Power tool and control method thereof

Abstract

The present invention discloses an electric tool and a control method thereof. The electric tool includes a motor having a multi-phase winding, wherein each phase winding of the motor can conduct at a first electrical angle in a first conduction mode and at a second electrical angle in a second conduction mode within a selected phase band; a torque detection module for detecting a first electromagnetic torque of the motor when conducting at the first electrical angle in the first conduction mode, and a second electromagnetic torque of the motor when conducting at the second electrical angle in the second conduction mode; and a controller electrically connected to at least the torque detection module and the motor. The controller is configured to: obtain the first electromagnetic torque and the second electromagnetic torque, and calculate the total torque of the motor per unit current within the phase band based on the first electromagnetic torque, the second electromagnetic torque, and the reluctance torque of the motor; and adjust the first electrical angle and the second electrical angle so that the total torque of the motor per unit current within the phase band is within a preset torque range. The present invention provides a low-energy electric tool.

Description

Technical Field

[0001] The present invention relates to the field of electric tools, and in particular to an electric tool and a control method thereof. Background Art

[0002] Permanent magnet motors (including inner-rotor and outer-rotor motors) all require speed regulation under varying loads or torque conditions. Common speed regulation methods include voltage regulation, field weakening, or sensor position-based speed regulation. However, voltage regulation carries a high cost, and field weakening, while readily available for electrically excited motors, is not applicable to permanent magnet motors, requiring speed regulation to be achieved using the armature effect.

[0003] Existing inductive magnetic weakening technology achieves speed regulation by changing the lead angle. However, increasing the speed by changing the lead angle causes the output speed to drop rapidly as the load increases, which means the speed is unstable. Furthermore, increased load also increases the motor's energy consumption. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, an object of the present invention is to provide a low-energy-consumption electric tool.

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

[0006] An electric tool comprises: a motor having a multi-phase winding, wherein each phase winding of the motor can conduct a first electrical angle in a first conduction mode and conduct a second electrical angle in a second conduction mode within a selected phase band; a torque detection module for detecting the first electromagnetic torque of the motor when conducting at the first electrical angle in the first conduction mode, and the second electromagnetic torque of the motor when conducting at the second electrical angle in the second conduction mode; a controller electrically connected to at least the torque detection module and the motor; the controller is configured to: obtain the first electromagnetic torque and the second electromagnetic torque, and calculate the total torque of the motor under unit current in the phase band based on the first electromagnetic torque, the second electromagnetic torque and the reluctance torque of the motor; adjust the first electrical angle and the second electrical angle so that the total torque of the motor under unit current in the phase band is within a preset torque range.

[0007] Furthermore, the reluctance torque of the motor is quasi-sine wave.

[0008] Furthermore, the first conduction mode includes conducting any two phase windings among the phase windings of the motor; and the second conduction mode includes conducting three phase windings among the phase windings of the motor.

[0009] Furthermore, the controller is configured to: detect the rotor position of the motor; in the first conduction mode, switch to the second conduction mode when the rotor position reaches a first preset position; in the second conduction mode, switch to the first conduction mode when the rotor position reaches a second preset position.

[0010] Furthermore, the ratio of the first electrical angle to the second electrical angle in the selected phase band is obtained by looking up a table according to the preset torque range.

[0011] A control method for an electric tool, the electric tool comprising: a motor having a multi-phase winding, wherein each phase winding of the motor can conduct a first electrical angle in a first conduction mode and conduct a second electrical angle in a second conduction mode within a selected phase band; a torque detection module for detecting a first electromagnetic torque of the motor when conducting at a first electrical angle in the first conduction mode, and a second electromagnetic torque of the motor when conducting at a second electrical angle in the second conduction mode; a controller electrically connected to at least the torque detection module and the motor; the control method comprising: obtaining the first electromagnetic torque and the second electromagnetic torque and calculating the total torque of the motor under unit current in the phase band based on the first electromagnetic torque, the second electromagnetic torque and the reluctance torque of the motor; and adjusting the first electrical angle and the second electrical angle so that the total torque of the motor under unit current in the phase band is within a preset torque range.

[0012] Furthermore, the reluctance torque of the motor is quasi-sine wave.

[0013] Furthermore, the first conduction mode includes conducting any two phase windings among the phase windings of the motor; and the second conduction mode includes conducting three phase windings among the phase windings of the motor.

[0014] Furthermore, the method also includes: detecting the rotor position of the motor; in the first conduction mode, switching to the second conduction mode when the rotor position reaches a first preset position; in the second conduction mode, switching to the first conduction mode when the rotor position reaches a second preset position.

[0015] Furthermore, the ratio of the first electrical angle to the second electrical angle in the selected phase band is obtained by looking up a table according to the preset torque range.

[0016] The present invention is beneficial in that the total torque of the motor is changed by adjusting the electrical angles of different conduction modes within the phase band to obtain the maximum torque per unit current, thereby reducing the working energy consumption of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 11 is a schematic structural diagram of an electric tool provided by an embodiment of the present invention;

[0018] Figure 2 This is a circuit block diagram of an electric tool provided by an embodiment of the present invention;

[0019] Figure 3 Schematic diagram of the change of magnetic potential in the motor when two motors are turned on, provided by an embodiment of the present invention;

[0020] Figure 4 Schematic diagram of magnetic potential change in a motor when three-three conduction is provided in an embodiment of the present invention;

[0021] Figure 5 Schematic diagram of the conduction mode of the winding in the selected phase band provided by an embodiment of the present invention;

[0022] Figure 6 Schematic diagram of magnetic potential synthesis provided by an embodiment of the present invention;

[0023] Figure 7 Schematic diagram of a winding conduction mode in a selected phase band combined with an advance angle provided by an embodiment of the present invention;

[0024] Figure 8a and Figure 8b 2 is a schematic diagram comparing the working capacity and magnetic weakening capacity of a motor provided by an embodiment of the present invention;

[0025] Figure 9 This is a circuit block diagram of an electric tool provided by an embodiment of the present invention;

[0026] Figure 10 and Figure 11 is a schematic diagram of electromagnetic torque provided by an embodiment of the present invention;

[0027] Figure 12 Schematic diagram of output performance of tools at different stages provided by an embodiment of the present invention;

[0028] Figure 13 This is a circuit block diagram of an electric tool provided by an embodiment of the present invention;

[0029] Figure 14 Schematic diagram of output performance of tools at different stages provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all of the components.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification are intended only to describe specific embodiments and are not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] The electric tools to which the technical solution of the present invention is applicable include grinding tools, electric drills, electric circular saws, reciprocating saws, miter saws, and any other electric tools that can adopt brushless and sensorless electric control. Other types of electric tools can fall within the scope of protection of the present invention as long as they can adopt the essential content of the technical solution disclosed below.

[0033] In the examples of this application, refer to Figure 1 Taking a sander as an example, the electric tool 100 comprises at least a housing 10, a motor 11 ( Figure 1 ), base plate 12 , transmission mechanism (not shown), grip portion 13 , and battery pack 14 .

[0034] 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 are respectively covered toward the middle from the left and right directions and fastened by screws. In one embodiment, the motor shaft of the motor is parallel to the base plate 12 and is built into the front end of the tool 100. The motor 11 drives the transmission mechanism to enable the sandpaper fixed on the base plate 12 to perform sanding. The transmission mechanism is at least used to connect the motor shaft and the output shaft, and can be a two-stage transmission gear. A gripping portion 13 is formed on the housing 10 for the user to hold in accordance with ergonomics. The tool 100 also includes an electronic membrane switch for controlling the power on and off. The battery pack 14 is inserted at the rear end of the tool. The longest side of the battery pack 14 is parallel to the plane of the base plate, and the overall size of the tool is relatively small.

[0035] refer to Figure 2 As shown in the circuit block diagram of the electric tool, the driving system of the motor 11 may at least include a driving circuit 20 , a power module 21 , a rotor position detection module 22 , an electrical parameter detection module 23 and a controller 24 .

[0036] In one embodiment, motor 11 is a brushless DC motor (BLDC). In one embodiment, motor 11 is a sensorless BLDC. In another embodiment, motor 11 is a sensored BLDC. In this application, the brushless DC motor can be either an inner rotor motor or an outer rotor motor. Motor 11 includes at least three-phase stator windings A, B, and C, which can be connected in either a star or delta configuration. In motor speed control, for BLDCs with Hall sensors or other hardware devices for detecting rotor position, the sensors can be used to directly detect the rotor position and adjust the motor speed accordingly. However, for sensorless BLDCs, since the motor lacks a rotor position sensor, the rotor position can be detected by detecting the back electromotive force of the windings or other methods. However, sensorless BLDCs cannot accurately determine the rotor position during startup or low-speed load operation, resulting in unstable output torque. Speed ​​control for sensorless BLDCs generally uses field weakening or voltage regulation. Voltage regulation is costly, while traditional field weakening significantly reduces the motor's work capacity. In this application, speed control by adjusting the stator magnetic potential can address this issue. Of course, in sensored BLDC, the motor speed can also be adjusted by adjusting the stator magnetic potential.

[0037] In one embodiment, the power source can be an AC power source, allowing the power module 21 to be connected to 120V or 220V AC mains power. In one embodiment, the power source can be 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 single power branch, forming a 1P battery pack. The output voltage of the battery pack is converted by a specific power control module, such as a DC-DC module, to output a supply voltage suitable for the drive circuit 20, motor 11, etc. to power them. Those skilled in the art will appreciate that the DC-DC module is a mature circuit structure that can be selected according to the specific parameter requirements of the power tool.

[0038] The rotor position detection module 22 is configured to identify the rotor position. In one embodiment, the rotor position detection module 22 may include a Hall sensor for detecting the rotor position. In one embodiment, the rotor position detection module 22 may estimate the rotor position based on motor parameters such as floating phase voltage or phase current. In this application, the rotor position detection module may also include any other method or hardware device capable of detecting the rotor position.

[0039] The electrical parameter detection module 23 can detect the electrical parameters of the motor 11 during operation, such as the motor speed, in real time. Optionally, the electrical parameter detection module 23 can also detect the output torque of the motor, or detect the work efficiency of the motor based on the speed and torque.

[0040] The drive circuit 20 is electrically connected to the stator windings A, B, and C of the motor 11 and is configured to transfer current from the power module 21 to the stator windings A, B, and C to drive the motor 10 to rotate. As one embodiment, the drive circuit 20 includes a plurality of switching elements Q1, Q2, Q3, Q4, Q5, and Q6. The gate terminal of each switching element is electrically connected to the controller 23 for receiving a control signal from the controller 23. The drain or source terminal of each switching element is connected to the stator windings A, B, and C of the motor 10. The switching elements Q1-Q6 receive control signals from the controller 23 to 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 can be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g., FETs, BJTs, IGBTs, etc.). It is understood that the switching elements can also be any other type of solid-state switch, such as an insulated gate bipolar transistor (IGBT) or a bipolar junction transistor (BJT).

[0041] To rotate motor 11, drive circuit 20 has multiple drive states. Controller 24, based on rotor position information, can output corresponding PWM drive signals to control switching elements within drive circuit 20, causing the drive circuit to switch between conduction states. This, in turn, changes the conduction phase of the motor's stator windings and the magnitude and direction of the current flowing through them. It should be noted that the different conduction phases of the stator windings and changes in the magnitude and direction of the current flowing through the windings will result in changes in the magnitude and direction of the stator magnetic potential.

[0042] like Figure 3 The figure shows the change of magnetic potential when two phases of the three-phase winding of the three-phase inductive BLDC are turned on, that is, two phases are turned on during the commutation process. The magnetic potential includes the magnetic potential of the motor rotor. and the stator magnetic potential of the stator winding Every time the rotor rotates 60 degrees electrical angle, the motor performs a phase change, that is, each phase winding occupies 60 degrees of phase band. The rotor corresponds to different position information in six different phase bands. The PWM drive signal output by the controller 24 can correspond to six different signal combinations. In one embodiment, signal 0 is used to represent the winding cut-off state, and signal 1 is used to represent the winding conduction state. In addition, Figure 3 The dashed line in the middle represents 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 position of the stator winding 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 conduction state of the corresponding stator windings are shown in Table 1:

[0043] Table 1

[0044]

[0045]

[0046] In Table 1, a 0 under the Hall Position indicates that the Hall Position of the corresponding winding is at the rotor's S level, and a 1 under the Hall Position indicates that the Hall Position of the corresponding winding is at the rotor's N level. In Table 1, a 0 under the PWM Signal Combination indicates that the lower transistor of the corresponding winding is conducting, a 1 under the PWM Signal Combination indicates that the upper transistor of the corresponding winding is conducting, and an X under the PWM Signal Combination indicates that neither the upper nor lower transistors of the corresponding winding are conducting.

[0047] Depend on Figure 3 It can be seen that within the 360° electrical angle range, the rotor magnetic potential is The direction keeps changing, The magnitude of the stator magnetic potential remains unchanged; It is synthesized by the magnetic potential of the two-phase stator winding. Its direction changes with the phase change of the stator winding. Its magnitude is also related to the conduction direction and conduction current of the conduction phase winding. For example, Figure 3 When the PWM signal output by the controller is (1, 0, X), the rotor rotates in the phase band of 30° to 90°, and the A and B windings are turned on in the form of A+B-. The rotor magnetic potential In the direction parallel to the rotor, the stator magnetic potential The magnetic potential of the A and B phase windings is synthesized. The rotor commutates once every 60 electrical degrees. The rotor commutates according to the drive signal shown in Table 1. Figure 3 The commutation process indicated by the arrow in the middle, the corresponding rotor magnetic potential and stator magnetic potential are also as follows Figure 3 Changes shown.

[0048] like Figure 4 The figure shows the change process of magnetic potential when all three phase windings are turned on (i.e., three-phase conduction) for a three-phase inductive BLDC. Table 2 shows the corresponding relationship between Hall position, PWM signal and conduction state of the motor stator winding when all three phase windings are turned on:

[0049] Table 2

[0050] Hall position PWM signal combination Stator winding conduction state (0，1，0) (1，0，0) A+BC- (0，1，1) (1，1，0) A+B+C- (0，0，1) (0，1，0) B+CA- (1，0，1) (0，1，1) B+C+A- (1，0，0) (0，0，1) C+AB- (1，1，0) (1，0，1) C+A+B-

[0051] Depend on Figure 4 It can be seen that within the 360° electrical angle range, the rotor magnetic potential is The direction keeps changing, The magnitude of the stator magnetic potential remains unchanged; It is synthesized by the magnetic potential of the three-phase stator winding. Its direction changes with the phase change of the stator winding, and its magnitude is also related to the conduction direction and conduction current of the three-phase winding. For example, Figure 4When the PWM signal output by the controller is (1, 0, 0), the rotor rotates within a phase range of 30° to 90°, and the A, B, and C windings are turned on in the form of A+BC-. The rotor magnetic field In the direction parallel to the rotor, the stator magnetic potential The magnetic potential of the A, B, and C phase windings is synthesized. The rotor commutates once every 60 electrical degrees. The rotor commutates according to the drive signal shown in Table 2. Figure 4 The commutation process indicated by the arrow in the middle, the corresponding rotor magnetic potential and stator magnetic potential are also as follows Figure 4 Changes shown.

[0052] Depend on Figure 3 and Figure 4 By comparison, it can be seen that the conduction mode of the motor stator winding affects the magnitude of the stator magnetic potential. Under unit current, the stator magnetic potential when all three phase windings are conducted is greater than the stator magnetic potential when the windings are conducted in pairs. Therefore, in order to obtain a larger stator magnetic potential within the selected phase band, the controller 24 can change the PWM signal to control the stator winding to operate in a combination of two-by-two conduction and three-by-three conduction. Specifically, Figure 5 As shown, within a 60° phase band, the motor's stator windings can be controlled to conduct three-on-three for an electrical angle of β° and two-on-two for an electrical angle of 60-β°, with β being the spread angle. In one embodiment, the two-on-two conduction within the selected phase band can be continuous or discontinuous. The so-called selected phase band can be of any size, and the size of the selected phase band is not limited in the embodiments of this application.

[0053] In one embodiment, the stator magnetic potential and the rotor magnetic potential can be synthesized in a certain way to obtain the synthetic magnetic potential of the motor. Figure 6 As shown, the first direction of the rotor position 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, a first synthetic magnetic potential in the direct axis direction and a second synthetic magnetic potential in the quadrature axis direction can be formed. Figure 6 The angle θ between the rotor and stator magnetic potentials can represent the motor's current excitation capability. For example, when the angle θ between the rotor and stator magnetic potentials is obtuse, the motor has field-weakening capability, while when the angle is acute, the motor has field-strengthening capability. In one embodiment, the angle θ is obtuse.

[0054] In this application, the first synthetic magnetic potential is the direct axis and As long as the magnetic potential after synthesis is greater than the original The smaller the size, the stronger the weak magnetic field ability of the motor is. Therefore, the size of the first synthetic magnetic potential represents the weak magnetic field ability of the motor. By adjusting the first synthetic magnetic potential, the speed of the motor can be adjusted. The second synthetic magnetic potential is the component of the stator magnetic potential on the quadrature axis. Based on the angle θ between the stator magnetic potential and the quadrature axis shown in Figure 6, the electromagnetic torque of the motor Where K is a fixed value, W represents the magnetic residual energy, and So the electromagnetic torque That is, the electromagnetic torque is related to the component of the stator magnetic potential on the quadrature axis, so the magnitude of the second synthetic magnetic potential represents the motor's work capacity. By adjusting the magnitude of the second synthetic magnetic potential, the electromagnetic torque can be adjusted to affect the motor's work capacity. Figure 6 As shown in the decomposition diagram of the synthetic magnetic potential, it is possible to adjust the stator magnetic potential to achieve the desired value for the second synthetic magnetic potential while maintaining the first synthetic magnetic potential. In other words, this application can ensure the motor's work capacity, i.e., its output efficiency, while increasing the motor speed.

[0055] In this application, the power efficiency of a motor is the efficiency of the motor's power output, which can represent the motor's work capacity.

[0056] Similarly, by Figure 6 It can be seen that the rotor position has a corresponding relationship with the rotor magnetic potential. When the rotor position is determined, the purpose of adjusting the synthetic magnetic potential of the two can be achieved by adjusting the stator magnetic potential, thereby controlling the electrical parameters output by the motor.

[0057] In one embodiment, Figure 7 As shown in the figure, to obtain higher magnetic weakening capability, the leading conduction angle α can be set. That is, whether in the two-two conduction mode or the three-three conduction mode, the winding has the leading conduction angle α.

[0058] Refer to the comparison chart of the weak magnetic capability and work capability of the motor shown in Figure 8, where the horizontal axis is 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 The center line 1 represents the work capacity of the motor when there is no lead angle and the windings are turned on in pairs, that is, the work capacity of the motor when the lead angle is 0 and the expansion angle is also 0; line 2 represents the work capacity of the motor when there is no lead angle and the windings are turned on in pairs and in combinations of three, that is, the work capacity of the motor when the lead angle is 0 and the expansion angle is not 0; line 3 represents the work capacity of the motor when there is a lead angle and the windings are turned on in pairs and in combinations of three, that is, the work capacity of the motor when the lead angle is not 0 and the expansion angle is not 0. Figure 8bThe middle line 1 represents the excitation capacity of the motor when there is no lead angle and the windings are turned on in pairs, that is, the excitation capacity of the motor when the lead angle is 0 and the expansion angle is also 0; line 2 represents the excitation capacity of the motor when there is no lead angle and the windings are turned on in pairs and in combinations of three, that is, the excitation capacity of the motor when the lead angle is 0 and the expansion angle is not 0; line 3 represents the excitation capacity of the motor when there is a lead angle and the windings are turned on in pairs and in combinations of three, that is, the excitation capacity of the motor when the lead angle is not 0 and the expansion angle is not 0. Among them, when the excitation is positive, it indicates strong magnetic capacity, and when the excitation is negative, it indicates weak magnetic capacity. Figure 8a It can be seen that setting a certain expansion angle can increase the work capacity of the motor. Preferably, the range of the expansion angle β is 0 to π / 3. Setting the lead angle α on the basis of setting the expansion angle will reduce the work capacity of the motor to a certain extent. However, even at π / 3, the difference between line 1 and line 3 is less than 0.2, which means that increasing the lead angle has little effect on the work capacity of the motor to a certain extent. Figure 8b It can be seen that setting the expansion angle β can increase the motor's field-weakening capability. On this basis, increasing the lead angle α will significantly improve the motor's field-weakening capability. In summary, adopting the appropriate expansion angle can achieve a balance between the motor's field-weakening capability and work performance, and can increase the motor speed while maintaining work performance.

[0059] In a specific implementation, the controller 24 can obtain rotor position information. Since the stator winding conduction mode varies depending on the rotor position, the stator magnetic potential varies under different winding conduction modes. Therefore, the controller 24 can control the change in the winding conduction state based on the rotor position information and thereby adjust the stator magnetic potential. The controller 24 can then determine the motor's composite magnetic potential based on the rotor magnetic potential and the adjusted stator magnetic potential. Under this composite magnetic potential, the electrical parameters output by the motor are within a preset parameter range. In other words, by adjusting the motor's composite magnetic potential, the motor can meet certain rotational characteristics. In one embodiment, the motor's electrical parameter can be the motor speed, or the power output 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 based on the rotor position information to ensure that the motor speed reaches a certain speed or increases the motor speed to a certain range while ensuring that the motor has a good power output efficiency. The winding conduction modes include two-by-two conduction, / or three-by-three conduction, and / or a combination of two-by-two conduction and three-by-three conduction, as well as the expansion angle and / or lead angle under different conduction modes.

[0060] Depend on Figure 3 and Figure 4It can be seen that the stator magnetic potential when any two-phase stator windings in the three-phase motor are turned on under unit current is less than the stator magnetic potential when all three-phase windings are turned on. Therefore, when the rotor is in the first preset position, the controller 24 can increase the stator magnetic potential by controlling the three-phase stator windings of the motor to be turned on and connected to the power module; when the rotor is in the second preset position, the controller 24 can reduce the stator magnetic potential by controlling any two stator windings of the motor to be turned on and connected to the power module. Increasing the stator magnetic potential can be to keep the current direction of the stator magnetic potential unchanged and increase the magnitude of the stator magnetic potential, or to change the direction of the stator magnetic potential and increase its magnitude at the same time. Reducing the stator magnetic potential can also be to keep the current direction of the stator magnetic potential unchanged and reduce the stator magnetic potential to zero or to a certain value, or to change the stator direction and reduce the stator magnetic potential to zero or to a certain value at the same time.

[0061] In one embodiment, when the rotor is in a first preset position, the controller can control the stator windings to switch from a two-by-two conduction mode to a three-by-three conduction mode, and when the rotor is in a second preset position, the controller can control the stator windings to switch from a three-by-three conduction mode to a two-by-two conduction mode. It is understandable that within a selected phase band, the two-by-two conduction mode or the three-by-three conduction mode can be switched multiple times. Therefore, the above-mentioned first preset position and second preset position are not fixed rotor positions, but rather the positions of the rotor when the combined magnetic potential of the motor changes during rotor rotation, causing the electrical parameters to exceed a preset range. 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.

[0062] That is to say, within the selected phase band, the stator magnetic potential can be adjusted by detecting the rotor position information and adjusting the conduction number of the stator winding, thereby affecting the synthetic magnetic potential, that is, affecting the first synthetic magnetic potential and the second synthetic magnetic potential, so as to increase the motor speed while having little impact on the motor's working capacity.

[0063] As can be seen from the above embodiment, the conduction mode of the three-phase sensorless BLDC stator windings within a selected phase band can be switched based on rotor position information, for example, between a first conduction mode in which two phase windings are conducting and a second conduction mode in which all three phase windings are conducting. In this embodiment, it is defined that in the first conduction mode (two-by-two conduction mode), the two-phase stator windings conduct for a first electrical angle, and in the second conduction mode (three-by-three conduction mode), the three-phase stator windings conduct for a second electrical angle. Thus, the motor exhibits a first electromagnetic torque when conducting at the first electrical angle in the first conduction mode, and a second electromagnetic torque when conducting at the second electrical angle in the second conduction mode. The so-called electromagnetic torque is the output torque of the motor and can represent the motor's work capacity.

[0064] Because motors inherently have reluctance torque that affects their performance, the reluctance torque and the electromagnetic torque under different conduction modes together contribute to the motor's total torque, which accurately reflects the motor's performance. It's understandable that the greater the motor's total torque per unit current, the more energy-efficient the tool. Therefore, while maintaining motor performance and increasing motor speed, energy consumption can be further reduced.

[0065] refer to Figure 9 The circuit block diagram of the power tool shown also includes a torque detection module 25 for detecting the output torque of the motor under different stator winding conduction modes. For example, the module can detect a first electromagnetic torque when the motor is conducted at a first electrical angle in a first conduction mode, and a second electromagnetic torque when the motor is conducted at a second electrical angle in a second conduction mode. It will be appreciated that the torque detection module 25 can also detect the motor's reluctance torque, which is caused by the difference in reluctance between the direct and quadrature axes of the motor's rotor.

[0066] refer to Figure 10 and Figure 11 The electromagnetic torque diagram shown in the figure shows that the horizontal axis represents the angle of rotation of the rotor, the vertical axis represents the magnitude of the torque, line 1 is the total torque of the motor in the first conduction mode, line 2 is the total torque of the motor in the second conduction mode, line 3 is the first electromagnetic torque of the motor in the first conduction mode, line 4 is the second electromagnetic torque of the motor in the second conduction mode, and line 5 is the reluctance torque of the motor. Figure 10 It can be seen that the reluctance torque of the motor is a quasi-sinusoidal waveform, that is, within a certain electrical angle, the reluctance torque can increase the total torque of the motor, and within a certain electrical angle, it can reduce the total torque of the motor. Therefore Figure 10 The middle shaded area represents the range of the rotor rotation angle when the motor has the maximum total torque. Preferably, the range of this range is 90° to 135°. In other words, the domain where the motor has the maximum total torque is 90° to 135°. Figure 11 The two shaded areas shown represent the first total torque when the first conduction mode is used under unit current and the second total torque when the second conduction mode is used. The sum of the two is the final required total torque of the motor. In other words, Figure 11 The maximum total torque of the motor under unit current corresponds to the maximum sum of the areas of the two shaded regions shown.

[0067] Based on this, the controller 24 can adjust the first electrical angle for conduction in the first conduction mode and the second electrical angle for conduction in the second conduction mode according to the position of the motor rotor, so that the total torque of the motor at a unit current in the selected phase band is within a preset torque range. It will be appreciated that different tools have different energy consumption and thus different preset torques. The preset torque range in this application can encompass the total torque values ​​of the motor corresponding to the different energy consumption requirements of different tools.

[0068] It can be understood that the above process of adjusting the conduction electrical angle of the stator winding under different conduction modes also affects the stator magnetic potential. Therefore, in the process of adjusting the total torque to reduce the energy consumption of the motor, the impact on the motor's work capacity and speed increase is relatively small.

[0069] In one embodiment, the ratio of the first electrical angle to the second electrical angle within the selected phase band can be obtained by looking up a table according to a preset torque range.

[0070] For different tools and their specific operating conditions, 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.

[0071] The operating phases of a typical tool can be divided into a high-speed operating phase and a low-speed operating phase. Different tools have different minimum motor speeds during the high-speed operating phase under different operating conditions, and different tools have different maximum motor speeds during the low-speed operating phase under different operating conditions. In one embodiment, the high-speed operating phase is defined as the first operating phase of the tool, and the low-speed operating phase is defined as the second operating phase of the tool. Generally, during the first operating phase, it is desirable for the motor to maintain a constant speed for a period of time and to transition to the second operating phase before the motor's operating parameters become overloaded. In this application, the motor is controlled using a conduction method that switches between two-to-two conduction and three-to-three conduction. Therefore, to achieve a substantially stable speed during the first operating phase, the controller adjusts the second electrical angle β at which the motor is conducting in the second conduction method, i.e., the three-to-three conduction method, during the first operating phase to maintain a substantially stable speed. Furthermore, during the second operating phase, the stator windings can be controlled to conduct at a first preset electrical angle, i.e., a fixed electrical angle, in the three-to-three conduction method. In particular, in the first and second operating stages, the motor switches between a two-by-two conduction mode and a three-by-three conduction mode. That is, in both operating stages, the motor has two conduction modes: two-by-two conduction and three-by-three conduction. Furthermore, the electrical angle of the two-by-two conduction mode in both operating stages is a fixed value, such as a second preset electrical angle. Therefore, this application does not describe the electrical angle of the two-by-two conduction mode of the motor in the two operating stages. In other words, the electrical angle of the three-by-three conduction mode changes continuously during the high-speed operation stage, remains fixed during the low-speed operation stage, and the electrical angle of the two-by-two conduction mode of the windings is a fixed value in both operating stages. In this embodiment, the magnitudes of the first and second preset electrical angles are not specifically limited.

[0072] In one embodiment, the controller 24 can maintain the motor's speed substantially constant by adjusting the electrical angle (spread angle β) of the motor's stator windings in the second conduction mode, namely, three-three conduction, while maintaining the stator windings at a fixed lead angle α. For example, in the first operating phase, if the stator windings have a lead angle of 15° and the spread angle of the three-three conduction varies from 0° to 45°, the motor's speed can be maintained at a relatively stable state.

[0073] 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 phase, the motor speed and output torque remain essentially unchanged, and line 1 is substantially parallel to the horizontal axis. However, in the first operating phase, the motor's current rises at a relatively fast rate, and the motor will be subjected to a relatively large current in a short period of time. Therefore, the duration of the first operating phase should not be too long. In one implementation, when the motor is in the first operating phase, the controller 24 can stop adjusting the electrical angle in the first conduction mode, causing the motor's stator winding to conduct at a third preset electrical angle while continuing to maintain a constant lead angle α, thereby reducing the motor's speed and the slope of change of the motor's operating current, thereby causing the motor to enter the second operating phase. The third preset electrical angle is a fixed electrical angle, and this application does not specifically limit its size. It is understood that if the motor maintains a high speed, it will cause severe heating. Therefore, when speed reduction is required, the controller can control the motor to enter the second operating phase.

[0074] In one embodiment, the controller may control the motor to enter the second operating phase when the conduction angle of the second conduction mode reaches an angle threshold. For example, when the spread angle changes from 0° to 45° during the first operating phase, the controller 24 no longer adjusts the spread angle, causing the motor windings to conduct at a 15° lead angle and a fixed spread angle of less than or equal to 45° during the second operating phase.

[0075] In one embodiment, Figure 13 As shown, the electric tool also includes a current detection module 26 for detecting the working current of the motor. After the controller 24 obtains the working current of the motor, it can calculate the change slope of the current. Furthermore, the controller can control the motor to switch to the second working stage according to the change slope of the motor current in the first working stage, that is, control the electrical angle of the motor stator winding to be turned on in the second conduction mode to be a first preset electrical angle. That is to say, in the second working stage, the lead angle α of the motor stator winding and the expansion angle β during three-three conduction are both fixed values. In this application, it is defined that the motor working current has a first change slope in the first working stage and a second change slope in the second working stage, such as Figure 14 As shown, the horizontal axis represents the motor output torque, and the vertical axis represents the motor working current. Figure 14It can be seen that the second change slope of the motor current in the second working stage is significantly smaller than the first change slope in the first working stage. Figure 12 and Figure 14 It can be seen that in the second working stage, the current change slope becomes smaller, but the working current value does not decrease, and the motor speed decreases.

[0076] In a specific implementation, when the controller 24 detects that the motor operating current reaches a current threshold at a first change slope during the first operating phase of the motor, it can control the motor to switch to the second operating phase, i.e., no longer adjusting the spread angle β. It is understood that when the motor operating current reaches the current threshold at the first change slope during the first operating phase, the spread angle β of the motor windings in the three-way conduction mode is the maximum electrical angle achievable in the second conduction mode. In the second operating phase, the fixed second electrical angle of the three-way conduction mode is less than or equal to the aforementioned maximum electrical angle. For example, when the spread angle of the three-way conduction mode is adjusted from 0° to 20° during the first operating phase, the motor operating current reaches the current threshold in the first operating phase. The controller then controls the motor to enter the second operating phase with a lead angle of 15° and a fixed spread angle of less than or equal to 20°. That is, when the motor operating current reaches the current threshold at the first current slope during the first operating phase, and the electrical angle in the second conduction mode is less than the angle threshold, the controller still controls the motor to enter the second operating phase.

[0077] By adjusting the expansion angle in the first working stage to maintain the motor's speed and output torque, it is possible to ensure that the motor can maintain stable output performance under different working conditions during the startup phase. By fixing the expansion angle so that the motor operates in the second stage, it is possible to avoid a continuous and rapid increase in current that could damage the motor.

[0078] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. An electric tool comprising: A motor having multi-phase windings, wherein each phase winding of the motor is capable of conducting a first electrical angle in a first conduction mode within a selected phase band and conducting a second electrical angle in a second conduction mode; wherein the first conduction mode includes conducting any two phase windings of the motor phase windings, and the second conduction mode includes conducting three phase windings of the motor phase windings; a torque detection module, configured to detect a first electromagnetic torque of the motor when the motor is turned on at a first electrical angle in the first conduction mode, and a second electromagnetic torque of the motor when the motor is turned on at a second electrical angle in the second conduction mode; a controller, electrically connected to at least the torque detection module and the motor; The controller is configured to: Obtaining the first electromagnetic torque and the second electromagnetic torque, and calculating a total torque of the motor at a unit current in the phase band according to the first electromagnetic torque, the second electromagnetic torque, and the reluctance torque of the motor; The first electrical angle and the second electrical angle are adjusted so that the total torque of the motor under unit current in the selected phase band is within a preset torque range.

2. The electric tool according to claim 1, wherein: The reluctance torque of the motor is quasi-sine wave.

3. The electric tool according to claim 1, wherein: The controller is configured to: detecting a rotor position of the motor; In the first conduction mode, when the rotor position reaches a first preset position, the conduction mode is switched to the second conduction mode; In the second conduction mode, the rotor position is switched to the first conduction mode when the rotor position reaches a second preset position.

4. The electric tool according to claim 1, wherein: The ratio of the first electrical angle to the second electrical angle in the selected phase band is obtained by looking up a table according to the preset torque range.

5. A method for controlling an electric tool, the electric tool comprising: A motor having multi-phase windings, wherein each phase winding of the motor is capable of conducting a first electrical angle in a first conduction mode within a selected phase band and conducting a second electrical angle in a second conduction mode; wherein the first conduction mode includes conducting any two phase windings of the motor phase windings, and the second conduction mode includes conducting three phase windings of the motor phase windings; a torque detection module, configured to detect a first electromagnetic torque of the motor when the motor is turned on at a first electrical angle in the first conduction mode, and a second electromagnetic torque of the motor when the motor is turned on at a second electrical angle in the second conduction mode; a controller, electrically connected to at least the torque detection module and the motor; The control method includes: Obtaining the first electromagnetic torque and the second electromagnetic torque and calculating a total torque of the motor under a unit current in the phase band according to the first electromagnetic torque, the second electromagnetic torque, and the reluctance torque of the motor; The first electrical angle and the second electrical angle are adjusted so that the total torque of the motor under the unit current in the phase band is within a preset torque range.

6. The method according to claim 5, characterized in that The reluctance torque of the motor is quasi-sine wave.

7. The method according to claim 5, characterized in that The method further comprises: detecting a rotor position of the motor; In the first conduction mode, when the rotor position reaches a first preset position, the conduction mode is switched to the second conduction mode; In the second conduction mode, the rotor position is switched to the first conduction mode when the rotor position reaches a second preset position.

8. The method according to claim 5, characterized in that The ratio of the first electrical angle to the second electrical angle in the selected phase band is obtained by looking up a table according to the preset torque range.

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