DE3230650A1 - Protection wiring on the LC input filter of a power circuit for networks having voltage which returns suddenly - Google Patents

Abstract

The invention relates to protection wiring on the LC input filter of a power circuit for networks having voltage which returns suddenly, having a controllable freewheeling circuit which is connected in parallel with the inductor and, when the network voltage returns and the capacitor is discharged or partially discharged, limits the rise in the voltage on the capacitor to a value which is increased above the rated voltage by a permissible voltage fluctuation, virtually short-circuits the inductor and converts its energy content into heat, especially for supplying railway converters. In order to create protection wiring which even withstands multiple, periodically occurring power interruptions without any reaction, and furthermore manages with a simple and small construction with cheap components and increases the operational readiness of the converter, it is proposed according to the invention that the series circuit of a thyristor (5) and of an uncontrolled valve (6) be used as the freewheeling circuit and that the thyristor (5) be driven as a function of the voltage reversal on the inductor (1) during self-induction, after completion of the charging process on the capacitor (2). <IMAGE>

Description

Protective circuit on the LC input filter

a power circuit for networks with sprungartiq recurring voltage The invention relates to a protective circuit as described in the preamble of Claim 1 is defined in more detail.

LC filters are usually used in front of converter circuits, in order to limit current ripples, such as those caused by retroactive effects in inverter operation develop. An overvoltage of an approved overvoltage arises on the capacitor A u fluctuating capacitor voltage Uc a. In addition, they are more appropriate Design suitable to dampen voltage peaks, i.e. the downstream arrangement, Here, for example, to protect the converter.

Voltage peaks occur, for example, in railway operations on the contact wire. In the event of voltage interruptions and then suddenly recurring voltage Problems often arise due to the transverse filter capacitor (buffer capacitor) occurring high voltages depending on the state of charge of the capacitor. These high With small attenuation of the power resonant circuit (normal), voltages can be up to to double the input voltage Ue. That makes protective measures for the Inverter and the connected consumers required and affects the Capacitor sizes. Brief voltage drops and voltage interruptions occur, for example, aperiodically through pantograph dancing and jumping stirrups, real, sometimes longer interruptions when driving over gaps in busbars in front of switches or stations. The voltage interruptions are in the millisecond range Jump for stirrups and reach in the seconds range for busbar gaps. In the case of longer interruptions, it must be assumed that the filter capacitor discharged through the further load on the inverter and at the critical In the event of a restart, the voltage is zero. A compensation process with shock-like high currents and voltages are the result. The condition is particularly critical when the inverter is unloaded. The voltage on the buffer capacitor has reached then with certainty twice the value of the input voltage Ue, and the capacitor is to be dimensioned accordingly. However, it only has to be used for this double voltage designed when it is not protected at all. Limiting measures against such dynamic overvoltages thus have a double function. You are supposed to protect the components including the downstream power semiconductors are used and also bring a reduction in size of the capacitor.

A circuit has already become known that counteracts surge currents and overvoltages at the buffer capacitor by the fact that gaps (interruptions) are detected in the input voltage Ue and then immediately by means of a logic Main contactor is switched off. The resonant circuit is then set via a series resistor aperiodically charged or recharged. During this time the ignition pulses for the inverter locked. After that, the resistance is fixed after a period of time has elapsed Time bridged again by an auxiliary contactor. However, this protection system means always an additional time delay of a few seconds, during which the capacitor is to be charged without temporal overvoltage. In the event of multiple voltage interruptions, especially in the millisecond range, this can seriously disrupt operation. The effort at logic and control circuit is with this Protection system not insignificant.

It is also known that the choke of the input filter has a voltage limiter, a U or Z diode, with an uncontrolled valve in series as a capacitive one Connect the free-wheeling circuit in parallel by using the energy stored in the choke is converted into heat (DE-OS 30 03 049). The voltage limiter is for a breakdown voltage around the permitted voltage fluctuation on the capacitor and for the maximum storable energy content of the choke in the worst case to interpret. The circuit contains only a few, but they are quite expensive and large Components. The U-diode in particular is expensive and has a large and therefore annoying one Construction volume.

The circuit is well suited for normal driving.

In the case of multiple, i.e. almost periodically traversable at short time intervals Busbar transitions, such as in shunting yards (up to 20 busbar gaps in 10 minutes), however, failures can occur due to overloading of the U diode. It is also disadvantageous that the voltage limitation in such U diodes of the Depending on the number of plates, it can only be carried out roughly in steps of 55 V. Even a more precise adjustment would be desirable here.

The object of the invention is to provide a real protective circuit create that also multiple, periodically occurring power interruptions without complaint tolerates, in addition, with a simple and small structure with cheap components gets by. The arrangement should include the filter capacitor and the semiconductors behind it of the inverter against dynamic overvoltages and the occurring Power interruptions really relate to the time of the power failure in the event of a gap in the busbar limit. This means that the interruption time for the converter should be kept as short as possible and its operational readiness thus increased.

This task is for a protective circuit of the aforementioned Kind according to the characterizing features of claim 1 solved.

When the choke voltage is short-circuited, the previously in current flowing through the load circuit to the parallel freewheeling circuit and thus relieves the load even in the event of a short circuit, the remaining circuit including switch where the arc pending. The circuit also has lower power losses than the previously known circuit with U diode, as the counter voltage applied by the freewheeling circuit with thyristor and diode (excluding forward voltage) and the resulting power loss are significant are lower. The time for the short-circuit process takes longer, the However, the main amount of energy is converted into heat in the throttle itself. This The process is harmless several times due to the heat storage capacity of the throttle iron core repeatable.

Further advantageous refinements can be found in the subclaims.

On the basis of an embodiment shown in the drawing the invention is explained in more detail below.

They show: FIG. 1 the circuit diagram of a protective circuit according to the invention, FIG. 2 shows the voltage profile on the filter capacitor, FIG. 3 shows the voltage profile the throttle.

In Fig. 1, the LC input filter of a power circuit is made up from a throttle 1 and the ground filter capacitor 2 shown. The DC input voltage Ue is applied to a main switch 3 Input a and the load output are denoted by b. The actual protective circuit is framed by dash-dotted lines and essentially consists of a dashed line power-bloc 4, consisting of a thyristor 5 with an uncontrolled series valve 6 and a control circuit for the thyristor 5 for short-circuiting the choke 1.

The further structure of the circuit is based on its functional description removable.

Normally, when the DC voltage Ue is applied, it flows in continuous current via main switch 3, choke 1 and output b to the load. Of the Filter capacitor 2 thus remains charged. In the case of busbar gaps with the voltage Zero at input a or an inverter short-circuit with tripping of the main switch 3, the capacitor 2 discharges through the load. When the tension returns the capacitor is recharged 2.

The applied voltage U first falls fully across the Choke 1 off, since the voltage on capacitor 2 is zero and charging takes place in the usual way according to a differential equation of the second order for two energy stores. Reference is also made to FIGS. 2 and 3 in this regard.

Fig. 2 shows the course of the capacitor voltage U2 according to a step function Ue at time t1 and FIG. 3 corresponding to the course of the throttle voltage U1. The energy initially stored in the choke 1 would be at the moment when the Capacitor 2 is fully charged, i.e. U = U2, the e U2, capacitor 2 up to 2 x Ue (dashed curve) overloaded. At time tx, when Ue = U2, the rotates Voltage at the choke 1 by self-induction. This time tx at which the throttle 1 starts to drive, is detected. A Charging diode 7 and a resistor-voltage divider 8/9 a circuit that is permanent and is engaged in parallel and allows a small current to flow, a capacitor 10 increased charged. If the voltage on the capacitor 10 reaches the defined trigger threshold of a diac 11, it breaks through (time t2) and discharges capacitor 10 the gate / cathode path of a thyristor 12, which is in cascade connection with thyristor 5 this ignites. The entire trigger circuit is short-circuited and thus becomes the driving voltage U2 at the choke 1 almost suddenly brought to zero. Of the Current flowing in the direction of the filter capacitor 2 commutates on the freewheeling circuit des power-blocs 4 and the voltage at the consumer goes back to Ue. About the relationship the optionally adjustable resistors 8 and 9 (multiplication factor Rg / R8 + Rg) any value of the response voltage for the diac 11, i.e.

the time t2 can be set. The currents there are in the mA range and are load independent. The monitoring circuit has the same elements practically usable for any such throttle and filter circuit, only the response values the resistors 8 and 9 must be set and the power bloc, if necessary, the Energy content of the throttle 1 can be adapted. The powerbloc is in its performance expandable almost at will. It should still be noted that the decisive factors the choke 1, the filter capacitor 2 and the input voltage U represent. Included there is a dependency e of the choke on the load and input voltage and of the filter capacitor 2 on the degree of filtering for the load circuit.

With 13 to 16 there are further wiring elements for the rubble - of the power blocs.

The implementation of the choke energy in the power bloc is not critical in a U diode, due to the low voltage drop of only approx. 2 V, thus the process is much slower here in a matter of seconds.

Claims (5)

Claims 1. Protective circuit on the LC input filter of a power circuit for networks with abruptly recurring voltage, with a parallel to the choke established controllable free-wheeling circuit, which occurs when the mains voltage returns and the discharged or partially discharged capacitor increases the voltage across the capacitor to one limited by a permissible voltage fluctuation above the nominal voltage, the choke practically short-circuits and converts its energy content into heat, in particular for the supply of railway converters, characterized in that as a free-wheeling circuit the series connection of a thyristor (5) and an uncontrolled valve (6) use and the control of the thyristor (5) depending on the voltage reversal at the throttle (1) with self-induction after completion of the charging process at the condenser sator (2) takes place. 2. Protective circuit according to claim 1, characterized in that between the thyristor (5) and the uncontrolled valve (6) of the free-wheeling circuit on the one hand and the choke (1) and the capacitor (2) of the input filter on the other a resistor-voltage divider (8/9) with series diode (7) is placed, the on the anode side facing the input filter, series diode (7) for charging a control capacitor (10) serves the one resistor (9) of the resistor-voltage divider (8/9) is parallel, which faces the free-wheeling circle. 3. Protective circuit according to claims 1 or 2, characterized in that that over one in the divider point between the resistors of the voltage divider (8/9) connected diac (11) the control electrode in cascade to the thyristor (5) of the free-wheeling circuit connected further thyristor (12) can be controlled. 4. Protective circuit according to one of claims 1 to 3, characterized in that that the thyristor (5) and the uncontrolled valve (6) of the free-wheeling circuit one Form a combined building block (power bloc). 5. Protective circuit according to one of claims 1 to 4, characterized in that that all components can be placed on a map of Europe as commercially available components are.