Electric Power Tool PWM Controller for Battery Overdischarge
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Solution Overview
Problem
Existing electric power tools with rechargeable batteries face overdischarging issues due to large inrush currents when the motor is started, which can shorten the battery life, and previous soft start control methods do not adequately address this problem.
Innovation Solution
An electric power tool with a controller and power switching unit that uses pulse width modulation (PWM) control signals to manage the duty ratio based on detected parameters such as battery temperature, voltage, and current to regulate the power supply to the motor, preventing excessive voltage drops and overdischarging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft start control is implemented to reduce inrush current, then motor starting is improved, but battery overdischarging may still occur due to excessive voltage drop
Solution Approach 1:
The control unit continuously monitors battery voltage and dynamically adjusts the PWM duty ratio based on the detected voltage level. When battery voltage drops below a threshold during motor startup, the control unit reduces the duty ratio to prevent overdischarging, while still allowing the motor to accelerate smoothly. This feedback mechanism resolves the contradiction by adapting the soft start control to battery conditions.
Solution Approach 2:
The system dynamically changes the PWM duty ratio during motor startup based on real-time battery voltage detection. Instead of using a fixed duty ratio, the control unit adjusts it adaptively: initially allowing higher duty ratios for smooth motor acceleration, then reducing them when battery voltage drops. This dynamic adjustment resolves the contradiction between maintaining reliable motor starting and preventing battery overdischarging.
2Speed
If high duty ratio is used during motor startup, then motor acceleration is improved, but battery voltage drops excessively causing overdischarging
Solution Approach 1:
The control unit applies partial action by using a duty ratio less than 100% during motor startup. Instead of applying full power immediately, it uses a controlled, reduced duty ratio that provides sufficient motor acceleration while limiting the current draw to prevent excessive battery voltage drop and overdischarging.
Solution Approach 2:
The system uses periodic PWM control to deliver power to the motor in controlled pulses rather than continuous full power. This periodic action with adjusted duty ratio allows the motor to accelerate while the battery experiences reduced stress, preventing excessive voltage drop and energy depletion.
3Loss of energy
If conventional soft start control is used, then inrush current is reduced, but battery life is shortened due to overdischarging
Solution Approach 1:
The control unit incorporates battery voltage feedback to monitor the state of charge during motor operation. When voltage drops indicate approaching overdischarge conditions, the system adjusts the duty ratio to prevent further voltage decline. This feedback mechanism extends battery life by preventing overdischarging events that would otherwise occur with conventional soft start control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces inrush currents and prevents overdischarging, extending the battery life by maintaining stable voltage levels and optimizing power delivery to the motor, thereby improving tool efficiency and reducing interruptions.
Implementation Method 1
The controller is configured to control the power switching unit using a pulse width modulation (PWM) control signal when the electric power tool is activated. The controller is configured to change a duty ratio of the PWM control signal in accordance with the detection signal of the detector.
Implementation Method 2
a motor; a motor driver connected to the motor
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An electric power tool (1) includes a rechargeable battery (21), a motor (11), a detector (15, 16, 17, 23, 24, 25) that detects a parameter that affects a voltage drop of the rechargeable battery (21) and outputs a detection signal corresponding to the detected parameter, a controller (13) that receives the detection signal and generates a control signal in accordance with the detection signal, and a power switching unit (31) operated in accordance with the control signal from the controller (13) to switch between a situation in which the rechargeable battery (21) supplies electric power to the motor (11) and a situation in which the rechargeable battery (21) stops supplying electric power to the motor (11). The controller (13) controls the power switching unit (31) using a pulse width modulation (PWM) control signal when the electric power tool is activated. The controller (13) changes a duty ratio of the PWM control signal in accordance with the detection signal of the detector (15, 16, 17, 23, 24, 25).