CN103280960A - Current-limiting device and current-limiting method - Google Patents

Abstract

The present invention relates to a current limiting device and a current limiting method. The method includes: when a nonlinear load is suddenly added to the circuit, a load impact signal is generated by detecting the change of the output current of the circuit; when the load impact is received signal, reduce the current-limiting threshold; compare the current-limiting threshold with the current value of the switching tube in the circuit, and when the current value of the switching tube is greater than the current-limiting threshold, a current-limiting enabling signal; according to the current limiting enabling signal, control the switching tube in the circuit to be turned off. The current limiting device and the current limiting method provided by the present invention keep the current stress of the power switch tube within a safe range when a non-linear load is suddenly applied, and at the same time ensure the normal current limiting function in the case of non-load impact.

Description

Current limiting device and current limiting method

technical field

The invention relates to the technical field of electronic circuits, in particular to a current limiting device and a current limiting method.

Background technique

Current inverter devices are all equipped with a current limiting circuit. The current limiting circuit of the inverter compares the detected switching tube current value with a fixed current limiting threshold value. If the switching tube current value exceeds the current limiting threshold value, a limiting The current-enabling signal is sent to the current-limiting circuit after level conversion, and the current-limiting circuit turns off the switch tube according to a certain sequence, so as to ensure that the current stress of the switch tube is within a safe range.

However, when the volume inductance of the inverter inductance is small, the di/dt of the inductance is very large due to the impact of the nonlinear load at the moment when the nonlinear load is connected. After detecting that the current of the inverter switching tube reaches the current limiting threshold, When the current limiting circuit operates to close the inverter switch tube, there will be a fixed transmission delay Δt (mainly including the inherent delay of each device on the signal transmission line and the signal debounce delay), Δt*di/dt will generate a Large current change value Δi. Assuming that the current-limiting threshold is I ₀ , the current of the actual switch tube will reach I ₀ +Δi when the current is limited. The smaller the inductance value of the inverter, the greater the Δi when the nonlinear load is suddenly applied. The greater the current stress I ₀ +Δi to bear, the current limiting method cannot ensure that the current stress I ₀ +Δi of the switch tube is within a safe range when the inductance value is small.

Due to the limitation of the hardware circuit itself, the delay Δt cannot be eliminated, so the current change value Δi must exist; at the same time, the minimum value of the current limiting threshold I ₀ cannot be lower than the upper limit of the steady-state load capacity of the inverter design, so it cannot be directly Reduce I ₀ to reduce the current stress of the power switch tube when the nonlinear load is suddenly added.

Contents of the invention

In view of this, the object of the present invention is to provide a current limiting device and a current limiting method, when a nonlinear load is suddenly added, the current stress of the power switch tube is within a safe range, while ensuring normal Current limiting function.

In order to achieve the above object, the first aspect of the present invention provides a current limiting device, said device comprising: a load impact detection circuit, a current limiting threshold generation circuit, a comparison circuit and a current limiting control circuit;

The load impact detection circuit is connected to the output terminal of the circuit, and is used to detect the change of the current output by the circuit, and when a nonlinear load is suddenly added to the circuit, a load impact signal is generated;

The current-limiting threshold generating circuit is connected with the load impact detection circuit, and is used to generate a variable current-limiting threshold, and when receiving the load impact signal output by the load impact detection circuit, reduces the current limit threshold;

The comparison circuit is connected with the detection terminal of the switching tube current in the circuit and the current-limiting threshold voltage generation circuit, and compares the current value of the switching tube with the current-limiting threshold, and when the switch When the current value of the tube is greater than the current limiting threshold, a current limiting enabling signal is generated;

The current-limiting control circuit is connected to the comparison circuit, and is used for controlling the switching tube in the circuit to turn off when receiving the current-limiting enable signal generated by the comparison circuit.

With reference to the first aspect, in a first possible implementation manner of the first aspect, the load impact detection circuit is a comparator, the input terminal of the comparator is connected to the output terminal of the circuit, and the The current output by the circuit is compared with a preset reference value, and when the current output by the circuit is greater than the preset reference value, the load impact signal is generated.

With reference to the first aspect, in a second possible implementation manner of the first aspect, the current-limiting threshold generating circuit delays the current-limiting threshold by a set delay time when the received load shock signal ends. Gradually restore to the initial current limit threshold.

With reference to the first aspect, in a third possible implementation manner of the first aspect, the current limiting control circuit includes: a level conversion circuit and a current limiting circuit;

The level conversion circuit is connected to the comparison circuit, and is used to perform level conversion on the current limit enable signal when receiving the current limit enable signal generated by the comparison circuit to generate an overcurrent flow logic signal;

The current limiting circuit is connected with the level shifting circuit, and is used to control the switching tubes in the circuit to turn off according to the set timing according to the overcurrent logic signal generated by the level shifting circuit.

In a second aspect, the present invention also provides a current limiting method, the method comprising:

When a non-linear load is suddenly added to the circuit, a load impact signal is generated by detecting the change of the current output by the circuit;

When receiving the load impact signal, reduce the current limiting threshold;

Comparing the current limiting threshold with the current value of the switching tube in the circuit, when the current value of the switching tube is greater than the current limiting threshold, generating a current limiting enabling signal;

According to the current limit enable signal, the switching tube in the circuit is controlled to be turned off.

With reference to the second aspect, in a first possible implementation manner of the second aspect, the generating the load impact signal by detecting the change of the current output by the circuit includes:

The current output by the circuit is compared with a preset reference value, and when the current output by the circuit is greater than the preset reference value, the load impact signal is generated.

With reference to the second aspect, in a second possible implementation manner of the second aspect, after the reducing the current limiting threshold when the load impact signal is received, the method further includes:

When the load impact signal ends, the current limiting threshold is gradually restored to the initial current limiting threshold according to a set delay.

With reference to the second aspect, in a third possible implementation manner of the second aspect, controlling the switching tube in the circuit to be turned off according to the current limiting enable signal includes:

performing level conversion on the current limiting enable signal to generate an overcurrent logic signal;

According to the overcurrent logic signal, the switches in the circuit are controlled to be turned off according to the set timing.

The current limiting device and current limiting method provided by the present invention can automatically reduce the current limiting threshold when a nonlinear load is suddenly added, and can ensure that the power switch tube current is within the safe current range when the load impacts; at the same time, when the load impact ends , after the inverter output load enters a steady state, the current limiting threshold is restored to the initial current limiting threshold, so as to ensure that the volume and inductance of the inverter inductance are small, and the current stress of the power switch tube is safe when impacted by the load. Within the range, while ensuring the normal current limiting function in the case of non-load impact.

Description of drawings

FIG. 1 is a schematic structural diagram of a current limiting device provided in Embodiment 1 of the present invention;

FIG. 2 is a schematic circuit diagram of a current-limiting threshold generation circuit provided by Embodiment 1 of the present invention;

FIG. 3 is a schematic diagram of a topological structure of an inverter output part provided by the present invention;

4 is a schematic diagram of the relationship between the inverter switch tube current and the inverter output current when the load impact is provided by the present invention;

FIG. 5 is a schematic diagram of the relationship between the change of the current limiting threshold when the load shock is provided by Embodiment 1 of the present invention;

FIG. 6 is a flow chart of the current limiting method provided by Embodiment 2 of the present invention.

Detailed ways

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

The current limiting device and current limiting method provided by the embodiments of the present invention are suitable for various circuits and devices that need to limit the current of power switch tubes, such as inverter devices, and are especially suitable for inverter inductors with small volume inductance. Inverter unit.

Embodiment one

FIG. 1 is a schematic diagram of a current limiting device provided in this embodiment. As shown in FIG. 1 , the current limiting device of the present invention includes: a load impact detection circuit 10 , a current limiting threshold generating circuit 20 , a comparing circuit 30 and a current limiting control circuit 40 .

The load impact detection circuit 10 is connected with the output terminal of the circuit, and is used to detect the change of the current output by the circuit, and when a nonlinear load is added to the circuit, a load impact signal is generated.

The load impact detection circuit 10 may, but is not limited to, use a comparator. The input terminal of the comparator is connected to the output terminal of the circuit, and the current output by the circuit is compared with a preset reference value. When the current output by the circuit is greater than the preset When the reference value of , the load shock signal is generated. The reference value may be a value artificially set according to actual experience.

Preferably, the load impact detection circuit 10 is connected to the output terminal of the circuit through the circuit output current detection circuit T1. The circuit output current detection circuit T1 can be a current transformer and other components as a sampling circuit to sample the current at the output terminal of the circuit and transmit it to The load impact detection circuit 10 performs detection.

The current-limiting threshold generation circuit 20 is connected with the load impact detection circuit 10 for generating a variable current-limiting threshold, and reduces the current-limiting threshold when receiving the load impact signal output by the load impact detection circuit 10 .

The current-limiting threshold generating circuit 20 gradually restores the current-limiting threshold to the initial current-limiting threshold according to a set delay when the received load shock signal ends.

The current-limiting threshold generating circuit 20 can be composed of, but not limited to, a triode and an RC circuit. Specifically, it can be shown in FIG. Connected through the voltage dividing resistors R1 and R2, the base of the switching tube Q1 is connected to the contacts of the voltage dividing resistors R1 and R2, the collector of the switching tube Q1 is connected to the reference voltage V_REF through the pull-up resistor R3, and through the voltage dividing Resistors R4 and R5 are connected to the switch tube Q2, the base of the switch tube Q2 is connected to the contacts of the voltage dividing resistors R4 and R5, the collector of the switch tube Q2 is connected to the reference voltage V_REF through the resistors R7 and R6, and the resistors R7, The middle contact of R6 serves as a variable current-limiting threshold voltage output terminal, and the emitters of the switching tubes Q1 and Q2 are grounded.

When the circuit is in a stable state, that is, when there is no load impact signal, the switches Q1 and Q2 in the current-limiting threshold generation circuit 20 are not turned on, and the output variable current-limiting threshold voltage is equal to the reference voltage V_REF. When there is a load impact signal, the switch tubes Q1 and Q2 in the current-limiting threshold generating circuit 20 are turned on, and the output variable current-limiting threshold voltage is equal to the voltage on the resistor R7, and an appropriate resistance value is selected to make the output current-limiting threshold voltage fulfil requirements. In addition, the charging and discharging time of the capacitor C1 can be controlled by adjusting the resistance values of the resistors R6 and R7, so that the output current-limiting threshold voltage gradually recovers to the initial current-limiting threshold according to a certain delay. Since there is a certain correspondence between the current and the voltage in the circuit, the current-limiting threshold of the current can be corresponding to the output current-limiting threshold voltage in the current-limiting threshold generation circuit 20 through a certain conversion relationship. It should be noted that the current-limiting threshold generating circuit 20 of the present invention can also be realized by other similar circuits, which are not exhaustively described here.

The comparison circuit 30 is connected with the detection terminal of the switching tube current in the circuit and the current limiting threshold voltage generating circuit 20, and compares the current value of the switching tube with the current limiting threshold, when the current of the switching tube When the value is greater than the current limit threshold, a current limit enable signal is generated.

The current-limiting control circuit 40 is connected to the comparison circuit 30 , and is used for controlling the switching tubes in the circuit to turn off when receiving the current-limiting enable signal generated by the comparison circuit 30 .

The current limiting control circuit 40 includes a level conversion circuit 401 and a current limiting circuit 402 . The level conversion circuit 401 is connected with the comparison circuit 30, and is used for performing level conversion on the current limit enable signal to generate an overcurrent logic signal when receiving the current limit enable signal generated by the comparison circuit 30.

The current limiting circuit 402 is connected with the level conversion circuit 401, and is used for controlling the switching tubes in the circuit to be turned off according to the set timing according to the overcurrent logic signal generated by the level conversion circuit 401.

The principle of the current limiting device of the embodiment of the present invention will be described below with reference to FIG. 3 , FIG. 4 and FIG. 5 .

Figure 3 is a schematic diagram of the topology of the output part of the inverter. As shown in Figure 3, the circuit of the inverter system includes an inductor L, and the output end of the circuit is connected to the output capacitor C ₀ . When the output end is connected to the load Load, The output capacitor C ₀ discharges to the load Load, and the current I _OUT output by the circuit increases rapidly. Due to the effect of the inductance L, the increase of the current I _L of the inductance L will lag behind the output current I _OUT of the circuit, as shown in Figure 4, so the sudden When a nonlinear load is added, the lead of the output current can be used to predict the sharp increase of the switching tube current _IL . When the current I _OUT output by the circuit exceeds the set threshold, a load impact signal will be generated. After the load impact signal is valid, the current limiting threshold will be reduced. After the load impact signal fails, the current limiting threshold will gradually recover according to the set delay. to the initial set value. As shown in Figure 5, when the circuit output current I _OUT exceeds the set load surge current reference value I _{OUT_REF} , a load surge signal I _{OUT_OC} is generated. The threshold I ₀ is reduced to the current-limiting threshold I ₀ ^/ . After the load impact disappears, the current-limiting threshold generation circuit 20 gradually restores the current-limiting threshold from the current-limiting threshold I ₀ ^/ to the initial current-limiting threshold I ₀ according to the set delay.

It can be seen that the current limiting device of the embodiment of the present invention can automatically reduce the current limiting threshold from I ₀ to I ₀ ^/ when a non-linear load is suddenly added (causing a load impact), so as to ensure the power switch tube when the load impacts The current stress I ₀ ^/ +Δi is within the safe current range; when the load impact is over, the current limiting threshold can be restored from I ₀ ^/ to I ₀ , which will not affect the normal load capacity of the inverter. Under the condition that the volume and inductance of the inverter inductance are small, the current stress problem of the power switch tube is solved, and the cost of the inductance is saved.

The above is a detailed description of the current limiting device provided by the present invention, and the current limiting method provided by the present invention will be described in detail below.

Embodiment two

Figure 6 is a flow chart of the current limiting method provided in this embodiment, as shown in Figure 6, the current limiting method of the present invention includes:

S101. When a non-linear load is suddenly applied to the circuit, a load impact signal is generated by detecting a change in the current output by the circuit.

Specifically, the current output by the circuit is compared with a preset reference value, and when the current output by the circuit is greater than the preset reference value, the load impact signal is generated.

When a non-linear load is added to the circuit, the output current of the circuit will increase rapidly, and when it exceeds the preset reference value, a load impact signal will be generated.

S102. Decrease the current limiting threshold when the load impact signal is received.

The current limiting threshold is reduced to ensure that the current stress of the power switch tube is also within the safe current range when there is a load impact.

When the load impact signal ends, the current limiting threshold is gradually restored to the initial current limiting threshold according to the set delay, without affecting the normal load capacity of the circuit.

S103. Compare the current limiting threshold with the current value of the switching tube in the circuit, and generate a current limiting enable signal when the current value of the switching tube is greater than the current limiting threshold.

When the load is connected, the characteristic that the current of the switch tube will lag behind the output current of the circuit is used. Before the load impact reaches the switch tube, the current limit threshold is lowered in advance through S102. The current value of the switch tube in the circuit is equal to the reduced limit Compared with the current threshold value, when the passing current is small and reaches the reduced current limit threshold value, the current limit enable signal is generated to ensure that when a large current change Δi is generated, the current stress of the switch tube can also be made within safe limits.

S104. According to the current limiting enable signal, control the switching tube in the circuit to be turned off.

Specifically, the method includes: converting the current-limiting enable signal to a level to generate an over-current logic signal; according to the over-current logic signal, controlling the switching tube in the circuit to be turned off according to a set timing.

The principle of the current limiting method provided by the embodiment of the present invention is the same as that in the first embodiment, and will not be repeated here.

The current limiting device and the current limiting method provided by the present invention, on the basis of the conventional current limiting circuit, add a load impact detection circuit, by using the characteristic that the output current of the system such as the inverter is ahead of the switching tube current, the load impact The signal is used as the reset control signal of the threshold voltage of the current-limiting comparator. When a large nonlinear load is suddenly added, the load impact signal can reset the threshold voltage of the current-limiting comparator, that is, reduce the wave-by-wave current-limiting threshold, so that the switching tube When the current is small (lower than the initial current-limiting threshold), the current-limiting enable signal can be triggered, and the system enters the current-limiting logic, ensuring that the switch current stress does not exceed the specification; after the load impact signal fails, the comparator valve The value voltage is gradually restored to the initial current-limiting threshold according to the set delay time, which solves the current stress problem of the power switch tube and can save the cost of the inductor. Under the conditions of medium power, large current and limited inductance volume and inductance, inverter inductance with small inductance can be used, and the current stress of the power switch tube does not exceed the specification when the load impacts, and at the same time, it ensures that it does not exceed the load impact condition. normal current limiting function.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (8)

1. A current-limiting device, characterized in that the device comprises: a load impact detection circuit, a current-limiting threshold generation circuit, a comparison circuit and a current-limiting control circuit; The load impact detection circuit is connected to the output terminal of the circuit, and is used to detect the change of the output current of the circuit, and when a non-linear load is suddenly added to the circuit, a load impact signal is generated; The current-limiting threshold generating circuit is connected with the load impact detection circuit, and is used to generate a variable current-limiting threshold, and when receiving the load impact signal output by the load impact detection circuit, reduces the current limit threshold; The comparison circuit is connected with the detection terminal of the switching tube current in the circuit and the current-limiting threshold voltage generation circuit, and compares the current value of the switching tube with the current-limiting threshold, and when the switch When the current value of the tube is greater than the current limiting threshold, a current limiting enabling signal is generated; The current-limiting control circuit is connected to the comparison circuit, and is used for controlling the switching tube in the circuit to turn off when receiving the current-limiting enable signal generated by the comparison circuit. 2. The device according to claim 1, wherein the load impact detection circuit is a comparator, the input terminal of the comparator is connected with the output terminal of the circuit, and the current output by the circuit Compared with a preset reference value, when the current output by the circuit is greater than the preset reference value, the load impact signal is generated. 3. The device according to claim 1, wherein the current-limiting threshold generation circuit gradually restores the current-limiting threshold to the initial value according to the set delay when the received load shock signal ends. current limit threshold. 4. The device according to claim 1, wherein the current limiting control circuit comprises: a level conversion circuit and a current limiting circuit; The level conversion circuit is connected to the comparison circuit, and is used to perform level conversion on the current limit enable signal when receiving the current limit enable signal generated by the comparison circuit to generate an overcurrent flow logic signal; The current limiting circuit is connected with the level shifting circuit, and is used to control the switching tubes in the circuit to turn off according to the set timing according to the overcurrent logic signal generated by the level shifting circuit. 5. A current limiting method, characterized in that the method comprises: When a non-linear load is suddenly added to the circuit, a load impact signal is generated by detecting the change of the current output by the circuit; When receiving the load impact signal, reduce the current limiting threshold; Comparing the current limiting threshold with the current value of the switching tube in the circuit, when the current value of the switching tube is greater than the current limiting threshold, generating a current limiting enabling signal; According to the current limit enable signal, the switching tube in the circuit is controlled to be turned off. 6. The method according to claim 5, wherein the generating a load impact signal by detecting the change of the current output by the circuit comprises: The current output by the circuit is compared with a preset reference value, and when the current output by the circuit is greater than the preset reference value, the load impact signal is generated. 7. The method according to claim 5, further comprising: after the load shock signal is received, after reducing the current limiting threshold: When the load impact signal ends, the current limiting threshold is gradually restored to the initial current limiting threshold according to a set delay. 8. The method according to claim 5, wherein, according to the current-limiting enable signal, controlling the switching tube in the circuit to be turned off comprises: performing level conversion on the current limiting enable signal to generate an overcurrent logic signal; According to the overcurrent logic signal, the switches in the circuit are controlled to be turned off according to the set timing.

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