Brushless Motor Position Sensor Offset for Phase Timing
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Solution Overview
Problem
Brushless motors in electric power tools face performance limitations due to delays in phase converting, which affect the precision and efficiency of rotor position detection, especially when rotating in reverse directions, leading to reduced performance and potential overheating.
Innovation Solution
The implementation of a driving system with position sensors advanced by an electrical angle of 20° to 40° from conventional positions, allowing for timely phase converting and improved control of the brushless motor's driving states, including six distinct states per electric cycle, to enhance motor performance and reduce delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If position sensors are positioned at conventional locations for detecting rotor positions, then the structure is simple and easy to manufacture, but phase converting delays occur reducing motor performance and efficiency
Solution Approach 1:
The position sensors are positioned in advance (ahead) of the conventional sensor locations, specifically at an angular offset of 15° to 25° electrical angle. This preliminary positioning allows the control system to detect rotor position earlier in the rotation cycle, enabling proactive phase converting before the actual commutation point is reached, thereby eliminating delays and improving motor rotation speed
2Productivity
If position sensors are advanced by 20° to 40° electrical angle, then phase converting timing is improved and motor performance increases, but sensor positioning precision requirements increase
Solution Approach 1:
The patent specifies an optimized angular offset range of 20° to 40° electrical angle between the advanced position sensors and the conventional sensor locations. This parameter optimization balances the benefits of early position detection (improved phase converting timing and motor performance) with practical manufacturing considerations, ensuring that the sensor positioning accuracy requirements remain achievable while maximizing motor rotation number and efficiency
3Use of energy by moving object
If conventional sensor positions are used, then device complexity is low, but current consumption increases especially under heavy loads
Solution Approach 1:
By positioning sensors in advance at the specified angular offset, the control system can anticipate rotor position and perform phase converting proactively, optimizing current waveform timing and reducing current peaks especially under heavy loads, thereby lowering overall current consumption without significantly increasing device complexity
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 configuration improves the brushless motor's performance by increasing the rotation number and reducing current consumption, especially under heavy loads, while ensuring reliable operation in both forward and reverse directions, thus extending the motor's service life.
Implementation Method 1
position sensors for detecting positions of the rotor
Implementation Method 2
a back electromotive force of the stator winding of at least one phase in the brushless motor is at a midpoint position of a waveform of the back electromotive force
Data Source
AI summary
An electric power tool and a method for driving a brushless motor in the electric power tool. The electric power tool includes a driving circuit for driving the brushless motor and position sensors (D1, D2, D3) for detecting positions of the rotor. The rotor of the brushless motor, when rotating in a normal direction, sequentially passes by a commutation position, where a signal of at least one of the position sensors (D1, D2, D3) in the brushless motor changes, and a reference position, where a back electromotive force of the stator winding of at least one phase in the brushless motor is at a midpoint position of the waveform of the back electromotive force. An electrical angle between the commutation position and the reference position ranges from 20° to 40°. The position sensors (D1, D2, D3) are configured such that performance of the brushless motor is improved.