Method for calculating leakage magnetic coefficient of closed slot in rotor of asynchronous motor

Abstract

The present invention relates to the technical field of motor design, and provides a method for calculating a leakage magnetic coefficient of a closed slot in a rotor of an asynchronous motor. According to the calculation method provided by the present invention, by means of diverting the magnetic flux of rotor teeth in combination with a relative magnetic permeability calculated from a magnetization curve, a closed slot is ultimately transformed equivalently into a semi-closed slot, thereby unifying the semi-closed-slot and closed-slot algorithms and improving the adaptability of the closed-slot algorithm. The present method provides a general algorithm for closed-slot parameters, takes into account the edge effects caused by punching and shearing of cold-rolled silicon steel sheets, and is applicable to closed slots of various rotor slot types. Compared to finite-element methods, the present method has a short calculation cycle and is suitable for programmatic processing.

Description

A method for calculating leakage magnetic coefficient of closed slot of rotor of asynchronous motor TECHNICAL FIELD

[0001] The present application relates to the field of motor design, in particular to a method for calculating leakage magnetic coefficient of closed slot of rotor of asynchronous motor. BACKGROUND

[0002] Motor is a kind of industrial product with large quantity and wide range, is the core of power system, and is the main equipment of industrial power. The design method of industrial three-phase asynchronous motor is divided into magnetic circuit method and finite element method in terms of algorithm. The magnetic circuit method calculates the performance parameters of the motor through the magnetic circuit parameters, which is the most commonly used method for electromagnetic design of asynchronous motor. The finite element method is generally used for the performance research of motors with special structure or special working conditions. Compared with the finite element design method, the magnetic circuit design method has obvious advantages in the whole machine electromagnetic design: short cycle: the design cycle of the magnetic circuit method is about one thousandth of that of the finite element method, which is very suitable for design tasks with tight time, heavy task and large number of types; high precision: after years of algorithm optimization and experience coefficient adjustment, the design parameters and test parameters can achieve high consistency; good consistency: the same motor design parameters, the results of the algorithm of different designers are completely consistent, and there is no error caused by modeling and partitioning.

[0003] The national standard GB18613-2020 "Motor Efficiency Limiting Value and Energy Efficiency Grade" has been formally implemented since June 2021. The 1st, 2nd and 3rd energy efficiency specified in the standard has been improved by one grade based on the original standard, and the 1st energy efficiency is equivalent to the IE5 efficiency of IEC60034-30-1:2014 standard. In the past motor design, due to the low standard of motor efficiency, semi-closed slot design (as shown in FIG. 1) is widely used in small and medium-sized three-phase asynchronous motors. However, with the higher requirements of national energy efficiency standard on motor efficiency, the application of closed slot (as shown in FIG. 2) in design is also increasing, which is used to reduce the pulse loss generated by rotor tooth slot during motor rotation, improve motor efficiency, and achieve the effect of energy saving and emission reduction. However, the algorithm for closed slot has not been improved, and the traditional table lookup method is still used. The table lookup method has the following problems: the table lookup method is an empirical algorithm, which has limitations on the bridge arch shape of the closed slot; the table lookup method comes from the era of hot-rolled silicon steel sheet, and cannot consider the punching and shearing deterioration problem caused by cold-rolled silicon steel sheet, which reduces the design precision.

[0004] SUMMARY

[0005] The present application aims to solve the problem of calculating the leakage magnetic coefficient of the closed slot, and provides a method for calculating the leakage magnetic coefficient of the closed slot of the rotor of the asynchronous motor.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The application provides a method for calculating a leakage coefficient of a closed slot of a rotor of an asynchronous motor.

[0008] Step 1), setting an initial width of a punching shear effect according to a closed slot preparation process of the motor, and setting an initial value of an equivalent slot thickness;

[0009] Step 2), setting a slot width of an equivalent half-closed slot of the motor closed slot;

[0010] Step 3), calculating motor performance according to the half-closed slot scheme, to obtain stator tooth magnetic density, stator yoke magnetic density and rotor tooth magnetic density;

[0011] Step 4), calculating tooth magnetic flux through the rotor tooth magnetic density;

[0012] Step 5), setting a slot leakage percentage to obtain leakage flux;

[0013] Step 6), calculating a rotor slot bridge arch magnetic resistance according to a bridge arch structure size, the leakage flux and a magnetization curve;

[0014] Step 7), calculating an equivalent stator tooth magnetic resistance according to the stator tooth magnetic density and the magnetization curve;

[0015] Step 8), calculating an equivalent air gap tooth magnetic resistance according to an air gap size;

[0016] Step 9), calculating an equivalent stator yoke magnetic resistance according to the stator yoke magnetic density and the magnetization curve;

[0017] Step 10), calculating the slot leakage percentage according to a magnetic resistance and magnetic flux in a magnetic circuit being inversely proportional;

[0018] Step 11), substituting the slot leakage percentage obtained in step 10) into step 5) for iterative calculation until an error is less than or equal to a first preset value;

[0019] Step 12), calculating a slot width of a half-closed slot with the same slot magnetic resistance according to the slot leakage percentage obtained through the iterative calculation in step 11);

[0020] Step 13), substituting the slot width of the half-closed slot obtained in step 12) into step 2) for iterative calculation until an error is less than or equal to a second preset value;

[0021] Step 14), calculating the leakage coefficient of the rotor closed slot according to a slot leakage resistance calculation method of the half-closed slot by using the slot width of the half-closed slot obtained in step 13).

[0022] Optionally, the first preset value is 0.001.

[0023] Optionally, the second preset value is 0.001.

[0024] Optionally, after step 14), the method further comprises: adjusting the initial value of the equivalent slot thickness in step 1) according to the measured data of the motor.

[0025] The beneficial effects of the present application include:

[0026] The present application provides a rotor closed slot slot leakage coefficient calculation method based on magnetic circuit calculation. By dividing the rotor tooth magnetic flux, combining the relative permeability calculated by the magnetization curve, the closed slot is finally equivalent to a half-closed slot, the half-closed slot and closed slot algorithm are unified, and the adaptability of the closed slot algorithm is improved. The present application provides a general algorithm for closed slot parameters, and considers the punching edge effect of cold-rolled silicon steel sheet, and can be applied to various rotor slot types of closed slot. Compared with the finite element method, the calculation period is short, and it is suitable for programming processing. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor.

[0028] Fig. 1 shows the structure of a three-phase asynchronous motor rotor half-closed slot in the prior art;

[0029] Fig. 2 shows the structure of a three-phase asynchronous motor rotor closed slot in the prior art;

[0030] Fig. 3 shows a rotor closed slot magnetic leakage coefficient calculation flowchart provided by the present application;

[0031] Fig. 4 shows a motor structure schematic diagram provided by the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0033] In the conventional motor design, due to the low motor efficiency standard, small and medium-sized three-phase asynchronous motor widely adopts semi-closed slot design (as shown in figure 1), but with the higher requirement of national energy efficiency standard on motor efficiency, the application of closed slot (as shown in figure 2) in the design is also more and more, to reduce the rotor tooth slot vibration loss when the motor rotates, improve the motor efficiency, achieve the effect of energy saving and emission reduction, but the algorithm for closed slot has not been improved, and the traditional table lookup method is still used, and the table lookup method has the following problems: the table lookup method is an empirical algorithm, and the bridge arch shape of the closed slot is limited; the table lookup method is derived from the hot-rolled silicon steel sheet era, and the punching shear deterioration problem caused by the cold-rolled silicon steel sheet cannot be considered, so the design precision is reduced.

[0034] Therefore, the asynchronous motor rotor closed slot leakage coefficient calculation method is provided to solve the problem of closed slot leakage coefficient calculation

[0035] As shown in figure 3, the asynchronous motor rotor closed slot leakage coefficient calculation method provided by the application comprises the following steps:

[0036] Step 1), according to the motor closed slot preparation process, the initial width h1 of the punching shear effect is set, and the initial value δ of the equivalent slot thickness is initially set.

[0037] Step 2), the slot width b02 of the equivalent semi-closed slot of the motor closed slot is initially set.

[0038] Step 3), the motor performance is calculated according to the semi-closed slot scheme, and the stator tooth magnetic density, the stator yoke magnetic density and the rotor tooth magnetic density are obtained. The specific operation of calculating the motor performance according to the semi-closed slot scheme can refer to the motor design magnetic circuit calculation method in the prior art.

[0039] Step 4), the tooth magnetic flux is calculated through the rotor tooth magnetic density. In step 4, since the purpose of calculation is to calculate the flow of the rotor tooth magnetic flux in the radial direction and the slot, the length of the motor core can be simultaneously divided, so the width of the magnetic circuit can be used instead of the cross-sectional area of the magnetic circuit for magnetic flux calculation.

[0040] Step 5), the slot leakage percentage La is initially set, and the leakage flux is obtained.

[0041] Step 6), according to the structure size of the bridge arch, the leakage flux, and the magnetization curve, the rotor slot bridge arch magnetic resistance is calculated.

[0042] Step 7), according to the stator tooth magnetic density, the equivalent stator tooth magnetic resistance is calculated in combination with the magnetization curve.

[0043] Step 8), according to the air gap size, the air gap equivalent tooth magnetic resistance is calculated.

[0044] Step 9), according to the stator yoke magnetic density, the equivalent stator yoke magnetic resistance is calculated in combination with the magnetization curve.

[0045] Step 10), according to the magnetic circuit in the magnetic resistance and magnetic flux is inversely proportional, the slot leakage percentage is calculated as La1.

[0046] Step 11), the slot leakage percentage La1 calculated in step 10) is substituted into step 5) for iterative calculation until the error is less than or equal to the first preset value ε, and optionally, the first preset value is 0.001.

[0047] Step 12), according to the slot leakage percentage calculated in step 11), the slot width b021 of the half-closed slot with the same slot leakage is calculated.

[0048] Step 13), the slot width b021 of the half-closed slot calculated in step 12) is substituted into step 2) for iterative calculation until the error is less than or equal to the second preset value ε1; the second preset value is 0.001, thereby obtaining the final bridge arch equivalent width.

[0049] Step 14), using the slot width of the half-closed slot calculated in step 13), the rotor closed slot leakage coefficient is calculated according to the slot leakage resistance calculation method of the half-closed slot. Optionally, after step 14), the method further comprises adjusting the initial value δ of the equivalent slot opening thickness in step 1) according to the measured data of the motor to correct the influence of the processing technology and characteristics of the material on the algorithm.

[0050] The present application proposes a rotor closed slot slot leakage resistance coefficient calculation method based on magnetic circuit calculation. By shunting the rotor tooth magnetic flux and combining the relative permeability calculated by the magnetization curve, the closed slot is finally equivalent to a half-closed slot, the algorithm of the half-closed slot and the closed slot is unified, and the adaptability of the closed slot algorithm is improved. The present application provides a general algorithm for closed slot parameters, and considers the edge effect problem of cold-rolled silicon steel sheet, and can be applied to various types of closed slots of rotor slots. Compared with the finite element method, the calculation period is short and suitable for programming processing.

[0051] The method proposed by the present application will be described in detail below taking a H225M-4, 45kW three-phase asynchronous motor as an example. The motor structure is shown in FIG. 4. As shown in FIG. 4, the motor structure is composed of a stator core A1, a winding A2, a rotor core A3, a shaft A4, and a cast aluminum cage A5. The motor line voltage effective value is 380VAC, the frequency is 50Hz, the pole number is 4 poles, and the detailed parameters are shown in Table 1:

[0052] Table 1 H225M-4 type three-phase asynchronous motor parameter table

[0053] For the motor of the parameters described in Table 1, the method of the application comprises the following steps: (1) initially setting the punching shear effect width h1 of the cold-rolled silicon steel sheet to 0.3 mm, obtaining the initial setting notch height δ = 0.5-0.3 = 0.2 mm; (2) initially setting the notch width b02 of the equivalent half-closed slot of the closed slot of the motor to 1 mm; (3) through calculation, when the motor is a half-closed slot, the calculated value of the stator tooth magnetic density of the motor is 15726 Gs, the calculated value of the stator yoke magnetic density is 12937 Gs, and the rotor tooth magnetic density is 13474 Gs; (4) according to the calculation of the rotor tooth width, the equivalent magnetic flux of the rotor is 143844 (since the calculation result is a ratio, in order to simplify the calculation, it is not converted into international units here, and the length of the motor can be divided, so the equivalent magnetic flux value obtained here is a relative value); (5) initially setting the leakage magnetic percentage to 10%, and the equivalent leakage magnetic at the notch is 14384.4; (6) since the rotor notch is composed of two parts of the shoulder and the bridge arch.The slot shoulder is trapezoidal in shape, which results in varying magnetic flux density at different locations. Since the magnetization curve is non-linear, the slot shoulder and slot opening are divided into 100 equal parts in the calculation (the number can be adjusted as needed; additionally, due to the symmetry of the magnetic circuit, the magnetic circuit of one slot shoulder and half a slot opening is calculated here). Then, based on the same magnetic flux and different magnetic circuit widths, the magnetic flux density at different locations is calculated, yielding the relative permeability: 5972.000, 6011.530, 6051.499, ..., 28.2448. The magnetic reluctance of each segment is then calculated using the permeability, and the reluctances are summed to obtain the magnetic reluctance at the slot shoulder: 0.000001354 + 0.000001363 + 0. .000001373+……+0.004426=0.152524;(7) The magnetic flux density of the stator teeth is 15726Gs, and the relative permeability is 1231.8592; the tooth height is 32.03mm, the equivalent width of the tooth is 7.57*48 / 40=9.08, and the relative magnetic reluctance of the stator tooth magnetic circuit is 0.002862;(8) The length of the air gap is 1mm, and the width of the air gap is the air gap circumference divided by the number of poles, and then divided by the number of rotor slots: 3.14*250 / 4 / 40=4.91, and the relative magnetic reluctance of the air gap is 0.05093;(9) The magnetic flux density of the stator yoke is 12937Gs, the yoke height is 35.03mm, and the yoke length is 139. 40mm, since the yoke is equivalent to parallel connection, the equivalent yoke height is 70.06mm and the equivalent yoke length is 69.70mm. The relative magnetic reluctance of the stator yoke magnetic circuit is 0.0001673; (10) Calculate the percentage of leakage flux at the slot opening of the rotor at this time: (0.002862+0.0001673+0.05093) / (0.002862+0.0001673+0.05093+0.152524)=26.13%; (11) Substitute the calculated value of 26.13% of the leakage flux at the slot opening of the rotor into step (5) for recalculation. After iterative iteration, the convergence value of the calculated percentage of leakage flux at the slot opening of the rotor is 21.94. %; (12) Using the rotor closed slot leakage magnetic percentage of 21.94%, calculate the width of the semi-closed slot with the same slot magnetic resistance as 0.09586mm; (13) Substitute the semi-closed slot width of 0.09586mm into step (2) for recalculation. After iterative iteration, the equivalent slot width is 0.09597; (14) According to the slot leakage resistance calculation method of semi-closed slot, the slot leakage resistance coefficient of closed slot rotor is 3.2130; (15) If the motor calculation result deviates from the test value, the punching and shearing effect deterioration width of cold rolled silicon steel sheet can be adjusted and substituted into step 1. Iterative iteration can be performed until the calculation result matches the test result. The punching and shearing performance of silicon steel sheet and the design parameters of motor can be obtained at this time.

[0054] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for calculating the leakage flux coefficient of a closed slot rotor in an asynchronous motor, characterized in that, The method includes the following steps: Step 1) Set the initial width of the punching and shearing effect according to the motor closed slot manufacturing process, and initially set the equivalent slot thickness. Step 2) Initially determine the slot width of the equivalent semi-closed slot for the motor closed slot; Step 3) Calculate the motor performance according to the semi-closed slot scheme to obtain the stator tooth magnetic flux density, stator yoke magnetic flux density, and rotor tooth magnetic flux density; Step 4) Calculate the magnetic flux of the tooth section using the rotor tooth magnetic flux density; Step 5) Initially set the leakage flux percentage at the slot opening to obtain the leakage flux; Step 6) Calculate the rotor slot bridge arch magnetic reluctance based on the structural dimensions and leakage flux of the bridge arch, combined with the magnetization curve; Step 7) Calculate the equivalent tooth reluctance of the stator based on the stator tooth magnetic flux density and the magnetization curve; Step 8) Calculate the equivalent tooth magnetic reluctance based on the air gap size; Step 9) Calculate the stator equivalent yoke reluctance based on the stator yoke magnetic flux density and the magnetization curve; Step 10) Calculate the percentage of magnetic leakage at the slot based on the inverse relationship between magnetic reluctance and magnetic flux in the magnetic circuit; Step 11) Substitute the percentage of leakage magnetic flux at the slot obtained in Step 10) into Step 5) for iterative calculation until the error is less than or equal to the first preset value; Step 12) Based on the leakage magnetic percentage of the slot opening calculated iteratively in Step 11), calculate the slot opening width of the semi-closed slot with the same magnetic reluctance. Step 13) Substitute the groove width of the semi-closed groove obtained in Step 12) into Step 2) for iterative calculation until the error is less than or equal to the second preset value. Step 14) Using the slot width of the semi-closed slot obtained in Step 13), calculate the leakage magnetic coefficient of the rotor closed slot according to the slot leakage reactance calculation method of the semi-closed slot.

2. The method for calculating the leakage flux coefficient of the closed slot of an asynchronous motor rotor according to claim 1, characterized in that, The first preset value is 0.

001.

3. The method for calculating the leakage flux coefficient of the closed slot of an asynchronous motor rotor according to claim 1, characterized in that, The second preset value is 0.

001.

4. The method for calculating the leakage flux coefficient of the closed slot of an asynchronous motor rotor according to claim 1, characterized in that, After step 14), the method further includes: adjusting the initial value of the equivalent slot thickness in step 1) based on the measured data of the motor.

Images