Method of intelligent protection for inverter undervoltage

Abstract

The invention discloses a method for intelligent undervoltage protection of a frequency converter, and relates to the technical field of frequency converters. The method detects the real-time voltage value of the frequency converter bus and calculates the standard value of the bus voltage within a period of time. If the standard value is lower than a first undervoltage threshold, the detected real-time voltage is corrected to eliminate the interference of the power supply ripple voltage on the bus voltage sampling signal, and obtain a more accurate bus voltage, so as to obtain the corrected bus voltage standard value. If the corrected bus voltage standard value is not greater than a second undervoltage threshold, it indicates that the power supply voltage is too low, and therefore the frequency converter motor is controlled to stop running. If the corrected bus voltage standard value is greater than the second undervoltage threshold, the bus current is calculated. If the bus current is not less than the first conduction current threshold, the boost module is started to increase the bus voltage. Otherwise, the boost module is not started, and the problem that the existing frequency converter motor is damaged due to unstable power supply is solved. The invention is suitable for frequency converters.

Description

Technical Field

[0001] The invention relates to the technical field of frequency converters, and in particular to a method for intelligent undervoltage protection of frequency converters. Background Art

[0002] The frequency converter converts the mains power into direct current, and then converts it into alternating current through an inverter to supply the motor.

[0003] The power supply conditions and operating environment of variable frequency motors are relatively bad. Usually, the AC voltage supplied by the power grid is not a stable voltage, and the voltage drop on the transmission line also changes due to changes in the load of the power grid. Due to these two reasons, the voltage at the load end is unstable and often fluctuates. If the power supply voltage is too much lower than the rated voltage of the variable frequency motor, the current of the motor will increase significantly, and even the motor will stop running with power on, which will cause the motor winding temperature to continue to rise and cause the motor to burn out. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for intelligent undervoltage protection of a frequency converter, so as to solve the problem that the existing frequency converter motor is damaged due to unstable power supply.

[0005] The present invention solves the above technical problems by adopting a technical solution: a method for intelligent undervoltage protection of a frequency converter, wherein the frequency converter is used to control a variable frequency motor, comprising the following steps:

[0006] S01, detecting the real-time bus voltage value of the inverter, obtaining the bus voltage standard value within a period of time, if the bus voltage standard value is less than the first undervoltage threshold, correcting the bus voltage detected within the period of time, obtaining the corrected bus voltage standard value, and entering step S02, otherwise, not entering undervoltage protection;

[0007] S02. If the corrected bus voltage standard value is not greater than the second undervoltage threshold, the variable frequency motor is controlled to stop running;

[0008] S03. If the corrected bus voltage standard value is greater than the second undervoltage threshold, the bus current is calculated; if the bus current is not less than the first conduction current threshold, the boost module is started to increase the bus voltage, otherwise, the boost module is not started.

[0009] Furthermore, in step S01, the standard value is an average value or an effective value.

[0010] Furthermore, in step S02, the variable frequency motor is controlled to stop running by setting the inverter input control signal to zero or disconnecting the inverter output.

[0011] Furthermore, in step S03, the calculation formula of the second undervoltage threshold is: Where K is a constant, ranging from 8% to 10%, V TF is the second undervoltage threshold, V TH is the first under-voltage threshold.

[0012] Furthermore, the formula for calculating the bus current is: Where P is power, is the power factor, V BUF is the corrected bus voltage standard value, I BUF is the bus current.

[0013] Furthermore, the variable frequency motor is applied to a variable frequency compressor.

[0014] Furthermore, the inverter is applied to an air conditioner or a refrigerator.

[0015] Beneficial effects of the present invention: The method for intelligent undervoltage protection of the frequency converter of the present invention detects the real-time voltage value of the frequency converter bus and calculates the standard value of the bus voltage within a period of time. If the standard value is lower than the first undervoltage threshold, the detected real-time voltage is corrected to eliminate the interference of the power supply ripple voltage on the bus voltage sampling signal, and obtain a more accurate bus voltage, so as to obtain the corrected bus voltage standard value. If the corrected bus voltage standard value is not greater than the second undervoltage threshold, it indicates that the power supply voltage is too low, so the frequency converter motor is controlled to stop running. If the corrected bus voltage standard value is greater than the second undervoltage threshold, the bus current is calculated. If the bus current is not less than the first conduction current threshold, the boost module is started to increase the bus voltage, otherwise the boost module is not started, thereby solving the problem of damage of the existing frequency converter motor due to unstable power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 It is a flow chart of the method for intelligent undervoltage protection of a frequency converter of the present invention. DETAILED DESCRIPTION

[0017] The method for intelligent protection of frequency converter undervoltage of the present invention is as follows Figure 1 As shown, the following steps are included:

[0018] S01, detecting the real-time bus voltage value of the inverter, obtaining the bus voltage standard value within a period of time, if the bus voltage standard value is less than the first undervoltage threshold, correcting the bus voltage detected within the period of time, obtaining the corrected bus voltage standard value, and entering step S02, otherwise, not entering undervoltage protection;

[0019] Specifically, the standard value is an average value or an effective value.

[0020] S02. If the corrected bus voltage standard value is not greater than the second undervoltage threshold, the variable frequency motor is controlled to stop running;

[0021] Specifically, the calculation formula of the second undervoltage threshold is: Where K is a constant, ranging from 8% to 10%, V TF is the second undervoltage threshold, V TH is the first undervoltage threshold, and the variable frequency motor is controlled to stop running by setting the inverter input control signal to zero or disconnecting the inverter output.

[0022] S03. If the corrected bus voltage standard value is greater than the second undervoltage threshold, the bus current is calculated; if the bus current is not less than the first conduction current threshold, the boost module is started to increase the bus voltage, otherwise, the boost module is not started.

[0023] Specifically, the formula for calculating the bus current is: Where P is power, is the power factor, V BUF is the corrected bus voltage standard value, I BUF is the bus current.

[0024] In the present application, the bus current is used as a comparison object, and combined with the use of a boost module, it is effectively avoided that the variable frequency motor is switched back and forth between the start and stop working states when the voltage hovers around the second under-voltage threshold, thereby improving the safety of the motor operation. For example, when the corrected bus voltage standard value is greater than the second under-voltage threshold, it will subsequently be lower than the second under-voltage threshold. When the bus voltage standard value is greater than the second under-voltage threshold, the bus current is calculated and compared with the bus current and the first conduction current threshold. After the boost module is started, the bus voltage will increase, and the situation of subsequently falling below the second under-voltage threshold will not occur.

[0025] In the present application, the bus voltage corresponding to the first on-current threshold is between the first undervoltage threshold and the second undervoltage threshold.

[0026] In the present application, the variable frequency motor can be applied to the variable frequency compressor. As the power source of the variable frequency compressor, the inverter can be applied to equipment such as air conditioners or refrigerators.

Claims

1. A method for intelligent undervoltage protection of a frequency converter, wherein the frequency converter is used to control a variable frequency motor, characterized in that: The following steps are involved: S01, detecting the real-time bus voltage value of the inverter, obtaining the bus voltage standard value within a period of time, if the bus voltage standard value is less than the first undervoltage threshold, correcting the bus voltage detected within the period of time, obtaining the corrected bus voltage standard value, and entering step S02, otherwise, not entering undervoltage protection; S02. If the corrected bus voltage standard value is not greater than the second undervoltage threshold, the variable frequency motor is controlled to stop running. The calculation formula of the second undervoltage threshold is: Where K is a constant, ranging from 8% to 10%, V TF is the second undervoltage threshold, V TH is the first undervoltage threshold; S03. If the corrected bus voltage standard value is greater than the second undervoltage threshold, the bus current is calculated; if the bus current is not less than the first conduction current threshold, the boost module is started to increase the bus voltage, otherwise, the boost module is not started.

2. The method for intelligent protection of frequency converter undervoltage according to claim 1, characterized in that: In step S01, the standard value is an average value or an effective value.

3. The method for intelligent protection of frequency converter undervoltage according to claim 1 or 2, characterized in that: In step S02, the variable frequency motor is controlled to stop running by setting the input control signal of the frequency converter to zero or disconnecting the output of the frequency converter.

4. The method for intelligent protection of frequency converter undervoltage according to claim 1 or 2, characterized in that: The formula for calculating the bus current is: Where P is power, is the power factor, V BUF is the corrected bus voltage standard value, I BUF is the bus current.

5. The method for intelligent protection of frequency converter undervoltage according to claim 1 or 2, characterized in that: The variable frequency motor is applied to a variable frequency compressor.

6. The method for intelligent protection of frequency converter undervoltage according to claim 5, characterized in that: The frequency converter is applied to an air conditioner or a refrigerator.

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