High-speed In-line Blower and Integrated Hybrid Controller for a Space Application Driven by a Permanent Magnet Motor on Active Magnetic Bearings
NASA, an independent agency of the U.S. federal government responsible for aeronautics and space research, was seeking to procure a next generation blower system for an exploration class CO2 removal system, which will be installed and tested on the international Space Station (ISS). The blower is a subcomponent of a larger system that processes the cabin air to remove carbon dioxide and maintain a breathable environment for the ISS inhabitants.
The current CDRA system on the ISS has relied upon a foil air bearing supported blower, which is no longer a readily available technology and the current technology must operate on the extreme end of performance envelope in order to meet the future CO2 removal requirements. Conventional bearing systems have a short life span, are usually susceptible to contamination, and usually require maintenance to meet the lifetime requirements of the system. NASA needed a highly reliable blower that could increase the life of the system, operate in the micro gravity space environment and withstand the ingestion of foreign particles in the air stream. The new blower also had to fit into the same length, width and height envelope as the foil bearing supported heritage blower.
Calnetix proposed using a high-speed permanent magnet motor on active magnetic bearings (AMBs) in an integral housing as a replacement to the existing blower. Calnetix machines on AMBs have been in operation for over 17 years in highly demanding applications. The company’s proven technology and know-how was applied to the NASA development.
Calnetix designed and built a blower system, which includes a compact Momentum™ In-line Blower on magnetic bearings and an integrated Continuum™ Dual Controller to drive the blower. The in-line blower consists of a centrally located five-axis Powerflux™ AMB system, backup bearings, an overhung Magnaforce™ permanent magnet motor and a centrifugal impeller in a very compact package. Magnetic bearings were used in place of conventional bearings to significantly increase the performance, reliability and lifespan of the system due to frictionless operation. AMBs also operate at very high speed, are tolerant to particle contaminants and provide oil-free and maintenance-free operation.
The dual controller consists of a Variable Speed Drive (VSD) for the motor and an AMB controller in a single compact package that supports speeds up to 60,000 RPM. Calnetix's AMBs were used to eliminate lubrication and rotating drag losses in the system. High-efficiency and high-speed switching technology for both the VSD and AMB controls were factored into the design. Two independent digital signal processors (DSPs), one dedicated for the VSD and a second for the AMB were used to achieve a fail-safe operation.
The key design challenge was that the active magnetic bearing system, including back up bearings and position sensors had to be miniaturized to fit into a highly constrained space. To help create a compact design, the bearing package located at the central part of the machine was used with a centrifugal impeller at the air inlet and an overhung permanent magnet synchronous motor at the outlet of the blower. The air flows through an annulus around the internal components.
This is the first time a magnetically levitated system has been qualified for use in a space station. The unique blower system design delivered by Calnetix meets the following requirements:
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