Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-04-18
2003-11-04
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S020000
Reexamination Certificate
active
06643148
ABSTRACT:
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION
Standards ETSI ETS 300 132-2 and ANSI T1.315 specify an allowable amount of audio band emissions (up to 20 kHz) that may be conducted from a telecom shelf onto DC power feeders supplying the shelf. Typically, the main source of these audio band conducted emissions is the forced air cooling system, which comprises fans or blowers drawing a current pulsed at less than 1 kHz. The invention suppresses the audio band conducted emissions resulting from the pulsed current sufficiently to comply with the stated standards.
FIGS. 1 and 2
show two prior art approaches of limiting audio band emissions conducted onto DC power feeders supplying a telecom shelf. In the first approach, shown in
FIG. 1
, a large passive L-C filter
10
is placed between the power feeder connection point on the shelf and a high bandwidth DC-DC converter
11
that supplies the fans or blowers
12
of the shelf's cooling system. The passive filter limits the amount of audio band emissions that are conducted from the DC-DC converter
11
back onto the DC power feeders. In the second approach, shown in
FIG. 2
, a low bandwidth active filter
14
is placed between the high bandwidth DC-DC converter
13
and the fans or blowers
15
. In this case the low bandwidth active filter limits the audio band emissions conducted through the DC-DC
13
converter onto the DC power feeders. In both approaches, the audio band emissions caused by the pulsed current used to drive the fans or blowers are sufficiently reduced before they are conducted back onto the DC power feeders, thereby enabling the telecom shelf to meet the aforementioned standards.
Regarding the first prior art approach, shown in
FIG. 1
, the main problem with this approach is that the physical size of the components required for the passive filter
10
is large, and therefore they occupy more than a desirable amount of shelf space, which is usually at a premium.
Regarding the second prior art approach, shown in
FIG. 2
, although the active filter
14
occupies less space than the passive filter
10
of
FIG. 1
, the approach still requires an amount of shelf space that could be further reduced. Additionally, a more complex thermal management solution is typically required due to resultant heating of a series pass element in the active filter.
Both approaches share a problem that is inherent to the high bandwidth DC-DC converters commonly used to regulate the DC voltage applied to the fan or blowers.
Typically, these converters are switch-mode power converters, which have an analog frequency control loop.
The frequency response of this control loop is set by the inherent characteristics of the power converter output filter and switch modulator, as well as the compensation network applied to the feedback error amplifier. In a power converter, it is very common to set the control loop bandwidth to a point well above the pulsed current frequency drawn by the fan or blower. In so doing, the power converter will react to any in band AC load applied to its output, thereby reflecting the AC current signature to its input and onto the power feeders for the shelf. Consequently, additional filtering is required to suppress the audio band noise reflected onto the power feeders.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
The present invention solves the above discussed problem by providing a switch-mode direct current-to-direct current power converter and method for supplying power from a direct current power feed to a forced air cooling system of a communication system, the forced air cooling system unit having an air forcing unit. The fans/blowers units require a DC power source only. Internal to the fan/blower unit is a motor drive circuit that derives from the DC source an AC voltage necessary to drive the fan/blower. The resulting load current signature from the fan/blower drawn from the DC source is an AC waveform with a DC offset. The power converter includes an input adapted to couple to the direct current power feed and an output adapted to electrically drive the air forcing element. In a preferred embodiment, an analog frequency control loop controls the amount of the direct current provided to the air forcing element, the control loop having a response bandwidth which is lower in frequency than that of the alternating current drawn from the output by the air forcing element. Preferably, the analog frequency control loop comprises a compensation network for providing the response bandwidth. Furthermore, the frequency of the alternating current is preferably below 1 kHz and a capacitor is coupled to the output.
REFERENCES:
patent: 4866367 (1989-09-01), Ridley et al.
patent: 5959853 (1999-09-01), Kos
patent: 6009000 (1999-12-01), Siri
patent: 6236578 (2001-05-01), Chen
Alcatel Canada Inc.
Vu Bao Q.
Zegeer Jim
LandOfFree
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