Claims:1. A system (100) comprising:
a converter (102) comprising a first switch (212) comprising one or more first controllable switches (216) coupled in parallel across at least one diode (218); and
a first controlling unit (106) operatively coupled to the converter (102), wherein the first controlling unit (106) is configured to:
determine a temperature of the one or more first controllable switches (216);
compare the determined temperature of the one or more first controllable switches (216) with a transition temperature at which a first power loss of the one or more first controllable switches (216) is equal to a second power loss of the at least one diode (218); and
control a switching state of the one or more first controllable switches (216) based on the comparison of the determined temperature with the transition temperature.

2. The system (100) of claim 1, wherein the one or more first controllable switches (216) comprise at least one of a silicon based switch and a wide-band gap device.

3. The system (100) of claim 1, wherein the converter (102) further comprises a second switch (214).

4. The system (100) of claim 1, wherein the first switch (212) comprises a freewheeling body diode coupled in parallel to each of the one or more first controllable switches (216).

5. The system (100) of claim 4, wherein a forward voltage drop of the at least one diode (218) is substantially less than a forward voltage drop of the freewheeling body diode.

6. The system (100) of claim 1, further comprising a sensing unit (601) operatively coupled to the converter (102).

7. The system (100) of claim 6, wherein the sensing unit (601) comprises a temperature sensor (602) operatively coupled to the one or more first controllable switches (216).

8. The system (100) of claim 7, wherein the sensing unit (601) further comprises a comparator (604) operatively coupled to the temperature sensor (602).

9. The system (100) of claim 8, further comprising a second controlling unit (614) operatively coupled to the sensing unit (601).

10. The system (100) of claim 9, wherein the sensing unit (601) is configured to:
determine a first voltage representative of the temperature of the one or more first controllable switches (216), using the temperature sensor (602);
compare the determined first voltage with a second voltage representative of the transition temperature, using the comparator (604); and
generate a first control signal for controlling the one or more first controllable switches (216) based on the comparison of the determined first voltage with the second voltage.

11. The system (100) of claim 10, wherein the sensing unit (601) is further configured to transmit the first control signal to the second controlling unit (614).

12. The system (100) of claim 11, wherein the second controlling unit (614) is configured to:
determine the temperature of the one or more first controllable switches (216), using the temperature sensor (602); and
generate a second control signal based on the determined temperature.

13. The system (100) of claim 12, wherein the second controlling unit is further configured to:
determine a value of variation of one or more parameters of one or more components of the sensing unit (601);
compare the second control signal with the first control signal based on the value of variation of the one or more parameters; and
control the switching state of the one or more first controllable switches (216) based on the comparison of the second control signal with the first control signal.

14. A method (700) comprising:
determining (702) a temperature of one or more first controllable switches (216) of a converter (102), wherein the one or more first controllable switches (216) is coupled in parallel across at least one diode (218) of the converter (102);
comparing (704) the determined temperature of the one or more first controllable switches (216) with a transition temperature at which a first power loss of the one or more first controllable switches (216) is equal to a second power loss of the at least one diode (218); and
controlling (708, 710) a switching state of the one or more first controllable switches (216) based on the comparison of the determined temperature with the transition temperature.

15. The method of claim 14, wherein the temperature of the one or more first controllable switches (216) is representative of a junction temperature of the one or more first controllable switches (216).

16. The method of claim 14, further comprising:
determining a first voltage representative of the temperature of the one or more first controllable switches (216), using a temperature sensor (602) of a sensing unit (601);
comparing the determined first voltage with a second voltage representative of the transition temperature, using a comparator (604) of the sensing unit (601); and
generating a first control signal for controlling the one or more first controllable switches (216) based on the comparison of the determined first voltage with the second voltage.

17. The method of claim 16, further comprising:
determining the temperature of the one or more first controllable switches (216), using a second controlling unit (614) operatively coupled to the sensing unit (601); and
generating a second control signal based on the determined temperature, using the second controlling unit (614).

18. The method of claim 17, further comprising:
determining, using the second controlling unit (614), a value of variation of one or more parameters of one or more components of the sensing unit (601);
comparing, using the second controlling unit (614), the second control signal with the first control signal based on the value of variation of the one or more parameters; and
controlling the switching state of the one or more first controllable switches (216) based on the comparison of the second control signal with the first control signal.

19. The method of claim 14, wherein determining the temperature of the one or more first controllable switches (216) comprises determining a load current.

20. The method of claim 19, wherein determining the temperature of the one or more first controllable switches (216) further comprises:
determining a current transmitted through the one or more first controllable switches (216) based on the determined load current; and
determining the temperature of the one or more first controllable switches (216) based on the current transmitted through the one or more first controllable switches (216).

21. The method of claim 19, wherein determining the temperature of the one or more first controllable switches (216) further comprises:
determining a duty cycle of a second switch (214) of the converter (102) based on the determined load current; and
determining the temperature of the one or more first controllable switches (216) based on the duty cycle of the second switch (214).

22. The method of claim 14, wherein determining the temperature of the one or more first controllable switches (216) comprises:
determining a filter current of a filtering circuit (108) coupled to the converter (102);
determining a magnitude of a switching harmonic component based on the determined filter current; and
determining the temperature of the one or more first controllable switches (216) based on the determined magnitude of the switching harmonic component.

23. The method of claim 14, wherein controlling the switching state of the one or more first controllable switches (216) comprises operating the converter (102) with the one or more first controllable switches (216) in a de-activated state if the determined temperature is greater than the transition temperature.

24. The method of claim 14, wherein controlling the switching state of the one or more first controllable switches (216) comprises operating the converter (102) with the one or more first controllable switches (216) in an activated state if the determined temperature is less than the transition temperature.

25. The method of claim 14, wherein the determined temperature of the one or more first controllable switches (216) comprises at least one of a maximum temperature and an average temperature of the one or more first controllable switches (216).
, Description:BACKGROUND
[0001] Embodiments of the present invention generally relate to power conversion systems
and more specifically to a power conversion system
[0002] embodiment, the temperature determination technique may include determining a
load current. A modulation signal or a duty cycle of the second controllable switch is
determined based on the determined load current. Subsequently, the temperature of the one
or more first controllable switches is determined based on the modulation signal or a duty cycle
of the configured to operate over a wide range of temperatures.
[0003] Currently, different DC-DC converters and AC-DC converters incorporating
synchronous rectification circuits at an output side are widely available. Typically, such
converters operate at a room temperature with higher efficiency (for example, >90%). For high
temperature operations, such converters may be designed by employing components which are
capable of withstanding high temperature. However, the converters designed for high
temperature operations are over-rated or require efficient thermal management solutions. The
over-rating of the converters and the use of advanced thermal management solutions make the
converter bulkier and costlier. Furthermore, life of the converters and the reliability of the
converters may be compromised.
[0004] When the converters designed for high temperature are operated at higher
temperatures (for example, above 85°C), the converters tend to lose efficiency. It may be
noted that several factors contribute to loss of efficiency at higher temperatures. In particular,
the semiconductor devices of the converters contribute significantly to the loss of efficiency.
Therefore, maintaining higher efficiency of the converters at higher temperatures and for a
wide range of operating temperatures is a challenging task.
[0005] Accordingly, there is a need for a power conversion system configured to operate
over a wide range of operating temperatures.
BRIEF DESCRIPTION
[0006] In accordance with one embodiment of the present invention, a system including a
converter is disclosed. The converter includes a first switch having one or more first
controllable switches coupled in parallel across at least one diode. A first controlling unit is
operatively coupled to the converter. The first controlling unit is configured to: determine a
temperature of the one or more first controllable switches. The first controlling unit is further
configured to compare the determined temperature of the one or more first controllable
switches with a transition temperature at which a first power loss of the one or more first
controllable switches is equal to a second power loss of the at least one diode. The first
controlling unit is further configured to control a switching state of the one or more first
controllable switches based on the comparison of the determined temperature with the
transition temperature.
[0007] In accordance with another embodiment of the present invention, a method is
disclosed. The method includes determining a temperature of one or more first controllable
switches of a converter. The one or more first controllable switches is coupled in parallel across
at least one diode of the converter. Further, the method includes comparing the determined
temperature of the one or more first controllable switches with a transition temperature at
which a first power loss of the one or more first controllable switches is equal to a second
power loss of the at least one diode. Further, the method includes controlling a switching state
of the one or more first controllable switches based on the comparison of the determined
temperature with the transition temperature.
DRAWINGS
[0008] These and other features, aspects, and advantages of the present disclosure will
become better understood when the following detailed description is read with reference to
the accompanying drawings in which like characters represent like parts throughout the
drawings, wherein:
[0009] FIG. 1 is a block diagram of a power conversion system in accordance with certain
embodiments of the present invention;
[0010] FIG. 2 is a diagrammatical representation of a power conversion system in
accordance with the embodiment of FIG. 1;
[0011] FIG. 3 is a graphical representation of variation of a forward voltage drop with
reference to operating temperature of a diode in accordance with the embodiment of FIG. 2;
and
[0012] FIG. 4 is a graphical representation of variation of ON state resistance (Rds,on) with
reference to operating temperature of a first controllable switch in accordance with the
embodiment of FIG. 2;
[0013] FIG. 5 is a graphical representation of a power loss characteristics of a first switch of
a converter in accordance with the embodiment of FIG. 1;
[0014] FIG. 6 is a diagrammatical representation of a sensing subsystem in accordance with
the embodiment of FIG. 1; and
[0015] FIG. 7 is a flow chart illustrating an exemplary method for operation of a power
conversion system in accordance with certain embodiments of the present invention.
DETAILED DESCRIPTION
[0016] Unless defined otherwise, technical and scientific terms used herein have the same
meaning as is commonly understood by one of ordinary skill in the art to which this
specification belongs. The terms “first”, “second”, and the like, as used herein do not denote
any order, quantity, or importance, but rather are used to distinguish one element from
another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote
the presence of at least one of the referenced items. The term “or” is meant to be inclusive
and mean one, some, or all of the listed items. The use of “including,” “comprising” or “having”
and variations thereof herein are meant to encompass the items listed thereafter and
equivalents thereof as well as additional items. The terms “connected” and “coupled” are not
restricted to physical or mechanical connections or couplings, and can include electrical
connections or couplings, whether direct or indirect. Furthermore, the terms “circuit”,
“circuitry”, and “controlling unit” may include either a single component or a plurality of
components, which are either active and/or passive and are connected or otherwise coupled
together to provide the described function. Also, the term “operatively coupled” as used
herein includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio
communication, software based communication, or combinations thereof.
[0017] As will be described in detail hereinafter, various embodiments of an exemplary
power conversion system and a method of operating the exemplary power conversion system
are disclosed. Specifically, the power conversion system includes a converter having a plurality
of switches configured to operate efficiently over a wide range of temperature. The use of such
switches in the converter enables the converter to be operated over a wide range of
temperature without compromising on the efficiency of the converter. The exemplary power
conversion system may find application in power supply systems employed in environments
prone to wide range of temperature fluctuation, such as in aircrafts, data centers, submarines,
oil and gas extraction systems, and the like.
[0018] Turning now to the drawings and by way of example in FIG. 1, a block diagram of a
power conversion system 100 in accordance with certain embodiments of the present
invention is shown. The power conversion system 100 includes a converter 102, a sensing
subsystem 104, a first controlling unit 106, and a filtering circuit 108. The converter 102 may
include a non-isolated converter or an isolated converter. The converter 102 includes one or
more first controllable switches (not shown in FIG. 1) and at least one second controllable
switch (not shown in FIG. 1). Furthermore, the converter 102 is operatively coupled to the
sensing subsystem 104 and the filtering circuit 108. The filtering circuit 108 is configured to
filter an output signal 110 generated by the converter 102. In one embodiment, the output
signal 110 may be representative of an output voltage or an output current.
[0019] In addition, the first controlling unit 106 is operatively coupled to the converter 102,
the sensing subsystem 104, and the filtering circuit 108. In one embodiment, the first
controlling unit 106 may be separated and disposed remotely from the power conversion
system 100. In particular, the first controlling unit 106 may be disposed in a controlled
temperature environment. The first controlling unit 106 includes an analog controlling unit or a
digital controlling unit.
[0020] In one embodiment, the first controlling unit 106 is configured to monitor, analyze,
and process parameters of the converter 102, the sensing subsystem 104, and the filtering
circuit 108. The parameters of the converter 102, the sensing subsystem 104, and the filtering
circuit 108 may include current, voltage, temperature, and the like.
[0021] Further, the first controlling unit 106 is configured to control operation of the
converter 102. In one embodiment, the first controlling unit 106 is configured to control a
switching state of the one or more first controllable switches and the at least one second
controllable switch of the converter 102. The term “switching state” as used herein may be
used to refer to activation or deactivation of the first and second controllable switches. The
term ‘activation’ of the switch, as used herein, refers to transitioning the switch to an ‘ON’ state
to provide a closed circuit or electrically conducting path. The term ‘deactivation’ of the switch,
as used herein, refers to transitioning the switch to an ‘OFF’ state to provide an open circuit or
electrically non-conducting path.
[0022] The first controlling unit 106 may include one or more processing units and
associated memory devices configured to execute at least one control algorithm. As used
herein, the term “processing unit” refers not only to integrated circuits included in a computer,
but also refers to a controller, a microcontroller, a microcomputer, a programmable logic
controller (PLC), an application specific integrated circuit, application-specific processors, digital
signal processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable
Gate Arrays (FPGAs), and/or any other programmable circuits.
[0023] Furthermore, the first controlling unit 106 may be operatively coupled to a data
repository (not shown in FIG. 1). The data repository includes a memory device. Further, the
memory device(s) may generally include memory element(s) including, but are not limited to,
computer readable medium (e.g., random access memory (RAM)), computer readable nonvolatile
medium (e.g., a flash memory), one or more hard disk drives, a floppy disk, a compact
disc-read only memory (CD-ROM), compact disk-read/write (CD-R/W) drives, a magneto-optical
disk (MOD), a digital versatile disc (DVD), flash drives, optical drives, solid-state storage devices,
and/or other suitable memory elements. The exemplary power conversion system 100 may be
used in applications such as in power supply systems for aviation, submarines, and the like.
[0024] In the illustrated embodiment, the first controlling unit 106 includes a first
temperature determination subunit 112, a first comparison subunit 114, and a first switching
subunit 116. The first temperature determination subunit 112 is configured to determine a
temperature corresponding to the one or more first controllable switches, using one or more
temperature determination techniques. The first comparison subunit 114 is configured to
compare the determined temperature with a transition temperature discussed in greater detail
below. The first switching subunit 116 is configured to control a switching state of the one or
more first controllable switches based on the comparison.
[0025] Referring to FIG. 2, a diagrammatical representation of the power conversion system
100 in accordance with certain embodiments of the present invention is disclosed. In the
illustrated embodiment, the converter 102 is a fly-back converter equipped with synchronous
rectification. The converter 102 is coupled to a source 204 and a load 206. In one
embodiment, the source 204 is a direct current (DC) voltage source or an alternating current
(AC) rectified voltage source. The converter 102 is coupled to the load 206 via a filtering circuit
108. The filtering circuit 108 includes a filter capacitor 208 and an inductor 207. In one
embodiment, the filtering circuit 108 includes either the inductor 207 or the capacitor 208.
Although in the illustrated embodiment, the converter 102 is a fly-back converter, in other
embodiments, the converter 102 may be an inductor-inductor-capacitor (LLC) converter, a buck
converter, a boost converter, a series resonant converter, a parallel resonant converter is also
envisaged.
[0026] The converter 102 includes a first switch 212 and a second switch 214. The first
switch 212 includes one or more first controllable switches 216 and at least one diode 218. For
the ease of illustration, only one first controllable switch 216 and one diode 218 are shown.
The diode 218 is coupled in parallel to the first controllable switch 216. The diode 218 is an
additional diode and is not a freewheeling body diode of the first controllable switch 216. In
the illustrated embodiment the first controllable switch 216 is a wide-band gap device. The
wide-band gap device is a high electron mobility transistor (HEMT) such as a gallium nitride
(GaN) based switch. In another embodiment, the wide-band gap device includes a silicon
carbide (SiC) based switch. In yet another embodiment, the first controllable switch 216
includes a silicon based switch such as an insulated gate bipolar transistor, a metal oxide
semiconductor field effect transistor, a field-effect transistor, an injection enhanced gate
transistor, an integrated gate commutated thyristor, or combinations thereof. In one
embodiment, the first controllable switch 216 includes a freewheeling body diode (not shown
in FIG. 2). The second switch 214 includes at least one second controllable switch. Reference
numeral 214 is used for referring to the second switch or the second controllable switch in the
subsequent detailed description. For ease of illustration, only one second controllable switch is
shown.
[0027] In the illustrated embodiment, the first switch 212 is configured to operate as a
synchronous rectifier of the converter 102. The second controllable switch 214 includes a
freewheeling body diode 215. The first controlling unit 106 is configured to control operation
of the converter 102. Specifically, the first controlling unit 106 is configured to control
activation and/or deactivation of the first and second controllable switches 216, 214. More
specifically, the switching subunit 116 of the first controlling unit 106 is configured to control
activation and/or deactivation of the first and second controllable switches 216, 214. In certain
embodiments, a plurality of first controllable switches 216 may be operatively coupled in
parallel to each other.
[0028] In one embodiment, the converter 102 further includes an isolation transformer 220.
The isolation transformer 220 includes a primary side 222 and a secondary side 224. The first
switch 212 is coupled to the secondary side 224 of the isolation transformer 220.
[0029] The use of the first switch 212 enables to operate the power conversion system 100
over a wide range of temperature. In one embodiment, the power conversion system 100 is
configured to operate at temperature a range of about -55 degrees centigrade to about +125
degrees centigrade.
[0030] Referring now to FIG. 3, a graphical representation 300 of a characteristic of a
forward voltage drop of the diode 218 of FIG. 2 with reference to temperature is shown. An xaxis
302 is representative of forward voltage drop in volts. Further, y-axis 304 is representative
of forward current in amperes. Further, curves 306, 308, 310, 312, and 314 are representative
of forward voltage-forward current characteristics for operating temperatures of about 25
degrees centigrade, 100 degrees centigrade, 150 degrees centigrade, 200 degrees centigrade,
and 250 degrees centigrade respectively.
[0031] In one embodiment, when the forward current is 8 amperes, the forward voltage
drop at an operating temperature of 250 degrees centigrade is 1.7 volts. Further, when the
forward current is 8 amperes, the forward voltage drop at an operating temperature of 150
degrees centigrade is 2.2 volts.
[0032] It may be noted herein that since the diode has a forward-voltage drop, there is
always an associated power loss in the diode. For a predefined forward current, the forward
voltage drop of the diode decreases when the operating temperature increases. The power
loss in the diode is proportional to the voltage. The power loss decreases when operating
temperature increases since the forward voltage drop of the diode decreases when the
operating temperature increases. Therefore, the diode may be advantageously operated at
higher temperatures without increasing power loss.
[0033] Referring now to FIG. 4, a graphical representation 400 of variation of ON state
resistance (Rds,on) with reference to variation in temperature of the first controllable switch 216
of FIG. 2, for example is shown. An x-axis 402 is representative of a junction temperature of the
first controllable switch in degrees centigrade. A y-axis 404 is representative of a normalized
ON state drain to source resistance of the first controllable switch. The term ‘normalized ON
state drain to source resistance’ refers to a normalized resistance with respect to a predefined
temperature
[0034] It may be noted herein that the power losses in the first controllable switch is due to
the ON state drain to source resistance (Rds,on). Curve 406 is representative of a variation of the
ON state drain to source resistance Rds,on with reference to operating temperature of the first
controllable switch. It may be noted herein that for a predefined current of the first
controllable switch, the ON state drain to source resistance Rds,on increases when the
temperature increases. Power loss is proportional to ON state drain to source resistance Rds,on.
Hence, when the operating temperature increases, the power loss in the first controllable
switch increases. When the operating temperature increases, the power loss in any wide-band
gap device also increases.
[0035] Referring now to FIG. 5, a graphical representation 500 of a power loss characteristic
of the first switch 212 of the converter 102 of FIG. 2, for example, is shown. An x-axis 502 is
representative of an operating temperature in degrees centigrade and a y-axis 504 is
representative of power loss in Watts.
[0036] Further, curve 506 is representative of power loss characteristics of the first
controllable switch and curve 508 is representative of power loss characteristics of the diode
218 shown in FIG. 2, for example. An intersecting point 510 of the curves 506, 508 is
representative of a transition temperature. The power loss of the first controllable switch may
be referred to as the first power loss and the power loss of the diode may be referred to as the
second power loss. At the transition temperature, the first power loss is equal to the second
power loss. Reference numeral 512 is representative of a curve along which the power loss of
the first switch is minimal over a wide range of operating temperature. The curve 512 is a
combination of portions of the curve 506 and the curve 508. In the illustrated embodiment, the
curve 512 is a combination of a portion of the curve 506 between points 513 and 510 and a
portion of the curve 508 between points 510 and 515. Further, reference numeral 514 is
representative of higher limit of the operating temperature of the first controllable switch.
[0037] Further, curve 508’ is representative of power loss characteristics in accordance with
another embodiment of diode 218. An intersecting point 510’ of the curves 506, 508’ is
representative of a transition temperature. Reference numeral 512’ is representative of a
curve along which the power loss of the first switch 212 is minimal over a wide range of
operating temperatures.
[0038] Referring again back to FIG. 2 in combination with FIG. 5, if the first controllable
switch 216 has a freewheeling body diode, the diode 218 is selected in such a way that the
forward voltage drop of the diode 218 is substantially less than the forward voltage drop of the
freewheeling body diode of the first controllable switch 216. In one embodiment, difference
between the forward voltage drop of the freewheeling body diode of the first controllable
switch 216 and the forward voltage drop of the diode 218 may be greater than or equal to 0.2
volts. In another embodiment, the power loss of the diode 218 is equal to the power loss of the
first controllable switch 216 at a temperature less than higher limit of the operating
temperature 514 (shown in FIG. 5) of the first controllable switch 216.
[0039] In yet another embodiment, the transition temperature at the point 510’ is
substantially less than the transition temperature at the point 510. Further, power loss of the
first switch 212 represented by the curve 512’ is substantially less than the power loss of the
first switch 212 represented by the curve 512 beyond the transition temperature 510’. In such
an embodiment, the cost of the diode 218 increases substantially. For an optimum design,
there needs to be a tradeoff between the power losses of the first switch 212 and the cost of
the diode 218.
[0040] The diode 218 provides a conducting path for the flow of current when the operating
temperature is greater than the transition temperature 510. The first controllable switch 216 is
activated at an operating temperature less than the transition temperature 510 for providing a
conducting path for the flow of current. When the first controllable switch 216 is activated, the
diode 218 does not provide a conducting path for the flow of current. As a result, power loss in
the converter 102 is reduced over a wide range of operating temperatures. In particular, the
power loss may be restricted along the curve 512 shown in FIG. 5, for example. Thus, the
converter 102 is operated over a wide range of operating temperatures without compromising
on the efficiency.
[0041] FIG. 6 is a diagrammatical representation of the sensing subsystem 104 in accordance
with the embodiment of FIG. 1. The sensing subsystem 104 is operatively coupled to the
converter 102. The sensing subsystem 104 includes a sensing unit 601, a second controlling
unit 614, and a control circuit 616. The second controlling unit 614 includes a second
temperature determination subunit 620, a second comparison subunit 622, and a second
switching subunit 624. The sensing unit 601 includes a temperature sensor 602 and an analog
circuit 612 used for determining switching state of the first controllable switch. The analog
circuit 612 includes a comparator 604, associated resistors, and capacitors. In the illustrated
embodiment, the temperature sensor 602 is a thermocouple. The numeral 602 may be used to
refer to either the temperature sensor or the thermocouple. In one embodiment, the second
controlling unit 614 is a digital controlling unit. In one specific embodiment, the second
controlling unit 614 and the first controlling unit 106 are integrated.
[0042] The thermocouple 602 is configured to produce a voltage signal as a result of a
thermoelectric effect. The voltage signal is representative of the measured temperature. The
thermocouple 602 is operatively coupled to the one or more first controllable switch of the
converter 102 and the comparator 604. The comparator 604, a resistor coupled to the
comparator 604, and a Zener diode 609 forms an analog circuit 612.
[0043] In the illustrated embodiment, the thermocouple 602 is configured to generate a first
voltage representative of the temperature of the first controllable switch. In one embodiment,
the comparator 604 is a hysteresis comparator. The comparator 604 includes an inverting input
terminal 608 and a non-inverting input terminal 606. A reference voltage Vref is generated at
the inverting input terminal 608, using the Zener diode 609. The reference voltage Vref is
representative of the transition temperature and may also be referred to as a second voltage.
[0044] The first voltage is transmitted to the non-inverting input terminal 606. In one
embodiment, the first voltage generated using the thermocouple 602 may be a substantially
low value and hence may not be detectable at the non-inverting input terminal 606 of the
comparator 604. In such an embodiment, an amplifier is used at an output of the
thermocouple 602 in order to amplify the first voltage. Accordingly, an amplified value of first
voltage is obtained.
[0045] In the illustrated embodiment, the first voltage is compared with the second voltage,
using the comparator 604. In particular, the amplified value of first voltage is compared with
the second voltage. The analog circuit 612 generates a first control signal 613 for controlling
the first controllable switch based on the comparison of the first voltage with the second
voltage. The first control signal 613 may be a high signal or a low signal.
[0046] At any instant, if the operating temperature of the first controllable switch is greater
than the transition temperature, then the first voltage transmitted to the non-inverting input
terminal 606 is greater than the reference voltage Vref (second voltage) transmitted to the
inverting input terminal 608. The analog circuit 612 generates a high signal at an output
terminal 610 of the comparator 604. If the high signal is transmitted to the control circuit 616,
the first controllable switch is disabled.
[0047] In an alternative embodiment, the second controlling unit 614 is configured to
directly acquire the temperature of the first controllable switch from the thermocouple 602. In
particular, the second temperature determination subunit 620 is configured to directly acquire
the temperature of the first controllable switch from the thermocouple 602. The determined
temperature is transmitted to an analog to digital converter and a digital value corresponding
to the determined temperature is obtained. Furthermore, the second controlling unit 614 is
configured to generate a second control signal 618 based on the determined temperature. In
particular, the second switching subunit 624 is configured to generate the second control signal
618 based on the determined temperature. More particularly, the second controlling unit 614
is configured to generate the second control signal 618 based on the digital value of
determined temperature. If the temperature of the first controllable switch is less than the
transition temperature, then the generated second control signal 618 is a low signal.
Accordingly, the first controllable switch is activated based on the generated second control
signal 618.
[0048] Furthermore, the second controlling unit 614 is configured to determine a value of
variation of a parameter of the one or more components of the sensing unit. In particular, the
second comparison subunit 622 is configured to determine a value of variation of a parameter
of the one or more components of the sensing unit. In one embodiment, the parameter may
be a resistance of the amplifier used at an output of the thermocouple 602.
[0049] The analog circuit 612 includes resistors, comparators, Zener diodes, and the like.
Hence, the analog circuit 612 is prone to issues associated with failure. In certain scenarios the
determination of temperature using the analog circuit 612 may be erroneous. Therefore, the
first control signal 613 generated by the analog circuit 612 need to be further analyzed by the
second controlling unit 614 to avoid any generation of errors. In one such embodiment, the
sensing unit 601 is configured to transmit the first control signal 613 to the second controlling
unit 614 for further analysis.
[0050] Subsequently, the second controlling unit 614, in particular, the second comparison
subunit 622 is configured to compare the second control signal 618 with the first control signal
613 based on the value of variation of the parameter of the one or more components of the
sensing unit. In one embodiment, the variation of the parameter may be a variation in
resistance of the amplifier used at the output of the thermocouple. In such an embodiment,
the variation in resistance may in turn cause a change in gain of the amplifier. In one
embodiment, if the first control signal 613 is a high signal and the second control signal 618 is a
low signal, then the comparison of both the first and the second control signal 613, 618 enables
to identify that the first control signal 613 is different from the second control signal 618.
[0051] The second controlling unit 614, in particular, the second switching subunit 624, is
further configured to control the switching state of the one or more first controllable switches
based on comparison of the second control signal 618 with the first control signal 613. As
noted hereinabove, the analog circuit 612 is prone to failure. Hence, in one embodiment, the
second switching subunit 624 is configured to prioritize the second control signal 618 over the
first control signal 613, when the first control signal 613 is different from the second control
signal 618. In another embodiment, the second switching subunit 624 may prioritize the
second control signal 618 over the first control signal 613 based on the value of variation of the
parameter of the one or more components of the sensing unit. Accordingly, a determination is
made to transmit the second control signal 618 to the control circuit 616. As a result, the first
controllable switch is activated.
[0052] The activation/deactivation of the first controllable switch is performed based on the
determination of operating temperature of the first controllable switch. Although in the
illustrated embodiment, a thermocouple is used, in other embodiments, other types of
temperature sensors are envisioned.
[0053] FIG. 7 is a flow chart 700 illustrating an exemplary method for operation of a power
conversion system in accordance with certain embodiments of the present invention. At step
702, a temperature of one or more first controllable switches is determined using a
temperature determination technique.
[0054] In one embodiment, the temperature determination technique may include
determining a filter current of the filtering circuit. Further, a magnitude of a switching
harmonic component is determined based on the determined filter current. In one
embodiment, the magnitude of switching harmonic component is determined by conducting a
Fast Fourier Transform (FFT) of the determined filter current. The temperature of the one or
more first controllable switches is determined based on the magnitude of the switching
harmonic component. In particular, the temperature of the one or more first controllable
switches is determined based on the magnitude of the switching harmonic component, using a
harmonic component look-up table. The harmonic component look-up table is stored in a data
repository operatively coupled to the first controlling unit.
[0055] In one embodiment, the harmonic component look up table may include a plurality
of sub-look-up tables, where each sub-look-up table corresponds to different ambient
temperatures. The sub-look-up table may be representative of a relation between different
switching harmonic component magnitudes and different values of junction temperature for a
predefined ambient temperature.
[0056] In another embodiment, the temperature determination technique may include
determining a load current. Further, a current transmitted through the one or more first
controllable switches is determined based on the determined load current. A temperature of
the one or more first controllable switches is determined based on the current transmitted
through the one or more first controllable switches.
[0057] The temperature of the one or more first controllable switches is representative of a
junction temperature of the one or more first controllable switches. In one embodiment, the
temperature of the one or more first controllable switches is determined using a first
monotonic function related to the load current and a temperature of the one or more first
controllable switches. One example of the first monotonic function is represented below in
equation (1).
???? ?? ???? ?? ?????? ???????? * ??????,???? * ???? ?? ????*??*??????
?? * ???????? ?? ??????????????..........(1)
, where Tj= temperature of the one or more first controllable switches;
Ta = ambient temperature;
Rja = junction to ambient thermal resistance;
k = constant of proportionality relating ON state current and root mean square (RMS)
current through one or more first controllable switches;
I= ON state current of the one or more first controllable switches;
V= OFF state voltage of the one or more first controllable switches;
fsw= switching frequency;
TON = ON time of the one or more first controllable switches; and
TOFF = OFF time of the one or more first controllable switches.
[0058] In yet another second controllable switch. In one embodiment, the temperature of
the one or more first controllable switches may be determined using a second monotonic
function related to a temperature of the one or more first controllable switches and the
modulation signal/duty cycle of the second controllable switch. One example of the second
monotonic function is represented below in equation (2).
???? ?? ???? ?? ?????? ??????*????????????
??????????
* ?????? * ?????? * ??????,?????? ?? ??????*????????????
??????????
* ?????? * ?????? * ??*??*??????
?? * ???????? ??
??????????????..........(2)
where Tj= temperature of the one or more first controllable switches;
Ta = ambient temperature;
Rja = junction to ambient thermal resistance;
D = Duty cycle of the second controllable switch;
Vin = Input voltage of a converter
Vo = Output voltage of a converter
Rfilt = Inductive filter resistance
c = constant of proportionality
I= ON state current of the one or more first controllable switches;
V= OFF state voltage of the one or more first controllable switches;
fsw= switching frequency;
TON = ON time of the one or more first controllable switches; and
TOFF = OFF time of the one or more first controllable switches.
[0059] In one embodiment, a Boolean operation may be performed on all results obtained
from the abovementioned temperature determination techniques by the first controlling unit
for determining a switching state of the one or more first controllable switches such as to avoid
any damage to the one or more first controllable switch. In particular, the Boolean operation
may be performed on all results obtained from the abovementioned temperature
determination techniques by the first comparison subunit of the first controlling unit.
[0060] In some embodiments, if the first switch includes a plurality of first controllable
switches, the temperature of each first controllable switch is determined using the
abovementioned temperature determination techniques. Accordingly, a determined
temperature is a maximum of the plurality of acquired values of temperature. In another
embodiment, the determined temperature is an average of the plurality of acquired values of
temperature.
[0061] Furthermore, at step 704, the determined temperature is compared with a transition
temperature. At step 706, a check is done to identify if the determined temperature is greater
than the transition temperature. If the determined temperature is greater than the transition
temperature the control may be transferred to step 708, else the control may be transferred to
step 710. At step 708, the one or more first controllable switches of the converter are
transitioned to a de-activated state. When the one or more first controllable switches are in a
de-activated state, the one or more diodes parallel to the one or more first controllable
switches provides a conducting path. Subsequent to step 708, the control may be shifted back
to step 702 and again the steps 702, 704, 706, and 708 or 710 may be repeated.
[0062] Further, at step 710, the one or more first controllable switches of the converter are
transitioned to an activated state. Subsequent to step 710, the control may be shifted back to
step 702 and the steps 702, 704, 706, and 708 or 710 may be repeated.
[0063] Steps 708, 710 allude to controlling a switching state of the one or more first
controllable switch based on the comparison of the determined temperature with the
transition temperature. In particular, steps 708 and 710 allude to deactivation and activation of
the one or more first controllable switches. In some embodiments, the activation refers to
activation of a plurality of first controllable switches. In another embodiment, the activation
refers to activation of a subset of the plurality of first controllable switches. In such a scenario,
the remaining subset of the plurality of first controllable switches is maintained in a deactivated
state.
[0064] The exemplary process steps may be implemented by suitable codes on a processorbased
system, such as a general-purpose or special-purpose computer. Some or all of the steps
described herein may be performed in different order or substantially concurrently.
Furthermore, the functions may be implemented in a variety of programming languages,
including but not limited to C++ or Java. Such code may be stored or adapted for storage on
one or more tangible, machine readable media, such as on data repository chips, local or
remote hard disks, optical disks (that is, CDs or DVDs), memory or other media, which may be
accessed by a processor-based system to execute the stored code. Note that the tangible
media may include paper or another suitable medium upon which the instructions are printed.
For instance, the instructions may be electronically captured via optical scanning of the paper
or other medium, then compiled, interpreted or otherwise processed in a suitable manner if
necessary, and then stored in the data repository or memory.
[0065] In accordance with the exemplary embodiments discussed herein, the power
conversion system includes a converter having switches that can be operated over a wide range
of temperatures, without compromising on the efficiency of the power conversion system. The
use of such switches in the power conversion system minimizes the need of advanced thermal
management solutions and over-rating of the converters.
[0066] While the invention has been described with reference to exemplary embodiments, it
will be understood by those skilled in the art that various changes may be made and
equivalents may be substituted for elements thereof without departing from the scope of the
invention. In addition, many modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from the essential scope thereof.