Application Of Sr Motors 2h6b37

Application of SR Motors

George Holling Rocky Mountain Technologies Inc. PO 1595, Riverton, UT 84065 ph.: (801) 446-8403 e-mail: [email protected]

Overview • The SR motor – physics and characteristics • Where to apply SR Motors • Pittfalls when applying SR motors • The future

The SR motor • the torque profile

The SR motor • the torque profile – at base speed

The SR motor • the torque profile – at base speed

efficiency 90.4% (above)

efficiency 87.6% (below)

The SR motor • the torque profile – changes with speed and load – changes with the motor geometry • rule of thumb: more phases less ripple • 4 phase vs. 3 phase motors

The SR motor • audible noise – audible noise and torque are related • reduced torque ripple -> reduced audible noise • more phases -> less noise • short flux path -> less noise – reducing audible noise results in • reduced performance, or • increased cost

The SR motor • size and geometry – it appears that SR motors require certain geometries to be efficient – length = diameter appears to be good geometry

• pancake motors appear less desirable • Very small diameter motor (<70mm) appear less desirable

– low number of poles per phase appears to improve performance

• exceptions exist • thermal considerations

The SR motor • efficiency – the efficiency of the SR motor is maximized at its rated load – while the SR motor will operate efficiently over a wide speed range it will not do so over a wide load range

Applying the SR motor • Advantages (perceived): – no magnets

• cost

– favors large motors

• contamination

– may not be significant in most applications

• internal and ambient temperature

– subject to magnet materials – sensorless SR motors can potentially operate in high temperature environments

– excitation waveform

• no waveform shaping – generic, simple, low cost control

• hall/optical sensor are very suitable – rugged, low cost solutions – hall sensors are more rugged that optical sensors

• very good performance at high speeds

Applying the SR motor • Advantages (perceived): – ease of sensorless control

• large inherent inductance changes – efficient algorithms to determine sensorless position

• low cost – cost of electronics less that sensors – no sensor wiring

• no devices on the motor – small size – high temperature environments

• reliability – no sensor wiring

Applying the SR motor • Disadvantages (perceived): – small airgap

• contamination • bearings and materials • assembly cost

– audible noise – new technology

• lack of infrastructure • lack of experience • inherent risk

Applying the SR motor • applications should focus on those areas where the SR is clearly superior – high efficiency at rated loads

• pumps • compressors • fans

– ease of sensorless

• highly efficient, hermetically sealed compressors

– high temperature ambient environments

• aerospace • drilling

– cost sensitive, large motors with high power density

• traction drives • linear SR motors

– good power density and efficiency at high speed

• high speed compressors • turbine starter/generators

Applying the SR motor • Single phase SR motors – Specialty applications • generators • electric assisted bike

Applying the SR motor • Two phase SR motors – low starting torque – audible noise • some patented technologies perform better – most suited for unidirectional operation • bi-directional operation is possible under certain conditions – typical applications include • blower • fan • pump • electric assist

Applying the SR motor • Three phase SR motors – variable speed applications – bi-directional operation – personal note: • least likely to succeed

Applying the SR motor • Four phase SR motors – fault tolerant operation • aerospace • fuel pump • drilling – low cost alternative • traction drives – high speed motor • generator

Applying the SR motor • More than four phase SR motors – Specialty applications

Pittfalls when applying SR motors • operation with suboptimal firing angles – power and efficiency can be significantly reduced – audible noise can be significantly higher – heating losses can be significantly higher

• sensors – Hall sensor can reduce performance

• duty cycle distortions reduce performance • sensors and magnet wheels are subject to heat related failure

– Optical sensors can reduce performance

• • •

duty cycle distortions reduce performance sensors and magnet wheels are subject to heat related failure sensors are subject to contamination

Pittfalls when applying SR motors • operation significantly below rated power – efficiency can be VERY poor

• production variations – production variations can be significantly larger than those of BLDC motors – high quality motor steels and good production methods are mandatory

Examples of SR motors & drives

Sensorless SR drive

Examples of SR motors & drives

SR Production Motor

Examples of SR motors & drives

SR Traction Drive

The future of SR motors • SR motor applications are proliferating • many OEM develop custom SR products in-house due to lack of “off the shelf” components

• SR motors will most likely penetrate selected niche applications at the OEM level