VFD Skip Frequency Bands for Cooling System Vibration Control
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Solution Overview
Problem
Existing cooling systems, such as refrigeration and HVAC systems, face challenges with excessive vibration and noise due to structural resonances, which are difficult to address through manual programming of lockout bands in VFD systems, requiring significant engineering resources and adding product cost.
Innovation Solution
A system and method that uses vibration sensors and a multi-channel data acquisition system to automatically determine lockout band frequencies for VFDs, allowing for automatic programming tailored to specific product configurations, reducing the need for special training and expertise, and incorporating expert rules to detect common faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manual programming of lockout bands is performed in factory, then vibration control can be achieved, but programming time and expertise requirements increase significantly
Solution Approach 1:
The system performs preliminary vibration testing and automatically determines lockout band frequencies during the manufacturing process, before the product is shipped to the customer. This preliminary action eliminates the need for time-consuming manual programming at the installation site while ensuring proper vibration control is established upfront.
Solution Approach 2:
The system uses self-service by automatically measuring the actual resonant frequencies of each specific product configuration through vibration testing, and then automatically programming the appropriate lockout bands without requiring external expert intervention. The product essentially programs itself based on its own measured characteristics.
2Reliability
If wide lockout bands are programmed to account for manufacturing variations, then vibration control is maintained across variations, but usable speed range is reduced
Solution Approach 1:
Instead of applying a uniform wide lockout band to all products, the system determines the specific resonant frequencies of each individual product configuration through vibration testing and programs precise, narrow lockout bands tailored to that local configuration. This local quality approach ensures vibration control is maintained while minimizing the impact on usable speed range.
Solution Approach 2:
The system changes the parameter of lockout band width from a fixed wide value to a variable value that is optimized for each specific product configuration. By measuring actual resonant frequencies and programming accordingly, the lockout band width adapts to the specific needs of each unit, maintaining reliability while maximizing usable speed range.
3Measurement precision
If individual vibration testing is performed on each unit, then accurate lockout band determination is achieved, but production time and cost increase significantly
Solution Approach 1:
The system replaces complex mechanical vibration testing instrumentation with a simplified automated testing apparatus that uses basic vibration sensors and a microprocessor to perform the measurements. This substitution maintains measurement precision while dramatically reducing the complexity and time required for individual unit testing.
Solution Approach 2:
The system uses a standardized testing procedure and data processing algorithm that can be rapidly applied to each unit without requiring complex custom setup. By copying the same simple testing and analysis process across all units, accurate resonant frequency determination is achieved efficiently at high production speeds.
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 effectively reduces excessive vibration and noise by automatically determining and implementing lockout bands, improving controllability and reducing production time, while minimizing the need for complex instrumentation and qualified technicians.
Implementation Method 1
Vibration sensors are mounted at a key location(s) on the structural system... A multi-channel data acquisition system acquires the sensor output signals and communicates with a controller/computer that calculates vibration level(s) during a frequency sweep
Implementation Method 2
Variable speed drive (VFD) systems... often by necessity must pass through frequencies that excite structural resonances. The resonances can lead to structural failure... the acquired vibration level versus speed curve is compared against an engineering specification. Using simple amplitude and rate of change information, the frequency bands over which the specification is exceeded is determined
Data Source
AI summary
A vibration control system for a variable speed cooling system includes a programmable controller in communication with a variable frequency drive (VFD). The programmable controller is programmed to command the VFD to operate at frequencies only outside of one or more frequency lockout bands automatically calculated by the programmable controller based on a comparison of newly acquired variable speed cooling system vibration data with previously stored variable speed cooling system vibration specification data.