BLDC Motor Controller Breakaway Detection via Back-EMF
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Solution Overview
Problem
Brushless DC motor controllers face issues with breakaway due to high external torque, where the brake function becomes ineffective, and existing solutions require additional sensors or complex calculations to detect this condition.
Innovation Solution
A controller for a brushless DC motor that temporarily opens switching means to short-circuit phase windings during braking, allowing detection of rotor movement and rotational speed, enabling identification of breakaway without additional sensors or significant construction changes, by using a measuring device to evaluate induced voltage as a rotor position signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the switching means are closed to short-circuit the phase windings for braking, then the braking effect is improved, but the ability to detect rotor movement and identify breakaway is worsened
Solution Approach 1:
The switching means are temporarily opened at specific periodic intervals during braking operation to allow back-emf detection. This periodic opening enables the measuring device to detect rotor movement and identify breakaway conditions, while maintaining braking effect during the majority of the braking cycle when the switching means remain closed.
2Reliability
If additional sensors are added to detect breakaway, then the reliability of breakaway identification is improved, but the device complexity and construction cost increase
Solution Approach 1:
The existing switching means and measuring device are made multi-functional. The switching means serve both braking function (when closed) and enable detection function (when temporarily opened). The measuring device evaluates back-emf for both normal rotor position detection and breakaway identification, eliminating the need for separate sensors and reducing system complexity.
Solution Approach 2:
The system uses its own existing components (switching means and back-emf measuring device) to perform the additional function of breakaway detection. No external or additional sensors are required - the system serves itself by utilizing the back-emf that naturally occurs during the temporary opening of switching means for both control and diagnostic purposes.
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
Effectively identifies breakaway conditions without reducing the braking effect, allowing for timely intervention and maintaining motor control, thus enhancing safety and efficiency in sensorless rotor-position detection.
Implementation Method 1
the induced voltage, the back-emf of a phase winding is detectable
Data Source
AI summary
A controller for a brushless direct-current motor having an upstream converter, which has a half-bridge having a pair of switching means for each phase winding of the motor, includes a measuring device or has a signal connection to a measuring device. The measuring device is associated with a half-bridge and by means of the measuring device, the induced voltage, the counterelectromotive force of a phase winding, can be detected for rotor position detection in the current-free state, for which purpose the controller, in an operating mode that causes the braking and in which the switching means cause a short circuit of the phase windings, briefly opens the switching means associated with the measuring device in order to determine a rotor motion.