A phase-shifted space vector modulation method for an H-bridge cascaded multi-level inverter

Abstract

The application discloses a phase-shifting space vector modulation method of an H-bridge cascaded multi-level inverter, on the basis of traditional alpha-beta coordinates, alpha coordinates are stretched to 3 times of the original value, beta coordinates are stretched to times of the original value to obtain p-q coordinates, basic vectors all fall on integer grids under the p-q coordinates; a space vector phase-shifting modulation algorithm realizes two-level space vectors under the p-q coordinates, modulates left half bridge arms and right half bridge arms of the cascaded inverter respectively, and appropriately shifts the reference vectors between adjacent two levels of the inverter, so as to realize control on the cascaded multi-level. The application has the advantages of simple and easy-to-implement modulation method and strong expansibility.

Description

Technical Field

[0001] This invention relates to the field of inverter modulation technology, and in particular to a phase-shifting space vector modulation method for an H-bridge cascaded multilevel inverter. Background Technology

[0002] Due to the limitations of capacity and voltage of power electronic devices, a single power electronic device cannot be used independently in high-voltage and high-power applications. To solve this problem, multiple electronic device modules can be cascaded to achieve high-voltage and high-power output, thus giving rise to cascaded multilevel inverters.

[0003] Each phase of an H-bridge cascaded multilevel inverter consists of several power units connected in series. It has advantages such as large output capacity, low harmonic content, modularity, and easy expansion. Therefore, it has been widely used in medium and high voltage speed regulation, high-power active power filtering, and AC flexible power supply.

[0004] The main modulation methods for H-bridge cascaded multilevel inverters include carrier phase shifting, carrier stacking, and space vector modulation.

[0005] Compared with carrier modulation, space vector modulation has advantages such as better harmonic characteristics, higher voltage utilization, and easier digital implementation.

[0006] However, as the number of power units connected in series increases, the redundancy of the switching states corresponding to the basic vector also increases. The calculation of the sector location of the reference vector and the action time of the basic vector becomes extremely complex, making it difficult to implement the space vector modulation algorithm and thus difficult to use in practical systems.

[0007] Therefore, it is necessary to design a phase-shifting space vector modulation method for H-bridge cascaded multilevel inverters. Summary of the Invention

[0008] The purpose of this invention is to provide a phase-shift space vector modulation method for an H-bridge cascaded multilevel inverter. This invention has the advantages of simple and easy-to-implement modulation method, and strong scalability.

[0009] The technical solution of this invention: A phase-shifting space vector modulation method for an H-bridge cascaded multilevel inverter, comprising the following steps:

[0010] S1. Transform the α-β coordinate system into the pq coordinate system: Stretch the α coordinates in the α-β coordinate system to three times their original value, and stretch the β coordinates back to their original value. Multiply by 1 to obtain the pq coordinate system;

[0011] S2. Establish a mathematical model of the two-level reference vector trajectory in the pq coordinate system. Where m is the modulation coefficient, 0 <m≤1,p rp is the horizontal coordinate of the reference vector r q is the vertical coordinate of the reference vector

[0012] S3, judging the sector where the reference vector V r (p r , q r ) is located, wherein V r (p r , q r ) is

[0013] S4, calculating the basic vector action time of the synthesized reference vector: determining the sector where the reference vector is located, determining the basic vector according to the sector where the reference vector is located, and calculating the basic vector action time by using the volt-second balance principle;

[0014] S5, switching path of the basic vector of the synthesized reference vector: switching by using the switch state vector corresponding to the basic vector.

[0015] In the aforementioned phase-shifted space vector modulation method of the H-bridge cascaded multi-level inverter, S1 converts the α-β coordinate system into the p-q coordinate system, and the specific content is as follows:

[0016] S1.1, the basic vector expression of the two-level space vector modulation method in the α-β coordinate system is:

[0017]

[0018] In formula (1), α and β are the horizontal coordinate and the vertical coordinate in the α-β coordinate system respectively, a, b and c are the level numbers of the half-bridge three-phase output of each H-bridge of the inverter and are integers, and can only take 0 and 1;

[0019] S1.2, after stretching the α coordinate in the α-β coordinate system to 3 times of the original value and stretching the β coordinate to 2 times of the original value, the p-q coordinate system is obtained, which is:

[0020]

[0021] In formula (2), p and q are the horizontal coordinate and the vertical coordinate in the p-q coordinate system respectively;

[0022] S1.3, six non-zero basic vectors V1(2, 0), V2(1, 1), V3(-1, 1), V4(-2, 0), V5(2, 0) and V6(1, -1) and one zero vector V0(0, 0) can be obtained from formula (2);

[0023] S1.4, six sectors are formed based on the non-zero vectors and the zero vector, and each sector is an isosceles right triangle, which are:

[0024] ​V0, V1, V6 constitute a first sector, namely sector I;

[0025] V0, V1, V2 constitute a second sector, namely sector II;

[0026] V0, V2, V3 constitute a third sector, namely sector III;

[0027] V0, V3, V4 constitute a fourth sector, namely sector IV;

[0028] V0, V4, V5 constitute a fifth sector, namely sector V;

[0029] V0, V5, V6 constitute a sixth sector, namely sector VI;

[0030] S1.5, define (a, b, c) as the basic vector V (p, q) switch state vector satisfying formula (2);

[0031] Six non-zero basic vectors and only one switch state vector, respectively: S1 (1, 0, 0), S2 (1, 1, 0), S3 (0, 1, 0), S4 (0, 1, 1), S5 (0, 0, 1), S6 (1, 0, 1);

[0032] Zero basic vector V0 (0, 0) corresponds to two switch state vectors, respectively: S0 (0, 0, 0), S7 (1, 1, 1).

[0033] In the phase-shifted space vector modulation method of the aforementioned H-bridge cascaded multilevel inverter, S2 establishes a mathematical model of a two-level reference vector trajectory in the p-q coordinate system The specific content is as follows:

[0034] S2.1, let the ideal three-phase sinusoidal voltage mathematical model be:

[0035]

[0036] In formula (3), U ra , U rb , U rc respectively represent the reference voltages A, B, and C three-phase voltage, and U rm is the amplitude of each phase of the reference voltage;

[0037] S2.2, substituting formula (3) into formula (1) gives the reference voltage vector U r in the α-β coordinate system as:

[0038]

[0039] As can be seen from formula (4), the reference voltage vector U r in the α-β coordinate system is a circular trajectory with a radius of U rm;

[0040] S2.3, divide formula (4) by E to normalize to obtain reference vector V r (α r , β r ) is:

[0041]

[0042] In formula (5), defined as reference vector V r The radius of the trajectory, E is the supply voltage of each cascaded H-bridge;

[0043] S2.4, by formula (1) and formula (5), reference vector V r The maximum radius of the trajectory

[0044] S2.5, reference vector V r Get the maximum radius value R rmax When, the input DC voltage utilization rate of the corresponding inverter is the highest, which is set to 1; Introducing parameter m to adjust the input DC voltage utilization rate of the inverter, get:

[0045]

[0046] S2.6, from formula (6) Substitute formula (5) to obtain reference vector V r (α r , β r ) is:

[0047]

[0048] S2.7, convert reference vector V r (α r , β r ) in α-β coordinate system to reference vector V r (p r , q r ) in p-q coordinate system, get:

[0049]

[0050] S2.8, from formula (8), the mathematical model of two-level reference vector trajectory in p-q coordinates can be obtained:

[0051]

[0052] In the phase-shifted space vector modulation method of the H-bridge cascaded multilevel inverter described above, S3 describes the judgment reference vector V r (pr , q r ) is located, and the specific content is:

[0053] If p r > 0 && q r > 0 && |p r |>|q r |, the reference vector V r is located in the first sector;

[0054] If p r > 0 && q r > 0 && |p r |>|q r |, the reference vector V r is located in the second sector;

[0055] If (p r > 0 && q r > 0 && |p r |<|q r |) OR (p r < 0 && q r > 0 && |p r |<|q r |), the reference vector V r is located in the third sector;

[0056] If p r < 0 && q r > 0 && |p r |>|q r |, the reference vector V r is located in the fourth sector;

[0057] If p r < 0 && q r < 0 && |p r |>|q r |, the reference vector V r is located in the fifth sector;

[0058] If (p r < 0 && q r < 0 && |p r |<|q r |) OR (p r > 0 && q r < 0 && |p r |<|q r |), the reference vector V r is located in the sixth sector.

[0059] In the phase-shifted space vector modulation method of the aforementioned H-bridge cascaded multi-level inverter, the basic vector action time of the synthesized reference vector is calculated according to S4, and the specific content is as follows:

[0060] S4.1, the basic vector action time of the synthesized reference vector V r is calculated according to the basic vectors V0, V1 and V6 in the first sector, and the synthesized reference vector V r is obtained as follows:

[0061]

[0062] S4.2, according to the coordinate values of the basic vectors and the reference vector, the following formula can be obtained:

[0063]

[0064] S4.3, the basic vector action time of the sector I is solved from formula (11) as follows:

[0065] t6=-q r *T s ;

[0066] S4.4, the basic vector action time of other sectors is obtained as follows:

[0067] Sector II: t2=q r *T s ;

[0068] Sector III: t0=(1-q r )*T s ,

[0069] Sector IV: t3=q r *T s ,

[0070] Sector V: t5=-q r *T s ;

[0071] Sector VI: t0=(1+q r )*T s ,

[0072] wherein t0, t1, t2, t3, t4, t5 and t6 respectively represent the action time of the basic vectors V0, V1, V2, V3, V4, V5 and V6, and T s represents the sampling period of the reference vector.

[0073] In the phase-shifted space vector modulation method of the aforementioned H-bridge cascaded multi-level inverter, the switching path of the sub-reference vector composed of the basic vectors of the reference vector is as follows:

[0074] Sector I: the switching path is S0(0, 0, 0)→S1(1, 0, 0)→S6(1, 0, 1)→S7(1, 1, 1)→S6(1, 0, 1)→S1(1, 0, 0)→S0(0, 0, 0), and the corresponding action time distribution in the switching path of the switch state vector is t0 / 4→t1 / 2→t6 / 2→t0 / 2→t6 / 2→t1 / 2→t0 / 4;

[0075] Sector II: the switching path is S0(0, 0, 0)→S1(1, 0, 0)→S2(1, 1, 0)→S7(1, 1, 1)→S2(1, 1, 0)→S1(1, 0, 0)→S0(0, 0, 0), and the action time distribution is t0 / 4→t1 / 2→t2 / 2→t0 / 2→t2 / 2→t1 / 2→t0 / 4;

[0076] Sector III: the switching path is S0(0, 0, 0)→S3(0, 1, 0)→S2(1, 1, 0)→S7(1, 1, 1)→S2(1, 1, 0)→S3(0, 1, 0)→S0(0, 0, 0), and the action time distribution is t0 / 4→t3 / 2→t2 / 2→t0 / 2→t2 / 2→t3 / 2→t0 / 4;

[0077] Sector IV: the switching path is S0(0, 0, 0)→S3(0, 1, 0)→S4(0, 1, 1)→S7(1, 1, 1)→S4(0, 1, 1)→S3(0, 1, 0)→S0(0, 0, 0), and the action time distribution is t0 / 4→t3 / 2→t4 / 2→t0 / 2→t4 / 2→t3 / 2→t0 / 4;

[0078] Sector V: the switching path is S0(0, 0, 0)→S5(0, 0, 1)→S4(0, 1, 1)→S7(1, 1, 1)→S4(0, 1, 1)→S5(0, 0, 1)→S0(0, 0, 0), and the action time distribution is t0 / 4→t5 / 2→t4 / 2→t0 / 2→t4 / 2→t5 / 2→t0 / 4;

[0079] Sector VI: the switching path is S0(0, 0, 0)→S5(0, 0, 1)→S6(1, 0, 1)→S7(1, 1, 1)→S6(1, 0, 1)→S5(0, 0, 1)→S0(0, 0, 0), and the action time distribution is t0 / 4→t5 / 2→t6 / 2→t0 / 2→t6 / 2→t5 / 2→t0 / 4.

[0080] Compared with the prior art, the application has the following beneficial effects:

[0081] Compared with the traditional space vector modulation method, the basic vectors of the traditional coordinate system all fall in non-integer coordinates, while the basic vectors of the p-q coordinate system of the application all fall in integer coordinates, thereby simplifying the calculation method and greatly improving the calculation speed.

[0082] Meanwhile, the basic vectors of the traditional space vector will increase the corresponding switch state vectors with the increase of the level number, thereby being not conducive to the realization of the space vector, while the switch state vectors corresponding to the basic vectors of the application are single and will not affect the number of the switch state vectors with the increase of the level number.

[0083] Therefore, the application has the advantages of simple and easy-to-implement modulation method and strong expansibility. BRIEF DESCRIPTION OF DRAWINGS

[0084] Figure 1 Reference vector trajectory and basic vector distribution diagram in the p-q coordinate system of the application;

[0085] Figure 2 Switching path and action time distribution diagram of the switch state vector in sector I of the application;

[0086] Figure 3 Topological diagram of three H-bridge cascaded inverters in the embodiment of the application;

[0087] Figure 4 Output phase voltage diagram of three H-bridge cascaded inverters in the embodiment of the application;

[0088] Figure 5 Topological diagram of n H-bridge cascaded inverters in the embodiment of the application. DETAILED DESCRIPTION

[0089] The application will be further described below in combination with the drawings and embodiments, but it is not used as the basis for limiting the application.

[0090] Embodiment. A phase-shifted space vector modulation method of H-bridge cascaded multilevel inverters, on the basis of the traditional alpha-beta coordinate, the alpha coordinate is stretched to 3 times of the original value, the beta coordinate is stretched to 3 times of the original value to obtain the p-q coordinate, the basic vectors all fall on the integer grid under the p-q coordinate; the space vector phase-shifted modulation algorithm realizes two-level space vectors under the p-q coordinate, modulates the left half bridge arm and the right half bridge arm of the multilevel cascaded inverter respectively, and appropriately shifts the phase of the reference vectors between the adjacent two levels of the inverter to realize the control of the cascaded multilevel;

[0091] The method comprises the following steps:

[0092] S1, converting the α-β coordinate system into the p-q coordinate system: stretching the α coordinate in the α-β coordinate system to 3 times the original value and the β coordinate to 2 times the original value to obtain the p-q coordinate system

[0093] S2, under the p-q coordinate, establishing a mathematical model of the two-level reference vector trajectory where m is a modulation coefficient, 0 r is the horizontal coordinate of the reference vector, and q r is the vertical coordinate of the reference vector

[0094] S3, judging the sector in which the reference vector V r (p r , q r ) is located, where V r (p r , q r ) is

[0095] S4, calculating the basic vector action time of the synthesized reference vector: determining the sector in which the reference vector is located, determining the basic vector according to the sector in which the reference vector is located, and calculating the basic vector action time by using the volt-second balance principle

[0096] S5, switching path of the basic vector of the synthesized reference vector: switching by using the switch state vector corresponding to the basic vector

[0097] S1, converting the α-β coordinate system into the p-q coordinate system, the specific content is as follows:

[0098] S1.1, the basic vector expression of the two-level space vector modulation method in the α-β coordinate system is:

[0099]

[0100] In formula (1), α and β are the horizontal coordinate and the vertical coordinate in the α-β coordinate system respectively, a, b and c are the level numbers of the half-bridge three-phase output of each H-bridge of the inverter and are integers, and can only be 0 and 1

[0101] As can be seen from formula (1), the basic vector (α, β) does not fall on the integer point in the α-β coordinate system

[0102] S1.2, after stretching the α coordinate in the α-β coordinate system to 3 times the original value and the β coordinate to 2 times the original value, the p-q coordinate system is obtained, which is:

[0103]

[0104] ​​In formula (2), p and q are horizontal and vertical coordinates in the p-q coordinate system, respectively.

[0105] As can be seen from formula (2), the basic vector (p, q) falls on an integer point in the p-q coordinate system, as shown in Figure 1

[0106] S1.3, six non-zero basic vectors V1(2, 0), V2(1, 1), V3(-1, 1), V4(-2, 0), V5(2, 0), V6(1, -1) and one zero vector V0(0, 0) can be obtained from formula (2);

[0107] S1.4, based on the non-zero vectors and the zero vector, six sectors are formed, each of which is an isosceles right triangle, and are respectively:

[0108] V0, V1 and V6 form the first sector, i.e. sector I;

[0109] V0, V1 and V2 form the second sector, i.e. sector II;

[0110] V0, V2 and V3 form the third sector, i.e. sector III;

[0111] V0, V3 and V4 form the fourth sector, i.e. sector IV;

[0112] V0, V4 and V5 form the fifth sector, i.e. sector V;

[0113] V0, V5 and V6 form the sixth sector, i.e. sector VI;

[0114] S1.5, define (a, b, c) satisfying formula (2) as the basic vector V(p, q) switch state vector;

[0115] The six non-zero basic vectors and only one switch state vector are respectively: S1(1, 0, 0), S2(1, 1, 0), S3(0, 1, 0), S4(0, 1, 1), S5(0, 0, 1), S6(1, 0, 1);

[0116] The zero basic vector V0(0, 0) corresponds to two switch state vectors, which are respectively: S0(0, 0, 0) and S7(1, 1, 1).

[0117] The ideal power supply for an alternating current motor is a three-phase sinusoidal voltage, i.e. the phase angles of A, B and C are sequentially different by 120°, and the space vector modulation method aims to take the ideal three-phase sinusoidal voltage as its reference voltage vector U r , and then the reference vector synthesized by the basic vectors is as close as possible to the ideal three-phase sinusoidal voltage signal.

[0118] ​The mathematical model described in S2 for establishing the trajectory of the two-level reference vector in the pq coordinate system. Its specific content is as follows:

[0119] S2.1. Let the mathematical model of an ideal three-phase sinusoidal voltage be:

[0120]

[0121] In equation (3), U ra U rb U rc These represent the reference voltages A, B, and C, respectively, and the three-phase voltages U. rm The amplitude of the reference voltage per phase;

[0122] S2.2 Substituting equation (3) into equation (1), we obtain the reference voltage vector U in the α-β coordinate system. r for:

[0123]

[0124] From equation (4), it can be seen that the reference voltage vector U r In the α-β coordinate system, the trajectory is a circle with radius U. rm ;

[0125] S2.3. Dividing equation (4) by E to normalize it yields the reference vector V. r (α r ,β r )for:

[0126]

[0127] In equation (5), Defined as reference vector V r The radius of the trajectory, E is the supply voltage for each cascaded H-bridge;

[0128] S2.4, combining equations (1) and (5), we obtain the reference vector V. r Maximum radius of trajectory

[0129] S2.5, Reference Vector V r Obtain the maximum radius value R rmax At this time, the inverter's input DC voltage utilization rate is the highest, which is set to 1; by introducing parameter m to adjust the inverter's input DC voltage utilization rate, we get:

[0130]

[0131] S2.6, From equation (6) we get Substituting into equation (5), we obtain the reference vector V. r(α r ,β r )for:

[0132]

[0133] S2.7, the reference vector V in the α-β coordinate system r (α r ,β r Convert to reference vector V in the pq coordinate system r (p r q r ),have to:

[0134]

[0135] S2.8 From equation (8), the mathematical model of the two-level reference vector trajectory in the pq coordinate system can be obtained as follows:

[0136] Its reference vector trajectory is shown in the appendix. Figure 1 As shown.

[0137] The reference vector V mentioned in S3 r (p r q r The sector containing the information is as follows:

[0138] If p r ≥0&&q r ≤0&&|p r |≥|q r |, then the reference vector V r Located in the first sector;

[0139] If p r >0&&q r >0&&|p r |>|q r |, then the reference vector V r Located in the second sector;

[0140] If (p) r >0&&q r >0&&|p r |<|q r |)OR(p r <0&&q r >0&&|p r |<|q r |), then the reference vector V r Located in the third sector;

[0141] If p r <0&&q r >0&&|pr |>|q r |, the reference vector V r is located in the fourth sector;

[0142] If p r <0&&q r <0&&|p r |>|q r |, the reference vector V r is located in the fifth sector;

[0143] If (p r <0&&q r <0&&|p r |<|q r |) OR (p r >0&&q r <0&&|p r |<|q r |), the reference vector V r is located in the sixth sector.

[0144] S4. The basic vector action time of the synthetic reference vector is calculated as described in S4, and the details are as follows:

[0145] S4.1, the basic vector action time of the synthetic reference vector V r is calculated as follows: Figure 1 r As shown in the attached , the basic vectors are V0, V1, and V6, and the synthetic reference vector V r is obtained as follows:

[0146]

[0147] S4.2, according to the coordinate values of the basic vectors and the reference vector, the following formula can be obtained:

[0148]

[0149] S4.3, the basic vector action time of sector I is solved from formula (11) as follows:

[0150] t6=-q s *T r ;

[0151] S4.4, the basic vector action time of other sectors is obtained as follows:

[0152] Sector II: t2=q s *T r ;

[0153] Sector III: t0=(1-q s )*T、

[0154] Sector IV: t3 = q r * s 、

[0155] Sector V: t5 = -q r * s ;

[0156] Sector VI: t0 = (1 + q r )*T s 、

[0157] where t0, t1, t2, t3, t4, t5, t6 represent the action time of basic vectors V0, V1, V2, V3, V4, V5, V6 respectively, and T s represents the reference vector sampling period.

[0158] The switching path of the basic vector of the reference vector composed according to S5 is to meet the minimum path switching principle (i.e. only one phase is allowed to change one level each time), and to meet the closure of the switching path, the switching of the basic vector corresponding switch state vector is adopted, and seven segment modulation method is adopted, and the specific content is:

[0159] As shown in the attached Figure 2 ,

[0160] Sector I: the switching path is S0(0, 0, 0)→S1(1, 0, 0)→S6(1, 0, 1)→S7(1, 1, 1)→S6(1, 0, 1)→S1(1, 0, 0)→S0(0, 0, 0), and the corresponding action time distribution in the switching path of the switch state vector is t0 / 4→t1 / 2→t6 / 2→t0 / 2→t6 / 2→t1 / 2→t0 / 4;

[0161] Sector II: the switching path is S0(0, 0, 0)→S1(1, 0, 0)→S2(1, 1, 0)→S7(1, 1, 1)→S2(1, 1, 0)→S1(1, 0, 0)→S0(0, 0, 0), and the action time distribution is t0 / 4→t1 / 2→t2 / 2→t0 / 2→t2 / 2→t1 / 2→t0 / 4;

[0162] Sector III: the switching path is S0(0, 0, 0)→S3(0, 1, 0)→S2(1, 1, 0)→S7(1, 1, 1)→S2(1, 1, 0)→S3(0, 1, 0)→S0(0, 0, 0), and the action time distribution is t0 / 4→t3 / 2→t2 / 2→t0 / 2→t2 / 2→t3 / 2→t0 / 4;

[0163] Sector IV: The switching path is S0(0,0,0)→S3(0,1,0)→S4(0,1,1)→S7(1,1,1)→S4(0,1,1)→S3(0,1,0)→S0(0,0,0), and the action time distribution is t0 / 4→t3 / 2→t4 / 2→t0 / 2→t4 / 2→t3 / 2→t0 / 4;

[0164] Sector V: The switching path is S0(0,0,0)→S5(0,0,1)→S4(0,1,1)→S7(1,1,1)→S4(0,1,1)→S5(0,0,1)→S0(0,0,0), and the action time distribution is t0 / 4→t5 / 2→t4 / 2→t0 / 2→t4 / 2→t5 / 2→t0 / 4;

[0165] Sector VI: The switching path is S0(0,0,0)→S5(0,0,1)→S6(1,0,1)→S7(1,1,1)→S6(1,0,1)→S5(0,0,1)→S0(0,0,0), and the action time distribution is t0 / 4→t5 / 2→t6 / 2→t0 / 2→t6 / 2→t5 / 2→t0 / 4.

[0166] Feasibility verification

[0167] like Figure 3 The diagram shows the topology of an inverter consisting of three cascaded H-bridges. The unit consisting of the first H-bridge in phases A, B, and C is called the first-level unit; the unit consisting of the second H-bridge in phases A, B, and C is called the second-level unit; and the unit consisting of the third H-bridge in phases A, B, and C is called the third-level unit.

[0168] The method of the present invention is used to control it, and the specific method is as follows:

[0169] The control signal allocation for each H-bridge in the first-level unit is as follows: six PWM signals generated by the two-level space vector modulation method in the pq coordinate system are used to control the left half of the H-bridge in the first-level unit. After shifting the reference vector in the left half of the H-bridge in the first-level unit by 180°, six PWM signals are used to control the right half of the H-bridge in the first-level unit.

[0170] The control signal allocation for each H-bridge in the second-level unit is as follows: the PWM control signal of the left half-bridge of the H-bridge in the first-level unit is shifted by π / 3k (where k = f). s / f, k is called the frequency ratio, f sAfter the phase shift of the PWM control signal of the left half-bridge of the first unit H-bridge by π / 3k, the phase-shifted PWM control signal is used as the PWM control signal of the left half-bridge of the second unit H-bridge; similarly, after the phase shift of the PWM control signal of the right half-bridge of the first unit H-bridge by π / 3k, the phase-shifted PWM control signal is used as the PWM control signal of the right half-bridge of the second unit H-bridge.

[0171] The PWM control signal of the left half-bridge of the first unit H-bridge is phase-shifted by 2π / 3k, and the phase-shifted PWM control signal is used as the PWM control signal of the left half-bridge of the third unit H-bridge; similarly, the PWM control signal of the right half-bridge of the first unit H-bridge is phase-shifted by 2π / 3k, and the phase-shifted PWM control signal is used as the PWM control signal of the right half-bridge of the third unit H-bridge.

[0172] As shown in FIG. 6, the simulation waveform of the phase voltage output by the three H-bridge cascaded inverters controlled based on the phase-shifted space vector modulation method in the p-q coordinate system is completely symmetrical, and thus the correctness of the present application can be illustrated. Figure 4 As shown in FIG. 7, the topology diagram of the n H-bridge cascaded inverter, the phase-shifted modulation method of the present application is still applicable to the n H-bridge cascaded inverter, and the specific control method is as follows:

[0173] As shown in FIG. 7, the topology diagram of the n H-bridge cascaded inverter, the phase-shifted modulation method of the present application is still applicable to the n H-bridge cascaded inverter, and the specific control method is as follows: Figure 5 The control method of the first unit is the same as that of the first unit of the three H-bridge cascaded inverter;

[0174] The PWM control signal of the left half-bridge of the first unit H-bridge is phase-shifted by π / nk (n is the number of H-bridge cascaded in each phase), and the phase-shifted PWM control signal is used as the PWM control signal of the left half-bridge of the second unit H-bridge; similarly, the PWM control signal of the right half-bridge of the first unit H-bridge is phase-shifted by π / nk, and the phase-shifted PWM control signal is used as the PWM control signal of the right half-bridge of the second unit H-bridge;

[0175] The PWM control signal of the left half-bridge of the first unit H-bridge is phase-shifted by (i-1)π / nk, and the phase-shifted PWM control signal is used as the PWM control signal of the left half-bridge of the i-th unit H-bridge; similarly, the PWM control signal of the right half-bridge of the first unit H-bridge is phase-shifted by (i-1)π / nk, and the phase-shifted PWM control signal is used as the PWM control signal of the right half-bridge of the i-th unit H-bridge;

[0176] The PWM control signal of the left half-bridge of the first unit H-bridge is phase-shifted by (i-1)π / nk, and the phase-shifted PWM control signal is used as the PWM control signal of the left half-bridge of the i-th unit H-bridge; similarly, the PWM control signal of the right half-bridge of the first unit H-bridge is phase-shifted by (i-1)π / nk, and the phase-shifted PWM control signal is used as the PWM control signal of the right half-bridge of the i-th unit H-bridge;

[0177] The H-bridge control signal distribution of the nth unit: the left half-bridge PWM control signal of the first unit H-bridge is phase shifted by (n-1)π / nk, and the phase shifted PWM is used as the corresponding left half-bridge PWM control signal of the nth unit H-bridge; similarly, the right half-bridge PWM control signal of the first unit H-bridge is phase shifted by (n-1)π / nk, and the phase shifted PWM is used as the corresponding right half-bridge PWM control signal of the nth unit H-bridge.

Claims

1. A phase-shifted space vector modulation method for an H-bridge cascaded multilevel inverter, characterized in that, It comprises the following steps: S1, to coordinate system conversion coordinate system: to in the coordinate system coordinate stretch to 3 times the original value, coordinate stretch to times the original value, obtain coordinate system; S2, in Under the coordinates, the mathematical model of two-level reference vector trajectory is established wherein is the modulation coefficient, , ; S3, judging the reference vector wherein = ; S4, calculating the basic vector action time of the synthesized reference vector: judging the sector where the reference vector is located, determining the basic vector according to the sector where the reference vector is located, and calculating the basic vector action time by using the volt-second balance principle; S5, switching path of the basic vector of the synthesized reference vector: switching by using the switch state vector corresponding to the basic vector; S1 said to coordinate system conversion coordinate system, which specifically includes, S1.1、 The basic vector expression of the two-level space vector modulation method under the coordinate system is （1）， In formula (1), , are respectively horizontal coordinate, vertical coordinate in the coordinate system, , , are respectively the number of levels of the half-bridge three-phase output of each H-bridge of the inverter and are integers, which can only take 0 and 1. S1.2, the coordinates in the coordinate system are stretched to 3 times the original value, coordinates in the coordinate system are stretched to 3 times the original value, coordinates in the coordinate system are stretched to 3 times the original value, coordinates in the coordinate system are stretched to 3 times the original value, coordinates in the coordinate system are stretched to 3 times the original value, （2）， In formula (2), , are respectively horizontal coordinate, vertical coordinate in the coordinate system; S1.3, from equation (2) six non-zero basic vectors , , , , , , one zero vector ; S1.4, six sectors are formed based on the non-zero vector and the zero vector, each sector is an isosceles right triangle, and each sector is, , , constitute a first sector, sector I; , , constitutes the second sector, sector II; , , constitutes the third sector, sector III; , , constitutes the fourth sector, sector IV; , , constitutes the fifth sector, i.e. sector V; , , constitutes the sixth sector, sector VI; S1.5, defining the as the basic vector switching state vector; Six non-zero basic vectors and only one switch state vector, respectively: , , , , , ; zero basic vector corresponding to two switching state vectors, respectively: , ; S3 the judgment reference vector The sector where the user is located, specifically, If then the reference vector is located in the first sector; If then the reference vector is located in the second sector; If then the reference vector is located in the third sector; If then the reference vector is located in the fourth sector; If then the reference vector is located in the fifth sector; If then the reference vector is located in the sixth sector.

2. The phase-shifted space vector modulation method of the H-bridge cascaded multi-level inverter according to claim 1, characterized in that, S2 said in Under the coordinates, the mathematical model of two-level reference vector trajectory is established S2.1, the mathematical model of the ideal three-phase sinusoidal wave voltage is: （3） In formula (3), , , respectively represent three-phase voltages of reference voltages A, B, C, is the amplitude of each phase of the reference voltage. S2.2, substituting equation (3) into equation (1) gives in the coordinate system the reference voltage vector is: （4） From equation (4), the reference voltage vector In The locus is a circle in the frame with a radius of ; S2.3, normalizing the equation (4) by E gives the reference vector is: （5） In formula (5), defined as a reference vector the radius of the trajectory, E is the supply voltage of each cascaded H-bridge; S2.4, refer to the vector Maximum radius of trajectory ; S2.5, reference vector Obtaining the maximum radius value At this time, the input DC voltage utilization rate of the corresponding inverter is the highest, and is set to 1; a parameter is introduced Adjusting the input DC voltage utilization rate of the inverter, we get: （6）； S2.6, from equation (6) , substituting into equation (5) gives the reference vector is: （7）； S2.7, the vector reference in the coordinate system vector reference in the coordinate system transformed into the coordinate system vector reference in the coordinate system , we have: = = （8）； S2.8, from equation (8), it can be derived that at The mathematical model of the two-level reference vector trajectory under the coordinates is: （9）。 3. The phase-shifted space vector modulation method of the H-bridge cascaded multi-level inverter according to claim 1, characterized in that, The specific content of the basic vector action time of the synthesized reference vector in S4 is: S4.1, the reference vector is In the first sector, the basic vector is , , The reference vector is synthesized by the basic vector , and the following is obtained: （10）； S4.2, according to the coordinate values of the basic vector and the reference vector, the following formula can be obtained: （11）； S4.3, the sector I basic vector action time is solved from formula (11) as follows: ； S4.4, similarly, the basic vector action time of other sectors is as follows: Sector II: ; Sector III: ; Sector IV: ; Sector V: ; Sector VI: ; 、 、 、 、 、 、 denote the action time of the basic vector 、 、 、 、 、 、 , denote the reference vector sampling period.

4. The phase-shifted space vector modulation method of the H-bridge cascaded multi-level inverter according to claim 3, characterized in that, The switching path of the basic vector of the synthesized reference vector in S5 adopts a seven-segment modulation method, and the specific content is: Sector I: switching path is , the corresponding action time distribution in the switching path of the switch state vector is ; Sector II: Switching path is , action time distribution ; Sector III: Switching path is , action time distribution ; Sector IV: Switching path is , action time distribution ; Sector V: Switching path is , action time distribution ; Sector VI: Switching path is , action time distribution .

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