A load balancing method suitable for the PID regulation system built into an air compressor

Abstract

The present invention discloses a load balancing method suitable for an air compressor with a built-in PID control system. The method fully utilizes the PID control principle of the device itself and achieves the goal of adjusting the load of a single unit by changing the output signal of a pressure sensor, thereby ultimately achieving load balancing of multiple units. A load balancing method suitable for an air compressor with a built-in PID control system comprises a centrifugal air compressor unit; the centrifugal air compressor unit comprises an intake valve, a bypass valve, a controller, a pressure sensor, a check valve, and a centrifugal air compressor; the intake valve is connected to the centrifugal air compressor via a pipeline, the centrifugal air compressor is connected to the inlet of the check valve via a pipeline, the outlet of the check valve is connected to the pressure sensor via a pipeline, and the outlet of the check valve is connected to the bypass valve via a pipeline; the controller is electrically connected to the intake valve, the pressure sensor, and the bypass valve respectively; and the exhaust gases of the two centrifugal air compressor units are combined on a main pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of air compressors, and in particular relates to a load balancing method suitable for an air compressor with a built-in PID regulation system. Background Art

[0002] Centrifugal air compressors are a general-purpose equipment widely used in industrial production. In a factory's air compressor station, a compressed air system is usually composed of multiple air compressors. In addition, the air compressors all have a built-in PID adjustment function. That is, according to the target pressure and the actual exhaust pressure of the unit, the PID adjustment is performed on the air compressor's intake valve to adjust the air supply of the air compressor. When the system air consumption increases, the intake valve opening will be gradually increased until it is adjusted to fully open, that is, full load.

[0003] However, as system usage decreases and exhaust pressure rises, the intake valve gradually closes, reducing the air supply from the compressor. This also causes the unit to depart from its high-efficiency operating range. When the unit reaches its minimum load (typically 70% of full load), the vent valve gradually opens to release excess compressed air directly into the atmosphere to prevent mechanical surge damage to the centrifugal unit, resulting in energy waste. From a single unit perspective, this is a mature design that both meets production needs and protects the unit.

[0004] However, when multiple units are connected to the network, the load of each unit will become unbalanced due to the difference in pipeline transmission pressure drop. Eventually, some units will be in a high-load operating state, while some units will be in a low-load operating state. In addition, the low-load unit will operate at the minimum load state, resulting in a wasteful situation where the bypass valve is opened to vent.

[0005] Although this situation can be resolved by resetting the unit's target pressure, in actual production, some centrifugal units are in operation for equipment protection and the target pressure cannot be adjusted (unless the unit is shut down first). Many production scenarios require continuous operation and do not require the air compressor to be stopped to reset the target pressure. Moreover, adjusting the target pressure of a single unit will ultimately affect the changes in the production air supply pressure, resulting in a decrease in system stability.

[0006] Similar problems also occur in variable frequency driven screw air compressors, because variable frequency screw units also calculate the actual pressure based on the target set pressure, and then control the speed by adjusting the inverter output to adjust the load. Summary of the Invention

[0007] In view of the shortcomings of the above background technology, the purpose of the present invention is to provide a load balancing method suitable for the air compressor with a built-in PID control system, which makes full use of the equipment's own PID control principle and achieves the goal of adjusting the load of a single unit by changing the output signal of the pressure sensor, and ultimately realizes the balancing of the loads of multiple units.

[0008] In order to solve the above-mentioned technical problems, the purpose of the present invention is achieved as follows:

[0009] A load balancing method suitable for an air compressor with a built-in PID control system, comprising a centrifugal air compressor unit; the centrifugal air compressor unit comprises an intake valve, a bypass valve, a controller, a pressure sensor, a check valve and a centrifugal air compressor;

[0010] The air intake valve is connected to the centrifugal air compressor through a pipeline, the centrifugal air compressor is connected to the inlet of the one-way valve through a pipeline, the outlet of the one-way valve is connected to the pressure sensor through a pipeline, and the outlet of the one-way valve is connected to the bypass valve through a pipeline; the controller is electrically connected to the air intake valve, the pressure sensor, and the bypass valve respectively;

[0011] The exhaust gas of the two centrifugal air compressor units is collected on the main pipe;

[0012] The following steps are involved:

[0013] S1, when the centrifugal air compressor is running, the controller collects the outlet pressure value P1 of the unit through the pressure sensor and compares it with the target pressure value P2 set in the controller;

[0014] S2: If the outlet pressure value P1 is lower than the target pressure value P2, the opening of the intake valve is gradually increased to allow the centrifugal air compressor to inhale more gas, thereby increasing the supply of compressed air. Otherwise, the opening of the intake valve is gradually reduced to allow the centrifugal air compressor to inhale less gas, thereby reducing the supply of compressed air.

[0015] S3, when the centrifugal air compressor inhaled gas is reduced to 70% of the rated flow, it is not appropriate to reduce it further; at this time the controller will open the bypass valve, the bypass valve opening is between 0~100%, and the bypass valve will discharge the excess compressed air directly into the atmosphere.

[0016] On the basis of the above scheme and as the preferred scheme of the above scheme: the exhaust gas of the two centrifugal air compressor units will be collected into the main pipe and a main pipe pressure value Pz will be established at the main pipe; the pressure change of the main pipe pressure value Pz depends on the common air supply of the two units and the compressed air consumption downstream of the main pipe, that is, in the production process.

[0017] On the basis of the above scheme and as the preferred scheme of the above scheme: the main pipe pressure value Pz before time t1 is low. At this stage, both centrifugal air compressor units are operating at full load, the intake valve opening is 100%, and the bypass valve opening is 0%. As the main pipe pressure value Pz rises, the expected pressure is reached at time t1. At this time, the resistance of the first centrifugal air compressor unit is large, causing its outlet pressure value P1-1 to begin to rise and gradually exceed the target pressure value of its controller. The intake valve IV-1 begins to close under the PID adjustment of the controller, the air supply flow of the first centrifugal air compressor unit decreases, and the outlet pressure value P1-1 of the first centrifugal air compressor unit begins to decrease. At time t2, the intake valve IV-1 reaches the minimum opening, and the outlet pressure value P1-1 is still higher than the target pressure value of the controller. The bypass valve BV-1 begins to open, and the first centrifugal air compressor unit is in a low-energy-efficiency operation state.

[0018] On the basis of the above solution and as a preferred solution of the above solution: further comprising a PLC controller; the controller is electrically connected to the PLC controller, and the pressure sensor is electrically connected to the controller through the PLC controller;

[0019] The outlet pressure value P1 signal of the pressure sensor first enters the newly added PLC controller and then enters the centrifugal air compressor controller. When it detects that the load of the two centrifugal air compressor units is unbalanced, the outlet pressure value collected by the low-load centrifugal air compressor unit is compared. The PLC controller calculates and outputs a reduced pressure signal value to the air compressor controller. The centrifugal air compressor maintains the opening of the intake valve through the internal PID adjustment of its controller, achieving no load drop or a minimal load drop.

[0020] Both centrifugal air compressor units are in the high-load area. The total air supply capacity exceeds the consumption of compressed air in production. The main pipe pressure value Pz begins to rise, causing the outlet pressure value P1 of the two centrifugal air compressor units to rise. Then, the PID of the controller of the centrifugal air compressor unit acts on each intake valve to achieve a nearly synchronous reduction in the opening of the intake valves of the two centrifugal air compressor units, thereby reducing the air supply and achieving a balance between supply and demand.

[0021] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects:

[0022] Compared with the prior art, the load balancing method of the present invention, which is suitable for the air compressor with a built-in PID adjustment system,

[0023] The present invention uses systematic reverse thinking to change the existing single target value variable to change the controller PID regulation, and proposes a method of changing the collected variable value, which provides another precise control method for centrifugal air compressors or variable frequency screw machines. It is also a very economical method because the control system usually already includes a PLC controller CPU. The control method and strategy only changes the pressure signal of the original air compressor to: first enter the PLC controller and then return to the air compressor controller. The method and principle are simple, there is basically no increase in hardware investment, and it is highly versatile, providing a new control method for energy saving of air compressor systems.

[0024] 1. Maintain the control process and protection mechanism of the original air compressor equipment to ensure the reliability of the equipment;

[0025] 2. Provides a general control method that has been put into practice in several projects;

[0026] 3. Implement control and algorithms on the existing hardware of the system control PLC, saving hardware costs;

[0027] 4. Achieved load balancing among multiple units and improved the energy efficiency of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the connection structure of a centrifugal air compressor unit.

[0029] Figure 2 It is a schematic diagram of the connection structure of two centrifugal air compressor units of the present invention.

[0030] Figure 3 It is a schematic diagram of regulating the resistance difference effect of the present invention.

[0031] Figure 4 It is a schematic diagram of the overall structure of the present invention.

[0032] Figure 5 It is a schematic diagram of the adjustment of two centrifugal air compressor units of the present invention.

[0033] Figure 6 It is a flow chart of the method system of the present invention.

[0034] Reference numerals: intake valve IV, bypass valve BV. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings;

[0036] The flow control system of a centrifugal air compressor usually includes a centrifugal air compressor, an intake valve, a bypass valve, a controller and a pressure sensor (see Figure 1 )

[0037] When the centrifugal air compressor is running, the controller collects the outlet pressure value P1 of the unit through the pressure sensor (the pressure of P1 depends on the downstream compressed air consumption. When the supply is greater than the consumption, it will increase, otherwise it will decrease) and compares it with the target pressure value P2 set in the controller. If it is lower than the target pressure value P2, the opening of the intake valve will be gradually increased to allow the centrifugal air compressor to inhale more gas, that is, to increase the supply of compressed air. Otherwise, the opening of the intake valve will be gradually reduced to allow the centrifugal air compressor to inhale less gas, reducing the supply of compressed air.

[0038] However, when the intake air flow rate drops to approximately 70% of the rated flow rate, further reduction is inappropriate because it can cause mechanical surge in the high-speed centrifuge, leading to equipment failure or even damage. At this point, the controller will open the bypass valve (opening degree between 0 and 100%). The bypass valve's function is to discharge excess compressed air directly into the atmosphere. Opening the bypass valve, regardless of its opening degree, wastes energy (compressed gas is released to avoid surge). Figure 1 This is the control logic diagram of the centrifugal air compressor unit:

[0039] Figure 2 In actual working conditions, there are usually multiple centrifugal air compressor units. Let's take two as an example (see Figure 2 ), the exhaust gases of the two units will be collected into the main pipe and establish the main pipe pressure Pz at the main pipe. Similarly, the pressure change of Pz depends on the combined air supply of the two units and the compressed air consumption downstream of the main pipe, that is, in the production process. If the supply is greater than the consumption, Pz will start to rise, thereby affecting the rise of P1, and then the controller will guide the intake valve to close, and vice versa.

[0040] In actual use, the target pressure P2 of the two centrifugal air compressors is usually set to the same value, but the transportation process from the outlet to the main pipe Pz of the two units will include pipelines, drying equipment, filters and other physical processes. When the gas flows through them, pressure differences △P1 and △P2 will be formed respectively. Assuming that both units are fully loaded at the beginning, that is, full flow gas supply, but if the channel composed of the pipeline, drying equipment, filter, etc. corresponding to △P1 of the first centrifugal air compressor is relatively narrow or the resistance is relatively high, that is, the pressure drop of the gas passing through is greater than that of the transportation process where △P2 is located, the first centrifugal air compressor will be The exhaust pressure P1 of one centrifuge will be higher than that of the other centrifuge. At this time, the PID controller of the first centrifuge will gradually close the opening of the intake valve IV because it detects that P1 is higher than the target pressure value P1, thereby reducing the air supply flow of the first machine. At this time, the pipeline, drying equipment, filter, etc. passing through the transportation process will have a reduced gas flow rate, and the △P1 formed will also become smaller. In the end, the pressure P1 of the two machines is the same, but the load of the first air compressor is at a lower level, while the other is at full load.

[0041] The actual situation is that even if both machines are running at less than full load, the different resistances of the pipes, drying equipment, filters, etc. where △P1 and △P2 are located will lead to unbalanced loads on the two units, and even one of them may be vented. This is the inevitable result of the difference in pipe resistance on the PID adjustment of the units, which ultimately guides the flow change to adapt to the different resistances of different pipes to achieve pressure balance.

[0042] ( Figure 3 ) describes the impact of the pipeline resistance difference effect on the unit load. Before time t1, because the main pipe pressure Pz is low, both units are operating at full load, the intake valve opening is 100%, and the bypass valve opening is 0%. As the main pipe pressure Pz rises, the expected pressure is reached at time t1. At this time, because the first unit has a large resistance due to △P1, its exhaust pressure P1-1 begins to rise and gradually exceeds the target pressure of its controller. At this time, the intake valve IV-1 begins to close under the controller PID adjustment, the unit's air supply flow decreases, and the amount of gas flowing through the △P1 physical pipeline process decreases. △P1 becomes smaller, and the P1-1 pressure of the first unit begins to decrease. At time t2, the intake valve IV-1 reaches the minimum opening (about 70%), but P1-1 is still slightly higher than the target pressure of the controller. The bypass valve BV-1 begins to open, and the first unit is in a low-efficiency operation state.

[0043] To address this common problem, changing the physical facilities that create resistance, such as pipes, drying equipment, and filters, is not practical to achieve load balancing between the two units. This is because once the plant is in production, it is difficult to stop, and the pipes, drying equipment, and filters will also experience irregular changes in resistance as they are used.

[0044] To overcome the influence of resistance differences during the transportation process, a more reasonable method is to dynamically set the target pressure value of each air compressor, so that the target pressure value of the unit with large resistance is relatively higher. In this way, the difference in resistance can be overcome, and the load of each unit can be more balanced. However, in practice, the openness of centrifugal air compressors of different brands is different. Some types of centrifugal air compressors can only modify the target pressure setting when the compressor is shut down, and some models cannot correct the target pressure value through communication. In most production situations, there are no conditions to stop the machine. Even if there is a shutdown scenario, the change in pipeline pressure resistance △P also changes with the change in the air supply flow in the pipeline, and it is not a fixed value.

[0045] (See Figure 4 ), the beauty of the present invention is that it solves the above-mentioned problems through a universal method. Still taking two centrifugal air compressors as an example, the intake valves are IV-1 and IV-2, and the bypass valves are BV-1 and BV-2; the outlet pressure value P1 signal first enters the newly added PLC controller, and then enters the air compressor controller. When the load of the two units is unbalanced, the actual pressure value collected by the lower load machine is calculated by the PLC controller to output a reduced pressure signal value to the air compressor controller. At this time, the controller will think that the outlet pressure value P1 is lower than the controller's target setting pressure P2, and thus maintain the intake valve at I through the internal PID adjustment of its controller. V-1, the opening of the intake valve IV-2, to achieve the load does not drop or the load drops less, at this time because the two units are in the high load area, the total air supply capacity exceeds the consumption of compressed air in production, the main pipe pressure value Pz begins to rise, causing the outlet pressure value P1 of the two units to rise slightly, and then through the PID of the unit controller acting on each intake valve, the intake valve IV-1 of the two units, the intake valve IV-2 opening is reduced almost synchronously, to achieve a reduction in air supply, and finally achieve a balance between supply and demand while the loads of the two units are relatively close, achieving the goal of load balance.

[0046] Figure 5 In program control, in order to ensure the stability of gas supply, the adjustment process is carried out gradually. Figure 5The following example illustrates a two-unit regulation process. Initially, unit 1 has a low exhaust volume (in the diagram, the vertical coordinate Q represents flow rate, and the horizontal coordinate T represents time). The pressure signal output by its pressure sensor is calculated by the PLC controller and then slightly reduced. This is then fed to the air compressor controller, prompting the PID controller within unit 1 to increase its load (Step 1). This increase in unit 1's supply flow increases the flow to the main pipe, resulting in a situation where the supply flow exceeds the main pipe's consumption flow. This causes a slight increase in main pipe pressure Pz, which in turn causes a slight increase in the pressure detected by unit 2's pressure sensor P1. After time t, unit 2 closes its intake valve IV to a certain degree, maintaining the total air flow of the two units at the original value. The pressure sensor of unit 1 then repeats the process, slightly increasing its load in Step 2. After time t, unit 2 experiences a slight load decrease, which leads to Steps 3 and 4. Ultimately, the load rates of the two units are close, achieving load balancing and avoiding waste caused by venting.

[0047] Similar logic and methods apply. If both machines are running at low load and venting occurs, and the total compressed air demand can be met by one of the machines, the above method can be used to increase the load of one machine and further reduce the load of the other machine, ultimately stopping the other machine.

[0048] Figure 6 The process of each step is briefly presented. Before the balancing control function is activated, relevant parameters need to be set according to the system properties (such as the number of machines, the response time properties of each machine, the pressure change properties of the rectification system, etc.), including: the identification and adjustment components of the load imbalance during the operation of each device; the correction amplitude of the pressure signal of each step (using a relative percentage value); the time period for waiting for the system to self-regulate after each step adjustment; the constraints for terminating the adjustment, etc.

[0049] When the system balancing control mode is started, the preset program will determine whether there is load imbalance in the system based on the current equipment operation status, and then automatically increase the load of the unit with the lowest load by a preset amplitude through a micro-reduction pressure signal, and then monitor the changes in the opening of the unit's intake valve IV, the current amplitude, etc., and the changes in the main pipe pressure to ensure the stability and reliability of the system; if the preset safety threshold is exceeded, the adjustment is exited and the adjustment process of the previous STEP is resumed. After a system response cycle, calculation and identification are performed to decide whether to enter Step 2.

[0050] This invention is a universal solution that is applicable to centrifuge equipment and different variable frequency air compressor equipment from different manufacturers. Through precise control, it allows the equipment to operate in the high-efficiency load range, improves the operating efficiency of the equipment, and achieves better process control and energy saving. Its core includes:

[0051] 1. Added the processing process of pressure sensor signal acquisition;

[0052] 2. The basic conditions for triggering signal regulation are determined;

[0053] 3. Determine the amplitude and period of each signal adjustment;

[0054] 4 determines the termination condition of signal conditioning.

[0055] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0056] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. In the present invention, unless otherwise clearly specified and limited, the terms "installed", "set", "connected", "fixed", "screwed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection;

[0057] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A load balancing method suitable for an air compressor's built-in PID control system, characterized by: Including centrifugal air compressor unit; the centrifugal air compressor unit includes an intake valve, a bypass valve, a controller, a pressure sensor, a check valve and a centrifugal air compressor; The air intake valve is connected to the centrifugal air compressor through a pipeline, the centrifugal air compressor is connected to the inlet of the one-way valve through a pipeline, the outlet of the one-way valve is connected to the pressure sensor through a pipeline, and the outlet of the one-way valve is connected to the bypass valve through a pipeline; the controller is electrically connected to the air intake valve, the pressure sensor, and the bypass valve respectively; The exhaust gas of the two centrifugal air compressor units is collected on the main pipe; The following steps are involved: S1, when the centrifugal air compressor is running, the controller collects the outlet pressure value P1 of the unit through the pressure sensor and compares it with the target pressure value P2 set in the controller; S2: If the outlet pressure value P1 is lower than the target pressure value P2, the opening of the intake valve is gradually increased to allow the centrifugal air compressor to inhale more gas, thereby increasing the supply of compressed air. Otherwise, the opening of the intake valve is gradually reduced to allow the centrifugal air compressor to inhale less gas, thereby reducing the supply of compressed air. S3, when the centrifugal air compressor inhaled gas is reduced to 70% of the rated flow, it is not suitable to reduce it further; at this time, the controller will open the bypass valve, the bypass valve opening is between 0~100%, and the bypass valve will discharge the excess compressed air directly into the atmosphere; The exhaust gas of the two centrifugal air compressor units will be combined into a main pipe and establish a main pipe pressure value Pz at the main pipe. The pressure change of the main pipe pressure value Pz depends on the combined air supply of the two units and the compressed air consumption downstream of the main pipe, that is, the production process. The system further includes a PLC controller; the controller of the centrifugal air compressor unit is connected to the PLC controller, and the pressure sensor is connected to the controller of the centrifugal air compressor unit through the PLC controller; the pressure value P1 signal of the pressure sensor first enters the newly added PLC controller and is then output to the controller of the centrifugal air compressor unit; when the load of the two centrifugal air compressor units is detected to be unbalanced, the PLC controller calculates and outputs a reduced pressure signal value to the controller of the low-load centrifugal air compressor unit by comparison; the centrifugal air compressor unit maintains the opening of the intake valve through the internal PID adjustment of its controller. When the load of the low-load unit increases, both centrifugal air compressor units are in the high-load area, and the total air supply capacity exceeds the compressed air consumption in production. The main pipe pressure value Pz begins to rise, causing the outlet pressure values P1 of the two centrifugal air compressor units to increase. The PID of the centrifugal air compressor unit controller then acts on the respective intake valves to achieve a nearly synchronous reduction in the intake valve opening of the two centrifugal air compressor units, thereby reducing the air supply volume and achieving a balance between supply and demand.

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