AC/DC chopper for power tool

• US 6,286,609 B1
• Filed: 03/16/2000
• Issued: 09/11/2001
• Est. Priority Date: 12/10/1999
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Carrier, David A., Seman, Andrew E. Jr., Woods, Samuel G., Yahnker, Christopher R.
• Primary Examiner(s): Smith, Scott A.
• Application Number:
  US09/526,682
• Time in Patent Office: 544 Days
• Field of Search: 173/217, 173/171, 173/117, 173/2, 173/1, 310/47, 310/50, 318/254, 318/439, 318/701, 318/492
• US Class Current: 173/1
• CPC Class Codes: B25F 5/008 Cooling means
• CPC Class Codes: B25F 5/02 Construction of casings, bodies or handles B25F5/006, B25F5/008 take precedence
• CPC Class Codes: H02H 7/0852 directly responsive to abnormal temperature by using a temperature sensor in a control circuit H02H7/0833
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: H02M 1/10 Arrangements incorporating converting means for enabling loads to be operated at will from different kinds of power supplies, e.g. from ac or dc
• CPC Class Codes: H02M 3/155 using semiconductor devices only
• CPC Class Codes: H02M 3/1555 for the generation of a regulated current to a load whose impedance is substantially inductive
• CPC Class Codes: H02P 7/288 using variable impedance
• CPC Class Codes: H02P 7/291 with on-off control between two set points, e.g. controlling by hysteresis

Abstract

A dual-mode system for inexpensively operating electrically powered double-insulated devices (12), such as hand-held power tools and appliances. The system includes a cordless battery power module (14) that supplies the power and current demands of the device (12) in a cordless mode or a chopper module (21) that supplies the necessary power and current demands in a physical envelope commensurate in size and interchangeable with that of the battery power module (14). The chopper module (21) is provided with a non-filtered high efficiency converter circuit that allows the chopper module (21) to generate the power and current required by the driven device (12). The inductance of the motor (11) for the driven device (12) is used to filter the output of the chopper module (21). Eliminating the output filter from the chopper module (16) significantly reduces the cost and size of the module (16). Additionally, the need for multiple battery packs and fast rechargers is minimized by the availability of a low-cost converter. The line power module (16) includes an EMI filter (15) for filtering AC or DC input power. The chopper module (21) chops the filtered voltage, providing a series of voltage pulses having a DC voltage level that is suitable for driving the motor (11).

Claims

1. A corded/cordless system for power tools comprising:

a low-voltage DC power tool operable in a preselected voltage range, said power tool having;

an exterior, an interior, a pre-defined interface for mechanically and electrically mating with a power module having a source of electric power, and a motor of a predetermined rating having a predetermined minimum inductance; and

a chopper module to convert input power from the source of electric power to an average DC motor voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said chopper module including a chopper circuit operable at a predetermined switching frequency to convert the input power to an output voltage comprising a series of voltage pulses that are averaged across the motor predetermined minimum inductance, thereby supplying the average DC motor voltage to the motor.

2. The corded/cordless system of claim 1 further comprising a cordless battery power module mechanically and electrically configured to mate with the power tool and to contain a battery assembly having a DC voltage at least equal to a lower limit of the preselected voltage range suitable for powering the low-voltage DC power tool, said battery power module to provide power to the DC power tool.

3. The corded/cordless system of claim 1 further comprising a corded AC power module mechanically and electrically configured to mate with the power tool, said AC power module coupled between a source of AC electric power and the power tool, such that input power from the source of AC electric power is provided to the chopper module.

4. The corded/cordless system of claim 3 further comprising:

a cordless battery power module for providing power to the DC power tool, mechanically and electrically configured to mate with the power tool and to include a battery assembly having a DC voltage at least equal to a lower limit of the preselected voltage range suitable for powering the low-voltage DC power tool;

wherein the power tool pre-defined interface further comprises a physical envelope configuration to accept either of said corded AC power module and said cordless battery power supply module.

5. The corded/cordless system of claim 4 wherein the chopper circuit changes the duty cycle of the voltage pulses to cause a change in the average DC motor voltage, thereby changing the operating speed.

6. The corded/cordless system of claim 1 wherein the series of voltage pulses have a duty cycle and the chopper module further comprises a chopper controller operable to control a chopper switch such that the duty cycle of the series of voltage pulses is controlled, thereby controlling the average DC motor voltage applied to the motor.

7. The corded/cordless system of claim 6 wherein the output voltage of the chopper module is not transformer-isolated from the source of electric power.

8. A corded/cordless system for power tools, comprising:

a low-voltage DC power tool operable in a preselected voltage range, said power tool including;

an exterior, an interior, and a pre-defined interface for mechanically and electrically mating with a power module;

a motor of a preselected rating having a predetermined minimum inductance and an operating speed; and

a tool module to control the operating speed of the motor; and

a corded chopper power module to convert line power from a source of electric power to a series of voltage pulses having an average DC voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said corded chopper power module mechanically and electrically configured to connect to the source of electric power and to mate with the low-voltage DC power tool, said corded chopper power module including a chopper circuit operable at a predetermined switching frequency, in response to said tool module, to convert the line power to said series of voltage pulses having a duty cycle, said voltage pulses being averaged across the motor predetermined minimum inductance, thereby applying the average DC voltage to the motor.

9. The corded/cordless system of claim 8 further comprising:

a cordless battery power module mechanically and electrically configured to mate with the power tool and to contain a battery assembly having a DC voltage at least equal to a lower limit of the preselected voltage range suitable for powering the low-voltage DC power tool, said battery power module to provide power to the DC power tool; and

wherein said tool module converts power from the cordless battery power module to a series of voltage pulses having an average DC motor voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said tool module including a chopper circuit operable at a predetermined switching frequency to convert the battery power module DC voltage to said series of voltage pulses having a duty cycle, said voltage pulses being averaged across the motor predetermined minimum inductance of said motor, thereby applying the average DC motor voltage to the motor;

wherein the power tool is configured to receive power from either the corded chopper power module or the battery power module.

10. The corded/cordless system of claim 8 wherein the chopper power module, in response to the tool module, controllably varies the duty cycle of the voltage pulses, thereby controlling the average DC motor voltage such that the operating speed of the motor is controlled.

11. The corded/cordless system of claim 10 wherein the tool module further comprises a first switch coupled between the chopper power module and the motor, said first switch having a conducting state and a non-conducting state.

12. The corded/cordless system of claim 11 wherein the first switch is continuously in the conducting state when the corded chopper power module is mated to the power tool.

13. The corded/cordless system of claim 11 wherein the chopper circuit includes a second switch for converting line power to the series of voltage pulses, said second switch having a conducting state and a non-conducting state, and wherein the first switch is switched to the conducting state a predetermined time before the second switch is switched to the conducting state.

14. The corded/cordless system of claim 11 wherein the tool module further comprises a conduction signal coupled to the chopper power module for providing a pulse width reference signal, wherein the chopper power module sets the pulse width of the series of voltage pulses to correspond with the conduction signal.

15. The corded/cordless system of claim 14 wherein the power tool further includes a sensor for providing a feedback signal corresponding to the motor operating speed.

16. The corded/cordless system of claim 15 wherein the sensor is selected from the group of:

a tachometer, a motor back EMF voltage monitor, motor current monitor, and a motor average voltage monitor, and a DSP of motor current commutation.

17. A corded/cordless system for power tools, comprising:

a low-voltage DC power tool operable in a preselected voltage range, said power tool including;

an exterior, an interior, a pre-defined interface for mechanically and electrically mating interchangeably with a power module;

a motor of a predetermined rating having a predetermined minimum inductance; and

a tool control to control the operating speed of the motor; and

a source power module to convert electric power from a source of electric power to a series of voltage pulses having an average DC motor voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said source power module mechanically and electrically configured to connect to the source of electric power and to mate with the low-voltage DC power tool, said source power module including a filterless chopper circuit operable at a predetermined switching frequency, in response to said tool control, to convert the electric power to the series of voltage pulses having a pulse width, said voltage pulses being averaged across the motor predetermined minimum inductance, thereby applying the average DC motor voltage to the motor.

18. The corded/cordless system of claim 17 wherein the source power module comprises a battery power module for supplying converted battery power to the corded/cordless system, said battery power module including a battery assembly for providing the electric power and a chopper circuit for converting the electric power to said series of voltage pulses, said battery assembly having a DC voltage at least equal to a lower limit of the preselected voltage range suitable for powering the power tool.

19. The corded/cordless system of claim 17 wherein the source module comprises a line module for supplying converted line power to the corded/cordless system, said line module including an electrical connector for supplying electric power from a line power source and a chopper circuit for converting the electric power to said series of voltage pulses.

20. The corded/cordless system of claim 17 wherein the source power module, responsive to the tool control, controllably varies the duty cycle of the voltage pulses over a predetermined operating range to control the average DC motor voltage, thereby setting the operating speed.

21. The corded/cordless system of claim 20 wherein the tool control further comprises a conduction signal coupled to the source power module for providing a pulse width reference signal, wherein the source power module sets the pulse width of the series of voltage pulses to correspond with the conduction signal.

22. The corded/cordless system of claim 21 wherein the power tool further includes a sensor for providing a feedback signal corresponding to the motor operating speed.

23. The corded/cordless system of claim 22 wherein the sensor is selected from the group of:

a tachometer, a motor back EMF voltage monitor, motor current monitor, motor average voltage monitor, and a DSP of motor current commutation.

24. The corded/cordless system of claim 17 wherein the source power module further comprises a power switch.

25. The corded/cordless system of claim 24 wherein the power switch is selected from the group of;

MOSFETs, IGBTs, MCT'"'"'s, and BJTs.

26. A method of supplying power to a DC power tool operable in a preselected voltage range, said power tool including exposed surfaces and a DC motor having a winding inductance, the method comprising the steps of:

determining the winding inductance of the motor;

providing electrical power from a source of power;

converting the electrical power to a series of voltage pulses having a duty cycle, an average voltage, and a predetermined operating frequency;

selecting the operating frequency of the voltage pulses to correspond with the winding inductance of the motor;

setting the duty cycle of the voltage pulses such that the average voltage is within the preselected range suitable for powering the DC motor;

coupling the series of voltage pulses to the DC motor, whereby the motor is powered from the source of electric power.

27. The method of claim 26 further comprising the step of insulating the exposed surfaces of the DC power tool to prevent the surfaces from becoming electrically energized, so that transformer-isolation of the source of power from the series of voltage pulses is not required.