CN108111091B - Method, device and storage medium for reducing total loss of asynchronous motor - Google Patents

Abstract

The invention provides a method, a device and a storage medium for reducing total loss of an asynchronous motor, wherein the method comprises the following steps: acquiring parameters of an asynchronous motor; when the parameters of the asynchronous motor meet the preset conditions, the frequency or the pressure-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor. The invention can at least solve the problem of low efficiency of the asynchronous motor under long-term light-load operation in the related art.

Description

Method, device and storage medium for reducing total loss of asynchronous motor

technical field

The invention relates to the technical field of asynchronous motors, and relates to a method, a device and a storage medium for reducing the total loss of an asynchronous motor.

Background technique

As an important power device, electric motors have been widely used in various sectors such as metallurgy, electric power, petrochemical, coal, papermaking, building materials manufacturing, etc. The electricity consumption of electric motors accounts for 60%-70% of the national industrial electricity consumption. However, due to the large wealth of equipment design and selection in my country, the equipment has been operating in low-load areas for a long time, and the phenomenon of "big horse-drawn carts" is serious. When the motor works near the rated load, its efficiency is very high, but in actual use, most motors often run under light load or even no load, the load rate of the motor is very low, its active current is very small, and there is no The power current is basically unchanged, so the power factor of the motor is very low at this time, and the efficiency is low. For the asynchronous motor under long-term light load operation, there is a lot of energy saving space.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a method, a device and a storage medium for reducing the total loss of an asynchronous motor, so as to at least solve the problem of low efficiency of the asynchronous motor under long-term light-load operation in the related art.

According to an embodiment of the present invention, a method for reducing the total loss of an asynchronous motor is provided, comprising: acquiring parameters of the asynchronous motor; and adjusting the asynchronous motor when the parameters of the asynchronous motor satisfy a preset condition The frequency or voltage-to-frequency ratio of the motor to reduce the total losses of the asynchronous motor.

According to an embodiment of the present invention, a device for reducing the total loss of an asynchronous motor is provided, comprising: a parameter acquisition unit for acquiring parameters of the asynchronous motor; and an adjustment unit for: when the asynchronous motor When the parameters of the asynchronous motor meet the preset conditions, the frequency or the voltage-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor.

According to yet another embodiment of the present invention, a storage medium is also provided. The storage medium is set to store program codes for executing the following steps: acquiring parameters of the asynchronous motor; adjusting the frequency or voltage-frequency ratio of the asynchronous motor when the parameters of the asynchronous motor meet preset conditions, In order to reduce the total loss of the asynchronous motor.

By means of the invention, the frequency or the voltage-frequency ratio of the asynchronous motor is adjusted under preset conditions to reduce the total loss of the asynchronous motor, so as to at least solve the problem of low efficiency of the asynchronous motor under long-term light-load operation in the related art , improve the operating efficiency of the asynchronous motor, and achieve the purpose of energy saving.

Description of drawings

The accompanying drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

1 is a flowchart of a method for reducing the total loss of an asynchronous motor according to an embodiment of the present invention;

2 is a block diagram of a device structure for reducing the total loss of an asynchronous motor according to an embodiment of the present invention;

3 is an equivalent circuit diagram of an asynchronous motor according to an embodiment of the present invention;

4 is a graph showing the relationship between frequency and electrical loss ΣP under a constant voltage-to-frequency ratio of an asynchronous motor according to an embodiment of the present invention;

5 is a graph showing the relationship between frequency and efficiency η under a constant voltage-to-frequency ratio of an asynchronous motor according to an embodiment of the present invention;

Fig. 6 is the relation diagram of frequency and ΣP under the constant voltage-frequency ratio of the asynchronous motor according to the embodiment of the present invention;

7 is a graph showing the relationship between frequency and efficiency η under a constant voltage-to-frequency ratio of an asynchronous motor according to an embodiment of the present invention;

8 is a diagram of electrical energy consumption of a 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation according to an embodiment of the present invention;

9 is a diagram of electrical energy consumption of a 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation according to an embodiment of the present invention;

FIG. 10 is a diagram of the electrical loss of a 5.5kW asynchronous motor with a non-constant voltage-to-frequency ratio and frequency modulation according to an embodiment of the present invention;

FIG. 11 is a diagram showing the total loss of a 5.5kW asynchronous motor with a non-constant voltage-to-frequency ratio and a frequency-modulated motor according to an embodiment of the present invention;

12 is a theoretical calculation relationship diagram of frequency modulation P1, U and f of a 5.5kW asynchronous motor according to an embodiment of the present invention;

Fig. 13 is the measured relation diagram of frequency modulation P1, U and f of the 5.5kW asynchronous motor according to the embodiment of the present invention;

14 is a diagram of electrical energy consumption of a 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation according to an embodiment of the present invention;

15 is a diagram of electrical energy consumption of a 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation according to an embodiment of the present invention;

FIG. 16 is a diagram showing the electrical loss of a 5.5kW asynchronous motor with a non-constant voltage-to-frequency ratio and frequency modulation according to an embodiment of the present invention;

17 is a loss diagram of a non-constant voltage-frequency-frequency-frequency-modulated motor of a 5.5kW asynchronous motor according to an embodiment of the present invention;

18 is a theoretical calculation relationship diagram of frequency modulation P1, U and f of a 5.5kW asynchronous motor according to an embodiment of the present invention;

FIG. 19 is an actual measured relationship diagram of frequency modulation P1, U and f of a 5.5kW asynchronous motor according to an embodiment of the present invention.

Detailed ways

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and in conjunction with embodiments. It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict.

It should be noted that the terms "first", "second" and the like in the description and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence.

Example 1

In this embodiment, a method for reducing the total loss of an asynchronous motor is provided, as shown in FIG. 1 , the method includes the following steps:

Step S101, acquiring the parameters of the asynchronous motor;

Step S102, when the parameters of the asynchronous motor meet the preset conditions, adjust the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.

Optionally, the preset conditions include a preset constant voltage-frequency ratio relationship and a preset non-constant voltage-frequency ratio relationship;

When the parameters of the asynchronous motor meet the preset constant voltage-frequency ratio relationship, adjust the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor;

When the parameters of the asynchronous motor meet the preset non-constant voltage-frequency ratio relationship, the voltage-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor.

Through the above steps, according to whether the parameters of the asynchronous motor meet the relationship of the constant voltage-frequency ratio, the frequency or the voltage-frequency ratio of the asynchronous motor is adjusted, the total loss of the asynchronous motor is reduced, the operating efficiency of the asynchronous motor is improved, and the purpose of energy saving is achieved.

Optionally, after acquiring the parameters of the asynchronous motor, the method further includes: adjusting the stator voltage of the asynchronous motor so that the ratio of the induced electromotive force of each phase winding of the stator of the asynchronous motor to the frequency of the asynchronous motor is constant.

It should be noted that, in the adjustment process, the ratio of the induced electromotive force of each phase winding of the asynchronous motor to the frequency of the asynchronous motor is kept constant in order to keep the magnetic flux unchanged. Therefore, when the frequency changes, the magnitude of the electromotive force must be changed by compensating for the voltage drop of the motor stator at the same time, so that the ratio E1/f of the electromotive force and the frequency is a constant value.

Optionally, the total loss of the asynchronous motor satisfies: ΣP=P _u +P _v , where P _v is the active power consumed by the resistors R ₁ and R' ₂ in the equivalent circuit of the asynchronous motor, and P _u is the equivalent circuit Power _dissipated across resistors R1 and _Rm .

其中，g为等效电导，满足：

其中，m₁为异步电动机的相数；U₁为每相绕组的电压；R₁为定子电阻；R_m为励磁阻抗；X₁为定子漏抗；X_m为励磁漏抗。Optionally, P _u satisfies:

Among them, g is the equivalent conductance, which satisfies:

Among them, m ₁ is the phase number of the asynchronous motor; U ₁ is the voltage of each phase winding; R ₁ is the stator resistance; R _m is the excitation impedance; X ₁ is the stator leakage reactance; X _m is the excitation leakage reactance.

Optionally, P _v satisfies:

其中，R₁为定子电阻；R'₂为转子电阻；c₁＝1+X₁/X_m，其中，X₁为定子漏抗；X_m为励磁漏抗。Among them, s is the slip ratio; T _e is the electromagnetic torque of the asynchronous motor; Ω ₁ is the synchronous mechanical angular velocity; R" ₁ =c ₁ R ₁ ;

Wherein, R ₁ is the stator resistance; R' ₂ is the rotor resistance; c ₁ =1+X ₁ /X _m , where X ₁ is the stator leakage reactance; X _m is the excitation leakage reactance.

Optionally, the frequency f ₁ of the regulated asynchronous motor satisfies:

其中，R₁为定子电阻；R'₂为转子电阻；c₁＝1+X₁/X_m，其中，X₁为定子漏抗；X_m为励磁漏抗；T_L为负载转矩；m₁为异步电动机的相数；p为异步电动机的功率；L_m为定、转子间互感；L₁为定子自感。Wherein, U ₁ is the power supply voltage; f ₁ is the frequency of the asynchronous motor; R ₁ is the stator resistance; R _m is the excitation impedance; R " ₁ =c ₁ R ₁ ;

Wherein, R ₁ is the stator resistance; R' ₂ is the rotor resistance; c ₁ =1+X ₁ /X _m , where X ₁ is the stator leakage reactance; X _m is the excitation leakage reactance; T _L is the load torque; m ₁ is the phase number of the asynchronous motor; p is the power of the asynchronous motor; L _m is the mutual inductance between the stator and the rotor; L ₁ is the stator self-inductance.

From the description of the above embodiments, those skilled in the art can clearly understand that the method according to the above embodiment can be implemented by means of software plus a necessary general hardware platform, and of course can also be implemented by hardware, but in many cases the former is better implementation. Based on this understanding, the technical solutions of the present invention can be embodied in the form of software products in essence or the parts that make contributions to the prior art, and the computer software products are stored in a storage medium (such as ROM/RAM, magnetic disk, CD-ROM), including several instructions to make a terminal device (which may be a mobile phone, a computer, a server, or a network device, etc.) to execute the methods of the various embodiments of the present invention.

Example 2

In this embodiment, a device for reducing the total loss of an asynchronous motor is also provided, and the device is used to implement the above-mentioned embodiments and preferred implementations, and what has been described will not be repeated. As used below, the term "unit" may be a combination of software and/or hardware that implements a predetermined function. Although the apparatus described in the following embodiments is preferably implemented in software, implementations in hardware, or a combination of software and hardware, are also possible and contemplated.

As shown in Figure 2, the device includes:

a parameter obtaining unit 10, used for obtaining parameters of the asynchronous motor;

The adjusting unit 20 is used for adjusting the frequency or the voltage-frequency ratio of the asynchronous motor when the parameters of the asynchronous motor meet the preset conditions, so as to reduce the total loss of the asynchronous motor.

Optionally, the preset conditions include a preset constant voltage-frequency ratio relationship and a preset non-constant voltage-frequency ratio relationship. When the parameters of the asynchronous motor meet the preset constant voltage-frequency ratio relationship, adjust the asynchronous motor. The frequency of the motor to reduce the total losses of the asynchronous motor;

When the parameters of the asynchronous motor meet the preset non-constant voltage-frequency ratio relationship, the voltage-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor.

Optionally, the device further includes a stator voltage adjustment unit, which is used to adjust the stator voltage of the asynchronous motor after acquiring the parameters of the asynchronous motor, so that the induction electromotive force of each phase winding of the stator of the asynchronous motor is related to the frequency of the asynchronous motor. ratio is constant.

It should be noted that the above-mentioned units can be implemented by software or hardware, and the latter can be implemented in the following ways, but not limited to this: the above-mentioned modules are all located in the same processor; or, the above-mentioned modules can be combined in any combination The forms are located in different processors.

Example 3

Embodiments of the present invention also provide a storage medium. Optionally, in this embodiment, the above-mentioned storage medium may be configured to store program codes for executing the following steps:

Obtain the parameters of the asynchronous motor; when the parameters of the asynchronous motor meet the preset conditions, adjust the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.

Optionally, the preset conditions include a preset constant voltage-frequency ratio relationship and a preset non-constant voltage-frequency ratio relationship;

When the parameters of the asynchronous motor meet the preset constant voltage-frequency ratio relationship, adjust the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor;

When the parameters of the asynchronous motor meet the preset non-constant voltage-frequency ratio relationship, the voltage-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor.

Optionally, in this embodiment, the above-mentioned storage medium may include but is not limited to: a U disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a mobile hard disk, a magnetic Various media that can store program codes, such as discs or optical discs.

Optionally, in this embodiment, the processor executes according to the program code stored in the storage medium:

Obtain the parameters of the asynchronous motor; when the parameters of the asynchronous motor meet the preset conditions, adjust the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.

Optionally, the preset conditions include a preset constant voltage-frequency ratio relationship and a preset non-constant voltage-frequency ratio relationship; when the parameters of the asynchronous motor meet the preset constant voltage-frequency ratio relationship, adjust the asynchronous The frequency of the motor is adjusted to reduce the total loss of the asynchronous motor; when the parameters of the asynchronous motor meet the preset non-constant voltage-frequency ratio relationship, the voltage-frequency ratio of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor.

Optionally, for specific examples in this embodiment, reference may be made to the examples described in the foregoing embodiments and optional implementation manners, and details are not described herein again in this embodiment.

Example 4

This embodiment is an optional embodiment of the present application, and is used to describe the present application in detail in combination with specific usage scenarios:

In the speed control system of the asynchronous motor, the variable voltage and frequency conversion speed control system is the system with the best control performance and the highest efficiency. The V/F control method is to change the voltage of the motor power supply while changing the frequency of the motor power supply, so that the magnetic flux of the motor is kept constant, and the efficiency and power factor of the motor do not decrease in a wide speed regulation range. Because the ratio of voltage and frequency (U/F) is controlled, it is called U/F control. In an asynchronous motor, the rotor speed is lower than the rotation speed of the air-gap rotating magnetic field, that is, the synchronous speed. Therefore, in the rotor circuit, a slip electromotive force will be generated, and the electromotive force will generate a rotor current. The rotor current interacts with the rotating magnetic field to generate electromagnetic torque. The formula for the effective value of the induced electromotive force of each phase winding of the asynchronous motor stator is:

E ₁ =4.44f ₁ N ₁ K _dp1 Φ _m (4-1)

In the formula, E ₁ is the effective value (V) of the induced electromotive force of the air-gap magnetic flux in each phase winding of the stator; f ₁ is the stator power supply frequency (Hz); N ₁ is the number of series turns of each phase winding of the stator; k _dp1 is the base Wave winding coefficient; Φ _m is the air gap flux (Wb) per pole.

Therefore, when the structural parameters of the motor are determined, it can be obtained according to the formula:

In addition, the electromagnetic torque of the motor is:

称为转矩因子；In the formula,

called torque factor;

——转子电压与电流的相位差；

- the phase difference between the rotor voltage and the current;

——转子每相电路功率因子；

- the power factor of each phase of the rotor circuit;

T——The electromagnetic torque of the motor (N·M).

It is inferred from equation (4-1) that if E ₁ remains unchanged, when the stator power supply frequency f ₁ increases, it will cause the air gap magnetic flux Φ _m to decrease, and it can be seen from the formula that the decrease of Φ _m causes the motor electromagnetic torque T to decrease, This results in an increase in frequency and a decrease in load capacity. When the value of E ₁ is constant, if the frequency f ₁ is lowered, the main magnetic flux Φ _m will increase. The main magnetic circuit of the motor is already a little saturated, and if Φ _m increases, the main magnetic is bound to pass through saturation, and the excitation current increases sharply, which is not allowed. For this reason, while adjusting the frequency, the stator voltage must be coordinated and controlled, but the control method varies with the operating frequency below the fundamental frequency and above the fundamental frequency.

When the speed is adjusted below the fundamental frequency, to keep the magnetic flux Φ _m constant, when the frequency f ₁ changes, the size of the electromotive force E ₁ must be changed at the same time, so that E1/f is a constant value, that is, the control method of constant electromotive force and frequency ratio is adopted. . Due to the difficulty in detecting and controlling the induced electromotive force of the motor, the steady-state performance of constant E1/f control is better than that of constant U1/f control. Constant E1/f control is the pursuit of compensating the motor stator voltage drop in constant U1/f control. The goal. According to the asynchronous motor stator voltage equation:

U ₁ =E ₁ +I ₁ Z ₁ (4-4)

where I ₁ — stator current (A);

Z ₁ - stator impedance (Ω).

When the output frequency of the inverter is lower than the rated power supply of the power supply, the variable frequency speed regulation system belongs to the constant torque speed regulation, but when the frequency is low, the voltage drop of the stator leakage impedance cannot be ignored, so artificially increase the stator voltage to compensate for the Voltage drop due to leakage reactance.

When the speed is adjusted above the fundamental frequency, when the voltage of the motor increases with the increase of the frequency, if the voltage of the motor has reached the rated voltage of the motor, continuing to increase the voltage may damage the insulation performance of the motor. For this reason, after the motor reaches the rated voltage, the motor voltage is maintained even if the frequency is increased. In this way, the power that the motor can output is determined by the product of the rated voltage and rated current of the motor, and does not change with the frequency. When the speed is adjusted above the base frequency, the frequency can be increased from the base frequency upward, but the voltage cannot exceed the rated voltage. At this time, the variable frequency speed control system belongs to the constant power speed control.

The loss analysis of the asynchronous motor after frequency conversion shows that the frequency conversion speed regulation of the asynchronous motor is to convert the power supply of the asynchronous motor through the frequency converter, and the entire speed regulation device is composed of the frequency converter and the motor. The loss refers to the difference between the input power and the output power of the entire device system. The main way to improve the efficiency of the whole system is to reduce the loss, so we must first analyze the losses of the frequency converter and the asynchronous motor.

The loss of the inverter is analyzed as follows: the loss of the inverter is mainly composed of the loss of the power electronic device itself and the driving loss. At present, the power electronic devices of the inverter are mainly IGBTs with low driving loss, and the driving loss can be ignored. In this way, the loss of the inverter is mainly the loss of the power electronic device, including the on-state loss and switching loss of the device. The on-state loss depends on the tube voltage drop and load current of the device, the switching loss depends on the switching frequency and load current, and the inverter loss increases with the increase of the rms value of the current, so the following loss expression can be established:

In the expression, P _inv is the loss of the inverter, K ₁ and K ₂ are the correlation coefficients determined by the switching _devices , and is the effective value of the phase current.

The loss of asynchronous motor is mainly divided into: ① the copper loss generated by the passage of current in the stator and rotor windings, which is finally dissipated in the form of heat, and is divided into two parts: stator copper loss and rotor copper loss; ② The magnetic field in the stator and rotor core produces Iron loss (including hysteresis loss and eddy current loss); ③ ventilation and friction loss caused by the rotation of the fan and bearing, also known as mechanical loss; ④ stray loss caused by higher harmonics of the air gap magnetic field.

The main research in this paper is the variable frequency speed regulation of the constant torque load of the asynchronous motor. The principle of the frequency converter speed regulation is: U ₁ /f ₁ =C is a constant, so that the power supply voltage U ₁ and the frequency f ₁ change in direct proportion to achieve Adjust the output. According to formula (4-1), we get:

Φ=U ₁ /4.44f ₁ N ₁ K _dp1 (4-6)

It can be seen from the formula (4-6) that for the asynchronous motor tested in the laboratory, 4.44, N ₁ , K _dp1 are constants. The frequency modulation is divided into two methods: constant voltage frequency ratio and non-constant voltage frequency ratio: for constant voltage frequency ratio frequency modulation, the magnetic flux φ of the asynchronous motor remains unchanged, so the stator and rotor currents remain unchanged; for non-constant voltage frequency ratio frequency modulation , due to the consideration of the magnetic flux saturation of the asynchronous motor, the loss increases, and the general voltage-to-frequency ratio is lowered, but it is not a constant value. The magnetic flux φ of the asynchronous motor decreases, and the stator and rotor currents decrease. When the frequency f ₁ is lowered by the frequency converter, the analysis of the loss changes of the asynchronous motor is as follows:

(1) Stator copper loss P _cu1 : under the constant voltage-frequency ratio of the asynchronous motor, since it is a constant voltage-frequency ratio, the magnetic flux φ of the motor remains unchanged, and the stator current remains unchanged, regardless of the influence of temperature on it, P _cu1 does not Change; under the non-constant voltage-frequency ratio, the magnetic flux φ of the motor decreases, and the stator current decreases, so P _cu1 decreases.

(2) Rotor copper loss P _cu2 : under the constant voltage-frequency ratio of the asynchronous motor, due to the constant voltage-frequency ratio, the magnetic flux φ of the motor remains unchanged, and the rotor current remains unchanged, regardless of the influence of temperature on it, P _cu2 does not Change; under the non-constant voltage-frequency ratio, the magnetic flux φ of the motor decreases, and the rotor current becomes smaller, so P _cu2 decreases.

(3) Iron loss P _Fe : From P _Fe =K·f ^1.3 ·B ² , it can be known that the frequency conversion of the asynchronous motor is a constant voltage-frequency ratio because of the constant voltage-frequency ratio, so the magnetic flux φ of the motor remains unchanged, when the frequency f When ₁ decreases, P _Fe also decreases; under the non-constant voltage-frequency ratio, the magnetic flux φ of the motor decreases, and when the frequency f ₁ decreases, P _Fe also decreases.

(4) Mechanical loss _pm : The mechanical loss depends on the speed of the asynchronous motor. Since the speed change from no-load to rated load is not obvious, it is generally considered to be a constant loss. However, when the frequency changes, the speed of the motor will also decrease, so no matter which way the frequency is adjusted, the mechanical loss will decrease.

(5) Spurious loss p _a : Since it is difficult to measure and calculate, it is generally calculated by means of estimation, so this paper assumes that it is unchanged for the time being.

It can be seen from the above analysis that when the asynchronous motor is frequency-regulated under the constant voltage-frequency ratio, the copper loss of the stator and rotor remains unchanged, the iron loss decreases, the mechanical loss decreases, the stray loss remains unchanged, and the total loss decreases; the asynchronous motor is under non-constant voltage-frequency ratio. Frequency modulation, the copper loss of the stator and rotor decreases, the iron loss decreases, the mechanical loss decreases, the stray loss remains unchanged, and the total loss decreases.

When the asynchronous motor is running in a steady state, its mechanical load only requires two operating parameters of torque T and speed n for the motor, that is, the asynchronous motor at a certain speed provides a specific electromagnetic torque [.

According to the rated voltage of the tested motor is 380v, the power frequency is 50Hz, and its voltage-frequency ratio K is 7.6. Available:

Substituting each parameter value into the above formula, we get:

Derive f by formula (4-7):

dΣP/df=0 (4-8)

When the load torque T of the asynchronous motor is its rated torque, there is no optimal frequency. When the constant voltage frequency ratio of the asynchronous motor is energy saving, the electrical loss decreases with the decrease of the frequency, so when the frequency is the smallest, the electrical loss is the smallest. When U1/f1 is equal to a constant and equal to 7.6, the main magnetic flux Φ _m of the asynchronous motor is close to a constant, and its maximum torque expression is:

According to the formula (4-9), when the frequency conversion of the asynchronous motor is used to ensure energy saving, the decrease of the frequency f leads to the reduction of Tm, but the Tm must be greater than the load torque value of the asynchronous motor, and a 20% margin is reserved.

According to the Γ-type equivalent circuit of the asynchronous motor (Fig. 3), set the total electrical loss of the asynchronous motor:

Depend on:

Substituting equation (4-10) into equation (4-9), we get:

make:

dΣP/dω=0 (4-13)

That is, the optimal voltage-to-frequency ratio can be obtained:

From formula (4-14), the optimal frequency f1 and optimal voltage U1 of the three-phase asynchronous motor under the non-constant voltage-frequency ratio energy saving can be deduced, which are:

or

From equation (4-14), it can be concluded that under a certain load, for a specific motor, there is an optimal voltage-frequency ratio to make the motor Electrical losses are minimal. That is, in actual engineering projects, for an asynchronous motor to drive different loads, under each load, as long as the voltage of the asynchronous motor is determined, the optimal frequency can be obtained to minimize the electrical loss of the motor.

For the variable frequency speed regulation of the asynchronous motor under the constant torque load, it is usually expected that the main magnetic flux of the motor should remain unchanged at the rated value. .

Now for the variable frequency speed regulation test of the constant voltage-frequency ratio of the asynchronous motor:

The following discusses the frequency conversion energy saving of the constant voltage-frequency ratio of the asynchronous motor under 1/4 load:

Now take a 5.5kW three-phase asynchronous motor as the research object, when it drives its 1/4 load with constant torque, the asynchronous motor can be saved by frequency conversion with a constant voltage-frequency ratio through the frequency converter. The test data is shown in Table 1:

Table 1 Energy consumption test data of 5.5kW asynchronous motor under constant voltage frequency ratio frequency modulation mode

The data of the asynchronous motor generated in Table 1 under constant torque and constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analytical parameters such as P _u , P _v and ΣP are calculated by formulas, and finally the power loss of the asynchronous motor is calculated. ΣP and output power P2 are added together to obtain P1, and the specific calculation results are shown in Table 2:

Table 2 Calculation and analysis of energy consumption of 5.5kW asynchronous motor under constant voltage frequency ratio frequency modulation mode

When U1/f1 is equal to a constant and equal to 7.6, the main magnetic flux Φ _m of the asynchronous motor is close to a constant. It can be seen from equation (4-9) that when the frequency f1 is reduced, its maximum torque Tm is not constant. See Table 3 for the specific calculated Tm values:

Table 3 The maximum torque value of the 5.5kW asynchronous motor under the constant voltage frequency ratio frequency modulation mode

It can be seen from Table 3 that the torque T of the 5.5kW asynchronous motor is 8.535 under the 1/4 load. The inverter saves energy through frequency conversion. Only when the frequency f1 is less than 10, the maximum torque T is less than the rated torque of the motor. Therefore, the constant voltage and frequency ratio of the asynchronous motor saves energy. When the frequency f1 is equal to 10, the electrical loss and total loss of the asynchronous motor are the smallest, but the efficiency of the asynchronous motor has decreased. As shown in Figure 4 and Figure 5, respectively. As can be seen from Figure 5, when the three-phase asynchronous motor is down-converted from the fundamental frequency for speed regulation, the efficiency is reduced. Because with the reduction of frequency f1, the output power P2 of the asynchronous motor decreases faster than the total loss ΣP of the asynchronous motor.

The following discusses the frequency conversion energy saving of the constant voltage-frequency ratio of the asynchronous motor under 1/3 load:

Now take a 5.5kW three-phase asynchronous motor as the research object, when it drives its 1/3 load with constant torque, the asynchronous motor can be converted to save energy by means of constant voltage-frequency ratio through the frequency converter. The test data is shown in Table 4

Table 4 Energy consumption test data of 5.5kW asynchronous motor under constant voltage frequency ratio frequency modulation mode

The data of the asynchronous motor generated in Table 4 under constant torque and constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analysis parameters such as P _u , P _v and ΣP are calculated by formulas. The specific calculation results are shown in Table 5. :

Table 5 Energy consumption test analysis of 5.5kW asynchronous motor under constant voltage frequency ratio frequency modulation mode

It can be seen from Table 5 and Figure 6 that the electrical loss ΣP of the asynchronous motor does not change much. Theoretically, the electrical loss value of the constant torque load variable frequency speed regulation asynchronous motor will decrease. However, in the frequency conversion experiment, the influence of various harmonics generated by the frequency converter on the test motor and the torque and speed measuring instrument, although the harmonic interference is avoided as much as possible, but it is still impossible to accurately measure the slightly changed value ΣP.

Since the stray loss p _a is approximately proportional to the square of the current, it can be seen from Table 4 that the current does not change, so it can be considered that the stray loss is basically unchanged.

The mechanical loss p _m depends on the speed of the asynchronous motor, which is generally a constant loss, but after frequency modulation, the speed n is proportional to the frequency f, and p _m is proportional to the cube of n. It can be seen from Table 5 that p _m The drop is huge.

Asynchronous motor efficiency:

η=P ₂ /P ₁ =P ₂ /(P ₂ +ΣP) (5-1)

According to Table 5, when the three-phase asynchronous motor is down-converted from the fundamental frequency, the efficiency is reduced. Mainly because when f < f _N , the output power P2 of the asynchronous motor decreases faster than the total loss ΣP of the asynchronous motor, as shown in Figure 7.

The following discusses the frequency conversion energy saving of asynchronous motors with non-constant voltage-frequency ratio under 1/4 load:

In the test, let the asynchronous motor drive 1/4 of the load, and the frequency is 5 groups of data from 50Hz to 30Hz. In order to prevent the increase of power loss caused by magnetic flux saturation in the process of frequency conversion of the asynchronous motor, the voltage or frequency regulation ratio should be adjusted within a range smaller than the rated voltage frequency ratio K=U _N /f _N =7.6. The selected voltage U ₁ =225V. The specific test data are shown in Table 6:

Table 6 Energy consumption test data of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation

The data of the asynchronous motor generated in Table 6 under constant torque and non-constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analysis parameters such as P _u , P _v and P1 are calculated by formulas, and the specific calculation results are shown in the table. 7:

Table 7 Energy consumption analysis of frequency modulation of 5.5kW asynchronous motor with non-constant voltage-frequency ratio

It can be seen from Table 7 that the asynchronous motor with non-constant voltage-frequency ratio speed regulation under constant load saves energy, and the total loss of the motor is the smallest when the frequency is 45Hz and the voltage-frequency ratio is 5. Use Matlab to calculate the formula, as shown in Figure 8.

In the test, let the asynchronous motor drive 1/4 of the load, and the frequency is 45Hz, and the voltage is 5 sets of data from 300V to 200V. In order to prevent the increase of power loss caused by magnetic flux saturation in the process of frequency conversion of the asynchronous motor, the voltage-to-frequency ratio must be adjusted within a range smaller than the rated voltage-to-frequency ratio K=U _N /f _N =7.6. The specific test data are shown in Table 8:

Table 8 Energy consumption test data of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation

The data of the asynchronous motor generated in Table 8 under constant torque and non-constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analysis parameters such as P _u , P _v and ΣP are calculated by formulas, and finally the loss of the asynchronous motor is calculated. The power ΣP and the output power P2 are added to obtain P1. The specific calculation results are shown in Table 9:

Table 9 Energy consumption analysis of frequency modulation of 5.5kW asynchronous motor with non-constant voltage-frequency ratio

It can be seen from Table 9 that the asynchronous motor with non-constant voltage-frequency ratio variable frequency speed regulation under 1/4 load saves energy. When the frequency is 45Hz, the voltage is 225V, and the voltage-frequency ratio is 5, the total loss of the motor is the smallest. Use Matlab for formula calculation, as shown in Figure 9.

The 5.5kW three-phase asynchronous motor saves energy in frequency regulation with non-constant voltage-frequency ratio. The voltage and frequency changes of the motor ensure that it can run under the optimal voltage and minimum energy consumption. The electrical loss of the motor under non-constant voltage-frequency ratio The graph and total loss graph are shown in Figure 10 and Figure 11.

The 5.5kW three-phase asynchronous motor saves energy by frequency regulation in a non-constant voltage-frequency ratio. The relationship between the input power P1 of the asynchronous motor, the voltage U and the frequency f is shown in Figure 12 in the theoretical calculation.

In the experiment, the 5.5kW asynchronous motor drives 1/4 of the load, and the magnetic powder brake is used as the load. Due to factors such as the heating of the magnetic powder brake, the load torque is unstable and has a little deviation. Therefore, the measured input power P1 _of the asynchronous motor is also too small. As shown in Figure 13.

The following discusses the frequency conversion energy saving of asynchronous motors with non-constant voltage-frequency ratio under 1/3 load:

In the test, let the asynchronous motor drive 1/3 of the load, and the frequency is 5 sets of data from 50Hz to 30Hz. In order to prevent the increase of power loss caused by magnetic flux saturation in the process of frequency conversion of the asynchronous motor, the voltage or frequency regulation ratio should be adjusted within a range smaller than the rated voltage frequency ratio K=U _N /f _N =7.6. The selected voltage U ₁ =240V. The specific test data are shown in Table 10:

Table 10 Energy consumption test data of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation

The data of the asynchronous motor generated in Table 10 under constant torque and non-constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analysis parameters such as P _u , P _v and ΣP are calculated respectively. The specific calculation results are shown in Table 11:

Table 11 Energy consumption test analysis of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency regulation

It can be seen from Table 11 that the asynchronous motor under constant load is not constant voltage-frequency ratio speed regulation and energy saving, and the total loss of the motor is the smallest when the frequency is 40Hz and the voltage-frequency ratio is 6. Use Matlab to calculate the formula, as shown in Figure 14.

In the test, let the asynchronous motor drive 1/3 of the load, and the frequency is 40Hz, and the voltage is 5 sets of data from 300V to 220V. The specific test data are shown in Table 12:

Table 12 Energy consumption test data of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency modulation

The data of the asynchronous motor generated in Table 12 under constant torque and non-constant voltage variable frequency ratio speed regulation are processed accordingly, and a series of analysis parameters such as P _u , P _v and ΣP are calculated by formulas. The specific calculation results are shown in the table. 13:

Table 13 Energy consumption test analysis of 5.5kW asynchronous motor with non-constant voltage-frequency ratio frequency regulation

It can be seen from Table 13 that the asynchronous motor under constant load is not constant voltage-frequency ratio speed regulation and energy saving, the frequency is 40Hz, the voltage is 240V, and the voltage-frequency ratio is 6 where the total loss of the motor is the smallest. Use Matlab to calculate the formula, as shown in Figure 15.

The 5.5kW three-phase asynchronous motor saves energy in frequency regulation with non-constant voltage-frequency ratio. The voltage and frequency changes of the motor ensure that it can run under the optimal voltage and minimum energy consumption. The electrical loss of the motor under non-constant voltage-frequency ratio The graph and total loss graph are shown in Figure 16 and Figure 17.

The 5.5kW three-phase asynchronous motor saves energy by frequency modulation in a non-constant voltage-frequency ratio. The theoretical calculation of the relationship between the input power P1 of the asynchronous motor, the voltage U and the frequency f is shown in Figure 18:

In the experiment, the 5.5kW asynchronous motor drives 1/3 of the load, and the magnetic powder brake is used as the load. Due to factors such as the heating of the magnetic powder brake, the load torque is unstable and there is a little deviation, so the measured input power P1 _of the asynchronous motor is also biased. large, as shown in Figure 19.

Obviously, those skilled in the art should understand that the above-mentioned modules, units or steps of the present invention can be implemented by a general-purpose computing device, and they can be centralized on a single computing device, or distributed in multiple computing devices. Alternatively, they may be implemented with program code executable by a computing device on a network composed of The steps shown or described may be performed in the sequence shown or described, either by fabricating them separately into individual integrated circuit modules, or by fabricating multiple modules or steps of them into a single integrated circuit module. As such, the present invention is not limited to any particular combination of hardware and software.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. a method for reducing the total loss of an asynchronous motor, comprising: obtain the parameters of the asynchronous motor; When the parameters of the asynchronous motor satisfy the preset constant voltage-frequency ratio relationship, adjusting the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor; When the parameters of the asynchronous motor satisfy a preset non-constant voltage-frequency ratio relationship, adjusting the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor; Wherein, the adjusted frequency f ₁ of the asynchronous motor satisfies:

in, U ₁ is the stator voltage; f ₁ is the frequency of the asynchronous motor; R1 is the stator resistance; Rm is the excitation resistance; R" ₁ =c ₁ R ₁ ;

in, R ₁ is the stator resistance; R' ₂ is the rotor resistance; c ₁ =1+X ₁ /X _m , where, X1 is the stator leakage reactance; Xm is the excitation leakage reactance; T _L is the load torque; m ₁ is the phase number of the asynchronous motor; p is the pole pair number of the asynchronous motor; Lm is the mutual inductance between stator and rotor; L1 is the stator self-inductance. 2. The method according to claim 1, wherein after acquiring the parameters of the asynchronous motor, the method further comprises: The stator voltage of the asynchronous motor is adjusted so that the ratio of the induced electromotive force of each phase winding of the stator of the asynchronous motor to the frequency of the asynchronous motor is constant. 3. The method according to claim 1, wherein the total loss of the asynchronous motor satisfies: ΣP=P _u +P _v , wherein P _v is the stator resistance R ₁ in the equivalent circuit of the asynchronous motor and the active power consumed by the rotor resistance R' ₂ , and P _u is the power consumed by the stator resistance R ₁ and the excitation resistance R _m in the equivalent circuit. 4. The method according to claim 3, wherein the P _u satisfies: P _u =m ₁ gU ₁ ² , Wherein, g is the equivalent conductance, satisfying: g=(R ₁ +R _m )/[(R ₁ +R _m ) ² +(X ₁ +X _m ) ² ] m ₁ is the phase number of the asynchronous motor; U ₁ is the stator voltage; R1 is the stator resistance; Rm is the excitation resistance; X1 is the stator leakage reactance; Xm is the excitation leakage reactance. 5. The method according to claim 3, wherein the P _v satisfies:

Among them, s is the slip rate; T _e is the electromagnetic torque of the asynchronous motor; Ω ₁ is the synchronous mechanical angular velocity; R" ₁ =c ₁ R ₁ ;

in, R ₁ is the stator resistance; R' ₂ is the rotor resistance; c ₁ =1+X ₁ /X _m , where, X1 is the stator leakage reactance; Xm is the excitation leakage reactance. 6. A device for reducing the total loss of an asynchronous motor, comprising: A parameter acquisition unit, used to acquire the parameters of the asynchronous motor; an adjustment unit, when the parameters of the asynchronous motor satisfy a preset constant voltage-frequency ratio relationship, adjust the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor; It is also used to adjust the voltage-frequency ratio of the asynchronous motor when the parameters of the asynchronous motor meet the preset non-constant voltage-frequency ratio relationship, so as to reduce the total loss of the asynchronous motor; Wherein, the adjusted frequency f ₁ of the asynchronous motor satisfies:

in, U ₁ is the stator voltage; f ₁ is the frequency of the asynchronous motor; R1 is the stator resistance; Rm is the excitation resistance; R" ₁ =c ₁ R ₁ ;

in, R ₁ is the stator resistance; R' ₂ is the rotor resistance; c ₁ =1+X ₁ /X _m , where, X1 is the stator leakage reactance; Xm is the excitation leakage reactance; T _L is the load torque; m ₁ is the phase number of the asynchronous motor; p is the pole pair number of the asynchronous motor; Lm is the mutual inductance between stator and rotor; L1 is the stator self-inductance. 7 . The device according to claim 6 , further comprising a stator voltage adjustment unit, the stator voltage adjustment unit is configured to adjust the stator voltage of the asynchronous motor after acquiring the parameters of the asynchronous motor, so that the The ratio of the induced electromotive force of each phase winding of the stator of the asynchronous motor to the frequency of the asynchronous motor is constant. 8 . A storage medium, characterized in that the storage medium comprises a stored program, wherein the method of any one of claims 1 to 5 is executed when the program is run.

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