Electric power conversion systems – Current conversion – With cooling means
Reexamination Certificate
2000-06-16
2001-04-17
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
With cooling means
C361S709000
Reexamination Certificate
active
06219266
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a self-commutated power converter of a voltage-impressing converter having n high-power modules, in particular IGBT high-power modules.
BACKGROUND INFORMATION
On the market, voltage-source converters are available for three-phase drives up to several MW whose self-commutated power converter has a plurality of high-power modules. When working with these amounts of power, the self-commutated power converter has two inverters which are electrically connected in parallel.
FIG. 1
shows an equivalent circuit diagram of a self-commutated power converter
2
of that kind. The two parallel-connected inverters
4
and
6
have IGBT high-power modules T
1
through T
6
and T
1
′ through T
6
′, respectively, as converter valves. IGBT high-power modules T
1
through T
6
of inverter
4
are mounted on a heat sink
8
(FIG.
2
). In the same way, IGBT high-power modules T
1
′ through T
6
′ of inverter
6
are mounted on a heat sink
10
(FIG.
2
).
In
FIG. 2
, these heat sinks
8
and
10
are illustrated with the appertaining IGBT high-power modules T
1
through T
6
and T
1
′ through T
6
′. It can be deduced from this representation that IGBT high-power modules T
1
through T
6
and T
1
′ through T
6
′, respectively, are arranged one over another in the direction of flow of the cooling air. The heat sink used is shown in e.g., FIG. 4 of European Patent 0 658 934.
A disadvantage of this design of the power section of inverters
4
and
6
is that at least uppermost modules T
1
and T
1
′ receive a heated cooling air. The cooling air flowing in it heat sinks
8
and
10
, respectively, heats up from IGBT module to IGBT module. Consequently, the cooling air can dissipate significantly less power loss at uppermost modules T
1
and T
1
′ than the cooling air at lowest modules T
6
and T
6
′. To prevent inverters
4
and
6
from failure due to overheating of uppermost modules T
1
and T
1
′, respectively, self-commutated power converter
2
is technically rated by uppermost modules T
1
and T
1
′, respectively. Because of this, a power reduction of 20% can occur for self-commutated power converter
2
. This means that, possibly, two IGBT high-power modules electrically connected in series must be provided per converter valve for a self-commutated heavy-duty power converter. In this manner, the illustrated problem would further intensify when working with an arrangement shown in
FIG. 2
, as a result of which one would have to expect a further increase in the power reduction. This means that the efficiency would further decline.
Moreover, these additional IGBT modules influence the size, the weight and the cost of the self-commutated power converter and, consequently, of the voltage-impressing converter, as well. Furthermore, when connecting at least two modules in series within such a converter arm, slightest differences in the switching times can already lead to unsymmetrical voltage sharing. Voltage differences of that kind can be prevented by an additional measure in the control. This additional outlay can be prevented by dividing the supply capacitor voltage into two parts by a center tap so that, in addition to the two potentials plus and minus, a potential zero results. By connecting the zero potential via in each case two additional midpoint diodes of each pair of arms, a “three-point power converter” results which is self-commutated.
In a paper entitled “Transistorwechselrichter für Nahverkehrstriebfahrzeuge [Transistor Inverters For Outer-Suburban Service Traction Vehicles]”, published in German Periodical “eb - Elektrische Bahnen [Electric Railways]” No. 11, pages 341 through 347, such a three-point inverter is depicted as self-commutated power converter. A three-point inverter of that kind uses the same number of modules per inverter arm as a two-point inverter having two modules per converter valve, respectively, but has significant advantages, which are discussed in chapter 3.1 of this paper.
Commercial IGBT modules are supplied as encapsulated modules which contain the actual IGBT and an antiparallel free-wheeling diode. Because of the isolated design of the semiconductors inside the module, the IGBT modules of the three-point inverter can be mounted on a shared heat sink without further measures for electrical isolation. The cooling air brushes over the lower side of the heat sink and does not come into contact with the electric components on the upper side. In this arrangement, only three IGBT modules are arranged side by side along the direction of flow of the cooling air. This arrangement has the disadvantage that, in the case of a fault of an inverter phase, the outlay for replacing one or more modules is quite considerable.
SUMMARY
An object of the present invention is to provide a self-commutated power converter having n high-power modules which no longer has the above mentioned disadvantages.
In an example embodiment according to the present invention of the self-commutated power converter, the high-power modules of a phase are detachably joined to a phase heat sink. These phase heat sinks are linked to a partition of the power converter. The cooling fins of each phase heat sink protrude through the openings of the partition into a ventilation space. Because of this, in the case of faults in the converter arms (phases), these defective modules can be removed relatively easily. The partition also assures that the cooling air brushes only over the cooling fins of the phase heat sinks without coming into contact with the electric components (high degree of protection for the power electronics area).
Because the cooling fins of the individual phase heat sinks run horizontally in the ventilation space and provision is made for an air-discharge duct which is designed in such a manner that the cooling air of the ventilation space flows laterally, in each case on both sides of the phase heat sinks, between the cooling fins into the air-discharge duct, all IGBT high-power modules are cooled uniformly so that the capacity of the each IGBT module can be fully utilized.
Because of this design of the phase modules, up to twelve high-power modules can be mounted per phase heat sink as a function of a required load current, the high-power modules being cooled in such a manner that no power reduction must be accepted. In comparison with a conventional design of a self-commutated power converter having the same number of modules, the cooling improves considerably, savings being made in terms of size, weight, and consequently, the cost, as well.
By arranging the cooling fins of the individual phase heat sinks in a ventilation space and using an air-discharge duct, it is achieved that all high-power modules can be cooled nearly equally so that the IGBT high-power modules available on the market (1200 A/3300 V) can be fully utilized in terms of capacity.
REFERENCES:
patent: 4296455 (1981-10-01), Leaycraft et al.
patent: 4315300 (1982-02-01), Parmerlee et al.
patent: 4682268 (1987-07-01), Okano et al.
patent: 5218516 (1993-06-01), Collin et al.
patent: 5477416 (1995-12-01), Schkrohowsky et al.
patent: 43 16 999 (1994-11-01), None
patent: 0 356 991 (1990-03-01), None
patent: 0 658 934 (1995-06-01), None
C. Tietze et al., “Transistorwechselrichter für Nahverkehrstriebfahrzeuge”, Elektrische Bahnen, 1993, No. 11, pp. 341-347*** .
BakerBotts L.L.P.
Nguyen Matthew
Siemens Aktiengesellschaft
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