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 driving circuit and a controller. The motor comprises a rotor and a multi-phase stator winding. The driving circuit has a plurality of switching elements for outputting switching signals to drive the motor to rotate. The controller is electrically connected with the driving circuit and the motor. The controller is configured to acquire rotor position information of the motor, and adjust a resultant magnetic potential of the motor according to the rotor position information, so that an output electric parameter of the motor corresponding to the resultant magnetic potential is within a preset parameter range. The electric tool provided by the application can guarantee the working capacity and effectively improve the rotating speed of the motor.

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] Permanent magnet electric motor, including inner rotor motor and outer rotor motor have different load or torque speed regulation requirements. Common speed regulation method is generally voltage regulation, field weakening or sensor position based speed regulation. However, the whole machine cost of voltage regulation is high, field weakening is very easy on electric excitation motor, and can only use armature effect to realize speed regulation on permanent magnet motor.

[0003] The existing field weakening technology can realize speed regulation by changing the lead angle, but when the lead angle is changed to increase the speed, the load will increase and the output speed will quickly decrease, that is, the speed is not stable, and at the same time, the output torque will also decrease due to the increase of the load, which affects the motor's doing function. SUMMARY

[0004] In order to solve the problems of the prior art, the purpose of the present application is to provide an electric power tool which can not only guarantee the doing function but also effectively improve the speed.

[0005] The present application adopts the following technical solutions:

[0006] An electric power tool, comprising: a motor comprising a rotor and a multi-phase stator winding; a drive circuit having a plurality of switching elements for outputting switching signals to drive the motor to rotate; a controller electrically connected with at least the drive circuit and the motor; the controller is configured to: obtain rotor position information of the motor; adjust a synthesized magnetic potential of the motor according to the rotor position information, so that an output electrical parameter of the motor corresponding to the synthesized magnetic potential is within a preset parameter range.

[0007] Further, the controller is configured to: control the on-off state of the drive circuit based on the rotor position information to adjust the stator magnetic potential of the stator winding; calculate the synthesized magnetic potential of the motor based on the rotor magnetic potential of the motor and the adjusted stator magnetic potential, so that the output electrical parameter of the motor corresponding to the synthesized magnetic potential is within the preset parameter range.

[0008] Further, it further comprises a rotor position detection module for detecting the rotor position of the motor; an electrical parameter detection module electrically connected with the motor for detecting the electrical parameter output by the motor.

[0009] Further, the rotor position detection module comprises a Hall sensor.

[0010] Further, the rotor position detection module is configured to:

[0011] estimating the rotor position based on back electromotive force of the stator winding or estimating the rotor position based on phase current of the stator winding.

[0012] Further, the controller is configured to: control the drive circuit to change the conduction state to increase the stator magnetic potential when the rotor is at a first preset position; and control the drive circuit to change the conduction state to decrease the stator magnetic potential when the rotor is at a second preset position.

[0013] Further, the electrical parameter includes a rotational speed of the motor.

[0014] Further, the controller is configured to: calculate a first resultant magnetic potential in a first direction and a second resultant magnetic potential in a second direction based on the rotor magnetic potential of the motor and the adjusted stator magnetic potential, so that the rotational speed of the motor corresponding to the first resultant magnetic potential is within a preset rotational speed range, and so that the output efficiency of the motor corresponding to the second resultant magnetic potential is within a preset efficiency range.

[0015] Further, the first direction is perpendicular to the second direction.

[0016] Further, the motor has a three-phase stator winding; and the controller is configured to: control the drive circuit to change the conduction state so that all the three-phase stator windings of the motor are connected to the power supply module when the rotor is at a first preset position; and control the drive circuit to change the conduction state so that any two of the three-phase stator windings of the motor are connected to the power supply module when the rotor is at a second preset position.

[0017] A control method of an electric tool, the electric tool comprising: a motor comprising a rotor multi-phase stator winding; a drive circuit having a plurality of switching elements for outputting switching signals to drive the motor to rotate; and a controller electrically connected with at least the drive circuit and the motor; the control method comprising: obtaining rotor position information of the motor; and adjusting a resultant magnetic potential of the motor according to the rotor position information, so that an output electrical parameter of the motor corresponding to the resultant magnetic potential is within a preset parameter range.

[0018] The electric tool provided by the application can effectively improve the working performance and rotational speed of the motor by adjusting the stator magnetic potential of the motor. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural schematic diagram of an electric tool provided by an embodiment of the application;

[0020] Figure 2 is a circuit block diagram of an electric tool provided by an embodiment of the application;

[0021] Figure 3 is a schematic diagram of magnetic potential change in a motor when two of the embodiments provided by the present application are conducted;

[0022] Figure 4 is a schematic diagram of magnetic potential change in a motor when three of the embodiments provided by the present application are conducted;

[0023] Figure 5 is a schematic diagram of a certain phase in-band winding conduction mode provided by the embodiments of the present application;

[0024] Figure 6 is a schematic diagram of magnetic potential synthesis provided by the embodiments of the present application;

[0025] Figure 7 is a schematic diagram of a certain phase in-band winding conduction mode provided by the embodiments of the present application;

[0026] Figure 8a and Figure 8b is a schematic diagram of motor power and field weakening capability provided by the embodiments of the present application;

[0027] Figure 9 is a circuit block diagram of an electric tool provided by the embodiments of the present application;

[0028] Figure 10 and Figure 11 is a schematic diagram of electromagnetic torque provided by the embodiments of the present application;

[0029] Figure 12 is a schematic diagram of output performance of a tool in different stages provided by the embodiments of the present application;

[0030] Figure 13 is a circuit block diagram of an electric tool provided by the embodiments of the present application;

[0031] Figure 14 is a schematic diagram of output performance of a tool in different stages provided by the embodiments of the present application. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with reference to the accompanying 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.

[0033] 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 this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] The electric tools to which the technical solution of this invention applies include grinding tools, electric drills, electric circular saws, reciprocating saws, miter saws, and any electric tools that can adopt a brushless and sensorless electric control method. Other types of electric tools can fall within the protection scope of this invention as long as they can adopt the substantive content of the technical solution disclosed below.

[0035] In the embodiments of this application, reference is made to Figure 1 Taking a sander as an example, the power tool 100 includes at least a housing 10 and a motor 11 inside the housing. Figure 1 (Not shown), base plate 12, transmission mechanism (not shown), grip part 13, battery pack 14.

[0036] A motor is built into the housing 10. In one embodiment, the housing 10 includes a left housing and a right housing. During assembly, the left and right housings close together from the left and right sides and are secured with screws. In one embodiment, the motor shaft is parallel to the base plate 12 and is built into the front end of the tool 100. The motor 11 drives a transmission mechanism to perform sanding work on sandpaper fixed on the base plate 12. The transmission mechanism is used to connect at least the motor shaft and the output shaft and can be a two-stage transmission gear. The housing 10 has an ergonomically designed grip 13 for the user to hold. The tool 100 also includes an electronic membrane switch for controlling the power on and off. A battery pack 14 is installed at the rear end of the tool, with the longest side of the battery pack 14 parallel to the plane of the base plate. The overall size of the tool is relatively small.

[0037] refer to Figure 2 The circuit block diagram of the power tool shown includes a drive system for motor 11 that may include at least a drive circuit 20, a power supply module 21, a rotor position detection module 22, an electrical parameter detection module 23, and a controller 24.

[0038] 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 windings or other methods. However, the sensorless BLDC cannot accurately determine the rotor position when starting or at low speed with 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 voltage regulation method has high cost, and the traditional field weakening method can greatly reduce the power of the motor. In this application, the stator magnetic potential is adjusted for speed control, which can solve the above problems. Of course, the stator magnetic potential can also be adjusted for speed control in a sensored BLDC.

[0039] 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 cells. For example, the battery cells can be connected in series 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 accordingly according to the specific parameters of the power tool.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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:

[0045] Table 1

[0046]

[0047]

[0048] In Table 1, a 0 below the Hall position indicates that the Hall position of the corresponding winding falls at the S-pole of the rotor, and a 1 below the Hall position indicates that the Hall position of the corresponding winding falls at the N-pole of the rotor. In Table 1, a 0 below the PWM signal combination indicates that the lower transistor of the corresponding winding is on, a 1 below the PWM signal combination indicates that the upper transistor of the corresponding winding is on, and an X below the PWM signal combination indicates that neither the upper nor lower transistor of the corresponding winding is on.

[0049] Depend on Figure 3 It can be seen that within the 360° electrical angle range, the rotor magnetomotive force during rotor rotation... The direction is constantly changing. The magnitude remains unchanged; while the stator magnetomotive force remains unchanged. The magnetomotive force is synthesized by the two conducting stator windings. Its direction changes with the commutation of the stator windings, and its magnitude is also related to the conduction direction and conduction current of the conducting phase windings. For example, Figure 3 When the PWM signal output by the controller is (1, 0, X), the rotor rotates within a phase band of 30° to 90°, and windings A and B are turned on in the A+B- configuration, and the rotor magnetomotive force... In the direction parallel to the rotor, the stator magnetomotive force The magnetomotive force of phases A and B is synthesized. Commutation occurs once every 60 electrical degrees of rotor rotation. The commutation process of the rotor according to the drive signals shown in Table 1 corresponds to... Figure 3 The commutation process indicated by the middle arrow also corresponds to the rotor magnetomotive force and stator magnetomotive force. Figure 3 The changes shown are as follows.

[0050] like Figure 4 The diagram illustrates the magnetomotive force (MF) change process when all three phases of a three-phase non-inductive BLDC motor are conducting (i.e., three-by-three conduction). Table 2 shows the correspondence between Hall position, PWM signal, and the conduction state of the motor stator windings under the three-phase winding all-conducting mode.

[0051] Table 2

[0052] 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-

[0053] Depend on Figure 4 It can be seen that within the 360° electrical angle range, the rotor magnetomotive force during rotor rotation... The direction is constantly changing. The magnitude remains unchanged; while the stator magnetomotive force remains unchanged. The magnetomotive force (MOMF) synthesized from the conducting three-phase stator windings changes direction with the commutation of the stator windings, and its magnitude is also related to the conduction direction and conduction current of the three-phase windings. For example, Figure 4The 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 .

[0054] 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 β° of electrical degrees, and in the two-by-two conduction mode for 60-β° of electrical degrees, 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.

[0055] 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 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.

[0056] In the present application, the first synthesized magnetic potential is the synthesis of and on the direct axis, and the second synthesized magnetic potential is the synthesis of 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.

[0057] In this application, the motor output efficiency is the efficiency of the motor power output, which represents the motor's work capacity.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 in 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.

[0063] 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 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.

[0064] 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.

[0065] 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, the two-phase stator windings are defined to conduct a first electrical angle in the first conducting mode, i.e., the two-by-two conducting mode, and the three-phase stator windings are defined to 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.

[0066] 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.

[0067] 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.

[0068] 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 final required total torque of the motor. 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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. 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.

[0078] 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, that is, 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.

[0079] By adjusting the expansion angle in the first working phase to maintain the speed and output torque of the motor, the stable output performance of the motor can be maintained 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.

[0080] 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, comprising a rotor and multiphase stator windings; The drive circuit has multiple switching elements for outputting switching signals to drive the motor to rotate. The controller is electrically connected to at least the drive circuit and the motor; The controller is configured to: Obtain the rotor position information of the motor; The combined magnetomotive force of the motor is adjusted according to the rotor position information so that the output electrical parameters of the motor corresponding to the combined magnetomotive force are within a preset parameter range; When the rotor is in the first preset position, the drive circuit is controlled to change the conduction state to increase the stator magnetomotive force; when the rotor is in the second preset position, the drive circuit is controlled to change the conduction state to decrease the stator magnetomotive force; wherein, the conduction state includes the multiphase stator windings being conducted in pairs and in triplets.

2. The power tool according to claim 1, characterized in that, The controller is configured to: The conduction state of the drive circuit is controlled based on the rotor position information to adjust the stator magnetomotive force of the stator winding; The combined magnetomotive force of the motor is calculated based on the rotor magnetomotive force and the adjusted stator magnetomotive force, so that the output electrical parameters of the motor corresponding to the combined magnetomotive force are within the preset parameter range.

3. The power tool according to claim 1, characterized in that, Also includes: A rotor position detection module is used to detect the rotor position of the motor; An electrical parameter detection module is electrically connected to the motor and is used to detect the electrical parameters output by the motor.

4. The power tool according to claim 3, characterized in that, The rotor position detection module includes a Hall sensor.

5. The power tool according to claim 3, characterized in that, The rotor position detection module is configured as follows: The rotor position is estimated based on the back electromotive force of the stator winding or based on the phase current of the stator winding.

6. The power tool according to claim 1, characterized in that, The controller is configured to: Based on the rotor magnetomotive force and the adjusted stator magnetomotive force of the motor, a first composite magnetomotive force in the first direction and a second composite magnetomotive force in the second direction are calculated, so that the speed of the motor corresponding to the first composite magnetomotive force is within a preset speed range, and the power output efficiency of the motor corresponding to the second composite magnetomotive force is within a preset efficiency range.

7. The power tool according to claim 6, characterized in that, The first direction is perpendicular to the second direction.

8. The power tool according to claim 4, characterized in that, The motor has a three-phase stator winding; The controller is configured to: When the rotor is in the first preset position, the drive circuit is controlled to change the conduction state so that all three phase stator windings of the motor are connected to the power module. When the rotor is in the second preset position, the drive circuit is controlled to change the conduction state so that any two phases of the stator winding of the motor are connected to the power module.

9. A control method for an electric tool, The power tool includes: An electric motor, comprising a rotor and multiphase stator windings; The drive circuit has multiple switching elements for outputting switching signals to drive the motor to rotate. The controller is electrically connected to at least the drive circuit and the motor; The control method is characterized by comprising: Obtain the rotor position information of the motor; The combined magnetomotive force of the motor is adjusted according to the rotor position information so that the output electrical parameters of the motor corresponding to the combined magnetomotive force are within a preset parameter range; When the rotor is in the first preset position, the drive circuit is controlled to change the conduction state to increase the stator magnetomotive force; when the rotor is in the second preset position, the drive circuit is controlled to change the conduction state to decrease the stator magnetomotive force; wherein, the conduction state includes the multiphase stator windings being conducted in pairs and in triplets.

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