Load balancing method suitable for PID (Proportion Integration Differentiation) regulating system of air compressor

Abstract

The invention discloses a load balancing method suitable for a PID (Proportion Integration Differentiation) adjusting system of an air compressor, which fully utilizes the PID adjusting principle of equipment, achieves the purpose of adjusting the load of a single unit by changing the output signal of a pressure sensor, and finally realizes the load balancing of a plurality of units. The invention discloses a load balancing method suitable for an air compressor with a PID (Proportion Integration Differentiation) adjusting system. The centrifugal air compressor unit comprises an air inlet valve, a bypass valve, a controller, a pressure sensor, a one-way valve and a centrifugal air compressor; the air inlet valve is communicated with the centrifugal air compressor through a pipeline, the centrifugal air compressor is communicated with an inlet of the one-way valve through a pipeline, an outlet of the one-way valve is communicated with the pressure sensor through a pipeline, and an outlet of the one-way valve is communicated with the bypass valve through a pipeline. The controller is electrically connected with the air inlet valve, the pressure sensor and the bypass valve. Exhaust of the two centrifugal air compressor units is gathered to a header 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 a PID regulating system provided in an air compressor. Background Art

[0002] Centrifugal air compressors are a general-purpose equipment widely used in industrial production. In the air compressor station of a factory, a compressed air system is usually composed of multiple air compressors. Moreover, the air compressors all have built-in PID adjustment function, that is, according to the target pressure and the actual exhaust pressure of the unit, the air intake valve of the air compressor is PID-adjusted to adjust the air supply of the air compressor. When the air consumption of the system increases, the opening of the air intake valve will be gradually increased until it is adjusted to be fully open, i.e. full load. However, as the system usage decreases and the exhaust pressure increases, the intake valve will gradually close to reduce the air supply of the air compressor, and it will also begin to deviate from the high-efficiency operation area of ​​the unit. When it is adjusted to the minimum load of the machine (usually 70% of the full load), in order to avoid mechanical surge damage to the centrifugal unit, the excess compressed air will be directly discharged into the atmosphere by gradually opening the vent valve, resulting in energy waste. From the perspective of a single unit, this is a mature design that meets production needs and protects the machine.

[0003] However, when multiple units are connected to the network, the difference in pipeline transmission pressure drop will cause an imbalance in the load of each unit. 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 in which the bypass valve is opened for venting.

[0004] Although this situation can be solved by resetting the target pressure of the unit, in actual production, some centrifugal units are in operation and are in the process of protecting the equipment, so the target pressure cannot be adjusted (unless they are shut down first). In many production scenarios, the units are in continuous operation and do not have the requirement to stop the air compressor to reset the target pressure. Moreover, the adjustment of the target pressure of a single unit will eventually affect the change of the production gas supply pressure, resulting in a decrease in system stability. Similar problems will also be faced in variable frequency driven screw air compressors, because variable frequency screw units also calculate based on the target set pressure and the actual pressure, and then adjust the speed by adjusting the inverter output to adjust the load. Summary of the invention

[0005] 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 PID control system, which makes full use of the equipment's own PID control principle, achieves the goal of adjusting the load of a single unit by changing the output signal of the pressure sensor, and finally realizes the load balancing of multiple units.

[0006] To solve the above technical problems, the purpose of the present invention is achieved as follows: A load balancing method suitable for an air compressor with a built-in PID adjustment 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; 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 so that the centrifugal air compressor can inhale more gas and increase the supply of compressed air. Otherwise, the opening of the intake valve is gradually reduced so that the centrifugal air compressor can inhale less gas and reduce 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.

[0007] On the basis of the above scheme and as a preferred scheme of the above scheme: the exhaust gases 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, i.e., in the production process.

[0008] 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 increases, 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.

[0009] On the basis of the above scheme and as a preferred scheme of the above scheme: 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; The outlet pressure value P1 signal of the pressure sensor first enters the newly added PLC controller and then enters the controller of the centrifugal air compressor; when the load of the two centrifugal air compressor units is detected to be unbalanced, the outlet pressure value collected by the low-load centrifugal air compressor unit is compared, and 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 to achieve no load reduction or a small load reduction; 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.

[0010] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects: Compared with the prior art, the load balancing method of the present invention, which is suitable for the PID adjustment system of the air compressor, The present invention changes the existing single adjustment target value variable to change the controller PID regulation through systematic reverse thinking, and proposes a method of changing the collected variable value, thereby providing 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 very versatile, providing a new control method for energy saving of air compressor systems.

[0011] 1. Maintain the control process and protection mechanism of the original air compressor equipment to ensure the reliability of the equipment; 2. Provides a general control method that has been put into practice in several projects; 3. Control and algorithm are implemented on the existing hardware of the system control PLC, saving hardware costs; 4. It realizes load balancing among multiple units and improves the energy efficiency of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the connection structure of a centrifugal air compressor unit.

[0013] Figure 2 It is a schematic diagram of the connection structure of two centrifugal air compressor units of the present invention.

[0014] Figure 3 It is a schematic diagram of regulating the resistance difference effect of the present invention.

[0015] Figure 4 It is a schematic diagram of the overall structure of the present invention.

[0016] Figure 5 It is a schematic diagram of regulating two centrifugal air compressor units of the present invention.

[0017] Figure 6 It is a schematic diagram of the process system of the present invention.

[0018] Reference numerals: intake valve IV, bypass valve BV. DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings; 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 ) 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 rise, otherwise it will fall) 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 is gradually increased so that the centrifugal air compressor can inhale more gas, that is, the supply of compressed air is increased. Otherwise, the opening of the intake valve is gradually reduced so that the centrifugal air compressor can inhale less gas and reduce the supply of compressed air.

[0020] However, when the suction gas is reduced to about 70% of the rated flow, it is not appropriate to reduce it further, because it will cause mechanical surge of the high-speed centrifuge, causing equipment failure or even damage. At this time, the controller will open the bypass valve (the opening degree is between 0~100%). The function of the bypass valve is to discharge the excess compressed air directly into the atmosphere. The opening of the bypass valve regardless of its opening degree is a waste of energy (in order to avoid surge, the compressed gas is released again). Figure 1 This is the control logic diagram of the centrifugal air compressor unit: Figure 2 In actual working conditions, there are usually multiple centrifugal air compressor units. We take two as an example (see Figure 2), the exhaust gases of the two units will be collected into the main pipe and the main pipe pressure Pz will be established at the main pipe. Similarly, the pressure change of Pz depends on the common air supply of the two units and the compressed air consumption in the downstream of the main pipe, that is, in the production process. If the supply is greater than the consumption, Pz will start to rise, which will in turn affect the rise of P1, and then the controller will guide the intake valve to close, and vice versa.

[0021] 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 physical processes such as pipelines, drying equipment, filters, etc., and the gas flow will form pressure differences △P1 and △P2 respectively when passing through them. 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 pipelines, drying equipment, filters, etc. that pass through the transportation process will have a decrease in the gas flow rate flowing through them, 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 in a small working condition, and the other is in a full load condition. The actual situation is that even if both machines are running at less than full load, the different resistances of the pipelines, 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 emptied. This is the inevitable result of the difference in pipeline resistance on the PID adjustment of the unit, which ultimately guides the flow change to adapt to the different resistances of different pipelines to balance the pressure. ( Figure 3 ) describes the impact of pipeline resistance difference effect on unit load. Before time t1, because the main pipe pressure Pz is low, both units are running at full load at this stage, 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 of △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 PID adjustment of the controller, the unit's air supply flow decreases, 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 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.

[0022] In view of the above common problem, in order to achieve load balancing between the two units, it is obviously not practical to change the physical facilities that form resistance such as pipelines, drying equipment, filters, etc., because once the factory is put into production, it will be difficult to stop, and the pipelines, drying equipment, filters, etc. will also have irregular resistance changes as they are used; 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 with large resistance is relatively higher, so that the resistance difference can be overcome, and at the same time, 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 they are shut down, and some models cannot correct the target pressure value through communication. In most cases in production, 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 of air supply flow in the pipeline, and it is not a fixed value.

[0023] (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 air inlet valves are IV-1 and IV-2, 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 machine with the lower load is calculated and output by the PLC controller as a reduced pressure signal value to the air compressor controller. At this time, the controller will consider that the outlet pressure value P1 is lower than the target setting pressure P2 of the controller, and thus maintain the air inlet 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 decrease or the load decreases slightly. At this time, because both 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's 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.

[0024] Figure 5 In program control, in order to ensure the stability of gas supply, the adjustment process is carried out gradually. Figure 5A regulation process of two machines is given. In the initial state, the exhaust volume of the No.1 machine is relatively low (the vertical coordinate Q in the figure represents the flow rate, and the horizontal coordinate T represents the time). The pressure value signal output by its pressure sensor is calculated by the PLC controller and then given a slight reduction and given to the air compressor controller, which will prompt the internal PID controller of the No.1 machine to increase the load of No.1, that is, step 1. Because the increase in the air supply flow of the No.1 machine will increase the flow to the main pipe, the supply flow will exceed the consumption flow of the main pipe, causing a slight increase in the main pipe pressure Pz, and then causing a slight increase in the pressure collected by the pressure sensor P1 of the No.2 machine. After time t, the No.2 machine will close the opening of the intake valve IV to a certain extent, so that the total air supply flow of the two units maintains the original total air supply flow. Then the pressure sensor of the No.1 machine repeats the above process and enters Step2 to achieve a slight increase in load. After time t, the No.2 unit achieves a slight decrease in load, and then enters Step3 and Step4, and finally achieves a close load rate of the two machines, achieves the goal of load balancing, and avoids waste caused by venting.

[0025] Similar logic and method, 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 also be used to increase the load of one of the machines and further reduce the load of the other, eventually stopping the other machine.

[0026] Figure 6 The process of each step is briefly presented. Before putting the balancing control function into use, 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: identification and adjustment of load imbalance during the operation of each device; correction amplitude of each Step pressure signal (using relative percentage value); the time period for waiting for system self-regulation after each Step adjustment; and constraint conditions for terminating adjustment.

[0027] When the system balance 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 monitor the changes in the main pipe pressure at the same time to ensure the stability and reliability of the system; if it exceeds the preset safety threshold, exit the adjustment and resume the adjustment process of the previous STEP, and perform calculations and identification after a system response cycle to decide whether to enter Step 2.

[0028] The present invention is a universal solution, applicable to centrifuge equipment and different variable frequency air compressor equipment from different manufacturers. Through precise control, the equipment can be operated in the high-efficiency load area, thus improving the operating efficiency of the equipment and achieving better process control and energy saving. Its core includes: 1. Added the processing process of pressure sensor signal acquisition; 2. The basic conditions for trigger signal regulation are determined; 3. Determine the amplitude and period of each signal adjustment; 4 determines the termination condition of signal conditioning.

[0029] 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. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element 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.

[0030] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot 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 "install", "set", "connect", "fix", "screw" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope 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 protection scope of the present invention.

Claims

1. A load balancing method suitable for the air compressor's built-in PID control system. Features: Including a 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 so that the centrifugal air compressor can inhale more gas and increase the supply of compressed air. Otherwise, the opening of the intake valve is gradually reduced so that the centrifugal air compressor can inhale less gas and reduce 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.

2. The load balancing method suitable for the air compressor's built-in PID adjustment system according to claim 1, Features: 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.

3. The load balancing method suitable for the air compressor's built-in PID adjustment system according to claim 2, Features: Before time t1, the main pipe pressure value Pz is low. At this stage, both centrifugal air compressor units are operating at full load, with the intake valve opening of 100% and the bypass valve opening of 0%. As the main pipe pressure value Pz increases, 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, and the air supply flow of the first centrifugal air compressor unit decreases. 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.

4. The load balancing method suitable for the air compressor's built-in PID adjustment system according to claim 1, Features: It also includes 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; The outlet pressure value P1 signal of the pressure sensor first enters the newly added PLC controller and then enters the controller of the centrifugal air compressor; when the load of the two centrifugal air compressor units is detected to be unbalanced, the outlet pressure value collected by the low-load centrifugal air compressor unit is compared, and 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 to achieve no load reduction or a small load reduction; 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.

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