Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electrical power distribution systems and devices
Reexamination Certificate
2003-06-05
2004-11-23
Chervinsky, Boris (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electrical power distribution systems and devices
C361S637000, C363S144000, C174S0720TR
Reexamination Certificate
active
06822850
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The field of the invention is power converters and more specifically converter configurations including heat sinks that reduce the overall space required to accommodate the configurations.
It is well known that variable speed drives of the type used to control industrial electric motors include numerous electronic components. Among the various electronic components used in typical variable-speed drives, all generate heat to a varying degree during operation. Typically, high-power switching devices such as IGBTs, diodes, SCRs and the like as well as storage devices such as capacitors are responsible for generating most of the heat in a variable-speed drive. It is for this reason, therefore, that most variable-speed drives include a heat sink(s) upon which the power switching devices are mounted. The heat sink(s) conducts potentially damaging heat from assembly components.
Selecting the size and design of a heat sink for a particular variable speed drive is somewhat of a challenge. First, a designer must be aware of the overall characteristics of the motor and drive pair. Second, the designer must understand the industrial application in which the motor and drive pair will be used, including the continuous and peak demands that will likely be placed on the motor and drive by the load. Third, the designer must accommodate, in the design, certain unexpected conditions that would deleteriously affect the heat transfer capability of the heat sink such as unexpectedly high ambient temperatures, physical damage to the heat sink such as mechanical damage, or a build up of a debris layer, as examples. Fourth, the heat sink(s) must be physically dimensioned so as to fit into the space allotted per customer requirements, cabinet or enclosure size, or the like.
In the past, air-cooled heat conducting plates were used to transfer thermal energy from electronic parts to the ambient air. These were passive heat-transfer devices and were generally formed of a light-weight aluminum extrusion including a set of fins. As a general rule, heat transfer effectiveness is based on the temperature differential between the power devices and the ambient air temperature. Of course, in order to provide adequate heat conduction, heat sinks of this type oftentimes are necessarily large and, therefore, bulky and expensive. If high ambient conditions exist, the heat sink becomes ineffective or useless as heat removal cannot be accomplished regardless of the size of the heat sink. If the variable speed drive was in an enclosed space the heat removed from the drive would need to be exhausted or conditioned for recirculation.
By forcing air over fins defined on the heat-conducting plate (e.g., an aluminum extrusion), improved cooling efficiency can be realized. Large blower motors are often used for this purpose. However, as the fins defined in the aluminum extrusions become dirty or corroded during use, the heat sinks become less effective or useless altogether. Blower motors cannot be used in environments where air cleanliness would clog filtration. Therefore, air conditioning equipment is often added to internally circulate and cool the air that is passed over the heat sink fins.
Liquid cooled heat sinks or cold plates have also been used for some applications but with limited success. Generally, a liquid cooled heat sink includes a series of chambers or channels that are formed internally within a sink body member that is formed of material (e.g., copper or aluminum) that readily conducts heat. The body member includes at least one mounting surface for receiving heat generating devices. The channels are typically configured so that at least one channel section is formed adjacent each surface segment to which a heat generating device is mounted—typical channel configurations are serpentine. A coolant liquid is pumped through the channels from one or more inlet ports to one or more outlet ports to cool the sink member and hence conduct heat away form the heat generating devices.
The industry has developed several ways in which to manufacture liquid cooled heat sinks and, each of the different ways to manufacture has different costs associated therewith. For instance, a liquid cooled sink can be constructed by forming a desired serpentine copper conduit path for liquid flow, placing the serpentine conduit construct within a sink mold, pouring molten liquid aluminum into the mold and allowing the molten aluminum to cool. While this manufacturing process has been used successfully, liquid molding processes are very difficult to control and the incidences of imperfect and or non-functioning product have been relatively high.
One other sink manufacturing process that has proven useful includes cutting a at least one channel out of a sink body member, hermetically sealing (e.g., vacuum brazing) a cover member to the body member to cover the channel and then forming an inlet and an outlet that open into opposite ends of the channel. This two part sealing process is much less expensive than the conduit-molten process described above.
When designing any liquid cooled heat sink several factors have to be considered including heat dissipating effectiveness, volume required to accommodate a resulting converter, and cost. With respect to heat dissipation, in the case of a power conversion assembly, there are typically several different heat generating devices that are similarly constructed and that operate in a similar fashion to convert power. For instance, as well known in the controls arts, an AC to DC rectifier typically includes a plurality of power switching devices that are arranged to form a bridge assembly. In the case of a three phase supply and load, the bridge assembly includes three phases, a separate switching phase for each of the three supply and load phases. Here, an exemplary phase may include first and second power switching devices linked at a common node to an associated supply line where the other terminals of the first and second switches are linked to positive and negative DC busses, respectively. A controller is configured to control all of the three phases of the bridge together to convert the three phase AC supply voltage to a DC potential across the positive and negative DC busses.
In a similar fashion, a three phase inverter assembly typically includes three separate phases that link positive and negative DC busses to three load supply lines. In the case of an inverter, each phase typically includes first and second power switching devices that are linked in series between the positive and negative DC busses with the common node between the first and second inverter switches linked to an associated phase of the load. Where the supply and load voltages are large, some rectifier/inverter converter assemblies may include several three phase bridges linked together thereby reducing the load handling of each switching device.
In the case of a rectifier-inverter conversion assembly, a drive circuit is provided that controls all of the switching devices together to create desired three phase output voltages to drive a load linked thereto. In this case, it is imperative that the switching devices operate in characteristic and substantially similar ways to simplify what is, by its very nature, an already complex switching scheme. For this reason, converter designers typically select switching devices having generally known operating characteristics (i.e., that operate within a range) to configure their conversion assemblies.
Nevertheless, as also well known, most switching devices have operating characteristics that are, at least in part, affected by the environments in which the devices operate. Specifically, for the purposes of the present invention, it should be appreciated that switching device operating characteristics change as a function of temperature. For instance, an internal switch resistance has been known to change as a function of temperature which in turn affects the voltage drop ac
Kasunich John M.
Pfeifer David W.
Sheppard Richard
Chervinsky Boris
Quarles & Brady LLP
Rockwell Automation Technologies Inc.
Walbrun William R.
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