WO2009144737A1

WO2009144737A1 - Wind turbine system with steady electric power output using air battery.

Info

Publication number: WO2009144737A1
Application number: PCT/IN2008/000810
Authority: WO
Inventors: Madhusudan Purshottam Patel
Original assignee: Mckinney, Hina
Priority date: 2008-05-05
Filing date: 2008-12-04
Publication date: 2009-12-03

Abstract

The invention presents a new approach and new design of Wind Turbine System with steady electric output using Air Battery regardless the rotating speed of the rotor. More particularly the system delivers constant voltage and constant frequency with controllable and presetable parameters. The major modules of the system incorporates, a wind powered rotor, Air Pump to charge Air Battery, Air Battery, Air Motor, Electric Generator driven by Air Motor, Control Components and interface controllers to deliver the power to utility grid or for use as stand alone power station.

Description

Title: WIND TURBINE SYSTEM WITH STEADY ELECTRIC POWER

OUTPUT USING AIR BATTERY.

DESCRIPTION

Background of the invention:

Prior art Wind Turbines use rotor with blades, Gear Box, Generator, Transformers and Controls. The prior art set-up has certain limitations. The invention described in this document, overcomes the limitations of the prior art wind turbines.

Limitations of prior art Technology (L.E.T.)

To overcome inertia and put the generator in working mode, grid connectivity is required, since the generator can deliver power only in a synchronous mode.

The speed of the propeller depends on the wind speed. Hence the speed of the generator varies according to the wind velocity.

This in turn effects output in terms of, (i) Voltage (ii) Frequency

The power output from Wind Generator can not be exported to the utility grid unless the power output from the generator is compatible with utility grid in terms of Voltage & Frequency. Compatible power output from such generator is not available all the times due to non constant speed of wind. Hence the total energy available from the wind is not converted into electrical energy. Only partial wind energy is converted.

This is described as "CUT - IN" speed & "CUT - OUT" speed of wind. Hence low speed wind and high speed wind both are wasted. That is there is big difference between the total wind energy available and wind energy usable.

When the wind speed is less than CUT - IN speed - the L.E.T. does not give any output. When the wind speed is more than CUT - OUT speed there is no output from L.E.T.

When the wind speed is less than CUT - IN speed, the L.E.T. draws power (i.e. import) power from the utility grid.

The net result of L.E.T. is that

♦ The conversion efficiency from wind to power is low (09 to 17%).

♦ The generator size is big.

♦ Can not be used as stand alone power plant. Must be connected to utility grid for IMPORT & EXPORT of power. ♦ When the speed of the wind is too high, the output from the generator is not suitable for connecting to the grid, and hence it is required to be disconnected from the grid.

This makes the propeller turn at runaway speed or free wheeling. To control the situation the generator is connected to a DUMP LOAD like resistors.

Some systems have added pitch control of the propeller blades; to adjust the speed and torque of the propeller. However this is quite bulky and is done at the cost of wasting the power available from the wind; and adding weight on mast (tower). The pitch control drive also needs servo motors, servo controllers and electric power, generally from storage batteries.

Prior art wind power system can not work as stand alone power station. It must have connectivity with the utility grid for its performance. There is also requirement for the turbine shaft to stay "in synchronism" which is difficult during mechanical and electrical faults. Even if the power is generated by the system; it can not be delivered to the grid, if it has lost synchronization with the grid. It then requires human intervention for a restart.

Prior art system lack capability to stay connected and drive / run through severe transient occurrences in the network especially 2 - phase short-circuit faults where induction generators will try to run as motors due to large transient negative - sequence voltage components during faults.

Prior art system has not been able to adopt cascading and parallel operations.

SUMMARY OF THE INVENTION

The invention presents a new approach and new design of wind turbine system with steady electric output using Air Pump, Air Battery, Air Motor and Generator.

To overcome inertia and to generate power, grid connectivity is not required.

The propeller (Air Rotor) drives the Air Pumps. The pumped air is stored into the Air Battery at high pressure. The volume is decided based on the requirement of the air supply period.

The pressurized stored air drives the "Air Motor" at a predetermined speed as per settings of the pneumatic controls.

The Air Motor drives the "Generator" at a steady speed.

The Generator runs at steady speed delivers steady power output. The Air Motor continues to run at a steady speed regardless of wind speed or even if there is no wind for some period; depending on the capacity of the Air battery. Air Batteries can be designed to store the wind energy to last for hours, days or months.

Brief Description of Drawings:

The invention and its operation can be better understood from block diagrams appended herewith:

Fig. 1 Shows the prior art which produces unregulated power.

Fig. 2 Shows the present invention delivering steady power because of introduction of AIR BATTERY and allied modules.

The propeller speed depends on the speed of the wind. This will produce varying output from the air pump, which will be stored in an air battery at high pressure. However the delivery of air from the air battery to the air motor can be regulated as desired to deliver constant speed to the generator. Hence generator is immune from the effect of variations in wind speed, and thus delivers steady power output regardless of the wind speed variations.

Fig. - 3

Shows how array of propellers with Air Pumps could be cascaded to charge the Air Battery. Distributed over the area but cascaded propellers can improve to a large extent continuous supply for pressurized air, thereby keeping the air battery charged almost all the time. The arrangement can also provide continuity of power, even if some turbine is under repair / maintenance.

Fig. - 4

Shows cascading of Air Batteries.

As shown in Fig. 3, like cascading of propellers, Air Batteries can also be cascaded. Cascading air batteries will result in additional storage of compressed air. Additional stock of Compressed Air can result in increase of autonomy of the power supply, even when, the wind is low or there is no wind for some time. Cascading can also help avoiding down time of the system, during need of maintainance. The arrangement can ensure continuity of power, even if some Air Battery is under repairs / maintenance. The system can also store the additional air, during non-peak hours, which can be used during peak hours, thereby increasing the PLF of the system.

Fig. - 5

Shows cascading of generators.

The arrangement can,

• Provide facility to add or deduct generators, depending on the load management requirements. This means control on despatchable power.

• Provide facility for maintainance and repairs on any generator while continuing to supply the power from the system.

By judicious combination of various cascading possibilities shown in fig. 3, 4 and 5, the wind farms can deliver steady and continuous power supply as per demand.

Fig. - 6

Shows the arrangement of dedicated controller. The Fig. 6 shows only two controllers to explain the basic arrangement, but any number of controllers can be used depending upon the requirements.

Controller (1) caters for stand alone supply terminal, which can cater to the surrounding localities directly without taking power from utility grid.

Controller (2) caters directly to utility grid to provide power to a given feeder. If there are more feeders, additional controllers can be installed. Separate dedicated controllers, can immunize the system, from short circuit fault on specific feeder.

Fig. - 7

Shows Programmable Logic Controller.

The figure shows standard PLC with 8 - I/O. (8 Inputs and 8 Outputs) configuration, readily available. The figure shows 5 - I/O. used. However spare 3 - I/O. can be used for additional functions at any time, or can be used as spare I/O for maintenance or stand by or for increasing the system reliability by programming them as "Either / OR" functions.

• One input can operate more than one output.

• More than one input can drive single item.

The relationships between inputs and outputs can be decided as per programming. e.g. input (3) & input (4) both act on "field control of generator" as shown in (3A) & (4A).

PLC provides control & automation of the system, alongwith data logging of all the units. DESCRIPTION OF PREFERRED EMBODIMENTS:

The power generation by wind mills has to fulfill many requirements. Wind mills essentially depend on the wind. It is well known that, the wind is a non constant entity and hence problems with wind mill generators. The most prominent is that the power output is not steady. The mechanical components have very high inertia. No power available during CUT - IN & CUT - OUT speeds of the rotor. Hence the wind energy available will only be partially converted into electric power. Prior art requires that the wind mill has connection with utility grid for import & export of power. It can not work as stand alone power station. In case of disturbance in the grid network, the system gets disconnected. This happens even in transient occurrences in the network, like 2 - phase short circuit faults. Once the system gets disconnected the wind mill tends to run at uncontrollable rate at highly accelerated speeds due to shaft relaxation process, commonly with resonance in the range of 1 - 2 Hz, not seen in simulations with stiff shafts (lumped mass consideration).

1 - 2 Hz is close to typical values of the electric power grid eigenfrequencies. There is thus a risk of oscillation between the wind turbines and the entire network.

During disconnections, the rotor will have runaway, uncontrollable speed. To damp the speed, the generator output requires to be loaded by dumping it into loading resistors.

In prior art, the electric generator is mounted at a height on the mast. Hence electrical system is exposed to the risk of lightening and electric atmospheric discharge.

The requirement is to achieve whole spectrum of throughput power, voltage and frequency control system to deliver steady power.

The present invention resolves all the draw backs described in the prior art. The generator is not mounted on the mast. Instead an air pump is mounted on the mast. It is a mechanical component hence not vulnerable to lightening like electric generator. The output from the wind pump is stored in a air battery as stored energy in the form of compressed air. During high speeds of the wind mill, for any reason, the air output will increase and may tend to over charge the air battery. The excess charge can be easily released by the safety pressure valves. If the mast is made from tubular structure, it can be used as air battery. This can save installation of separate tank. The air motor and generator can be installed at a suitable distance in a covered room; thereby automatic protection from vulnerability of environmental effects.

With present invention it is now possible to operate wind mills in parallel, to charge the common air battery to provide steady power output through air motor. Common air battery can facilitate handling the varying demand of power grid by varying the volume of the air to the air motor.

It is also possible to increase the size of the air batteries to store more energy which can last for days or months or to be used as per the needs.

The air batteries will be charged all times regardless the speed of the rotor.

The invention has also made possible to cascade the generators and air batteries (instead of a large generator) to meet the varying load demands. By making proper matrix the number of wind motors and number of generators connected to the Air Batteries, a very efficient and reliable power management can be achieved. Thus the invention also makes it possible to run the set-up as stand alone power station.

The invention eliminates the need of pitch control of propeller blades. For pitch control the previous art employs servo motors of ratings varying from 2.5 kW to 10 kW. The pitch rate associated with emergency feathering is usually anywhere from 2.5 to 10 degrees per second depending upon the type of turbine. Generally the assumed rate is 7 degrees per second for the purpose of calculation. The energy storage requirement for pitch control motors need about 50 Amps and size depending on the duty cycles of servo motors. The present art eliminates the need of controlling the pitch. However for any reason, pitch control is to be incorporated, it could be done by using pneumatic motors or cylinders, which could be powered from the Air Battery and separate power pack will not be required.

In case of previous art, the generator is not running at constant speed. Hence the generator can not deliver the rated output. The best output so far known is 30% of the rating of the generator.

The invention drives the generator continuously at the rated speed. Hence the output from the generator is nearly equal to the rated output of generator, say 100%. This will result in reduction in size of generators and will also drastically reduce the payback period of the investment made in the equipment.

According to the present invention the generator and other equipment (except air pump) is installed on the ground in a shed. This protects the equipment and makes it easy for maintenance.

In the previous art the induction type generators do not contribute to regulation of voltage or frequency. The present art does both.

The invention permits the installation of generators on the ground and well protected. This opens the possibility of using high- voltage generators, thereby eliminating the need of a transformer for voltage conversion. Transformers have loses in the range of 20%. This itself is a big gain. The inventive arrangement is cost effective, more reliable, easier to maintain and also reduces the payback period. Regarding developers, owners, insurance companies, power utilities and grid operators it is judged worth to communicate the novelties and advantages to them too. These are listed in the COMPARISON TABLE.

Industrial Field of Application:

Where Wind Energy / Fluid Energy is converted into electrical energy.

Where variable wind energy is to be harvested, and to be used as a steady reliable air supply.

Where wind energy is to be harvested and stored for use as desired.

The invention will bring a revolution in the field of wind energy farming. The invention has made it possible to get steady electric power from wind energy.

The invention has made it possible to make stand alone power stations without the support of utility grid.

The invention has also greatly improved the power output and load factor of wind energy system. Has made it economical and drastically reduced the payback period.

The invention can be used for applications like direct pumping of water using air batteries and motors.

The invention can eliminate need of lead - Acid and other batteries in certain applications.

Since the invention makes it possible to have stand alone power stations; it can be used in remote and border areas for meeting needs of electric power. Armed forces in border areas can be helped by this type of power stations.

Although favourable the scope of the invention must not be limited by the embodiments presented but also certain embodiments obvious to a person skilled in the art. It should also be appreciated that by various modifications, adaptations, and alternative embodiments thereof may be made within the scope and the spirit of the present invention. The invention is further described by the following claims.

Claims

CLAIMS:

1. A system to harness wind energy comprising a wind propeller connected to drive an air compressor, the compressed air being stored in a storage tank, the storage tank is connected to a pneumatic controller which supplies constant flow of air to run a Air Motor and the Air motor is connected to run a generator, the output of generator being connected to utility grid through control panel, transformer and safety devices.

2. A system of claim 1 wherein control panel is connected to standalone supply terminal.

3. A system of claim 1 or 2 wherein a gear box is connected between wind propeller and the air compressor.

4. A system of claim 1 or 2 or 3 wherein the storage tank is provided with a relief valve.

5. A system of claim 1 or 2 or 3 wherein pneumatic controller contains a solenoid valve with a load sensor device.

6. A system of claim 1 wherein the storage tank is provided with a relief valve.

7. A system of claim 1 wherein the wind turbine is directly connected to run a mechanical contrivance.

8. A system of 1 wherein the air tank provides a damping effect on the propeller when it is full.

9. A system of claim 1 wherein a plurality of propellers are connected to a plurality of storage tanks to run a plurality of generators to produce more power.

10. A system of claim 1 or 9 wherein the system is operated by a computer and PLC with the help of lab view or custom built software.

11. A system of claim 10 wherein the air tanks are provided with pressure sensors and volume sensors.

12. A system of claim 10 wherein the pneumatic controller is provided with pressure and flow sensors.

13. A system of claim 10 wherein speed sensors are provided for the wind turbines and connected to PLC to control the airflow in the pneumatic controllers.

14. A method of harnessing wind energy to produce power comprising the steps of: Running wind propeller by wind force to drive an air compressor, storing the compressed air in storage tank which has a relief valve, connecting the storage tank to a pneumatic controller which supplies steady flow of air to run a Air Motor and the air motor is connected to run a generator and tapping the electrical energy for use.

15. A method of claim 14 wherein the wind turbine is directly connected to run any mechanical device.

16. A method of claim 14 wherein a plurality of propellers are connected to a plurality of storage tanks to run a plurality of generators to produce more power.

17. A method of claim 16 wherein sensors are provided for air tanks, pneumatic controllers and wind turbines and are logically controlled by PLC and computer.

18. A system to harness wind energy substantially as herein defined particularly with reference to the figures of the accompanying drawings.

19. A method of harnessing wind energy substantially as herein defined and illustrated in the figures of the accompanying drawings.