10-08-2012, 04:50 PM
42V POWERNET WITH SUPERCAPACITOR AND BATTERY FOR AUTOMOTIVE APPLICATION
42V POWERNET WITH SUPERCAPACITOR.pdf (Size: 1.82 MB / Downloads: 197)
INTRODUCTION
For many years 6V electrical system was the standard employed by the
majority of the world’s automobile manufactures .In the mid of 1950’s it was clear
that 6V system had serious electrical limitations and the 12V system quickly became
its successor.
The 12V electric system have served the automobile very well. However with
the development of technology new on board electronic equipments increased such as
active suspension, navigation equipments etc. Along with this luxury like heated
seats, wind shield etc increased the electric power demand. Maintaining the same
12V results in increase in current which increases cost of power electronic
components inside. It also affects the life of the battery. Due to high current flow the
entire system will get heated up which will damage the system. So the only way to go
with the increase in demand is to increase the operating voltage there by reducing the
current flow through the system. But increase in the voltage has certain limitations.
Taking into consideration human tolerance to electric shock Society of Automotive
Engineers tech committee on Vehicle Electric Power Supply System recommended
voltage below 65V(SAE J2232). The German standard-making body, VDE, also
determined that peak bus voltage should not exceed 60V DC (VDE01004/410). After
much discussion in the industry, a group known A Forum Brodnetz has recommended
42V as new automotive electrical standard.[1]
42V system (42V PowerNet) requires battery voltage of 36V, Charging
voltage 42V, and a maximum dynamic overvoltage is 58 V which is below the
suggested voltage of 60V. Unlike previous systems that employed only a battery and
an alternator as the principle energy source, the 42V system utilises additional energy
storage devices like supercapacitors as those are optimum storage medium for
absorbing and releasing large amount of energy quickly.
Replacing of the entire car power system by 42V won’t be economical and not
necessary .In order to provide high power for newly added parts a power converter
can be used to step up the voltage .So a system with both 12V and 42V system can be
used, such a system will be more economical than replacing of entire 42V system .For
such a system a Boost converter is used to step up the 12V to 42V with some transient
time. To supply power during that transient time supercapacitor are employed which
discharges when the battery circuit output voltage is below 42V and charges when
battery attains steady state. A bidirectional Buck-Boost converter is used for the
above Buck conveter to step down output voltage(42V) to charge capacitor and Boost
converter to step up capacitor voltage from 12 to 42 V(discharging).Voltage control is
used for the closed loop control of Boost converter and voltage and current control for
Buck- Boost converter.
OBJECTIVE
The objective of this project is to develop a 42V system using a 12V battery . At first
the 12V from the battery need to be stepped up to give 42V. Output of this level take
some time (transient) to attain the desired value .So using an ultracapacitor in parallel
voltage is applied during the transient time .A bi-directional Buck-Boost converter is
used .While discharging the 12V is stepped up and current flows from supercapacitor
to load , while charging 42 V is stepped down to 12V recharged and during this time
current flows from load to supercapacitor. The simulation of the entire circuit is
implemented in MATLAB/SIMULINK. Hardware implementation is to be done and
an appropriate control algorithm to satisfy the above requirement and to be
implemented in a microcontroller.
PROJECT OUTLINE
Also objective and outline of the project.
Chapter 2 dedicated to literature review on various power electronic
components ,circuits and control strategies
Chapter 3 dedicated to system description
Chapter4 gives the simulation results
Chapter 5 discuss about the Hardware implementation
Chapter 6 gives conclusion and future scope of the project
Chapter 7 gives the bibliography.
LITERATURE REVIEW
INTRODUCTION
This project consists of two voltage levels 12V and 42V .Battery voltage need
to be stepped up to meet the load demand. On the other hand ultracapacitor charging
and discharging requires stepping up/down. Thus a detailed study of DC- DC
converters its types and control are necessary before making a choice of the
converters. This chapter is an elobaration of the above mention study along with other
requirements in the project like ultracapacitor , Battery etc.
REVIEW OF DC-DC CONVERTERS
A DC-DC converter converts dc voltage of one level to another level. A dc
converter can be considered as DC equivalent to an ac transformer with a
continuously varying turns ratio. Like a transformer, it can be used to step down or
step up a DC voltage. Switch mode DC-DC converters utilize one or more switches to
transform dc from one level to another. This can be done by adjusting the switch on
and switch off durations (ton and toff). The average output voltage Vo depends on the
ton and toff. Varying the on duration will vary the average output voltage. The ratio of
the on duration time to the switching time period is called as Duty ratio (D) is
expressed in equation 2.1.[2] Thus by varying the duty ratio the average output
voltage of a DC-DC converter can be varied. The equation for the switching
frequency is given in eqn.2.2.