FIELD OF THE INVENTION
The present invention relates to a reliable and energy-efficient PM-alternator for
auxiliary power applications.
BACKGROUND OF THE INVENTION
The conventional alternators are excited with field winding"s". As the field windings
are mounted on a rotor, the supply to field winding is given through a slip ring and a
brush gear. The PM alternator is excited by several magnets mounted on the rotor and
requires no winding nor slip ring & brush gear. Currently inductor alternators with
voltage regulators, batteries and inverters are used for energizing fan, lights in
industrial and railway applications. The inductor alternators of the prior art have field
winding for excitation and hence it is bulky. The alternator output voltage is rectified
using a controller rectifier, a magnetic amplifier, and due to this, the response of the
alternator is very slow. Hence the efficiency of the inductor alternator system is low.
OBJECT OF THE INVENTION
The object of invention is to propose a reliable and energy efficient PM-alternator for
auxiliary power applications.
SUMMARY OF THE INVENTION
According to the invention, a permanent magnet (PM) alternator "is",
electromagnetically and mechanically optimized with voltage regulator. The rotation of
the permanent magnet rotor induces three phase voltages in the stator winding. The
output voltage of the alternator changes in magnitude and frequency due to change in
process speed. Hence it is rectified and controlled using voltage regulators. The dc
output power of the regulator is used for charging the batteries. Even though the
alternator has no field control, the alternator is controlled by a thyristor controller to
keep the full load voltage of the alternator within ±2% of its rated value.
The invention thus provides a compact PM Alternator with enhanced efficiency by
using high energy NdFeB magnets. The efficiency of the inventive PM alternator is
91%, which is 4% higher than prior art inductor alternators used for industrial power
applications. The average weight of the optimized PM alternator is only 70% of weight
of Standard Inductor alternator.
According to the invention, the magnets are optimized for operation of the alternator
right from 400rpm to2500rpm to produce rated output with enhanced efficiency. The
winding, stator & rotor slots, diameter, and core are configured to achieve (i) maximum
output with minimum weight and (ii) sinusoidal waveform with regulation <2%.
The optimization of the magnet size, winding, main "dimension", stator stamping
enables achieving a "91"% efficiency which is 4% higher than the existing one. The,
use of active material is further optimized to get 70% of weight of a standard
alternator.
The alternator has 3 phases A.C. winding in the stator, and the magnets are inserted
in the periphery of the rotor. Stator core is built with 0.5m thick silicon steel having a
minimum loss.
The inventive alternator is optimized electromagnetically based on a developed flux
plot. This plot shows the distribution of flux line and density at different parts of the
magnetic circuit. The dimension of the magnetic circuit is varied to minimize leakage
of the flux. Stator, rotor, winding details and their material properties are fed into
developed magnet software and the flux plot is outputted.
The invention provides a compact PM alternator, having a plurality of high energy
NdFeB magnets. The developed PM alternator has no field winding, hence efficiency
is better and more reliable than standard alternators. It has no field control and hence
the response is fast. With the absence of field winding, the PM alternator is more
compact than a standard alternator.
BRIEF DESCRIPTOR OF THE ACCOMPANYING DRAWINGS
Fig. 1 shows a flux plot for a "16 & 12 poles" PM alternators" according to the present
invention.
Fig. 2. shows an assembly drawing for the PM alternator of the invention.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention the permanent magnet alternators consists of a stator
having three phase winding and rotor with a plurality of high energy permanent
magnets inserted inside its slots. The rotation of the rotor in the permanent magnets
induces three phase voltages in the stator winding. The magnets are not only fixed by
adhesive inside the rotor slots but are also mechanically locked on both ends of the
rotor by end plates. The output voltage of the alternator changes in magnitude and
frequency due to change in operational speed. Hence, the output voltage is rectified
and controlled using voltage regulator "for charging batteries. The flux plot of
the inventive PM Alternator is shown in Fig.1.Even though the alternator has no field
control, the alternator is controlled by a thyristor controller to keep the full load of the
alternator within ±2% of its rated value.
As shown in figure-2, a stack (1) is assembled into a stator frame (3), a rotor hub (2)
onto a shaft (4), bearings (5) into end covers (6&7). An optimized winding (8) and an
air gap is maintained between the stator stack (1) and the rotor hub (2). After fixing
the magnets into the rotor hub (2), the rotor assembly is inserted into the stator
assembly with a screw jack fixture. Table-I depicts the technical parameters of the
inventive PM alternator. The technical parameters are decided through optimizing of
the design data of the alternator in a magnet software. The stator and rotor diameter,
slot sizes, magnet size, winding details enables enhancement in efficiency and
performance of the alternator.
WE CLAIM:
1. A reliable and energy-efficient permanent magnet based alternator for auxiliary
power applications, comprising:
-a stator stack disposed "in" a stator frame;
a rotor stack with rotor hub disposed on a rotatable shaft;
-a plurality of "optimized" high power magnets placed inside a corresponding number
of slots configured on the rotor hub;
-the rotor shaft supported by at least one each drive end and non-drive end bearing,
the bearings being provided with end covers; the stator stack is configured with
optimized stator windings maintaining a gap between the stator stack and the rotor
hub.
2. A reliable and energy-efficient permanent magnet based alternator for auxiliary
power applications, as substantially described and illustrated herein with reference to
the accompanying drawings.

A reliable and energy-efficient permanent magnet based alternator "for" auxiliary
power applications, comprising a stator stack disposed "in" a stator frame; a rotor
stack with rotor hub disposed on a rotatable shaft; a plurality of high power magnets
placed inside a corresponding number of slots configured on the rotor hub; the rotor
shaft supported by at least one each drive end and non-drive end bearing, the
bearings being provided with end covers; wherein the stator stack is configured with
optimized stator windings maintaing a gap between the stator stack and the rotor hub.