FIELD OF THE INVENTION
The present invention relates to a bidirectional switching power converter. More
particularly, the present invention relates to a push-pull based isolated
bidirectional switching power converter.
The bi-directional DC-DC converters are involved in power flow between two de
sources to allow power flow in either and/or both direction without change in
polarity of voltage. The converter are used in DC uninterruptible power supplies
and battery charging circuits.
Conventional uninterrupted Power Supply (UPS) units used in domestic use, have
two different circuits namely a battery charger that operates when mains supply
is present and a discharge or inverter that operate during mains power supply is
in off condition.
The implementation of this converter topology for a battery chargerldischarger
circuit, with applications in DC UPS systems according to the prior art, is based
on a half-bridge on the primary and a current fed push-pull on the secondary
side of a high frequency isolation transformer.
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3 1 0 SEP 70\1
US Patent No. 6,094,363 provides an uninterruptible power supply having sine
wave AC output and an energy recycle function with simple circuit structure
thereby providing high quality and high efficiency uninterruptible power. The
inverter is formed by four MOS transistors respectively controlled by the
microcontroller whereby two MOS transistor pairs are alternatively switched on to
convert the full-wave rectified shaped DC voltage to a sine wave AC voltage. The
DC/AC converter is implemented by a push-pull circuit structure and the energy
recycle charger is implemented by a flyback circuit structure. This patent
discloses recycling the redundant energy from high frequency transformer and
fed to battery.
Publication No. WO 9941826 describes a PWM controller suitable for use with
open loop DC to AC type converters. The PWM controller is adapted to provide
the required signals to control the various possible open loop converter
topologies. The controller functions to generate a PWM signal that is used to
generate a half wave sine wave signal. The controller includes the necessary
functionality to control the duty cycle of the generated PWM signal so as to
produce a full wave sine wave at the output of the output bridge circuit. The
controller of the invention is suitable for use with a variety of open loop
converter topologies such as buck, boost, forward, push-pull and any other
continuous mode. PWM controlled topology. This invention generates a sine
signal (ring generator) by suitable PWM.
\ 8 SEP ?MI
US Patent No. 4,788,451 describes an AC stabilizer that supplies stable, clean AC
power, even when the network that is feeding it is unstable and distorted. This
type of stable, sinusoidal voltage is highly recommended for computers and
other sorts of sensitive electronic equipment. The basic part of the apparatus
according to the invention is a conventional push-pull power amplifier output
stage. This invention uses one directional push-pull circuit.
US Patent No. 4,916,329 describes a highly efficient, reliable and light weight
transmission of electrical power from AC input source to load during normal line
conditions and the maintenance of the UPS device in the normal mode during
minor voltage variations of the line. The loose coupling of the standby inverter to
the load facilitates using PWM techniques, with the high reactive impedance of
the loose coupling forming the necessary inductance to smooth the PWM pulses
into a sinusoidal output waveform. The comparators produce square wave
signals out of phase with the precision sine wave signal when the AC sample
signal exceeds either one of the limit signals. In the standby mode, the pulse
width modulated, push-pull inverter drives switched DC electrical power from
battery through a second primary winding of transformer to the secondary
winding 60 and load terminals. This invention utilizes existing push-pull winding
and extra turns added to it, that saves copper.
1 8 SEP 7014
Publication No. CN 1022882417 provides an uninterrupted power supply (UPS)
isolation type bidirectional direct-current converter characterized by comprising a
push-pull circuit, a half-bridge circuit and a transformer, wherein a switch tube is
built in the push-pull circuit to control unidirectional connection or disconnection.
A low-voltage winding of the transformer is connected onto a backup power
source through the push-pull circuit, and a high-voltage winding of the
transformer is connected onto a direct-current busbar capacitor through the halfbridge
circuit. This invention is specific for UPS whereas the present invention is
related to any backup system or power supply.
Publication No. CN 102082526 describes a self-exited push-pull converter,
comprising an input soft starting circuit, a bipolar push-pull circuit, a coupling
transformer and an output filter circuit, wherein the input soft starting circuit, the
bipolar push-pull circuit, the coupling transformer and the output filter circuit
are connected in order; the bipolar push-pull circuit comprises two triodes and a
high frequency self-exited suppression circuit, wherein the two triodes are in
push-pull connection; the emitters of the two triodes are grounded; the bases of
the two triodes are respectively connected with two ends of a feed back winding
of the coupling transformer; the collectors of the two triodes are connected with
two ends of a primary winding of the coupling transformer; the high frequency
l 8 SEP 7011
self-exited suppression circuit is used for removing sine vibration generated due
to high characteristic frequency when the triodes are electrified; and the high
frequency self-exited suppression circuit is connected in the bipolar push-pull
circuit. This is self-exited push-pull converter without using additional PWM
source.
Publication No. GB 2489467 describes a grid tied inverter connectable to an
electricity grid, the grid tied inverter comprising a DC to DC current fed push-pull
converter operable to generate a current waveform from a DC voltage source,
the current waveform being substantially synchronized to the electricity grid, the
push-pull converter comprising a transformer having a first side connectable to a
battery and a second side connectable to the grid, wherein each of the two
primary sides is connected to ground via a switching transistor; and respective
voltage clamps are connected between the respective primary side of the
transformer and the respective switching transistor, the voltage clamp
commutating the current from the respective primary side of the transformer
when the switching transistor is tuned off. This invention utilizes current fed push
pull circuit and operates in one direction i.e. battery to grid.
Reference may be made to a non-patent literature entitled "Bi-directional DC-DC
converter for low power application" by Manu lain ( The Department of Electrical
and Computer Engineering; Concordia University, 1998) that teaches about a
1 8 SEP 20\!
topology for a bi-directional dc-dc converter for use in low power applications.
The implementation of this converter topology for a battery chargerldischarger
circuit, with applications in DC UPS systems, demonstrates its feasibility and
advantages when compared to the conventionally used circuit. The topology is
based on a half-bridge on the primary and a current fed push-pull on the
secondary side of a high frequency isolation transformer.
Usually high frequency (HF) transformer turns ratio in a bidirectional dc-dc
converter is designed to deliver power even under low battery voltage during an
inverter mode. This imposes restriction while charging and may not give
sufficient voltage to charge the battery. To overcome this drawback usually
current fed push-pull, boost derived full-bridge, boost derived half bridge are
employed during charging. But added inductance in the dc-link reduces
efficiency.
Therefore, the present invention provides a bidirectional power converter with an
auxiliary winding at the push-pull side of the HF converter while retaining the
center-tapped nature of HF transformer low voltage side which is essential for
push-pull converter operation.
OBJECTS OF THE INVENTION
8 SEP
It is therefore an object of the present invention to propose a bidirectional power
converter with an auxiliary winding at the push-pull side of high frequency (HF)
converter that smoothens the charging and discharging modes battery chargers
of Home UPS/UPS/Inverters.
Another object of the invention is to propose a bidirectional power converter with
an auxiliary winding at the push-pull side of high frequency (HF) converter that
smoothens the charging and discharging modes battery chargers of Home
UPS/UPS/Inverters which retains the centre-ta pped nature of HF transformer on
voltage side.
A still another object of the present invention is to propose a bidirectional power
converter with an auxiliary winding at the push-pull side of high frequency (HF)
converter that smoothens the charging and discharging modes battery chargers
of Home UPS/UPS/Inverters that performs both functions of battery charging and
discharging in a single power conversion unit with highest component utilization
factor.
Yet another object of the present invention is to propose a bidirectional power
converter with an auxiliary winding at the push-pull side of high frequency (HF)
converter that smoothens the charging and discharging modes battery chargers
of Home UPS/UPS/Inverters that provides the nominal charging current till half of
the mains voltage and delivers power to the load with nominal voltage even
under low battery condition during back-up mode of home UPS.
A further object of the present invention is to propose a bidirectional power
converter with an auxiliary winding at the push-pull side of high frequency (HF)
converter that smoothens the charging and discharging modes battery chargers
of Home UPS/UPS/Inverters which is high efficient with galvanically isolated
topology for a low power bi-directional dc-dc converter achieving bi-directional
flow of power using the same power components.
A still further object of the present invention is to propose a bidirectional power
converter with an auxiliary winding at the push-pull side of high frequency (HF)
converter that smoothens the charging and discharging modes battery chargers
of Home UPS/UPS/Inverters which is flexible to adopt conventional topologies
like full-bridge circuit or half bridge circuit on primary side and push pull with
auxiliary winding on secondary side that results in simple in structure and low in
cost.
\ 8 SEP 7Mh
SUMMARY OF THE INVENTION
Accordingly, there is provided a bidire4ctional switching power converter
comprising bi-directional dc-dc converters of one of a full bridge circuit and half
bridge circuit on the high voltage side of the high frequency transformer and a
push-pull circuit on the battery side that are operated in charging and
discharging mode respectively. The push-pull side of the converter comprises an
additional winding while retaining the center-tapped nature of the high frequency
(HF) transformer on low voltage side and provides different turn's ratios in
charging and discharging modes. The present invention provides both functions
of battery charging and discharging in a single power conversion unit with its
bidirectional power flow capability and effectively reduces the overall system cost
and increases the component utilization factor.
In an embodiment according to the present invention, an additional winding is
incorporated at the push-pull side while retaining the center-tapped nature of
high frequency transformer on low voltage side which is essential for push-pull
converter operation. The added winding i.e. auxiliary winding is utilized only
during charging the battery and during discharging or inverter mode the auxiliary
winding is made ineffective.
\ 8 SEP 3QM
In another embodiment according to the present invention, the additional
winding in battery side achieves high efficiency during discharging mode as this
does not include a boosting inductor on the battery side as in case of current-fed
push-pull converter. Also during the discharging mode, the high turns ratio
maintain high dc voltage which interalia allows the output to preserve its shape
at low battery condition, hence avoid clipping of the output waveform at low
battery voltages and satisfies the THD requirement. The additional winding
remains non-operative during discharging mode by using diode, switch or relay
combination as shown in the figures.
BRIEF DESCRIPTION OF THE 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
and wherein:
Figure 1 shows a block diagram of a bi-directional converter and H-bridge
inverter utilized in Home UPS application.
Figure 2 shows an auxiliary switch in the form of IGBT without anti-parallel diode
according to the present invention.
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\ a SEP 20\4
Figure 3 shows an auxiliary switch using MOSFET and MOSFET (as Diode)
combination according to the present invention.
Figure 4 shows an auxiliary switch using RELAY and DIODE combination
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a bidirectional converter which provides both
functions of battery charging and discharging in a single power conversion unit
with its bidirectional power flow capability and effectively reduces the overall
system cost. The complete block diagram is shown in Figure 1, wherein a bidirectional
converter including a H-bridge inverter is utilized in Home UPS
application. The novel Bidirectional push-pull converter is implemented in Home
UPS system as shown in Figure 1, along with critical protections that are
incorporated to enhance reliability of the system.
Figure 2 shows an auxiliary switch acting as an IGBT without an anti-parallel
diode wherein the bidirectional converter comprising a bi-directional dc-dc
converter consisting of a full bridge circuit of half bridge circuit on the high
voltage side of a high frequency transformer and push-pull circuit on the battery
end with one or more additional windings integrated with a center tapped
winding. IGBTs (ASl, AS2) operating in charging mode and MOSFETs (MSl,
MS2) operate in discharging/ inverter mode as shown in a first embodiment
(Figure 1). A second embodiment is shown in Figure 3 which comprises
MOSFETs (ASl, AS2) and diodes (DAl, DA2) operating in charging mode. The
diodes operate in a charging mode and the MOSFEFs MSl and MS2 operate in
discharging / inverter mode. Another embodiment is shown in Figure 4 which
comprises DIODE and RELAY combination (SWl) that operates in charging
mode, MOSFET (MSl, and MS2 operate in discharging / back-up mode. ,
According to the invention, an additional winding at the push-pull side is
provided while retaining the center-tapped type of the high frequency
transformer on low voltage side which is essential for push-pull converter
operation. The added winding i.e. auxiliary windi9ng is utilized only during
charging the battery, wherein during discharging or inverter mode, the auxiliary
winding is made ineffective by reverse biasing the auxiliary switch combination.
The control of the auxiliary switch is vital for successful operation of the novel
bi-directional converter, because if it is ON during the inverter/discharging mode,
the diode gets forward biased due to the switching operation of the push-pull
\ 8 SEP ?M4
mosfets MS1 and MS2 that leads to failure of the same. Hence the auxiliary
winding is forced to be OFF during the discharging mode and only turned ON
during charging mode. Also for precise battery voltage and battery current
monitoring, an isolated amplifier based sensing is implemented using ADuM3190
that can provide high isolation between input (battery) and output (ac output) of
the Home UPS ensures high safety.
The extra winding in the battery side achieves high efficiency in the discharging
mode as this does not include a boosting inductor on the battery side as in case
of the current-fed push-pull topology. Also during the discharging mode, the high
turns ratio maintains a high dc voltage which allows the output to preserve its
shape at low battery condition, hence avoid clipping of the output waveform at
low battery voltages. The extra winding during discharging mode is made
inoperative by using the diode, switch or relay combination as shown in the
figure.
During the charging mode, the extra winding is made operative by suitably using
the diode, switch or relay combination to charge the batteries with lower turns
ratio. Hence the present configuration provides two different turn ratios that
smoothens the charging and discharging modes of the power backup systems
(UPS) switch mode power supply based battery chargers even under low battery
and low mains voltage conditions.
In order to compensate the error of the system for measuring the battery
voltage and system current, a calibration is done. In voltage calibration, the
system is given fixed predefined voltage from a constant voltage source. The
sense value is captured and the error in measurement is measured based on the
real values and predefined values stored in a non-volatile memory. This error
value is compensated continuously for the measurement of the system
parameters. This error value is compensated continuously for the measurement
of the system parameters. Similar is the case with calibration of current for
charging and discharging current.
The Peak current limit sensed from the analog circuit is fed to a driver for turning
off the inverter IGBT gate pulse, ensuring pulse by pulse protection for
instantaneous protection. This action is also communicated to a controller for
decision making. The member of such pulses are counted in the controller and
after specific counts, the inverter is shut off permanently depending on overload
or short circuit conditions. Figure 5 shows the sequence of operation during
short circuit protection.
Numerous modifications and adaptation of the system of the present invention
will be apparent to those skilled in the art, and thus it is intended by the
appended claims to cover all such modifications and adaptations which fall within
the true spirit and scope of the invention.
\ 8 SEP 9o\l
WE CLAIM:
1. A bidirectional converter comprising an auxiliary switch without antiparallel
diode, the auxiliary switch acting as an IGBT, as well as MOSFET,
wherein the bidirectional converter is a bi-directional dc-dc converter
consisting of a full bridge circuit or half bridge circuit on the high voltage
side of a high frequency transformer, a push-pull circuit constructed on
the battery end, and one or more additional windings integrated with the
center tapped winding of the transformer,
characterized in that the high frequency transformer is provided with an
additional winding / auxiliary winding at the push-pull side while retaining
The center-tapped winding of the high frequency transformer at low
voltage side to enable push-pull converter operation, in that the
additional winding / auxiliary winding is made operative only during
charging of the battery, and in that the additional winding is made
inoperative during discharging of the battery or operation of the system
under inverter mode.
\ 8 SEP MI4
2. The bidirectional converter as claimed in claim 1, wherein the auxiliary
switch comprises the IGBT (ASl, AS2) which operates in charging mode
and wherein the MOSFFT (MSl, MS2) operates in discharginglinverter
mode.
3. The bidirectional converter as claimed in claim 1, wherein the auxiliary
switch comprises IGBT (AS1, AS2) which operates in charging mode,
wherein MOSFET (MSl, MS2), operates in discharging/ inverter mode, and
wherein the diodes, DAl, DA2) operating in charging mode.
4. The bidirectional converter, as claimed in claim 1, the additional winding in
the battery side allows to achieve high efficiency in discharging mode of the
battery due to absence of a boosting inductor on the battery side .
5. The bidirectional converter as claimed in claim 1, wherein during the
discharging mode, the high turns ratio enables to maintain high dc voltage
which allows the output of the transformer to preserve its shape even
at low battery condition thereby avoiding clipping of the output waveform
at low battery voltages.
ORIGINAL
19 2-7 ~ OD3E I-l 0 SEP 7011
6. The bidirectional converter as claimed in claim 1, wherein during the
battery charging mode, the additional winding is activated using a
combination of diode, switch or relay and wherein the battery is charged
with lower turns ratio voltage.
7. The bidirectional converter as claimed in claim 1, wherein two different
turn ratios are provided which smoothens the charging and discharging
modes of the power backup systems including the switch mode power
supply based battery chargers even under low battery and low mains
voltage condition.