Methods for preventing overload of variable frequency screw compressor motor

Abstract

The present invention provides a method for preventing overload in a variable-frequency screw compressor motor, comprising the following steps: setting a motor current ratio-inverse time curve for the inverter's overload time limit and a corresponding table for the inverter's overload time limit-frequency adjustment range; collecting data on the motor's operating current; calculating the current ratio between the operating current and the motor's rated current; applying the current ratio to the inverse time curve to calculate the overload time limit; applying the overload time limit to the corresponding table to calculate the frequency adjustment range; and adjusting the inverter's original set frequency according to the frequency adjustment range to change the motor speed and adjust the motor's operating current to below the rated current. This preventive method takes effect before the motor reaches an overload shutdown, ensuring the normal operation of the variable-frequency screw compressor.

Description

Technical Field

[0001] The present invention relates to the technical field of compressors, and in particular to a method for preventing overload of a variable frequency screw compressor motor. Background Art

[0002] Variable-frequency screw compressors are a widely used piece of mechanical equipment, finding crucial applications in the fields of machinery, metallurgy, textiles, and food. The motor, the primary drive source, can experience overloads during operation due to factors such as excessive load, voltage fluctuations, and excessive temperatures. This can affect the motor's normal operation, potentially causing damage or even safety accidents. Therefore, motor overload protection is essential, typically implemented using an inverse time curve strategy. Specifically, when the motor's operating current reaches different multiples of the rated current, corresponding overload time limits are established. Upon reaching this time limit, the motor stops operating.

[0003] Although the inverse time curve strategy can effectively protect the motor, it also has some problems. Once the operating current of the motor reaches a certain multiple of the rated current, it can only wait for the overload time limit to shut down, which is very passive and affects the operation of the variable frequency screw compressor and user use. Summary of the Invention

[0004] In view of the above situation, the present invention provides a variable frequency screw compressor motor overload prevention method to solve the problem that the existing inverse time curve strategy can only wait for the motor overload time limit to perform shutdown protection, affecting the overall operation of the compressor.

[0005] To achieve the above object, the technical solution adopted by the present invention is to provide a method for preventing overload of a variable frequency screw compressor motor, which comprises the following steps:

[0006] Set the inverse time curve of the motor current ratio-inverter overload time limit and the corresponding table of the inverter overload time limit-frequency adjustment range;

[0007] Collecting data on the running current of the motor;

[0008] calculating a current ratio between the operating current and the rated current of the motor;

[0009] Introducing the current ratio into the inverse time curve to calculate the overload time limit;

[0010] The overload time limit is introduced into the corresponding table to calculate the frequency adjustment amplitude;

[0011] The original set frequency of the frequency converter is adjusted according to the frequency adjustment range to change the rotation speed of the motor so that the operating current of the motor is adjusted to be lower than the rated current.

[0012] Furthermore, the inverse time curve and the corresponding table are set in a controller, the controller is connected to the frequency converter, and the controller collects the operating current data through the frequency converter and calculates the current ratio, the overload time limit and the frequency adjustment amplitude.

[0013] Furthermore, the operating current is the output current of the inverter.

[0014] Furthermore, the controller transmits the frequency adjustment amplitude to the frequency converter, and the frequency converter changes the original set frequency by reducing the magnitude of the frequency adjustment amplitude based on the original set frequency.

[0015] Furthermore, the inverse time curve is set according to the specific model and operation requirements of the inverter.

[0016] The beneficial effect of the present invention is that the present invention provides a method for preventing overload of a variable frequency screw compressor motor, which collects data on the motor's operating current, calculates the current ratio of the operating current to the rated current, compares the inverse time curve, obtains different overload time limits, and then compares the corresponding table to calculate the required frequency adjustment amplitude of the frequency converter and transmits it to the frequency converter. The frequency converter adjusts the original set frequency according to the frequency adjustment amplitude, thereby adjusting the motor speed to reduce the operating current, so that the motor is away from the overload curve within the overload time limit, thereby forming a motor overload prevention method to ensure the normal operation of the variable frequency screw compressor. The present invention adopts a prevention mechanism method rather than a pure overload shutdown protection, that is, it does not perform shutdown protection after the motor of the variable frequency screw compressor has been overloaded, but rather performs prevention before the motor reaches the overload shutdown, thereby ensuring the normal operation of the variable frequency screw compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 The present invention is a flow chart of a method for preventing overload of a variable frequency screw compressor motor.

[0019] Figure 2 The present invention is a schematic diagram of the connection between the motor, the controller and the frequency converter of the variable frequency screw compressor motor overload prevention method.

[0020] Figure 3 It is a schematic diagram of an inverse time curve of the variable frequency screw compressor motor overload prevention method of the present invention.

[0021] Figure 4 The invention provides a corresponding table of inverse time multiples and inverse time limits of the variable frequency screw compressor motor overload prevention method and a corresponding table of overload time limits and frequency adjustment amplitudes of the frequency converter.

[0022] The corresponding relationship between the reference numerals and components is as follows:

[0023] 11-controller; 12-inverter; 13-motor; 14-variable frequency screw compressor. DETAILED DESCRIPTION

[0024] To facilitate understanding of the present invention, the following description is given with reference to the accompanying drawings and embodiments.

[0025] See also Figure 1 The present invention provides a method for preventing overload of a variable frequency screw compressor motor, comprising the following steps:

[0026] S1, set the inverse time curve of the motor current ratio-the overload time limit of the inverter and the corresponding table of the overload time limit of the inverter-the frequency adjustment range;

[0027] S2, collecting data on the running current of the motor;

[0028] S3. Calculate the current ratio between the operating current and the rated current of the motor;

[0029] S4. Introduce the current ratio into the inverse time curve and calculate the overload time limit;

[0030] S5. Introduce the overload time limit into the corresponding table and calculate the frequency adjustment range;

[0031] S6. Adjust the original set frequency of the inverter according to the frequency adjustment range to change the motor speed and adjust the motor's operating current to be lower than the rated current.

[0032] Specifically, motor 13 is connected to an inverter 121 that drives motor 14 and detects the operating current data of motor 14. Inverter 12 is connected to controller 11. An inverse time curve and a corresponding table are set in controller 11. Controller 11 collects operating current data through inverter 12 and calculates the current ratio. It then calculates the overload time limit by introducing the current ratio into the inverse time curve. By introducing the overload time limit into the corresponding table, a frequency adjustment amplitude is assigned to the overload time limit according to the corresponding table, thereby calculating the frequency adjustment amplitude. The controller transmits the frequency adjustment amplitude to inverter 12. Inverter 12 reduces the frequency adjustment amplitude based on the original set frequency to form a new set frequency, further changing the power frequency supplied to motor 13, thereby reducing the speed and operating current of motor 13, allowing motor 13 to stay away from the overload curve within the overload time limit. This forms a method for preventing overload of motor 13 and ensures the normal operation of the variable frequency screw compressor.

[0033] Because the output current of the inverter 12 is the input current of the motor 13, and the input current of the motor 13 is the operating current of the motor 13, the controller 11 can collect the operating current data of the motor 13 by collecting the output current of the inverter 12. When the operating current of the motor 13 decreases due to a decrease in speed, the output current of the inverter 12 also decreases, and the current ratio measured by the controller 11 decreases.

[0034] The inverse time curve is set according to the specific model and operation requirements of the inverter 12.

[0035] Different overload time limits of the inverter in the corresponding table correspond to different frequency adjustment ranges, and the frequency adjustment range is the empirical data in actual work.

[0036] like Figure 2 As shown, a variable frequency screw compressor motor mainly includes a controller 11, a frequency converter 12, and a motor 13. The motor 13 is the main driving source of the variable frequency screw compressor 14. The controller 11 operates to monitor and measure the process parameters and running / shutdown status of the variable frequency screw compressor 14 and diagnose faults. The frequency converter 12 drives the motor 14 and detects the operating current of the motor 13. The controller 11 and the frequency converter 12 are connected to the motor 13.

[0037] The specific implementation steps of the variable frequency screw compressor motor overload prevention method of the present invention are as follows:

[0038] S10, set the inverse time curve of the motor current ratio-inverter overload time limit and the corresponding table of the inverter overload time limit-frequency adjustment range on the controller 11. This inverse time curve can be set according to the specific model and operation requirements of the inverter 12 in the variable frequency screw compressor 14. For example, the inverse time curve of the inverter 12 can be set as follows, Figure 3 The solid line in the figure shows:

[0039] 1. Current ratio 1.25 times, overload time limit 2400S;

[0040] 2. Current ratio 1.35 times, overload time limit 900S;

[0041] 3. Current ratio 1.45 times, overload time limit 360S;

[0042] 4. Current ratio 1.55 times, overload time limit 240S;

[0043] 5. Current ratio 1.65 times, overload time limit 150S;

[0044] 6. Current ratio 1.75 times, overload time limit 120S;

[0045] 7. Current ratio 1.85 times, overload time limit 90S;

[0046] 8. Current ratio 1.95 times, overload time limit 60S;

[0047] 9. Current ratio 2.25 times, overload time limit 30S;

[0048] 10. Current ratio 2.45 times, overload time limit 10S;

[0049] This correspondence table is the empirical data in actual work, so the correspondence table can be set as follows, such as Figure 4 The diagram in the dotted box is shown below:

[0050] 1. Overload (adjustment) time limit 2400S, frequency adjustment range 1.0%;

[0051] 2. Overload (adjustment) time limit 900S; frequency adjustment range 2.0%

[0052] 3. Overload (adjustment) time limit 360S, frequency adjustment range 3.0%;

[0053] 4. Overload (adjustment) time limit 240S, frequency adjustment range 5.0%;

[0054] 5. Overload (adjustment) time limit 150S, frequency adjustment range 7.5.0%;

[0055] 6. Overload (adjustment) time limit 120S, frequency adjustment range 10.0%;

[0056] 7. Overload (adjustment) time limit 90S, frequency adjustment range 12.5%;

[0057] 8. Overload (adjustment) time limit 60S, frequency adjustment range 15.0%;

[0058] 9. Overload (adjustment) time limit 30S, frequency adjustment range 17.5%;

[0059] 10. Overload (adjustment) time limit 10S, frequency adjustment range 20.0%;

[0060] S20 , when the screw compressor 14 is running, the inverter 12 detects the operating current data of the motor 13 , and then transmits the data to the controller 11 via communication so that the controller 11 can process the data.

[0061] S30 , the controller 11 compares the operating current of the motor 13 with the rated current of the motor 13 in real time, and calculates the current ratio of the operating current to the rated current. If the current ratio is greater than 1, it means that the motor 13 may be overloaded.

[0062] S40, the controller 11 obtains different overload time limits according to different current ratios and inverse time curves, and the controller 11 introduces the overload time limits into the corresponding table to obtain the frequency adjustment amplitude, and then transmits it to the inverter 12 via communication. Figure 3 and Figure 4 As shown, when the current ratio of the motor 13 reaches 2.45, the overload (adjustment) time limit is 10s, and the frequency adjustment range is 20%; when the current ratio of the motor 13 reaches 1.35, the overload (adjustment) time limit is 900s, and the frequency adjustment range is 2%, and so on.

[0063] Preferably, if Figure 4 As shown in the solid line frame, the integer current ratio is used as the inverse time multiple to form an inverse time correspondence table of inverse time multiple-inverse time limit. For example, the inverse time multiple is 1.25, 1.35, 1.45, etc., which corresponds to Figure 3 The calculated current ratio is compared with the inverse time multiple. When the current ratio is close to or equal to the inverse time multiple, the measured current ratio is Figure 3 Within the dashed lines on both sides of the solid line, the inverse time limit (i.e., overload time limit) is calculated using the inverse time correspondence table. For example, if the calculated current ratio is close to or equal to 1.25, then the inverse time multiplier is calculated to be 1.25. Using the inverse time correspondence table, the corresponding inverse time limit (i.e., overload time limit) is 2400s.

[0064] S50, the frequency converter 12 adjusts the original set frequency according to the frequency adjustment amplitude of the controller 11, and the new set frequency is automatically generated by subtracting the frequency adjustment amplitude from the original set frequency, thereby adjusting the speed of the motor 13 to reduce the operating current. This allows the motor 13 to stay away from the overload curve within the overload time limit, avoiding overload operation of the motor 13 and reducing the risk of damage. For example, Figure 3 As shown, when the current ratio of the motor 13 reaches 2.45, the frequency adjustment range is 20%, and the new set frequency is 80%; when the current ratio of the motor 13 reaches 1.35, the frequency adjustment range is 2%, and the new set frequency is 98%, and so on.

[0065] The present invention employs a preventative approach, rather than purely overload shutdown protection. Specifically, rather than performing shutdown protection only after the motor 13 of the variable-frequency screw compressor 14 has already overloaded, the present invention implements preventative measures before the motor 13 reaches an overload shutdown, thereby ensuring the normal operation of the variable-frequency screw compressor 14. The controller 11 can flexibly adjust the frequency amplitude value based on the specific operating status and requirements of the motor 13 to achieve optimal operating results. This approach not only effectively prevents the motor 13 from overloading, but also ensures the normal operation of the variable-frequency screw compressor 14.

[0066] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preventing overload of a variable frequency screw compressor motor, characterized in that: The following steps are involved: Set the inverse time curve of the motor current ratio-inverter overload time limit and the corresponding table of the inverter overload time limit-frequency adjustment range; Collecting data on the running current of the motor; calculating a current ratio between the operating current and the rated current of the motor; Introducing the current ratio into the inverse time curve to calculate the overload time limit; The overload time limit is introduced into the corresponding table to calculate the frequency adjustment amplitude; Adjusting the original set frequency of the frequency converter according to the frequency adjustment range to change the speed of the motor and adjust the operating current of the motor to be lower than the rated current; The inverse time curve and the corresponding table are set in a controller, the controller is connected to the frequency converter, the controller collects the operating current data through the frequency converter, and calculates the current ratio, the overload time limit, and the frequency adjustment range; The operating current is the output current of the inverter; The controller transmits the frequency adjustment amplitude to the frequency converter, and the frequency converter changes the original set frequency by reducing the magnitude of the frequency adjustment amplitude based on the original set frequency; The inverse time curve is set according to the specific model and operation requirements of the inverter.

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