A method for constant pressure oscillation control of variable frequency air compressor

Abstract

This application provides a constant pressure oscillation control method for a variable frequency air compressor. The method includes: S1: Real-time detection of air compressor pressure and current, and calculation of pressure change rate e(t), pressure change acceleration a(t), and current change rate i(t); S2: Construction of a pressure dynamic instability index E, which is calculated based on the pressure change rate e(t), pressure change acceleration a(t), and motor current change rate; S3: Comparison of the pressure dynamic instability index E with preset first and second thresholds, and selection of a preset control mode to control the air compressor based on the comparison result; S4: Execution of a control algorithm corresponding to the selected control mode to generate frequency commands for the inverter and control the air compressor speed. This method detects air compressor oscillations by constructing a pressure dynamic instability index and adaptively switches control modes accordingly, thereby effectively suppressing oscillations under various complex operating conditions.

Description

Technical Field

[0001] This application relates to the field of air compressor control, and in particular to a constant pressure oscillation control method for a variable frequency air compressor. Background Technology

[0002] In industrial production, variable frequency air compressors are widely used to provide a stable air supply, and their constant pressure control performance directly affects energy consumption, equipment lifespan, and the quality of processes at the air-consuming end. However, due to the inherent characteristics of air compressor systems—large inertia and significant hysteresis—and the randomness and abrupt changes in downstream air loads, traditional constant pressure control methods, such as conventional PID control, are clearly insufficient to handle such complex operating conditions. Fixed-parameter PID controllers struggle to achieve the optimal balance between response speed and control stability, often resulting in continuous oscillations of system pressure around the setpoint or significant overshoot and slow recovery during load abrupt changes. This pressure oscillation not only increases additional energy consumption but also accelerates fatigue damage to mechanical components, shortening equipment lifespan.

[0003] While existing technologies employ intelligent methods such as fuzzy control to improve performance, their control rules are often fixed and lack quantitative perception and forward-looking judgment of the degree of dynamic instability of the system. They cannot implement targeted control strategies according to different risk levels, and therefore cannot fundamentally suppress oscillations when dealing with drastic load changes or operating under low flow conditions.

[0004] Therefore, there is an urgent need in this field for a control method to achieve stable, efficient, and reliable constant pressure control of variable frequency air compressors. Summary of the Invention

[0005] This application provides a constant pressure oscillation control method for a variable frequency air compressor. This method constructs a pressure dynamic instability index to perceive the oscillation risk of the air compressor in real time, and adaptively switches between three control modes: precise tracking, smooth suppression, and feedforward hold. This achieves a shift from passive correction to active prevention, thereby effectively suppressing oscillations under various complex operating conditions, significantly improving the stability and response speed of constant pressure control. At the same time, by avoiding unnecessary control actions and realizing intelligent sleep management, it achieves the comprehensive beneficial effects of reducing system energy consumption and extending equipment life.

[0006] Firstly, a method for controlling constant pressure oscillation in a variable frequency air compressor is provided, the method comprising: S1: Real-time detection of air compressor pressure and current, and calculation of pressure change rate e(t), pressure change acceleration a(t), and current change rate i(t); S2: Construct a pressure dynamic instability index E, which is calculated based on the pressure change rate e(t), pressure change acceleration a(t), and motor current change rate. S3: Compare the pressure dynamic instability index E with the preset first threshold and second threshold, and select a mode from the preset control modes to control the air compressor based on the comparison result. The preset control modes include: precise tracking mode, smooth suppression mode and feedforward holding mode. S4: Run the control algorithm corresponding to the selected control mode to generate the frequency command of the inverter and control the speed of the air compressor.

[0007] It should be understood that by constructing a pressure dynamic instability index E, the tendency of system instability can be detected in advance; based on the threshold judgment of this index, the control mode can be switched precisely, transforming the traditional passive response control method to pressure deviation into an active intervention strategy based on system stability prediction. This allows for the implementation of corresponding suppression measures before oscillations occur, resolving the technical contradiction between response speed and system stability in constant pressure control, and significantly improving the system's control quality, anti-interference ability, and operating efficiency.

[0008] It should be understood that the pressure change rate e(t) characterizes the instantaneous trend of system pressure change, the pressure change acceleration a(t) reveals the intensification or deceleration of this trend, and the motor current change rate i(t) provides direct and rapid electrical feedback on load-side disturbances. By integrating these three key dynamic parameters—pressure change rate e(t), pressure change acceleration a(t), and motor current change rate i(t)—a pressure dynamic instability index E is constructed. This index not only quantifies the instantaneous instability of the current system but also allows for proactive prediction of future oscillation risks based on acceleration and current abrupt changes, thus providing accurate decision-making basis for intelligent switching of control modes.

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the formula for calculating the pressure dynamic instability index E is as follows: , in, These are pre-calibrated non-negative weighting coefficients.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, the selection of the preset control mode includes: When the pressure dynamic instability index E is less than the first threshold, the precise tracking mode is activated; When the first threshold < the pressure dynamic instability index E < the second threshold, the smoothing suppression mode is activated; When the pressure dynamic instability index E is greater than or equal to the second threshold, the feedforward hold mode is activated.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, the method includes: In the precise tracking mode, a conventional proportional-integral control algorithm is used; In the smoothing suppression mode, a proportional-integral control algorithm is employed; In the feedforward hold mode, at least a feedforward frequency compensation amount is calculated based on the current change rate, and this compensation amount is used as the dominant output, while the integral operation in the proportional-integral control algorithm is paused.

[0012] It should be understood that the multi-mode switching control based on the threshold criterion of the pressure dynamic instability index E transforms the traditional single control strategy into adaptive control that matches the real-time risk assessment of the system: when the E value is low, the precise tracking mode is used to ensure control accuracy; when the E value increases, the smoothing suppression mode actively dampens the system oscillation trend; when the E value reaches the high-risk threshold, the system switches to the feedforward hold mode, directly generating compensation commands through the current change rate and pausing integral calculation. This utilizes the speed of feedforward control while avoiding the control lag caused by integral saturation, thus enabling the implementation of the optimal control strategy under different risk levels and achieving a balance between control accuracy and system stability.

[0013] In conjunction with the first aspect, in some implementations of the first aspect, the formula for calculating the feedforward frequency compensation amount in the feedforward hold mode is as follows: , in, K This is the feedforward gain coefficient.

[0014] In conjunction with the first aspect, in some implementations of the first aspect, when switching back from the smoothing suppression mode or the feedforward hold mode to the precise tracking mode, the integral term of the proportional-integral controller is reset.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes low-load condition management: When the pressure dynamic instability index E is lower than the third threshold for a continuous time T, and the average value of the current for the continuous time T is lower than the set current threshold, it is determined that the air compressor has entered a low load condition, and the air compressor is controlled to enter the pulse maintenance mode. In the pulse maintenance mode, when the pressure drops to the start pressure threshold, the air compressor is controlled to start running at a preset speed until the pressure reaches the target pressure value and then stops.

[0016] It should be understood that in feedforward hold mode, the feedforward compensation is calculated based on the current change rate and by specifying the gain coefficient K, which enables rapid and accurate compensation for load disturbances. At the same time, combined with the reset operation of the integral term during mode switching, the control lag problem caused by integral saturation is effectively avoided. Furthermore, by introducing an intelligent identification and pulsation maintenance mechanism for low-load conditions based on the pressure dynamic instability index E and the average current, the ineffective running time of the air compressor under low-load conditions is significantly reduced while ensuring pressure stability. This improves the dynamic response performance of the system and optimizes energy consumption and reduces equipment wear.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, the values ​​of the first threshold and the second threshold can be adjusted according to the target pressure value. Attached Figure Description

[0018] Figure 1 A flowchart illustrating the implementation of a constant pressure oscillation control method for a variable frequency air compressor, as provided in this application embodiment. Detailed Implementation

[0019] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” “the,” “the,” and “this” are intended to also include expressions such as “one or more,” unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, “at least one” and “one or more” refer to one, two, or more than two. The term “and / or” is used to describe the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can indicate: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character “ / ” generally indicates that the preceding and following related objects are in an “or” relationship.

[0020] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0021] In industrial production, the constant pressure control performance of variable frequency air compressors directly affects energy consumption, equipment lifespan, and process quality. However, air compressor systems exhibit significant inertia and hysteresis, coupled with sudden changes in air load, making it difficult for traditional PID control to balance response speed and stability. This often leads to continuous pressure oscillations or overshoot, increasing energy consumption and accelerating equipment wear. Existing improvement methods, such as fuzzy control, still lack the ability to quantitatively perceive the dynamic instability of the system due to fixed control rules. They cannot implement targeted strategies based on risk levels and have limited effectiveness in dealing with drastic load changes and low-flow conditions.

[0022] Therefore, there is an urgent need for a new method that can achieve stable and efficient constant pressure control.

[0023] This application provides a constant pressure oscillation control method for a variable frequency air compressor, which can effectively overcome the above-mentioned problems.

[0024] The technical solutions provided in the embodiments of this application will be described below with reference to the accompanying drawings.

[0025] Figure 1 A flowchart illustrating the implementation of a constant pressure oscillation control method for a variable frequency air compressor, as provided in this application embodiment.

[0026] refer to Figure 1 In some examples, the method includes: S1: Real-time detection of air compressor pressure and current, and calculation of pressure change rate e(t), pressure change acceleration a(t), and current change rate i(t); S2: Construct a pressure dynamic instability index E, which is calculated based on the pressure change rate e(t), pressure change acceleration a(t), and motor current change rate. S3: Compare the pressure dynamic instability index E with the preset first threshold and second threshold, and select a mode from the preset control modes to control the air compressor based on the comparison result. The preset control modes include: precise tracking mode, smooth suppression mode and feedforward holding mode. S4: Run the control algorithm corresponding to the selected control mode to generate the frequency command of the inverter and control the speed of the air compressor.

[0027] In some examples, the formula for calculating the pressure dynamic instability index E is as follows: , in, These are pre-calibrated non-negative weighting coefficients.

[0028] In some examples, the selection of the preset control mode includes: When the pressure dynamic instability index E is less than the first threshold, the precise tracking mode is activated; When the first threshold < the pressure dynamic instability index E < the second threshold, the smoothing suppression mode is activated; When the pressure dynamic instability index E is greater than or equal to the second threshold, the feedforward hold mode is activated.

[0029] In some examples, the method includes: In the precise tracking mode, a conventional proportional-integral control algorithm is used; In the smoothing suppression mode, a proportional-integral control algorithm is employed; In the feedforward hold mode, at least a feedforward frequency compensation amount is calculated based on the current change rate, and this compensation amount is used as the dominant output, while the integral operation in the proportional-integral control algorithm is paused.

[0030] In some examples, under the feedforward hold mode, the formula for calculating the feedforward frequency compensation is: , Where K is the feedforward gain coefficient.

[0031] In some examples, when switching back from the smoothing suppression mode or the feedforward hold mode to the precise tracking mode, the integral term of the proportional-integral controller is reset.

[0032] In some examples, the method also includes low-load condition management: When the pressure dynamic instability index E is lower than the third threshold for a continuous time T, and the average value of the current for the continuous time T is lower than the set current threshold, it is determined that the air compressor has entered a low load condition, and the air compressor is controlled to enter the pulse maintenance mode. In the pulse maintenance mode, when the pressure drops to the start pressure threshold, the air compressor is controlled to start running at a preset speed until the pressure reaches the target pressure value and then stops.

[0033] In some examples, the values ​​of the first threshold and the second threshold can be adjusted according to the target pressure value.

[0034] In one possible implementation, the air compressor pressure and current are monitored in real time at a sampling frequency of 100Hz. The pressure change rate e(t) and pressure change acceleration a(t) are obtained through differential calculation, and the current change rate i(t) is calculated simultaneously. Weighting coefficients α=0.5, β=0.3, and θ=0.2 are used. The pressure dynamic instability index E is calculated in real time according to the formula E=0.5|e(t)|+0.3|a(t)|+0.2|i(t)|. A first threshold of 0.4 and a second threshold of 0.8 are set. When E<0.4, conventional proportional-integral control is used to ensure accurate pressure tracking. When 0.4≤E<0.8, a first-order inertial loop with a time constant of 0.5s is connected to the output of the proportional-integral control. The system uses smooth control commands. When E≥0.8, it calculates the feedforward compensation based on ΔF=2*i(t) according to the feedforward gain K=2 and outputs it directly, while pausing the integral term of the proportional-integral controller. When the system returns to stability and switches back to the precise tracking mode, the integral term of the proportional-integral controller is cleared and reset. When the pressure dynamic instability index E is below the third threshold for 30 consecutive seconds, and the average motor current is below 20% of the rated current during this period, the system determines that it has entered a small load condition and switches to the pulse maintenance mode. In this mode, when the system pressure is detected to drop to the starting threshold, the controller immediately starts the air compressor at a preset speed for rapid pressure replenishment, and immediately controls the air compressor to stop when the pressure returns to the target value.

[0035] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or variations made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A variable frequency air compressor constant pressure surge control method, characterized by, The method includes: S1: Real-time detection of air compressor pressure and current, and calculation of pressure change rate e(t), pressure change acceleration a(t), and current change rate i(t); S2: Construct a pressure dynamic instability index E, which is calculated based on the pressure change rate e(t), pressure change acceleration a(t), and motor current change rate. S3: Compare the pressure dynamic instability index E with the preset first threshold and second threshold, and select a mode from the preset control modes to control the air compressor based on the comparison result. The preset control modes include: precise tracking mode, smooth suppression mode and feedforward holding mode. S4: Run the control algorithm corresponding to the selected control mode to generate the frequency command of the inverter and control the speed of the air compressor.

2. The method of claim 1, wherein, The formula for calculating the pressure dynamic instability index E is as follows: ， wherein, are the pre-calibrated non-negative weight coefficients.

3. The method of claim 1, wherein, The selection of the preset control mode includes: When the pressure dynamic instability index E is less than the first threshold, the precise tracking mode is activated; When the first threshold < the pressure dynamic instability index E < the second threshold, the smoothing suppression mode is activated; When the pressure dynamic instability index E is greater than or equal to the second threshold, the feedforward hold mode is activated.

4. The method of claim 3, wherein, The method includes: In the precise tracking mode, a conventional proportional-integral control algorithm is used; In the smoothing suppression mode, a proportional-integral control algorithm is employed; In the feedforward hold mode, at least a feedforward frequency compensation amount is calculated based on the current change rate, and this compensation amount is used as the dominant output, while the integral operation in the proportional-integral control algorithm is paused.

5. The method of claim 4, wherein, In the feedforward hold mode, the formula for calculating the feedforward frequency compensation is: ， wherein K is a feedforward gain coefficient.

6. The method of claim 5, wherein, When switching back to the precise tracking mode from the smoothing suppression mode or the feedforward hold mode, the integral term of the proportional-integral controller is reset.

7. The method of claim 1, wherein, The method also includes low-load condition management: When the pressure dynamic instability index E is lower than the third threshold for a continuous time T, and the average value of the current for the continuous time T is lower than the set current threshold, it is determined that the air compressor has entered a low load condition, and the air compressor is controlled to enter the pulse maintenance mode. In the pulse maintenance mode, when the pressure drops to the start pressure threshold, the air compressor is controlled to start running at a preset speed until the pressure reaches the target pressure value and then stops.

8. The method of claim 6, wherein, The values ​​of the first threshold and the second threshold can be adjusted according to the target pressure value.

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