AUTOTRANSFORMER RECTIFIER UNIT

Abstract

The present improvement essentially integrates a DC link inductance within an interphase power transformer (IPT). The integration is achieved by creating auxiliary magnetic paths for leakage inductance inside the IPT core. The magnetic path can be created, for example, by incorporating extra portions of magnetic material commonly referred to hereinafter as shunts. The IPT flux shared between windings does not cross these shunts. Therefore, this magnetic path increases the self-inductance of the IPT but does not contribute to the mutual inductance between windings. This extra magnetic path allows for leakage inductance of a much higher quantity than that achievable with a conventional IPT.

Claims

1. An interphase transformer comprising: a core defining three or more limbs (N.sub.1-N.sub.n); and a winding provided around each limb; characterised by means incorporated in or on said core for creating auxiliary magnetic paths for flux generated by at least one of the windings.

2. The interphase transformer of claim 1, wherein the means for creating auxiliary magnetic paths comprises a shunt of magnetic material provided between adjacent wound limbs (N.sub.1-N.sub.n).

3. The interphase transformer of claim 1, wherein the means for creating auxiliary magnetic paths comprises an additional limb defined by the core between adjacent limbs with windings, the additional limb not having a winding; the additional limb interrupted by an air gap.

4. The interphase transformer of claim 1, wherein the means for creating auxiliary magnetic paths comprises an additional number of turns in one or more of the windings.

5. The interphase transformer of claim 1, wherein the means for creating auxiliary magnetic paths comprises limbs of magnetic material formed external to and adjacent the core.

6. A system for converting AC electric power to DC electric power, the system comprising: an n×6 pulse autotransformer, where n is an integer of 3 or more; n rectifier bridges; and two interphase transformers (IPT1, IPT2) comprising n limbs (N.sub.1-N.sub.n) with windings there around, at least a first one of said two interphase transformers being an interphase transformer comprising: a core defining three or more limbs (N.sub.1-N.sub.n); and a winding provided around each limb; characterised by means incorporated in or on said core for creating auxiliary magnetic paths for flux generated by at least one of the windings.

7. The system of claim 6, wherein the means for creating auxiliary magnetic paths comprises a shunt of magnetic material provided between adjacent wound limbs (N.sub.1-N.sub.n).

8. The system of claim 6, wherein the means for creating auxiliary magnetic paths comprises an additional limb defined by the core between adjacent limbs with windings, the additional limb not having a winding; the additional limb interrupted by an air gap.

9. The system of claim 6, wherein the means for creating auxiliary magnetic paths comprises an additional number of turns in one or more of the windings.

10. The system of claim 6, wherein the means for creating auxiliary magnetic paths comprises limbs of magnetic material formed external to and adjacent the core.

11. The system of claim 6, wherein a second one of the at least two interphase transformers is an interphase transformer comprising: a core defining three or more limbs (N.sub.1-N.sub.n); and a winding provided around each limb; characterised by means incorporated in or on said core for creating auxiliary magnetic paths for flux generated by at least one of the windings.

12. A method of providing a smoothing choke effect to an AC to DC power converter, the method comprising: providing an the AC to DC power converter, the converter including an interphase transformer; and creating auxiliary magnetic paths in the interphase transformer of the AC to DC power converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Preferred embodiments will now be described by way of example only, with reference to the accompanying drawings.

[0022] FIG. 1 is a circuit diagram showing a known 12-pulse ATRU.

[0023] FIG. 2 is a circuit diagram of a known 18-pulse converter.

[0024] FIG. 3 is a circuit diagram of an 18-pulse ATRU.

[0025] FIG. 4 shows the equivalent reluctance model, equivalent electrical model and design equations for an arrangement such as shown in FIG. 5.

[0026] FIG. 5 shows the three windings of an IPT for an 18-pulse ATRU with shunts of magnetic material arranged between the core legs.

[0027] FIG. 6 shows the windings of an IPT for an 18-pulse ATRU with alternative ways of increasing leakage inductance according to the present disclosure.

[0028] FIG. 7 shows IPT windings and how the concept could be applied to “greater than 18”-pulse systems.

DETAILED DESCRIPTION

[0029] One embodiment will be described in relation to an 18-pulse ATRU. The disclosure can also be implemented and provide advantages in relation to topologies with more than 18 pulses, e.g. 24-pulse systems.

[0030] FIG. 2 shows a conventional 18-pulse converter with an ATRU (shown in detail in FIG. 3).

[0031] In contrast to a 12-pulse system described above, and shown in FIG. 1, an 18-pulse system is comprised of three 6-pulse systems. As seen in FIG. 2, the power converter 110 includes front-end filter 118, autotransformer rectifier unit (ATRU) 120 and DC link filter 122.

[0032] The front-end filter 118 is as known in the art, such as described in U.S. Pat. No. 8,729,844 and will not be described in further detail. The inductors L2, L3, L4 and resistors R1, R2 and R3 with capacitors C1, C2 and C3 act to damp the filter. Filtering can prevent unwanted harmonics generated by ATRU 120 from being propagated to the power distribution network. This is just one example, other front-end filters are also suitable.

[0033] ATRU 120, shown in more detail in FIG. 3, converts the AC input provided by front-end filter 118 to a DC output via DC link filter 122.

[0034] ATRU 120 includes an asymmetrical phase shift autotransformer and a rectifier unit.

[0035] ATRU 20 includes 18-pulse autotransformer 130, diode bridge (DB) rectifiers DB1, DB2 and DB3, and interphase transformers IPT1 and IPT2.

[0036] Autotransformer 130 includes, in the example shown, first AC input terminals In1, In4 and In7. Each labelled input terminal represents a terminal connection point to the windings associated with autotransformer 130. The first AC input terminals In1, In4, In7 are connected directly to a first group of output terminals Out1, Out4, Out7 connected to resistors R1, R2 and R3. In this example, first AC input terminals In1, In4 and In7 are connected to receive AC power labelled VA, VB and VC, respectively. In an aircraft application, for example, this may be 230 volt AC power provided by an on-board generator. Of course, other autotransformer configurations may be used.

[0037] The output terminals Out3, Out6 and Out9 are connected to diode bridge DB3, output terminals Out2, Out5 and Out8 are connected to diode bridge DB2. Input terminals In1, In4 and In7 are connected to diode bridge DB1 via resistors R1, R2 and R3 in a configuration that bypasses autotransformer 130. Resistors R1, R2 and R3 are sized to match the resistance of windings associated with autotransformer 130 to balance output impedance of the outputs provided to the diode bridges DB1, DB2 and DB3.

[0038] The diode bridges convert the received AC input to a DC output having a positive component and a negative component. The positive DC output from each diode bridge is provided to interphase transformer IPT1 which provides an output that is combined to generate the positive DC output DC+. The negative DC output from each diode bridge is provided to the interphase transformer IPT2 which provides an output which is combined to generate the negative DC output DC−.

[0039] The IPTs provide parallel connection of the rectified output voltages and, for an 18-pulse system, each one comprises three windings 60. For higher order pulse systems, the IPTs will have more windings (i.e. for n×6-pulse systems, the IPTs have n windings). Generally speaking, an IPT comprises a magnetic core 50 which defines a number (n) of legs or limbs N1-Nn around each of which is provided an inductive winding 60.

[0040] The DC link 122, with DC inductor choke L5 serves to smooth the DC output voltage, as described above.

[0041] The present improvement essentially integrates a DC link inductance within an interphase power transformer (IPT). The integration is achieved by creating auxiliary magnetic paths for leakage inductance inside the IPT core 50. The magnetic paths can be created, for example, by incorporating extra portions of magnetic material commonly referred to hereinafter as shunts. The IPT flux shared between windings 60 does not cross these shunts. Therefore, this magnetic path increases the self-inductance of the IPT but does not contribute to the mutual inductance between windings. This extra magnetic path allows for leakage inductance of a much higher quantity than that achievable with a conventional IPT.

[0042] The additional magnetic leakage inductance can be realised as shown in FIG. 5, where shunts (100) or portions of magnetic material are provided between the wound core legs or limbs (N1, N2, N3) of the IPT.

[0043] Other ways of increasing the leakage inductance of the IPT are also envisaged and are within the scope of the disclosure. One such implementation is shown in FIG. 6A in which the IPT core 50 is provided or formed with additional gapped limbs (200), i.e. limbs without a winding but having an interruption 80 in the limb to form an air gap 70 along the length or across the limb, rather than shunts.

[0044] An alternative implementation is shown in FIG. 6B in which additional or external limbs (300) are mounted on or around the IPT core as a separate magnetic circuit to provide an auxiliary magnetic path that does not interfere with the path of the wound limbs of the IPT.

[0045] Referring now to the equivalent circuits shown in FIG. 4, the equivalent reluctance circuit shows the core limbs represented by resistor Rm and reluctance of leakage paths created by the shunts represented by resistors RI.

[0046] This is also represented in the equivalent electrical model. The equations at the bottom of FIG. 4 relate the reluctance model and the electrical model, where N is the number of turns per winding and i1, i2 and i3 are the currents on each winding.

[0047] As can be seen, adding magnetic shunts or auxiliary magnetic paths increases the self-inductance L and reduces the mutual inductance M, therefore increasing the difference L−2 M. This difference contributes to differential mode current filtering and, therefore, has the same effect as a conventional DC link choke.

[0048] The advantages of this concept can be achieved by integrating the DC link inductance with one IPT or several.

[0049] As mentioned above, although the disclosure describes an 18-pulse system, the concepts equally apply to higher order systems e.g. 24-pulse, 30-pulse, 36-pulse systems. FIG. 7 illustrates an implementation of a solution for 6×n-pulse systems (where n is an integer of 3 or more), thus having n limbs N.sub.1-N.sub.n, each provided with a winding 60. FIG. 7 shows the inductance increased by shunts 100 (as in FIG. 5) but, again, there are other ways of providing increased leakage inductance, such as, for example, shown in FIGS. 6a and 6b).