An IGBT overcurrent protection circuit and protection method for photovoltaic inverter

Abstract

The present invention discloses an IGBT overcurrent protection circuit and protection method for a photovoltaic inverter, comprising a voltage sampling circuit, a sampling conditioning circuit and an overcurrent threshold acquisition circuit, wherein the output end of the voltage sampling circuit is connected to the input end of the sampling conditioning circuit, the output end of the sampling conditioning circuit is connected to the input end of the overcurrent threshold acquisition circuit, and the overcurrent threshold acquisition circuit outputs a maximum voltage threshold and a minimum voltage threshold. The present invention has a simple structure, comprising a voltage sampling circuit, a sampling voltage conditioning circuit and an overcurrent threshold acquisition circuit. The voltage threshold output by the sampling voltage conditioning circuit is determined by the voltage sampling circuit, and the upper and lower current thresholds output by the overcurrent threshold acquisition circuit are determined by the sampling voltage conditioning circuit, so as to achieve the purpose of obtaining the corresponding IGBT overcurrent threshold according to different DC bus voltages, so as to protect the IGBT in time.

Description

Technical Field

[0001] The present invention relates to the application field of IGBT technology, and in particular to an IGBT overcurrent protection circuit and a protection method applied to a photovoltaic grid-connected inverter. Background Art

[0002] Power semiconductor devices have made great progress since the last century. IGBT integrates high-voltage and high-current thyristor manufacturing technology and large-scale integrated circuit micro-machining technology, showing good comprehensive performance and strong vitality in the high-power field. Compared with other power electronic devices, IGBT has the characteristics of high reliability, simple driving, easy protection, voltage-type driving, low driving power, low saturation voltage drop, and high voltage and high current resistance. It has been widely used in various traditional and emerging fields such as automotive electronics, consumer electronics, rail transportation, power field, new energy, etc.

[0003] IGBTs work in a harsh environment of high voltage and high current, and often fail and get damaged due to various reasons. The types of failure and damage mainly include: overheating damage, damage caused by locking effect due to exceeding the shutdown safe working area, and IGBT breakdown caused by overvoltage. Almost all damages are related to excessive collector current Ic. Therefore, in order to ensure the smooth, normal and intelligent operation of the entire system, real-time monitoring of IGBT current is very important. In the field of photovoltaic grid-connected inverters, using current sensors to detect AC bus current is a common detection method. If current abnormality occurs, a fault signal is issued and relevant processing is performed.

[0004] However, the safe operating area of ​​IGBT is not fixed under high voltage and high current conditions. Figure 1 As shown in the figure, when the IGBT is subjected to a high voltage, the current value it can withstand needs to be reduced. If the overcurrent threshold of the IGBT under the high voltage is not adjusted in time, the IGBT will inevitably be damaged by overcurrent. Therefore, it is very important to obtain an IGBT overcurrent protection circuit and protection method for photovoltaic inverters to solve the problem that the IGBT overcurrent threshold cannot be adjusted in time with the change of the DC bus voltage in the prior art. Summary of the invention

[0005] To solve the above technical problems, on the one hand, the present invention provides an IGBT overcurrent protection circuit for a photovoltaic inverter, comprising a voltage sampling circuit, a sampling and conditioning circuit and an overcurrent threshold acquisition circuit, wherein the output end of the voltage sampling circuit is connected to the input end of the sampling and conditioning circuit, the output end of the sampling and conditioning circuit is connected to the input end of the overcurrent threshold acquisition circuit, and the overcurrent threshold acquisition circuit outputs a maximum voltage threshold and a minimum voltage threshold.

[0006] The voltage sampling circuit includes a first operational amplifier unit U1, the in-phase input terminal of the first operational amplifier unit U1 is connected to the positive pole of the DC bus voltage through at least one connecting resistor, the in-phase input terminal of the first operational amplifier unit U1 is connected to the negative pole of the DC bus voltage after being connected in series with the first inductor L1 through the tenth resistor R10, the output terminal of the first operational amplifier unit U1 is connected to the inverting input terminal of the first operational amplifier unit U1, and the tenth resistor R10 is connected in parallel with the first capacitor C1. The connecting resistors include a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9 connected in series.

[0007] The output voltage V of the voltage sampling circuit dect =R10*(Vbus + -Vbus - ) / (R1+R2+R3+R4+R5+R6+R7+R8+R9+R10).

[0008] The sampling and conditioning circuit includes a third operational amplifier unit U3, the inverting input terminal of the third operational amplifier unit U3 is connected to the output terminal of the voltage sampling circuit through an eleventh resistor R11, the output terminal of the third operational amplifier unit U3 is connected to its inverting input terminal through a twelfth resistor R12, the twelfth resistor R12 is connected in parallel with a fourth capacitor, the non-inverting input terminal of the third operational amplifier unit U3 is grounded through a third capacitor C3, the non-inverting input terminal of the third operational amplifier unit U3 is connected to a 1 / 2 reference voltage source Vcc through a thirteenth resistor R13, and the non-inverting input terminal of the third operational amplifier unit U3 is connected to the reference voltage source Vcc.

[0009] The sampling and conditioning circuit also includes a second operational amplifier unit U2, the output end of the second operational amplifier unit U2 is connected to the non-inverting input end of the third operational amplifier unit U2 through a sixteenth resistor R16, the non-inverting input end of the second operational amplifier unit U2 is connected to the reference voltage source Vcc through a fourteenth resistor R14, the non-inverting input end of the second operational amplifier unit U2 is grounded through a fifteenth resistor R15, the second operational amplifier unit U2 is grounded through a second capacitor C2, and the output end connector of the second operational amplifier unit U2 is connected to the inverting input end.

[0010] The sampling and conditioning circuit also includes a regional clamping circuit, which includes a first diode D1 and a second diode D2. The output end of the third operational amplifier unit U3 is connected to the anode of the first diode D1 through a seventeenth resistor R17 and then connected to the output end of the second operational amplifier unit U2. The output end of the third operational amplifier unit U3 is connected to the cathode of the second diode D2 through the seventeenth resistor R17 and then grounded.

[0011] The output voltage V of the sampling voltage conditioning circuit O =(V ov *R13-V 1 *R12+1 / 2Vcc*R16) / R11.

[0012] Where V ov =Vcc*R15 / (R14+R15).

[0013] The overcurrent threshold acquisition circuit includes a fourth operational amplifier unit U4, the output signal of the sampling and conditioning circuit is connected to the non-inverting input terminal of the fourth operational amplifier unit U4 through a nineteenth resistor R19, the inverting input terminal of the fourth operational amplifier unit U4 is grounded through an eighteenth resistor R18, the output terminal of the fourth operational amplifier unit U4 is connected to the inverting input terminal of the sixth capacitor C6 connector, the sixth capacitor C6 is connected in parallel with a twentieth resistor R20, the non-inverting input terminal of the fourth operational amplifier U4 is grounded through a fifth capacitor C5, the fifth capacitor C5 is connected in parallel with a twenty-eighth resistor R28, the output terminal of the fourth operational amplifier unit U4 is connected to the reference voltage source Vcc through a twenty-first resistor R21 and a seventh capacitor C7, and the output terminal of the fourth operational amplifier unit U4 outputs the highest voltage threshold through the twenty-first resistor R21.

[0014] The overcurrent threshold acquisition circuit includes a fifth operational amplifier unit U5, the inverting input terminal of the fifth operational amplifier unit U5 is connected to the output signal of the sampling and conditioning circuit through a twenty-seventh resistor, the non-inverting input terminal of the fifth operational amplifier unit U5 is connected to a 3.3V voltage through a twenty-sixth resistor R26, the non-inverting input terminal of the fifth operational amplifier unit U5 is grounded through a tenth capacitor C10, the tenth capacitor C10 is connected in parallel with a twenty-fifth resistor R25, the output terminal of the fifth operational amplifier unit U5 is connected to the inverting input terminal through a ninth capacitor C9 connector, the ninth capacitor C9 is connected in parallel with a twenty-fourth resistor R24, the output terminal of the fifth operational amplifier unit U5 is connected to a reference voltage source Vcc through a twenty-third resistor R23 and an eighth capacitor C8, and the output terminal of the fifth operational amplifier unit U5 outputs a minimum voltage threshold through the twenty-third resistor R23.

[0015] It also includes a twenty-second resistor R22, a first end of the twenty-second resistor R22 is connected to the connection between the twenty-first resistor R21 and the seventh capacitor C7, and the other end is connected to the connection between the twenty-third resistor R23 and the eighth capacitor C8. When there is a need to adjust the threshold, the highest and lowest thresholds can be adjusted simultaneously by adjusting the twenty-second resistor R22, that is, symmetrical adjustment is performed with 1 / 2Vcc as the center.

[0016] According to the above, the overcurrent upper threshold voltage is: V I_REF_H =V O;

[0017] The overcurrent upper threshold voltage is: V I_REF_L =Vcc-V O .

[0018] On the other hand, the present invention provides a protection method for an IGBT overcurrent protection circuit of a photovoltaic inverter, wherein the input end of the voltage sampling circuit is connected to the positive and negative poles of the DC bus voltage respectively, and the voltages of different IGBTs are obtained to obtain the corresponding maximum voltage threshold and minimum voltage threshold of the IGBT.

[0019] Compared with the prior art, the advantages of the present invention are: the present invention has a simple structure, including a voltage sampling circuit, a sampling voltage conditioning circuit and an overcurrent threshold acquisition circuit. The voltage threshold output by the sampling voltage conditioning circuit is determined by the voltage sampling circuit, and the upper and lower current thresholds output by the overcurrent threshold acquisition circuit are determined by the sampling voltage conditioning circuit, so as to achieve the purpose of obtaining the corresponding IGBT overcurrent threshold according to different voltages, which can fully utilize the capacity of the IGBT and avoid overcurrent damage to the IGBT, so as to protect the IGBT in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the reverse bias safe operating area (RBSOA) of the IGBT;

[0021] Figure 2 It is a structural block diagram of the present invention;

[0022] Figure 3 This is the IGBT voltage sampling circuit diagram proposed by the present invention;

[0023] Figure 4 This is the IGBT sampling voltage conditioning circuit diagram proposed by the present invention;

[0024] Figure 5 This is a circuit diagram for obtaining the IGBT overcurrent threshold value proposed by the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the present invention, and thus to more clearly define the scope of the protection claimed in the present invention, the present invention is described in detail with respect to certain specific embodiments of the present invention. It should be noted that the following are only certain specific implementations of the present invention, which are only some embodiments of the present invention, wherein the specific and direct description of the relevant structures is only for the convenience of understanding the present invention, and each specific feature does not naturally and directly limit the scope of implementation of the present invention.

[0026] Referring to the accompanying drawings, the present invention adopts the following technical scheme. On the one hand, the present invention provides an IGBT overcurrent protection circuit for a photovoltaic inverter, including a voltage sampling circuit, a sampling and conditioning circuit, and an overcurrent threshold acquisition circuit. The output end of the voltage sampling circuit is connected to the input end of the sampling and conditioning circuit, and the output end of the sampling and conditioning circuit is connected to the input end of the overcurrent threshold acquisition circuit. The overcurrent threshold acquisition circuit outputs a maximum voltage threshold and a minimum voltage threshold.

[0027] The voltage sampling circuit includes a first operational amplifier unit U1, the in-phase input terminal of the first operational amplifier unit U1 is connected to the positive pole of the DC bus voltage through at least one connecting resistor, the in-phase input terminal of the operational amplifier unit U1 is connected to the negative pole of the DC bus voltage after being connected in series with a first inductor through a tenth resistor R10, the output terminal of the first operational amplifier unit U1 is connected to the inverting input terminal of the first operational amplifier unit U1, and the tenth resistor R10 is connected in parallel with a first capacitor C1. The connecting resistors include a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9 connected in series.

[0028] The output voltage V of the voltage sampling circuit dect =R10*(Vbus+-Vbus-) / (R1+R2+R3+R4+R5+R6+R7+R8+R9+R10).

[0029] The sampling and conditioning circuit includes a third operational amplifier unit U3, the inverting input terminal of the third operational amplifier unit U3 is connected to the output terminal of the voltage sampling circuit through an eleventh resistor R11, the output terminal of the third operational amplifier unit U3 is connected to its inverting input terminal through a twelfth resistor R12, the twelfth resistor R12 is connected in parallel with a fourth capacitor C4, the non-inverting input terminal of the third operational amplifier unit U3 is grounded through a third capacitor C3, the non-inverting input terminal of the third operational amplifier unit U3 is connected to a 1 / 2 reference voltage source Vcc through a thirteenth resistor R13, and the non-inverting input terminal of the third operational amplifier unit U3 is connected to the reference voltage source Vcc. Figure 2 As shown, it is a structural block diagram of the present invention. The differential amplifier in the figure is the third operational amplifier unit U3, and its in-phase input terminal is connected to the reference voltage source Vcc. The voltage of the reference voltage source can be 3.3V. The reference voltage source Vcc can be set separately according to parameters. In the figure, Vbus is the bus voltage sampling value, the horizontal axis represents the bus voltage scalar, and the vertical axis represents the voltage value, wherein G represents the differential gain.

[0030] The sampling and conditioning circuit also includes a second operational amplifier unit U2, the output end of the second operational amplifier unit U2 is connected to the non-inverting input end of the third operational amplifier unit U3 through a sixteenth resistor, the non-inverting input end of the second operational amplifier unit U2 is connected to the reference voltage source Vcc through a fourteenth resistor R14, the non-inverting input end of the second operational amplifier unit U2 is grounded through a fifteenth resistor R15, the second operational amplifier unit U2 is grounded through a second capacitor C2, and the output end connector of the second operational amplifier unit U2 is connected to the inverting input end.

[0031] The sampling and conditioning circuit also includes a regional clamping circuit, which includes a first diode D1 and a second diode D2. The output end of the third operational amplifier unit U3 is connected to the anode of the first diode D1 through a seventeenth resistor R17 and then connected to the output end of the second operational amplifier unit U2. The output end of the third operational amplifier unit U3 is connected to the cathode of the second diode D2 through the seventeenth resistor R17 and then grounded.

[0032] The output voltage V of the sampling voltage conditioning circuit O =(V ov *R13-V 1 *R12+1 / 2Vcc*R16) / R11.

[0033] Where V ov =3.3*R15 / (R14+R15).

[0034] The overcurrent threshold acquisition circuit includes a fourth operational amplifier unit U4, the output signal of the sampling and conditioning circuit is connected to the non-inverting input terminal of the fourth operational amplifier unit U4 through a nineteenth resistor R19, the inverting input terminal of the fourth operational amplifier unit U4 is grounded through an eighteenth resistor R18, the output terminal of the fourth operational amplifier unit U4 is connected to the inverting input terminal of the sixth capacitor C6 connector, the sixth capacitor C6 is connected in parallel with a twentieth resistor R20, the non-inverting input terminal of the fourth operational amplifier U4 is grounded through a fifth capacitor C5, the fifth capacitor C5 is connected in parallel with a twenty-eighth resistor R28, the output terminal of the fourth operational amplifier unit U4 is connected to the reference voltage source Vcc through a twenty-first resistor R21 and a seventh capacitor C7, and the output terminal of the fourth operational amplifier unit U4 outputs the highest voltage threshold through the twenty-first resistor R21.

[0035] The overcurrent threshold acquisition circuit includes a fifth operational amplifier unit U5, the inverting input terminal of the fifth operational amplifier unit U5 is connected to the output signal of the sampling and conditioning circuit through a twenty-seventh resistor R27, the non-inverting input terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc through a twenty-sixth resistor R26, the non-inverting input terminal of the fifth operational amplifier unit U5 is grounded through a tenth capacitor C10, the tenth capacitor C10 is connected in parallel with a twenty-fifth resistor R25, the output terminal of the fifth operational amplifier unit U5 is connected to the inverting input terminal through a ninth capacitor C9 connector, the ninth capacitor C9 is connected in parallel with a twenty-fourth resistor R24, the output terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc after passing through a twenty-third resistor R23 and an eighth capacitor C8, and the output terminal of the fifth operational amplifier unit U3 outputs the lowest voltage threshold through the twenty-third resistor R23.

[0036] It also includes a twenty-second resistor R22, a first end of the twenty-second resistor R22 is connected to the connection between the twenty-first resistor R21 and the seventh capacitor C7, and the other end is connected to the connection between the twenty-third resistor R23 and the eighth capacitor C8. When there is a need to adjust the threshold, the highest and lowest thresholds can be adjusted simultaneously by adjusting the twenty-second resistor R22, that is, symmetrical adjustment is performed with 1 / 2Vcc as the center.

[0037] According to the above, the overcurrent upper threshold voltage is: V I_REF_H =V O ;

[0038] The overcurrent upper threshold voltage is: V I_REF_L =3.3VV O .

[0039] On the other hand, the present invention provides a protection method for an IGBT overcurrent protection circuit of a photovoltaic inverter, wherein the input end of the voltage sampling circuit is connected to the positive and negative poles of the DC bus voltage respectively, and the voltages of different IGBTs are obtained to obtain the corresponding maximum voltage threshold and minimum voltage threshold of the IGBT.

[0040] Compared with the prior art, the advantages of the present invention are: the present invention has a simple structure, including a voltage sampling circuit, a sampling voltage conditioning circuit and an overcurrent threshold acquisition circuit. The voltage threshold output by the sampling voltage conditioning circuit is determined by the voltage sampling circuit, and the upper and lower current thresholds output by the overcurrent threshold acquisition circuit are determined by the sampling voltage conditioning circuit, so as to achieve the purpose of obtaining the corresponding IGBT overcurrent threshold according to different DC bus voltages, so as to protect the IGBT in time.

[0041] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An IGBT overcurrent protection circuit for photovoltaic inverters, Features: It includes a voltage sampling circuit for collecting the DC bus voltage where the IGBT is located, a sampling conditioning circuit for conditioning the output voltage of the voltage sampling circuit, and an overcurrent threshold value acquisition circuit for obtaining the overcurrent threshold value of the IGBT through the output voltage of the sampling conditioning circuit, the output end of the voltage sampling circuit is connected to the input end of the sampling conditioning circuit, the output end of the sampling conditioning circuit is connected to the input end of the overcurrent threshold value acquisition circuit, the overcurrent threshold value acquisition circuit outputs the highest voltage threshold value and / or the lowest voltage threshold value, and the input end of the voltage sampling circuit is connected to the DC bus; The overcurrent threshold acquisition circuit includes a fourth operational amplifier unit U4, the output signal of the sampling and conditioning circuit is connected to the non-inverting input terminal of the fourth operational amplifier unit U4, the output terminal of the fourth operational amplifier unit U4 is connected to the reference voltage source Vcc, and the output terminal of the fourth operational amplifier unit U4 outputs the highest voltage threshold; The overcurrent threshold acquisition circuit includes a fifth operational amplifier unit U5, the inverting input terminal of the fifth operational amplifier unit U5 is connected to the output signal of the sampling and conditioning circuit, the non-inverting input terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc, the output terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc, and the output terminal of the fifth operational amplifier unit U5 outputs the lowest voltage threshold; It also includes a twenty-second resistor R22, a first end of which is connected to the output end of the fourth operational amplifier unit U4, and the other end is connected to the output end of the fifth operational amplifier unit U5. When there is a need to adjust the threshold, the highest and lowest thresholds can be adjusted simultaneously by adjusting the twenty-second resistor R22, that is, symmetrical adjustment is performed with 1 / 2Vcc as the center.

2. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 1, Features: The voltage sampling circuit includes a first operational amplifier unit U1, the in-phase input terminal of the first operational amplifier unit U1 is connected to the positive electrode of the DC bus voltage through at least one connecting resistor, the in-phase input terminal of the first operational amplifier unit U1 is connected to the negative electrode of the DC bus voltage through a tenth resistor R10, and the output terminal of the first operational amplifier unit U1 is connected to the inverting input terminal of the first operational amplifier unit.

3. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 2, Features: The connection resistors include a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9 connected in series.

4. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 1, Features: The sampling and conditioning circuit includes a third operational amplifier unit U3, the inverting input terminal of the third operational amplifier unit U3 is connected to the output terminal of the voltage sampling circuit through an eleventh resistor R11, the output terminal of the third operational amplifier unit U3 is connected to its inverting input terminal through a twelfth resistor R12, the non-inverting input terminal of the third operational amplifier unit U3 is connected to a 1 / 2 reference voltage source Vcc through a thirteenth resistor R13, and the non-inverting input terminal of the third operational amplifier unit U3 is connected to the reference voltage source Vcc.

5. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 4, Features: The sampling and conditioning circuit also includes a second operational amplifier unit U2, the output end of the second operational amplifier unit U2 is connected to the non-inverting input end of the third operational amplifier unit U3 through a sixteenth resistor R16, the non-inverting input end of the second operational amplifier unit U2 is connected to the reference voltage source Vcc through a fourteenth resistor R14, the non-inverting input end of the second operational amplifier unit U2 is grounded through a fifteenth resistor R15, and the output end of the second operational amplifier unit U2 is connected to the inverting input end.

6. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 5, Features: The sampling and conditioning circuit also includes a regional clamping circuit, which includes a first diode D1 and a second diode D2. The output end of the third operational amplifier unit U3 is connected to the anode of the first diode D1 and then to the output end of the second operational amplifier unit U2. The output end of the third operational amplifier unit U3 is connected to the cathode of the second diode D2 and then to ground.

7. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 1, Features: The overcurrent threshold acquisition circuit includes a fourth operational amplifier unit U4, the output signal of the sampling and conditioning circuit is connected to the non-inverting input terminal of the fourth operational amplifier unit U4 through a nineteenth resistor R19, the inverting input terminal of the fourth operational amplifier unit U4 is grounded through an eighteenth resistor R18, the output terminal of the fourth operational amplifier unit U4 is connected to the reference voltage source Vcc through a twenty-first resistor R21 and a seventh capacitor U7, and the output terminal of the fourth operational amplifier unit U4 outputs the highest voltage threshold.

8. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 7, Features: The overcurrent threshold acquisition circuit includes a fifth operational amplifier unit U5, the inverting input terminal of the fifth operational amplifier unit U5 is connected to the output signal of the sampling and conditioning circuit through a twenty-seventh resistor R27, the non-inverting input terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc through a twenty-sixth resistor R26, the output terminal of the fifth operational amplifier unit U5 is connected to the reference voltage source Vcc through a twenty-third resistor R23 and an eighth capacitor C8, and the output terminal of the fifth operational amplifier unit U5 outputs the lowest voltage threshold.

9. The IGBT overcurrent protection circuit for photovoltaic inverter according to claim 8, Features: A twenty-second resistor R22 is also included, a first end of the twenty-second resistor R22 is connected to the output end of the fourth operational amplifier unit U4, and the other end of the twenty-second resistor R22 is connected to the output end of the fifth operational amplifier U5.

10. A protection method for an IGBT overcurrent protection circuit for a photovoltaic inverter according to any one of claims 1 to 9, Features: The input end of the voltage sampling circuit is connected to the positive and negative electrodes of the DC bus voltage respectively, and the corresponding maximum voltage threshold and minimum voltage threshold of the IGBT are obtained by obtaining different DC bus voltages.

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