|Title of Invention||
A DEVICE FOR THE STORAGE AND RETRIEVAL OF ELECTRICAL ENERGY
|Abstract||(57) Abstract: A device for tbe stroage and reterived of electrical energy comporising a first Unit incorporating first control means for reciving electric power a source and regulating tho power output ttherform to a.b.c. bus; a second limit incorporating second control means for receiving the power from the bus and regulating the power output therefrom to a load; a third limit incorporating an Induotion motor coupled to a Sywheel, said induction motor being connected to the said d.c. bus through an invention such the whenever the d.c- bus vottage falls below a predetermined value, power in fed to the said bus from the third unit by the fly wheel driving the induction motor; and whenever the d-c. bus voltage is equal to or above the predetermined value. the third unit its made to absorb poiver from the bufl to boost the speed of the flywheel; and a microcontrolled for controlling the power flows flows the said units.|
This invention relates to a device for the storage and retrieval of electrical energy.
In many high power drives and production processes the power drawn needs to be highly variable to meet the demands of a specific application. Often peak power is required for a short duration. Although peak power is required only intermittently for brief periods, the system will, nonetheless, have to be designed for such peaks.
On the other hand, if the peaks could be levelled, the supply side could be rated for the average power, which is often far below peak power. The advantage of such levelling is obvious. In fact many utilities charge for peak power in addition to that for the energy utilised.
Another instance of the advantage of averaging power is in hybrid vehicles where the energy ultimately comes from a heat engine which drives a generator which in turn charges a bank of batteries, whenever all of its output is not required by the traction motor(3). The batteries augment the generator output when traction
requirements peak. The advantage is that often the engine can be of half the power (or even less com¬pared to what it would have had to be if it had to meet the traction duty on its own.
This invention proposes a device for the storage and retrieval of electrical energy to even out the power input to a system which needs fluctuating power levels.
The device for the storage and retrieval of electrical energy, according to the invention comprises a first unit incorporating first control means for receiving electric power from a source and regulating the power output therefrom to a d.c bus; a second unit incorpo¬rating second control means for receiving the power from the bus and regulating the power output therefrom to a load; a third unit incorporating an induction motor coupled to a flywheel, said induction motor being connected to the said d.c. bus through an inverter such that whenever the d.c. bus voltage falls below a prede¬termined value, power is fed to the said bus from the third unit by the flywheel driving the induction motor; and whenever the d.c. bus voltage is equal to or above
the predetermined value, the third unit is made to
absorb power from the bus to boost the speed of the
flywheel; and a rnicrocontroller for/ controlling the
power flows throught the said units.
This invention will now be described with reference to the aGGompanying drawings which illustrate, by way of example, one of the possible embodiments of the device proposed herein
Fig.l illustrating the circuit layout of the embodiment
Fig.2 illustrating the power demands of a hypothetical city bug negotiating city traffic
Fig.3 illustrating a typical power demand pattern of a small factory.
A first unit illustrated as Block 1 incorporates first control means for receiving electric power from a source and regulating the power output therefrom to a d.c bus. Input of power to the system is assumed to be from the three phase utility power grid. Block 1
converts this to a a.c. voltage ana also regulates the power flow. The control means in Block 1 comprises a converter to convert the a.c. input to d.c. and a controlled chopper to regulate the d.c.output. If the power input is d.c. the converter is not required.
The second unit is illustrated by Block 2 which incorporates second control means comprising an inverter. It converts the d.c. Input power supply to 3 phase a.c. power output, which is assumed to be the desired form of load supply. The inverter can be controlled to regulate power flow. On the other hand, if the load requires a d.c. power supply, the inverter will be replaced toy a controlled chopper.
The third unit is illustrated by Block 3 which incorpo¬rates an induction motor coupled to a flywheel. The induction motor is connected to the d.c. bus through an inverter. The inverter is controlled to supply or extract power from the flywheel. The power flows through the three blocks are controlled by a microcon¬troller. The flow of power through Block 2 is con¬trolled according to the requirements of the load. In the case where regenerative braking is feasible, power
can be made to flow in the opposite sense.
When the d.c. bus voltage falls below the prescribed value, power is fed to it from Block 3 by letting the flywheel drive the induction machine. When the d.c. bus voltage is equal to or above the prescribed voltage, power is drawn from it by Block 3 to increase the speed of the flywheel.
Once the flywheel's maximum permissible speed is attained, no further power is drawn from the d.c. bus. Block 1 is controlled to firstly ensure that the power drawn from the source (the grid or engine driven alter¬nator or fuel cells etc.) is limited to the specified magnitude; secondly to supply the full load demand as far as possible; and thirdly when load demand is below the input power limit of Block 1, to accelerate the flywheel if it is below a set speed.
As can be seen, the system can limit the power drawn from the mains while permitting the consumer to draw as much as the sum of the power drawn from the mains and that from the induction machine coupled to a flywheel for short intervals. The rating of the induction machine is selected to ensure that peak demand is met.
The limit for the input power is set at slightly above average power. The flywheel will store sufficient energy to make good the shortfall in energy drawn from the main grid for all periods when power demand ex¬ceeds the average value.
The main advantages of this invention are:
A bank of batteries employed to meet the requirements would mean that one is compelled to use large batteries even though only a small fraction of the energy storage capacity is needed. The cost of such batteries and their service life makes the proposition unattractive. The best possible charge-discharge efficiency for lead acid batteries is less than 60% as compared to 80% in the case of this invention.
compressed air storage of energy for smoothing power flow would need an electric motor driven compressor, high pressure tank, and air motor driven generator. Even assuming the most efficient compressors and pneu-matic motors the charge discharge efficiency will be less than 40%. Investment for the same power will in any event be much more than in the case of this inven-
A diesel driven generator can be used to augment mains power such as to keep the maximum power drawn from the grid below a set limit; but this does not make economic sense given the difference in price between power from the grid and that from diesel.
The most efficient system for smoothing electrical power flow is likely to be a super conducting magnet but although some experimental units have been built, it is not yet commercially available.
Fig.2 graphically illustrates the power demands of a hypothetical city bus negotiating city traffic with its stops for traffic signals and bus stops. Though the peak power is over 80 kW the average power over the 2 min. depicted works out to Just 35 kW.
Fig.3 illustrates a typical power demand pattern of a small scale factory, the area under the power curve represents energy and the diagram has been drawn to illustrate the energy exchange between the d.c. bus and the flywheel if this invention were to be adopted to regulate the power supply from the grid to the
enterprise so as to limit the peak to 75 kW. The areas marked as N1 NZ etc. represent the energy gained by the flywheel from the grid and the areas marked P1 P2 P3 etc.represent the energy which the flywheel has to supply to the load to avoid excessive demand from the mains. The value in kJ of these are:
It may be noted that the flywheel will have to store at least 1071 kJ or say 1350 kJ to be safe. This can be achieved by a wheel spinning at a peak speed of 6000 rpm if it has a mass of just 55 kg, even using steel.
The terms and expressions in this specification are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and decsribed, but it is understood that various other
embodiments of the device proposed herein are possible without departing from the scope and ambit of this invention.
1,A device for the storage and retrieval of electrical energy comprising a first unit incorporating first control means for receiving electric power from a source and regulating the power output therefrom to a d.c bus; a second unit incorporating second control means for receiving the power from the bus and regulat¬ing the power output therefrom to a load; a third unit incorporating an induction motor coupled to a flywheel, said induction motor being connected to the said d.c. bus through an inverter such that whenever the d.c. bus voltage falls below a predetermined value, power is fed to the said bus from the third unit by the fly¬wheel driving the-induction motor; and whenever the d.c. bus voltage is equal to or above the predetermined value, the third unit is made to absorb power from the bus to boost the- speed of the flywheel; and a microcontroller for controlled the power flows through the said units.
2.A device as claimed in Claim 1 wherein the said source is an a.c source and the first control means comprise a converter and a controlled chopper, the said converter for converting the a.c to d.c and the con-
trolled chopper to regulate the power output.
3.A device as claimed in Claim 1 wherein the said source is a d.c. source and the first control means comprise a controlled chopper for regulating the power out put.
4.A device as claimed in Claim 1 wherein, when the load is an a.c. load, the second control means comprise an inverter for converting the d.c. from the bus to a.c. and regulating the a.c power output to the said load.
5.A device as claimed in Claim 1 wherein, when the load is a d.c. load, the-second control means comprise a controlled chopper to regulate the d.c. power output to the said load.
6.A device for the storage and retrieval of electrical energy substantially as herein described with reference to, and as illustrated in, the accompanying drawings.
|Indian Patent Application Number||1454/MAS/1996|
|PG Journal Number||30/2009|
|Date of Filing||19-Aug-1996|
|Name of Patentee||ELECTRONICS RESEARCH & DEVELOPMENT CENTRE|
|Applicant Address||AN INDIAN SCIENTIFIC SOCIETY, VELLAYAMBALAM, THIRUVANANTHAPURAM 695033|
|PCT International Classification Number||H02M 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|