A method for obtaining shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter

Abstract

The present invention relates to the technical field of permanent magnet shielded motors, and in particular to a method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter. The method can effectively solve the problem that the shielding sleeve loss calculation requires measured current waveform data. In addition, the method does not use the superposition method when considering the harmonic loss of the shielding sleeve, so it has the advantages of high precision, simple calculation, and saving calculation time, and provides a reference for the design and optimization of the permanent magnet shielded motor powered by the frequency converter. The method includes the following steps: first, determine the input power of the frequency converter, the loss of the frequency converter, the copper loss of the motor stator winding, and the core loss of the motor stator; second, establish an air gap magnetic field analytical model and an electromagnetic power calculation model to calculate the electromagnetic power; finally, use the power balance equation to obtain the shielding sleeve loss of the permanent magnet shielded motor powered by the frequency converter.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet shielded motors, and in particular to a method for obtaining the loss of a shielding sleeve of a permanent magnet shielded motor powered by a frequency converter. Background Art

[0002] Compared with traditional motors, permanent magnet shielded motors have the advantages of simple maintenance, cleanliness, and no leakage. These advantages make it widely used in pharmaceutical, chemical, chip manufacturing and other fields as a mechanical seal-free vacuum pump drive motor. Structurally, the stator of the permanent magnet shielded motor is separated by a thin, metal, cylindrical shielding sleeve to prevent vacuum leakage. The shielding sleeve is affected by the rotating magnetic field of the air gap, inducing eddy currents and generating eddy current losses, which are called shielding sleeve losses. The shielding sleeve loss accounts for about 5%-15% of the total loss of the permanent magnet shielded motor and has a great impact on the motor performance. Therefore, the acquisition of the shielding sleeve loss plays a vital role in the performance calculation and optimization design of the permanent magnet shielded motor.

[0003] Currently, there are two main methods for obtaining the shielding sleeve loss: one is the finite element method. Although this method can accurately obtain the shielding sleeve loss, it requires the use of oscilloscopes and other equipment to provide measured current waveform data when considering the power supply situation of the inverter. This not only increases the calculation cost, but also has problems such as long calculation time.

[0004] Another method is to combine the finite element method with the analytical method. Liang Yanping and others from Harbin University of Science and Technology proposed a shielding sleeve loss calculation method combining finite element and analytical methods in the paper "Calculation and analysis of can losses of canned induction motor". This method first obtains the magnetic flux density of the shielding sleeve through the static magnetic field, and then brings the magnetic flux density into the shielding sleeve loss calculation formula. Although this method can well consider the time harmonics and magnetic circuit saturation problems, it assumes that the harmonic loss of the shielding sleeve is linearly superimposable, which reduces the calculation accuracy of the shielding sleeve loss. Summary of the invention

[0005] The present invention aims at the defects in the prior art and provides a method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter.

[0006] To achieve the above object, the present invention adopts the following technical solution, including the following steps:

[0007] First, determine the inverter input power, inverter loss, motor stator winding copper loss and motor stator core loss;

[0008] Secondly, the air gap magnetic field analytical model and electromagnetic power calculation model are established to calculate the electromagnetic power;

[0009] Finally, the power balance equation is used to obtain the shielding sleeve loss of the inverter-powered permanent magnet shielded motor.

[0010] Furthermore, the shielding sleeve loss is obtained by a loss separation method.

[0011] Furthermore, the electromagnetic power calculation model is established based on the Poynting vector.

[0012] Furthermore, the inverter input power P1 is determined using the formula:

[0013] P1=UI (1)

[0014] Among them, U is the DC bus voltage of the inverter, and I is the DC bus current of the inverter;

[0015] Determine the inverter loss p inv Using the formula:

[0016] p inv =P1(1-η) (2)

[0017] Where, η is the inverter efficiency;

[0018] Calculate the copper loss of the motor stator winding:

[0019] p cu =mI1 2 R1 (3)

[0020] Among them, m is the number of motor phases, I1 is the stator winding phase current, and R1 is the stator winding phase resistance;

[0021] Calculate the motor stator core loss:

[0022] p Fe =C Fe f 1.3 B m 2 G (4)

[0023] Among them, C Fe is the core loss coefficient, f is the stator current frequency, B m is the magnetic flux density of the stator core, and G is the mass of the stator core.

[0024] Furthermore, establishing the air gap magnetic field analytical model includes:

[0025] The air gap magnetic field of the permanent magnet shielded motor is a two-dimensional parallel plane field. The air gap magnetic field is solved by solving the vector magnetic potential A in polar coordinates. z The scalar Laplace equation is realized by solving

[0026]

[0027] In the formula, θ is the tangential direction of the motor, r is the radial direction of the motor, is a differential operator;

[0028] The boundary conditions of the permanent magnet shielded motor magnetic field are as follows:

[0029]

[0030] In the formula, H θ is the tangential component of the magnetic field intensity in the air gap, K1 and K2 are the amplitudes of the stator and rotor equivalent current sheets, R1 is the inner radius of the shielding sleeve, R2 is the outer radius of the rotor, and t is the time;

[0031] Then the air gap A z The general solution expression is:

[0032] A z =(C p r p +D p r -p )cos(ωt-pθ)+(E p r p +F p r -p )cos(ωt-pθ-pδ 12 ) (7)

[0033] Where p is the number of motor pole pairs, δ 12 is the motor power angle, C p , D p , E p , F p is the general solution coefficient, ω is the rotor angular frequency;

[0034] According to the boundary condition formula (6), the coefficients in the general solution are obtained:

[0035]

[0036] Where μ0 is the magnetic permeability of air;

[0037] Then the tangential component of the magnetic field intensity in the air gap is H θ for:

[0038]

[0039] The electric field strength in the air gap has only the z-axis component E z for:

[0040]

[0041] Furthermore, establishing the electromagnetic power calculation model to calculate the electromagnetic power includes:

[0042] The electromagnetic power depends on the radial component Πr of the Poynting vector:

[0043] Π r =(E×H) r =E θ H z -E z H θ =-E z H θ (11)

[0044] In the formula, E θ is the tangential component of the electric field intensity in the air gap, H z is the axial component of the magnetic field intensity in the air gap;

[0045] From equations (9), (10) and (11), we can get that at any radius r of the air gap, the active power transferred from the stator to the rotor, i.e., the electromagnetic power P e for,

[0046]

[0047] Where l is the axial length of the motor.

[0048] Furthermore, the shielding sleeve loss is obtained by the loss separation method including:

[0049] According to the power balance equation on the stator side of the permanent magnet shielded motor powered by the inverter:

[0050] p can =P1-p inv -p cu -p fe -P e (13)

[0051] Where P1 is the input power, p inv is the inverter loss, p cu is the stator winding copper loss, p fe is the stator core iron loss, P e is the electromagnetic power, p can is the shielding sleeve loss.

[0052] Specifically, first, the DC bus voltage and DC bus current of the inverter can be viewed on the inverter display menu or measured by a voltmeter and an ammeter.

[0053] 2. The inverter efficiency can be obtained by consulting the inverter user manual.

[0054] 3. The number of motor phases, stator winding phase current and stator winding phase resistance are motor design parameters and can be obtained from the motor design plan.

[0055] 4. The core loss coefficient is provided by the manufacturer of the silicon steel sheet model used, and the remaining parameters are obtained from the motor design plan.

[0056] 5. Laplace equation is solved by separation of variables method.

[0057] Compared with the prior art, the present invention has beneficial effects.

[0058] The present invention can effectively solve the problem that the shielding sleeve loss calculation requires measured current waveform data. In addition, the method does not use the superposition method when considering the harmonic loss of the shielding sleeve. Therefore, it has the advantages of high accuracy, simple calculation, and saving calculation time. It provides a reference for the design and optimization of inverter-powered permanent magnet shielded motors. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. The protection scope of the present invention is not limited to the following description.

[0060] Figure 1 This is a flow chart of a method for obtaining the shield sleeve loss of a permanent magnet shielded motor powered by an inverter.

[0061] Figure 2 It is a flow chart for solving the air gap magnetic field of permanent magnet shielded motor.

[0062] Figure 3 It is the air gap flux density result obtained by the air gap flux density calculation model of the present invention.

[0063] Figure 4 This is the shielding sleeve loss acquisition result provided by the specific embodiment.

[0064] Figure 5 It is the shielding sleeve loss result calculated by the finite element method in the specific embodiment. DETAILED DESCRIPTION

[0065] like Figure 1 As shown, a specific embodiment: a method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter, and the specific operation process is as follows:

[0066] 1) A three-phase permanent magnet shielded motor with a rated power of 1.5 kW, a rated voltage of 200 V, a rated current of 5.7 A, and a rated speed of 9000 r / min is selected as the research object. The material of the motor stator shield is 304 stainless steel. First, the DC bus current and DC bus voltage of the motor under different load conditions are read on the inverter display menu, and the input power under different loads is calculated by formula (1).

[0067] 2) The motor is powered by a KEWO AD800N inverter. By referring to the inverter user manual, we know that its efficiency is 98.2%. The inverter loss under different loads can be obtained through formula (2).

[0068] 3) The electromagnetic design of the motor can be used to determine the stator winding copper loss and core loss under different load conditions.

[0069] 4) Establish an analytical model of the air gap magnetic field of the permanent magnet shielded motor. The air gap magnetic field solution process is as shown in the attached Figure 2 As shown in the figure, the air gap magnetic flux waveform calculated by this model is as follows Figure 3 shown.

[0070] 5) Establish an electromagnetic power analytical calculation model, input the magnetic field analysis results and motor-related parameters into the electromagnetic power calculation model, and then the electromagnetic power of the motor under different loads can be obtained.

[0071] 6) The losses and powers obtained from the above steps can be separated according to the loss separation method to obtain the shielding sleeve loss of the permanent magnet shielded motor powered by the inverter under different load conditions. Figure 4 shown.

[0072] 7) In order to verify the accuracy of the present invention, the two-dimensional finite element method was used to calculate the loss of the motor shielding sleeve of the embodiment. The results are shown in the attached figure. Figure 5 By comparing the attached Figure 4 and attached Figure 5 It can be seen that the method proposed by the present invention is effective and accurate.

[0073] The present invention provides a method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter. Since it does not require actual current waveform data and does not use the superposition method when considering the harmonic loss of the shielding sleeve, it ensures that the shielding sleeve loss obtaining method saves calculation time under the premise of high accuracy, has the advantages of simple calculation and strong feasibility, and provides a theoretical basis for the optimized design of the permanent magnet shielded motor powered by the frequency converter. The present invention provides a method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter with high speed and high accuracy.

[0074] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the protection scope of the present invention.

Claims

1. A method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter, characterized in that: The steps include: First, determine the inverter input power, inverter loss, motor stator winding copper loss and motor stator core loss; Secondly, the air gap magnetic field analytical model and electromagnetic power calculation model are established to calculate the electromagnetic power; Finally, the power balance equation is used to obtain the shield loss of the permanent magnet shielded motor powered by the inverter; The air gap magnetic field analytical model is established including: The air gap magnetic field of the permanent magnet shielded motor is a two-dimensional parallel plane field. The air gap magnetic field is solved by solving the vector magnetic potential A in polar coordinates. z The scalar Laplace equation is realized by solving In the formula, θ is the tangential direction of the motor, r is the radial direction of the motor, is a differential operator; The boundary conditions of the permanent magnet shielded motor magnetic field are as follows: In the formula, H θ is the tangential component of the magnetic field intensity in the air gap, K1 and K2 are the amplitudes of the stator and rotor equivalent current sheets, R1 is the inner radius of the shielding sleeve, R2 is the outer radius of the rotor, and t is the time; Then the air gap A z The general solution expression is: A z =(C p r p +D p r -p )cos(ωt-pθ)+(E p r p +F p r -p )cos(ωt-pθ-pδ 12 ) (7) Where p is the number of motor pole pairs, δ 12 is the motor power angle, C p , D p , E p , F p is the general solution coefficient, ω is the rotor angular frequency; According to the boundary condition formula (6), the coefficients in the general solution are obtained: Where μ0 is the magnetic permeability of air; Then the tangential component of the magnetic field intensity in the air gap is H θ for: The electric field strength in the air gap has only the z-axis component E z for: Establishing the electromagnetic power calculation model to calculate the electromagnetic power includes: The electromagnetic power depends on the radial component Πr of the Poynting vector: Π r =(E×H) r =E θ H z -E z H θ =-E z H θ (11) In the formula, E θ is the tangential component of the electric field intensity in the air gap, H z is the axial component of the magnetic field intensity in the air gap; From equations (9), (10) and (11), we can get that at any radius of the air gap, the active power transferred from the stator to the rotor, i.e., the electromagnetic power P e for, Where l is the axial length of the motor.

2. The method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter according to claim 1, characterized in that: The shielding sleeve loss is obtained by a loss separation method.

3. The method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter according to claim 1, characterized in that: The electromagnetic power calculation model is established based on the Poynting vector.

4. The method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter according to claim 1, characterized in that: The formula used to determine the inverter input power P1 is: P1=UI (1) Among them, U is the DC bus voltage of the inverter, and I is the DC bus current of the inverter; Determine the inverter loss p inv Using the formula: p inv = P1(1-n) (2) Where, η is the inverter efficiency; Calculate the copper loss of the motor stator winding: p cu =mI1 2 R1 (3) Among them, m is the number of motor phases, I1 is the stator winding phase current, and R1 is the stator winding phase resistance; Calculate the motor stator core loss: p Fe =C Fe 1.3 B m 2 G (4) Among them, C Fe is the core loss coefficient, f is the stator current frequency, B m is the magnetic flux density of the stator core, and G is the mass of the stator core.

5. The method for obtaining the shielding sleeve loss of a permanent magnet shielded motor powered by a frequency converter according to claim 1, characterized in that: The shielding sleeve loss is obtained by loss separation method including: According to the power balance equation on the stator side of the permanent magnet shielded motor powered by the inverter: p can = P1-p inv -p cu -p fe -P e (13) Where P1 is the input power, p inv is the inverter loss, p cu is the stator winding copper loss, p fe is the stator core iron loss, P e is the electromagnetic power, p can is the shielding sleeve loss.

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