U.S. patent application number 09/858341 was filed with the patent office on 2001-11-08 for switching circuit of power conversion apparatus.
Invention is credited to Itoh, Kazuyuki, Okita, Yoshihisa, Tanaka, Katsuaki.
Application Number | 20010038540 09/858341 |
Document ID | / |
Family ID | 17362902 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038540 |
Kind Code |
A1 |
Itoh, Kazuyuki ; et
al. |
November 8, 2001 |
Switching circuit of power conversion apparatus
Abstract
A switching circuit for a power conversion apparatus capable of
reducing conduction loss to provide a higher efficiency, and
achieving downsizing and weight-reduction and higher driving
frequency based on the improved efficiency is disclosed. A driving
transistor is connected to a switching main transistor to supply a
driving power for ON-OFF driving thereto, and an auxiliary power
source composed of a current transformer is provided between the
main transistor and the driving transistor. An auxiliary transistor
having a lower switching loss than that of the main transistor is
connected in parallel with the main transistor to form a main
switch in combination with the main transistor. A current-driven
type transistor serves as the main transistor, and voltage-driven
type transistors serve as both of the driving transistor and the
auxiliary transistor. The auxiliary transistor is adapted to be
driven at a higher speed than that of the main transistor when the
main transistor is turned on, and adapted to be driven at a lower
speed than that of the main transistor when the main transistor is
turned off.
Inventors: |
Itoh, Kazuyuki; (Tokyo,
JP) ; Okita, Yoshihisa; (Tokyo, JP) ; Tanaka,
Katsuaki; (Tokyo, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN &
LANGER & CHICK, PC
767 THIRD AVENUE
25TH AVE
NEW YORK
NY
10017-2023
US
|
Family ID: |
17362902 |
Appl. No.: |
09/858341 |
Filed: |
May 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09858341 |
May 14, 2001 |
|
|
|
PCT/JP00/06253 |
Sep 13, 2000 |
|
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Current U.S.
Class: |
363/17 |
Current CPC
Class: |
H02M 3/33576 20130101;
H02M 3/1584 20130101; H02M 7/5387 20130101 |
Class at
Publication: |
363/17 |
International
Class: |
H02M 003/335 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 1999 |
JP |
11-261509 |
Claims
What is claimed is:
1. A switching circuit for a power conversion apparatus, wherein a
driving transistor is connected to a switching main transistor to
supply a driving power for ON-OFF driving thereto, an auxiliary
power source composed of a current transformer being provided
between said main transistor and said driving transistor, an
auxiliary transistor having a lower switching loss than that of
said main transistor being connected in parallel with said main
transistor to form a main switch in combination with said main
transistor, said switching circuit comprising; a current-driven
type transistor serving as said main transistor, and voltage-driven
type transistors serving as both of said driving transistor and
said auxiliary transistor, wherein said auxiliary transistor is
adapted to be driven at a higher speed than that of said main
transistor when said main transistor is turned on, and adapted to
be driven at a lower speed than that of said main transistor when
said main transistor is turned off.
2. A switching circuit as defined in claim 1, wherein said main
transistor is adapted to have a period of OFF state within a half
cycle of an AC output of said power transformer apparatus in the
state when a driving control signal is transmitted only to said
auxiliary transistor to bring said auxiliary transistor into ON
state.
3. A switching circuit as defined in claim 2, which further
includes a regenerative diode for regenerating power from an output
of said main switch to said auxiliary power source in said period
when said driving control signal is transmitted only to said
auxiliary transistor.
4. A switching circuit as defined in either one of claims 1 to 3,
wherein said auxiliary transistor is adapted to be driven only
during an activation period of said main switch.
5. A switching circuit as defined in either one of claims 1 to 4,
which further includes an activating power source for supplying an
activating power to said auxiliary power source only during said
activation period of said main switch.
6. A switching circuit for a power conversion apparatus, wherein a
driving transistor is connected to a switching main transistor to
supply a driving power for ON-OFF driving thereto, and an auxiliary
power source composed of a current transformer is provided between
said main transistor and said driving transistor, so as to supply a
power from said auxiliary power source to said driving transistor
through a rectifier circuit, said switching circuit comprising: a
current-driven type transistor serving as said main transistor, and
a voltage-driven type transistor serving as said driving
transistor, and an activating device for applying a bias power to
said auxiliary power source in an earlier timing than that of an
activation of said main transistor when said main transistor is
turn on.
Description
TECHNICAL FIELD
[0001] The present invention relates to a switching circuit of a
switching type power conversion apparatus. In particular, the
present invention relates to a type of switching circuit in which a
driving transistor is connected to a switching main transistor to
supply a driving power for ON-OFF driving thereto in response to a
control signal, and an auxiliary power source is provided between
the main transistor and the driving transistor.
BACKGROUND ART
[0002] In view of efficient utilization of energy, a power
conversion apparatus using a semiconductor switching element or
switching transistor has an extremely widespread availability due
to its excellent characteristics in power conversion efficiency.
The semiconductor switching transistor includes a voltage-driven
type transistor, such as an isolated-gate bipolar transistor
(IGBT), static-induction transistor (SIT) and field-effect
transistor (FET), and a current-driven type transistor, such as a
bipolar-mode static-induction transistor (BSIT) and bipolar
junction transistor (BJT).
[0003] The voltage driven type transistor may be directly driven by
a voltage signal so that a driving circuit may be readily
simplified and its driving frequency may also be arranged higher.
In applications requiring a withstand voltage of 250V or more,
several types of switching transistors are selectively used
depending on requirements for capacity and driving frequency.
Specifically, in case of using the switching transistors in a
driving frequency range of several KHz to several hundred KHz, the
IGBT excellent in overall balance of voltage drop in ON state and
switching performance and the FEA having small current capacity but
capable of high speed operation are widely employed in the power
conversion apparatus.
[0004] On the other hand, since the current-driven switching type
transistor is driven by applying current to a control terminal, a
driving circuit tends to be complexified and to have a lower
operation speed than that of the voltage-driven type transistor.
However, the current-driven type switching transistor has an
advantageous feature that the voltage drop in ON state is about
one-third to one-sixth of that of the voltage-driven type
transistor, and thereby provides a lower conduction loss. This
proves that the current-driven type switching transistor is more
suitable for providing a downsized power conversion apparatus.
[0005] While there are broadly classified two types of
semiconductor switching elements or switching transistor available
for the power conversion apparatus, as described above, it has been
often the case that the voltage-driven type switching transistor
having a low switching loss and facilitating a high frequency
driving was employed in view of downsizing of components,
simplification of circuits, downsizing based on high driving
frequency, cost reduction and other. However, considering how to
coping with social needs for achieving an enhanced efficiency and
downsizing with an eye to the future, the level of voltage drop in
ON state of the voltage-driven type element will be an obstacle as
long as holding over the technique using the current voltage-driven
switching transistor. In particular, observing the current
situation, the voltage drop in ON state of the IGBT et al. being a
mainstream voltage-driven switching transistor has already been
improved closely up to the theoretical value. All the more because
of its current high percentage of completion, it cannot be expected
to reduce the conduction loss drastically.
[0006] As to switching loss, loss recovery techniques utilizing
resonance phenomenon and soft switching techniques have been
developed for preventing electromagnetic environment pollution and
reducing power loss. In contrast, a conduction loss in transistors
serving as a switching element inevitably arises when a current is
passed through the element and the level of the loss depends on the
performance of the element. Thus, the conduction loss cannot be
readily reduced only by a simple modification but a radical review
of circuit topology.
[0007] In the technical field of the power conversion apparatus,
various efforts are currently continued to achieve further
downsized apparatus as a whole, higher power density, and higher
efficiency et al.
[0008] Two primary losses arise in the semiconductor switching
transistor of the power conversion apparatus; one is a switching
loss arising in the course of changing the transistor from ON state
to OFF state or from OFF state to ON state; and the other is a
conduction loss caused by a voltage drop arising in the transistor
when this transistor is in ON state. Thus, in order to provide a
power conversion apparatus capable of meeting the need in response
to the demand for further downsizing the current power conversion
apparatus and enhancing its power density, it is necessary to
develop a technique capable of achieving higher efficiency by
comprehensively reducing both of the conduction loss caused by the
voltage drop in ON state of the switching transistor and the
switching loss which lead to a power loss.
[0009] Heretofore, there have been very few cases reporting that
the conduction loss in the switching transistor was reduced by an
effective improvement in circuit. Giving some examples from among
such few cases, Japanese Patent Laid-Open Publication No. Hei
1-97173 discloses a technology for reducing both a switching loss
and conduction loss in a PWM full-bridge power conversion
apparatus, such as a PWM inverter, by applying a semiconductor
switching element having a small conduction loss, such as a bipolar
transistor, to an arm switched by commercial frequency, and a
semiconductor switching element having a small switching loss, such
as a static-induction transistor (SIT), to an arm switched by
high-frequency, so as to make up a bridge circuit in the apparatus.
The Journal of the Institute of Electrical Engineers of Japan,
Section D, vol. 116, No. 12, 1996, pp. 1205-1210, also discloses a
modification in circuit for reducing a conduction loss in a power
conversion apparatus using semiconductor switching elements.
However, these prior arts involve problems, such as an actual
restriction of their driving frequency, due to insufficient studies
in terms of optimization of the conduction loss, reduction of the
loss in their driving circuit, downsizing et al. For example, the
aforementioned Japanese Patent Laid-Open Publication includes no
specific teaching about how to drive the bipolar transistor serving
as a current control switching element. However, when a constant
current is applied to a base of the transistor as in conventional
methods for driving transistors, the efficiency in low load will be
particularly deteriorated due to the driving loss in no load state
or low load state. In the technique described in the aforementioned
Journal of the Institute of electrical Engineers of Japan, two
transistors each having a small conduction loss are selectively
used among the switching transistors to couple with each other in
the form of the Darlington-connection, and its initial-stage
transistor serves as a driving transistor. Further, an auxiliary
power source composed of a current transformer (CT) is interposed
between the driving transistor and the other or main transistor.
This disclosure describes that this circuitry may reduce the
conduction loss to one-third. However, in the circuit described in
this disclosure, it is necessary for the couple of
Darlington-connected transistors to have a high withstand voltage
characteristic. Generally, as a withstand voltage of a
semiconductor switching element is increased, the element has an
increased voltage drop and a lowered switching speed. Thus, this
technique has its limits in achieving an improved efficiency and
enhanced driving frequency.
DISCLOSURE OF THE INVENTION
[0010] In view of the aforementioned problems in the prior arts, it
is an object of the present invention to provide a switching
circuit for a power conversion apparatus capable of reducing
conduction loss to provide a higher efficiency, and achieving
downsizing and weight-reduction and higher driving frequency based
on the improved efficiency.
[0011] In order to achieve the aforementioned object, in a
switching circuit for a power conversion apparatus according to the
present invention, a driving transistor is connected to a switching
main transistor to supply a driving power for ON-OFF driving
thereto, and an auxiliary power source composed of a current
transformer is provided between the main transistor and the driving
transistor. Further, an auxiliary transistor having a lower
switching loss than that of the main transistor is connected in
parallel with the main transistor to form a main switch in
combination with the main transistor. In the present invention, a
current-driven type transistor serves as the main transistor, and
voltage-driven type transistors serve as both of the driving
transistor and the auxiliary transistor. The auxiliary transistor
is adapted to be driven at a higher speed timing than that of the
main transistor when the main transistor is turned on, and adapted
to be driven at a lower speed than that of the main transistor when
the main transistor is turned off.
[0012] In a preferred embodiment of the present invention, the main
transistor is adapted to have a period of OFF state in the state
when a driving control signal is transmitted only to the auxiliary
transistor to bring the auxiliary transistor into ON state. In this
case, a regenerative diode is preferably provided to regenerate
power from an output of the main switch to the auxiliary power
source in the period when the driving control signal is transmitted
only to the auxiliary transistor. In another embodiment of the
present invention, the auxiliary transistor may be adapted to be
driven only during an activation period of the main switch.
Further, in another embodiment of the present invention, an
activating power source may be provided for supplying an activating
power to the auxiliary power source only during the activation
period of the main switch.
[0013] In another aspect of the present invention, there is
provided a switching circuit for a power conversion apparatus,
wherein a driving transistor is connected to a switching main
transistor to supply a driving power for ON-OFF driving thereto,
and an auxiliary power source composed of a current transformer is
provided between the main transistor and the driving transistor, so
as to supply a power from the auxiliary power source to the driving
transistor through a rectifier circuit. In this case, a
current-driven type transistor serves as the main transistor, and
voltage-driven type transistors serves as the driving transistor.
An activating device is also provided for applying a bias power to
the auxiliary power source in an earlier timing than that of an
activation of the main transistor when the main transistor is turn
on.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a circuit diagram of a switching circuit showing
one embodiment of the present invention;
[0015] FIG. 2 is a circuit diagram showing a structure of a power
conversion apparatus using the switching circuit of FIG. 1;
[0016] FIG. 3 is a diagram showing a switching timing in the power
conversion apparatus of FIG. 2;
[0017] FIG. 4(a) is a circuit diagram showing an arrangement of an
activating power supply transistor;
[0018] FIG. 5(b) is a circuit diagram showing another arrangement
of an activating power supply transistor; and
[0019] FIG. 6 is a circuit diagram showing an example of power
conversion apparatus using a switching circuit provided with the
activating power supply transistor.
BEST MODE OF CARRING OUT THE INVENTION
[0020] With reference to the drawings, embodiments of the present
invention will now be described. Firstly, referring to FIG. 1, a
switching circuit implementing the present invention includes a
main transistor S1 composed of a current-driven type semiconductor
switching element, and a driving transistor S2 connected to a base
of the main transistor S1 to apply a driving signal to the base the
main transistor S1. As one feature of the present invention, the
driving transistor is composed of a voltage-driven type
semiconductor element. An auxiliary transistor S3 is connected in
parallel with the main transistor S1. This auxiliary transistor S3
is also composed of a voltage-driven type semiconductor element. A
drain of the auxiliary transistor S3 is connected to a collector of
the main transistor S1, and a source of the auxiliary transistor S3
is connected to an emitter of the main transistor S1. The main
transistor S1 and auxiliary transistor S3 make up a main switch
MS.
[0021] The collector of the main switch S1 is connected to one
electrode of a DC power source through a connecting terminal 1, and
the emitter of the main transistor S1 is connected to the other
electrode of the DC power source through a connecting terminal 2.
The main switch MS and the driving transistor S2 are connected to
the connecting terminal 1 through a current transformer CT. A
primary winging CT1 of the current transformer CT is connected in
series with the main transistor S1, and a secondary winging CT2 of
the current transformer CT is connected to the driving transistor
S2 through a rectifier circuit composed of a diode Dl and a
capacitor Cl. Each diode D2, D3 is connected in parallel with the
primary winding CT1 of the current transformer CT. Specifically, a
drain of the driving transistor S2 is connected to the secondary
winding of the current transformer CT, and a source of the driving
transistor S2 is connected to the base of the main transistor
S1.
[0022] In this switching circuit, terminals 3 and 4 are provided
for receiving input signals applied to respective gates of the
driving transistor S2 and the auxiliary transistor S3,
respectively. An operation of the current transformer is the same
as that described in the aforementioned disclosure of the Journal
of the Institute of Electrical Engineers of Japan. Specifically, a
driving current corresponding to an input current of the main
switch is supplied to the base of the main transistor S1 through
the driving transistor S2. In the illustrated switching circuit,
since one end of the secondary winding of the current transformer
CT is connected to the drain of the driving transistor S2 and the
other end of the secondary winding is connected to the emitter of
the main transistor S1, a withstand voltage required to the driving
transistor S2 becomes lower than that of the main transistor S1.
Thus, a relatively inexpensive transistor having a low withstand
voltage characteristic, a fast switching speed, and a low voltage
drop may be used as the driving transistor S2. Since the driving
transistor S2 for supplying the driving current to the main
transistor S1 is composed of a voltage-driven type of transistor,
the driving transistor S2 may be driven by a suitable control
signal having power saving effect.
[0023] FIG. 2 shows one example of a power conversion apparatus
using the switching circuit shown in FIG. 1. This power conversion
apparatus includes four switching circuits having the structure
shown in FIG. 1, and the reference numbers B1, B2, B3, B4 indicates
each switching circuit. In FIG. 2, while circuit elements and their
connection are shown for the switching circuit B1 as with FIG. 1,
such detail has been omitted for other switching circuits B2, B3,
B4.
[0024] In FIG. 2, terminals 1 of the switching circuits B1, B4 are
connected to a positive electrode of a DC power source E, and each
emitter of main transistors S1 of the switching circuits B2, B3 are
connected to a negative electrode of the DC power supply E.
Emitters of main transistors S1 of the switching circuit B1, B4 and
terminals 1 of the switching circuit B2, B3 are connected to an
output circuit 6, and the output circuit 6 is connected to a load
7. A signal corresponding to an output is input to a control
circuit 8. Signals S11, S12, S13, S14 indicating respective
currents flowing through main transistors S1 of the switching
circuits B1, B2, B3, B4 are input to the control circuit 8. The
control circuit 8 generates a switching signal by receiving these
input signals. The switching signal includes main transistor
driving signals SS1, SS2, SS3, SS4 to be applied to respective
driving transistors S2 of the switching circuits B1, B2, B3, B4,
and auxiliary transistor driving signals SF1, SF2, SF3, SF4 to be
applied to respective auxiliary transistors S3 of the switching
circuits B1, B2, B3, B4.
[0025] FIG. 3(a) is a time chart showing an operation timing of
each switching transistor in the power conversion apparatus shown
in FIG. 2. For setting the operation timing of each switching
transistor, a half cycle of an AC output is divided into two
sections, and different timings are set in each section. In the
waveforms of the AC output shown in FIG. 3(b), the half cycle
comprises a period T1 in which an output current is higher than a
given rate to a peak value of the output current, and a period T2
in which the output current is lower than the given rate to the
peak value.
[0026] As sown in FIG. 3(a), in the period T1, the driving signals
SS1, SS3 indicated by (A) in FIG. 3(a) are applied to the driving
transistors S2 of the switching circuits B1, B3, respectively, and
thereby a current indicated by (B) in FIG. 3(a) flows through each
of the switching circuits B1, B3. The driving signals SF1, SF3
indicated by (C) in FIG. 3(a) are also applied to the auxiliary
transistors S3 of the switching circuits B1, B3, respectively, and
thereby a current indicated by (D) in FIG. 3(a) flows through each
of the switching circuits B1, B3. As is apparent from FIG. 3(a),
the driving signal applied to the auxiliary transistors S3 is
initiated in an earlier timing than that of the driving signal
applied to the driving transistors S2, and it is held on after the
driving signal of the driving transistors S2 is turned off. While
the current of the auxiliary transistors S3 flows until the current
of the main transistor S1 raises up, the current of the auxiliary
transistors S3 gradually decreases after the current starts flowing
through the main transistor S1 and becomes zero during the current
equivalent to the output current flows through the main transistor
S1. This arises because the current-driven type main transistor S1
has a lower resistance to the current flow, and thereby the current
flows toward the main transistor.
[0027] According to the above control, when the main switch MS is
turn on, the rectifier circuit provided on the side of the
secondary winding of the current transformer CT serving as an
auxiliary power source is activated, and thereby the auxiliary
power source may function without any delay upon the turn-on of the
main switch. Further, when the main switch MS is turn off, the
switching operation arising a switching loss is carried out by the
element having a faster switching speed than that of the main
transistor S1. This allows the switching loss to be reduced.
Further, since the current-driven type transistor having a low
conduction loss is conducted during the most part of a period in
which the main switch is conducted, the conduction loss may also be
reduced. Thus, the loss of the switching circuit may be reduced as
a whole.
[0028] In this circuit, the auxiliary transistor S3 may be
controllably operated only during the activation period of the main
switch MS. The term "the activation period of the main switch MS"
herein means a period of an initial operation in which the
initially activated main switch MS enters into a regular operation
state. For this control, the driving signal is supplied to the
auxiliary transistor S3 in response to a charging voltage of the
capacitor Cl of the rectifier circuit connected to the secondary
winding CT2 of the current transformer CT. More specifically,
during the activation period of the main switch, the driving signal
is applied to the gate of the auxiliary transistor S3 until a given
electric charge is accumulated in the capacitor Cl. Then, after the
given electric charge has been accumulated in the capacitor Cl, the
driving signal of the auxiliary transistor is stopped. After the
given electric charge has been accumulated in the capacitor Cl, the
power from the auxiliary power source is applied to the driving
transistor S2 to activate the regular switching operation of the
main switch MS. In this control, the auxiliary transistor S3 is
operated only in the initial operation of the main switch. This
allows a component having a low capacity to be used as the
auxiliary transistor S3. Further, the operation of the main switch
MS is controlled only by the action of main transistor S1 during a
period other than the activation period of the main switch. Thus,
the operating, or driving, frequency of the main switch depends on
the characteristic of the main transistor.
[0029] As shown in FIG. 3(a), the operating timings of the
switching circuits B2, B4 are shifted by a half cycle with respect
to those of the switching circuit B1, B3.
[0030] In the period T2 in which the output current becomes lower
than the given rate of the peak value of the output current, the
driving signals SS1, SS3 for the driving transistors S2 is stopped,
and the switching operation is carried out only by the activation
of the auxiliary transistor S3, as shown in FIG. 3(a). In this
case, the accumulated energy in the secondary winding CT2 of the
transformer CT serving as the auxiliary power source may be
regenerated from a terminal 5 having a diode D4 shown in FIGS. 1
and 2, and this regenerated energy may, for example, be supplied to
the auxiliary power supply of any other switching circuit. In order
to achieve this operation, as shown in FIG. 4, a bias transistor T
is connected to the circuit connected to the secondary winding CT2
of the current transformer CT to supply an activating power through
an anti-reverse-voltage diode D4, for example. Then, the
regenerated energy at any other switching circuit may be supplied
this switching circuit during the activation period of the main
switch.
[0031] Further, a circuit including the transistor T shown in FIG.
4(a) is useful for an activating circuit of the main switch.
Specifically, during the activation period of the main switch MS,
the activating power may be supplied from the transistor T to the
main switch, and after the activation period, the transistor T may
be controllably turn off. This activation process is advantageous
to allow the main switch to be activated with a lower voltage.
Thus, the auxiliary transistor S3 in FIG. 1 may be omitted and the
anti-reverse-voltage diode may be alternatively used. Furthermore,
a circuit including the transistor T shown in FIG. 4(a) is also
useful for an activating circuit of the main switch. Specifically,
during the activation period of the main switch MS, the activating
power may be supplied from the transistor T to the main switch, and
after the activation period, the transistor T may be controllably
turn off. This activation process is advantageous to allow the main
switch to be activated with a lower voltage. Thus, the auxiliary
transistor S3 in FIG. 1 may be omitted and the anti-reverse-voltage
diode may be alternatively used. FIG. 5 shows one example of a
power conversion apparatus using a switching circuit constructed as
describe above. In FIG. 5, a diode connected in parallel with the
main transistor S1 is designated by the reference number D6.
* * * * *