Brushless Motor Control via Phase Voltage Measurement
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Solution Overview
Problem
Brushless motors in power tool systems face challenges in starting efficiently and maintaining high operating efficiency due to the reliance on sensor-based control methods, which are inaccurate and costly, especially when the rotor is stationary or difficult to rotate, leading to insufficient torque output.
Innovation Solution
A method for controlling a brushless motor in a power tool system that determines the driving state corresponding to the rotor's position without a position sensor by measuring voltage and current parameters across phase windings, switching between different winding configurations to match the rotor's position, thereby optimizing torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If sensory control with position sensor is used, then control logic is simplified and control is more direct, but the cost increases and measurement precision deteriorates when assembly problems occur
Solution Approach 1:
The patent extracts the position detection function from the mechanical sensor system and implements it through electrical parameter measurement. By measuring voltage and current parameters of the phase windings, the system determines rotor position without physical contact, eliminating assembly-related precision problems while maintaining simple control logic.
Solution Approach 2:
The patent replaces the mechanical position sensor system with an electrical measurement system. Instead of using physical sensors that require precise assembly, the system uses voltage and current measurements of the phase windings to infer rotor position, substituting mechanical detection with electrical detection.
2Ease of manufacture
If sensorless control with forced rotation is used, then cost is reduced, but torque output is insufficient and the method fails when rotor cannot rotate initially
Solution Approach 1:
The patent performs preliminary action by measuring electrical parameters (voltage and current) of the phase windings before initiating rotor rotation. This allows the system to determine the initial rotor position and select the appropriate driving state in advance, ensuring maximum torque output from the start without requiring forced rotation or sacrificing torque performance.
3Speed
If forced rotation is applied to start the motor, then the rotor can begin rotating, but the brushless motor cannot output enough torque because the driving state does not correspond to the position of the rotor
Solution Approach 1:
The patent performs preliminary measurement of electrical parameters before rotation to determine rotor position in advance. This ensures that when rotation begins, the driving state is already correctly matched to the rotor position, eliminating the torque loss that occurs in forced-rotation methods where the driving state lags behind the actual rotor position.
Solution Approach 2:
The patent uses feedback from electrical parameter measurements (voltage and current of phase windings) to continuously monitor and determine rotor position. This feedback mechanism ensures the driving state remains synchronized with rotor position during acceleration, maintaining optimal torque output throughout the speed transition.
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 method improves the operating efficiency of brushless motors by accurately determining and matching the driving state to the rotor's position, enhancing torque output and reducing the reliance on position sensors, especially in applications with loads or starting difficulties.
Implementation Method 1
measuring a voltage of a higher-voltage one of the two of the phase input ends to which the driving voltage is applied and defining the voltage of the higher-voltage phase input end as a higher-voltage-end voltage; measuring a voltage at the phase input end which is kept floating when the driving voltage is applied
Implementation Method 2
the phase commutation of the brushless motor is continuously performed by electronic control so that a winding generates an electromagnetic field whose direction is continuously changing and a rotator rotates under the interaction of a magnetic field and the electromagnetic field
Implementation Method 3
a rotator rotates under the interaction of a magnetic field and the electromagnetic field
Data Source
AI summary
Provided is a method for controlling a brushless motor (101) in a power tool system. The brushless motor (101) includes multiple phase windings (u, v, w). The control method includes: operating the brushless motor (101) in each driving state for a period of time separately; measuring a voltage of a higher-voltage one of two phase input ends to which a driving voltage is applied and defining this voltage as a higher-voltage end voltage; measuring a voltage of a phase input end of one of the multiple phase windings which is kept floating when the driving voltage is applied and defining this voltage as a floating end voltage; determining whether values of the higher-voltage end voltage and the floating end voltage meet a preset condition; and when the values of the higher-voltage end voltage and the floating end voltage meet the preset condition, using any one of the multiple phase windings not serving as the current floating phase as a next floating phase. This method helps improve the running efficiency of the brushless motor (101).