Two-Phase Braking for Brushless DC Motors
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Solution Overview
Problem
Existing braking techniques for single-coil brushless DC motors, such as fixed time-based and speed-sensing methods, face challenges in adapting to changing motor characteristics and can result in reverse spinning, especially during rapid deceleration, as they rely on back EMF voltage sensing which is limited to three-coil designs.
Innovation Solution
A motor control circuit that implements a two-phase braking approach, where active braking is followed by back electromotive force (BEMF) voltage sensing, with distinct low speed thresholds to ensure precise deceleration and prevent reverse spinning, using a magnetic field sensor and output bridge circuit to manage drive current and braking phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back EMF voltage sensing is used for speed detection during braking, then speed sensing capability is provided, but it is limited to three-coil motor designs and cannot be applied to single-coil motors
Solution Approach 1:
The patent applies universality by enabling back EMF voltage sensing to function in both three-coil and single-coil motor designs. The method allows the same sensing technique to be universally applied across different motor configurations by utilizing the coil that is not currently active during braking, making the speed sensing capability adaptable to various motor topologies.
2Ease of operation
If fixed time-based braking control is used, then control simplicity is maintained, but it does not adapt to changing motor characteristics and can allow reverse spinning
Solution Approach 1:
The patent implements feedback by continuously monitoring the back EMF voltage during braking to detect actual motor speed. This feedback mechanism allows the control system to adjust braking duration dynamically based on real-time speed conditions, preventing reverse spinning and adapting to changing motor characteristics while maintaining relatively simple control logic.
3Speed
If active braking with Hall-effect sensor feedback is used, then faster deceleration is achieved, but device complexity increases due to additional sensors
Solution Approach 1:
The patent applies self-service by utilizing the motor's own back EMF voltage as the sensing signal, eliminating the need for external Hall-effect sensors or other dedicated speed sensing components. The motor structure itself provides the necessary feedback signal through its back EMF generation, achieving fast deceleration control without adding external sensing hardware.
4Reliability
If braking duration is extended to ensure complete stop, then reverse spinning is prevented, but braking time increases and efficiency decreases
Solution Approach 1:
The patent implements dynamics by making the braking duration variable rather than fixed. The braking process dynamically adjusts its duration based on real-time back EMF voltage measurements, extending braking only as long as necessary to reach complete stop and prevent reverse spinning, then terminating immediately. This dynamic adaptation optimizes braking time while ensuring reliability.
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 solution allows for efficient and adaptive braking in single-coil motors, achieving fast deceleration while preventing reverse spinning by combining time-based and voltage-based speed sensing, effectively controlling motor speed to near zero RPM.
Implementation Method 1
A brushless DC (BLDC) motor is braked by generating a negative torque which slows the rotation of the motor
Implementation Method 2
One prior technique for braking uses the back electromotive force (EMF) voltage induced in a coil of the motor
Data Source
AI summary
A motor control circuit that features a smart, two-phase braking operation is presented. The motor control circuit includes a motor drive circuit to apply a brake current to a coil of an external motor for active braking of the motor. The motor control circuit further includes a braking control circuit, coupled to the motor drive circuit and responsive to an externally generated control signal, to control the active braking by the motor drive circuit so that the active braking occurs in two phases. The two phases include a first phase that includes a first portion of the active braking and a second phase that includes back electromotive force (BEMF) voltage sensing and a second portion of the active braking.