A calculation method for PWM harmonic current and harmonic AC copper loss of permanent magnet motor

Abstract

The present invention discloses a method for calculating PWM harmonic current and harmonic AC copper loss of a permanent magnet motor. Using frequency-domain finite element calculation results, a mapping relationship between high-frequency harmonic voltage and harmonic current is established, and the relationship between high-frequency AC resistance and frequency is extracted. The harmonic current corresponding to each harmonic voltage is calculated using an incremental sensing matrix at different frequencies and rotor positions. Finally, the total spectrum of all harmonic currents is calculated using the superposition principle on a locally linearized model. The PWM harmonic AC copper loss is then calculated from the harmonic current and high-frequency AC resistance. Compared to traditional methods for calculating PWM harmonic current and harmonic AC copper loss based on transient finite elements, this method improves calculation speed while ensuring calculation accuracy.

Description

Technical Field

[0001] The present invention relates to a method for calculating the loss of a permanent magnet synchronous motor, and in particular to a method for calculating PWM harmonic current and harmonic AC copper loss of a permanent magnet motor. Background Art

[0002] To regulate the output power and speed of permanent magnet motors in real time, they are typically used in conjunction with a PWM (Pulse Width Modulated) voltage source inverter. However, the PWM harmonic currents generated by the PWM voltage source inverter generate PWM harmonic AC copper losses in the motor windings. This PWM harmonic AC copper loss significantly impacts the motor's operating efficiency, making it necessary to accurately and quantitatively calculate these PWM harmonic currents and AC losses during the motor system design phase to facilitate targeted measures to reduce losses and improve efficiency. The copper loss generated by motor operation differs from iron loss in that iron loss is primarily divided into hysteresis loss and eddy current loss, which are generated in the motor's core. Copper loss, on the other hand, describes the heat loss caused by current flowing through the motor windings. Therefore, the calculation method for copper loss is completely different from that for iron loss.

[0003] Currently, the traditional transient field-circuit coupled finite element calculation method that uses a PWM voltage source or a harmonic current source as input requires a very small step size to resolve the high-frequency PWM harmonic voltage, which makes the traditional method very time-consuming when calculating this part of the high-frequency harmonic current and loss. Summary of the Invention

[0004] Purpose of the invention: In order to solve the technical problems mentioned in the above background technology, the present invention proposes a method for calculating the PWM harmonic current and harmonic AC copper loss of a permanent magnet motor, which can improve the calculation efficiency while ensuring the calculation accuracy.

[0005] Technical solution: In order to achieve the above technical objectives, the technical solution adopted by the present invention is a permanent magnet motor PWM harmonic current, comprising the following steps:

[0006] (1) Based on the sinusoidal fundamental current of the permanent magnet motor, the transient finite element method is used to calculate the magnetic flux density distribution of the silicon steel sheet;

[0007] (2) According to the magnetic flux density distribution, the frozen frequency-varying complex increment tensor reluctance of each grid is calculated, and a frequency domain small signal model of the rotor at different positions is constructed; the calculation of the frozen frequency-varying complex increment tensor reluctance includes the following steps:

[0008] (21) Based on the DC operating point, the scalar incremental permeability is determined under low frequency conditions by using the hysteresis model of silicon steel sheets while ignoring the eddy current response.

[0009] (22) The frequency-dependent complex scalar incremental permeability is determined based on the operating frequency of the operating point and the scalar incremental permeability. The calculation formula is:

[0010]

[0011] in: is the frequency-dependent complex scalar incremental permeability, μ h is the scalar incremental permeability under low frequency conditions ignoring eddy current reaction, t is the thickness of the silicon steel sheet, △ is the skin depth, σ is the electrical conductivity of the silicon steel sheet, and f is the alternating magnetic flux density frequency;

[0012] (23) According to the relationship between the complex permeability and frequency, the frequency-dependent complex tensor incremental reluctance is obtained in combination with the vector hysteresis model.

[0013] (3) Based on the frequency domain small signal model, the time-harmonic finite element method is used to calculate the harmonic currents caused by the d-axis and q-axis harmonic voltages under separate excitation, and the incremental sensing parameters at different rotor positions under the d-axis and q-axis voltage excitation are extracted according to the excitation voltage and the harmonic current; the incremental sensing parameters corresponding to at least three typical frequencies are calculated, and the incremental sensing parameters of the rotor at any frequency at different positions are obtained by interpolation and extrapolation;

[0014] The incremental sensing parameters at different rotor positions under d-axis and q-axis voltage excitation are extracted according to the excitation voltage and the harmonic current, including the following process: when only d-axis voltage excitation is used, G is calculated according to the harmonic current. dd , G qd When only q-axis voltage is excited, G is calculated based on the harmonic current dq , G qq .

[0015] (4) An incremental sensing matrix is ​​constructed based on the incremental sensing parameters, and the d-axis and q-axis harmonic currents generated by the rotor at different positions are calculated using the incremental sensing matrix and the d-axis and q-axis harmonic voltages; the calculation formula is:

[0016]

[0017] where u dh and u qh Represents d and q axis harmonic voltages respectively, i dh and i qh Represents d-axis and q-axis harmonic currents, G dd , G dq , G qd , G dq The matrix formed is called the incremental perception matrix.

[0018] (5) Perform fast Fourier transform on the phase current generated by each harmonic voltage, and correct the harmonic current spectrum obtained by fast Fourier transforming the complex harmonic current according to the actual frequency of the harmonic voltage to obtain the actual harmonic current spectrum generated by the harmonic voltage, and superimpose it on the total PWM harmonic current spectrum.

[0019] The harmonic current spectrum obtained by performing fast Fourier transform on the complex harmonic current according to the actual frequency of the harmonic voltage is corrected by the following calculation formula:

[0020] i mod (j) = i mod (j)+i a (mod(j,N s )),

[0021] i mod (j) = i mod (j)+i a (N s ), mod(j,N s )=0

[0022] Where j represents the harmonic frequency, i mod (j) represents the actual harmonic current generated by the jth harmonic after correction, the initial value is 0, i a represents the uncorrected harmonic current calculated by the harmonic voltage and incremental sensing matrix, mod(j, N s ) represents j and N s The result obtained by taking the remainder; f h Indicates the frequency corresponding to a certain frequency harmonic voltage, f0 indicates the fundamental frequency, N s Indicates the number of different rotor positions in one complete cycle.

[0023] Based on the above-mentioned method for calculating PWM harmonic current, the present invention proposes a method for calculating PWM harmonic AC copper loss of a permanent magnet motor, comprising the following steps:

[0024] (1) Based on the sinusoidal fundamental current of the permanent magnet motor, the transient finite element method is used to calculate the magnetic flux density distribution of the silicon steel sheet;

[0025] (2) According to the magnetic flux density distribution, the frozen frequency-variable complex increment tensor reluctance of each grid is calculated to construct a frequency domain small signal model of the rotor at different positions;

[0026] (3) Based on the frequency domain small signal model, the time-harmonic finite element method is used to calculate the harmonic current and conductor copper loss caused by the d-axis and q-axis harmonic voltages under separate excitation, and the incremental sensing parameters at different rotor positions under the d-axis and q-axis voltage excitation are extracted according to the excitation voltage and the harmonic current. The AC resistance under the d-axis and q-axis harmonic voltage excitation is extracted according to the harmonic current and the conductor copper loss; the incremental sensing parameters corresponding to at least three typical frequencies are calculated, and the incremental sensing parameters of the rotor at any frequency at different positions are obtained by interpolation and extrapolation;

[0027] The AC resistance under the d-axis and q-axis harmonic voltage excitations is extracted based on the harmonic current and conductor copper loss, and the calculation formula is:

[0028] R ac d (θ r , f)=2P d / (|i ah | 2 +|i bh | 2 +|i ch | 2 )

[0029] Among them, R ac d (θ r , f) represents the AC resistance under the d-axis harmonic voltage excitation alone, P d is the total copper loss of the slot conductor calculated by time-harmonic field, i ah ,i bh ,i ch It is the three-phase current generated by the d-axis and q-axis voltages alone; the q-axis AC resistance is extracted in the same way.

[0030] (4) constructing an incremental sensing matrix according to the incremental sensing parameters, and calculating the d-axis and q-axis harmonic currents generated by the rotor at different positions using the incremental sensing matrix and the PWM voltage spectrum;

[0031] (5) Perform fast Fourier transform on the phase current generated by each harmonic voltage, and correct the harmonic current spectrum obtained by fast Fourier transforming the complex harmonic current according to the actual frequency of the harmonic voltage to obtain the actual harmonic current spectrum generated by the harmonic voltage, and superimpose it on the total PWM harmonic current spectrum;

[0032] (6) Calculate the PWM harmonic AC copper loss using the PWM harmonic current spectrum and the AC resistance.

[0033] The calculation method of the PWM harmonic AC copper loss is:

[0034]

[0035] in, Indicates PWM harmonic AC copper loss, f h Represents the frequency of a component in the current spectrum, i ah (f h ) is the amplitude of the harmonic current component, and They represent the average values ​​of the AC resistance at different rotor positions under the excitation of the d-axis and q-axis harmonic voltages respectively. Indicates the terminal resistance, f c Indicates the switching frequency.

[0036] Based on the above-mentioned method for calculating AC copper loss, the present invention proposes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the above-mentioned method for calculating the PWM harmonic AC copper loss of a permanent magnet motor are implemented.

[0037] Accordingly, the present invention further proposes a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above-mentioned method for calculating the PWM harmonic AC copper loss of a permanent magnet motor when executed by a processor.

[0038] Beneficial effect: Compared with the existing technology, the calculation method designed by the present invention does not need to use transient finite element calculation under PWM voltage power supply to calculate the harmonic current and harmonic AC copper loss caused by PWM, but only requires dozens of steps of linear frequency domain finite element calculation. Through the frequency domain finite element calculation results, the mapping relationship between high-frequency harmonic voltage and harmonic current and AC copper loss and harmonic current is established. The incremental sensing matrix and AC resistance can be obtained by using the excitation results of several special dq voltages at different frequencies. Then, the harmonic current generated by any harmonic can be obtained by using the incremental sensing matrix of the harmonic voltage at different frequencies and rotor positions. Finally, the superposition principle is applied to the locally linearized model to calculate all PWM harmonic current spectra. And the PWM harmonic AC copper loss can be calculated based on the obtained PWM harmonic current and the previously obtained AC resistance. Compared with the traditional method, the calculation speed of this method at one working point is increased by about 8 times. More importantly, after establishing the mapping relationship between harmonic voltage and harmonic current, the PWM harmonic AC copper loss can be easily obtained through AC resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of the method for calculating the PWM harmonic AC copper loss of a permanent magnet motor according to the present invention;

[0040] Figure 2 This is a flow chart for extracting incremental inductance and AC resistance under d-axis and q-axis voltage excitation according to the present invention;

[0041] Figure 3 This is a flow chart of calculating harmonic currents using an incremental susceptibility matrix according to the present invention;

[0042] Figure 4 This is the current waveform obtained by traditional transient finite element calculation under PWM line voltage power supply;

[0043] Figure 5 It is the harmonic current spectrum obtained by combining traditional transient finite element analysis with fast Fourier transform calculation under PWM voltage power supply;

[0044] Figure 6 This is a PWM harmonic current spectrum diagram quickly calculated by the method of the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] Example 1

[0047] This embodiment takes a 120-slot 20-pole permanent magnet motor as an example to calculate the PWM harmonic current of the motor. The motor speed is 1500rpm, the fundamental frequency f is 250Hz, and the current i d =-60A,i q Take the operating condition when =157.990506A as an example. The DC bus voltage of the PWM inverter is 450V, the switching frequency is 5kHz, and the SVPWM modulation strategy is adopted.

[0048] The method for calculating the PWM harmonic current of the permanent magnet motor comprises the following steps:

[0049] (1) Based on the sinusoidal fundamental current of the permanent magnet motor under the above working conditions, the transient finite element method is used to calculate the magnetic flux density distribution of the silicon steel sheet;

[0050] (2) According to the magnetic flux density distribution, the frozen frequency-varying complex increment tensor reluctance of each grid is calculated, and a frequency domain small signal model of the rotor at different positions is constructed; the calculation of the frozen frequency-varying complex increment tensor reluctance includes the following steps:

[0051] (21) Based on the DC operating point, the scalar incremental permeability is determined under low frequency conditions by using the hysteresis model of silicon steel sheets while ignoring the eddy current response.

[0052] (22) The frequency-dependent complex scalar incremental permeability is determined based on the operating frequency of the operating point and the scalar incremental permeability. The calculation formula is:

[0053]

[0054] in: is the frequency-dependent complex scalar incremental permeability, μ h is the scalar incremental permeability under low frequency conditions ignoring eddy current reaction, t is the thickness of the silicon steel sheet, △ is the skin depth, σ is the electrical conductivity of the silicon steel sheet, and f is the alternating magnetic flux density frequency;

[0055] (23) According to the relationship between the complex permeability and frequency, the frequency-dependent complex tensor incremental reluctance is obtained in combination with the vector hysteresis model.

[0056] (3) Based on the frequency domain small signal model, the time-harmonic finite element method is used to calculate the harmonic currents caused by the d-axis and q-axis harmonic voltage excitations respectively, and the incremental sensing parameters at different rotor positions under the d-axis and q-axis voltage excitations are extracted according to the excitation voltage and the harmonic current; the incremental sensing parameters corresponding to at least three typical frequencies are calculated, and the incremental sensing parameters of the rotor at any frequency at different positions are obtained by interpolation and extrapolation; the incremental sensing parameters under the d-axis and q-axis voltage excitations are extracted, and the process is as follows: Figure 2 shown.

[0057] The incremental sensing parameters at different rotor positions under d-axis and q-axis voltage excitation are extracted according to the excitation voltage and the harmonic current, including the following process: when only d-axis voltage excitation is used, G is calculated according to the harmonic current. dd , G qd When only q-axis voltage is excited, G is calculated based on the harmonic current dq , G qq .

[0058] (4) An incremental sensing matrix is ​​constructed based on the incremental sensing parameters, and the d-axis and q-axis harmonic currents generated by the rotor at different positions are calculated using the incremental sensing matrix and the d-axis and q-axis harmonic voltages; the calculation formula is:

[0059]

[0060] where u dh and u qh Represents d and q axis harmonic voltages respectively, i dh and i qh Represents d-axis and q-axis harmonic currents, G dd , G dq , G qd , G dq The matrix formed is called the incremental perception matrix.

[0061] (5) Perform fast Fourier transform on the phase current generated by each harmonic voltage, and correct the harmonic current spectrum obtained by fast Fourier transforming the complex harmonic current according to the actual frequency of the harmonic voltage to obtain the actual harmonic current spectrum generated by the harmonic voltage, and superimpose it on the total PWM harmonic current spectrum.

[0062] The harmonic current spectrum obtained by performing fast Fourier transform on the complex harmonic current according to the actual frequency of the harmonic voltage is corrected by the following calculation formula:

[0063] i mod (j) = i mod (j)+i a (mod(j,N s )),

[0064] i mod (j) = i mod (j)+i a (N s ), mod(j,N s )=0

[0065] Where j represents the harmonic frequency, i mod (j) represents the actual harmonic current generated by the jth harmonic after correction, the initial value is 0, i a represents the uncorrected harmonic current calculated by the harmonic voltage and incremental sensing matrix, mod(j, N s ) represents j and N s The result obtained by taking the remainder; f h Indicates the frequency corresponding to a certain frequency harmonic voltage, f0 indicates the fundamental frequency, N s Indicates the number of different rotor positions in one complete cycle.

[0066] Example 2

[0067] This embodiment takes a 120-slot 20-pole permanent magnet motor as an example to calculate the PWM harmonic AC copper loss of the motor. The motor speed is 1500rpm, the fundamental frequency f is 250Hz, and the current i d =-60A,i q Take the operating condition when =157.990506A as an example. The DC bus voltage of the PWM inverter is 450V, the switching frequency is 5kHz, and the SVPWM modulation strategy is adopted.

[0068] The calculation method of the permanent magnet motor PWM harmonic AC copper loss is as follows: Figure 1 As shown, the following steps are included:

[0069] Step 1: For the permanent magnet motor, the d-axis and q-axis currents required under the above operating conditions are known. Convert them into three-phase currents, A, B, C, and C. Use these as input for a transient finite element calculation of 1 / 6 cycle.

[0070] Step 2: Based on the magnetic flux density of each grid in the silicon steel sheet calculated within 1 / 6 electrical cycle in step (1), calculate the frozen frequency-variable complex incremental tensor reluctance of each grid, thereby constructing a frequency domain small signal model of the permanent magnet motor at different rotor positions.

[0071] In this embodiment, the above step 2 is implemented using the following solution:

[0072] First, according to the DC operating point B dc , using the hysteresis model of silicon steel sheets, determine the scalar incremental permeability μ under low frequency conditions, ignoring eddy current reactions h .

[0073] Then, the frequency-dependent complex scalar incremental permeability is determined according to the operating frequency and permeability of the operating point:

[0074]

[0075] Where: μ h is the incremental magnetic permeability under low frequency conditions, t is the thickness of the silicon steel sheet, Δ is the skin depth, σ is the electrical conductivity of the silicon steel sheet, and f is the alternating magnetic flux density frequency.

[0076] Finally, based on the relationship between the complex permeability and frequency and combined with the vector hysteresis model, the frequency-dependent complex tensor incremental reluctance is obtained.

[0077] Step 3: When the rotor is at different positions within 1 / 6 electrical cycle, the time-harmonic finite element method is used based on the permanent magnet motor frequency domain small signal model to calculate the harmonic current and conductor copper loss caused by the d-axis and q-axis harmonic voltage excitations respectively.

[0078] Step 4: Extract the AC resistance under the excitation of d-axis and q-axis harmonic voltages based on the three-phase ABC currents and conductor copper loss. The process of extracting the AC resistance under the excitation of d-axis and q-axis voltages is as follows: Figure 2 shown.

[0079] In this embodiment, the above step 4 is implemented using the following solution:

[0080] Given the resulting three-phase voltages A, B, C, and AC copper losses under the conditions of separate excitation of the d-axis and q-axis voltages, the d-axis or q-axis AC resistance can be extracted using the following formula:

[0081] R ac d (θ r , f)=2P d / (|i ah | 2 +|i bh | 2 +|i ch | 2 )

[0082] Among them, P d is the total AC loss of the slot conductor calculated by time-harmonic field, i ah ,i bh ,i ch is the three-phase harmonic current generated by the d-axis and q-axis voltage excitation. The same principle applies to extracting the q-axis AC resistance.

[0083] Step 5: Convert the three-phase current into the current in the d and q coordinate systems.

[0084] Step 6: Extract the incremental sensing parameters G at different rotor positions under d-axis and q-axis voltage excitation according to the d and q response currents at different rotor positions and the known input d and q excitation voltages. dd , G qd , G dq , G qq .

[0085] In this embodiment, the above step 6 is implemented using the following solution:

[0086] At high frequencies, the mapping relationship between harmonic voltage excitation and harmonic current response can be described as:

[0087]

[0088] where u dh and u qh Represents d and q axis harmonic voltages respectively, i dh and i qh Represent the d-axis and q-axis harmonic currents respectively. Here, G dd , G dq , G qd , G dq The 2×2 matrix composed of is called the incremental inductance matrix, which is the inverse matrix of the incremental inductance matrix. Consider them as frequency f and rotor electrical angle θ r When there is only d-axis voltage excitation, G can be calculated based on the harmonic current obtained from the time-harmonic field. dd , G qd Similarly, when only q-axis voltage is excited, G can be calculated dq , G qq .

[0089] Step 7: Repeat steps (3) to (6) 5 times to calculate the incremental inductance and AC resistance within 1 / 6 cycle at five typical frequencies respectively; these five frequencies are f c / 2,f c , 2f c , 4f c , 8f c , where f c is the switching frequency, fc =10000 Hz. This step can be implemented by selecting three or more typical frequencies, and here five typical frequencies are preferably used for calculation.

[0090] Step 8: Extend the incremental inductance and AC resistance to a full cycle.

[0091] Step 9: Use the stationary dq transform to calculate the d-axis and q-axis PWM voltage spectra when the rotor is at different positions.

[0092] Step 10: Use the incremental sensing matrix to calculate the d-axis and q-axis harmonic currents generated by each harmonic component in the PWM voltage spectrum at each different rotor position in the first 1 / 6 cycle. The flowchart for calculating harmonic currents using the incremental sensing matrix is ​​as follows: Figure 3 shown.

[0093] In this embodiment, the above step 10 is implemented using the following scheme:

[0094] Since the fundamental frequency is f0=250Hz, the high-frequency harmonic voltage frequency range used to verify this method is selected to be 20f0~400f0, that is, the 20th harmonic to the 400th harmonic, and the frequency range is 5000Hz~100000Hz (f c / 2~10f c ), three or more typical frequencies can be selected within this range, with five typical frequencies being preferred. When solving for harmonic currents at different subharmonic voltages, the incremental sensing matrix at the subharmonic frequency must first be obtained. By interpolating and extrapolating the incremental sensing coefficients at different rotor positions for the five existing typical frequencies, the incremental sensing coefficients at other arbitrary frequencies and different rotor positions can be obtained. The harmonic currents at different frequencies and rotor positions are then obtained based on the mapping relationship in step 6.

[0095] Step 11: Obtain the ABC three-phase currents generated by each harmonic component according to the static dq inverse transformation.

[0096] Step 12: The harmonic current spectrum obtained by performing FFT on the complex harmonic current is corrected according to the real frequency of the harmonic voltage to obtain the real harmonic current spectrum generated by the harmonic voltage, and superimposed on the total PWM harmonic current spectrum.

[0097] In this embodiment, the above step 12 is implemented using the following scheme:

[0098] The harmonic current spectrum obtained by fast Fourier transform of the complex harmonic current is corrected according to the real frequency of the harmonic voltage. The correction formula is:

[0099] i mod (j) = i mod (j)+ia (mod(j,N s )),

[0100] When mod(j, N s )=0,

[0101] i mod (j) = i mod (j)+i a (N s )

[0102] Where j represents the harmonic frequency, i mod (j) represents the actual harmonic current generated by the jth harmonic after correction, the initial value is 0, i a represents the uncorrected harmonic current calculated by the harmonic voltage and incremental sensing matrix, mod(j, N s ) represents j and N s The result obtained by taking the remainder; f h Indicates the frequency corresponding to a certain frequency harmonic voltage, f0 indicates the fundamental frequency, N s Indicates the number of different rotor positions in one complete cycle.

[0103] Step 13: Extend the harmonic current spectrum to a whole cycle.

[0104] Step 14: Calculate the PWM harmonic AC copper loss.

[0105] In this embodiment, the above step 14 is implemented using the following preferred solution:

[0106] After obtaining the PWM harmonic current spectrum for a complete cycle, the calculation method for PWM harmonic AC copper loss is:

[0107]

[0108] Where: f h Represents the frequency of a component in the current spectrum, i ah (f h ) is the amplitude of the harmonic current component, and Respectively represent R ac d (f h ,θ r ) and R ac q (f h ,θ r ) at different rotor positions. Initially, the current frequency range for calculating AC copper loss is set at f c / 2 to 10f cA reasonable upper cutoff frequency can be obtained by trying several different values ​​and performing error analysis to speed up the calculation.

[0109] Figure 4 The three-phase current waveforms obtained by traditional transient finite element calculation under PWM inverter power supply are shown, taking the operating condition of 1500r / min current id=-60A, iq=157.990506A as an example. Figure 5 The transient finite element analysis is performed using PWM voltage as input, and the harmonic current spectrum is calculated by fast Fourier transform of the current time domain waveform. Figure 6 The harmonic current spectrum obtained by the method of the present invention is shown. It can be seen that the calculation results of the two methods are very consistent. Table 1 compares the calculation time of the method of the present invention and the traditional transient finite element method. It can be seen that the calculation speed of the method of the present invention is increased by 8 times. Table 2 compares the error between the calculated harmonic AC copper loss and the actual harmonic AC copper loss. Due to the certain error in the generated PWM voltage, there is a certain numerical error between the loss generated by the PWM fundamental wave and the loss generated under sinusoidal power supply. Therefore, a certain correction is made to the loss generated under SCS power supply. FFT is performed on the current generated under PWM inverter power supply to obtain the fundamental component. Since the harmonic AC copper loss is proportional to the square of the current, the square sum of the fundamental amplitude of the ABC three-phase current under PWM power supply is divided by the square sum of the fundamental components of the ABC three-phase current under sinusoidal power supply to obtain the proportional coefficient. The loss obtained under SCS power supply is multiplied by the proportional coefficient, which is the loss generated by the actual PWM voltage fundamental wave.

[0110] Table 1 Comparison of calculation time between the method of the present invention and the traditional finite element method

[0111]

[0112] Table 2 Errors in calculating harmonic AC copper loss using the method of the present invention

[0113]

[0114] The above embodiment is described by taking an embedded permanent magnet synchronous motor as an example. The present invention is not limited to this type of permanent magnet motor, but is also applicable to all other types of permanent magnet motors such as surface mount type.

[0115] Example 2

[0116] In one embodiment, a computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the above-mentioned method for calculating the PWM harmonic AC copper loss of a permanent magnet motor are implemented.

[0117] Example 3

[0118] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned method for calculating the PWM harmonic AC copper loss of a permanent magnet motor.

[0119] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0120] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0121] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0122] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

Claims

1. A method for calculating PWM harmonic current of a permanent magnet motor, characterized in that: The following steps are involved: (1) Based on the sinusoidal fundamental current of the permanent magnet motor, the transient finite element method is used to calculate the magnetic flux density distribution of the silicon steel sheet; (2) According to the magnetic flux density distribution, the frozen frequency-variable complex increment tensor reluctance of each grid is calculated to construct a frequency domain small signal model of the rotor at different positions; (3) Based on the frequency domain small signal model, the time-harmonic finite element method is used to calculate the harmonic currents caused by the d-axis and q-axis harmonic voltages under separate excitation, and the incremental sensing parameters at different rotor positions under the d-axis and q-axis voltage excitation are extracted according to the excitation voltage and the harmonic current; the incremental sensing parameters corresponding to at least three typical frequencies are calculated, and the incremental sensing parameters of the rotor at any frequency at different positions are obtained by interpolation and extrapolation; (4) constructing an incremental sensing matrix according to the incremental sensing parameters, and calculating the d-axis and q-axis harmonic currents generated by the rotor at different positions using the incremental sensing matrix and the d-axis and q-axis harmonic voltages; (5) Perform fast Fourier transform on the phase current generated by each harmonic voltage, and correct the harmonic current spectrum obtained by fast Fourier transforming the complex harmonic current according to the actual frequency of the harmonic voltage to obtain the actual harmonic current spectrum generated by the harmonic voltage, and superimpose it on the total PWM harmonic current spectrum.

2. The method for calculating the PWM harmonic current of a permanent magnet motor according to claim 1, characterized in that: The calculation of the frozen frequency-variant complex increment tensor magnetoresistance comprises the following steps: (21) Based on the DC operating point, the scalar incremental permeability is determined under low frequency conditions by using the hysteresis model of silicon steel sheets while ignoring the eddy current response. (22) The frequency-dependent complex scalar incremental permeability is determined based on the operating frequency of the operating point and the scalar incremental permeability. The calculation formula is: in: is the frequency-dependent complex scalar incremental permeability, μ h is the scalar incremental permeability under low frequency conditions ignoring eddy current reaction, t is the thickness of the silicon steel sheet, Δ is the skin depth, σ is the electrical conductivity of the silicon steel sheet, and f is the alternating magnetic flux density frequency; (23) According to the relationship between the complex permeability and frequency, the frequency-dependent complex tensor incremental reluctance is obtained in combination with the vector hysteresis model.

3. The method for calculating PWM harmonic current of a permanent magnet motor according to claim 1, wherein: The method of extracting the incremental sensing parameters at different rotor positions under d-axis and q-axis voltage excitation respectively according to the excitation voltage and the harmonic current includes the following process: when only d-axis voltage excitation is used, G is calculated according to the harmonic current. dd , G qd When only q-axis voltage is excited, G is calculated based on the harmonic current dq , G qq .

4. The method for calculating PWM harmonic current of a permanent magnet motor according to claim 1, wherein: The d-axis and q-axis harmonic currents generated by the rotor at different positions are calculated using the incremental sensing matrix and the d-axis and q-axis harmonic voltages. The calculation formula is: where u dh and u qh Represents d and q axis harmonic voltages respectively, i dh and i qh Represents d-axis and q-axis harmonic currents, G dd , G dq , G qd , G dq The matrix formed is called the incremental perception matrix.

5. The method for calculating PWM harmonic current of a permanent magnet motor according to claim 1, wherein: The harmonic current spectrum obtained by performing fast Fourier transform on the complex harmonic current according to the actual frequency of the harmonic voltage is corrected by the following calculation formula: i mod (j)=i mod (j)+i a (mod(j,N s )), j>0 i mod (j)=i mod (j)+i a (N s ), mod(j,N s )=0 Where j represents the harmonic frequency, i mod (j) represents the actual harmonic current generated by the jth harmonic after correction, the initial value is 0, i a represents the uncorrected harmonic current calculated by the harmonic voltage and incremental sensing matrix, mod(j,N s ) represents j and N s The result obtained by taking the remainder; f h Indicates the frequency corresponding to a certain frequency harmonic voltage, f0 indicates the fundamental frequency, N s Indicates the number of different rotor positions in one complete cycle.

6. A method for calculating the PWM harmonic AC copper loss of a permanent magnet motor, characterized in that: The following steps are involved: (1) Based on the sinusoidal fundamental current of the permanent magnet motor, the transient finite element method is used to calculate the magnetic flux density distribution of the silicon steel sheet; (2) According to the magnetic flux density distribution, the frozen frequency-variable complex increment tensor reluctance of each grid is calculated to construct a frequency domain small signal model of the rotor at different positions; (3) Based on the frequency domain small signal model, the time-harmonic finite element method is used to calculate the harmonic current and conductor copper loss caused by the d-axis and q-axis harmonic voltages when they are excited separately. The incremental sensing parameters at different rotor positions under the d-axis and q-axis voltage excitations are extracted according to the excitation voltage and the harmonic current. The AC resistance under the d-axis and q-axis harmonic voltage excitations is extracted according to the harmonic current and the conductor copper loss. Calculate the incremental sensing parameters corresponding to at least three typical frequencies, and use interpolation and extrapolation methods to obtain the incremental sensing parameters of any frequency at different rotor positions; (4) constructing an incremental sensing matrix according to the incremental sensing parameters, and calculating the d-axis and q-axis harmonic currents generated by the rotor at different positions using the incremental sensing matrix and the PWM voltage spectrum; (5) Perform fast Fourier transform on the phase current generated by each harmonic voltage, and correct the harmonic current spectrum obtained by fast Fourier transforming the complex harmonic current according to the actual frequency of the harmonic voltage to obtain the actual harmonic current spectrum generated by the harmonic voltage, and superimpose it on the total PWM harmonic current spectrum; (6) Calculate the PWM harmonic AC copper loss using the PWM harmonic current spectrum and the AC resistance.

7. The method for calculating the PWM harmonic AC copper loss of a permanent magnet motor according to claim 6, characterized in that: The AC resistance under the d-axis and q-axis harmonic voltage excitations is extracted based on the harmonic current and conductor copper loss, and the calculation formula is: R ac d (θ r ,f)=2P d / (|i ah | 2 +|i bh | 2 +|i ch | 2 ) Among them, R ac d (θr r ,f) represents the AC resistance under the d-axis harmonic voltage excitation alone, P d is the total copper loss of the slot conductor calculated by time-harmonic field, i ah ,i bh ,i ch It is the three-phase current generated by the d-axis and q-axis voltages alone; the q-axis AC resistance is extracted in the same way.

8. The method for calculating the PWM harmonic AC copper loss of a permanent magnet motor according to claim 6, characterized in that: The calculation method of the PWM harmonic AC copper loss is: in, Indicates PWM harmonic AC copper loss, f h Represents the frequency of a component in the current spectrum, i ah (f h ) is the amplitude of the harmonic current component, and They represent the average values ​​of the AC resistance at different rotor positions under the excitation of the d-axis and q-axis harmonic voltages respectively. Indicates the terminal resistance, f c Indicates the switching frequency.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method for calculating the PWM harmonic AC copper loss of the permanent magnet motor according to any one of claims 6 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for calculating the PWM harmonic AC copper loss of a permanent magnet motor according to any one of claims 6 to 8 are implemented.

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