A method for improving the operating ability of a variable frequency compressor

Abstract

The present invention mainly relates to the technical field of variable-frequency compressors. In order to solve the problem that during the actual control process, the power supply voltage fluctuation causes the torque and speed of the variable-frequency compressor to deviate from the rated load torque of the variable-frequency compressor and the speed when the variable-frequency compressor operates stably under the rated power supply voltage, resulting in poor control performance of the variable-frequency compressor, the present invention provides a method for improving the operating ability of the variable-frequency compressor. On the one hand, the method of the present invention adopts the constant torque control method of the frequency converter to control the electromagnetic torque of the permanent magnet synchronous motor of the variable-frequency compressor to follow the rated load torque of the permanent magnet synchronous motor in real time, and improves the adverse impact of torque fluctuation on the actual operation of the variable-frequency compressor. On the other hand, the method of the constant speed control of the frequency converter is adopted to control the dynamic operating speed of the variable-frequency compressor to be consistent with the operating speed when the variable-frequency compressor operates stably under the rated power supply voltage, and offsets the influence of voltage imbalance on the field weakening control of the frequency converter.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of variable frequency compressors, and in particular to a method for improving the operating capacity of variable frequency compressors. Background Art

[0002] During the actual use of the compressor, there are inevitable fluctuations in the power supply voltage. The voltage fluctuation will cause great harm to the inverter control system using vector closed-loop control, and then affect the electromagnetic torque output of the permanent magnet synchronous motor of the variable frequency compressor. The electromagnetic torque of the permanent magnet synchronous motor is in direct proportion to the power supply voltage, resulting in the inability to accurately control the electromagnetic torque of the permanent magnet synchronous motor in real time according to the operating state of the controlled motor, causing a steady-state deviation between the electromagnetic torque of the permanent magnet synchronous motor of the variable frequency compressor and the rated load torque, resulting in poor dynamic control performance of the variable frequency compressor and low operating speed control accuracy, so that the overall use effect of the refrigerator does not reach the ideal state. Summary of the invention

[0003] The technical problems to be solved by the present invention are:

[0004] A method for improving the operating capacity of a variable frequency compressor is provided to solve the problem that the torque and speed of the variable frequency compressor deviate from the rated load torque and given operating speed of the variable frequency compressor during operation due to power supply voltage fluctuation, resulting in poor dynamic control performance of the variable frequency compressor.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] A method for improving the operating capacity of a variable frequency compressor comprises the following steps:

[0007] S1: Connect the variable frequency compressor system to the rated power supply voltage and record the speed n when the variable frequency compressor is running stably c , and calculate the rated load torque T of the variable frequency compressor permanent magnet synchronous motor B , enter S2;

[0008] S2: Connect the variable frequency compressor and the inverter to the actual test control system to determine the input power supply voltage V of the inverter. IN Is it greater than or equal to the rated power supply voltage V B And it is less than the maximum working voltage of the compressor. If so, go to S3, if not, go to S4;

[0009] S3: Start the first constant torque control module of the frequency conversion software, and adjust the rated load torque T B The actual torque T of the permanent magnet synchronous motor e1 The difference between N to make compensation;

[0010] S4: Determine whether the input power supply voltage is greater than or equal to the minimum operating voltage of the compressor and less than or equal to the rated power supply voltage V B , if not, go to S5; if so, go to S6;

[0011] S5: Control the variable-frequency compressor to stop running;

[0012] S6: Start the second constant-torque control module of the variable-frequency software to compensate for the difference T B between the rated load torque T e2 of the permanent magnet synchronous motor and the actual torque T p of the permanent magnet synchronous motor, and then go to S7;

[0013] S7: Determine whether the dynamic operating speed n of the variable-frequency compressor is equal to the speed n during the stable operation of the variable-frequency compressor c , if so, go to S8; if not, go to S9;

[0014] S8: The variable-frequency compressor system is in a normal operating state and continues to run;

[0015] S9: Determine whether the dynamic operating speed n of the variable-frequency compressor is less than the maximum operating speed n of the variable-frequency compressor MAX , if not, go to S10; if so, go to S11;

[0016] S10: Start the first constant-speed control module of the variable-frequency software to control the dynamic operating speed n of the compressor to be consistent with the given operating speed n c by controlling the input frequency of the frequency converter;

[0017] S11: Start the second constant-speed control module of the variable-frequency software to control the dynamic operating speed n of the variable-frequency compressor to be consistent with the given operating speed n c by adjusting the weak magnetic control PI controller and the weak magnetic control starting modulation rate;

[0018] Furthermore, the first constant-torque control module includes a first electromagnetic torque sampling module and a first comparator module. The first electromagnetic torque sampling module is used to collect the actual electromagnetic torque T e1 of the first permanent magnet synchronous motor of the variable-frequency compressor. The first comparator module is used to compare the rated load torque T B of the permanent magnet synchronous motor with the actual electromagnetic torque T e1 of the first permanent magnet synchronous motor, calculate the negative compensation torque T N , and complete the output of the negative compensation torque T N .

[0019] Further, the second constant torque control module includes a second electromagnetic torque sampling module and a second comparator module. The second electromagnetic torque sampling module is used to collect the actual electromagnetic torque T of the second permanent magnet synchronous motor of the variable frequency compressor. e2 The second comparator module is used to compare the rated load torque T of the permanent magnet synchronous motor. B with the actual electromagnetic torque T of the second permanent magnet synchronous motor. e2 to calculate the positive compensation torque T. P and complete the output of the positive compensation torque T. P

[0020] Further, the specific method for controlling the variable frequency compressor to stop running in step S5: Set the input frequency of the frequency converter to zero, stop the variable frequency compressor from running, and at the same time control the LED fault light of the frequency converter to flash to report a voltage fault.

[0021] Further, the specific method of step S10: The first constant speed control module calculates the difference f between the input frequency of the variable frequency compressor during dynamic operation and the input frequency during stable operation under the rated power supply voltage, and controls the dynamic operation speed n of the variable frequency compressor to be consistent with the speed n during stable operation under the rated power supply voltage through frequency compensation. The calculation method of the frequency difference f of the frequency converter is: f = p(n - n c ) / 60, where p is the number of pole pairs of the motor. c

[0022] Further, the specific method of step S11 is: The second constant speed control module controls the dynamic operation speed of the variable frequency compressor by adjusting the weak magnetic control PI controller and the weak magnetic control start modulation rate.

[0023] The weak magnetic control PI controller takes the output dynamic voltage U of the frequency converter detected by the frequency converter software as the input quantity of the weak magnetic regulator, compares it with the maximum output voltage U of the frequency converter. MAX The deviation between the two is used as the input of the weak magnetic control PI controller. After the deviation is adjusted by proportional regulation and integral regulation, it is linearly combined to adjust the input of the second d-axis current and the second q-axis current, so that the second d-axis current weakens the permanent magnet magnetic potential within the weak magnetic range to achieve the purpose of weak magnetic control. The weak magnetic control start modulation rate is used to adjust the weak magnetic start threshold, so that the permanent magnet synchronous motor enters the weak magnetic state in advance. Under the condition of ensuring voltage balance, the dynamic operation speed n of the variable frequency compressor is increased to the given operation speed n. c The calculation formula of the maximum output voltage U of the frequency converter is: U MAX = V MAX * λ, where λ is a proportionality constant. IN

[0024] Further, the preferred value range of λ is 85% - 90%.

[0025] Advantages of the present invention:

[0026] On the one hand, the method of the present invention adopts the constant torque control of the frequency converter to control the electromagnetic torque of the permanent magnet synchronous motor of the variable frequency compressor to follow the rated load torque of the permanent magnet synchronous motor in real time, improving the adverse effect of torque fluctuation on the actual operation of the variable frequency compressor and enhancing the operation ability of the variable frequency compressor. On the other hand, the method adopts the constant speed control of the frequency converter to control the dynamic operation speed of the variable frequency compressor to be consistent with the operation speed during stable operation under the rated power supply voltage, offsetting the adverse effect of voltage imbalance caused by low power supply voltage on the field weakening control of the frequency converter, thereby further improving the operation stability of the variable frequency compressor control system. At the same time, the method of the present invention also has the characteristics of low cost and convenient operation. Description of the drawings

[0027] Figure 1 It is a step flow chart of a method for improving the operation ability of a variable frequency compressor according to the present invention. Detailed implementation manners

[0028] Firstly, adopt the constant torque control method of the frequency converter to compensate the electromagnetic torque of the permanent magnet synchronous motor of the variable frequency compressor according to the change of the input power supply voltage monitored by the frequency converter software in real time, so as to realize the real-time dynamic following of the electromagnetic torque of the permanent magnet synchronous motor of the variable frequency compressor with the rated load torque of the permanent magnet synchronous motor. At the same time, adopt the constant speed control method of the frequency converter. The frequency converter software monitors the dynamic operation speed of the variable frequency compressor under low power supply voltage in real time, and realizes the control of the dynamic operation speed of the variable frequency compressor to be consistent with the given operation speed by compensating the frequency difference of the input frequency of the frequency converter and adjusting the field weakening control PI controller and the field weakening control starting modulation rate. The specific method steps are as Figure 1 shown:

[0029] S1: The rated power supply voltage of the variable frequency compressor system is V B , set the input voltage of the variable frequency compressor system to be constantly the rated power supply voltage V B , select n c as the given input within the operating speed range of the variable frequency compressor (in actual applications, the value of n c can be selected according to the actual situation of the specific compressor system), and record the output power P out of the permanent magnet synchronous motor, and calculate the rated load torque T B of the permanent magnet synchronous motor of the variable frequency compressor. The calculation method of the rated load torque T B is: T B = 9.55 * P out / n c .

[0030] S2: Under the same test conditions, connect the variable-frequency compressor system to an actual control system such as a refrigerator, and input the given operating speed n into the above control system. c After the compressor system receives the power supply, the input power supply voltage V of the frequency converter during the operation of the variable-frequency compressor is monitored in real time through the frequency converter software. IN Judge whether the input power supply voltage V IN is greater than the rated power supply voltage V B and less than or equal to the maximum working voltage of the compressor system. If so, go to step S3; if not, go to step S4.

[0031] S3: Start the first constant torque control module of the frequency converter software. The first constant torque control module includes a first electromagnetic torque sampling module and a first comparator module. The first electromagnetic torque sampling module is used to collect the electromagnetic torque T of the first permanent magnet synchronous motor of the variable-frequency compressor. e1 The first comparator module is used to compare and perform a difference operation on the rated load torque T of the permanent magnet synchronous motor B and the electromagnetic torque T of the first permanent magnet synchronous motor e1 to complete the output of the negative compensation torque T N The negative compensation torque T N is equal to the difference between the rated load torque T of the permanent magnet synchronous motor B and the electromagnetic torque T of the first permanent magnet synchronous motor e1 That is, T N = T B - T e1 The calculation formula for the electromagnetic torque T of the first permanent magnet synchronous motor of the variable-frequency compressor e1 is: T e1 = 1.5pi q1 [Ψ f + (L d - L q )i d1 ; where p is the number of pole pairs of the motor, i q1 is the first q-axis current, Ψ f is the amplitude of the equivalent d-axis permanent magnet flux linkage, L d is the d-axis inductance, L q is the q-axis inductance, i d1 is the first d-axis current.

[0032] S4: Judge whether the input power supply voltage V of the frequency converter IN is greater than or equal to the minimum working voltage of the compressor system and less than the rated power supply voltage V B If so, go to step S6; if not, go to step S5, set the input frequency of the frequency converter to zero, control the variable-frequency compressor to stop running, and make the LED fault light of the frequency converter flash to report a voltage fault.

[0033] S6: Start the second constant torque control module of the frequency converter software and enter step S7. The second constant torque control module includes a second electromagnetic torque sampling module and a second comparator module. The second electromagnetic torque sampling module is used to collect the electromagnetic torque T of the second permanent magnet synchronous motor of the variable frequency compressor e2 , and the second comparator module is used to compare and perform a difference operation on the rated load torque T of the permanent magnet synchronous motor B and the electromagnetic torque T of the second permanent magnet synchronous motor e2 to complete the output of the positive compensation torque T P . The positive compensation torque T P is equal to the difference between the rated load torque T of the permanent magnet synchronous motor B and the electromagnetic torque T of the second permanent magnet synchronous motor e2 , that is, T P = T B - T e2 . The calculation formula for the electromagnetic torque T of the second permanent magnet synchronous motor of the variable frequency compressor e2 is: T e2 = 1.5pi q2 [Ψ f +(L d - L q )i d2 , where i q2 is the second q-axis current and i d2 is the second d-axis current

[0034] S7: Real-time monitor the dynamic operating speed n of the variable frequency compressor through the frequency converter software, and determine whether the dynamic operating speed n of the variable frequency compressor is equal to the given operating speed n c . If so, enter step S8, and the compressor control system continues to operate. If not, enter step S9

[0035] S9: Determine whether the dynamic operating speed n of the variable frequency compressor is less than the maximum dynamic operating speed n of the variable frequency compressor MAX . If not, enter step S10. If so, enter step S11. The calculation method for the maximum dynamic operating speed n of the variable frequency compressor MAX is: n MAX = V IN / k e , where k e is the back electromotive force coefficient of the permanent magnet synchronous motor of the variable frequency compressor

[0036] S10: Start the first constant speed control module of the frequency converter software. The first constant speed module controls the dynamic operating speed n of the variable frequency compressor and the given operating speed n by compensating the frequency difference f of the input frequency of the frequency converter cKeeping the same, the inverter input frequency f calculation formula is: f = p (nn c ) / 60, where p is the number of motor pole pairs.

[0037] S11: Start the second constant speed control module of the inverter software. The second constant speed control module adjusts the weak magnetic control PI controller and the weak magnetic control start modulation rate to control the dynamic operating speed n of the variable frequency compressor and the given operating speed n. c The weak magnetic control PI regulator uses the output dynamic voltage U of the inverter detected by the inverter software as the input of the weak magnetic regulator and compares it with the maximum output voltage U of the inverter. MAX The deviation between the two is used as the input of the weak magnetic control PI regulator. The proportion P and integral I of the deviation are linearly combined to form the control quantity to adjust the second d-axis current i d2 and the second q-axis current i q2 The input makes the second d-axis current i d2 The magnetic potential of the permanent magnet is weakened within the weak magnetic range to achieve the purpose of weak magnetic control. The weak magnetic control start modulation rate is used to adjust the weak magnetic start threshold so that the permanent magnet synchronous motor enters the weak magnetic state in advance, so as to ensure that the dynamic operating speed n of the variable frequency compressor is increased to the given operating speed n under the condition of ensuring voltage balance. c , the maximum output voltage U of the inverter MAX The calculation formula is: U MAX =V IN *λ, where λ is a proportional constant, wherein the preferred value range of the proportional constant λ is 85% to 90%.

Claims

1. A method for improving the operating ability of a variable-frequency compressor, characterized in that, it includes the following steps: S1: Connect the variable-frequency compressor system to the rated power supply voltage, select n within the operating speed range of the variable-frequency compressor as the given input, and calculate the rated load torque T of the permanent magnet synchronous motor of the variable-frequency compressor, then enter S2; c B ​​ S2: Connect the variable-frequency compressor and the frequency converter to the actual test control system, and determine whether the input power supply voltage V of the frequency converter IN is greater than or equal to the rated power supply voltage V B and less than the maximum operating voltage of the compressor. If so, proceed to S3; if not, proceed to S4; S3: Start the first constant torque control module of the variable frequency software to compensate for the difference T between the rated load torque T B and the actual torque T e1 of the permanent magnet synchronous motor; N ​ S4: Determine whether the input power supply voltage is greater than or equal to the minimum operating voltage of the compressor and less than or equal to the rated power supply voltage V B , if not, go to S5, if so, go to S6; S5: Control the variable-frequency compressor to stop running; S6: Start the second constant torque control module of the variable frequency software to compensate for the difference T between the rated load torque T B and the actual torque T e2 of the permanent magnet synchronous motor, and enter S7; p ​ S7: Determine whether the dynamic operating speed n of the variable-frequency compressor is equal to the speed n during stable operation of the variable-frequency compressor. c If so, proceed to S8; if not, proceed to S9. S8: The variable-frequency compressor system is in a normal operating state and continues to run; S9: Determine whether the dynamic operating speed n of the variable-frequency compressor is less than the maximum operating speed n of the variable-frequency compressor MAX . If not, go to S10; if so, go to S11; S10: Activate the first constant speed control module of the variable frequency software, and control the dynamic operating speed n of the compressor to be consistent with the given operating speed n by controlling the input frequency of the frequency converter; c Keep consistent; S11: Activate the second constant speed control module of the variable frequency software, and adjust the dynamic operating speed n of the variable frequency compressor by regulating the weak magnetic control PI controller and the weak magnetic control starting modulation rate to be consistent with the given operating speed n. c Keep consistent.

2. The method for improving the operating ability of a variable-frequency compressor according to claim 1, characterized in that, The first constant torque control module includes a first electromagnetic torque sampling module and a first comparator module. The first electromagnetic torque sampling module is used to collect the actual electromagnetic torque T of the first permanent magnet synchronous motor of the variable frequency compressor e1 , and the first comparator module is used to compare the rated load torque T of the permanent magnet synchronous motor B with the actual electromagnetic torque T of the first permanent magnet synchronous motor e1 , calculate the negative compensation torque T N , and complete the output of the negative compensation torque T N .

3. The method for improving the operating ability of a variable-frequency compressor according to claim 2, characterized in that, The second constant torque control module includes a second electromagnetic torque sampling module and a second comparator module. The second electromagnetic torque sampling module is used to collect the actual electromagnetic torque T of the second permanent magnet synchronous motor of the variable frequency compressor e2 , and the second comparator module is used to compare the rated load torque T of the permanent magnet synchronous motor B with the actual electromagnetic torque T of the second permanent magnet synchronous motor e2 to calculate the positive compensation torque T P , and complete the output of the positive compensation torque T P .

4. The method for improving the operating ability of a variable-frequency compressor according to claim 3, characterized in that, The specific method for controlling the variable-frequency compressor to stop running in step S5: Set the input frequency of the frequency converter to zero, stop the variable-frequency compressor from running, and at the same time control the LED fault light of the frequency converter to flash to report a voltage fault.

5. The method for improving the operating ability of a variable-frequency compressor according to claim 4, characterized in that, Specific method of step S10: The first constant speed control module calculates the difference f between the input frequency of the variable frequency compressor during dynamic operation and the stable operation under the rated power supply voltage, and controls the dynamic operation speed n of the variable frequency compressor to be consistent with the given operation speed n through frequency compensation, where the calculation method of the frequency difference f of the frequency converter is: f = p(n - n c ) / 60, where p is the number of pole pairs of the motor. c ) / 60, where p is the number of pole pairs of the motor.

6. The method for improving the operating ability of a variable-frequency compressor according to any one of claims 1-5, characterized in that, The specific method of step S11 is: The second constant-speed control module controls the dynamic operating speed of the variable-frequency compressor by adjusting the weak magnetic control PI controller and the weak magnetic control starting modulation rate; The weak magnetic control PI controller uses the inverter output dynamic voltage U detected by the inverter software as the input of the weak magnetic regulator and compares it with the inverter's maximum output voltage U MAX The deviation between the two is used as the input of the weak magnetic control PI controller. The deviation is adjusted by proportional regulation and integral regulation and then linearly combined to adjust the input of the second d-axis current and the second q-axis current, so that the second d-axis current weakens the magnetic potential of the permanent magnet within the weak magnetic range to achieve the purpose of weak magnetic control. The weak magnetic control starting modulation rate is used to adjust the weak magnetic starting threshold value so that the permanent magnet synchronous motor enters the weak magnetic state in advance. Under the condition of ensuring voltage balance, the dynamic operating speed n of the variable frequency compressor is increased to the given operating speed n. c , the maximum output voltage U of the inverter MAX The calculation formula is: U MAX =V IN *λ, where λ is the proportionality constant.

7. The method for improving the operating ability of a variable-frequency compressor according to claim 6, characterized in that, The value range of λ is 85% to 90%.

Images