A full-speed-range multiphase cobalt-iron alloy motor core loss calculation method and system

Abstract

The application discloses a kind of full speed domain multiphase cobalt iron alloy motor core loss calculation method, system, and multiphase cobalt iron alloy motor is decoupled to fundamental wave subplane and harmonic subplane by coordinate transformation, reduces the core loss generated by low frequency harmonic current using maximum six-vector SVPWM control strategy, improves control performance;Obtain magnetic flux density from the sideband harmonic current under the stationary coordinate system, and substitute into the traditional core loss separation formula, re-fitting, obtain the core loss separation formula, for the formulation of motor modulation strategy under different conditions, to suppress the core loss generated by high frequency harmonic current, improve the efficiency of motor control system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of multiphase motor drive control, and particularly relates to a core loss calculation method for a multiphase cobalt-iron alloy motor. BACKGROUND

[0002] A multiphase permanent magnet motor has the characteristics of small torque ripple, excellent fault tolerance performance, and high control flexibility, and has been widely concerned in all-electric aircraft and ship electric propulsion systems. Compared with traditional silicon steel alloy materials, cobalt-iron alloy materials have higher saturation magnetic flux, so they can achieve high-efficiency and lightweight design while having better electromagnetic performance. However, cobalt-iron alloy materials produce greater core loss, the main reason for which is that the magnetic flux density amplitude of cobalt-iron alloy materials is much larger than that of traditional silicon steel alloy materials, and the loss is positively correlated with the magnetic flux density amplitude, and cobalt-iron alloy materials have a higher loss coefficient than traditional silicon steel alloy materials. Core loss is mainly caused by fundamental current and high-frequency harmonic current, so it is of great significance to analyze the change of core loss caused by high-frequency harmonic current in the full speed range. SUMMARY

[0003] Therefore, the application provides a core loss calculation method for a full-speed-range multiphase cobalt-iron alloy motor.

[0004] The application achieves the above technical purpose through the following technical means.

[0005] A core loss calculation method for a full-speed-range multiphase cobalt-iron alloy motor:

[0006] The multiphase cobalt-iron alloy motor is decoupled to a fundamental subplane and a harmonic subplane through coordinate transformation, and the maximum six-vector SVPWM control strategy is used to select the six largest vectors in the fundamental subplane closest to the reference voltage vector, so that the projections of the six largest vectors in the harmonic subplane are zero, thereby reducing the core loss caused by low-frequency harmonic current;

[0007] The sideband harmonic voltage at one to five times the switching frequency in the stationary coordinate system is determined from the phase voltage expression, the sideband harmonic voltage in the stationary coordinate system is converted into the sideband harmonic voltage in the rotating coordinate system through coordinate transformation, and then the sideband harmonic current in the rotating coordinate system is determined, and the sideband harmonic current in the stationary coordinate system is converted into the sideband harmonic current in the stationary coordinate system through coordinate transformation; the magnetic flux is obtained from the sideband harmonic current in the stationary coordinate system, and is substituted into the traditional core loss separation formula to perform fitting again, thereby obtaining the core loss separation formula for formulating the motor modulation strategy under different operating conditions, and thereby suppressing the core loss caused by high-frequency harmonic current.

[0008] Further, the projections of the six large vectors in the harmonic subplane are made to be zero, specifically: the six large vectors closest to the reference voltage vector in the fundamental subplane are synthesized, the vector action time is calculated, the switching sequence of the maximum six-vector SVPWM is determined, and a centering process is performed once.

[0009] Further, the phase voltage expression is obtained based on the modulation wave expression, in the maximum six-vector SVPWM control strategy, the zero vector is evenly divided, thereby determining the expression of the modulation wave, through Fourier analysis, rewriting the expression of the modulation wave and simplifying, and further determining the phase voltage expression.

[0010] Further, the core loss separation formula is obtained by refitting, specifically:

[0011] P Fe =χ h fi α +χ c f 2 i 2 +χ e f 1.5 i 1.5

[0012] In the formula, P Fe is the core loss, f is the frequency, i is the sideband harmonic current in the stationary coordinate system, χ h , χ c , χ e are the hysteresis loss coefficient, the eddy current loss coefficient and the additional loss coefficient obtained by refitting respectively, and α is the hysteresis loss index.

[0013] Further, the coordinate transformation is performed by using the Clark transformation matrix and the Park transformation matrix of the polyphase cobalt-iron alloy motor, and the Clark transformation matrix and the Park transformation matrix are obtained according to the vector space decoupling principle.

[0014] A core loss calculation system of a full-speed-range polyphase cobalt-iron alloy motor, comprising:

[0015] A maximum six-vector SVPWM control module, programs of a maximum six-vector control strategy are burned into a digital signal processor through a code debugger, the digital signal processor outputs gate signals to switching devices through a driving circuit after amplification, and the control of the maximum six-vector is realized.

[0016] A core loss calculation module, in MATLAB, data fitting is performed using the least squares method, the coefficients of the core loss are confirmed by minimizing the sum of squares of errors, and the core loss is calculated.

[0017] An electronic device, comprising a memory and a processor.

[0018] The memory is used for storing a computer program;

[0019] The processor is used for executing the computer program and realizing the core loss calculation method of the full-speed-range multiphase cobalt-iron alloy motor when the computer program is executed.

[0020] A storage medium stores a computer program, and the computer program makes the processor execute the core loss calculation method of the full-speed-range multiphase cobalt-iron alloy motor when the processor executes the computer program.

[0021] The present application has the following beneficial effects:

[0022] 1) The present application proposes a control strategy based on maximum six-vector SVPWM, effectively suppresses low-frequency harmonic current, and improves control performance.

[0023] 2) The present application obtains high-frequency harmonic current from one to five times the switching frequency, which greatly affects the core loss, and helps to analyze the change rule of high-frequency harmonic in the full-speed range.

[0024] 3) The present application re-fits the core loss separation formula, which is conducive to calculating the core loss generated by high-frequency harmonic current under different working conditions.

[0025] 4) By comparing the core loss generated by high-frequency current in the full-speed range, the modulation strategy of the motor can be adjusted according to different working conditions to suppress the core loss and improve the efficiency of the motor control system. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The winding connection topology diagram of the three neutral point multiphase permanent magnet motor is provided.

[0027] Figure 2 The maximum six-vector SVPWM control block diagram is provided.

[0028] Figure 3(a) is a schematic diagram of the fundamental subplane vector according to the present application;

[0029] Figure 3(b) is a schematic diagram of the z1-z2 subplane vector according to the present application;

[0030] Figure 3(c) is a schematic diagram of the z3-z4 subplane vector according to the present application;

[0031] Figure 4 The core loss amplitude diagram in the full-speed range obtained by the experiment is provided.

[0032] Figure 5(a) is a schematic diagram of the sideband harmonic current theoretical value at one switching frequency in the stationary coordinate system according to the present application;

[0033] Fig. 5(b) is a schematic diagram of experimental values of sideband harmonic currents at one times the switching frequency in the stationary reference frame according to the present application;

[0034] Fig. 5(c) is a schematic diagram of theoretical values of sideband harmonic currents at two times the switching frequency in the stationary reference frame according to the present application;

[0035] Fig. 5(d) is a schematic diagram of experimental values of sideband harmonic currents at two times the switching frequency in the stationary reference frame according to the present application;

[0036] Fig. 5(e) is a schematic diagram of theoretical values of sideband harmonic currents at three times the switching frequency in the stationary reference frame according to the present application;

[0037] Fig. 5(f) is a schematic diagram of experimental values of sideband harmonic currents at three times the switching frequency in the stationary reference frame according to the present application;

[0038] Fig. 5(g) is a schematic diagram of theoretical values of sideband harmonic currents at four times the switching frequency in the stationary reference frame according to the present application;

[0039] Fig. 5(h) is a schematic diagram of experimental values of sideband harmonic currents at four times the switching frequency in the stationary reference frame according to the present application;

[0040] Fig. 5(i) is a schematic diagram of theoretical values of sideband harmonic currents at five times the switching frequency in the stationary reference frame according to the present application;

[0041] Fig. 5(j) is a schematic diagram of experimental values of sideband harmonic currents at five times the switching frequency in the stationary reference frame according to the present application;

[0042] Figure 6 Fig. 5(k) is a comparison chart of core losses due to different high-frequency harmonic currents in the full speed range according to the present application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0044] The core loss calculation method of the full speed range multiphase cobalt-iron alloy motor according to the present embodiment includes three parts: maximum six-vector SVPWM control strategy, derivation of high-frequency harmonic current expression, and re-fitting of core loss. The specific embodiment will be described in detail below in combination with Figures 1-6 .

[0045] Step 1) The multiphase permanent magnet motor is a system with strong coupling, nonlinearity and multiple variables, so it is necessary to realize the control of the motor through coordinate transformation. The present embodiment selects the Park transformation as Figure 1The nine-phase permanent magnet motor control system shown is based on the vector space decoupling principle to obtain the Clark transformation matrix and the Park transformation matrix of the multi-phase permanent magnet motor:

[0046]

[0047] In the formula, θ is the rotor position angle, T αβ is the transformation matrix from the stationary coordinate system to the α-β coordinate system, T dq is the transformation matrix from the α-β coordinate system to the rotating coordinate system, d represents the d-axis component of the current, voltage, and flux linkage, q represents the q-axis component of the current, voltage, and flux linkage, z1 represents the z1-axis component of the current, voltage, and flux linkage, z2 represents the z2-axis component of the current, voltage, and flux linkage, z3 represents the z3-axis component of the current, voltage, and flux linkage, z4 represents the z4-axis component of the current, voltage, and flux linkage, o1, o2, and o3 are zero sequence components.

[0048] Step 2) Based on the Clark transformation matrix and the Park transformation matrix of step 1), the nine-phase permanent magnet motor is decoupled to the fundamental wave subplane, the z1-z2 subplane, and the z3-z4 subplane through coordinate transformation, respectively referring to Figure 3(a) 、 3(b) , 3(c), wherein the z1-z2 subplane and the z3-z4 subplane do not participate in the electromechanical energy conversion.

[0049] The maximum six-vector SVPWM is to select the six large vectors closest to the reference voltage vector in the fundamental wave subplane, so that their projections in the two harmonic subplanes (z1-z2 subplane and z3-z4 subplane) are zero, to suppress low-frequency harmonic currents, reduce core loss generated by low-frequency harmonic currents, and have the largest bus voltage utilization rate.

[0050] Taking the first sector (I in FIG. 3(a)) as an example, voltage vectors v70, v57, v71, v56, v58, and v69 are selected for synthesis, the vector action time is calculated, the switching sequence of the maximum six-vector SVPWM is determined, and a centralization process is performed once to realize the projection of v70, v57, v71, v56, v58, and v69 in the z1-z2 subplane and the z3-z4 subplane is zero. The vector action time is calculated in the following way:

[0051]

[0052] In the formula, V α is the α-axis component of the voltage vector, V β is the β-axis component of the voltage vector, V z1 is the z1-axis component of the voltage vector, V z2 is the z2-axis component of the voltage vector, V z3 is the z3-axis component of the voltage vector, Vz4 is the axis component of the voltage vector z4, T s is the action time of one switching period, U dc is the DC bus voltage, is the axis component of the six large vectors, is the axis component of the six large vectors, is the z1 axis component of the six large vectors, is the z2 axis component of the six large vectors, is the z3 axis component of the six large vectors, is the z4 axis component of the six large vectors, T1…T6 is the action time of the six large vectors.

[0053] The control block diagram of the maximum six-vector SVPWM is shown in Figure 2 , wherein n is the feedback speed, n * is the given speed, i q is the q-axis feedback current, i d is the d-axis feedback current, is the d-axis given current, i z1 is the z1-axis feedback current, is the z1-axis given current, i z2 is the z2-axis feedback current, is the z2-axis given current, i z3 is the z3-axis feedback current, is the z3-axis given current, i z4 is the z4-axis feedback current, is the z4-axis given current, θ e is the rotor position angle, i s is the phase current.

[0054] The low-frequency harmonic current is suppressed by the maximum six-vector SVPWM control strategy, and the core loss generated by the low-frequency harmonic current is reduced; however, the core loss generated by the high-frequency harmonic current accounts for a large proportion in the total core loss, so the calculation of the core loss generated by the high-frequency harmonic current is realized in the following manner.

[0055] Step 3) Since the zero vector is evenly divided in the maximum six-vector SVPWM control strategy, the expression of the modulation wave is:

[0056]

[0057] In the formula, a is the modulation range, and 0≤a≤1, ω o is the fundamental angular frequency.

[0058] Through Fourier analysis, the expression (formula (1)) of the modulation wave is rewritten in the following form:

[0059]

[0060] where n = 6k + 3, k = 0, 1, 2,...

[0061] Equation (2) is further simplified as:

[0062] y(t) ≈ (sin(ω o t) + μ sin(3ω o t))(3)

[0063] where the intermediate quantity the intermediate quantity

[0064] The expression of the modulation wave shown in equation (3) is the expression of the A-phase voltage of the nine-phase permanent magnet motor:

[0065]

[0066] where ω c is the carrier angular velocity, u a is the A-phase voltage, the intermediate quantity A0 = 2M(sin(ω o t) + μ sin(3ω o t)),

[0067]

[0068] Because the sideband current harmonics from one switching frequency to five switching frequencies have a greater impact on core loss, the high-frequency harmonic currents at ω c ± 2ω o , 2ω c ± ω o , 3ω c ± 2ω o , 4ω c ± ω o , 5ω c ± 2ω o frequencies have the most significant impact on core loss, the sideband harmonic voltages from one switching frequency to five switching frequencies in the stationary coordinate system are further determined based on the expression of the A-phase voltage.

[0069] The sideband harmonic voltage at one switching frequency in the stationary coordinate system can be expressed as:

[0070] ε1≈β 1-2 cos((ω c ± 2ω o )t)(5)

[0071] where the intermediate quantity J0 is a zero-order Bessel function, J1 is a first-order Bessel function, J2 is a second-order Bessel function, and J4 is a fourth-order Bessel function.

[0072] The sideband harmonic voltage at the double switching frequency in the stationary coordinate system can be expressed as:

[0073] ε2≈β 2-1 sin(2ω c ±ω o )(6)

[0074] In the formula, the intermediate quantity

[0075] The sideband harmonic voltage at the triple switching frequency in the stationary coordinate system can be expressed as:

[0076] ε3≈β 3-2 cos((3ω c ±2ω o )t)(7)

[0077] In the formula, the intermediate quantity

[0078] The sideband harmonic voltage at the quadruple switching frequency in the stationary coordinate system can be expressed as:

[0079] ε4≈β 4-1 sin(4ω c ±ω o ) (8)

[0080] In the formula, the intermediate quantity

[0081] The sideband harmonic voltage at the quintuple switching frequency in the stationary coordinate system can be expressed as:

[0082] ε5≈β 5-2 cos((5ω c ±2ω o )t) (9)

[0083] In the formula, the intermediate quantity

[0084] Step 4) For further in-depth analysis, based on the Clark transformation matrix and the Park transformation matrix of step 1), the sideband harmonic voltage in the stationary coordinate system is converted into the sideband harmonic voltage in the rotating coordinate system through coordinate transformation.

[0085] The sideband harmonic voltage at the double switching frequency in the stationary coordinate system can be expressed as:

[0086]

[0087] In the formula: φ0 represents an initial torque angle;

[0088] The sideband harmonic voltage at the double switching frequency in the rotating coordinate system is expressed as:

[0089]

[0090] The sideband harmonic voltage at the triple switching frequency in the rotating coordinate system is expressed as:

[0091]

[0092] The sideband harmonic voltage at the quadruple switching frequency in the rotating coordinate system is expressed as:

[0093]

[0094] The sideband harmonic voltage at the quintuple switching frequency in the rotating coordinate system is expressed as:

[0095]

[0096] Therefore, the sideband harmonic current expression in the rotating coordinate system can be further obtained as:

[0097]

[0098]

[0099] Step 5) The sideband harmonic current expression in the rotating coordinate system is converted to the stationary coordinate system by coordinate transformation to obtain the sideband harmonic current expression in the stationary coordinate system:

[0100]

[0101] In the formula, the intermediate quantity L d is the d-axis inductance, and L q is the q-axis inductance.

[0102] Step 6) The traditional core loss separation formula is a function of the magnetic flux density, which is not conducive to calculating the core loss in the full speed range; the traditional core loss separation formula is:

[0103] P Fe = k h fB α +k c f 2 B 2 +k e f 1.5 B 1.5 (35)

[0104] In the formula, P Fe is the core loss, k h , kc , k e are the coefficients of hysteresis loss, eddy current loss, additional loss, respectively, a is the hysteresis loss index, f is the frequency, and B is the magnetic flux density.

[0105] Since the current is positively correlated with the magnetic flux density, the expression of the sideband harmonic current in the stationary coordinate system obtained in step 5) is substituted into the following formula:

[0106] F = Ni = HL (36)

[0107] The magnetomotive force F is calculated, and the magnetic flux density B is calculated by substituting the following formula:

[0108] B = μH = μF / L = μNi / L (37)

[0109] The calculated magnetic flux density B is substituted into the traditional core loss separation formula, and a new core loss separation formula is obtained by refitting:

[0110] P Fe = χ h f α i c + χ 2 f 2 i e + χ 1.5 f 1.5 i h (38)

[0111] In the formula, i is the sideband harmonic current in the stationary coordinate system, N is the number of turns of the coil, H is the magnetic field strength, L is the length of the magnetic circuit, μ is the vacuum permeability, χ c , χ e are the coefficients of hysteresis loss, eddy current loss, additional loss of the refitted core loss separation formula.

[0112] The refitted core loss separation formula will change with the change of the modulation range, which is beneficial to the analysis of high-frequency core loss.

[0113] The amplitude of the core loss of the nine-phase cobalt-iron alloy motor in the full speed range obtained by experiment is shown in FIG. 5(a), (b), (c), (d), (e), (f), (g), (h), (i), (j), and it can be seen that the increase of the core loss is more obvious as the speed increases. Figure 4

[0114] The theoretical value and experimental value of the high-frequency current harmonic in the full speed range are compared as shown in FIG. 5(a), (b), (c), (d), (e), (f), (g), (h), (i), (j), and the change rule of the experimental data basically conforms to the theoretical derivation, which shows that the expression of the sideband harmonic current in the stationary coordinate system obtained in step 5) is correct.

[0115] ​Core losses generated by high frequency harmonic currents at different frequencies change the dominant core loss as the modulation range changes, as shown in FIG. Figure 6

[0116] The full-speed-range multiphase cobalt-iron alloy motor core loss calculation system provided by the embodiment of the application comprises:

[0117] The maximum six-vector SVPWM control module programs the maximum six-vector control strategy into a DSP (Digital Signal Processing) through a CCS (Code Composer Studio, code debugger), and the DSP outputs gate signals to switching devices through a driving circuit to realize maximum six-vector control.

[0118] The core loss calculation module uses the least square method to perform data fitting in MATLAB, confirms the core loss coefficient by minimizing the sum of squares of errors, and then performs core loss calculation.

[0119] The phase current of the nine-phase permanent magnet motor is recorded by an oscilloscope, input into ANSYS software, simulated through a finite element simulation model, and subjected to Fourier analysis to obtain the core loss amplitude at each switching frequency, and compared with the core loss value obtained by the new core loss separation formula.

[0120] It should be noted that the embodiments of the present application can be realized by hardware, software or a combination of software and hardware. The hardware part can be realized by special logic; the software part can be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or a specially designed hardware. Those skilled in the art can understand that the above-mentioned devices and methods can be realized by computer executable instructions and / or included in processor control code, such as provided on a carrier medium, such as a magnetic disk, CD or DVD-ROM, a programmable memory, such as a read-only memory (firmware), or a data carrier, such as an optical or electronic signal carrier. The devices of the present application and their modules can be realized by hardware circuits, such as very large scale integrated circuits or gate arrays, semiconductors, such as logic chips, transistors, etc., or programmable hardware devices, such as field programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0121] ​The above examples are only used for illustrating the design idea and characteristics of the present application, and the purpose is to enable the person skilled in the art to understand the present application and to implement it, and to obtain the multi-phase cobalt-iron alloy motor core loss calculation method. Therefore, any equivalent changes or modifications made according to the principles and design ideas disclosed by the present application are within the protection scope of the present application.

Claims

1. A method for calculating core loss of a full-speed-range multiphase cobalt-iron alloy motor, characterized in that: the multiphase cobalt-iron alloy motor is decoupled into a fundamental subplane and a harmonic subplane through coordinate transformation, and a maximum six-vector SVPWM control strategy is used to select six large vectors closest to a reference voltage vector in the fundamental subplane, so that the projections of the six large vectors in the harmonic subplane are zero, thereby reducing core loss caused by low-frequency harmonic current; sideband harmonic voltage at one to five times the switching frequency in a stationary coordinate system is determined from a phase voltage expression, the sideband harmonic voltage in the stationary coordinate system is converted into sideband harmonic voltage in a rotating coordinate system through coordinate transformation, and then sideband harmonic current in the rotating coordinate system is determined, and the sideband harmonic current in the rotating coordinate system is converted into sideband harmonic current in the stationary coordinate system through coordinate transformation; the magnetic flux density is obtained from the sideband harmonic current in the stationary coordinate system, and substituted into a core loss separation formula to perform re-fitting, thereby obtaining a re-fitted core loss separation formula for formulating motor modulation strategies under different operating conditions, and thereby suppressing core loss caused by high-frequency harmonic current; the core loss separation formula is re-fitted as follows: so that the projections of the six large vectors in the harmonic subplane are zero, and specifically: the six large vectors closest to the reference voltage vector in the fundamental subplane are synthesized, the vector action time is calculated, the switching sequence of the maximum six-vector SVPWM is determined, and a first centering process is performed. The phase voltage expression is obtained based on a modulation wave expression, in the maximum six-vector SVPWM control strategy, the zero vector is evenly divided, thereby determining the expression of the modulation wave, rewriting the expression of the modulation wave through Fourier analysis, and simplifying, and then determining the phase voltage expression. The coordinate transformation is performed using a Clark transformation matrix and a Park transformation matrix of the multiphase cobalt-iron alloy motor, and the Clark transformation matrix and the Park transformation matrix are obtained according to the vector space decoupling principle. It comprises: P Fe =χ h fi α +χ c f 2 i 2 +χ e f 1.5 i 1.5 In the formula, P Fe is the core loss, f is the frequency, i is the sideband harmonic current in the stationary coordinate system, χ h , χ c , χ e are the hysteresis loss coefficient, the eddy current loss coefficient and the additional loss coefficient respectively, and α is the hysteresis loss index.

2. The method of calculating core loss of a full speed range multiphase cobalt-iron alloy electrical machine according to claim 1, wherein, a maximum six-vector SVPWM control module, which programs the maximum six-vector control strategy into a digital signal processor through a code debugger, the digital signal processor amplifies the gate signal through a drive circuit and outputs it to a switching device, thereby realizing maximum six-vector control; 3. The method of claim 1, wherein, a core loss calculation module, which uses the least squares method to perform data fitting in MATLAB, confirms the coefficients of core loss by minimizing the sum of squares of errors, and then calculates the core loss.

4. The method of claim 1, wherein, It comprises a memory and a processor; 5. A system for implementing the method of calculating core loss of a full speed range multiphase cobalt-iron alloy electric machine according to any one of claims 1-4, characterized in that, The memory is used to store a computer program; The processor is used to execute the computer program and realize the core loss calculation method of the full-speed-range multiphase cobalt-iron alloy motor according to any one of claims 1-4 when executing the computer program. The storage medium stores a computer program, and the computer program makes the processor execute the core loss calculation method of the full-speed-range multiphase cobalt-iron alloy motor according to any one of claims 1-4 when executed by the processor.

6. An electronic device, comprising: ​ ​ ​ 7. A storage medium, characterized by ​

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