque of the motor under the second conduction mode, and line 5 is the reluctance torque of the motor. It can be seen from Figure 10 that the reluctance torque of the motor is a sinusoidal waveform, that is, within a certain electric angle, the reluctance torque can increase the total torque of the motor, and within a certain electric angle, it can reduce the total torque of the motor, so Figure 10 the shaded area in the figure represents the interval range of the rotor rotation angle when the motor has the maximum total torque. Preferably, the range of the interval is 90°-135°. That is, the definition domain of the motor having the maximum total torque is 90°-135°. Further, as Figure 11 shown in FIG. 6, the two shaded intervals respectively represent the first total torque under the first conduction mode and the second total torque under the second conduction mode under unit current, and the sum of the two is the total torque of the motor required finally. That is, Figure 11 the sum of the areas of the two shaded areas in FIG. 6 is the maximum total torque of the motor under unit current.

[0066] Based on this, the controller 24 can adjust the first electric angle conducted under the first conduction mode and the second electric angle conducted under the second conduction mode according to the position of the rotor of the motor, so that the total torque of the motor under unit current in the selected phase band is within the preset torque range. It can be understood that the energy consumption of different tools is different, and the preset torque is also different. The preset torque range in the present application can cover the total torque values of the motor corresponding to different energy consumption requirements of different tools. ​

[0067] It can be understood that the process of adjusting the conduction electrical angle of the stator winding in different conduction modes is also a process of affecting the stator magnetic potential, and therefore has a relatively small effect on the improvement of the motor's power and speed in the process of adjusting the total torque to reduce the motor's energy consumption.

[0068] In an embodiment, the ratio of the first electrical angle and the second electrical angle in the selected phase band can be obtained by table lookup according to a preset torque range.

[0069] For different tools and different specific use conditions of the tools, the conduction mode of the motor stator winding can be controlled to ensure that the power tool has stable output performance under different working conditions and has a large output power.

[0070] The running stage of a general tool can be divided into a high-speed running stage and a low-speed running stage. The minimum speed of the motor in the high-speed running stage of different tools under different working conditions is different, and the maximum speed of the motor in the low-speed running stage of different tools under different working conditions is also different. In an embodiment, the high-speed running stage is defined as the first working stage of the tool, and the low-speed running stage is defined as the second working stage of the tool. Generally, in the first working stage, it is desired that the motor maintains a constant speed for a period of time before the working parameters of the motor are overloaded and the motor switches to the second working stage. In the present application, the motor adopts a conduction mode of switching between two-by-two conduction and three-by-three conduction to control the motor running, and therefore, to obtain a basically stable speed in the first working stage, the controller adjusts the second electrical angle β of the motor in the second conduction mode, i.e., the three-by-three conduction mode, in the first working stage, so as to maintain the speed of the motor in a basically stable state. Further, in the second working stage, the stator winding can be controlled to be conducted in the first preset electrical angle in the three-by-three conduction mode, i.e., in a fixed electrical angle. In particular, in the first working stage and the second working stage, the motor is switched between the two-by-two conduction and the three-by-three conduction, i.e., in the two working stages, the motor exists in two conduction working modes, i.e., the two-by-two conduction and the three-by-three conduction, and the electrical angle of the two-by-two conduction in the two working stages is a fixed value, for example, the second preset electrical angle. Therefore, the present application does not describe the electrical angle of the two-by-two conduction of the motor in the two working stages. That is to say, the electrical angle of the three-by-three conduction of the tool in the high-speed running stage is constantly changing, the electrical angle of the three-by-three conduction of the tool in the low-speed running stage is fixed, and the electrical angle of the two-by-two conduction in the two running stages is a fixed value. In the present embodiment, the sizes of the first preset electrical angle and the second preset electrical angle are not specifically limited.

[0071] In one embodiment, the controller 24 adjusts the electrical angle (expansion angle β) of the motor stator winding in the second conduction mode, i.e., 3x3 conduction, while maintaining the stator winding at a fixed lead angle α, thus keeping the motor speed essentially constant. For example, if the stator winding has a lead angle of 15° in the first operating stage, and the expansion angle of the 3x3 conduction changes from 0° to 45°, the motor speed can be maintained in a relatively stable state.

[0072] like Figure 12 As shown, the horizontal axis represents the motor's output torque T, and the vertical axis represents the motor's speed n. In the first operating stage, the motor speed and output torque remain essentially constant, and line 1 is basically parallel to the horizontal axis. However, the motor current rises rapidly in the first operating stage, and the motor will bear a large current in a short period of time. Therefore, the duration of the first operating stage should not be too long. In one implementation, when the motor is in the first operating stage, the controller 24 can stop adjusting the electrical angle under the first conduction mode, so that the stator winding of the motor conducts at a third preset electrical angle, while maintaining a constant lead angle α, thereby reducing the motor speed and the slope of the change in the motor's operating current, allowing the motor to enter the second operating stage. The third preset electrical angle is a fixed electrical angle, and its size is not specifically limited in this application. It is understood that if the motor maintains a high speed continuously, it will lead to severe overheating. Therefore, when a speed reduction is needed, the controller can control the motor to enter the second operating stage.

[0073] In one embodiment, the controller can control the motor to enter the second operating stage when the conduction angle of the second conduction mode reaches an angle threshold. For example, when the extension angle changes from 0° to 45° in the first operating stage, the controller 24 no longer adjusts the extension angle, so that the motor windings conduct with a 15° lead angle and a fixed extension angle less than or equal to 45° to enter the second operating stage.

[0074] In one embodiment, such as Figure 13 As shown, the power tool also includes a current detection module 26 for detecting the motor's operating current. After acquiring the motor's operating current, the controller 24 can calculate the slope of the current change. Furthermore, the controller can control the motor to switch to the second operating stage based on the slope of the motor current change in the first operating stage, that is, control the electrical angle of the second conduction mode of the motor stator winding to be a first preset electrical angle. In other words, in the second operating stage, the lead angle α of the motor stator winding and the extension angle β when conducting in a 3x3 configuration are both fixed values. In this application, the motor operating current is defined to have a first slope in the first operating stage and a second slope in the second operating stage, as follows: Figure 14 As shown, the horizontal axis represents the motor output torque, and the vertical axis represents the motor operating current. Figure 14It can be seen that the second change slope of the motor current in the second working phase is obviously smaller than the first change slope in the first working phase. In combination with Figure 12 and Figure 14 It can be seen that in the second working phase, the current change slope becomes smaller, but the working current value does not decrease, and the motor speed decreases.

[0075] In the specific implementation, when the controller 24 detects that the motor working current reaches the current threshold at the first change slope in the first working phase of the motor, the controller can control the motor to switch to the second working phase, i.e., no longer adjust the expansion angle β. It can be understood that when the motor working current reaches the current threshold at the first change slope in the first working phase, the expansion angle β of the motor winding three-phase conduction is the maximum electrical angle that can be reached in the second conduction mode. In the second working phase, the fixed second electrical angle of three-phase conduction is smaller than or equal to the maximum electrical angle. For example, when the expansion angle of three-phase conduction is adjusted from 0° to 20° in the first working phase, the motor working current reaches the current threshold in the first working phase, and the controller controls the motor to conduct in the second working phase with a lead angle of 15° and a fixed expansion angle smaller than or equal to 20°. That is, when the motor working current reaches the current threshold at the first current slope in the first working phase, and the electrical angle in the second conduction mode is smaller than the angle threshold, the controller still controls the motor to enter the second working phase.

[0076] By adjusting the expansion angle in the first working phase to maintain the speed and output torque of the motor, the output performance of the motor can be maintained stable in different working conditions in the starting phase. By fixing the expansion angle to make the motor work in the second phase, the continuous and rapid increase of the current can be avoided, and the motor can be damaged.

[0077] Note that the above is only the preferred embodiment of the present application and the technical principle applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, readjustments and substitutions without departing from the scope of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims.

Claims

1. An electric tool, comprising: An electric motor has a multi-phase stator winding, wherein each phase winding of the motor can be turned on in a first conduction mode and a second conduction mode within a selected phase band; A torque detection module is used to detect the output torque of the motor. A speed detection module is used to detect the speed of the motor; The controller is electrically connected to at least the torque detection module, the speed detection module, and the motor; The controller is configured to: Obtain the output torque and speed of the motor; In the first working stage, the electrical angle of the motor is adjusted to operate in the second conduction mode so that the motor speed is maintained in a basically stable state; In the second working phase, the stator winding is controlled to conduct at a first preset electrical angle under the second conduction mode; In the first working stage, when the slope of the change in the motor's operating current reaches a current threshold, the motor is controlled to enter the second working stage.

2. The power tool according to claim 1, characterized in that, The controller is configured to: In the first and second working phases, the stator winding is controlled to conduct at a second preset electrical angle in the first conduction mode.

3. The power tool according to claim 1, characterized in that, The controller is configured to: In the first working stage, when the electrical angle of the motor operating in the second conduction mode reaches a preset angle threshold, the stator winding is controlled to conduct in the second conduction mode at a third preset electrical angle.

4. The power tool according to claim 1, characterized in that, Also includes: A current detection module is used to detect the operating current of the motor; The controller is configured to: Obtain the operating current of the motor and calculate the slope of the change in the operating current; When the operating current of the motor reaches the current threshold under the first change slope in the first working stage, the stator winding is controlled to conduct at the first preset electrical angle so that the motor enters the second working stage.

5. The power tool according to claim 4, characterized in that, During the first operating phase, the output current of the motor has the first change slope, and during the second operating phase, the output current of the motor has the second change slope. The first slope of change is greater than the second slope of change.

6. The power tool according to claim 3, characterized in that, When the operating current of the motor reaches the current threshold under the first change slope during the first working stage, the electrical angle of the stator winding in the second conduction mode is the maximum electrical angle that can be achieved under the second conduction mode.

7. The power tool according to claim 6, characterized in that, The first preset electrical angle is less than or equal to the maximum electrical angle at which the stator winding is turned on in the second conduction mode during the first working phase.

8. The power tool according to claim 1, characterized in that, The first conduction method includes conducting any two phase windings of the motor; The second conduction method includes conducting three-phase windings in each phase winding of the motor.

9. A method for controlling an electric tool, the electric tool comprising: An electric motor has a multi-phase stator winding, wherein each phase winding of the motor can be turned on in a first conduction mode and a second conduction mode within a selected phase band; A torque detection module is used to detect the output torque of the motor. A speed detection module is used to detect the speed of the motor; The controller is electrically connected to at least the torque detection module, the speed detection module, and the motor; The control method includes: Obtain the output torque and speed of the motor; In the first working stage, the electrical angle of the motor is adjusted to operate in the second conduction mode so that the motor speed is maintained in a basically stable state; In the second working phase, the stator winding is controlled to conduct at a first preset electrical angle under the second conduction mode; In the first working stage, when the slope of the change in the motor's operating current reaches a current threshold, the motor is controlled to enter the second working stage.

10. The method according to claim 9, characterized in that, The method further includes: In the first and second working phases, the stator winding is controlled to conduct at a second preset electrical angle in the first conduction mode.

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