Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2001-03-28
2003-02-04
Berhane, Adolf Denske (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C323S222000
Reexamination Certificate
active
06515883
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to single-stage power converters, and more particularly to single-stage power converters having an AC, a DC, or an AC/DC input and providing power factor correction.
BACKGROUND OF THE INVENTION
As the number of computers and sophisticated electronics continues to grow, so to does the requirement for high-quality electric power to supply the growing demand presented by these devices. Unfortunately, the ability of electric power utilities to supply the power quality required by such equipment at the point of utilization has simply not kept up with the need for such power. As a result, there is a greatly increased need for power conversion and conditioning equipment that is capable of supplying reliable, high-quality power for use by these devices. Additionally, despite the essential role that such power conversion and conditioning equipment plays, there is increased market pressure for such equipment to be as low-cost and complexity as possible to achieve the required reliability demanded by the consuming public.
Uninterruptible power supplies (UPSs) make up one class of such power conversion and conditioning equipment in increased demand. These UPSs are needed to supply reliable high-quality power to the consumer and commercial electronics industries to maintain operation of this equipment in the face of degraded or absent utility power. A typical UPS includes power conversion circuitry capable of conditioning poor quality AC voltage from the utility line, as well as generating high-quality output power from electric storage batteries. The typical UPS utilizes a multistage power converter to fulfill all of the requirements of the UPS system. These requirements may include maintaining the charge of the electric storage batteries during AC power line usage, performing power factor correction on the input power draw from the utility line, and generating an AC output voltage from the electric storage batteries during periods of loss or sufficient degradation of the power quality of the utility line voltage. Unfortunately, such increased complexity also tends to drive up the cost of such UPS equipment.
Various single-stage power converter topologies are known in the power conversion industry. Unfortunately, most are limited to simple DC-to-DC conversion. One such single-stage power converter, which has found wide application as a DC-to-DC converter, is known as the Ćuk converter after its inventor, Dr. Slobodan Ćuk of the California Institute of Technology. This single-stage switched mode DC-to-DC converter
400
illustrated in
FIG. 4
operates from a DC input voltage source
402
and delivers an output DC voltage to the connected load
416
. The DC source
402
is coupled through input inductor
404
and coupled across switching device
406
. The converter
400
includes capacitor
408
and diode
410
, as well as an output inductor
412
and filter capacitor
414
. The control and operation of the Ćuk converter
400
is well known, and has an output transfer function defined by the following equation:
V
OUT
=
-
V
IN
×
T
ON
T
OFF
,
where T
on
and T
off
are the on and off times of the switching element
406
.
As will be recognized by those skilled in the art, this converter may be operated in a boost or buck fashion. As will also be recognized, the Ćuk converter
400
is inverting, that is the output voltage is of opposite polarity to the input voltage. It is of interest to note that the Ćuk converter
400
allows for a continuous input current and a continuous output current. However, limitations on this circuit require that the input voltage be equal to or greater than zero, thereby constraining its operation to applications having DC input voltages only. As such, the Ćuk converter
400
has not found applicability where AC input voltage is used.
Another switched mode single-stage power converter that has found wide applicability is the single ended primary induction converter (SEPIC)
500
as illustrated in FIG.
5
. As with the Ćuk converter
400
, the SEPIC converter
500
is a DC-to-DC converter. Unlike the Ćuk converter
400
, the SEPIC converter
500
is non-inverting. Its output transfer function is defined by
V
OUT
=
V
IN
×
T
ON
T
OFF
,
where T
ON
and T
OFF
are the on and off times of switching element
506
.
The actual construction of the SEPIC converter
500
is also very similar to the Ćuk converter, utilizing a DC input voltage source
502
coupled through an input inductor
504
across switching element
506
and across inductor
508
. Unlike the Ćuk converter
400
, the SEPIC converter
500
utilizes an output diode
512
, coupling inductor
510
between capacitor
508
and diode
512
to ground. The output capacitor
514
is coupled in parallel with the output load
516
. While the input current from the positive DC voltage source
502
may be continuous, the structure of the SEPIC converter
500
results in an output current that is discontinuous. This discontinuity in the output current tends to increase the output distortion, and further limits application of the SEPIC converter to applications that can tolerate such increased output waveform distortion. This SEPIC converter
500
is also limited to applications that have only a positive DC input voltage, therefore prohibiting its application where AC line voltage must be used.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a new and improved single-stage power converter. More particularly, it is an object of the present invention to provide a new and improved single-stage switched mode power converter providing power factor correction.
In one embodiment of the present invention a single-stage power converter comprises an input that receives an electric power input from an external source, a first circuit portion coupled to the input and operative during a first phase to produce an output power to an external coupled load. The converter further includes a second circuit portion coupled to the input and operative during a second phase to produce the output power. In this embodiment, the first circuit portion is configured as either a Ćuk converter or a single-ended primary inductance converter (SEPIC) and the second circuit portion is configured as either a Ćuk converter or a single-ended primary inductance converter (SEPIC). Unlike a typical SEPIC converter, the output power produced by each of the first and the second circuit portions is continuous.
In an embodiment of the present invention, the first circuit portion includes an output inductor through which the output power is supplied during the first phase. The second circuit portion shares this output inductor. For an embodiment where the input electric power is AC and the output electric power is DC, the first circuit portion is configured as a Ćuk converter and the second portion is configured as a SEPIC converter. In this embodiment the first circuit portion is operative during a negative half-cycle of the AC input electric power, and the second circuit portion is operative during a positive half-cycle of the AC input electric power.
For an embodiment where the input electric power is AC and the output electric power is also AC, the first circuit portion is configured as a Ćuk converter and the second circuit portion is also configured as a Ćuk converter. The first circuit portion is operative during a positive half-cycle of the AC input electric power, and the second circuit portion is operative during a negative half-cycle of the AC input electric power. With this embodiment the output electric power is inverted relative to the input electric power.
For an embodiment where the input electric power is AC and the output electric power is AC, the first circuit portion is configured as a SEPIC converter and the second circuit portion is also configured as a SEPIC converter. In this embodiment the first circuit portion is operati
Berhane Adolf Denske
Leydig Voit & Mayer LTD
Powerware Corporation
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