Brushless Motor Power-On Self-Test for Short Circuit Detection
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Solution Overview
Problem
Existing power-on self-test methods for electric power tools with brushless direct current motors are inadequate in detecting short circuits, leading to potential machine damage and prolonged boot times, which compromise user experience and safety.
Innovation Solution
A power-on self-test method that involves monitoring the power-on signal to detect the position of the rotor of the brushless motor when motionless, using phase or line voltages to determine if switching elements are short-circuited, and preventing the motor from starting if a short circuit is detected, thereby ensuring safety and reducing boot time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage between switching elements is detected before starting up to determine short circuit, then safety of electric power tool is improved, but boot time is prolonged
Solution Approach 1:
The patent combines the short circuit detection function with the rotor position detection function into a single integrated process. By using the same voltage detection circuit and control logic to perform both tasks simultaneously during the power-on phase, the detection of switching element voltages and determination of rotor position are merged into one unified operation, eliminating the need for separate detection steps and thereby reducing boot time while maintaining safety.
Solution Approach 2:
The patent performs short circuit detection during the rotor position detection phase, which occurs before the motor starts rotating. By completing the voltage detection and short circuit determination as a preliminary action during the initial position detection routine, the system ensures safety checks are performed in advance without requiring additional time after position detection, thus preventing boot time extension.
2Reliability
If voltage between switching elements is detected before starting up, then short circuit detection capability is improved, but detection precision is insufficient
Solution Approach 1:
The patent employs feedback mechanisms where the detected voltage signals from the switching elements are continuously monitored and compared against predetermined threshold values. The control unit adjusts its detection strategy based on the feedback from initial voltage readings, and uses the rotor position information as additional feedback to refine the short circuit determination, thereby improving detection precision through iterative verification.
Solution Approach 2:
The patent enhances detection precision by adding another dimension to the detection process - utilizing rotor position information as an additional parameter alongside voltage measurements. By combining voltage magnitude detection with angular position data, the system creates a two-dimensional detection space that allows for more accurate short circuit identification, distinguishing between actual short circuits and normal operational voltage variations.
Data Source
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AI summary
Provided are a power-on self-test method for an electric power tool and an electric power tool. The power-on self-test method includes steps described below. In response to monitoring a power-on signal of the electric power tool, a controller outputs a driving signal to a motor driving circuit and acquires a position of a rotor of a brushless motor. During acquiring the position of the rotor of the brushless motor, a phase voltage or a line voltage of a winding of the brushless motor is detected through the voltage detection circuit. Whether an upper bridge arm switching element, a lower bridge arm switching element, and/or the brushless motor is short-circuited is determined according to the phase voltage or the line voltage of the winding of the brushless motor. In the solution provided by embodiments of the present disclosure, during detecting the position of the rotor of the brushless motor, whether the switching element and the brushless motor are short-circuited is determined according to the phase voltage or the line voltage of the winding of the brushless motor, so as to reduce the risk of burning machine when the electric power tool is turned on. This method is simple and quick, and can save the boot time of the electric power tool.