Power tool and control method thereof

Abstract

The application discloses an electric tool and a control method thereof, which comprises a shell, an alternating current power input device, a motor and a driving circuit. The driving circuit comprises a plurality of electronic switch current detection modules and a control module. The phase current value of the motor is acquired in real time by the current detection module within a periodic time interval. When the acquired phase current value exceeds a preset current threshold value, the electronic switch in the on state is turned off within the remaining time of the current time interval, and the electronic switch currently controlled by the control module is turned on at the end of the current driving signal cycle. The cycle of the driving signal randomly changes within a second preset cycle range. The above technical scheme can provide a control method suitable for the current electric tool and the current limiting control method, so that the electric tool can effectively inhibit the large current and improve the user's feeling under the heavy load working condition.

Description

Technical Field

[0001] This invention relates to a power tool, and more specifically to a control method applicable to AC power tools. Background Technology

[0002] Under heavy-duty conditions, especially for high-voltage brushless tools, AC power tools are prone to overcurrent due to the large power supply capacity of the power grid. This not only damages electronic components but also significantly affects the feel of the power tool. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a current limiting control method suitable for AC power tools, which can effectively suppress large currents under heavy-load conditions without affecting the user experience of the power tool.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An electric tool includes: a housing; an AC power input device for connecting to a power source required for the tool to operate; a motor disposed within the housing; a drive circuit including multiple electronic switches; a current detection module for acquiring the phase current value of the motor; and a control module electrically connected to the drive circuit, wherein the control module outputs a drive signal to control the drive circuit to operate the motor. The control module is further configured to: acquire the phase current value of the motor in real time via the current detection module during periodic time intervals; when the acquired phase current value exceeds a preset current threshold, turn off the electronic switches currently in a conducting state for the remaining time of the current time interval; and turn on the electronic switches currently controlled by the control module at the end of the current drive signal cycle. The duration of each time interval in the periodic time interval is the same as the current cycle of the drive signal; the cycle of the drive signal randomly varies within a second preset cycle range.

[0006] Furthermore, the random changes within the second preset period range follow the law of normal distribution.

[0007] Furthermore, it also includes: a rectifier module, configured to be electrically connected to an AC power input device to convert AC power into DC power for use by the power tool; a power supply circuit, electrically connected to the rectifier module, configured to supply power to at least the control module; and a capacitor circuit, electrically connected between the rectifier module and the drive circuit.

[0008] Furthermore, the current detection module includes multiple current sensing resistors.

[0009] Furthermore, the motor is configured as a brushless DC motor.

[0010] Furthermore, the brushless DC motor is controlled by the drive signal.

[0011] Furthermore, the capacitor circuit includes at least one electrolytic capacitor.

[0012] A control method for an electric tool, the electric tool comprising: a housing; an AC power input device for connecting to a power source required for the electric tool to operate; a motor disposed within the housing; a drive circuit including multiple electronic switches; a current detection module for acquiring the phase current value of the motor; and a control module electrically connected to the drive circuit.

[0013] The control method includes: the control module outputting a drive signal to control the drive circuit to operate the motor, and limiting the current of the motor within a periodic time interval; the control module acquiring the phase current value of the motor in real time through the current detection module within the periodic time interval; if the phase current value exceeds the preset current threshold, turning off the electronic switch that is currently in the conducting state for the remaining time of the current time interval, and then turning on the electronic switch that the control module is currently controlling to conduct at the end of the current drive signal cycle; the duration of each time interval in the periodic time interval is the same as the period corresponding to the current drive signal; the period of the drive signal varies randomly within a second preset period range.

[0014] Furthermore, the random changes within the second preset period range follow the law of normal distribution.

[0015] This invention discloses an electric tool and its control method, which effectively limits the high current of the electric tool under heavy load conditions. By setting the period of the drive signal within a preset range to satisfy the random variation of the normal distribution law, the EMI characteristics of the drive circuit are reduced through a frequency dithering strategy, which greatly optimizes the user experience of the electric tool and improves its reliability and lifespan. Attached Figure Description

[0016] Figure 1 This is a perspective view of a power tool as one embodiment;

[0017] Figure 2 This is a circuit block diagram of a circuit system as one embodiment;

[0018] Figure 3 This is a circuit block diagram of a rectifier module as one embodiment;

[0019] Figure 4 This is a circuit block diagram of a current detection module as one embodiment;

[0020] Figure 5 This is a circuit block diagram of a current detection module as another embodiment;

[0021] Figure 6 This is a waveform diagram of the motor control signal as one embodiment;

[0022] Figure 7 This is a waveform diagram of a motor current limiting control method as one embodiment;

[0023] Figure 8 This is a flowchart of a motor current limiting control method as one embodiment;

[0024] Figure 9 This is a waveform diagram showing the continuous frequency variation of a PWM signal as one example;

[0025] Figure 10 This is a waveform diagram showing the continuous frequency variation of a PWM signal as one example;

[0026] Figure 11 This is a flowchart of a motor control method as one embodiment;

[0027] Figure 12 This is a waveform diagram of the PWM signal and current limiting period as another embodiment;

[0028] Figure 13 This is a flowchart of a motor control method as another embodiment;

[0029] Figure 14 This is a waveform diagram of the PWM signal and current limiting period as another embodiment;

[0030] Figure 15 This is a flowchart of a motor control method as another embodiment. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0032] The power tools of this invention can be handheld power tools, garden tools, or garden vehicles such as vehicle-mounted lawnmowers, and are not limited thereto. The power tools of this invention include, but are not limited to, AC power tools such as sanders, drills, impact screwdrivers, tapping machines, and fastener screwdrivers, as long as these power tools adopt the substantive content of the technical solutions disclosed below, they fall within the protection scope of this invention. It should also be noted that, for ease of description, the accompanying drawings only show the parts relevant to this invention, not the entire structure.

[0033] refer to Figure 1As shown, an exemplary power tool 10 is illustrated, which is an angle grinder. The power tool 10 mainly includes: a housing 11, a motor 13, a functional component 14, an AC power input device 15, and a circuit system 12 located within the housing 11.

[0034] Motor 13 includes stator windings and a rotor. In some embodiments, motor 13 is a three-phase brushless motor, including a rotor with permanent magnets and electronically commutated three-phase stator windings U, V, and W. In some embodiments, the three-phase stator windings U, V, and W are star-connected. In other embodiments, the three-phase stator windings U, V, and W are delta-connected. However, it must be understood that other types of brushless motors are also within the scope of this disclosure. Brushless motors may include fewer or more than three phases.

[0035] Functional component 14 is used to perform the functions of power tool 10. Functional component 14 is driven by motor 13. The functional component varies for different power tools. For an angle grinder, functional component 14 is an angle grinding disc, used to perform grinding or cutting functions.

[0036] The AC power input device 15 is used to connect to the power supply required for the operation of the power tool 10. As one specific embodiment, the power supply in this embodiment may optionally be set to an AC power supply. Specifically, the AC power input device 15 includes an AC plug for connecting to 120V or 220V AC mains power.

[0037] Reference Figure 2 The circuit system 12 of one embodiment of the power tool 10 shown mainly includes a rectifier module 21, a capacitor circuit 22, a power supply circuit 23, a drive circuit 24, a control module 25, a speed detection module 26, and a current detection module 27.

[0038] The rectifier module 21 constitutes the 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, to convert the AC power input from the AC power input device 15 into pulsating DC power output. The rectifier module 21 is electrically connected to the AC power input device 15. As one specific embodiment, see... Figure 3 As shown, the rectifier module 21 includes a rectifier bridge composed of four diodes D1, D2, D3, and D4, which uses the unidirectional conductivity and voltage drop of the diodes to convert AC power into pulsating DC power output in the same direction.

[0039] The capacitor circuit 22 is connected in parallel to the DC bus of the power tool 10, that is, in parallel between the positive and negative terminals of the DC unit in the circuit system 12. In one specific embodiment, the capacitor circuit 22 may optionally be connected in parallel between the rectifier module 21 and the drive circuit 24. Specifically, the capacitor circuit 22 includes an electrolytic capacitor C. The capacitor circuit 22 is electrically connected to the rectifier module 21, and the pulsating DC output from the rectifier module 21 is filtered by the electrolytic capacitor C and converted into smooth DC output to reduce harmonic interference in the pulsating DC. Preferably, the ratio of the capacitance of the electrolytic capacitor C to the rated power of the motor 13 is greater than 20μF / KW and less than 80μF / KW. This saves space and ensures that there are no physically large capacitor components in the hardware circuit.

[0040] The power supply circuit 23 is used to supply power to at least the control module 25. In one specific embodiment, the power supply circuit 23 is electrically connected to the rectifier module 21, converting the rectified electrical energy into a supply voltage output suitable for the control module 25. For example, to supply power to the control module 25, the power supply circuit 23 reduces the voltage from the AC power input device 15, after rectification by the rectifier module 21, to 15V to supply power to the control module 25.

[0041] The drive circuit 24 is electrically connected to the rectifier module 21 and is used to drive the motor 13. The input terminal of the drive circuit 24 receives voltage from the rectifier module 21 and, driven by the drive signal output by the control module 25, distributes the voltage to each phase winding of the stator of the motor 13 according to a certain logical relationship, so that the motor 13 starts and generates continuous torque. Specifically, the drive circuit 24 includes multiple electronic switches. In some embodiments, the electronic switches include field-effect transistors (FETs), and in other embodiments, the electronic switches include insulated-gate bipolar transistors (IGBTs), etc. In some embodiments, the drive circuit 24 is a three-phase bridge circuit. The drive circuit 24 includes three electronic switches Q1, Q3, and Q5 configured as high-side switches and three electronic switches Q2, Q4, and Q6 configured as low-side switches.

[0042] Three electronic switches, Q1, Q3, and Q5, serving as high-side switches, are respectively located between the power supply line of the rectifier module 21 and each phase coil of the motor 13. Three electronic switches, Q2, Q4, and Q6, serving as low-side switches, are respectively located between each phase coil of the motor 22 and the ground wire.

[0043] The gate terminals UH, UL, VH, VL, WH, and WL of the six electronic switches Q1-Q6 are electrically connected to the control module 25, and the drain or source of each electronic switch is connected to the stator winding of the motor 13. The electronic switches Q1-Q6 change their on or off states at a certain frequency according to the drive signal output by the control module 25, thereby changing the power state applied to the motor 13 winding by the rectifier circuit 21.

[0044] The drive circuit 24 is used to drive the motor 13 to rotate by switching the energizing state of each phase winding and controlling the energizing current of each phase winding. The conduction sequence and timing of each phase winding depend on the rotor position. To make the motor 13 rotate, the drive circuit 24 has multiple drive states. In one drive state, the stator winding of the motor 13 generates a magnetic field. The control module 25 outputs control signals based on different rotor positions to control the drive circuit 24 to switch drive states so that the magnetic field generated by the stator winding rotates to drive the rotor to rotate, thereby driving the motor 13.

[0045] The speed detection module 26 is used to acquire at least one of the measured speed of the motor 13 and the position of the rotor. In some embodiments, the speed detection module 26 includes a sensor capable of directly detecting the speed and position of the motor 13, such as a Hall sensor. In other embodiments, the speed detection module 26 is configured to estimate the rotor position of the motor 13 based at least on the phase voltage and stator winding current values ​​of the motor 13.

[0046] The current detection module 27 is used to collect the current of the motor 13, which can be the bus current of the motor 13 or the phase current of each phase winding of the motor 13. In one specific embodiment, the current detection module 27 detects the phase current of each phase winding of the motor 13. The bus current of the motor 13 can be calculated from the detected three-phase current values. In some embodiments, the current detection module 27 includes a Hall current sensor to directly detect the phase current of each phase winding of the motor 13. As another specific embodiment, refer to... Figure 4 As shown, current-sensing resistors R1, R2, and R3 are connected in series between each phase winding of the drive circuit 24 and the motor 13. The current detection module 27 can calculate the phase current or bus current of each phase winding by detecting the voltage across the detection resistors. Specifically, the current detection module 27 can calculate the phase currents U, V, and W of the three-phase stator windings by detecting the voltage across each current-sensing resistor R1, R2, and R3. See another specific embodiment for further details. Figure 5 As shown, the current detection module 27 is used to detect the internal resistance of the electronic switch in the conducting state in the drive circuit 24. Based on the internal resistance of the electronic switch in the conducting state and the voltage value across its terminals, the current passing through the electronic switch is calculated. The current of the electronic switch is the phase current of the corresponding motor 13 winding. Specifically, the current detection module 27 detects the voltage across the three drive switches Q1, Q3, and Q5 of the high-side switch to calculate the corresponding phase currents U, V, and W of the three-phase stator windings. In this way, the power tool can detect the phase current of the corresponding motor 22 winding without adding hardware, saving costs.

[0047] The control module 25 is electrically connected to at least the power supply circuit 23, the drive circuit 24, and the current detection module 27 to control the operation of the drive circuit 24. In some embodiments, the control module 25 uses a dedicated control chip (e.g., MCU, Microcontroller Unit).

[0048] In some specific implementations, refer to Figure 6 and Figure 7 As shown, the control module 25 outputs a drive signal with a period of T1 and a frequency of f1, which is used to control the conduction state of multiple electronic switches Q1-Q6 to drive the motor 13. Preferably, the motor 13 is a three-phase brushless DC motor, and the drive signal can optionally be set as a PWM signal. Simultaneously, the control module 25 limits the current of the motor 13 within a periodic time interval T2. Those skilled in the art will understand that this periodic time interval can be understood as the current-limiting period of the motor; T2 is defined below as the current-limiting period of the motor 13.

[0049] As one specific embodiment, refer to Figure 7 As shown, the current limiting period T2 is set to be the same as the period T1 of the PWM signal. The control module 25 is configured to acquire the phase current value of the motor 13 in real time through the current detection module 27 within the current limiting period T2, and compare the phase current value with a preset current threshold. If the phase current value exceeds the preset current threshold, the electronic switch is turned off for the remaining time of the current limiting period T2, thereby disconnecting the current flowing to the motor 13. The electronic switch is then turned on at the end of the current PWM signal period T1 to restore the current flowing to the motor 13. Specifically, the preset current threshold can be set according to the motor selection and actual application scenario. This invention does not limit the method for setting the preset current. It should also be noted that the electronic switch turned off in the above technical solution is the electronic switch currently in the on state, and the electronic switch turned on is the electronic switch controlled by the current drive signal.

[0050] Under heavy-load conditions, motor 13 may experience overcurrent due to the sufficiently high grid voltage, which can damage components in the power tool and reduce its lifespan. (Refer to...) Figure 7 As shown, motor 13 experienced overcurrent under heavy load conditions, as indicated by point b in the figure. Using the aforementioned current-limiting technology, the phase current value I... phase Exceeding the preset current threshold I refWhen the current cycle of the PWM signal ends, as shown by point a in the figure, the control module 25 immediately turns off the electronic switch, preventing the current flowing through the motor 13 from increasing further. At the end of the current cycle of the PWM signal, as shown by point c in the figure, the control module 25 turns the electronic switch back on, thereby restoring the current flowing to the motor 13. It should be noted that the current detection module in this invention primarily detects the phase current of the motor 13 to achieve cycle-by-cycle current limiting. Those skilled in the art will understand that cycle-by-cycle current limiting can also be achieved by detecting the motor's bus current value, which will not be described in detail here.

[0051] The following will combine Figure 8 The following describes a control method for a current-limiting cycle of the motor 13 in the power tool 10, which includes the following steps:

[0052] S101, obtain the motor phase current value.

[0053] S102, determine whether the phase current value of the motor exceeds the preset current threshold. If yes, proceed to step S103; otherwise, proceed to step S104.

[0054] S103, turn off the currently active electronic switch.

[0055] S104. Determine whether the current rate limiting period has ended. If yes, proceed to step S105; otherwise, proceed to step S101.

[0056] S105, turn on the electronic switch controlled by the current drive signal, and return to step S101.

[0057] In some specific embodiments, the grid voltage fluctuates when the grid load increases or decreases significantly, thus affecting the user's experience. To address this, the present invention proposes to effectively compensate for the grid voltage while simultaneously limiting the motor current. Combined with... Figure 9 As shown, specifically, the control module 25 controls the period T1 of the PWM signal used to drive the motor 13 to continuously change within a first preset period range, while setting the current limiting period T2 of the motor 13 to be the same as the period T1 of the PWM signal. The first preset period range can optionally be set to [0.5T0, 2T0], where T0 is the initial period of the PWM signal. Specifically, when the grid voltage is lower than or equal to the current back EMF of the motor 13, the period T1 of the PWM signal remains unchanged; conversely, when the grid voltage is higher than the current back EMF of the motor 13, the period T1 of the PWM signal continuously changes within the first preset range. Specifically, combined with... Figure 9 and Figure 10 As shown, the period T1 of the driving signal, which is set to a continuous variation within a preset period range, can be obtained by the following formula:

[0058]

[0059] Where f0 is the initial frequency corresponding to the initial period T0 of the PWM signal, f1 is the frequency corresponding to the period T1 of the PWM signal, and θ is the phase of the current grid voltage.

[0060] The following will combine Figure 11 A cycle-by-cycle current limiting control method for the motor 13 in the power tool 10 is described in detail. The method includes the following steps:

[0061] S201, obtain the phase current value of the motor.

[0062] S202, determine whether the phase current value of the motor exceeds the preset current threshold. If yes, proceed to step S203; otherwise, proceed to step S204.

[0063] S203, turn off the currently active electronic switch.

[0064] S204. Determine whether the current rate limiting period has ended. If yes, proceed to step S205; otherwise, proceed to step S206.

[0065] S205, turn on the electronic switch controlled by the current drive signal.

[0066] S206, obtain the grid voltage and motor back EMF.

[0067] S207. Determine whether the current back electromotive force of the motor exceeds the grid voltage. If yes, proceed to step S208; otherwise, proceed to step S201.

[0068] S208, reset the period T1 of the drive signal.

[0069] S209, reset the current limiting period T2, and return to step S201.

[0070] In the above embodiments, the present invention discloses a cycle-by-cycle current limiting control method for power tools. The current limiting cycle is always the same as the cycle of the PWM signal. When the detected motor phase current is greater than a preset current threshold, the electronic switch is turned off. At the end of the current cycle of the PWM signal, the electronic switch is turned back on, while the phase current of the motor continues to be monitored in real time. On the other hand, the cycle of the PWM signal is set to continuously change within a first preset cycle range according to the fluctuation of the grid voltage, which can effectively compensate for the fluctuation of the grid voltage, improve the user experience and extend the service life of the power tool.

[0071] In other specific embodiments, the control module 25 controls the period T1 of the PWM signal used to drive the motor 13 to vary randomly within a second preset period range, and sets the current limiting period T2 of the motor 13 to always be the same as the period T1 of the PWM signal. See also Figure 12 As shown, specifically, the period T1 of the PWM signal varies randomly within a second preset period range, which can be set to follow a normal distribution after adding white noise to the initial period T0 of the PWM signal. Specifically, the initial period T0 of the PWM signal used to drive the motor 13 is set to 100us, and the period T1 of the PWM signal after adding white noise varies randomly within the second preset period range [98us, 102us], and the variation follows a normal distribution. It should be noted that the second preset range set by those skilled in the art can be set by themselves according to the actual application scenario of the power tool.

[0072] The following will combine Figure 13 This section describes another control method for cycle-by-cycle current limiting of the motor 13 in the power tool 10, which includes the following steps:

[0073] S301, obtain the phase current value of the motor.

[0074] S302, determine whether the phase current value of the motor exceeds the preset current threshold. If yes, proceed to step S303; otherwise, proceed to step S304.

[0075] S303, Turn off the currently active electronic switch.

[0076] S304. Determine whether the current rate limiting period has ended. If yes, proceed to step S305; otherwise, proceed to step S301.

[0077] S305, reset the period T1 of the drive signal.

[0078] S305 sets the current limiting period T2 based on the period T1 of the reset drive signal.

[0079] S305, turn on the electronic switch controlled by the current drive signal, and return to step S301.

[0080] In the above embodiments, this invention discloses another control method for cycle-by-cycle current limiting of power tools. The current limiting cycle is always the same as the cycle of the PWM signal. When the detected motor phase current is greater than a preset current threshold, the electronic switch is turned off. At the end of the current cycle of the PWM signal, the electronic switch is turned back on, while the phase current of the motor continues to be monitored in real time. On the other hand, the cycle of the PWM signal is set to vary randomly within a second preset cycle range, and the random variation follows a normal distribution. This embodiment reduces the EMI of the drive circuit and improves the reliability of the power tool by setting the cycle of the PWM signal to a random variation within a preset range that follows a normal distribution, and by using a frequency dithering strategy.

[0081] In other specific embodiments, the control module 25 outputs a PWM signal with an initial period of T0, controlling the drive circuit 24 to drive the motor 13. Simultaneously, 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. See also... Figure 14 As shown, specifically, the preset current range includes a first preset current threshold I. ref1 Second preset current threshold I ref2 The first preset current threshold I ref1 Set to the upper limit value, second preset current threshold I ref2 Set as the lower limit. When the phase current value of motor 13 obtained by control module 25 is higher than the first preset current threshold I. ref1 When the current condition is met, the control module 25 immediately turns off the electronic switch that is currently in the conducting state; once the phase current value of the motor 13 obtained by the control module 25 is lower than the second preset current threshold I... ref2 At that time, the control module 25 controls the electronic switch that is turned on by the current drive signal. In the specific setting process, the first preset current threshold I... ref1 With the second preset current threshold I ref2 The difference is inversely proportional to the motor inductance and directly proportional to the back electromotive force during normal operation of the motor. Those skilled in the art can reasonably design the preset current range according to the motor selection and actual application scenarios.

[0082] The following will combine Figure 15 This section describes another control method for cycle-by-cycle current limiting of the motor 13 in the power tool 10, which includes the following steps:

[0083] S401, obtain the phase current value of the motor.

[0084] S402, determine whether the phase current value of the motor is higher than the first preset current threshold. If yes, proceed to step S403; otherwise, proceed to step S404.

[0085] S403, turn off the currently active electronic switch.

[0086] S404, determine whether the motor phase current value is lower than the second preset current threshold. If yes, proceed to step S405; otherwise, proceed to step S401.

[0087] S405, turn on the electronic switch controlled by the current drive signal. Return to step S401.

[0088] In the above embodiments, this invention discloses another control method for cycle-by-cycle current limiting of power tools. The method involves acquiring the phase current of the motor through a current detection module. Once the phase current exceeds a first preset current threshold, the electronic switch is turned off; once the phase current value of the motor is lower than a second preset current threshold, the electronic switch is turned on, restoring the current flowing to the motor. The technical solution in the above embodiments can simply and effectively suppress large currents during motor operation without affecting the feel of the power tool.

[0089] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. An electric tool, comprising: case; An AC power input device is provided for connecting the power source required when the power tool is working. The motor is housed within the housing; The driving circuit includes multiple electronic switches; A current detection module is used to obtain the phase current value of the motor; A control module is electrically connected to the drive circuit, and the control module outputs drive signals to control the drive circuit to run the motor; The control module is also configured to: The phase current value of the motor is acquired in real time through the current detection module at periodic time intervals; When the obtained phase current value exceeds the preset current threshold, the electronic switch that is in the conducting state is turned off during the remaining time of the current time interval, and the electronic switch that is currently controlled to be turned on is turned on by the control module at the end of the current driving signal cycle. Its features are, The duration of each time interval in the periodic time interval is the same as the period corresponding to the current driving signal; When the grid voltage is lower than or equal to the back electromotive force of the motor, the period of the drive signal remains unchanged; When the grid voltage is higher than the back electromotive force of the motor, the period of the drive signal changes randomly within a second preset period range.

2. The power tool according to claim 1, characterized in that, The random changes within the second preset period range follow the law of normal distribution.

3. The power tool according to claim 1, characterized in that, Also includes: The rectifier module is configured to be electrically connected to the AC power input device to convert AC power into DC power for use by the power tool; The power supply circuit is electrically connected to the rectifier module and is configured to supply power to at least the control module; A capacitor circuit is electrically connected between the rectifier module and the drive circuit.

4. The power tool according to claim 1, characterized in that, The current detection module includes multiple current sensing resistors.

5. The power tool according to claim 1, characterized in that, The motor is a brushless DC motor.

6. The power tool according to claim 5, characterized in that, The brushless DC motor is controlled by the drive signal.

7. The power tool according to claim 3, characterized in that, The capacitor circuit includes at least one electrolytic capacitor.

8. A control method for an electric tool, the electric tool comprising a housing; an AC power input device for connecting to a power source required for the electric tool to operate; A motor is disposed within the housing; a drive circuit includes multiple electronic switches; A current detection module is used to obtain the phase current value of the motor; The control module is electrically connected to the drive circuit; The control method includes: The control module outputs a drive signal to control the drive circuit to run the motor, and limits the current of the motor at periodic time intervals; The control module acquires the phase current value of the motor in real time through the current detection module during the periodic time interval; if the phase current value exceeds the preset current threshold, the electronic switch that is in the conducting state is turned off during the remaining time of the current time interval, and then the electronic switch that the control module is currently controlling to conduct is turned on at the end of the current drive signal cycle. Its features are, The duration of each time interval in the periodic time interval is the same as the period corresponding to the current driving signal; When the grid voltage is lower than or equal to the back EMF of the motor, the period of the drive signal remains unchanged; when the grid voltage is higher than the back EMF of the motor, the period of the drive signal changes randomly within a second preset period range.

9. The control method according to claim 8, characterized in that, The random changes within the second preset period range follow the law of normal distribution.

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