CN108111091B - Method, device and storage medium for reducing total loss of asynchronous motor - Google Patents
Method, device and storage medium for reducing total loss of asynchronous motor Download PDFInfo
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- H—ELECTRICITY
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- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
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- H—ELECTRICITY
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- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
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- H02P2207/01—Asynchronous machines
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
Technical Field
The invention relates to the technical field of asynchronous motors, in particular to a method, a device and a storage medium for reducing the total loss of an asynchronous motor.
Background
The motor is used as an important power device and is widely applied to various departments of metallurgy, electric power, petrifaction, coal, papermaking, building material manufacturing and the like in China, and the power consumption of the motor accounts for 60% -70% of the national industrial power consumption. However, because the design and selection of equipment in China have large surplus, the equipment runs in a low-load area for a long time, and the phenomenon of 'large horse pulls a trolley' is serious. When the motor works near the rated load, the efficiency is very high, in practical use, most motors often run under light load or even no load, the load rate of the motors is very low, the active current is very small, and the reactive current basically has no change, so that the power factor of the motors is very low, the efficiency is low, and a very large energy-saving space exists for the asynchronous motors running under the light load for a long time.
Disclosure of Invention
The embodiment of the invention provides a method, a device and a storage medium for reducing the total loss of an asynchronous motor, which are used for at least solving the problem of low efficiency of the asynchronous motor under the condition of long-term light-load operation in the related art.
According to an embodiment of the present invention, there is provided a method of reducing total loss of an asynchronous motor, including: acquiring parameters of the asynchronous motor; and when the parameters of the asynchronous motor meet the preset conditions, adjusting the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.
According to an embodiment of the present invention, there is provided an apparatus for reducing total loss of an asynchronous motor, including: a parameter acquisition unit for acquiring parameters of the asynchronous motor; an adjustment unit to: and when the parameters of the asynchronous motor meet the preset conditions, adjusting the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.
According to still another embodiment of the present invention, there is also provided a storage medium. The storage medium is configured to store program code for performing the steps of: acquiring parameters of the asynchronous motor; and when the parameters of the asynchronous motor meet the preset conditions, adjusting the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.
According to the invention, under the preset condition, the frequency or the voltage-frequency ratio of the asynchronous motor is adjusted, and the total loss of the asynchronous motor is reduced, so that the problem that the efficiency of the asynchronous motor is low under long-term light-load operation in the related art is at least solved, the operation efficiency of the asynchronous motor is improved, and the purpose of saving energy is achieved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a flow chart of a method of reducing total losses in an asynchronous motor according to an embodiment of the present invention;
fig. 2 is a block diagram of an apparatus for reducing total loss of an asynchronous motor according to an embodiment of the present invention;
fig. 3 is an equivalent circuit diagram of an asynchronous motor according to an embodiment of the present invention;
FIG. 4 is a graph of frequency versus electrical loss Σ P for a constant voltage frequency ratio for an asynchronous motor in accordance with an embodiment of the present invention;
fig. 5 is a graph of frequency versus efficiency η for a constant voltage frequency ratio of an asynchronous motor according to an embodiment of the present invention;
FIG. 6 is a graph of frequency versus Σ P for a constant voltage frequency ratio for an asynchronous motor in accordance with an embodiment of the present invention;
fig. 7 is a graph of frequency versus efficiency η for a constant voltage frequency ratio of an asynchronous motor according to an embodiment of the present invention;
FIG. 8 is a graph of electrical energy consumption for frequency modulation at a non-constant voltage frequency ratio for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 9 is a graph of electrical energy consumption for frequency modulation at a non-constant voltage frequency ratio for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 10 is a graph of non-constant voltage frequency ratio frequency modulated electrical losses for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 11 is a graph of total loss for a non-constant voltage frequency ratio FM motor for a 5.5kW asynchronous motor according to an embodiment of the present invention;
FIG. 12 is a graph of theoretical calculations of frequency modulation P1, U and f for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 13 is a graph of measured frequency P1, U and f for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 14 is a graph of electrical energy consumption for frequency modulation at a non-constant voltage frequency ratio for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 15 is a graph of electrical energy consumption for frequency modulation at a non-constant voltage frequency ratio for a 5.5kW asynchronous motor in accordance with an embodiment of the invention;
FIG. 16 is a graph of non-constant voltage frequency ratio frequency modulated electrical losses for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 17 is a graph of non-constant voltage frequency ratio FM motor losses for a 5.5kW asynchronous motor according to an embodiment of the present invention;
FIG. 18 is a graph of theoretical calculations of frequency modulation P1, U and f for a 5.5kW asynchronous motor according to an embodiment of the invention;
FIG. 19 is a graph of measured frequency P1, U, and f for a 5.5kW asynchronous motor according to an embodiment of the invention.
Detailed Description
The invention will be described in detail hereinafter with reference to the accompanying drawings in conjunction with embodiments. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Example 1
In the present embodiment, a method for reducing the total loss of an asynchronous motor is provided, as shown in fig. 1, the method comprising the steps of:
step S101, acquiring parameters of an asynchronous motor;
and step S102, when the parameters of the asynchronous motor meet the preset conditions, adjusting the frequency or the voltage-frequency ratio of the asynchronous motor to reduce the total loss of the asynchronous motor.
Optionally, the preset condition includes 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, adjusting the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor;
and when the parameters of the asynchronous motor meet the 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.
Through the steps, the frequency or the voltage-frequency ratio of the asynchronous motor is adjusted according to whether the parameters of the asynchronous motor meet the relation of the constant voltage-frequency ratio, the total loss of the asynchronous motor is reduced, the running efficiency of the asynchronous motor is improved, and the purpose of energy conservation is achieved.
Optionally, 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.
It should be noted that, during the regulation, 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 kept constant in order to keep the magnetic flux constant. For this reason, when the frequency is changed, the electromotive force must be changed in magnitude in a manner of compensating for the voltage drop of the stator of the motor so that the ratio E1/f of the electromotive force to the frequency is constant.
Optionally, the total loss of the asynchronous motor satisfies: sigma P ═ Pu+PvWherein P isvResistance R in equivalent circuit for asynchronous motor1And R'2Active power consumed, PuFor resistance R in equivalent circuit1And RmThe power consumed.
Alternatively, PuSatisfies the following conditions:
wherein g is equivalent conductance, satisfying:
wherein m is1Is the number of phases of the asynchronous motor; u shape1Is the voltage of each phase winding; r1Is a stator resistor; rmIs the excitation impedance; x1Is stator leakage reactance; xmIs an excitation leakage reactance.
Alternatively, PvSatisfies the following conditions:
wherein s is the slip; t iseIs the electromagnetic torque of the asynchronous motor; omega1Synchronous mechanical angular velocity; r'1＝c1R1；
Wherein R is1Is a stator resistor; r'2Is the rotor resistance; c. C1＝1+X1/XmWherein X is1Is stator leakage reactance; xmIs an excitation leakage reactance.
Optionally, the frequency f of the asynchronous motor is adjusted1Satisfies the following conditions:
wherein, U1Is the supply voltage; f. of1Is the frequency of the asynchronous motor; r1Is a stator resistor; rmIs the excitation impedance; r'1＝c1R1；
Wherein R is1Is a stator resistor; r'2Is the rotor resistance; c. C1＝1+X1/XmWherein X is1Is stator leakage reactance; xmIs an excitation leakage reactance; t isLIs the load torque; m is1Is the number of phases of the asynchronous motor; p is the power of the asynchronous motor; l ismMutual inductance between the stator and the rotor; l is1The stator self-inductance.
Through the above description of the embodiments, those skilled in the art can clearly understand that the method according to the above embodiments can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware, but the former is a better implementation mode in many cases. Based on such understanding, the technical solutions of the present invention may be embodied in the form of a software product, which is stored in a storage medium (such as ROM/RAM, magnetic disk, optical disk) and includes instructions for enabling a terminal device (such as a mobile phone, a computer, a server, or a network device) to execute the method according to the embodiments of the present invention.
Example 2
In this embodiment, a device for reducing the total loss of the asynchronous motor is also provided, and the device is used to implement the above embodiments and preferred embodiments, which have already been described and will not be described again. As used below, the term "unit" may be a combination of software and/or hardware that implements a predetermined function. Although the means described in the embodiments below are preferably implemented in software, an implementation in hardware, or a combination of software and hardware is also possible and contemplated.
As shown in fig. 2, the apparatus includes:
a parameter acquisition unit 10 for acquiring parameters of the asynchronous motor;
an adjustment unit 20 for: 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.
Optionally, the preset condition includes a preset constant voltage frequency ratio relationship and a preset non-constant voltage frequency ratio relationship, and when the parameter of the asynchronous motor satisfies the preset constant voltage frequency ratio relationship, the frequency of the asynchronous motor is adjusted to reduce the total loss of the asynchronous motor;
and when the parameters of the asynchronous motor meet the 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.
Optionally, the apparatus further comprises a stator voltage adjusting unit for adjusting the stator voltage of the asynchronous motor after acquiring the parameter 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, the above units may be implemented by software or hardware, and for the latter, the following may be implemented, but not limited to: the modules are all positioned in the same processor; alternatively, the modules are respectively located in different processors in any combination.
Example 3
The embodiment of the invention also provides a storage medium. Alternatively, in the present embodiment, the storage medium may be configured to store program codes for performing 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.
Optionally, the preset condition includes 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, adjusting the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor;
and when the parameters of the asynchronous motor meet the 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.
Optionally, in this embodiment, the storage medium may include, but is not limited to: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.
Optionally, in this embodiment, the processor executes, according to the program code stored in the storage medium:
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.
Optionally, the preset condition includes 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, adjusting the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor; and when the parameters of the asynchronous motor meet the 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.
Optionally, the specific examples in this embodiment may refer to the examples described in the above embodiments and optional implementation manners, and this embodiment is not described herein again.
Example 4
The embodiment is an optional embodiment of the present application, and is used to describe the present application in detail with reference to specific usage scenarios:
among the speed regulating systems of asynchronous motors, the variable-voltage variable-frequency speed regulating system has the best control performance and the highest efficiency. The V/F control mode is to change the frequency of the motor power supply and the voltage of the motor power supply to keep the magnetic flux of the motor constant, and the efficiency and power factor of the motor are not reduced in a wide speed regulation range. This is called U/F control because it is the ratio of voltage to frequency (U/F) that is controlled. In the asynchronous motor, the rotor speed is lower than the synchronous speed, which is the speed of rotation of the air-gap rotating magnetic field, and therefore, in the rotor circuit, slip electromotive force is generated, which generates rotor current, and the rotor current interacts with the rotating magnetic field to generate electromagnetic torque. The effective value formula of the induced electromotive force of each phase winding of the stator of the asynchronous motor is as follows:
E1＝4.44f1N1Kdp1Φm(4-1)
in the formula, E1An effective value (V) of the electromotive force induced in each phase winding of the stator for the air gap flux; f. of1Is the stator supply frequency (Hz); n is a radical of1The number of turns of each phase winding of the stator is connected in series; k is a radical ofdp1Is the fundamental winding coefficient; phimIs the air gap per pole magnetic flux (Wb).
Therefore, when the structural parameters of the motor are determined, the following formula is obtained:
in addition, the electromagnetic torque of the motor is:
in the formula (I), the compound is shown in the specification,
referred to as the torque factor;
t is the electromagnetic torque (N.M) of the motor.
By inference from formula (4-1) if E1Constant when the stator supply frequency f1Increase will cause air gap flux phimDecrease, and as can be seen from equation phimThe reduction in turn causes a reduction in the motor electromagnetic torque T, which occurs when the frequency increases and the load capacity decreases. When E is1Timing, if the frequency f is reduced1Then main magnetic flux phimTo be increased. The main magnetic circuit of the motor is inherently saturated to a certain extent, phimAnd the main magnetic flux is required to be oversaturated, and the exciting current is increased suddenly, which is not allowed. For this reason, the stator voltage must be controlled in coordination while adjusting the frequency, but the manner of control differs depending on the operating frequency below and above the fundamental frequency.
For regulating speed below fundamental frequency, the magnetic flux phi is maintainedmUnchanged when the frequency f is1When changing, the electromotive force E must be changed simultaneously1The value of E1/f is constant, that is, a control method of constant electromotive force to frequency ratio is adopted. Because the induced electromotive force detection and control of the motor are difficult, the steady-state performance of the constant E1/f control is superior to that of the constant U1/f control, and the constant E1/f control is the target pursued after compensating the stator voltage drop of the motor in the constant U1/f control. According to the asynchronous motor stator voltage equation:
U1＝E1+I1Z1(4-4)
in the formula I1-a stator current (a);
Z1-stator impedance (Ω).
When the output frequency of the frequency converter is lower than the rated power supply of power supply, the frequency conversion speed regulation system belongs to constant torque speed regulation, but when the frequency is lower, the voltage drop of the leakage impedance of the stator cannot be ignored, so the voltage of the stator is artificially increased to compensate the voltage drop caused by the leakage impedance.
When the speed is adjusted above the fundamental frequency, if the voltage of the motor increases with the increase of the frequency and the voltage of the motor reaches the rated voltage of the motor, the insulation performance of the motor may be damaged by continuously increasing the voltage. For this reason, after the motor reaches the rated voltage, the motor voltage is maintained constant even if the frequency increases. Thus, the power that can be output by the motor is determined by the product of the rated voltage and the rated current of the motor, and does not change with the change of the frequency. When the speed is regulated above the fundamental frequency, the frequency can be increased from the fundamental frequency to the top, but the voltage cannot exceed the rated voltage, and at the moment, the variable frequency speed regulation system belongs to constant power speed regulation.
For loss analysis after the frequency conversion of the asynchronous motor, the frequency conversion speed regulation of the asynchronous motor is realized by frequency conversion of a power supply of the asynchronous motor through a frequency converter, and the whole speed regulation device consists of the frequency converter and the motor. The loss is the difference between the input power and the output power of the whole device system. The main way to improve the efficiency of the whole system is to reduce the loss, so we firstly analyze the losses of the frequency converter and the asynchronous motor.
The losses of the frequency converter were analyzed as follows: the loss of the frequency converter is mainly composed of the loss of a power electronic device and the loss of a drive. The power electronic device of the current frequency converter mainly uses an IGBT with low driving loss, and the driving loss of the IGBT can be ignored, so that the loss of the frequency converter mainly refers to the loss of the power electronic device and mainly comprises the on-state loss and the switching loss of the device. The on-state loss depends on the tube voltage drop of the device and the load current, the switching loss depends on the switching frequency and the load current, and the converter loss increases with the increase of the effective value of the current, so that the following loss expression can be established:
in the expression, PinvIs loss of frequency converter, K1、K2Is a correlation coefficient, i, determined by a switching devicesIs the effective value of the phase current.
The losses of an asynchronous motor are mainly divided into: firstly, the copper loss generated by the current passing in the stator winding and the rotor winding is finally dissipated in the form of heat and is divided into two parts of stator copper loss and rotor copper loss; iron loss (including hysteresis loss and eddy current loss) generated by a magnetic field in the iron core of the stator and the rotor; ventilation and friction loss caused by the rotation of the fan and the bearing, also called mechanical loss; stray loss generated by higher harmonics of the air gap magnetic field.
For the main research of the present document, the constant torque load variable frequency speed regulation of the asynchronous motor is performed, and the speed regulation principle of the frequency converter is as follows: u shape1/f1C is constant, and makes the power supply voltage U1And frequency f1And the output is adjusted by changing in direct proportion. According to formula (4-1):
Φ＝U1/4.44f1N1Kdp1(4-6)
as can be seen from the equation (4-6), for the asynchronous motor tested in the laboratory, 4.44, N1，Kdp1Is a constant. The frequency modulation is divided into two modes of constant voltage frequency ratio and non-constant voltage frequency ratio: for constant voltage frequency ratio frequency modulation, the magnetic flux phi of the asynchronous motor is unchanged, so that the stator and rotor currents are kept unchanged; for non-constant voltage frequency ratio frequency modulation, the voltage frequency ratio is generally adjusted downward, but not constant, due to the increased losses due to the magnetic flux saturation of the asynchronous motor. The magnetic flux phi of the asynchronous motor is reduced, and the stator and rotor currents are reduced. When the frequency f1The frequency converter is adjusted downwards, and various loss changes of the asynchronous motor are analyzed as follows:
(1) stator copper loss Pcu1: because the constant-voltage frequency ratio is adopted in the constant-voltage frequency ratio down-conversion of the asynchronous motor, the magnetic flux phi of the motor is kept unchanged, the stator current is unchanged, the influence of the temperature on the stator current is not counted, and P is the constant-voltage frequency ratiocu1The change is not changed; at a non-constant voltage frequency ratio, the magnetic flux phi of the motor is reduced, the stator current is reduced, so Pcu1And decreases.
(2) Rotor copper loss Pcu2: because the constant-voltage frequency ratio is adopted in the down-conversion of the constant-voltage frequency ratio of the asynchronous motor, the magnetic flux phi of the motor is kept unchanged, the rotor current is unchanged, the influence of the temperature on the rotor current is not counted, and P is the constant-voltage frequency ratiocu2The change is not changed; at a non-constant voltage frequency ratio, the magnetic flux phi of the motor decreases, the rotor current becomes smaller, so Pcu2And decreases.
(3) Iron loss PFe: from PFe＝K·f1.3·B2It is known that the constant voltage frequency ratio down-conversion in the asynchronous motor is a constant voltage frequency ratio, and therefore, the electromotive motor is drivenThe magnetic flux phi of the machine remains constant at frequency f1At the time of descent, PFeAlso decreases; at a non-constant voltage frequency ratio, the magnetic flux phi of the motor decreases when the frequency f1At the time of descent, PFeAnd likewise decreases.
(4) Mechanical loss pm: the mechanical losses depend on the speed of the asynchronous motor and are generally regarded as constant losses since the speed does not vary significantly from no load to the nominal load. However, since the rotational speed of the motor also decreases when the frequency changes, the mechanical loss decreases regardless of the frequency modulation method.
(5) Stray loss pa: the calculation is generally carried out in an estimation mode due to the difficulty of measurement and calculation, so the method is considered unchanged temporarily in the text.
From the analysis, the frequency of the asynchronous motor is modulated under a constant voltage frequency ratio, the copper loss of the stator and the rotor is unchanged, the iron loss is reduced, the mechanical loss is reduced, the stray loss is unchanged, and the total loss is reduced; the frequency of the asynchronous motor is modulated under a non-constant voltage frequency ratio, the copper loss, the iron loss, the mechanical loss, the stray loss and the total loss of the stator and the rotor are reduced.
When the asynchronous motor is in steady-state operation, the mechanical load of the asynchronous motor only requires two operation parameters of torque T and rotating speed n for the motor, namely the asynchronous motor provides specific electromagnetic torque at a certain rotating speed.
According to the fact that the rated voltage of the tested motor is 380v, the power frequency is 50Hz, and the voltage-frequency ratio K is 7.6. The following can be obtained:
substituting the parameter values into the formula to obtain:
derivation of f is performed by equation (4-7):
dΣP/df＝0 (4-8)
when the load torque T of the asynchronous motor is the rated torque, the load torque T is not optimalFrequency. When the constant voltage frequency of the asynchronous motor is lower than the variable frequency, the electric loss is reduced along with the reduction of the frequency, so that the electric loss is minimum when the frequency is minimum. When U1/f1 is equal to a constant and equal to 7.6, the main flux phi of the asynchronous motormApproximately constant, its maximum torque expression is:
when the variable frequency energy saving of the asynchronous motor is ensured by the equation (4-9), the Tm is reduced due to the reduction of the frequency f, but the Tm is required to be larger than the load torque value of the asynchronous motor, and meanwhile, the margin of 20% is reserved.
According to the type equivalent circuit of the asynchronous motor (fig. 3), the total electrical loss of the asynchronous motor is set:
consists of:
substituting formula (4-10) into formula (4-9) to obtain:
order:
dΣP/dω＝0 (4-13)
namely, the optimal pressure-frequency ratio can be obtained:
from the equation (4-14), the optimal frequency f1 and the optimal voltage U1 of the three-phase asynchronous motor under the energy saving of the non-constant voltage frequency ratio can be continuously derived, which are respectively:
or
From the equation (4-14), it can be concluded that the asynchronous motor can save energy by frequency modulation of the frequency converter with a non-constant voltage-to-frequency ratio for a specific motor under a certain load, and an optimal voltage-to-frequency ratio exists so that the electrical loss of the motor is minimum. That is, in an actual engineering project, for an asynchronous motor to drive different loads, the optimum frequency can be found to minimize the electrical loss of the motor by determining the voltage of the asynchronous motor for each load.
The asynchronous motor is subjected to variable frequency speed regulation under a constant torque load, and the requirement that the main flux of the motor is not changed is met because the main flux of the asynchronous motor is expected to keep a rated value unchanged generally and the variable frequency mode of the frequency converter is a constant voltage-frequency ratio.
The frequency conversion speed regulation test of the constant voltage frequency ratio of the asynchronous motor comprises the following steps:
the following discussion discusses the energy saving of the constant voltage frequency ratio of the asynchronous motor under the 1/4 load:
a three-phase asynchronous motor of 5.5kW is taken as a research object, and when the motor drags 1/4 to load a constant torque, the asynchronous motor is subjected to frequency conversion and energy saving in a constant voltage frequency ratio mode through a frequency converter. The data tested are shown in table 1:
TABLE 1 energy consumption test data of 5.5kW asynchronous motor in constant voltage frequency ratio frequency modulation mode
Correspondingly processing the data of the asynchronous motor generated in the table 1 under the condition of constant torque, constant voltage, variable frequency ratio and speed regulation, and respectively calculating P through a formulau、PvAnd a series of analysis parameters such as sigma P, and finally, adding the loss power sigma P of the asynchronous motor and the output power P2 to obtain P1, wherein the specific calculation results are shown in Table 2:
TABLE 2 energy consumption calculation analysis of 5.5kW asynchronous motor in constant voltage frequency ratio frequency modulation mode
When U1/f1 is equal to a constant and equal to 7.6, the main flux phi of the asynchronous motormAs shown by the equation (4-9), the maximum torque Tm is not constant when the frequency f1 is lowered. The calculated values of Tm are shown in Table 3:
TABLE 3 maximum Torque value of 5.5kW asynchronous motor under constant pressure frequency ratio frequency modulation mode
As can be seen from table 3, the 5.5kW asynchronous motor has a torque T of 8.535 under 1/4 load, and the energy is saved by frequency conversion of the frequency converter, and the maximum torque T is less than the rated torque of the motor only when the frequency f1 is less than 10. Therefore, the constant voltage frequency of the asynchronous motor is more energy-saving than the frequency conversion, when the frequency f1 is equal to 10, the electrical loss and the total loss of the asynchronous motor are minimum, but the efficiency of the asynchronous motor is reduced. As shown in fig. 4 and 5, respectively. As can be seen from fig. 5, when the three-phase asynchronous motor is frequency-down regulated, the efficiency is reduced. Because with the down-regulation of the frequency f1, the output power P2 of the asynchronous motor falls faster than the total loss Σ P of the asynchronous motor.
The following discussion discusses the energy saving of the constant voltage frequency ratio of the asynchronous motor under the 1/3 load:
a three-phase asynchronous motor of 5.5kW is taken as a research object, and when the motor drags 1/3 to load a constant torque, the asynchronous motor is subjected to frequency conversion and energy saving in a constant voltage frequency ratio mode through a frequency converter. The data of the test are shown in Table 4
TABLE 4 energy consumption test data of 5.5kW asynchronous motor in constant voltage frequency ratio frequency modulation mode
For the asynchronous motor generated in table 4, the torque is constantThe data under the pressure-variable frequency ratio speed regulation is correspondingly processed, and P is respectively calculated through a formulau、PvAnd a series of analysis parameters such as sigma-delta P, and specific calculation results are shown in Table 5:
TABLE 5 energy consumption test analysis of 5.5kW asynchronous motor in constant voltage frequency ratio frequency modulation mode
It can be seen from table 5 and fig. 6 that the electrical loss Σ P of the asynchronous motor does not change much, and theoretically, the electrical loss value of the constant-torque load variable-frequency speed control asynchronous motor is analyzed to be decreased. However, in the frequency conversion experiment, various harmonic waves generated by the frequency converter influence the test motor and the torque and rotation speed measuring instrument, and although harmonic interference is avoided as much as possible, the numerical value Σ P with small change cannot be accurately measured.
Stray loss paThe stray losses can be considered to be substantially constant since they are approximately proportional to the square of the current, which is constant as seen from table 4.
Mechanical loss pmDepending on the speed of the asynchronous motor, which is normally a constant loss, but after frequency modulation, the speed n is proportional to the frequency f and pmProportional to the cube of n, as can be seen from Table 5, pmThe magnitude of the drop is large.
Efficiency of asynchronous motor:
η＝P2/P1＝P2/(P2+ΣP) (5-1)
as can be seen from table 5, the efficiency is reduced when the three-phase asynchronous motor is frequency-down regulated. Mainly because f < fNThe output power P2 of the asynchronous motor decreases faster than the total loss sigma P of the asynchronous motor, see fig. 7.
The following discussion discusses the energy saving of the non-constant voltage frequency ratio of the asynchronous motor under the 1/4 load:
in the test, an asynchronous motor is used for dragging 1/4 load, and the frequency is changed by a frequency converter to regulate the speed, wherein the frequency is 5 groups of data from 50Hz to 30 Hz. To prevent the process of frequency conversion of asynchronous motorsIn the above case, since the magnetic flux saturation causes the power loss to increase, the voltage-to-frequency ratio is set to be smaller than the rated voltage-to-frequency ratio K ═ UN/fNThe voltage or frequency is adjusted within a small range of 7.6. Selected voltage U1225V. Specific test data are shown in table 6:
energy consumption test data of frequency modulation under non-constant voltage frequency ratio of table 65.5 kW asynchronous motor
Correspondingly processing the data of the asynchronous motor generated in the table 6 under the constant-torque non-constant-voltage variable-frequency-ratio speed regulation, and respectively calculating P through a formulau、PvAnd P1, and the specific calculation results are shown in Table 7:
energy consumption analysis of frequency modulation under non-constant voltage frequency ratio of table 75.5 kW asynchronous motor
As can be seen from table 7: the non-constant voltage frequency ratio speed regulation of the asynchronous motor under the constant load is energy-saving, and the total loss of the motor is the minimum when the frequency is 45Hz and the voltage-frequency ratio is 5. The formula calculation was performed using Matlab, see fig. 8.
In the test, an asynchronous motor is used for dragging 1/4 load, and the speed is regulated through the non-constant voltage frequency ratio variable frequency of a frequency converter, wherein the frequency is 45Hz, and the voltage is 5 groups of data from 300V to 200V. In order to prevent the power loss from increasing due to the saturation of magnetic flux during the frequency conversion of the asynchronous motor, the voltage-frequency ratio is less than the rated voltage-frequency ratio K ═ UN/fNThe voltage is adjusted within a small range of 7.6. Specific test data are shown in table 8:
energy consumption test data of frequency modulation under non-constant voltage frequency ratio of table 85.5 kW asynchronous motor
The asynchronous motor generated in the counter 8 is subjected to constant-torque non-constant-voltage variable-frequency-ratio speed regulationThe data is correspondingly processed, and P is respectively calculated through a formulau、PvAnd a series of analysis parameters such as sigma-P, and finally, the loss power sigma-P of the asynchronous motor and the output power P2 are added to obtain P1, and the specific calculation results are shown in table 9:
energy consumption analysis of frequency modulation under non-constant voltage frequency ratio of table 95.5 kW asynchronous motor
As can be seen from table 9: 1/4 the asynchronous motor under load has energy saving by non-constant voltage frequency ratio frequency conversion speed regulation, when the frequency is 45Hz and the voltage is 225V, the total loss of the motor at the voltage frequency ratio of 5 is the minimum. The formula calculation was performed using Matlab, see fig. 9.
The 5.5kW three-phase asynchronous motor is frequency-modulated and energy-saving under the non-constant voltage frequency ratio, the voltage and frequency changes of the motor are ensured to be operated under the optimal voltage and the minimum energy consumption, and the electric loss graph and the total loss graph of the motor under the non-constant voltage frequency ratio are shown in figures 10 and 11.
The 5.5kW three-phase asynchronous motor is frequency-modulated and energy-saving under the condition of non-constant voltage frequency ratio, and the relation between the input power P1 of the asynchronous motor and the voltage U and the frequency f is shown in the theoretical calculation as shown in figure 12.
In the experiment, the 5.5kW asynchronous motor drags 1/4 load, a magnetic powder brake is used as the load, and because the magnetic powder brake generates heat and other factors, the load torque is unstable and has a point deviation, the actually measured input power P of the asynchronous motor1It is also small. As shown in fig. 13.
The following discussion discusses the energy saving of the non-constant voltage frequency ratio of the asynchronous motor under the 1/3 load:
in the test, an asynchronous motor is used for dragging 1/3 load, and the frequency is changed by a frequency converter to regulate the speed, wherein the frequency is 5 groups of data from 50Hz to 30 Hz. 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-frequency regulating ratio is smaller than the rated voltage-frequency ratio K-UN/fNThe voltage or frequency is adjusted within a small range of 7.6. Selected voltage U1240V. Specific test data are shown in table 10:
energy consumption test data of frequency modulation under non-constant voltage frequency ratio of table 105.5 kW asynchronous motor
Correspondingly processing the data of the asynchronous motor generated in the table 10 under the constant-torque non-constant-voltage variable-frequency-ratio speed regulation, and respectively calculating Pu、PvAnd a series of analysis parameters such as sigma-delta P, and the specific calculation results are shown in table 11:
energy consumption test analysis of frequency modulation under non-constant voltage frequency ratio of asynchronous motor with 115.5 kW in table
As can be seen from table 11: the asynchronous motor speed regulation under the constant load is energy-saving due to the non-constant voltage frequency ratio, and the total loss of the motor is the minimum when the frequency is 40Hz and the voltage-frequency ratio is 6. The formula calculation was performed using Matlab, see fig. 14.
In the test, an asynchronous motor is used for dragging 1/3 load, and the speed is regulated through the non-constant voltage frequency ratio variable frequency of a frequency converter, wherein the frequency is 40Hz, and the voltage is 5 groups of data from 300V to 220V. Specific test data are shown in table 12:
energy consumption test data of frequency modulation under non-constant voltage frequency ratio of table 125.5 kW asynchronous motor
Correspondingly processing the data of the asynchronous motor generated in the table 12 under the constant-torque non-constant-voltage variable-frequency-ratio speed regulation, and respectively calculating P through a formulau、PvAnd a series of analysis parameters such as sigma P, and the specific calculation results are shown in Table 13:
energy consumption test analysis of frequency modulation under non-constant voltage frequency ratio of table 135.5 kW asynchronous motor
As can be seen from table 13: the asynchronous motor speed regulation under the constant load is energy-saving due to the non-constant voltage frequency ratio, the frequency is 40Hz, the voltage is 240V, and the total loss of the motor at the voltage-frequency ratio of 6 is the minimum. The formula calculation was performed using Matlab, see fig. 15.
The 5.5kW three-phase asynchronous motor is frequency-modulated and energy-saving under the non-constant voltage frequency ratio, the voltage and frequency changes of the motor are ensured to be operated under the optimal voltage and the minimum energy consumption, and the electric loss graph and the total loss graph of the motor under the non-constant voltage frequency ratio are shown in figures 16 and 17.
The frequency-modulation energy-saving of the 5.5kW three-phase asynchronous motor under the non-constant voltage frequency ratio is realized, and the relation between the input power P1 of the asynchronous motor and the voltage U and the frequency f is shown in the theoretical calculation of FIG. 18:
in the experiment, the 5.5kW asynchronous motor drags 1/3 load, the magnetic powder brake is used as the load, and the load torque is unstable and has a slight deviation due to factors such as heating of the magnetic powder brake, so the actually measured input power P of the asynchronous motor1And also larger as shown in fig. 19.
It will be apparent to those skilled in the art that the modules, units or steps of the invention described above may be implemented by a general purpose computing device, they may be centralized on a single computing device or distributed over a network of multiple computing devices, and alternatively, they may be implemented by program code executable by a computing device, such that they may be stored in a storage device and executed by a computing device, and in some cases, the steps shown or described may be executed out of order, or fabricated separately as individual integrated circuit modules, or multiple ones of them may be fabricated into a single integrated circuit module. Thus, the present invention is not limited to any specific combination of hardware and software.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A method of reducing the total losses of an asynchronous motor, comprising:
acquiring parameters of the asynchronous motor;
when the parameters of the asynchronous motor meet 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 meet the 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 frequency f of the asynchronous motor is adjusted1Satisfies the following conditions:
wherein the content of the first and second substances,
U1is the stator voltage;
f1is the frequency of the asynchronous motor;
r1 is stator resistance;
rm is an excitation resistor;
R"1＝c1R1；
wherein the content of the first and second substances,
R1is a stator resistor;
R'2is the rotor resistance;
c1＝1+X1/Xmwherein, in the step (A),
x1 is stator leakage reactance;
xm is an excitation leakage reactance;
TLis the load torque;
m1is the number of phases of the asynchronous motor;
p is the pole pair number of the asynchronous motor;
lm is mutual inductance between the stator and the rotor;
l1 is the stator self inductance.
2. The method of claim 1, wherein after obtaining 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 of claim 1, wherein the total loss of the asynchronous motor satisfies: sigma P ═ Pu+PvWherein P isvFor stator resistance R in equivalent circuit of said asynchronous motor1And rotor resistance R'2Active power consumed, PuFor the stator resistance R in the equivalent circuit1And an excitation resistor RmThe power consumed.
4. The method of claim 3, wherein P isuSatisfies the following conditions: pu＝m1gU1 2，
Wherein g is equivalent conductance, satisfying: g ═ R1+Rm)/[(R1+Rm)2+(X1+Xm)2]
m1Is the number of phases of the asynchronous motor;
U1is the stator voltage;
r1 is stator resistance;
rm is an excitation resistor;
x1 is stator leakage reactance;
xm is the leakage reactance of the excitation.
5. The method of claim 3, wherein P isvSatisfies the following conditions:
wherein s is the slip;
Teis the electromagnetic torque of the asynchronous motor;
Ω1synchronous mechanical angular velocity;
R"1＝c1R1；
wherein the content of the first and second substances,
R1is a stator resistor;
R'2is the rotor resistance;
c1＝1+X1/Xmwherein, in the step (A),
x1 is stator leakage reactance;
xm is the leakage reactance of the excitation.
6. An apparatus for reducing the total loss of an asynchronous motor, comprising:
a parameter acquisition unit for acquiring parameters of the asynchronous motor;
the adjusting unit is used for adjusting the frequency of the asynchronous motor to reduce the total loss of the asynchronous motor when the parameter of the asynchronous motor meets the preset constant voltage frequency ratio relation;
the asynchronous motor control circuit is also used for adjusting the voltage-frequency ratio 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 relation;
wherein the frequency f of the asynchronous motor is adjusted1Satisfies the following conditions:
wherein the content of the first and second substances,
U1is the stator voltage;
f1is the frequency of the asynchronous motor;
r1 is stator resistance;
rm is an excitation resistor;
R"1＝c1R1；
wherein the content of the first and second substances,
R1is a stator resistor;
R'2is the rotor resistance;
c1＝1+X1/Xmwherein, in the step (A),
x1 is stator leakage reactance;
xm is an excitation leakage reactance;
TLis the load torque;
m1is the number of phases of the asynchronous motor;
p is the pole pair number of the asynchronous motor;
lm is mutual inductance between the stator and the rotor;
l1 is the stator self inductance.
7. The apparatus of claim 6, further comprising a stator voltage adjusting unit, wherein the stator voltage adjusting unit is configured to adjust the stator voltage of the asynchronous motor after acquiring the parameter 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.
8. A storage medium, comprising a stored program, wherein the program when executed performs the method of any one of claims 1 to 5.
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