HK1214678B - Method for operating an on-load tap changer having semiconductor switching elements - Google Patents

Description

The invention relates to a method for operating a load step switch for voltage control with semiconductor switch elements on a control transformer with control winding. The step switch is known from DE 10 2011 012 080 A1. The step switch has two parallel load branches, in which both load branches are connected in series with semiconductor switches. Each of these has a semi-conductor switch unit of the first and second load branches opposite in pairs. Switching between these two alternating switches allows the load switches to be connected in parallel with a partial winding and a bridge. The partial winding is of different secondary lengths. The partial winding can be adjusted by using a high voltage or current resistance to maintain a constant voltage or current resistance, which can also be adjusted by using a high voltage and current resistance ratio between the IGBT and the transformer.

The purpose of the invention is to provide a load step switch for voltage regulation with semiconductor switching elements that has lower switching losses, requires a smaller cooling device and is therefore cost-effective and safe.

This task is solved by a method according to the invention for operating a load switch for voltage regulation as claimed 1. Preferred embodiments are defined in the dependent claims.

The general idea of the invention is to use two anti-serial IGBTs with inverter diodes as semiconductor switching elements and to take into account the direction of current and the direction of voltage at the sub-winding in the pulse width modulation in order not to switch part of a load branch and thus to avoid switching losses.

According to the preferred embodiment of the invention, the load-level switch for voltage regulation has semiconductor switching elements and is mounted on a control transformer with control windings. This is located between a fixed, unregulated part of the control windings and a load-level switch. Furthermore, the load-level switch has a first load branch and a second load branch parallel to it, with a partial winding 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 load-level switch comprises at least one load-level switch, which comprises the first and second load-load mode.

In a further embodiment of the invention, each semiconductor switch element consists of a first IGBT and a second IGBT, each of which is antiserieally connected to each other. The IGBTs are each equipped with an inverse diode such that an anode of an inverse diode is connected to an emitter connection and a cathode of the inverse diode to a collector connection of the first IGBT and the second IGBT. The semiconductor switches of the first and second load branches are optional.

In another embodiment, the load step switch consists of a first switch module, a second switch module and a third switch module, each with a different winding ratio between the sub-winding of each switch module, e.g. 9:3:1.

The method of operation of the load switcher according to the invention first determines which positions of a partial winding of a control module are to be switched between: in a starting position, the windings of the partial winding are subtracted from a control winding; in an additional position, the windings of the partial winding are added to the control winding; and in a nominal position, the partial winding is omitted entirely.

A further step in the process of the invention is to determine the active and passive sides of the switch module, activating the semiconductor switching elements on the active side of the switch module and setting them to a specified switching state on the opposite side.

After determining the direction of a current and the direction of a voltage at the sub-coil, the switching states of the semiconductor switching elements of the switching module are determined. The IGBTs connected to the alternating current-carrying inverse diodes of the respective active side of the first semiconductor switch element or second semiconductor switch element are constantly locking. Of the two alternating current-carrying IGBTs, one of the active side is constantly conductive, namely the IGBT whose collector connection is connected to a negative pole and the emitter connection to a positive pole of the sub-coil.

When the current flow direction and the positive and negative poles on the sub-winding are changed, it is determined which IGBTs of the semiconductor switch elements are clocked or conductive on the active side, conductive or non-conductive on the passive side and generally which side is active or passive.

These and other features and advantages of the embodiment described here are better understood by reference to the following description and drawings, whereby the same reference marks consistently indicate the same elements. Figure 1 a schematic representation of a step switch in connection with a transformer;Figure 2 a schematic representation of the step switch with semiconductor switching elements;Figure 3 a diagram of the electronic structure of the semiconductor switching elements;Figure 4a -4a diagram of the different switching positions of the load switching element;Figure 5 a diagram of the semiconductor switching elements in a switching position;Figure 6 a further diagram of a switching position of the semiconductor switching element; andFigure 7 a schematic representation of the switching of three switching modules.

The same or similar elements of the invention are identified by identical reference marks. The example shown is merely a possible design of the switch element in accordance with the invention.

In Figure 1 a load switch 1 for voltage regulation is shown in a control transformer 2 and a control winding 3.

As shown in Figure 2, the load step switch 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 parallel to it. The first and second load branches 6, 7 of the switching module 5 are connected by a conductive sub-coil 8. The first load branch 6 has a first semiconductor switch element 61 between the control coil 3 and the sub-coil 8 and a second semiconductor switch element 62 after the sub-coil 8, i.e. to the discharge 4. The second load branch 7 also has a first semiconductor switch element 71 before the coil 8 and a second semiconductor switch element 72 after the coil 8.

Figure 3 shows that each of the semiconductor switch elements 61, 62, 71 and 72 consists of a first Insulated Gate Bipolar Transistor (IGBT) 11 and a second IGBT 12 that are anti-serial switched. The first IGBT 11 and the second IGBT 12 are each equipped with an inverse diode 14. Each IGBT 11 and 12 has a collector port C, an emitter port E and a gate port G. Each of the individual leads 14 is connected to the emitter port E with its anode and the cathode to the collider port C of the respective IGBT 11 or 12.

First, as shown in Figures 4a to 4d, it is determined which of the positions takes up the sub-coil 8; in a position in paragraph 20 (Fig. 4a), the windings of the sub-coil 8 are subtracted from the fixed part of the control coil 3; the current I flows independently of direction through the first semiconductor switch element 61 in the first load branch 6, the sub-coil 8 and the second semiconductor switch element 72 in the second load branch 7.

In an additional position 21 (Fig. 4b), the windings of sub-coil 8 are added to the fixed part of the control coil 3 and current I flows independently through the first semiconductor switch element 71 in the second load branch 7, the sub-coil 8 and the second semiconductor switch element 62 in the first load branch 6.

In a nominal position 22 (Figures 4c and 4d), current I is passed at the sub-winding 8 either through the first or second load branch 6, 7 and in this position the windings of the sub-winding 8 have no effect on the control winding 3.

In order to implement a fine-level control and to create an intermediate stage, pulse width modulation is used to clock between two of the three positions described. If switching is made between the number 22 and the number 20 or the number 21 respectively, a passive and an active side of the switch module 5 must be determined; this is the rule. Each side always includes the semiconductor switch elements 61 and 71 and 62 and 72 respectively, which are on the same side before or after the sub-winding 8. Thus it must be determined whether the first semiconductor switch element 61 of the first switch branch 6 and the first semiconductor load element 71 of the second load branch 7 and the second semiconductor load element 62 of the first second load branch 6 and the second semiconductor load element 72 are actively rotated.Depending on this definition, the IGBTs 11 and 12 of the semiconductor switch elements 61, 62, 71 and 72 must be switched differently. The semiconductor switches on the specified passive side are always kept conductive or blocking during the procedure, with one semiconductor switch element conducting and the other not conducting. On the active side, the semiconductor switch elements are actively switched on due to the pulse width modulation performed, i.e. they assume different states. When switching between paragraph 20 and Appendix 21 both sides are active.

In the example in Figure 5, the active side of the modules 5 shown consists of the first semiconductor switch element 61 of the first load branch 6 and the first semiconductor switch element 71 of the second load branch 7. Consequently, the passive side in Figure 5 consists of the second semiconductor switch element 62 of the first load branch 6 and the second semiconductor switch element 72 of the second load branch 7.

On the passive side, the second semiconductor switch element 72 of the second load branch 7 is always conductive. The second semiconductor switch element 62 of the first load branch 6 is always non-conductive. The current I thus flows through either the first IGBT 11 and the inverse diode 14 which is connected to the second IGBT 12 upstream in the opposite direction through the second IGBT 12 and the inverse diode 14 which is connected to the first IGBT 11. The first and second IGBT's 11 and 12 of the second semiconductor switch element 62 in the first load branch 6 are, however, continuously blocking, so that no current I flows here.

Err1:Expecting ',' delimiter: line 1 column 511 (char 510)

The IGBT of the respective semiconductor switch element shall be switched on immediately before the current is switched off to ensure a safe current path during the current change.

Err1:Expecting ',' delimiter: line 1 column 170 (char 169)

After each change in voltage or current direction, it is always redefined which IGBTs are conductive, which are locking and which are clocked.

For purely ohmic loads of the load switch 1, the direction of current I and the direction of voltage U at sub-coil 8 change at the same time; for inductive and capacitive loads, the direction of voltage U changes in response to the change in direction of current I.

Err1:Expecting ',' delimiter: line 1 column 641 (char 640)

Err1:Expecting ',' delimiter: line 1 column 868 (char 867)

Because a semiconductor switch element 61, 62, 71 or 72 is always continuous on the active side, i.e. low-permeability, during the process the switch losses that occur in the state of the art when the switch from the high-ohm state to the low-ohm state are significantly reduced. This reduces the heat generation at the switch module 5, so that less heat energy has to be dissipated through the cooling.

Figure 7 shows a load step switch 1 in which a first switch module 51, a second switch module 52 and a third switch module 53 are switched in series. The sub-winding 8 of these switching modules 51, 52 and 53 have different winding ratios.

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.