Spread-Spectrum Fan Control for Vibration Reduction
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Solution Overview
Problem
Current fan control technologies in server systems result in high amplitude mechanical and acoustical vibrations due to constant blade-passing frequencies, leading to functional failures and customer acceptance issues, as they fail to effectively manage the increasing heat dissipation needs of advanced electronic components.
Innovation Solution
A spread-spectrum fan control system that continuously and randomly modulates the blade-passing frequencies of cooling fans within a defined range around a set point, independent of temperature fluctuations, using noise generators to vary the duty cycles of PWM signals and reduce coupled vibrations and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If constant PWM control signals are used to maintain stable fan operation, then fan speed stability is improved, but mechanical and acoustical vibration amplitude increases due to fixed blade-passing frequencies
Solution Approach 1:
The patent applies dynamics by continuously varying the PWM control signals to dynamically change the blade-passing frequencies of cooling fans. Instead of using constant frequencies, the system modulates fan speeds to create time-varying frequencies that avoid fixed resonant points, thereby reducing mechanical and acoustical vibrations while maintaining stable cooling performance through controlled frequency transitions.
Solution Approach 2:
The patent implements parameter changes by modifying the PWM duty cycle parameters to vary blade-passing frequencies over time. The system changes the frequency parameter dynamically within a defined range, transforming the static frequency operation into a dynamic one that spreads spectral energy and minimizes vibration coupling to the chassis at any given frequency.
2Power
If multiple high-power cooling fans are used to handle increasing heat-generating components, then cooling capacity is improved, but mechanical vibration coupling to chassis increases
Solution Approach 1:
The patent applies dynamics by coordinating multiple cooling fans to operate with dynamically varying speeds rather than constant speeds. The system continuously adjusts the rotational speeds of multiple fans to vary their blade-passing frequencies, preventing synchronized vibration and reducing mechanical coupling to the chassis while maintaining the required cooling capacity.
Solution Approach 2:
The patent implements periodic action through spread-spectrum modulation techniques that periodically vary the fan speeds in a controlled manner. By applying periodic frequency modulation to the PWM control signals, the system creates time-varying blade-passing frequencies that distribute vibrational energy across a broader spectrum, minimizing peak vibrations and reducing mechanical coupling to the chassis.
3Device complexity
If fan blade-passing frequencies are kept constant for extended periods, then control simplicity is improved, but acoustical noise perception worsens due to strong tonal centers
Solution Approach 1:
The patent applies dynamics by implementing continuous frequency modulation of fan speeds through variable PWM control signals. Instead of maintaining constant frequencies, the system dynamically adjusts blade-passing frequencies within a defined range, which disperses the concentrated tonal noise centers and reduces perceptible acoustical noise while maintaining manageable control complexity through automated spread-spectrum algorithms.
Data Source
AI summary
A system and method of spread-spectrum fan control for an air-cooled system is provided for reducing the vibrational and acoustical noise associated with the air-cooled system. The method includes generating a first control signal that controls a blade-passing frequency of a first cooling fan and a second control signal that controls a blade-passing frequency of a second cooling fan, wherein the first and second control signals may be pulse width modulated (“PWM”) signals. One or more noise generators independently vary duty cycles for the first and second PWM signals within a range around respective first and second blade-passing frequency set points. As a result, the blade-passing frequencies for the first and second cooling fans are independently and randomly modulated within a range around the respective first and second blade-passing frequency set points.