FIELD OF THE INVENTION
The present invention generally relates to the electrical machines. More particularly, the invention relates to a process for maintaining the designed movement of sun tracker of a solar panel under strong wind flow environment. The invention further relates to an electromagnetic brake for reducing undesired oscillations of solar panels due to strong wind.
BACKGROUND OF THE INVENTION
Due to scarcity of non-renewable sources of energy, alternate sources of energy are being exploited. Solar energy is the most abundant among all other available energy resources and it is relatively easy to convert it into electrical energy. Hence installation and operation of solar panels has become very popular to generate electrical energy. Instead of fixed solar panels whose movement is fixed irrespective of the position of sun, solar panels along with sun tracking arrangement are being widely used for maximum absorption of solar energy. Unlike fixed solar panel, the sun tracking solar panel is perpendicular to the sun at any given time in a day absorbing the maximum solar energy possible. A major difficulty in operating such sun tracking solar panels is that though the solar panel moves in small steps from east to west in a day, it is subjected to greater torque in the presence of large wind causing unwanted oscillations.
WO2007025618A1 describes a slaving system for solar plants which can be attached, which is swivelling around a vertical axle, in order to make the azimuth adjustment of a solar panel. A Schwenkkopf propelled by a gear motor, which influences over a mitre gear. A circling price increase drives a middle tappet out vertically, in order to make a daily temporal change of the inclination of the solar panel. An auxiliary curve overlays this daily temporal

movement, in order to adapt the inclination of the seasonal change of the position of the sun.
DE102005042478A1 describes a tracking system for solar units comprising a pivot head for mounting on a stand which may be rotated about a vertical axis in order to carry out the azimuthal orientation of a solar panel. The pivot head is driven by a geared motor, acting by means of a bevel gear. A cam control extends a middle pin vertically, to carry out a change in inclination of the solar panel dependent on the time of day. An additional cam control overlays the time of day movement in order to adjust for the inclination due to the change of sun position dependent on the time of year.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a process for maintaining the designed movement of the sun tracking arrangement to reduce the solar panel oscillations due to strong wind force.
Another object of the invention is to propose an electromagnetic brake for reducing undesired oscillations of solar panels due to strong wind.
SUMMARY OF THE INVENTION:
According to one aspect of the invention, an electromagnetic brake is proposed for reducing the oscillations of the solar panel that are caused due to strong wind. The electromagnetic brake works on the principle of creation of an electromagnetic filed between the rotating part and the static part of the solar panel so as to generate a torque opposing the motion of the rotating part.

The electromagnetic brake proposed in the present invention is designed as an electrical machine with inner and outer rotors and stator. The inner and outer rotors are fixed to a flange which is welded to one of the cross beams. The inner rotor of the electromagnetic brake carries permanent magnets on the outer surface while the outer rotor carries permanent magnets on the inner surface.
The stator of the electromagnetic brake is mounted to a column having windings on both inner surface and outer surface. The winding on the inner surface of the stator faces the permanent magnets arranged on the outer surface of the inner rotor wherein the winding on the outer surface of the stator faces the permanent magnets arranged on the inner surface of the outer rotor.
The amount of torque developed depends on the strength of the magnetic field between the rotor and the stator. It also depends on the rate of the change of magnetic flux. The more the rate of change of flux the more will be the torque generated in the electromagnetic brake. The rate of change of flux is proportional to the speed at which the rotating part moves. Thus the greater amount of torque will generate opposing the motion of the rotating part due to large winds while allowing the solar panel to move in smaller steps for sun tracking as the generated torque in this case is of very low value.
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 view of the solar panel supported by beams and columns.
Fig. 2 is a view of the solar panel along with the electromagnetic brake.

DETAILED DESCRIPTION OF THE INVENTION
A central beam 101 which is free to rotate through anti friction bearing system 102 is supported by two columns 103 as shown in Fig. 1. Solar panel 104 is mounted over the cross beams 105 which are supported by a central beam 101 as shown in Fig. 1. In order to absorb the maximum solar energy, the solar panel is coupled to the stepper motor for tracking the sun. Unlike fixed solar panel, the sun tracking solar panel is perpendicular to the sun at any given time in a day absorbing the maximum solar energy possible. Though the solar panel moves in small steps from east to west in a day, it is subjected to greater torque in the presence of large wind causing unwanted oscillations. The object of the invention is to reduce these unwanted oscillations due to wind by developing counter torque with the help of electromagnetic brake proposed in the present invention.
The working principle of electromagnetic brake is creation of electromagnetic field between the rotating part and the static part which will establish a torque opposing the motion of the rotating part. The electromagnetic brake proposed in the present invention is a sector of the electrical machine which comprises of inner rotor 201, outer rotor 202 and stator 203 as shown in Fig. 1.
One end of the stator of electromagnetic brake is mounted to the column as shown in Fig. 2 while the other end of the stator of electromagnetic brake is left freely. The stator of electromagnetic brake consists of copper windings 204 on both inner surface and outer surface as shown in Fig. 2. The circumferential length of the stator has to be chosen to be maximum but at the same time it must be ensured that the stator doesn’t hit the solar panel when it comes to its extreme position.

The inner rotor of electromagnetic brake consists of permanent magnets 205 with alternate north and south poles on the outer surface while the outer rotor consists of permanent magnets with alternate north and south poles on the inner surface as shown in Fig. 2. One end of the inner rotor is fixed to the flange 206 which is welded to one of the cross beams while the other end of the inner rotor is left freely as shown in Fig. 2. Similarly one end of the outer rotor is also fixed to the flange below the inner rotor while the other end of the outer rotor is left freely as shown in Fig. 2. The circumferential length of the rotors has to be chosen to be maximum but at the same time it must be ensured that the rotors don’t hit the column when the solar panel comes to its extreme position.
The inner and outer rotors and stator are to be aligned such that the stator passes in between the inner and outer rotors as the solar panel moves. When the stator is in between the inner rotor and outer rotor, the winding on the inner surface of the stator faces the permanent magnets arranged on the outer surface of the inner rotor while the winding on the outer surface of the stator faces the permanent magnets arranged on the inner surface of the outer rotor.
The braking torque developed is proportional to the strength of the magnetic field between the rotor and the stator. It means the stronger the permanent magnets used in the electromagnetic brake the stronger will be the braking torque developed. The braking torque is also proportional to the rate of the change of magnetic flux. The more the rate of change of flux the more will be the torque generated in the electromagnetic brake. The rate of change of flux is proportional to the speed at which the rotating part moves. Thus the greater amount of torque will generate opposing the motion of the rotating part due to large winds while allowing the solar panel to move in smaller

steps for sun tracking as the generated torque in this case is of very low value.
The materials used for manufacture of rotor and stator are of solid instead of laminations because the more the eddy currents that are induced in the rotor and stator the more will be the opposing torque generated to the unwanted solar panel oscillations created due to wind. The ferromagnetic material which has higher core losses is preferred compared to the ferromagnetic material which has lower core losses for manufacture of rotor and stator parts.
Though stator with windings on both the inner diameter and outer diameter along with inner rotor and outer rotor is used as an electromagnetic brake for purpose of illustrating the present invention, a single sided structure alone can be used if the braking torque generated is sufficient. It is also proposed that the windings in the stator need not be used if the sufficient braking torque is generated due to the eddy currents induced in the stator and rotor parts due to change in the magnetic flux.

WE CLAIM :
1. The invention further relates to an electromagnetic brake for reducing
undesired oscillations of solar panels due to strong wind, the solar
panel (104) mounted over cross (105) supported by a central beam
(101), the central beam (101) being free to rotate though an anti-
friction bearing (102) and supported by a pair of vertical columns
(103), the electromagnetic brake comprising :-
- an inner rotor (201), an outer rotor (202);
- a stator (203) consisting of copper windings (204) on both inner surface and outer surface;
- a first plurality of permanent magnets (205) placed on the outer surface of the inner rotor (201), and a second plurality of permanent magnets (205) disposed on the inner surface of the outer rotor (202);
- one each flange (206) welded respectively on first side of the inner rotor (201)and on a second side of the outer rotor (202),
wherein the inner and outer rotors including the stator are aligned such that the stator is enabled to pass through the passage between the inner rotor and the outer rotor corresponding to the movement of the solar panel, and wherein the electromagnetic brake generates an electromagnetic field between said rotating and static components so as to establish a matching torque opposing any undesired oscillating motion of the solar panel.
2. The brake as claimed in claim 1, wherein the rotor and stator are
made of solid material instead of laminations as more eddy currents
are induced in it resulting in increase in the braking torque.

3. The brake as claimed in claim 1, wherein the stator does not use the
copper windings when sufficient braking torque as generated due to the eddy currents induced in the stator and rotor parts due to change in the magnetic flux.