Brushless DC Motor Startup Stability via Back-EMF Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor control systems struggle to start a three-phase brushless DC motor stably when the load torque is not constant, as the fixed application time of drive current can lead to unstable startup.
Innovation Solution
The motor drive system employs a 120-degree conduction method with adjustable current patterns and a semiconductor device that detects back electromotive force to determine the optimal time for applying starting torque, allowing for adaptive control based on rotor position and load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the application time of drive current is fixed, then the control system is simple, but the motor cannot start up stably when load torque is not constant
Solution Approach 1:
The patent applies dynamics by making the drive current application time variable rather than fixed. The control system dynamically adjusts the application time based on detected rotor position and back electromotive force characteristics, allowing the motor to start stably under varying load torque conditions while maintaining manageable system complexity through structured control logic.
Solution Approach 2:
The patent implements feedback by detecting the back electromotive force generated in the non-conducting phase and using this information to determine the optimal application time for drive current. This feedback mechanism enables the control system to adapt to different load conditions and achieve reliable startup without requiring overly complex control architecture.
2Force
If the application time of drive current is extended, then the motor can overcome higher load torque, but the startup time increases
Solution Approach 1:
The patent uses dynamics to optimize the drive current application time based on real-time rotor position and back electromotive force detection. By dynamically adjusting the application time, the system achieves sufficient starting torque to overcome load torque while minimizing the duration of current application, thus reducing overall startup time compared to fixed or extended application times.
Solution Approach 2:
The patent applies parameter changes by varying the drive current application time according to detected motor state parameters (rotor position, back electromotive force characteristics). This allows the system to use shorter application times when possible, reducing startup time, while still achieving the necessary starting torque through optimized parameter selection.
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 approach enables stable startup of the motor even under varying load torque conditions by optimizing the duration and phase of drive current application, ensuring efficient torque application and reducing startup time.
Implementation Method 1
back electromotive force (BEMF) is generated in a stator winding in a non-conducting phase when a rotor of the motor rotates
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present disclosure starts up a three-phase motor in a stable manner. During a start-up operation of a brushless DC motor, a motor drive system detects the position of a particularly suitable rotor while the rotor is resting, and applies a drive current to two phases in accordance with the detected position of the rotor. A controller changes the time of drive current application in accordance with the magnitude of back electromotive force that is in a non-conducting phase and detected by a detector during drive current application.