A control method of a vacuum drying system

Abstract

This invention relates to the field of vacuum drying technology, and provides a control method for a vacuum drying system. The vacuum drying system includes: a vacuum pump, a motor, a frequency converter, and a controller; the controller is signal-connected to the frequency converter; the frequency converter is signal-connected to the motor, and the frequency converter controls the frequency of the motor; the motor is drive-connected to the vacuum pump; an inlet pressure sensor is installed at the inlet of the vacuum pump to collect inlet pressure; an outlet pressure sensor is installed at the outlet of the vacuum pump to collect outlet pressure; a bearing temperature sensor is installed at the bearing of the vacuum pump to collect bearing temperature; a pump body temperature sensor is installed on the outer casing of the vacuum pump to collect vacuum pump temperature; and a Hall sensor is installed at the bearing of the vacuum pump to collect the actual rotational speed of the vacuum pump. The vacuum drying system employs PID control. This invention can improve drying effect, reduce water consumption, and improve control efficiency and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum drying, in particular to a control method of a vacuum drying system. BACKGROUND

[0002] In the field of medicine, food and other high hygiene level requirements, oil-free cleaning vacuum process scene is needed; the vacuum drying system can be vacuumized.

[0003] At present, the vacuum drying system that meets the needs of the medical industry in the market needs a stable water circulation system to provide the water flow required for its work. Such a vacuum drying system consumes a large amount of water, seriously wasting water resources, and the water circulation system increases power consumption; and the pipeline is complex, occupies a large area, has harsh installation and use requirements, and has a high use cost, which does not meet the current energy saving and consumption reduction needs. In addition, the current vacuum drying system uses fixed frequency control, which has the disadvantages of low control efficiency and high power consumption. SUMMARY

[0004] The present application mainly solves the problem of high water consumption of the existing vacuum drying system which must rely on the operation of the water system, and proposes a vacuum drying system with zero water consumption to improve the drying effect and reduce water consumption, save water resources; no lubricating oil is needed to lubricate the seal, which realizes oil-free and pollution-free, and improves the control efficiency and stability.

[0005] The present application provides a control method of a vacuum drying system, comprising: a vacuum pump, a motor, a frequency converter and a controller;

[0006] The controller is signal connected with the frequency converter; the frequency converter is signal connected with the motor, and the frequency converter controls the frequency of the motor; the motor is drivingly connected with the vacuum pump;

[0007] An inlet pressure sensor is arranged at the inlet of the vacuum pump for collecting the inlet pressure;

[0008] An outlet pressure sensor is arranged at the outlet of the vacuum pump for collecting the outlet pressure;

[0009] A bearing temperature sensor is arranged at the bearing of the vacuum pump for collecting the bearing temperature;

[0010] A pump body temperature sensor is arranged on the shell of the vacuum pump for collecting the temperature of the vacuum pump;

[0011] A Hall sensor is arranged at the bearing of the vacuum pump for collecting the actual rotating speed of the vacuum pump;

[0012] The inlet pressure sensor, the outlet pressure sensor, the bearing temperature sensor, the pump body temperature sensor and the Hall sensor are respectively signal connected with the controller.

[0013] Preferably, the controller uses the single-chip microcomputer STM32F103VE, and the controller is integrated with analog input channels, digital input channels, digital output channels, and PWM output channels.

[0014] Preferably, an RS232 interface and a hardware protection circuit are further provided on the controller.

[0015] Preferably, the frequency converter is a functional unit, including: a rectification unit, a high-capacity capacitor, an inverter, and a frequency conversion control unit.

[0016] Preferably, the vacuum drying system adopts PID control, and the control process is as follows:

[0017] Step 1, collect the current operating state data of the vacuum pump; wherein, the current operating state data of the vacuum pump includes: the bearing temperature t, the inlet pressure Pin, the outlet pressure Pout, the rotational speed r, and the pump body temperature tb;

[0018] Step 2, the controller obtains the current operating state data of the above-mentioned vacuum pump, reads the set outlet pressure threshold P, reads the set bearing operating temperature threshold T, and obtains the bearing temperature difference and the outlet pressure difference based on the current operating state data of the vacuum pump, so as to determine the temperature difference change rate a and the outlet pressure change rate b;

[0019] Step 3, the controller enters the PID operating mode according to the obtained current operating state data of the vacuum pump, and judges whether to perform PID frequency regulation depending on temperature or depending on pressure by setting the temperature threshold Tmin; when Tmin < a, perform PID frequency regulation depending on temperature and execute Step 4; when Tmin >= a, perform PID frequency regulation depending on pressure and execute Step 5;

[0020] Step 4, the controller gives the frequency f of the frequency converter according to the bearing temperature t and the temperature difference change rate a, and the frequency converter controls the motor rotational speed r according to the frequency f;

[0021] Step 5, give the frequency f of the frequency converter according to the outlet pressure P and the outlet pressure change rate b, and the frequency converter controls the motor rotational speed r according to the frequency f.

[0022] Preferably, in Step 2, the difference between the bearing operating temperature threshold and the bearing temperature (bearing temperature difference) A = T - t;

[0023] The difference between the outlet pressure threshold and the outlet pressure (outlet pressure difference) B = P - Pout;

[0024] The determination method of the temperature difference change rate a:

[0025] When A>100, a =A / 10; when A>10, a=10; A<=10, a=A;

[0026] Method for determining the rate of change of export pressure, b:

[0027] When B > 100, b = B / 10; when B > 10, b = 10; when B <= 10, b = B.

[0028] Preferably, the method for adjusting the PID frequency is as follows:

[0029] out=Kp×e(k)+Ki×∑e(k)+Kd×[e(k)-e(k-1)];

[0030] out represents the frequency output of the frequency converter, Kp represents the proportional control coefficient, Ki represents the integral control coefficient, Kd is the derivative control coefficient, e(k) represents the deviation of the current bearing temperature t from the bearing operating temperature threshold T or the deviation of the outlet pressure Pout from the outlet pressure threshold P, e(k-1) represents the deviation of the previous bearing temperature t from the bearing operating temperature threshold T or the deviation of the outlet pressure Pout from the outlet pressure threshold P; ∑e(k) represents the cumulative sum of e(k) and previous deviations, where k is 1, 2, 3...

[0031] Preferably, the vacuum pump includes: a pump body;

[0032] The pump body includes: a pump casing, a front cover, and a rotor;

[0033] The front cover is installed at the front end of the pump housing, and an air inlet and an air outlet are respectively opened on the front cover; an air inlet channel is provided on one side of the pump housing, and an air outlet channel is provided on the corresponding other side; the air inlet channel is connected to the air inlet, and the air outlet channel is connected to the air outlet.

[0034] The rotor is eccentrically disposed within the pump casing; the rotor has multiple grooves evenly distributed in the circumferential direction; a sliding vane is movably disposed in each groove;

[0035] The motor's output shaft is axially connected to the rotor;

[0036] The pump casing has a rear cover at its rear end, which is connected to the motor; the output shaft of the motor passes through the rear cover.

[0037] Preferably, the rear cover is mounted on the output shaft of the motor via a bearing.

[0038] Preferably, a sealing ring is filled in the center hole of the rear cover.

[0039] The control method for a vacuum drying system provided by this invention has the following advantages compared with the prior art:

[0040] 1. The control system features high integration, small size, high efficiency and reliability, practical functions, and simple operation. The integrated design combines the motor, controller, and vacuum pump into a single unit, resulting in high output and a simple structure.

[0041] 2. The vacuum pump requires no circulating water system, consuming zero water and saving water resources; it also eliminates the need for lubricating oil to lubricate the seals, achieving oil-free and pollution-free operation. The system has a simple structure, is easy to install, small in size, and low in cost.

[0042] 3. The vacuum pump uses a motor to rotate a rotor, which in turn drives the sliding vanes. Two adjacent vanes carry away the gas entering from the inlet channel, rotating it to the outlet channel for discharge, thus achieving vacuuming. This provides excellent vacuuming performance and improves production efficiency. A small amount of condensate may be produced during operation, but the equipment can still function normally.

[0043] 4. This invention can be applied to oil-free clean vacuum processes and has good application prospects in fields with high hygiene requirements, such as medicine and food.

[0044] 5. The vacuum drying system employs PID control to adjust the inverter's output frequency, forming a negative feedback system to stabilize the controlled variable at the target value. This is suitable for process control such as flow control, pressure control, and temperature control. This invention utilizes a temperature-regulating PID to quickly preheat the bearings to achieve the optimal stable operating temperature, and a pressure-regulating PID to reliably and stably achieve the system's ideal pressure value, fulfilling vacuum pump control requirements, improving system lifespan and stability, increasing control efficiency, and reducing energy consumption. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the system composition of the vacuum drying system provided by the present invention;

[0046] Figure 2 This is a schematic diagram of the controller provided by the present invention;

[0047] Figure 3 This is a schematic diagram of the inverter provided by the present invention;

[0048] Figure 4 This is a schematic diagram of the vacuum pump and motor provided by the present invention;

[0049] Figure 5 This is a schematic diagram of the vacuum pump provided by the present invention;

[0050] Figure 6 This is an exploded view of the vacuum pump provided by the present invention. Detailed Implementation

[0051] To make the technical problems solved by this invention, the technical solutions adopted, and the technical effects achieved clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings, not all of them.

[0052] like Figure 1 As shown, the control method for the vacuum drying system provided in this embodiment of the invention includes: a vacuum pump, a motor, a frequency converter, and a controller.

[0053] The controller is connected to the frequency converter via signal transmission. The frequency converter is connected to the motor via signal transmission, and the frequency converter controls the frequency of the motor. The motor is connected to the vacuum pump via drive, providing the vacuum pump with rotational power.

[0054] An inlet pressure sensor is installed at the inlet of the vacuum pump to collect the inlet pressure, which is the actual inlet pressure of the vacuum drying system.

[0055] An outlet pressure sensor is installed at the outlet of the vacuum pump to collect the outlet pressure, which is the actual outlet pressure of the vacuum drying system.

[0056] A bearing temperature sensor is installed at the bearing of the vacuum pump to collect the bearing temperature; the bearing is an important component of the vacuum pump, and it is necessary to monitor the bearing temperature.

[0057] The vacuum pump casing is equipped with a pump body temperature sensor for collecting the vacuum pump temperature.

[0058] A Hall sensor is installed at the bearing of the vacuum pump to collect the actual rotational speed of the vacuum pump.

[0059] The inlet pressure sensor, outlet pressure sensor, bearing temperature sensor, pump body temperature sensor, and Hall sensor are respectively connected to the controller signal.

[0060] like Figure 2 As shown, the controller uses an STM32F103VE microcontroller and integrates analog input channels, digital input channels, digital output channels, and PWM output channels. The controller also features an RS232 interface and hardware protection circuitry.

[0061] like Figure 3 As shown, the frequency converter is a functional unit, including: a rectifier unit, a high-capacity capacitor, an inverter, and a frequency conversion control unit.

[0062] A frequency converter is a power control device that uses frequency conversion technology and microelectronics technology to control an AC motor by changing the frequency of the motor's power supply.

[0063] A frequency converter mainly consists of a rectification unit (AC to DC), a filter, an inverter (DC to AC), a braking unit, a drive unit, a detection unit, and a microprocessor unit. The frequency converter adjusts the output voltage and frequency by switching its internal IGBTs, providing the required power voltage according to the actual needs of the motor, thereby achieving energy saving and speed regulation. In addition, the frequency converter has many protection functions, such as overcurrent, overvoltage, and overload protection.

[0064] The rectifier unit converts AC power with a fixed operating frequency into DC power.

[0065] The high-capacity capacitor stores the converted electrical energy.

[0066] The inverter: uses high-power IGBT electronic switches to convert direct current into square waves of different frequencies, widths, and amplitudes.

[0067] The frequency conversion control unit operates according to a set program, controlling the amplitude and pulse width of the output square wave to superimpose it into an approximately sinusoidal alternating current to drive the AC motor.

[0068] The vacuum drying system employs PID control, a process control method. PID control adjusts the inverter's output frequency by performing proportional, integral, and derivative operations on the difference between the controlled variable's feedback signal and the target variable signal, thus creating a negative feedback system that stabilizes the controlled variable at the target value. It is suitable for process control applications such as flow control, pressure control, and temperature control.

[0069] The specific control process of this invention is as follows:

[0070] Step 1: Collect the current operating status data of the vacuum pump; wherein, the current operating status data of the vacuum pump includes: bearing temperature t, inlet pressure Pin, outlet pressure Pout, rotational speed r, and pump body temperature tb.

[0071] The bearing temperature sensor collects the bearing temperature t, the inlet pressure sensor collects the inlet pressure Pin, the outlet pressure sensor collects the outlet pressure Pout, the Hall sensor collects the rotational speed r, and the pump body temperature sensor collects the pump body temperature tb.

[0072] Step 2: The controller acquires the current operating status data of the vacuum pump, reads the set outlet pressure threshold P, reads the set bearing operating temperature threshold T, and obtains the bearing temperature difference and outlet pressure difference based on the current operating status data of the vacuum pump, thereby determining the temperature difference change rate a and the outlet pressure change rate b.

[0073] Wherein, the difference between the bearing operating temperature threshold and the bearing temperature (bearing temperature difference) is A = Tt.

[0074] The difference between the outlet pressure threshold and the outlet pressure (outlet pressure difference) B = P - Pout.

[0075] The method for determining the rate of change of the temperature difference a:

[0076] When A > 100, a = A / 10; when A > 10, a = 10; when A <= 10, a = A.

[0077] The method for determining the rate of change of the outlet pressure b:

[0078] When B > 100, b = B / 10; when B > 10, b = 10; when B <= 10, b = B.

[0079] Step 3: Based on the currently obtained operating state data of the vacuum pump, the controller enters the PID operating mode and determines whether to perform PID frequency adjustment based on temperature or pressure by setting the temperature threshold Tmin.

[0080] When Tmin < a, perform PID frequency adjustment based on temperature and execute Step 4; when Tmin >= a, perform PID frequency adjustment based on pressure and execute Step 5.

[0081] Among them, the temperature threshold Tmin can be set to multiple values according to the actual working conditions for multi - gear selection. For example, setting different temperature thresholds Tmin in different seasons for control can better adapt to environmental changes.

[0082] The method of the above - mentioned PID frequency adjustment is as follows:

[0083] out = Kp×e(k)+Ki×∑e(k)+Kd×[e(k)-e(k - 1)];

[0084] out represents the frequency output of the frequency converter, Kp represents the proportional adjustment coefficient, Ki represents the integral adjustment coefficient, Kd is the differential adjustment coefficient, e(k) represents the deviation between the current bearing temperature t and the bearing operating temperature threshold T (the current bearing temperature difference) or the deviation between the outlet pressure Pout and the outlet pressure threshold P (the current outlet pressure difference), and e(k - 1) represents the deviation between the previous bearing temperature t and the bearing operating temperature threshold T (the previous bearing temperature difference) or the deviation between the outlet pressure Pout and the outlet pressure threshold P (the previous outlet pressure difference). ∑e(k) represents the cumulative sum of e(k) and the previous deviations, where k is 1, 2, 3….

[0085] The integral control coefficient Ki and the derivative control coefficient Kd are obtained through system settings. The integral control coefficient Ki in the PID controller eliminates residuals and adjusts the steady-state time. The derivative control coefficient Kd in the PID controller improves the system's dynamic performance, predicts error trends, and corrects errors in advance.

[0086] Step 4: The controller sets the frequency f of the frequency converter based on the bearing temperature t and the rate of change of temperature difference a. The frequency converter controls the motor speed r based on the frequency f.

[0087] The inverter frequency f starts from the set initial frequency fint01 and operates within the range of the minimum operating frequency Fmin and the maximum operating frequency Fmax. The specific operating frequency value is automatically obtained through PID control.

[0088] When executing step 4, the proportional gain Kp is obtained through the rate of change of the temperature difference, a, where Kp = X1 * a, and the coefficient X1 needs to be set. In a PID controller, the proportional gain Kp plays a role in accelerating the system's response speed, improving the system's regulation accuracy, and quickly adjusting errors.

[0089] This step uses PID control based on the bearing temperature t and the rate of change of temperature difference a to achieve the desired effect. By changing the frequency output, the bearing operating temperature is adjusted to reach the optimal working temperature. This working mode is the preheating stage.

[0090] Step 5: Based on the outlet pressure P and the outlet pressure change rate b, the frequency f of the frequency converter is given, and the frequency converter controls the motor speed r according to the frequency f.

[0091] The inverter frequency f starts from the set initial frequency fint02 and operates within the range of the minimum operating frequency Fmin and the maximum operating frequency Fmax. The specific operating frequency value is automatically obtained through PID control.

[0092] When performing step 5, the proportional adjustment coefficient Kp is obtained through the outlet pressure change rate b, Kp = X2 * b, and the X2 coefficient needs to be set.

[0093] The purpose is achieved by using PID control to control the outlet pressure P and the outlet pressure change rate b. This project uses a master control method, where the outlet pressure Pout and inlet pressure Pin are set, and the inverter frequency f is controlled to change the motor speed r, thereby adjusting the outlet pressure P and achieving a stable operating mode within the set value range.

[0094] This invention can achieve the design of various control modes through the rising steps: full steam working mode control mode, steam and condensate mixed working mode control mode, and pressure holding working mode.

[0095] like Figure 4 As shown, the vacuum pump includes: a pump body.

[0096] like Figures 5-6 As shown, the pump body includes: pump casing 1, front cover 2 and rotor 5.

[0097] The front cover 2 is installed at the front end of the pump housing 1. An air inlet 7 and an air outlet 8 are respectively opened on the front cover 2. An air inlet channel 9 is provided on one side of the pump housing 1, and an air outlet channel is provided on the corresponding other side. The air inlet channel 9 is connected to the air inlet 7, and the air outlet channel is connected to the air outlet 8.

[0098] The rotor 5 is eccentrically positioned inside the pump casing 1; the rotor 5 has multiple grooves evenly distributed in the circumferential direction; a sliding plate 6 is movably disposed in each groove. The multiple grooves are distributed in a radiating pattern and are located in a non-radial direction.

[0099] The output shaft of motor 4 is axially connected to rotor 5. The rotation of the output shaft of motor 4 drives the rotor 5 to rotate.

[0100] A rear cover 3 is provided at the rear end of the pump housing 1, and the rear cover 3 is connected to the motor 4; the output shaft of the motor 4 passes through the rear cover 3. The rear cover 3 is mounted on the output shaft of the motor 4 via a bearing 11. A sealing ring is filled in the center hole of the rear cover 3.

[0101] In addition, a motor mount 10 is provided at the bottom of the motor 4 to facilitate motor installation.

[0102] The working principle of the vacuum pump of this invention is as follows: The output shaft of the motor 4 rotates, driving the rotor 5 to rotate. Under the action of centrifugal force, the rotor 5 causes the sliding vanes 6 in the groove to slide outwards, while the vanes 6 remain in contact with the inner wall of the pump housing 1 due to the constraint of the pump housing 1. The rotor 5 is eccentrically positioned, with varying distances between its outer periphery and the inner wall of the pump housing 1. When the vanes 6 rotate from the area with smaller distances to the area with larger distances, they slide outwards; when they rotate from the area with larger distances to the area with smaller distances, they slide inwards due to the constraint of the pump housing 1, maintaining contact with the inner wall of the pump housing 1. Two adjacent vanes 6, the outer periphery of the rotor 5, and the inner wall of the pump housing 1 can form a movable gas space. When the vanes 6 rotate to the inlet channel 9, the two adjacent vanes 6 carry away the gas entering from the inlet channel 9, rotating it to the outlet channel for discharge.

[0103] The vacuum pump of this invention is used to evacuate the equipment, thereby purging the gas inside the equipment. It is also applicable if there is a small amount of liquid in the equipment, and it can also purge the liquid.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some or all of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a vacuum drying system, characterized in that, Including: a vacuum pump, a motor, a frequency converter and a controller; The controller is signal-connected to the frequency converter; the frequency converter is signal-connected to the motor, and the frequency converter controls the frequency of the motor; the motor is drivingly connected to the vacuum pump; An inlet pressure sensor is provided at the inlet of the vacuum pump for collecting the inlet pressure; An outlet pressure sensor is provided at the outlet of the vacuum pump for collecting the outlet pressure; A bearing temperature sensor is provided at the bearing of the vacuum pump for collecting the bearing temperature; A pump body temperature sensor is provided on the housing of the vacuum pump for collecting the temperature of the vacuum pump; A Hall sensor is provided at the bearing of the vacuum pump for collecting the actual rotational speed of the vacuum pump; The inlet pressure sensor, the outlet pressure sensor, the bearing temperature sensor, the pump body temperature sensor, and the Hall sensor are respectively signal-connected to the controller; The vacuum drying system adopts PID control, and the PID control method is as follows: Step 1: Collect the current operating status data of the vacuum pump; wherein, the current operating status data of the vacuum pump includes: bearing temperature t, inlet pressure Pin, outlet pressure Pout, rotational speed r, and pump body temperature t b ; Step 2, the controller obtains the current operating state data of the above-mentioned vacuum pump, reads the set outlet pressure threshold P, reads the set bearing operating temperature threshold T, and based on the current operating state data of the vacuum pump, obtains the bearing temperature difference and the outlet pressure difference, so as to determine the temperature difference change rate a and the outlet pressure change rate b; In step 2, the difference A between the bearing operating temperature threshold and the bearing temperature = T - t; The difference B between the outlet pressure threshold and the outlet pressure = P - Pout; The determination method of the temperature difference change rate a: When A > 100, a = A / 10; when A > 10, a = 10; when A <= 10, a = A; The determination method of the outlet pressure change rate b: When B > 100, b = B / 10; when B > 10, b = 10; when B <= 10, b = B; Step 3, the controller enters the PID operation mode according to the obtained current operating state data of the vacuum pump, and determines whether to perform PID frequency adjustment depending on temperature or depending on pressure by setting the temperature threshold Tmin; when Tmin < a, perform PID frequency adjustment depending on temperature and execute step 4; when Tmin >= a, perform PID frequency adjustment depending on pressure and execute step 5; The method of the PID frequency adjustment is as follows: out = Kp × e(k) + Ki × ∑e(k) + Kd × [e(k) - e(k - 1)]; out represents the frequency output of the frequency converter, Kp represents the proportional adjustment coefficient, Ki represents the integral adjustment coefficient, Kd is the differential adjustment coefficient, e(k) represents the deviation between the current bearing temperature t and the bearing operating temperature threshold T or the deviation between the outlet pressure Pout and the outlet pressure threshold P, e(k - 1) represents the deviation between the previous bearing temperature t and the bearing operating temperature threshold T or the deviation between the outlet pressure Pout and the outlet pressure threshold P; ∑e(k) represents the cumulative sum of e(k) and the previous deviations, where k is 1, 2, 3...; the integral adjustment coefficient Ki and the differential adjustment coefficient Kd are obtained through system settings; Step 4: The controller sets the inverter frequency f based on the bearing temperature t and the temperature difference change rate a. The inverter controls the motor speed r based on the inverter frequency f. When executing step 4, the proportional adjustment coefficient Kp is obtained through the temperature difference change rate a. Kp = X1 * a. The coefficient X1 needs to be set. Step 5: Based on the outlet pressure Pout and the outlet pressure change rate b, the frequency converter frequency f is given, and the frequency converter controls the motor speed r according to the frequency converter frequency f. When executing step 5, the proportional adjustment coefficient Kp is obtained through the outlet pressure change rate b, Kp = X2 * b, and the X2 coefficient needs to be set.

2. The control method for the vacuum drying system according to claim 1, characterized in that, The controller uses an STM32F103VE microcontroller and integrates analog input channels, digital input channels, digital output channels, and PWM output channels.

3. The control method for the vacuum drying system according to claim 2, characterized in that, The controller is also equipped with an RS232 interface and hardware protection circuit.

4. The control method for the vacuum drying system according to claim 1, characterized in that, The frequency converter is a functional unit, including: a rectifier unit, a high-capacity capacitor, an inverter, and a frequency conversion control unit.

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