Electric power conversion systems – Current conversion – With starting arrangement
Reexamination Certificate
2002-02-13
2004-06-01
Berhane, Adolf (Department: 2838)
Electric power conversion systems
Current conversion
With starting arrangement
C323S908000
Reexamination Certificate
active
06744644
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a soft-start system in an electrical power system and in particular to the soft-start of DC links for capacitor banks of aerospace/industrial power electronics and drive systems.
BACKGROUND OF THE INVENTION
Soft-start systems are used in power conversion and distribution systems to limit the in-rush currents generated therein. For example, when charging capacitor banks the initial in-rush current causes very large transient current and voltage excursions. These transient voltages and currents can over-stress semiconductors and may damage other circuit components such as DC link capacitors and Electromagnetic Interference (EMI) filter components.
FIG. 1
illustrates a conventional soft-start circuit. Traditional soft-start circuits use a resistor
110
and a switching device
120
in the DC link
180
power pass that results in significant power dissipation. Additionally, the traditional soft-start design requires a high current rating of the controlled switching device
120
because the switching device
120
must accommodate the full current supplied to the back-end inverter
170
or other load. Further, an isolated power supply is required for triggering the soft-start supply because the switch is at the same high voltage as the DC link
180
.
In the circuit of
FIG. 1
, the soft-start system interfaces between a front-end rectifier
160
and the back-end inverter
170
. The front-end rectifier
160
receives AC power from a 3 phase AC power source
150
and converts it into DC power. However, the DC power poses a problem if applied directly to the capacitor bank
130
because the capacitor bank appears as a short circuit when the DC voltage is first applied. Therefore, a current limiting resistor
110
is inserted into the circuit to limit the in-rush current when the DC voltage from front-end rectifier
160
is first applied. After the capacitor bank
130
is charged, the current draw from the capacitor bank essentially becomes zero. Additionally, the voltage across the DC bus
182
,
184
approaches the output voltage of the front-end rectifier
160
. The triggering circuit
140
detects this voltage and triggers the switching device
120
when the voltage reaches a predetermined threshold. Switching device
120
when activated shorts out resistor
110
. However, as noted above, this disadvantageously place switching device
120
in series with the back-end inverter, which results in switching device
120
having to conduct the full current drawn by the back-end inverter. Thus, the switching device must be sized for this full current rating. Typically, the switching device
120
, heat sink (not shown) and related components will be relatively large and expensive.
FIG. 1
shows a conventional soft-start system that is used for preventing excessive current/voltage excursions during the initial starting of a power electronic system using a DC link. This design requires a high voltage and high current switching device with excessive power dissipation during normal operation. Alternatively, a relay can be used that is very expensive and bulky due to the high current and high voltage rating of the relay. Therefore, this soft-start system is difficult to implement and requires a large physical envelope for the components.
Therefore, it is desired to have a soft-start system that does not require the switching device, either solid state or electromechanical relay, to continuously carry the full current of the power system
SUMMARY OF THE INVENTION
In accordance with the present invention, the deficiencies in prior systems are overcome by providing a soft-start device for electrical power systems that has the switching device removed from the DC link power pass. According to the present invention, the switching device and resistor are placed in series with a capacitor bank out of the DC link power pass. According to an embodiment of the present invention, the soft-start system includes: a rectifier that receives AC power from a source and converts the AC power into DC power in a DC link; a capacitor connected to a first bus of said DC link; a resistor connected a second bus of said DC link, wherein said resistor and capacitor are connected in series; a switching device connected in parallel with said resistor; and a triggering circuit for measuring a DC voltage on the DC link and activating the switching device to short circuit the resistor.
According to another embodiment of the invention, a method for soft-starting a DC link in an electrical power system comprises: charging a capacitor connected to a first bus of the DC link, wherein a resistor is connected to a second bus of the DC link, and wherein the resistor and capacitor are connected in series; measuring the charge of the capacitor; and activating a switching device, wherein the switching device is connected in parallel with the resistor, and wherein the switching device when activated short circuits the resistor.
REFERENCES:
patent: 4573113 (1986-02-01), Bauman
patent: 5030844 (1991-07-01), Li et al.
patent: 5483142 (1996-01-01), Skibinski et al.
patent: 5570277 (1996-10-01), Ito et al.
patent: 5808880 (1998-09-01), Marvin
patent: 5973419 (1999-10-01), Kruppa et al.
patent: 5978236 (1999-11-01), Faberman et al.
patent: 5986434 (1999-11-01), Roy et al.
patent: 5993039 (1999-11-01), Crill
patent: 5995392 (1999-11-01), Turner
patent: 6005377 (1999-12-01), Chen et al.
patent: 6009008 (1999-12-01), Pelly
patent: 6038155 (2000-03-01), Pelly
patent: 6051941 (2000-04-01), Sudhoff et al.
patent: 6093186 (2000-07-01), Goble
patent: 6097108 (2000-08-01), Tweed
patent: 6128204 (2000-10-01), Munro et al.
patent: 6137705 (2000-10-01), Maekawa et al.
patent: 6157168 (2000-12-01), Malik
patent: 6222749 (2001-04-01), Peron
Berhane Adolf
Honeywell International , Inc.
Palguta Larry J.
LandOfFree
Soft-start of DC link capacitors for power electronics and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Soft-start of DC link capacitors for power electronics and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft-start of DC link capacitors for power electronics and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3364477