CN102455240A - Method for detecting load inertia of variable-frequency motor - Google Patents

Abstract

The invention relates to a method for detecting the load inertia of a variable-frequency motor. The method for detecting the load inertia comprises the following steps of: firstly, controlling the variable-frequency motor to rotate to certain speed SPEED1, and calculating an average torque T1 output by the motor according to an output signal of a PI controller of a frequency converter and the rotating speed of the motor; secondly, controlling the variable-frequency motor to accelerate to speed SPEED2 at constant speed, and calculating an average torque T2 output by the motor according to the output signal of the PI controller of the frequency converter and the rotating speed; and finally, calculating the load inertia J of the variable-frequency motor according to a difference value between the torque T1 and the torque T2 and an acceleration value. The load inertia is calculated according to the output signal of the PI controller of the frequency converter and the rotating speed of the motor, and an extra hardware circuit is not needed, so the method has the advantage of low cost; and a product of a sampling period and the number of sampling points is equal to the integral multiple of the rotating period of load during calculation of the average torques, so the method has the advantage of high detection precision.

Description

A kind of inertia detection method of variable-frequency motor load

Technical field

Patent of the present invention relates to the measuring method of load inertia, particularly a kind of inertia detection method of variable-frequency motor load.

Background technology

Variable-frequency motor comprises motor and frequency converter.Along with the development of Power Electronic Technique and microcontroller technology, the frequency converter price is more and more lower, and it not only is used in the Industry Control now in a large number, and gets in a large number in the civil equipment, like the variable-frequency washing machine in the white domestic appliances, air-conditioning, refrigerator etc.

For dynamic property and the stability that improves frequency converter itself, just need adjust the parameter of the PI controller of frequency converter according to the size of motor load inertia; System also can be according to the size of detected motor load inertia, the motion flow of automatic adjustment system, thus make system obtain best effect.Be that example describes below with the washing machine: during automatic washing machine work, hope can obtain the capacity of clothing in the washing machine, thereby can select suitable water level and wash time etc. in view of the above automatically, realizes the fuzzy control of laundry processes.And the capacity of clothing can obtain through the inertia of measuring the washing machine rotating cylinder in the washing machine; Therefore; The detection that how to realize washing machine rotating cylinder inertia is one of the important technology in washing machine field; It is irregularly shaped and washing machine is as load, definite more complicated of its torque, and the inertia that therefore how to detect such load still is technological difficulties in washing machine field at present.Therefore, how realizing that the inertia of motor load detects, is the important gordian technique that the technician in motor and frequency converter field need solve.

Summary of the invention

The technical matters that the present invention will solve provides the inertia detection method of the variable-frequency motor load that a kind of inertia that can realize motor load detects.

The present invention is in order to solve the problems of the technologies described above; A kind of technical scheme is provided: the inertia detection method of variable-frequency motor load adopts the output signal of the PI controller of frequency converter; Come the inertia of sensing lead in conjunction with motor speed, may further comprise the steps: the control of conversion motor forwards certain speed SPEED1 to; Output signal and motor speed according to the PI controller calculate the average torque T1 of motor output; The control of conversion motor forwards certain speed SPEED2 to; Output signal and motor speed according to the PI controller calculate the average torque T2 of motor output; Acceleration magnitude according between the difference of torque T1 and torque T2 and SPEED1, the SPEED2 is calculated the inertia J of variable-frequency motor load.The output signal of said PI controller is in voltage, electric current, the power signal.The process that the control of conversion motor forwards certain speed SPEED2 to is even accelerator.When calculating the average torque of motor output, the product in sampling number and sampling period equals the integral multiple of the rotation period of motor load.

After having adopted technique scheme, the beneficial effect that the present invention brings: (1) the present invention does not need the additional hardware circuit according to the output signal of the PI controller of frequency converter and the inertia of motor speed computational load, has the low advantage of cost.Testing result can be used for regulating automatically the parameter of the PI controller of frequency converter, also can be used for control system and according to the inertia size Based Intelligent Control or fuzzy control is carried out in the operation of system, thereby improve performance, efficient, self-adaptation and the stability of system.

(2), thereby has good suitability owing to can carry out the detection of load inertia according to the multiple output signal of PI controller.

(3) because in detecting the load inertia process, the process of control of conversion motor speed is even accelerator, therefore has the advantage of accuracy of detection height, good stability.

(4) product owing to sampling period and sampling number when calculating average torque equals the integral multiple of the rotation period of load, thereby has the high advantage of accuracy of detection, can be widely used in technical fields such as white domestic appliances frequency converter, industrial frequency transformer.

Description of drawings

For content of the present invention is expressly understood more easily,, the present invention is done further detailed explanation, wherein below according to specific embodiment and combine accompanying drawing

Fig. 1 is the application system block diagram.

Fig. 2 is a PI controller block diagram.

Fig. 3 is an inertia detection speed curve.

Fig. 4 is variable-frequency motor load inertia testing process figure.

Embodiment

(embodiment 1)

The application system block diagram is as shown in Figure 1, and the present invention is applied to the system of a variable-frequency motor and load composition thereof, and this system comprises frequency converter, motor and load, and frequency converter comprises this software module of PI controller.

PI controller block diagram is as shown in Figure 2; The input signal of PI controller is the error of target velocity and feedback speed; Obtain exporting signal through the PI algorithm; Be the control voltage of motor, more by formula 1 calculate motor according to the control voltage of motor the output torque, then by formula 2 according to the output torque of motor and the inertia of motor speed calculating motor load.

$T=\frac{k_{1}V{c}^2}{{\mathrm{\ω}}^2}---\left(1\right)$

J＝(T2-T1)/(dω/dt) (2)

In the formula: J is the load inertia of motor, and T is the output torque of motor, and ω is a motor speed, and d ω/dt is the acceleration of motor, k ₁It is constant.

The speed control curve of inertia testing process is as shown in Figure 3, between t1～t2, measures average torque T1, between t3～t4, measures average torque T2, and time span requires the product of sampling period and sampling number to equal the integral multiple of the rotation period of load equipment;

Testing process of the present invention is as shown in Figure 4, and concrete steps are following:

At first the control of conversion motor forwards certain speed SPEED1 to; Wait for that motor speed is stabilized to SPEED1;

Output voltage and motor speed according to the PI controller calculate the average torque T1 of motor output;

The even speed SPEED2 that accelerates to of control of conversion motor;

According to the average torque T2 that exports in the output voltage of the PI controller of frequency converter and the even accelerator of revolution speed calculating motor;

At last calculate the inertia J of variable-frequency motor load according to the acceleration magnitude between the difference of torque T1 and torque T2 and SPEED1, the SPEED2.

(embodiment 2)

The testing process of present embodiment such as embodiment 1; The PI controller of different is present embodiment is output as current signal; Again by formula 3 calculate motor according to the electric current of motor the output torque, then by formula 2 according to the output torque of motor and the inertia of motor speed calculating motor load.

$T=\frac{k_2{I}^2}{{\mathrm{\ω}}^2}---\left(3\right)$

In the formula: k ₂It is constant.

(embodiment 3)

The testing process of present embodiment such as embodiment 1; The PI controller of different is present embodiment is output as power signal; 4 output torques by formula again according to the power calculation motor of motor, then by formula 2 calculate motor load according to the output torque and the motor speed of motor inertia.

$T=\frac{k_{3}P}{{\mathrm{\ω}}^2}---\left(4\right)$

In the formula: k ₃It is constant.

The above only is a typical application of the present invention; Should be understood that; For the person of ordinary skill of the art, under the prerequisite that does not break away from principle of the present invention, described software algorithm or software flow are made some changes and retouching; Such as change to detect and computing velocity SPEED1, SPEED2 between the method for operating etc. of even acceleration average torque T2, these changes and retouching also should be regarded as protection scope of the present invention.

Claims (4)

1. the inertia detection method of a variable-frequency motor load is characterized in that adopting the output signal of the PI controller of frequency converter, comes the inertia of computational load in conjunction with motor speed, may further comprise the steps:

S1. the control of conversion motor forwards certain speed SPEED1 to;

S2. output signal and the motor speed according to the PI controller calculates the average torque T1 of motor output;

S3. the control of conversion motor forwards certain speed SPEED2 to;

S4. output signal and the motor speed according to the PI controller calculates the average torque T2 of motor output;

S5. calculate the inertia J of variable-frequency motor load according to the acceleration magnitude between the difference of torque T1 and torque T2 and SPEED1, the SPEED2.

2. the inertia detection method of a kind of variable-frequency motor load according to claim 1 is characterized in that: the output signal of said PI controller is in voltage, electric current, the power signal.

3. the inertia detection method of a kind of variable-frequency motor load according to claim 1 is characterized in that: the process that the control of conversion motor forwards certain speed SPEED2 to is even accelerator.

4. the inertia detection method of a kind of variable-frequency motor load according to claim 1 is characterized in that: when calculating the average torque of motor output, the product in sampling number and sampling period equals the integral multiple of the rotation period of motor load.

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