DE2910788A1 - Overvoltage protection circuit for mains commutated static converter - has damping choke in series with resistor and cut=out thyristor circuit - Google Patents

Abstract

The overvoltage protection circuit has a non-linear de-excitation circuit damping ch oke in the de-excitation circuit in series with the limiting resistor and the de-excitation thyristor circuit. A processing circu it is provided and consists of a pulse generator, a control angle setter and a time measurer. The pulse generator's outputs are connected to the pulse amplifier for controlling the de-excitation thyristors to the control angle setter which is connected to the turn-on pulse control and to the timemeasurer which is connected to the mains side of the circuit.

Description

• ■ · ·

VEB Elektroprojekt and Berlin, March 1, 1979 Plant construction Berlin

Overvoltage protection device for power converters with mains connection

The invention relates to a device for protecting power converters, the loads with high inductance against overvoltages caused by switching operations. In consumers with high inductance (> 1 H), e.g. the fields of equilibrium drum machines an energy of 1Cr J bia 1Cr J is stored. In the event of a shutdown, i.e. interruption of the circuit, this high energy converted into thermal energy. This happens in the form of an arc over the switching point, furthermore, so high a voltage arises at the consumer that the electronic components of the converter are destroyed.

To avoid these destructive effects, it is necessary to switch off the consumer current at the moment of switch-off to open up a way via circuit elements in such a way that the energy turnover without the formation of a dangerous overvoltage is carried out. On a representative circuit (Fig. 1) of a converter with the valves V in a fully controlled three-phase bridge circuit, the currently known measures and their shortcomings are explained. The switching paths S are the switches arranged in or in front of a converter or fuses that can switch in any combination. In particular, the switches represent S 1 switching devices such as contactors in the power

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judge feed lines R, S, T, while the switches S 2 ] \

mainly represent branch fuses. The ver i>

consumer 1 iat by connecting R and L in series shown »

The arrangement of a zero valve Vj. (Diode) parallel to consumer 1 leads to a voltage close to zero across consumer 1. Ea, however, the operating behavior of the converter is influenced in that inverter operation (demagnetization of L with negative voltage on the consumer) is no longer possible. The antiparallel arrangement of a second converter (reverse operation) is not possible because the zero valve V _{n represents} a short circuit for it.

The arrangement of a parallel resistor Rp leads to Overvoltages within permissible limits if the value of the parallel resistance Rp is around 3 to 4 times the value of the consumer resistance R limited §j

will. Due to the power loss of the parallel resistor; ^;

Standes Rp, however, the efficiency of the entire facility is reduced by 25% to 30%. Farther :

the dynamic behavior (current i, as a function [ _:;

the time) has a significantly negative effect. ί

The arrangement of a non-linear element Rp _n results in f _: according to the UI characteristic of the available

standing components (varistors, selenium limiters) for fi

Overvoltage just barely permissible. p

The power loss in normal operation is also |

(Nominal voltage on the element) very low. These elements |

can only be a fraction of what is in the consumer i |

convert stored energy and after a short |

Current conduction time can be relieved. |

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■ J ·: ^·: i 2310788

^:; The arrangement of a controlled zero valve V _n

(Thyristor) is a frequently used measure to limit voltage. If a certain V overvoltage is exceeded when switching off, the thyristor V _{n r} ; ignited and acts as a zero valve. Also in j converters that do not contain switches S 2 (converters with string fuses) at least § thyristors V 3 (Fig. 1) are _{operated as controlled zero valves by means of an ignition device according to ignition V N} _ (DT-AS 1 283 358) . The arrangement of controlled zero valves, however, has some deficiencies under the conditions of real converter operation, which call the operational safety into question.

Under real operation is to be understood in addition to the arrangement according to Fig.1 that the converter contains capacitors which serve to dampen the so-called carrier jam effect and the point suppression, and that the control device generating the ignition pulses is also connected to the input of the converter. The disadvantageous phenomena that occur are to be explained using a two-pulse converter (Pig.2) with a capacitor C at the input as an initial variable for the capacitors mentioned in the converter. A non-linear element R, which preferably protects the converter against overvoltages coming from the network, is arranged at the input of the converter.
At the time of shutdown by the switching path S1, the valves V1.1 and V2.2 of the converter should be conductive. The current i, becomes null and void Ii

ύ linear element R _n and the capacitor C

tj is charged to the overvoltage dropping across R.

(u _c in the direction of the arrow). The controlled zero valve V _n

! is ignited, with the delay that is necessary

there is no ignition during normal operation

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due to overvoltages in the network. With the ignition of the controlled zero valve V «, the converter valves V1.1 and V2.2 become non-conductive, the control device 2 is supplied from the capacitor C and ignites the converter valves V2.1 and 1.2, whereby the zero valve V _{n is} triggered by a negative anode voltage pulse" The current i, now flows in the opposite direction through the non-linear element R _n and the capacitor C is reloaded, and if the overspax detection 3 is dynamically able to ignite the zero valve V ^, the process is repeated · If the zero valve V «is not ignited, the current i, - flows continuously, only in an alternating direction, through the non-linear element R. The mains-deleted circuit of the converter works as a self-extinguished inverter when it is switched off by the switching path S1, with energy supplied from the inductance L of the consumer 1 further, with 'the non-linear element R being overwhelmed in terms of energy consumption ird and the control device 2 receives overvoltage for an inadmissibly long time. This oscillation effect leads to further disadvantageous phenomena with a three-phase bridge connection.If a mains supply line fails (switching one of the switches S1 in Pig. 1), the converter can still deliver load current via the remaining mains supply lines under the conditions of oscillation operation and the amplitude of the overvoltage is at the Line side of the converter higher than on the output side. A further disadvantage is that by ignition of the controlled zero valve V ~ by coming from the network overvoltages a short circuit over the zero valve V ~ arises particularly in antiparallelter arrangement of a second power converter · It is common to _n for limiting the current in series with the zero valve V

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.Λ.

■ lilt ft J * ·

to switch off a resistor and the formation of the ignition pulses to suppress in the control device. However, the latter measure means a malfunction.

The invention is based on the object, under the conditions of the real converter operation Effective overvoltage protection device that avoids breakdowns to protect highly inductive To create power converters that supply power to the power supply by switching operations on the converters associated switching paths are caused. In particular, it should also be used with a high rated current operated converters work in reverse operation without interference.

The object is achieved according to the invention in that in a de-energizing circuit known per se, consisting of the series arrangement of a limiting resistor and a de-energizing valve arrangement, a non-linear de-energizing circuit attenuation adrosael with high initial inductance is connected in series and the overvoltage protection device with information processing, consisting of a pulse generator, a control angle adjuster and a Wirkdauexmeßeinrichtung, is combined. The pulse generator has one input each for voltage detection on the mains and direct current side and signal outputs which are sent simultaneously to the pulse amplifier for de-energizing valve control, to the control angle adjuster, which is connected to the ignition pulse control device via a signal output, and to the operating duration measuring device, which has a signal output with the mains-side switching path is connected, are guided ·

Further advantageous embodiments of the invention consist in

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- that the signal inputs provided on the pulse generator

gears to the line and DC side voltage |

acquisition OR- linked to a Schwoll- I

Wertbildner are performed and the excitation of the de-energizing valve control that takes place by means of a pulse train is executed with a time delay j

- That a time-limited signal is derived from the first pulse of the pulse generator in the control angle adjuster which is in the ignition pulse control I direction adjusts the ignition pulses to the ff value of about 90 ° electrically;

- That the control angle of the ignition pulses around its basic setting in the total command time at least once, alternating in both directions by one Angle d is shifted;

- That the active duration measuring device contains a pulse counting circuit which, after a certain f Number of pulses a switch-off command for the current-> ' judge triggers. Here is the number of pulses, | which leads to the disconnection of the converter, a § Functor. of the mean pulse spacing, namely the- I type that no switch-off command is given in the case of pulses at a great distance. §1

The invention is described below in an exemplary \\

example explained in more detail using a circuit arrangement. |

The i "ig.3 shows a converter known per se

arrangement in anti-parallel circuit consisting of £

Valves V and the usual condenser arrangement |

(not shown) for carrier congestion damping and |

for point suppression, the switching sections S1 and S2 and f the mains switch S3, the usual mains-side non-linear protective elements R .., the ignition pulse control device 2 and the highly inductive consumer 1 with

9098S1 / 0578

$ - 7 -

^\: \ The resistive and inductive load component R and L. This ^v [converter arrangement is provided with a protective device, Λ consisting of a per se known Entregerventil- (arrangement with the anti-parallel thyristors Vg and 7 in series with the limiting resistor R ₁₇ and the. De-energizing circuit damping throttle Lg according to the invention equipped.

Parallel is the consumer 1 as well as to the described protection device, the nonlinear element R _n2 · The protective device is an information processing 4, consisting of a pulse generator 5, a ■■ '■, control angle plate 6 and a Wirkdauermeßeinrichtung 7, associated with that supplied by a power supply 8 which is advantageously designed in such a way that its output voltage is maintained in the event of failure of the voltage of a mains supply line or a short circuit of the same% to another supply line.

?; <In the pulse generator 5, the OR-linked

% Signal inputs Si1 and Si2 the voltage on the input |; i input and output side of the converter detected * At; If an adjustable threshold is exceeded, square-wave pulses (with an H width of approx. 100 / us and a spacing of approx. 250 #us) are generated ^{for the duration of the exceedance!} s generated via a pulse amplifier 9 to the H control electrode of the just to be ignited Entregerven-; ' tils Vg and cause the de-energizing valve circuit to be switched on. To avoid the generation of pulses by overvoltage of short duration i from the network, which cannot be attributed to a switching action on the switching paths S1 to S3, the excitation is carried out with a time delay, so that in the event of a switching action, the non-linear elements R- and R _n2 in the The time between the occurrence of the overvoltage and its prevention by switching on the de-energizing valve is a small part of the time in the

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χ. a ^ - *

Have to convert inductance L of the consumer 1 contained energy. By generating a pulse train the effect is that a de-energizing circuit is then also formed if due to an overvoltage of a longer duration from the network, e.g. by disconnecting one from the same network lying converter arrangement with loads of high inductivity, an excitation has taken place and afterwards Switching operations can be carried out on switching paths S1 to S3.

To avoid a malfunction in the form that especially with anti-parallel connection of the converter According to Pig · 3, an excitation takes place through overvoltage from the network, and through connection of the de-energizing circuit an additional load caused by the limiting resistor Rg is generated in the control angle adjuster 6 by the first pulse from the pulse generator a short-term (approx. 30 ms long) command is formed, which in the ignition pulse control device 2 a Adjustment of the ignition pulses for the converter valves V to the value of about 90 ° electrically effected. As a result, there is almost only AC voltage and the current-carrying de-energizing valve at the output of the converter Y-, becomes non-conductive due to a negative anode voltage, and after the control command is withdrawn normal operating status is restored. When excited by overvoltage from the network occurs alongside the effect depending on the occurrence of the stimulus as an additional load circuit due to the limiting resistor, it also has the effect of a deenergizing circuit. However, this circumstance has an effect on converters in reverse operation with a high rated current adversely affect the required accuracy of the control angle setting, whereby the desired shutdown of the de-energizing circuit is not always guaranteed. To with both effects

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the non-conductive state in the energized de-energizing valve To achieve this, the control angle in the ignition pulse control device must be given special consideration the non-linear characteristic of the de-energizing circuit damping choke can be electrically adjusted fairly accurately to a nominal value of 87 °. Especially with converters with a high rated current, some 100 A, is required because of a small limiting resistor and an inductance characteristic that is independent of the rated current of the converter der Entregerkreisdämpfunssdroasel the time constant of the Entregerkreis so large that under The non-conductive state of the de-energizing valve does not apply to real tolerances of the 87 ° electrical control angle position is to achieve.

Therefore, the Entregerkreises is arranged in advance SWITCH ON ^"1 tung (about 30 ms long) formed command by overvoltage from the network in the control angle plate by the first pulse from the pulse generator is a short-time to switch off, in the Zündimpul33teuereinrichtung for the controllable valves of the converter adjustment which results in ignition pulses with a time response as shown in Pig. 4.

Under the condition that the time of the shift by the angle d is greater than twice the pulse time of the converter is, and is shifted at least once in each direction by the angle d in the total command time, it is ensured that a correct setting always appears dynamically to switch off the deenergizing circuit leads·

The size of the angle d depends on the tolerances of the basic setting 87 ° electrical and is about »5 % of the same. The puncture is not necessarily tied to the rectangular course of the control angle position shown in Pig. 4. Deviations from the constant displacement d are also possible,

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eg a sinusoidal curve, if only ensured t

is that one in both directions around the basic setting %

symmetrical around the course DAR I specified conditions is given according to the before.

The duration measuring device 7 determines the time of the Occurrence of an overvoltage by counting the pulses detected from the pulse generator 5 and after a certain number of pulses a command to turn off the Converter to the switching path S3 in the event that, in particular due to the failure of a power supply line ί continuously the oscillation effect already described on- I; occurs and an impermissibly long overvoltage f

load leads. |

According to the time-dependent overload capacity of the |

nonlinear elements R ^ and R _n2 is the number of §

Impulse that leads to shutdown, a puncture of the I.

mean impulse from st and it in such a way that with Im- Ü. pulse at large intervals, no shutdown command is issued. ·

Bur ch the inventive insertion of the exciter circuit "■ damping throttle L _£ , the occurrence of the non-conductive state of the current-carrying de-excitation nerve

tils Vg prevented in the swinging effect. With a corresponding design of the deenergizing circuit damping choke Lg it is achieved that the described negative anode voltage pulse that occurs with the oscillation effect does not result in a current zero crossing. To ensure the damping effect, the de-energizing circuit damping choke L «must have _{a high inductance with a small current i T} and can have a small inductance with a high current. Demzu-: follow the steering angle adjuster iat the Entregerkreisdämpfungsdrossel as a so-called non-linear choke with current dependent on the inductance executed as v tion to secure the required punk is where How-i de rum a small inductance as possible is required. yyy

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The overvoltage protection device according to the invention iat

'not only on converter circuits according to Fig.1 and

Q is limited, but equally advantageous, for example, for a

'■: 2pula bridge adjustment or 3pula midpoint adjustment,

(I. as well as for converters in the facility operation.

(i If a converter does not contain switching sections S2,

1 so only the signal detection Si1 on the network side

I of the converter is used and the DC side

The non-linear element R ₀ can be replaced by a high-ohmic resistor to prevent overvoltages from I residual currents, which are caused by the holding current of the thyristors V and V _p . If Ea is also possible, instead of sensing the voltage indirectly, the current through the nonlinear elements I as the effect of an overvoltage load on the

ί to lead signal inputs Si1 and Si2.

I The overvoltage protection device also works in the

I described white if in place of the nonlinear

I elements of energy storage in the form of non-reactive

I connected capacitors aind arranged, where

I under non-reactive e.g. the connection via a

% Rectifier bridge connection is to be understood.

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List of the reference marks used

1 R. 2 5 8th Consumers with L. 3 6th 9 ohmic Laat component 4th 7th S1 ... S3 inductive Laat component R, S, T Ignition pulse control device V Over-tension detection ^V N Information processing with ^V Ng Pulse generator ^V Eg1 ... 2 St euervainkelst eller Rp _n , R _n , R _n -,.,. Operating time measuring device Rp power adapter ^R E Pulse amplifier L ₂ Switchgear C. Converter lead OX I · · · C. Converter valve ¹ L Zero valve (diode) ^U C Zero valve, controlled (thyristor) De-energizing valve 2 non-linear protection element Parallel resistance Limitation v / id purchased . Deenergizing circuit damping throttle capacitor Sip, killing it current Condenser voltage tension

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Claims (6)

Patent claims: Berapensiona protective device for mains-powered converters feeding highly inductive loads, in particular reversing converters with controllable valves, the converter having switching paths in the converter feed lines and two converters, while on the network side overvoltage protection elements and an ignition pulse control device for the converter valves are connected and a DC-side internal voltage element is connected in parallel with the consumer is, the de-energizing circuit having a series connection of a limiting resistor with a de-energizing valve arrangement, each consisting of a controllable valve for each current direction controlled by a pulse amplifier, characterized in that in the de-energizing circuit in series with the limiting resistor (Rg) and the de-energizing valve arrangement (V ™ 2 ) a nonlinear Entregerkreiadämpfungsdrossel (Lg) with high initial inductivity is inserted, and that di e Überapannungaachutzeinrichtung to an information processing (4) consisting aua a pulse generator (5), a Steuerwinkelstel- l} ler (6), and a Wirkdauermeßeinrichtung (7), combination [I ned, the pulse generator (5) each having a signal f- naleingang for mains and DC-side voltage detection (SH; S12) and signal outputs from Pulse generator (5) at the same time on the pulse amplifier (9) to control the de-energizing valve Control angle adjuster (6), which is connected to the ignition pulse control device (2) via a signal output, and to the effective duration measuring device (7), which has a signal output with the network-side switching path (S3) is connected. 909851/0578 2. Overvoltage protection device according to claim 1, characterized marked that the line and DC side Voltage detection provided signal inputs (Si1; Si2) of the pulse generator (5) OR-linked and fed to a threshold generator are, and that the excitation of the de-energizing valve control, which takes place by means of a pulse train, is delayed is executed. 3 · Overvoltage protection device according to claim 1, characterized characterized in that in the control angle adjuster (6) from the eraten pulse of the pulse generator (5) a temporal Limited signal is derived, which in the ignition pulse control device (2) a setting which causes ignition pulses to a value of about 90 ° electrically. 4. Overvoltage protection device according to claim 1 and 3, characterized in that the control angle of the ignition pulses is a basic setting in the total command time at least once alternately in both directions by an angle d iat. 5. Overvoltage protection device according to claim 1, characterized characterized in that the V / irkdauermeßeinrichtung (7) contains a pulse counting circuit, which after A shutdown command for the converter is issued after a certain number of pulses has elapsed. 6. Overvoltage protection device according to Anapruch 5, thereby characterized in that the number of pulses which leads to the disconnection of the converter is a puncture dea middle impulaabatandea iat in such a way that No shutdown command for pulses at a large distance he follows, - In addition 3 sheets of drawings - 909851/0578