Negative voltage drive circuit of IGBT of variable frequency motor

Abstract

The invention discloses a negative voltage driving circuit of a variable frequency motor IGBT, comprising a triode cascade module and a negative voltage driving module, wherein the triode cascade module is electrically connected to the negative voltage driving module, and a control terminal voltage turns the triode cascade module on or off, thereby turning on or quickly turning off the negative voltage driving module. The negative voltage driving circuit of the variable frequency motor IGBT of the invention accelerates the IGBT turn-off time by using a negative voltage driving circuit constructed by discrete devices, has low cost, and has obvious improvement effect, while not increasing the MCU control signal, and the control signal is reused with the original motor drive circuit control signal, thereby saving MCU resources.

Description

Technical Field

[0001] The invention belongs to the technical field of direct current frequency conversion, and in particular relates to a negative voltage drive circuit of an IGBT of a frequency conversion motor. Background Art

[0002] The driving circuit of the DC variable frequency motor is a bridge circuit, which is divided into an upper bridge arm and a lower bridge arm. The main driving device of each bridge arm is a power device IGBT, which connects the input voltage and the motor winding and plays a switch role in controlling the voltage input to the motor.

[0003] However, there is junction capacitance inside the IGBT. During the shutdown process, the junction capacitance discharges slowly until it is completely discharged, and the IGBT will be completely shut down. The IGBTs in the upper and lower arms of the motor drive circuit are prohibited from being in the on state at the same time, otherwise it will cause a short circuit between the power supply and the ground. Therefore, the drive circuit design requires that the IGBT shutdown time be as short as possible to ensure that the system will not have a short circuit fault. At present, there is no perfect solution for how to speed up the shutdown time of the IGBT. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a negative voltage driving circuit for an IGBT of a variable frequency motor, which accelerates the IGBT turn-off time, has low cost and obvious improvement effect.

[0005] The technical solution adopted by the present invention is:

[0006] A negative voltage driving circuit for an IGBT of a variable frequency motor comprises a triode cascade module and a negative voltage driving module. The triode cascade module is electrically connected to the negative voltage driving module. A control terminal voltage turns the triode cascade module on or off, thereby turning on or quickly turning off the negative voltage driving module.

[0007] Preferably, the triode cascade module comprises a first triode module, a second triode module, a third triode module and a fourth triode module, and the first triode module is sequentially connected to the second triode module, the third triode module and the fourth triode module.

[0008] Preferably, the first transistor module includes a first transistor Q1 and a second transistor Q2, the base of the first transistor Q1 is connected in parallel to one end of the first resistor R1 and one end of the second resistor R2, the other end of the first resistor R1 is connected to the control end voltage, the base of the second transistor Q2 is connected to one end of the third resistor R3 and the collector of the first transistor Q1, the emitter of the second transistor Q2 and the other end of the third resistor R3 are both connected to a power supply, and the emitter of the second transistor Q2 and the other end of the second resistor R2 are grounded.

[0009] Preferably, the second transistor module includes a fifth transistor Q5 and a seventh transistor Q7, the base of the fifth transistor Q5 is connected in parallel to one end of the fourth resistor R4 and one end of the sixth resistor R6, the other end of the sixth resistor R6 is connected to the emitter of the fifth transistor Q5, the other end of the fourth resistor R4 is connected to the collector of the second transistor Q2 and one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected in parallel to the base of the seventh transistor Q7 and one end of the tenth resistor R10, the collector of the seventh transistor Q7 is connected in series with the eleventh resistor R11 and then to the power supply, and the other end of the tenth resistor R10 and the emitter of the seventh transistor Q7 are grounded.

[0010] Preferably, the third triode module includes a third triode Q3 and a fourth triode Q4, the base of the third triode Q3 is connected in parallel to the base of the fourth triode Q4, the collector of the fifth triode Q5 and one end of the seventh resistor R7, the other end of the seventh resistor R7 and the collector of the third triode Q3 are connected to a power supply, the collector of the fourth triode Q4 is connected to the emitter of the fifth triode Q5, and the emitter of the third triode Q3 is connected to the emitter of the fourth triode Q4.

[0011] Preferably, the fourth transistor module includes a sixth transistor Q6, the base of the sixth transistor Q6 is connected in parallel to one end of the eighth resistor R8 and one end of the ninth resistor R9, the other end of the eighth resistor R8 is connected to the emitter of the third transistor Q3 and the emitter of the fourth transistor Q4, the collector of the sixth transistor Q6 is connected in series with the first capacitor C1 and then connected to the collector of the seventh transistor Q7, and the emitter of the sixth transistor Q6 and the other end of the ninth resistor R9 are grounded.

[0012] Preferably, the negative voltage driving module includes a fourth IGBT tube M4, one end of the gate parallel capacitor C of the fourth IGBT tube M4, one end of a twelfth resistor R12, and one end of a thirteenth resistor R13, the other end of the twelfth resistor R12 is connected to the emitter of the fourth triode Q4 and the emitter of the third triode Q3, and the other end of the thirteenth resistor R13, the other end of the capacitor C, and the emitter of the fourth IGBT tube M4 are grounded.

[0013] Preferably, it also includes a motor driving module for driving a DC variable frequency motor, and the motor driving module is connected to the negative pressure driving module.

[0014] Preferably, the motor drive module includes a first IGBT tube M1, a second IGBT tube M2, a third IGBT tube M3, a fourth IGBT tube M4, a fifth IGBT tube M5 and a sixth IGBT tube M6, the collector of the first IGBT tube M1, the collector of the second IGBT tube M2 and the collector of the third IGBT tube M3 are all connected to a high-voltage power supply, the high-voltage power supply is connected in parallel with a first capacitor C1, a second capacitor C2 and a third capacitor C3 and then grounded, the emitter of the first IGBT tube M1 is connected to the collector of the fourth IGBT tube M4 and the U phase of the motor, the emitter of the second IGBT tube M2 is connected to the collector of the fifth IGBT tube M5 and the V phase of the motor, the emitter of the third IGBT tube M3 is connected to the collector of the sixth IGBT tube M6 and the W phase of the motor, and the emitter of the fourth IGBT tube M4, the emitter of the fifth IGBT tube M5 and the emitter of the sixth IGBT tube M6 are all grounded.

[0015] Preferably, the first transistor Q1 , the third transistor Q3 , the fifth transistor Q5 , the sixth transistor Q6 and the seventh transistor Q7 are all NPN transistors, and the second transistor Q2 and the fourth transistor Q4 are all PNP transistors.

[0016] Compared with the prior art, the negative voltage drive circuit of the variable frequency motor IGBT of the present invention accelerates the IGBT shutdown time by constructing a negative voltage drive circuit with discrete devices, has low cost and obvious improvement effect, and does not increase the MCU control signal. Its control signal is multiplexed with the original motor drive circuit control signal, saving MCU resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a circuit diagram of a negative voltage driving circuit of an IGBT of a variable frequency motor provided by an embodiment of the present invention;

[0018] Figure 2 It is a circuit diagram of a motor drive module of a negative voltage drive circuit of an IGBT of a variable frequency motor provided by an embodiment of the present invention;

[0019] Figure 3 It is a schematic diagram of a negative voltage driving circuit of a negative voltage driving circuit of an IGBT of a variable frequency motor provided by an embodiment of the present invention;

[0020] Figure 4 It is a method for implementing a negative voltage driving circuit of a negative voltage driving circuit of an IGBT of a variable frequency motor provided by an embodiment of the present invention;

[0021] Figure 5 The invention provides an equivalent circuit of a negative voltage driving circuit of an IGBT of a variable frequency motor when the IGBT is turned on.

[0022] Figure 6The invention provides an equivalent circuit of a negative voltage driving circuit of an IGBT of a variable frequency motor when the IGBT is turned off.

[0023] Description of Reference Numerals

[0024] 1-transistor cascade module, 11-first transistor module, 12-second transistor module, 13-third transistor module, 14-fourth transistor module, 2-negative pressure drive module, 3-motor drive module. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. 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.

[0026] Example

[0027] The embodiment of the present invention provides a negative voltage driving circuit of an IGBT of a variable frequency motor, such as Figure 1 As shown, it includes a transistor cascade module 1 and a negative voltage driving module 2. The transistor cascade module 1 is electrically connected to the negative voltage driving module 2. The control terminal voltage turns the transistor cascade module 1 on or off, thereby turning on or quickly turning off the negative voltage driving module 2.

[0028] In this way, the transistor cascade module 1 is turned on or off by controlling the terminal voltage, thereby turning on or quickly turning off the negative voltage drive module 2, thereby accelerating the IGBT turn-off time. The cost is low and the improvement effect is obvious. At the same time, the MCU control signal is not increased, and its control signal is reused with the original motor drive circuit control signal, saving MCU resources.

[0029] Among them, IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar transistor) and MOS (insulated gate field effect transistor), which has the advantages of both MOSFET's high input impedance and GTR's low on-state voltage drop. GTR has a low saturation voltage drop and a large current density, but a large driving current; MOSFET has a very small driving power and a fast switching speed, but a large on-state voltage drop and a low current density. IGBT combines the advantages of the above two devices, with low driving power and low saturation voltage drop. It is very suitable for use in converter systems with a DC voltage of 600V and above, such as AC motors, inverters, switching power supplies, lighting circuits, traction drives and other fields.

[0030] The triode cascade module 1 comprises a first triode module 11 , a second triode module 12 , a third triode module 13 and a fourth triode module 14 , wherein the first triode module 11 is connected to the second triode module 12 , the third triode module 13 and the fourth triode module 14 in sequence.

[0031] In this way, the first triode module 11 is connected in sequence to the second triode module 12 , the third triode module 13 and the fourth triode module 14 to output high and low levels, thereby turning on or quickly turning off the negative voltage driving module 2 .

[0032] The first transistor module 11 includes a first transistor Q1 and a second transistor Q2, the base of the first transistor Q1 is connected in parallel to one end of a first resistor R1 and one end of a second resistor R2, the other end of the first resistor R1 is connected to a control terminal voltage, the base of the second transistor Q2 is connected to one end of a third resistor R3 and the collector of the first transistor Q1, the emitter of the second transistor Q2 and the other end of the third resistor R3 are both connected to a power supply, the emitter of the second transistor Q2 and the other end of the second resistor R2 are grounded, wherein the first transistor Q1 is an NPN transistor, and the second transistor Q2 is a PNP transistor.

[0033] In this way, the first transistor Q1 and the second transistor Q2 are turned on or off by controlling the high and low voltages of the terminal voltages.

[0034] The second transistor module 12 includes a fifth transistor Q5 and a seventh transistor Q7, the base of the fifth transistor Q5 is connected in parallel to one end of the fourth resistor R4 and one end of the sixth resistor R6, the other end of the sixth resistor R6 is connected to the emitter of the fifth transistor Q5, the other end of the fourth resistor R4 is connected to the collector of the second transistor Q2 and one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected in parallel to the base of the seventh transistor Q7 and one end of the tenth resistor R10, the collector of the seventh transistor Q7 is connected in series with the eleventh resistor R11 and then connected to the power supply, the other end of the tenth resistor R10 and the emitter of the seventh transistor Q7 are grounded, wherein the fifth transistor Q5 and the seventh transistor Q7 are both NPN transistors.

[0035] In this way, the fifth transistor Q5 and the seventh transistor Q7 are turned on or off by turning on or off the first transistor module 11 .

[0036] The third triode module 13 includes a third triode Q3 and a fourth triode Q4, the base of the third triode Q3 is connected in parallel to the base of the fourth triode Q4, the collector of the fifth triode Q5 and one end of the seventh resistor R7, the other end of the seventh resistor R7 and the collector of the third triode Q3 are connected to a power supply, the collector of the fourth triode Q4 is connected to the emitter of the fifth triode Q5, and the emitter of the third triode Q3 is connected to the emitter of the fourth triode Q4, wherein the third triode Q3 is an NPN triode, and the fourth triode Q4 is a PNP triode.

[0037] In this way, the third transistor Q3 and the fourth transistor Q4 are turned on or off by turning on or off the second transistor module 12 .

[0038] The fourth transistor module 14 includes a sixth transistor Q6, a base of the sixth transistor Q6 is connected in parallel to one end of an eighth resistor R8 and one end of a ninth resistor R9, the other end of the eighth resistor R8 is connected to the emitter of the third transistor Q3 and the emitter of the fourth transistor Q4, the collector of the sixth transistor Q6 is connected in series to the first capacitor C1 and then connected to the collector of the seventh transistor Q7, the emitter of the sixth transistor Q6 and the other end of the ninth resistor R9 are grounded, wherein the sixth transistor Q6 is an NPN transistor.

[0039] In this way, the sixth transistor Q6 is turned on or off by turning on or off the third transistor module 13 .

[0040] The negative voltage driving module 2 includes a fourth IGBT tube M4, one end of the gate parallel capacitor C of the fourth IGBT tube M4, one end of the twelfth resistor R12, and one end of the thirteenth resistor R13, the other end of the twelfth resistor R12 is connected to the emitter of the fourth triode Q4 and the emitter of the third triode Q3, and the other end of the thirteenth resistor R13, the other end of the capacitor C and the emitter of the fourth IGBT tube M4 are grounded.

[0041] In this way, the fourth IGBT tube M4 is turned on or quickly turned off by turning on or off the triode cascade module 1 .

[0042] like Figure 2 As shown, it also includes a motor driving module 3 for driving a DC variable frequency motor, and the motor driving module 3 is connected to the negative pressure driving module 2.

[0043] In this way, the motor driving module 3 can be driven by the negative pressure driving module 2, thereby making the DC variable frequency motor run normally.

[0044] The motor drive module 3 includes a first IGBT tube M1, a second IGBT tube M2, a third IGBT tube M3, a fourth IGBT tube M4, a fifth IGBT tube M5 and a sixth IGBT tube M6. The collector of the first IGBT tube M1, the collector of the second IGBT tube M2 and the collector of the third IGBT tube M3 are all connected to a high-voltage power supply, and the high-voltage power supply is connected in parallel with a first capacitor C1, a second capacitor C2 and a third capacitor C3 and then grounded. The emitter of the first IGBT tube M1 is connected to the collector of the fourth IGBT tube M4 and the U phase of the motor, the emitter of the second IGBT tube M2 is connected to the collector of the fifth IGBT tube M5 and the V phase of the motor, the emitter of the third IGBT tube M3 is connected to the collector of the sixth IGBT tube M6 and the W phase of the motor, and the emitter of the fourth IGBT tube M4, the emitter of the fifth IGBT tube M5 and the emitter of the sixth IGBT tube M6 are all grounded.

[0045] In this way, the U, V, and W phases of the three-phase DC variable frequency motor are controlled by bridge arms U, V, and W respectively. Each bridge arm is divided into two upper and lower bridge arms, and IGBTs (M1 to M6) are used as power switch devices. The figure shows the current direction when the U phase is connected to a high voltage of 24V and the W phase is connected to the ground terminal.

[0046] a. When the upper bridge arm IGBT is turned on, the corresponding phase is connected to a high voltage of 24V, and when the upper bridge arm IGBT is turned off, the corresponding phase is disconnected from a high voltage of 24V;

[0047] b. When the lower bridge arm IGBT is turned on, the corresponding phase is connected to the ground terminal, and when the lower bridge arm IGBT is turned off, the corresponding phase is disconnected from the ground terminal;

[0048] c. When controlling the IGBT switch, it is strictly forbidden to turn on the upper and lower bridge arm IGBTs of the same bridge arm at the same time, otherwise it will cause a short circuit between +24V and the ground.

[0049] The negative voltage driving circuit of the variable frequency motor IGBT of the present invention adopts NPN transistors and PNP transistors as main components to build the negative voltage driving circuit. When the U_L_OUT terminal of the IGBT is at a high level of 12V, the IGBT is turned on, and when the U_L_OUT terminal of the IGBT is at a low level, the IGBT is turned off.

[0050] like Figure 3 As shown in the figure, it is the working principle of the negative pressure driving circuit:

[0051] a. IGBT has internal junction capacitance C. When it is turned on, the junction capacitance C is fully charged. When it is turned off, the junction capacitance C discharges to the resistor R10. The IGBT is not completely turned off until the junction capacitance C is completely discharged.

[0052] b. The voltage waveform of the control terminal of the IGBT shows a tailing phenomenon. The discharge is fast in the initial stage, the terminal voltage drops rapidly, and the discharge is slow in the middle and later stages. When the terminal voltage slowly drops to close to 0V, the IGBT is completely turned off, which takes a long time. The problem to be solved is that when the IGBT terminal voltage drops to 5V (i.e. point e), the IGBT needs to be turned off.

[0053] c. Negative voltage drive circuit: Add capacitor C1 to the original circuit. When the IGBT is turned on, C1 is charged to 12V. When the IGBT is turned off, the high voltage end of C1 is connected to the ground (GND), and the low voltage end of C1 forms a negative voltage of -12V.

[0054] d. Because the junction capacitance C is at the middle point, the voltage value of the junction capacitance C is half of the IGBT voltage value (i.e. half of -12V). At the same time, due to other loads in the circuit, it is equivalent to converting the lower limit of the original tail curve 0V to about -5V. When the IGBT terminal voltage drops to point e (i.e. reaches 0V), the IGBT is completely turned off, and the shutdown time is greatly reduced.

[0055] like Figure 4 As shown, this is the implementation of the negative voltage drive circuit:

[0056] a. Energy storage: When the IGBT is turned on, C1 is charged to 12V.

[0057] b. Energy output: When the IGBT is turned off, C1 is reversely connected to the circuit, forming a negative voltage with a voltage difference of 12V.

[0058] c. This is the square wave signal used by the MCU to control the motor. Assume that when the MCU outputs a low level, the IGBT is turned on, the negative end of the capacitor C1 is grounded, and the capacitor C1 is charged to 12V. When the MCU outputs a high level, the IGBT is turned off, the positive end of the capacitor C1 is grounded and the negative end is connected to form a -12V voltage, and begins to discharge. This cycle repeats.

[0059] In the negative voltage driving circuit of the variable frequency motor IGBT of the present invention, U_L_IN is a control signal output by the MCU with an amplitude of 0 to 3.3V, and U_L_OUT is a control signal for driving the IGBT with an amplitude of 0 to 12V.

[0060] like Figure 5 As shown, a. When U_L_IN=0V, B of NPN transistor Q1 is low level and Q1 is turned off, B of PNP transistor Q2 is high level and Q2 is turned off, B of NPN transistor Q5 is low level and Q5 is turned off, B of NPN transistor Q7 is low level and Q7 is turned off, B of NPN transistor Q3 is high level and Q3 is turned on, B of PNP transistor Q4 is high level and Q4 is turned off, B of NPN transistor Q6 is high level and Q6 is turned on, and the control terminal U_L_OUT of M4 is high level and M4 is turned on, so the equivalent circuit is as follows Figure 5 The arrow direction is the current direction, at this time the negative end of capacitor C1 is grounded, and capacitor C1 is charged to 12V.

[0061] like Figure 6 As shown, b. When U_L_IN=3.3V, B of NPN transistor Q1 is high level and Q1 is turned on, B of PNP transistor Q2 is low level and Q2 is turned on, B of NPN transistor Q5 is high level and Q5 is turned on, B of NPN transistor Q7 is high level and Q7 is turned on, B of NPN transistor Q3 is low level and Q3 is turned off, B of PNP transistor Q4 is low level and Q4 is turned on, B of NPN transistor Q6 is low level and Q6 is turned off, so the equivalent circuit is as follows Figure 6 The arrow direction is the current direction. At this time, the positive end of capacitor C1 is grounded to the negative end to form a -12V voltage, and discharge begins. The voltage at the control end U_L_OUT of M4 drops rapidly to 0V. At this time, the IGBT is completely turned off. After that, as the discharge slowly tails, the voltage at U_L_OUT slowly drops to -5V.

[0062] c. As the MCU controls the U_L_IN square wave repeatedly, the above processes a and b are repeated in sequence, achieving the effect of fast IGBT shutdown by relying on a single MCU signal during the motor control process.

[0063] The negative voltage drive circuit of the variable frequency motor IGBT of the present invention accelerates the IGBT shutdown time by constructing a negative voltage drive circuit with discrete devices, has low cost and obvious improvement effect, and does not increase the MCU control signal. Its control signal is multiplexed with the original motor drive circuit control signal, saving MCU resources.

[0064] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A negative voltage drive circuit for an IGBT of a variable frequency motor, characterized in that: The invention comprises a triode cascade module (1) and a negative voltage driving module (2), wherein the triode cascade module (1) is electrically connected to the negative voltage driving module (2), and a control terminal voltage causes the triode cascade module (1) to be turned on or off, thereby causing the negative voltage driving module (2) to be turned on or off quickly; the triode cascade module (1) comprises a first triode module (11), a second triode module (12), a third triode module (13) and a fourth triode module (14), wherein the first triode module (11) is connected in sequence to the second triode module (12), the third triode module (13) and the fourth triode module (14). (13) and a fourth transistor module (14); the second transistor module (12) comprises a fifth transistor Q5 and a seventh transistor Q7, the base of the fifth transistor Q5 is connected in parallel to one end of a fourth resistor R4 and one end of a sixth resistor R6, the other end of the sixth resistor R6 is connected to the emitter of the fifth transistor Q5, the other end of the fourth resistor R4 is connected to the collector of the second transistor Q2 and one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected in parallel to the base of the seventh transistor Q7 and one end of the tenth resistor R10, the seventh transistor The collector of the transistor Q7 is connected in series with an eleventh resistor R11 and then connected to a power supply, and the other end of the tenth resistor R10 and the emitter of the seventh transistor Q7 are grounded; the third transistor module (13) comprises a third transistor Q3 and a fourth transistor Q4, the base of the third transistor Q3 is connected in parallel with the base of the fourth transistor Q4, the collector of the fifth transistor Q5 and one end of the seventh resistor R7, the other end of the seventh resistor R7 and the collector of the third transistor Q3 are connected to a power supply, and the collector of the fourth transistor Q4 is connected to the emitter of the fifth transistor Q5. The emitter of the third triode Q3 is connected to the emitter of the fourth triode Q4; the fourth triode module (14) comprises a sixth triode Q6, the base of the sixth triode Q6 is connected in parallel to one end of an eighth resistor R8 and one end of a ninth resistor R9, the other end of the eighth resistor R8 is connected to the emitter of the third triode Q3 and the emitter of the fourth triode Q4, the collector of the sixth triode Q6 is connected in series with the first capacitor C1 and then connected to the collector of the seventh triode Q7, and the emitter of the sixth triode Q6 and the other end of the ninth resistor R9 are grounded.

2. The negative voltage driving circuit of the variable frequency motor IGBT according to claim 1, characterized in that: The first transistor module (11) comprises a first transistor Q1 and a second transistor Q2, the base of the first transistor Q1 is connected in parallel to one end of a first resistor R1 and one end of a second resistor R2, the other end of the first resistor R1 is connected to a control terminal voltage, the base of the second transistor Q2 is connected to one end of a third resistor R3 and the collector of the first transistor Q1, the emitter of the second transistor Q2 and the other end of the third resistor R3 are both connected to a power supply, and the emitter of the first transistor Q1 and the other end of the second resistor R2 are grounded.

3. The negative voltage driving circuit of the variable frequency motor IGBT according to any one of claims 1-2, characterized in that: The negative voltage driving module (2) comprises a fourth IGBT tube M4, one end of a gate parallel capacitor C of the fourth IGBT tube M4, one end of a twelfth resistor R12, and one end of a thirteenth resistor R13, the other end of the twelfth resistor R12 is connected to the emitter of the fourth triode Q4 and the emitter of the third triode Q3, and the other end of the thirteenth resistor R13, the other end of the capacitor C, and the emitter of the fourth IGBT tube M4 are grounded.

4. The negative voltage driving circuit of the variable frequency motor IGBT according to claim 3, characterized in that: It also comprises a motor drive module (3) for driving a DC variable frequency motor, wherein the motor drive module (3) is connected to the negative pressure drive module (2).

5. The negative voltage driving circuit of the variable frequency motor IGBT according to claim 4, characterized in that: The motor drive module (3) comprises a first IGBT tube M1, a second IGBT tube M2, a third IGBT tube M3, a fourth IGBT tube M4, a fifth IGBT tube M5 and a sixth IGBT tube M6; the collector of the first IGBT tube M1, the collector of the second IGBT tube M2 and the collector of the third IGBT tube M3 are all connected to a high-voltage power supply; the high-voltage power supply is connected in parallel to a first capacitor C1, a second capacitor C2 and a third capacitor C3 and then grounded; the emitter of the first IGBT tube M1 is connected to the collector of the fourth IGBT tube M4 and the U phase of the motor; the emitter of the second IGBT tube M2 is connected to the collector of the fifth IGBT tube M5 and the V phase of the motor; the emitter of the third IGBT tube M3 is connected to the collector of the sixth IGBT tube M6 and the W phase of the motor; the emitter of the fourth IGBT tube M4, the emitter of the fifth IGBT tube M5 and the emitter of the sixth IGBT tube M6 are all grounded.

6. The negative voltage driving circuit of the variable frequency motor IGBT according to claim 5, characterized in that: The first transistor Q1 , the third transistor Q3 , the fifth transistor Q5 , the sixth transistor Q6 and the seventh transistor Q7 are all NPN transistors, and the second transistor Q2 and the fourth transistor Q4 are all PNP transistors.

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