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Claims  |
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What is claimed is:
1. A boost power converter apparatus for transferring power form an input
voltage source to a load at a load voltage of magnitude greater than the
magnitude of the voltage of said input voltage source, comprising
a magnetic circuit,
a switch connected in series with said input source and a portion of said
magnetic circuit,
a first capacitor connected between said magnetic circuit and the junction
of said switch and said input source, a portion of said magnetic circuit
thereby being connected in series with said capacitor and said switch,
said capacitor cooperating with said magnetic circuit to define a
characteristic time constant for the time variation of the sinusoidal
component of the switch current which flows after said switch is closed,
a switch controller for turning said switch on and off at times when the
current in said switch is zero, said turn on times being controlled to
regulate the ratio of the voltage across said load to the average value of
voltage across said input source, said ratio being greater than or equal
to one, and
a first unidirectional conducting device connected between said magnetic
circuit and said load, said unidirectional conducting device being poled
to permit current to flow in the direction of said load,
wherein said magnetic circuit comprises an input terminal, an output
terminal an a shunt terminal, said input source being connected to said
input terminal, said switch being connected to said shunt terminal and
said first capacitor and said first unidirectional conducting device being
connected to said output terminal, and
wherein said magnetic circuit comprises a non-saturating coupled inductor
having a first winding and a second winding, said first winding being
connected between said input terminal and said shunt terminal, said second
winding being connected between said shunt terminal and said output
terminal, the polarity of said windings being arranged so that imposition
of a positive voltage between said input terminal and said shunt terminal
induces a positive voltage to appear between said output terminal and said
shunt terminal.
2. A boost power converter apparatus for transferring power form an input
voltage source to a load at a load voltage of magnitude greater than the
magnitude of the voltage of said input voltage source, comprising
a magnetic circuit,
a switch connected in series with said input source and a portion of said
magnetic circuit,
a first capacitor connected between said magnetic circuit and the junction
of said switch and said input source, a portion of said magnetic circuit
thereby being connected in series with said capacitor and said switch,
said capacitor cooperating with said magnetic circuit to define a
characteristic time constant for the time variation of the sinusoidal
component of the switch current which flows after said switch is closed,
a switch controller for turning said switch on and off at times when the
current in said switch is zero, said turn on times being controlled to
regulate the traction of the voltage across said load to the average value
of voltage across said input source, said ration being grater than or
equal to one, and
a first unidirectional conducting device connected between said magnetic
circuit and said load, said unidirectional conducting device being poled
to permit current to flow int eh direction of said load,
wherein said magnetic circuit comprises an input terminal, an output
terminal and a shunt terminals, and input source being connected to said
input terminal, said switch being connected to said shunt terminal and
said first capacitor and said first unidirectional conducting device being
connected to said output terminal, and
wherein said magnetic circuit comprises a non-saturating coupled inductor
having a first winding and a second winding, said first winding being
connected between said input terminal and said output terminal, said
second winding being connected between said shunt terminal and said output
terminal, the polarity of said windings being arranged so that imposition
of a positive voltage between said input terminal and said output terminal
induces a positive voltage to appear between said output terminal and said
shunt terminal.
3. The apparatus of claim 1 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said first winding.
4. The apparatus of claim 1 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said second winding.
5. The apparatus of claim 2 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said first winding.
6. The apparatus of claim 2 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said second winding.
7. The apparatus of claim 2 wherein said magnetic circuit further comprises
a second coupled inductor having a third winding and a fourth winding,
said third winding connected to said input terminal and in series with
said first winding and said fourth winding connected between the junction
of said first and second windings and said output terminal.
8. The apparatus of claim 7 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said third winding.
9. The apparatus of claim 7 wherein said magnetic circuit further comprises
a discrete inductor connected in series with said fourth winding.
10. The apparatus of claim 7 wherein said magnetic circuit further
comprises a discrete inductor connected in series with said second
winding.
11. A boost power converter apparatus for transferring power from an input
voltage source to a voltage-sinking load at a load voltage of magnitude
greater than the magnitude of the voltage of said input voltage source,
comprising
a switch
a non-saturating coupled inductor comprising a first winding, having N1
turns, connected to and in series with a second winding, having N2 turns,
the polarities of said first and said second windings being arranged so
that a voltage across said first winding will induce a voltage across said
second winding which adds to said voltage across said first winding, said
first winding being connected to said input source, both of said windings
of said coupled inductor being connected in series with said input source
and said switch, said coupled inductor being characterized by a turns
ratio, a=N1/N2; a total first winding inductance, Lpri; a total second
winding inductance, Lsec; first and second winding leakage inductances,
Ll1 and Ll2, respectively; and a magnetizing inductance, Lm, where
Lpri=Lm+Ll1 and Lsec=Ll2+Lm/a.sup.2,
a first capacitor, of value C, connected between the junction of said first
winding and said second winding and the junction of said input source and
said switch,
a first unidirectional conducting device connected between said load and
the junction of said first winding and said second winding, said
unidirectional conducting device being poled to conduct current from said
input source to said load after said switch is opened,
a switch controller for turning said switch on and off at times when the
current in said switch is zero,
said coupled inductor and said first capacitor defining a characteristic
time scale,
##EQU16##
for the time variation of the sinusoidal component of the switch current
which flows after turning said switch on, the ratio of the voltage across
said load to the average value of voltage across said input source being
varied by varying the rate at which said turn on times are initiated, said
ratio being greater than or equal to one.
12. A boost power converter apparatus for transferring power from an input
voltage source to a voltage-sinking load at a load voltage of magnitude
greater than the magnitude of the voltage of said input voltage source,
comprising
a first capacitor, of value C,
a non-saturation coupled inductor comprising a first winding, having N1
turns, connected to and in series with a second winding, having N2 turns,
the polarities of said first and said second windings being arranged so
that a voltage across said first winding will induce a voltage across said
second winding which is in opposition to said voltage across said first
winding, said first winding being connected to said input source, both of
said windings of said coupled inductor being connected in series with said
input source and said first capacitor, said coupled inductor being
characterized by a turns ratio, a=N1/N2; a total first winding inductance,
Lpri; a total second winding inductance, Lsec; first and second winding
leakage inductances, Ll1 and Ll2, respectively; and a magnetizing
inductance, Lm, where Lpri=Lm+Ll1 and Lsec=Ll2+Lm/a.sup.2,
a switch connected between the junction of said first winding and said
second winding and the junction of said input source and said first
capacitor,
a first unidirectional conducting device connected between said load and
the junction of said second winding and said first capacitor, said
unidirectional conducting device being poled to conduct current from said
input source to said load after said switch is opened,
a switch controller for turning said switch on and off at times when the
current in said switch is zero,
said first inductance and said first capacitor defining a characteristic
time scale,
##EQU17##
for the time variation of the sinusoidal component of the switch current
which flows after turning said switch on, the ratio of the voltage across
said load to the average value of voltage across said input source being
varied by varying the rate at which said turn on times are initiated, said
ratio being greater than or equal to one.
13. The boost power converter apparatus of any one of claims 1 through 10,
11, or 12 further comprising a second unidirectional conducting device
connected in series between said input source and said boost power
converter apparatus.
14. The boost power converter apparatus of any one of claims 1 through 10,
11, or 12 wherein said input source is an AC source and further comprising
a full-wave rectifier connected between said AC source and said boost
power converter apparatus.
15. The apparatus of claim 13 further comprising a third unidirectional
conducting device connected between the input of said boost power
converter and said load, said third unidirectional conducting device being
poled so that current flowing back toward said input source which is
blocked by said second unidirectional conducting device can flow through
said third unidirectional conducting device in the direction of said load.
16. The apparatus of claim 14 further comprising a third unidirectional
conducting device connected between the input of said boost power
converter and said load, said third unidirectional conducting device being
poled so that current which flows back form the input of said boost power
converter in the direction of said input source, and which is inhibited
from flowing back into said input source by said second unidirectional
conducting device, can flow through said third unidirectional conducting
device int eh direction of said load.
17. The apparatus of any one of claim 1 through 10, 11, or 12 wherein said
controller is arranged to turn said switch off at essentially the first
instant in time, following the time when said switch is turned on, when
the current in said switch returns to zero
18. The apparatus of any one of claim 1 through 10, 11, or 12 wherein said
controller is arranged to turn said switch off at essentially the second
instant in time, following the time when said switch is turned on, when
the current in said switch returns to zero.
19. The apparatus of any one of claim 1 through 10, 11, or 12 further
comprising an output capacitor in parallel with said load, the capacitance
of said output capacitor being large enough so that it smooths the effect
of time variations int eh output current delivered to said load so that
the output voltage of the converter is an essentially DC value.
20. The apparatus of any one of claim 1 through 10, 11, or 12 further
comprising an output voltage controller which varies the frequency of the
switch turn-on times in response to the output voltage at the load.
21. The apparatus of claim 14 further comprising an output voltage
controller which varies the frequency of the switch turn-on times in
response to the output voltage at the load.
22. The apparatus of claim 20 wherein said output voltage controller
comprises
a reference signal, indicative of a desired value of output voltage of said
converter apparatus,
a divider which delivers a second signal, indicative of the actual output
voltage of said converter apparatus,
an error amplifier which compares said reference signal to said second
signal and which delivers an output indicative of the difference between
said desired value of converter output voltage and said actual converter
output voltage, and
a variable frequency control circuit which accepts the output of said error
amplifier and delivers a third signal to said switch controller, said
third signal being indicative of the rate at which switch turn-on ties are
to be initiated so as to maintain said actual converter output voltage
essentially equal to said desired value of converter output voltage.
23. The apparatus of claim 21 wherein said output voltage controller is a
power factor preregulating controller, said power factor preregulating
controller maintaining said output voltage at or above both the peak value
of the voltage delivered by said AC source and the minimum operating
voltage of said load while simultaneously forcing the input current drawn
by said boost power converter to follow the time varying waveform of said
AC source.
24. The apparatus of claim 11 or 12 wherein said switch comprises a
bidirect two-terminal switch capable of carrying bipolar current when on
and capable of withstanding a unipolar voltage when off, said
bidirectional two-terminal switch comprising
a unipolar switch capable of withstanding a unipolar voltage when turned
off, the polarity of said unipolar voltage defining positive and negative
poles on said switch, and capable of carrying a unipolar current, when
turned on, between said positive and negative poles, and
a first unidirectional conducting device connected in parallel with said
unipolar switch, said first unidirectional conducting device being poled
so that it conducts current in a direction opposite of that which can be
carried by said unipolar switch.
25. The apparatus of claim 11 or 12 wherein said switch comprises a
bidirectional two-terminal switch capable of carrying unipolar current
when on and capable of withstanding a bipolar voltage when off, said
bidirectional two-terminal switch comprising
a unipolar switch capable of withstanding a unipolar voltage when turned
off, the polarity of said unipolar voltage defining positive and negative
poles on said switch, and capable of carrying a unipolar current, when
turned on, between said positive and negative poles, and
a first unidirectional conducting device connected in series with said
unipolar switch, said first unidirectional conducting device being poled
so that it conducts current in the same direction as said unipolar switch.
26. The apparatus of claim 24 wherein said unipolar switch comprises a
bipolar transistor.
27. The apparatus of claim 25 wherein said unipolar switch comprises a
bipolar transistor.
28. The apparatus of claim 24 wherein said unipolar switch comprises a
field effect transistor.
29. The apparatus of claim 25 wherein said unipolar switch comprises a
field effect transistor.
30. The apparatus of claim 24 wherein said unipolar switch comprises an
insulated gate bipolar transistor.
31. The apparatus of claim 25 wherein said unipolar switch comprises an
insulated gate bipolar transistor.
32. The apparatus of claim 24 wherein said unipolar switch comprises a
field effect transistor in series with a second unidirectional conducting
device, said second unidirectional conducting device being poled so that
it carries current in the same direction as said field effect transistor. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to boost switching power converters.
Boost switching power converters accept power from an input voltage source
and deliver power to a load at a controllable load voltage value which is
greater than the voltage delivered by the input source. Such converters
are useful in applications where a load must be supplied with a voltage
greater in magnitude than the available source voltage, or where the
magnitude of the voltage delivered by an input source may, under either
steady-state or transient conditions, drop below the minimum value of
operating voltage required by the load. In one increasingly important
application, a boost switching converter forms the core element of a power
factor correcting AC to DC preregulator. In such preregulators, an AC
voltage source is rectified and delivered to the input of a boost
switching power converter. The boost switching power converter is
controlled so as to maintain the load voltage at or above both the peak
value of the AC source voltage and the minimum operating voltage of the
load, while simultaneously forcing the boost converter input current to
follow the time varying periodic waveform of the AC source. In this way,
the voltage delivered by the boost switching converter is controlled to be
within the operating voltage range of the load, while the power factor
presented to the AC source is kept at essentially unity. Examples of
preregulators of this type are described in Wilkerson, U.S. Pat. No.
4,677,366, Williams, U.S. Pat. No. 4,940,929, and Vinciarelli, U.S. patent
application Ser. No. 07/642,232, filed Jan. 16, 1991. One such prior art
boost switching converter is shown in FIG. 1. In the Figure, an input
inductor 12 is connected in series with an input voltage source 14, of
magnitude Vin, and a switch 16. A diode 18, connected between the junction
of the input inductor and the switch, is poled to carry current towards an
output capacitor 20 and a load 22. In operation, the frequency at which
the switch 16 is turned on and off during a converter operating cycle is
fixed, and the duty cycle of the switch (i.e., the fraction, D, of the
time that the switch is on during an operating cycle) is varied as a means
of controlling the converter output voltage, Vo. The inductor smooths the
input current, I1, keeping it essentially constant throughout the
operating cycle, and the output capacitor smooths the effect of variations
in the current Io so that the converter delivers an essentially DC output
voltage. When the switch is on, the voltage across the switch is zero
(assuming ideal circuit elements) and all of the input current flows
losslessly in the switch; when the switch is off all of the input current
flows through the diode toward the capacitor and the load and the voltage
across the switch is equal to the output voltage Vo. Under steady state
conditions, the average voltage across the input inductor must be zero,
else the average value, Iin, of the input current, I1, will vary. Thus,
the average value of the voltage across the switch, (1-D).multidot.Vo,
must equal Vin, hence Vo=Vin/(1-D). Since D must be between zero and one,
Vo>Vin. In prior art boost switching converters of the kind illustrated in
FIG. 1, neither the switch nor the diode is ideal, and both elements
contribute to converter losses. When the switch is turned on it is exposed
to both the current flowing in the input inductor and to a reverse current
which flows from the output capacitor back through the diode during the
diode reverse recovery time. Switch turn-off occurs when the switch is
carrying the full converter input current. Since both the rise and fall
time of the switch are finite, the presence of switch voltage and current
during the switch transition times will cause power to be dissipated in
the switch, and, all other conditions being equal, these switching losses
will increase directly with converter operating frequency. Thus, although
increased operating frequency is desirable in that it allows reducing the
size of the input inductor and the output capacitor (and hence the size of
the converter), prior art converters inherently must trade power density
against operating efficiency. As a practical matter, as the operating
frequency of a prior art boost switching power converter is raised much
beyond 100 KHz, efficiency declines rapidly and the thermal and electrical
stresses on the switch become unmanageable. Another characteristic of
prior art boost switching converters is that two or more units connected
to a common input source and load will not inherently share load power if
operated synchronously. Current sharing between units connected in this
way is first-order dependent on second-order effects (e.g., diode voltage
drops, switch impedance).
SUMMARY OF THE INVENTION
A zero-current switching boost converter according to the present invention
offers improved performance over prior art converters. By essentially
eliminating switching losses, a zero-current switching boost converter
reduces losses in, and stresses on, the switching elements included within
the converter and overcomes the operating frequency barrier exhibited by
prior art converters. As a result, a zero-current switching boost
converter can be operated at higher converter operating frequencies than a
prior art converter with a corresponding improvement in converter power
density. A zero-current switching boost switching converter incorporates
the natural power sharing mechanism inherent to quantized power converters
(note Vinciarelli, U.S. Pat. No. 4,648,020), thereby allowing two or more
such converters to simultaneously supply power to a common load, with each
converter carrying an essentially fixed share of the total load power.
Thus, in general, in one aspect, the invention features apparatus for
controlling transfer of power from an input current source to an output
voltage sink. The apparatus includes a switch for controllably permitting
or inhibiting delivery of current from the source to the output sink when
the switch is, respectively, off or on; circuit elements defining a
characteristic time scale for the time variation of the flow of current in
the switch after the switch is turned on; a switch controller for turning
the switch on and off at times when the current in the switch is zero, the
turn on times being controlled to regulate the ratio of the voltage across
the output voltage sink to the average value of voltage across the input
source, the ratio being greater than or equal to one, and a unidirectional
conducting device poled to permit current flow into the output voltage
sink after the switch is opened and to prevent current flow in reverse
from the output voltage sink back toward the input source.
The invention includes the following preferred embodiments.
The circuit elements which define the characteristic time scale are an
inductor and a capacitor. In some embodiments, the inductor and the switch
form a series circuit and the capacitor is connected in parallel with the
series circuit. In other embodiments, the inductor and the capacitor form
a series leg connected in parallel with the switch. The first inductance
and the first capacitor define the characteristic time scale as
Tc=pi.sqrt(L1.C), for the sinusoidal component of the switch current which
flows after turning the switch on.
In some embodiments, the controller is arranged to turn the switch off at
essentially the first instant in time, following the time when the switch
is turned on, when the current in the switch returns to zero. In other
embodiments, the switch is turned off at essentially the second instant in
time when the current in the switch returns to zero.
In general, in another aspect, the invention features a boost power
converter apparatus in which a switch is connected in series with the
input source and with a portion of a magnetic circuit, a first capacitor
is connected between the magnetic circuit and the junction of the switch
and the input source, a portion of the magnetic circuit thereby being
connected in series with the capacitor and the switch. The capacitor and
the magnetic circuit cooperate with the magnetic circuit to define a
characteristic time constant for the time variation of the sinusoidal
component of the switch current which flows after the switch is closed.
Preferred embodiments of the invention include the following features. The
magnetic circuit comprises an input terminal, an output terminal and a
shunt terminal, the input source being connected to the input terminal,
the switch being connected to the shunt terminal and the first capacitor
and the first unidirectional conducting device being connected to the
output terminal. In some embodiments, the magnetic circuit comprises a
first discrete inductor connected between the input terminal and the shunt
terminal, and a second discrete inductor connected between the shunt
terminal and the output terminal. In other embodiments, the magnetic
circuit comprises a first discrete inductor connected between the input
terminal and the output terminal, and a second discrete inductor connected
between the shunt terminal and the output terminal.
In some embodiments, the magnetic circuit comprises a coupled inductor
having a first winding and a second winding, the first winding being
connected between the input terminal and the shunt terminal, the second
winding being connected between the shunt terminal and the output
terminal, the polarity of the windings being arranged so that imposition
of a positive voltage between the input terminal and the shunt terminal
induces a positive voltage to appear between the output terminal and the
shunt terminal. In other embodiments, the magnetic circuit comprises a
coupled inductor having a first winding and a second winding, the first
winding being connected between the input terminal and the output
terminal, the second winding being connected between the shunt terminal
and the output terminal, the polarity of the windings being arranged so
that imposition of a positive voltage between the input terminal and the
output terminal induces a positive voltage to appear between the output
terminal and the shunt terminal. The magnetic circuit may also include a
discrete inductor connected in series with the first winding, or in series
with the second winding. The magnetic circuit may include a second coupled
inductor having a third winding and a fourth winding, the third winding
connected to the input terminal and in series with the first winding and
the fourth winding connected between the junction of the first and second
windings and the output terminal. A discrete inductor may be connected in
series with the third winding or with the fourth winding.
In some embodiments, the switch comprises a bidirectional two-terminal
switch capable of carrying bipolar current when on and capable of
withstanding a unipolar voltage when off, the bidirectional two-terminal
switch comprising a unipolar switch capable of withstanding a unipolar
voltage when turned off, the polarity of the unipolar voltage defining
positive and negative poles on the switch, and capable of carrying a
unipolar current, when turned on, between the positive and negative poles;
and a first unidirectional conducting device connected in parallel with
the unipolar switch, the first unidirectional conducting device being
poled so that it conducts current in a direction opposite of that which
can be carried by the unipolar switch.
In other embodiments of the bidirectional two-terminal switch, the first
unidirectional conducting device is connected in series with the unipolar
switch, the first unidirectional conducting device being poled so that it
conducts current in the same direction as the unipolar switch.
The unipolar switch may comprise a bipolar transistor, a field effect
transistor, an insulated gate bipolar transistor, or (in the case of a
parallel connection between the unidirectional conducting device and the
unipolar switch) a field effect transistor in series with a second
unidirectional conducting device, the second unidirectional conducting
device being poled so that it carries current in the same direction as the
field effect transistor.
In general, in another aspect, the invention features a boost power
converter apparatus for transferring power from an input voltage source to
a load at a load voltage of magnitude greater than the magnitude of the
voltage of the input voltage source. An input inductance and a switching
circuit (of the kind referred to above) are connected in series with the
input voltage source.
In some embodiments, the converter includes an input inductance, of value
L2, and the switching circuit connected in series with the input voltage
source; and the first inductance, the input inductance, and the first
capacitor define a characteristic time scale, Tc=pi.sqrt(Lp.C), where
Lp=(L1.L2)/(L1+L2), for the sinusoidal component of the switch current
which flows after turning the switch on.
In other embodiments, the first inductance and the first capacitor define a
characteristic time scale, Tc=pi.sqrt(L1.C), for the sinusoidal component
of the switch current which flows after turning the switch on.
In preferred embodiments, a unidirectional conduction device is connected
to the source; e.g., a full-wave rectifier may be connected between an AC
input source and the switching circuit. An output capacitor may be
connected in parallel with the load, the capacitance of the output
capacitor being large enough so that it smooths the effect of time
variations in the output current delivered to the load so that the output
voltage of the converter is an essentially DC value. An output voltage
controller may be used to control the frequency of the switch turn-on
times in response to the output voltage at the load. The output voltage
controller may include a reference signal, indicative of a desired value
of output voltage of the converter apparatus; a divider which delivers a
second signal, indicative of actual output voltage of the converter
apparatus; an error amplifier which compares the reference signal to the
second signal and which delivers an output indicative of the difference
between the desired value of converter output voltage and the actual
converter output voltage; and a variable frequency control circuit which
accepts the output of the error amplifier and delivers a third signal to
the switch controller, the third signal being indicative of the rate at
which switch turn-on times are to be initiated so as to maintain the
actual converter output voltage essentially equal to the desired value of
converter output voltage.
In some embodiments, the output voltage controller is a power factor
preregulating controller which maintains the output voltage at or above
both the peak value of the voltage delivered by the AC source and the
minimum operating voltage of the load while simultaneously forcing the
input current drawn by the boost power converter to follow the time
varying waveform of the AC source.
In general, in other aspects, the invention includes methods for
controlling transfer of power.
Other advantages and features will become apparent from the following
description of the preferred embodiment and from the claims.
DESCRIPTION
We first briefly describe the drawings:
FIG. 1 shows a prior art boost switching power converter.
FIG. 2 shows a prior art current-commutating switch.
FIGS. 3A, 3B, and 3C show operating waveforms for the current-commutating
switch of FIG. 2.
FIGS. 4A and 4B show two embodiments of a zero-current-switching
current-commutating switch.
FIGS. 5A through 5F show operating waveforms for either of the switches of
FIG. 4A or FIG. 4B in an operating mode called the short cycle mode.
FIGS. 6A through 6F show operating waveforms for either of the switches of
FIG. 4A or FIG. 4B in an operating mode called the long cycle mode.
FIG. 7 is a zero-current-switching boost switching power converter which
includes a zero-current-switching current-commutating switch of the kind
shown in FIG. 4A.
FIG. 8 is a zero-current-switching boost switching power converter which
includes a zero-current-switching current-commutating switch of the kind
shown in FIG. 4B.
FIG. 9 shows an array of zero-current-switching boost switching power
converters.
FIGS. 10A through 10F show waveforms for a converter of the kind shown in
FIG. 7, operating in the short cycle operating mode, wherein the ratio of
the inductance values, L1 and L2, is finite.
FIGS. 11A through 11F show waveforms for a converter of the kind shown in
FIG. 7, operating int he long cycle operating mode, wherein the ratio of
the inductance values, L1 and L2, is finite.
FIGS. 12A through 12F show waveforms for a converter of the kind shown in
FIG. 8, operating in the short cycle operating mode, wherein the ratio of
the inductance values, L1 and L2, is finite.
FIGS. 13A through 13F show waveforms for a converter of the kind shown in
FIG. 8, operating in the long cycle operating mode, wherein the ratio of
the inductance values, L1 and L2, is finite.
FIG. 14 is a generalized circuit model, illustrating a general magnetic
circuit structure, for a zero-current switching boost converter.
FIG. 15A through 15E illustrate embodiments of zero-current switching boost
converters which include coupled inductors.
FIG. 16 is a circuit model for a coupled inductor.
FIG. 17 shows the converter of FIG. 15A with the coupled inductor replaced
with the circuit model of FIG. 16.
FIG. 18 shows the converter of FIG. 15B with the coupled inductor replaced
with the circuit model of FIG. 16.
FIG. 19 is a table of equations for the switch voltage, just prior to
closure of the switch, for the converter of FIG. 17, for different
coupling conditions.
FIG. 20 is a table of equations for the switch voltage, just prior to
closure of the switch, for the converter of FIG. 18, for different
coupling conditions.
FIGS. 21 and 21A are a Thevenin's equivalent circuit model (and associated
equations) which combines the circuit effects of the input source and the
coupled inductor, with the switch closed, for the converter of FIG. 17.
FIGS. 22 and 22A are a Thevenin's equivalent circuit model (and associated
equations) which combines the circuit effects of the input source and the
coupled inductor, with the switch closed, for the converter of FIG. 18.
FIG. 23 is a table of equations for the current flowing in the switch in
the converter of FIG. 17 during the energy transfer phase.
FIG. 24 is a table of equations for the current flowing in the switch in
the converter of FIG. 18 during the energy transfer phase.
FIGS. 25 and 25A illustrate use of a unidirectional conducting device at
the input of a zero-current-switching boost switching power converter.
FIGS. 26A through 26C show waveforms which illustrate the change in
characteristic time constant associated with discontinuous flow of input
current during the active portion of an operating cycle.
FIG. 27A through 27D show embodiments of zero-current switching boost
converters which incorporate a forward diode.
FIGS. 28A through 28E show waveforms for the converter of FIG. 27B.
FIGS. 29A and 29B show other embodiments of a zero-current switching boost
converter.
FIGS. 30A through 30C embodiments of a two-terminal switch for use in a
zero-current-switching boost switching power converter which operates in
the long cycle operating mode.
FIGS. 31A through 32C show embodiments of a two-terminal switch for use in
a zero-current-switching boost switching power converter which operates in
the short cycle operating mode.
FIG. 32 shows a zero-current-switching boost switching power converter and
a controller for maintaining the output voltage of the converter at some
desired value as the converter input voltage and load vary.
FIG. 33 shows an implementation of a switch controller suitable for
operating a ZCB converter in the short cycle mode.
FIG. 34 shows another implementation of a switch controller for operating a
ZCB converter in the long cycle mode.
Structure and Operation
FIG. 1 shows a circuit model of one kind of prior art boost switching
converter 10 which delivers power from an input voltage source 14, of
value Vin, to a load 22, at a load voltage Vo, where Vo>Vin. The converter
includes a current-commutating switch 17, an input inductor 12, and an
output capacitor 20. The current commutating switch 17 consists of a
two-terminal switch 16 and a diode 18. A switch control signal 19,
delivered to the current commutating switch at a switch control input,
turns the two-terminal switch 16 on and off. When the two-terminal switch
is on, the current, I1, flowing into the input terminal 24 of the
current-commutating switch 17, flows out of the shunt terminal 21 (i.e.,
Is=I1) and the switched voltage, Vs, is zero. When the two-terminal switch
16 is turned off, the current, I1, flowing into the input terminal of the
current-commutating switch, flows through the diode 18 and out of the
output terminal 25 (i.e., Io=I1), and the switched voltage, Vs, is equal
to the output voltage, Vo. Assuming ideal components, there is no switch
loss associated with the flow of currents Is and Io. Both the basic
operating principles and the performance limitations of the prior art
converter may be illustrated, without loss of generality, by assuming that
the rate at which the two-terminal switch is turned on and off (i.e., the
converter operating frequency) is fixed; that the switch is operated at a
fixed duty cycle, D (where D is the fraction of the time that the switch
is on during a converter operating cycle); that the average value of the
current, I1, flowing in the input inductor is Iin; that the value, L1, of
the input inductor is large enough so that the flow of I1 is maintained in
the direction indicated in the Figure throughout the operating cycle; and
that the value, Co, of the output capacitor is also large enough so that,
by smoothing the effects of variations of the current Io during an
operating cycle, the converter delivers an essentially DC output voltage,
Vo. It should be apparent that the size of both the input inductor and the
output capacitor (and hence the size of the converter) can be reduced as
the converter operating frequency is increased. Under these conditions,
the average value of the current Io will be (1-D).multidot.Iin, the
average value of the current Is will be D.multidot.Iin, and the average
value of the switched voltage, Vs, will be (1-D).multidot.Vo. Under
steady-state conditions the average voltage across the input inductor,
Vin-(1-D).multidot.Vo, must be zero, else the average value of the input
current, Iin, will increase or decrease until this condition is met.
Therefore, the steady-state DC output voltage will be
Vo=Vin/(1-D)=Rv.multidot.Vin, and the ratio of converter output voltage to
converter input voltage, Rv, will be maintained independent of converter
loading. This property inherent to the converter, where development of
nonzero average voltage across the converter input inductor causes the
converter input current to self-adjust until a ratio of output to input
voltage is achieved which returns the average input inductor voltage back
to zero, will be referred to as "volt-second" regulation. Thus, under
steady state conditions, Pin=Vin.multidot.In=Pout=Vo.multidot.Iload, and
the average values of the currents and voltages are: Iin=Pin/Vin;
Io=Iin/Rv; Is=D.multidot.Iin; Vs=Vin; and Vo=Rv.multidot.Vin. Since 1>D>0,
Vo must be | | |
