Start-stop control systems and methods for gas foil bearing machine
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Solution Overview
Problem
Gas foil bearings in HVAC compressors experience accelerated wear during start-up and shutdown due to running below liftoff speed and compressor surge events, leading to reduced lifespan and increased maintenance needs.
Innovation Solution
A controller system that manages the start-up and shutdown of centrifugal compressors by operating an unloading device to remove and reapply load, accelerating the motor to a speed above the liftoff speed of the gas foil bearings but below the operating speed, and decelerating to a minimum speed greater than zero before coasting to stop, thereby minimizing wear and surge events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor is started or stopped quickly, then productivity is improved, but wear on gas foil bearings increases due to running below liftoff speed
Solution Approach 1:
Before stopping the compressor, the controller预先 removes the load from the compressor using an unloading device, then decelerates the motor to a minimum speed greater than zero before coasting to stop. This preliminary load removal prevents surge events and reduces bearing wear during the shutdown process.
Solution Approach 2:
The controller dynamically adjusts motor speed during start-up and shutdown operations. During start-up, the motor is accelerated to a first speed above liftoff speed but below operating speed, held for a period, then accelerated to full operating speed. During shutdown, the motor is decelerated to a minimum speed greater than zero before coasting to stop, preventing the motor from running below liftoff speed where bearing wear occurs.
2Productivity
If the compressor operates at high speed, then productivity is improved, but surge events increase in severity causing bearing damage
Solution Approach 1:
Before decelerating the compressor during shutdown, the controller预先 removes the load using an unloading device. This preliminary action prevents surge events from occurring during the speed reduction process, allowing the compressor to safely transition through speed ranges where surge is likely.
Solution Approach 2:
The controller continuously monitors compressor operation and adjusts motor speed and unloading device operation based on real-time conditions. This feedback control ensures the compressor operates above liftoff speed during transitions and prevents surge events by coordinating load removal with speed changes.
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 reduces wear on gas foil bearings, minimizes the number and severity of surge events, and extends the lifespan of the bearings by optimizing operational speeds during critical phases of compressor operation.
Implementation Method 1
The shaft and gas foil bearing are separated by the gas's high pressure, which is generated by the rotation that pulls gas into the bearing via viscosity effects.
Implementation Method 2
The shaft and gas foil bearing are separated by the gas's high pressure
Implementation Method 3
operating the unloading device to remove a load from the centrifugal compressor, accelerating the motor to a first speed above a liftoff speed
Implementation Method 4
removing power from the motor when the speed of the motor reaches the minimum speed and allowing the motor to coast to a stop
Data Source
AI summary
An HVAC system includes an unloading device, a centrifugal compressor, a gas foil bearing, a VFD and a controller. The controller is programmed to start the centrifugal compressor from a stopped condition by operating the unloading device to remove a load from the centrifugal compressor, accelerating the motor to a first speed above a liftoff speed of the gas foil bearing and below an operating speed of the centrifugal compressor, running the motor for a period of time, operating the unloading device to apply the load to the centrifugal compressor, and accelerating the motor to the operating speed.