|
Technology
| The E-core Transverse Flux Machine (ETFM) is a new mechanical design of the Switched Reluctance Machine (SRM). The new design is patented by Aalborg University, Institute of Energy Technology in Denmark. |
The ETFM is a transverse flux machine, which means the flux is running in the axial direction,
in contrast to traditional switched reluctance machines, where the flux runs radial. The
stator and rotor poles are constructed of traditional EI-cores, which are well-known
from transformers. The stator poles consist of
the E-cores and the rotor poles consist of the
I-cores. Due to the transverse flux path, the
stator poles are operated locally and the
space in the centre of the machine is “free”.
A rotor is of course necessary to fasten the
I-cores, but there is left space, where a
gearbox can be integrated.
|
Cross sectional view of the ETFM |
| The segmental construction of the ETFM makes it possible to make the pole configuration almost free. The SRM has some fixed pole configurations, like 6/4, 12/8, 18/12 for three phase machines. Any combination in between are impossible because of the flux path. The ETFM has both the traditional pole configuration, but also some uneven numbers, like the 15/10 shown in the right figure. This flexible pole configuration makes it very easy to design the machine for any application. |
The ETFM is operated exactly like the
traditional switched reluctance machine.
The reluctance principle of the switched
reluctance motor was discovered in 1838,
but the motor could not realize its full potential until the modern era of power electronics
and FEM. Especially in the late 1980s and in
the 1990s has the switched reluctance motor become interesting, due to the development
of MOSFETS and IGBT’s
|
|
The ETFM can operate in all four quadrants depending on the topology of the power electronic converter. AWS has developed a power electronic converter for 24 V battery systems, which are commonly used in automotive. The power stage consists of three asymmetrical H-bridges, one for each phase, which makes four quadrant operations possible. The power stage has also a brake chopper circuit for dumping excessive energy during deceleration or generator operation. The power electronic converter is easily scaled to any battery voltage system in the range 12-48 V.
The potential of the ETFM is very interesting, because the new mechanical design makes it possible to integrate the ETFM in applications, where the axial length of the machine must be short. An example is the indoor cycle, eTenzor, developed by AWS Technology. The ETFM, with integrated gearbox, is placed directly between the pedals, which make the design homogeneous.
The key features of the ETFM are:
· Robustness – The ETFM is simple in structure and the machine is fault tolerant, due to the
separated phase-windings. No windings or magnets on the rotor.
· Efficiency – Maintains higher efficiency over a wide speed and load area.
· Starting Torque – The ETFM provides a high starting torque, up to 3-4 times nominal.
· High speed – Wide speed range, up to 10,000 rpm.
· Low speed – Maintain full rated torque down to zero speed.
· 4 Quadrant operation – Depending on the power electronic converter.
· Low cost – Simple construction and thereby low manufacturing cost.
· Gearbox – A gearbox can be integrated in the machine without increasing the physical size.
· Shape – The ETFM has a short axial length, approximately the width of the E-cores
|
|
_________________________________________________________________________ |
|
