Electric tool and control method thereof

Abstract

The invention discloses an electric tool and a control method thereof. The electric tool comprises a motor, a power supply module, a driving circuit and a control module, and the control module is used for outputting a pulse width modulation signal to control the driving circuit; the control module is configured to obtain a current load parameter of the motor when the motor operates in a first mode; when the current load parameter meets the first condition, the motor operates in a second mode, and the duty ratio of the pulse width modulation signal is controlled to be reduced to the first duty ratio; wherein in the first mode, the maximum current of the motor does not exceed a current threshold value; the first duty ratio is smaller than or equal to a preset duty ratio, and the preset duty ratio is the minimum duty ratio of the pulse width modulation signal in the first mode. By the adoption of the technical scheme, a user can be reminded of the current load state and load removal during heavy load, so that damage to a drive circuit or demagnetization of a motor are prevented, and the reliability of the electric tool is improved.

Description

Technical Field

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

[0002] High-voltage brushless motors are becoming more and more popular in the field of power tools, especially heavy-duty power tools, due to their high power and small size. High-voltage brushless motors are powered by AC mains rather than DC battery packs.

[0003] High-voltage brushless motors use semiconductor switching devices to achieve electronic commutation, that is, electronic switching devices replace traditional contact commutators and brushes. It has the advantages of high reliability, no commutation sparks, and low mechanical noise, and is widely used in various power tools.

[0004] When the load on the power tool is heavy, the power tool needs to have a feedback mechanism to remind the user to remove the load, otherwise it may cause irreversible damage to the motor.

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

[0006] One object of the present application is to solve or at least alleviate part or all of the above problems. To this end, one object of the present application is to provide an electric tool and a control method thereof that can prevent damage to a drive circuit or demagnetization of a motor.

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

[0008] In some embodiments, the present application provides an electric tool, comprising: a motor, comprising a rotor and a multi-phase stator winding; a power supply module, supplying power to the electric tool; a drive circuit, electrically connected to the motor and the power supply module, for loading the electric energy provided by the power supply module to the motor; a control module, for outputting a pulse width modulation signal to control the drive circuit; the control module is configured to: when the motor operates in a first mode, obtain the current load parameters of the motor; when the current load parameters meet a first condition, the motor operates in a second mode, and controls the duty cycle of the pulse width modulation signal to drop to a first duty cycle; wherein, in the first mode, the maximum current of the motor does not exceed a current threshold; the first duty cycle is less than or equal to a preset duty cycle, and the preset duty cycle is the minimum duty cycle of the pulse width modulation signal in the first mode.

[0009] In some embodiments, the current load parameter includes a current rotational speed; and the first condition includes that the current rotational speed is less than a first rotational speed.

[0010] In some embodiments, the control module is further configured to: control the duty cycle of the pulse width modulation signal to drop to a first duty cycle, and then increase the duty cycle of the pulse width modulation signal at a first preset rate; when the current load parameter meets a second condition, control the duty cycle of the pulse width modulation signal to drop to a second duty cycle.

[0011] In some embodiments, the control module is further configured to: when the current load parameter does not satisfy a second condition, control the motor to return to the first mode.

[0012] In some embodiments, the current load parameter includes a current rotational speed; and the second condition includes that the current rotational speed is less than or equal to a second rotational speed.

[0013] In some embodiments, the current load parameter includes a current current; and the second condition includes that the current current is greater than or equal to a second current.

[0014] In some embodiments, the control module is further configured to: control the duty cycle of the pulse width modulation signal to drop to a second duty cycle, and then increase the duty cycle of the pulse width modulation signal at a second preset rate; when the current load parameters meet a third condition and no autonomous commutation of the motor is detected within a preset time period, control the motor to enter a forced commutation state; wherein, in the forced commutation state, the motor is controlled to be forced to commutate at a fixed period.

[0015] In some embodiments, the control module is further configured to: when the current load parameter does not satisfy a third condition, control the motor to return to the first mode.

[0016] In some embodiments, the current load parameter includes a current rotational speed; and the third condition includes that the current rotational speed is less than a third rotational speed.

[0017] In some embodiments, the current load parameter includes a current current; and the third condition includes that the current current is greater than or equal to a third current.

[0018] In some embodiments, the current load parameters include a current speed; the control module is also configured to: start timing after the motor enters a forced commutation state; if when the timing time reaches a first time, the current speed does not exceed a fourth speed, or the current current is greater than or equal to a fourth current, the motor is controlled to stop.

[0019] In some embodiments, the control module is further configured to control the motor to return to the first mode if the timing time has not reached the first time, the current speed exceeds a fourth speed, or the current current is greater than or equal to a fourth current.

[0020] In some embodiments, the present application further provides a method for controlling an electric tool, for controlling any of the above-mentioned electric tools, characterized by comprising: in a first mode, obtaining a current load parameter of the motor;

[0021] Determine whether the current load parameter satisfies a first condition; when the current load parameter satisfies the first condition, control the duty cycle of the pulse width modulation signal to drop to a first duty cycle; wherein, in the first mode, the maximum current of the motor does not exceed the current threshold; the first duty cycle is less than or equal to a preset duty cycle, and the preset duty cycle is the minimum duty cycle of the pulse width modulation signal in the first mode.

[0022] In some embodiments, after controlling the duty cycle of the pulse width modulation signal to drop to a first duty cycle when the current load parameter satisfies a first condition, it also includes: increasing the duty cycle of the pulse width modulation signal at a first preset rate; determining whether the current load parameter satisfies a second condition; and when the current load parameter satisfies the second condition, controlling the duty cycle of the pulse width modulation signal to drop to a second duty cycle.

[0023] In some embodiments, after controlling the duty cycle of the pulse width modulation signal to decrease to the second duty cycle when the current current is greater than or equal to the second current, the method further includes: increasing the duty cycle of the pulse width modulation signal at a second preset rate; determining whether the current load parameter satisfies a third condition;

[0024] When the current load parameter satisfies the third condition and autonomous commutation of the motor is not detected within a preset time period, the motor is controlled to enter a forced commutation state; wherein, in the forced commutation state, the motor is controlled to forced commutation at a fixed period.

[0025] The benefit of the present application lies in that: by obtaining the current load parameters of the motor in the first mode, when the current load parameters meet the first condition, the duty cycle of the pulse width modulation signal is controlled to drop to a first duty cycle that is less than the preset duty cycle. In this way, when the load is heavy, the user can be prompted to the current load status and to remove the load to prevent damage to the drive circuit or demagnetization of the motor, thereby improving the reliability of the power tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a three-dimensional diagram of an angle grinder provided in an embodiment of the present application;

[0027] Figure 2 is a circuit system block diagram provided by an embodiment of the present application;

[0028] Figure 3 is another circuit system block diagram provided by an embodiment of the present application;

[0029] Figure 4 A schematic diagram of the structure of a detection circuit provided in an embodiment of the present application;

[0030] Figure 5 A flow chart of a control method for an electric tool provided in an embodiment of the present application;

[0031] Figure 6 A flow chart of another method for controlling an electric tool provided in an embodiment of the present application;

[0032] Figure 7 For Figure 6 A flowchart of a control method associated with the embodiment;

[0033] Figure 8 A flow chart of another method for controlling an electric tool provided in an embodiment of the present application;

[0034] Fig. 9 A flowchart of another method for controlling an electric tool provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] Before any embodiments of the 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 above drawings.

[0036] In this application, the terms "comprises", "includes", "has" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0037] In this application, the term "and / or" is a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects before and after are in an "and / or" relationship.

[0038] In the present 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, direct connection refers to two parts or components being connected together without the need for an intermediate piece, and indirect connection refers to two parts or components being connected to at least one intermediate piece respectively, and the two parts or components being connected via the intermediate piece. In addition, "connect" and "couple" are not limited to physical or mechanical connections or couplings, and may include electrical connections or couplings.

[0039] In the present application, it will be understood by those of ordinary skill 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 tolerances caused by manufacturing, assembly, and use associated with a specific value, and the like. 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).

[0040] In this application, it will be understood by those skilled in the art that the function performed by a component can be performed by one component, multiple components, one part, or multiple parts. Similarly, the function performed by a part can also be performed by one part, one component, or a combination of multiple parts.

[0041] 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 another element "upper" or "lower", but also indirectly connected to another 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, the bottom can include directly below, lower left, lower right, lower front, and lower back, etc.

[0042] In this application, the terms "controller", "processor", "central processing unit", "CPU", and "MCU" are interchangeable. When a unit "controller", "processor", "central processing unit", "CPU", or "MCU" is used to perform a specific function, unless otherwise specified, these functions can be performed by a single unit or multiple units.

[0043] In the present application, the terms “device”, “module” or “unit” may be implemented in the form of hardware or software to achieve specific functions.

[0044] 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.).

[0045] In order to control the brushless motor, it is necessary to detect the position of the rotor, which refers to the rotational position of the rotor relative to the stator. The existing technology for detecting the rotor position is divided into two different technologies: one is sensory control, that is, using a position sensor to directly detect the position of the rotor and generate a corresponding control signal; the other is sensorless control, that is, judging the position of the rotor or the change of the position according to the change of the electrical parameters of the winding and then controlling the start-up commutation of the brushless motor.

[0046] Although the use of sensory control can simplify the control logic and make the control more direct, when the position sensor itself is inaccurate due to assembly or other problems, it will have a greater impact on the drive of the brushless motor.

[0047] The cost of using sensorless control is lower. The existing sensorless control often uses the method of forcing the rotor to rotate without considering the rotor position. After the rotor reaches a certain speed, it gradually switches according to the rotor phase change control until the drive state corresponding to the rotor position is reached, and then normal driving is performed. That is, the brushless motor first uses open-loop control to force the rotor to change phase, and then closes the loop to perform normal driving.

[0048] Although the rotor rotates during forced driving in the existing sensorless control method, the brushless motor cannot output sufficient torque because the driving state does not correspond to the rotor position. In addition, this control method relies on the rotor being able to rotate at a certain initial speed first. When the rotor of the brushless motor cannot or is difficult to rotate for some reason, this control method makes it difficult to put the brushless motor in the correct driving state.

[0049] In the field of power tools, load starting and heavy loads are relatively common, so existing brushless motors with sensorless control are not well suited for power tools. Especially for existing angle grinders and other grinding tool power tools, due to the large rotational inertia of the grinding disc, when using sensorless starting, if the initial position of the rotor is not found correctly, it is easy to cause the motor to fail to start, generate a high current spike in the motor, and even cause the motor to demagnetize. In the heavy load stage, due to the large rotational inertia of the grinding disc, if the rotor position cannot be accurately and timely identified, it is also easy to generate a high current spike, resulting in shutdown protection, and may even cause the motor to demagnetize.

[0050] High-voltage brushless motors are becoming increasingly popular in the field of power tools, especially heavy-duty power tools, due to their high power and small size. High-voltage brushless motors are powered by AC mains rather than DC battery packs. Although the technical solution disclosed in this application belongs to the field of high-voltage brushless motors, some of the concepts may also be applied to the field of DC-powered power tools.

[0051] High-voltage brushless motors use semiconductor switching devices to achieve electronic commutation, that is, electronic switching devices replace traditional contact commutators and brushes. It has the advantages of high reliability, no commutation sparks, and low mechanical noise, and is widely used in various power tools.

[0052] The present application provides an electric tool using a brushless motor, which can reduce high current spikes caused by rotor recognition errors under heavy load conditions (such as electric angle grinders). In one embodiment, the brushless motor is a high-voltage brushless motor using no position sensor.

[0053] like Figure 1 As shown, the electric tool may be an angle grinder 10. In other embodiments, the electric tool may also be other electric tools with heavy loads, such as grinding or polishing tools such as grinders and sanding machines. For the convenience of explanation, the electric tool takes an angle grinder as an example. Of course, the electric tool may also be other tools that can convert the output torque into other forms of motion. These tools may be used to grind workpieces, such as sanders; these tools may also be used to cut workpieces, such as reciprocating saws, circular saws, and jigsaws; these tools may also be used for impact, such as electric hammers; these tools may also be garden tools, such as pruning machines and chain saws; these tools may also be vehicle-type electric tools, such as riding lawn mowers; in addition, these tools may also be used for other purposes, such as blenders. As long as these electric tools include a motor that drives the movement of their working parts, the substantive content of the technical solution disclosed below can be adopted.

[0054] The angle grinder 10 can be mainly used for cutting, grinding and brushing metal and stone. Figure 1The descriptions of the directions front, rear, top, bottom, left and right are all based on the positions of the power tool relative to the user when in use.

[0055] like Figure 1 As shown, the angle grinder 10 includes a housing 11, a brushless motor 12, a power cord 13 and a control mainboard (not shown). The control mainboard is used to drive the brushless motor 12 to rotate to realize the operation of the power tool. The brushless motor 12 is a DC motor without a position sensor. The brushless motor 12 is supported on the housing 11, and the power cord 13 is connected to an AC power supply. The power cord 13 and the brushless motor 12 are both electrically connected to the control mainboard. The brushless motor 12 of the angle grinder 10 of this embodiment can be an AC brushless motor without a position sensor.

[0056] The circuit system 100 of the power tool may be as follows Figure 2 The circuit shown includes: a brushless motor 12 , a power supply module 101 , a drive circuit 102 , a detection module 103 and a control module 104 .

[0057] The brushless motor 12 may include three-phase windings u, v, and w forming a Y-type connection, and their connection terminals are respectively defined as phase access terminal A, phase access terminal B, and phase access terminal C. In other embodiments, the three-phase windings of the brushless motor 12 may also be connected in a triangle.

[0058] The drive circuit 102 is electrically connected to the power supply module 101, and the drive circuit 102 includes a plurality of switch elements. The drive circuit 102 is electrically connected to the control module 104 and the brushless motor 12, and can control the operation of the brushless motor 12 according to the control signal output by the control module 104. As an embodiment, the brushless motor 12 is a three-phase motor having a three-phase winding, and the drive circuit 102 is specifically electrically connected to the three-phase winding of the brushless motor 12. The drive circuit 102 specifically includes a switch circuit, and the switch circuit is used to drive the rotor of the motor to operate according to the control signal of the control module 104. In order to make the motor rotate, the drive circuit 102 has a plurality of drive states, and in a drive state, the stator winding of the motor generates a magnetic field, and the control module 104 is configured to output a corresponding drive signal to the drive circuit 102 according to the rotation position of the rotor of the brushless motor 12 so that the drive circuit 102 switches the drive state, thereby changing the state of the voltage and / or current loaded on the winding of the brushless motor 12, generating an alternating magnetic field to drive the rotor to rotate, and then realizing the drive of the motor. Exemplarily, the drive circuit 102 includes switch elements Q1, Q2, Q3, Q4, Q5, and Q6. Among them, Q1, Q3, and Q5 are high-side switch elements, and Q2, Q4, and Q6 are low-side switch elements. Any phase stator winding of the brushless motor 12 is connected to a high-side switch element and a low-side switch element. The gate terminal of each switch element in the drive circuit 102 is electrically connected to the control module 104 for receiving a control signal from the control module 104, and the control signal may be a PWM signal. In one embodiment, if the switch element is a MOS tube, the drain or source of each switch element is connected to the stator winding of the brushless motor 12. In one embodiment, if the switch element is an IGBT tube, the collector and emitter of each switch element are connected to the stator winding of the brushless motor 12. The switch elements Q1-Q6 receive control signals from the control module 104 to change their respective conduction states, thereby changing the current loaded on the stator winding of the brushless motor 12 by the power supply module 101.

[0059] The detection module 103 is electrically connected to the multi-phase stator winding of the brushless motor 12, and is used to detect the electrical parameters of the multi-phase stator winding during the operation of the brushless motor 12. Specifically, the electrical parameters can be electrical parameters that can be directly detected, such as voltage or current, or can be parameters calculated based on the voltage or current, such as slope or derivative.

[0060] The control module 104 is electrically connected to at least the detection module 103 and the drive circuit 102, and is used to control the conduction status of the switch element of the drive circuit 102, thereby controlling the working mode and driving state of the brushless motor 12. In some embodiments, the control module 104 uses a dedicated controller, such as some dedicated control chips (e.g., MCU, Microcontroller Unit). The control module 104 is integrated with a signal processing unit, wherein the signal processing unit is used to process the acquisition of relevant parameter signals, and has functions such as calculation, comparison, and judgment. After the signal processing unit processes the signal, it can generate a control signal and output it to the drive circuit 102 to drive the brushless motor 12 to operate.

[0061] The power supply module 101 includes a power supply. In this embodiment, the power supply is an AC power supply.

[0062] The DC brushless motor 12 without position sensor has two working modes: open-loop mode and closed-loop mode. Since there is no position sensor, the brushless motor needs to first use the open-loop mode to find the position of the rotor after starting. After confirming the position of the rotor, the control module 104 can control the brushless motor 12 to switch from the open-loop mode to the closed-loop mode. In some embodiments, when the brushless motor is overloaded, if the rotor position cannot be identified in time, the brushless motor 12 can also be controlled to switch from the closed-loop mode to the open-loop mode to prevent the generation of a higher current spike and damage to the brushless motor 12. After the rotor position is found or the load is removed, it is switched to the closed-loop mode.

[0063] When the control module 104 controls the drive circuit 102 to drive the brushless motor 12, the drive state output by the control module 104 should be compatible with the position of the rotor of the brushless motor 12 so that the rotor can obtain a larger torque. In other words, the control module 104 needs to control the switching of the drive state according to the position of the rotor. When the drive state does not correspond to the rotor position, the efficiency and capacity of the brushless motor 12 will be lost.

[0064] In some embodiments, the control module 104 controls the electrical signal of the driving circuit by outputting a pulse width modulation (PWM) signal to the switching element of the driving circuit 102 .

[0065] The control module 104 is configured to: when the motor operates in the first mode, obtain the current load parameter of the motor; when the current load parameter meets the first condition, the motor operates in the second mode and controls the duty cycle of the pulse width modulation signal to decrease to the first duty cycle.

[0066] It should be emphasized here that the first mode and the second mode can be different working states of the motor. For example, in the first mode, the working parameters of the motor meet one type of indicators; while in the second mode, the working parameters of the motor meet another type of indicators. The "working parameters" here can be any one or more of the parameters such as voltage, current, and speed.

[0067] In some embodiments, the first mode may be a constant speed mode, that is, the electric tool is controlled to operate at a constant speed. It should be noted that when the electric tool is started normally and reaches a stable operation of the motor speed, it is usually in the first mode. The "constant speed" here does not necessarily mean that the motor speed is completely unchanged, but means that the motor speed can fluctuate slightly around a constant value. In the second mode, the maximum current of the motor does not exceed the current threshold, wherein the current threshold is the maximum current allowed in the constant current mode. The first duty cycle is less than or equal to the preset duty cycle, and the preset duty cycle is the minimum duty cycle of the pulse width modulation signal in the second mode. In some embodiments, the minimum duty cycle of the pulse width modulation signal in the second mode is 20%. In some embodiments, the first duty cycle can be 8%. It can be understood that the smaller the value of the first duty cycle, that is, the greater the difference between the preset duty cycle and the first duty cycle, when the duty cycle of the pulse width modulation signal drops to the first duty cycle, the easier it is for the user to feel the change in the speed of the motor, so as to prompt the user to remove the load. In some embodiments, the first condition can be that the current load parameter of the motor is greater than the load threshold of the motor. In some embodiments, the current load parameter of the motor may include the current speed of the motor, and in this case, the first condition is that the current speed is less than the first speed, wherein the first speed is greater than or equal to the minimum speed allowed in the first mode. For example, the first speed may be 8000 rpm / min.

[0068] Specifically, in the first mode, by acquiring the current load parameters of the motor in real time, when the current load parameters of the motor meet the first condition, that is, when the current load of the motor is too large, the duty cycle of the modulation signal that controls the pulse width is reduced to the first duty cycle, so that the motor can be continuously driven with the first duty cycle. In this way, the user can be prompted that the current load is too large, so that the user can remove the load in time, thereby preventing damage to the drive circuit or demagnetization of the motor, thereby improving the reliability of the power tool; compared with the prior art of directly switching the motor state to a forced commutation state or directly shutting down when overloaded, the present application optimizes the user's feel of the angle grinder when it is in the overload stage.

[0069] In some embodiments, the control module 104 is further configured to: after controlling the duty cycle of the pulse width modulation signal to drop to a first duty cycle, increase the duty cycle of the pulse width modulation signal at a first preset rate; when the current load parameters meet a second condition, control the duty cycle of the pulse width modulation signal to drop to a second duty cycle.

[0070] Wherein, the first preset rate can be determined according to the performance parameters of the motor. The second condition can be that the current load parameter is greater than the load threshold of the motor. In some embodiments, the current load parameter of the motor may include the current speed of the motor, at which point the second condition includes that the current speed is less than the second speed. Wherein, the second speed is greater than or equal to the minimum speed allowed by the motor at the current duty cycle, and exemplarily, the second speed may be 4000rpm / min. In some embodiments, the current load parameter of the motor may include the current current of the motor, at which point the second condition includes that the current current is greater than or equal to the second current. Wherein, the second current is less than or equal to the minimum current allowed by the motor at the current duty cycle, and exemplarily, the second current may be 16A. In some embodiments, the current load parameter of the motor may include the current speed and current current of the motor, at which point the second condition includes that the current speed is less than the second speed, and the current current is greater than or equal to the second current, so that it is possible to more accurately determine whether the user is unloading, further improving the reliability of the power tool.

[0071] The second duty cycle is less than or equal to the preset duty cycle to be able to remind the user of overload. In some embodiments, the second duty cycle may be the same as or different from the first duty cycle, and the second duty cycle may be greater than or less than the first duty cycle.

[0072] In some embodiments, the control module 104 is further configured to control the motor to return to the first mode when the current load parameter does not satisfy the second condition.

[0073] It is understandable that the current load parameter does not meet the second condition, that is, when the user removes the load, the load of the motor is small at this time, and the motor can operate normally, thereby controlling the motor to return to the original first mode. In some embodiments, the first mode of the motor is a constant speed mode, and the second mode of the motor is a flow mode. In the constant speed mode, the speed of the motor is controlled to be a constant speed value. In the constant current mode, the current of the motor is controlled to be less than a current threshold.

[0074] Specifically, after the duty cycle of the pulse width modulation signal is controlled to drop to the first duty cycle to prompt the user to remove the load, the duty cycle of the pulse width modulation signal is increased at a first preset rate, and when the current load parameters meet the second condition, that is, when the user has not removed the load, the duty cycle of the pulse width modulation signal is controlled to drop to the second duty cycle to remind the user to remove the load again.

[0075] In some embodiments, the control module 104 is further configured to: control the duty cycle of the pulse width modulation signal to decrease to a second duty cycle, and then increase the duty cycle of the pulse width modulation signal at a second preset rate; when the current load parameters meet the third condition and the autonomous commutation of the motor is not detected within a preset time period, control the motor to enter a forced commutation state.

[0076] In the forced commutation state, the motor is controlled to be forced to commutate at a fixed period.

[0077] The second preset rate can be determined according to the performance parameters of the motor. In some embodiments, the second preset rate can be equal to the first preset rate. The third condition can be that the current load parameter is greater than the load threshold of the motor. In some embodiments, the current load parameter of the motor may include the current speed of the motor, at which point the third condition includes that the current speed is less than the third speed. Wherein the third speed is greater than or equal to the minimum speed allowed by the motor at the current duty cycle, and in some embodiments, the third speed may be equal to the second speed. In some embodiments, the current load parameter of the motor may include the current current of the motor, at which point the third condition includes that the current current is greater than or equal to the third current. Wherein the third current is less than or equal to the minimum current allowed by the motor at the current duty cycle, and in some embodiments, the third current may be equal to the second current. In some embodiments, the current load parameter of the motor may include the current speed and current current of the motor, at which point the third condition includes that the current speed is less than the third speed, and the current current is greater than or equal to the third current.

[0078] If the autonomous commutation of the motor is not detected within a preset time period, that is, the motor cannot correctly identify the rotor position under the current load, then the efficiency and capacity of the motor 12 will be lost.

[0079] In some embodiments, the control module 104 is further configured to: when the current load parameter does not satisfy the third condition, control the motor to return to the first mode.

[0080] It is understandable that when the load parameter does not meet the third condition, that is, when the user removes the load, at this time, the load of the motor is small and the motor can operate normally, so the motor is controlled to return to the first mode.

[0081] In some embodiments, the control module 104 is further configured to: start timing after the motor enters the forced commutation state; if when the timing reaches the first time, the current speed does not exceed the fourth speed, or the current current is greater than or equal to the fourth current, the motor is controlled to stop.

[0082] In some embodiments, the first time may be 5 seconds. The fourth speed is greater than or equal to the minimum speed allowed by the motor under the current duty cycle, and the current speed does not exceed the fourth speed, that is, it is used for unloaded. Since the driving state does not correspond to the rotor position in the forced commutation state, the motor cannot output sufficient torque, so it is necessary to control the motor to stop in time.

[0083] In some embodiments, the control module 104 is further configured to control the motor to return to the first mode if the timing time has not reached the first time, the current speed exceeds the fourth speed, or the current current is greater than or equal to the fourth current.

[0084] It is understandable that when the current speed exceeds the fourth speed, or the current current is greater than or equal to the fourth current, that is, when the user removes the load, the load on the motor is small and the motor can operate normally, thereby controlling the motor to return to the first mode.

[0085] In another embodiment, the control module 104 is configured to: obtain the current load parameter of the motor; and when the current load parameter satisfies the first condition, control the current of the motor to drop to the second current to prompt the user to remove the load.

[0086] In some embodiments, the current load parameter of the motor may include the current power, current speed and / or current current of the motor. When the current load parameter of the motor includes the current current of the motor, the first condition may be that the current current of the motor is greater than or equal to a threshold current, wherein the threshold current may be the maximum current that the motor can reach according to the characteristic curve of the motor, and illustratively, the threshold current may be 20A.

[0087] In some embodiments, the second current is less than the threshold current, and illustratively, the second current may be 10 A. It is understandable that the smaller the second current is, the more the motor speed decreases, and the user is more likely to feel the change in the motor speed, thereby prompting the user that the current load is too large and needs to be removed.

[0088] In some embodiments, the control module 104 is further configured to: after the current of the control motor drops to the second current, if the current load parameters acquired within a preset time all meet the second condition, then the current of the control motor continues to decrease or remains at the second current.

[0089] In some embodiments, when the current load parameter of the motor includes the current power of the motor, the second condition may be that the current power of the motor is greater than a threshold power, wherein the threshold power is the maximum power that the motor can reach under the current current; illustratively, the second condition may be that the current power of the motor is greater than 2600 W. It is understandable that the current load parameter satisfies the second condition, that is, the user has not removed the load. At this time, by controlling the current of the motor to continuously decrease or maintain the second current, the speed of the motor is continuously reduced, thereby continuously reminding the user to remove the load.

[0090] In some embodiments, the control module 104 is further configured to: if the load parameter of the motor does not meet the second condition within the threshold time T, that is, the user removes the load, then stop limiting the current of the motor, and at this time, the motor returns to a normal working state.

[0091] In some embodiments, the control module 104 is further configured to: if within the threshold time T, the load parameters of the motor all meet the second condition, that is, the user has not removed the load, then control the motor to shut down to protect the motor.

[0092] It is understandable that by reducing the current of the motor to prompt the user to remove the load, when the speed of the motor drops to a certain value, the motor will be blocked and cannot work normally. Therefore, the motor can be controlled to stop in time when the speed is low to prevent the motor from blocking.

[0093] In some embodiments, the control module 104 is further configured to: obtain the speed and current of the motor; start timing when the obtained current is greater than or equal to the second current and the obtained speed is less than the first speed; determine the stop time of the motor based on the timing time and the obtained speed, wherein the speed is always greater than zero.

[0094] Wherein, the second current is less than or equal to the threshold current, wherein the threshold current is the maximum current allowed by the motor. If the current current of the motor is greater than the threshold current, the components of the circuit board may be damaged by overcurrent. In some embodiments, when the current of the motor is greater than the second current and the output torque of the motor is the first torque, the speed of the motor is the first preset speed; on the characteristic curve of the motor, the speed corresponding to the first torque is the second preset speed; the first preset speed is less than or equal to the second preset speed, that is, under the second current, the speed of the motor is lower than the speed under the same torque on the characteristic curve of the motor to prevent damage to the motor. That is, when the current is greater than the second current, due to the current limiting behavior of the power tool, the speed of the motor may be lower than the speed of the same torque on the motor characteristic curve. The first speed can be less than or equal to the minimum speed allowed under the current current.

[0095] Specifically, by acquiring the rotation speed and current of the motor, the motor is controlled to stop after a period of time when the acquired current is greater than the second current and the acquired rotation speed is less than the first rotation speed, thereby preventing the motor from being damaged.

[0096] In some embodiments, the control module 104 is specifically configured to: if the rotation speeds at each moment acquired are less than the set rotation speed when the timing time reaches the set time, then control the motor to stop.

[0097] The setting time can be set according to the temperature rise test results of the motor at different speeds. When the set speed is different, the setting time is different. In this way, the user's use feel can be kept consistent before the motor stops.

[0098] In some embodiments, the control module 104 is specifically configured as follows: if the speed obtained at each moment is less than the first set speed when the timing time reaches the first set time, the motor is controlled to stop; if the speed obtained at each moment is less than the second set speed when the timing time reaches the second set time, the motor is controlled to stop.

[0099] Among them, the first set time is less than the second set time, and the first set speed is less than the second set speed, that is, the set time is proportional to the set speed. In this way, the working time of the motor can be longer while ensuring that the motor will not be damaged.

[0100] In some embodiments, the angle grinder is further provided with a motor temperature sensor, which can be provided on the motor to monitor the temperature of the motor. The control module 104 is further configured to: obtain the temperature of the motor; if the temperature of the motor is greater than or equal to the first temperature when the start signal is detected, then after the motor is started, determine whether the electrical parameter is greater than the preset electrical parameter; when the electrical parameter is greater than the preset electrical parameter, control the motor to stop.

[0101] The motor can be remotely controlled by an external device or by a button, and detecting the start signal means receiving a signal sent by an external device or a button to start the motor. The first temperature is lower than the shutdown temperature of the motor. For example, the first temperature may be 67°C. In some embodiments, the electrical parameters may include the current and / or power of the motor. The preset electrical parameters may be less than or equal to the set electrical parameters of the motor, wherein the set electrical parameters of the motor may be the maximum electrical parameters that can be reached when the motor is operating normally.

[0102] In some embodiments, the control module 104 is further configured to: after the motor is started, if the acquired temperature of the motor is lower than the second temperature, stop judging whether the electrical parameter is higher than the preset electrical parameter.

[0103] The second temperature is lower than the first temperature. For example, the second temperature may be 60°C.

[0104] In some embodiments, the control module 104 is further configured to: obtain the temperature of the motor in real time; if the temperature of the motor is lower than the first temperature when the start signal is detected, then after the motor starts, when the obtained temperature of the motor is greater than or equal to the third temperature, the motor is controlled to stop.

[0105] The third temperature is greater than the first temperature. For example, the third temperature may be 70°C.

[0106] Specifically, the temperature of the motor is obtained in real time. When the start signal is detected, if the temperature of the motor is greater than or equal to the first temperature, it means that the temperature of the motor is too high and it is easy to rise to the shutdown temperature during operation. Therefore, it is necessary to determine in real time whether the electrical parameters of the motor are greater than the preset electrical parameters after the motor is started, so as to control the motor to stop in time when the electrical parameters are greater than the preset electrical parameters to prevent the motor from being damaged by overheating. After the motor is started, if the temperature of the motor obtained is less than the second temperature, it means that the temperature of the motor has recovered to a lower temperature. At this time, the motor will not be at risk of being damaged by overheating. Therefore, the judgment of whether the electrical parameters are greater than the preset electrical parameters can be stopped, thereby saving the computing power of the control module 104. If the temperature of the motor is less than the first temperature when the start signal is detected, the temperature of the motor can be monitored after the motor is started. When the temperature of the motor is greater than or equal to the third temperature, the motor can be controlled to stop to prevent the motor from being damaged by overheating, which is beneficial to improving the service life of the angle grinder.

[0107] Figure 3 Another circuit system block diagram provided for an embodiment of the present application. The present application also provides an electric tool, the power supply of which is alternating current. For ease of description, this embodiment only describes the differences from the above-mentioned embodiment, and the same or similar components as the above-mentioned embodiment are marked with the same reference numerals. The parts of the above-mentioned embodiment that are compatible with the present embodiment can all be applied to the present embodiment, and only the differences between the present embodiment and the above-mentioned embodiment are described below.

[0108] The circuit system 200 of the electric tool of this embodiment includes a brushless motor 12 , a power supply module 201 , a drive circuit 202 , a detection module 203 , a control module 204 and a rectification module 205 .

[0109] The three-phase winding of the brushless motor 12 can be Y-connected or △-connected. In some embodiments, the brushless motor 12 can be a three-phase winding l, m, and n that form a △-connection. The difference between the △-connection and the Y-connection is that their connection ends are respectively connected to different ends of the windings, that is, one of the two connection ends of the winding l is connected to a connection end of the winding m, and the other is connected to the connection end of the winding n; according to this connection method, the connection ends of the three-phase windings l, m, and n are connected end to end in sequence, so that the three-phase windings forming the angle connection are essentially manifested as three winding access ends, which are respectively defined as winding access end D, winding access end E, and winding access end F.

[0110] The detection module 203 is electrically connected to the multi-phase stator winding of the brushless motor 12, and is used to detect the electrical parameters of the stator winding during the operation of the brushless motor 12. In a specific embodiment, the detection module 203 detects the electrical parameters of the connection between the detection module 203 and the stator winding during the operation of the brushless motor 12.

[0111] The driving circuit 202 is electrically connected to the power supply module 201 , and the driving circuit 202 includes a plurality of switch elements.

[0112] The control module 204 is electrically connected to at least the detection module 203 and the driving circuit 202 , and is used to control the conduction status of the switch element of the driving circuit 202 , thereby controlling the working mode and driving state of the brushless motor 12 .

[0113] The power supply module 201 includes an AC power source. The circuit system 200 also includes a rectifier module 205 for converting AC power into DC power.

[0114] For high-voltage brushless motors, the rated operating voltage is generally 220V-240V. Due to voltage fluctuations, high-voltage brushless motors are required to work normally within a larger voltage range. In one embodiment, the high-voltage brushless motor is required to work normally within a voltage range of 170V-285V. Such a wide voltage range will affect the positioning of the rotor position when the motor starts. For example, if a positioning pulse with a fixed width is used, inaccurate positioning is prone to occur at low voltage, making it impossible for the motor to obtain a large torque; at high voltage, excessive current is prone to occur, causing the motor to start short-circuit protection or even burn the motor.

[0115] In this embodiment, different positioning pulses are set according to different starting voltages to solve the problem of inaccurate rotor positioning of the high-voltage brushless motor in a wide voltage range, which is beneficial to improving the reliability of the high-voltage brushless motor.

[0116] In this embodiment, the control module 104 is further configured to: obtain the voltage of the motor in real time, and determine the width of the positioning pulse according to the voltage of the motor.

[0117] In some embodiments, the voltage of the motor can be the phase voltage or bus voltage of the motor. In some embodiments, the voltage of the motor is inversely proportional to the width of the positioning pulse, that is, when the voltage of the motor is low, a positioning pulse with a larger width can be set, and when the voltage of the motor is high, a positioning pulse with a smaller width can be set, so that when the motor is started at different voltages, the rotor can be accurately positioned, thereby improving the reliability of the high-voltage brushless motor and bringing a better user experience to users without increasing costs.

[0118] One MCU detection analog unit can only detect one analog signal. When multiple analog signals need to be detected, the MCU is often required to have at least a corresponding number of detection analog units. However, the number of analog detection units of the MCU of the power tool is often limited. Therefore, when the number of detection analog units of the MCU is limited, how to use one MCU analog detection unit to detect two different analog signals has become a technical problem that needs to be solved in this field.

[0119] Figure 4 This is a schematic diagram of a detection circuit provided in an embodiment of the present application. Figure 4 As shown, in the detection circuit provided by this embodiment, the I / O port TEM_CON of the MUC is connected to the control end of the first transistor Q25 through the resistor R105, the first power supply VCC25 is connected to the first end of the temperature sensor J4 of the motor through the resistor R41, the second end of the temperature sensor J4 is connected to the input end of the first transistor Q25, and the output end of the first transistor Q25 is grounded; the first end of the temperature sensor J4 is also connected to the detection analog unit AD-TEMP of the MCU; the control end of the second transistor Q26 is connected to the I / O port TEM_CON of the MUC through the resistor R99, the input end of the second transistor Q26 is connected to the second power supply VCC33 through the resistor R99, and the output end of the second transistor Q26 is grounded; the control end of the third transistor Q27 is connected to the I / O port TEM_CON of the MUC through the resistor R100 CON is connected, the input end of the third transistor Q27 is connected to the second power supply VCC33 through the resistor R99, and the output end of the third transistor Q27 is grounded; in this way, the detection circuit provided in this embodiment, when the I / O port TEM_CON of the MUC is at a low level, Q27 is not connected, resulting in Q26 being turned on, and Q25 being not turned on, at this time, the detection analog unit AD-TEMP of the MCU collects the signal of RT, wherein RT is a temperature sensor, and illustratively, the temperature sensor RT is used to collect the temperature of the IGBT; correspondingly, when the I / O port TEM_CON of the MUC is at a high level, Q27 is turned on, resulting in Q26 being blocked, and Q25 being turned on, at this time, the detection analog unit AD-TEMP of the MCU collects the signal of J4, wherein J4 can be the temperature sensor of the motor, and J4 is used to collect the temperature of the motor. In this way, when the TEM_CON signal received by the I / O port of the MUC is alternating between high and low levels, an MCU detection simulation unit can collect two different analog signals in time-sharing, that is, the MCU's detection simulation unit can alternately collect the temperature of the IGBT and the temperature of the motor, thereby saving resources and reducing the cost of power tools.

[0120] Figure 5 This is a flow chart of a control method for an electric tool provided in an embodiment of the present application. This application also provides a control method for an electric tool, such as Figure 5 As shown, the control method includes:

[0121] S110 . In the first mode, obtain current load parameters of the motor.

[0122] S120: Determine whether the current load parameters meet the first condition.

[0123] It should be noted that the first condition here is used to determine whether the user has removed the load. If the user has removed the load, the current load parameter does not meet the first condition; if the user has not removed the load, the current load parameter meets the first condition.

[0124] S130: If yes, control the duty cycle of the pulse width modulation signal to decrease to the first duty cycle.

[0125] It should be noted that if the front load parameter meets the first condition and the user does not remove the load, the power tool enters a second mode different from the first mode to operate. The first duty cycle is less than or equal to the preset duty cycle, which is the minimum duty cycle of the pulse width modulation signal in the second mode.

[0126] Figure 6 This is a flow chart of another method for controlling an electric tool provided in an embodiment of the present application. In some embodiments, the present application further provides a method for controlling an electric tool, further comprising:

[0127] S140 . After controlling the duty cycle of the pulse width modulation signal to decrease to the first duty cycle, increase the duty cycle of the pulse width modulation signal at a first preset rate.

[0128] S150: Determine whether the current load parameters meet the second condition.

[0129] It should be noted that the second condition here is used to determine whether the user has removed the load. If the user has removed the load, the current load parameter does not meet the second condition; if the user has not removed the load, the current load parameter meets the second condition.

[0130] S160: If yes, control the duty cycle of the pulse width modulation signal to decrease to a second duty cycle.

[0131] In some embodiments, if the current load parameter does not satisfy the second condition, the motor is controlled to return to the first mode, and the motor continues to operate in the original mode.

[0132] It should be noted that the third condition here is used to determine whether the user has removed the load. If the user has removed the load, the current load parameter does not meet the third condition; if the user has not removed the load, the current load parameter meets the third condition.

[0133] S170. Increase the duty cycle of the pulse width modulation signal at a second preset rate.

[0134] S180: Determine whether the current load parameters meet the third condition.

[0135] S190: If yes, determine whether autonomous commutation of the motor is detected within a preset time period.

[0136] S1100: If not, control the motor to enter the forced commutation state.

[0137] In the forced commutation state, the motor is controlled to be forced to commutate at a fixed period.

[0138] In some embodiments, if the timing time does not reach the first time and the current load parameter does not meet the third condition, the motor is controlled to return to the first mode.

[0139] In some embodiments, after the motor enters the forced commutation state, timing starts; if when the timing reaches the first time, the current speed does not exceed the fourth speed, or the current current is greater than or equal to the fourth current, the motor is controlled to stop.

[0140] Any two or three of the first condition, the second condition and the third condition involved in the present application may use the same load parameter for judgment. When the same load parameter is used, the specific value of the load parameter may be the same or different.

[0141] Figure 7 The flowchart revealed Figure 6 The flowchart disclosed is associated with Figure 7 As shown, the control method includes:

[0142] S150: Determine whether the current load parameters meet the second condition.

[0143] S161: If yes, the duty cycle of the pulse width modulation signal is controlled to decrease to the second duty cycle, and timing is started.

[0144] In some embodiments, if the current load parameter does not satisfy the second condition, the motor is controlled to return to the first mode without timing.

[0145] S171, determining whether the timing time reaches the preset time.

[0146] S181: If yes, determine whether the motor returns to the first mode.

[0147] S191, if not, control the motor to stop.

[0148] In some embodiments, the preset time may be 5 seconds. When the acquired timing time reaches the preset time and the electric tool has not returned to the first mode, the motor is controlled to stop. Figure 7 Step S150 of the flowchart shown in FIG. Figure 6 The step S150 of the flowchart shown is the same, and the subsequent steps are performed when the current load parameter meets the second condition. Therefore, the time point when the timing time reaches the preset time may be at Figure 6Any step between S170 and S1100 in the above process, that is, the control motor shutdown of step S191 may occur at any time between S170 and S1100. Figure 6 When the control cycle shown cycles for a certain period of time and the user does not respond to the load removal, the power tool can actively shut down to avoid further damage to components such as the motor and the control board.

[0149] Figure 8 This is a flow chart of another method for controlling an electric tool provided in an embodiment of the present application. The present application also provides a method for controlling an electric tool, such as Figure 8 As shown, the control method includes:

[0150] S210, obtaining the rotation speed and current value of the motor.

[0151] S220: Determine whether the acquired current value is greater than the first current value.

[0152] S230: If yes, determine whether the acquired rotation speed is less than the first rotation speed;

[0153] S240: If yes, start timing.

[0154] S250: Determine the stop time of the motor according to the timing time and the acquired rotation speed.

[0155] In some embodiments, the motor shutdown time is determined according to the timing time and the rotation speed, including: when the timing time reaches the set time, judging whether the rotation speeds at each time obtained are all less than the set rotation speed; if the rotation speeds at each time obtained are all less than the set rotation speed, the motor is controlled to shut down. The rotation speed here is always greater than zero.

[0156] In some embodiments, Fig. 9 As shown, the control method also includes:

[0157] S310: Obtain the temperature and electrical parameters of the motor.

[0158] S320: When a start signal is detected, determine whether the temperature of the motor is greater than or equal to a first temperature.

[0159] S330: If yes, after the motor is started, determine whether the electrical parameter is greater than the preset electrical parameter.

[0160] In some embodiments, if the temperature of the motor is lower than the first temperature when the start signal is detected, then after the motor is started, it is determined whether the acquired temperature of the motor is greater than or equal to a third temperature; if the acquired temperature of the motor is greater than or equal to the third temperature, the motor is controlled to stop.

[0161] The third temperature is greater than the first temperature.

[0162] In some embodiments, if after the motor is started, if the acquired temperature of the motor is lower than the second temperature, the determination of whether the electrical parameter is higher than the preset electrical parameter is stopped.

[0163] The second temperature is lower than the first temperature.

[0164] S340: If yes, the motor is controlled to stop.

[0165] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the above embodiments do not limit the present application in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present application.

Claims

1. An electric tool, characterized in that: include: An electric machine, including a rotor and a multi-phase stator winding; A power supply module, for supplying power to the electric tool; A drive circuit, electrically connected to the motor and the power supply module, and configured to load the electric energy provided by the power supply module to the motor; A control module, used for outputting a pulse width modulation signal to control the driving circuit; The control module is configured to: when the motor is running in the first mode, obtain the current load parameter of the motor; when the current load parameter meets the first condition, the motor is running in the second mode, and the duty cycle of the pulse width modulation signal is controlled to be reduced to the first duty cycle; wherein, in the second mode, the maximum current of the motor does not exceed the current threshold; The first duty cycle is less than or equal to a preset duty cycle, and the preset duty cycle is the minimum duty cycle of the pulse width modulation signal in the second mode.

2. The electric tool according to claim 1, characterized in that: The current load parameter includes a current speed or a current current; when the current load parameter is a current speed, the first condition includes that the current speed is less than a first speed; When the current load parameter is a current current, the first condition includes that the current current is greater than a first current.

3. The electric tool according to claim 1, characterized in that: The control module is further configured to: after controlling the duty cycle of the pulse width modulation signal to decrease to the first duty cycle, increase the duty cycle of the pulse width modulation signal at a first preset rate; When the current load parameter satisfies a second condition, the duty cycle of the pulse width modulation signal is controlled to decrease to a second duty cycle.

4. The electric tool according to claim 3, characterized in that: The control module is further configured to control the motor to return to the first mode when the current load parameter does not satisfy a second condition.

5. The electric tool according to any one of claims 3 or 4, characterized in that: The current load parameter includes a current rotation speed; and the second condition includes that the current rotation speed is less than or equal to a second rotation speed.

6. The electric tool according to any one of claims 3 or 4, characterized in that: The current load parameter includes a current current; and the second condition includes that the current current is greater than or equal to a second current.

7. The electric tool according to claim 3, characterized in that: The control module is further configured to: after controlling the duty cycle of the pulse width modulation signal to decrease to a second duty cycle, increase the duty cycle of the pulse width modulation signal at a second preset rate; When the current load parameter satisfies the third condition and autonomous commutation of the motor is not detected within a preset time period, the motor is controlled to enter a forced commutation state; wherein, in the forced commutation state, the motor is controlled to forced commutation at an artificially set period.

8. The electric tool according to claim 7, characterized in that: The control module is further configured to control the motor to return to the second mode when the current load parameter does not satisfy a third condition.

9. The electric tool according to any one of claims 7 or 8, characterized in that: The current load parameter includes a current rotation speed; and the third condition includes that the current rotation speed is less than a third rotation speed.

10. The electric tool according to any one of claims 7 or 8, characterized in that: The current load parameter includes a current current; and the third condition includes that the current current is greater than or equal to a third current.

11. The electric tool according to any one of claims 5 or 6, characterized in that: The current load parameter includes the current speed; The control module is also configured to: start timing when the current load parameter meets the second condition; if when the timing reaches the first time, the current speed does not exceed the fourth speed, or the current current is greater than or equal to the fourth current, control the motor to stop.

12. The electric tool according to claim 11, characterized in that: The control module is further configured to control the motor to return to the first mode if the timing time does not reach the first time, the current speed exceeds a fourth speed, or the current current is less than a fourth current.

13. A method for controlling an electric tool, used for controlling the electric tool according to any one of claims 1 to 12, characterized in that: include: In the first mode, obtaining current load parameters of the motor; Determining whether the current load parameter satisfies a first condition; When the current load parameter satisfies a first condition, controlling the duty cycle of the pulse width modulation signal to decrease to a first duty cycle; wherein, in the first mode, the maximum current of the motor does not exceed a current threshold; The first duty cycle is less than or equal to a preset duty cycle, and the preset duty cycle is the minimum duty cycle of the pulse width modulation signal in the first mode.

14. The control method of the electric tool according to claim 13, characterized in that: When the current load parameter satisfies the first condition, after controlling the duty cycle of the pulse width modulation signal to decrease to the first duty cycle, the method further includes: increasing the duty cycle of the pulse width modulation signal at a first predetermined rate; Determining whether the current load parameter satisfies a second condition; When the current load parameter satisfies the second condition, the duty cycle of the pulse width modulation signal is controlled to decrease to a second duty cycle.

15. The control method of the electric tool according to claim 14, characterized in that: When the current current is greater than or equal to the second current, after controlling the duty cycle of the pulse width modulation signal to decrease to the second duty cycle, the method further includes: increasing the duty cycle of the pulse width modulation signal at a second predetermined rate; Determining whether the current load parameter satisfies a third condition; When the current load parameter satisfies the third condition and autonomous commutation of the motor is not detected within a preset time period, the motor is controlled to enter a forced commutation state; wherein, in the forced commutation state, the motor is controlled to forced commutation at a fixed period.

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