Applicant's Name: VALAGAM RAJAGOPAL RAGHUNATHAN

Application no: 1830/CHE/2013

FIELD OF THE INVENTION

This invention generally relates to a wind turbine and braking system, and more particularly to an eddy current braking system for safely stopping the wind turbine during shut down or emergency stop.

BACKGROUND OF THE INVENTION

In recent times, wind turbines have received better attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines with protective braking system to avoid damage at shut down and emergency stop/high condition.

The conventional wind turbines include disk brakes or drum brakes or mechanical braking system for stopping the wind turbine, but these are not acceptable since they are subjected to high wear.

To avoid the above problems, some turbines have the capability to vary the pitch of the blades to reduce the rotational speed of the turbine. This prevents the turbine from rotating at an unsafe speed, but such systems are complex.

The prior art PCT/IN2012/000082 discloses about a system for controlling the rotational speed of the wind turbine by means of drag device. The prior art comprises of drag device pivoted at the arms which is held in no drag position by the tension spring as long as the turbine operates within the rated speed. While the turbine exceeds the rated speed, the centrifugal force corresponding to that speed exceeds the designed value of spring which causes it to lose the tension over the drag device. The created drag force retards the rotation of the turbine and brings the rotational speed under control. The drag device is

art needs external braking system to slow down the speed of the wind turbine.

As per the above explanations, we consider all the types of braking system such as disk brakes, drum brakes, mechanical brakes systems and individual pitch control system are capable of stop or reduce the speed of the wind turbine in unsafe wind speed condition and then friction loss, high wear and practical usage studied. It was realized that the present invention could have an improved safety features and could safely and easily slow down the speed of the wind turbine without any additional braking system.

Thus, there is a need for braking system to gradually control the rotational speed of the wind turbine without any external braking system arrangements.

OBJECT OF THE INVENTION

An object of the invention is to provide a control system for controlling the speed of wind turbine during shut down or emergency stop.

Another object of the invention is to eliminate the need of external braking system.

Yet another object of the invention is to utilize a generator as a braking system.

Yet another object of the invention is to utilize a selected number of generators as a braking system among the plurality of generators.

Yet another object of the invention is to utilize generated power of plurality of generators for braking the turbine.

Yet another object of the invention is to enable eddy current braking on selected number of generators for braking the wind turbine.

Further object of the invention is to control a wind turbine at real time.

SUMMARY OF THE INVENTION

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wind speed and stopping/protecting the turbine at predetermined conditions such as shut down, emergency stop, etc.

The wind turbine with braking system comprises of a main driving means, a plurality of generators, a small driving means, a tower assembly, a control means, a sensing means, a power supply means and a rotor assembly.

Each generator of the wind turbine having at least one small driving means which is rigidly attached with generator shaft. Each of the above mentioned small driving means rotatably and frictionally _, engaged with the main driving means. The control means monitors the required parameters by means of plurality of sensing means for controlling the wind turbine while braking and power generation.

Power generation: At rated wind speed/sufficient wind speed, the main driving means rotates along with the rotor assembly thereby plurality of small driving means are driven for generating power.

Braking or emergency stop: At emergency stop condition, the control means allows generated power supply of plurality of generators into the primary filed of the selected number of generators thereby emf induced in a secondary field so speed of the wind turbine is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 illustrates one of the embodiment of the invention which shows the block diagram of the wind turbine braking system.

Fig 2 illustrates one of the embodiment of the invention which clearly shows braking system of the wind turbine with multi generator assembly. DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses about a wind turbine with braking system for generating power at rated wind speed and stopping/protecting the turbine at predetermined conditions such as shut down, emergeney-stop etcT ^{^} Hereafter w components orthe wind turbine, while power generation it performs as a generator, while braking it performs as a motor.

One of the preferred, embodiment of the invention discloses about a wind turbine with braking system for generating power at rated wind speed and stopping the turbine at predetermined conditions by means of plurality of generators, the said wind turbine with braking system comprises of a main driving means, a plurality of generators, a small driving means, a tower assembly, a control means, a power 95 _, supply means and a rotor assembly. The said main driving means is rotatably secured on the said tower assembly along with plurality of generators, each of the said generators having rigidly attached to - at least one said small driving means and said each small driving means rotatably and frictionally engaged with the said main driving means, wherein the said main driving means rotates along with the said rotor assembly at rated wind speed thereby main driving means drives the plurality of driving 100 means for generating power, wherein, when the control means detects the predetermined stopping condition then the said control means diverts the generated power supply of plurality of generators into the said primary filed of the said selected number of generators thereby emf induced in a secondary field thereby speed of the wind turbine is lowered.

105 Another preferred embodiment of the present invention discloses about a wind turbine with braking system for generating power at rated wind speed and stopping the turbine at predetermined conditions by means of plurality of generators. The said wind turbine with braking system comprises of a main driving means, a plurality of generators, a small driving means, a tower assembly, a control means, a power supply means and a rotor assembly. The main driving means is rotatably secured on the said no tower assembly along with plurality of generators, each of the generators having rigidly attached to at least one said small driving means and each small driving means rotatably and frictionally engaged with the main driving means, wherein the said main driving means rotates along with the said rotor assembly at rated wind speed thereby main driving means drives the plurality of driving means for generating power. Wherein, when the control means detects the predetermined stopping condition then the said lis control means allows power supply from the power source to the said primary filed of the said plurality of generators thereby emf induced in a short-circuited secondary field thereby speed of the wind turbine is lowered. Wherein the said power source can be a stored power or grid power or generated power of plurality of generators or self-excited power of generators or combination thereof.

120 Yet another embodiment of the invention showed in figure 1 , which discloses about VFD based control — ._— system of wind turbine. Where 6 motors are controlled by VFD. Two motors are used for braking and four motors are used for power generation. Regenerative braking system is used for run the two braking motors.

125 Yet another embodiment of the invention discloses about control means, wherein the control means may be a programme logic controller or VFD or SCADA or micro controller or microprocessor for controlling braking action based on plurality of sensing means. _ Yet another embodiment of the invention discloses about driving means which is a combination of main driving means and small driving means. The main driving means and small driving means are driven by - gear or gearless means.

Yet another embodiment of the invention discloses about a method for controlling a speed of the vertical axis wind turbine by means of speed control system (shown in figure 3). The method comprises the steps of:

Step 1 : detecting a speed of the turbine and comparing with predetermined speed limit,

Step 2: allowing the control system to keep the plurality of or selected number of motors in generation mode,

Step 3: allowing the control system to enable eddy current braking for selected number/plurality of generators by using generated power and/or gird power and/or stored power source to control the speed of the wind turbine.

wherein, if the detected speed limit of step 1 is below the predetermined speed condition, step 2 is repeated until change in turbine speed limit,

wherein, if the detected speed limit of step 1 is above the predetermined speed limit step 3 is repeated until change in turbine speed limit.

Yet another embodiment of the invention discloses about a predetermined stopping condition of wind turbine. The stopping condition is determined based on various parameters such as wind speed, rotor speed, generator speed, temperature of components or combination of thereof.

Yet another embodiment of the invention discloses about a horizontal axis wind turbine with eddy current braking system for generating power at rated wind speed and stopping the turbine at predetermined conditions by means of plurality of generators, the said wind turbine with braking system comprises of a main driving means, a plurality of generators, a small driving means, a tower assembly, a control means, a power supply means and a rotor assembly. The said main driving means is rotatably secured on the said tower assembly (Horizontal axis) along with plurality of generators(Horizontal Vertical axis), each of the said generators having rigidly attached to at least one said small driving means and said each small driving means rotatably and frictionally engaged with the said main driving means, wherein the said main driving means rotates along with the said rotor assembly at rated wind speed thereby main driving means drives the plurality of driving means for generating power, wherein, when the control means detects the predetermined stopping condition then the said control means diverts the generated power supply of plurality of generators into the said primary filed of the said selected number of generators thereby emf induced in a secondary field thereby speed of the wind turbine is lowered.

165 -

Yet another embodiment of the invention discloses about a Vertical axis wind turbine with eddy current braking system for generating power at rated wind speed and stopping the turbine at predetermined conditions by means of plurality of generators, the said wind turbine with braking system comprises of a main driving means, a plurality of generators, a small driving means, a tower assembly, a control

170 means, a power supply means and a rotor assembly. The said main driving means is rotatably secured on the said tower assembly (Vertical axis) along with plurality of generators(Horizontal/Vertical axis), each of the said generators having rigidly attached to at least one said small driving means and said each small driving means rotatably and frictionally engaged with the said main driving means, wherein the said main driving means rotates along with the said rotor assembly at rated wind speed thereby

175 main driving means drives the plurality of driving means for generating power, wherein, when the control means detects the predetermined stopping condition then the said control means diverts the generated power supply of plurality of generators into the said primary filed of the said selected number of generators thereby emf induced in a secondary field thereby speed of the wind turbine is lowered.

180 Yet another embodiment of the invention discloses about single generator braking system of wind turbine. The eddy current braking system can be used for single generator wind turbine also.

Further embodiment of the invention discloses about an operating power supply of braking system. The braking system can be operated by means of DC or AC power supply. The generated power supply of 185 plurality of generators directly diverted into selected number of generators or through a filter means.

ADVANTAGE OF THE INVENTION

1. The system reduces the need of additional braking system thereby overall weight and maintenance of the turbine can be minimized—

1902. The rotating speed of the turbine is either controlled or stopped in high wind speed condition.

3. The system reducing the external braking system cost.

4. The system allows variable speed control which rotates the turbine and generates electricity even in high wind speed condition therefore efficiency will be improved.

5. The system increases the life time of the turbine components due to smooth eddy current braking.

1956. The system eliminates the need of existing complex braking system.

7. The system eliminates the need of external braking system. The system controls the braking system automatically in high wind speed condition.

- While considerable emphasis has been placed herein on the various components of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.