Field of Invention
5
[001] The embodiments herein generally relates to a charging system. More specifically, the
embodiments described herein relate to a system and method for maintaining a constant charging
current in a battery based charging system. Particularly, relates to a system and method for
maintaining a constant and low THD charging current in a charging system comprising the step
10 of modulating the duty cycle as per mains signal.
Background of the Invention
[002] Batteries and other energy storage devices store energy so that it can be used when
15 needed. Battery banks connected to the grid, with an appropriate inverter, may work as an
uninterruptable power supply to make energy available during a power outage for all or some of
the electrical loads in a home or business. Typical battery charging system deploys bi-directional
power conversion techniques to achieve battery charging and inverter functions. Major system
variables that determine the duty cycle are driven by the leakage inductance of the transformer,
20 line input voltage, and Battery voltage/State of charge. These variables are commonly modeled
into the control system with experimental data at a given “optimal” operating point for the
system.
[003] As input mains is sinusoidal in nature which results in higher peak current at crest and
25 trough levels of mains and almost zero current near zero crossings. These high charging peaks
can damage the MOSFET switches resulting in complete system failure. Also at Low AC mains
voltages say 150V, these peaks become dangerously high and so, we are forced to reduce the
target charging current to avoid such high peaks. This result in increased charging time and in
turn reduced power backup time in areas where AC voltage is low. More over this will inject
30 high harmonics to the grid and loss in power distribution in grid.
3
[004] In existing systems during charging, control loop is applied every mains cycle (50 Hz)
depending on average charging current for last cycle and remains constant throughout complete
cycle. Due to this same duty cycle applied for complete mains cycle, the charging current peak at
crest and trough becomes high. And at near to zero crossing, current reduces to zero so energy at
this point was not 5 being utilized.
[005] Techniques that are commonly deployed to prevent are to either change the charging
current across line input voltage/battery voltage such that the converter remains in DCM
throughout the line cycle or to disable charging for a specific duration across the line cycle in
10 order to maintain a constant average charging current. The former results in inconsistent
charging times for the battery, because of inconsistent charging currents, while the later results in
poor reliability and thermal performance since transformer RMS currents required during the line
cycle period that charging is enabled are higher. All of the above situations have the
disadvantage of poor overall system efficiency across the operating input line voltage range and
15 more power loss.
[001] Therefore, there is a need in the prior art to develop a system and method for maintaining
a uniform charging current to overcome the problem associated with the prior arts.
20 Objects of the Invention
[002] Some of the objects of the present disclosure are described herein below:
[003] A main object of the present invention is to provide a system and method for maintaining
25 a constant charging current in a charging system.
[004] Another object of the present invention is to provide a method for maintaining a constant
and low THD charging current in a charging system comprising the step of modulating the duty
cycle as per mains signal.
30
4
[005] Still another object of the present invention is to provide a method and system of
maintaining a constant charging current by modulating the duty cycle as per instantaneous value
of mains, RMS value of mains and Peak value of mains signal.
[006] Yet another object of the present invention is to provide a method 5 and system wherein
duty cycle is modulated as per instantaneous value of the main signal to have a maximum duty
cycle at an edge of a sine wave and a minimum duty cycle at a peak of the sine wave.
[007] Another object of the present invention is to provide a method and system wherein duty
10 cycle is further modulated by peak value of the main signal to limit peak current in a safe
threshold value.
[008] The other objects and advantages of the present invention will be apparent from the
following description when read in conjunction with the accompanying drawings which are
15 incorporated for illustration of preferred embodiments of the present invention and are not
intended to limit the scope thereof.
Summary of the Invention
20 [009] In view of the foregoing, an embodiment herein provides a system and method for
maintaining a constant and low THD charging current in a charging system comprising the step
of modulating the duty cycle as per mains signal. According to an embodiment, a method of
maintaining a constant charging current by modulating the duty cycle as per different parameters
of mains signal like instantaneous value of mains, RMS value of mains and Peak value of mains
25 signal.
[0010] According to an embodiment, wherein duty cycle is modulated as per instantaneous value
of the main signal to have a maximum duty cycle at an edge of a sine wave and a minimum duty
cycle at a peak of the sine wave. In an embodiment, a method wherein duty cycle is further
30 modulated by peak value of the main signal to limit peak current in a safe threshold value.
5
[0011] According to an embodiment, the system for maintaining a constant and Low THD
charging current in a charging system comprising an input energy supply unit which is
operatively connected to a charging unit through a battery driving unit. The system further
comprises a controller unit which is disposed between the input energy supply unit (101) and a
battery driving unit (103) and wherein said controller unit is adapted to perform 5 modulating a
duty cycle as per mains signal. Wherein said controller unit is adapted to perform modulating a
duty cycle as per instantaneous value of mains, RMS value of mains and Peak value of mains of
the mains signal.
10 [0012] These and other aspects of the embodiments herein will be better appreciated and
understood when considered in conjunction with the following description and the
accompanying drawings. It should be understood, however, that the following descriptions,
while indicating preferred embodiments and numerous specific details thereof, are given by way
of illustration and not of limitation. Many changes and modifications may be made within the
15 scope of the embodiments herein without departing from the spirit thereof, and the embodiments
herein include all such modifications.
Brief Description of the Drawings
20 [0013] The detailed description is set forth with reference to the accompanying figures. In the
figures, the use of the same reference numbers in different figures indicates similar or identical
items.
[0014] Figure 1 illustrates a block diagram of a system for maintaining a constant and Low THD
25 charging current in a charging system, according to an embodiment therein;
[0015] Figure 2 illustrates a schematic electronic configuration of the battery charging system,
according to an embodiment therein;
30 [0016] Figure 3 illustrates a flow process for modulating duty cycle as per mains signal, according to
an embodiment therein;
6
[0017] Figure 4a & 4b illustrates a graphical representation of charging current waveforms for 150V
mains signal, according to an embodiment therein; and
[0018] Figure 5a & 5b illustrates a graphical representation of charging current waveforms for 200V
mains signal, according to an embodiment 5 therein.
Detailed Description of the Preferred Embodiments
[0019] The embodiments herein and the various features and advantageous details thereof are
10 explained more fully with reference to the non-limiting embodiments and detailed in the
following description. Descriptions of well-known components and processing techniques are
omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein
are intended merely to facilitate an understanding of ways in which the embodiments herein may
be practiced and to further enable those of skill in the art to practice the embodiments herein.
15 Accordingly, the examples should not be construed as limiting the scope of the embodiments
herein.
[0020] As mentioned above, there remains a need for a system and method for maintaining a
constant and Low THD charging current in a charging system. The embodiments herein achieve
20 this by modulating a duty cycle as per mains signal for maintaining a constant and Low THD
charging current in a charging system. Referring now to drawings, and more particularly to
FIGS. 1 through 5b, where similar reference characters denote corresponding features
consistently throughout the figures, there are shown preferred embodiments.
25 [0021] Figure 1 illustrates a block diagram of a system for maintaining a constant and Low THD
charging current in a charging system 100, according to an embodiment. The system (100)
includes various electronic components of an input energy supply unit (101), a controller unit
(102), a battery driving unit (103) and a charging unit (104). The input energy supply unit (101)
comprises an input sense main transformer with an input signal processing stage and the
30 Controller unit (102) is a microcontroller. The input sense mains transformer converts the input
AC mains voltage to low voltage by using a step down sense transformer. The input signal
7
processing stage is used for processing all input signals like AC mains and battery voltage for
feeding to the microcontroller for measurement. For example, the AC mains sense signal is
provided with a biasing voltage of 2.5 V so that the sense signal rides over this 2.5 V offset. This
is required to capture both the amplitude and polarity of signal so that crest and trough both are
available to microcontroller 5 for measurement.
[0022] In an embodiment, the battery driving unit (103) is a Pulse Width Modulation (PWM)
driver stage following by a charging unit (104). This PWM driver employs an H-bridge
convertor for battery charging and also for charging unit (104). Further, battery voltage signal is
10 also processed to keep it within sensing range of the microcontroller. Further, the microcontroller
senses all the input signals, measures the input signals and processes the measured data. It also
drives the PWM signals as per the target current and the duty cycle. It is capable of handling
different fault condition and system protection also. The PWM driver stage drives a MOSFET
according to the signal from the microcontroller stage. This stage applies the digital TTL signal
15 coming from microcontroller to power section through the MOSFET. The drain of MOSFET is
further connected to a charging unit (104). This is the power stage transformer to which Mains
input is connected on high voltage winding of transformer. At low voltage winding side the
MOSFET Bridge is connected. MOSFET are being driven through Microcontroller to get the
desired charging current.
20
[0023] According to a preferred embodiment, the system for maintaining a constant and Low
THD charging current in a charging system comprising the input energy supply unit (101) which
is operatively connected to a charging unit (104) through the battery driving unit (103). The
controller unit (102) is disposed between the input energy supply unit (101) and a battery driving
25 unit (103) and wherein said controller unit (102) is adapted to perform modulating a duty cycle
as per mains signal.
[0024] According to an embodiment, Figure 2 illustrates a schematic detailed component level
schematic diagram of the charging section (200).
30
8
[0025] According to an embodiment, the method for maintaining a constant and Low THD
charging current in a charging system comprising modulating a duty cycle as per mains signal.
The duty cycle is modulated by varying the parameters of instantaneous value of mains, RMS
value of mains and Peak value of mains of said main signal and wherein said duty cycle is varied
through 5 a controller unit.
[0026] According to an embodiment, Figure 3 illustrates a flow process (300) for modulating
duty cycle as per mains signal. At first step 301, the system checks for presence of mains supply
at step 302. If mains supply is present, threshold values of instantaneous values of main supply,
10 RMS value of mains and peak value of mains is set at step 304. Measuring the average charging
current, input mains voltage and last cycle peak voltage and RMS voltage of the mains supply at
step 305. Duty cycle and error are calculated by using the formulas given at step 306. Checking
if peak voltage is above threshold at step 307. If the peak voltage is above the threshold value,
checking if RMS voltage is above the threshold value at step 308. If the RMS voltage is
15 threshold value above, modulation factor as per the instantaneous value is calculated at step 309.
Further the duty cycle is modulated as per the modulation factor at step 310. Checking if duty
cycle is in predefined limits at step 311. If the duty cycle is in predefined limits, apply duty cycle
is at MOSFET gate through microcontroller at step 313. If the duty cycle is not in predefined
limit at step 311.
20
[0027] According to an embodiment, with mains voltage, the duty cycle can be modulated
depending upon different parameters of AC mains voltage. This modulation of duty cycle can be
done with respect to three aspects of mains signal such as instantaneous value of mains, RMS
value of mains and Peak value of mains of the mains signal.
25
[0028] According to an embodiment, modulating the duty cycle as per instantaneous value of
mains signal and thereby the near edge of sine wave have maximum duty cycle and at the peak
have minimum duty cycle. This will reduce the peak current and in turn will reduce the THD of
charging current. So this will induce less harmonics into the grid and hence lesser loss in power
30 distribution in the grid.
9
[0029] In an example embodiment, a user may experience a high voltage glitch due to some
malfunctioning in input mains line. This may result in high current at that instant. But this instant
limiting of duty cycle as per instantaneous value of mains signal by sensing such high value will
reduce the extent of damage. This is like being proactive because by the time this 5 high voltage is
sensed in terms of average current the damage to MOSFET could have been done.
[0030] According to an embodiment, modulating the duty cycle as per RMS value of mains
signal, wherein during low main signal, RMS value calculated in last mains cycle is used to
10 disable/reduce mains modulation to have maximum available current at low voltage. If RMS
voltage is less than 150V, we can disable/reduce this modulation factor so that the charging
current is good even at this voltage. As the improvement required was mainly in high RMS say
greater than 150V, so disabling/reducing of modulation factor at low voltage will not affect
system performance.
15
[0031] According to an embodiment, modulating the duty cycle as per peak value of mains
signal near the peak values of mains input voltage, the charging current peak becomes
dangerously high. So the user need to further modulate or even clip the duty cycle to a certain
threshold so that components are safe in terms of allowed peak current.
20
[0032] In an example embodiment, with varying mains voltage, the user may need to have
varying duty cycle depending upon instantaneous level and RMS or peak level of mains input
voltage. The higher the instantaneous value, lower is the duty cycle applied. Also the user needs
to calculate the RMS value of full mains cycle to calculate the factor for instantaneous
25 modulation.
[0033] Figure 4a & 4b illustrates a graphical representation of charging current waveforms for
150V mains signal (400), according to an embodiment. Figure 5a & 5b illustrates a graphical
representation of charging current waveforms for 200V mains signal (500), according to an
30 embodiment.
10
[0034] In an example embodiment, the user can allow 94% duty cycle near the zero crossings
with the proposed system of maintaining a constant and Low THD charging current in a charging
system. This duty cycle will be reduced as we get higher values of instantaneous mains. At the
peak side we can even reduce it to 20% duty cycle so that peak current is in control. 5 So we need
to follow the AC mains envelop and modulate the duty cycle accordingly.
[0035] According to an embodiment, figure 4a illustrates charging signals without modulation at
150 V and figure 4b illustrates charging signals with modulation at 150 V. Further, the below
10 table provides detailed representation of mains modulation effect at 150V mains signal:
[0036] According to an embodiment, figure 5a illustrates charging signals without modulation at
200 V and figure 5b illustrates charging signals with modulation at 200 V. Further, the below
15 table provides detailed representation of mains modulation effect at 200 V mains signal:
Parameter Without Modulation With Modulation Remarks
Peak O/P Current 26.8 A 20.6 A Reduced Peak current
RMS O/P Current 13.6 A 11.5 A Reduced RMS current
Average O/P Current 9.5 A 9A Stable Target achieved
I/P Current THD 36.1% 19.1% Improved THD
[0037] According to an embodiment, the proposed system ensures to provide Increased
Reliability due to Reduced Peak Current and Temperature, Low Input current THD and Uniform
20 Current throughout the range. As Peak current reduced by 40% resulting in reduction of
temperature by 20oC resulting in increased reliability as we are operating much lower than
maximum rated operating conditions which results in Increased Reliability due to Reduced Peak
Current and Temperature. Further, Current THD reduced to 9% from 22% resulting in less
Parameter Without Modulation With Modulation Remarks
Peak O/P Current 35.2 A 22A Reduced Peak current
RMS O/P Current 19.3A 15.7A Reduced RMS current
Average O/P Current 6.7A 9A Stable Target achieved
I/P Current THD 22.2% 9.4% Improved THD
11
harmonics induced to grid and hence less power loss in distribution system of Grid which results
in Low Input current THD. Further, uniform current is achieved throughout the rated input
voltage range with the proposed system.
[0038] It is to be understood that the above description is intended to be illustrative, 5 and not
restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and
understanding the above description. Although the present invention has been described with
reference to specific exemplary embodiments, it will be recognized that the invention is not
limited to the embodiments described, but can be practiced with modification and alteration
10 within the spirit and scope of the appended claims. Accordingly, the specification and drawings
are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the
invention should, therefore, be determined with reference to the appended claims, along with the
full scope of equivalents to which such claims are entitled.

We Claim:
1. A method of maintaining a constant and Low THD charging current in 5 a charging system
comprising:
modulating a duty cycle as per mains signal;
wherein said duty cycle is modulated by varying the parameters of instantaneous value of mains,
RMS value of mains and Peak value of mains of said main signal; and
10 wherein said duty cycle is varied through a controller unit (102).
2. The method as claimed in claim 1, wherein said duty cycle is modulated as per instantaneous
value of the main signal to have a maximum duty cycle at an edge of a sine wave and a minimum
duty cycle at a peak of the sine wave.
15
3. The method as claimed in claim 1, wherein during low main signal, RMS value calculated in a
last cycle disables mains modulation to have maximum available current at low voltage.
4. The method as claimed in claim 1, wherein said duty cycle is further modulated as per the
20 peak value of the main signal to limit peak current in a safe threshold value.
5. A system for maintaining a constant and Low THD charging current in a charging system
comprising:
an input energy supply unit (101) is operatively connected to a charging unit (104) through a
25 battery driving unit (103);
a controller unit (102) is disposed between the input energy supply unit (101) and a battery
driving unit (103) and wherein said controller unit (102) is adapted to perform modulating a duty
cycle as per mains signal.
30 6. The system as claimed in claim 5, wherein said controller unit (102) is adapted to perform
modulating a duty cycle as per instantaneous value of mains, RMS value of mains and Peak
value of mains of the mains signal.
13
7. The system as claimed in claim 5, wherein said controller unit (102) is a microcontroller
connected to the battery driving unit (103) for processing the sensed signals of the input AC
mains and the battery voltage and generating a control signal for driving the battery 5 driving unit
(103).
8. The system as claimed in claim 5, wherein said battery driving unit (103) is a power converter
comprising a `H’ bridge circuit.
10
9. The system as claimed in claim 5, wherein said battery driving unit (103) is a pulse Width
modulator (PWM) circuit.
10. The system as claimed in claim 5, wherein said controller unit (103) is adapted to provide
15 constant current charging operation over a wide operating input AC voltage ranging from 150 V
and 280V.