DE2117602A1 - Converter arrangement consisting of several half-controlled converter bridges - Google Patents

Description

Sn / os

Converter arrangement consisting of several semi-controlled

Converter bridges

For the control of single-phase alternating current traction vehicles with thyristors, asymmetrical semi-controlled ones are predominantly used Converter bridges used.

The disadvantage is that these converters take up a lot of reactive power when partially driven and also have strong harmonics cause in the rush current.

This flowing in the contact line and over the rails (in the case of railways) flowing, strongly harmonic-containing current has an effect now inductively on the telecommunication cables, which mostly run in parallel at a short distance !!. This results in loud noises in the

Telephone, malfunctions in the telex precaution and influences Pernsteueranla ^ s.

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As a rule, therefore, only low-power locomotives are used equipped with a single bridge. In the case of high-performance locomotives, several are used, operated in series Converter bridges, which means only a fraction of the total power is implemented in the phase control with an unfavorable power factor and the resulting harmonics with filter elements can be weakened sufficiently.

It is known to connect several half-controlled bridges in series on the DC side ™. For example, there are locomotives in Japan with Jj bridges in series.

Significant disadvantages of this known type of circuit, however, can be seen in the fact that, firstly, the transformer has a complicated structure is because it requires several galvanically isolated and as well decoupled secondary windings as possible and, secondly, many

> and diodes
Thyristors ^ with a relatively small reverse voltage are required.

The latter is very uneconomical, as there are no difficult- W ^ nd diodes today

prepares thyristors ^ for high reverse voltages to build.

Another disadvantage is due to the fact that at full level the commutation takes place slowly because the driving alternating voltage is small (this increases the Commutation reactive power).

.first

In order to avoid the aforementioned disadvantages, * an alternating current

proposed series connection with sequential control, the function of which is briefly explained schematically with reference to FIG.

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In this figure, 1 denotes a converter transformer, 2 and 2 are diodes and 3.3 'to 6.6' are thyristors. The control circuit is not specifically shown.

In order to continuously adjust the output voltage from zero to maximum, first the thyristors 3 and 3 ^{1 are switched} to open, then 4 and 4 ', 5 and 5' and finally 6 and 6 '. It should be understood that the thyristors 3, ^, 5, 6, for example, each work during the positive half-wave and the thyristors 31, 4 ', 5 *, 6' during the negative half-wave. So z. B. the current at a half-wave from plus via the consumer to minus, from there via the diode 2 ', the transformer secondary winding and the thyristor 6 back to plus. For the other half-wave of plus, consumer, minus, thyristor 6 ', transformer secondary winding and diode 2.

A major disadvantage of this circuit, however, is that each thyristor branch for the full current and the maximum reverse voltage must be measured.

The object of the invention is to eliminate the disadvantages of the known.

This object is achieved according to the invention in that a first secondary winding of a converter transformer R, designed with taps, has at least two alternating currents semi-controlled converter bridges connected in series

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are connected, with a center tap of the first secondary winding to the connection between the anode and Cathode of the non-controllable semiconductor valves is guided, which all these semi-controlled converter bridges represent common uncontrolled 3 back part and that continue to these alternating current in series, but direct current half-controlled converter bridges lying in parallel, another one is connected in series with direct current, plural marriage, to a second secondary winding of the converter transformer connected.

A particular advantage of the invention is to be seen in the fact that only two galvanically separated secondary windings of a converter transformer are needed. Compared to two direct current Semi-controlled bridges connected in series (with only two secondary windings also being required) results in the inventive Stromriehteranorndung also a significant improvement in the power factor and a significant reduction of the harmonics in the mains current-r

If, according to a preferred embodiment, the first and second Secondary winding are designed with the same total number of turns, the control circuit can be implemented more easily.

It is recommended that the first secondary winding only have a center tap. It can only do so two alternating current connected in series,]

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Converter bridges connected v / earth, but the arrangement (including control circuit) is characterized by a favorable Simplicity.

A considerable reduction in the harmonic content in the mains current without increasing the reactive power requirement is according to a further advantageous embodiment by switching on a choke coil in the voη leading away from the central tap Cable run possible.

If the first secondary winding is provided with taps after 1/4 and 1/2 of its total number of turns, three semi-controlled Converter bridges can be connected in series in terms of alternating currents. This results in a further reduction in Harmonics.

Here it is recommended to use after 1/4 of the total number of turns to switch on a choke coil leading away from the cable run.

Exemplary embodiments of the subject matter of the invention are shown in the drawing shown in simplified form.

It shows :

1 shows an arrangement belonging to the state of the art,

Pig. 2 an embodiment of the invention,

Fig. 3 shows a modification of the arrangement of Fig. 2,

FIG. 4a is a voltage-time diagram,

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4b shows a current-time diagram,
Fig. 5 shows a control circuit.

According to FIG. 2, the reference numbers mean the following: 7 a converter transformer with a first secondary winding 7a and a second secondary winding 7b, 8,9,10 and 11 diodes, 12,13, 14, 15, 16 and 17 thyristors and 18 a choke coil. A load resistance through which a current I flows is indicated by FL. S denotes a connection and U ₇ is the total voltage of the first secondary winding.

In Fig. 3, 7a 'is a modified first secondary winding of the converter transformer 7 and 20, 21 are referred to as diodes. Reference numerals 22, 23, 24, 25, 26 and 27 are Thyristors provided.

In FIGS. 4a and 4b, the time axes are identified by t.

The meaning of the reference numbers in Fig. 5 is as follows: 30, 31, 33, 34, 49, 50, 51, 52, 53 and 54 are resistors, 32 is an operational amplifier, 35, 26, 37, 38 are comparators (level detectors ), 39, 40, 41 are bistable multivibrators * The reference numerals 42, 43 and 44 denote electronic switches and 45 is an AND element. An OR gate was given the designation 46, while 47 and 48 represent amplifiers. The output voltages of the operational amplifier 32 and the amplifiers 47 and 48 were represented by U, ~, U,,,, and Ui. _Q noted. U ₁ is an auxiliary

32 4 1 * to J.

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voltage, U- an alternating voltage, ^u _{should be} a nominal voltage and U is the voltage at the input of the operational amplifier 32. The voltage arrows point from plus to minus. El ₃ E2 and el, e2 are inputs of the comparators or bistable multivibrators, the outputs of which are marked with A1, A2 or al, a2. D denotes the dynamic input of a bistable multivibrator.

The mode of operation of the current cord arrangement according to the invention

will first be explained with reference to FIG. *

It must still be prepended that the two secondary windings 7a and 7b have the same number of turns.

If the DC output voltage is to be zero, not a single thyristor is triggered.

The aim now is to show how the DC output voltage can be continuously adjusted up to its maximum value.

For this purpose, the thyristors I ^ and 15 are first known V / or on controlled, i.e. during a half-round e.g. 14 and during the other 15, the ignition of which is initially carried out in such a way that they only remain conductive for a short time and are thus out of the Cut out only small sections of the AC mains voltage (gate control) * To increase the DC output voltage the thyristors are fired earlier and earlier until

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at full output of the thyristor 14 e.g. the complete positive voltage half-wave passes and 15 the subsequent negative.

The thyristors 14 and 15 together with the diodes 10 form and 11 a half-controlled converter bridge and the thyristors 16 and 17 with the same diodes 10 and 11 another.

During the modulation of the thyristors I ^ and 15, the current flows during the positive voltage half-wave from the upper half of the first secondary winding 7a, via the thyristor 14, the diodes 9 and 10, from plus to minus via the consumer Rj ₁ , the diode 11 and via the connection S back via the choke coil 18 and the center tap. In the case of the negative voltage half-cycle, the current flows from the center tap via connection S, the choke coil 18, the diodes 10, 9 and 8, from plus to minus via the consumer f the thyristor 15 and back into the upper half of the first secondary winding «

When the thyristors 14 and 15 are fully driven, there is a DC output voltage of a quarter of the maximum possible available.

If full modulation is reached, according to the invention is in place of the thyristor 14, the thyristor 17 is ignited and the thyristor replaces the thyristor 15.

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The thyristors 1H and 15 can now be turned on again, with the result that the DC output voltage can be continuously adjusted from a quarter to a half of the maximum size.

There are the two half-controlled converter bridges, on the one hand from 16,17,10,11 and on the other hand from 14,15, 10,11, connected in series in terms of alternating current, what comes from the sound reinforcement the first secondary winding 7a follows. The connection S is the anode or. Cathode of diodes 10 and 11 with the center tap tied together.

V / enn full modulation of the two thyristors 1 * 1 and 15 again is present, a switch is made to the next stage, that is, the semi-controlled one located on the second secondary winding 7b The converter bridge with the diodes 8, 9 and thyristors 12, 13 is fully controlled, while none of the thyristors 14, 15, 16 or 17 is ignited. There is therefore a current change in the second secondary winding from the first without any change the DC voltage, since 7a and 7b generate the same voltages.

Then again by increasing the thyristors 1H and 15 (with fully controlled thyristors 12 and 13) the output DC voltage is continuously increased from half to three quarters of the maximum value.

As already described above, the thyristors 16 then take over

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and 17, while with 1H and 15 the range up to the maximum of the output DC voltage can be continuously adjusted.

According to the description above, only the two thyristors I ¹ I and 15 are used for stepless voltage changes, while the remaining semi-controlled converters (16, 17, 10, 11; 12, 13, 8, 9) are used to set the four coarse voltage levels.

When the thyristors 1h and 15 are partially driven and the current only flows through one half of the winding of the first secondary winding 7a, the converter transformer 7 translates this current smaller to the primary side. However, this also means that the interfering harmonics are transmitted to the AC network in a smaller manner.

In addition, the rate of current change in the! Commutation ^ on the higher voltage thyristors in this converter arrangement relatively small, because the phase control only takes place with a quarter of the total voltage.

As a result, higher-frequency harmonics are created with less strength.

If, despite this advantageous harmonic reduction, the permissible level is exceeded, it is advisable to use a To switch the choke coil l8 into the cable run from the center tap of the first secondary winding 7a to the connection S.

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The Y / effect of this choke coil 18 is best from the Diagrams of FIG. 4 can be seen.

In the voltage-time diagram of Fig. 4a, the sinusoidal

ü _7a
The course of the voltages Uy ₈ and ■■ is shown. The hatching indicates when these voltages are effective when the thyristors 16, 17 are fully controlled (i.e. ignition at the earliest possible point in time; i.e. when the current flowing through the thyristor to be detached has dropped to zero) and the thyristors 14, 15 fail be fired with a delay of about a quarter period. The full voltage Uy _{3 of} the first secondary winding 7a is effective as soon as the thyristors 14 »15 carry the current.

With the firing of the thyristors 16, 17, the current I is from the path via the diodes 10, 11 (freewheeling) in the lower half of the Secondary winding 7a deflected. The current flow through the upper half begins when the thyristors 14, 15 are triggered.

According to the current-time diagram in FIG. 4b, the alternating current i increases in the primary winding of the converter transformer 7 suddenly starts after each thyristor ignition. The steepness this jump in current depends on the inductivity of the commutation circuit. For example, the commutation circuit includes when firing the thyristor 17, the lower half of the first

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Secondary winding 7a, the choke coil 18, the diode 11 (in the opposite direction , The current is reduced) and the thyristor 17

With the choke coil 18, the rate of increase in current can be controlled 'reduce, which is equivalent to a reduced

Qt

reduced occurrence of harmonics.

A detrimental effect of inductance in the commutation

circuit generally consists in the fact that the current commutation is slow, especially after the AC voltage has crossed zero he follows. This leads to a phase shift between alternating currents and voltage, which is equivalent to increased reactive power consumption.

When considering the course of the current in Flg. 2 shows the extremely advantageous fact that the choke coil 18 is only effective when the thyristors 17 and 16 as well as 14 and 15 are switched on, but not when commutating after the voltage zero crossing. This is explained in more detail below.

After the thyristor 17 has been triggered, the current I flows through the lower half of the first secondary winding 7a, the choke coil and further via mode 10. The current rise is delayed, because the choke coil 18 absorbs energy.

When the thyristor 14 is switched on, the current I begins

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on the way via the thyristor 17, the entire first secondary winding 7a and the thyristor 14 to change over. First of all, however, the choke coil 18 endeavors to maintain the current flowing through it and thereby reduces the energy stored in it. For this purpose, this choke coil 18 drives a current via the diode 10 and in the opposite direction via the open thyristor 14 and also against the voltage induced in the upper half of the first secondary winding 7a. Only when this current has decayed can the full current, which has now risen in accordance with the increased voltage, via the thyristor 14 (or 15 for the next half-wave) fHessen.3i3 the next time the thyristors 16 or 17 are triggered, the choke coil 18 remains de-energized. In particular, it is not effective during the commutation on the diodes 10, 11 after the zero crossing of the alternating voltage and does not slow down this commutation process.

In a modification of FIG. 2, the first secondary winding " Taps according to / 4 and / 2 their total number of turns on how it is illustrated in FIG. 3.

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Accordingly, it also feeds three half-controlled, alternating currents converter bridges connected in series. The diodes 20 and 21 again represent the non-controllable ones that are common to all bridges Part.

In order to set a DC output voltage from zero to the maximum value here, the thyristors 22 and 23 turned up, bringing the range from 0 to 1/8 of the maximum Output voltage is available.

Then these thyristors remain fully modulated and with the thyristors 24 and 25, the output DC voltage is stepless increased up to 1/4 of the maximum voltage.

When this point is reached, the thyristors 26 take over and 27 with full output control the current flow, while 22, 23, 24 and 25 block.

Furthermore, by continuously opening thyristors 22 and 23 first and then 24 and 25 in the previously described (but with fully controlled thyristors 26 and 27) half of the maximum possible output DC voltage can be achieved.

Then the upper half-controlled converter bridge takes over again, which is fed from the second secondary winding 7b, the current, while that fed from the secondary winding 7a

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half-controlled converter bridges can be controlled again as if from zero.

The in Fig. 3 shown and compared to FIG. 2 modified detail has the effect that the converter arrangement can be set in 8 coarse voltage levels.

Even fewer higher-frequency harmonics are generated and the harmonics that occur are transformed into lower strength on the primary side of the converter transformer 7. The power factor is also increased because a smaller proportion of the power is converted in the phase control. If a choke coil is also to be provided in this converter arrangement to reduce harmonics, it is recommended it is appropriate to attach this in accordance with the choke coil 28 in FIG. 3. Then those in connection with the Choke coil IS (Fig.2) exploited advantages discussed.

Finally, a possible control circuit is to be shown and described with reference to FIG. 5, which is used for operating the circuit shown in FIG The converter arrangement shown is used.

First of all, the actual ignition devices for the thyristors are widely known and are therefore no longer shown. You only have to meet the condition that the control angle oC for the thyristors is inversely proportional to the control voltage (^ ₂ > ^U 2i7> ^u JiR '^ variable

means that e.g. with a control voltage of zero volts the

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Control angle ° C - ISO is present, whereby the thyristors are fully controlled, while z. B. applies at + 10 volts Ut-O and thus the thyristors are constantly blocked.

Before the mode of operation of the control circuit is discussed, the standard structural units used should be briefly described be characterized.

As is known, the operational amplifier 32 supplies a control voltage according to the formula:

33
U, = - U , where R, _T and R, ^ are the resistance

⁵ values of the resistors 33, 34 are.

Since that

Ratio - ^ is constant, it will be used in the following for the sake of simplicity are no longer observed. Note, however, the change in sign.

The level detectors 35, 36 and 37 have the property that the signal logic L is present at the outputs A1 as soon as the voltage at E2 is equal to or greater than that at El.Der inverting Output A2 always shows the logical opposite of A1; So if the signal L is applied to Al, A2 shows that Signal O.

The level detector 38 is in principle global, but there is one Input to ground and the other receives a voltage proportional to the mains AC voltage. As a result, appears at the exit

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output a square-wave signal that changes synchronously with the AC mains voltage from L to O and vice versa.

With the bistable multivibrators 39, 40 and ^l \ l , the outputs: al always have the same signal as at the inputs el or at a2 the same as e2. It is important, however, that the static inputs el and e2 only have a preparatory function; This means that the outputs only follow when a dynamic signal arrives at D. Under dynamic signal there is a LO transition or. To understand OL transition.

The electronic switches 42, 43 and 44 are designed so that they switch through as soon as they are triggered with a logical L signal.

The AND gate 45 is only on one negated input (black point), according to which an L signal only appears at the output if L- and at the direct input negated input 0 signal is present.

The OR gate 46 provides a low output signal when on one or the other or both inputs have an L signal.

The amplifiers 47 and 48 are only used to adapt the power to the downstream, but not shown, Igniters.

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• It should also be noted that the signals are logical L and 0 can be any voltage values, such as B. + 10 V and -10 V, + 10 V and OV or +20 V and -3V etc. In adaptation, to The ignition devices will, however, be chosen as logic L, the ground potential (i.e. 0 volts), while logic 0 corresponds to a voltage of + loV. (These values are taken for granted to be understood only as an example, since they are based on the example information selected above, according to which + 10 volts corresponds to a control angle ° £ = 0.)

Now, assume that the target tension ^ _o n continuously from zero to the maximum value is increased in order to explain the operation of the control circuit.

At U '= 0, as a result of the effect of the voltage division between the resistors 30 and 31 and as a result of the voltage U. which is negative with respect to ground, the voltage U _e = -10 V (for example). Taking into account the change in sign, a control voltage U-, ρ of + 10 volts is available. This means that the thyristors I ^ and 15 are blocked.

However, as soon as U .. is increased, U ₅₂ drops and the thyristors I ^ and 15 work in partial modulation.

When U _{30n has reached} the value, the thyristors I ¹ J and 15 are fully controlled (U ^ ₂ = 0). At the same time, however, the comparator 25 emits an L signal at its output A1,

since now his input El, which is fixed to r, is not

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is more due to a higher potential than · E2.

This L signal at A1 and the O signal at A2 now prepare the bistable flip-flop 39 before switching. As soon as a LO or OL transition comes from the comparator 36, Al appears at the output also L signal.

Incidentally, the purpose of synchronizing the tilting processes of the bistable triggering stages is to ensure that such a blatant change in the | Control angle as from full modulation to zero and vice versa always takes place at the times of the mains voltage zero crossings.

With the L signal at the output A1 of the bistable multivibrator 39, on the one hand, the AND condition for the AND element 45 is met, so that now the control voltage U _1. "To L potential, via the OR element 46 and the amplifier 47" so zero volts, is converted. This means that the thyristors 16 and 17 are controlled fully utilized like.

On the other hand, this L signal at the output A1 of 39 »causes that the electronic switch 42 turns on. So that the resistor 49 becomes effective, whereby the voltage divider ratio

^ on.

is changed so far that U ^ - 10 V drops and U, "again

e ever.

Assumes 4-10 volts. The thyristors 14 and 15 are thus complete locked and are only controlled again by further increasing the setpoint voltage U ...

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The resistors 52, 53 and 54 now form a voltage divider which means that the input E2 of the comparator 3β is only present when U _{3011 has reached} the value. When this is reached, the same procedure as before

but now
Described * ^ at the output A1 of the bistable multivibrator 40j an L-signal appears, which causes the thyristors 12 and 13 to be fully modulated via the amplifier 48 and at the same time again the complete blocking of the thyristors 14 and 15 by means of the electronic switch 43 and the resistor 50 brings about. In addition, the AND condition at the AND element 45 is not met by the L signal at the inverting input, so that the thyristors 16 and 17 ^ -ή dependence on Uj, ₇ ) are also fully. are blocked "

By further increasing the nominal voltage, the thyristors 14 and 15 are again turned on depending on U_ _p or U _e ,

5-U
until at U 1, - —so _{as a result of the} voltage divider 52, 53, 54 the condition for the tilting of the comparator 37 is met.

For example, 150 Qi for 52, 50 5L for 53 and 100 Sh for resistor 54 would be suitable.

With the tilting of the bistable multivibrator 4l, the electronic switch 44 and the resistor 51 again cause U ₅₂ = 10 V (for example) and thus the thyristors 14 and 15 are blocked. At the same time, however, the L signal arrives from the output A1 of the bistable multivibrator 41 via the OR element

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and the amplifier 47 to act so that the thyristors 16 and 17 can be fully controlled.

If the nominal voltage U ,, is increased further up to the maximum value, the maximum possible output DC voltage of the converter arrangement according to FIG. 2 is thus also achieved.

When you steer back from U ,, the previously described run Operations only in reverse order.

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Claims (6)

- 22 - 39/71 Claims ( 1st converter arrangement consisting of several half-controlled converter bridges, characterized in that at least two half-controlled converter bridges connected in series with alternating current are connected to a first secondary winding of a converter transformer (7) with taps a Connection (S) between the anode and cathode of the non-controllable semiconductor valves (10, 11; 20, 21) is performed, which represent the uncontrolled bridge part common to all of these semi-controlled flow straightener bridges and that, furthermore, are in series with these in terms of alternating currents, but in parallel in terms of direct current Converter bridges another direct current is connected in series, which is connected to a second secondary winding (7b) of the converter transformer (7). 2. Converter arrangement according to claim 1, characterized in that the first (7a, 7a ^f ) and the second secondary winding (7b) of the converter transformer (7) are designed with the same total number of turns. 3. converter arrangement according to claim 2, characterized in that the first secondary winding (7a) with exclusively a center tap is carried out. 209840/0534 - 23 - 39/71 4. converter arrangement according to claim 3 »characterized in that in the leading away from the center tap A choke coil (18) is switched on. 5. Converter arrangement according to claim 2, characterized in that the first secondary winding (7a ¹ ) is designed with taps after 1/4 and 1/2 of their total number of turns. 6. converter arrangement according to claim 5 »characterized in that that a choke coil (28) is switched on in the line running away after 1/4 of the total number of turns is. AKTIENGESELLSCHAFT BROWN, BOVERI & CIE 209840/0534