Air-cooled variable frequency control method, system and storage medium for oil-free screw air compressor

Abstract

This application relates to the technical field of air-cooled control of air compressors, and discloses an air-cooled variable frequency control method, system, and storage medium for an oil-free screw air compressor. The method includes: acquiring the lubricating oil temperature and the secondary intake air temperature in real time; if both the lubricating oil temperature and the secondary intake air temperature are lower than the minimum control temperature, controlling the fan to operate at a first low frequency; if the secondary intake air temperature rises and crosses the minimum control temperature for the first time, delaying the fan control for a first duration; if the secondary intake air temperature exceeds the minimum temperature and the first difference between the two reaches a first set temperature difference value, adjusting the fan control frequency; if the lubricating oil temperature rises and crosses the minimum control temperature for the first time, increasing the control frequency at a second speed; and after the lubricating oil temperature and the secondary intake air temperature gradually decrease to the minimum control temperature, decreasing the fan control frequency at a third speed; this method can improve the energy-saving effect of the entire unit.

Description

Technical Field

[0001] This application relates to the technical field of air-cooled control of air compressors, and in particular to an air-cooled variable frequency control method, system and storage medium for an oil-free screw air compressor. Background Technology

[0002] Oil-free screw air-cooled air compressors are devices that achieve gas compression through non-contact rotor meshing. They dissipate the heat generated during compression via an air-cooling system, producing oil-free compressed air. These compressors are widely used in industries with stringent air quality requirements, such as food, pharmaceuticals, and semiconductors. The equipment utilizes synchronous gears to maintain rotor clearance and a multi-stage sealing structure to prevent oil from entering the compression chamber, ensuring the purity of the compressed air. Most oil-free screw air compressors use fixed-frequency air cooling for heat dissipation. Due to the multi-stage compression characteristics of the equipment, there are significant differences in the intake and exhaust temperatures, lubricating oil temperatures, and motor temperatures at each stage of the compressor, making it difficult to achieve dynamic temperature balance throughout the unit. To avoid localized overheating and equipment failure, the fan typically maintains a fixed-frequency, high-speed operation. Even in low ambient temperatures, the fan will not reduce its frequency. Because the fan operates at a fixed frequency, it cannot adjust its heat dissipation capacity according to the actual temperature requirements of the unit. This results in significant energy waste when the ambient temperature is low or the unit is under partial load. This not only increases the operating cost of the equipment but also significantly reduces the overall energy-saving effect of the unit. Summary of the Invention

[0003] To improve the energy efficiency of the entire unit, this application provides an air-cooled variable frequency control method, system, and storage medium for an oil-free screw air compressor.

[0004] In a first aspect, this application provides an air-cooled variable frequency control method for an oil-free screw air compressor, employing the following technical solution: A method for air-cooled variable frequency control of an oil-free screw air compressor includes the following steps: The lubricating oil temperature value is obtained in real time based on the preset lubricating oil temperature sensor, and the secondary intake air temperature value is obtained in real time based on the temperature sensor set at the secondary compression air inlet. If both the lubricating oil temperature and the secondary intake air temperature are lower than the preset minimum control temperature, the fan will be controlled to operate at the preset first low frequency. If the secondary intake air temperature rises and crosses the minimum control temperature for the first time, the fan is delayed for a preset first duration. Then, if the secondary intake air temperature exceeds the minimum temperature and the first difference between the two reaches a preset first set temperature difference, the fan control frequency is adjusted according to a preset first control algorithm. The control frequency is positively correlated with the set temperature difference; the larger the set temperature difference, the higher the control frequency; the smaller the set temperature difference, the lower the control frequency. If the lubricating oil temperature rises and exceeds the minimum control temperature for the first time, the fan control frequency will be increased according to the preset second speed. Then, as the lubricating oil temperature and the secondary intake air temperature gradually decrease to the minimum control temperature, the fan control frequency is reduced according to the preset third speed.

[0005] By adopting the above technical solution, the lubricating oil temperature and the secondary intake air temperature at the secondary compressor inlet are acquired in real time. When both the lubricating oil temperature and the secondary intake air temperature are lower than the minimum control temperature, the fan is controlled to operate at a first low frequency to reduce energy consumption under low load conditions. When the secondary intake air temperature first exceeds the minimum control temperature, the fan is delayed for a preset first duration. Then, based on whether the first difference between the secondary intake air temperature and the minimum control temperature reaches a preset first set temperature difference value, the fan control frequency is adjusted according to the first control algorithm. This avoids frequent fan starts and stops and accurately matches the heat dissipation requirements of the secondary intake air temperature. When the lubricating oil temperature first exceeds the minimum control temperature, the fan control frequency is increased at a second speed to quickly suppress the rise in lubricating oil temperature. When the lubricating oil temperature and the secondary intake air temperature gradually decrease to the minimum control temperature, the fan control frequency is decreased at a preset third speed to stably maintain temperature balance and avoid energy waste, thereby improving the energy-saving effect of the entire unit.

[0006] Optionally, the first control algorithm includes the following steps: The difference between the second-stage intake temperature and the minimum temperature is calculated as the step difference. Record the time taken for the step difference to reach the preset first step point. Adjust the first time according to the positive correlation bar of the step time. The longer the step time, the longer the first time; the shorter the step time, the shorter the first time. The fan's control frequency is adjusted according to a preset adjustment algorithm.

[0007] By adopting the above technical solution, and through the correlation adjustment of the step difference, the first step point and the span duration in the first control algorithm, the adjustment of the first duration and the fan control frequency is made to better match the actual temperature change rate, which helps to improve the accuracy of temperature control response.

[0008] Optionally, the adjustment algorithm is a PID algorithm or a PD algorithm; The ratio between the span duration and the preset reference duration is called the span ratio. Based on the positive correlation between the span ratio and the P parameter in the control adjustment algorithm, the larger the span ratio, the larger the P parameter, and the smaller the span ratio, the smaller the P parameter.

[0009] By adopting the above technical solutions, based on the adaptive adjustment characteristics of PID or PD algorithms, and combined with the positive correlation control of the P parameter in the algorithm, the adjustment of the fan control frequency is made more adaptable to the temperature change rhythm, which helps to alleviate temperature control overshoot or lag and improves the stability of the unit's air-cooling frequency control effect.

[0010] Optionally, a second difference between the lubricating oil temperature value and the controlled minimum temperature value is calculated, and the second speed is adjusted according to the positive correlation of the second difference. The larger the second difference, the larger the second speed; the smaller the second difference, the smaller the second speed.

[0011] By adopting the above technical solution, the second speed is positively correlated with the second difference, so that the rate of increase of the fan control frequency is precisely matched with the rate of increase of the lubricating oil temperature.

[0012] Optionally, if only the lubricating oil temperature value is lower than the minimum control temperature value, then within a preset calculation time, the first rate of decrease before the lubricating oil temperature value falls below the minimum control temperature value is calculated. The ratio between the first deceleration speed and the preset reference deceleration speed is calculated as the first deceleration ratio. The third speed is adjusted inversely based on the first deceleration ratio. The larger the first deceleration ratio, the slower the third speed; the smaller the first deceleration ratio, the faster the third speed.

[0013] By adopting the above technical solution, the first reduction speed ratio to the reference reduction speed is calculated, and then the third speed is adjusted inversely to make the reduction rate of the fan control frequency match the control environment corresponding to the previous downward trend of the lubricating oil temperature; only when the lubricating oil temperature value is lower than the minimum control temperature value, the temperature of the whole unit has a low probability of rapid rebound.

[0014] Optionally, if only the secondary intake temperature is lower than the minimum control temperature, the second reduction rate before the secondary intake temperature falls below the minimum control temperature is calculated within a preset calculation time. The ratio between the second deceleration speed and the preset reference deceleration speed is calculated as the second deceleration ratio. The third speed is adjusted according to the positive correlation of the second deceleration ratio. The larger the second deceleration ratio, the faster the third speed, and the smaller the second deceleration ratio, the slower the third speed.

[0015] By adopting the above technical solution, the second reduction speed ratio between the second reduction speed and the reference reduction speed is calculated, and then the third speed is positively adjusted so that the reduction rate of the fan control frequency matches the control environment corresponding to the previous downward trend of the secondary intake temperature; only when the secondary intake temperature value is lower than the minimum control temperature value, the temperature of the whole unit has a high probability of rapid rebound.

[0016] Optionally, if both the lubricating oil temperature and the secondary intake air temperature are lower than the minimum control temperature, then within a preset calculation time, the first rate of decrease before the lubricating oil temperature falls below the minimum control temperature is calculated, and the second rate of decrease before the secondary intake air temperature falls below the minimum control temperature is calculated. The combined deceleration rate is calculated based on the first deceleration rate and the second deceleration rate; The ratio between the calculated overall deceleration rate and the preset reference deceleration rate is called the overall deceleration ratio. The calculation time is adjusted according to the inverse correlation of the overall deceleration rate; the larger the overall deceleration ratio, the shorter the calculation time, and the smaller the overall deceleration ratio, the longer the calculation time.

[0017] By adopting the above technical solution, the comprehensive reduction speed is calculated based on the first and second reduction speeds. Then, the calculation time is adjusted according to the inverse correlation between the comprehensive reduction speed and the reference reduction speed, so that the calculation time adapts to the temperature change trend of the entire machine. This avoids the adjustment lag caused by excessively long calculation time when the temperature drops rapidly, or the judgment deviation caused by excessively short calculation time when the temperature drops slowly, highlighting the accuracy of multi-parameter collaborative control.

[0018] Optionally, the exhaust temperature value is obtained in real time based on a temperature sensor installed at the compressor exhaust port; Once the exhaust temperature reaches the preset exhaust temperature control point, the fan control frequency will be increased to the preset full-load frequency. Once the exhaust temperature drops below the preset exhaust temperature control point, the fan control frequency is reduced to the preset half-load frequency.

[0019] By adopting the above technical solution, the compressor exhaust temperature is protected.

[0020] Secondly, this application provides an air-cooled variable frequency control system for an oil-free screw air compressor, employing the following technical solution: An air-cooled variable frequency control system for an oil-free screw air compressor includes a processor, wherein the processor executes the steps of the air-cooled variable frequency control method for the oil-free screw air compressor as described in any of the preceding claims.

[0021] Thirdly, this application provides a storage medium, which adopts the following technical solution: A storage medium storing a program, which, when executed by a processor, implements the steps of the air-cooled variable frequency control method for an oil-free screw air compressor as described in any one of the preceding claims.

[0022] In summary, this application includes at least one of the following beneficial technical effects: real-time acquisition of lubricating oil temperature and secondary intake air temperature at the secondary compressor inlet; when both lubricating oil temperature and secondary intake air temperature are below the minimum control temperature, the fan is controlled to operate at a first low frequency to reduce energy consumption under low load conditions; when the secondary intake air temperature first crosses the minimum control temperature, the fan is delayed for a preset first duration, and then the fan control frequency is adjusted according to a first control algorithm based on whether the first difference between the secondary intake air temperature and the minimum control temperature reaches a preset first set temperature difference value, which can avoid frequent fan start-stop and accurately match the heat dissipation requirements of the secondary intake air temperature; when the lubricating oil temperature first crosses the minimum control temperature, the fan control frequency is increased at a second speed to quickly suppress the rise in lubricating oil temperature; and when the lubricating oil temperature and secondary intake air temperature gradually drop to the minimum control temperature, the fan control frequency is reduced at a preset third speed to stably maintain temperature balance and avoid energy waste, thereby improving the energy-saving effect of the entire unit. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow for the air-cooled variable frequency control method of an oil-free screw air compressor.

[0024] Figure 2 It is a temperature curve after air-cooled inverter control.

[0025] Figure 3 It is a curve showing the relationship between fan speed and power.

[0026] Figure 4 It is a temperature curve diagram controlled by the fan of the cooler after the back is artificially blocked. Detailed Implementation

[0027] The embodiments of this application are described in detail below, and examples of the embodiments are shown in the accompanying drawings.

[0028] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0029] This application discloses an air-cooled variable frequency control method for an oil-free screw air compressor, referring to... Figures 1 to 3 It includes the following steps: The lubricating oil temperature is acquired in real time based on a preset lubricating oil temperature sensor, and the secondary intake air temperature is acquired in real time based on a temperature sensor located at the secondary compression intake port. The lubricating oil temperature sensor can be one of a platinum resistance temperature sensor, a thermocouple temperature sensor, or an integrated temperature sensor. The secondary compression intake air temperature sensor can also be one of a platinum resistance temperature sensor, a thermocouple temperature sensor, an integrated temperature sensor, or a surface-mount temperature sensor. Furthermore, the lubricating oil temperature and secondary intake air temperature values ​​can be smoothed and filtered.

[0030] like Figure 2 As shown, if both the lubricating oil temperature and the secondary intake air temperature are lower than the preset minimum control temperature, the fan will operate at a preset first low frequency. Maintaining this first low frequency minimizes fan energy consumption, approximately 1 / 6 of the power consumption of a fixed-frequency fan, resulting in significant energy savings. When the secondary exhaust temperature and the overall exhaust temperature rise, stepped temperature trigger points can be set separately. Upon temperature triggering, the fan operates at the stepped trigger speed to ensure overall thermal balance.

[0031] If the secondary intake air temperature rises and exceeds the minimum control temperature for the first time, the control fan will be delayed for a preset first duration. The first duration can be preset to 30 seconds, that is, the control frequency of the fan will remain unchanged within 30 seconds, and the control frequency of the fan will be adjusted after 30 seconds.

[0032] Then, if the secondary intake air temperature exceeds the minimum temperature and the first difference between the two reaches the preset first set temperature difference value, the fan control frequency is adjusted according to the preset first control algorithm. The control frequency is positively correlated with the set temperature difference value; the larger the set temperature difference value, the higher the control frequency, and vice versa.

[0033] The first control algorithm also includes the following steps: The difference between the second-stage intake temperature and the minimum temperature is calculated as the step difference.

[0034] Record the time taken for the step difference to reach the preset first step point, where the first step point can be preset to 0.6℃ or other temperature values. Adjust the first time based on the positive correlation bar of the step time. The longer the step time, the longer the first time; the shorter the step time, the shorter the first time.

[0035] Set the adjustment algorithm to PID or PD; adjust the fan control frequency according to the algorithm. Set the minimum control temperature value to the PID control point or PID temperature control point. By adjusting the step difference, first step point, and span duration in the first control algorithm, the adjustment of the first duration and fan control frequency more closely matches the actual temperature change rate, improving the accuracy of temperature control response. Based on the actual operating environment of the air compressor, the fan will automatically perform constant temperature control and determine the target speed, stabilizing at a suitable speed to achieve energy savings. If the adjustment algorithm cannot achieve constant temperature control, the fan will operate at maximum capacity to protect the air compressor's temperature safety.

[0036] The ratio between the calculated span duration and the preset reference duration is called the span ratio. Based on the positive correlation between the span ratio and the P parameter in the control algorithm, the larger the span ratio, the larger the P parameter; conversely, the smaller the span ratio, the smaller the P parameter. By leveraging the adaptive adjustment characteristics of PID or PD algorithms and combining the positive correlation between the span ratio and the P parameter in the algorithm, the fan control frequency adjustment becomes more adapted to the temperature change rhythm, which helps alleviate temperature control overshoot or lag and improves the stability of the unit's air-cooled frequency control effect.

[0037] like Figure 2 As shown, after the stage 2 intake air temperature first reaches the PID temperature control point, the fan adjusts again after a delay of approximately 30 seconds. Once the stage 2 intake air temperature exceeds the PID temperature control point by 0.6°C, PID control begins to gradually increase the fan control frequency, meaning the fan gradually accelerates. After the stage 2 intake air temperature gradually decreases back to the PID temperature control point, the fan control frequency gradually stabilizes, meaning the fan speed gradually stabilizes. The fan speed can be automatically determined based on the PID temperature control point to achieve a suitable speed and achieve energy savings.

[0038] If the lubricating oil temperature rises and exceeds the minimum control temperature for the first time, the fan control frequency is increased according to the preset second speed. The second difference between the lubricating oil temperature and the minimum control temperature is calculated, and the second speed is adjusted in a positive correlation with this difference: the larger the difference, the higher the second speed; the smaller the difference, the lower the second speed. This positive correlation adjustment of the second speed using the second difference ensures a precise match between the rate of increase in the fan control frequency and the magnitude of the lubricating oil temperature rise.

[0039] Once the lubricating oil temperature and the secondary intake air temperature have gradually decreased to the minimum control temperature, the fan control frequency will be reduced according to the preset third speed.

[0040] like Figure 2 As shown, the oil temperature subsequently reached the PID temperature control point for the first time, and the fan gradually accelerated from its initial stable speed. After the oil temperature and the second-stage intake air temperature gradually decreased to the PID temperature control point, the fan speed gradually decreased and then stabilized.

[0041] If only the lubricating oil temperature is lower than the minimum control temperature, then within a preset calculation period, the first reduction speed before the lubricating oil temperature falls below the minimum control temperature is calculated. The ratio between the calculated first reduction speed and the preset reference reduction speed is the first reduction speed ratio. The third speed is adjusted inversely based on the first reduction speed ratio; the larger the first reduction speed ratio, the slower the third speed, and the smaller the first reduction speed ratio, the faster the third speed.

[0042] Calculate the first reduction speed ratio to the reference reduction speed, and then adjust the third speed inversely to make the fan control frequency reduction rate match the control environment corresponding to the previous downward trend of lubricating oil temperature; only when the lubricating oil temperature value is lower than the minimum control temperature value, the temperature of the whole unit has a low probability of rapid rebound.

[0043] If only the secondary intake air temperature is lower than the minimum control temperature, within a preset calculation time, the second reduction speed before the secondary intake air temperature falls below the minimum control temperature is calculated. The ratio between the calculated second reduction speed and the preset reference reduction speed is the second reduction speed ratio. The third speed is adjusted according to the positive correlation of the second reduction speed ratio; the larger the second reduction speed ratio, the faster the third speed, and the smaller the second reduction speed ratio, the slower the third speed.

[0044] Calculate the second reduction speed ratio to the reference reduction speed, and then adjust the third speed in a positive correlation to match the rate of decrease of the fan control frequency with the control environment corresponding to the previous downward trend of the secondary intake temperature; only when the secondary intake temperature value is lower than the minimum control temperature value, the temperature of the whole unit has a high probability of rapid rebound.

[0045] If both the lubricating oil temperature and the secondary intake air temperature are lower than the minimum control temperature, then within the preset calculation time, the first rate of decrease before the lubricating oil temperature falls below the minimum control temperature is calculated, and the second rate of decrease before the secondary intake air temperature falls below the minimum control temperature is calculated.

[0046] The combined deceleration rate is calculated based on the first deceleration rate and the second deceleration rate.

[0047] The ratio between the calculated overall deceleration rate and the preset reference deceleration rate is called the overall deceleration ratio. The calculation time is adjusted according to the inverse correlation of the overall deceleration rate; the larger the overall deceleration ratio, the shorter the calculation time, and the smaller the overall deceleration ratio, the longer the calculation time.

[0048] The combined reduction speed is calculated based on the first and second reduction speeds. Then, the calculation time is adjusted inversely based on the ratio of the combined reduction speed to the reference reduction speed to adapt the calculation time to the overall temperature change trend. This avoids excessively long calculation times when cooling is rapid, leading to adjustment lag, or excessively short calculation times when cooling is slow, causing judgment errors, thus highlighting the accuracy of multi-parameter coordinated control.

[0049] like Figure 2 and Figure 3 As shown, when the stage 2 intake air temperature and oil temperature gradually rise, the oil temperature reaches the PID temperature control point first, and the fan gradually accelerates from its initial stable speed. When the oil temperature and stage 2 intake air temperature gradually decrease, ensuring both remain below the PID temperature control point, the fan speed gradually decreases and stabilizes. After stabilization, PID control is applied based on the higher of the stage 2 intake air temperature and oil temperature, maintaining both fan speed and temperature stability. When the oil temperature and stage 2 intake air temperature rise further, and the oil temperature cannot drop below the PID temperature control point, the fan operates at its maximum speed. The fan speed can be adjusted according to the environment, allowing it to output at its maximum speed even in the worst conditions, thus ensuring safe oil and stage 2 intake air temperatures.

[0050] The compressor uses a temperature sensor located at the exhaust port to acquire the exhaust temperature value in real time. When the exhaust temperature reaches a preset exhaust temperature control point, the fan control frequency is increased to a preset full-load frequency. When the exhaust temperature falls below the preset exhaust temperature control point, the fan control frequency is reduced to a preset half-load frequency. This protects the compressor's exhaust temperature.

[0051] like Figure 4 As shown, when the cooler was manually blocked, the compressor exhaust temperature rose to 60°C, while the oil temperature was 48°C and the stage 2 intake temperature was 55°C, neither of which triggered the PID algorithm. Once the compressor exhaust temperature reached the 60°C exhaust temperature control point, the safety protection point was triggered. When the exhaust temperature exceeded 60°C, the fan switched from a 50% half-load frequency to a 100% full-load frequency. When the exhaust temperature was below 60°C, the fan switched from a 100% full-load frequency to a 50% half-load frequency. After removing the baffle from the cooler, the compressor exhaust temperature dropped from 60°C to approximately 42.7°C. The stage 2 intake temperature rose from 47.8°C to approximately 54°C. The stage 2 exhaust temperature reached the protection point after one minute. The secondary exhaust temperature protection value of 175℃ was triggered. 175℃ is the program correction value. When the secondary exhaust temperature exceeds 175℃, the fan control frequency switches from 50% to 100% operation. When the secondary exhaust temperature is below 175℃, the fan control frequency switches from 100% to 50% operation.

[0052] The system acquires real-time lubricating oil temperature and secondary intake air temperature at the secondary compressor inlet. When both lubricating oil temperature and secondary intake air temperature are below the minimum control temperature, the fan operates at a first low frequency to reduce energy consumption under low load conditions. When the secondary intake air temperature first exceeds the minimum control temperature, the fan is delayed for a preset first duration. Then, based on whether the first difference between the secondary intake air temperature and the minimum control temperature reaches a preset first temperature difference value, the fan control frequency is adjusted according to the first control algorithm. This avoids frequent fan starts and stops and accurately matches the heat dissipation requirements of the secondary intake air temperature. When the lubricating oil temperature first exceeds the minimum control temperature, the fan control frequency is increased at a second speed to quickly suppress the rise in lubricating oil temperature. As the lubricating oil temperature and secondary intake air temperature gradually decrease to the minimum control temperature, the fan control frequency is decreased at a preset third speed to stably maintain temperature balance and avoid energy waste, thereby improving the overall energy-saving effect of the unit.

[0053] This application also discloses an air-cooled variable frequency control system for an oil-free screw air compressor, including a processor, wherein the processor executes the steps of the air-cooled variable frequency control method for the oil-free screw air compressor as described in any of the above embodiments.

[0054] This application also discloses a storage medium storing a program, which, when executed by a processor, implements the steps of the air-cooled variable frequency control method for an oil-free screw air compressor as described in any of the above embodiments.

[0055] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for air-cooled variable frequency control of an oil-free screw air compressor, characterized in that, Includes the following steps: The lubricating oil temperature value is obtained in real time based on the preset lubricating oil temperature sensor, and the secondary intake air temperature value is obtained in real time based on the temperature sensor set at the secondary compression air inlet. If both the lubricating oil temperature and the secondary intake air temperature are lower than the preset minimum control temperature, the fan will be controlled to operate at the preset first low frequency. If the secondary intake air temperature rises and exceeds the minimum control temperature for the first time, the fan is controlled after a preset first time delay. Then, if the secondary intake air temperature exceeds the minimum temperature and the first difference between the two reaches a preset first set temperature difference value, the fan control frequency is adjusted according to a preset first control algorithm. The control frequency is positively correlated with the set temperature difference value. The larger the set temperature difference value, the higher the control frequency; the smaller the set temperature difference value, the lower the control frequency. If the lubricating oil temperature rises and exceeds the minimum control temperature for the first time, the fan control frequency will be increased according to the preset second speed. Then, as the lubricating oil temperature and the secondary intake air temperature gradually decrease to the minimum control temperature, the fan control frequency is reduced according to the preset third speed. The first control algorithm includes the following steps: The difference between the second-stage intake temperature and the minimum temperature is calculated as the step difference. Record the time taken for the step difference to reach the preset first step point, and adjust the first time according to the positive correlation between the step time and the step time. The longer the step time, the longer the first time; the shorter the step time, the shorter the first time. The fan's control frequency is adjusted according to a preset adjustment algorithm.

2. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 1, characterized in that, The control algorithm is either PID or PD. The ratio between the span duration and the preset reference duration is called the span ratio. Based on the positive correlation between the span ratio and the P parameter in the control adjustment algorithm, the larger the span ratio, the larger the P parameter, and the smaller the span ratio, the smaller the P parameter.

3. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 1 or 2, characterized in that, Calculate the second difference between the lubricating oil temperature value and the minimum control temperature value. Adjust the second speed according to the positive correlation between the second difference and the second speed. The larger the second difference, the larger the second speed, and the smaller the second difference, the smaller the second speed.

4. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 1, characterized in that, If only the lubricating oil temperature is lower than the minimum control temperature, then within the preset calculation time, the first rate of decrease before the lubricating oil temperature falls below the minimum control temperature will be calculated. The ratio between the first deceleration speed and the preset reference deceleration speed is calculated as the first deceleration ratio. The third speed is adjusted inversely based on the first deceleration ratio. The larger the first deceleration ratio, the slower the third speed; the smaller the first deceleration ratio, the faster the third speed.

5. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 1, characterized in that, If only the secondary intake air temperature is lower than the minimum control temperature, the second reduction rate before the secondary intake air temperature falls below the minimum control temperature is calculated within the preset calculation time. The ratio between the second deceleration speed and the preset reference deceleration speed is calculated as the second deceleration ratio. The third speed is adjusted according to the positive correlation of the second deceleration ratio. The larger the second deceleration ratio, the faster the third speed, and the smaller the second deceleration ratio, the slower the third speed.

6. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 4 or 5, characterized in that, If both the lubricating oil temperature and the secondary intake air temperature are lower than the minimum control temperature, then within the preset calculation time, the first rate of decrease before the lubricating oil temperature falls below the minimum control temperature is calculated, and the second rate of decrease before the secondary intake air temperature falls below the minimum control temperature is calculated. The combined deceleration rate is calculated based on the first deceleration rate and the second deceleration rate; The ratio between the overall deceleration rate and the preset reference deceleration rate is the overall deceleration ratio. The calculation time is adjusted according to the inverse correlation of the overall deceleration rate. The higher the overall speed reduction ratio, the shorter the calculation time; the lower the overall speed reduction ratio, the longer the calculation time.

7. The air-cooled variable frequency control method for an oil-free screw air compressor according to claim 6, characterized in that, The exhaust temperature value is obtained in real time based on a temperature sensor installed at the compressor exhaust port; Once the exhaust temperature reaches the preset exhaust temperature control point, the fan control frequency will be increased to the preset full-load frequency. Once the exhaust temperature drops below the preset exhaust temperature control point, the fan control frequency is reduced to the preset half-load frequency.

8. A wind-cooled variable frequency control system for an oil-free screw air compressor, characterized in that, Includes a processor, wherein the processor performs the steps of the air-cooled variable frequency control method for an oil-free screw air compressor as described in any one of claims 1-7.

9. A storage medium, characterized in that, The storage medium stores a program that, when executed by a processor, implements the steps of the air-cooled variable frequency control method for the oil-free screw air compressor according to any one of claims 1-7.

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