Advanced pulse width modulation method and device for minimizing torque ripple

Abstract

The invention relates to the technical field of pulse width modulation, in particular to an advanced pulse width modulation method and device for minimizing torque ripple, and the method comprises the steps: constructing a stator flux linkage offline calculation model; reconstructing a motor output torque waveform based on the stator flux linkage offline calculation model; constructing a transcendental equation set taking the minimum torque ripple as a target based on the motor output torque waveform; and calculating an initial value of a transcendental equation set by using a low-order torque harmonic minimum principle, solving the transcendental equation set based on the initial value of the transcendental equation set, obtaining a switching angle table with minimum torque fluctuation, and completing pulse width modulation through the switching angle table. The torque reconstruction method and the torque ripple minimum pulse width modulation strategy can be widely applied to the industrial field, and the operation reliability and safety of the motor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pulse width modulation, and particularly to an advanced pulse width modulation method and device for minimizing torque ripple. Background Art

[0002] In a traction speed control system, due to limitations of switching losses and heat dissipation conditions, the switching devices of an inverter usually operate at a frequency lower than 1 kHz. At such a low frequency, the system operates under a low carrier ratio condition, resulting in an increase in system harmonic content. If only traditional pulse width modulation strategies are adopted, it will lead to a serious decline in the harmonic characteristics of the system. Excessive harmonic content in the output waveform of the inverter will increase motor losses, raise the temperature, and cause fluctuations in motor torque. To maintain the harmonic performance of the system, a relatively large filter usually needs to be installed, but this will not only reduce the efficiency of the inverter but also may cause low-frequency resonance. To solve this problem, adopting a specific pulse width modulation strategy (Pulsewidth modulation, PWM) can reduce torque ripple, optimize current THD, improve system efficiency, and reduce the demand for filters. For the special modulation mode under a low carrier ratio, there are already various solutions. Among them, the synchronous optimization modulation mode has been widely applied due to its flexible optimization target configuration and excellent steady-state performance.

[0003] The optimized modulation mode is a modulation technique that distributes the inverter switching time through fixed targets. This modulation technique calculates the switching angles based on specific targets and stores them in the controller memory in the form of a table. When the control system needs to output PWM, the switching angle table is called in real time. Currently, the relatively mature one is the Selected Harmonic Elimination PWM (SHEPWM). SHEPWM decomposes the periodic PWM voltage waveform through Fourier technology and calculates the switching angles for eliminating the selected low-order harmonics. However, SHEPWM has two defects. The first is that eliminating low-order harmonics may increase the amplitudes of adjacent high-order harmonics, which not only leads to an increase in the current harmonic distortion rate but also causes a significant rise in torque ripple. The second is that SHEPWM cannot directly suppress torque ripple. Even though SHEPWM can indirectly optimize torque ripple by suppressing low-order harmonics, it cannot achieve the minimum torque ripple. Another existing technical solution is the Current Harmonic Minimization PWM (CHMPWM). This modulation mode aims to minimize the current harmonic distortion rate. The configured switching sequence can minimize the THD in the load, which is helpful for high-performance closed-loop control and comprehensively optimizes multiple aspects such as the harmonic loss, torque ripple, and current peak of the system. However, it still cannot directly optimize torque ripple. The optimization target of CHMPWM is the magnitude of the current THD, and the switching sequence calculated according to this technical solution cannot achieve the minimum torque ripple. Therefore, the present invention proposes an advanced pulse width modulation method and device for minimizing torque ripple. Summary of the Invention

[0004] The object of the present invention is to provide an advanced pulse width modulation method and device for minimizing torque ripple, reducing torque fluctuation, and improving the operation reliability and safety of the motor.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] An advanced pulse width modulation method for minimizing torque ripple, comprising:

[0007] Constructing an off-line calculation model of the stator flux linkage;

[0008] Reconstructing the motor output torque waveform based on the off-line calculation model of the stator flux linkage;

[0009] Constructing a transcendental equation set with the minimum torque fluctuation as the target based on the motor output torque waveform;

[0010] Calculate the initial values of the transcendental equations using the principle of minimizing the low-order torque harmonics, and solve the transcendental equations based on the initial values of the transcendental equations to obtain a switching angle table with the minimum torque ripple. Complete pulse width modulation through the switching angle table.

[0011] Optionally, construct the stator flux linkage offline calculation model as:

[0012]

[0013] where, ψ s (θ) is the stator flux linkage within one fundamental wave period, θ is the fundamental wave phase, is the desired stator flux linkage, M is the modulation index, is the coordinate transformation matrix, U abc is the reconstructed three-phase stator voltage of the motor, ψ off is the bias of the stator flux linkage during the reconstruction process.

[0014] Optionally, reconstruct the motor output torque waveform based on the stator flux linkage offline calculation model, including:

[0015] Obtain the reconstructed stator flux linkage based on the stator flux linkage offline calculation model;

[0016] Calculate the stator flux linkage vector phase and the angle between the stator and rotor, and construct a torque waveform reconstruction model;

[0017] Obtain the reconstructed motor output torque waveform based on the torque waveform reconstruction model.

[0018] Optionally, the torque waveform reconstruction model is:

[0019]

[0020] where, T e is the reconstructed motor torque, N p is the number of pole pairs of the motor, X m is the mutual inductance of the motor, σ is the leakage inductance coefficient, X s is the stator inductance, X r is the rotor inductance, ψ r is the rotor flux linkage vector.

[0021] Optionally, construct a transcendental equation with the goal of minimizing torque ripple based on the motor output torque waveform, including:

[0022] After obtaining the reconstructed motor output torque waveform, construct the transcendental equation with the torque ripple magnitude as the goal and the relationship between the desired fundamental wave voltage and the switching angle sequence as the constraint.

[0023] Optionally, the transcendental equation is:

[0024]

[0025] Among them, J opt is the cost function for torque ripple minimization, is the amplitude of torque fluctuation in one fundamental wave period, M is the modulation index, and α i is the switching angle, and N is the number of switching angles.

[0026] Optionally, using the principle of minimizing low-order torque harmonics to calculate the initial value of the transcendental equation set as:

[0027]

[0028] Among them, I 6k+1 is the 6k + 1 order current harmonic, and I 6k-1 is the 6k - 1 order current harmonic.

[0029] Optionally, based on the initial value of the transcendental equation set, solve the transcendental equation set to obtain the switching angle table with the minimum torque fluctuation, including:

[0030] Use the interior point method to solve the transcendental equation set, and at the same time optimize the solution process based on the initial value of the transcendental equation set to obtain the final solution of each modulation degree, and construct the switching angle table with the minimum torque fluctuation.

[0031] To further achieve the above object, the present invention also provides an advanced pulse width modulation device for minimizing torque ripple, including:

[0032] A model construction module for constructing an off-line calculation model of the stator magnetic flux;

[0033] A torque reconstruction module for reconstructing the motor output torque waveform based on the off-line calculation model of the stator magnetic flux;

[0034] A transcendental equation set construction module for constructing a transcendental equation set with the goal of minimizing torque fluctuation based on the motor output torque waveform;

[0035] An initial value calculation module for calculating the initial value of the transcendental equation set using the principle of minimizing low-order torque harmonics;

[0036] A transcendental equation set solving module for solving the transcendental equation set based on the initial value of the transcendental equation set to obtain the switching angle table with the minimum torque fluctuation, and completing pulse width modulation through the switching angle table.

[0037] The beneficial effects of the present invention are:

[0038] The torque reconstruction method and the torque ripple minimum PWM modulation strategy proposed by the present invention can be widely applied to the industrial field, improving the operation reliability and safety of motors. The application scope of the present invention is wide. By reducing the vibration at the motor shaft end, it can effectively reduce mechanical vibration noise, thereby extending the service life of the equipment. These improvements not only enhance the performance of the equipment, but also have a positive impact on the social and economic levels. Specifically, the application of the present invention can reduce maintenance costs, improve transportation efficiency, and reduce energy consumption, thus having significant advantages in terms of social value and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0040] Figure 1 Flowchart of an advanced pulse width modulation method for minimizing torque ripple according to an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of the stator flux linkage in the simulation and the reconstructed stator flux linkage according to an embodiment of the present invention;

[0042] Figure 3 Schematic diagram of the motor output torque in the simulation and the reconstructed motor output torque according to an embodiment of the present invention;

[0043] Figure 4 Schematic diagram of the switching angle solution set according to an embodiment of the present invention;

[0044] Figure 5 Schematic diagram of the experimental platform according to an embodiment of the present invention;

[0045] Figure 6 Torque fluctuation comparison diagram when the modulation index M is 0.85 according to an embodiment of the present invention;

[0046] Figure 7 Torque fluctuation comparison diagram when the modulation index M is 0.95 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0048] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] This embodiment provides an advanced pulse width modulation method for minimizing torque ripple, as Figure 1 shown, including:

[0050] Construct an offline calculation model of the stator flux linkage;

[0051] Reconstruct the motor output torque waveform based on the offline calculation model of the stator flux linkage;

[0052] Construct a transcendental equation set with the goal of minimizing torque fluctuation based on the motor output torque waveform;

[0053] Calculate the initial value of the transcendental equation set using the principle of minimizing low-order torque harmonics, and solve the transcendental equation set based on the initial value of the transcendental equation set to obtain a switching angle table with the minimum torque fluctuation, and complete pulse width modulation through the switching angle table.

[0054] Specifically, the torque reconstruction method and the minimum torque ripple PWM modulation strategy proposed in this embodiment can be widely applied in the industrial field to improve the operation reliability and safety of the motor. The application scope of this embodiment is wide. By reducing the vibration at the motor shaft end, mechanical vibration noise can be effectively reduced, and thus the service life of the equipment can be extended. These improvements not only enhance the performance of the equipment, but also have a positive impact on the social and economic aspects. The application of this embodiment can reduce maintenance costs, improve transportation efficiency, and reduce energy consumption, thus having significant advantages in terms of social value and economic value.

[0055] Specifically, it includes the following content:

[0056] (1) Construct an offline calculation model of the stator flux linkage: When considering the stator voltage of the inverter connected to the motor, the stator flux linkage is deduced based on the three-phase switching states output by the inverter.

[0057] When considering the stator voltage of the inverter connected to the motor, the stator flux trajectory can be deduced from the three-phase switching waveforms U abc output by the inverter. The three-phase stator voltage U abc of the motor is reconstructed through the following formula:

[0058] U abc (ω s t) = f(α 1 ,...α i ,ω s ,t), i = 1, 2, 3,..., N;

[0059] In the case of ignoring the bus voltage fluctuation, the three-phase stator voltages in the stationary reference frame are obtained by the following formula:

[0060]

[0061] where is the coordinate transformation matrix. When the motor speed is relatively high, the voltage drop across the stator resistance can be ignored, and the stator flux linkage is equal to the integral of the voltage vector. A fundamental wave period stator flux linkage is obtained according to the following formula:

[0062]

[0063] where ψ s (t) represents the stator flux linkage vector at time t. By mapping the variable t in the integral to the variable θ, the stator flux expression can be obtained as a function of the angular variable θ:

[0064]

[0065] Using the relationship between the modulation index M and the expected amplitude of the stator flux linkage The expression of the stator flux linkage relative to the modulation degree and the reference flux linkage is obtained by the following formula:

[0066]

[0067] Since the purpose of this embodiment is to calculate the switching angle table offline, the calculation process is for a complete fundamental wave period, i.e., θ ∈ [0, 2π], and real-time applications do not need to be considered. The stator flux linkage within a fundamental wave period for offline calculation is obtained by the following formula:

[0068]

[0069] There will be a bias in the offline calculation of this stator flux linkage, and the bias is:

[0070]

[0071] Finally, the offline calculation model of the stator flux linkage is obtained:

[0072]

[0073] (2) Reconstruct the motor output torque: Reconstruct the complete waveform of the motor output torque in a fundamental wave period based on the reconstructed stator flux linkage.

[0074] Obtain the reconstructed stator flux linkage based on the offline calculation model of the stator flux linkage; calculate the phase of the stator flux linkage vector and the angle between the stator and the rotor, and construct a torque waveform reconstruction model; obtain the reconstructed motor output torque waveform based on the torque waveform reconstruction model.

[0075] In this step, the torque expression of the induction motor is obtained by the following formula:

[0076]

[0077] where ψ s =[ψ sα ψ sβ T is the stator flux vector, ψ r =[ψ rα ψ rβ T is the rotor flux vector, and γ is the angle between the stator flux vector and the rotor flux. Since the rotor flux has a relatively large time constant, it can be considered to remain unchanged during actual operation, forming an ideal flux circle. The torque ripple of the motor is mainly determined by the magnitude of the stator flux and the angle between the stator and rotor fluxes.

[0078] In addition, using the torque equation, after obtaining the angle between the stator flux and the rotor flux, the torque can be reconstructed from the stator flux vector result. The angle between the stator and rotor flux vectors can be expressed as:

[0079]

[0080] The phase of the stator flux vector can be obtained through the relationship in the stationary coordinate system. The phase of the stator flux vector is calculated by the following formula:

[0081]

[0082] In the rotor flux oriented system, the angle of the rotor flux is equal to the fundamental wave phase, that is Furthermore, the angle between the stator and rotor is obtained by the following formula:

[0083]

[0084] The stator flux is a function of θ, and the finally reconstructed motor torque is obtained by the following formula:

[0085]

[0086] In addition, the change in the length of the stator flux also affects the torque ripple. However, under traction conditions, due to the large rotational inertia, in order to maintain the required stator flux amplitude of the motor, the modulation index is usually adjusted proportionally to the stator frequency.

[0087] (3) Construct a transcendental equation set based on minimum torque ripple: Preset the output torque ripple of the induction motor as the objective function, and construct a transcendental equation set based on minimum torque ripple according to the relationship between the desired fundamental wave voltage constraint and the switching angle sequence size.

[0088] ​​After obtaining the reconstructed motor output torque waveform, taking the torque ripple magnitude as the objective and the relationship between the desired fundamental voltage and the switching angle sequence as the constraint, the transcendental equations are constructed.

[0089] During the construction implementation process, by substituting the switching angle and phase into the formula, the torque waveform of one fundamental period can be reconstructed. The torque ripple amplitude of one fundamental period is calculated by the following formula:

[0090]

[0091] In this torque ripple model, all other parameters are known variables, and the torque ripple model is completely a function of U abc In optimizing the synchronous modulation mode, U abc is a function of the switching angle α i ; therefore, the magnitude of the torque ripple is completely determined by the switching angle distribution α i .

[0092] The above can complete the reconstruction of the torque waveform of one fundamental period. The maximum and minimum values of the torque can only be calculated after the torque reconstruction is completed. The torque ripple can be expressed as a function of the motor parameters, inverter parameters, and pulse modulation. Specifically, the expression of the torque ripple consists of two components. The first is a constant scaling factor, and its expression is:

[0093]

[0094] It involves the DC bus voltage, motor parameters, and fundamental frequency. This component depends on the voltage level and the type of motor model. The second component depends on the pulse modulation. Different pulse modulation schemes have different switching angles, and the voltage sequence U abc in the equation is completely determined by the pulse modulation. Finding the switching angle that generates the minimum torque ripple is actually an optimization problem subject to two sets of conditions. The cost function with the torque ripple magnitude as the objective is obtained by the following formula:

[0095]

[0096] In the motor control system, in addition to meeting the optimization objective of harmonic performance, there are also two strong constraints; the first is that the final amplitude of the fundamental voltage component in the pulse mode must be equal to the expected value. The constraint for satisfying the modulation index M is obtained by the following formula:

[0097]

[0098] The switching angles must follow an increasing sequence. The constraint for satisfying the switching angle sequence relationship is obtained by the following formula:

[0099]

[0100] Finally, the present invention constructs a transcendental equation set with the minimum torque ripple as the optimization objective:

[0101]

[0102] Solving this equation set can obtain the switch angle combination with the minimum torque ripple. This transcendental equation set is applicable to all cases with different numbers of switch angles. As can be seen from the above formula, the technical solution for solving the optimal pulsating switch angle proposed by the present invention does not depend on specific motor parameters, and its solution has the same effect when applied above any induction point.

[0103] (4) Solving the switch angle table characterized by the minimum torque ripple: Derive the solution process of the transcendental equation set, and based on the optimization algorithm, solve the switch angle table that satisfies the minimum torque ripple, and set the initial value given scheme.

[0104] Calculate the initial value of the transcendental equation set according to the principle of the minimum low-order torque harmonic, and use the interior point method to solve the transcendental equation set based on the calculated initial value of the transcendental equation set to obtain the switch angle table with the minimum torque ripple, and complete the pulse width modulation through the switch angle table.

[0105] After completing the construction of the above transcendental equation, it is necessary to solve this equation set. Solving this transcendental equation is essentially a non-linear programming problem with both equality constraints and inequality constraints. In this embodiment, the interior point method is used to solve this non-linear optimization problem. Since the solution of the interior point method is seriously affected by the initial value, in the optimization process, the following two key sub-steps are taken in this embodiment to accurately determine the optimal switch angle.

[0106] Sub-step 1: First, the torque harmonic expression can be obtained through the following formula:

[0107]

[0108] Calculate the initial value of the transcendental equation set using the principle of the minimum low-order harmonic, that is, the initial value of the switch angle,

[0109]

[0110] Sub-step 2: Next, according to the preliminary solution set of each modulation index interval, set the initial value of the switch angle for specific different modulation index intervals, so as to obtain the final solution of each modulation index. These final solutions represent the optimized switch angles, ensuring the efficiency and accuracy of the PWM modulation strategy.

[0111] (5) Generate PWM based on the switch angle table; According to the given voltage and determine the frequency and duty cycle of the PWM, and use the enhanced ePWM module of DSP28335 to configure the pulse generation.

[0112] The method of generating PWM based on the switching angle table generally involves the following steps:

[0113] (5.1) Determine the frequency and duty cycle of PWM: The frequency and duty cycle of PWM can be controlled by the values of the carrier period and duty cycle. Specifically, the counter increments by one cycle size in each system clock cycle. When the value of the counter is less than the duty cycle, the output PWM is 0; when the value of the counter is greater than or equal to the duty cycle, the output PWM is set to 1.

[0114] (5.2) Calculate the PWM parameters: The period and frequency of PWM can be calculated from the period and frequency of the system clock.

[0115] (5.3) Configure pulse generation using the enhanced ePWM module of DSP28335: In the DSP28335 microcontroller, PWM can be generated by configuring the timer. When programming to achieve PWM output, the duty cycle of PWM can be adjusted by setting the count comparison value of the timer.

[0116] The following combines Figures 2 - 7 to specifically implement and verify an advanced pulse width modulation method for minimizing torque ripple proposed in this embodiment, as follows:

[0117] (1) Construct a torque reconstruction model based on the switching angle and verify it with the Simulink simulation results;

[0118] In the electrical simulation of Simulink, the corresponding environment is available to simulate the induction motor and the actual motor torque can be output. The motor library of Simulink is highly recognized in the field involved in the present invention. Therefore, the torque reconstruction model based on the switching angle constructed in this embodiment will be verified in Simulink. First, compare whether the torque waveforms reconstructed offline with specific switching angles are consistent with the torque waveforms output by the simulation results. This implementation scheme includes three key steps: reconstructing the voltage waveform, reconstructing the magnetic flux waveform, and reconstructing the torque waveform.

[0119] When selecting the number of switching angles N = 2 for torque waveform reconstruction, the power of the induction motor used in the simulation is 1.1 kW, the bus voltage is 300 V, the rated frequency is 50 Hz, the stator resistance is 1.696 Ω, the rotor resistance is 1.364 Ω, the stator inductance is 0.103 H, the rotor inductance is 0.103 H, the mutual inductance is 0.941 H, and the moment of inertia of the motor is 0.12 kg·m 2 . The selected simulation condition is that the given modulation degree is 0.90 and the given stator frequency is 45 Hz. At this time, the switching angles α 1 = 21.0699, α 2 = 27.9762 (°), and the reconstructed waveform of the stator magnetic flux is as shown in Figure 2As shown. Torque reconstruction is an optimal technical solution. The torque waveform obtained by the torque waveform reconstruction method proposed in this embodiment is compared with the Simulink simulation output waveform as Figure 3 shown.

[0120] (2) Construct a switching angle calculation scheme for the modulation strategy with the minimum torque ripple;

[0121] After verifying the effectiveness of the torque waveform reconstruction strategy in Simulink, implement the modulation strategy with the minimum torque ripple. Calculate the torque ripple according to the proposed torque ripple calculation model with respect to the switching angle. Construct a constraint equation that satisfies the fundamental voltage expectation value, construct a constraint equation that the switching angle must follow an increasing sequence, and establish a cost function with the torque ripple as the optimization objective. The general interior point method is selected as the solution method. Select the number of switching angles N = 2 to solve the minimum torque ripple switching angle table. The initial values of the switching angles for different modulation depths are calculated by the following formula as shown below:

[0122]

[0123] Substitute the calculated switching angles as the initial values into the optimization solution process of the following transcendental equation:

[0124]

[0125] During the operation of the motor, the switching angle table is called by the modulation depth, that is, the ratio of the given fundamental voltage amplitude to the bus voltage. The solution set of the switching angles within the full modulation depth range obtained by the solution is as Figure 4 shown.

[0126] (3) Experimental analysis and comparative verification based on MCU as DSP28335;

[0127] Conduct experimental verification in the experimental platform that has been built in the laboratory. The experimental platform consists of a core controller, a power driver, a power supply, an induction motor, and measuring equipment. The core controller is the floating-point operation chip DSP28335 of Texas Instruments, and the V / F part of the control algorithm is executed by DSP28335; the power drive device selects the EVAL-M1-IM828-A drive module of Infineon Technologies, which combines six 1200V CoolSiC TMA MOSFET and an optimized 6-channel SOI gate driver, applicable to three-phase motor drive; the power supply is powered by a regulated DC power supply with a bus voltage of 300V; the induction motor is selected as the ABB motor M2BAF - 1.1KW, the power of the used induction motor is 1.1kW, the rated frequency is 50Hz, the stator resistance is 1.696Ω, the rotor resistance is 1.364Ω, the stator inductance is 0.103H, the rotor inductance is 0.103H, and the mutual inductance is 0.941H, and the moment of inertia of the motor is 0.12kg·m 2 The experimental test equipment is a 6-channel oscilloscope of Tektronix MSO464 - BW - 200 with a sampling rate of 6.25GS / s. The current probe uses TCP0030A with a probe bandwidth of 120MHz, and the measurement error range is plus or minus 0.5‰. The experimental platform is as Figure 5 shown. Two target operating conditions with modulation indices of 0.85 and 0.95 are selected respectively, and the torque ripple magnitudes of the modulation strategy proposed in this embodiment are compared with those of the traditional modulation strategies SHEPWM and CHMPWM respectively to verify the effectiveness of the strategy proposed in this embodiment. The experimental comparison results of the two target operating conditions with modulation indices of 0.85 and 0.95 are as Figure 6 and Figure 7 shown.

[0128] To further optimize the technical solution, this embodiment also provides an advanced pulse width modulation device for minimizing torque ripple, including:

[0129] A model construction module for constructing an off-line calculation model of the stator flux linkage;

[0130] A torque reconstruction module for reconstructing the motor output torque waveform based on the off-line calculation model of the stator flux linkage;

[0131] A transcendental equation construction module for constructing a transcendental equation with the goal of minimizing torque ripple based on the motor output torque waveform;

[0132] An initial value calculation module for calculating the initial value of the transcendental equation using the principle of minimizing low-order torque harmonics;

[0133] A transcendental equation solving module for solving the transcendental equation based on the initial value of the transcendental equation to obtain a switching angle table with the minimum torque ripple, and completing pulse width modulation through the switching angle table.

[0134] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An advanced pulse width modulation method for minimizing torque ripple, characterized in that: include: Construct stator flux offline calculation model; Reconstructing the motor output torque waveform based on the stator flux offline calculation model; Based on the motor output torque waveform, a transcendental equation group is constructed with the goal of minimizing torque fluctuation; The initial values ​​of the transcendental equations are calculated using the minimum low-order torque harmonic principle, and the transcendental equations are solved based on the initial values ​​to obtain a switching angle table with the minimum torque fluctuation, and pulse width modulation is completed through the switching angle table.

2. The advanced pulse width modulation method for minimizing torque ripple according to claim 1, characterized in that: The stator flux offline calculation model is constructed as follows: Among them, ψ s (θ) is the stator flux in one fundamental wave period, θ is the fundamental wave phase, is the desired stator flux, M is the modulation index, is the coordinate transformation matrix, U abc is the three-phase stator voltage of the reconstructed motor, ψ off is the bias of the stator flux during the reconstruction process.

3. The advanced pulse width modulation method for minimizing torque ripple according to claim 1, characterized in that: Reconstructing the motor output torque waveform based on the stator flux offline calculation model includes: Acquiring a reconstructed stator flux based on the stator flux offline calculation model; Calculate the stator flux vector phase and the angle between the stator and rotor to build a torque waveform reconstruction model; A reconstructed motor output torque waveform is obtained based on the torque waveform reconstruction model.

4. The advanced pulse width modulation method for minimizing torque ripple according to claim 3, characterized in that: The torque waveform reconstruction model is: Among them, T e is the reconstructed motor torque, N p is the number of motor pole pairs, X m is the motor mutual inductance, σ is the leakage inductance coefficient, X s is the stator inductance, X r is the rotor inductance, ψ r is the rotor flux vector.

5. The advanced pulse width modulation method for minimizing torque ripple according to claim 1, characterized in that: The transcendental equations for minimizing torque fluctuation based on the motor output torque waveform include: After obtaining the reconstructed motor output torque waveform, the transcendental equation group is constructed with the torque fluctuation size as the target and the expected fundamental voltage and the switching angle sequence relationship as the constraint.

6. The advanced pulse width modulation method for minimizing torque ripple according to claim 5, characterized in that: The transcendental equations are: Among them, J opt is the cost function for minimizing the torque ripple, is the torque fluctuation amplitude of a fundamental wave cycle, M is the modulation index, α i is the switching angle, and N is the number of switching angles.

7. The advanced pulse width modulation method for minimizing torque ripple according to claim 6, characterized in that: The initial value of the transcendental equations is calculated using the minimum principle of low-order torque harmonics as follows: Among them, I 6k+1 is 6k+1th current harmonic, I 6k-1 It is 6k-1 current harmonic.

8. The advanced pulse width modulation method for minimizing torque ripple according to claim 7, characterized in that: Solving the transcendental equations based on the initial values ​​of the transcendental equations to obtain a switching angle table with the minimum torque fluctuation includes: The transcendental equations are solved by the interior point method, and the solution process is optimized based on the initial values ​​of the transcendental equations to obtain the final solution of each modulation index and construct a switching angle table with the minimum torque fluctuation.

9. An advanced pulse width modulation device for minimizing torque ripple, characterized in that: include: Model building module, used to build stator flux offline calculation model; A torque reconstruction module, used for reconstructing the motor output torque waveform based on the stator flux offline calculation model; A transcendental equation group construction module, used for constructing a transcendental equation group with the goal of minimizing torque fluctuation based on the motor output torque waveform; An initial value calculation module is used to calculate the initial value of the transcendental equation group using the minimum principle of low-order torque harmonics; The transcendental equations solving module is used to solve the transcendental equations based on the initial values ​​of the transcendental equations, obtain a switching angle table with the minimum torque fluctuation, and complete pulse width modulation through the switching angle table.

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