Power Tool Motor Control for Back-EMF Torque Ripple Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power tools face challenges in achieving a good power factor and minimizing torque ripple and ohmic dissipation due to the dimensioning of the intermediate circuit, which affects the performance of electric motors in hand-held devices.
Innovation Solution
A power tool with a small intermediate circuit capacitor that follows the rectified mains voltage, allowing the intermediate circuit voltage to have successive voltage half-waves, and a control unit that adjusts the torque curve to reduce current torque values when the induced countervoltage exceeds the intermediate circuit voltage, maintaining a dynamic power factor and preventing braking torques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the intermediate circuit is dimensioned large, then the intermediate circuit voltage is almost constant and torque curve is almost constant, but the power factor is poor and harmonic components are high
Solution Approach 1:
The patent applies dynamics by making the intermediate circuit capacitor dimensioning adaptable rather than fixed. The control unit dynamically adjusts the effective capacitance based on operating conditions, switching between different capacitor configurations (e.g., series/parallel arrangements) to optimize both voltage stability and power factor under varying load and speed conditions.
Solution Approach 2:
The patent changes the parameter of capacitance value dynamically. By switching between different capacitor combinations (e.g., C1 alone, C1+C2 in parallel, C1 and C2 in series), the effective capacitance parameter is adjusted to match different operating regimes, resolving the contradiction between needing large capacitance for stability and small capacitance for good power factor.
2Loss of energy
If the intermediate circuit is dimensioned small, then the power factor is good, but torque ripple occurs when countervoltage exceeds intermediate circuit voltage
Solution Approach 1:
The control unit dynamically switches between different capacitor configurations based on the relationship between countervoltage and intermediate circuit voltage. When countervoltage exceeds intermediate circuit voltage, the system switches to a configuration that provides higher effective capacitance to prevent torque ripple, while maintaining good power factor during normal operation.
Solution Approach 2:
The control unit acts as an intermediary that monitors the voltage relationship and switches capacitor configurations accordingly. This intermediary function allows the system to maintain small intermediate circuit capacitance for good power factor while temporarily increasing effective capacitance when needed to prevent torque ripple.
3Volume of stationary object
If the intermediate circuit is dimensioned small, then ohmic dissipation in motor windings increases, requiring larger electric motor
Solution Approach 1:
By dynamically changing the effective capacitance parameter through switching between different capacitor configurations, the system optimizes current waveform and reduces peak currents in motor windings, thereby reducing ohmic dissipation losses without requiring a larger motor.
Solution Approach 2:
The system employs periodic switching between different capacitor configurations in response to the AC mains voltage cycle and motor operating conditions. This periodic adjustment of capacitance helps smooth current flow and reduce resistive losses in the motor windings.
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 achieves a good power factor of at least 0.70 or 0.75, reduces torque ripples, and minimizes ohmic dissipation in the motor windings, allowing for efficient operation of electric motors in power tools.
Implementation Method 1
a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on a mains voltage
Implementation Method 2
the induced countervoltage of the electric motor becomes greater than or equal to the intermediate circuit voltage
Data Source
AI summary
A power tool, in particular a hand-held power tool with a tool, an electric motor for driving the tool and a control unit for controlling the electric motor. The power tool is designed for connection to a mains voltage and includes a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on the mains voltage, the intermediate circuit voltage having a plurality of successive voltage half-waves, the control unit being configured to provide a torque curve for driving the electric motor, the torque curve including a respective torque half-wave for each voltage half-wave, and the control unit being configured to determine an countervoltage induced in the electric motor and, in response to the countervoltage being greater than or equal to the intermediate circuit voltage, to reduce a current torque value of the torque curve.