DE3727996A1 - Method and device for suppressing unacceptable attempts to turn off power semiconductors which can be switched off - Google Patents

Abstract

The method for suppressing unacceptable attempts to turn off power semiconductors which can be switched off prevents an anode current being switched off in the case of gate turn off thyristors (V1...V6), when said anode current is greater than the maximum anode current (iAmax) which can be switched. To this end, the instantaneous anode current (iAO) of the semiconductor and the time derivative of the instantaneous anode current (diAO/dt) are detected. The time derivative of the anode current is multiplied by the maximum switch-off delay time. The two variables are added and compared with the maximum anode current (iAmax) which can be switched. The turn-off command is suppressed if the measurement variable (M(t0)) formed reaches or exceeds the maximum anode current (iAmax) which can be switched. The instantaneous load current (iL) can also be used instead of the instantaneous anode current (iAO). <IMAGE>

Description

The invention relates to a method of suppression of impermissible deletion attempts with disconnectable Power semiconductors according to the preamble of the claim 1 and a device for this purpose.

One application is, for example, in GTO pulse inverters possible for traction drives.

Such a method of suppressing impermissible Extinguishing attempts with disconnectable power semiconductors is known from DE-OS 34 34 607.

Power semiconductors that can be switched off, in particular GTO thyristors, can conduct high overcurrents, but can no longer switch them off. When switching off an anode current that is above the maximum, periodically switchable anode current I _TQM , GTO thyristors are usually destroyed.

To prevent such an unauthorized shutdown, has been proposed to determine the anode currents of GTO thyristors to measure and a latch of the GTO thyristor to effect in the conductive state, if a to high anode current is detected (see e.g. "The Electronics Technician", No. 11/1985, H. Graffert, "Dimensioning Critical Parameters when using GTO thyristors ", page 44, 45). However, this is a disadvantageous own current measuring element in each GTO branch of a converter required, which incurs additional costs. Furthermore, delays due to the principle between the time of issuing a shutdown command to taken into account for its execution by the GTO thyristor (command runtime, storage time). There is no more possibility of a control intervention if a Switch-off command is issued and only then a Overcurrent occurs. This is the reason why the threshold is to put the anode current detection so low, that the anode current of the GTO thyristor during the command run time under no circumstances to impermissible Values can rise. This continues the utilization of the GTO thyristor considerably down.

From DE-OS 34 34 607 mentioned at the beginning it is known initially every attempt to turn off a GTO thyristor and during the shutdown attempt based on the current measured switch-off delay time (Storage time) of the GTO thyristor to determine whether the Shutdown attempt with regard to the expected current is permissible. If this is not the case, the GTO thyristor will immediately turned back on to a destruction to prevent. This process uses the GTO thyristor exposed to high stress as everyone Attempt to switch off is started first. So that results there is a residual risk of destruction of the GTO thyristor, especially with multiple shutdown attempts. In addition, is the storage time of the GTO thyristor used as the measured variable strongly dependent on temperature, which leads to a large inaccuracy the response current leads. Here too is an underutilization of the GTO thyristor is the result.

On this basis, the invention is based on the object a method of suppressing impermissible Extinguishing attempts with disconnectable power semiconductors indicate that a high utilization rate in a simple manner of the power semiconductor. Furthermore should a device for this should be developed.

This task is related to the procedure with the features of the preamble according to the invention by those specified in the characterizing part of claim 1 Features solved.

The task is related to the device by the im Claim 4 characterized features solved.

The advantages that can be achieved with the invention are in particular in that not every GTO branch has its own Current measuring element is required. The use of additional Measuring sensor especially for the shut-off lock is avoided, since only measuring elements are necessary, which in any case to control or to protect a Converters with GTO thyristors are required, such as Current rise detection devices (necessary for the Short-circuit protection) and phase current detection devices (necessary for control purposes). The procedure is not temperature-dependent and enables a high degree of utilization the GTO thyristors, as the response threshold relatively high for inadmissible attempts at extinguishing can be. Dangerous conditions are simple Way recognized and the shutdown command to the relevant GTO thyristor is reliably suppressed. It is there advantageously not necessary to attempt a shutdown first to begin, and then to turn it back if necessary suppress.

Advantageous embodiments of the invention are shown in Characterized subclaims.

The invention is described below with reference to the in the drawing illustrated embodiments explained.

It shows:

Fig. 1 shows the diagram of an inverter with current and current rise detecting means,

Fig. 2 shows the time course of the actual and the estimated disconnected anode current,

Fig. 3 is a transmitter for suppressing illegal extinguishing tests.

In Fig. 1, the scheme of an inverter with current and current rise detection devices is shown. A three-phase inverter 1 can be seen in a bridge circuit, which is connected on the direct current side to a positive or negative direct current connection 2 or 3 and on the alternating current side to three-phase connections 4, 5, 6 . The inverter 1 has six branches, each with a GTO thyristor V 1 , V 2,. . . V 6 as the main valve. Each GTO thyristor V 1 . . . V 6 is a diode D 1 , D 2 . . . D 6 antiparallel.

The GTO thyristors V 1 . . . V 6 are each via throttles 7 . . . 12 and current rise detection devices 13 . . . 18 connected to the direct current connections, the first, third and fifth branches being connected to the positive connection 2 and the second, fourth and sixth branches being connected to the negative connection 3 . The GTO thyristors V 1 , V 2 of the first and second branches are connected to one another and connected to the three-phase connection 4 via a phase current detection device 19. The GTO thyristors V 3 , V 4 of the third and fourth branches are also connected to one another and connected to the three-phase connection 5 via a further phase current detection device 20. Finally, the interconnected GTO thyristors V 5 , V 6 are connected to the three-phase connection 6 via a third phase current detection device 21.

To control, ie to ignite and extinguish the GTO thyristors V 1 . . . V 6 is used by a control device 22 . This control device 22 is connected on the output side to the control connections of the GTO thyristors and receives, inter alia, the signals K 1 · i _{L 1} or K 1 · i _{L 2} or K 1 · i _{L 3 of} the phase current detection devices 19 or 20 or 21 and the signals K 2 · di _{A 1} / dt and K 2 · di _{A 2} / dt and K 2 · di _{A 3} / dt and K 2 · di _{A 4} / dt and K 2 · di _{A 5, respectively} / dt or K 2 · di _{A 6} / dt of the current rise detection devices 13 or 14 or 15 or 16 or 17 or 18 , where

K 1 = converter factor of the current measurement;
K 2 = converter factor of the di / dt measurement;
i _{A 1} , i _{A 2} . . . i _{A 6} = anode current of the GTO thyristors V 1 , V 2 . . . V 6 ;
i _{L 1} . . . i _{L 3} = load current.

The control electronics 22 contain, inter alia, evaluation electronics for suppressing impermissible attempts at deletion, to which the aforementioned signals are to be fed on the input side and which reliably suppress impermissible shutdown commands.

The three-phase connections 4, 5, 6 are connected to a three-phase (inductive) load 33 , e.g. B. with a traction drive (asynchronous machine).

In the proposed method for suppressing impermissible attempts to extinguish power semiconductors that can be switched off, it is essential that the switch-off lock is activated in two cases, namely in the event of overcurrent and in the event of a short circuit. The shut-off lock is effective as long as at least one of the two cases is present in the conductive GTO thyristors. The switch-off lock is activated as soon as a measured variable M (t ₀) (= estimated anode current to be switched) is greater than an adjustable threshold value (= response current = maximum switchable anode current) i _Amax . The measurand M (t ₀) results from:

M (t ₀) = K 1 ( i _A ( t ₀) + K 2 K 3 di _A (t) / dt)

For i _A ( t ₀) = i _{A 0} , the current anode current i _{A 1} is in each case. . . i _{A 6} to be used at time t . For di _A ( t ₀) / dt = di _{A 0} / dt , the current time derivative (steepness, slope of the anode current) is di _{A 1} / dt . . . di _{A 6} / dt to be used. K 3 = maximum switch-off delay time of the GTO thyristor (= command runtime between the time a switch-off command is issued and the time it is executed by the GTO thyristor: time t ₀ indicates the current time at which the switch-off command is to be issued, gives the measured variable M (t ₀) at the time of the switch-off command an estimate for the maximum anode current i _A that is expected to flow in the GTO thyristor at the actual switching instant the negative consequences of Ausschaltverzugszeit largely avoided, that it is not necessary to turn off the GTO thyristor initially and to prevent destruction then possibly back on, but the decision is made on the GTO switching off the current time t ₀ where the Shutdown command is about to be issued Furthermore, the proposed method is not temperature-dependent, so that the response current can be set relatively precisely. This results in an optimal utilization of the GTO thyristor.

To explain the proposed method, FIG. 2 shows the time course of the actual and the estimated anode current to be switched off. The actual course i _A ( t) is shown as a solid line and the estimated course of the anode current is shown as a dashed line. At the current point in time t ₀ (= start of the extinguishing attempt), the current has the value i _A ( t ₀) = i _{A 0} (= current anode current). After an "actual trial time" has elapsed at time t ₁, the actual current has the value i _{A '} (= anode current actually to be switched). After the maximum switch-off delay time K 2 has elapsed at time t 2, the estimated anode current has the value M (t ₀) (estimated anode current to be switched).

For explanation, the maximum switchable anode current i _Amax (= adjustable threshold value, response current) is shown. Since the measured variable M (t ₀) is smaller than the threshold value i _Amax , the deletion attempt sketched as an example is permissible, ie the shut-off lock is not activated.

The overcurrent release described is only intended to cause a quenching block in the event of an excessive output current of the converter. In the event of an internal short circuit, the steepness of the anode current and thus the term K 2 · K 3 · di _{A 0} / dt are so great that the quenching lock is activated by this alone. This makes it possible, instead of the measured value of the real anode current of the GTO thyristor, to use the measured value of the load current i _{L, which is} to be generated anyway for control tasks, as a substitute value. Therefore, no additional separate current detection devices are required in each GTO branch for the extinguishing lock, but rather the phase current detection devices 19, 20, 21 are sufficient. Half-wave rectifiers in the evaluation circuit suppress the measured values of those components of the phase currents that do not flow through the power semiconductors under consideration

The current rise detection devices 13 . . . 18 for determining the steepness of the anode currents di _A / dt are included in the short-circuit detection, which is also already present, the short-circuit detection also taking care of the triggering of the short-circuit in addition to other tasks. Thus, the overcurrent tripping does not require any additional measuring elements with regard to the rise in current (steepness). In summary, the proposed method of the extinguishing lock does not require its own measured value recorders, but only evaluation electronics which, as a function of the output signals of the current rise detection devices 13 . . . 18 and the phase current detection devices 19 . . . 21 decides on the admissibility of an intended deletion attempt.

In Fig. 3, an electronic evaluation system for suppressing impermissible deletion attempts is shown. The evaluation electronics are part of the control device 22 and have a half-wave rectifier 23 , which receives the signal K 2 · di _{A 1} / dt of the current increase detection device 13 on the input side (U _e = input signal, U _a = output signal), and on the output side a signal

S 1 = 1/2 (1 + Sign ( di _{A 1} / dt)) K 2 · di _{A 1} / dt

outputs to a multiplier 24. The multiplier 24 forwards a signal K 3 · S 1 to an addition point 25 . The addition point 25 is also an output signal

S 2 = 1/2 (1 + Sign ( i _{L 1} )) K 1 · i _{L 1}

a half-wave rectifier 26 , to which the signal K 1 · i _{L 1 of} the phase current detection device 19 is applied on the input side. The addition point 25 outputs the sum signal S 2 + K 3 · S 1 corresponding to the estimated anode current M (t ₀) to be switched to a threshold switch 27 . The threshold switch 27 emits the output signal S 3 = 0 (“low”) when the input signal S 2 + K 3 · S 1 is greater than the maximum switchable anode current i _Amax . The threshold switch 27 emits the output signal S 3 = 1 ("high") when the input signal S 2 + K 3 · S 1 is less than the maximum switchable anode current i _Amax , with a switching hysteresis Δ i _A having to be taken into account when there is a the input signal S 2 + K 3 · S 1 changes from larger to smaller values, ie the low-high transition takes place at a value U _e = i _Amax - Δ i _A and the high-low transition takes place at a value U _e = i _Amax .

Contains the transmitter further comprises a half-wave rectifier 28, the input side of the signal K 2 _{A 2} di / dt of the current increase detection means 14 receives a signal on the output side

S 5 = 1/2 (1 + Sign ( di _{A 2} / dt )) K 2 di _{A 2} / dt)

outputs to a multiplier 29. The multiplier forwards a signal K 3 · S 5 to an addition point 30 . The addition point 30 also becomes an output signal

S 4 = 1/2 (1 + Sign ( i _{L 1} )) K 1 · i _{L 1}

a half-wave rectifier 31 , to which the signal K 1 · i _{L 1 of} the phase current detection device 19 is applied on the input side. The addition point 30 outputs the sum signal S 4 + K 3 · S 5 corresponding to the estimated anode current M (t ₀) to be switched to a threshold value switch 32 . The threshold switch 32 emits the output signal S 6 = 0 (low) when the input signal S 4 + K 3 · S 5 is greater than the maximum switchable anode current i _Amax .

The threshold switch 27 emits the output signal S 6 = 1 (high) when the input signal S 4 + K 3 · S 5 is less than the maximum switchable anode current i _Amax , the switching hysteresis Δ i _A also having to be taken into account.

The evaluation electronics contain further limiters, multipliers, Addition points and threshold switches for Processing of the other signals

K 2 · di _{A 3} / dt,. . . K 2 · di _{A 6} / dt as well as K 1 · i _{L 2} and K 1 · i _{L 3}

in the manner described above. It is essential that each GTO thyristor is assigned its own device for the switch-off lock. The factor K 3 simulates the maximum switch-off delay time. The output signals of the threshold switches directly affect the control of the GTO thyristors V 1 . . . V 6 on , ie when a signal S 3 , S 6 occurs . . . = 0 (low), the switch-off command to the GTO thyristor in question and thus the intended deletion attempt are suppressed in order to prevent destruction by an impermissibly high current. When a signal S 3 , S 6 occurs . . . = 1 (high) the deletion attempt is evaluated as permissible and the shutdown command is executed.

Claims (8)

1. A method for suppressing impermissible deletion attempts in disconnectable power semiconductors in converters, characterized in that one is derived from the current anode current ( i _{A 0} ) of the semiconductor and the product of the time derivative of this current anode current ( di _{A 0} / dt) and the Maximum switch-off delay time K 3 ) composing measured variable ( M (t ₀)) is formed and compared with an adjustable, maximum switchable anode current ( i _Amax ), with erase commands that occur are suppressed if the measured variable formed ( M (t ₀)) exceeds the maximum switchable Anode current ( i _Amax ) reached or exceeded. 2. The method according to claim 1, characterized in that the load current ( i _L ) is used as the current anode current (i _{A 0).} 3. The method according to any one of claims 1 and / or 2, characterized in that the converter factor ( K 1 ) of the current measurement is taken into account in the formation of the current anode current (i _{A 0).} 4. Device for performing the method according to one of claims 1 to 3, characterized in that each power semiconductor ( V 1 ... V 6 ) which can be switched off is assigned its own current rise detection device ( 13 ... 18 ), the output signals of which
( K 2 · di _{A 1} / dt... K 2 · di _{A 6} / dt)
can be fed to an electronic evaluation system that phase current detection devices ( 19 ... 21 ) are provided, the output signals of which
( K 1 · i _{L 1} ... K 1 · i _{L 3} )
also get to the evaluation electronics that the evaluation electronics adding points ( 25, 30 ) to the summation of the current load currents ( i _{L 1} ... i _{L 3} ) evaluated with a converter factor (K 1 ) with those with a converter factor ( K 2 ) and the maximum Switch-off delay time ( K 3 ) evaluated time derivatives of the current anode currents ( di _{A 0} / dt) , and that threshold value switches (27, 32 ) are used to compare the measured variable formed with the predeterminable, maximum switchable anode current ( i _Amax ). 5. Apparatus according to claim 4, characterized in that each half-wave rectifier ( 23, 26, 28, 31 ) for the input signals ( K 2 · di _A / dt , K 1 · i _L ) of the evaluation electronics are provided, which can be switched off in each case Assign power semiconductors. 6. Device according to one of claims 4 and / or 5, characterized in that multipliers ( 24, 29 ) are provided for evaluating the input signals ( K 2 · di _A / dt) of the evaluation electronics with the maximum switch-off delay time ( K 3 ). 7. Apparatus according to claim 4, characterized in that threshold switches ( 27, 32 ) with switching hysteresis ( Δ i _A ) are provided. 8. Device according to one of claims 4 to 7, characterized in that each power semiconductor that can be switched off ( V 1 ... V 6 ) is assigned its own device for the switch-off lock.