A dynamic current sharing system for parallel IGBTs based on gate resistance control

Abstract

The invention belongs to the technical field of IGBTs, and discloses a parallel IGBT dynamic current balancing system based on gate resistance control. The parallel current balancing is achieved by reducing the gate resistance of the IGBT that is turned on and off later, so the switching frequency will not be reduced due to the slowing down of the transient current change of the IGBT, and this switch adjustment method is suitable for digital control systems. In addition, compared with the method of adjusting the delay of the driving signal, the method of changing the gate resistance is simpler and more convenient; the transient change rate of the current of the IGBT is changed by adjusting the gate resistance, so as to achieve the purpose of parallel current balancing; the gate resistance is divided into two parts, one of which is connected in parallel with a switch, and the on and off of the switch is controlled to change the gate resistance; the on and off time of the IGBT is judged to be advanced or delayed based on the current amplitude and the change rate, and then the switch is determined to be turned on or off.

Description

Technical Field

[0001] The invention belongs to the technical field of IGBTs, and in particular relates to a parallel IGBT dynamic current sharing system based on gate resistance control. Background Art

[0002] Limited by the current capacity of a single IGBT, the solution of paralleling IGBTs has been increasingly widely used in many high-power scenarios. Due to the inconsistency of the IGBT's own and external parameters and the asymmetry of the circuit layout, the current of different IGBTs may be different. This will cause some IGBTs to be damaged due to excessive current, reduce the stability and reliability of the system, and even trigger a chain reaction, causing the entire system to crash. Therefore, they must be connected in parallel to share the current.

[0003] The gate resistance control method is one of the methods for current balancing of IGBTs in parallel. Its principle is to change the transient change of the current of the IGBT by adjusting the gate resistance of the IGBT. The on and off process of the IGBT can be equivalent to the charging and discharging process of the gate-emitter capacitance. When the gate resistance increases, the time constant of charging and discharging also becomes larger, and the gate-emitter voltage of the IGBT changes more slowly. According to the transfer characteristics of the IGBT, the current of the IGBT increases with the increase of the gate-emitter voltage, so the current of the IGBT changes more slowly in the transient state, that is, the process of turning on and off the IGBT slows down. Conversely, when the gate resistance decreases, the current of the IGBT changes faster. Therefore, when the current of the parallel IGBT is unbalanced, the gate resistance of the IGBT that is turned on and off later can be reduced to make its current change faster; or the gate resistance of the IGBT that is turned on and off first can be increased to make its current change slower, and finally the current difference of the parallel IGBT is reduced.

[0004] Some scholars have proposed a method to achieve current balance of parallel IGBTs by dynamic gate resistance control. By dynamically changing the gate resistance, current balance of parallel IGBTs can be achieved without high-frequency digital logic or complex delay circuits. This method has been proven to be simpler than directly controlling the gate delay and can achieve C without limiting the gate drive current. GCThe charge and discharge of the IGBT. However, it is difficult to determine the specific turn-on and turn-off delay times, and increasing the gate resistance of the IGBT that is turned on and off first will cause the current change rate of the IGBT to decrease, thereby reducing the switching frequency. Some scholars have also proposed a gate driver chip with programmable output resistance, which can achieve current balance of parallel IGBTs. By dynamically adjusting the gate drive resistance to reduce the on / off delay difference between parallel IGBTs, the current imbalance in each switching cycle can be compensated. The programmable gate drive resistance is implemented using segmented output stage technology, which has a simple process, does not require additional chip area, and is easy to integrate and manage with a digital control system. However, this method lacks a discharge mechanism in the on state. Summary of the invention

[0005] The object of the present invention is to provide a parallel IGBT dynamic current sharing system based on gate resistance control to overcome the defects of the existing method such as complex control strategy, reduced switching frequency, and high cost and loss.

[0006] To achieve the above object, the present invention adopts the following technical solution: a parallel IGBT dynamic current sharing system based on gate resistance control, comprising:

[0007] Multiple parallel IGBTs (Q1, ..., Q k , …, Q n );

[0008] and the IGBT (Q1, ..., Q k , …, Q n ) connected to the gate resistor;

[0009] and a control strategy unit connected to the gate resistor;

[0010] and the current (I1, ..., I k ,…,I n );

[0011] The gate resistor includes R ga and R gb , the R ga and R gb connected in series, and the R ga A switch (S) is connected in parallel.

[0012] Furthermore, the control strategy unit is connected to the switch (S).

[0013] Furthermore, the R gb The plurality of IGBTs (Q1, ..., Q k , …, Q n )’s gate is connected.

[0014] Furthermore, the control strategy unit includes the following:

[0015] When the current I1, ..., I k ,…,I n When one of the two conditions is met, the output is high level to turn on the switch (S), otherwise the output is low level to turn off the switch (S).

[0016] Furthermore, the two conditions include:

[0017] a.I k is less than the average current and I k The slope is positive;

[0018] B.I k is greater than the average current and I1,…,I k ,…,I n At least one of the slopes is negative.

[0019] Furthermore, when I k When the control strategy is not satisfied, it is a normal situation, indicating that Q k The turn-on and turn-off time of the switch S is ahead of the average value, and the output is low level to turn off the switch S. At this time, the equivalent gate resistance is R ga With R gb sum.

[0020] Furthermore, when I k When the control strategy is satisfied, it means Q k The turn-on and turn-off time lags behind the average value, and the output high level turns on the switch (S). At this time, the equivalent gate resistance is reduced to R gb , so I k The change of is accelerated, and finally the difference between it and the average current is reduced.

[0021] Technical effects and advantages of the present invention: Compared with the prior art, the present invention provides a parallel IGBT dynamic current sharing system based on gate resistance control, which has the following advantages:

[0022] 1. The present invention is mainly composed of multiple groups of parallel IGBTs, gate resistors, control strategy units, switches and other components. The parallel current sharing is achieved by reducing the gate resistance of the IGBT that is turned on and off later. Therefore, the switching frequency will not be reduced due to the slowing down of the transient current change of the IGBT, and this method of adjusting the switch is suitable for digital control systems. In addition, compared with the method of adjusting the delay of the driving signal, the method of changing the gate resistance is simpler and more convenient, and can achieve dynamic current sharing of multiple parallel IGBTs, ensure the safe and stable operation of the IGBT, reduce the transient current imbalance of the IGBT, and do not require complex delay circuits and control algorithms;

[0023] 2. By adjusting the gate resistance, the transient rate of change of the IGBT current can be changed to achieve the purpose of parallel current sharing;

[0024] 3. Divide the gate resistor into two parts, connect one part in parallel with a switch, and control the on and off of the switch to change the gate resistor size;

[0025] 4. Based on the current amplitude and change rate, determine whether the IGBT's turn-on and turn-off time is advanced or delayed, and then decide whether the switch is turned on or off. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The schematic diagram of the parallel IGBT dynamic current sharing system based on gate resistance control of the present invention;

[0027] Figure 2 is a schematic diagram of a test circuit based on a BUCK circuit in an embodiment of the present invention;

[0028] Figure 3 is a current waveform diagram of the instantaneous opening state when there is no current sharing in the embodiment of the present invention;

[0029] Figure 4 The current waveform of the instantaneous state after the method proposed in the embodiment of the present invention is applied and the driving voltage waveform of the switch S;

[0030] Figure 5 is a current waveform diagram of the shutdown transient state when there is no current sharing in an embodiment of the present invention;

[0031] Figure 6 The figure is a diagram of the current waveform of the turn-off transient state and the driving voltage waveform of the switch S after applying the proposed method in the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, but not all of the embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] The present invention provides a parallel IGBT dynamic current sharing system based on gate resistance control, the principle of which is as follows: Figure 1 As shown. Where n is the number of parallel IGBTs, Q k It is the kth IGBT, and the gate resistance is divided into R ga and Rgb Two parts, R ga In parallel with a switch S, I1,…,I k ,…,I n They are Q1,…,Q k , …, Q n The control strategy unit is connected to the switch S, R gb With multiple parallel IGBTs (Q1, ..., Q k , …, Q n ) is connected to the gate of

[0035] When I k When the control strategy is not satisfied, it is a normal situation, indicating that Q k The turn-on and turn-off time of the switch S is ahead of the average value, and the output low level turns off the switch S. At this time, the equivalent gate resistance is R ga With R gb When I k When the control strategy is satisfied, it means Q k The turn-on and turn-off time lags behind the average value, and the output high level turns on the switch S. At this time, the equivalent gate resistance is reduced to R gb (Here we assume that S is an ideal switch), so I k The change of is accelerated, and finally the difference between it and the average current is reduced.

[0036] The control strategy is as follows: When the current I1, ..., I k ,…,I n When one of the following two conditions is met, the output high level turns on the switch S, otherwise the output low level turns off the switch S:

[0037] a.I k is less than the average current and I k The slope is positive.

[0038] b.I k is greater than the average current and I1,…,I k ,…,I n At least one of the slopes is negative.

[0039] Obviously, the proposed solution realizes parallel current sharing by reducing the gate resistance of the IGBT that is turned on and off later, so the switching frequency will not be reduced due to slowing down the transient current change of the IGBT. Moreover, this method of adjusting the switch is suitable for digital control systems. In addition, compared with the method of adjusting the delay of the driving signal, the method of changing the gate resistance is simpler and more convenient.

[0040] The gate resistance is adjusted to change the transient rate of change of the IGBT current, thereby achieving the purpose of parallel current sharing. The gate resistance is divided into two parts, one of which is connected in parallel with a switch. The on and off of the switch is controlled to change the gate resistance. The current amplitude and change rate are used as the basis to determine whether the IGBT's turn-on and turn-off time is advanced or delayed, and then determine whether the switch is turned on or off.

[0041] Example 2

[0042] Figure 2 The schematic diagram of the test circuit based on the BUCK circuit of the present invention, Q1 and Q2 are two parallel IGBTs, wherein the driving signal of Q1 lags behind that of Q2 by 10ns, and the DC power supply voltage V dc The voltage is 400V, the filter capacitor C is 68μF, the filter inductor L is 680μH, D is a freewheeling diode, the load resistor R is 2Ω, the switching frequency of the IGBT is 20kHz, and the duty cycle is 50%. When there is no current sharing, the gate resistance of the IGBT is 15Ω; when the solution of the present invention is adopted, R ga 5Ω, R gb When there is no current sharing and the present invention is applied, the current waveforms of the turn-on transient state are as follows: Figure 3 and 4 As shown, the current waveforms of the turn-off transient are as follows: Figure 5 and 6 shown.

[0043] from Figure 3 It can be seen that since the driving signal of Q2 is ahead of Q1, its current rises first and there is a large gap with the current of Q1, which will affect the performance of Q2 and reduce the stability and reliability of the system. After applying the solution in the present invention, since the current of Q1 is less than the average value and its slope is positive at the turn-on transient, the first item in the control strategy is met, so the driving signal of its switch S is high, that is, the switch S is turned on, so that the equivalent gate resistance value of Q1 decreases, causing its current to rise faster, and the current gap with Q2 is reduced, and finally the function of parallel current sharing is realized, such as Figure 4 shown.

[0044] like Figure 5 As shown, in the shutdown transient state, Q2's current drops in advance due to the advance of the driving signal, causing Q1 to produce a current spike due to the excessive current. After applying the solution in the present invention, since the current of Q1 is greater than the average value and the current slope of Q2 is negative, the second item in the control strategy is satisfied, so its corresponding switch S is turned on, causing the equivalent gate resistance value to decrease, and its current is reduced compared to when there is no current sharing, thereby reducing the current imbalance, which is beneficial to the performance optimization of the IGBT and the safe and stable operation of the system. Figure 6 shown.

[0045] It can realize dynamic current sharing of multiple parallel IGBTs, ensure the safe and stable operation of IGBTs, reduce the transient current imbalance of IGBTs, and avoid reducing the switching frequency without the need for complex delay circuits and control algorithms. It is suitable for digital control systems.

[0046] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, a technician in this field can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A parallel IGBT dynamic current sharing system based on gate resistance control, characterized in that: include: Multiple parallel IGBTs (Q1, ..., Q k , …, Q n ); and the IGBT (Q1, ..., Q k , …, Q n ) connected to the gate resistor; and a control strategy unit connected to the gate resistor; and the current (I1, ..., I k ,…,I n ); The gate resistor includes R ga and R gb , the R ga and R gb connected in series, and the R ga A switch S is connected in parallel on the control strategy unit; the control strategy unit is connected to the switch S; The control strategy unit includes the following: When the current I1, ..., I k ,…,I n When one of the two conditions is met, the output is high level to turn on the switch S, otherwise the output is low level to turn off the switch S; The two conditions include: a.I k is less than the average current and I k The slope is positive; B.I k is greater than the average current and I1,…,I k ,…,I n At least one of the slopes is negative.

2. The parallel IGBT dynamic current sharing system based on gate resistance control according to claim 1, characterized in that: The R gb The plurality of IGBTs (Q1, ..., Q k , …, Q n )’s gate is connected.

3. The parallel IGBT dynamic current sharing system based on gate resistance control according to claim 2, characterized in that: When I k When the control strategy is not satisfied, it is a normal situation, indicating that Q k The turn-on and turn-off time of the switch S is ahead of the average value, and the output low level turns off the switch S. At this time, the equivalent gate resistance is R ga With R gb sum.

4. The parallel IGBT dynamic current sharing system based on gate resistance control according to claim 3 is characterized in that: When I k When the control strategy is satisfied, it means Q k The turn-on and turn-off time lags behind the average value, and the output high level turns on the switch S. At this time, the equivalent gate resistance is reduced to R gb , so I k The change of is accelerated, and finally the difference between it and the average current is reduced.

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