Power converters with AC and DC operating modes and methods...

Details Power converters with AC and DC operating modes and methods... Power converters with AC and DC operating modes and methods...

2001-12-10

2002-11-19

Vu, Bao Q. (Department: 2838)

Electric power conversion systems

Current conversion

Using semiconductor-type converter

C363S142000, C363S058000, C363S037000, C307S066000

Reexamination Certificate

active

06483730

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to electrical power devices and methods of operation thereof, and more particularly, to power conversion devices and methods of operation thereof.
BACKGROUND OF THE INVENTION
Uninterruptible power supplies (UPSs) are power conversion devices that are commonly used to provide conditioned, reliable power for computer networks, telecommunications networks, medical equipment and the like. UPSs are widely used with computers and similar computing devices, including but not limited to personal computers, workstations, mini computers, network servers, disk arrays and mainframe computers, to insure that valuable data is not lost and that the device can continue to operate notwithstanding temporary loss of an AC utility source. UPSs typically provide power to such electronic equipment from a secondary source, such as a battery, in the event that a primary alternating current (AC) utility source drops out (blackout) or fails to provide a proper voltage (brownout).
Conventional UPSs may be classified into categories. Referring to
FIG. 1
, a typical conventional off-line UPS disconnects a load from a primary AC source
10
when the primary AC source fails or is operating in a degraded manner, allowing the load to be served from a secondary source such as a battery. The AC power source
10
is connected in series with a switch SI, producing an AC voltage across a load
20
when the switch S
1
is closed. Energy storage is typically provided in the form of a storage capacitor C
S
. The secondary power source, here a battery B, is connected to the load
20
via a low voltage converter
30
and a transformer T. When the AC power source
10
fails, the switch SI is opened, causing the load to draw power from the battery B. The low voltage converter
30
typically is an inverter that produces a quasi-square wave or sine wave voltage on a first winding L
1
of the transformer T from a DC voltage produced by the battery B. The first winding L
1
is coupled to a second winding L
2
of the transformer T connected across the load
20
. When the AC power source is operational, i.e., when the switch S
1
is closed, the battery B may be charged using the low-voltage converter
30
or a separate battery charger circuit (not shown).
A line interactive (LIA) UPS topology is illustrated in FIG.
2
. Here, the transformer T has a third winding L
3
that may be connected in series with the load
20
using switches S
2
, S
3
to “buck” or “boost” the voltage applied to the load
20
. As with the offline UPS topology of
FIG. 1
, when the AC power source
10
fails, the switch S
1
can be opened to allow the load
20
to run off the battery B.
As illustrated in
FIG. 3
, a typical on-line UPS includes a rectifier
40
that receives an AC voltage from an AC power source
10
, producing a DC voltage across a storage capacitor C
S
at an intermediate node
45
. An inverter
50
is connected between the intermediate node
45
, and is operative to produce an AC voltage across a load
20
from the DC voltage. As shown, a battery B is connected to the intermediate node
45
via a DC/DC converter
60
, supplying auxiliary power. Alternatively, the DC/DC converter can be eliminated and a high-voltage battery (not shown) connected directly to the intermediate node
45
.
Each of these topologies may have disadvantages. For example, typical conventional on-line and LIA UPSs for 60 Hz applications use 60 Hz magnetic components (e.g., transformers and inductors) that are sized for such frequencies, and thus may be large, heavy and expensive. LIA UPSs often exhibit step voltage changes that can affect the performance of the load. Conventional off-line, LIA and on-line UPSs often use large storage capacitors, which tend to be bulky and expensive, in order to maintain an acceptable output voltage under heavy loading conditions. Moreover, because conventional UPSs are typically designed to operate in only one of the above-described off-line, LIA or on-line modes, sellers of UPSs may be required to maintain large inventories including several different types of UPSs in order to meet a variety of different customer applications.
SUMMARY OF THE INVENTION
According to embodiments of the present invention, a power converter, such as one that might be utilized in an uninterruptible power supply (UPS), includes first and second voltage busses, a first input port having a first terminal coupled to one of the first and second voltage busses, a neutral bus and an output terminal. A first switching circuit selectively couples a second terminal of the first input port to the first and second voltage busses. A second switching circuit selectively couples the first and second voltage busses to the output terminal. A third switching circuit selectively couples the first and second voltage busses to the neutral bus. Preferably, the first, second and third switching circuits are operative to produce an AC output voltage at the output terminal from a DC input voltage at the first input port such that alternating ones of the first and second terminals of the first input port are referenced to the neutral bus for successive first and second half cycles of the AC output voltage.
In embodiments of the present invention, the first switching circuit includes a first inductance having first and second terminals, the first terminal of the first inductance coupled to the second terminal of the first input port. The first switching circuit further includes a first switch is operative to couple and decouple the second terminal of the first inductance and the first voltage bus and a second switch operative to couple and decouple the second terminal of the first inductance and the second voltage bus. The second switching circuit includes a second inductance having first and second terminals, the first terminal of the second inductance coupled to the output terminal. The second switching circuit further includes a third switch operative to couple and decouple the second terminal of the second inductance and the first voltage bus and a fourth switch operative to couple and decouple the second terminal of the second inductance and the second voltage bus. The third switching circuit includes a third inductance having first and second terminals, the first terminal of the third inductance connected to the neutral bus. The third switching circuit also includes a fifth switch operative to couple and decouple the second terminal of the third inductance and the first voltage bus and sixth switch operative to couple and decouple the second terminal of the third inductance and the second voltage bus.
In other embodiments of the present invention, a power converter further includes a second input port. A fourth switching circuit concurrently couples the second terminal of the first input port to the second voltage bus, decouples the second terminal of the first input port from the first switching circuit, and couples the first switching circuit to a first terminal of the second input port, in a first mode. The fourth switching circuit concurrently couples the second terminal of the first input port to the first switching circuit, decouples the second terminal of the first input port from the second voltage bus, and decouples the first terminal of the second input port from the first switching circuit, in a second mode.
According to other aspects of the present invention, a power converter includes first and second voltage busses, a neutral bus, and an output terminal. A DC voltage generating circuit is operative to produce respective first and second DC voltages on the first and second voltage busses. A first switching circuit is operative to selectively couple the first and second voltage busses to the output terminal. A storage circuit is connected to the output terminal, and includes a capacitive storage element, a rectifying circuit coupling the capacitive storage element to the output terminal and operative to produce a DC voltage across the capacitive storage element from an AC output voltage at the output term

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