A molecular pump shutdown braking method

Abstract

The present invention discloses a molecular pump stop braking method, which is based on a motor control system. The system includes a power module, a DC bus, a main controller, an inverter, a DC bus voltage sampling unit, and an energy release unit. The braking method includes: s1. Upon receiving a shutdown command, the system performs vector control braking and reduces the motor speed to a speed threshold; s2. The power module disconnects the power supply to the DC bus, and the system performs resistance braking. First, the highest-order energy release subunit is connected, and the back electromotive force generated on the DC bus is consumed by an energy-consuming resistor. When the back electromotive force on the DC bus drops to a voltage threshold, the energy release subunit of this order is disconnected and switched to the next-order energy release subunit. Thereafter, the system operates sequentially according to the above rules until the lowest-order energy release subunit is disconnected. A multi-modal braking method combining vector control braking and resistance braking is adopted, which can prevent the molecular pump rotor from losing stability and oscillation, and can also quickly complete braking.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular pumps, and in particular to a molecular pump shutdown braking method. Background Art

[0002] Molecular pumps are also called vacuum pumps. In the natural shutdown state, due to the small air resistance, the motor rotor takes tens of minutes or even hours to completely stop. In the semiconductor process, repeated starting and stopping of the molecular pump is an essential operation. Excessive shutdown time will affect the duration of the entire process and also affect the continuity of the entire semiconductor process. At present, the conventional practice is to manually or through a dedicated inflation valve to fill the molecular pump cavity with air or nitrogen to increase the rotor resistance and make it stop quickly. However, in a high vacuum environment, filling with air or nitrogen will cause a large load impact on the molecular pump impeller. The control response cannot keep up with the rate of change of the load impact, which can easily cause the rotor to become unstable and oscillate or even fall, ultimately causing damage to the equipment. Therefore, it is necessary to consider optimizing the design and operation of the molecular pump to reduce downtime and ensure safe and stable shutdown of the molecular pump, thereby improving the efficiency and continuity of the entire semiconductor processing technology. Summary of the Invention

[0003] The object of the present invention is to provide a molecular pump braking method for stopping, aiming to solve at least one of the technical problems existing in the above-mentioned prior art. To achieve the above-mentioned object, the technical solution adopted is as follows:

[0004] A molecular pump shutdown braking method is based on a motor control system. The system includes a power module, a DC bus, a main controller, and an inverter. The power module is connected to the input end of the DC bus to provide DC power to the DC bus. The output end of the DC bus is connected to the input end of the main controller. The main controller is used to control and monitor the entire system. The output end of the main controller is connected to the input end of the inverter. The inverter is used to convert DC power into AC power and power the motor. The system also includes a DC bus voltage sampling unit and an energy release unit. The DC bus voltage sampling unit is used to detect the voltage of the DC bus and feed it back to the main controller. The energy release unit includes a plurality of energy release subunits arranged in order from high order to low order. Each energy release subunit includes a MOS tube and an energy dissipation resistor. The input end of the MOS tube is connected to the DC bus, the output end is connected to the energy dissipation resistor, and the control end is connected to the main controller. The resistance value of the energy dissipation resistor in the previous order energy release subunit is greater than the resistance value of the energy dissipation resistor in the next order energy release subunit.

[0005] The braking method comprises the following steps:

[0006] s1. The main controller receives a shutdown command, and the system performs vector control braking and reduces the motor speed to the speed threshold;

[0007] s2. The power module disconnects the DC bus from power, and the system performs resistance braking. The highest-order energy release subunit is connected first, and the back EMF generated on the DC bus is dissipated through the energy-dissipating resistor. When the back EMF on the DC bus drops to the voltage threshold, the energy release subunit of that order is disconnected and the next-order energy release subunit is switched to. The system then operates sequentially according to the above rules until the lowest-order energy release subunit is disconnected.

[0008] s3. Brake by short-circuiting the motor windings until the motor speed drops to zero;

[0009] s4. The power module resumes supplying power to the DC bus, preparing for the next motor start-up.

[0010] Preferably, the energy release unit comprises a three-stage energy release subunit.

[0011] Preferably, in step s1, the vector control braking is specifically as follows: the main controller controls the motor drive current output by the inverter to gradually decrease, and at the same time reverses the direction of the rotor magnetic field of the motor.

[0012] Preferably, in step s1, the speed threshold is 30%-40% of the rated speed of the motor.

[0013] Preferably, in step s2, the voltage threshold is 10% of the back electromotive force on the DC bus when the energy release sub-unit of this stage is connected.

[0014] Preferably, the main controller is powered by a UPS uninterruptible power supply.

[0015] Preferably, the system further comprises a pressure sensor unit, the pressure sensor unit being used to detect the pressure in the molecular pump cavity and feed back the pressure to the main controller;

[0016] In step s1, if a pressure rise is detected, the process directly proceeds to step s2.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a molecular pump stopping braking method, which adopts a multi-modal braking method combining vector control braking and resistance braking, which can not only prevent the molecular pump rotor from losing stability and oscillation, but also enable the molecular pump to quickly complete a safe and stable braking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are only some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic diagram of the vector control braking principle of the present invention.

[0021] Figure 2 This is a schematic diagram of the principle of the resistance braking connected to the first-order energy release subunit of the present invention.

[0022] Figure 3 This is a schematic diagram of the principle of the resistance braking connected to the second-order energy release subunit of the present invention.

[0023] Figure 4 This is a schematic diagram of the principle of the resistance braking connected to the third-order energy release subunit of the present invention.

[0024] Figure 5 This is a schematic diagram of the motor winding short-circuit braking principle of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections; they may refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0027] A preferred embodiment of the present invention provides a molecular pump shutdown braking method based on a motor control system, which includes a power module, a DC bus, a main controller, an inverter, a pressure sensor unit, a DC bus voltage sampling unit and an energy release unit.

[0028] The power module is connected to the input end of the DC bus to provide stable DC power for the DC bus. The output end of the DC bus is connected to the input end of the main controller. The main controller is powered by a UPS uninterruptible power supply and is used to control and monitor the entire power system. The output end of the main controller is connected to the input end of the inverter. The output end of the inverter is connected to the motor. The inverter is used to convert DC power into AC power and power the motor.

[0029] The pressure sensor unit is used to detect the pressure in the molecular pump cavity and feed it back to the main controller. The DC bus voltage sampling unit is used to detect the voltage of the DC bus and feed it back to the main controller. The energy release unit includes a plurality of energy release sub-units arranged in sequence from high order to low order. The present invention preferably has three-order energy release sub-units, namely: a first-order energy release sub-unit, a second-order energy release sub-unit and a third-order energy release sub-unit. Each order of energy release sub-unit includes a MOS tube and an energy-consuming resistor, and the input end of the MOS tube is connected to the DC bus, the output end is connected to the energy-consuming resistor, and the control end is connected to the main controller, wherein the resistance value of the energy-consuming resistor in the previous order energy release sub-unit is greater than the resistance value of the energy-consuming resistor in the next order energy release sub-unit.

[0030] The braking method comprises the following steps:

[0031] s1. The main controller receives a stop command and the system performs vector control braking to reduce the motor speed to the speed threshold.

[0032] like Figure 1 As shown in the figure, during vector control braking, the main controller monitors the motor's current, speed, position and other parameters, and controls the motor's operating status based on these parameters, thereby achieving precise control of the motor. During vector control braking, the main controller controls the motor drive current output by the inverter to gradually decrease, while reversing the direction of the motor's rotor magnetic field.

[0033] Since the molecular pump motor has the problem of low-speed stability, especially the molecular pump using a permanent magnet synchronous motor has the more prominent inherent low-speed stability, the vector control braking will become unstable at a certain speed. In order to prevent the motor from becoming unstable, after experimental testing, the speed threshold of this embodiment is 30%-40% of the rated speed of the motor, preferably 35%.

[0034] In practice, to further shorten downtime due to process adjustments or emergency situations, operators may fill the molecular pump chamber with air or nitrogen. If gas is added in step s1, the pressure sensor unit will detect a pressure increase. At this point, even if the motor speed has not dropped to the speed threshold, the system must proceed directly to step s2. This is because large amounts of gas in the molecular pump chamber can cause instability in vector control braking, preventing the rotor from oscillating and potentially falling, which could damage the equipment.

[0035] s2. The power module disconnects the DC bus from power supply, and the system performs resistance braking.

[0036] First, connect the highest-order energy release subunit, that is, the first-order energy release subunit, such as Figure 2As shown, the back EMF generated on the DC bus is consumed by the energy dissipation resistor. When the back EMF on the DC bus drops to the voltage threshold, the energy release sub-unit of this stage is disconnected and switched to the next stage energy release sub-unit. The voltage threshold is 10% of the back EMF on the DC bus when the first stage energy release sub-unit is connected. Then, the second stage energy release sub-unit and the third stage energy release sub-unit are connected in sequence according to the above rules, as shown in FIG. Figure 3-Figure 4 As shown, the process continues until the lowest-order energy release subunit, ie, the third-order energy release subunit, is disconnected.

[0037] It should be noted that the resistance of the energy-consuming resistor needs to be selected according to the power required for braking. The parameters considered for resistance calculation include the braking speed range, the molecular pump's moment of inertia, the molecular pump's motor parameters, etc.

[0038] s3. Use motor winding short circuit to brake, such as Figure 5 until the motor speed drops to zero.

[0039] s4. The power module resumes supplying power to the DC bus, preparing for the next motor start-up.

[0040] In summary, the molecular pump stopping braking method described in an embodiment of the present invention adopts a multi-modal braking method that combines vector control braking and resistance braking, which can not only prevent the problem of molecular pump rotor instability and oscillation, but also enable the molecular pump to quickly complete a safe and stable braking process.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A molecular pump braking method based on a motor control system, the system comprising a power module, a DC bus, a main controller, and an inverter, wherein the power module is connected to the input of the DC bus to provide DC power to the DC bus, the output of the DC bus is connected to the input of the main controller, the main controller is used to control and monitor the entire system, the output of the main controller is connected to the input of the inverter, the inverter is used to convert DC power into AC power and supply power to the motor, and is characterized in that: The system also includes a DC bus voltage sampling unit, an energy release unit, and a pressure sensor unit. The DC bus voltage sampling unit is used to detect the voltage of the DC bus and feed it back to the main controller. The energy release unit includes a plurality of energy release sub-units arranged in sequence from high order to low order. Each energy release sub-unit includes a MOS tube and an energy dissipation resistor. The input end of the MOS tube is connected to the DC bus, the output end is connected to the energy dissipation resistor, and the control end is connected to the main controller. The resistance of the energy dissipation resistor in the previous order energy release sub-unit is greater than the resistance of the energy dissipation resistor in the next order energy release sub-unit. The pressure sensor unit is used to detect the pressure in the molecular pump cavity and feed it back to the main controller. The braking method comprises the following steps: s1. The main controller receives a shutdown command, and the system performs vector control braking and reduces the motor speed to the speed threshold; In step s1, if it is detected that the pressure in the molecular pump chamber rises, the process directly proceeds to step s2; s2. The power module disconnects the DC bus from power, and the system performs resistance braking. The highest-order energy release subunit is connected first, and the back EMF generated on the DC bus is dissipated through the energy-dissipating resistor. When the back EMF on the DC bus drops to the voltage threshold, the energy release subunit of that order is disconnected and the next-order energy release subunit is switched to. The system then operates sequentially according to the above rules until the lowest-order energy release subunit is disconnected. s3. Brake by short-circuiting the motor windings until the motor speed drops to zero; s4. The power module resumes supplying power to the DC bus, preparing for the next motor start-up.

2. A molecular pump stopping and braking method according to claim 1, characterized in that: The energy release unit includes three-stage energy release subunits.

3. A molecular pump stopping and braking method according to claim 1, characterized in that: In step s1 , the vector control braking is specifically as follows: the main controller controls the motor drive current output by the inverter to gradually decrease, and at the same time reverses the direction of the rotor magnetic field of the motor.

4. A molecular pump stopping and braking method according to claim 1, characterized in that: In step s1, the speed threshold is 30%-40% of the rated speed of the motor.

5. A molecular pump stopping and braking method according to claim 1, characterized in that: In step s2, the voltage threshold is 10% of the back electromotive force on the DC bus when the energy release sub-unit of this stage is connected.

6. A molecular pump stopping and braking method according to claim 1, characterized in that: The main controller is powered by a UPS uninterruptible power supply.

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