19-05-2014, 12:15 PM
Charging and Discharging of Supercapacitor Major Project Report
Abstract
A new technology, the supercapacitor, has emerged with the potential
to enable major advances in energy storage. Supercapacitors are governed
by the same fundamental equations as conventional capacitors, but utilize
higher surface area electrodes and thinner dielectrics to achieve greater ca-
pacitances. This allows for energy densities greater than those of conventional
capacitors and power densities greater than those of batteries. As a result,
supercapacitors may become an attractive power solution for an increasing
number of applications.
A simple resistive capacitive equivalent circuit is sufficient to characterize
its internal behavior. The equivalent model consists of three R-C branches.
The internal parameters of supercapacitor is explained by using practical
charging and discharging characteristics. With the help of internal parame-
ters of supercapacitor the exact behavior of supercapacitor for charging and
discharging characteristics can be obtained. By changing these internal pa-
rameters the required charging discharging characteristics can be achieved.
To replace the battery with supercapacitor it is required to have charging and
discharging characteristics of supercapacitor same as battery. To obtain same
characteristics as battery with the help of supercapacitor modification in its
internal parameters is required. And to get performance of supercapacitor
same as battery it is require to have internal parameters of supercapacitor
equivalent to battery. To obtain the desired value of internal parameters of
supercapacitor modification in material used in supercapacitor is required.
By choosing such material which increase the value of electrical series resis-
tance (ESR) the capacitance value will decreases.
Introduction
A capacitor is a device that stores energy in an electric field between two
charged “plates” for a short period of time. A capacitor is a passive elec-
tronic component consisting of a pair of conductors separated by a dielectric
(insulator). When there is a potential difference (voltage) across the con-
ductors, a static electric field develops across the dielectric, causing positive
charge to collect on one plate and negative charge on the other plate. Energy
is stored in the electrostatic field. An ideal capacitor is characterized by a
single constant value, capacitance, measured in farads. This is the ratio of the
electric charge on each conductor to the potential difference between them.
Capacitors are widely used in electronic circuits for blocking direct current
while allowing alternating current to pass, in filter networks, for smoothing
the output of power supplies, in the resonant circuits that tune radios to
particular frequencies and for many other purposes.
Theory of Operation
A capacitor consists of two conductors separated by a non-conductive region.
The non-conductive region is called the dielectric or the dielectric medium.
In simpler terms, the dielectric is just an electrical insulator. Examples of
dielectric mediums are glass, air, paper, vacuum, and even a semiconductor
depletion region chemically identical to the conductors. A capacitor is as-
sumed to be self-contained and isolated, with no net electric charge and no
influence from any external electric field. The conductors thus hold equal
and opposite charges on their facing surfaces, and the dielectric develops an
electric field. In SI units, a capacitance of one farad means that one coulomb
of charge on each conductor causes a voltage of one volt across the device.
Supercapacitor
Supercapacitor is a electro-chemical capacitor. It is also known as a electric
double-layer capacitor (EDLC), supercondenser, electrochemical double layer
capacitor, or ultracapacitor.Compared to conventional electrolytic capacitors
the energy density is typically on the order of hundreds of times greater .
In comparison with conventional batteries or fuel cells, supercapacitor also
have a much higher power density.