Patent Application
20170133151
The present invention relates to providing power and, more specifically, to providing a compact, high-voltage, high-frequency transformer to provide power.
Power converters are used to convert power from an input to a needed power for provision to a load. One type of power converter is a transformer. Transformers may be designed to convert a fixed AC input voltage into a higher or lower AC voltage. The architecture chosen may provide for high frequency operation, pulse-width-modulation, isolation, and the like.
Different types of transformers may be used depending on a particular application. A typical power transformer includes one or more input windings and one or more output windings. The input and output coils are both wrapped around a core formed of a magnetic material. An alternating current provided at the input (e.g., primary) windings causes a varying magnetic flux in the transformer core. This flux leads to a time varying magnetic field that includes a voltage in the output (e.g., secondary) windings of the transformer.
In some cases, the core is so-called “closed-core.” An example of closed-core is a “shell form” core. In a shell form, the primary and secondary windings are both wrapped around a central core arm and a both surrounded by outer arms. In some cases, more than one primary winding is provided and multiple secondary windings may also be provided. In such systems, based on the input and to which of the primary windings that input is provided (of course, power could also be provided to more than one primary winding in some instances) different output voltages can be created at each of the secondary windings.
Some power transformers operate at high voltages and/or currents. Such power transformers may produce strong electromagnetic (EM) fields. One approach to deal with the electric fields and parasitic currents they produce is to shield one or both of the primary and secondary windings. This may be especially important where the power transformer operates in high, very-high or ultra-high frequency bands. An example is a power transformer used in a microwave power module.
In some applications, the cost of high frequency and/or high voltage transformers for use in compact equipment can be high relative to the cost of the equipment as a whole or compared to other elements in the equipment. Further, in some cases, the transformer can be difficult to make or prone to failures.
According to one embodiment a transformer that includes a core having a central arm and first and second outer arms on opposite sides of the of the central arm is disclosed. The transformer includes a first input winding surrounding the central arm, a first output winding surrounding the central arm, a first input winding shield surrounding the first input winding, and a first output winding shield surrounding the first output winding. In this embodiment, the first input winding and the first input winding shield are connected to a steady potential at the input side and the first output winding and the first output winding shield are connected to a steady potential at the output side.
According to another embodiment, a transformer that includes a core having a central arm and first and second outer arms on opposite sides of the of the central arm, a first input winding surrounding the central arm and a first output winding surrounding the central arm is disclosed. The transformer also includes a first input winding shield surrounding the first input winding, the first input winding shield having only flat or arcuate edges in cross section and a first output winding shield surrounding the first output winding, the first output winding shield having only flat or arcuate edges in cross section.
According to another embodiment, a method of forming a transformer is disclosed. The method includes: providing a core; providing a first input winding; proving first output winding; surrounding the first input winding with a first input winding shield, the first input winding shield having only flat or arcuate edges in cross section; surrounding the second input winding with a second input winding shield, the second input winding shield having only flat or arcuate edges in cross section; and disposing the input and output windings around portions of the core.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
As will be described below, a multiple primary and second winding transformer is disclosed. The windings are printed on one or more printed circuit boards (PCBs) and the primary windings are shielded from the secondary windings by surrounding one or both in an outer case that includes a substantially smooth shaped shield disposed therein. As will be become clear below, the shape of the shield may reduce or eliminate discharges due to EM fields near sharp edges typically present in prior art shields.
As illustrated, the transformer 100 includes four primary windings, each having a single turn and are labeled as a first primary winding W1-1, a second primary winding W2-1, a third primary winding W1-2 and a fourth primary winding W2-1. In this and other examples, the primary windings are part of the so-called “low voltage” side of the transformer and each include 1 turn. The illustrated transformer includes two secondary windings W3 and W4 both formed of three turns. In this and other examples, the secondary windings are part of the so-called “high voltage” side of the transformer and each include 3 turns. A low voltage provided to the one or more of the primary winding creates a higher voltage in the secondary windings. Of course, if the number of turns one the primary and secondary could be changes and, accordingly the naming secondary would be low voltage side.
In the example shown in
It has been discovered that sharp edges in a high voltage (HV) region (e.g., near the secondary windings W3, W4) provide locations where partial discharges (coronas) may form. However, foil-based shields and windings made with small diameter wire (in the range of several mils) may create such edges leading to a high-intensity electric field that forms such partial discharges.
For example,
In some cases high-voltage, high-frequency transformers often use flat, “pan cake” windings to reduce the transformer primary-to-secondary equivalent capacitance. This could lead to a solution where a shield may not be needed. These windings, however, can be labor intensive to use.
Another approach to reduce transformer cost is to form planar windings on a printed circuit board (PCB). However, such windings are not used because winding traces may have sharp edges that further increase electric field intensity issues that are present in foil shields described above.
The transformer 300 includes a core 302. The core 302, as described above, may be formed a metal or other magnetically conductive material. Examples includes include ferromagnetic metal such as iron, or ferromagnetic compounds such as ferrites. Other examples include laminated silicon steel. The illustrated core 302 is of the closed variety, and in particular to a shell core, having a central arm 304 and outer arms 306, 308.
As illustrated, the transformer includes a first pair of primary windings 310, 312 and a second pair of primary windings 314, 316. Each of these windings are illustrated as being formed of a single turn. Of course, the number of and turns of each primary windings may be limited varied as long as one primary winding is provided that has at least one turn. In embodiments herein, one or more of the primary windings 310, 312, 314, 316 are planar windings formed on and supported by a substrate. As illustrated, each winding 310, 312, 314, 316 is formed on and supported by a substrate labeled as 311, 313, 315, 317 formed of a dielectric material.
The transformer 300 also includes secondary windings 318, 320. Each of these windings is illustrated as being formed of three turns. Of course, the number of and turns of each secondary winding 318, 320 may be limited varied as long as one secondary winding is provided that has at least one turn. In embodiments herein, one or more of the secondary windings 318, 320 are planar windings formed on and supported by a substrate. As illustrated, each winding 318, 320 is formed on and supported by a substrate labeled as 319, 321 formed of a dielectric material.
In this manner, one or more of the primary and secondary windings may be formed as part of a printed circuit board. In the prior art using such windings was typically avoided as the traces forming the windings have sharp edges that further increase electric field intensity at those locations and can lead the same or similar problems discussed above with respect to sharp shield edges.
To overcome one or more of the possible problems described above, one or more toroid-shaped shields are provided. As illustrated, each winding 310, 312, 314, 316, 318, 320 is surrounded by a toroid shaped shield. In particular, windings 310, 312, 314, 316, 318, 320 are surrounded by shields 330, 332, 334, 336, 338, 340, respectively. That is, in this embodiment, each winding includes its own shield. In an alternative embodiment, and as shown in
Each of the substrates 311, 313, 315, 317, 319 and 321 may be supported within their respective shields by a respective support member 311a-321a. The support member may be formed of a dielectric or other not conductive material in one embodiment. The support members can be formed at part of the substrate and sided and arranged such that contact a top and bottom surface of the shields to provide a rigid support from which its respective substrate may extend.
In one embodiment, each shield 330, 332, 334, 336, 338, 340 is surrounded by a respective insulting tube 350, 352, 354, 356, 358, 360. (as shown, the tubes are in the form of a hollow toroid) The tube may be formed of any non-conductive material. One or more of the insulating tube 350, 352, 354, 356, 358, 360 may include an optional offset member 362 that provides a means to slightly separate the insulating tubes from one another.
According to one embodiment, one or more of the shields 330, 332, 334, 336, 338, 340 may be shaped such that a portion that is not flat is arcuate. That is, one embodiment, one or more of the shields may be shaped such that, in cross section, they do not have any sharp edges, corners, or discontinuous surfaces. However, as will be discussed below, one or more cuts may be made to the shields but these, while they may introduce a discontinuity at the location of the cut, the cut does not change the shape of the cross-section of the shield. The shields function to change the contour of the HV electric field (e.g., emerging from the flat windings) to reduce its intensity and eliminate ionization.
With reference now to
To avoid shorting the transformer, the shield 400 has to have a single cut formed therein. This is due to the fact that if a shield forms a continuous loop around the center leg of the core, it will act as a shorted turn of the winding and, in effect, short circuit the transformer. However, the location of the cut may create edges leading to high intensity field in its immediate vicinity bringing back the initial corona problem discussed above. To address this situation, and as shown in
In
With reference to
In order to place the windings 310, and support structures 311, 311a in the shield 330 and outer casing 370, both the shield 330 and outer casing 370 are cut. In particular, outer casing 370 is cut along cut line 610.
The shield 330 in this embodiment, includes an inner and outer metallic layers 504, 506. To ensure that the cut of the shield 330 does not create high intensity field in its immediate vicinity (identical to the previous problem regarding the vertical cut in the shield 330), the cuts in the inner and outer metallic layers 504, 506 are displaced into different horizontal planes B and C. As the inner and outer metallic layers 504, 506 are closely spaced, their composite electric field has a low intensity and does not lead to the problems discussed above.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof
The corresponding structures, materials, acts and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material or act for performing the function in combination with other claimed elements as claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
While embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.
