Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2001-09-20
2003-04-15
Berhane, Adolf Denske (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C307S105000
Reexamination Certificate
active
06549434
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
This invention relates to harmonic mitigating devices for electrical power distribution systems and more particularly to a passive harmonic mitigating device for connection between a power distribution system and one or more harmonic-generating loads that reduces the level of harmonic currents flowing into the power distribution system.
Electrical distribution systems used to distribute electrical power to buildings, manufacturing facilities, etc., are often subjected to harmonic currents generated by non-linear loads such as electronic equipment, adjustable speed drives (ASD), uninterruptible power supplies (UPS), power rectifiers, etc. Among other harmonics, it is known that these loads are capable of routinely causing 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th etc. harmonics in the power distribution system.
As well known in the art, load generated harmonic currents cause many problems in power distribution systems including increasing the voltage total harmonic distortion level, reducing the electromagnetic compatibility of the loads, reducing reliability of the power distribution equipment, increasing power losses, reducing system power factor, etc.
Prior art systems for mitigating harmonic currents have included configurations that can be grouped into many different categories. One important category of mitigating system is generally referred to as a passive filter network. Passive networks are systems wherein devices within the networks are selected to configure filters based on desired operating characteristics and then, as the name implies, the networks themselves operate, independent of controllers or the like, to reduce harmonics.
One type of passive filter network includes a plurality of trap filters that are individually tuned to eliminate specific harmonics. For instance, because the 5
th
, 7
th
and 11
th
harmonics typically have the largest magnitudes, one exemplary passive network includes three trap filters arranged in parallel between the source and load, one filter for each of the 5
th
, 7
th
and 11
th
harmonics. Often the filter that mitigates the 11
th
harmonic will be designed to mitigate higher order harmonics as well. Each filter includes a reactor including inductive windings disposed on a core, capacitors and typically resistors wherein the capacitors and resistors are arranged in either a delta or wye configuration. Another exemplary passive filter network includes three trap filters arranged in series between the source and load, each filter tuned to mitigate specific harmonics and including a separate core, inductive windings, resistors and capacitors.
These multi-filter networks are advantageous in that the fluxes generated by the windings are relatively simple and easy to comprehend and therefore the networks are easy to design and construct. To this end, because multi-filter networks include separate cores for each of the trap filters, there is no need to account for mutual inductance between filter windings during design.
Unfortunately, while simple to design and construct, the multi-filter networks require a large number of components including resistors, capacitors, windings and a separate core for each of the filters in the network. Not only are the large number of components expensive but the number of components increases overall space required to house the networks.
In an effort to reduce network size and component related costs, another type of passive filter network has been developed which is referred to generally as a broad band filter network. Instead of requiring separate resistors and capacitors for each harmonic to be mitigated, broadband networks typically include first and second line reactors, a trap reactor and a delta or wye connected capacitive and resistive assembly. The first line reactor includes a separate winding for each of the three supply lines in a three phase system, each winding disposed on a first reactor core and linked to a separate one of the supply lines at a first end and to a separate one of three central nodes at a second end. Similarly, the second line reactor includes a separate winding for each of the three supply lines in a three phase system where each winding is disposed on a second reactor core and is linked to a separate one of the central nodes at a first end and to the load at a second end. Thus, in series between each supply line and the load are separate windings corresponding to each of the first and second reactors. The trap reactor includes a third core on which are disposed three separate trap windings, a separate one of the trap windings linked to a separate one of the central nodes at one end and linked to the capacitive/resistive assembly at the other end.
In this case the first and second line reactors provide large reactance to harmonics traveling along the supply line while the trap reactor is tuned to provide minimal reactance to the harmonics such that the harmonics travel into the trap circuit where they are effectively “trapped” (hence the label “trap circuit”) within the capacitive/resistive network.
While advantageous over the multi-filter designs because component count is reduced appreciably and therefore cost and required volume are reduced, three core broadband filters as described above are disadvantageous in that they still require three separate cores (i.e., a separate core for each of the first, second and trap reactors). Again, any design requiring additional components typically increases overall network cost and space required to house the network.
Recently some single core broadband filter networks have been designed that reduce overall network size appreciably. To this end, U.S. Pat. No. 6,127,743 (hereinafter “the '743 patent”) teaches a filter network that includes all network windings on a single core. Specifically, the '743 patent teaches a first set of reactor windings including a separate first winding for each of the supply lines, a second set of reactor windings including a separate second winding for each of the supply lines wherein a separate one of the second windings is linked in series with a separate one of the first windings between the supply and the load and a set of trap reactor windings that are linked to central nodes between the first and second windings of each line. As in the case of three core broad band networks described above, the '743 patent network also includes a capacitive/resistive assembly linked to the trap reactor windings. Importantly, the '743 patent teaches that the first and second windings are disposed on the core in opposite orientations (i.e., the first winding in each series is in a first orientation and the second winding in each series is in an opposite orientation). The '743 patent teaches that this opposing orientation is necessary in order to minimize the voltage drop across the filter network while still mitigating supply line harmonics.
Thus, the '743 patent claims that the networks disclosed therein have many advantages and it would be advantageous to have other network configurations that could provide similar advantages.
In addition, while the '743 patent advantageously reduces the core material required to configure a workable network and therefore reduces system costs, unfortunately, the task of designing and constructing finely tuned single core networks is exacerbated by the fact that the inductances between the single core windings become relatively complex due to mutual inductances between the separate first, second and trap windings. In some cases the extra design and construction costs needed to account for the mutual inductances may be greater than the costs associated with the savings in core material. Thus, it would be advantageous to have a filter network configuration which has some of the advantages associated with a reduced number of cores and components while being characterized by inductance pa
Buchholz Brian R.
Guskov Nick N.
Maslowski Walt A.
Skibinski Gary L.
Zhou Dongsheng
Berhane Adolf Denske
Gerasimow Alexander M.
Jaskolski Michael A.
Rockwell Automation Technologies Inc.
Walbrun William R.
LandOfFree
Harmonic mitigating method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Harmonic mitigating method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Harmonic mitigating method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3003511