Patent Application
20120092108
1. Field of the Invention
Embodiments of the subject matter disclosed herein generally relate to magnetic components, and more particularly, to a multiple mega-Watts (MW) level dry type power transformer operating at voltage levels in the kV range and capable of operating at a fundamental frequency ranging from about hundreds of Hz up to about 1 kHz in a power converter.
2. Description of the Prior Art
Most commercial solutions presently implement dry-type transformers which are either air-cooled or which implement direct cooling for windings (such as hollow metallic tubes that conduct both a cooling fluid and electrical current in the tube). Air-cooled transformers at this power level and frequency approach sizes that are undesirably large. Direct-liquid-cooled tubes exhibit poor packing factors and result in large windows for the winding(s). Further, directly cooled windings exhibit high losses since they cannot be transposed and stranded like litz-wire.
The liquid cooling system of the transformer preferably shares the cooling liquid with the cooling circuit of a power converter. The cooling fluid(s) in modern power electronics is typically in direct contact with several parts of the system. It is known that de-ionized (DI) water interacts with aluminum heat sinks of the converter that are used for cooling semiconductors. The use of copper for cooling tubes of the transformer in such a system should desirably be avoided in the thermal path to eliminate electrochemical interaction that leads to corrosion of the aluminum heat sinks, thus ruling out any direct cooling solution via hollow copper tubes for the transformer. Directly cooled transformer solutions using indirect cooling allows use of Litz wire resulting in a much lower coil loss.
In view of the foregoing, there is a need for a multiple MWs level dry type power transformer capable of operating at a fundamental frequency ranging from about hundreds of Hz up to about 1 kHz in a power converter. The power transformer should avoid the foregoing electrochemical effects, provide a superior packing factor when compared to a hollow aluminum design, and should have a substantially higher efficiency than known solutions.
According to one exemplary embodiment, a magnetic component comprises one or more first litz-wire windings; and one or more first metallic cooling tube windings, wherein each first litz-wire winding is wound together with a corresponding first metallic cooling tube winding on a common bobbin to provide an indirectly-cooled magnetic component spindle assembly.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
Particular embodiments of MWs-level transformer winding configuration 10 described in further detail herein are constructed with a magnetic core and litz-wire windings. Each phase in the transformer winding 10 comprises a first winding and a second winding. The windings are cooled by hollow metal cooling tubes that are wound on the same winding form as the windings. In particular embodiments, the first windings comprise a first litz-wire winding 12 and a corresponding metal cooling tube 13. The second windings comprise a second litz-wire winding 14 and a corresponding metal cooling tube 15. The metal cooling tubes and the windings are embedded in a resin or epoxy to maximize thermal conductivity between the windings and the metal tubes according to one aspect of the disclosure. The metal tubes carry a fluid such as DI water or other suitable fluid that works to extract heat away from the windings. According to one embodiment, the fluid is sustained through a closed loop thermal system that comprises a heat exchanger to accept the rejected heat from the windings.
The transformer core described in further detail herein is cooled through cold-plates that are attached to the surfaces of the magnetic core. The cold-plates sustain fluid flow that removes heat away from the core to the central heat exchanger, similar to the winding cooling loop, also described in further detail herein.
Further details of transformer winding 10 that is configured to support multi-megawatts power applications operating at high fundamental frequencies, e.g. about 100 Hz to about 1 kHz, are now described herein with reference to
According to one aspect, transformer core 20 is cooled through metallic cold plates 40, 42 that are attached to the surfaces of the core 20.
According to one embodiment, a race-track shaped bobbin 62 shown in
With continued reference to
A layer of litz-wire is wound on top of the cooling tube 64 winding to provide a first litz-wire winding 68 for each leg. The litz-wire comprises several, e.g. hundreds or thousands, of smaller wire strands housed in a bundle. The strands are designed to exhibit a diameter that is much smaller than the skin-depth at the frequency of operation. This is done in order to reduce circulating currents in the strands due to skin-effect and proximity effect. According to one aspect, each litz-wire bundle is wrapped with electrical-insulation tape prior to winding in order to withstand the turn-to-turn voltage induced in the winding. Cooling tube 64 winding together with the litz-wire winding 68 form the first winding for the transformer 10.
A layer of insulating material 74 is wound on the first litz-wire winding 68. The thickness of the insulating material 74 is configured to provide sufficient insulation between the second winding discussed in further detail herein and the first winding.
A layer of litz-wire with a predetermined number of turns is wound on top of the insulating material 74 to provide a second litz-wire winding 70 for each leg. The construction of the second winding is similar to that of the first winding.
A hollow cooling tube 66 comprising a metallic material such as aluminum or stainless steel is wound on the second litz-wire winding 70. According to one aspect, cooling tube 66 comprises the same number of turns as the second electrical winding 70. Cooling tube 66 is wrapped with sufficient electrical-insulation tape such as Nomex prior to winding in order to withstand the turn-turn voltage that may exist between each turn of the cooling tube 66 according to one embodiment.
According to one embodiment, each spindle assembly is comprised of bobbin 62, cooling tubes 64, 66, first litz-wire winding 68, second litz-wire winding 70 and second winding-first winding insulation layer 74 is embedded in an insulating medium such as resin or epoxy prior to its installation one of the magnetic core legs 22, 24, 26. The embedding process according to particular embodiments comprises a standard epoxy-case process or a vacuum pressure impregnation process, wherein the bobbin assembly is immersed in the resin or epoxy and heat treated for curing.
The cross-sectional area of the litz-wire bundles 68, 70 for second and first windings, the dimensions of the hollow cooling tubes 64, 66 and the choice of epoxy or resin are interrelated in that they are co-optimized for maximizing the thermal conductivity of the processed spindle assembly in order to effectively remove heat. The litz-wire bundles 68, 70 may be rectangular, square, circular, or elliptical according to particular embodiments. The cooling tubes 64, 66 may also be rectangular or circular in cross-section according to particular embodiments. According to one aspect, the cooling tubes 64, 66 serve an additional purpose of providing a means to sense the voltage. The metallic tube 64 abutting the first litz-wire winding 68 essentially comprises a tertiary winding that sustains the same voltage as the first litz-wire winding 68. This voltage can be integrated, for example, to yield an estimate of the flux in the magnetic core 20. Cooling circuits 64 and 66 are each connected with the external cooling system, comprising the heat exchanger, through electrically insulating connections such as rubber tubes according to one aspect.
According to particular embodiments, the second windings and the first windings can be configured in a star or a delta fashion. According to one embodiment, the second windings are configured as an open star connection and the first windings are configured as a delta connection, such as depicted in
The embodiments described herein advantageously provide without limitation, a high power, multi-megawatts level, high fundamental frequency, e.g. up to about 1 kHz, dry-type transformer with indirect cooling for windings and the magnetic core to yield a high efficiency and high power density transformer. Advantages provided using the principles described herein comprise 1) advanced cooling in the windings and the magnetic core, 2) a lightweight structure through use of a smaller magnetic core, 3) high power density, e.g. about 2.5 kVA per kg, relative to about 1 kVA per kg of oil cooled solutions for the same applications, and 4) competitive efficiency between about 98% and about 99% due to its smaller size.
The embodiments described herein further provide commercial advantages that comprise without limitation, 1) a lightweight power conversion system that is devoid of copper in the coolant path and thus avoids contaminating shared cooling DI water that may run through heat sinks constructed from aluminum, 2) ease of shipping a lightweight transformer, and 3) weighs only about 2500 kg as compared to about 5000 kg for competitive designs.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, comprising making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may comprise other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010516326.1 | Oct 2010 | CN | national |
