Neutral-point potential balancing method for three-level SVPWM (Space Vector Pulse Width Modulation) control based on multi-segment small vector

Abstract

The invention discloses a multi-segment small vector-based three-level SVPWM (Space Vector Pulse Width Modulation) controlled neutral-point potential balancing method, which comprises the following steps of: S1, judging a current sector in a 60-degree coordinate system according to an internally acquired target voltage value; s2, calculating the action time T1, T2 and T3 of the basic vector of the sector by using the existing universal method and technology; and S3, if the current sector belongs to a special sector using a multi-segment vector sequence, obtaining current adjustment coefficients K1 and K2 according to a midpoint potential adjustment coefficient operation rule, then calculating switching time Ta1, Ta2, Tb1, Tb2, Tc1 and Tc2 of a space vector according to the coefficients, and if the current sector is a common sector, directly using an existing general technical method to calculate switching time Ta1, Ta2, Tb1, Tb2, Tc1 and Tc2 of the space vector in the common sector. The neutral-point potential adjustment coefficients K1 and K2 are added when paired small vectors are used according to the switching time Ta1, Ta2, Tb1, Tb2, Tc1 and Tc2 of the corresponding space vectors, and the neutral-point potential adjustment capability of the control method is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of midpoint potential balancing, and in particular to a midpoint potential balancing method of three-level SVPWM control based on multi-segment small vectors. Background Art

[0002] With the development of power electronics technology, inverters are increasingly used in various fields. As an advanced inverter structure, the three-level NPC inverter has the advantages of high output waveform quality, low switching device withstand voltage, and redundant design. Therefore, it is widely used in uninterruptible power supply, DC transmission, electric locomotives and other fields.

[0003] The output performance of the three-level inverter mainly depends on the modulation algorithm. SVPWM technology is widely used in three-level inverters due to its easy digital implementation and high voltage utilization. The traditional seven-segment SVPWM algorithm cannot use small vectors symmetrically when constructing the vector sequence, which will introduce the problem of midpoint potential fluctuation. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies in the prior art, the present invention provides a midpoint potential balancing method for three-level SVPWM control based on multi-segment small vectors to solve the problems raised in the above background technology.

[0006] (II) Technical solution

[0007] To achieve the above object, the present invention provides the following technical solution: a midpoint potential balancing method for three-level SVPWM control based on multi-segment small vectors, the midpoint potential balancing method comprising:

[0008] S1, based on the internally acquired target voltage value, determine the current sector in the 60° coordinate system;

[0009] S2, using existing general methods and technologies, calculate the action time T1, T2, T3 of the basic vector of the sector;

[0010] S3, if the current sector belongs to a special sector using a multi-segment vector sequence, then according to the midpoint potential adjustment coefficient operation rule, obtain the current adjustment coefficients K1 and K2, and then calculate the switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector according to the coefficient; if it is a common sector, directly use the existing general technical method to calculate the corresponding switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector in the common sector;

[0011] S4, according to the adjustment coefficients K1 and K2 described in S3, it is necessary to make real-time adjustments according to the deviation of the midpoint potential detected during the real-time control process and the direction of the midpoint current at the midpoint position, the value range of K1 is between 0 and 2 (excluding the boundary), and the value range of K2 is between 0 and 1 (excluding the boundary);

[0012] S5, calculate the space vector switching time, define the time points of space vector switching of phases A, B, and C as Ta1, Ta2, Tb1, Tb2, Tc1, and Tc2, respectively, where Ta1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase A, Ta2 is the switching time of the inner tube of the upper bridge arm IGBT of phase A, Tb1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase B, Tb2 is the switching time of the inner tube of the upper bridge arm IGBT of phase B, Tc1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase C, and Tc2 is the switching time of the inner tube of the upper bridge arm IGBT of phase C. Define Ts as the PWM switching cycle time.

[0013] As a preferred solution, S4 adopts the following rules:

[0014] Rule 1: When Ud is greater than the positive adjustment start threshold (positive number), if io>0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will decrease the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged;

[0015] Rule 2: When Ud is less than the negative adjustment threshold (negative number), if io>0, K1 and K2 will reduce the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged.

[0016] As a preferred solution, in S4, Ud is set as the difference between the actual sampled bus midpoint voltage and half of the actual bus total voltage, and io is set as the current value at the midpoint position at the current moment, with the direction of the current flow from the midpoint position being positive.

[0017] As a preferred solution, in S5, the corresponding midpoint potential balance calculation formula in each sector is as follows:

[0018] In sector I-①:

[0019] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0020] Ta2 = 0;

[0021] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0022] Tb2=(K1*T1) / 4;

[0023] Tc1 = Ts / 2;

[0024] Tc2=(K1*T1) / 4+(K2*T2) / 4;

[0025] Ogi Ward I-③ Middle:

[0026] Ta1=(K1*T1) / 4+(K2*T2) / 4;

[0027] Ta2 = 0;

[0028] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0029] Tb2=(K1*T1) / 4;

[0030] Tc1 = Ts / 2;

[0031] Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0032] Ogi Ward II-① Middle:

[0033] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0034] Ta2=(K1*T1) / 4;

[0035] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0036] Tb2 = 0;

[0037] Tc1 = Ts / 2;

[0038] Tc2=(K1*T1) / 4+(K2*T2) / 4;

[0039] Ogi Ward II-③ Middle:

[0040] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0041] Ta2=(K1*T1) / 4;

[0042] Tb1=(K1*T1) / 4+(K2*T2) / 4;

[0043] Tb2 = 0;

[0044] Tc1=Ts / 2;

[0045] Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0046] In Sector III-①:

[0047] Ta1=Ts / 2;

[0048] Ta2=(K1*T1) / 4+(K2*T2) / 4;

[0049] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0050] Tb2 = 0;

[0051] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4;

[0052] In Sector III-③:

[0053] Ta1=Ts / 2;

[0054] Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0055] Tb1=(K1*T1) / 4+(K2*T2) / 4;

[0056] Tb2 = 0;

[0057] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4;

[0058] In Sector IV-①:

[0059] Ta1=Ts / 2;

[0060] Ta2=(K1*T1) / 4+(K2*T2) / 4;

[0061] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4;

[0062] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0063] Tc2 = 0;

[0064] Ogi Ward IV-③ Middle:

[0065] Ta1 = Ts / 2;

[0066] Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0067] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4;

[0068] Tc1=(K1*T1) / 4+(K2*T2) / 4;

[0069] Tc2 = 0;

[0070] Ogi Ward V-① Middle:

[0071] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0072] Tb1 = Ts / 2;

[0073] Tb2=(K1*T1) / 4+(K2*T2) / 4;

[0074] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0075] Tc2 = 0;

[0076] Ogi Ward V-③ Middle:

[0077] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0078] Tb1 = Ts / 2;

[0079] Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0080] Tc1=(K1*T1) / 4+(K2*T2) / 4;

[0081] Tc2 = 0;

[0082] In Sector VI-①:

[0083] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0084] Ta2 = 0;

[0085] Tb1 = Ts / 2;

[0086] Tb2=(K1*T1) / 4+(K2*T2) / 4;

[0087] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0088] Tc2 = (K1*T1) / 4;

[0089] In Sector VI-③:

[0090] Ta1=(K1*T1) / 4+(K2*T2) / 4;

[0091] Ta2 = 0;

[0092] Tb1 = Ts / 2;

[0093] Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0094] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0095] Tc2 = (K1*T1) / 4.

[0096] (III) Beneficial effects

[0097] Compared with the prior art, the present invention provides a midpoint potential balancing method for three-level SVPWM control based on multi-segment small vectors, which has the following beneficial effects: for the traditional seven-segment SVPWM algorithm, the small vectors cannot be used symmetrically when constructing the vector sequence, which will introduce the problem of midpoint potential fluctuation, and a multi-segment SVPWM control method is designed. The new method uses paired small vectors and other vectors to form a multi-segment control method in a specific sector. At the same time, the midpoint potential adjustment coefficients K1 and K2 are added when paired small vectors are used, thereby enhancing the control method's ability to adjust the midpoint potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Figure 1This is a flow chart of a midpoint potential balancing method of three-level SVPWM control based on multi-segment small vectors according to the present invention;

[0099] Figure 2 A midpoint adjustment coefficient operation rule diagram of a midpoint potential balancing method of a three-level SVPWM control based on multi-segment small vectors according to the present invention;

[0100] Figure 3 The sector division diagram of the midpoint potential balancing method of the three-level SVPWM control based on multi-segment small vectors of the present invention. DETAILED DESCRIPTION

[0101] In order to better understand the purpose, structure and function of the present invention, the specific implementation mode of the present invention is now described with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

[0102] refer to Figure 1-3 The present invention provides a midpoint potential balancing method for three-level SVPWM control based on multi-segment small vectors, the midpoint potential balancing method comprising:

[0103] S1, based on the internally acquired target voltage value, determine the current sector in the 60° coordinate system;

[0104] S2, using existing general methods and technologies, calculate the action time T1, T2, T3 of the basic vector of the sector;

[0105] S3, if the current sector belongs to a special sector using a multi-segment vector sequence, then according to the midpoint potential adjustment coefficient operation rule, obtain the current adjustment coefficients K1 and K2, and then calculate the switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector according to the coefficient; if it is a common sector, directly use the existing general technical method to calculate the corresponding switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector in the common sector;

[0106] S4, according to the adjustment coefficients K1 and K2 described in S3, it is necessary to make real-time adjustments according to the deviation of the midpoint potential detected during the real-time control process and the direction of the midpoint current at the midpoint position, the value range of K1 is between 0 and 2 (excluding the boundary), and the value range of K2 is between 0 and 1 (excluding the boundary);

[0107] S5, calculate the space vector switching time, define the time points of space vector switching of phases A, B, and C as Ta1, Ta2, Tb1, Tb2, Tc1, and Tc2, respectively, where Ta1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase A, Ta2 is the switching time of the inner tube of the upper bridge arm IGBT of phase A, Tb1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase B, Tb2 is the switching time of the inner tube of the upper bridge arm IGBT of phase B, Tc1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase C, and Tc2 is the switching time of the inner tube of the upper bridge arm IGBT of phase C. Define Ts as the PWM switching cycle time.

[0108] S4 adopts the following rules:

[0109] Rule 1: When Ud is greater than the positive adjustment start threshold (positive number), if io>0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will decrease the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged;

[0110] Rule 2: When Ud is less than the negative adjustment threshold (negative number), if io>0, K1 and K2 will reduce the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged.

[0111] In S4, Ud is set as the difference between the actual sampled bus midpoint voltage and half of the actual bus total voltage, and io is set as the current value at the midpoint position at the current moment, with the direction of the current flow from the midpoint position being positive.

[0112] like Figure 2 As shown in , the entire area is divided into 6 large sectors, namely sector I, sector II, sector III, sector IV, sector V, and sector VI. Each large sector is further divided into 4 small sectors, namely ①, ②, ③, and ④. V0, V1, V2, ..., V18 in the figure are the names of the defined basic vectors.

[0113] Table 1 gives the specific definitions of all vectors. V0 is the vector corresponding to the origin, and V1~V6 are small vectors, which are divided into positive small vectors and negative small vectors. In the following table, p represents a positive vector and n represents a negative vector. For example, the positive vector of V1 is V1p, and the negative vector is V1n. V7~V12 correspond to medium vectors, and V13~V18 correspond to large vectors. Both medium vectors and large vectors are unique.

[0114]

[0115]

[0116] Table 1 Vector definition table

[0117] In all sectors, all small sectors containing two small vectors need to use a multi-segment sequence, including small sectors ① and ③ in sectors I to VI. The construction of the vector sequence in this method starts with a negative small vector.

[0118] This part of the sector division and related definitions are currently common methods and are classified as existing technology types.

[0119] 1.1 Multi-segment sequence corresponding to sector I

[0120] The modulation sequence of sector I-① vector is as follows:

[0121]

[0122]

[0123] Table 2 Sector I-① vector modulation sequence Sector I-③ vector modulation sequence is as follows

[0124]

[0125] Table 3 Sector I-③ vector modulation sequence

[0126] In Table 2, T1, T2, and T3 correspond to the total time of the action of vectors V1, V2, and V0, respectively.

[0127] In Table 3, T1, T2, and T3 correspond to the total time of the action of vectors V1, V2, and V7, respectively.

[0128] In Table 2 and Table 3, coefficient K is the midpoint potential adjustment coefficient, which needs to be adjusted and set according to the change of the current midpoint voltage. The K mentioned below is the same coefficient.

[0129] 1.2 Multi-segment sequence corresponding to sector II

[0130] The modulation sequence of sector II-① vector is as follows:

[0131]

[0132]

[0133] Table 4 Sector II-① vector modulation sequence Sector II-③ vector modulation sequence is as follows

[0134]

[0135] Table 5 Sector II-③ vector modulation sequence

[0136] In Table 4, T1, T2, and T3 correspond to the total time of the action of vectors V3, V2, and V0, respectively. In Table 5, T1, T2, and T3 correspond to the total time of the action of vectors V3, V2, and V8, respectively. 1.3 Multi-segment sequence corresponding to sector III The modulation sequence of sector III-① vector is as follows

[0137]

[0138] Table 6 Sector III-① vector modulation sequence Sector III-③ vector modulation sequence is as follows

[0139]

[0140] Table 7 Sector III-③ vector modulation sequence In Table 6, T1, T2, and T3 correspond to the total time of the action of vectors V3, V4, and V0, respectively. In Table 7, T1, T2, and T3 correspond to the total time of the action of vectors V3, V4, and V9, respectively. 1.4 Multi-segment sequence corresponding to sector IV The modulation sequence of sector IV-① vector is as follows

[0141]

[0142] Table 8 Sector IV-① vector modulation sequence Sector IV-③ vector modulation sequence is as follows

[0143]

[0144]

[0145] Table 9 Sector IV-③ vector modulation sequence

[0146] In Table 8, T1, T2, and T3 correspond to the total time of the action of vectors V5, V4, and V0, respectively. In Table 9, T1, T2, and T3 correspond to the total time of the action of vectors V5, V4, and V10, respectively. The modulation sequence of the multi-segment sequence sector V-① vector corresponding to 1.5 sector V is as follows:

[0147]

[0148] Table 10 Sector V-① vector modulation sequence Sector V-③ vector modulation sequence is as follows

[0149]

[0150]

[0151] Table 11 Sector V-③ vector modulation sequence

[0152] In Table 10, T1, T2, and T3 correspond to the total time of the action of vectors V5, V6, and V0, respectively.

[0153] In Table 11, T1, T2, and T3 correspond to the total time of action of vectors V5, V6, and V11, respectively.

[0154] 1.6 Multi-segment sequence corresponding to sector VI

[0155] The modulation sequence of the sector VI-① vector is as follows:

[0156]

[0157] Table 12 Sector VI-① vector modulation sequence Sector VI-③ vector modulation sequence is as follows

[0158]

[0159] Table 13 Sector VI-③ vector modulation sequence

[0160] In Table 10, T1, T2, and T3 correspond to the total time of the action of vectors V1, V6, and V0, respectively.

[0161] In Table 11, T1, T2, and T3 correspond to the total time of action of vectors V1, V6, and V12, respectively.

[0162] For the calculation of space vector switching time, in each sector, the action time of the three basic vectors is defined as T1, T2, and T3 respectively. The time points of space vector switching of phases A, B, and C are defined as Ta1, Ta2, Tb1, Tb2, Tc1, and Tc2 respectively, where Ta1 is the switching time point of the external IGBT tube of the upper bridge arm of phase A, Ta2 is the switching time of the internal IGBT tube of the upper bridge arm of phase A, Tb1 is the switching time point of the external IGBT tube of the upper bridge arm of phase B, Tb2 is the switching time of the internal IGBT tube of the upper bridge arm of phase B, Tc1 is the switching time point of the external IGBT tube of the upper bridge arm of phase C, and Tc2 is the switching time of the internal IGBT tube of the upper bridge arm of phase C. Ts is defined as the PWM switching cycle time.

[0163] In sector I-①:

[0164] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0165] Ta2 = 0;

[0166] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2;

[0167] Tb2 = (K1*T1) / 4;

[0168] Tc1=Ts / 2;

[0169] Tc2=(K1*T1) / 4+(K2*T2) / 4;

[0170] In sector I-③:

[0171] Ta1=(K1*T1) / 4+(K2*T2) / 4;

[0172] Ta2 = 0;

[0173] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4;

[0174] Tc1=Ts / 2;

[0175] Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0176] In Sector II-①:

[0177] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0178] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0179] Tb2 = 0;

[0180] Tc1=Ts / 2;

[0181] Tc2=(K1*T1) / 4+(K2*T2) / 4;

[0182] In Sector II-③:

[0183] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0184] Tb1=(K1*T1) / 4+(K2*T2) / 4;

[0185] Tb2 = 0;

[0186] Tc1=Ts / 2;

[0187] Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0188] In Sector III-①:

[0189] Ta1 = Ts / 2;

[0190] Ta2=(K1*T1) / 4+(K2*T2) / 4;

[0191] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0192] Tb2 = 0;

[0193] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4;

[0194] Ogi Ward III-③ Middle:

[0195] Ta1 = Ts / 2;

[0196] Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0197] Tb1=(K1*T1) / 4+(K2*T2) / 4;

[0198] Tb2 = 0;

[0199] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4;

[0200] Ogi Ward IV-① Middle:

[0201] Ta1 = Ts / 2;

[0202] Ta2=(K1*T1) / 4+(K2*T2) / 4;

[0203] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4;

[0204] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0205] Tc2 = 0;

[0206] Ogi Ward IV-③ Middle:

[0207] Ta1 = Ts / 2;

[0208] Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0209] Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4;

[0210] Tc1=(K1*T1) / 4+(K2*T2) / 4;

[0211] Tc2 = 0;

[0212] In sector V-①:

[0213] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0214] Tb1 = Ts / 2;

[0215] Tb2=(K1*T1) / 4+(K2*T2) / 4;

[0216] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0217] Tc2 = 0;

[0218] In sector V-③:

[0219] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4;

[0220] Tb1 = Ts / 2;

[0221] Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0222] Tc1=(K1*T1) / 4+(K2*T2) / 4;

[0223] Tc2 = 0;

[0224] In Sector VI-①:

[0225] Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0226] Ta2 = 0;

[0227] Tb1 = Ts / 2;

[0228] Tb2=(K1*T1) / 4+(K2*T2) / 4;

[0229] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4;

[0230] In Sector VI-③:

[0231] Ta1=(K1*T1) / 4+(K2*T2) / 4;

[0232] Ta2 = 0;

[0233] Tb1 = Ts / 2;

[0234] Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2;

[0235] Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4.

[0236] For the conventional seven-segment sequence and space vector switching time calculation of other sectors, except for the special sectors mentioned in 1.1 to 1.6 that use the new multi-segment modulation sequence, other sectors use the conventional seven-segment sequence for modulation. At the same time, the switching time of the space vector is also the conventional formula.

[0237] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A midpoint potential balancing method for three-level SVPWM control based on multi-segment small vectors, characterized in that: The midpoint potential balance method includes: S1, based on the internally acquired target voltage value, determine the current sector in the 60° coordinate system; S2, using existing general methods and technologies, calculate the action time T1, T2, T3 of the basic vector of the sector; S3, if the current sector belongs to a special sector using a multi-segment vector sequence, then according to the midpoint potential adjustment coefficient operation rule, obtain the current adjustment coefficients K1 and K2, and then calculate the switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector according to the coefficient; if it is a common sector, directly use the existing general technical method to calculate the corresponding switching time Ta1, Ta2, Tb1, Tb2, Tc1, Tc2 of the space vector in the common sector; S4, according to the adjustment coefficients K1 and K2 described in S3, it is necessary to make real-time adjustments according to the deviation of the midpoint potential detected during the real-time control process and the direction of the midpoint current at the midpoint position, the value range of K1 is between 0 and 2 (excluding the boundary), and the value range of K2 is between 0 and 1 (excluding the boundary); S5, calculate the space vector switching time, define the time points of space vector switching of phases A, B, and C as Ta1, Ta2, Tb1, Tb2, Tc1, and Tc2, respectively, where Ta1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase A, Ta2 is the switching time of the inner tube of the upper bridge arm IGBT of phase A, Tb1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase B, Tb2 is the switching time of the inner tube of the upper bridge arm IGBT of phase B, Tc1 is the switching time point of the outer tube of the upper bridge arm IGBT of phase C, and Tc2 is the switching time of the inner tube of the upper bridge arm IGBT of phase C. Define Ts as the PWM switching cycle time.

2. The midpoint potential balancing method of three-level SVPWM control based on multi-segment small vector according to claim 1 is characterized in that: The S4 adopts the following rules: Rule 1: When Ud is greater than the positive adjustment start threshold (positive number), if io>0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will decrease the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged; Rule 2: When Ud is less than the negative adjustment threshold (negative number), if io>0, K1 and K2 will reduce the adjustment step size based on their current values ​​respectively; if io<0, K1 and K2 will increase the adjustment step size based on their current values ​​respectively; if io=0, K1 and K2 will remain unchanged.

3. The midpoint potential balancing method of three-level SVPWM control based on multi-segment small vector according to claim 1 is characterized in that: In S4, Ud is set as the difference between the actual sampled bus midpoint voltage and half of the actual bus total voltage, and io is set as the current value at the midpoint position at the current moment, with the direction of the current flow from the midpoint position being positive.

4. The midpoint potential balancing method of three-level SVPWM control based on multi-segment small vector according to claim 1 is characterized in that: In S5, the corresponding midpoint potential balance calculation formula in each sector is as follows: In sector I-①: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Ta2 = 0; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2 = (K1*T1) / 4; Tc1=Ts / 2; Tc2=(K1*T1) / 4+(K2*T2) / 4; In sector I-③: Ta1=(K1*T1) / 4+(K2*T2) / 4; Ta2 = 0; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2 = (K1*T1) / 4; Tc1=Ts / 2; Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; In Sector II-①: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tb2 = 0; Tc1=Ts / 2; Tc2=(K1*T1) / 4+(K2*T2) / 4; In Sector II-③: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4; Tb1=(K1*T1) / 4+(K2*T2) / 4; Tb2 = 0; Tc1=Ts / 2; Tc2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; In Sector III-①: Ta1=Ts / 2; Ta2=(K1*T1) / 4+(K2*T2) / 4; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tb2 = 0; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4; In Sector III-③: Ta1=Ts / 2; Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tb1=(K1*T1) / 4+(K2*T2) / 4; Tb2 = 0; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4; In Sector IV-①: Ta1=Ts / 2; Ta2=(K1*T1) / 4+(K2*T2) / 4; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tc2 = 0; In Sector IV-③: Ta1=Ts / 2; Ta2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tb1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tb2=(K1*T1) / 4; Tc1=(K1*T1) / 4+(K2*T2) / 4; Tc2 = 0; Ogi Ward V-① Middle: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4; Tb1 = Ts / 2; Tb2=(K1*T1) / 4+(K2*T2) / 4; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tc2 = 0; Ogi Ward V-③ Middle: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Ta2=(K1*T1) / 4; Tb1 = Ts / 2; Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tc1=(K1*T1) / 4+(K2*T2) / 4; Tc2 = 0; Ogi Ward VI-① Middle: Ta1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Ta2 = 0; Tb1 = Ts / 2; Tb2=(K1*T1) / 4+(K2*T2) / 4; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4; Ogi Ward VI-③ Middle: Ta1=(K1*T1) / 4+(K2*T2) / 4; Ta2 = 0; Tb1 = Ts / 2; Tb2=(K1*T1) / 4+(K2*T2) / 4+T3 / 2; Tc1=(K1*T1) / 4+(K2*T2) / 4+T3 / 2+(2-K1) / 4=T1 / 2+(K2*T2) / 4+T3 / 2; Tc2=(K1*T1) / 4.

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