BLDC Motor Control Module for AC Power Tools
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Solution Overview
Problem
Conventional motor control schemes for brushless DC motors powered by AC sources face challenges due to non-linear voltage waveforms and inherent electrical characteristics, leading to reduced power factor and motor efficiency.
Innovation Solution
A control module that regulates the switching operation of power switches in a brushless DC motor, halting or reducing PWM switching between specific thresholds to prevent current flow during zero-crossings of the AC power supply voltage waveform, and adjusting the PWM duty cycle based on target and actual rotational speeds to optimize power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional motor control schemes are used with AC power supply, then the motor can operate, but power factor and motor efficiency are reduced due to non-linear voltage waveform and current spikes
Solution Approach 1:
The control module dynamically adjusts the PWM duty cycle based on the instantaneous AC voltage waveform, specifically reducing or halting switching operation near zero-crossings where voltage is low. This dynamic adaptation to the AC power supply characteristics eliminates current spikes and improves both motor efficiency and power factor without requiring complex additional hardware.
2Duration of action of stationary object
If PWM switching operation continues through zero-crossings of AC voltage waveform, then continuous power delivery is maintained, but current spikes occur and harmonic content increases
Solution Approach 1:
The control module preemptively reduces or halts PWM switching operation before the AC voltage reaches zero-crossings, preventing the conditions that would cause current spikes and harmonic distortion. By anticipating the problematic voltage conditions and adjusting switching accordingly, the system avoids harmful current transients while maintaining continuous and smooth power delivery through the AC cycle.
3Ease of operation
If switching operation is halted near zero-crossings to reduce current spikes, then power factor improves, but power delivery is reduced during low voltage periods
Solution Approach 1:
The control module changes the PWM duty cycle parameter in response to the AC voltage waveform characteristics, reducing or halting switching near zero-crossings where voltage is low and current spikes would occur. During higher voltage portions of the AC cycle, normal PWM switching resumes to maintain adequate power delivery. This parameter adaptation resolves the contradiction by optimizing both power factor and power delivery at different points in the AC cycle.
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 approach improves power factor and harmonic content of the AC line current, reducing current spikes and enhancing motor efficiency by synchronizing current draw with the AC input line voltage waveform.
Implementation Method 1
a rectifier configured to receive an alternative current from an alternating current (AC) power supply and output a rectified signal supplied to a DC power bus
Implementation Method 2
a brushless DC (BLDC) motor arranged within the housing and having a stator and a rotor rotatably disposed within the stator
Data Source
AI summary
A power tool is provided including a brushless DC (BLDC) motor, a rectifier that receives an alternative current from a power supply and outputs a rectified signal supplied to a DC power bus, and an inverter circuit having motor switches connected electrically between the DC power bus and the motor. A control module controls a switching operation of the power switches to regulate supply power from the power supply to the motor. The control module controls the switching operation so as to, within a half cycle of the AC power supply voltage waveform, increase current draw from the power supply from a first threshold at or after a first zero-crossing of the half cycle up to a second threshold, and reduce current draw from the power supply from the second threshold up to a third threshold at or prior to a second zero-crossing of the half cycle.