EP2959492B1 - Method for operating an on-load tap changer having semiconductor switching elements - Google Patents

Description

The invention relates to a method for operating an on-load tap changer for voltage regulation with semiconductor switching elements on a control transformer with a control winding. From the DE 10 2011 012 080 A1 is a tap changer for voltage regulation with semiconductor switching units known. The tap changer has two parallel load branches, wherein in both load branches semiconductor switching units are connected in series. In each case, a semiconductor switching unit of the first load branch and the second load branch are in pairs opposite. In each case alternately between these paired semiconductor switching units, a partial winding and a bridge are connected in parallel between the two load branches. The partial windings have different numbers of turns. The semiconductor switching units may be formed as thyristor or IGBT pairs. By skillfully interconnecting the semiconductor switching units, the windings can be switched on or off. As a result, the transmission ratio of the transformer can be adjusted and the secondary-side voltage can thus be regulated. By the use of IGBT's it is also possible with the help of a pulse width modulation to realize an alternating switching on or off of a partial winding and thereby to implement a fine-level voltage regulation. Constant switching on and off of the semiconductor switching units causes switching losses, and the semiconductor switching units heat up, which places a high demand on the cooling device.

The object of the invention is to provide an on-load tap changer for voltage regulation with semiconductor switching elements, which has lower switching losses, requires a smaller cooling device and is thus inexpensive and safe.

This object is achieved by a method according to the invention for operating an on-load tap-changer Voltage regulation solved according to claim 1. Preferred embodiments are defined in the dependent claims. The operation according to the invention of the on-load tap-changer with semiconductor switching elements enables lower switching losses, reduced heat development and increased safety.

The general inventive idea is to use two anti-serially connected IGBTs with inverse diodes as semiconductor switching elements and to take into account the direction of the current and orientation of the voltage at the partial winding in the pulse width modulation, thereby not switching a part of a load branch and thus switching losses avoid.

According to the preferred embodiment of the invention, the on-load tap changer for voltage regulation has semiconductor switching elements and is arranged on a regulating transformer with regulating windings. This is arranged between a fixed, unregulated part of the control winding and a load derivation. Furthermore, the on-load tap changer has a first load branch and a second load branch arranged parallel thereto, wherein a partial winding is arranged between the load branches. The first load branch has a first semiconductor switching element before the partial winding and a second semiconductor switching element after the partial winding. The second load branch also has a first semiconductor switching element before the partial winding and a second semiconductor switching element after the partial winding. The on-load tap-changer comprises at least one switching module, which comprises the first load branch and the second load branch.

According to a further embodiment of the invention, each semiconductor switching element consists in each case of a first IGBT and a second IGBT which are interconnected antiserially to one another. The IGBTs are each provided with an inverse diode such that an anode of an inverse diode having an emitter terminal and a cathode of the inverse diode are connected to a collector terminal of the first IGBT and the second IGBT. The semiconductor switching elements of the first load branch and the second load branch are selectively switched off.

According to a further embodiment, the on-load tap changer comprises a first switching module, a second switching module and a third switching module. They own the Partial windings of each switching module with each other a different turns ratio, for example, 9: 3: 1.

In the method according to the invention for operating the on-load tap-changer, it is first determined between which positions a partial winding of a switching module is to be changed. In a sales position turns of the partial winding are subtracted from a control winding, in an additional position turns of the partial winding are added to the control winding and at a nominal position, the partial winding is completely omitted.

Another step according to the method of the invention relates to the definition of an active and a passive side of the switching module. On the active side of the switching module, the semiconductor switching elements are actuated, while on the opposite side they are set in a predetermined switching state.

After determining the direction of a current and the orientation of a voltage at the partial winding, the switching states of the semiconductor switching elements of the switching module are determined. In this case, the IGBTs of the first semiconductor switching elements or second semiconductor switching elements connected to the alternating current-carrying inverse diodes of the respective active side are always blocking. Of the two alternating current-carrying IGBT's of the active side, one is always conducting, namely that IGBT whose collector terminal is connected to a negative pole and emitter terminal to a positive pole of the partial winding. Of the two alternating current-carrying IGBT's of the active side, one is clocked, namely the one whose collector terminal is connected to the positive pole and the emitter terminal is connected to the negative pole of the partial winding. On the passive side of a semiconductor switching element is always locked and the other semiconductor switching element always conductive.

By changing the direction of the current flow and the orientation of the positive pole and the negative pole on the partial winding, it is determined which IGBT's of the semiconductor switching elements on the active side are clocked or turned on, on the passive side turned on or off, and generally which the pages is active or passive.

Figur 1

eine schematische Darstellung eines Stufenschalters in Verbindung mit einem Transformator;

Figur 2

eine schematische Darstellung des Stufenschalters mit Halbleiter-Schaltelementen;

Figur 3

eine Darstellung des elektronischen Aufbaus der Halbleiter-Schaltelemente;

Figur 4a -4d

eine Darstellung der verschiedenen Schaltstellungen des Laststufenschalters;

Figur 5

eine Darstellung der Halbleiter-Schaltelemente in einer Schaltstellung;

Figur 6

eine weitere Darstellung einer Schaltstellung des Halbleiter-Schaltelements; und

Figur 7

eine schematische Darstellung der Verschaltung von drei Schaltmodulen.

These and other features and advantages of the embodiment disclosed herein will become better understood with reference to the following description and drawings, wherein like reference numerals refer to like elements throughout. Show it:

FIG. 1

a schematic representation of a tap changer in conjunction with a transformer;

FIG. 2

a schematic representation of the tap changer with semiconductor switching elements;

FIG. 3

a representation of the electronic structure of the semiconductor switching elements;

Figure 4a -4d

a representation of the various switching positions of the on-load tap-changer;

FIG. 5

a representation of the semiconductor switching elements in a switching position;

FIG. 6

a further illustration of a switching position of the semiconductor switching element; and

FIG. 7

a schematic representation of the interconnection of three switching modules.

For identical or equivalent elements of the invention, identical reference numerals are used. The illustrated embodiment represents only one way in which the switching element according to the invention can be configured.

In FIG. 1 is an on-load tap changer 1 for voltage regulation in a control transformer 2 and a control winding 3 shown. The on-load tap-changer 1 is arranged between the fixed, unregulated part of the control winding 3 and a load discharge line 4.

As in FIG. 2 illustrated, the on-load tap-changer 1 consists of at least one switching module 5. The switching module 5 has a first load branch 6 and a second load branch 7 arranged parallel thereto. The first and the second load branch 6, 7 of the switching module 5 is conductively connected to one another via a partial winding 8. The first load branch 6 has a first semiconductor switching element 61 between the control winding 3 and the partial winding 8 and a second semiconductor switching element 62 after the partial winding 8, ie towards the discharge line 4, on. The second load branch 7 likewise has a first semiconductor switching element 71 in front of the partial winding 8 and a second semiconductor switching element 72 after the partial winding 8.

In FIG. 3 It is shown that each of the semiconductor switching elements 61, 62, 71 and 72 consists of a first insulated gate bipolar transistor (IGBT) 11 and a second IGBT 12, which are connected in antiseries. The first IGBT 11 and the second IGBT 12 are each provided with an inverse diode 14. Each IGBT 11 and 12 has a collector terminal C, an emitter terminal E and a gate G. Each of the inverse diodes 14 has its anode connected to the emitter terminal E and the cathode connected to the collector terminal C of FIG IGBT 11 or 12 connected.

First, as in the FIGS. 4a-4d shown determines which of the positions the sub-winding 8 assumes. In a paragraph 20 ( Fig. 4a ), the turns of the partial winding 8 are subtracted from the fixed part of the control winding 3. In this case, the current I flows independently of the direction through the first semiconductor switching element 61 in the first load branch 6, the partial winding 8 and the second semiconductor switching element 72 in the second load branch 7.

In an additional position 21 ( Fig. 4b ), the turns of the partial winding 8 are added to the fixed part of the control winding 3. In this case, the current I flows irrespective of the direction through the first semiconductor switching element 71 in the second load branch 7, the partial winding 8 and the second semiconductor switching element 62 in the first load branch 6.

In a nominal position 22 ( Fig. 4c and 4d ), the current I is selectively guided past the partial winding 8 either via the first or the second load branch 6, 7. In this position, the turns of the partial winding 8 have no influence on the control winding third

In order to implement a fine-level control and to be able to generate an intermediate stage, pulse-width modulation is used to clock between two of the three explained positions. If switching between the nominal position 22 and the offset position 20 or additional position 21, a passive and an active side of the switching module 5 must be set; this is the rule. Each one side always includes the semiconductor switching elements 61 and 71 or 62 and 72, which lie on the same side before or after the partial winding 8. Thus, it must be determined whether the first semiconductor switching element 61 of the first load branch 6 and the first semiconductor switching element 71 of the second load branch 7 are active and the second semiconductor switching element 62 of the first load branch 6 and the second semiconductor switching element 72 of the second load branch 7 are passive or vice versa. Depending on this setting, the IGBTs 11 and 12 of the semiconductor switching elements 61, 62, 71, and 72 need to be switched differently. The semiconductor switching elements on the fixed, passive side are always held during the process as conductive or blocking, wherein a semiconductor switching element is conductive and the other is not conductive. On the active side, the semiconductor switching elements are actively switched due to the pulse width modulation carried out, ie they assume different states. When switching between sales position 20 and additional position 21 both sides are active.

In the example of FIG. 5 is the active side of the illustrated switching module 5 of the first semiconductor switching element 61 of the first load branch 6 and the first semiconductor switching element 71 of the second load branch 7. Consequently, the passive side in FIG. 5 from the second semiconductor switching element 62 of the first load branch 6 and the second semiconductor switching element 72 of the second load branch 7.

On the passive side, the second semiconductor switching element 72 of the second load branch 7 is always conductive. By contrast, the second semiconductor switching element 62 of the first load branch 6 is always nonconductive. The current I thus flows either through the first IGBT 11 and the inverse diode 14 which is connected to the second IGBT 12 in the reverse direction by the second IGBT 12 and the inverse diode 14, which is connected to the first IGBT 11. By contrast, the first and second IGBTs 11 and 12 of the second semiconductor switching element 62 in the first load branch 6 are always blocking, so that no current I flows here.

On the active side, the first or second IGBTs 11 or 12 of the first semiconductor switching elements 61 and 71, whose forward direction does not correspond to the current flow direction, are turned off. Of the remaining two IGBTs 11 or 12 of the first semiconductor switching elements 61 and 71 one is always conducting, namely the one whose collector terminal C is connected to a negative pole " "and the emitter terminal E is connected to a positive pole" + "of the partial winding 8, possibly via other IGBT's or inverse diodes. Finally, the fourth IGBT of the active side is clocked with a duty cycle corresponding to the intermediate stage to be achieved. The collector terminal C of this IGBT thus lies at the positive pole "+" and at the emitter terminal E at the negative pole "-".

Shortly before the current zero crossing of the clocked IGBT antiserial IGBT of the respective semiconductor switching element is turned on to ensure a safe current path when Stromrichtungswechsel.

In the example in FIG. 5 is the orientation of the voltage U such that on the upper side of the partial winding 8, the positive pole "+" and on the lower side of the negative pole "-" abut. Since the current I flows from left to right, the first IGBTs 11 of the first semiconductor switching elements 61 and 71 and the inverse diodes 14 connected in parallel to the second IGBT 12 of the first semiconductor switching elements 61 and 71 are used for this purpose. Considering the first IGBTs 11 of the first semiconductor switching elements 61 and 71, the positive terminal "+" of the partial winding 8 and the emitter terminal is located at the collector terminal C of the first IGBT 11 of the first semiconductor switching element 71 in the second load branch 7 E the negative pole "-" of the partial winding 8 at. This is thus clocked, while the first IGBT 11 of the first semiconductor switching element 61 in the first load branch 6 is permanently conductive. The second IGBT 12 of the first semiconductor switching element 71 in the second load branch 7 is turned on shortly before the current zero crossing, ie before the change of direction of the current I.

After each change of voltage or current direction is always redefined which IGBT's conducting, which blocking and which are clocked. In this case, a change of the active and passive sides of the uniform distribution of losses serve and thus lead to an extension of the life of the components.

In purely resistive loads of the on-load tap-changer 1, the direction of the current I and the orientation of the voltage U at the partial winding 8 change at the same time. For inductive and capacitive loads, the orientation of the voltage U changes offset to the change in direction of the current I.

In FIG. 6 is the switching module 5 off FIG. 5 displayed. The left side of the switching module 5 with the semiconductor switching elements 61 and 71 is still active as previously determined and the right side of the switching module 5 with the semiconductor switching elements 62 and 72 is passive. Here, the direction of the current I has changed, so that it flows from the right side to the left side of the switching module 5. Based on an ohmic load, the orientation of the voltage U at the partial winding 8 has also been reversed. At the upper end of the partial winding 8 are now the negative pole "-" and at the lower end of the partial winding 8 of the positive pole "+" on.

On the passive side, the current I through the second semiconductor switching element 72 in the second load branch 7, in particular the second IGBT 12 of the second semiconductor switching element 72 and the inverse diode 14, the first IGBT 11 of the second semiconductor switching element 72 is connected in parallel, guided. The second semiconductor switching element 62 in the first load branch is always non-conductive. On the active side of the switching module 5, the current I can only via the inverse diodes 14, which are connected in parallel to the first IGBTs 11 of the first and second semiconductor switching elements 61 and 71, and the second IGBTs 12 of the first and second semiconductor switching element 61 and 71 flow. At the collector terminal C of the second IGBT 12 of the first semiconductor switching element 71, the positive pole "+" is present in the second load branch 7; thus this is clocked. Since the second IGBT 12 of the first semiconductor switching element 71 is clocked in the second load branch 7, the second IGBT 12 of the first semiconductor switching element 61 in the first load branch 6 is thus switched permanently conducting.

Due to the fact that during the process, a semiconductor switching element 61, 62, 71, or 72 on the active side is always conducting, i. Low impedance, switching losses, which arise in the prior art in the transition from the high-impedance state to the low-impedance state, significantly reduced. As a result, the heat generation decreases at the switching module 5, so that less heat energy has to be dissipated by the cooling. In general, when using this method, a spatially smaller and thus cheaper cooling system can be used.

In FIG. 7 is an on-load tap-changer 1 shown, in which a first switching module 51, a second switching module 52 and a third switching module 53 are connected in series. The partial windings 8 of these switching modules 51, 52 and 53 have different Windungsverhältnisse. Particularly advantageous is the distribution of Windungsverhältnisse 9: 3: 1. By applying the method according to the invention in one of these switching modules 51, 52 or 53, it is possible to combine the finer intermediate stages produced here with the stages of the other switching modules 51, 52 and 53.

Claims (8)

1. Method of operating an on-load tap changer (1) for voltage regulation with semiconductor switching elements (61, 62, 71, 72) at a regulating transformer (2) with a regulating winding (3), wherein

   - the on-load tap changer (1) is arranged between a feed line (4'), which is connected with a fixed unregulated part of the regulating winding (3), and a load diverter (4);

   - the on-load tap changer (1) consists of at least one switching module (5), which has a first load branch (6), a second load branch (7), arranged parallel thereto and a sub-winding (8) therebetween;

   - the first load branch (6) comprises a first semiconductor switching element (61) between the feed line (4') and the sub-winding (8) and a second semiconductor switching element (62) between the sub-winding (8) and the load diverter (4);

   - the second load branch (7) comprises a first semiconductor switching element (71) between the feed line (4') and the sub-winding (8) and a second semiconductor switching element (72) between the sub-winding (8) and the load diverter (4);

   comprising the following steps:

   - determining the desired intermediate stage of the sub-winding (8);

   - subtraction of the windings of the sub-winding (8) from the unregulated part of the regulating winding (3) in a first setting of the switching module (5), i.e. the reducing setting;

   - addition of the windings of the sub-winding (8) to the unregulated part of the regulating winding in a second setting of the switching module (5), i.e. the increasing setting;

   - completely leaving out the sub-winding in a third setting of the switching module (5), i.e. the nominal setting;

   - producing the intermediate stage in that switching over between the third setting and the first or second setting is carried out;

   - characterised by

   - determining an active and a passive side of the respective switching module (5) for the desired intermediate stage, wherein the active side comprises the first semiconductor switching elements (61, 71) and the passive side comprises the second semiconductor switching elements (62, 72) or vice versa;

   - determining the switching states of the semiconductor switching elements (61, 62, 71, 72) of the switching module (5) in that

   - for switching over between the third and second settings on the active side of the respective switching module (5) the semiconductor switching element (61) of the first load branch (6) is conducting and the switching element (71) of the second load branch (7) is cycled by pulse width modulation and on the passive side of the respective switching module (5) the semiconductor switching element (62) of the first load branch (6) is non-conducting and the semiconductor switching element (72) of the second load branch (7) is conducting; and

   - for switching over between the third and first settings on the active side of the respective switching module (5) the semiconductor switching element (61) of the first load branch (6) is cycled by pulse width modulation and the switching element (71) of the second load branch (7) is conducting and on the passive side of the respective switching module (5) the semiconductor switching element (62) of the first load branch (6) is conducting and the semiconductor switching element (72) of the second load branch (7) is non-conducting.
2. Method according to claim 1, wherein

   - each semiconductor switching element (61, 62, 71, 72) consists of a respective first IGBT (11) and second IGBT (12), which are connected anti-serially with respect to one another;

   - the first IGBT (11) and the second IGBT (12) are each provided with an inverse diode (14) in such a way that an anode of one inverse diode (14) is connected with an emitter terminal (E) and a cathode of the inverse diode (14) is connected with a collector terminal (C) of the first IGBT (11) and the second IGBT (12); and

   - the semiconductor switching elements (61, 62, 71, 72) of the first load branch (6) and the second load branch (7) are selectably switchable off.
3. Method according to claim 2, wherein

   - the IGBTs (11, 12), which are connected with the alternately current-conducting inverse diodes (14) of the respective active side, of the first semiconductor switching elements (61, 71) or second semiconductor switching elements (62, 72) are constantly blocking;

   - of the two alternately current-conducting IGBTs (11, 12) of the active side one is always conducting and, in particular, that IGBT (11, 12) of which the collector terminal (C) is connected with a negative pole (-) and the emitter terminal (E) is connected with a positive pole (+) of the sub-winding (8);

   - of the two alternately current-conducting IGBTs (11, 12) of the active side one is cycled and, in particular that of which the collector terminal (C) is connected with the positive pole (+) and the emitter terminal (E) with the negative pole (-) of the sub-winding (8); and

   - at a passive side one semiconductor switching element (61, 62, 71, 72) is always blocked and the other semiconductor switching element (61, 62, 71, 72) is always conducting.
4. Method according to any one of the preceding claims, wherein

   - in the case of change in the direction of the current flow (I) and the orientation of the positive pole (+) and the negative pole (-) it is detected at the sub-winding (8) which IGBTs (11, 12) of the semiconductor switching element (61, 62, 71, 72) on the active side are cycled or switched to be conducting.
5. Method according to claim 4, wherein

   - in the case of change in the direction of the current flow (I) and the orientation of the positive pole (+) and the negative pole (-) it is detected at the sub-winding (8) which IGBTs (11, 12) of the semiconductor switching element (61, 62, 71, 72) on the passive side are switched to be conducting or non-conducting.
6. Method according to claim 5, wherein

   - in the case of change in direction of the current flow (I) and the orientation of the positive pole (+) and the negative pole (-) the active side and the passive side are determined at the sub-winding (8).
7. Method according to any one of the preceding claims, wherein

   - the on-load tap changer (1) consists of a first switching module (51), a second switching module (52) and a third switching module (53); and

   - the sub-windings (8) of the switching modules (51, 52, 53) have different winding ratios with respect to one another.
8. Method according to claim 7, wherein

   - the winding ratio of the sub-windings (8) is 9:3:1.

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