CN115940747A - Electric tool and control method thereof - Google Patents

Abstract

The invention discloses an electric tool and a control method thereof, comprising the following steps: the device comprises a shell, an alternating current power supply input device, a motor and a drive circuit, wherein the drive circuit comprises a plurality of electronic switch current detection modules and a control module, and the phase current value of the motor is acquired in real time through the current detection modules at periodic time intervals; and if the obtained phase current value is higher than a first preset current threshold value, closing the electronic switch in the conducting state, and starting the electronic switch which is controlled to be conducted by the control module at present until the obtained phase current value is lower than a second preset current threshold value. By adopting the technical scheme, the cycle-by-cycle current-limiting control method suitable for the alternating current electric tool can be provided, so that the electric tool can effectively inhibit large current under heavy load working conditions and improve the use hand feeling of users.

Description

Electric tool and control method thereof

Technical Field

The invention relates to an electric tool, in particular to a control method suitable for an alternating current electric tool.

Background

Under the heavy load working condition, especially for a high-voltage brushless tool, the alternating current electric tool is easy to generate an overcurrent phenomenon due to the fact that the power supply capacity of a power grid is large enough, electronic components are easy to damage, and the use hand feeling of the electric tool is obviously influenced to a large extent.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides the current-limiting control method suitable for the alternating current electric tool, which can effectively inhibit large current under a heavy-load working condition and does not influence the use hand feeling of the electric tool.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a power tool, comprising: a housing; the alternating current power supply input device is used for accessing a power supply required by the electric tool during working; a motor disposed within the housing; a drive circuit comprising a plurality of electronic switches; the current detection module is used for acquiring a phase current value of the motor; the control module is electrically connected with the drive circuit and outputs a drive signal with a given period to control the drive circuit to operate the motor; the current detection module acquires the phase current value of the motor in real time; the control module is further configured to: if the obtained phase current value is higher than a first preset current threshold value, the electronic switch in the conducting state is closed, and the electronic switch which is controlled to be conducted by the control module at present is opened until the obtained phase current value is lower than a second preset current threshold value.

Further, the first preset current threshold is greater than the second preset current threshold.

Further, still include: the rectifier module is electrically connected with the alternating current power supply input device and converts alternating current into direct current for the electric tool to use; the power supply circuit is electrically connected with the rectification module and is arranged to at least supply power to the control module; and the capacitor circuit is electrically connected between the rectifying module and the driving circuit.

Further, the current detection module comprises a plurality of current detection resistors.

Further, the motor is configured as a brushless dc motor.

Further, the brushless dc motor is controlled by the driving signal.

Further, the capacitor circuit comprises at least one electrolytic capacitor.

A control method of a power tool, the power tool including a housing; the alternating current power supply input device is used for accessing a power supply required by the electric tool during working; a motor disposed within the housing; a drive circuit comprising a plurality of electronic switches; the current detection module is used for acquiring a phase current value of the motor; the control module is electrically connected with the driving circuit;

the control method comprises the following steps: the control module outputs a drive signal with a given period to control the drive circuit to operate the motor; the current detection module is used for acquiring the phase current value of the motor in real time; if the obtained phase current value is higher than a first preset current threshold value, the control module closes the electronic switch which is in a conducting state, and the electronic switch which is controlled to be conducted by the control module at present is opened until the obtained phase current value is lower than a second preset current threshold value.

Further, the first preset current threshold is greater than the second preset current threshold.

The invention discloses an electric tool and a control method thereof.A first preset current threshold and a second current threshold are set, and once the phase current is detected to exceed the first preset current threshold, an electronic switch is turned off; and once the phase current value of the motor is lower than a second preset current threshold value, the electronic switch is started to recover the current flowing to the motor. The motor can simply and effectively inhibit the large current generated during the working of the motor, simultaneously does not influence the use hand feeling of the electric tool, optimizes the use hand feeling of the electric tool to a greater extent, and improves the reliability and the service life of the electric tool.

Drawings

Fig. 1 is a perspective view of a power tool as an embodiment;

FIG. 2 is a circuit block diagram of circuitry for one embodiment;

FIG. 3 is a circuit block diagram of a rectification module as one embodiment;

FIG. 4 is a block circuit diagram of a current detection module as one embodiment;

FIG. 5 is a block circuit diagram of a current sensing module as another embodiment;

fig. 6 is a waveform diagram of a motor control signal as an embodiment;

FIG. 7 is a waveform diagram of a motor current limit control method as an embodiment;

FIG. 8 is a flow chart of a motor current limit control method as one embodiment;

fig. 9 is a waveform diagram of a frequency continuous variation of a PWM signal as an embodiment;

fig. 10 is a waveform diagram of a frequency continuous variation of a PWM signal as an embodiment;

fig. 11 is a flowchart of a control method of a motor as an embodiment;

fig. 12 is a waveform diagram of a PWM signal and a current limit period as another embodiment;

fig. 13 is a flowchart of a control method of a motor as another embodiment;

fig. 14 is a waveform diagram of a PWM signal and a current limit period as a further embodiment;

fig. 15 is a flowchart of a control method of a motor as still another embodiment.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

The power tool of the present invention may be a hand-held power tool, a garden-type vehicle such as a vehicle-type lawn mower, but is not limited thereto. The power tool of the present invention includes, but is not limited to, alternating current power tools such as sanders, drills, impact drivers, tappers, fastener drivers, etc., as long as they can adopt the essence of the technical solution disclosed below, and thus fall within the scope of the present invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

Referring to fig. 1, an exemplary power tool 10 is shown, which is an angle grinder. The electric power tool 10 mainly includes: a housing 11, a motor 13, a function 14, an ac power input 15, and circuitry 12 located within the housing 11.

The motor 13 includes a stator winding and a rotor. In some embodiments, the electric machine 13 is a three-phase brushless electric machine comprising a rotor with permanent magnets and electronically commutated three-phase stator windings U, V, W. In some embodiments, a star connection is used between the three phase stator windings U, V, W. In other embodiments, the three-phase stator windings U, V, W are connected in an angular fashion. However, it must be understood that other types of brushless motors are also within the scope of the present disclosure. The brushless motor may include less or more than three phases.

The function element 14 is used to implement the function of the power tool 10. The function 14 is driven by the motor 13. The functional elements are different for different power tools. For angle grinders, the function 14 is an angle grinder disc for performing a grinding or cutting function.

The ac power input device 15 is used to receive power required for the operation of the power tool 10. As one of specific embodiments, the power supply of the present embodiment is optionally configured as an ac power supply. Specifically, the ac power input device 15 includes an ac plug to receive ac commercial power of 120V or 220V.

Referring to fig. 2, the circuit system 12 of the power tool 10 of one embodiment mainly includes a rectifier module 21, a capacitor circuit 22, a power supply circuit 23, a driving circuit 24, a control module 25, a rotation speed detection module 26, and a current detection module 27.

The rectifier module 21 constitutes a dc unit of the power tool 10. The rectifier module 21 is configured to receive ac power from the ac power input device 15 and output dc bus voltage, that is, convert ac power input by the ac power input device 15 into pulsating dc power for output. The rectifying module 21 is electrically connected to the ac power input device 15. As one specific embodiment, referring to fig. 3, the rectifier module 21 includes a rectifier bridge composed of four diodes D1, D2, D3, and D4, and converts the alternating current into pulsating direct current in the same direction by using the unidirectional conductivity of the diodes and the tube voltage drop.

The capacitor circuit 22 is connected in parallel to the dc bus of the power tool 10, i.e., between the positive and negative poles of the dc unit in the circuit system 12. As one of the specific embodiments, the capacitor circuit 22 is optionally connected in parallel between the rectifier module 21 and the driving circuit 24. Specifically, the capacitor circuit 22 includes an electrolytic capacitor C. The capacitor circuit 22 is electrically connected with the rectifying module 21, and the pulsating direct current output by the rectifying module 21 is converted into smooth direct current through filtering of the electrolytic capacitor C and is output, so that harmonic interference in the pulsating direct current is reduced. Preferably, the ratio of the capacity value of the electrolytic capacitor C to the rated power of the motor 13 is greater than 20 μ F/KW and less than 80 μ F/KW. Therefore, the space can be saved, and the capacitor element with larger physical size does not exist in the hardware circuit.

The power supply circuit 23 is used to supply power to at least the control module 25. As an embodiment, the power supply circuit 23 is electrically connected to the rectifying module 21, and converts the electric energy rectified by the rectifying module 21 into a supply voltage suitable for the control module 25. For example, to power the control module 25, the power supply circuit 23 reduces the voltage rectified by the rectifying module 21 from the ac power input device 15 to 15V to power the control module 25.

The driving circuit 24 is electrically connected to the rectifier module 21 for driving the motor 13,. The input terminal of the driving circuit 24 receives the voltage from the rectifier module 21, and the voltage is distributed to each phase winding on the stator of the motor 13 in a certain logic relation under the driving of the driving signal output by the control module 25, so that the motor 13 is started and generates continuous torque. Specifically, the drive circuit 24 includes a plurality of electronic switches. In some embodiments, the electronic switch comprises a Field Effect Transistor (FET), and in other embodiments, the electronic switch comprises an insulated gate bipolar transistor (IG-BT), or the like. In some embodiments, the driving circuit 24 is a three-phase bridge circuit. The driver circuit 24 includes three electronic switches Q1, Q3, Q5 arranged as high-side switches and three electronic switches Q2, Q4, Q6 arranged as low-side switches.

Three electronic switches Q1, Q3, Q5 as high-side switches are provided between the power supply line of the rectifier module 21 and the coils of the respective phases of the motor 13, respectively. Three electronic switches Q2, Q4, Q6 as low-side switches are provided between the coils of the respective phases of the motor 22 and the ground, respectively.

The respective gate terminals UH, UL, VH, VL, WH, WL of the six electronic switches Q1-Q6 are electrically connected to the control module 25, and each drain or source of the electronic switches is connected to the stator winding of the electric motor 13. The electronic switches Q1-Q6 change the on or off state at a certain frequency according to the driving signal output by the control module 25, thereby changing the power state of the rectifying circuit 21 applied to the winding of the motor 13.

The drive circuit 24 is a circuit for switching the energization state of each phase winding of the motor 13 and controlling the energization current of each phase winding to rotationally drive the motor 13. The turn-on sequence and timing of the phase windings depends on the position of the rotor. In order to rotate the motor 13, the driving circuit 24 has a plurality of driving states, in which a stator winding of the motor 13 generates a magnetic field, and the control module 25 outputs a control signal based on different rotor positions to control the driving circuit 24 to switch the driving states so that the magnetic field generated by the stator winding rotates to drive the rotor to rotate, thereby driving the motor 13.

The rotation speed detection module 26 is configured to obtain at least one of a measured rotation speed of the motor 13 and a position of the rotor. In some embodiments, the speed detection module 26 includes sensors capable of directly detecting the speed and position of the motor 13, such as hall sensors. In other embodiments, the speed detection module 26 is configured to estimate the rotor position of the electric machine 13 based on at least the phase voltages of the electric machine 13 and the current values of the stator windings.

The current detection module 27 is configured to collect a current of the motor 13, where the current may be a bus current of the motor 13 or a phase current of each phase winding of the motor 13. As one of specific embodiments, the current detection module 27 detects phase currents of windings of each phase of the motor 13, and the bus current of the motor 13 can be calculated from the detected three-phase current values, and in some embodiments, the current detection module 27 includes hall current sensors to directly detect the phase currents of the windings of each phase of the motor 13. As another specific embodiment, referring to fig. 4, current detecting resistors R1, R2, and R3 are respectively connected in series between the driving circuit 24 and each phase winding of the motor 13, and the current detecting module 27 can calculate the phase current or the bus current of each phase winding by detecting the voltage across the detecting resistors. Specifically, the current detection module 27 detects voltages at two ends of the current detection resistors R1, R2, and R3, respectively, to calculate phase currents of the three-phase stator windings U, V, and W. As another specific embodiment, referring to fig. 5, the current detecting module 27 is configured to detect an internal resistance of an electronic switch in a conducting state in the driving circuit 24, and calculate a current through the electronic switch based on the internal resistance of the electronic switch in the conducting state and a voltage value across the electronic switch, where the current of the electronic switch is a phase current of a winding of the corresponding motor 13. Specifically, the current detection module 27 detects voltages at two ends of three driving switches Q1, Q3, and Q5 of the high-side switch respectively to calculate phase currents of the corresponding three-phase stator windings U, V, and W. Thus, the electric tool can detect the phase current corresponding to the winding of the motor 22 without adding hardware, and the cost is saved.

The control module 25 is electrically connected to at least the power supply circuit 23, the driving circuit 24 and the current detecting module 27 for controlling the operation of the driving circuit 24. In some embodiments, the control module 25 employs a dedicated control chip (e.g., MCU, micro control Unit, microcontroller Unit).

In some embodiments, referring to fig. 6 and 7, the control module 25 outputs a period T ₁ Frequency of f ₁ For controlling the conductive state of the plurality of electronic switches Q1-Q6 to drive the motor 13. Preferably, the motor 13 is provided as a three-phase brushless dc motor, and the drive signal is optionally provided as a PWM signal. Meanwhile, the control module 25 limits the current of the motor 13 for a periodic time interval T2, which is understood by those skilled in the art as a current limiting period of the motor, and T2 is defined as a current limiting period of the motor 13.

Referring to fig. 7, as one of the embodiments, the current limiting period T ₂ Set to be equal to the period T of the PWM signal ₁ And the consistency is maintained. The control module 25 is configured to limit the current period T ₂ The current detection module 27 obtains the phase current value of the motor 13 in real time in the current-limiting period T, compares the phase current value with the preset current threshold, and if the phase current value exceeds the preset current threshold, determines that the current-limiting period T is within the current-limiting period T ₂ Turns off the electronic switch for the remaining time of the previous one cycle, thereby cutting off the current flowing to the motor 13, and for the period T of the previous one PWM signal ₁ At the end, the electronic switch is turned on to resume the current to the motor 13. In particular, the setting of a preset current thresholdThe setting can be additionally set according to the type selection of the motor in practical application and practical application scenes, and the setting method for presetting the current is not limited in the invention. It should be further noted that, in the above technical solution, the turned-off electronic switch is specifically an electronic switch currently in a turned-on state, and the turned-on electronic switch is an electronic switch controlled to be turned on by a current driving signal.

Under the heavy-load working condition, the motor 13 has enough power supply capacity of the power grid voltage, so that the overcurrent phenomenon can occur, components in the electric tool are damaged, and the service life of the electric tool is shortened. Referring to fig. 7, under a heavy load condition, the motor 13 has an overcurrent phenomenon, i.e., indicated by point b. By adopting the technical scheme of current limiting, the phase current value I _phase Exceeds a predetermined current threshold I _ref At this time, the control module 25 immediately turns off the electronic switch so that the current flowing through the motor 13 does not rise any more, i.e., as shown by point a. At the end of the current cycle of the PWM signal, indicated at point c, the control module 25 re-opens the electronic switch to restore current to the motor 13. It should be noted that, in the present invention, a current detection module is mainly provided to detect a phase current of the motor 13 for implementing cycle-by-cycle current limiting of the motor, and those skilled in the art can understand that the current detection module can also be used to implement cycle-by-cycle current limiting of the motor by detecting a bus current value of the motor, which is not described in detail herein.

A method for controlling a current limiting period of the motor 13 in the power tool 10 will be described in detail with reference to fig. 8, and the method includes the following steps:

and S101, acquiring a motor phase current value.

S102, judging whether the phase current value of the motor exceeds a preset current threshold value, if so, executing a step S103; if not, go to step S104.

And S103, turning off the currently turned-on electronic switch.

S104, judging whether the current limiting period is finished or not, if so, executing a step S105; if not, step S101 is executed.

And S105, turning on the electronic switch controlled to be turned on by the current driving signal, and returning to the step S101.

In other embodiments, the grid voltage fluctuates when the grid load is increased or decreased to a greater extent, thereby affecting the user's hand feeling. Therefore, the invention provides that the current of the motor is effectively limited, and the voltage of the power grid is effectively compensated. In particular, as shown in connection with fig. 9, the control module 25 controls the period T of the PWM signal for driving the motor 13 ₁ Continuously varying within a first predetermined period while setting a current limiting period T of the motor 13 ₂ With period T of the PWM signal ₁ And the consistency is maintained. Wherein the first preset period range is optionally set to [0.5T ] ₀ ，2T ₀ ]，T ₀ Is the initial period of the PWM signal. In particular, the period T of the PWM signal is such that when the grid voltage is lower than or equal to the back emf of the present motor 13 ₁ Keeping the same; conversely, when the grid voltage is higher than the present back emf of the motor 13, the period T of the PWM signal ₁ Continuously varying within a first preset range. Specifically, as shown in conjunction with fig. 9 and 10, the period T of the drive signal ₁ The continuous variation set within the preset period range can be obtained by the following formula:

wherein f is ₀ Is the initial period T of the PWM signal ₀ Corresponding initial frequency, f ₁ Is equal to the period T of the PWM signal ₁ The corresponding frequency, θ, is the phase of the current grid voltage.

A method for controlling the cycle-by-cycle current limiting of the motor 13 in the electric tool 10 will be described in detail with reference to fig. 11, and the method includes the following steps:

s201, acquiring a phase current value of the motor.

S202, judging whether the phase current value of the motor exceeds a preset current threshold value, if so, executing a step S203; if not, go to step S204.

And S203, turning off the currently turned-on electronic switch.

S204, judging whether the current limiting period is finished, if so, executing a step S205; if not, go to step S206.

And S205, turning on the electronic switch controlled to be turned on by the current driving signal.

And S206, acquiring the grid voltage and the motor back electromotive force.

And S207, judging whether the back electromotive force of the current motor exceeds the voltage of the power grid, if so, executing a step S208, and if not, executing a step S201.

S208, the period T1 of the drive signal is reset.

S209 resets the current limit period T2, and returns to step S201.

In the above embodiment, the present invention discloses a cycle-by-cycle current-limiting control method for an electric tool, wherein a current-limiting cycle is always consistent with a cycle of a PWM signal, when a detected phase current of a motor is greater than a preset current threshold, an electronic switch is turned off, when a current cycle of the PWM signal is finished, the electronic switch is turned on again, and simultaneously, a real-time detection of the phase current of the motor is continued. On the other hand, the period of the PWM signal is continuously changed in a first preset period range along with the fluctuation of the power grid voltage, so that the fluctuation of the power grid voltage can be effectively compensated, the use hand feeling of a user is improved, and the service life of an electric tool is prolonged.

In other embodiments, the control module 25 controls the period T of the PWM signal used to drive the motor 13 ₁ Randomly varying within a second predetermined period and setting a current limit period T of the motor 13 ₂ Always in agreement with the period T1 of the PWM signal. Referring to FIG. 12, specifically, the period T of the PWM signal ₁ Randomly varying within a second predetermined period range may be set to the initial period T of the PWM signal ₀ And the change of the normal distribution rule is met after white noise is superposed. Specifically, the initial period T of the PWM signal for driving the motor 13 ₀ Set to 100us, the period T of the PWM signal after white noise is superimposed ₁ In a second predetermined period range [98us,102us ]]And the change is internal random, and the change meets the rule of normal distribution. It should be noted here that the second preset range of the setting of the present invention can be set by those skilled in the art according to the actual application scenario of the electric tool。

Another method for controlling the cycle-by-cycle current limiting of the motor 13 in the power tool 10 will be described in detail with reference to fig. 13, and the method includes the following steps:

and S301, acquiring a phase current value of the motor.

S302, judging whether the phase current value of the motor exceeds a preset current threshold value, if so, executing a step S303; if not, go to step S304.

And S303, turning off the currently turned-on electronic switch.

S304, judging whether the current limiting period is finished, if so, executing the step S305; if not, step S301 is executed.

S305, the period T1 of the driving signal is reset.

S305, a current limit period T2 is set according to the reset period T1 of the driving signal.

S305, turning on the electronic switch controlled to be turned on by the current driving signal, and returning to the step S301.

In the above embodiment, the present invention discloses another control method for cycle-by-cycle current limiting of an electric tool, wherein a current limiting cycle is always consistent with a cycle of a PWM signal, when a detected phase current of a motor is greater than a preset current threshold, an electronic switch is turned off, and when a current cycle of the PWM signal is ended, the electronic switch is turned on again, and meanwhile, the phase current of the motor is continuously detected in real time. And on the other hand, the period of the PWM signal is set to randomly change within a second preset period range, and the random change meets the rule of normal distribution. The embodiment reduces the EMI of the driving circuit through the jitter frequency strategy by setting the period of the PWM signal to meet the random variation of the normal distribution rule within the preset range, and improves the reliability of the electric tool.

In other embodiments, control module 25 outputs an initial period of T ₀ Controls the drive circuit 24 for driving the operation of the motor 13. Meanwhile, the control module 25 also acquires the phase current value of the motor 13 in real time through the current detection module 27 at periodic time intervals, and compares the acquired real-time phase current value with a preset current range. Referring to fig. 14, in particular,the preset current range comprises a first preset current threshold I _ref1 And a second predetermined current threshold I _ref2 First predetermined current threshold I _ref1 Set to an upper limit value, a second predetermined current threshold value I _ref2 Set to the lower limit value. When the phase current value of the motor 13 acquired by the control module 25 is higher than the first preset current threshold I _ref1 When the electronic switch is turned off, the control module 25 immediately turns off the electronic switch which is currently in the on state; once the control module 25 determines that the phase current value of the motor 13 is lower than the second predetermined current threshold I _ref2 At this time, the control module 25 controls to turn on the electronic switch controlled to be turned on by the current driving signal. In a specific setting process, a first preset current threshold value I _ref1 And a second predetermined current threshold I _ref2 The difference value of the motor is inversely proportional to the inductance value of the motor and is directly proportional to the back electromotive force of the motor in the normal working process, and a person skilled in the art can reasonably design a preset current range according to the type selection of the motor and the actual application scene.

Another method for controlling the cycle-by-cycle current limiting of the motor 13 in the power tool 10 will be described in detail with reference to fig. 15, and the method includes the following steps:

s401, acquiring a phase current value of the motor.

S402, judging whether the phase current value of the motor is higher than a first preset current threshold value, if so, executing a step S403; if not, go to step S404.

And S403, turning off the currently turned-on electronic switch.

And S404, judging whether the motor phase current value is lower than a second preset current threshold value, if so, executing a step S405, and if not, executing a step S401.

And S405, turning on the electronic switch controlled to be turned on by the current driving signal. The process returns to step S401.

In the above embodiment, the invention discloses another control method for cycle-by-cycle current limiting of an electric tool, which includes obtaining a phase current of a motor through a current detection module, and turning off an electronic switch once the phase current is detected to exceed a first preset current threshold; and once the phase current value of the motor is lower than a second preset current threshold value, the electronic switch is started to recover the current flowing to the motor. According to the technical scheme in the embodiment, the use hand feeling of the electric tool is not influenced while the large current generated in the working process of the motor can be simply and effectively inhibited.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (9)

1. A power tool, comprising:

a housing;

the alternating current power supply input device is used for accessing a power supply required by the electric tool during working;

a motor disposed within the housing;

a drive circuit comprising a plurality of electronic switches;

the current detection module is used for acquiring a phase current value of the motor;

the control module is electrically connected with the drive circuit and outputs a drive signal with a given period to control the drive circuit to operate the motor; the current detection module acquires the phase current value of the motor in real time;

it is characterized in that the preparation method is characterized in that,

the control module is further configured to:

if the obtained phase current value is higher than a first preset current threshold value, the electronic switch in the conducting state is closed, and the electronic switch which is controlled to be conducted by the control module at present is opened until the obtained phase current value is lower than a second preset current threshold value.

2. The power tool of claim 1,

the first preset current threshold is greater than the second preset current threshold.

3. The power tool of claim 1,

further comprising:

the rectifier module is electrically connected with the alternating current power supply input device and converts alternating current into direct current for the electric tool to use;

the power supply circuit is electrically connected with the rectification module and is arranged to at least supply power to the control module;

and the capacitor circuit is electrically connected between the rectifying module and the driving circuit.

4. The power tool of claim 1,

the current detection module comprises a plurality of current detection resistors.

5. The power tool according to claim 1,

the motor is set as a brushless direct current motor.

6. The power tool according to claim 5,

the brushless DC motor is controlled by the driving signal.

7. The power tool of claim 1,

the capacitor circuit comprises at least one electrolytic capacitor.

8. A control method of a power tool, the power tool including a housing; the alternating current power supply input device is used for accessing a power supply required by the electric tool during working; a motor disposed within the housing; a drive circuit comprising a plurality of electronic switches; the current detection module is used for acquiring a phase current value of the motor; the control module is electrically connected with the driving circuit;

the control method comprises the following steps:

the control module outputs a drive signal with a given period to control the drive circuit to operate the motor; the current detection module is used for acquiring the phase current value of the motor in real time;

it is characterized in that the preparation method is characterized in that,

if the obtained phase current value is higher than a first preset current threshold value, the control module closes the electronic switch which is in a conducting state, and the electronic switch which is controlled to be conducted by the control module at present is opened until the obtained phase current value is lower than a second preset current threshold value.

9. The control method according to claim 8,

the first preset current threshold is greater than the second preset current threshold.

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