Magnetic Bearing Induction Motor for Direct-Drive Centrifugal Compressors
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Solution Overview
Problem
High-speed permanent magnet motors used in centrifugal compressors require expensive rare-earth materials and complex variable speed drives, while low-pressure refrigerants allow for the use of larger impellers and slower speeds, enabling the potential for high-speed direct drive induction motors with simplified VSDs at reduced costs.
Innovation Solution
A semi-hermetically-sealed induction motor with magnetic bearing assemblies supporting the shaft in both radial and axial directions, directly driving a centrifugal compressor using low-pressure refrigerants, which reduces the need for rare-earth materials and simplifies the VSD, allowing for efficient operation with a direct drive connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed permanent magnet motors are used in centrifugal compressors, then motor performance and speed capability are improved, but material cost increases due to expensive rare-earth materials and device complexity increases due to specialized variable speed drives
Solution Approach 1:
The patent replaces the permanent magnet motor system with an induction motor system that uses magnetic bearing assemblies for support. This substitution eliminates the need for rare-earth permanent magnets and complex specialized VSDs, while maintaining high-speed capability through the use of magnetic bearings that reduce friction and enable higher rotational speeds
Solution Approach 2:
The patent changes the motor type from permanent magnet to induction motor, and changes the bearing type from conventional to magnetic bearings. These parameter changes allow the system to achieve high-speed operation without requiring expensive rare-earth materials or complex control systems, thereby reducing both material cost and device complexity
2Stress or pressure
If medium pressure refrigerant is used in centrifugal compressors, then pressure rise requirement is met, but operating speed must be high which limits motor options
Solution Approach 1:
The patent introduces magnetic bearing assemblies as an intermediary technology that enables the compressor to operate at high speeds required for medium pressure refrigerant applications. The magnetic bearings provide frictionless support that allows the induction motor to achieve the necessary rotational speeds to meet pressure rise requirements, bridging the gap between motor type selection and compressor performance
3Speed
If low pressure refrigerant is used in centrifugal compressors, then larger diameter impellers can be used with slower operating speeds, but motor type selection is restricted
Solution Approach 1:
The patent segments the motor system into distinct functional components: an induction motor for cost-effective and simple manufacturing, and separate magnetic bearing assemblies for enabling high-speed operation. This segmentation allows the motor to be manufactured using conventional, simpler processes while still achieving the performance characteristics needed for low pressure refrigerant applications
4Ease of manufacture
If induction motor technology is used with simplified VSDs, then cost is reduced, but performance may be compromised compared to permanent magnet motors
Solution Approach 1:
The patent substitutes the permanent magnet motor system with an induction motor system enhanced by magnetic bearing assemblies. This substitution maintains motor performance and reliability by using magnetic bearings to eliminate friction and enable high-speed operation, while simultaneously reducing manufacturing cost by eliminating rare-earth materials and simplifying the VSD requirements
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 solution enables similar performance to permanent magnet motors at lower costs by utilizing low-pressure refrigerants and magnetic bearings, reducing material expenses and VSD complexity, while maintaining efficient operation and aerodynamic performance.
Implementation Method 1
a first magnetic bearing assembly located proximate the first end of the shaft and a second magnetic bearing assembly located proximate the second end of the shaft. The first and the second magnetic bearing assemblies are configured to support the shaft and associated loads
Implementation Method 2
a stator, a rotor, and a shaft with a first end and a second end. The rotor and the shaft are configured to rotate relative to the stator
Data Source
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AI summary
A sealed induction motor for a chiller assembly is provided. The induction motor includes a stator, a rotor, and a shaft with a first end and a second end. The rotor and the shaft are configured to rotate relative to the stator. The induction motor further includes a first magnetic bearing assembly located proximate the first end of the shaft and a second magnetic bearing assembly located proximate the second end of the shaft. The first and the second magnetic bearing assemblies are configured to support the shaft. The shaft is coupled to a centrifugal compressor using a direct drive connection.