Motor braking using selectively connectable resistance
Apparatus and method for motor braking using selectively connectable resistance. The method includes controlling, using a motor controller of the power tool, a power switching network to drive a motor of the power tool in response to actuation of a user input and determining, using the motor controller, a variable tool characteristic. The method further includes determining, using the motor controller, that the user input is de-actuated. The method also includes controlling, using the motor controller, the power switching network to brake the motor when the variable tool characteristic satisfies the tool characteristic threshold and controlling, using the motor controller, a braking circuit to brake the motor when the variable tool characteristic does not satisfy the tool characteristic threshold. The braking circuit includes one or more resistive loads and is selectively coupled to the motor terminals of the motor.
1. A power tool comprising:
a battery pack;
a three-phase motor including three motor terminals;
a power switching network coupled between the battery pack and the motor, wherein the power switching network includes a first power switching element and a second power switching element;
a user input configured to be actuated to drive the motor;
a braking circuit including a resistor and a braking switching element connected to each motor terminal, wherein each braking switching element is configured to selectively connect a respective resistor to a respective motor terminal, and wherein the braking circuit is configured to selectively couple each motor terminal to one selected from the group consisting of ground and a terminal of the battery pack; and
a motor controller connected to the power switching network and the braking circuit and configured to:
control the power switching network to drive the motor in response to actuation of the user input,
determine a variable tool characteristic,
determine that the user input is de-actuated,
determine whether the variable tool characteristic satisfies a tool characteristic threshold in response to the user input being de-actuated,
in response to the variable tool characteristic satisfying the tool characteristic threshold:
control the power switching network to brake the motor,
enable the first power switching element to induce a freewheeling current to flow through the first power switching element, wherein the freewheeling current flows through a diode of the second power switching element, and
disable the first power switching element to provide the freewheeling current to the battery pack, and
control the braking circuit to brake the motor when the variable tool characteristic does not satisfy the tool characteristic threshold.
2. The power tool of claim 1 , wherein the braking switching element includes a Field Effect Transistor (FET) configured to be controlled by the motor controller.
3. The power tool of claim 1 , wherein the motor controller is configured to:
perform a pulse width modulation control of the braking switching element to brake the motor using the braking circuit.
4. The power tool of claim 1 , wherein, to control the braking circuit to brake the motor, the motor controller is configured to:
control each braking switching element to couple the respective resistor to the respective motor terminal.
5. The power tool of claim 4 , wherein, when the braking circuit is coupled to the motor terminals, the braking circuit forms a closed circuit with the motor terminals and the motor current flows through the resistors.
6. The power tool of claim 1 , further comprising:
a straight connect power interface such that a connection between the battery pack and the power switching network is provided without an on/off switch controlled by the user input.
7. The power tool of claim 1 , wherein the motor controller is further configured to:
determine that the variable tool characteristic has decreased below the regenerative braking threshold when braking the motor using the braking circuit; and
switch from controlling the braking circuit to brake the motor to controlling the power switching network to brake the motor in response to the variable tool characteristic having decreased below the regenerative braking threshold.
8. The power tool of claim 1 , wherein a resistance value of the one or more resistive loads is selected based on a prescribed stopping time.
9. A method for braking a three-phase motor of a power tool, the method comprising:
controlling, using a motor controller of the power tool, a power switching network to drive the motor of the power tool in response to actuation of a user input, wherein the power switching network includes a first power switching element and a second power switching element;
determining, using the motor controller, a variable tool characteristic;
determining, using the motor controller, that the user input is de-actuated;
determining, using the motor controller, whether the variable tool characteristic satisfies a tool characteristic threshold in response to the user input being de-actuated;
in response to the variable tool characteristic satisfying the tool characteristic threshold:
controlling, using the motor controller, the power switching network to brake the motor,
enabling, using the motor controller, the first power switching element to induce a freewheeling current to flow through the first power switching element, wherein the freewheeling current flows through a diode of the second switching element, and
disabling, using the motor controller, the first power switching element to provide the freewheeling current to a battery pack connected to the power tool; and
controlling, using the motor controller, a braking circuit to brake the motor in response to the variable tool characteristic not satisfying the tool characteristic threshold, the braking circuit including a respective resistor and a respective braking switching element connected to a respective terminal of the motor, and wherein each respective braking switching element is configured to selectively couple the respective resistor to the respective terminal of the motor.
10. The method of claim 9 , wherein selectively coupling the respective resistor to the respective terminal of the motor further comprises:
controlling, using the motor controller, each respective braking switching element to couple the respective resistor to the respective terminal of the motor.
11. The method of claim 10 , wherein, when the braking circuit is coupled to the motor terminals, the braking circuit forms a closed circuit with the motor terminals and the motor current flows through the resistors.
12. The method of claim 9 , further comprising:
performing, using the motor controller, a pulse width modulation control of the braking switching elements to brake the motor using the braking circuit.
13. The method of claim 9 , further comprising:
determining, using the motor controller, that the variable tool characteristic has decreased below the regenerative braking threshold when braking the motor using the braking circuit; and
switching from controlling the braking circuit to brake the motor to controlling the power switching network to brake the motor in response to determining that the variable tool characteristic has decreased below the regenerative braking threshold.
14. A method for braking a motor of a power tool, the method comprising:
controlling, in response to actuation of a user input, a power switching network to drive the motor, wherein the power switching network is coupled between a power source and the motor;
determining a variable tool characteristic;
determining that the user input is de-actuated;
determining, in response to the user input being de-actuated, whether the variable tool characteristic satisfies a tool characteristic threshold;
controlling, in response to the variable tool characteristic satisfying the tool characteristic threshold, the power switching network to brake the motor; and
controlling, in response to the variable tool characteristic not satisfying the tool characteristic threshold, a braking circuit to brake the motor, the braking circuit including one or more resistive loads, the braking circuit configured to be selectively coupled to motor terminals of the motor, the braking circuit configured to selectively couple the motor terminals to one selected from the group consisting of ground and a terminal of the power source,
wherein the variable tool characteristic is a system impedance, and
wherein the variable tool characteristic satisfies the tool characteristic threshold when the system impedance is above a system impedance threshold.
15. The method of claim 14 , wherein the braking circuit includes one or more braking switches, the method further comprising:
controlling the braking circuit by controlling the one or more braking switches to selectively couple one or more braking resistors to the motor terminals.
16. The method of claim 15 , further comprising:
controlling the braking circuit by performing a pulse width modulation control of the one or more braking switches to brake the motor.
17. The method of claim 14 , wherein controlling the power switching network to brake the motor includes performing a regenerative braking using the power switching network to redirect braking current to the power source.
18. The method of claim 17 , wherein performing regenerative braking includes selectively enabling a low-side Field Effect Transistor (FET) of the power switching network to enable a freewheeling current.
19. The method of claim 14 , wherein the system impedance includes a power source impedance, the method further comprising:
measuring the power source impedance using a voltage sensor and a current sensor.
20. The method of claim 14 , wherein the system impedance includes a power source impedance, the method further comprising:
retrieving the power source impedance by communicating with the power source.