DE3727996C2 - - Google Patents

Description

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

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

Such a method of suppressing inadmissible Attempt to erase power semiconductors that can be switched off 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 off. GTO thyristors are generally destroyed when an anode current is switched off which is above the maximum periodically switchable anode current I _TQM .

To prevent such an impermissible shutdown, The anode currents of the GTO thyristors have been proposed to measure and lock the GTO thyristor effect in the conductive state, if one too high anode current is detected (see, for example, "The Electronics Technician", No. 11/1985, H. Graffert, "Dimensioning critical Parameters when using GTO thyristors ", page 44, 45). However, this is disadvantageous separate current measuring element in each GTO branch of a converter required, which incurs additional costs. In addition, there must be delays between the time a shutdown command is issued until considered for its execution by the GTO thyristor (command runtime, storage time). There is no possibility of tax intervention if a Shutdown command is issued and only then Overcurrent occurs. For this reason, the response threshold the anode current detection so low that the anode current of the GTO thyristor during the instruction runtime under no circumstances to impermissible Values can rise. This implies the utilization of the GTO thyristor considerably down.

From the aforementioned DE-OS 34 34 607 it is known every attempt to switch off a GTO thyristor begin and during the shutdown attempt based on the current measured switch-off delay time (Storage time) of the GTO thyristor to determine whether the Attempt to switch off with regard to the expected current is permissible, d. H. during the shutdown process of the thyristor the detected gate current becomes an integration variable formed and an overload signal is generated, if this integration quantity has a given one Threshold exceeded. When the overload signal appears the thyristor is then returned to the Controlled current-controlled state to destruction to prevent. In this process, the GTO thyristor exposed to a high burden since everyone Switch-off attempt is started first. So that results there is a residual risk of destruction of the GTO thyristor,  especially when trying to switch off several times. In addition is the storage time of the GTO thyristor used as measured variable strongly temperature-dependent, leading to great inaccuracy of the response current. Here too Underutilization of the GTO thyristor results.

From DE 34 08 788 A1 is an electronic security device for semiconductor switches to protect against Overcurrent is known at which the load current of the semiconductor switch if there is an overcurrent due to ignition a circuit breaker located in a parallel branch is dismantled, with an overcurrent detection device when a certain current threshold is exceeded delivers a corresponding ignition pulse.

Furthermore, from DE 37 00 788 A1 is a blockable non-mechanical breaker for an AC circuit known with an inductive load, with a shutdown thyristor, the one to open and close a the AC circuit containing the inductive load serves, with a parallel to the anode-cathode path arranged RCD protection circuit is provided. Farther are the thyristor's anode-cathode path and its Protection circuit with the AC power source through a Two-way rectifier connected while one Voltage limiting device at the connections of this Rectifier device is provided.

Based on this, the object of the invention is a method of suppressing inadmissible Attempt to erase power semiconductors that can be switched off indicate that in a simple way high utilization of the power semiconductor enables. Furthermore should a device to be developed for this.

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 performed on the device by the Characteristics characterized claim 4 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 Sensor especially for the shutdown lock is avoided since only measuring elements are necessary, which in any case to control or protect a Power 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 of the GTO thyristors because the response threshold relatively high for inadmissible deletion attempts can be. Dangerous conditions are simple Way recognized and the shutdown command to the concerned  GTO thyristor is reliably suppressed. It is advantageously not necessary, a switch-off attempt first to start and then close it again if necessary suppress.

Advantageous embodiments of the invention are in the Subclaims marked.

The invention is described below with reference to 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 evaluation electronics to suppress inadmissible deletion attempts.

In Fig. 1, the scheme is shown of an inverter with current and current rise detecting means. A three-phase inverter 1 can be seen in a bridge circuit, which is connected on the DC side to a positive or negative DC connection 2 or 3 and on the AC side with 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 anti-parallel.

The GTO thyristors V 1 . . . V 6 are each via chokes 7 . . . 12 and current rise detection devices 13 . . . 18 connected to the DC connections, the first, third and fifth branches being at the positive connection 2 and the second, fourth and sixth branches at 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 . Likewise, the GTO thyristors V 3 , V 4 of the third and fourth branches are 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 serves a control device 22 . On the output side, this control device 22 is connected to the control connections of the GTO thyristors and receives, among other things, 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 or K 2 · di _{A 2} / dt or K 2 · di _{A 3} / dt or K 2 · di _{A 4} / dt or K 2 · di _{A 5} / 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 converter factors K 1 , K 2 generally express the factor by which the current currents or derivatives of the currents differ from the measurement signals.

The control device 22 contains, among other things, evaluation electronics for suppressing impermissible deletion attempts, to which the signals mentioned are to be supplied on the input side and which reliably suppresses impermissible switch-off commands.

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

In the proposed method for suppressing inadmissible deletion attempts in the case of power semiconductors which can be switched off, it is essential that the switch-off lock is activated in two cases, namely in the event of overcurrent and short circuit. The shutdown lock is effective as long as there is at least one of the two cases with conductive GTO thyristors. The shutdown lock is activated as soon as a measured variable M (t₀) (= estimated anode current to be switched) is greater than an adjustable threshold value (= response current = maximum switchable anode current) i _Amax . The measured variable M (t₀) results in:

M (t₀) = K 1 (i _A (t₀) + K 2 · K 3 · di _A (t) / dt)

For i _A (t₀) = i _{A 0} , the current anode current is i _{A 1} . . . i Use _{A 6} at time t. For di _A (t₀) / dt = di _{A 0} / dt, the current time derivative (slope, slope of the anode current) is di _{A 1} / dt. . . to use di _{A 6} / dt. K 3 = maximum switch-off delay time of the GTO thyristor (= command runtime between the point in time when a switch-off command is issued and the point in time when it is executed by the GTO thyristor. If time t₀ indicates the current point in time at which the switch-off command is to be issued, the measured variable M gives (t₀) at the time of the switch-off command an estimate for the maximum anode current i _A , which is likely to flow in the GTO thyristor at the actual switching instant. In addition to the current value of the anode current, its estimated future development in overcurrent monitoring is also taken into account Consequences of the switch-off delay time largely avoided, i.e. it is not necessary to switch off the GTO thyristor first and then switch it on again afterwards in order to prevent destruction, but the decision about the GTO switch-off is made at the current time t₀, at which the switch-off command was just issued Furthermore, the proposed method is not temperature-dependent, which means that the response current can be set relatively precisely. This results in optimal use of the GTO thyristor.

FIG. 2 shows the course over time of the actual and the estimated anode current to be switched off to explain the proposed method. 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 time t₀ (= start of the quenching attempt), the current has the value i _A (t₀) = i _{A 0} (= current anode current). After an "actual test time" 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 3 at time t 2 , the estimated anode current has the value M (t₀) (estimated anode current to be switched).

Finally, the maximum switchable anode current i _Amax (= adjustable threshold value, response current) is shown for explanation. Since the measured variable M (t₀) is smaller than the threshold value i _Amax , the deletion attempt sketched as an example is permissible, ie the shutdown lock is not activated.

The described overcurrent release is only intended to block the extinguishing if the output current of the converter is excessive. When an internal short circuit, the slope of the anode current and thus the term K 2 · K 3 · _{A 0} are di / dt already so large that the erasure preventing device is already activated solely thereby. This results in the possibility, instead of the measured value of the real anode current of the GTO thyristor, of using the measured value of the load current i _{L, which is} to be generated anyway for process control tasks, as a substitute value. Therefore, no additional separate current detection devices are required in each GTO branch for the extinguishing block, but the phase current detection devices 19, 20, 21 are sufficient. The measured values of those portions of the phase currents which do not flow through the power semiconductors under consideration are suppressed by one-way rectifiers in the evaluation circuit

The current rise detection devices 13 . . . 18 for determining the steepness of the anode currents di _A / dt are also contained in the short-circuit detection, which is already present anyway, the short-circuit detection also carrying out the short-circuit triggering in addition to other tasks. This means that overcurrent tripping does not require any additional measuring elements with regard to the current increases (slopes). In summary, the proposed method of the extinguishing block does not require its own measuring sensor, but only an electronic evaluation system, which is dependent on 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, a transmitter is shown for suppressing illegal extinguishing tests. The evaluation electronics is part of the control device 22 and has a one-way rectifier 23 , which receives the signal K 2 · di _{A 1} / dt of the current rise detection device 13 on the input side (U _e = input signal, U _a = output signal), and a signal on the output side

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 also becomes an output signal

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

a one-way rectifier 26 , to which the signal K 1 · i _{L 1 of} the phase current detection device 19 is present 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 (t₀) to be switched to a threshold switch 27 . The threshold switch 27 outputs 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 outputs 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 , a switching hysteresis Δi _A having to be taken into account if that Input signal S 2 + K 3 · S 1 changed from larger to smaller values, ie the low-high transition occurs at a value U _e = i _Amax -Δi _A and the high-low transition occurs 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 one-way 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 (t₀) to be switched to a threshold switch 32 . The threshold switch 32 outputs 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 outputs 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 Δi _A also having to be taken into account.

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

K 2 · di _{A 3} / dt,. . . K 2 · di _{A 6} / dt
such 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 shutdown 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 extinguishing 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 rated as permissible and the shutdown command is executed.

Claims (8)

1. A method for suppressing inadmissible extinguishing attempts in the case of power semiconductors which can be switched off in power converters, characterized in that 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 (t₀)) and compared with an adjustable, maximum switchable anode current (i _Amax ), deletion commands occurring are suppressed if the measured variable (M (t₀)) forms 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 switchable power semiconductor (V 1 ... V 6 ) is assigned its own current rise detection device ( 13 ... 18 ), the output signals
(K 2 · di _{A 1} / dt.. K 2 · di _{A 6} / dt)
can be fed to an evaluation electronics that phase current detection devices ( 19 .... 21 ) are provided, their output signals
(K 1 · I _{L 1} .. K 1 · i _{L 3} )
also arrive at the evaluation electronics that the evaluation electronics add points ( 25, 30 ) for summing 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 ) has evaluated time derivatives of the current anode currents (di _{A 0} / dt), and that threshold switches ( 27, 32 ) serve to compare the measured variable formed with the specifiable, maximum switchable anode current (i _Amax ). 5. Apparatus according to claim 4, characterized in that one-way rectifiers ( 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 ) for evaluating the input signals (K 2 · di _A / dt) of the evaluation electronics with the maximum switch-off delay time (K 3 ) are provided. 7. The device according to claim 4, characterized in that threshold switches ( 27, 32 ) with switching hysteresis (Δi _A ) are provided. 8. Device according to one of claims 4 to 7, characterized in that each switchable power semiconductor (V 1 ... V 6 ) is assigned its own device for a shutdown lock to suppress inadmissible deletion attempts.