Inductor devices – Winding formed of plural coils
Reexamination Certificate
2002-11-21
2004-09-07
Mai, Anh (Department: 2832)
Inductor devices
Winding formed of plural coils
C336S180000, C336S182000
Reexamination Certificate
active
06788180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to controllable inductive devices. More particularly, the invention relates to controllable transformers.
BACKGROUND OF THE INVENTION
A transformer comprising orthogonal windings is previously known from U.S. Pat. No. 4,210,859, to Meretsky et al. of Apr. 18, 1978 (hereinafter “Meretsky”). However, the known solution manifests several disadvantages. Some of these disadvantages are described below.
In general, the problem with the prior art as illustrated by Meretsky is that it does not present a complete picture of how the manipulation of the domains with a DC control current affects the magnetisation in relation to the connection between two orthogonal windings. In Meretsky, a device is described which is developed on the basis of a test conducted on a ferrite pot core with dimensions 18×11 mm, and with current levels in the mA range. Ferrite, however, is not suitable for use at high power levels, for example, because of the high material costs associated with it. The high costs limit the size of a ferrite core from the production engineering point of view. Further, higher power levels can be transferred by increasing the frequency of the voltage that has to be converted, but this requires complicated and expensive power electronics.
Meretsky illustrates a connection diagram for a variable transformer solution with 4 windings: a primary main winding, a secondary main winding arranged at a right angle to the primary winding, and two control windings, one for each main winding. The mode of operation is such that a variable DC current in both control windings will result in a transfer of AC voltage from the primary winding to the secondary winding. A transformer of this kind cannot be considered a realistic option, particularly if it is to be applied outside the mA range, because a DC current in the control windings will rotate the domains in the magnetic material in an unfavourable direction for connection in one half cycle of the primary voltage. These domain rotations cause harmonics in the secondary voltage. This phenomenon, is not taken into consideration in Meretsky.
In order to be able to implement a realistic solution for a variable power transformer, the problem arises that the control winding on the primary side is transformatively connected to the primary winding and will be under voltage from the primary side, thereby making it very difficult to regulate without extensive filtering.
Meretsky also discloses a transformer connection (
FIG. 18
) where windings with right-angled axes are interconnected in series two by two. The publication states that the core's utilisation can be increased by using such a connection. This is not correct, however, since the magnetic fields for the windings are summed vectorially and the described effect will not be achieved.
Meretsky also describes (
FIG. 20
) a variable delay between the input and output voltage in a case where the control windings each carry current and are interconnected in series. Phase distortion is involved here since the fields through the primary and the secondary winding are shifted via the domain directions. With the control windings connected in this manner, the device will not work for a power transformer used as a phase inverter, since the connection from the primary winding will influence the control current to such an extent that in principle the same connection as mentioned earlier (
FIG. 18
) will be obtained.
SUMMARY OF THE INVENTION
The present invention addresses the shortcomings of the prior art by implementing a transformer in which the domain rotation is controlled.
In one aspect of the invention, a magnetisation in a transformer core provides a connection from a primary side to a secondary side by means of a current in a control winding. As a result of the orientation of a primary winding, a secondary winding and the control winding, two magnetisation currents, which are orthogonal, are summed in such a manner that the domain direction is changed linearly in a direction that is at an angle to the secondary winding. Further, an induced voltage in the secondary winding will be dependent on the size of this angle.
In one embodiment, the magnetisation of the transformer is controlled by means of a pulsed DC or a pulsed AC control current in the control winding which is located orthogonal to the primary control winding. The direction of the domains can be held constant as a result of the controlled magnetisation. The domain control also can be used to avoid a simultaneous change of the domain direction and the field strength of magnetisation. In a version of this embodiment, a constant domain direction is achieved by means of accurate dosing of the control current in relation to the primary winding's magnetisation current and the ampere-turn balance with the secondary winding.
In a further embodiment of the invention, a core plate is used which has special properties with regard to permeability. In a version of this embodiment, a laminar material is used where the magnetisation curve is the same for all directions in the plate. This involves the use of non-directional plate. However, in yet another embodiment of the invention, a directionally oriented plate is used.
The invention can also be implemented in a variable transformer/frequency converter device comprising a body of a magnetic material, a primary winding (or first main winding) wound round the body about a first axis, a secondary winding (or third main winding) wound round the body about a second axis at right angles to the first axis, and a control winding (or second main winding) wound around the body about a third axis, coincident with the second axis.
In another aspect, the invention concerns a method for controllable conversion of a primary alternating electrical signal to a secondary alternating electrical signal by the use of a device comprising a body of a magnetic material, a primary winding (or first main winding) wound round the body about a first axis, a secondary winding (or third main winding) wound round the body about a second axis at right angles to the first axis, and a control Winding (or second main winding) wound around the body about a third axis, coincident with the second axis. In one embodiment, the primary winding is supplied with a primary alternating electrical signal, the control winding is supplied with an alternating voltage which is either in phase or shifted by 180° relative to the primary alternating electrical signal, and the control winding is supplied with a variable current. As a result the transformer's conversion ratio is controlled by means of the variable current.
In a further embodiment, an amplitude adjustment of the alternating voltage changes at least one of domain directions in the magnetic material and a magnetisation angle between the primary winding and the secondary winding. An inductance is introduced in the control circuit, an electromagnetic force from the secondary winding is added to an electromagnetic force from the control winding, and a phase angle rotation between the primary winding and the secondary winding is compensated. This embodiment results in a change in the voltage transfer of the transformer and a phase angle rotation that varies according to load conditions. Additionally, the magnetisation angle between the primary winding and the secondary winding is influenced by the added electromagnetic force. Also, the effect of a direct transformative connection between the secondary winding and the control winding is suppressed. A resulting controlled transformation effect is achieved by obtaining a primary winding response to a load change in a secondary load.
In still another embodiment, the transformer device includes a hollow magnetisable core with an internal winding compartment for internal windings and an external winding compartment for external windings. In a version of this embodiment, the transformer device includes three windings: a primary winding located in the external winding compartment; an
Haugs Espen
Strand Frank
Magtech AS
Mai Anh
Testa Hurwitz & Thibeault LLP
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