Reference vector positioning and common-mode voltage suppression method for SVM strategy of cascaded H-bridge converter

Abstract

The invention discloses a reference vector positioning and common-mode voltage suppression method for a cascaded H-bridge converter SVM strategy, and the method comprises the steps: carrying out the sampling of three phase voltage reference signals, and obtaining a reference vector under a conventional alpha-beta coordinate system through calculation; positioning the reference vector by using the characteristic factor; according to the second volt balance principle, the action time of the three basic vectors of the synthesized reference vector is calculated; calculating the maximum switching state by using the correction factor, and directly obtaining the corrected switching state with the minimum common-mode voltage according to the correction factor; and performing time-sharing action on the corrected switch state to complete SVM in a single period. Reference vector positioning under a traditional alpha-beta coordinate system is simplified, a coordinate calculation formula and action time calculation of three basic vectors for synthesizing the reference vector are simplified, and the iteration problem of calculating the minimum switching state of the common-mode voltage through Clark inverse transformation in the traditional SVM process is avoided in the common-mode voltage suppression process. And the calculation of three basic vector switch states is simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of cascaded H-bridge converter modulation, and particularly relates to a method for reference vector positioning and common-mode voltage suppression of the SVM strategy for cascaded H-bridge converters. Background Technique

[0002] Space vector modulation technology was initially applied to three-phase motor drive systems. Its core idea is to convert three-phase symmetrical voltage signals into space vectors, and by controlling the action time of the space vectors, precise control of the output voltage waveform is achieved. Specifically, SVM selects the three space vectors closest to the reference vector according to the trajectory of the reference vector, and adjusts the PWM drive of the converter according to their action time, thereby realizing the modulation of the output waveform of the converter. SVM technology has high DC voltage utilization rate, low switching frequency and excellent output power quality, and is widely used in three-level and five-level converters.

[0003] However, with the increase in the number of levels, the reference vector positioning in the space vector modulation process becomes increasingly complex. With the increase in the number of levels of the multilevel converter, the number of space vectors increases significantly, and at the same time, the number of switching states corresponding to the space vectors also increases significantly, making the calculation of switching states and the selection of switching sequences extremely complex. This complexity poses a great challenge to the implementation of the SVM algorithm for multilevel converters. Especially in the case of a high number of levels, the execution efficiency and accuracy of the modulation algorithm are affected.

[0004] In addition, a common-mode voltage is generated during the modulation of the multilevel converter. This voltage may pose a serious threat to the insulation performance of the motor. The large common-mode voltage is coupled through the capacitance between the stator and rotor of the motor, which may cause a large bearing current, resulting in damage to the motor bearings and even electromagnetic interference (EMI) to other equipment in the power grid, affecting the normal operation of the equipment. Therefore, how to effectively control the common-mode voltage, reduce the bearing current and reduce electromagnetic interference has become a key issue in the design of cascaded H-bridge converters. Summary of the Invention

[0005] The present invention provides a method for reference vector positioning and common-mode voltage suppression of the SVM strategy for cascaded H-bridge converters, aiming to solve problems in the prior art such as complex reference vector positioning, inconsistent calculation formulas for upper and lower triangular sectors, and difficulty in suppressing the common-mode voltage within the minimum range during the space vector modulation process of cascaded H-bridge converters.

[0006] The present invention provides a method for reference vector positioning and common-mode voltage suppression of the SVM strategy for cascaded H-bridge converters, including:

[0007] Step 1: Let n be the number of sub-modules of the H-bridge in a single phase of the three-phase cascaded H-bridge, for the three-phase voltage reference signals ura , u rb , u rc Sample and calculate the reference vector V in the αβ coordinate system r (α r , β r ).

[0008]

[0009] Wherein, u ra , u rb , u rc are the three-phase reference voltages, and α r , β r are the coordinate components of the reference vector in the αβ coordinate system.

[0010] Step 2: Perform vector positioning on the reference vector V r (α r , β r ) in the αβ coordinate system according to the characteristic factors. First, calculate two characteristic factors J and K, which determine the unique rhombus sector where the reference vector is located; then use these two characteristic factors to calculate the coordinates V z (α z , β z ) of the midpoint of this rhombus sector in the αβ coordinate system; finally, use the midpoint coordinates to calculate the coordinates V4(α4, β4), V3(α3, β3), V0(α0, β0) of the three basic vectors adjacent to the reference vector in the αβ coordinate system. The specific steps are as follows:

[0011] Step 2.1: Calculate two characteristic factors J and K of the rhombus sector according to the coordinate components α r , β r of the reference vector in the αβ coordinate system.

[0012]

[0013] Wherein, α r , β r are the coordinate components of the reference vector, J and K are the two characteristic factors of the rhombus sector, and floor(*) is the floor function.

[0014] Step 2.2: Calculate the coordinates V r , β r of the midpoint of the rhombus sector according to the two characteristic factors α z (α z , β z ).

[0015]

[0016] Where J and K are two characteristic factors of the rhombus sector, and α z , β z are the coordinate components of the midpoint of the rhombus sector.

[0017] Step 2.3: Calculate three basic vectors V4(α4, β4), V3(α3, β3), and V0(α0, β0) according to the coordinate components α z , β z of the midpoint of the rhombus sector.

[0018]

[0019] Where α z , β z are the midpoint coordinates of the rhombus sector, V4, V3, and V0 are three basic vectors, and sign(*) is the sign function.

[0020] Step 3: Calculate the action times t4, t3, and t0 of the three basic vectors V4, V3, and V0 according to the volt-second balance principle.

[0021]

[0022] Where T s is the sampling period, α z , β z are the coordinate components of the midpoint of the rhombus sector, α r , β r are the coordinate components of the reference vector, t4, t3, and t0 are the action times of the three basic vectors V4, V3, and V0, and abs(*) is the absolute value function.

[0023] Step 4: Calculate the switching state with the minimum common-mode voltage corresponding to the basic vector according to the correction coefficient. First, calculate the correction factors of the three basic vectors V4(α4, β4), V3(α3, β3), and V0(α0, β0) according to the characteristic factors, and calculate the maximum switching states S4(a4, b4, c4), S3(a3, b3, c3), and S0(a0, b0, c0) of the three basic vectors according to the correction factors; then calculate the common-mode voltage of the maximum switching state and the number of redundant switching states of the basic space vector, and determine the correction coefficients of the three basic vectors based on this; finally, use the correction coefficients to calculate the corrected switching states S 44 (a 44 , b 44 , c 44 ), S 33 (a 33 , b 33 , c 33 ), S 00 (a 00 , b 00,c 00 )。The specific steps are as follows:

[0024] Step 4.1: Calculate the correction factors of V4, V3, and V0 according to the two characteristic factors of the rhombus sector.

[0025] For the basic vector V4, its correction factors p4 and q4 are calculated as follows:

[0026]

[0027] For the basic vector V3, its correction factors p3 and q3 are calculated as follows:

[0028]

[0029] For the basic vector V0, its correction factors p0 and q0 are calculated as follows:

[0030]

[0031] Step 4.2: Calculate the maximum switching states of V4, V3, and V0 according to the correction factors.

[0032] For the basic vector V4, its correction factors are p4 and q4, and the maximum switching state is S4(a4, b4, c4).

[0033] If p4 ≥ 0 and q4 ≥ 0, then w 41 = 1, w 42 = 0, w 43 = 0.

[0034] If p4 < 0 and (q4 - p4) ≥ 0, then w 41 = 0, w 42 = 1, w 43 = 0.

[0035] If q4 < 0 and (q4 - p4) < 0, then w 41 = 0, w 42 = 0, w 43 = 1.

[0036] The maximum switching state S4(a4, b4, c4) is calculated as follows:

[0037]

[0038] For the basic vector V3, its correction factors are p3 and q3, and the maximum switching state is S3(a3, b3, c3).

[0039] If p3 ≥ 0 and q3 ≥ 0, then w 31 = 1, w 32 = 0, w 33 = 0.

[0040] If p3 < 0 and (q3 - p3) ≥ 0, then w 31 = 0, w 32 = 1, w 33 = 0.

[0041] If q3 < 0 and (q3 - p3) < 0, then w 31 = 0, w 32 = 0, w 33 = 1.

[0042] The maximum switching state S3(a3, b3, c3) is calculated as follows:

[0043]

[0044] For the basic vector V0, its correction factors are p0 and q0, and the maximum switching state is S0(a0, b0, c0).

[0045] If p0 ≥ 0 and q0 ≥ 0, then w 01 = 1, w 02 = 0, w 03 = 0.

[0046] If p0 < 0 and (q0 - p0) ≥ 0, then w 01 = 0, w 02 = 1, w 03 = 0.

[0047] If q0 < 0 and (q0 - p0) < 0, then w 01 = 0, w 02 = 0, w 03 = 1.

[0048] The maximum switching state S0(a0, b0, c0) is calculated as follows:

[0049]

[0050] Step 4.3: Calculate the number of redundant switching states R4, R3, and R0 of V4, V3, and V0.

[0051] For the basic vector V4, the number of redundant switching states R4 is calculated as follows:

[0052]

[0053] For the basic vector V3, the number of redundant switching states R3 is calculated as follows:

[0054]

[0055] For the basic vector V0, the number of redundant switching states R0 is calculated as follows:

[0056]

[0057] Step 4.4: Calculate the common-mode voltages N4, N3, and N0 of the maximum switching states S4(a4, b4, c4), S3(a3, b3, c3), and S0(a0, b0, c0) according to the definition of the common-mode voltage.

[0058]

[0059] Step 4.5: Calculate the correction factors H4, H3, and H0 of V4, V3, and V0.

[0060] For the basic vector V4, its correction factor H4 is determined as follows:

[0061] If the common-mode voltage N4 ≤ 0, then H4 = 0.

[0062] If the common-mode voltage N4 > 0, then H4 = min(round(N4), (R4 - 1)).

[0063] For the basic vector V3, its correction factor H3 is determined as follows:

[0064] If the common-mode voltage N3 ≤ 0, then H3 = 0.

[0065] If the common-mode voltage N3 > 0, then H3 = min(round(N3), (R3 - 1)).

[0066] For the basic vector V0, its correction factor H0 is determined as follows:

[0067] If the common-mode voltage N0 ≤ 0, then H0 = 0.

[0068] If the common-mode voltage N0 > 0, then H0 = min(round(N0), (R0 - 1)).

[0069] Step 4.6: Calculate the corrected switching states according to the correction factors.

[0070] For the basic vector V4, its correction factor is H4, and the corrected switching state is S 44 (a 44 , b 44 , c 44 ) is calculated as follows:

[0071]

[0072] For the basic vector V3, its correction factor is H3, and the corrected switching state is S 33 (a 33 , b 33 , c 33) is calculated as follows:

[0073]

[0074] For the basic vector V0, its correction coefficient is H0, and the corrected switching state is S 00 (a 00 ,b 00 ,c 00 ) is calculated as follows:

[0075]

[0076] Step 5: Use the corrected switch state to determine the switching path of the switch state in a time-sharing manner, and enter the next sampling period, repeat the steps, and complete the space vector modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings involved in the description of the embodiments. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0078] Figure 1 A flowchart of a reference vector positioning and common mode voltage suppression method of a cascaded H-bridge converter SVM strategy provided by an embodiment of the present invention;

[0079] Figure 2 A topology diagram of a three-phase n-level H-bridge cascade converter provided in one embodiment of the present invention;

[0080] Figure 3 A diamond sector positioning diagram of a reference vector provided by an embodiment of the present invention;

[0081] Figure 4 A space vector switching timing diagram of a synthetic reference vector provided by an embodiment of the present invention;

[0082] Figure 5 This is a simulated output voltage waveform diagram of a 5-level H-bridge cascade converter provided in one embodiment of the present invention. Specific implementation methods

[0084] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0085] Please refer to Figure 1 , which shows the flow chart of the reference vector positioning and common-mode voltage suppression method for the SVM strategy of a cascaded H-bridge converter in this application.

[0086] As Figure 1 shown, the reference vector positioning and common-mode voltage suppression method for the SVM strategy of a cascaded H-bridge converter specifically includes the following steps:

[0087] In this embodiment, taking a three-phase n-level H-bridge cascaded converter as an example, each phase of the converter is composed of n voltage-source H-bridge inverter sub-modules connected in series, and each H-bridge inverter sub-module is composed of four IGBTs and anti-parallel diodes (as Figure 2 shown).

[0088] The three-phase voltage reference signals u ra , u rb , u rc are:

[0089]

[0090] In the formula, n is the number of H-bridge inverter sub-modules connected in series in each phase of the converter, m is the modulation coefficient, 0 < m ≤ 1, and ω is the angular frequency of the reference voltage signal.

[0091] Step 1: Sample the three-phase voltage reference signals u ra , u rb , u rc , and calculate the reference vector V r (α r , β r ) in the αβ coordinate system. The positions of V r (α r , β r ) are as Figure 3 shown, and the calculation formula is as follows:

[0092]

[0093] In the formula, u ra , u rb , u rc are the three-phase reference voltages, and α r , β r are the coordinate components of the reference vector in the αβ coordinate system.

[0094] Step 2.1: Calculate the two characteristic factors J and K of the rhombus sector according to the coordinate components α r , β r of the reference vector in the αβ coordinate system. The rhombus sector is as Figure 3 shown, and the calculation formula is as follows:

[0095]

[0096] Wherein, α r , β r are the coordinate components of the reference vector, J and K are two characteristic factors of the rhombus sector, and floor(*) is the floor function.

[0097] Step 2.2: Calculate the coordinates V r of the midpoint of the rhombus sector according to the two characteristic factors α r , β z (α z , β z ). The positions of V z (α z , β z ) are as shown in Figure 3 , and the calculation formula is as follows:

[0098]

[0099] Wherein, J and K are two characteristic factors of the rhombus sector, and α z , β z are the coordinate components of the midpoint of the rhombus sector.

[0100] Step 2.3: Calculate the three basic vectors V4(α4, β4), V3(α3, β3), V0(α0, β0) according to the coordinate components α z , β z of the midpoint of the rhombus sector. Their positions are as shown in Figure 3 . Even if the reference vector may fall in the upper triangular sector or the lower triangular sector of the rhombus sector as shown in the left and right figures of Figure 3 , the same formula can be used in this method to calculate the coordinates of the three basic vectors. The calculation formula is as follows:

[0101]

[0102] Wherein, α z , β z are the midpoint coordinates of the rhombus sector, V4, V3, and V0 are the three basic vectors, and sign(*) is the sign function.

[0103] Step 3: Calculate the action times t4, t3, and t0 of the three basic vectors V4, V3, and V0 according to the volt-second balance principle.

[0104]

[0105] Wherein, T s is the sampling period, α z , β z are the coordinate components of the midpoint of the rhombus sector, and α r, β r are the coordinate components of the reference vector, t4, t3, and t0 are the action times of the three basic vectors V4, V3, and V0, and abs(*) is the absolute value function.

[0106] In this embodiment, for the cascaded H-bridge converter, one basic vector may correspond to multiple switching states with different common-mode voltages. Through the following algorithm, the switching state with the minimum common-mode voltage corresponding to the basic vector can be quickly obtained with only a finite number of comparison judgments and four arithmetic operations.

[0107] Since the reference vector is synthesized by three adjacent basic vectors, each step of the following calculation steps has three parts. However, the method of the present invention unifies the formula for calculating the switching state of the three basic vectors, and the same calculation formula is used regardless of which basic vector is used to calculate the switching state.

[0108] Step 4.1: Calculate the correction factors of V4, V3, and V0 according to the two characteristic factors of the rhombus sector.

[0109] For the basic vector V4, its correction factors p4 and q4 are calculated as follows:

[0110]

[0111] For the basic vector V3, its correction factors p3 and q3 are calculated as follows:

[0112]

[0113] For the basic vector V0, its correction factors p0 and q0 are calculated as follows:

[0114]

[0115] Step 4.2: Calculate the maximum switching state of V4, V3, and V0 according to the correction factors.

[0116] For the basic vector V4, its correction factors are p4 and q4, and the maximum switching state is S4(a4, b4, c4).

[0117] If p4 ≥ 0 and q4 ≥ 0, then w 41 = 1, w 42 = 0, w 43 = 0.

[0118] If p4 < 0 and (q4 - p4) ≥ 0, then w 41 = 0, w 42 = 1, w 43 = 0.

[0119] If q4 < 0 and (q4 - p4) < 0, then w 41 = 0, w42 = 0, w 43 = 1.

[0120] The maximum switching state S4(a4, b4, c4) is calculated as follows:

[0121]

[0122] For the basic vector V3, its correction factors are p3 and q3, and the maximum switching state is S3(a3, b3, c3).

[0123] If p3 ≥ 0 and q3 ≥ 0, then w 31 = 1, w 32 = 0, w 33 = 0.

[0124] If p3 < 0 and (q3 - p3) ≥ 0, then w 31 = 0, w 32 = 1, w 33 = 0.

[0125] If q3 < 0 and (q3 - p3) < 0, then w 31 = 0, w 32 = 0, w 33 = 1.

[0126] The maximum switching state S3(a3, b3, c3) is calculated as follows:

[0127]

[0128] For the basic vector V0, its correction factors are p0 and q0, and the maximum switching state is S0(a0, b0, c0).

[0129] If p0 ≥ 0 and q0 ≥ 0, then w 01 = 1, w 02 = 0, w 03 = 0.

[0130] If p0 < 0 and (q0 - p0) ≥ 0, then w 01 = 0, w 02 = 1, w 03 = 0.

[0131] If q0 < 0 and (q0 - p0) < 0, then w 01 = 0, w 02 = 0, w 03 = 1.

[0132] The maximum switching state S0(a0, b0, c0) is calculated as follows:

[0133]

[0134] Step 4.3: Calculate the number of redundant switching states R4, R3, and R0 of V4, V3, and V0.

[0135] For the basic vector V4, the number of redundant switching states R4 is calculated as follows:

[0136]

[0137] For the basic vector V3, the number of redundant switching states R3 is calculated as follows:

[0138]

[0139] For the basic vector V0, the number of redundant switching states R0 is calculated as follows:

[0140]

[0141] Step 4.4: Calculate the common-mode voltages N4, N3, and N0 of the maximum switching states S4(a4, b4, c4), S3(a3, b3, c3), and S0(a0, b0, c0) according to the definition of the common-mode voltage.

[0142]

[0143] Step 4.5: Calculate the correction factors H4, H3, and H0 of V4, V3, and V0.

[0144] For the basic vector V4, the correction factor H4 is determined as follows:

[0145] If the common-mode voltage N4 ≤ 0, then H4 = 0.

[0146] If the common-mode voltage N4 > 0, then H4 = min(round(N4), (R4 - 1)).

[0147] For the basic vector V3, the correction factor H3 is determined as follows:

[0148] If the common-mode voltage N3 ≤ 0, then H3 = 0.

[0149] If the common-mode voltage N3 > 0, then H3 = min(round(N3), (R3 - 1)).

[0150] For the basic vector V0, the correction factor H0 is determined as follows:

[0151] If the common-mode voltage N0 ≤ 0, then H0 = 0.

[0152] If the common-mode voltage N0 > 0, then H0 = min(round(N0), (R0 - 1)).

[0153] Step 4.6: Calculate the corrected switching state according to the correction factor.

[0154] For the basic vector V4, its correction factor is H4, and the corrected switching state is S 44 (a 44 , b 44 , c 44 ) The calculation is as follows:

[0155]

[0156] For the basic vector V3, its correction factor is H3, and the corrected switching state is S 33 (a 33 , b 33 , c 33 ) The calculation is as follows:

[0157]

[0158] For the basic vector V0, its correction factor H0, and the corrected switching state is S 00 (a 00 , b 00 , c 00 ) The calculation is as follows:

[0159]

[0160] Step 5: Apply the corrected switching state time-divisionally to determine its switching path, and perform the next sampling period. Repeat Steps 1 to 4 to complete space vector modulation. In this embodiment, using the five-segment algorithm, the switching path of the switching state is determined. Taking V3 as the starting point and V0 as the ending point as an example, the switching path is S3→S4→S0→S4→S3, and the action times of the switching states are t3 / 2→t4 / 2→t0→t4 / 2→t3 / 2 (as Figure 4 shown). Perform the next sampling period, repeat Steps 1 to 4 to complete space vector modulation.

[0161] In summary, the method of the present invention simplifies the positioning of the reference vector and the calculation of the action time of the basic vector in the traditional αβ coordinate system, unifies the calculation formulas of the adjacent three basic vector coordinates and the action time of the basic vector in the upper triangular sector and the lower triangular sector, and directly obtains the maximum switching state corresponding to the basic vector according to the condition judgment of the correction factor, and then introduces a correction coefficient to correct the maximum switching state, so as to obtain the switching state corresponding to the minimum common-mode voltage of the basic vector, avoiding the iterative problem of calculating the switching state using the Clark inverse transformation in the traditional space vector modulation process and reducing the complexity of the implementation of the SVM algorithm.

[0162] In a specific embodiment, taking a 5-level H-bridge cascaded converter as an example, let the modulation coefficient m = 0.92, n = 5, the angular frequency ω of the reference voltage signal = 100π, and the sampling period T s = 0.1 ms. When sampling the reference voltage signal at t = 2.4 ms, we get u ra = 3.872, u rb = 1.213, u rc = -5.085. Calculate the reference vector according to formula (2) to get V r (α r , β r ) = (3.872, 3.636). Calculate the characteristic factors according to formula (3) to get J = 2, K = 8. Calculate the coordinates of the midpoint of the rhombus sector according to formula (4) to get V z (α z , β z ) = (3.668, 3.464). Calculate the three adjacent basic vectors of the synthesized reference vector according to formula (5) to get V4(α4, β4) = (4.000, 3.464), V3(α3, β3) = (3.333, 3.464), V0(α0, β0) = (3.668, 4.041). Calculate the action times of the three basic vectors according to formula (6) to get t4 = 65.91 us, t3 = 4.307 us, t0 = 29.78 us. Calculate the correction factors of the basic vector V4 according to formula (7) to get p4 = 3, q4 = 9. Calculate the correction factors of the basic vector V3 according to formula (8) to get p3 = 2, q3 = 8. Calculate the correction factors of the basic vector V0 according to formula (9) to get p0 = 2, q0 = 9. Calculate the maximum switching state of the basic vector V4 according to formula (10) to get S4(a4, b4, c4) = (5, 2, -4). Calculate the maximum switching state of the basic vector V3 according to formula (11) to get S3(a3, b3, c3) = (5, 3, -3). Calculate the maximum switching state of the basic vector V0 according to formula (12) to get S0(a0, b0, c0) = (5, 3, -4). Calculate the number of redundant switching states of the basic vector V4 according to formula (13) to get R4 = 2. Calculate the number of redundant switching states of the basic vector V3 according to formula (14) to get R3 = 3. Calculate the number of redundant switching states of the basic vector V0 according to formula (15) to get R0 = 2. Calculate the common-mode voltages of the maximum switching states of the three basic vectors according to formula (16) to get N4 = 1, N3 = 1.667, N0 = 1.333. Determine the correction coefficients of the three basic vectors according to step 4.5 to get H4 = 1, H3 = 2, H0 = 1. Calculate the switching state with the minimum common-mode voltage after correction of the basic vector V4 according to formula (17) to get S 44 (a 44 , b 44 , c 44) = (4, 1, -5), calculate the switching state with the minimum common-mode voltage after correcting the basic vector V3 according to formula (18) to get S 33 (a 33 , b 33 , c 33 ) = (3, 1, -5), calculate the switching state with the minimum common-mode voltage after correcting the basic vector V0 according to formula (19) to get S 00 (a 00 , b 00 , c 00 ) = (4, 2, -5). Finally, use the five-segment algorithm to determine the switching path of the switching state. Taking V3 as the starting point and V0 as the ending point as an example, the switching path is S3 → S4 → S0 → S4 → S3, and the action times of the switching states are t3 / 2 → t4 / 2 → t0 → t4 / 2 → t3 / 2 (as Figure 5 shown).

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A reference vector positioning and common mode voltage suppression method for a cascaded H-bridge converter SVM strategy, characterized in that: include: Step 1: Let n be the number of single-phase H-bridge submodules in the three-phase cascade H-bridge, and the three-phase voltage reference signals u ra 、u rb 、u rc Sampling, calculating the reference vector V in the αβ coordinate system r (α r ,β r ); Step 2: In the αβ coordinate system, the reference vector V is calculated according to the characteristic factor r (α r ,β r ) for vector positioning; first calculate two characteristic factors J and K, which determine the unique diamond sector where the reference vector is located; then use these two characteristic factors to calculate the coordinates V of the midpoint of the diamond sector in the αβ coordinate system z (α z ,β z ); finally, the coordinates of the three basic vectors adjacent to the reference vector in the αβ coordinate system are calculated using the midpoint coordinates V4(α4,β4), V3(α3,β3), and V0(α0,β0); Step 3: Calculate the action time t4, t3, t0 of the three basic vectors V4, V3, V0 according to the volt-second balance principle; Step 4: Calculate the switching state of the basic vector with the minimum common-mode voltage based on the correction coefficient; first, calculate the correction factors of the three basic vectors V4 (α4, β4), V3 (α3, β3), and V0 (α0, β0) based on the characteristic factors, and calculate the maximum switching state S4 (a4, b4, c4), S3 (a3, b3, c3), and S0 (a0, b0, c0) of the three basic vectors based on the correction factors; then calculate the common-mode voltage of the maximum switching state and the number of redundant switching states of the basic space vector, and use this to determine the correction coefficients of the three basic vectors; finally, use the correction coefficients to calculate the corrected switching state S of the three basic vectors 44 (a 44 ,b 44 ,c 44 ), S 33 (a 33 ,b 33 ,c 33 ), S 00 (a 00 ,b 00 ,c 00 ); Step 5: Use the corrected switch state to determine the switching path of the switch state in a time-sharing manner, and enter the next sampling period, repeat the steps, and complete the space vector modulation.

2. The reference vector positioning and common mode voltage suppression method of the cascaded H-bridge converter SVM strategy according to claim 1, characterized in that: The steps 1 to 3 are the reference vector positioning part, and the detailed steps are as follows: Step 1: Let n be the number of single-phase H-bridge submodules in the three-phase cascade H-bridge, and the three-phase voltage reference signals u ra 、u rb 、u rc Sampling, calculating the reference vector V in the αβ coordinate system r (α r ,β r ); In the formula, α r , β r are the coordinate components of the reference vector in the αβ coordinate system; Step 2.1: According to the coordinate component α of the reference vector in the αβ coordinate system r , β r Calculate the two characteristic factors J and K of the diamond sector; In the formula, J and K are two characteristic factors of the diamond sector, and floor(*) is the floor rounding function; Step 2.2: According to the two characteristic factors α of the diamond sector r , β r Calculate the coordinates V of the midpoint of the rhombus sector z (α z ,β z ); In the formula, α z , β z are the coordinate components of the midpoint of the rhombus sector; Step 2.3: According to the coordinate component α of the midpoint of the diamond sector z , β z Calculate three basic vectors V4(α4,β4), V3(α3,β3), and V0(α0,β0); Where V4, V3, and V0 are three basic vectors, and sign(*) is the sign function; Step 3: Calculate the action time t4, t3, t0 of the three basic vectors V4, V3, V0 according to the volt-second balance principle; Where, T s is the sampling period, t4, t3, t0 are the action times of the three basic vectors V4, V3, V0, and abs(*) is the absolute value function.

3. The reference vector positioning and common mode voltage suppression method of the cascaded H-bridge converter SVM strategy according to claim 1, characterized in that: The step 4 is the common mode voltage suppression part, and the detailed steps are as follows: Step 4.1: Calculate the correction factors of V4, V3, and V0 based on the two characteristic factors of the diamond sector; For the basic vector V4, the correction factors p4 and q4 are calculated as follows: For the basic vector V3, the correction factors p3 and q3 are calculated as follows: For the basic vector V0, the correction factors p0 and q0 are calculated as follows: Step 4.2: Calculate the maximum switching state of V4, V3, and V0 according to the correction factor; where i = 4, 3, 0; For the basic vector V i The correction factor is p i ,q i , the maximum switch state is S i (a i ,b i ,c i ); If p i ≥0 and q i ≥0, then w i1 =1,w i2 =0,w i3 =0; If p i <0 and (q i -p i )≥0, then w i1 =0,w i2 =1,w i3 =0; If q i <0 and (q i -p i )<0, then w i1 =0,w i2 =0,w i3 =1; Maximum switching state S i (a i ,b i ,c i ) is calculated as follows: Step 4.3: Calculate the number of redundant switch states R4, R3, R0 of V4, V3, V0; where i = 4, 3, 0; For the basic vector V i The number of redundant switch states R i The calculation is as follows: Step 4.4: Calculate the common mode voltages N4, N3, and N0 of the maximum switching states S4 (a4, b4, c4), S3 (a3, b3, c3), and S0 (a0, b0, c0) according to the definition of common mode voltage; where i = 4, 3, 0; Step 4.5: Calculate the correction coefficients H4, H3, H0 of V4, V3, V0; where i = 4, 3, 0; For the basic vector V i Its correction factor H i Determine as follows: If the common mode voltage N i ≤0, then H i =0; If the common mode voltage N i >0, then H i =min(round(N i ),(R i -1); Step 4.6: Calculate the corrected switch state according to the correction coefficient; where i = 4, 3, 0; For the basic vector V i Its correction factor is H i , the corrected switch state is S ii (a ii ,b ii ,c ii ) is calculated as follows:

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