Power Tool Motor Control for Bus Voltage Spike Protection
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Solution Overview
Problem
Existing power tools using traditional square-wave control driver circuits face issues with motor burnout due to voltage spikes caused by capacitors, which affect the bus voltage amplitude and current levels.
Innovation Solution
Incorporating a first capacitor in parallel with the driver circuit, coupled with a voltage collection device and a controller that adjusts the duty cycle of control signals based on bus voltage amplitude to maintain normal voltage and current levels, and includes modules for current and rotational speed detection to optimize motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a capacitor is provided in the circuit to improve the power factor, then the power factor is improved, but the bus voltage has a spike resulting in a risk of burning out the electric motor
Solution Approach 1:
The controller includes a voltage detection unit that detects the bus voltage in real-time and feeds this information back to the control unit. The control unit adjusts the duty cycle of the square wave signal based on the detected voltage to maintain the bus voltage within a safe range, preventing motor burnout while maintaining power factor improvement
Solution Approach 2:
The duty cycle of the square wave control signal is made dynamically adjustable based on the detected bus voltage. When voltage spikes are detected, the duty cycle is reduced to lower the voltage; when voltage is normal, the duty cycle can be increased to maintain good power factor. This dynamic adjustment resolves the contradiction between power factor improvement and motor protection
2Speed
If the duty cycle of the square wave signal is adjusted to control motor speed and torque, then speed and torque control is achieved, but voltage spikes occur that risk burning out the motor
Solution Approach 1:
The voltage detection unit continuously monitors the bus voltage and provides feedback to the control unit. Based on this feedback, the control unit dynamically adjusts the duty cycle to ensure that speed and torque control objectives are met while preventing voltage spikes that could burn out the motor
Solution Approach 2:
The control unit proactively reduces the duty cycle when voltage spikes are detected or anticipated, preventing the harmful effect of motor burnout before it occurs. This preliminary protective action allows the system to maintain both speed control capability and motor safety
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
Prevents motor burnout by stabilizing voltage and current, ensuring efficient and safe operation of the electric motor, while maintaining the power tool's performance and torque output.
Implementation Method 1
The first capacitor is connected in parallel between the power supply device and the driver circuit
Implementation Method 2
The electric motor is disposed in the housing and includes stator windings and a rotor rotating about the stator windings
Data Source
AI summary
A power tool includes a housing, an electric motor, a power supply device, a driver circuit, a controller, a first capacitor, and a voltage collection device. The power supply device is used for outputting a power signal to the driver circuit; and the driver circuit is used for outputting a drive signal to the electric motor according to the power signal and a control signal provided by the controller. The first capacitor is connected in parallel between the power supply device and the driver circuit. The voltage collection device is used for collecting a bus voltage signal at the front end of the driver circuit and transmitting the bus voltage signal to the controller. The controller can control the duty cycle of the control signal to decrease when the amplitude of the bus voltage is greater than a preset amplitude.