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TECHNOLOGY AND TREND OF HIGH FREQUENCY BATTERY CHARGER FOR LEAD-ACID BATTERY

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 622-628. Article ID: IJMET_10_03_064
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
TECHNOLOGY AND TREND OF HIGH
FREQUENCY BATTERY CHARGER FOR
LEAD-ACID BATTERY
Min Ho Kim
Department of Control Measurement Engineering, Kongju National University,
Chungnam, Cheonan, Republic of Korea
Bok Gil Choi
Department of Electrical Engineering, Kongju National University,
Chungnam, Cheonan, Republic of Korea
Haeng Muk Cho*
Division of Automotive Mechanical and Engineering, Kongju National University,
Chungnam, Cheonan, Republic of Korea
*Corresponding Author
ABSTRACT
Though battery use increases more and more and the capacity is increased as a
result of short battery use time, research and development is in progress with the
purpose of reducing the charging time and increasing the charging speed due to the
physical limitations and the limitations on technology development. High speed
chargers and high frequency battery chargers used with AC power utilize two
conversion circuit designing methods, and the efficiency and performance of chargers
have been enhanced by using additional PFC, filter, safety circuit, etc. If a lead-acid
battery is charged with a slow charger for general battery, sulfuric acid accumulates
as a by-product of the chemical reaction, which leads to battery performance
deterioration. In order to charge such a battery turning it into the state of initial
performance, a charger which employs high frequency wave is used to prevent
performance deterioration. As it is also important to check the battery state at this
time to ensure quick charging and prevent performance deterioration, we intend to
look into various methods of checking the battery state, changes in the charger
efficiency, and the difference between a high frequency battery charger and a general
slow battery charger.
Keywords: Lead-acid battery, High-frequency, SOC, LLC, Transformer.
Cite this Article Min Ho Kim, Bok Gil Choi, Haeng Muk Cho, Technology and Trend of
High Frequency Battery Charger for Lead-Acid Battery, International Journal of Mechanical
Engineering and Technology, 10(3), 2019, pp. 622-628.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3
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Technology and Trend of High Frequency Battery Charger for Lead-Acid Battery
1. INTRODUCTION
A battery is a storage medium that stores electric energy, and the reliability of the battery
power should be enhanced so that the battery can be protected against blackouts resulting
from a fire, natural disaster, repair, or checkup. For this reason, the reliability of the power
supplied by a battery that is responsible for the operation of equipment even in an unforeseen
situation is very important. Also, increasing the duration of a battery by lowering its
discharging rate is the most important part for the equipment which operates using electric
energy. [1] Among such batteries, we see that lead-acid battery developed in the 1860s of
which the manufacturing unit price is inexpensive is utilized in various fields for wide variety
of applications including an auxiliary battery such as ESS or UPS for emergency, those for
industries, automobile and photovoltaic power generation even at this point in time when
diverse batteries such as lithium ion/polymer batteries have been developed, and battery
discharge takes place as the equipment operates and the battery is required to be charged for
continuous operation of the equipment.
Charging method is divided into two, general charging method and quick charging
method, based on the charging time as shown in Figure 1, and the charging time could have
been greatly reduced through quick charging which uses high voltage and high current.
However, the SOC (State of Charge) should be estimated as the time a lead-acid battery can
be used should be estimated because the battery should be protected against overcharge when
it is quick-charged and over-discharge should be prevented when it is consumed, and there are
various methods of estimating it such as discharge experiment, coulomb counting method,
open circuit voltage, etc. Among the methods mentioned above, the focus will be put on the
method of estimating the SOC based on the data provided by the manufacturer and the
method of grasping the SOC by analyzing the voltage value through a discharge experiment.
[2]
Figure 1 Speed Comparison Graph of Quick Charger and Slow Charger
In this paper, we show how to make up for efficiency drop caused by increase in heat
generation and occurrence of loss when the performance of the charger of which the circuit is
organized utilizing semi-conductor devices is enhanced, present a direction to enable the most
suitable charger to be selected depending on the structure and condition of the battery, and
introduce a method that can save energy and enhance efficiency by changing the converter
circuit, among the circuits of the charger, that converts electric power.
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Min Ho Kim, Bok Gil Choi, Haeng Muk Cho
2. LEAD-ACID BATTERY
Lead-acid battery is a type of secondary battery and is utilized in many fields until today due
to its cheap price compared to that of lithium iron or lithium polymer battery, excellent
stability, high reliability and long service life. A lead-acid battery converts chemical energy
into electric energy through a discharging reaction where PbO2 of the cathode and Pb of the
anode react with sulfate ions to produce PbSO4 and water, and the reaction formula is as
Expression (1). Also, it returns to the original state capable of discharging through a charging
reaction where PbSO4 and water are decomposed and reduced to PbO2 and Pb (Equation 2).
Charging and discharging take place as such a process is repeated, and sulphate accumulates
during the chemical reaction at the time of discharge and continued accumulation of sulphate
causes gradual degradation of alternating current leading to performance deterioration of the
battery. [2][3]
(Reaction at the cathode of a lead-acid battery)
(1)
⇔
(Reaction at the anode of a lead-acid battery)
⇔
(Reaction in a whole lead-acid battery)
(2)
⇔
As to the method of removing sulphate during charging, when the battery is charged using
a high frequency charger, the high frequency band decomposes the packed sulphate to prevent
performance deterioration caused by sulphate and also reduces the charging time.
To use such a high frequency charger, the low frequency band should be removed from
the circuit inside the charger and the output should be provided through a switching circuit so
that only the high frequency band can be output. For outputting high frequency wave, there
exist diverse methods such as the case of obtaining it through the switching device after
converting AC power into DC power, the method of making it using a film condenser, and the
method of directly outputting it from the transformer.
3. LEAD-ACID BATTERY CHARGER
3.1. High frequency output
To implement high frequency, high frequency switching operation is required. The devices
that create switching operation include MOSFET and IGBT, SIT and capacitor, resonant
capacitor and inverter, which can be used to design and organize two switching circuits by
hardware switching method and PWM converter switching method but the efficiency of the
PWM converter is low due to the high switching loss. Also in the case of the hardware
switching, it is difficult to maintain the soft switching condition when a load is applied due to
loss, heat generation, etc.
A PFC circuit is added or an LLC converter is added to the terminal in order to recover
the efficiency decreased like this. In the case of an LLC converter, the soft switching
condition can be maintained even when a load is applied and, as it has a wide output voltage
in single phase, it can be used for a high frequency quick charger. [4] Though there are
different methods of enhancing efficiency, it is impossible to quickly charge a battery from 0
% to 100 %. If quick charging is carried out up to 80 ~ 90 % through the switching function
also in a quick charger, though the subsequent charging should be able to automatically
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Technology and Trend of High Frequency Battery Charger for Lead-Acid Battery
complete battery charging up to 100 % through slow charging, it seems that quick chargers do
not have other functions.
3.2. LLC Charger using a converter
The thing devised to make up for efficiency while maintaining the soft switching condition of
LLC converter even in a state where a load is applied is LLC resonant converter. It minimizes
frequency change by making the ratio of the resonant inductance and the magnetizing
inductance to be 1 or smaller using two transformers. While the size cannot help but grow if
this ratio is made to be 1 or smaller using one transformer, as the ratio of the resonant
inductance and the magnetizing inductance does not exceed 1 using two transformers, the
frequency change resulting from the change in the input voltage can be minimized. Also, as
two small size transformers can be used, though the efficiency is higher than that of a big
transformer and power consumption can be also reduced, it cannot be regarded as a good
solution because the area, weight and the complexity of the circuit increase. [5] Though the
performance improves if two graphic cards are used being interlocked, if there is no software
that can support this, the speed rather decreases than when one device is used due to a
bottleneck phenomenon. Like this, if the complexity of the circuit increases as a result of
using two transformers or there is no other device that can support it, it is more desirable to
use one transformer, and the shape or material quality of the existing transformer should be
changed or tuned to change the efficiency.
3.3. Transformer conversion circuit
The current situation is that environment-friendliness and frugality have become important
issues, and companies are making a lot of effort to reduce energy consumption by, for
example, conserving electric power and reducing power consumption, and many studies are
carried out also to enhance the efficiency. Enhancing efficiency is a method of reducing loss,
and reducing loss is a way of utilizing energy to the utmost. [6] As the biggest amount of
electric power is consumed by the transformer of the converter where electric power is
converted and much energy loss takes place due to conversion of the energy form as a result
of heat generation, we intend to prevent loss by changing the shape of the coil, a component
of transformer, which is one of the methods of preventing it.
Figure 2 Transformer of Sandwich Technique Shape
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Figure 3 Troidal Transformer Shape
To improve the coupling of an existing transformer, the sandwich technique is used as
shown in Figure 2. However, to maintain the most ideal transformer coupling and high
efficiency, the gap between the first primary winding and the secondary winding should be
very small and, in the sandwich technique, the gap between the first primary winding and the
secondary winding cannot be reduced due to a structural problem. Accordingly, it can be seen
that the gap between the first primary winding and the secondary winding can be reduced in
the case of the coaxial winding of a troidal shape as shown in Figure 3, and also the coupling
and the efficiency are superior to those of the transformer for which the sandwich technique is
used [7].
As there is a case where the efficiency of a transformer with the biggest loss is enhanced
by changing the shape from the existing sandwich shape to another shape, if studies are
carried out to improve the coupling and enhance efficiency by changing the coil shape and the
winding method, better output can be obtained while making up for the shortcomings of the
existing transformers.
4. SOC ESTIMATION METHOD
The reliability of this battery that plays the most important role as a main energy source of the
electric power storage device is very important and, for this reason, the information required
for stable operation is accurate information about battery SOC (State Of Charge). Though
SOC can be obtained by different methods, as it is sometimes distorted by noise, we introduce
the method of obtaining accurate information.
4.1. Estimation of SOC using a Kalman filter
Estimation of SOC using a Kalman filter can be realized in real-time and shows a property
strong against noise. Though a Kalman filter is mainly used due to the non-linear
characteristic of battery, it has a disadvantage that, if the status variable changes, the
calculation time increases to that extent. [8] Accordingly, accurate SOC can be estimated
when modeling is carried out using a model of a battery with distinct operating characteristics
and the simplified equivalent circuit. The equivalent circuit is comprised of an open loop,
which are based on OCV (Open Circuit Voltage) and RC-ladder (
,
) and OCV is
the most important data here. When we look into the graph in Figure 4, the characteristic of
the OCV is similar to that of a hysteresis and shows a flat graph in the remaining area other
than the areas below 10 % and above 90 %.
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Technology and Trend of High Frequency Battery Charger for Lead-Acid Battery
Figure 4 OCV Hysteresis Characteristics Graph [9]
The equipment which shows such a phenomenon most easily is the battery of a
smartphone. Though the SOC estimation algorithms of different manufacturers may differ
from each other, people may have experienced a phenomenon where the battery is quickly
consumed in one section and lasts long in another section as if it is slowly consumed. To
prevent such a phenomenon, it is said that such a phenomenon can be improved by adjusting
the SOC estimation interval to be smaller than the existing one and by adding a noise model.
[9][10].
4.2. SOC estimation using the Puekert’s Equation
This method carries out a modeling of a lead-acid battery based on the data of the
specification table provided by the manufacturer and verifies the reliability of the model by
comparatively analyzing the values obtained by discharging certain current and power with
the data in the specification table, and estimates the remaining capacity of the battery from the
open circuit voltage. To model the battery first, a battery equivalent circuit is organized as
shown in Figure 5 and the data values to be used for simulation are determined by entering the
data values of the specification table into the expression to obtain the Peukert’s coefficient.
However, as the terminal voltage changes in line with the depth of discharge (effective
amount of battery to be used), the Peukert’ coefficient should be calculated taking into
account the error and the SOC should be estimated in the simulation.
Figure 5 Battery Equivalent Circuit Model
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SOC can be estimated using the Matlab simulation program and, though such a method
can be employed to estimate the reliability of the battery model and SOC using only the
specification values and it has a disadvantage that, the higher the discharge rate is, the more
the error from the specification values grows, it is thought to be a method required for
development of a model that estimates battery SOC following temperature change or external
environment change [11].
5. CONCLUSIONS
We have found that the performance of a lead-acid battery deteriorates because sulphate is
generated in the chemical reaction during charging and introduced that the sulphate can be
removed using high frequency wave. We have also introduced diverse circuits and methods
that can be used to generate high frequency wave and, if this is added to improve the existing
one and batteries are charged using an accurate SOC, the obstacles to battery charging caused
by noise or environmental factors are expected to be overcome.
ACKNOWLEDGEMENTS
This work (Grants No. S2591854) was supported by Business for Cooperative R&D between
Industry, Academy, and Research Institute funded Korea Small and Medium Business
Administration in 2018.
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