NL8800001A - Compact transformer for electronic lamp, ballast or HF converter - uses superconducting material and magnetic screening to reduce capacitive coupling - Google Patents

Abstract

The transformer is designed for use in h.f. resonant d.c. -d.c. converters. The prim. (2) and sec. (6) coils are made from superconducting material so that the coils can be placed close together to achieve the required coupling factor. The transformer stack has a sandwich construction with outer superconducting screens (1,7). Between the prim. and sec. coils are superconducting screens (3,4). Layers of electrical insulating material are interposed between all the other elements of the transformer. There may be a number of auxiliary windings strongly coupled with the prim. coil.

Description

-1- \ t k s

Nedap N.V.

Groenlo

Compact transformer.

The invention relates to a transformer, such as is used in high-frequency electronic lamp ballasts, or in DC-DC converters with a high-frequency transformer. In particular, this concerns the category of converters in which a so-called electrode transformer is used. Converters employing such transformers are described, inter alia, in the publication EUR 0105541 and in the publication "High-Frequency Resonant Transistor DC-DC converters", IEEE-transactions on Industrial Electronics, 10 Vol IE-31, no. 2, May 1984 .

The leakage inductance of the transformer and in the first case also the primary self-induction is used to store an amount of energy per switching cycle. In order to achieve this, commonly used ferrite cores have 15 air gaps, in which the major part of the energy storage takes place. In order to be able to store a maximum amount of energy per switching cycle and thus to transmit a large amount of power, the ferrite cores are operated with flux densities as high as 20 permissible in connection with temperature increase due to core losses. The copper of the transformer windings also contributes to the energy loss as a result of the resonant currents in the primary winding and by heating as a result of magnetic stray fields, the so-called proximity effect. Although litz winding wire reduces the latter losses, the copper losses in the above type of converters remain relatively high. Furthermore, the transformer in a resonant converter, as mentioned above, takes up relatively much space.

The object of the invention is to enable the construction of a high-frequency electrode transformer with small dimensions and low losses. This goal is achieved by using superconducting material for the coils and by not using a transformer core.

The current development in superconducting materials justifies the expectation that materials will become available soon which will be superconducting at room temperature or even higher temperatures. Most suitable is a material that retains its superconducting property up to temperatures of 100 degrees Celsius or higher so that it can be used in an environment heated by the presence of electronic circuits.

.88 0000 1 f -2- ί

Of course, a form of cooling can also be used, such as, for example, with the aid of peltier elements.

With conventional copper winding wire, a core-less construction would also be possible, but this would lead to very large coils with a lot of copper losses, in order to achieve the required value of inductance and leakage inductance.

In the conventional electrode transformer, as described in publication EUR 0105541, the energy storage per switching cycle takes place mainly in the air gap between the core halves and in the space between the primary and the secondary coils. In fact, the core serves to bundle the ampere turns of the primary coil into the air gap. In this way, the required inductance can be achieved by relatively few turns and without excessive copper losses in the occurring currents.

When air coils of superconducting material are used, the energy is stored in the air around the coil. A large number of turns is required at a given diameter to achieve the desired inductance, but since the coils show almost no copper losses, this is not a problem.

The primary and secondary windings must be close to each other. The desired coupling factor can be obtained by correctly selecting the distance between the primary and the secondary coils 25. Short circuit of the secondary coil must change the magnetic field distribution around the primary coil so much, if it is driven with an AC voltage source, that the desired ratio between the self-inductance of the primary winding on an open secondary winding and the self-inductance of the primary winding on an short-circuited secondary winding is achieved.

For the converter as described in EUR 0105541, this ratio is around 2: 1. A possible construction of the transformer according to the invention is shown in the form of a cross-section in figure 1 and consists of a sandwich construction of a superconducting screen (1 and 7), which serves to separate the electric and magnetic fields of the transformer. screens, a superconducting coil (2), 40 two superconducting electrical screens (3 and 4), which can be connected to the reference potentials of the primary and secondary circuit and a secondary coil (6), while all said layers are separated from each other separated by insulating layers (8), which can also serve as 45 carriers for the superconducting materials. The shape is assumed to be circular here, but any other shape such as rectangular is of course also possible.

.8800001 -3-

Many converters use auxiliary windings on the primary side to provide control power for the switching transistors and to power the primary control and control circuits. In this embodiment, layer 2 of figure 1 will consist of several, strongly coupled coils.

Many converters supply more than one output voltage. In that case the layer 6 of figure 1 must consist of several strongly coupled coils.

. 880000 1

Claims (5)

1. Transformer, characterized in that it contains at least one primary coil and at least one secondary coil, which are made of superconducting material and that these coils are placed so close together that the desired coupling factor is achieved and that these coils have so many turns require that the desired inductance and the desired transformer ratio be achieved in order to work properly in converters as described in EUR 0105541 or in the publication "High Frequency 10 Resonant Transistor DC-DC Converters, "IEEE Transactions on Industrial Electronics, Vol IE-31, No. 2, May 1984, or in comparable converters. 2. Transformer according to claim 1, characterized in that one or more superconducting screens are used on the outside of the transformer to shield the electric and magnetic fields of the transformer. 3. Transformer according to one or both of the preceding claims, characterized in that one or more electrical screens are arranged between the primary and the secondary windings to reduce capacitive coupling between the primary and the secondary coils. 4. Transformer according to one or more of the preceding claims, characterized in that one or more auxiliary windings are provided, which are strongly coupled to the primary coil. Transformer according to one or more of the preceding claims, characterized in that several secondary coils are provided, which are strongly coupled to each other. . 8 8 6 0 D 01