Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2002-06-04
2004-04-27
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S125000, C307S066000
Reexamination Certificate
active
06728119
ABSTRACT:
FIELD OF THE INVENTION
Embodiments of the present invention are directed generally to a method and an apparatus for converting a DC voltage to an AC voltage. More specifically, embodiments of the present invention are directed to methods and apparatus for converting DC voltages to AC voltages using resonant bridge inverter circuits in devices such as uninterruptible power supplies.
BACKGROUND OF THE INVENTION
The use of uninterruptible power supplies (UPSs) having battery back-up systems to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems, and other data processing systems is well known.
FIG. 1
shows a typical prior art UPS
10
used to provide regulated uninterrupted power. The UPS
10
includes an input filter/surge protector
12
, a transfer switch
14
, a controller
16
, a battery
18
, a battery charger
19
, an inverter
20
, and a DC—DC converter
23
. The UPS also includes an input
24
for coupling to an AC power source and an outlet
26
for coupling to a load.
The UPS
10
operates as follows. The filter/surge protector
12
receives input AC power from the AC power source through the input
24
, filters the input AC power and provides filtered AC power to the transfer switch and the battery charger. The transfer switch
14
receives the AC power from the filter/surge protector
12
and also receives AC power from the inverter
20
. The controller
16
determines whether the AC power available from the filter/surge protector is within predetermined tolerances, and if so, controls the transfer switch to provide the AC power from the filter/surge protector to the outlet
26
. If the AC power from the rectifier is not within the predetermined tolerances, which may occur because of “brown out,” “high line,” or “black out” conditions, or due to power surges, then the controller controls the transfer switch to provide the AC power from the inverter
20
. The DC—DC converter
23
is an optional component that converts the output of the battery to a voltage that is compatible with the inverter. Depending on the particular inverter and battery used the inverter may be operatively coupled to the battery either directly or through a DCDC converter.
The inverter
20
of the prior art UPS
10
receives DC power from the DC—DC converter
23
, converts the DC voltage to AC voltage, and regulates the AC voltage to predetermined specifications. The inverter
20
provides the regulated AC voltage to the transfer switch. Depending on the capacity of the battery and the power requirements of the load, the UPS
10
can provide power to the load during brief power source “dropouts” or for extended power outages.
In typical medium power, low cost inverters, such as inverter
20
of UPS
10
, the Z waveform of the AC voltage has a rectangular shape rather than a sinusoidal shape. A typical prior art inverter circuit
100
is shown in
FIG. 2
coupled to a DC voltage source
18
a
and coupled to a typical load
126
comprising a load resistor
128
and a load capacitor
130
. The DC voltage source
18
a
may be a battery, or may include a battery
18
coupled to a DC—DC converter
23
and a capacitor
25
as shown in FIG.
2
A. Typical loads have a capacitive component due to the presence of an EMI filter in the load. The inverter circuit
100
includes four switches S
1
, S
2
, S
3
and S
4
. Each of the switches is implemented using power MOSFET devices which consist of a transistor
106
,
112
,
118
,
124
having an intrinsic diode
104
,
110
,
116
, and
122
. Each of the transistors
106
,
112
,
118
and
124
has a gate, respectively
107
,
109
,
111
and
113
. As understood by those skilled in the art, each of the switches S
1
-S
4
can be controlled using a control signal input to its gate.
FIG. 3
provides timing waveforms for the switches to generate an output AC voltage waveform Vout (also shown in
FIG. 3
) across the capacitor
130
and the resistor
128
.
A major drawback of the prior art inverter circuit
100
is that for loads having a capacitive component, a significant amount of power is dissipated as the load capacitance is charged and discharged during each half-cycle of the AC waveform. This power is absorbed by the switches S
1
, S
2
, S
3
, S
4
, which typically requires the switches to be mounted to relatively large heat sinks. The issue of power dissipation becomes greater for high voltage systems, in which the energy required to charge the load capacitance is greater. The dissipation of power in the switches dramatically reduces the efficiency of the inverter, and accordingly, reduces the run-time of the battery
18
in the UPS
10
. The rise in temperature of the switches also becomes a large concern.
SUMMARY OF THE INVENTION
In one general aspect, the present invention features an uninterruptible power supply for providing AC power to a load having a capacitive element. The uninterruptible power supply includes an input to receive AC power from an AC power source, an output that provides AC power, a DC voltage source that provides DC power, the DC voltage source having an energy storage device, an inverter operatively coupled to the DC voltage source to receive DC power and to provide AC power, the inverter including first and second output nodes to provide AC power to the load having the capacitive element, first and second input nodes to receive DC power from the DC voltage source, a resonant element having a first terminal and a second terminal, the second terminal being electrically coupled to the first output node, a first switch electrically coupled between the first terminal of the resonant element and the first input node, wherein during a first time period, the first switch is controlled to allow an electrical current path to connect the resonant element to the capacitive element, an electrical current of the path storing energy in the resonant element and charging the capacitive element to a first voltage level, and during a second time period, the first switch is controlled to block the current path to cause the stored energy in the resonant element to further charge the capacitive element to a second voltage level during the second time period, a set of switches operatively coupled between the first and second output nodes and the first and second input nodes and controlled to generate AC power from the DC power, and a transfer switch constructed and arranged to select one of the AC power source and the DC voltage source as an output power source for the uninterruptible power supply.
Other features may include one or more of the following: the first voltage level is a portion of a voltage source and the second voltage level is substantially the voltage source; the set of switches includes a second switch electrically coupled between the second output node and the second input node, a third switch electrically coupled between the second output node and the first input node, a fourth switch electrically coupled between the first output node and the first input node, and a fifth switch electrically coupled between the first output node and the second input node; the inverter further includes a sixth switch electrically coupled between the first terminal of the resonant element and the second input node; the resonant element includes an inductor; each of the switches includes a transistor; the energy storage device includes a battery; and the transfer switch is constructed and arranged to receive the AC power from the input and to receive the AC power from the inverter and to provide one of the AC power from the input and the AC power from the inverter to the load.
In another general aspect, the uninterruptible power supply includes an input to receive AC power from an AC power source, an output that provides AC power, a voltage source that provides DC power, the voltage source having an energy storage device, an inverter operatively coupled to the voltage source to receive DC power and having an output to provide AC power, the inverter including means for charging the capacitive element to
Curtis Jeffrey
Landsman Emanuel E.
Reilly David E.
American Power Conversion
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Patel Rajnikant B.
LandOfFree
Method and apparatus for converting a DC voltage to an AC... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for converting a DC voltage to an AC..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for converting a DC voltage to an AC... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3201781