IGBT overvoltage protection circuit and overvoltage protection method

Abstract

The invention discloses an IGBT (Insulated Gate Bipolar Translator) overvoltage protection circuit and an overvoltage protection method, and mainly solves the technical problems that the existing IGBT overvoltage protection cannot realize effective clamping protection and has a relatively large device failure risk. The overvoltage protection circuit comprises a control unit, an active clamping unit and a sampling unit, wherein the active clamping unit is correspondingly connected between a collector electrode and a grid electrode of the IGBT; the sampling unit is electrically connected between the active clamping unit and the control unit and is used for correspondingly sampling clamping voltage; the conduction unit, the normal turn-off unit and the soft turn-off unit are connected in parallel between the control unit and the IGBT grid electrode and are correspondingly controlled by the control unit to be conducted or turned off according to the sampling data of the sampling unit. The corresponding overvoltage protection method is high in anti-interference capability, high in reliability and high in response speed, and the overvoltage protection effect of the IGBT can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly relates to an IGBT overvoltage protection circuit and an overvoltage protection method. Background Art

[0002] The semiconductor device insulated gate bipolar transistor (IGBT) has characteristics such as high efficiency and energy saving, high reliability, and easy control, and is widely used in the field of power electronics, especially in application scenarios that require high voltage and large current, such as frequency converters, electric vehicle drive systems, and solar inverters.

[0003] The IGBT has three electrodes: the gate (G), the collector (C), and the emitter (E). It internally contains a MOSFET (metal oxide semiconductor field effect transistor) and a PNP bipolar transistor, which are connected through a specific circuit. This structure enables the IGBT to have both the high input impedance and high-speed switching characteristics of the MOSFET and the high current density and low on-state voltage drop characteristics of the BJT.

[0004] The IGBT can be regarded as a switch controlled by the gate voltage. Its turn-on and turn-off protection are crucial. In an actual circuit, there is significant stray inductance in the main circuit from the capacitor side to the IGBT module. The stray inductance refers to the equivalent inductance presented by conductors in the circuit (such as connecting wires, component leads, component bodies, etc.). At this time, the voltage between the collector and emitter of the IGBT is V ce =U dc +L s *dI c / dt , where L s is the stray inductance, U dc is the capacitor voltage, I c is the collector current. When the IGBT turns off, the collector current drops rapidly, and an overshoot electromotive force U ov = L s *dI c / dt will be generated on the stray inductance, resulting in a large surge voltage between the collector and emitter of the IGBT and may exceed the rated voltage of the IGBT, posing a risk of device damage to the IGBT.

[0005] However, since the stray inductance is generated by the power device layout and the connection structure loop, it can only be reduced but not eliminated. Therefore, when the IGBT is turned off, there must be a turn-off spike voltage during the current drop process, which may cause overvoltage damage to the IGBT.

[0006] In order to effectively control the IGBT during the turn-off process dI c / dt and reduce the reverse voltage impact caused by the stray inductance of the DC bus, the inventor is aware of a method of an active clamping protection circuit and method. See Figure 1 , which utilizes the V generated when the IGBT is turned off ce overvoltage to break down the TVS tube D z . The TVS clamping voltage is lower than the IGBT tolerance voltage, and the TVS current is fed back to the control gate, raising the gate voltage, thereby slowing down the gate voltage drop and controlling the IGBT turn-off process dI c / dt is reduced, thereby realizing the suppression of the IGBT device turn-off overvoltage.

[0007] However, during the process of implementing the technical solution in the embodiment of the present application, the inventor of the present application found that when the TVS clamping action occurs in the existing active clamping protection circuit, the V ce voltage is approximately the TVS clamping voltage, and the TVS current I z flows into the gate through the TVS. Since a relatively small turn-off resistor R is usually selected during normal turn-off g to reduce the turn-off loss, the I ee current flowing to the V out terminal is large during turn-off, consuming most of the TVS current, thereby slowing down the rise of the gate voltage dI c / dt and resulting in a worse effect. As a result, the TVS flows through a larger breakdown current and operates in the deep saturation region. See Figure 2 . As the breakdown current increases, the breakdown clamping voltage also increases accordingly, so effective clamping protection cannot be achieved; in addition, the transient power consumption of the TVS tube is very large, and there is a great risk of failure.

[0008] The information disclosed in this background art section is only used to deepen the understanding of the background art of the present disclosure, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0009] In view of at least one of the above technical problems, the present disclosure provides an IGBT overvoltage protection circuit and an overvoltage protection method, mainly solving the technical problems that the existing IGBT overvoltage protection cannot achieve effective clamping protection and there is a great risk of device failure.

[0010] According to one aspect of the present disclosure, an IGBT overvoltage protection circuit is provided, which includes a control unit, an active clamping unit correspondingly connected between the collector and the gate of the IGBT, a sampling unit electrically connected between the active clamping unit and the control unit for correspondingly sampling the clamping voltage, a conduction unit, a normal turn-off unit, and a soft turn-off unit connected in parallel between the control unit and the IGBT gate and controlled to conduct or turn off correspondingly by the control unit according to the sampling data of the sampling unit.

[0011] In some embodiments of the present disclosure, the control unit is a programmable logic device FPGA or CPLD.

[0012] In some embodiments of the present disclosure, the active clamping unit includes at least one transient voltage suppression device TVS, and the clamping voltage of the active clamping unit is less than the withstand voltage of the IGBT.

[0013] In some embodiments of the present disclosure, the sampling unit includes a sampling resistor for correspondingly converting the clamping breakdown current of the active clamping unit into a corresponding sampling voltage, and a voltage dividing module for correspondingly dividing the sampling voltage and introducing it into the control unit.

[0014] In some embodiments of the present disclosure, the conduction unit, the normal turn-off unit, and the soft turn-off unit respectively include a MOS tube driving resistor, a MOS tube, and an action resistor connected in series in sequence, and the resistance value of the action resistor of the normal turn-off unit is less than the resistance value of the action resistor of the soft turn-off unit.

[0015] According to another aspect of the present disclosure, an IGBT overvoltage protection method is provided, which is implemented based on the above IGBT overvoltage protection circuit; during the turn-off process of the IGBT, when the voltage input to the control unit after voltage division by the sampling unit is higher than the action voltage of the control unit, the control unit correspondingly turns off the turn-off unit and turns on the soft turn-off unit, until the clamping current of the active clamping unit subsides and the voltage input to the control unit after voltage division by the sampling unit is lower than the action voltage of the control unit, the control unit correspondingly turns off the soft turn-off unit and turns on the turn-off unit.

[0016] In some embodiments of the present disclosure, the action voltage of the control unit is set to 1.5V.

[0017] One or more technical solutions provided in the embodiments of the present disclosure have at least the following technical effects or advantages: The detection of the clamping action current is achieved through a sampling unit, and the sampling unit is configured according to the actual action threshold voltage. By conducting and turning off different corresponding stages, based on the detection signal of the control unit, the on / off of the conduction unit, the normal turn-off unit, and the soft turn-off unit is correspondingly controlled, which can effectively suppress the overshoot voltage between the collector and emitter of the IGBT, slow down the turn-off process of the IGBT, and the corresponding overvoltage protection method has strong anti-interference ability, high reliability, and fast response speed, which can significantly improve the overvoltage protection effect of the IGBT. Description of the Drawings

[0018] Figure 1 This is the circuit schematic diagram of the existing active clamping protection circuit in the background technology of this application.

[0019] Figure 2 This is the working characteristic curve diagram of the TVS in the existing active clamping protection circuit in the background technology of this application.

[0020] Figure 3 This is the principle block diagram of the IGBT overvoltage protection circuit in an embodiment of this application.

[0021] Figure 4 This is the circuit schematic diagram of the IGBT overvoltage protection circuit in an embodiment of this application.

[0022] Figure 5 This is the working characteristic curve diagram of the IGBT in an embodiment of this application. Detailed Embodiments

[0023] The programs involved or relied on in the following embodiments are all conventional programs or simple programs in this technical field, and those skilled in the art can make conventional selections or adaptive adjustments according to specific application scenarios.

[0024] The devices and the like involved in the following embodiments are all conventional commercially available products without special instructions.

[0025] In order to better understand the technical solution of the present invention, the above technical solution will be described in detail below in conjunction with the specification drawings and specific embodiments.

[0026] To solve the technical problems of the existing IGBT overvoltage active clamping protection that when the IGBT is turned off, the TVS works in the deep saturation region due to the large breakdown current flowing through it, resulting in an increase in the breakdown clamping voltage, which cannot effectively clamp and protect the IGBT, and due to the large transient power consumption of the TVS tube, there is a large risk of device failure, this example discloses an IGBT overvoltage protection circuit. Taking an IGBT tube with a withstand voltage of 4500V as an example, see Figure 3, which includes a control unit, an active clamping unit correspondingly connected between the collector C and the gate G of the IGBT, a sampling unit electrically connected between the active clamping unit and the control unit for correspondingly sampling the clamping voltage, a conduction unit, a normal turn-off unit, and a soft turn-off unit connected in parallel between the control unit and the IGBT gate.

[0027] Specifically, the active clamping unit is connected between the collector and the gate of the IGBT. When the collector potential is too high, the voltage is clamped to a value lower than the withstand voltage of the IGBT, and part of the current enters the IGBT gate, causing the gate potential to rise accordingly, thereby avoiding an overly steep turn-off current and achieving the purpose of reducing the voltage spike. Specifically, in this embodiment, refer to Figure 4 , the active clamping unit includes a transient voltage suppression device TVS tube and an anti-reverse diode D1 connected in series. At least one transient voltage suppression device TVS tube is provided to achieve voltage clamping, and it is necessary to ensure that the clamping voltage is less than the withstand voltage of the IGBT. In this example, a total of 11 TVS tubes are connected in series, including 10 TVS tubes with a voltage of 350V and 1 TVS tube with a voltage of 300V. After being connected in series in this way, the clamping voltage of the TVS tube group can reach 3800V. When the IGBT is turned off and the collector voltage of the IGBT is too high, the TVS tube group is broken down and clamped to 3800V, which is less than the withstand voltage of 4500V of the IGBT to be protected. Additionally, in this embodiment, the anti-reverse diode D1 correspondingly connected in series in the active clamping unit is used to prevent the gate voltage from flowing back into the subsequent sampling unit.

[0028] The sampling unit collects the voltage and correspondingly transmits it to the control unit to be used as the basis for judging the turn-off process. In this embodiment, refer to Figure 4 , the sampling unit includes a sampling resistor R p and a voltage division module. The sampling resistor R p is connected in series with the TVS tube. Among them, the line ACL_IN between the two is the test point, which is connected to the voltage division module through a high-speed switching diode D2. The voltage division module includes a voltage division resistor R1 and R2 connected in series. In this example, the resistance value of R1 is 2KΩ, and the resistance value of R2 is 2KΩ; after the voltage division of the voltage division module, a signal line is correspondingly led out at the test point of the input pin of the control unit corresponding to ACL_ERR and electrically connected to the input terminal of the control unit. Among them, in this example, an input protection diode D3 is correspondingly connected at the led-out signal line, so that when the voltage is greater than 3.3V, the branch where the input protection diode D3 is located conducts, thereby ensuring the input safety of the control unit and avoiding damage to the control unit due to excessive input voltage.

[0029] Specifically, when a clamping action occurs, that is, after the TVS tube is broken down and the voltage is clamped to a value lower than the IGBT withstand voltage, the clamping current flows into the sampling unit and into the gate of the IGBT through the branch where the anti-reverse diode D1 is located, thereby raising the gate potential. A part of the clamping current Iz flowing into the sampling unit generates a voltage drop across the sampling resistor, and then is divided by the voltage dividing resistors R1 and R2 in the voltage dividing module and input into the control unit.

[0030] The control unit includes a programmable chip. In this embodiment, the programmable chip specifically uses a complex programmable logic device (CPLD). In some other embodiments, the programmable chip uses a field-programmable gate array (FPGA). In addition, the corresponding output pins of the control unit are respectively electrically connected to a conduction unit, a normal turn-off unit, and a soft turn-off unit. Specifically, the control unit determines whether the ACL_ERR voltage is higher than its preset action voltage by detecting the voltage of the pin ACL_ERR corresponding to the sampling unit input to the CPLD, and then outputs corresponding control instructions according to the IGBT conduction or turn-off process to control the conduction or turn-off of the corresponding units in the conduction unit, the normal turn-off unit, and the soft turn-off unit connected in parallel downstream, so as to reduce the dI c / dt turn-off slope during IGBT turn-off and protect the IGBT from being damaged by overshoot voltage caused by stray inductance during the turn-off process.

[0031] The conduction unit, the normal turn-off unit, and the soft turn-off unit each include a MOS tube drive circuit. Specifically, refer to Figure 4 , the conduction unit includes a PMOS tube drive resistor R3, a PMOS tube Q1, and a conduction action resistor R connected in series in sequence ON1 ; the normal turn-off unit includes an NMOS tube drive resistor R4, an NMOS tube Q2, and a conduction action resistor R connected in series in sequence OFF1 ; the soft turn-off unit includes an NMOS tube drive resistor R5, an NMOS tube Q3, and a conduction action resistor R connected in series in sequence OFF2 . Among them, the resistance value of the conduction action resistor of the normal turn-off unit is smaller than the resistance value of the action resistor of the soft turn-off unit, that is, the soft turn-off unit uses an action resistor with a larger resistance value, so that the turn-off current can be switched to a smaller soft turn-off current, and then most of the breakdown current of the TVS tube acts on the voltage rise of the gate, achieving the purpose of reducing the dI c / dt turn-off slope during IGBT turn-off.

[0032] In addition, this example also discloses an IGBT overvoltage protection method, which is implemented based on the above-mentioned IGBT overvoltage protection circuit. Specifically, in this embodiment, the operating voltage of the programmable chip CPLD in the control unit is set to 1.5V. When the IGBT is conducting normally, the voltage in the circuit does not reach the breakdown threshold of the TVS diode in the active clamping unit, and the TVS diode presents a high impedance state at this time, and the current I Z is zero. Further, after being divided by the voltage-dividing resistors R1 and R2, the voltage at ACL_ERR is zero, which is much lower than the operating voltage of the CPLD. Therefore, the corresponding pin of the CPLD detects a low level, and through logical judgment, it is determined that there is no need for the soft turn-off circuit to intervene. At this time, the conducting unit is turned on, and the normal turn-off unit and the soft turn-off unit are turned off.

[0033] During the turn-off process of the IGBT, the voltage in the circuit reaches the breakdown threshold of 3800V of the TVS diode in the active clamping unit. At this time, the TVS diode is broken down and conducts, and the breakdown current I Z is input to the sampling unit and sampled by the sampling resistor R p and its current is about 30mA. The voltage at ACL_IN is about 2.4V, and after being divided by the corresponding voltage-dividing resistors R1 and R2, the voltage at ACL_ERR is about 1.5V, which is exactly the operating voltage threshold value of 1.5V of the programmable chip CPLD in the control unit. At this time, the pin of the programmable chip CPLD detects a high level, the NMOS transistor Q2 of the normal turn-off unit is correspondingly turned off, and the NMOS transistor Q3 in the soft turn-off unit is driven to conduct, so that the turn-off current is switched to a smaller soft turn-off current. As a result, most of the TVS current acts on the gate voltage rise of the IGBT, reducing dI c / dt the turn-off slope and controlling the voltage Vce between the collector and emitter of the IGBT to be basically close to the operating threshold of the TVS of 3800V. After the decline is completed, as the TVS clamping current subsides, when the detection voltage of the detection pin of the control unit corresponding to ACL_ERR is lower than the preset operating voltage threshold of the CPLD, the CPLD switches to the normal turn-off process, and uses the smaller operating resistance in the normal turn-off unit compared to the soft turn-off unit to reduce the turn-off loss.

[0034] To verify the effectiveness of the IGBT overvoltage protection circuit and the overvoltage protection method disclosed in the present invention, this example conducts experiments based on the above-mentioned IGBT overvoltage protection circuit. The experimental result curve is shown in Figure 5 . The CH1 curve in the figure represents the IGBT gate voltage V GE , the CH2 curve represents the IGBT collector current I C , the CH3 curve represents the voltage V CE between the collector and emitter of the IGBT. It can be seen that when the IGBT collector current I CDuring the descending process, due to the clamping effect of the active clamping unit, V CE The overshoot voltage is suppressed. The suppressed overshoot voltage is 320V higher than the wiring voltage, and the maximum is 3922V, which is lower than the withstand voltage of the device, 4500V. This can ensure the safety of the device and achieve the effect of overvoltage protection.

[0035] Although some preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0036] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of its inventive concept. Thus, if these modifications and variations to the present disclosure fall within the scope of the claims of this application and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. An IGBT overvoltage protection circuit, characterized in that, It includes a control unit, an active clamping unit correspondingly connected between the collector and the gate of the IGBT, a sampling unit electrically connected between the active clamping unit and the control unit for correspondingly sampling the clamping voltage, a conduction unit connected in parallel between the control unit and the IGBT gate and controlled to conduct or turn off by the control unit according to the sampling data sampled by the sampling unit, a normal turn-off unit, and a soft turn-off unit.

2. The IGBT overvoltage protection circuit according to claim 1, wherein, The control unit is a programmable logic device FPGA or CPLD.

3. The IGBT overvoltage protection circuit according to claim 1, characterized in that, The active clamping unit includes at least one transient voltage suppression device TVS, and the clamping voltage of the active clamping unit is less than the withstand voltage of the IGBT.

4. The IGBT overvoltage protection circuit according to claim 1 or 3, characterized in that The sampling unit includes a sampling resistor for correspondingly converting the clamping breakdown current of the active clamping unit into a corresponding sampling voltage, and a voltage division module for correspondingly dividing the sampling voltage and introducing it into the control unit.

5. The IGBT overvoltage protection circuit according to claim 1, wherein The conduction unit, the normal turn-off unit, and the soft turn-off unit respectively include a MOS transistor driving resistor, a MOS transistor, and an action resistor connected in series in sequence, and the resistance value of the action resistor of the normal turn-off unit is less than the resistance value of the action resistor of the soft turn-off unit.

6. An IGBT overvoltage protection method, characterized in that, It is implemented based on the IGBT overvoltage protection circuit described in claim 1; during the turn-off process of the IGBT, when the voltage input to the control unit after voltage division by the sampling unit is higher than the action voltage of the control unit, the control unit correspondingly turns off the turn-off unit and turns on the soft turn-off unit. After the clamping current of the active clamping unit subsides and the voltage input to the control unit after voltage division by the sampling unit is lower than the action voltage of the control unit, the control unit correspondingly turns off the soft turn-off unit and turns on the turn-off unit.

7. The IGBT overvoltage protection method according to claim 6, characterized in that, Set the action voltage of the control unit to 1.5V.

Images