DE2843087A1 - EXTINGUISHING DEVICE AND OVERCURRENT PROTECTION FOR AN INTERMEDIATE CONVERTER OR SELF-ADJUSTED INVERTER - Google Patents

Description

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Extinguishing device and overcurrent protection for a DC link converter or self-commutated inverter

The invention relates to an extinguishing device and an overcurrent protection for a DC link converter or self-commutated inverter according to the preamble of the claim "J ..

Circuits for self-commutated converters are known in which transistors are used to erase thyristors. The advantageous properties of the thyristors and the transistors are used here. With transistors this is in first and foremost the ability to be switched off via the control current and at Thyristors, it is mainly the low price compared to transistors.

Compared to thyristors, power transistors in self-commutated converters do not have commutation circuits, which are made up of capacitors, inductors and auxiliary thyristors. On the other hand, the control of power transistors is more complex because the power transistors are due to their lower current gain to control with relatively high control currents, which moreover during the

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must be applied throughout the entire current carrying time. For switching off, the control current is not only to zero switch, but to impress negatively for a short time.

The advantage that the power transistors can be switched off via the control connection is the complicated control as well as the low current overload capacity and the higher price.

Power transistors have grown in recent years by improving their limit data and lowering their manufacturing costs for power electronics gained increasing importance.

From DE-OS 25 38 317 an arrangement is known in which the transistor is parallel to the thyristor. The thyristor is used to switch on and conduct the current, while the transistor switches off the circuit arrangement by briefly taking over the thyristor current. It is switched on by igniting the thyristor with a short control current pulse Iq. The thyristor takes over current if the circuit allows it and carries this current up to the point in time at which the transistor is controlled _{with a control signal i ß.}

The transistor must then carry current as long as the thyristor needs time to become free. The transistor will subsequently

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switched off by taking away its control signal i _ß .

The advantages of the known arrangement are that commutation circuits as in self-commutated converters are not required, and that, on the other hand, the control power requirement measured against that for power transistors is low. In addition, the transistor in this circuit arrangement can be used to a greater extent, since in it neither switch-on nor Passage losses arise. The upper frequency limit of this valve arrangement depends on the release time of the valve used Thyristors. The valve arrangement can be operated at any low operating frequency (in borderline cases with direct current).

In the case of intermediate circuit converters or self-commutated inverters, the discharges in the intermediate circuit or in parallel the DC voltage terminals of the inverter arranged smoothing capacitor in the event of an inverter tilt or a short circuit at the output of the inverter like a surge through the inverter valves. So that the valves are not destroyed by this, in known arrangements the peak value of the current is limited by a protective inductor and the surge current in the event of a tilt is taken over by an additional thyristor (short-circuit thyristor) at the input of the inverter or is arranged in the intermediate circuit and relieves the valves.

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The surge currents occurring in these known arrangements stress the capacitors, in particular the power supply lines to a considerable extent, as a result of which both the capacitance and the service life of the capacitors are reduced.

In addition, a special thyristor is required as a short-circuit thyristor, which must carry the high surge current. In addition, switches or fuses are required that interrupt the power supply from the mains.

From the "Scientific Reports" AEG-TELEFUNKEN 50 (1977), Issue 1/2, page 46, an overcurrent protection for a self-commutated inverter with thyristors is known in which A power transistor is arranged between the smoothing capacitance and the inverter.

If, for whatever reason, a valve in the inverter can no longer extinguish or if it receives an incorrect pulse, it triggers the inverter, whereby the smoothing capacitor is impulsive would be discharged through the inverter. In this case the transistor can be switched off instantly, so that an overcurrent is avoided because the current does not increase significantly during the turn-off time of the transistor could.

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With this known overcurrent protection, neither the inverter valves the smoothing capacitors are still burdened by surge currents. In the event of a tilt, neither safety devices speak quick switch on, so that operational interruptions are avoided.

The object of the present invention is the known arrangements To simplify the deletion of the converter valves of a DC link converter or self-commutated inverter and at the same time to create an effective overcurrent protection, which ensures that when the Wechselbzw. Converter, neither fuses nor high-speed switches respond and the smoothing capacitors do not respond in an impulse current fashion are claimed.

According to the invention, this object is achieved by the characteristics of claim 1 listed features solved.

Variants of the extinguishing and protection device according to the invention

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are due to the characteristics of claims 2 and 3 listed Characteristics given.

The solution according to the invention includes a significant simplification of known commutation circuits (quenching circuits) and thus a reduction in price with increased reliability at the same time by reducing the circuit breakers required for commutation.

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The overcurrent protection integrated in the extinguishing device ensures that if the inverter or converter tilts neither fuses nor high-speed switches respond and the smoothing capacitors are not subjected to surge currents will. In addition, it is ensured that the semiconductor arrangement provided for overcurrent protection can be switched off is not flowed through by the load current but only by the superimposed alternating current, i.e. the capacitor current.

Since the inverter current due to the smoothing reactor in the intermediate circuit after the overcurrent protection has responded only increases slowly, the inverter can be switched off without further effort. After that the inverter is without further measures are immediately ready for operation again.

Based on the execution examples shown in the drawing the idea on which the invention is based is to be explained in more detail.

Show it

Figure 1 and 2 a three-phase self-commutated inverter with DC voltage intermediate circuit and a sum clearing circuit formed from two semiconductor switches and

Figure 3 shows a three-phase self-commutated

Inverter with DC voltage.

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intermediate circuit and an overcurrent protection as well as two independent extinguishing circuits.

The three-phase self-commutated inverter shown in Figure 1 with the inverter thyristors 1 to 6 and the reverse current diodes 7 to 12 and a DC voltage intermediate circuit have a quenching circuit that causes that with each deletion process all inverter thyristors are deleted at the same time.

The clearing circuit, also known as the total clearing circuit consists of two semiconductor switches (transistors or GTO thyristors) T1 and T2.

One semiconductor switch arrangement is formed from a transistor (or GTO) Tl as the first semiconductor switch and a diode D1 connected in antiparallel to this. It is in series with the smoothing capacitor C of the DC voltage intermediate circuit.

According to the invention, this arrangement serves as overcurrent protection for the downstream inverter.

The actual deletion branch is parallel to this. It consists of a second semiconductor switch T2 and a voltage source E with a voltage opposite to the intermediate circuit voltage Polarity. The function of the extinguishing and overcurrent protection device according to the invention is as follows:

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If an inverter thyristor is to be deleted, the first semiconductor switch Tl is first blocked in order to prevent that when switching on the extinguishing circuit T2, E the intermediate circuit

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capacitor C is short-circuited.

Both the load current i and the intermediate circuit current I, commutate to the quenching circuit. After the time off has expired

of the inverter thyristor to be deleted, the second semiconductor switch T2 is blocked, so that the first semiconductor switch Tl become conductive again. The current then commutates back to the inverter thyristors, their ignition was not interrupted. In addition, another thyristor is ignited.

As can also be seen from this figure, in

(Tl / Dl ^ Normal operation of the semiconductor device - Vnot from the load current but only the capacitor current flows through it. Is one the thyristors of the inverter are not able to delete or if it receives a missing pulse, this will be in normal operation first semiconductor switch Tl held in the conductive state is switched off immediately, so that an overcurrent is avoided. Only during the switch-off time of the semiconductor switch Tl there is a brief increase in the current, but this does not endanger the inverter thyristors and the smoothing capacitor C.

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The three-phase self-commutated shown in Figure 2, from the inverter thyristors 1 to 6 and the reverse current diodes 7 to 12 inverters with a DC voltage intermediate circuit have a quenching circuit made up of two semiconductor switches (Transistors or GTO thyristors).

The one semiconductor switch arrangement is formed from one Transistor (or GTO) Tl with a diode Dl connected in anti-parallel. The intermediate circuit capacitor C is connected in series

This arrangement also serves as overcurrent protection for the downstream inverter.

The inverter reverse current diodes are from the inverter thyristors decoupled via the blocking diodes D2 and D3. It is thus possible to alternate between the anode side and the cathode side connected inverter thyristors. This ensures that the current in the inverter during the extinguishing phase commutates on the freewheeling diodes.

The quenching switch arrangement, which can be referred to as a commutation switch, consists of a second semiconductor switch (transistor or GTO) T2, a quenching voltage source E of fixed polarity and constant voltage and four auxiliary thyristors T3 to T6.

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Each deletion process starts with the blocking of the first semiconductor switch Tl initiated. This prevents the commutation switch to be switched on from the DC voltage intermediate circuit capacitor C shorts.

Should, for example, the main thyristors connected on the anode side are deleted, branches T3, T2, E and T6 of the commutation switch must be switched on. The negative Reverse voltage, which is provided by the erase voltage source E, can then be used via the relevant reverse current diodes get to the thyristors to be deleted.

After the respective inverter thyristor has become free, the quenching circuit with the second semiconductor switch T2 interrupted so that the first semiconductor switch Tl can be switched on again. Is there an operating mode of the inverter? before, in which the inverter thyristors l80 ° el. are ignited, the current commutates again on the inverter thyristor, whose ignition was not interrupted during the extinguishing period. In addition, another inverter thyristor is used ignited.

The mode of operation of the overcurrent protection corresponds to that in Figure 1 explained mode of operation.

The three-phase self-commutated inverter shown in FIG corresponds to the inverter shown in FIG. 2 and described with reference to this figure.

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However, there are two independent quenching circuits with the semiconductor switches T2 and T3 and the quenching voltage sources E here . or E 2 instead of the auxiliary thyristor bridge circuit T3 ... T6 according to FIG. This has the advantage that each switch is only used at half the switching frequency.

The mode of operation of this arrangement corresponds to that based on

Figure 2 explained functional catfish

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Claims (3)

Licentia Patent-Verwaltungs-GmbH 6000 Frankfurt 70, Theodor-Stern-Kai 1 Ninnemann-rt EE2-B 78/36 Nm Claims {1.! Extinguishing device and overcurrent protection for an intermediate circuit converter with smoothing capacity in the intermediate circuit or self-commutated inverter with input-side smoothing capacity, characterized in that in series with the smoothing capacitance (C) a first semiconductor switch (Tl) is connected and that parallel to the series connection of smoothing capacitance (C) and first semiconductor switch CTl) the series connection of a second semiconductor switch (T2) and a voltage source (El) is arranged with the intermediate circuit voltage of opposite polarity. 2. Extinguishing device and overcurrent protection according to claim 1, characterized in that 030 015/0477 - 2 - EE2-B 78/36 Nm that in series with the second semiconductor switch (T2) and the voltage source (El) each have an auxiliary thyristor (T3, T5) to the thyristors (1 to 3 or 4 to 6) of the inverter connected on the anode side or cathode side to be quenched and One auxiliary thyristor (T4, T6) each to the reverse current diodes (7 to 9 or to 12) of the inverter are connected, the reverse current diodes (7 to 12) via blocking diodes (D2, D3) of the thyristors (1 to 6) of the inverter are decoupled. 3. Extinguishing device and overcurrent protection according to claim 1, characterized. that parallel to the series connection of smoothing capacitance (C) and the first semiconductor switch (Tl), the series connection of a third semiconductor switch (T3) and a second Voltage source (E2) with the intermediate circuit voltage of opposite polarity arranged via a first blocking diode (D2) is, and that the series connection of the second semiconductor switch (T2) and the first voltage source (El) over a second blocking diode (D3) parallel to the series connection of the smoothing capacitance (C) and the first semiconductor switch (Tl) is switched. - 3 030015/0477