Power tool and control method thereof
A power tool includes a housing, an electric motor, a driver circuit, a control module, and a current detection module. The control module is configured to: acquire a phase current value of the electric motor in real time within periodic time intervals; and turn off an on-state electronic switch within remaining time of a present time interval when the acquired phase current value exceeds a preset current threshold, and turn on an electronic switch which is controlled by the control module at present to be on when a present period of the drive signal ends, where the duration of each time interval among the periodic time intervals is the same as a period corresponding to the drive signal at present, and a period of the drive signal varies randomly within a second preset period range.
1 . A power tool, comprising:
a housing;
an electric motor disposed in the housing;
a current detection module configured to acquire a current value of the electric motor in real time;
a driver circuit, comprising a plurality of electronic switches, selectively providing electrical signals to drive the electric motor; and
a control module electrically connected to the driver circuit and configured to acquire a grid voltage of the electric motor, use the grid voltage to determine a time period for each of a series of drive signal time intervals, turn off an on-state electronic switch among the plurality of electronic switches within a remaining time period of each one of the series of drive signal time intervals when the current value acquired by the current detection module exceeds a preset current threshold, and turn on an electronic switch among the plurality of electronic switches which is controlled by the control module at present to be on when the time period of each one of the series of drive signal time intervals ends;
wherein the determined time period for each of the series of drive signal time intervals is varied within a present period range when the grid voltage is higher than a present counter-electromotive force of the electric motor; the determined time period for each of the series of drive signal time intervals keeps constant when the grid voltage is lower than or equal to the present counter-electromotive force of the electric motor.
2 . The power tool according to claim 1 , wherein variations of the time periods associated with the series of drive signal time intervals follows a law of a normal distribution.
3 . The power tool according to claim 1 , wherein the preset current threshold has a value that follows a preset waveform.
4 . The power tool according to claim 3 , wherein a time period of the preset waveform is the same as the time period of each of the series of drive signal time intervals.
5 . The power tool according to claim 4 , wherein the preset waveform is set as a triangular waveform or a waveform comprising a curve.
6 . The power tool according to claim 5 , wherein the preset current threshold corresponding to an end of a first one of the series of drive signal time intervals is less than the preset current threshold corresponding to a beginning of the first one of the series of drive signal time i intervals.
7 . The power tool according to claim 1 , further comprising a power supply input device and a rectifier module, wherein the power supply input device is configured to access a power supply required by the power tool when working, and the rectifier module is configured to be electrically connected to the power supply input device and convert electrical energy of the power supply input device into a direct current for the power tool to use.
8 . The power tool according to claim 7 , further comprising a power supply circuit and a capacitor circuit, wherein the power supply circuit is electrically connected to the rectifier module to supply power to at least the control module, and the capacitor circuit is electrically connected between the rectifier module and the driver circuit.
9 . The power tool according to claim 8 , wherein the capacitor circuit comprises at least one electrolytic capacitor.
10 . The power tool according to claim 9 , wherein a ratio of a capacitance value of the electrolytic capacitor to rated power of the electric motor is higher than 20 μF/kW and lower than 80 μF/kW.
11 . The power tool according to claim 10 , wherein the rectifier module comprises a rectifier bridge constituted by four diodes D 1 , D 2 , D 3 , and D 4 .
12 . The power tool according to claim 11 , wherein the current detection module is electrically connected between the control module and the electric motor and comprises a plurality of current detection resistors.
13 . The power tool according to claim 1 , wherein the electric motor is configured to be a brushless direct current motor.
14 . The power tool according to claim 1 , further comprising a rotational speed detection module configured to acquire a rotational speed of the electric motor and a position of a rotor of the electric motor.
15 . A control method of a power tool comprising a housing, an electric motor disposed in the housing, a driver circuit comprising a plurality of electronic switches, a current detection module configured to acquire a current value of the electric motor, and a control module electrically connected to the driver circuit, the control method comprising:
outputting, by the control module, a drive signal to control the driver circuit to cause the electric motor to operate;
limiting, by the control module, a current of the electric motor within periodic time intervals;
acquiring, by the control module, a current value of the electric motor in real time through the current detection module within the periodic time intervals;
turning off, by the control module, an on-state electronic switch among the plurality of electronic switches within a remaining time of a present time interval when the current value exceeds a preset current threshold; and
turning on, by the control module, an electronic switch among the plurality of electronic switches which is controlled by the control module at present to be on when a present period of the drive signal ends;
wherein a duration of each time interval among the periodic time intervals is the same as a period corresponding to the drive signal at present and a period of the drive signal is determined by the controller by comparing a grid voltage of the electric motor to a present counter-electromotive force of the electric motor.