DC Motor Control Circuit Using Dynamic Amplitude Ratio
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Solution Overview
Problem
DC motor control systems face challenges in maintaining stable operation and reducing mechanical noise due to Back Electro-Motive Force (BEMF) effects, which cause sharp changes in current, affecting the performance and noise levels of DC motor fans in high-performance personal computers.
Innovation Solution
A DC motor control method and circuit that compares a positive full-wave signal and a triangular wave signal to generate a control signal, adjusting their amplitudes based on the needed speed of the motor, increasing the amplitude ratio for high speeds and decreasing it for low speeds, thereby reducing noise and maintaining stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the DC motor operates at high speed, then the cooling performance is improved, but the mechanical noise increases due to sharp current changes
Solution Approach 1:
The patent applies dynamics by making the signal amplitudes adjustable based on operating conditions. The first periodic signal amplitude is increased relative to the second periodic signal amplitude when high speed is needed, and decreased when low noise is needed. This dynamic adjustment of signal characteristics allows the system to adapt to different operational requirements and resolve the contradiction between speed and noise.
Solution Approach 2:
The patent changes the amplitude parameters of the periodic signals used in PWM generation. By varying the amplitude ratio between the first and second periodic signals, the control system can optimize the duty cycle waveform to reduce current ripple and mechanical noise at different speed levels, thereby resolving the contradiction between high-speed performance and noise reduction.
2Speed
If the amplitude ratio of the first periodic signal to the second periodic signal is increased for high speed, then the motor speed is improved, but the current waveform becomes sharper causing more noise
Solution Approach 1:
The system dynamically adjusts the amplitude relationship between the first and second periodic signals based on the required motor speed. When high speed is needed, the first signal's amplitude is increased; when noise reduction is prioritized, the amplitude ratio is decreased. This dynamic parameter adjustment allows flexible optimization of the PWM duty cycle to achieve the desired balance between speed and current waveform quality.
Solution Approach 2:
The patent modifies the amplitude parameters of the input periodic signals to the comparator. By changing these amplitude parameters, the resulting PWM duty cycle waveform is optimized to produce smoother current characteristics at different operating points, thereby controlling both motor speed and current waveform sharpness through parameter variation.
3Object-generated harmful factors
If the amplitude ratio of the first periodic signal to the second periodic signal is decreased for low noise, then the mechanical noise is reduced, but the motor speed decreases
Solution Approach 1:
The system employs dynamic adjustment of signal amplitudes to accommodate different operational priorities. When low noise operation is required, the amplitude ratio is decreased to smooth the current waveform; when high speed is needed, the ratio is increased. This dynamic adaptability allows the system to optimize performance based on real-time requirements.
Solution Approach 2:
The patent utilizes parameter changes in the periodic signal amplitudes to control the PWM generation characteristics. By varying these parameters, the system can produce duty cycle waveforms that minimize current ripple and mechanical noise when needed, while maintaining the capability to achieve high speeds when required, thus resolving the speed-noise trade-off through parameter optimization.
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
The method effectively controls DC motor speed, reducing mechanical noise and maintaining stable operation by smoothing the current waveform, achieving high speeds with low noise characteristics, and avoiding sharp current changes during phase transitions.
Implementation Method 1
comparing a first periodic signal and a second periodic signal for generating a control signal
Implementation Method 2
when the single-phase DC motor 130 rotates, a Back Electro-Motive Force (BEMF) must be generated in the single-phase DC motor 130, wherein polarity of the BEMF is opposite to that of the applied voltage
Data Source
AI summary
The present disclosure provides a DC motor control method comprising comparing a first periodic signal and a second periodic signal for generating a control signal, wherein the frequency of the first periodic signal is lower than the frequency of the second periodic signal; configuring the amplitudes of the first periodic signal and the second periodic signal according to the needed speed of the DC motor, wherein increasing the ratio of the amplitude of the first periodic signal to the amplitude of the second periodic signal when the needed speed of the DC motor is increased, and decreasing the ratio of the amplitude of the first periodic signal to the amplitude of the second periodic signal when the needed speed of the DC motor is decreased.