Modulation compensation method and device based on synchronous SVPWM

Abstract

The present invention provides a modulation index compensation method based on synchronous SVPWM, comprising: presetting a theoretical modulation index, and determining a sampling angle according to a frequency division number and a preset modulation strategy; calculating a comparison value at the sampling angle according to the theoretical modulation index; calculating a U-phase voltage pulse switching angle according to the comparison value; calculating an actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle; calculating an actual output line voltage effective value according to the actual phase voltage fundamental peak value; calculating an actual modulation index according to a ratio of the actual output line voltage effective value to a DC bus voltage; determining a formula for calculating the theoretical modulation index through the actual modulation index, obtaining a theoretical modulation index corresponding to each actual modulation index under each frequency division number, and storing a corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3; in application, querying the corresponding relationship through the current demand modulation index to obtain the corresponding current theoretical modulation index, so as to compensate for the current demand modulation index.

Description

Technical Field

[0001] The present invention relates to the technical field of digital signal processing, and in particular to a modulation index compensation method and device based on synchronous space vector pulse width modulation (SVPWM). Background Art

[0002] High-power traction drive systems, such as those used in EMUs and subways, feature high voltages and high currents, resulting in significant power device losses. However, the power modules have limited heat dissipation capabilities, and the system's maximum switching frequency is typically limited to below a few hundred hertz. Furthermore, some motors have a large number of pole pairs, requiring a fundamental frequency exceeding 250Hz. Therefore, to improve output voltage symmetry and reduce current harmonic distortion, synchronous modulation is employed in medium and high-speed sections.

[0003] Synchronous SVPWM, as a near-optimal modulation strategy, features a simple algorithm, consumes minimal computing resources, and is easily digitally implemented. It can flexibly implement a variety of modulation strategies based on the number of sampling angles, their positions, and the order in which the sampling angle vectors are applied. Selecting the appropriate modulation method can reduce current harmonics, current spikes, and electromagnetic noise. Therefore, synchronous SVPWM remains widely used in traction drive systems.

[0004] However, when the synchronous SVPWM frequency division number is small, the actual generated flux trajectory deviates greatly from the reference flux circle, resulting in a certain difference between the actual modulation index and the theoretical modulation index. If it is directly adopted, it will cause the decoupling current to fail to keep up, the torque control to deviate, and the current to have a certain impact and be prone to overcurrent due to the discontinuous modulation index during frequency cutting. Therefore, in practical applications, it is necessary to compensate and correct the actual modulation index when the frequency division number is small. The existing method uses the required modulation index multiplied by the maximum theoretical modulation index for compensation when the frequency division number is greater than 3. The actual modulation index calculated by this method is approximately linear with the theoretical modulation index, based on the ratio of the actual modulation index to the maximum achievable modulation index with the current frequency division. However, in practice, the actual modulation index and the theoretical modulation index have a nonlinear relationship, which inevitably leads to deviations during application and affects control. When the frequency division number exceeds 3, it is difficult to determine the compensation formula, and existing methods do not address nonlinear compensation. Therefore, given these issues, the segmented synchronous SVPWM modulation index nonlinear compensation method is particularly important. Summary of the Invention

[0005] An object of the embodiments of the present invention is to provide a modulation degree compensation method and apparatus based on synchronous SVPWM, so as to perform synchronous SVPWM modulation degree nonlinear compensation.

[0006] In a first aspect, the present invention provides a modulation index compensation method based on synchronous SVPWM, the method comprising:

[0007] Preset theoretical modulation index, and determine the sampling angle according to the frequency division number and preset modulation strategy;

[0008] Calculating the comparison value at the sampling angle according to the theoretical modulation index;

[0009] Calculating the U-phase voltage pulse switching angle according to the comparison value;

[0010] Calculating the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle;

[0011] Calculating the actual output line voltage effective value according to the actual phase voltage fundamental peak value;

[0012] Calculate the actual modulation index based on the ratio of the actual output line voltage RMS value to the DC bus voltage;

[0013] Determine a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula, and store the corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3;

[0014] In the application, the corresponding relationship is queried through the current demand modulation degree to obtain the current theoretical modulation degree corresponding to the current demand modulation degree, and the current theoretical modulation degree is used as the compensation modulation degree to compensate the current demand modulation degree.

[0015] In a possible implementation, the comparison value includes two non-zero vector action times and one zero vector action time, and calculating the comparison value at the sampling angle according to the theoretical modulation index specifically includes:

[0016] According to the sampling angle, the modulation period and the theoretical modulation degree, two non-zero vector action times and one zero vector action time at the sampling angle are calculated.

[0017] In one possible implementation, when the frequency division number is greater than 3, determining a formula for calculating the theoretical modulation degree by deriving the actual modulation degree, obtaining the theoretical modulation degree corresponding to each actual modulation degree under each frequency division number by using the formula, and storing the corresponding relationship between the actual modulation degree and the theoretical modulation degree when the frequency division number is greater than 3 specifically includes:

[0018] Assign an initial value to the actual modulation index in the formula, and calculate a theoretical modulation index through calculation tools;

[0019] According to a preset step size, the actual modulation index is incremented from an initial value to obtain a theoretical modulation index after each increment;

[0020] The actual modulation index and the corresponding theoretical modulation index after each increment are stored.

[0021] In a possible implementation, storing the actual modulation index and the corresponding theoretical modulation index after each increment specifically includes:

[0022] The initial value of the actual modulation index is used as the first element in the first array, and the theoretical modulation index corresponding to the initial value is used as the second element in the first array;

[0023] The actual modulation index after each increment of the initial value is used as the first element in the subsequent array, and the corresponding theoretical modulation index is used as the second element in the array; the number of arrays is the number of increments plus 1.

[0024] In a possible implementation, the method further includes:

[0025] When the frequency division number is 3, according to the formula Derive theoretical modulation;

[0026] Among them, m is the actual modulation index, and m' is the theoretical modulation index.

[0027] In a possible implementation, the method further includes:

[0028] The first processor determines the currently required modulation degree according to the currently required effective value of the line voltage and the DC bus voltage;

[0029] Determine whether to cut frequency according to the current required modulation index and stator frequency;

[0030] Through the correspondence between the actual modulation index and the theoretical modulation index, the current theoretical modulation index corresponding to the current demand modulation index is queried, and the current theoretical modulation index is used as the compensation modulation index to compensate the current demand modulation index;

[0031] Calculating the modulation period of the current cycle according to the frequency division number and the stator frequency; calculating the comparison value at the sampling angle according to the modulation period, the sampling angle and the current theoretical modulation index;

[0032] Determine the angle of the three-phase pulse switch angle in this cycle according to the comparison value; determine the initial level of the three-phase pulse according to the initial time vector of this cycle; wherein the initial time vector of this cycle is determined by the modulation strategy and sampling angle adopted by the current frequency division;

[0033] The modulation period, the angle of the three-phase pulse switching angle and the initial level are sent to the second processor so that the second processor can perform pulse control.

[0034] In a possible implementation, calculating the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle specifically includes:

[0035] Perform FFT analysis on the U-phase voltage pulse switching angle to calculate the actual phase voltage fundamental peak value.

[0036] In a second aspect, the present invention provides a modulation index compensation device based on synchronous SVPWM, the device comprising:

[0037] A determination module, the determination module is used to preset a theoretical modulation index and determine a sampling angle according to a frequency division number and a preset modulation strategy;

[0038] a calculation module, configured to calculate a comparison value at the sampling angle according to the theoretical modulation index;

[0039] The calculation module is further used to calculate the U-phase voltage pulse switching angle according to the comparison value;

[0040] The calculation module is further used to calculate the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle;

[0041] The calculation module is further configured to calculate the effective value of the line voltage actually output according to the actual phase voltage fundamental peak value;

[0042] The calculation module is further used to calculate the actual modulation index according to the ratio of the actual output line voltage effective value and the DC bus voltage;

[0043] The determining module is further configured to determine a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula;

[0044] A storage module, the storage module being used to store a correspondence between an actual modulation index with a frequency division number greater than 3 and a theoretical modulation index;

[0045] A query module is used in an application to query the corresponding relationship through the current demand modulation index, obtain the current theoretical modulation index corresponding to the current demand modulation index, and use the current theoretical modulation index as the compensation modulation index to compensate for the current demand modulation index.

[0046] In a third aspect, the present invention provides a computer server comprising: a memory, a processor, and a transceiver;

[0047] The processor is configured to be coupled to the memory, read and execute instructions in the memory, so as to implement the modulation degree compensation method based on synchronous SVPWM according to any one of the first aspects;

[0048] The transceiver is coupled to the processor, and the processor controls the transceiver to send and receive messages.

[0049] In a fourth aspect, the present invention provides a storage medium comprising a program or instruction, which, when executed on a computer, implements the modulation index compensation method based on synchronous SVPWM as described in any one of the first aspects.

[0050] Therefore, by applying the modulation index compensation method based on synchronous SVPWM provided by the present invention, different modulation index compensation arrays are stored according to the different segmented synchronous SVPWM strategies selected. The modulation index compensation array is directly read according to the frequency division segment in which it is located. After compensation, the current actual modulation index is continuous before and after the switching between the frequency divisions, the switching process is smooth, and there is no obvious current shock. For the frequency division with a large difference between the theoretical modulation index and the actual modulation index, the current theoretical modulation index corresponding to the actual modulation index is called to realize the compensation of the current demand system by the current theoretical modulation index, thereby ensuring the control accuracy. Among them, the present application adopts the FFT analysis method to compare and analyze the theoretical modulation index with the actual output modulation index. For compensation with a frequency division number greater than 3, an offline array method is adopted. It can be directly read in actual application to realize real-time compensation of nonlinear multi-frequency modulation index. The 3-frequency division is compensated in the form of a formula, and its theoretical modulation index The corresponding actual output modulation is After nonlinear compensation for the modulation depth, the 3-frequency division can be seamlessly switched with the square wave without any special overmodulation processing. Furthermore, the pulse generation of this application adopts the architecture of the first processor + the second processor, adopts the method of matching the switching angle with the initial level, and has only one switching angle per modulation cycle, which can flexibly generate any form of synchronous pulse. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the synchronous SVPWM modulation nonlinear compensation method provided in Example 1 of the present invention;

[0052] Figure 2 A schematic flow chart of a modulation index compensation method based on synchronous SVPWM provided in the first embodiment of the present invention;

[0053] Figure 3A Schematic diagram of the actual output flux and ideal flux of the AZCS_5 frequency division provided in Example 1 of the present invention;

[0054] Figure 3B Schematic diagram of the actual output flux and ideal flux of the CSVS_3 frequency division provided in Example 1 of the present invention;

[0055] Figure 4 The voltage vector diagram of the AZCS_5 frequency division in the first sector space provided in the first embodiment of the present invention;

[0056] Figure 5 This is the AZCS_5 frequency-divided U-phase pulse switch angle distribution diagram provided in Example 1 of the present invention;

[0057] Figure 6 A corresponding curve diagram of the actual modulation index and the theoretical modulation index of the AZCS_5 and CSVS_3 frequency divisions provided in the first embodiment of the present invention;

[0058] Figure 7 This is a diagram showing the relative error between the actual modulation depth and the theoretical modulation depth of the AZCS_5 and CSVS_3 frequency divisions provided in Example 1 of the present invention;

[0059] Figure 8 A schematic flow chart of an SVPWM method for a modulation index compensation method based on synchronous SVPWM provided in the first embodiment of the present invention;

[0060] Figure 9 Schematic diagram of FPGA PWM pulse generation provided in Example 1 of the present invention;

[0061] Figure 10 This is a structural diagram of a modulation index compensation device based on synchronous SVPWM provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0062] The present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the relevant invention and are not intended to limit the invention. It should also be noted that, for ease of description, only portions relevant to the relevant invention are shown in the accompanying drawings.

[0063] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0064] Figure 1 The principle diagram of the synchronous SVPWM modulation nonlinear compensation method provided by the embodiment of the present invention is as follows: Figure 1As shown, the maximum switching frequency of high-power traction drive systems is typically limited to a few hundred hertz, but the fundamental frequency can reach up to 250 Hz. Therefore, a synchronous modulation strategy is adopted in medium- and high-speed ranges. A segmented synchronous SVPWM method can be used to reduce the switching frequency while ensuring output voltage symmetry and current harmonic distortion. However, when the frequency division factor is low, the error between the actual modulation index and the theoretical modulation index is large. Therefore, compensation is required for the current desired modulation index (i.e., the actual desired modulation index). The synchronous SVPWM modulation period, switching angle, and initial level are calculated based on the compensated current desired modulation index (i.e., the current theoretical modulation index). This is then executed by a second processor. The switching angle refers to the fundamental phase value corresponding to the power device's operation.

[0065] Figure 2 The present invention provides a flow chart of a modulation index compensation method based on synchronous SVPWM. The execution subject of the method can be a processor, such as a digital signal processing (DSP). Figure 2 As shown, this application includes the following steps:

[0066] Step 210: preset a theoretical modulation index and determine a sampling angle according to the frequency division number and the preset modulation strategy;

[0067] Specifically, in the train traction system, the traction inverter is the core of the traction system. The traction inverter is generally a two-level three-phase inverter. For a two-level three-phase inverter, there are 6 switching devices. According to the different switching states of the devices, 2 3 = 8 different spatial voltage vectors, including two zero voltage vectors and six effective voltage vectors. The six effective voltage vectors are represented by (1, 2, ..., 6), and the two zero voltage vectors are represented by (0, 7). The effective voltage vectors divide the entire complex plane into six sectors, each 60°. Taking the first sector as an example, 0 and 7 represent zero voltage vectors, and 1 and 2 represent effective voltage vectors.

[0068] Based on the number of sampling angles in each sector, the sampling angles of the sampling angles, and the order of the sampling angle vectors, synchronous SVPWM modulation can be further divided into conventional space vector strategy (CSVS), boundary sampling strategy (BSS), asymmetric zero-vector switching strategy (AZCS), and basic bus clamping strategy (BBCS). In order to reduce electromagnetic noise, current harmonics, and current spikes in the full-speed range of the train, the modulation strategies of the segmented synchronous SVPWM in this application are CSVS_15, CSVS_12, CSVS_9, BSS_7, AZCS_5, and CSVS_3, hereinafter referred to as 15-division, 12-division, 9-division, 7-division, 5-division, and 3-division.

[0069] The order in which the sampling angle vectors are applied is explained using the first sector as an example. The first sector has four vectors: 0, 1, 2, and 7, with 0 and 7 being zero vectors. The SVPWM modulation method operates in a specific order, such as 0127 and 7210. This order is determined by the specific modulation strategy selected. For example, if CSVS is used, the switching sequence can only be 0127 or 7120.

[0070] The frequency division number is the ratio of the switching frequency to the fundamental frequency, that is, the stator frequency. For synchronous SVPWM with a low frequency division number, such as a frequency division number not greater than 5, the actual generated flux trajectory deviates greatly from the reference flux circle. The flux trajectory is the terminal trajectory of the stator flux vector during the control process, and the reference flux circle is the ideal flux circle, such as Figure 3A and Figure 3B As shown, Figure 3A The track with arrows in the middle is the 5-frequency magnetic flux track, and the dotted arc corresponding to the arrow is the reference magnetic flux circle track. Figure 3B The arrowed trajectory is the 3-way flux trajectory, and the dotted arc corresponding to the arrow is the reference flux trajectory. The discrepancy between the two causes the actual modulation index to be inconsistent with the theoretical modulation index. This application uses AZCS_5 and CSVS_3-way (hereinafter referred to as 5-way and 3-way) as examples to illustrate how to compensate for the current required modulation index.

[0071] The modulation strategy and sampling angle of the first sector in this application are shown in Table 1:

[0072] Frequency division number Modulation strategy First sector sampling angle 15 CSVS 6°，18°，30°，42°，54° 12 CSVS 7.5°，22.5°，37.5°，42.5° 9 CSVS 10°，30°，50° 7 BSS 0°，20°，40° 5 AZCS 15°，45° 3 CSVS 30° Square Wave / /

[0073] Table 1

[0074] As shown in Table 1, the sampling angles of the first sector of the 5-frequency division are 15° and 45°, and the carrier ratio N is 12. The sampling angle of the first sector of the 3-frequency division is 30°, and the carrier ratio N is 6. The carrier ratio is the ratio of the carrier frequency to the fundamental frequency (stator frequency).

[0075] The theoretical modulation index can be expressed as m′, and a theoretical modulation index can be preset to facilitate the subsequent derivation of the relationship between the actual modulation index and the theoretical modulation index.

[0076] Step 220, calculating the comparison value at the sampling angle according to the theoretical modulation index;

[0077] According to the volt-second balance principle, Figure 4 As shown, the two basic voltage vector action times T1 and T2 and the zero vector action time T0 of the two sampling angles θ1 and θ2 in the first sector of the 5-frequency division are respectively:

[0078]

[0079] in, Therefore, T 11 =T 22 , similarly T 12 =T 21 ; m′ is the theoretical modulation index. The zero vector action time at the sampling angle θ1 is T 10 , the action time of the two basic voltage vectors is T 11 、T 12 , the zero vector action time at the sampling angle θ2 is T 20 , the action time of the two basic voltage vectors is T 21 、T 22 .

[0080] The action time of each vector of the 3-frequency division when the sampling angle is 30° is:

[0081]

[0082] Among them, the action time of a zero vector is T0, and the action time of two basic voltage vectors is T1 and T2.

[0083] In order to facilitate the calculation of the fundamental wave period value of this application, 2π is selected, and the 5-frequency modulation period value is 3-frequency modulation period value

[0084] Step 230, calculating the U-phase voltage pulse switching angle according to the comparison value;

[0085] Specifically, since the U-phase voltage pulses of the 5-frequency division and the 3-frequency division are symmetrical about π, it is only necessary to calculate the switching angle in the [0,π] interval, as shown in the following example: Figure 5As shown, the 5-frequency U-phase voltage pulse switching angles α0, α1...α5 are:

[0086]

[0087] Among them, α0, α1, ..., α5 are the 6 switching angles of the 5-frequency U-phase voltage pulse in the interval [0,π].

[0088] The switching angles α0, α1, α2, and α3 of the 3-frequency U-phase voltage pulse series are:

[0089]

[0090] Among them, α0, α1, α2, and α3 are the four switching angles of the three-frequency U-phase voltage pulse in the interval [0,π], and T0 is the zero vector action time when the frequency is divided by three.

[0091] Step 240, calculating the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle;

[0092] Specifically, the actual phase voltage fundamental peak value refers to the maximum value of the fundamental wave of the phase voltage.

[0093] Perform fast Fourier transform (FFT) analysis on the U phase pulse voltage to calculate the actual phase voltage fundamental peak value U n1 Since the U-phase voltage pulse is symmetrical about the π pair, the coefficient A in its expression is o , B1 is 0, and there is only A1, so the actual phase voltage fundamental peak value of 5-frequency division is:

[0094]

[0095] Among them, ωt is the angular frequency variable, A o , A1, B1 are Fourier coefficients, if they are even symmetric, then A o , B1 is 0, only A1.

[0096] The actual phase voltage fundamental peak value of 3-frequency division is:

[0097]

[0098] Step 250, calculating the actual output line voltage effective value according to the actual phase voltage fundamental peak value;

[0099] Specifically, the actual output line voltage effective value can be obtained by multiplying the actual phase voltage fundamental peak value by the preset threshold value. The preset threshold value can be Right now

[0100] Step 260, calculating the actual modulation index based on the ratio of the actual output line voltage effective value to the DC bus voltage;

[0101] Specifically, the effective value of the line voltage actually output by the 5-frequency division is:

[0102]

[0103] The effective value of the line voltage of the 3-frequency divider is:

[0104]

[0105] The actual modulation index of the 5-frequency output is:

[0106]

[0107] The actual modulation index of the 3-way frequency output is:

[0108]

[0109] Among them, m is the actual modulation index.

[0110] Step 270: Determine a formula for calculating the theoretical modulation index from the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index at each frequency division number through the formula. The corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3 is stored.

[0111] Specifically, for a frequency division number greater than 3, determine the first formula of the theoretical modulation index and the actual modulation index, reversely deduce the second formula of the actual modulation index and the theoretical modulation index, and use the second formula to obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number.

[0112] Among them, the formula It can be regarded as the first formula, and its reverse deduction can be regarded as the second formula. Since the formula between the actual modulation index and the theoretical modulation index contains multiple trigonometric functions, it is directly solved in reverse to solve m′=f -1 (m) is too difficult, so this application can use reverse calculation tools, such as using MATLAB to reversely solve the theoretical modulation index m′ corresponding to the actual modulation index.

[0113] Step 270 specifically includes: assigning an initial value to the actual modulation index in the formula, and calculating a theoretical modulation index using a calculation tool; incrementing the actual modulation index from the initial value according to a preset step size to obtain the theoretical modulation index after each increment; and storing the actual modulation index and the corresponding theoretical modulation index after each increment. Thus, the corresponding relationship between the actual modulation index and the theoretical modulation index under each frequency division number can be calculated and stored. In order to ensure the accuracy of the corresponding relationship, the increment value of the actual modulation index can be set to 0.001, and the initial value can be 0.0005. For example, if the current required modulation index is in the range of 0.612≤m<0.613, the array a

[612] is read, and the value stored in a

[612] is the theoretical modulation index corresponding to the actual modulation index of 0.6125, thereby improving the accuracy of the corresponding relationship.

[0114] The storage here refers to using the initial value of the actual modulation index as the first element in the first array, and the theoretical modulation index corresponding to the initial value as the second element in the first array; the actual modulation index after each increment of the initial value is used as the first element in the subsequent array, and the corresponding theoretical modulation index is used as the second element in the array; the number of arrays is the number of increments plus 1.

[0115] For example, when the frequency is divided by 5, the maximum actual modulation index that can be output is 0.737. According to the initial value of 0.0005 and the increment by 0.001, 738 actual modulation indexes and the corresponding theoretical modulation indexes are obtained. Each actual modulation index and the corresponding theoretical modulation index are stored in an array in the order of gradually increasing from the initial value. Array a5

[738] represents the theoretical modulation index array corresponding to the actual modulation indexes 0 to 0.737.

[0116] Furthermore, in one example, for a 3-frequency division, the above formula can be used: The formula for inversely calculating the actual modulation index and theoretical modulation index of the 3-way frequency division is:

[0117]

[0118] Where m' is the theoretical modulation index, and m is the actual modulation index. This formula assigns a numerical value to each actual modulation index, allowing the theoretical modulation index corresponding to the actual modulation index to be calculated. In practical applications, when the current demand modulation index is known, this formula can be used to directly calculate the theoretical modulation index corresponding to the current demand modulation index. This theoretical modulation index can then be used as the compensation modulation index to compensate for the current demand modulation index.

[0119] Step 280: In the application, query the corresponding relationship through the current demand modulation index to obtain the current theoretical modulation index corresponding to the current demand modulation index, and use the current theoretical modulation index as the compensation modulation index to compensate the current demand modulation index.

[0120] Specifically, in actual applications, when the current demand modulation index is known, that is, the actual modulation index that is to be output, the current demand modulation index is consistent with a certain value in the actual modulation index in the corresponding relationship. At this time, the theoretical modulation index corresponding to the actual modulation index in the array is directly called, and the theoretical modulation index is used as the compensation modulation index. The current demand modulation index is compensated by the theoretical modulation index. For example, when the frequency is divided by 5, the current demand modulation index m=0.612, then the theoretical modulation index of the array a5

[612] is directly read, which means directly reading the 613th number in the array, thereby realizing compensation for the current demand modulation index by reading the theoretical modulation index.

[0121]

[0122] Among them, a k [z k ]、a r [z r ] are k and r frequency divisions respectively, the modulation index compensation offline array, m is the actual modulation index, and m′ is the theoretical modulation index.

[0123] The array used in this embodiment has an appropriately chosen step size and moderate array memory usage, ensuring that both DSP memory usage and control accuracy are within reasonable ranges. Furthermore, to maximize control accuracy, the value m selected during the reverse calculation of the m' offline array is the midpoint between two adjacent data points. When the modulation index is low, asynchronous modulation or synchronous modulation with a high frequency division ratio is typically used to ensure current harmonics. In the low frequency division ratio range, the modulation index is typically greater than 0.500, resulting in a control error of ≤0.1%, fully meeting practical application requirements.

[0124] Furthermore, the corresponding curves and relative errors of the actual modulation index of 5 and 3 frequency division and the current theoretical modulation index are as follows: Figure 6 、 7 As shown. Figure 7 The relative error of the modulation index is

[0125] The actual modulation index of 5-way frequency division can reach up to 0.737, and that of 3-way frequency division can reach up to The actual output modulation depth is the same as that of a square wave. Therefore, after modulation depth compensation, the 3-way divider can smoothly transition to the square wave without any special overmodulation processing. With the 5-way divider, the relative error decreases from a positive deviation of 4.0% to a negative deviation of -4.1% as the modulation depth increases; with the 3-way divider, the relative error decreases from 0 to -9.3% as the modulation depth increases.

[0126] This method is now combined with the segmented synchronous SVPWM method for further explanation.

[0127] Figure 8 This is a flow chart of a method based on segmented synchronous SVPWM provided in the first embodiment of the present invention. The method is executed by a first processor, which may be a digital signal processing (DSP). Figure 8 As shown, the method includes the following steps:

[0128] Step 810: The first processor determines the current required modulation degree based on the motor line voltage and the DC bus voltage;

[0129] The currently required modulation index can be determined based on the ratio of the currently required line voltage effective value to the DC bus voltage. The currently required line voltage effective value can be set based on actual needs.

[0130] Step 820, judging whether to cut frequency based on the current demand modulation index and stator frequency;

[0131] Specifically, the judgment of whether to cut frequency includes: when accelerating, if the current required modulation index is greater than the preset first threshold, or the stator frequency is greater than the preset second threshold, the frequency division number is switched from high frequency to low frequency; when the theoretical modulation index is less than the preset third threshold, or the stator frequency is less than the preset fourth threshold during deceleration, the frequency division number is switched from low frequency to high frequency.

[0132] When accelerating, if the frequency division is determined, the frequency division number can be switched from high frequency to low frequency. As for how many frequency divisions to switch to, it is generally switched to an adjacent frequency division number, for example, from 5 divisions to 3 divisions. When decelerating, the frequency division number can be switched from low frequency to high frequency, for example, from 3 divisions to 5 divisions.

[0133] Among them, the first threshold, the second threshold, the third threshold and the fourth threshold are empirical values from multiple experiments. The modulation index compensation method of this application is applied when the frequency division number is small. Therefore, after multiple experiments, the first threshold can be 0.730 and the third threshold can be 0.700.

[0134] Step 830: Query the current theoretical modulation index corresponding to the current demand modulation index based on the correspondence between the actual modulation index and the theoretical modulation index, and use the current theoretical modulation index as the compensation modulation index to compensate the current demand modulation index.

[0135] Specifically, the current demand modulation index is the actual modulation index that is desired to be output. In actual applications, when the frequency division number meets the requirements of step 820 and the frequency needs to be cut and the current demand modulation index needs to be compensated when the frequency is cut, the theoretical modulation index corresponding to the actual modulation index under each frequency division number has been calculated according to the present application. Figure 2 The modulation degree compensation method is stored, and the theoretical modulation degree corresponding to the current demand modulation degree is directly called, and the corresponding current theoretical modulation degree is used as the compensation modulation degree for the current demand modulation degree.

[0136] Step 840, calculate the modulation period of the current cycle according to the frequency division number and the stator frequency; calculate the comparison value at the sampling angle according to the modulation period, the sampling angle and the current theoretical modulation index.

[0137] Specifically, the modulation period of this cycle is determined based on the product of the carrier ratio corresponding to the frequency division number and the stator frequency. The modulation period can be calculated according to the following formula:

[0138]

[0139] Among them, T pwm is the modulation period, N is the carrier ratio, F s is the stator frequency.

[0140] According to the SVPWM volt-second balance principle, in an interval with two sampling angles θ1 and θ2, the comparison value at the sampling angle θ1 includes the zero vector action time T 01 and the two basic voltage vector action time T 11 、T 21 , the comparison value at the sampling angle θ2 includes the zero vector action time T 02 and the two basic voltage vector action time T 12 、T 22 , the comparison value can be expressed as the following formula:

[0141]

[0142] Where m″ is the current theoretical modulation index.

[0143] In an example, the vector action time for 15° and 45° divided by 5 is:

[0144]

[0145] Among them, T pwm is the modulation period, F s is the stator frequency, and the comparison value at 15° includes the zero vector action time T 10 and the two basic voltage vector action time T 11 、T 12, the comparison value at 45° includes the zero vector action time T 20 and the two basic voltage vector action time T 21 、T 22 .

[0146] In another example, the vector action time for a 30° division by 3 is:

[0147]

[0148] in, The comparison value at 30° includes the zero vector action time T0 and the two basic voltage vector action times T1 and T2.

[0149] Step 850: Determine the switching angle of the three-phase pulse in this cycle according to the comparison value; and determine the initial level of the three-phase pulse according to the initial time vector of this cycle.

[0150] The initial time vector of the current cycle is determined by the modulation strategy and sampling angle used for the current frequency division. Specifically, the modulation strategy, sampling angle, and initial time vector corresponding to the frequency division number can be pre-stored, for example, in a table in a database. By querying, the initial time vector of the current cycle corresponding to the modulation strategy and sampling angle used for the current frequency division number can be determined.

[0151] In one modulation cycle, each phase pulse has at most one switching angle, 0 indicates that the initial level of this modulation cycle is low, 1 indicates that the initial level is high, and the initial level is determined by the initial time vector of this modulation cycle.

[0152] Specifically, calculate the three-phase pulse switching angle α of this modulation cycle u , α v , α w As shown below:

[0153] α=f(T1,T2,T0)

[0154] Among them, α represents the three-phase pulse switching angle, including α u , α v , α w ,α u Indicates the U-phase switching angle, α v1 Indicates the V-phase switching angle, α w represents the W-phase switching angle, T1 and T2 represent the action time of two basic voltage vectors, and T0 represents the action time of zero vector.

[0155] In an example, taking the frequency division by 3 in the first sector as an example, the sampling angle is 30° and the switching angle is:

[0156]

[0157] Among them, the modulation strategy used for the 3-frequency division is CSVS. When the sampling angle is 30°, the initial moment vector is the 0 vector, and the initial levels of the U, V, and W three-phase pulses are 0, 0, and 0.

[0158] In another example, taking the sampling angles of 15° and 45° in the first sector of the 5-frequency division as an example, the U, V, and W three-phase pulse switching angles at 15° are:

[0159]

[0160] The modulation strategy used for the 5-frequency division is AZCS. When the sampling angle is 15°, the initial vector is the 0 vector, and the initial levels of the U, V, and W three-phase pulses are 0, 0, and 0.

[0161] When the angle is 45°, the U, V, and W three-phase pulse switching angles are:

[0162]

[0163] The modulation strategy used for the 5-frequency division is AZCS. When the sampling angle is 45°, the initial vector is 1 vector, and the initial levels of the U, V, and W three-phase pulses are 1, 0, and 0.

[0164] Step 860: Send the modulation period value, the three-phase pulse switching angle, and the initial level to the second processor so that the second processor can perform pulse control.

[0165] Specifically, the second processor performs pulse control according to the three-phase pulse switching angle and the initial level. Taking the second processor as a Field Programmable Gate Array (FPGA) as an example, the FPGA determines the level at the initial moment of the modulation cycle based on the initial level. When a valid switching angle is encountered, the level is flipped. When there is no valid switching angle, the modulation cycle level remains unchanged according to the initial level. Figure 9 shown.

[0166] Among them, the effective switching angle refers to the switching angle value 0<α<T pwm. The initial level of pulse 1 in modulation cycle 1 is 0. When encountering the effective switching angle α0, the level flips to 1; the initial level of pulse 1 in modulation cycle 2 is 1. When encountering the effective switching angle α1, the level flips to 0. The initial level of pulse 2 in modulation cycle 1 is 0. When encountering the effective switching angle α0, the level flips to 1; the initial level of pulse 2 in modulation cycle 2 is 0. When encountering the effective switching angle α1, the level flips to 1. The initial level of pulse 3 in modulation cycle 1 is 1. When encountering the effective switching angle α0, the level flips to 0; the initial level of pulse 0 in modulation cycle 2. When encountering the effective switching angle α1, the level flips to 1. The initial level of pulse 4 in modulation cycle 1 is 1. When encountering the effective switching angle α0, the level flips to 0; the initial level of pulse 1 in modulation cycle 2. When encountering the effective switching angle α1, the level flips to 0.

[0167] When the first sector of the 5-frequency division is 15°, α u , α v is the effective switching angle, α w is the invalid switching angle; when 45°, α v , α w is the effective switching angle, α u Therefore, the pulse generation adopts the method of combining the initial level with the switching angle, and the method of flipping the initial level and the level when encountering a valid switching angle can flexibly generate the required synchronous pulse.

[0168] Therefore, by applying the modulation index compensation method based on synchronous SVPWM provided by the present invention, different modulation index compensation arrays are stored according to the different segmented synchronous SVPWM strategies selected. The modulation index compensation array is directly read according to the frequency division segment in which it is located. After compensation, the current actual modulation index is continuous before and after the switching between the frequency divisions, the switching process is smooth, and there is no obvious current shock. For the frequency division with a large difference between the theoretical modulation index and the actual modulation index, the current theoretical modulation index corresponding to the actual modulation index is called to realize the compensation of the current demand system by the current theoretical modulation index, thereby ensuring the control accuracy. Among them, the present application adopts the FFT analysis method to compare and analyze the theoretical modulation index with the actual output modulation index. For compensation with a frequency division number greater than 3, an offline array method is adopted. It can be directly read in actual application to realize real-time compensation of nonlinear multi-frequency modulation index. The 3-frequency division is compensated in the form of a formula, and its theoretical modulation index The corresponding actual output modulation is After nonlinear compensation for the modulation depth, the 3-frequency division can be seamlessly switched with the square wave without any special overmodulation processing. Furthermore, the pulse generation of this application adopts the architecture of the first processor + the second processor, adopts the method of matching the switching angle with the initial level, and has only one switching angle per modulation cycle, which can flexibly generate any form of synchronous pulse.

[0169] Example 2

[0170] The second embodiment of the present invention provides a modulation compensation device based on synchronous SVPWM, such as Figure 10 As shown, the device includes: a determination module 1010, a calculation module 1020, a storage module 1030 and a query module 1040.

[0171] The determination module 1010 is used to preset a theoretical modulation index and determine a sampling angle according to a frequency division number and a preset modulation strategy;

[0172] The calculation module 1020 is used to calculate the comparison value at the sampling angle according to the theoretical modulation index;

[0173] The calculation module 1020 is further configured to calculate the U-phase voltage pulse switching angle according to the comparison value;

[0174] The calculation module 1020 is further configured to calculate the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle;

[0175] The calculation module 1020 is further configured to calculate the actual output line voltage effective value according to the actual phase voltage fundamental peak value;

[0176] The calculation module 1020 is further configured to calculate the actual modulation index based on the ratio of the actual output line voltage effective value to the DC bus voltage;

[0177] The determining module 1010 is further configured to determine a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula;

[0178] The storage module 1030 is used to store the correspondence between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3;

[0179] The query module 1040 is used to query the corresponding relationship through the current demand modulation degree in the application, obtain the current theoretical modulation degree corresponding to the current demand modulation degree, and use the current theoretical modulation degree as the compensation modulation degree to compensate the current demand modulation degree.

[0180] Furthermore, the comparison value includes two non-zero vector action times and one zero vector action time. The calculation module 1020 calculates the comparison value at the sampling angle according to the theoretical modulation index, specifically including: calculating the two non-zero vector action times and one zero vector action time at the sampling angle according to the sampling angle, modulation period and theoretical modulation index.

[0181] Furthermore, when the frequency division number is greater than 3, the determination module 1010 determines a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtains the theoretical modulation index corresponding to each actual modulation index under each frequency division number through the formula. The storage module 1030 stores the corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3. Specifically, the following steps are performed:

[0182] The determination module 1010 assigns an initial value to the actual modulation index in the formula and calculates a theoretical modulation index through a calculation tool; the actual modulation index is incremented from the initial value according to a preset step size to obtain the theoretical modulation index after each increment; the storage module 1030 stores the actual modulation index after each increment and the corresponding theoretical modulation index.

[0183] Furthermore, the storage module 1030 stores the actual modulation index and the corresponding theoretical modulation index after each increment, specifically including: taking the initial value of the actual modulation index as the first element in the first array, and taking the theoretical modulation index corresponding to the initial value as the second element in the first array; the actual modulation index after each increment of the initial value as the first element in the subsequent array, and the corresponding theoretical modulation index as the second element in the array; wherein the number of arrays is the number of increments plus 1.

[0184] Furthermore, the calculation module 1020 is further configured to, when the frequency division number is 3, calculate the value of Derive the theoretical modulation index; where m is the actual modulation index and m′ is the theoretical modulation index.

[0185] Furthermore, the calculation module 1020 is also used to determine the current required modulation index based on the current required line voltage effective value and DC bus voltage; determine whether to cut the frequency based on the current required modulation index and stator frequency; query the current theoretical modulation index corresponding to the current required modulation index through the correspondence between the actual modulation index and the theoretical modulation index, and use the current theoretical modulation index as the compensation modulation index to compensate for the current required modulation index; calculate the modulation period of this cycle based on the frequency division number and the stator frequency; calculate the comparison value at the sampling angle based on the modulation period, sampling angle and current theoretical modulation index; determine the angle of the three-phase pulse switching angle of this cycle based on the comparison value; determine the initial level of the three-phase pulse based on the initial time vector of this cycle; wherein the initial time vector of this cycle is determined by the modulation strategy and sampling angle adopted by the current frequency division; send the modulation period, the angle of the three-phase pulse switching angle and the initial level to the second processor so that the second processor can perform pulse control.

[0186] Furthermore, the calculation module 1020 calculates the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle, which specifically includes: performing FFT analysis on the U-phase voltage pulse switching angle to calculate the actual phase voltage fundamental peak value.

[0187] Example 3

[0188] A third embodiment of the present invention provides a computer server, comprising: a memory, a processor, and a transceiver;

[0189] The processor is configured to be coupled to the memory, read and execute instructions in the memory, so as to implement the modulation index compensation method based on synchronous SVPWM according to any one of the first embodiments;

[0190] The transceiver is coupled to the processor, and the processor controls the transceiver to send and receive messages.

[0191] Example 4

[0192] A fourth embodiment of the present invention provides a storage medium including a program or an instruction. When the program or the instruction is executed on a computer, the modulation index compensation method based on synchronous SVPWM described in any one of the first embodiments is implemented.

[0193] Professionals should also be further aware that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0194] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein may be implemented using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0195] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modulation compensation method based on synchronous SVPWM, characterized in that: The method comprises: Preset theoretical modulation index, and determine the sampling angle according to the frequency division number and preset modulation strategy; Calculating the comparison value at the sampling angle according to the theoretical modulation index; Calculating the U-phase voltage pulse switching angle according to the comparison value; Calculating the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle; Calculating the actual output line voltage effective value according to the actual phase voltage fundamental peak value; Calculate the actual modulation index based on the ratio of the actual output line voltage RMS value to the DC bus voltage; Determine a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula, and store the corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3; In the application, the corresponding relationship is queried through the current demand modulation degree to obtain the current theoretical modulation degree corresponding to the current demand modulation degree, and the current theoretical modulation degree is used as the compensation modulation degree to compensate the current demand modulation degree.

2. The method according to claim 1, characterized in that The comparison value includes two non-zero vector action times and one zero vector action time. The calculation of the comparison value at the sampling angle according to the theoretical modulation index specifically includes: According to the sampling angle, the modulation period and the theoretical modulation degree, two non-zero vector action times and one zero vector action time at the sampling angle are calculated.

3. The method according to claim 1, characterized in that When the frequency division number is greater than 3, determining a formula for calculating the theoretical modulation index by deriving the actual modulation index, obtaining the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula, and storing the corresponding relationship between the actual modulation index and the theoretical modulation index when the frequency division number is greater than 3 specifically includes: Assign an initial value to the actual modulation index in the formula, and calculate a theoretical modulation index through calculation tools; According to a preset step size, the actual modulation index is incremented from an initial value to obtain a theoretical modulation index after each increment; The actual modulation index and the corresponding theoretical modulation index after each increment are stored.

4. The method according to claim 3, characterized in that The storing of the actual modulation index and the corresponding theoretical modulation index after each increment specifically includes: The initial value of the actual modulation index is used as the first element in the first array, and the theoretical modulation index corresponding to the initial value is used as the second element in the first array; The actual modulation index after each increment of the initial value is used as the first element in the subsequent array, and the corresponding theoretical modulation index is used as the second element in the array; the number of arrays is the number of increments plus 1.

5. The method according to claim 1, wherein The method further comprises: When the frequency division number is 3, according to the formula Derive theoretical modulation; Among them, m is the actual modulation index, and m' is the theoretical modulation index.

6. The method according to claim 1, characterized in that The method further comprises: The first processor determines the currently required modulation degree according to the currently required effective value of the line voltage and the DC bus voltage; Determine whether to cut frequency according to the current required modulation index and stator frequency; Through the correspondence between the actual modulation index and the theoretical modulation index, the current theoretical modulation index corresponding to the current demand modulation index is queried, and the current theoretical modulation index is used as the compensation modulation index to compensate the current demand modulation index; Calculating the modulation period of the current cycle according to the frequency division number and the stator frequency; calculating the comparison value at the sampling angle according to the modulation period, the sampling angle and the current theoretical modulation index; Determine the angle of the three-phase pulse switch angle in this cycle according to the comparison value; determine the initial level of the three-phase pulse according to the initial time vector of this cycle; wherein the initial time vector of this cycle is determined by the modulation strategy and sampling angle adopted by the current frequency division; The modulation period, the angle of the three-phase pulse switching angle and the initial level are sent to the second processor so that the second processor can perform pulse control.

7. The method according to claim 1, characterized in that Calculating the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle specifically includes: Perform FFT analysis on the U-phase voltage pulse switching angle to calculate the actual phase voltage fundamental peak value.

8. A modulation compensation device based on synchronous SVPWM, characterized in that: The device comprises: A determination module, the determination module is used to preset a theoretical modulation index and determine a sampling angle according to a frequency division number and a preset modulation strategy; a calculation module, configured to calculate a comparison value at the sampling angle according to the theoretical modulation index; The calculation module is further used to calculate the U-phase voltage pulse switching angle according to the comparison value; The calculation module is further used to calculate the actual phase voltage fundamental peak value according to the U-phase voltage pulse switching angle; The calculation module is further configured to calculate the effective value of the line voltage actually output according to the actual phase voltage fundamental peak value; The calculation module is further used to calculate the actual modulation index according to the ratio of the actual output line voltage effective value and the DC bus voltage; The determining module is further configured to determine a formula for calculating the theoretical modulation index by deriving the actual modulation index, and obtain the theoretical modulation index corresponding to each actual modulation index under each frequency division number by using the formula; A storage module, the storage module being used to store a correspondence between an actual modulation index with a frequency division number greater than 3 and a theoretical modulation index; A query module is used in an application to query the corresponding relationship through the current demand modulation index, obtain the current theoretical modulation index corresponding to the current demand modulation index, and use the current theoretical modulation index as the compensation modulation index to compensate for the current demand modulation index.

9. A computer server, characterized in that: include: memory, processors, and transceivers; The processor is configured to be coupled to the memory, read and execute instructions in the memory, so as to implement the modulation compensation method based on synchronous SVPWM according to any one of claims 1 to 7; The transceiver is coupled to the processor, and the processor controls the transceiver to send and receive messages.

10. A storage medium, characterized in that: The method comprises a program or an instruction, and when the program or the instruction is run on a computer, the method for compensating the modulation index based on synchronous SVPWM as claimed in any one of claims 1 to 7 is implemented.

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