Electric tool and control method therefor

Abstract

An electric tool, comprising: a housing; a brushless motor; a power interface supplying power to the brushless motor; a driving circuit comprising a plurality of switching elements and configured to apply a driving voltage to a winding of each phase of the brushless motor; a controller electrically connected to the driving circuit and configured to generate a target voltage vector by means of current closed-loop control and output a pulse width modulation signal to control the on state of the plurality of switching elements to control the operation of the brushless motor; a voltage estimation unit configured to obtain a motor parameter of the brushless motor, and estimate, on the basis of the motor parameter and a direct-axis voltage equation, a theoretical voltage vector corresponding to the target voltage vector; and an electrical angle correction unit configured to determine an electrical angle offset on the basis of the target voltage vector and the theoretical voltage vector, and correct a rotor position signal on the basis of the electrical angle offset.

Description

Power tool and control method thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 28, 2024, with application number 202410372678.6. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of electric tools, for example, to an electric tool and a control method thereof. Background Art

[0003] Portable power tools can be used in a variety of scenarios in production and life. By configuring a rechargeable battery pack to power the power tools, the power tools are freed from the constraints of wires and are more convenient for users to use.

[0004] Power tools feature motors controlled by controllers. In field-oriented control (FOC), the observed electrical angle often exhibits significant errors at low motor speeds, resulting in weak load capacity and poor stability. Currently, sensored FOC is primarily used to address these issues, replacing sensorless FOC. However, sensored FOC increases mechanical installation complexity and material costs.

[0005] This section provides background information related to the present application which is not necessarily prior art. Summary of the Invention

[0006] In order to address the deficiencies of the related art, the purpose of the present application is to provide an electric tool and a control method thereof, in which the motor has better load capacity and stability when the motor speed of the electric tool is low.

[0007] In order to achieve the above objectives, this application adopts the following technical solutions:

[0008] An electric tool comprises: a housing; a brushless motor, at least partially disposed in the housing, comprising a stator and a rotor; a power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit, comprising a plurality of switching elements, configured to apply a drive voltage to windings of each phase of the brushless motor; a controller, electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of the plurality of switching elements, thereby controlling the operation of the brushless motor; a voltage estimation unit, configured to obtain motor parameters of the brushless motor, and estimate a theoretical voltage vector corresponding to the target voltage vector based on the motor parameters and a direct-axis voltage equation; an electrical angle correction unit, configured to determine an electrical angle offset based on the target voltage vector and the theoretical voltage vector, and to correct a rotor position signal based on the electrical angle offset.

[0009] In some embodiments, the power tool further includes a rotor position estimation unit configured to output a rotor position signal representing the rotor position in electrical degrees; the rotor position estimation unit includes a flux observer.

[0010] In some embodiments, the flux observer is configured to determine the rotor flux based on the observed stator flux, and determine the electrical angle based on the rotor flux; wherein, before determining the observed stator flux, a phase gain is obtained, and the phase gain is set according to the speed of the brushless motor.

[0011] In some embodiments, when the rotation speed of the brushless motor is greater than 0, the phase gain is 1; when the rotation speed of the brushless motor is less than 0, the phase gain is -1.

[0012] In some embodiments, the voltage estimation unit is configured to obtain an electrical angle compensation value before the electrical angle correction unit determines the electrical angle offset, and the electrical angle compensation value is used to correct the electrical angle offset.

[0013] In some embodiments, the voltage estimation unit is configured to set the electrical angle compensation value to a preset value when the electrical angle compensation value cannot be obtained.

[0014] In some embodiments, the electrical angle correction unit is configured to: obtain an electrical angle compensation value, and update the electrical angle compensation value based on the rotation speed, the target voltage vector, and the theoretical voltage vector of the brushless motor.

[0015] In some embodiments, when the speed of the brushless motor is greater than 0 and the target voltage vector is greater than the first theoretical voltage vector, the electrical angle correction unit is configured to: obtain an electrical angle compensation value, and reduce the electrical angle compensation value to update the electrical angle compensation value.

[0016] In some embodiments, when the speed of the brushless motor is greater than 0 and the target voltage vector is less than the second theoretical voltage vector, the electrical angle correction unit is configured to: obtain an electrical angle compensation value, and increase the electrical angle compensation value to update the electrical angle compensation value.

[0017] In some embodiments, when the speed of the brushless motor is less than 0 and the target voltage vector is less than the third theoretical voltage vector, the electrical angle correction unit is configured to: obtain an electrical angle compensation value, and increase the electrical angle compensation value to update the electrical angle compensation value.

[0018] In some embodiments, when the speed of the brushless motor is less than 0 and the target voltage vector is greater than the fourth theoretical voltage vector, the electrical angle correction unit is configured to: obtain an electrical angle compensation value, and reduce the electrical angle compensation value to update the electrical angle compensation value.

[0019] In some embodiments, the electrical angle correction unit is configured to correct the rotor position signal based on the updated electrical angle compensation value; and the controller is configured to generate an updated target voltage vector through current closed-loop control based on the corrected rotor position signal.

[0020] In some embodiments, the absolute value of the rotation speed of the brushless motor is lower than a preset rotation speed threshold.

[0021] In some embodiments, the electrical angle correction unit is configured to determine an electrical angle offset based on the updated target voltage vector and the theoretical voltage vector, and correct the rotor position signal based on the electrical angle offset.

[0022] In some embodiments, correcting the rotor position signal by using the electrical angle offset includes: correcting the rotor position signal by using the electrical angle compensation value.

[0023] In some embodiments, an electric tool includes: a housing; a brushless motor, at least partially disposed in the housing, including a stator and a rotor; a power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit, including multiple switching elements, configured to apply a drive voltage to the windings of each phase of the brushless motor; a controller, electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of multiple switching elements to control the operation of the brushless motor; a voltage estimation unit, configured to estimate a theoretical voltage vector corresponding to the target voltage vector; an electrical angle correction unit, configured to determine an electrical angle offset based on the target voltage vector and the theoretical voltage vector when the absolute value of the speed of the brushless motor is lower than a preset speed threshold, and to correct the rotor position signal based on the electrical angle offset.

[0024] In some embodiments, the voltage estimation unit is configured to obtain an electrical angle compensation value before the electrical angle correction unit determines the electrical angle offset, and the electrical angle compensation value is used to correct the electrical angle offset.

[0025] In some embodiments, the voltage estimation unit is configured to set the electrical angle compensation value to a preset value when the electrical angle compensation value cannot be obtained.

[0026] In some embodiments, a control method for an electric tool is provided, wherein the electric tool includes: a housing; a brushless motor, at least partially disposed in the housing, including a stator and a rotor; a power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit, including multiple switching elements, configured to apply a drive voltage to the windings of each phase of the brushless motor; and a controller, electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of multiple switching elements to control the operation of the brushless motor; the control method includes: obtaining the speed of the brushless motor, obtaining the target voltage vector and theoretical voltage vector of the direct axis when the absolute value of the speed is lower than a preset speed threshold; determining an electrical angle offset based on the target voltage vector and the theoretical voltage vector; and correcting the rotor position signal based on the electrical angle offset.

[0027] In some embodiments, the control method includes: obtaining an electrical angle compensation value, and updating the electrical angle compensation value based on the speed, target voltage vector and theoretical voltage vector of the brushless motor; wherein the electrical angle compensation value is used to correct the electrical angle offset.

[0028] The benefit of the present application is that after the electrical angle offset is determined by the electrical angle correction unit and the rotor position signal is corrected, the observation error of the brushless motor is corrected, thereby enhancing the load capacity and stability of the brushless motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a schematic diagram of a power tool according to an embodiment;

[0030] FIG2 is a schematic circuit block diagram of the power tool in FIG1 ;

[0031] FIG3 is a schematic diagram of a process for estimating an observation angle according to an embodiment;

[0032] FIG4 is a schematic diagram of the electric control principle of the controller in FIG2 for controlling the operation of the motor;

[0033] FIG5 is a flowchart of a method for controlling a power tool according to an embodiment;

[0034] FIG6 is a detailed flow chart of the control method in FIG5 ;

[0035] FIG. 7 is a schematic diagram of a flow chart of updating the electrical angle compensation value based on the target voltage vector and the theoretical voltage vector in FIG. 6 . DETAILED DESCRIPTION

[0036] Before any embodiments of the present application are explained in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the foregoing drawings.

[0037] In this application, the terms "comprises," "includes," "has," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0038] In this application, the term "and / or" describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Additionally, the character " / " in this application generally indicates that the related objects are in an "and / or" relationship.

[0039] In this application, the terms "connect," "combine," "couple," and "install" may refer to direct connection, combination, coupling, or installation, or indirect connection, combination, coupling, or installation. For example, a direct connection refers to two parts or components being connected together without an intermediary, and an indirect connection refers to two parts or components being connected to at least one intermediary, with the two parts or components being connected via the intermediary. Furthermore, "connect" and "couple" are not limited to physical or mechanical connections or couplings and may include electrical connections or couplings.

[0040] In this application, it will be understood by those skilled in the art that relative terms (e.g., "about," "approximately," "substantially," etc.) used in conjunction with quantities or conditions include the values ​​and have the meaning indicated by the context. For example, the relative terms include at least the degree of error associated with the measurement of a specific value, the tolerance caused by manufacturing, assembly, use, etc. associated with a specific value. Such terms should also be considered to disclose a range defined by the absolute values ​​of the two endpoints. Relative terms may refer to plus or minus a certain percentage (e.g., 1%, 5%, 10% or more) of the indicated value. Numerical values ​​that do not use relative terms should also be disclosed as specific values ​​with tolerances. In addition, "substantially" may refer to plus or minus a certain degree (e.g., 1 degree, 5 degrees, 10 degrees or more) on the basis of the indicated angle when expressing a relative angular position relationship (e.g., substantially parallel, substantially perpendicular).

[0041] In this application, it will be understood by those skilled in the art that the function performed by an assembly can be performed by one assembly, multiple assemblies, one part, or multiple parts. Similarly, the function performed by a part can also be performed by one part, one assembly, or a combination of multiple parts.

[0042] In the present application, the terms "upper", "lower", "left", "right", "front", "back" and other directional words are described based on the orientation and positional relationship shown in the accompanying drawings, and should not be understood as limiting the embodiments of the present application. In addition, in the context, it is also necessary to understand that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to the other element "upper" or "lower", but also be indirectly connected to the other element "upper" or "lower" through an intermediate element. It should also be understood that directional words such as upper side, lower side, left side, right side, front side, back side, etc. not only represent the positive orientation, but can also be understood as the lateral orientation. For example, below can include directly below, lower left, lower right, lower front and lower back, etc.

[0043] In this application, the terms "controller," "processor," "central processing unit," "CPU," and "MCU" are used interchangeably. Where a unit "controller," "processor," "central processing unit," "CPU," or "MCU" is used to perform a particular function, unless otherwise specified, the function may be performed by a single unit or multiple units.

[0044] In this application, the terms "device", "module" or "unit" can be implemented in the form of hardware or software to achieve specific functions.

[0045] In this application, the terms "calculate", "judge", "control", "determine", "identify", etc. refer to the operations and processes of a computer system or similar electronic computing device (e.g., controller, processor, etc.).

[0046] FIG1 shows an electric tool 100 as an embodiment of the present application. The electric tool 100 shown in FIG1 is a screwdriver. The electric tool 100 in other embodiments may also be a handheld power tool, such as a drill, a pruner, a sander, etc. Alternatively, the electric tool 100 may also be a bench tool, such as a table saw, a miter saw, etc. Alternatively, the electric tool 100 may also be a hand-push power tool, such as a hand-push lawn mower or a hand-push snow blower. Alternatively, the electric tool 100 may also be a riding power tool, such as a riding lawn mower, a riding vehicle, an all-terrain vehicle, etc. Alternatively, the electric tool 100 may also be a robot tool, such as a lawn mowing robot or a snow blower robot, etc.

[0047] As shown in Figure 1, the power tool 100 includes a housing 110, a power interface 120, a functional part 130 and a brushless motor 200. Among them, the housing 110 constitutes the main body of the power tool 100, which connects or supports the above-mentioned components and forms a storage space, which can accommodate or partially accommodate the above-mentioned components. The power interface 120 is configured to connect to a power source to supply power to the brushless motor 200. The functional part 130 is the component in the power tool 100 that actually performs operations such as cutting, tightening, grinding, and impacting. The brushless motor 200 is at least partially disposed in the housing 110, and the brushless motor 200 includes a stator 210 and a rotor 220. As shown in Figure 1, this application takes the brushless motor 200 as an inner rotor motor as an example. In addition, the brushless motor 200 can also be an outer rotor motor, which is not limited in this application.

[0048] Referring to the circuit block diagram of the power tool 100 shown in FIG2 , the drive system of the brushless motor 200 may include at least a power supply 300, a control circuit 400, a detection module 500, a voltage estimation unit 600, and an electrical angle correction unit 700. The control circuit 400 may include a drive circuit 410 and a controller 420. Optionally, the present application describes the brushless motor 200 as a sensorless brushless motor. In the present application, the brushless motor 200 may be an inner rotor motor or an outer rotor motor. The brushless motor 200 includes at least three-phase stator windings A, B, and C. The three-phase windings may be connected in a star configuration or a delta configuration.

[0049] In one embodiment, the power supply 300 can be an AC power source, i.e., it can be connected to 120V or 220V AC mains electricity via the power interface 120. In one embodiment, the power supply 300 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 power controller, such as a DC-DC module, to output a supply voltage suitable for controlling the brushless motor 200, 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 based on the specific parameter requirements of the power tool.

[0050] The drive circuit 410 is electrically connected to the stator windings A, B, and C of the brushless motor 200 and is used to transfer current from the power supply 300 to the stator windings A, B, and C, that is, to apply a drive voltage to the windings of each phase of the brushless motor 200 to drive the brushless motor 200 to rotate. In one embodiment, the drive circuit 410 includes a plurality of switching elements Q1, Q2, Q3, Q4, Q5, and Q6. Among them, Q1, Q3, and Q5 are high-side switching elements, and Q2, Q4, and Q6 are low-side switching elements. Any phase stator winding of the brushless motor 200 is connected to a high-side switching element and a low-side switching element.

[0051] The controller 420 can be a microcontroller unit (MCU), a high-performance RISC microprocessor (ARM), a general-purpose digital signal processor (DSP), etc. The controller 420 is electrically connected to the gate terminal of each switching element in the drive circuit 410. The controller 420 can run a related control program and output control signals such as pulse-width modulation (PWM) signals to the drive circuit 410 to control the brushless motor 200 to operate in the intended manner. The controller 420 outputs the PWM signal through current closed-loop control and also generates the target voltage vector Udm through current closed-loop control.

[0052] The drive circuit 410 is located between the power supply 300 and the brushless motor 200 and is electrically connected to both. The drive circuit 410 is also connected to the controller 420 and receives control signals, such as pulse-width modulated (PWM) signals, from the controller 420. The drain or source of each switching element in the drive circuit 410 is connected to the stator windings A, B, and C of the brushless motor 200. Switching elements Q1-Q6 receive PWM signals from the controller 420 to change their respective conduction states, thereby varying the current applied by the power supply 300 to the stator windings A, B, and C of the brushless motor 200. The controller 420 controls the operation of the brushless motor 200.

[0053] In one embodiment, the driver circuit 410 may be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g., field-effect transistors (FETs), bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), etc.). It will be appreciated that the switching elements may also be any other type of solid-state switches, such as insulated gate bipolar transistors (IGBTs) and bipolar junction transistors (BJTs).

[0054] The detection module 500 is electrically connected to the brushless motor 200 and the voltage estimation unit 600. It can detect motor parameters of the brushless motor 200 and transmit them to the voltage estimation unit 600. For example, the detection module 500 can detect at least one motor parameter of the brushless motor 200 and transmit it to the voltage estimation unit 600. In some embodiments, the motor parameters of the brushless motor 200 detected by the detection module 500 include, but are not limited to, the current, voltage, speed, torque, freewheeling time, and temperature of the brushless motor 200. The current of the brushless motor 200 may include phase current, bus current, etc., the voltage of the brushless motor 200 may include phase voltage, bus voltage, etc., and the temperature of the brushless motor 200 may include metal-oxide-semiconductor (MOS) temperature, ambient temperature, etc.

[0055] Optionally, the voltage estimation unit 600 and the electrical angle correction unit 700 may be the controller 420, that is, the voltage estimation unit 600 and the electrical angle correction unit 700 are functional units within the controller 420, and the functions of the voltage estimation unit 600 and the electrical angle correction unit 700 are directly implemented by the controller 420. Optionally, the voltage estimation unit 600 and the electrical angle correction unit 700 may also be other controllers other than the controller 420, that is, the voltage estimation unit 600 is a separate controller, the electrical angle correction unit 700 is a separate controller, or the voltage estimation unit 600 and the electrical angle correction unit 700 together are a controller other than the controller 420. This application is specifically described using the example of the voltage estimation unit 600 and the electrical angle correction unit 700 being other controllers other than the controller 420.

[0056] As shown in FIG2 , the voltage estimation unit 600 is electrically connected to the detection module 500 and the electrical angle correction unit 700. The electrical angle correction unit 700 is electrically connected to the voltage estimation unit 600 and the controller 420. The voltage estimation unit 600 obtains the motor parameters of the brushless motor 200 from the detection module 500 and estimates a theoretical voltage vector Udn corresponding to the target voltage vector Udm based on the motor parameters of the brushless motor 200 and the direct-axis voltage equation. The electrical angle correction unit 700 determines the electrical angle offset θ based on the target voltage vector Udm generated by the controller 420 and the theoretical voltage vector Udn estimated by the voltage estimation unit 600. err , and based on the electrical angle offset θ err To correct the rotor position signal.

[0057] In some embodiments, the power tool 100 further includes a rotor position estimation unit 800, which is electrically connected to the detection module 500. The rotor position estimation unit 800 outputs the power angle θ eThe rotor position signal represents the rotor position, where the electrical angle θ e That is the observation angle θ e Optionally, the rotor position estimation unit 800 includes a flux observer 810 , based on which the observation angle θ can be estimated. e .

[0058] As shown in Figure 3, the estimated observation angle θ e The following steps are included: e All motor parameters of the brushless motor 200 involved in the above are detected by the detection module 500 and transmitted to the rotor position estimation unit 800 .

[0059] Step 310: Calculate the amplitude gain λ.

[0060] In some embodiments, the amplitude gain λ can be calculated based on the voltage utilization of the brushless motor 200. Alternatively, the amplitude gain λ can be calculated according to the formula Calculated. Among them, the amplitude gain λ is any value within the stable range, ω e is the speed of the brushless motor 200, ψ e is the permanent magnet flux of the brushless motor 200.

[0061] Step 320 : Set the phase gain k according to the rotation speed of the brushless motor 200 .

[0062] In some embodiments, at the speed ω of the brushless motor 200 e When it is greater than 0, the phase gain k is 1. e When it is less than 0, the phase gain k is -1.

[0063] Step 330: Calculate the observation error err.

[0064] In some embodiments, the observation error err is based on the formula Calculated. Among them, ψ r is the rotor flux of the brushless motor 200. That is, the observation error err is calculated by the square difference between the permanent magnet flux of the brushless motor 200 and the rotor flux of the brushless motor 200.

[0065] Step 340: Calculate the back electromotive force y.

[0066] In some embodiments, the back electromotive force y is based on the formula y=u αβ -R s i αβ Calculated. Among them, u αβis the voltage of the brushless motor 200, and the voltage of the brushless motor 200 is represented by the vector relationship between the voltage of the α-axis and the voltage of the β-axis. αβ is the current of the brushless motor 200, and the current of the brushless motor 200 is represented by the vector relationship between the current of the α-axis and the current of the β-axis. s is the stator resistance of the brushless motor 200 .

[0067] Step 350: Calculate the observed stator flux.

[0068] The flux observer 810 is based on the formula Observe the stator flux, where ψ s is the stator flux of the brushless motor 200 , and γ is the phase gradient optimization gain of the brushless motor 200 .

[0069] For the observation angle θ e The gradient optimization calculation results are as follows:

[0070] To eliminate The influence of the item, setting Then the formula of flux observer 810 is simplified to in, The rotor flux of the brushless motor 200 leads by 90 degrees.

[0071] Based on the simplified formula of the flux observer 810, combined with the observation error err based on the above step 330 and the back electromotive force y in step 340, The observed stator flux is obtained by multiplying the formula by the calculation period and integrating it:

[0072] Step 360: Calculate the observed rotor flux.

[0073] After the stator flux of the brushless motor 200 is calculated in step 350, the rotor flux can be calculated based on the stator flux. For example, the rotor flux is calculated based on the formula Among them, L s is the phase inductance of the brushless motor 200 .

[0074] Step 370: Calculate the observation angle θ e .

[0075] Observation angle θ e By calculating the inverse tangent of the rotor flux observed in step 360, it can be obtained, for example, the calculation formula is: in, is the stator flux of the β axis, is the stator flux linkage about the α-axis.

[0076] Compared with the conventional estimated observation angle θ e In the process, the present application adds phase information on the basis of the traditional flux observer, and also adds a phase gain k in the control parameter. Therefore, the observation accuracy of the flux observer 810 in the present application is improved, so that the accuracy of the observed stator flux and rotor flux is improved, thereby making it possible to estimate the observation angle θ. e More accurate.

[0077] However, in the sensorless FOC control of the brushless motor 200, the electrical angle observation error at low speed is often relatively large, that is, the estimated observation angle θ e There is still a certain error, so the voltage estimation unit 600 and the electrical angle correction unit 700 are required to determine the electrical angle offset θ err , to correct the observation angle θ e , that is, correct the rotor position signal.

[0078] In some embodiments, referring to FIG4 , the controller 420 may include a speed loop, a current distribution unit, a first current loop, a second current loop, a current conversion unit, a voltage conversion unit, and a vector modulation unit. The detection module 500 may include a current detection module and a position / speed detection module. The speed loop is configured with a target speed n0 and is connected to the speed detection module to obtain the actual speed n of the brushless motor 200. The speed loop determines the current target current Is0 of the brushless motor 200 based on the target speed n0 and the actual speed n.

[0079] The current distribution unit is connected to the above-mentioned speed loop, and distributes the direct-axis target current Id0 and the quadrature-axis target current Iq0 based on the target current Iso. The above-mentioned target current Iso, the direct-axis target current Id0, and the quadrature-axis target current Iq0 are all vectors with magnitude and direction. The direct-axis target current Id0 and the quadrature-axis target current Iq0 are perpendicular to each other, and the target current Is0 can be synthesized by the above-mentioned two.

[0080] The current conversion unit is connected to the current detection module and can obtain the phase currents Iu, Iv, and Iw of the three-phase winding and convert them from a three-phase stationary coordinate system to a two-phase rotating coordinate system to obtain the direct-axis actual current Id and the quadrature-axis actual current Iq. The first current loop is connected to the current distribution unit and the current conversion unit and can obtain and determine the first regulated voltage Ud based on the direct-axis target current Id0 and the direct-axis actual current Id. The second current loop is connected to the current distribution unit and the current conversion unit and can obtain and determine the second regulated voltage Uq based on the quadrature-axis target current Iq0 and the quadrature-axis actual current Iq.

[0081] The voltage conversion unit is connected to the first and second current loops and is capable of acquiring the first and second regulated voltages Ud and Uq and converting them from a two-phase rotating coordinate system to a two-phase stationary coordinate system to obtain the first and second voltage control variables Uα and Uβ. The vector modulation unit is connected to the voltage conversion unit and is capable of acquiring the first and second voltage control variables Uα and Uβ. Based on the current modulation index, it linearly modulates or overmodulates the first and second voltage control variables Uα and Uβ, generating corresponding pulse-width modulation signals and outputting them to the drive circuit 410. The specific process by which the controller 420 outputs the pulse-width modulation signal through current closed-loop control is as described above. The target voltage vector Udm generated by the controller 420 through current closed-loop control is the first regulated voltage Ud.

[0082] In some embodiments, since the electrical angle observation error is often large at low speeds in the sensorless FOC control of the brushless motor 200, the observation angle θ is corrected when the brushless motor 200 is at low speeds. e Therefore, the theoretical voltage vector Udn is estimated when the brushless motor 200 is at a low speed. e The absolute value of is lower than the preset speed threshold value, which is considered a low speed. Optionally, the preset speed threshold value may be 5% of the rated speed. Optionally, the preset speed threshold value may be 10% of the rated speed. Optionally, the preset speed threshold value may be 15% of the rated speed. In addition, the preset speed threshold value may also be other percentages of the rated speed that meet the requirements, which is not limited in this application.

[0083] In some embodiments, the voltage estimation unit 600 determines the speed ω of the brushless motor 200. e After the absolute value of is lower than the preset speed threshold, the voltage estimation unit 600 estimates the theoretical voltage vector Udn corresponding to the target voltage vector Udm. For example, the theoretical voltage vector Udn is obtained by the formula Udn=-ω e L q I q Calculated, where ω e is the speed of the brushless motor 200, Lq is the quadrature-axis inductance of the brushless motor 200, and Iq is the actual quadrature-axis current of the brushless motor 200. e , Lq, and Iq can all be detected by the detection module 500 and transmitted to the voltage estimation unit 600.

[0084] In some embodiments, the electrical angle correction unit 700 determines the electrical angle offset θ based on the target voltage vector Udm and the theoretical voltage vector Udn. err Before, it is also necessary to determine the speed ω of the brushless motor 200 eIs the absolute value of lower than the preset speed threshold, at the speed ω of the brushless motor 200? e When the absolute value of is lower than the preset speed threshold, the electrical angle offset θ is determined. err .

[0085] In some embodiments, the electrical angle correction unit 700 determines the electrical angle offset θ err Before, you need to obtain the electrical angle compensation value θ, which is used to correct the electrical angle offset θ err For example, by dividing the electrical angle compensation value θ by the electrical angle offset θ err Add to correct the electrical angle offset θ err After the voltage estimation unit 600 obtains the electrical angle compensation value θ, the electrical angle correction unit 700 obtains the electrical angle compensation value θ from the voltage estimation unit 600 .

[0086] Optionally, if the voltage estimation unit 600 cannot obtain the electrical angle compensation value θ, the electrical angle compensation value θ is set to a preset value, i.e., an initial value of the electrical angle compensation value θ. Optionally, the preset value of the electrical angle compensation value θ can be 0. Optionally, the preset value of the electrical angle compensation value θ can also be any other angle value, which is not limited in this application.

[0087] In some embodiments, at the speed ω of the brushless motor 200 e When the absolute value of is lower than the preset speed threshold, after the electrical angle correction unit 700 obtains the electrical angle compensation value θ, the electrical angle offset θ is determined according to the target voltage vector Udm and the theoretical voltage vector Udn. err And correct the electrical angle offset θ err Divided into the speed of the brushless motor 200 ω e Greater than 0 and the speed ω of the brushless motor 200 e When it is less than 0, the specific correction process is as follows:

[0088] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is greater than 0 and the target voltage vector Udm is greater than the first theoretical voltage vector Udn1, the theoretical voltage vector Udn is negative according to the formula, and the first theoretical voltage vector Udn1 is also negative. err The offset is large and is a leading offset. The electrical angle offset θ is corrected by reducing the electrical angle compensation value θ. err. At this time, the electrical angle compensation value θ is updated to the reduced electrical angle compensation value θ. The first theoretical voltage vector Udn1 is less than or equal to the theoretical voltage vector Udn. Optionally, the first theoretical voltage vector Udn1 = 0.5*Udn. Optionally, the first theoretical voltage vector Udn1 = 0.3*Udn. Optionally, the first theoretical voltage vector Udn1 = 0.7*Udn. The present application does not limit the reduction value of the electrical angle compensation value θ, and the electrical angle compensation value θ needs to be reduced within an appropriate range.

[0089] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is greater than 0 and is less than the second theoretical voltage vector Udn2, the theoretical voltage vector Udn is negative according to the formula, and the second theoretical voltage vector Udn2 is also negative. err The offset is large and is a hysteresis offset. The electrical angle offset θ is corrected by increasing the electrical angle compensation value θ. err . At this time, the electrical angle compensation value θ is updated to the increased electrical angle compensation value θ. The second theoretical voltage vector Udn2 is greater than or equal to the theoretical voltage vector Udn. Optionally, the second theoretical voltage vector Udn2 = 1.5*Udn. Optionally, the second theoretical voltage vector Udn2 = 2*Udn. Optionally, the second theoretical voltage vector Udn2 = 3*Udn. The present application does not limit the increase in the electrical angle compensation value θ, and the electrical angle compensation value θ needs to be increased within an appropriate range.

[0090] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is greater than 0 and is neither greater than the first theoretical voltage vector Udn1 nor less than the second theoretical voltage vector Udn2, that is, the target voltage vector Udm is greater than or equal to the second theoretical voltage vector Udn2 and less than or equal to the first theoretical voltage vector Udn1, the electrical angle offset θ is determined. err Small, no correction is performed.

[0091] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is less than 0 and the target voltage vector Udm is less than the third theoretical voltage vector Udn3, the theoretical voltage vector Udn is a positive number according to the formula, and the third theoretical voltage vector Udn3 is also a positive number. err The offset is large and is a hysteresis offset. The electrical angle offset θ is corrected by increasing the electrical angle compensation value θ. err. At this time, the electrical angle compensation value θ is updated to the increased electrical angle compensation value θ. Among them, the third theoretical voltage vector Udn3 is less than or equal to the theoretical voltage vector Udn. Optionally, the third theoretical voltage vector Udn3 can be equal to the absolute value of the first theoretical voltage vector Udn1, or can be different from the absolute value of the first theoretical voltage vector Udn1, and this application does not limit it. Optionally, the third theoretical voltage vector Udn3 = 0.5*Udn. Optionally, the third theoretical voltage vector Udn3 = 0.3*Udn. Optionally, the third theoretical voltage vector Udn3 = 0.7*Udn. Among them, this application does not limit the increase value of the electrical angle compensation value θ, and the electrical angle compensation value θ needs to increase within an appropriate range.

[0092] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is less than 0 and is greater than the fourth theoretical voltage vector Udn4, the theoretical voltage vector Udn is a positive number calculated according to the formula, and the fourth theoretical voltage vector Udn4 is also a positive number. err The offset is large and is a leading offset. The electrical angle offset θ is corrected by reducing the electrical angle compensation value θ. err . At this time, the electrical angle compensation value θ is updated to the reduced electrical angle compensation value θ. Among them, the fourth theoretical voltage vector Udn4 is greater than or equal to the theoretical voltage vector Udn. Optionally, the fourth theoretical voltage vector Udn4 can be equal to the absolute value of the second theoretical voltage vector Udn2, or can be different from the absolute value of the second theoretical voltage vector Udn2, and this application does not limit it. Optionally, the fourth theoretical voltage vector Udn4 = 1.5*Udn. Optionally, the fourth theoretical voltage vector Udn4 = 2*Udn. Optionally, the fourth theoretical voltage vector Udn4 = 3*Udn. Among them, this application does not limit the reduction value of the electrical angle compensation value θ, and the electrical angle compensation value θ needs to be reduced within an appropriate range.

[0093] When the speed of the brushless motor 200 ω e When the target voltage vector Udm is less than 0 and is both less than the third theoretical voltage vector Udn3 and not greater than the fourth theoretical voltage vector Udn4, that is, the target voltage vector Udm is greater than or equal to the third theoretical voltage vector Udn3 and less than or equal to the fourth theoretical voltage vector Udn4, the electrical angle offset θ is determined. err Small, no correction is performed.

[0094] In some embodiments, at the speed ω of the brushless motor 200 e When the absolute value of is greater than or equal to the preset speed threshold, it represents the speed ω of the brushless motor 200. eTherefore, when the electrical angle compensation value θ is obtained by the electrical angle correction unit 700, if the electrical angle compensation value θ is greater than 0, the electrical angle compensation value θ is reduced to update the electrical angle compensation value θ; if the electrical angle compensation value θ is less than 0, the electrical angle compensation value θ is increased to update the electrical angle compensation value θ. In this way, the electrical angle compensation value θ is as close to 0 as possible, so as to achieve the goal of not offsetting the electrical angle offset θ. err The present application does not limit the value of the electrical angle compensation value θ to be reduced or increased, and the electrical angle compensation value θ needs to be reduced or increased within an appropriate range.

[0095] After the electrical angle compensation value θ is updated and determined according to the above process, since the observation angle θ e The electrical angle offset θ is included in err , then the electrical angle compensation value θ and the observation angle θ e Add and correct the observation angle θ e , thereby correcting the rotor position signal. After correcting the rotor position signal, the controller 420 generates an updated target voltage vector Udm again through current closed-loop control based on the corrected rotor position signal. Thus, the electrical angle correction unit 700 corrects the observed angle θ based on the updated target voltage vector Udm. e , thereby correcting the rotor position signal. The correction process at this time is divided into the speed ω of the brushless motor 200 as described above in this application. e The absolute value of the speed of the brushless motor 200 is lower than the preset speed threshold value. e Greater than 0 and the speed ω of the brushless motor 200 e The case where θ is less than 0 is not described here. The electrical angle compensation value θ used at this time is the electrical angle compensation value θ determined after updating in the above process, and after this round of calibration process, the electrical angle compensation value θ will be updated again for use in the next round of calibration process.

[0096] Correspondingly, FIG5 shows a flow chart of a control method of the electric tool 100, which may include:

[0097] Step 510: Obtain the speed ω of the brushless motor 200 e , at the speed ω e When the absolute value of is lower than the preset speed threshold, the target voltage vector Udm and the theoretical voltage vector Udn of the direct axis are obtained.

[0098] Step 520: Determine the electrical angle offset θ based on the target voltage vector Udm and the theoretical voltage vector Udn err .

[0099] Step 530: Based on the electrical angle offset θ err To correct the rotor position signal.

[0100] As shown in FIG6 , a detailed process of a control method of a power tool 100 is as follows:

[0101] Step 610: Obtain the observation angle θ estimated by the flux observer 810 e .

[0102] The flux observer 810 estimates the observation angle θ e The specific process is as described in step 310 to step 370 in FIG3 of the present application, and will not be repeated here. e It can be obtained by the voltage estimation unit 600 or the electrical angle correction unit 700. In this application, the voltage estimation unit 600 is used to obtain the observation angle θ e Take this as an example for specific explanation.

[0103] Step 620: Generate a target voltage vector Udm.

[0104] The specific process of the controller 420 generating the target voltage vector Udm through the current closed-loop control is as described in the corresponding process of FIG. 4 , which will not be repeated here.

[0105] Step 630: Obtain the electrical angle compensation value θ.

[0106] The electrical angle compensation value θ can be obtained by the voltage estimation unit 600 or by the electrical angle correction unit 700. This application specifically describes the electrical angle compensation value θ obtained by the voltage estimation unit 600. If the voltage estimation unit 600 cannot obtain the electrical angle compensation value θ, the electrical angle compensation value θ is set to a preset value.

[0107] Step 640: Determine the speed of the brushless motor 200 ω e Whether the absolute value of is lower than the preset speed threshold.

[0108] The voltage estimation unit 600 obtains the speed ω of the brushless motor 200 from the detection module 500. e , and judge the speed ω e Is the absolute value of the speed lower than the preset speed threshold? e When the absolute value of is lower than the preset speed threshold, the process goes to step 650A; e When the absolute value of is greater than or equal to the preset speed threshold, proceed to step 650B.

[0109] Step 650A: Estimate the theoretical voltage vector Udn corresponding to the target voltage vector Udm.

[0110] At the speed ω e When the absolute value of is lower than the preset speed threshold, the voltage estimation unit 600 is based on the speed ω of the brushless motor 200.e , the quadrature-axis inductance Lq and the quadrature-axis actual current Iq to estimate the theoretical voltage vector Udn.

[0111] Step 660: Update the electrical angle compensation value θ based on the target voltage vector Udm and the theoretical voltage vector Udn.

[0112] After estimating the theoretical voltage vector Udn in step 650A, the electrical angle correction unit 700 updates the electrical angle compensation value θ based on the target voltage vector Udm and the theoretical voltage vector Udn. The detailed process is shown in FIG7 . The electrical angle correction unit 700 obtains and updates the electrical angle compensation value θ from the voltage estimation unit 600. After completing the electrical angle compensation value θ update, the process proceeds to step 670.

[0113] Step 650B: Determine whether the electrical angle compensation value θ is greater than 0.

[0114] After the voltage estimation unit 600 obtains the electrical angle compensation value θ, the electrical angle correction unit 700 determines whether the electrical angle compensation value θ is greater than 0. If the electrical angle compensation value θ is greater than 0, the process proceeds to step 651B; otherwise, the process proceeds to step 652B.

[0115] Step 651B: Reduce the electrical angle compensation value θ.

[0116] At the speed ω e When the absolute value of is greater than or equal to the preset speed threshold, electrical angle compensation is not required for brushless motor 200. Therefore, after electrical angle correction unit 700 obtains electrical angle compensation value θ, if electrical angle compensation value θ is greater than 0, electrical angle compensation value θ is reduced to update electrical angle compensation value θ, and then the process proceeds to step 670.

[0117] Step 652B: Determine whether the electrical angle compensation value θ is less than 0.

[0118] The electrical angle correction unit 700 determines whether the electrical angle compensation value θ is less than 0. If the electrical angle compensation value θ is less than 0, the process proceeds to step 653B; otherwise, the process proceeds to step 670 .

[0119] Step 653B: Increase the electrical angle compensation value θ.

[0120] At the speed ω e When the absolute value of is greater than or equal to the preset speed threshold, no electrical angle compensation is required for the brushless motor 200. Therefore, after the electrical angle correction unit 700 obtains the electrical angle compensation value θ, if the electrical angle compensation value θ is less than 0, the electrical angle compensation value θ is increased to update the electrical angle compensation value θ, and then the process proceeds to step 670.

[0121] Step 670: Compare the electrical angle compensation value θ with the observation angle θ e Add.

[0122] The electrical angle correction unit 700 compares the acquired electrical angle compensation value θ with the observation angle θ e Add to correct the electrical angle offset θ err , that is, to correct the rotor position signal. The electrical angle compensation value θ obtained by the electrical angle correction unit 700 may be the updated electrical angle compensation value θ or the unupdated electrical angle compensation value θ. The observation angle θ obtained by the electrical angle correction unit 700 e The observation angle θ obtained by the voltage estimation unit 600 is: e And transmitted to the electrical angle correction unit 700.

[0123] Step 680: Generate an updated target voltage vector Udm.

[0124] After correcting the rotor position signal in step 670 , the controller 420 generates an updated target voltage vector Udm again through current closed-loop control based on the corrected rotor position signal, and then executes the process again starting from step 630 to correct a new round of rotor position signals.

[0125] As shown in FIG7 , the above step 660 updates the electrical angle compensation value θ based on the target voltage vector Udm and the theoretical voltage vector Udn as follows:

[0126] Step 710: Determine the speed ω of the brushless motor 200 e Is it greater than 0?

[0127] The electrical angle correction unit 700 obtains the rotation speed ω of the brushless motor 200 from the voltage estimation unit 600. e , and judge the speed ω of the brushless motor 200 e Is it greater than 0. At the speed ω of the brushless motor 200 e When the speed of the brushless motor 200 is greater than 0, the process goes to step 720A. e When it is less than 0, go to step 720B.

[0128] Step 720A: Determine whether the target voltage vector Udm is greater than the first theoretical voltage vector Udn1.

[0129] The electrical angle correction unit 700 determines whether the target voltage vector Udm is greater than the first theoretical voltage vector Udn1. When the target voltage vector Udm is greater than the first theoretical voltage vector Udn1, the process proceeds to step 730. When the target voltage vector Udm is less than or equal to the first theoretical voltage vector Udn1, the process proceeds to step 740.

[0130] Step 730: Reduce the electrical angle compensation value θ.

[0131] The electrical angle correction unit 700 determines the electrical angle offset θ at this time. err If the offset is large and is a leading offset, reduce the electrical angle compensation value θ to correct the electrical angle offset θ err , so that the electrical angle compensation value θ is updated to the reduced electrical angle compensation value θ. After reducing the electrical angle compensation value θ, the process proceeds to step 670 in FIG6 .

[0132] Step 740: Determine whether the target voltage vector Udm is smaller than the second theoretical voltage vector Udn2.

[0133] The electrical angle correction unit 700 determines whether the target voltage vector Udm is less than the second theoretical voltage vector Udn2. When the target voltage vector Udm is less than the second theoretical voltage vector Udn2, the process proceeds to step 750. When the target voltage vector Udm is greater than or equal to the second theoretical voltage vector Udn2, no processing is performed on the electrical angle compensation value θ, and the process proceeds to step 670 in FIG. 6 .

[0134] Step 750: Increase the electrical angle compensation value θ.

[0135] The electrical angle correction unit 700 determines the electrical angle offset θ at this time. err If the offset is large and is a hysteresis offset, increase the electrical angle compensation value θ to correct the electrical angle offset θ err , so that the electrical angle compensation value θ is updated to the increased electrical angle compensation value θ. After the electrical angle compensation value θ is increased, the process proceeds to step 670 in FIG6 .

[0136] Step 720B: Determine whether the target voltage vector Udm is smaller than the third theoretical voltage vector Udn3.

[0137] The electrical angle correction unit 700 determines whether the target voltage vector Udm is less than the third theoretical voltage vector Udn3. When the target voltage vector Udm is less than the third theoretical voltage vector Udn3, the process proceeds to step 760. When the target voltage vector Udm is greater than or equal to the third theoretical voltage vector Udn3, the process proceeds to step 770.

[0138] Step 760: Increase the electrical angle compensation value θ.

[0139] The electrical angle correction unit 700 determines the electrical angle offset θ at this time. err If the offset is large and is a hysteresis offset, increase the electrical angle compensation value θ to correct the electrical angle offset θ err , so that the electrical angle compensation value θ is updated to the increased electrical angle compensation value θ. After the electrical angle compensation value θ is increased, the process proceeds to step 670 in FIG6 .

[0140] Step 770: Determine whether the target voltage vector Udm is greater than the fourth theoretical voltage vector Udn4.

[0141] The electrical angle correction unit 700 determines whether the target voltage vector Udm is greater than the fourth theoretical voltage vector Udn4. When the target voltage vector Udm is greater than the fourth theoretical voltage vector Udn4, the process proceeds to step 780. When the target voltage vector Udm is less than or equal to the fourth theoretical voltage vector Udn4, no processing is performed on the electrical angle compensation value θ, and the process proceeds to step 670 in Figure 6.

[0142] Step 780: Reduce the electrical angle compensation value θ.

[0143] The electrical angle correction unit 700 determines the electrical angle offset θ at this time. err If the offset is large and is a leading offset, reduce the electrical angle compensation value θ to correct the electrical angle offset θ err , so that the electrical angle compensation value θ is updated to the reduced electrical angle compensation value θ. After reducing the electrical angle compensation value θ, the process proceeds to step 670 in FIG6 .

[0144] In some embodiments, the electrical angle correction unit 700 determines the electrical angle offset θ err Previously, the electrical angle correction unit 700 did not need to obtain the electrical angle compensation value θ from the voltage estimation unit 600, and the voltage estimation unit 600 did not need to set the electrical angle compensation value θ to a preset value. e When the absolute value of is lower than the preset speed threshold, the electrical angle correction unit 700 can directly calculate the electrical angle offset θ according to the formula err And correct the electrical angle offset θ err For example, the relationship between the target voltage vector Udm and the theoretical voltage vector Udn is:

[0145] Udm=Udncosθ err +Uqnsinθ err ;

[0146] Among them, Udm and Udn are known items, and Uqn is the theoretical voltage vector of the brushless motor 200 on the quadrature axis, and Uqn is obtained by the formula Calculated. Where Rs is the stator resistance of the brushless motor 200, Iq is the actual quadrature axis current of the brushless motor 200, Lq is the quadrature axis inductance of the brushless motor 200, ω e is the speed of the brushless motor 200, ψ e is the permanent magnet flux linkage of the brushless motor 200 , and f is the frequency of the brushless motor 200 .

[0147] The above parameters can all be obtained through the detection module 500, so the electrical angle offset θ err Thus, the electrical angle correction unit 700 can directly set the electrical angle compensation value θ=-θ err, thereby the electrical angle compensation value θ and the electrical angle offset θ err The electrical angle offset θ can be eliminated by adding err , that is, the electrical angle compensation value θ and the observation angle θ e Adding them together can eliminate the observation angle θ e The electrical angle offset θ in err .

[0148] In addition, since the electrical angle correction unit 700 does not obtain the electrical angle compensation value θ, at the rotation speed ω of the brushless motor 200 e When the absolute value of is greater than or equal to the preset speed threshold, there is no electrical angle compensation value θ, and no processing is required at this time.

[0149] With the above solution, at the speed ω of the brushless motor 200 e The absolute value of is less than the preset speed threshold, that is, when the brushless motor 200 is in the low speed mode, the electrical angle offset θ generated by the brushless motor 200 is err Use the electrical angle compensation value θ to compensate and reduce or eliminate the electrical angle offset θ err This reduces the observation error of the brushless motor 200 at low speeds, corrects the rotor position signal, and enhances the load capacity and stability of the sensorless motor 200. Furthermore, the proposed solution reduces costs compared to replacing sensorless FOC with sensored FOC and eliminates the need for mechanical installation.

[0150] The above shows and describes the basic principles, main features and advantages of this application. Those skilled in the art should understand that the above embodiments do not limit this application in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the scope of protection of this application.

Claims

1. An electric tool comprising: case; a brushless motor, at least partially disposed in the housing, comprising a stator and a rotor; A power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit including a plurality of switching elements configured to apply a drive voltage to a winding of each phase of the brushless motor; a controller electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of the plurality of switching elements, thereby controlling the operation of the brushless motor; a voltage estimation unit configured to obtain motor parameters of the brushless motor and estimate a theoretical voltage vector corresponding to the target voltage vector based on the motor parameters and a direct-axis voltage equation; The electrical angle correction unit is configured to determine an electrical angle offset based on the target voltage vector and the theoretical voltage vector, and correct the rotor position signal based on the electrical angle offset.

2. The electric tool according to claim 1, further comprising a rotor position estimation unit configured to output the rotor position signal representing the rotor position in electrical degrees; the rotor position estimation unit comprises a flux observer.

3. The electric tool according to claim 2, wherein: The flux observer is configured to determine the rotor flux based on the observed stator flux, and determine the electrical angle based on the rotor flux; wherein, before determining the observed stator flux, a phase gain is obtained, and the phase gain is set according to the rotational speed of the brushless motor.

4. The electric tool according to claim 3, wherein: When the rotation speed of the brushless motor is greater than 0, the phase gain is 1; when the rotation speed of the brushless motor is less than 0, the phase gain is -1.

5. The electric power tool according to claim 1, wherein: The voltage estimation unit is configured to obtain an electrical angle compensation value before the electrical angle correction unit determines the electrical angle offset, and the electrical angle compensation value is used to correct the electrical angle offset.

6. The electric power tool according to claim 5, wherein: The voltage estimation unit is configured to: when the electrical angle compensation value cannot be obtained, set the electrical angle compensation value to a preset value.

7. The electric power tool according to claim 5, wherein: The electrical angle correction unit is configured to obtain the electrical angle compensation value and update the electrical angle compensation value based on the rotation speed of the brushless motor, the target voltage vector, and the theoretical voltage vector.

8. The electric power tool according to claim 5, wherein: When the speed of the brushless motor is greater than 0 and the target voltage vector is greater than a first theoretical voltage vector, the electrical angle correction unit is configured to: obtain the electrical angle compensation value, and reduce the electrical angle compensation value to update the electrical angle compensation value.

9. The electric power tool according to claim 5, wherein: When the speed of the brushless motor is greater than 0 and the target voltage vector is less than a second theoretical voltage vector, the electrical angle correction unit is configured to: obtain the electrical angle compensation value, and increase the electrical angle compensation value to update the electrical angle compensation value.

10. The electric power tool according to claim 5, wherein: When the speed of the brushless motor is less than 0 and the target voltage vector is less than a third theoretical voltage vector, the electrical angle correction unit is configured to: obtain the electrical angle compensation value, and increase the electrical angle compensation value to update the electrical angle compensation value.

11. The electric power tool according to claim 5, wherein: When the speed of the brushless motor is less than 0 and the target voltage vector is greater than a fourth theoretical voltage vector, the electrical angle correction unit is configured to: obtain the electrical angle compensation value, and reduce the electrical angle compensation value to update the electrical angle compensation value.

12. The electric tool according to any one of claims 8 to 11, wherein: The electrical angle correction unit is configured to correct the rotor position signal based on the updated electrical angle compensation value; and the controller is configured to generate the updated target voltage vector through current closed-loop control based on the corrected rotor position signal.

13. The electric power tool according to claim 12, wherein: The absolute value of the rotation speed of the brushless motor is lower than a preset rotation speed threshold.

14. The electric power tool according to claim 12, wherein: The electrical angle correction unit is configured to determine the electrical angle offset based on the updated target voltage vector and the theoretical voltage vector, and correct the rotor position signal based on the electrical angle offset.

15. The electric power tool according to claim 14, wherein: Correcting the rotor position signal by using the electrical angle offset includes: correcting the rotor position signal by using the electrical angle compensation value to correct the electrical angle offset.

16. An electric tool comprising: case; a brushless motor, at least partially disposed in the housing, comprising a stator and a rotor; A power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit including a plurality of switching elements configured to apply a drive voltage to a winding of each phase of the brushless motor; a controller electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of the plurality of switching elements, thereby controlling the operation of the brushless motor; a voltage estimation unit configured to estimate a theoretical voltage vector corresponding to the target voltage vector; The electrical angle correction unit is configured to determine an electrical angle offset based on the target voltage vector and the theoretical voltage vector when the absolute value of the rotational speed of the brushless motor is lower than a preset rotational speed threshold, and correct the rotor position signal based on the electrical angle offset.

17. The electric power tool according to claim 16, wherein: The voltage estimation unit is configured to obtain an electrical angle compensation value before the electrical angle correction unit determines the electrical angle offset, and the electrical angle compensation value is used to correct the electrical angle offset.

18. The electric power tool according to claim 17, wherein: The voltage estimation unit is configured to: when the electrical angle compensation value cannot be obtained, set the electrical angle compensation value to a preset value.

19. A method for controlling an electric tool, wherein: The electric tool comprises: case; a brushless motor, at least partially disposed in the housing, comprising a stator and a rotor; A power interface, configured to connect to a power source to supply power to the brushless motor; a drive circuit including a plurality of switching elements configured to apply a drive voltage to a winding of each phase of the brushless motor; and a controller electrically connected to the drive circuit, the controller being configured to generate a target voltage vector through current closed-loop control and output a pulse width modulation signal to control the conduction state of the plurality of switching elements, thereby controlling the operation of the brushless motor; The control method includes: Acquiring the rotational speed of the brushless motor, and acquiring the target voltage vector and the theoretical voltage vector of the direct axis when the absolute value of the rotational speed is lower than a preset rotational speed threshold; determining an electrical angle offset based on the target voltage vector and the theoretical voltage vector; The rotor position signal is corrected based on the electrical angle offset.

20. The control method of the electric tool according to claim 19, further comprising: An electrical angle compensation value is obtained, and the electrical angle compensation value is updated based on the rotational speed of the brushless motor, the target voltage vector, and the theoretical voltage vector; wherein the electrical angle compensation value is used to correct the electrical angle offset.

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