FIELD OF INVENTION:
The present invention is generally related to the electrical machines.
More particularly, the invention relates to the hybrid excited
synchronous machine comprising permanent magnets and excitation
windings.
BACKGROUND OF INVENTION:
In order to provide magnetic flux for machine operation, many
synchronous generators are designed by using either excitation windings,
which is fed by a regulated source, or permanent magnets. Synchronous
generators containing excitation windings to produce magnetic flux can
be regulated over a wide range but winding losses occurs in the wound
field machines which results in decreasing the machine efficiency. In
order to improve the efficiency of synchronous generators, permanent
magnets can be used for providing magnetic flux instead of excitation
windings but permanent magnet synchronous generators cannot be
regulated though higher efficiency can be achieved.
The advantages of the excitation control of conventional synchronous
generators and the advantages of higher efficiency of permanent magnet
synchronous generators can be attained by a hybrid excited synchronous
generators comprising both excitation windings and permanent magnets
in the rotor core.
The parallel hybrid excitation generator (PHEG) has advantage of good
flux regulation as compared to series hybrid excitation generator (SHEG).

In addition to this advantage, the parallel hybrid excitation generator also
avoids demagnetization of permanent magnets which usually occurs in
series hybrid excitation generator. The PHEG can be further categorized
into two types according to location of the excitation source, namely the
parallel hybrid rotor excitation topology generators (PHRETG) with
excitation source located in the rotor core and the parallel hybrid stator
excitation topology generators (PHSETG) with excitation source located in
the stator core as disclosed in Y. Wang, Z. Deng, "Parallel hybrid
excitation machines and their control schemes for DC generation
system," IET Electr. Power Appl. 2012, Vol. 6, Iss. 9, pp. 669-680.
The parallel hybrid rotor excitation topology machines proposed so far
have utilized two rotor cores. A parallel hybrid excitation machine with
rotor excitation topology was proposed based on permanent magnet
synchronous machine and reluctance machine in the prior art. One rotor
core of this parallel hybrid excitation machine has permanent magnets
and the other rotor core of this machine is axially laminated anisotropic
part as disclosed in Chalmers, B. J., Akmese, R., Musaba, L., " Design
and field-weakening performance of permanent-magnet/reluctance motor
with two-part rotor," IET Electr. Power Appl. 1998, 145, (2), pp. 133-139.
Another type of parallel hybrid excitation machine with rotor excitation
topology was proposed based on permanent magnet synchronous
machine and conventional salient-pole synchronous machine in the prior
art. One rotor core of this parallel hybrid excitation machine has
permanent magnets and the other rotor core of this machine has
excitation windings as disclosed in Naoe, N, Fukami, T, Trial production
of a hybrid excitation type synchronous machine," Proc. Int. Con. on
Electrical Machines and Drives (IEMDC), Cambridge, USA, August 2001,
pp. 545-547.

Another type of parallel hybrid excitation machine, which uses two rotor
cores, with rotor excitation topology was proposed based on interior
permanent magnet synchronous machine and brushless synchronous
machine having two additional air gaps and electrical excitation in the
prior art. as disclosed in Zhuoran, Z., Jingjie, Z., Yangguang, Y., Bo, Z.,
"Construction and opearation principle of a novel coordinates structure
hybrid excitation synchronous machine," Proc. Chin. Soc. Electr. Eng.,
2009, 29, (33), pp. 83-89.
From the above existing rotor excitation topologies of parallel hybrid
excitation generators that is Chalmers, B. J., Akmese, R., Musaba, L., "
Design and field-weakening performance of permanent-
magnet/reluctance motor with two-part rotor," IET Electr. Power Appl.
1998, 145, (2), pp. 133-139, Naoe, N, Fukami, T, "Trial production of a
hybrid excitation type synchronous machine," Proc. Int. Con. on
Electrical Machines and Drives (IEMDC), Cambridge, USA, August 2001,
pp. 545-547, Zhuoran, Z., Jingjie, Z., Yangguang, Y., Bo, Z.,
"Construction and opearation principle of a novel coordinates structure
hybrid excitation synchronous machine," Proc. Chin. Soc. Electr. Eng.,
2009, 29, (33), pp. 83-89], it is observed that two rotor cores are being
used in the machine for flux regulation, which increases the volume of
the machine. So the rotor excitation topology of hybrid excitation
generator which utilizes only one rotor core is proposed in the present
invention to reduce the volume of the machine.
OBJECTS OF THE INVENTION:
An object of the invention is to propose an invention for accommodating
both the excitation windings and permanent magnets in the rotor core of
a hybrid excited synchronous generator.

Another object of the invention is to introduce a hybrid excited
synchronous machine which results in wide regulation of output voltage
and no risk of demagnetization of permanent magnets.
Another object of the invention is to make the hybrid excited
synchronous generator of reduced size.
SUMMARY OF THE INVENTION:
According to an aspect of the invention, an approach for accommodating
both excitation windings and permanent magnets in the rotor core of a
hybrid excited synchronous machine is proposed for achieving wide
regulation in the output voltage.
The rotor of the hybrid excited synchronous machine is significant in that
it has excitation windings slots provided at the bottom of the permanent
magnet slots as shown in Fig. 1.
The rotor of the hybrid excited synchronous machine is also significant in
that the slot openings for placing excitation windings in the excitation
winding slots of the rotor core are provided over the outer diameter of
rotor core and in between the permanent magnet slots and excitation
winding slots.
The size of the hybrid excitation generator is reduced by using only one
rotor core and wide voltage regulation with no risk of demagnetization of
permanent magnets is also achieved by innovative arrangement of
excitation windings and permanent magnets.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The advantages of the present invention will become apparent from the
following detailed description of embodiments with reference to the
accompanying drawings, in which:
Fig. 1 is a sectional view of the hybrid excited synchronous machine
comprising both permanent magnets and excitation windings.
Fig. 2 is the flux plot of the hybrid excited synchronous machine shown
in Fig. 1 when field windings are not excited.
Fig. 3 is output voltage of the hybrid excited synchronous machine
shown in Fig. 1 when field windings are not excited.
Fig. 4 is the flux plot of the hybrid excited synchronous machine shown
in Fig. 1 when field windings are excited.
Fig. 5 is output voltage of the hybrid excited synchronous machine
shown in Fig. 1 when field windings are excited.

DETAILED DESCRIPTION OF A PREFFERED EMBODIEMENT OF THE
INVENTION:
A hybrid excited synchronous machine is designed with rotor
configuration in which permanent magnet slots (102) are made per pole
with sufficient space between them as shown in Fig. 1. The excitation
winding slots (103) for placing field windings are made at the bottom of
the permanent magnets as shown in Fig. 1. The sufficient space between
the permanent magnet slots per pole is created for the magnetic flux path

of excitation windings. Exploiting the periodicity of hybrid excited
synchronous generator, only half of the cross section of hybrid excited
synchronous generator with proposed changes in the rotor (101) is shown
in Fig. 1.
The rotor of the hybrid excited synchronous machine is designed such
that the slot openings (104) for placing excitation windings in the
excitation winding slots of the rotor core are provided over the outer
diameter of rotor core and in between the permanent magnet slots and
excitation winding slots as shown in Fig. 1.
The invention suggests accommodating both excitation windings and
permanent magnets in the rotor core of a hybrid excited synchronous
generator achieves wide regulation in the output voltage along with
reduction in size of the generator.
The transient analysis using FEM software has been carried out on the
proposed hybrid excited synchronous generator with zero excitation of
field windings to determine and plot the flow of flux lines as shown in Fig.
2 and the output voltage as shown in Fig. 3. The rms value of the output
voltage obtained in this case is 168 V.
The transient analysis using FEM software has also been carried out on
the proposed hybrid excited synchronous machine with field windings
under rated excitation of 1500 Ampere turns per pole to determine and
plot the flow of flux lines as shown in Fig. 4 and the output voltage as
shown in Fig. 5. The rms value of the output voltage obtained in this case
is 327 V. Thus the output voltage in this case is 94% more when
compared to that in the case where field windings are not excited.
As the field windings are being excited such that the magnetic flux of

excitation windings always aids the magnetic flux of permanent magnets,
there will be no risk of demagnetization of permanent magnets. Thus the
proposed hybrid rotor excitation topology generator is compact in size
having wide voltage regulation capability with no risk of demagnetization
of permanent magnets.
Though four-pole hybrid excited synchronous machine is used for the
purpose of illustrating the invention, the present invention can be
extended to machines having more or less than four poles.

WE CLAIM:
1. A modified hybrid excited synchronous machine configured to
accommodate atleast a excitation winding slot (103) and a permanent
magnet slot (102) in a rotor core of the said machine wherein that
permanent magnet slot in positioned in the rotor core (101) occupying a
substantial space; wherein the excitation winding slot (103) in disposed
beneath the permanent magnet slot (102); wherein slot opening (104)
for placing excitation winding slot (103) in the excitation winding slots
(103) of the rotor core (101) and in between the said permanent
magnetic slots (102) and said excitation winding slot (103).
2. The modified hybrid excited synchronous machine as claimed in claim
1, wherein the hybrid excited synchronous is 2 pole or more.
3. The modified hybrid excited synchronous machine as claimed in claim
1, wherein the size of machine is compact and the risk of
demagnetisation of permanent magnets is zero.
4. The modified hybrid excited synchronous machine as claimed in claim
1, wherein the permanent magnetic slots are distanced to provide
magnetic flux path of excitation winding.
5. The modified hybrid excited synchronous machine as claimed in claim
1, wherein as illustrated in the accompanying drawings.