A three-stage vacuum pump set using a water-cooled variable frequency integrated motor and a control method

Abstract

The application relates to a three-stage vacuum pump set using a water-cooled variable-frequency integrated motor and a control method. The application comprises a Roots vacuum pump, a Roots pump support frame, a rack and an air inlet flange, and is characterized in that the application further comprises a two-stage dry vacuum pump, an upper-lower pump connecting flange, an electric control system, an exhaust silencer, a communication line joint and a power line joint; the two-stage dry vacuum pump is composed of a high-pressure-difference Roots vacuum pump and a dry screw vacuum pump, the two-stage dry vacuum pump is installed on the rack, and the two-stage dry vacuum pump is located directly below the Roots vacuum pump; the Roots vacuum pump air outlet is connected with the two-stage dry vacuum pump air inlet through the upper-lower pump connecting flange; the exhaust silencer is connected with the two-stage dry vacuum pump air outlet; the high-pressure-difference Roots vacuum pump shell and the dry screw vacuum pump shell are both provided with cooling water jackets. The application has reasonable structure design, small volume, can cope with large load working conditions and reduce the overall failure rate of the Roots vacuum pump.

Description

Technical Field

[0001] The present invention relates to a three-stage vacuum pump unit and a control method using a water-cooled variable-frequency integrated motor, and in particular to a unit consisting of a Roots vacuum pump and a two-stage dry vacuum pump, which is mainly used in the fields of semiconductors, lithium batteries, chemical medicine, photovoltaics, etc. Background Art

[0002] At present, the application of two-stage vacuum pump groups and three-stage vacuum pump groups is becoming more and more common.

[0003] Commonly used two-stage vacuum pump groups have the following main problems: 1. Under working conditions of high pumping speed and high load, the stability of the Roots vacuum pump will be reduced, and the vacuum pump is prone to jamming; 2. It cannot cope with working conditions requiring a wide range of pumping speeds and can only maintain a higher or lower pumping speed, and cannot take into account multiple pumping speed requirements.

[0004] The commonly used three-stage vacuum pump group has the following main problems: 1. The overall structure of the three-stage vacuum pump group is complex, and it is prone to problems such as resonance and abnormal noise; 2. The overall size of the three-stage vacuum pump group is large, and a larger space is required for installation. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned shortcomings in the prior art and to provide a three-stage vacuum pump group and control method using a water-cooled variable frequency integrated motor, which has a reasonable structural design, a small size, can cope with large load conditions, and reduce the overall failure rate of the Roots vacuum pump.

[0006] The technical solution adopted by the present invention to solve the above problems is: the three-stage vacuum pump group using a water-cooled variable frequency integrated motor includes a Roots vacuum pump, a Roots pump support frame, a frame and an air inlet flange, the Roots vacuum pump is fixed to the frame through the Roots pump support frame, and the air inlet flange is installed at the air inlet of the Roots vacuum pump. Its structural characteristics are: it also includes a two-stage dry vacuum pump, upper and lower pump connecting flanges, an electric control system, an exhaust muffler, a cooling water inlet connector, a cooling water return connector, a communication line connector and a power line connector, the two-stage dry vacuum pump consists of a high-pressure differential Roots vacuum pump and a dry screw vacuum pump, and the two-stage dry vacuum pump is installed on the frame. And the two-stage dry vacuum pump is located directly below the Roots vacuum pump; the air outlet of the Roots vacuum pump is connected to the air inlet of the two-stage dry vacuum pump through the upper and lower pump connecting flanges, and the exhaust muffler is connected to the air outlet of the two-stage dry vacuum pump; the housing of the high-pressure differential Roots vacuum pump and the housing of the dry screw vacuum pump in the two-stage dry vacuum pump are both provided with cooling water jackets, and the cooling water inlet joint and the cooling water return joint are connected to the cooling water jackets through cooling water pipes; the electronic control system, communication line connector and power line connector are all installed on the frame, and the electronic control system, communication line connector and power line connector are all connected to the Roots vacuum pump and the two-stage dry vacuum pump.

[0007] Preferably, the three-stage vacuum pump assembly of the present invention further includes casters and foot cups, and the casters and foot cups are both fixed to the bottom of the frame.

[0008] Preferably, the drive motors in the Roots vacuum pump and the two-stage dry vacuum pump of the present invention are both water-cooled variable frequency integrated motors.

[0009] Preferably, the air inlet of the two-stage dry vacuum pump of the present invention is located directly below the air outlet of the Roots vacuum pump, and the upper and lower pump connecting flanges are vertical structures.

[0010] Preferably, sheet metal is provided on the frame of the present invention.

[0011] A control method for a three-stage vacuum pump group using a water-cooled variable frequency integrated motor is characterized in that: the gas circuit of the three-stage vacuum pump group is connected to the gas pipeline of the client through an air inlet flange and an exhaust muffler to realize gas transportation; the water circuit of the three-stage vacuum pump group is connected to the cooling water system of the client through a cooling water inlet joint and a cooling water return joint to realize cooling water circulation; the three-stage vacuum pump group is connected to the power supply system of the client and the upper computer electronic control system through a power line joint and a communication line joint respectively to realize the operation of the three-stage vacuum pump group;

[0012] The steps of the control method are as follows: the dry screw vacuum pump in the two-stage dry vacuum pump is started first, and after the delayed start program set by the electronic control system, the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump is started again, and finally, after the delayed start program set by the electronic control system, the Roots vacuum pump is started last; wherein, the frequency of the Roots vacuum pump is connected to the communication line connector by the client's upper computer electronic control system through a communication line and transmits an analog quantity to give the required operating frequency. In addition, the electronic control system adjusts the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump by collecting the operating frequency and current data of the Roots vacuum pump, and adaptively adjusts the zero frequency setting of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump according to the load, so as to meet the operating conditions of high pumping speed and low pumping speed; at the same time, the electronic control system sets the frequency of the Roots vacuum pump and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump through an algorithm to achieve an operating frequency plan and achieve minimum energy consumption while meeting process requirements.

[0013] Preferably, the electronic control system of the present invention adjusts the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump by collecting the operating frequency and current data of the Roots vacuum pump, and adaptively adjusts the zero frequency setting of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump according to the load, which is achieved by the following method:

[0014] When I bp ≤ I th , and F bp ≤ Fth / k, F bstr = F th / k ;

[0015] When I bp > I th When F bstr = F bp / q;

[0016] In other cases, F bstr = F bp / k ;

[0017] In the above formula:

[0018] F bp : operating frequency of Roots vacuum pump;

[0019] I bp : Operating current of Roots vacuum pump;

[0020] I th : The threshold current of the Roots vacuum pump is set;

[0021] F th : The threshold frequency of the Roots vacuum pump is set;

[0022] k: The ratio of the frequency of the Roots vacuum pump to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump at minimum power consumption;

[0023] q: Under abnormal conditions, the ratio of the frequency of the Roots vacuum pump to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump;

[0024] F bstr : The operating frequency of the high-pressure differential Roots vacuum pump in a two-stage dry vacuum pump.

[0025] Preferably, the electronic control system of the present invention sets the frequency of the Roots vacuum pump and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump through an algorithm to achieve an operating frequency scheme and achieve minimum energy consumption while meeting process requirements. This is achieved by the following method:

[0026] W = W bp +W bstr = V bp * (P mid -P in ) + V bstr * (P out -P mid );

[0027] P in , P mid , P out= f(F bp , F bstr );

[0028] Establish the objective function of minimum power consumption, and calculate the ratio k = F between the operating frequency of the Roots vacuum pump at the lowest power consumption and the operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump through the optimization algorithm. bp / F bstr ;

[0029] In the above formula:

[0030] P in : Inlet pressure of Roots vacuum pump;

[0031] P mid : Exhaust pressure of Roots vacuum pump;

[0032] P out : The exhaust pressure of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump;

[0033] W bp : The work required by the Roots vacuum pump;

[0034] W bstr : The work required for the high-pressure differential Roots vacuum pump in a two-stage dry vacuum pump;

[0035] V bp : Exhaust volume of Roots vacuum pump;

[0036] F bp : operating frequency of Roots vacuum pump;

[0037] F bstr : The operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump;

[0038] W: The work required by the three-stage vacuum pump group.

[0039] Compared with the existing technology, this invention has the following advantages and effects: 1. The Roots vacuum pump and the two-stage dry vacuum pump are connected using upper and lower pump connection flanges. The Roots vacuum pump is supported by a Roots pump support frame. The two-stage dry vacuum pump is an integrated structure. Therefore, the entire three-stage vacuum pump assembly has the same connection interface as a conventional two-stage vacuum pump. The overall rigidity is stronger, which can more effectively reduce the occurrence of vibration and abnormal noise, and the operation is smoother and the failure rate is lower. The average vibration can be reduced by 0.5-1mm / s (the original vibration average is about 2.5mm / s), which can improve between 20% and 40%.

[0040] 2. The two-stage dry vacuum pump uses a high-differential Roots vacuum pump. Under heavy load conditions, the high-differential Roots vacuum pump in the two-stage dry vacuum pump bears most of the pressure differential, while the Roots vacuum pump bears a smaller portion. This ensures that the pressure differential between the Roots vacuum pump and the high-differential Roots vacuum pump in the two-stage dry vacuum pump does not exceed the maximum allowable pressure differential, enabling long-term stable operation under heavy load conditions.

[0041] 3. The three-stage pump structure can minimize the working pressure difference of the Roots vacuum pump and effectively improve the volumetric efficiency from an average of 75% to an average of 85%.

[0042] 4. High-pressure differential between Roots vacuum pumps and two-stage dry vacuum pumps. Roots vacuum pumps synchronize frequency adjustment during use through an electronic control system, enabling independent control of their operating frequencies. This allows the unit to meet both high and low pumping speed applications without any adjustments, accommodating a variety of process requirements. Compared to a two-stage vacuum pump of the same pumping speed, the minimum pumping speed can be reduced by 30-35%. Due to improved volumetric efficiency, the maximum pumping speed can be increased by 5-10%, resulting in an overall increase in process adaptability by approximately 40%.

[0043] 5. The front pump of the unit adopts an integrated two-stage dry vacuum pump, which has a more compact overall structure, stronger rigidity, and a more stable center of gravity. It can effectively reduce the probability of abnormal vibration and abnormal noise, making the unit run more smoothly and reducing the failure rate of the unit.

[0044] 6. The dry screw vacuum pump part of the two-stage dry vacuum pump and the high-pressure differential Roots vacuum pump part have cooling water jackets on their shells, which enable the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump, which bears a larger load in the unit system, to have a better cooling effect and reduce the failure rate. The overall monthly failure rate can be reduced by 5% to 10%.

[0045] 7. The water-cooled variable frequency integrated motor can provide a stable power source for the unit operation. The excellent sealing and efficient heat dissipation effect can ensure the long-term stable operation of the unit in harsh working environments and under harsh working conditions.

[0046] 8. The water-cooled variable frequency integrated motor completely isolates the motor's power source from the motor's control source, eliminating the need to consider the inverter's heat dissipation requirements when designing the electrical control cabinet. This can effectively improve the sealing of the electrical control cabinet, thereby improving the stability of the entire electrical control system and reducing the failure rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention and / or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments and / or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 It is a schematic diagram of the three-dimensional structure of a three-stage vacuum pump group using a water-cooled variable frequency integrated motor in an embodiment of the present invention.

[0049] Figure 2 It is a schematic diagram of the three-stage structure of the three-stage vacuum pump group using a water-cooled variable frequency integrated motor in an embodiment of the present invention from another perspective.

[0050] Figure 3 This is a schematic diagram of the main structure of a three-stage vacuum pump group using a water-cooled variable frequency integrated motor in an embodiment of the present invention.

[0051] In the figure: 1-Roots vacuum pump; 2-two-stage dry vacuum pump; 3-upper and lower pump connection flange; 4-Roots pump support frame; 5-electronic control system; 6-frame; 7-inlet flange; 8-exhaust muffler; 9-castor; 10-foot cup; 11-cooling water inlet connector; 12-cooling water return connector; 13-communication line connector; 14-power line connector. DETAILED DESCRIPTION

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0053] Example

[0054] See also Figures 1 to 3 The three-stage vacuum pump group using a water-cooled variable frequency integrated motor in this embodiment includes a Roots vacuum pump 1, a two-stage dry vacuum pump 2, upper and lower pump connecting flanges 3, a Roots pump support frame 4, an electronic control system 5, a frame 6, an air inlet flange 7, an exhaust muffler 8, casters 9, a foot cup 10, a cooling water inlet connector 11, a cooling water return connector 12, a communication line connector 13 and a power line connector 14, wherein the casters 9 and the foot cup 10 are both fixed to the bottom of the frame 6.

[0055] The Roots vacuum pump 1 in this embodiment is fixed to the frame 6 via a Roots pump support frame 4, and the air inlet flange 7 is installed at the air inlet of the Roots vacuum pump 1. The two-stage dry vacuum pump 2 consists of a high-pressure differential Roots vacuum pump and a dry screw vacuum pump. The two-stage dry vacuum pump 2 is installed on the frame 6, and the two-stage dry vacuum pump 2 is located directly below the Roots vacuum pump 1. The air inlet of the two-stage dry vacuum pump 2 is located directly below the air outlet of the Roots vacuum pump 1.

[0056] The air outlet of the Roots vacuum pump 1 in this embodiment is connected to the air inlet of the two-stage dry vacuum pump 2 through the upper and lower pump connecting flanges 3. The upper and lower pump connecting flanges 3 are vertical structures, and the exhaust muffler 8 is connected to the air outlet of the two-stage dry vacuum pump 2.

[0057] In this embodiment, the housings of the high-pressure differential Roots vacuum pump and the dry screw vacuum pump in the two-stage dry vacuum pump 2 are both provided with cooling water jackets, and the cooling water inlet connector 11 and the cooling water return connector 12 are connected to the cooling water jackets through cooling water pipes; the electronic control system 5, the communication line connector 13 and the power line connector 14 are all installed on the frame 6, and the electronic control system 5, the communication line connector 13 and the power line connector 14 are all connected to the Roots vacuum pump 1 and the two-stage dry vacuum pump 2.

[0058] The drive motors in the Roots vacuum pump 1 and the two-stage dry vacuum pump 2 in this embodiment are both water-cooled variable frequency integrated motors, and sheet metal is usually provided on the frame 6 .

[0059] When the three-stage vacuum pump group using a water-cooled variable frequency integrated motor in this embodiment is in use, the gas path of the three-stage vacuum pump group is connected to the gas pipeline of the client through the air inlet flange 7 and the exhaust muffler 8 to realize gas transportation; the water path of the three-stage vacuum pump group is connected to the cooling water system of the client through the cooling water inlet joint 11 and the cooling water return joint 12 to realize the circulation of the cooling water path; the three-stage vacuum pump group is connected to the power supply system of the client and the upper computer electronic control system through the power line joint 14 and the communication line joint 13 respectively to realize the operation of the three-stage vacuum pump group.

[0060] The steps of the control method of the three-stage vacuum pump group using a water-cooled variable frequency integrated motor in this embodiment are as follows: the dry screw vacuum pump in the two-stage dry vacuum pump 2 is started first, and after the delayed start program set by the electronic control system 5, the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 is started again, and finally after the delayed start program set by the electronic control system 5, the Roots vacuum pump 1 is started last; wherein, the frequency of the Roots vacuum pump 1 is connected to the communication line connector 13 by the upper computer electronic control system of the client through the communication line and transmits the analog quantity, and the required operation is given. In addition, the electronic control system 5 adjusts the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 by collecting the operating frequency and current data of the Roots vacuum pump 1, and adaptively adjusts the zero frequency setting of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 according to the load, so as to meet the operating conditions of high pumping speed and low pumping speed; at the same time, the electronic control system 5 sets the frequencies of the Roots vacuum pump 1 and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 through an algorithm to achieve an operating frequency plan and realize minimum energy consumption while meeting the process requirements.

[0061] The electronic control system 5 in this embodiment adjusts the frequency of the high-differential Roots vacuum pump in the two-stage dry vacuum pump 2 by collecting the operating frequency and current data of the Roots vacuum pump 1, and adaptively adjusts the zero frequency setting of the high-differential Roots vacuum pump in the two-stage dry vacuum pump 2 according to the load. This is achieved by the following method:

[0062] When I bp ≤ I th , and F bp ≤ F th / k, F bstr = F th / k ;

[0063] When I bp > I th When F bstr = F bp / q;

[0064] In other cases, F bstr = F bp / k ;

[0065] In the above formula:

[0066] F bp : operating frequency of Roots vacuum pump 1;

[0067] I bp : Operating current of Roots vacuum pump 1;

[0068] I th : The threshold current of Roots vacuum pump 1 is set;

[0069] F th : The threshold frequency of Roots vacuum pump 1 is set;

[0070] k: The ratio of the frequency of the Roots vacuum pump 1 to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 at minimum power consumption;

[0071] q: Under abnormal conditions, the ratio of the frequency of Roots vacuum pump 1 to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2;

[0072] F bstr : The operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2.

[0073] The electronic control system 5 in this embodiment sets the frequencies of the Roots vacuum pump 1 and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 through an algorithm to achieve an operating frequency scheme that minimizes energy consumption while meeting process requirements. This is achieved using the following method:

[0074] W = W bp+W bstr = V bp * (P mid -P in ) + V bstr * (P out -P mid );

[0075] P in , P mid , P out = f(F bp , F bstr );

[0076] Establish the objective function of minimum power consumption and calculate the ratio k = F between the operating frequency of Roots vacuum pump 1 and the operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2 when the power consumption is the lowest. bp / F bstr ;

[0077] In the above formula:

[0078] P in : Inlet pressure of Roots vacuum pump 1;

[0079] P mid : Exhaust pressure of Roots vacuum pump 1;

[0080] P out : Exhaust pressure of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2;

[0081] W bp : The work required by Roots vacuum pump 1;

[0082] W bstr : The work required by the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump 2;

[0083] V bp : exhaust volume of Roots vacuum pump 1;

[0084] F bp : operating frequency of Roots vacuum pump 1;

[0085] F bstr : The operating frequency of the high-differential Roots vacuum pump in the two-stage dry vacuum pump 2;

[0086] W: The work required by the three-stage vacuum pump group.

[0087] In addition, it should be noted that the shapes and names of the parts and components of the specific embodiments described in this specification may be different, and the above content described in this specification is only an example of the structure of the present invention. Any equivalent changes or simple changes made based on the structure, features and principles described in the patent concept of the present invention are included in the protection scope of the patent of the present invention. Those skilled in the art of the technology to which the present invention belongs can make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A control method for a three-stage vacuum pump group using a water-cooled variable frequency integrated motor, the three-stage vacuum pump group using a water-cooled variable frequency integrated motor comprising a Roots vacuum pump (1), a Roots pump support frame (4), a frame (6), an air intake flange (7), a two-stage dry vacuum pump (2), upper and lower pump connection flanges (3), an electric control system (5), an exhaust muffler (8), a cooling water inlet connector (11), a cooling water return connector (12), a communication line connector (13) and a power line connector (14), the Roots vacuum pump (1) being fixed to the frame (6) via the Roots pump support frame (4), the air intake flange (7) being mounted on the air inlet of the Roots vacuum pump (1), the two-stage dry vacuum pump (2) being composed of a high-pressure differential Roots vacuum pump and a dry screw vacuum pump, the two-stage dry vacuum pump (2) being mounted on the frame (6), and the The two-stage dry vacuum pump (2) is located directly below the Roots vacuum pump (1); the air outlet of the Roots vacuum pump (1) is connected to the air inlet of the two-stage dry vacuum pump (2) through the upper and lower pump connecting flanges (3), and the exhaust muffler (8) is connected to the air outlet of the two-stage dry vacuum pump (2); the housing of the high-pressure differential Roots vacuum pump and the housing of the dry screw vacuum pump in the two-stage dry vacuum pump (2) are both provided with cooling water jackets, and the cooling water inlet joint (11) and the cooling water return joint (12) are connected to the cooling water jackets through cooling water pipes; the electric control system (5), the communication line joint (13) and the power line joint (14) are all installed on the frame (6), and the electric control system (5), the communication line joint (13) and the power line joint (14) are all connected to the Roots vacuum pump (1) and the two-stage dry vacuum pump (2); it is characterized in that: The gas path of the three-stage vacuum pump group is connected to the gas pipeline of the client through the air inlet flange (7) and the exhaust silencer (8) to realize the transportation of gas; the water path of the three-stage vacuum pump group is connected to the cooling water system of the client through the cooling water inlet joint (11) and the cooling water return joint (12) to realize the circulation of the cooling water path; the three-stage vacuum pump group is connected to the power supply system of the client and the upper computer electronic control system through the power line joint (14) and the communication line joint (13) respectively to realize the operation of the three-stage vacuum pump group; The control method comprises the following steps: the dry screw vacuum pump in the two-stage dry vacuum pump (2) is started first, and after the delay start program set by the electronic control system (5), the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) is started again, and finally after the delay start program set by the electronic control system (5), the Roots vacuum pump (1) is started last; wherein, the frequency of the Roots vacuum pump (1) is connected to the communication line connector (13) by the client's upper computer electronic control system through the communication line and transmits analog quantity, and the required operating frequency is given. In addition, the electronic control system (5) adjusts the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) by collecting the operating frequency and current data of the Roots vacuum pump (1), according to The load adaptively adjusts the zero frequency setting of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) to meet the operating conditions of high pumping speed and low pumping speed; at the same time, the electric control system (5) sets the frequencies of the Roots vacuum pump (1) and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) through an algorithm to achieve an operating frequency scheme and realize minimum energy consumption under the condition of meeting process requirements; wherein, the electric control system (5) adjusts the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) by collecting the operating frequency and current data of the Roots vacuum pump (1), and adaptively adjusts the zero frequency setting of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) according to the load, which is achieved by the following method: When I bp ≤ I th , and F bp ≤ F th / k, F bstr = F th / k ; When I bp > I th When F bstr = F bp / q; In other cases, F bstr = F bp / k ; F bp : operating frequency of the Roots vacuum pump (1); I bp : operating current of the Roots vacuum pump (1); I th : The threshold current of the Roots vacuum pump (1) is set; F th : The threshold frequency of the roots vacuum pump (1) is set; k: ratio of the frequency of the Roots vacuum pump (1) to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) at minimum power consumption; q: ratio of the frequency of the Roots vacuum pump (1) to the frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) under abnormal conditions; F bstr : Operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2).

2. The control method of a three-stage vacuum pump unit using a water-cooled variable frequency integrated motor according to claim 1, characterized in that: The electronic control system (5) sets the frequency of the Roots vacuum pump (1) and the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) through an algorithm to achieve an operating frequency scheme and achieve minimum energy consumption while meeting process requirements. This is achieved by the following method: W = W bp +W bstr = V bp * (P mid - P in ) + V bstr * (P out - P mid ); P in , P mid , P out = f(F bp , F bstr ); Establish the objective function of minimum power consumption, and calculate the ratio k = F between the operating frequency of the Roots vacuum pump (1) at the lowest power consumption and the operating frequency of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2) through the optimization algorithm. bp / F bstr ; P in : Inlet pressure of Roots vacuum pump (1); P mid : exhaust pressure of Roots vacuum pump (1); P out : The exhaust pressure of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2); W bp : The work required by the Roots vacuum pump (1); W bstr : The work required by the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2); V bp : exhaust volume of Roots vacuum pump (1); V bstr : Exhaust volume of the high-pressure differential Roots vacuum pump in the two-stage dry vacuum pump (2); W: The work required by the three-stage vacuum pump group.

3. The control method of a three-stage vacuum pump assembly using a water-cooled variable frequency integrated motor according to claim 1, characterized in that: The three-stage vacuum pump assembly further comprises a caster (9) and a foot cup (10), and the caster (9) and the foot cup (10) are both fixed to the bottom of the frame (6).

4. The control method of a three-stage vacuum pump assembly using a water-cooled variable frequency integrated motor according to claim 1, characterized in that: The drive motors in the Roots vacuum pump (1) and the two-stage dry vacuum pump (2) are both water-cooled variable frequency integrated motors.

5. The control method of a three-stage vacuum pump assembly using a water-cooled variable frequency integrated motor according to claim 1, characterized in that: The air inlet of the two-stage dry vacuum pump (2) is located directly below the air outlet of the Roots vacuum pump (1), and the upper and lower pump connecting flanges (3) are in a vertical structure.

6. The control method of a three-stage vacuum pump assembly using a water-cooled variable frequency integrated motor according to claim 1, characterized in that: The frame (6) is provided with sheet metal.

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