Variable Speed Compressor Control for Motor Overload Prevention
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Solution Overview
Problem
Variable speed dynamic compressors face challenges in preventing choke conditions and motor overload, making it difficult to maintain efficient operation while avoiding excessive motor winding temperatures, as direct power measurement is hard to achieve, leading to the need for fixed speed and power limits that are not suitable for commercial operation.
Innovation Solution
A method of controlling the compressor using continuous measurement of gas inlet temperature, motor winding temperature, and motor speed to set maximum motor speed limits, employing a double PID loop control system that adjusts motor speed based on delivery pressure and winding temperature to prevent choke and manage power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If compressor speed is increased to increase air flow rate, then productivity is improved, but motor winding temperature increases leading to motor overload
Solution Approach 1:
The control system continuously monitors motor winding temperature and uses this feedback to dynamically adjust the maximum permissible compressor speed. When temperature approaches critical levels, the system reduces speed to prevent motor overload, creating a closed-loop control that balances productivity with thermal safety
Solution Approach 2:
The system transitions from fixed speed limits to dynamic speed adjustment based on real-time temperature conditions. The maximum speed is no longer a static parameter but varies continuously with motor winding temperature, allowing optimal productivity while preventing thermal damage
2Reliability
If fixed speed and power limits are imposed to protect from motor overload, then motor protection is improved, but compressor efficiency deteriorates
Solution Approach 1:
The system replaces static power limits with dynamic temperature-based speed limits. By monitoring actual motor winding temperature and adjusting speed accordingly, the system provides motor protection tailored to real-time conditions rather than imposing conservative fixed limits that reduce efficiency
Solution Approach 2:
The control approach shifts from limiting power consumption to limiting speed based on temperature parameters. This parameter change allows the system to operate at optimal efficiency points while still protecting the motor, as speed adjustment directly controls both productivity and thermal load
Data Source
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AI summary
The invention relates to improvements in compressors and, in particular, to an improvement in a method of controlling variable speed dynamic compressors to avoid 'motor overload as a result of choking.1 The invention therefore comprises a method of controlling a compressor to provide compressed gas at a target delivery pressure (Pt) and prevent excessive motor power consumption, the compressor being driven by a variable speed motor which has motor windings, wherein the gas inlet temperature (Tin), gas output delivery pressure (Pd), motor speed (Vm) and the motor winding temperature (Tmw) are continuously measured during operation of the compressor. The gas inlet temperature (Tin) is used to determine a predetermined maximum motor winding temperature (Tmwmax) limit. The maximum motor winding temperature (Tmwmax) is used (to set a maximum motor speed (Vmmax) limit. The maximum motor speed (Vmmax), target (Pt) and gas output delivery (Pd) pressures are used to control the actual motor speed (Vm) below the maximum motor speed limit (Vmmax).