DE3823922C2 - - Google Patents

Description

The invention relates to an electronic Schaltvor direction with performance monitoring and integrated Absi Protection for electrical circuits according to the Oberbe handle of claim 1, as described in DE 35 15 133 A1, DE 34 45 340 A1 and the literature "Advances in Solid State Switchgear Technology for Large Space Power Systems (NASA Technical Memorandum 83652), 1984, are known.

In these known switching devices, as exemplified in FIG. 1, the closing and opening of the electrical circuit to be protected is carried out by a semiconductor, such as a line transistor TR or a field effect transistor (MOS). This function is controlled by an external low power electrical signal that is either set or not, as in a simple ON / OFF control.

The current measuring circuit consisting of a shunt and an amplifier A 1 , controlled by a transistor TR, ensures the limitation of the operating current. This limitation is necessary so that the limits for the current through the transistor are not exceeded when the maximum permissible continuous load is exceeded for a certain time, the maximum permissible continuous load being essentially determined by the performance characteristics of the transistor. This is the switch off function.

An integrator IT imparts inertia to the device to avoid unwanted shutdowns. In which described structure, the problem arises first, that the switching transistor during the current limitation extreme thermal stress  is exposed. The picked up by the transistor TR Power can reach the switching power if the consumer is short-circuited. There are two ways of destroying the transistor Prevent TR: the duration of the tax phases of the Current before switching off can be limited or the Transistor TR can be oversized.

If the time before switching off is too short, a switch of this kind for motor and capacitive Loads unusable. The burdens take for a few milliseconds of current that up to five times their nominal current.

The oversizing of the transistor TR is problematic because transistors with large powers are very expensive, especially in MOS technology. A Parallel connection of several transistors with less Performance is excluded because of the linear control this prohibits.

The reason for this is the spread of the Charak teristics of the transistors.

The second problem is the difficulty that the circuit to be controlled opens progressively and is closed to overvoltages and overcurrents limit generating voltage and current jumps. The first problem is solved very quickly Transitions (jumps) generated what the requirement contradicts the slow switching. To the About to limit tensions and overcurrents back to auxiliary circuits for switching.

Another problem is the current control. The arrangement of transistor TR, shunt Sh and amplifier A 1 represents a control. This control has a limited stability and limited response times, which make a very fast amplifier in the range of 50 V / ms necessary.

The invention is based, to be to eliminate written disadvantages.

To solve the problem is fiction according to an electronic switching device Claim 1 proposed.

Advantageous refinements of the inventive concept are protected in the subclaims.

The switching device according to the invention combines following functions:

• - Closing and opening an electrical switch circle,
• - regulation and limitation of the current,
• - Controlled and timed shutdown.

The opening and closing is carried out by means of an arrangement of transistors TR ₁ to TR _n in parallel.

The naming of the transistors indicates the type of semiconductors, such as line transistors, MOS circuits, thyristors, triacs and GTO thyristors. The selection depends on the type of current to be monitored (direct current or alternating current) and the power to be controlled. The current limitation is perceived by resistors R ₁ to R _n . The resistors can absorb significant overloads in very short times. In order to prevent the resistors from being destroyed, the heat removed is dissipated using a conventional cooling device. The resistors are in series with the transistors described. They are so dimensioned that the current is below the interference current of the transistor in each of the arrangements even when the consumer is short-circuited.

An electronic sequence switch provides sure that the arrangements "resistor transistor" successively with the help of suitable means measure the current through the circuit.

For direct current in the electrical circuit the semiconductor switches (line transistors or MOS transistors) in series with the resistors interconnected and the means for measuring the current through the circuit are using a shunt formed a voltage comparator.

For alternating current in the electrical circuit are the semiconductor switches bidirectional switches, d. H. Triacs, transistors connected in opposite directions or oppositely connected MOS circuits. In this case, the means for measuring the current formed by the circuit of a current transformer, which is assigned to a comparator. Closes to activate the external control of the circuit in any case the sequence switch a first Circuit arrangement, namely the one with the greatest resistance, then a second with one lower resistance etc. until the last arrangement, that has no series resistance and everyone else Arrangements shorts because of that in the circuit flowing current is the nominal current corresponding to the load has reached.

The circuit provides an electronic rheostat represents its slope from the number of parallel  interconnected arrangements and size which depends on resistances.

If the number of orders is large, the order is circuit moderate. The course of the slope can by means of resistors with different values be adapted to the load to be controlled. This is for non-linear loads, such as motors, of interest.

If the number of resistors is small, the result is the smallest resistance and switching takes place suddenly. This is the case with linear Loads, such as resistors, and inductive loads.

With the command "Open circuit" the opens Sequence switches accordingly all arrangements in the reverse order of closing. The aim of this gradual opening is to open up damping switching currents and the changes limit the electrically generated load.

If before the close command and during the Electrical overload occurs the current detector controls the sequence switch so that it opens the last switch, which has no series resistance. Thus the current in the system because of the resistances in limited the switching arrangements.

If the error persists, open it all transistors and the switch turns off. If the error disappears during the limitation phase, so the sequence switch closes the last one Switch without series resistance again.  

All overload conditions are possible. If an overload occurs before the command to close the circuit (starting an engine or charging a capacitor), the sequence switch leaves the first arrangement TR ₁ to TR _n in the conductive state. Otherwise (the overload remains) the switch goes into the switched off state. It should be noted that the reference voltage is controlled by the sequence switch during the start-up phase and is reversed in accordance with a law that approximates the characteristic of starting motors or charging capacitors. The overload currents acceptably follow this characteristic and can assume three to five times the value of the nominal current for a fraction of a second.

The input voltage is not passed through during operation switches, the sequence switch using of a company supply circuit (MST) this lock conforms to an ON / OFF command; thus eliminated this new structure has the main disadvantages of the conventional structure.

• 1. The transistors are not thermally stressed. They only work in saturation or in the restricted area; the power losses are very low, they are in the range of a few watts. The way of working allows you Parallel operation of several transistors with the corresponding cost advantages.
• 2. The ver. By sudden opening and closing are caused by overvoltages and overcurrents because of the gradual openings and closings suppressed.  
• 3. The circuit for monitoring and controlling the Transistors have no special requirements in terms of speed and stability.

The present invention is more preferred below Embodiments with reference to the Drawings explained in more detail with further details.

Show:

Fig. 1 shows a conventional electronic Schaltvor direction;

Fig. 2 shows an embodiment of the switching device according to the Invention for a DC circuit;

FIG. 3 shows the switching device of Figure 2 in detail.

Fig. 4, 5 and 6 the waveforms of various currents in the switching device according to the invention, circuitry is provided and

Fig. 7 shows an embodiment of the circuit device according to the invention for an AC circuit.

According to FIG. 2 according to the invention, gear changes direction is 3 between a DC power source 1 and a load R _c. It is controlled by an ON / OFF switch 12 .

The circuit comprises a plurality of parallel switchgear systems TR ₁ -R _1, TR _n -R _n, which semiconductor switch TR ₁ to TR _n each comprise in series with resistors R ₁ to R _n.

The last branch of the circuit does not include a stand, but only a semiconductor switch TR _p . The current is measured using a shunt 6 in conjunction with a voltage comparator 7 . The information obtained, here in digital form, is used to control a sequence switch 4 , which controls the various transistors TR ₁ to TR _n and TR _{p in} succession corresponding to the course of the current in the circuit. A circuit 2 for monitoring the voltage of the supply source 1 , which comprises a comparator and a transistor in series, drives the sequence switch 4 in the same way as the ON / OFF switch 12 .

Fig. 3, the details of construction shows the circuit of Fig. 2. The part of the power circuit is to T _n of the MOS transistors T _1, T _n-1 and T formed _p, which are to R _n interconnected with limiting resistors R ₁ . The shunt 6 is connected to comparators 7 , 8 and 9 in order to monitor the current control of the switching device.

The comparator 7 ensures the current monitoring during the undervoltage setting and in the idle state. Its reference voltage U is supplied by a circuit 5 . This voltage, which corresponds to the current to be monitored, changes over time. It is large when the voltage is switched on and then gradually assumes a fixed value which corresponds to the rated current of the switching device. The changes are controlled by the sequence switch 4 , which also ensures the monitoring of the transistors T ₁ to T _p . The sequence switch 4 is controlled by a ramp generator 11 , which comprises a capacitor in series with two parallel resistors, the ramp generator being controlled by the ON / OFF switch 12 or by a supervisor 2 for the supply.

The comparator 8 is used for the main monitoring of the limiting current, which is set to a value between three and five times the nominal current I _N. If the comparator 8 reverses, a thyristor 10 becomes conductive. The state of the conduction of the thyristor causes the ON / OFF switch 12 to be blocked, which in turn causes the transistors T ₁ to T _{p to} open immediately. The switch 12 is galvanically isolated from the circuit, for example by means of an optocoupler 14 .

The switching device is switched on again by switching the switch 12 to "OFF", which puts the thyristor 10 out of operation.

The comparator 9 is used to monitor the minimum current of about ½ the nominal value only the transistor T ₁ and the resistor R ₁ in the conduction state.

This monitoring is necessary in the event that the consumer is disconnected and then reconnected, with the switch 12 in the ON position. Without this precaution when disconnecting the consumer, the currents mentioned would be very large, which would entail the risk of the transistor TR _{p being destroyed} . By means of this circuit, the MOS transistors are left in a successively conductive state.

The electronic circuits of the device are fed by means of a converter 13 , which draws its energy from a supply voltage V _e .

Fig. 4 shows the signals before switching on. The time and current values are given for information. They can change depending on the application. The end of the signals corresponds to opening switch 12 . The drawing shows:

• - Curve a: the rise time a 1 of the current is much longer than the fall time a₂,
• Curve b: the conduction state of the transistor T₁,
• Curve c: the conduction state of the transistor T _n-1 ,
• Curve d: the conduction state of the transistor T _n ,
• Curve e: the conduction state of the transistor T _p ,
• Curve f: the output signal of the circuit 5 , the curve of the triggering of the switching device.

Fig. 5 shows various forms of the currents flowing through the device.

Curve g represents the current drawn by a motor. When the circuit is closed, the current g ₁ of tripping fluctuates until it assumes an idle state below the nominal current. A first temporary overload occurs at g ₂ . This temporarily blocks the transistor T _p (h ₁ ). After this overload has subsided, the transistor T _p returns to the conduction state. A series of overloads g ₃ then occurs, which repeatedly block the transistor T _p . A circuit RC 15 at the output of the comparator 7 integrates this error and controls the conduction of the thyristor 10 . The switch is open.

Fig. 6 shows the effects of disconnecting a motor load when the device is in the conduction state. Disconnection is possible if a switch is connected between the load and the device.

According to the curve k, the current through the Load interrupted because the load is disconnected.

Curve 1 represents the state of the comparator 9 , which then changes the state of the opening of the circuit. This change in state causes:

• - The discharge of the capacitor in the circuit 11 ;
• - The change in the state of the comparator in the circuit 4 , which causes the opening of the transistors T _n-1 to T _p , with only the transistor T ₁ remaining in the conductive state, as the curves m, n, o and p illustrate;
• - The change in the state of the comparator in the circuit 4 , which causes a change in the circuit 5 . This has a comparator at one of the inputs, which are connected to the outputs of the comparators of the sequence switch 4 . The order switch 4 performs the regulation of the current to the maximum allowable value, for example 3I _N, so as g from the curve of the line is represented k. ₁

If the load is disconnected, the current on the line increases immediately, which puts the comparator 9 in a new state. This new state allows:

• - Put the branches T _n-1 to T _p into the conduction state one after the other by means of the circuit 4 and
• - To monitor the current by means of the circuit 5 .

In Fig. 7 a switching device is shown for monitoring alternating current circuits. The switching arrangements are implemented by means of bidirectional switches 70 , 71 and 72 , such as thyristors or MOS circuits, the latter being connected to one another in opposite directions. Triacs can also be used. In this embodiment, the device for current measurement comprises a current transformer 73 with a comparator 74 .

The invention particularly relates to static Switch and on power control relay on the Aviation area.

Claims (7)

1. Electronic switching device with power monitoring and integrated protection for electrical circuits, with an electronic switch, a current monitor and a device that controls the electronic switch depending on the current flow through the electronic switch, characterized in that the electronic switch is formed by a parallel connection of several switching arrangements, each comprising a semiconductor switch (T) in series with a resistor (R), these arrangements having different characteristics and being successively controlled by an electronic sequence switch ( 4 ), one of which is controlled by one external control ( 12 ) and the other is controlled by the current monitor ( 6, 7 ). 2. Switching device according to claim 1, characterized in that for monitoring a DC circuit, the semiconductor switches in series with resistors connected surfaces are transistors (T) and that the current monitor is formed by a voltage comparator ( 7 ) assigned shunt ( 6 ). 3. Switching device according to claim 1, characterized in that for monitoring a DC circuit, the semiconductor switches in series with resistors MOS transistors are transistors and that the current monitor is formed by a voltage amplifier ( 7 ) associated shunt ( 6 ). 4. Switching device according to claim 1, characterized in that for monitoring an AC circuit, the semiconductor switches are bidirectional switches ( 70 ) and that the current monitor comprises a current measuring device with a comparator ( 74 ) and a current transformer ( 73 ). 5. Switching device according to claim 4, characterized characterized that the bidirectional Switches are triacs. 6. Switching device according to claim 4, characterized characterized that the bidirectional Switch connected in opposite directions Are thyristors. 7. Switching device according to claim 4, characterized characterized that the bidirectional Switch connected in opposite directions MOS circuits are.