FIELD OF THE INVENTION:
The present invention is generally related to the electrical machines. More particularly,
the invention relates to the hybrid excitation synchronous machines comprising
permanent magnets and excitation windings.
BACKGROUND AND PRIOR ARTS OF THE 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 has advantage of good flux regulation as compared to series hybrid excitation
generator. While the series hybrid excitation generator has a simple structure, the
parallel hybrid excitation generators proposed so far have either complex structures or
large size to overcome the drawbacks of series hybrid excitation generator. Few rotor
excitation topologies are discussed in the patents US9356479B2, EP2599196B1,
JP5673640B2, DE112013000314T5 and WO2014006294A1. Hence in order to achieve
the wide flux regulation in series hybrid excitation alternator like in parallel hybrid
excitation alternator, a new rotor configuration is proposed in the present invention.
OBJECTS OF THE INVENTION:
It is therefore an object of the invention is to propose a series hybrid excitation
alternator which will have wide flux regulation like parallel hybrid excitation alternator.
Another object of the invention is to propose an approach for accommodating both the
excitation windings and permanent magnets in the rotor of series hybrid excitation
alternator by proposing a suitable permanent magnet and excitation winding slot
configuration in the rotor.
SUMMARY OF THE INVENTION:
According to the aspect of the invention, a new rotor configuration for accommodating
both excitation windings and permanent magnets in the rotor of a series hybrid
excitation alternator is proposed for achieving wide regulation in the output voltage.

The rotor of the series hybrid excitation alternator is significant in that the permanent
magnet slots are made in the rotor by leaving space around each permanent magnet
slot. It means there is space left between outer diameter of rotor and permanent
magnet slot, space left in between permanent magnet slots and space left between
permanent magnet slot and excitation winding slot. The purpose of leaving space
around each permanent magnet slot is to allow the magnetic flux leakage within the
rotor.
The rotor of the series hybrid excitation alternator is also significant in that its excitation
winding slots are provided at the bottom of the permanent magnet slots. The slot
openings to the excitation winding slots are provided in between permanent magnet
poles so that the replacement of filed winding will become easy in the case of failure of
field winding. The slot openings to the excitation winding slots also act as magnetic flux
barrier between permanent magnet poles.
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 series hybrid excitation alternator comprising both
permanent magnets and excitation windings.

Fig. 2 is the flux line plot of the series hybrid excitation alternator when field windings
are positively excited.
Fig. 3 is the air gap flux density plot of the series hybrid excitation alternator when field
windings are positively excited.
Fig. 4 is output voltage of the series hybrid excitation alternator when field windings are
positively excited.
Fig. 5 is the flux line plot of the series hybrid excitation alternator when field windings
are not excited.
Fig. 6 is the air gap flux density plot of the series hybrid excitation alternator when field
windings are not excited.
Fig. 7 is output voltage of the series hybrid excitation alternator when field windings are
not excited.
Fig. 8 is the flux line plot of the series hybrid excitation alternator when field windings
are negatively excited.
Fig. 9 is the air gap flux density plot of the series hybrid excitation alternator when field
windings are negatively excited.
Fig. 10 is output voltage of the series hybrid excitation alternator when field windings
are negatively excited.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF
THE INVENTION:
A new rotor configuration is proposed in the present invention for a series hybrid

excitation alternator to achieve wide flux regulation capability. The rotor configuration
with permanent magnet slots and excitation windings slots is as shown in Fig. 1. The
permanent magnet slots 101 are made in the rotor by leaving sufficient space below the
outer diameter of the rotor. Sufficient amount of space is also left in between the
permanent magnet slots in the rotor. The excitation winding slots 102 are made below
the permanent magnet slots by leaving some space between permanent magnet slots
and excitation winding slots. The purpose of leaving space around the permanent
magnet slot is to allow the permanent magnetic flux to leak within the rotor so that the
net amount of air gap flux linking the stator winding will reduce. The series hybrid
excitation alternator shown in Fig. 1 is designed for four poles. Twelve number of
permanent magnet slots are made in the rotor cross section for easy assembly of
permanent magnets into the rotor. It means three permanent magnet slots will be used
for one number of pole.
The slot openings 103 for placing the filed winding into excitation winding slots are
provided in between the permanent magnet poles. As the slot openings to excitation
winding slots are provided separately without through permanent magnet slots, the
placement of field winding can be carried out even after the placement of permanent
magnets. The other advantage of this kind of providing slot openings is that the
replacement of field winding can easily be carried out in the case of failure of filed

winding during operation. The slot openings of excitation winding slots also act as flux
barriers between permanent magnet poles of rotor.
When the field windings are not excited, some of the magnetic flux will leak within the
rotor and only some of the magnetic flux will link the stator winding. When the field
windings are positively excited (electromagnet pole and permanent magnet pole are
same), the leakage flux within the rotor reduces and the air gap flux will increase to the
maximum value. Similarly when the field windings are negatively excited
(electromagnet pole and permanent magnet pole are different), the leakage flux within
the rotor increases to the maximum value and hence the air gap flux will decrease.
Thus in the present invention, an approach proposed for accommodating both
excitation windings and permanent magnets in the rotor of a series hybrid excitation
alternator achieves wide regulation in the magnetic flux density.
The transient analysis using FEM, software has been carried out on the proposed series
hybrid excitation alternator with field windings positively excited to determine and plot
the flow of flux lines (as shown in Fig. 2), the air gap magnetic flux density (as shown
in Fig. 3) and the output voltage waveform (as shown in Fig. 4). The peak air gap
magnetic flux density is 0.47 T. The RMS value of phase output voltage is 388 V. The
transient analysis using FEM software has also been carried out on the proposed series
hybrid excitation alternator with field windings unexcited to determine the plot the flow
of flux lines (as shown in Fig. 5), the air gap magnetic flux density (as shown in Fig. 6)

and the output voltage waveform (as shown in Fig. 7). The peak air gap magnetic flux
density is 0.3 T. The RMS value of phase output voltage is 257 V. Similarly the transient
analysis using FEM software has also been carried out on the proposed series hybrid
excitation alternator with field windings negatively excited to determine the plot the
flow of flux lines (as shown in Fig. 8), the air gap magnetic flux density (as shown in
Fig. 9) and the output voltage waveform (as shown in Fig. 10). The peak air gap
magnetic flux density is 0.11 T. The RMS value of phase output voltage is 66 V.

WE CLAIM:
1) A rotor (100) for a series hybrid excitation alternator configured to accommodate
both excitation windings and permanent magnets,
characterized by, slots (101) for permanent magnets, and slots (102) for
separate excitation winding.
2) The rotor (100) as claimed in claim 1, wherein, permanent magnet slots (101)
are configured to leave sufficient space below the outer diameter of the rotor (1)
and in between two permanent magnet slots, characterized to allow magnetic
flux to leak within the rotor for regulation.
3) The rotor (100) as claimed in claim 1, wherein, excitation winding slots (102)
below the permanent magnet slots (101) are configured to leave some space
between permanent magnet slots and excitation winding slots (102),
characterized to allow magnetic flux to leak within the rotor for regulation.
4) The rotor (100) as claimed in claim 1, wherein slot openings (103) for excitation
winding are provided in between permanent magnet poles, facilitating to act as
flux barriers between permanent magnet poles of rotor and replacement of field
winding.

5) A series excited hybrid excitation alternator (200) along with the rotor (100),
wherein, wide regulation of flux path in the alternator provides wide regulation in
the output voltage.