CN216598978U - Inner tube protection circuit of ANPC circuit, converter and inverter - Google Patents

Abstract

The utility model discloses an inner tube protection circuit, a converter and an inverter of an ANPC circuit. The inner tube protection circuit of the ANPC circuit comprises two groups of active clamp circuits, and the input of the two groups of active clamp circuits The terminals are respectively connected to the collectors of the two inner tubes, and the output terminals are respectively connected to the gates of the two inner tubes; they are respectively used when the voltage between the collectors and the emitters of the two inner tubes is greater than or equal to the overvoltage threshold It works to make the charge of the collector of the inner tube flow to the gate to delay the turn-off speed of the inner tube; it will be turned off when the voltage between the collector and the emitter of the inner tube is lower than the overvoltage threshold. On the basis of protecting the inner tube of the ANPC circuit from being damaged by overvoltage, the utility model maximizes the output capability of the switch tube and improves the product performance.

Description

Inner tube protection circuit, converter and inverter of ANPC circuit

technical field

The utility model relates to the technical field of power electronics, in particular to an inner tube protection circuit, a converter and an inverter of an ANPC circuit.

Background technique

The ANPC topology is an improved version based on the NPC topology. On the basis of the NPC-I structure, a switch is incorporated into each of the clamping diodes. By adjusting the switching mode to control the current flow path, the power device loss balance can be achieved, and the output power and converter efficiency can be improved.

The topology of the ANPC is shown in Figure 1, which respectively includes six IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor) switch tubes T1-T6 and diodes at both ends of the six switch tubes. There is a modulation method: the switching tubes T1, T4, T5, and T6 are high-frequency tubes, that is, they work at high-frequency (such as a few KHz to a dozen KHz) switching frequency; T2, T3 are power frequency tubes, that is Work in the working state of the power frequency (50Hz) switching frequency. This modulation method can control the mutual switching of each commutation circuit, make full use of the output current of each tube, and balance the loss and junction temperature.

Figure 2 and Figure 3 are the P-O and N-O commutation circuits of ANPC in this modulation mode. It can be seen from the figure that the commutation circuits are all inside the same half-bridge module, and the commutation circuits are small; but when the zero-point commutation is performed, as shown in Figure 4 As shown, the commutation loop exists between different modules, and the commutation loop is relatively large, and during zero-crossing commutation, the switching logic generally performs commutation through the switching of the inner tubes T2 and T3.

Through experimental measurement, when the small loop is commutated, the stray inductance is 45 to 70nH, and when the large loop is commutated, the stray inductance is 340 to 370nH. In the case of large miscellaneous inductance, when the turn-off speed of the IGBT is fast, a large instantaneous current peak will be generated. At this time, the voltage Vce between the collector and the emitter of the inner tubes T2 and T3 exceeds the withstand voltage of the IGBT. risk of damage to the inner tube.

At present, the common solution is to increase the resistance of the gate turn-off resistors of the two inner tubes to reduce the turn-off speed of the IGBT. However, when Vce is small, the turn-off resistance will still reduce the turn-off speed of the IGBT. It can be seen that this method brings unnecessary switching loss of the IGBT, which makes the switching loss of the IGBT switch tube larger.

Utility model content

The main purpose of the utility model is to provide an inner tube protection circuit, a converter and an inverter of an ANPC circuit, which aims to solve the problem that the switching loss of the switch tube is relatively large when the inner tube of the ANPC topology circuit is protected.

In order to achieve the above purpose, the present invention provides an inner tube protection circuit of an ANPC circuit, the ANPC circuit includes six switch tubes and six diodes, wherein each switch tube is inversely connected to a diode; A switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, the collector of the first switch tube is connected to the positive pole of the bus bar, and the emitter of the fourth switch tube is connected to the negative pole of the bus bar , the emitter of the first switch tube is connected to the collector of the second switch tube and the fifth switch, the collector of the fourth switch tube is connected to the emitter of the third switch tube and the sixth switch tube, the emitter of the fifth switch tube, The collectors of the sixth switch tube are all connected to the midpoint of the bus, the emitter of the second switch tube and the collector of the third switch tube are connected together to form a bridge arm end; the first switch tube, the fourth switch tube, the third switch tube Both the fifth switch tube and the sixth switch tube work in a working state where the switching frequency is a high frequency, and the second switch tube and the third switch tube work in a working state where the switching frequency is a power frequency;

The inner tube protection circuit of the ANPC circuit includes two groups of active clamp circuits,

Wherein, in a group of the active clamp circuits, the input end is connected to the collector of the second switch tube, and the output end is connected to the gate electrode of the second switch tube; It works when the voltage between the collector and the emitter is greater than or equal to the overvoltage threshold, so that the charge of the collector of the second switch tube flows to the gate, so as to delay the turn-off speed of the second switch tube; Turn off when the voltage between the collector and the emitter of the second switch tube is lower than the overvoltage threshold;

Another group of the active clamp circuits, the input end is connected to the collector of the third switch tube, and the output end is connected to the gate of the third switch tube; it is used when the collector of the third switch tube is working when the voltage between the electrode and the emitter is greater than or equal to the overvoltage threshold, so that the charge of the collector of the third switch tube flows to the gate, so as to delay the turn-off speed of the third switch tube; in the The third switch is turned off when the voltage between the collector and the emitter is lower than the overvoltage threshold.

Optionally, the active clamp circuit includes a clamp unit and an anti-backflow unit; the active clamp circuit includes a clamp unit and an anti-voltage backflow unit; the first end of the clamp unit is the input end of the active clamp circuit, the second end is connected to the first end of the anti-voltage back-feed unit, and the second end of the voltage back-feed unit is the output end of the active clamp circuit;

The clamping unit is configured to conduct when the voltage between the first end and the second end exceeds the overvoltage threshold, and clamp the voltage between the first end and the second end to a first safe voltage.

Optionally, the clamping unit includes a clamping device; the first end of the clamping device is the first end of the clamping unit, and the second end of the clamping device is the second end;

The anti-voltage backfill unit includes a diode; the anode of the diode is the first end of the voltage backfill unit, and the cathode of the diode is the second end of the voltage backfill unit.

Optionally, the clamping device is a TVS diode, a bidirectional TVS diode or a Zener tube.

Optionally, the inner tube protection circuit of the ANPC circuit further includes two drive units;

Wherein, the first end of a driving unit is connected with the gate of the second switch tube, and the second end is connected with the emitter of the second switch tube;

The first end of the other driving unit is connected to the gate of the third switch tube, and the second end is connected to the emitter of the third switch tube.

Optionally, the driving unit includes a resistor and a capacitor; the first end of the resistor is connected to the first end of the capacitor, and the second end of the resistor is connected to the second end of the capacitor; the first end of the resistor is connected The common terminal connected to the first terminal of the capacitor is the first terminal of the driving unit, and the common terminal connected to the second terminal of the resistor and the second terminal of the capacitor is the second terminal of the driving unit.

In addition, in order to achieve the above purpose, the present invention also provides a converter, which includes an ANPC circuit and an inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used when two of the ANPC circuits are protected. When both ends of the inner tube are over-voltage, the inner tube is protected respectively; the inner tube protection circuit of the ANPC circuit is configured as the inner tube protection circuit of the ANPC circuit described above.

In addition, in order to achieve the above purpose, the present invention also provides an inverter, which includes an ANPC circuit and an inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used when two of the ANPC circuits are protected. When both ends of the inner tube are over-voltage, the inner tube is protected respectively; the inner tube protection circuit of the ANPC circuit is configured as the inner tube protection circuit of the ANPC circuit as described above.

In the present invention, an active clamp circuit is respectively arranged between the collectors and gates of the two inner tubes of the ANPC circuit, namely the second switch tube and the third switch tube; Too fast, when the voltage Vce between the collector and the emitter reaches the overvoltage threshold, the active clamp circuit operates to re-inject the collector charge to the G level, so that the second switch is turned on again, thereby delaying the The turn-off speed of the second switch tube reduces the instantaneous current spike and reduces the voltage between the collector and the emitter; when Vce is reduced to less than the overvoltage threshold, the active clamp circuit resumes the blocking state, that is, it is turned off, The switch tube is turned off under the action of the turn-off level. Therefore, the active clamp circuit works when the inner tube of the ANPC circuit may be damaged due to too high Vce to protect the two switching tubes; it does not work when the Vce is small, which does not affect the turn-off speed of the switching tube and will not affect the switching tube. Therefore, the output capability of the switch tube is improved as much as possible, and the product performance is indirectly improved.

Description of drawings

In order to more clearly illustrate the embodiments of the present utility model or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are just some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained based on the structures shown in these drawings without any creative effort.

Fig. 1 is the topology structure schematic diagram of existing ANPC;

2 to 3 are schematic diagrams of the commutation circuits of P-O and N-O of the ANPC topology in FIG. 1;

Fig. 4 is the schematic diagram of the zero-point commutation loop of the ANPC topology in Fig. 1;

5 is a schematic block diagram of an embodiment of the inner tube protection circuit of the ANPC circuit of the present invention;

FIG. 6 is a schematic diagram of the circuit structure of the embodiment of FIG. 5 .

The realization, functional characteristics and advantages of the purpose of the present utility model will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Description of reference numbers:

label name label name 100 ANPC circuit T1～T6 The first switch tube to the sixth switch tube 10 Active Clamp Circuit Z1 clamp device 20 Clamping unit Z2 second clamping device twenty one Anti backfill unit Z3 third clamping device 30 Drive unit Z4 Fourth clamping device T2_C Collector of the second switch tube Z5 diode T2_E The emitter of the second switch tube C1 capacitance T2_G The gate of the second switch tube R1 resistance

Detailed ways

It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not intended to limit the present invention.

The technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, not all of them. Example. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the difference between the various components under a certain posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly.

In addition, the descriptions involving "first", "second", etc. in the present invention are only for description purposes, and should not be understood as indicating or implying their relative importance or implicitly indicating the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the realization by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist. , is not within the scope of protection required by the present utility model.

The utility model provides an inner tube protection circuit of an ANPC circuit. Referring to FIG. 5 , the ANPC circuit includes six switch tubes and six diodes, wherein each switch tube is inversely connected to a diode; the six switch tubes are the first The switch tube T1, the second switch tube T2, the third switch tube T3, the fourth switch tube T4, the fifth switch tube T5 and the sixth switch tube T6, the collector of the first switch tube T1 is connected to the positive pole of the bus bar DC+, and the fourth switch tube The emitter of the tube T4 is connected to the negative pole of the bus bar DC-, the emitter of the first switch tube T1 is connected to the collector of the second switch tube T2 and the fifth switch T5, and the collector of the fourth switch tube T4 is connected to the third switch tube T3, The emitter of the six switches T6, the emitter of the fifth switch T5, and the collector of the sixth switch T6 are all connected to the midpoint of the bus, and the emitter of the second switch T2 and the collector of the third switch T3 are connected The bridge arm terminal OUT is formed together; in one embodiment, the first switch tube T1, the fourth switch tube T4, the fifth switch tube T5 and the sixth switch tube T6 of the ANPC circuit all work at a high-frequency switching frequency. Working state, the second switch tube T2 and the third switch tube T3 work in a working state where the switching frequency is the power frequency;

The inner tube protection circuit of the ANPC circuit includes two groups of active clamp circuits,

Among them, a group of the active clamp circuits 10, the input end is connected to the collector of the second switch tube T2, and the output end is connected to the gate of the second switch tube T2; When the voltage between the collector and the emitter of the switch tube T2 is greater than or equal to the overvoltage threshold, it works, so that the charge of the collector of the second switch tube T2 flows to the gate, so as to delay the voltage of the second switch tube T2. turn-off speed; cut-off when the voltage between the collector and the emitter of the second switch tube T2 is lower than the overvoltage threshold;

Another group of the active clamp circuits 10, the input end is connected to the collector of the third switch tube T3, and the output end is connected to the gate of the third switch tube T3; used when the third switch tube T3 When the voltage between the collector and the emitter of the transistor T3 is greater than or equal to the overvoltage threshold, it works, so that the charge of the collector of the third switch transistor T3 flows to the gate, so as to delay the turn-off of the third switch transistor T3. Turn off speed; cut off when the voltage between the collector and the emitter of the third switch tube T3 is lower than the overvoltage threshold.

The above-mentioned overvoltage threshold can be set in combination with the actual circuit. For example, if the six switches of the ANPC circuit are IGBTs with a withstand voltage of 1200V, the overvoltage threshold of the active clamp circuit 10 can be set to 1060V.

It should be noted that the ANPC circuit of this circuit structure has two modulation modes, one of which is that the first switch tube T1, the fourth switch tube T4, the fifth switch tube T5 and the sixth switch tube T6 all work at a switching frequency of The working state of the power frequency, the second switch tube T2 and the third switch tube T3 work in the working state where the switching frequency is high frequency; when this modulation method is designed, the T1, T4, T5, T6 tubes can be The tube with low conduction loss is selected, while T2 and T3 use high-speed switching devices, such as MOS, SIC, etc.; however, the commutation loop of this topology is large, and the stray inductance of the loop is difficult to deal with when the half-bridge module is used to build the circuit. , so it is not suitable for high-power converters, and this scheme will not be discussed too much.

This embodiment is another modulation method. The first switch tube T1, the fourth switch tube T4, the fifth switch tube T5 and the sixth switch tube T6 all work in a working state where the switching frequency is high frequency, and the second switch tube The tube T2 and the third switch tube T3 work in a working state where the switching frequency is the power frequency. Among them, the high frequency can be changed according to the actual circuit, such as 3.2KHz ~ more than ten KHz. The above switch tubes can also be selected according to actual needs, for example, all of them are IGBTs. The IGBT will generate a certain voltage spike when it is turned off under normal conditions, but the value will not be too high. However, when the inner tube of the ANPC circuit is commutated at zero, and when the converter is overloaded or the bridge arm is short-circuited, the voltage spikes generated in these cases are very high, and the IGBT is at risk of being damaged.

The active clamp circuit 10 detects Vce, it does not work when it is normal, and works when it is too high, it can clamp the collector potential of the IGBT so that it does not reach a too high level, delay the turn-off of the IGBT, and limit the di/dt and Voltage spikes to avoid voltage spikes that are too high or too steep at turn-off, threatening the IGBT.

Specifically, when the turn-off speed of the second switch T2 is too fast, the voltage Vce between the collector and the emitter reaches the overvoltage threshold, and the active clamp circuit 10 connected to it operates to reduce the charge on the collector. Re-injecting the G level of the second switch tube T2 can make the second switch tube T2 turn on again, thereby delaying the turn-off speed of the second switch tube T2; when the Vce voltage decreases, the active clamp circuit 10 resumes blocking In the state, the G-level charge continues to be pulled away from the second switch tube T2 under the action of the off level, so that the second switch tube T2 is turned off. The principle of the third switch tube T3 is the same. When the turn-off speed of the third switch tube T3 is too fast, the voltage Vce between the collector and the emitter reaches the overvoltage threshold, and the active clamp circuit 10 connected to it operates. , the charge of the collector is re-injected into the G level of the third switch tube T3, which can make the third switch tube T3 turn on again, thereby delaying the turn-off speed of the third switch tube T3; when the Vce voltage decreases, the active clamp The bit circuit 10 is restored to the blocking state, and the G-level charge continues to be pulled away from the third switch tube T3 under the action of the off level, so that the third switch tube T3 is turned off.

In this solution, active clamp circuits are respectively set between the collectors and gates of the second switch tube T2 and the third switch tube T3; taking the second switch tube T2 as an example, when the turn-off speed is too fast, its collector and When the voltage Vce between the emitters reaches the overvoltage threshold, the active clamp circuit 10 operates to re-inject the collector charge to the G level, so that the second switch tube T2 is turned on again, thereby delaying the second switch tube T2 The turn-off speed reduces the instantaneous current spike and reduces the voltage between the collector and the emitter; when Vce is reduced to less than the overvoltage threshold, the active clamp circuit 10 returns to the blocking state, that is, it is turned off, and the switch is in the Shut down under the action of the shutdown level. Therefore, the active clamp circuit 10 works when the inner tube of the ANPC circuit may be damaged due to high Vce, and protects the switch tube; it does not work when the Vce is small, does not affect the turn-off speed of the switch tube, and will not affect the switch tube. Therefore, the output capability of the switch tube is improved as much as possible, the product performance is indirectly improved, the ability to protect the inner tube from overvoltage is improved, and the safety of the circuit is improved.

Further, referring to FIG. 6 , FIG. 6 takes the active clamp circuit 10 connected to the second switch tube T2 as an example. The active clamp circuit 10 includes a clamp unit 20 and an anti-voltage backflow unit 21 ; the The first end of the clamping unit 20 is the input end of the active clamping circuit 10 , the second end is connected to the first end of the anti-voltage backfill unit 21 , and the second end of the anti-voltage backfill unit 21 The terminal is the output terminal of the active clamp circuit 10;

The clamping unit 21 is used to conduct when the voltage between the first end and the second end exceeds the overvoltage threshold, and clamp the voltage between the first end and the second end at the first safe voltage .

The first end of the clamping unit 20 is connected to the collector C of the IGBT, and the second end is connected to the gate G of the IGBT through the anti-backflow unit 20; the value of the first safety voltage can be set according to the actual circuit, such as the first The safe voltage is the same value as the overvoltage threshold.

When the Vce of the switch tube reaches the overvoltage threshold, the clamping unit 20 works to clamp the Vce of the IGBT at the first safe voltage; when the Vce is lower than the overvoltage threshold, the clamping unit 20 stops working so as not to affect the IGBT's Vce normal work. By arranging the anti-backflow unit 20, when the IGBT is normally turned on, the clamping unit 20 can be prevented from being turned on under the action of the voltage of the gate electrode G, thereby pulling down the voltage of the gate electrode G.

Further, the structures of the clamping unit 20 and the anti-backflow unit 21 can be set according to actual needs. For example, the clamping unit 20 includes a clamping device Z1; the first end of the clamping device Z1 is the clamping device Z1. The first end of the unit 20, the second end of the clamping device Z1 is the second end of the clamping unit 20; the anti-voltage backflow unit 21 includes a diode Z5; the anode of the diode Z5 is the The first end of the anti-voltage backfill unit 21 , and the cathode of the diode Z5 is the second end of the voltage backfill unit 21 .

It should be noted that the clamping device Z1 may be a single device, or may be formed by connecting multiple devices in series. For example, the clamping device Z1 can also be connected in series with the second clamping device Z2, the third clamping device Z3 and the fourth clamping device Z4. The diode Z5 may be a common diode, a Zener diode or a bidirectional transient voltage suppression diode, which is not limited herein.

Further, the clamping device Z1 is a transient voltage suppression diode TVS, a bidirectional transient voltage suppression diode or a Zener tube. When the clamping device Z1 is a transient voltage suppression diode TVS or a Zener tube, the cathode of the transient voltage suppression diode TVS or the Zener tube is the first end of the clamping device Z1, and the anode is the first terminal of the clamping device Z1. two ends.

Based on the above hardware structure, the working process of the inner tube protection circuit of the ANPC circuit can be as follows:

When the IGBT turn-off speed is too fast, when the Vce voltage reaches the threshold of the clamping device Z1, the clamping device Z1 acts to re-inject the charge into the G-level of the IGBT to delay the IGBT turn-off speed; when the Vce voltage decreases, the clamping device The device Z1 returns to the blocking state, and the G-level charge continues to pull away from the IGBT under the action of the off level, thereby turning off the IGBT;

When the IGBT is normally turned on, the diode Z5 is in a blocking state.

To sum up, based on the above hardware structure, although in engineering applications, the stray inductance of the loop must exist; the overvoltage of Vce generally occurs when the output power is large. Therefore, when the output current does not reach the threshold value of the clamping device Z1, the turn-off of the IGBT is independent of the clamping device Z1. When the output current is large and the stress of Vce reaches the active clamping threshold, the clamping device Z1 will work again.

This method and the method of increasing the turn-off resistance are both to delay the turn-off of the IGBT, but increasing the turn-off resistance will work every time the IGBT operates, and increasing the active clamp clamp circuit protection is only in the Vce It will only act when there is a real overvoltage, and it will not work when the output power is low. Therefore, in this scheme, an active clamp circuit is added to the inner tube (T2, T3) of the three-level ANPC to ensure that the Vce of the IGBT is within a safe range, and on the basis of protecting the inner tube of the ANPC circuit from being damaged by overvoltage The output capability of the switch tube has been improved as much as possible, and the product performance has been improved.

Further, the inner tube protection circuit further includes two drive units 30;

Wherein, the first end of a driving unit 30 is connected to the gate of the second switch tube T2, and the second end is connected to the emitter of the second switch tube T2;

The first end of the other driving unit 30 is connected to the gate electrode of the third switch transistor T3 (not shown), and the second end is connected to the emitter electrode of the third switch transistor T3. The two driving units are IGBT driving circuits, which enhance the switching capability of the second switch tube T2 and the third switch tube T3.

Further, the driving unit 30 includes a resistor R1 and a capacitor C1; the first end of the resistor R1 is connected to the first end of the capacitor C1, and the second end of the resistor R1 is connected to the second end of the capacitor C1; The common terminal connected to the first terminal of the resistor R1 and the first terminal of the capacitor C1 is the first terminal of the driving unit 30, and the common terminal connected to the second terminal of the resistor R1 and the second terminal of the capacitor C1 is the first terminal of the driving unit 30. the second end of the drive unit 30 . It should be noted that the selection of the resistor R1 and the capacitor C1 does not need to be limited, and those skilled in the art can refer to common techniques in the art for setting, and only need to implement the above-mentioned corresponding functions.

The utility model also provides a converter, which includes an ANPC circuit and an inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used when the two inner tubes of the ANPC circuit are two When the terminal is over-voltage, the inner tubes are respectively protected; the structure of the inner tube protection circuit of the ANPC circuit can refer to the above-mentioned embodiments, and details are not repeated here. Naturally, since the converter of this embodiment adopts the technical solution of the inner tube protection circuit of the ANPC circuit, the converter has all the beneficial effects of the inner tube protection circuit of the ANPC circuit.

The utility model also provides an inverter, the inverter ANPC circuit and the inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used when the two ends of the two inner tubes of the ANPC circuit are In case of overvoltage, the inner tubes are respectively protected; the structure of the inner tube protection circuit of the ANPC circuit can refer to the above-mentioned embodiments, and details are not repeated here. Naturally, since the inverter of this embodiment adopts the technical solution of the inner tube protection circuit of the ANPC circuit, the inverter has all the beneficial effects of the inner tube protection circuit of the ANPC circuit.

The above are only optional embodiments of the present utility model, which are not intended to limit the scope of the present utility model patent. Any equivalent structure or equivalent process transformation made by using the contents of the present utility model description and accompanying drawings, or directly or indirectly applied to other Relevant technical fields are similarly included in the scope of patent protection of the present invention.

Claims (8)

1. An inner tube protection circuit of an ANPC circuit, the ANPC circuit comprises six switch tubes and six diodes, wherein each switch tube is reversed with a diode; The second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the sixth switch tube, the collector of the first switch tube is connected to the positive pole of the bus bar, the emitter of the fourth switch tube is connected to the negative pole of the bus bar, and the first switch tube The emitter of the second switch is connected to the collector of the fifth switch, the collector of the fourth switch is connected to the emitter of the third switch and the sixth switch, the emitter of the fifth switch and the sixth switch are The collectors are all connected to the midpoint of the bus, the emitter of the second switch tube and the collector of the third switch tube are connected together to form a bridge arm end; it is characterized in that the first switch tube, the fourth switch tube, the fifth switch tube Both the switch tube and the sixth switch tube work in a working state where the switching frequency is a high frequency, and the second switch tube and the third switch tube work in a working state where the switching frequency is a power frequency; The inner tube protection circuit of the ANPC circuit includes two groups of active clamp circuits, Wherein, in a group of the active clamp circuits, the input end is connected to the collector of the second switch tube, and the output end is connected to the gate electrode of the second switch tube; It works when the voltage between the collector and the emitter is greater than or equal to the overvoltage threshold, so that the charge of the collector of the second switch tube flows to the gate, so as to delay the turn-off speed of the second switch tube; Turn off when the voltage between the collector and the emitter of the second switch tube is lower than the overvoltage threshold; Another group of the active clamp circuits, the input end is connected to the collector of the third switch tube, and the output end is connected to the gate of the third switch tube; it is used when the collector of the third switch tube is working when the voltage between the electrode and the emitter is greater than or equal to the overvoltage threshold, so that the charge of the collector of the third switch tube flows to the gate, so as to delay the turn-off speed of the third switch tube; in the The third switch is turned off when the voltage between the collector and the emitter is lower than the overvoltage threshold. 2. The inner tube protection circuit of the ANPC circuit according to claim 1, wherein the active clamping circuit comprises a clamping unit and an anti-voltage backflow unit; the first end of the clamping unit is a the input end of the active clamp circuit, the second end is connected to the first end of the anti-voltage back-feed unit, and the second end of the voltage back-feed unit is the output end of the active clamp circuit; The clamping unit is configured to conduct when the voltage between the first end and the second end exceeds the overvoltage threshold, and clamp the voltage between the first end and the second end to a first safe voltage. 3 . The inner tube protection circuit of the ANPC circuit according to claim 2 , wherein the clamping unit comprises a clamping device; the first end of the clamping device is the first end of the clamping unit. 4 . , the second end of the clamping device is the second end of the clamping unit; The anti-voltage backfill unit includes a diode; the anode of the diode is the first end of the voltage backfill unit, and the cathode of the diode is the second end of the voltage backfill unit. 4 . The inner tube protection circuit of the ANPC circuit according to claim 3 , wherein the clamping device is a transient voltage suppression diode, a bidirectional transient voltage suppression diode or a Zener tube. 5 . 5. The inner tube protection circuit of the ANPC circuit according to any one of claims 1-4, wherein the inner tube protection circuit of the ANPC circuit further comprises two drive units; Wherein, the first end of a driving unit is connected with the gate of the second switch tube, and the second end is connected with the emitter of the second switch tube; The first end of the other driving unit is connected to the gate of the third switch tube, and the second end is connected to the emitter of the third switch tube. 6 . The inner tube protection circuit of the ANPC circuit according to claim 5 , wherein the driving unit comprises a resistor and a capacitor; the first end of the resistor is connected to the first end of the capacitor, and the first end of the resistor is connected to the first end of the capacitor. 7 . The two ends are connected to the second end of the capacitor; the common end connected to the first end of the resistor and the first end of the capacitor is the first end of the driving unit, and the second end of the resistor and the second end of the capacitor The connected common terminal is the second terminal of the driving unit. 7. A converter, characterized in that it comprises an ANPC circuit and an inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used when the two ends of the two inner tubes of the ANPC circuit are overvoltage When the inner tube is protected, the inner tube protection circuit of the ANPC circuit is configured as the inner tube protection circuit of the ANPC circuit according to any one of claims 1-6. 8. An inverter, characterized in that it comprises an ANPC circuit and an inner tube protection circuit of the ANPC circuit; the inner tube protection circuit of the ANPC circuit is used for overvoltage at both ends of the two inner tubes of the ANPC circuit When the inner tube is protected, the inner tube protection circuit of the ANPC circuit is configured as the inner tube protection circuit of the ANPC circuit according to any one of claims 1-6.

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