FIELD OF INVENTION:
The present invention relates to a method for increasing efficiency of
H-bridge boost converter for battery charging operation by using
control elements in the electronic circuit of the inverter. The present
invention in particular relates to a control unit with an H-bridge
boost converter element.
BACKGROUND OF THE INVENTION:
A battery operated bidirectional line frequency transformer based
inverter broadly performs two functions. First in case where mains
is not available or out of specified voltage limit i.e. main is higher or
lower than specified voltage limit or frequency is out of limit' it acts
as a backup system i.e. battery DC voltage is converted into 50/60
Hzs AC by using a H-bridge converter employing four nos power
switches SW1 to SW4 followed by step-up transformer plus post LC
filter to produce sine-wave output (fig. 1). There are two nos
frequency operating to complete this task. First is the line frequency
or fundamental frequency (50/60Hz) on which power transformer
works and same line frequency is delivered to load connected as a
sinusoidal output. Second is switching frequency to produce sinewave
output from battery energy.
The second function of this bidirectional system is to charge the
battery through H-bridge boost converter when mains is available
and is within specified limit of voltage and frequency. Power
switches SW1 to SW4 performs H-bridge boost converter during
battery charging operation. At the same time, as mains is healthy
and within specified limit, the mains is directly bypassed to load
connected through switch RELAY 1.
2
Battery charging operation is performed by AC mains voltage step
down by power transformer followed by H-bridge boost converter
employing SW1 to SW4. Power transformer is designed in such a
way that its step down peak voltage should not reach to battery
voltage else uncontrolled charging current will follow through body
diode of SW1 to SW4 acting as full-wave rectifier.
To perform a controlled battery charging, peak voltage of step down
AC voltage should be less than battery voltage. So that body diode of
SW1 to SW4 shouldn't forward bias with uncontrolled charging. To
perform a controlled battery charging current, available step down
AC voltage is boosted in controlled environment i.e. inductor of
secondary side of power transformer and H-bridge convertor using
SW1 to SW4.
Variable. PWM (Pulse-width modulation) switching frequency is
applied to lower switches of H-bridge converter i.e. SW2 and SW3
simultaneously. There is a close loop circuit to control battery
charging current. More the PWM, more AC step down voltage is
boosted as accordingly battery charging current follows. Battery
charging current is sensed by micro-controller and accordingly PWM
duty cycle varies (fig. 2).
During positive half cycle PWM applies simultaneously to lower
switches of H-bridge converter i.e. SW3 and SW4. When switches
SW3 and SW4 are "ON", energy is stored in inductor of secondary
winding of power transformer. When switches SW3 and SW4 are
"OFF" voltage of stepped down AC voltage i.e. secondary side of
power transformer is boosted due to inductive effect of transformer
winding. PWM duty cycle increases in such a way that its peak
voltage crosses the battery voltage level. Once this boost voltage
3
crosses the battery voltage level, body diode of SW1 and SW4 is
forward biased. In this manner, PWM duty cycle of SW3 and SW4
varies based on close loop feedback of battery charging current
sense through shunt and battery charging current is achieved in
controlled environment.
During negative half cycle PWM applies simultaneously to lower
switches of H-bridge converter i.e. SW3 and SW4. When switches
SW3 and SW4 are "ON", energy is stored in inductor of secondary
winding of power transformer. When switches SW3 and SW4 are
"OFF", voltage of stepped down AC voltage i.e. secondary side of
power transformer is boosted due to inductive effect of transformer
winding. PWM duty cycle increases in such a way that its peak
voltage crosses the battery voltage level. Once this boost voltage
crosses the battery voltage level, body diode of SW2 and SW3 is
forward biased which is opposite to switches conducts during
positive half cycle.
In this manner PWM duty cycle of SW3 and SW4 varies based on
close loop feedback of battery charging current sense through shunt
and battery charging current is achieved in controlled environment.
US Publication No. 20060062026 for "High Efficiency Power
Conversion Circuits" describes high frequency, switched mode
electronic power converters. A composite high voltage schottky
rectifier applied in a boost converter provides a forward voltage
slightly larger than a low voltage schottky rectifier combined with a
high voltage breakdown capability.
Publication No. EP1427091 for "Resonant Converter with
Integrated Boost Means" describes a switched-mode power supply
comprising a boost means showing a boost inductor and being
4
capable of transforming a rectified AC input voltage Uin into a
primary regulated output voltage Upri at a first load terminal and a
resonant converter means connected in series to said boost means
and being capable of transforming said primary regulated output
voltage into at least one secondary regulated output voltage Uout
across a load connected between a second and a third load
terminal; The driver circuit comprises the Schottky-diodes, a driver
transformator and minimum load resistors.
US Patent No. 5,315,533 for "Back-up uninterruptible Power
System" relates to a back-up uninterruptible power system having a
power supply path from input terminals connected to AC power
system lines to normally supply power to a load. During normal
operation, wherein AC power is available from the AC power system
lines, the primary winding acts as a secondary, providing stepped
down voltage which is rectified by the diodes on alternate halfcycles,
and is passed through a filter composed of a parallel
capacitor and series inductor, through a schottky diode and thence
on a line which is connected to the DC bus line. Power flows from
the battery charger on a line to the bus and through protective fuses
to the battery to the common. A boost controller is connected
between the output of the inductor and common to provide boost
control regulation of the voltage to the battery. The capacitor
connected between the bus line and common serves to filter out the
peaks in the power on the line so that a relatively smooth DC
voltage charging level is provided to the battery.
US Patent No. 7,812,579 for "High Efficiency DC/DC Voltage
Converter including Capacitive Switching Pre-converter and up
inductive switching post-regulator" provides a DC/DC converter that
includes a pre-converter stage, which may include a charge pump,
5
and a post-regulator stage, which may include a boost converter.
Charge pump comprises four MOSFETs, configured in an Hbridge
arrangement. One or more of the MOSFETs in
the charge pump pre-converter may be used to limit
the charge pump's inrush current during the charging or
discharging of its flying capacitors. A Schottky diode may be
included in parallel with MOSFET but with series inductance may
not operate fast enough to divert current from forward biasing
intrinsic diode.
Publication No. EP1563590 for "Power Converter Circuitry and
Method" describes a system for regulating the operation of a
plurality of different types of switching power converters. The
switching power supply controller begins to operate circuit as a
boost converter, whose source is battery and switching power supply
controller regulates boost operation to regulate supply. One set of
outputs might be described to the regulation hardware block as
being connected in the configuration of a buck converter. An
adjacent set of outputs could be defined to the regulation hardware
block as a boost converter or a half bridge, a sepic, or other
topology. One of the efficiency optimizations in switching power
supplies is to attempt to minimize the power dissipated by the
Schottky diode that will typically either be inserted in the circuit
across the lower transistor or is intrinsic to a FET. The system
implements substantially all of a power converter's expected
functions, such as maintaining a steady output voltage that is
substantially independent of the current drawn from the power
supply or maintaining a steady output current that is substantially
independent on the load applied to the power supply, deciding when
to shed loads, and measuring the state of charge in a battery,
charging the battery, and performing battery sequencing.
6
Publication No. WO03012966 for "Fuel Cell Inverter" provides a
device for converting direct current (DC) electrical voltage from a DC
power source to an alternating current (AC) voltage. The system
includes a DC-to-AC inverter, a DC bus coupled to the DC to-AC
inverter (e. g., an H-bridge inverter), and a battery coupled to the DC
bus via a charge /discharge controller. Also, the system\ includes a
converter (e. g., a boost converter) coupled to the DC bus and to the
fuel cell. Charge/discharge controller includes a small MOSFET
coupled in anti-parallel with a diode. The diode can be the body
diode of MOSFET or a separate diode, like a Schottky diode.
US Patent No. 7,777,459 for "High Efficiency DC/DC Voltage
Converter including Capacitive Switching Pre-converter and up
inductive switching post-regulator" provides a DC/DC converter that
includes a pre-converter stage, which may include a charge pump,
and a post-regulator stage, which may include a Buck converter.
The synchronous rectifier MOSFET may be eliminated and
recirculation current carried entirely by diode, which preferably
should comprise a Schottky metal-semiconductor diode rather than
a P-N junction diode.
US Publication No. 20100320839 for "Bidirectional Power
Converter" describes circuits for bidirectional power conversion. DC
to DC converters may be implemented in a similar bidirectional
configuration, including, but not limited to buck, boost, buck-boost,
inverting, flyback, push-pull, H-bridge, Cuk or SEPIC configurations
for bidirectional power conversion. In the case where switch is a PNP
power transistor, Schottky diodes may be coupled in parallel to
avoid transistor saturation in one or both directions.
7
Publication No. EP2493061 for "Converter" provides technology for
simplifying the structure of a converter utilizing synchronous
rectification, especially the structure of a gate drive circuit in the
converter. The semiconductor element includes a diode region in
addition to the MISFET region. The diode region is constituted by
the n<+> substrate, the n<-> drift layer, the drain electrode and the
Schottky electrode. A Schottky barrier diode (SBD) is formed in the
diode region.
Publication No. WO2013004453 for "An Isolated Boost Flyback
Power Converter" provides an isolated boost power converter
comprising a magnetically permeable multi-legged core comprising
first and second outer legs and a center leg having an air gap
arranged therein. The rectifying element and/or the rectification
circuit each may comprise one or more semiconductor di- ode(s),
diode-coupled transistor(s) or synchronously controlled transistor
switch (es). Each of the semiconductor diodes may comprise a MOS
diode, a bipolar diode, a Schottky diode or any combination thereof.
The driver may comprise a half-bridge or an H-bridge with two or
four MOS transistors, respectively.
US Publication No. 20090108677 for "Bidirectional Power
Converters" describes bidirectional power converters that may be
used to covert power in two different directions. Any other suitable
DC to DC converters may be implemented in a similar bidirectional
configuration, including, but not limited to buck, boost, buck-boost,
inverting, flyback, push-pull, H-bridge, Cuk or SEPIC configurations
for bidirectional power conversion. The switches may be
implemented as any suitable semiconductor or armature type
switches with any suitable polarity or configuration. In the case
where switch is a PNP power transistor, schottky diodes may be
8
coupled in parallel to avoid transistor saturation in one or both
directions.
US Patent No. 7,002,328 for "Switching Power Converter Method"
describes a method for producing a switching power converter. One
of the efficiency optimizations in switching power supplies is to
attempt to minimize the power dissipated by the Schottky diode that
will typically either be inserted in the circuit across the lower
transistor or is intrinsic to a FET. When very high voltages are
required (i.e., a cold cathode fluorescent light bulb or even a
photographic strobe in a digital camera), topologies such as halfbridge
may be used.
US Patent No. 7,092,265 for "Switching Power Converter
Controller" provides a robust switching power supply which is
capable of providing power to a number of different regulated power
sources within a given circuit. The switching power supply controller
charge battery through converter, operating either in buck or boost
mode, when an external DC supply voltage (e.g., 12 15 volts) is
available at terminal and draw power from battery, operating in
boost mode, when the external DC supply voltage at terminal is not
available. The expected voltage at terminal falls as the gate drive to
QT.sub.l is turned off and drops to the point where it is caught by
the Schottky diode, then in the subsequent time QB.sub. 1 is turned
on pulling the voltage back up to the supply rail.
US Publication No. 20090039869 for "Cascode current sensor for
Discrete Power Semiconductor Devices" provides a cascode current
sensor that includes a main MOSFET and a sense MOSFET. The
main and sense MOSFETs may be either N-channel or P-channel
devices, and the cascode current sensor may be used with a wide
variety of power devices, including, for example, P-channel and N-
9
channel MOSFETs, P-channel and N-channel insulated-gate bipolar
transistors (IGBTs), an N-channel junction field-effect transistors
(JFETs) or static inductor transistors (SITs), thyristors, bipolar
transistors, P-I-N rectifiers and Schottky diodes, regardless of the
specific manufacturing process used to fabricate the power device.
Cree, Inc. provides silicon carbide schottky diodes which are ideal
devices for CCM PFC boost diode applications because of the
superior reverse recovery characteristics - zero reverse recovery
current.
Reference may be made to an article entitled "High efficiency power
converter for low voltage high power applications" by Morten
Nymand (Technical University of Denmark, 2010) that talks about
high efficiency power electronic dc-to-dc boost converters for highpower,
low-input-voltage to high-output-voltage applications. The
use of silicon carbide Schottky diodes and a low inductance layout
provides very fast current-switching speed, significantly reducing
switching losses.
Schematic Diagrams provides active PFC boost
converter which perform an active power factor correction boost
converter. This is why the SiC Schottky diode has been used to
avoid the switching loss in the diode itself and in order to meet
efficiency and thermal specifications.
Freescale provides a monolithic quad H-Bridge power IC ideal for
portable electronic applications containing tiny bipolar stepper
motors and/or brush DC-motors powered by two-to-four cell
NiCd/NiMH batteries. The device features an on-board DC/DC boost
converter that allows motor operation all the way down to 1.6 V (the
10
boost converter supplies the gate-drive voltage for each of the four
independent H-bridge output stages. The LX terminal is the opendrain
output of the internal DC/DC converter circuit. It is the
junction for the external inductor and the anode of the external
Schottky diode.
Reference may be made to an article entitled "Low-cost off-grid solar
panel inverter with maximum power-point tracking" by Andrew
O'Connell, et al (ECE, 2008) that talks about a solar panel inverter
which could be used as backup power during outages, battery
charging, or for typical household applications. The key features of
the system are a true 60Hz, 120Vrms sinusoidal voltage output, a
wide input range, and maximum power-point tracking (MPPT), and a
power output of up to 500W. The high side switching is
accomplished by providing a bootstrap capacitor of luF capacitor
and a 1N5819 Schottky diode.
Ken Sarkies provides a full H-Bridge buck-boost converter which
provides somewhat better efficiency at higher currents than the half
H-bridge. To avoid battery discharging back through the MOSFETs
and coil during the startup phase, the charger is kept turned off
after power on or reset until the analogue circuitry has settled and a
steady battery terminal voltage can be read. The Schottky diode (1A
capacity) that bypasses the upper boost MOSFET can provide the
boost function adequately with the low currents that occur during
this stage.
Vincotech GmbH provides a high efficient bi-directional
inverter/converter comprising boost circuit with MOSFET
(600V/45mQ), SiC rectifier, bypass diode for maximum power (when
exceeding nominal power), H-bridge with 75A/600V IGBTs, SiC
11
rectifier in the high side and MOSFET (600V/45mfi) in the low side,
temperature sensor.
But there are 5 major types of losses in this battery charging
operation as describe below.
1st is conduction losses of switches SW1 to SW4; when current is
passing through switches during "ON" condition, the losses are due
to its resistive behavior.
2nd is switching losses of SW3/SW4; switching losses are basically
voltage and current overlap during ON to OFF and vice-versa of
SW3/SW4.
3rd are losses due to forward voltage drop of body diode of SW1,
SW4, during positive half cycle and losses due to forward voltage of
body diode of SW2, SW3 of negative half cycle.
4th are reverse recovery losses of body diode of SW4 during positive
half cycle and reverse recovery losses of body diode of SW3 during
negative half cycle.
5th are conduction losses of copper wire and PCB traces.
By doing power losses calculation for lower voltage battery systems
i.e. 12V to 24V battery systems, it can be seen that the majority of
losses are due to forward voltage drop losses of body diode of
switches SW1 to SW4.
Therefore, in view of the above prior arts, the present invention
provides a method to increase the efficiency of H-bridge boost
converter for battery charging operations.
12
OBJECTS OF THE INVENTION:
The principal object of the present invention is to provide a method
for increasing the efficiency of H- bridge boost converter during
battery charging operation.
Another object of the present invention is to provide a method for
increasing the efficiency of H- bridge boost converter which
minimizes half the forward voltage diode drop conduction losses in
bidirectional H-bridge converter.
Yet another object of the present invention is to provide a method for
increasing the efficiency of H- bridge boost converter which
simplifies the charging circuits while avoiding the generation of
harmonics to the source.
Still another object of the present invention is to provide a method
for increasing the efficiency of H- bridge boost converter where there
is a gain of about 6% in overall efficiency as compared to prior art
bidirectional H-bridge converter.
The foregoing has outlined some of the pertinent objects of the
invention. These objects should be construed to be merely
illustrative of some of the more prominent features and applications
of the intended invention. Many other beneficial results can be
attained by applying the disclosed invention in a different manner or
modifying the invention within the scope of disclosure. Accordingly,
other objects and a full understanding of the invention and the
detailed description of the preferred embodiment in addition to the
scope of the invention are to be defined by the claims taken in
conjunction with the accompanying drawings.
13
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more
apparent from the ensuing description when read in conjunction
with'the accompanying drawings wherein:
Fig. 1 illustrates circuit for battery charging using H-bridge
converter employing four power switches SW1 to SW4
followed by step-up transformer plus post LC filter;
Fig. 2 illustrates positive half cycles of the ac input voltage;
Fig. 3 illustrates negative half cycle of the ac input voltage;
Fig. 4 illustrates positive half cycles of the ac input voltage
according to present invention;
Fig.5 illustrates negative half cycles of the ac input voltage
•-» according to present invention.
Fig. 6 illustrates method of eliminating forward voltage drop of
"SW3" and "SW4" by using analog circuit.
While the invention is described in conjunction with the
illustrated embodiments, it is understood that it is not intended to
limit the invention to such embodiments. On the contrary, it is
intended to cover all alternatives, modifications and equivalents may
be included within the spirit and scope of the invention disclosure
as defined by the claims.
STATEMENT OF THE INVENTION;
According to the invention there is provided a method for increasing
efficiency of H-bridge boost converter during battery charging
comprising H-bridge converter employing four power switches SW1
to SW4 in conjunction with step-up transformer, post LC filter and a
relay where, during positive and negative half cycles of mains AC
14
voltage, one terminal of power transformer secondary winding tie
with -ve battery terminal through "SW4" and "SW3" respectively
while second terminal of power transformer secondary winding
checks switching frequency using PWM at the gate of "SW3" and
"SW4" respectively.
DETAILED DESCRIPTION OF THE INVENTION;
At the outset of the description, which follows, it is to be understood
that the ensuing description only illustrates a particular form of the
invention. However, such a particular form is only an exemplary
embodiment and the teachings of the invention are not intended to
be taken restrictively.
Accordingly, the present invention provides a control circuit with an
H-bridge boost converter element method for increasing the
efficiency of H -bridge boost converter during battery charging
operations comprising H-bridge employing four power switches SW1
to SW4 in conjunction with step-up transformer, post AC filler and a
relay the present invention minimizes half the forward voltage diode
drop conduction losses in bidirectional H-bridge converter which are
converted into ON state conduction losses which are negligible. At
the same time, full reverse recovery losses of body diode are also
removed.
During positive half cycle of mains AC voltage (fig. 4), one terminal of
power transformer secondary winding tie with -ve battery terminal
through "SW4" as the gate is permanently "ON" during positive half
cycle of mains AC voltage. The second terminal of power transformer
secondary winding checks switching frequency using PWM at the
gate of "SW3". When PWM is "ON" at the gate of "SW3", the
magnetizing energy is stored in the power transformer secondary
15
winding and when PWM if "OFF" at the gate of "SW3", the sapped
down AC voltage is boosted above battery voltage.
During PWM "OFF" state, the battery charging current passes
through SW1 and SW4. As "SW4" is permanently "ON" during
positive half cycle of input AC mains. So there is only ON state
conductions losses in "SW4" which is negligible as compare to body
diode forward voltage drop losses with the same MOSFET.
At the same time as "SW4" is permanently in "ON" state during
positive half cycle of input AC mains. So it acts as resistor, therefore
no reverse recovery losses of body diode. This situation persists
during lOmesc of positive half cycle of input AC mains.
During negative half cycle of mains AC voltage (fig. 5), one terminal
of power transformer secondary winding tie with -ve battery terminal
through "SW3" as gate is permanently "ON" during negative half
cycle of mains AC voltage. Second terminal of power transformer
secondary winding, checks the switching frequency using PWM at
the gate of "SW4".
When PWM is "ON" at the gate of "SW4", the magnetizing energy is
stored in the power transformer secondary winding and when PWM
if "OFF" at the gate of "SW4" said sapped down AC voltage is boosted
above battery voltage.
During PWM "OFF" state, the battery charging current passes
through SW2 and SW3. As "SW3" is permanently "ON" during
positive half cycle of input AC mains. So there is only ON state
conduction losses in "SW3" which is negligible as compare to body
diode forward voltage drop losses with the same MOSFET. At the
same time as "SW3" is permanently in "ON" state during positive
half cycle of input AC mains. So it acts as resistor, therefore no
16
reverse recovery losses of body diode. This situation persists during
lOmesc of positive half cycle of input AC mains.
In an aspect according to the present invention, this PWM scheme is
acheived by overlapping zero cross circuit to the PWM output of
microcontroller during charging operation of said H-bridge
converter.
In the prior art a single PWM for "SW3" and "SW4" has been used
from micro-controller. During first half of input mains and PWM in
"ON STATE" one switch say "SW3" connect to battery ground and
second one "SW4" will be act as boost converter along with
inductance of transformer. During first half of input mains and
PWM in "OFF STATE", battery charging current will flow through
"SW3" and "SW2" body diode. Since body diode forward voltage is
big enough to result bad efficiency during this charging operation.
During second half of input mains and PWM in "ON STATE" one
switch "SW4" connect to battery ground and another one "SW3" will
be act as boost converter along with inductance of transformer.
During second half of input mains and PWM in "OFF STATE",
battery charging current will flow through "SW4" and "SW1" body
diode. Same result with bad efficiency due to forward voltage drop of
body diode.
Figure-6 shows the method of eliminating forward voltage drop of
"SW3" and "SW4" by using analog circuit. During first half of input
mains and PWM in "ON STATE" one switch say "SW3" connect to
battery ground and second one "SW4" will be act as boost converter
along with inductance of transformer. During first half of input
mains and PWM in "OFF STATE", transistor "positive half PWM" will
17
still turn ON "SW3" battery charging current will flow through
"SW3" as close switch and "SW2" body diode. Since SW3 RDSon will
take place during battery charging efficiency will be improved.
Same is true for second half of input mains "negative half PWM" will
keep turn ON "SW4" and connect to battery ground. During boost
operation i.e. PWM in ON state it will connect one terminal of power
transformer winding to battery ground. And during battery charging
current will pass through it as close switch i.e. through RDSon,
hence efficiency will be improved.
These two blocks "positive half PWM" and "negative half PWM"
should be disable during backup mode i.e. inverter mode of
operation of h-bridge converter. So "Inverter ON" command will
disable the function "positive half PWM" and "negative half PWM"
blocks.
It is to be noted that the present invention is susceptible to
modifications, adaptations and changes by those skilled in the art.
Sucji variant embodiments employing the concepts and features of
this invention are intended to be within the scope of the present
invention, which will be further set forth under the claims.
18

WE CLAIM;
1. A method for increasing efficiency of H-bridge boost converter
during battery charging comprising H-bridge converter
employing four power switches SWl to SW4 in conjunction
with step-up transformer, post LC filter and a relay where,
during positive and negative half cycles of mains AC voltage,
one terminal of power transformer secondary winding tie with
-ve battery terminal through "SW4" and "SWS" respectively
,, while second terminal of power transformer secondary winding
checks switching frequency using PWM at the gate of "SWS"
and "SW4'' respectively.
2. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein during positive half cycle of mains AC voltage when
PWM is "ON" at the gate of "SWS", the magnetizing energy is
stored in the power transformer secondary winding and when
PWM if "OFF" at the gate of "SWS" the sapped down AC
voltage is boosted above battery voltage.
3. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein during positive half cycle of mains AC voltage when
PWM is "OFF", the battery charging current passes through
switches SWl and SW4.
4. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein during negative half cycle of mains AC voltage when
19
, ^ PWM is "ON" at the gate of "SW4'', the magnetizing energy is
stored in the power transformer secondary winding and when
PWM if "OFF" at the gate of "SW4" the sapped down AC
voltage is boosted above battery voltage.
5. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein during negative half cycle of mains AC voltage during
PWM "OFF" state, the battery charging current passes through
switches SW2 and SW3.
6.' The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein the losses are converted into ON state conduction
losses, which are negligible.
7. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein the full reverse recovery losses of body diode are
removed.
8,. The method for increasing efficiency of H-bridge boost
converter during battery charging as claimed in claim 1,
wherein the PWM scheme is acheived by overlapping zero
cross circuit to the PWM output of microcontroller during
charging operation of said H-bi-idge converter.
20
9. A method for increasing efficiency of H-bridge boost converter
during battery charging as substantially described herein with
reference to accompanying figures.