Brushless DC Motor PWM Control for Stable Startup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing motor driving methods for single phase brushless DC motors experience unstable rotation and generate back electromotive voltage and noise due to distortion in the Hall signal, particularly during startup, which affects the soft switching operation.
Innovation Solution
A motor driving circuit comprising an inverter circuit, a position detection sensor, and a controller that controls the PWM signal by maintaining a constant pulse width during a specific time period after the position detection signal zero-crosses and then narrows the pulse width, stabilizing the rotation and suppressing back electromotive voltage and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft switching operation is performed using PWM signal based on voltage amplitude of Hall signal at startup, then motor can be driven, but back electromotive voltage and noise are generated when voltage amplitude is large, and rotating speed decreases when voltage amplitude is small
Solution Approach 1:
The controller performs preliminary action by detecting zero-crossing points of the Hall signal in advance and using this information to determine the PWM pulse width timing. This preliminary detection allows the system to synchronize the PWM switching with the back electromotive voltage waveform, ensuring that switching occurs at optimal moments that prevent voltage spikes and noise generation while maintaining stable motor rotation.
2Reliability
If PWM pulse width is varied based on Hall signal voltage amplitude, then soft switching is achieved, but rotation becomes unstable and vibration occurs due to Hall signal distortion near zero cross
Solution Approach 1:
The zero-crossing detection of the Hall signal serves as an intermediary reference that mediates between the PWM control and the motor's back electromotive voltage waveform. By using the zero-crossing point as a reference timestamp, the controller can accurately determine PWM pulse width without being directly influenced by the distorted Hall signal amplitude variations, thus achieving both soft switching and rotation stability.
3Measurement precision
If Hall signal is amplified to improve detection, then signal strength increases, but distortion near zero cross increases causing waveform distortion in driving signal
Solution Approach 1:
The controller segments the PWM pulse width control into two distinct parts: a fixed time period determined by zero-crossing detection and a variable time period adjusted according to Hall signal amplitude. This segmentation allows the system to use the accurate zero-crossing timing for the critical portion of the pulse width while using amplitude-based adjustment only for the remaining portion, thereby reducing the overall distortion in the driving signal waveform.
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 configuration ensures stable motor rotation during startup and reduces the generation of back electromotive voltage and noise, improving the motor's performance and reliability.
Implementation Method 1
a position detection sensor which detects a magnetic pole position of a magnet rotor
Implementation Method 2
an inverter circuit which supplies a driving current to a coil of a single phase brushless DC motor
Data Source
AI summary
A motor driving circuit includes an inverter circuit which supplies a driving current to a coil of a single phase brushless DC motor, a position detection sensor which detects a magnetic pole position of a magnet rotor of the motor and outputs a position detection signal, and a controller which controls the inverter circuit based on the position detection signal and a speed instruction signal for instructing a rotating speed of the motor. At a time of startup of the motor, the controller makes a pulse width of a PWM signal for controlling the inverter circuit constant in a first time period which starts after the position detection signal zero-crosses and lasts until the position detection signal zero-crosses next time, and narrows the pulse width of the PWM signal as time elapses in a second time period immediately after the first time period.