BLDC Motor Phase Compensation Using Back-EMF Freewheeling Detection
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Solution Overview
Problem
Existing phase compensation methods for brushless direct current (BLDC) motors are either time-consuming and inefficient, requiring manual adjustments, or increase hardware costs by needing additional sensors to detect zero-crossing events for automatic phase correction.
Innovation Solution
A sinusoidal pulse width modulation scheme is implemented, using a control unit, driving circuit, and back electromotive force circuit to automatically update initial angles of driving currents based on the duration of the freewheeling period of the back electromotive force voltage, allowing for commutation and phase compensation without manual intervention or increased hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual phase compensation method is used to adjust current phase, then phase compensation can be achieved, but it is time consuming and requires back and forth debugging
Solution Approach 1:
The patent uses feedback by detecting the zero-crossing point of back electromotive force voltage and comparing it with the zero-crossing point of driving current to automatically determine phase difference, eliminating manual trial-and-error adjustment and significantly reducing phase compensation time while maintaining accuracy
Solution Approach 2:
The patent introduces an intermediary measurement approach by using the zero-crossing point detection as a mediator to indirectly measure phase difference, avoiding direct complex phase measurement and enabling automatic compensation without manual intervention
2Extent of automation
If phase current detector and back electromotive force detector are added to detect zero-crossing information, then automatic phase compensation can be achieved, but hardware cost increases
Solution Approach 1:
The patent makes the back electromotive force detector serve multiple functions: it not only detects back electromotive force voltage for motor control but also provides zero-crossing information for phase compensation, eliminating the need for separate phase current detectors and reducing hardware complexity
Solution Approach 2:
The system uses its own back electromotive force detection capability to automatically perform phase compensation without requiring external additional sensors, making the system self-sufficient and avoiding increased hardware costs
3Productivity
If original optimal phase compensation value is used when load changes, then system operation continues, but motor efficiency decreases
Solution Approach 1:
The patent implements dynamic phase compensation by continuously detecting zero-crossing points and automatically adjusting phase compensation values in real-time according to load changes, ensuring motor operates at optimal efficiency rather than using fixed original values
Solution Approach 2:
The system uses feedback from zero-crossing point detection to continuously monitor and adjust phase compensation in real-time, automatically adapting to load changes and maintaining optimal motor efficiency without manual intervention
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 enables quick and efficient phase compensation, improving motor efficiency by synchronizing back electromotive force voltage and driving current, reducing phase correction time, and maintaining efficiency even with changing loads without increasing hardware costs.
Implementation Method 1
a back electromotive force circuit and a control unit. The back electromotive force circuit is coupled to the first winding, the second winding and the third winding
Implementation Method 2
in the freewheeling period, a current continues to flow through a body diode of the first high-side switch or a body diode of the first low-side switch
Data Source
AI summary
A motor system includes a brushless direct current motor, a back electromotive force (EMF) circuit, and a control unit. The brushless direct current motor includes first to third windings. The back EMF circuit is coupled to the first to the third windings. The control unit is coupled to the back EMF circuit for floating the first winding, energizing the second winding, and energizing the third winding prior to detect a zero-crossing event. The back EMF detects a duration of a freewheeling period of a back EMF signal of the first winding and a zero-crossing event. The control unit updates respective initial angles of respective driving currents of the first to the third windings according to the duration of a freewheeling period, and performs commutation according to respective updated initial angles of the respective driving currents of the first to the third windings upon detecting the zero-crossing event.