RU2460163C1 - Method of breakless switching between transformer winding taps with stepped voltage control - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the method of breakless switching between two taps (tap n, tap n+1) of a transformer winding with stepped voltage control, besides, each of both winding taps via an appropriate mechanical switch (DS) and a circuit arranged subsequently with it from two opposite IGBT (I_p, I_n) may be connected with a common loading outlet.

EFFECT: higher functionality.

3 cl, 3 dwg

Description

The invention relates to a method for seamless switching using semiconductor switching elements between the taps of the transformer winding with step voltage regulation.

A similar method using semiconductor switching elements is known from WO 01/22447. The method described there works with both electrical switching means, such as insulated gate bipolar transistors (IGBTs), and with mechanical contacts. It is designed in such a way that the load switching itself is carried out when the load current passes through zero with two IGBTs with diodes in the Graetz circuit (bridge rectification circuit on four diodes). A necessary component of this known method is the recognition and determination of the corresponding transition through zero current as a prerequisite for the introduction of load switching at this point in time.

Another method is known from WO 97/05536 with an IGBT switching device, in which the taps of the control winding of a power transformer are connected via a series connection of two IGBTs to a common load terminal. This known method works according to the principle of pulse width modulation; at the next stage of the method, the loop current is limited by means of transient reactivity of the winding with taps.

This method requires specific coordination of the step switch of the transformer windings with the corresponding transformer with step voltage regulation, which must be mounted. In other words, a transformer with step voltage regulation and a step switch of the transformer windings are matched to each other and interact electrically. Therefore, this known method is not suitable for use in a separate, universally applicable, not designed for a particular transformer switch of the steps of the transformer windings.

The objective of the invention is to propose a method of the type described above, which is simple to implement, has high functionality and in which it is not necessary to carry out switching only precisely when the load current passes through zero. Another objective of the invention is to propose an appropriate method that is workable in any case, that is, without tuning to a specific transformer with step voltage regulation, which must be mounted.

This problem is solved by a method with the features of the first claim. The dependent clause relates to a particularly preferred embodiment of the invention.

This problem is also solved in a modified way with the signs of a subordinate third claim.

Corresponding to the invention, the methods proceed from the general inventive idea that varistors should not be used, as has long been known in the prior art, as components for overvoltage protection, but for switching the load current of the transformer winding stage switch from one side to the other, there is from the winding tap turned on so far to a new connected tap of the winding, by applying the corresponding steps of the method.

In the method according to the invention, the varistors which are specially calculated parallel to each IGBT and which are turned on, perform a new function: after switching the supplied, created by the mains voltage of the load current disconnecting IGBT to the parallel-connected varistor (small switching circuit), the varistor streamlined by the load current forms according to its current-voltage (IU) characteristic voltage that shows a relatively insignificant dependence on the instantaneous current value and remains during the OLTC switching process Xia is almost constant.

In this case, the varistors are selected in such a way that the varistor voltage, which manifests itself under load with the peak value of the maximum current, still has a sufficient safe gap with respect to the maximum blocking voltage IGBT.

On the other hand, the clamping voltage (limitation) of the varistor (U _Var at 1 mA) should be noticeably higher than the peak value of the maximum step voltage so that the load current of the disconnected OLTC side can be switched via the step voltage to the side receiving the load current (large switching circuit).

The difference ΔU between the instantaneous value of the voltage drop across the varistor and the instantaneous value of the voltage of the stage causes the switching of the load current through the stray inductance of the winding with taps and the line inductance to the receiving side of the stage switch and determines the di / dt of the switching process

It is obvious that the varistors in the framework of the corresponding invention of the method do not act, as is known in the prior art, to reduce transient overvoltages. In the proposed method, varistors take on the following functions not typical of their purpose and not arising from the prior art as part of the method:

- reception of load current from hard-off IGBTs,

- the formation of a voltage drop, which regardless of the instantaneous value of the load current should be in the voltage range between the maximum blocking voltage IGBT and the peak value of the maximum voltage of the stage,

- providing a voltage-time region, which the load current from the current-carrying side of the stage switch through the oppositely directed voltage of the stage commutes to the receiving side of the stage switch:

The provision of the above functions by means of varistors simplifies and offloads the power electronic switching process in a crucial way:

- Very little energy input to hard-switched IGBTs.

- Loss energy, forcibly transferred to the disconnecting side during the switching process

especially in the case of high switching requirements (high instantaneous value of the load current, high instantaneous value of the oppositely directed voltage of the stage, large parasitic inductance of the switched stage), it is predominantly accepted by the varistor and only in a small part of the disconnected IGBT.

- This state of affairs provides a very simple and economical design of power electronic groups of compounds, since the energy-receiving volume in the case of a varistor is flexibly variable and significantly larger than a much smaller, expensive and commensurate with the volume only hardly-varied volume of the IGBT chip.

- As an additional positive effect, passing the load current through the varistors, providing the required voltage-time switching region by means of the varistors and receiving the loss energy due to it also by the varistors leads to a very large tolerance field regarding the synchronization of the turn-off time of the switched-off IGBT group and the turn-on time of the receiving IGBT groups. The following switching modes are possible and valid:

- Incomplete (with a pass)

The process of switching off the switched side is carried out before the switching process of the receiving side. The current flow time for the load current through one of both varistors of the disconnecting side is accordingly extended.

- simultaneous

The disconnection process and the inclusion process of both IGBT groups is carried out simultaneously. The standard case, without additional load current - the load time on the varistor.

- overlapping

. Это приводит к повышению приходящейся на отключающуюся сторону энергии потерь коммутации и к затягиванию процесса коммутации.The process of switching on the receiving side of the step switch is carried out before the process of switching off the switched side. During the overlap time, both IGBT groups are closed, so that the voltage of the stage begins to form a circulation current in this time interval. di / dt of the generated circulation current depends on the instantaneous value of the step voltage in the time interval of the overlap and on the loop inductance of the circulation current. The circulation current is summed up on the disconnecting side with the load current and, at the time of the shutdown process, leads to a gradual increase in the current, which must be switched in total

. This leads to an increase in switching losses per switching side energy and to a delay in the switching process.

Compared to the prior art, the methods of the invention have several advantages:

The smallest losses and the shortest switching times are achieved when both IGBT groups are turned off and on.

If, during the year of operation, due to the aging of the components and the displacement of the operating point in the control electronics, a switching mode with overlapping or gaps with an order of magnitude of approximately ± 10 μs arises, this does not pose a threat to functioning in the case of the switching principle in accordance with the invention.

The only consequences are moderately increasing switching losses and a slightly longer switching time.

- With all three of the switching modes described above, ohmic / resistive energy reception by varistors causes excellent attenuation of currents and voltages during the switching process as an important positive side effect. The interference oscillations that would be expected with such fast switching processes (of the order of 10 μs) in connection with the capacitances of the windings and the parasitic inductances of the sectioned windings cannot occur due to the strong attenuating effect of the varistors. In addition, the voltage formed on the varistors, as a result of the flow of the load current, is relatively constant and, as a result, a constant di / dt is formed during the switching process. Due to this state of affairs, strong vibrational excitation is additionally impeded.

- In the case of very high load currents, it is a possible known method to foresee the detection of current transitions through zero and to carry out the switching or switching process at very low instantaneous values of the load current, in the time proximity to the transition through zero current.

This measure leads to a significant reduction in the current load of IGBTs and varistors, as well as the energy of switching losses and to a reduction in switching time.

Switching near the transitions through zero current provides a significant increase in the nominal data on the switching power of the switch of the steps of the transformer windings with the same hardware of power electronic components.

The method is further explained in more detail with reference to the drawings, which show the following:

Figure 1 - schematic representation of the implementation of the first method corresponding to the invention,

Figure 2 - the first circuit with IGBT and with parallel to each IGBT enabled varistors, especially suitable for performing the method,

Figure 3 is another diagram for performing the method,

4 is a schematic representation of the implementation of the second, simplified method corresponding to the invention.

Figure 1 shows a schematic representation of the implementation of the first method corresponding to the invention. The method proceeds from the fact that in the switch of steps of the transformer windings, by means of which switching from the current tap of the transformer winding with step voltage regulation to the new tap of the winding is carried out, there are two load branches, which are connected through the mechanical switch DS _a , DS _b and sequentially to them an arrangement of a serial connection from, respectively, two oppositely connected IGBTs I _an , I _ap ; I _bn , I _bp , with the corresponding parallel diode d _an , d _ap ; d _bn , d _bp can be electrically connected to a common load terminal, and that in parallel to each of the named IGBTs a corresponding varistor V _an , V _{ap is} connected; V _bn , V _bp . Each of the two load branches should be able to be bypassed through the continuous main contact MC _a or MC _b .

At the first stage, all mechanical switches DS _a and DS _b acting as free switching contacts on both sides are closed.

Then, the gate voltage IGBT I _an , I _{ap of the} disconnected side is applied.

Then the continuous main contact MC _{a of the} disconnected side is unlocked.

Then, the load current I _L is switched again to the IGBT of the disconnected side.

These IGBTs of the disconnected side I _an , I _ap now receive a shutdown command, and the IGBTs of the disconnected side I _bn , I _bp , on the contrary, receive a shutdown command.

As a result, the IGBT I _an and I _{ap of the} disconnected side are hard-disconnected.

The load current is now, in accordance with the invention, switched on the varistors V _an and V _{ap of the} disconnected side.

Then this load current is switched to the IGBT of the receiving, connected side I _bn , I _bp .

Once again, the continuous main contact MC _{b of the} receiving side closes.

Then, the IGBTs of the receiving side I _bn , I _bp switch to a non-conductive state.

The last step of the method consists in opening the mechanical contacts DS _a , DS _b , which protect the IGBT from transient voltage loads that can act on the winding with taps.

Figure 2 shows a diagram particularly suitable for implementing the method of figure 1. Moreover, each of both taps n, n + 1 of the winding through a mechanical switch DS _a , DS _{b is} connected to the serial circuit of respectively two oppositely connected IGBTs I _an and I _ap on the side n, as well as I _bn and I _bp on the side n +1 with the output of the step switch of the transformer windings. In parallel to each IGBT, a diode d _an , d _{ap is} provided; d _bn , d _bp , and both diodes in each load branch are connected oppositely to each other.

In parallel to each individual IGBT, a varistor V _an , V _{ap is} again respectively provided; V _bn , V _bp .

Finally, the corresponding continuous main contacts MC _a or MC _{b on} each side are also shown shunting the entire switching device in stationary mode. IGBT of both sides I _an , I _ap ; I _bn , I _{bp are} controlled by a common, only schematically known, prior art IGBT pathogen.

The varistors V _an , V _ap or V _bn , V _{bp are} designed in such a way that their varistor voltage is lower than the maximum blocking voltage of the corresponding parallel IGBTs, but greater than the maximum instantaneous voltage value of the stage.

Further, the method according to the invention, that is, the switching sequence, for example, from branch n to branch n + 1, will be considered in more detail using this scheme: in the main position, the load current flows through the long main contact MC _a from branch n to branch Y of the stage switch transformer windings.

At the first stage of the switching sequence, the free switching contacts DS _a and DS _b close.

Then, a gate voltage is applied to the IGBT gates I _an and I _ap . The continuous main contact MC _{a is} now unlocked and the load current I _L switches to the IGBT group I _an / I _ap . After less than 10 ms of the current I _L flowing through the IGBT group I _an / I _ap, these IGBTs receive a shutdown command, and the IGBT group I _bn / I _bp receive a turn-on command simultaneously (at least in the standard case).

The voltage generated on the disconnected IGBT is transferred to a parallel varistor. If after several 100 ns the varistor fixing voltage is reached, then the varistor goes into a conducting state, the voltage on the IGBT is divided into two components:

- still slightly increasing varistor voltage,

малого контура коммутации между IGBT и параллельным варистором.-

small switching circuit between the IGBT and the parallel varistor.

Due to the very low-induction connection of the varistor with IGBT, the switching of the maximum load current from IGBT to the varistor occurs during the interval from 0.1 to 1 μs.

The varistor is calculated in such a way that the voltage of the varistor streamlined by the load current changes, on the one hand, below the maximum blocking voltage of the parallel IGBTs, and on the other hand, above the maximum instantaneous value of the stage voltage.

The excess of the instantaneous value of the varistor voltage over the instantaneous value of the voltage of the stage causes the switching of the load current with an almost constant di / dt from side A and transfer through the voltage of the stage and the stray inductance of the winding with taps L _σ (large switching circuit) with the same di / dt (in this case positive) to side B. Despite the continuously decreasing current that flows through the varistor on side A, the varistor voltage, to a first approximation, remains constant.

After approximately 10 μs, the entire load current is switched from the side A streamlined by the varistor to the side B conductive IGBTs. When the side A current approaches 0, the voltage at connection group A changes as follows:

исчезает, и на группе А IGBT-варистора появляется напряжение ступени, которое создается в зависимости от полярности на блокированном IGBT и соответствующем параллельно расположенном варисторе. Даже при нагрузке пиковым значением напряжения ступени варистор еще не допускает никакого значительного протекания тока.Varistor voltage drops, transient state

disappears, and a step voltage appears on group A of the IGBT varistor, which is created depending on the polarity on the blocked IGBT and the corresponding parallel varistor. Even with a peak load of the step voltage, the varistor still does not allow any significant current flow.

Less than 10 ms after the power electronic switching of the load current from side A to side B, the continuous main contact MC _b closes and shunts the IGBT group B. Then, IGBT I _bn / I _{bp are} switched to a non-conducting state through the gate control.

The switching sequence ends with the opening of the mechanical free switching contacts DS _a and DS _b , which protect the IGBT from transient voltage loads that can act on the tapped winding.

Figure 3 shows a modified circuit for performing the method according to paragraph 1 of the claims, in which both varistors of the corresponding one side V _an , V _ap or V _bn , V _bp are reduced to the corresponding common varistor V _a or V _b . In this case, the corresponding mechanical switch on each side of DS _a or DS _b and the corresponding varistor of the associated side V _a or V _b also form a series connection to a common load terminal.

Figure 4 shows another modified method according to the invention, which proceeds from the simplification of the process and in which mechanical switches are not provided. The general idea of the invention — to apply varistors for switching the load current — is also realized with this method.

This additional method proceeds from the fact that two load branches are again provided in the transformer winding stage switch, each of both load branches comprising a series connection circuit of two oppositely connected IGBTs I _an , I _ap ; I _bn , I _bp , to which respectively a diode d _an , d _{ap is} connected in parallel; d _bn , d _bp . In parallel to each of the named IGBTs I _an , I _ap ; I _bn , I _bp respectively included varistor V _an , V _ap ; V _bn , V _bp .

To the beginning of the switching of the IGBT of the disconnected side, I _an and I _ap conduct a load current.

Then these IGBTs receive a shutdown command, the IGBTs of the connected side I _bn and I _bp receive a turn-on command; The IGBTs of the disconnected side I _an , I _{ap are} hard disconnected.

Then, the load current in accordance with the invention is switched to the varistors V _an , V _{ap of the} disconnected side.

Then again, the load current is switched on the IGBT of the receiving side I _bn and I _bp and passed by them.

As already explained, this simplified method proceeds from the step switch of the transformer windings, which does not contain mechanical free switching contacts and mechanical continuous main contacts, but in which the load current in stationary mode is carried out by means of IGBT.

Both methods, both presented in figure 1 and presented in figure 4, follow the same idea of the invention and solve the problem of the invention in the same way.

In conclusion, it should be cited once again already explained in detail above the advantages of the method according to the invention in relation to the prior art:

- Ability to switch at any arbitrary instantaneous value of the load current without thermal overload IGBT.

- Extremely fast process of switching the load current of the side of the stage switch A → B or B → A for about 10 μs.

- Elimination of interfering vibrations.

- There is no task-specific matching of each stage switch with the specific nominal stage data for a custom case (stage voltage, rated transmittance, spurious inductance) if the limit values for the step voltage and rated transmittance are not exceeded.

- Reliable, safe switching principle with a very large tolerance range with respect to the switching time drift of both groups of IGBT connections. No additional adjustment is required after a long working time.

Claims (3)

1. A method of seamless switching between the taps of a transformer winding with step-wise voltage regulation with two load branches (branch n, branch n + 1), each of both load branches (branch n, branch n + 1) through a mechanical switch (DS _a , DS _b ) and a series-connected series circuit of two oppositely connected IGBTs (I _an , I _ap ; I _bn , I _bp ) can be connected to a common load terminal,
and in parallel to each IGBT (I _an , I _ap ; I _bn , I _bp ) a diode is provided (d _an , d _ap ; d _bn , d _bp ), and in parallel to each IGBT (I _an , I _ap ; I _bn , I _bp ) a varistor (V _an , V _ap ; V _bn , V _bp ) is provided, and each of both load branches (branch n, branch n + 1) can be bridged by means of a mechanical continuous main contact (MC _a , MC _b ), characterized in the following steps of the method: closing the free switching contacts DS _a and DS _{b on} both sides, applying the unlocking voltage to the gate IGBT I _an , I _{ap of the} disconnected side and thereby turning them on, unlocking rodolzhitelnogo main contact MS _and disconnectable hand, switching the load current I _L on the IGBT switchable side IGBT off switchable side I _an, I _ap and switch IGBT plug-side I _bn, I _bp so that IGBT I _an and I _ap switchable hand " hard off
then switching the load current to the varistors V _an and V _{ap of the} disconnected side,
switching then the load current again on the IGBT of the receiving side I _bn , I _bp ,
closing the long main contact MC _{b of the} receiving side,
disconnecting the IGBT of the receiving side I _bn , I _bp , and opening the mechanical contacts DS _a , DS _{b on} both sides. 2. The method according to claim 1, characterized in that it additionally detects the transitions through zero current and the process of switching or switching in time proximity to the transition through zero load current. 3. A method for seamless switching between the taps of a transformer winding with stepwise voltage regulation with two load branches (branch n, branch n + 1), each of both load branches (branch n, branch n + 1) contains a series connection circuit of two oppositely connected IGBT (I _an , I _ap ; I _bn , I _bp ), and in parallel with each IGBT (I _an , I _ap ; I _bn , I _bp ) a diode (d _an , d _ap ; d _bn , d _bp ) is turned on, and parallel to each _{IGBT (I an, I ap;} I bn, I bp) included varistor _{(V an, V ap; V} bn, V bp), characterized by the following method steps: passing nagruzoch th current first through IGBT switchable side I _an and I _ap, subsequent disconnection IGBT switchable side and switch IGBT plug-side I _bn and I _bp so that IGBT switchable side I _an, I _ap "rigidly" deactivated, the subsequent switching of the load current varistors V _an , V _{ap of the} disconnected side, subsequent switching again of the load current to the IGBT of the receiving side I _bn and I _bp and passing the load current through them.

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