24-03-2011, 11:08 AM
PRESENTED BY:-
GEETHA.K
ASHA.T.R
SHWETHA.G
VINAYA NAYAK
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ABSTRACT
The recent developments in both wireless technologies and low power electronic devices consume less power – ENERGY HARVESTING.
Wireless Sensor Networks (WSNs), powered by harvesters, has been increasing over the last decade, especially those using thermal energy harvesting.
In this research work, a low temperature thermal energy harvesting system -- which can harvest heat energy from a temperature gradient and convert it into electrical energy with mechanical systems.
Our prototype is divided into three subsystems: 1. Thermal Harvesting, 2. DC-DC converter, 3. Control unit – is presented to extract heat energy from a radiator and use it to power ZigBee application. (wireless protocol).
In our thesis, a remote controlled controlling unit is used to control two different applications – for efficient operation of the thermal energy system.
The efficiency of the system is achievable to 15 percent.
OBJECTIVE OF THE PROJECT
Design of Harvesting system using Thermal Energy generator.
To efficiently control the operation of steam and electrical output.
Easier installation and environment friendly.
To Achieve 15% efficiency from the Thermal System.
Video file
PROBLEM FORMULATION
1. Harvesting energy – is a desirable and increasingly important capability in several emerging applications.
2. Designing an efficient energy harvesting system that actually requires an in-depth understanding of several complex tradeoffs.
3. These tradeoffs arise due to the characteristics of the harvesting transducers, chemistry and capacity of the batteries used (if any), power supply requirements, etc.
In our project, we are going to design the module that effectively harvest waste thermal energy.
The module uses TE (Thermal Energy) generator to harvest thermal energy, and convert the harvested energy.
The design techniques are described in our thesis, which target high conversion and storage efficiency for wireless sensor applications.
INTRODUTION
Nowadays, some very low power wireless – marketplace. Applications to carry out complex tasks without human intervention.
The power supply is the most challenging technological hurdle in development of WSNs (wireless sensor network).
Batteries are the dominant energy source for WSNs but they are not the optimal choice for wireless electronics.
1. lifetime is limited and 2. battery leakage can pose serious environmental pollution.
Recent developments in thermoelectric materials and structures -- interest in TE power generation.
Initial literature surveys indicates, simple TE generator is made by heating one face of TE module, and cooling the other face causing an electrical current to be generated for load – Tomas see back in 1882.
A TE generator has characteristics of 1. long life cycle, 2. no moving parts, 3. simple and high reliability.
However, here some significant research is being carried out to develop new materials and module constructions, which promise harvesting efficiency of more than 10%.
LITERATURE SURVEY
DESCRIPTION OF THE RESEARCH WORK
The Fig.1 shown is the simplified block diagram of Thermal Harvesting System.
The Block diagram consist of
1. Thermal Harvesting unit – Radiator and Thermal Generator.
2. DC-DC converter and Driver circuit.
3. Controlling unit – Microcontroller
4. ZigBee.
THERMAL HARVESTING UNIT
A highly efficient system is the basic requirement for a successful harvesting system design.
The Harvesting system consist of radiator and thermal generator.
The radiator is used to generate the heat and generator to convert into electrical energy.
Basically, the efficiency of the TE generator is dependent on two factors:
1. Efficiency of the TE module and
2. Heat temperature level
The temperature difference across the module is another significant factor in determining the efficiency of the whole harvesting system.
DC-DC CONVERTER
The MAX668 constant-frequency, pulse-width modulating (PWM), DC-DC controller is used in our project.
The MAX668, optimized for low input voltages with a guaranteed start-up voltage of 1.8V. It supports output voltages up to 28V.
The conversion efficiencies of dc-dc converter is 90%. (Maxim’s proprietary Idle Mode™ control scheme).
The MAX668 operates with inputs as low as 3V and can be connected in either a bootstrapped or non-bootstrapped (IC powered from input supply or other source) configuration.
Low operating current (220μA).
MICROCONTROLLER(89S52)
The important features of microcontroller includes
8K byte of flash memory.
256 bytes of RAM.
32 I/O lines, 2 data pointers.
Three 16bit timers/counters.
Full duplex serial communication.
On chip oscillator and clock circuit.
16- bit timer/ counter.
Fully static operation: 0 HZ to 33 HZ
IMPORTANCE OF 89S52
THERMAL ENERGY GENERATOR
Thermoelectric generators are all solid-state devices that convert heat into electricity.
A thermoelectric produces electrical power from heat flow across a temperature gradient.
As the heat flows from hot to cold, free charge carriers (electrons or holes) in the material are also driven to the cold end .
The Seebeck coefficient, α, (V = αΔT).
A good thermoelectric material has a Seebeck coefficient between 100 μV/K and 300 μV/K;
A thermoelectric generator converts heat (Q) into electrical power (P) with efficiency η.
The amount of heat, Q, that can be directed though the thermoelectric materials frequently depends:
Size of the heat exchangers used to harvest the heat on the hot side and reject it on the cold side.
ZIGBEE(Wireless protocol)
ZigBee is a worldwide open standard for wireless radio networks in the monitoring and control fields.
The standard was developed by the ZigBee Alliance (an association of international companies) to meet the following principal needs:
low cost
ultra-low power consumption
use of unlicensed radio bands
cheap and easy installation
flexible and extendable networks
integrated intelligence for network set-up and message routing
FUTURE SCOPE OF THE PROJECT
Basically, a permanent harvesting system with high efficiency, simple and compact construction, is considered as an idea battery replacement for WSNs.
The concept of maximum power point tracking system, for higher efficiency of the system.
To enhance the system's efficiency, an improved DC-DC converter subsystem can be designed ---convert low harvesting voltages from the TE modules.
The S-882Z charge pump IC can be added to work as start-up circuit to deliver the required voltages for a boost converter.
A piezoelectric, thermopiles harvesting system can be implemented.
An advance circuit can be designed to supply the driving voltage (~mV) for efficient cooling of modern microprocessor.
An wrist watch can be designed by body heat converted into the electrical power by the thermoelectric.
CONCLUSION
Society’s demand for power will continue to grow as new technologies are invented. This is a reality of living in an industrialized age.
Our power suppliers are given the burden of supplying us with a constant power supply, but this burden cannot always be met.
The subsystem of harvesting system consists of subsystems, thermal energy harvesting, driver circuit, controlling unit, ZigBee.
The heart of circuit is the controlling part, consisting of advance microcontroller.
The microcontroller along with the Zigbee protocol does two different applications.
If there is a rise in temperature beyond the controlling the amount of steam, which gives the signal to the microcontroller with the help of a buzzer.
Another application is to control the electrical output for efficient operation of thermal energy harvesting system.
Various design considerations for designing a high efficient TE generator have been presented and also architecture of the TE generator is designed to reduce the system’s complexity.
Thermal energy harvesting is a promising approach to alleviate the power supply challenge in ultra low power systems.
