H-bridge cascaded multi-level inverter based on phase-shifted space vector modulation method

Abstract

The application discloses a kind of H bridge cascaded multilevel inverter based on phase-shifted space vector modulation method, including inverter body and controller;The controller is used to send PWM signal to switch tube in inverter body;The inverter body is composed of A, B, C three phases, and each phase is formed by n H bridge cascaded;Each H bridge is formed by four switch tubes and a DC power supply in parallel, and H bridge has two AC output ends, and the connection mode of four switch tubes is that each two switch tubes are connected in series and then connected in parallel as a whole;The DC power supply of each H bridge is independent power supply;The n H bridge cascaded of each phase is specifically formed by the end-to-end series connection of one end of the AC output of n H bridge;The modulation method executed by the controller is based on phase-shifted space vector modulation method;The application has the advantages of simple modulation method and strong expansibility.

Description

Technical Field

[0001] This invention relates to the field of inverter modulation technology, and in particular to an H-bridge cascaded multilevel inverter based on a phase-shifted space vector modulation method. 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 an H-bridge cascaded multilevel inverter based on the phase-shifted space vector modulation method. Summary of the Invention

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

[0009] The technical solution of the present invention is as follows: an H-bridge cascaded multilevel inverter based on phase-shift space vector modulation method, comprising an inverter body and a controller; the controller is used to send PWM signals to the switching transistors in the inverter body; the inverter body consists of three phases A, B and C, each phase being composed of n cascaded H-bridges;

[0010] Each H-bridge consists of four switching transistors and a DC power supply connected in parallel. The H-bridge has two AC output terminals. The four switching transistors are connected in series with two transistors and then connected in parallel. Each H-bridge has an independent DC power supply.

[0011] The cascading of n H-bridges in each phase is specifically formed by connecting the AC output ends of the n H-bridges one after the other.

[0012] Connect the spare end of the AC output terminal of the nth H-bridge in the three phases to the same node, which is called the zero point or neutral point of the inverter; connect the spare end of the AC output terminal of the 1st H-bridge in the three phases to the A, B, and C phase outputs respectively, which are called the three-phase output terminals of the inverter.

[0013] The switching transistor is driven by a PWM signal;

[0014] The modulation method executed by the controller is a phase-shift space vector modulation method.

[0015] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shift space vector modulation, the modulation method includes the following steps:

[0016] 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;

[0017] 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 r Let q be the x-coordinate of the reference vector. r The ordinate of the reference vector;

[0018] S3. Determine the reference vector V r (p r q r The sector where V is located. r (p r q r )for

[0019] S4. Calculate the basic vector action time of the composite reference vector: Determine the sector where the reference vector is located, determine the basic vector based on the sector where the reference vector is located, and calculate the basic vector action time using the volt-second balance principle.

[0020] S5. The switching path of the basic vector for allocating the composite reference vector: switch using the switch state vector corresponding to the basic vector.

[0021] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, the conversion of the α-β coordinate system to the pq coordinate system described in S1 is as follows:

[0022] The basic vector expression for the two-level space vector modulation method in the S1.1, α-β coordinate system is:

[0023]

[0024] In equation (1), α and β are the abscissa and ordinate of the α-β coordinate system, respectively, and a, b, and c are the number of half-bridge three-phase output levels of each H-bridge of the inverter, which are integers and can only be 0 and 1.

[0025] S1.2, Stretch the α coordinate in the α-β coordinate system to three times its original value, and stretch the β coordinate back to its original value. After multiplying, the pq coordinate system is obtained as follows:

[0026]

[0027] In equation (2), p and q are the abscissa and ordinate in the pq coordinate system, respectively;

[0028] S1.3 From equation (2), we can obtain 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);

[0029] S1.4. Six sectors are constructed based on non-zero and zero vectors. Each sector is an isosceles right triangle, as follows:

[0030] V0, V1, and V6 constitute the first sector, i.e., sector I.

[0031] V0, V1, and V2 constitute the second sector, namely sector II;

[0032] V0, V2, and V3 constitute the third sector, namely sector III;

[0033] V0, V3, and V4 constitute the fourth sector, namely sector IV;

[0034] V0, V4, and V5 constitute the fifth sector, namely sector V;

[0035] V0, V5, and V6 constitute the sixth sector, namely sector VI.

[0036] S1.5. Define (a,b,c) that satisfies equation (2) as the basic vector V(p,q) switch state vector;

[0037] There are six non-zero basic vectors and only one switch state vector, namely: S1(1,0,0), S2(1,1,0), S3(0,1,0), S4(0,1,1), S5(0,0,1), S6(1,0,1);

[0038] The zero fundamental vector V0(0,0) corresponds to two switch state vectors: S0(0,0,0) and S7(1,1,1).

[0039] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, the mathematical model described in S2 for establishing the two-level reference vector trajectories in the pq coordinate system... Its specific content is as follows:

[0040] S2.1. Let the mathematical model of an ideal three-phase sinusoidal voltage be:

[0041]

[0042] 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;

[0043] S2.2 Substituting equation (3) into equation (1), we obtain the reference voltage vector U in the α-β coordinate system. r for:

[0044]

[0045] 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 ;

[0046] S2.3. Dividing equation (4) by E to normalize it yields the reference vector V. r (α r ,β r )for:

[0047]

[0048] In equation (5), Defined as reference vector V r The radius of the trajectory, E is the supply voltage for each cascaded H-bridge;

[0049] S2.4, combining equations (1) and (5), we obtain the reference vector V. r Maximum radius of trajectory

[0050] 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:

[0051]

[0052] S2.6, From equation (6) we get Substituting into equation (5), we obtain the reference vector V. r (α r ,β r )for:

[0053]

[0054] 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:

[0055]

[0056] 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:

[0057]

[0058] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, the reference vector V mentioned in S3 is... r (p r q r The sector containing the information is as follows:

[0059] If p r ≥0&&q r ≤0&&|p r |≥|q r |, then the reference vector V r Located in the first sector;

[0060] If p r >0&&q r >0&&|p r |>|q r |, then the reference vector V r Located in the second sector;

[0061] 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;

[0062] If p r <0&&q r >0&&|p r |>|q r |, then the reference vector V r Located in the fourth sector;

[0063] If p r <0&&q r <0&&|p r |>|q r |, then the reference vector V r Located in the fifth sector;

[0064] 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 sector six.

[0065] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, the calculation of the basic vector action time of the synthesized reference vector described in S4 is as follows:

[0066] S4.1, with reference vector V r Taking the first sector as an example, the basic vectors are V0, V1, and V6. The reference vector V is synthesized using the basic vectors. r ,have to:

[0067]

[0068] S4.2. Based on the coordinate values ​​of the basic vector and the reference vector, the following formula can be derived:

[0069]

[0070] S4.3, Solving equation (11) yields the action time of the basic vector of sector I:

[0071] t6 = -q r *T s ;

[0072] S4.4 Similarly, the action time of the basic vectors in other sectors is as follows:

[0073] Sector II:

[0074] Sector III:

[0075] Sector IV:

[0076] Sector V:

[0077] Sector VI:

[0078] Where t0, t1, t2, t3, t4, t5, and t6 represent the durations of action of the basic vectors V0, V1, V2, V3, V4, V5, and V6, respectively, and T s This indicates the sampling period of the reference vector.

[0079] In the aforementioned H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, the switching path of the basic vector for allocating the synthesized reference vector, as described in S5, employs a seven-segment modulation method, specifically as follows:

[0080] 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 state vector switching path is t0 / 4→t1 / 2→t6 / 2→t0 / 2→t6 / 2→t1 / 2→t0 / 4;

[0081] 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→t1 / 2→t0 / 2→t2 / 2→t1 / 2→t0 / 4;

[0082] 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;

[0083] 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;

[0084] 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;

[0085] 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.

[0086] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0087] Compared to traditional space vector modulation methods, where the fundamental vectors of a traditional coordinate system all lie in non-integer coordinates, this invention, based on the pq coordinate system, ensures that all fundamental vectors lie in integer coordinates, thus simplifying the calculation method and significantly improving the calculation speed. Furthermore, in traditional space vector methods, the number of switching state vectors corresponding to the fundamental vectors increases with the number of voltage levels, which is detrimental to the implementation of space vectors. In contrast, the fundamental vectors of this invention correspond to a single switching state vector, and the number of switching state vectors is not affected by the increase in the number of voltage levels.

[0088] Therefore, the present invention has the advantages of simple and easy-to-implement modulation method and strong scalability. Attached Figure Description

[0089] Figure 1 This is a diagram showing the reference vector trajectory and basic vector distribution in the pq coordinate system of this invention.

[0090] Figure 2 This is a diagram showing the switching vector path and time allocation of the switch state in sector I of this invention;

[0091] Figure 3 This is a topology diagram of three H-bridge cascaded inverters in an embodiment of the present invention;

[0092] Figure 4 This is a diagram showing the output phase voltages of the three cascaded H-bridge inverters in an embodiment of the present invention.

[0093] Figure 5 This is a topology diagram of an inverter with n cascaded H-bridges in an embodiment of the present invention. Detailed Implementation

[0094] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0095] Example. An H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation method, which, based on the traditional α-β coordinate system, stretches the α coordinate to three times its original value and the β coordinate to its original value. The pq coordinates are obtained by multiplying the coordinates. The basic vectors in the pq coordinates all fall on the integer grid. The space vector phase shift modulation algorithm realizes two-level space vectors in the pq coordinates, modulates the left and right half-bridge arms of the multi-level cascaded inverter respectively, and appropriately shifts the reference vectors between adjacent stages of the inverter to achieve control of the cascaded multilevel.

[0096] It includes an inverter body and a controller; the controller is used to send PWM signals to the switching transistors in the inverter body; the inverter body consists of three phases A, B and C, and each phase is composed of n cascaded H-bridges.

[0097] Each H-bridge consists of four switching transistors and a DC power supply connected in parallel. The H-bridge has two AC output terminals. The four switching transistors are connected in series with two transistors and then connected in parallel. Each H-bridge has an independent DC power supply.

[0098] The cascading of n H-bridges in each phase is specifically formed by connecting the AC output ends of the n H-bridges one after the other.

[0099] Connect the spare end of the AC output terminal of the nth H-bridge in the three phases to the same node, which is called the zero point or neutral point of the inverter; connect the spare end of the AC output terminal of the 1st H-bridge in the three phases to the A, B, and C phase outputs respectively, which are called the three-phase output terminals of the inverter.

[0100] The switching transistor is driven by a PWM signal;

[0101] The modulation method executed by the controller is a phase-shift space vector modulation method.

[0102] The modulation method is written into the controller to output a PWM signal. The controller is composed of a DSP and an FPGA.

[0103] The modulation method includes the following steps:

[0104] 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;

[0105] 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 r Let q be the x-coordinate of the reference vector. rThe ordinate of the reference vector;

[0106] S3. Determine the reference vector V r (p r q r The sector where V is located. r (p r q r )for

[0107] S4. Calculate the basic vector action time of the composite reference vector: Determine the sector where the reference vector is located, determine the basic vector based on the sector where the reference vector is located, and calculate the basic vector action time using the volt-second balance principle.

[0108] S5. The switching path of the basic vector for allocating the composite reference vector: switch using the switch state vector corresponding to the basic vector.

[0109] The specific details of converting the α-β coordinate system to the pq coordinate system described in S1 are as follows:

[0110] The basic vector expression for the two-level space vector modulation method in the S1.1, α-β coordinate system is:

[0111]

[0112] In equation (1), α and β are the abscissa and ordinate of the α-β coordinate system, respectively, and a, b, and c are the number of half-bridge three-phase output levels of each H-bridge of the inverter, which are integers and can only be 0 and 1.

[0113] As can be seen from equation (1), the basic vector (α,β) does not fall on integer points in the α-β coordinate system;

[0114] S1.2, Stretch the α coordinate in the α-β coordinate system to three times its original value, and stretch the β coordinate back to its original value. After multiplying, the pq coordinate system is obtained as follows:

[0115]

[0116] In equation (2), p and q are the abscissa and ordinate in the pq coordinate system, respectively;

[0117] As can be seen from equation (2), the basic vector (p,q) lies on integer points in the pq coordinate system, such as... Figure 1 As shown;

[0118] S1.3 From equation (2), we can obtain 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);

[0119] S1.4. Six sectors are constructed based on non-zero and zero vectors. Each sector is an isosceles right triangle, as follows:

[0120] V0, V1, and V6 constitute the first sector, i.e., sector I.

[0121] V0, V1, and V2 constitute the second sector, namely sector II;

[0122] V0, V2, and V3 constitute the third sector, namely sector III;

[0123] V0, V3, and V4 constitute the fourth sector, namely sector IV;

[0124] V0, V4, and V5 constitute the fifth sector, namely sector V;

[0125] V0, V5, and V6 constitute the sixth sector, namely sector VI.

[0126] S1.5. Define (a,b,c) that satisfies equation (2) as the basic vector V(p,q) switch state vector;

[0127] There are six non-zero basic vectors and only one switch state vector, namely: S1(1,0,0), S2(1,1,0), S3(0,1,0), S4(0,1,1), S5(0,0,1), S6(1,0,1);

[0128] The zero fundamental vector V0(0,0) corresponds to two switch state vectors: S0(0,0,0) and S7(1,1,1).

[0129] The ideal power supply for an AC motor is a three-phase sinusoidal voltage, where the phase angles of phases A, B, and C differ by 120° sequentially. The goal of the space vector modulation method is to use this ideal three-phase sinusoidal voltage as its reference voltage vector U. r Then, the reference vector synthesized from the basic vectors approximates the ideal three-phase sinusoidal voltage signal as closely as possible.

[0130] 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:

[0131] S2.1. Let the mathematical model of an ideal three-phase sinusoidal voltage be:

[0132]

[0133] 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;

[0134] S2.2 Substituting equation (3) into equation (1), we obtain the reference voltage vector U in the α-β coordinate system. r for:

[0135]

[0136] 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 ;

[0137] S2.3. Dividing equation (4) by E to normalize it yields the reference vector V. r (α r ,β r )for:

[0138]

[0139] In equation (5), Defined as reference vector V r The radius of the trajectory, E is the supply voltage for each cascaded H-bridge;

[0140] S2.4, combining equations (1) and (5), we obtain the reference vector V. r Maximum radius of trajectory

[0141] 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:

[0142]

[0143] S2.6, From equation (6) we get Substituting into equation (5), we obtain the reference vector V. r (α r ,β r )for:

[0144]

[0145] 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:

[0146]

[0147] 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:

[0148] Its reference vector trajectory is shown in the appendix. Figure 1 As shown.

[0149] The reference vector V mentioned in S3 r (p r q r The sector containing the information is as follows:

[0150] If p r ≥0&&q r ≤0&&|p r |≥|q r |, then the reference vector V r Located in the first sector;

[0151] If p r >0&&q r >0&&|p r |>|q r |, then the reference vector V r Located in the second sector;

[0152] 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;

[0153] If p r <0&&q r >0&&|p r |>|q r |, then the reference vector V r Located in the fourth sector;

[0154] If p r <0&&q r <0&&|p r |>|q r |, then the reference vector V r Located in the fifth sector;

[0155] 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 sector six.

[0156] The calculation of the basic vector action time of the composite reference vector described in S4 is as follows:

[0157] S4.1, with reference vector V r Taking the first sector as an example, see attached... Figure 1 As shown, the basic vectors are V0, V1, and V6. The reference vector V is synthesized using these basic vectors. r ,have to:

[0158]

[0159] S4.2. Based on the coordinate values ​​of the basic vector and the reference vector, the following formula can be derived:

[0160]

[0161] S4.3, Solving equation (11) yields the action time of the basic vector of sector I:

[0162]

[0163] S4.4 Similarly, the action time of the basic vectors in other sectors is as follows:

[0164] Sector II:

[0165] Sector III:

[0166] Sector IV:

[0167] Sector V:

[0168] Sector VI:

[0169] Where t0, t1, t2, t3, t4, t5, and t6 represent the durations of action of the basic vectors V0, V1, V2, V3, V4, V5, and V6, respectively, and T s This indicates the sampling period of the reference vector.

[0170] The switching path of the basic vector for allocating the synthetic reference vector described in S5, in order to satisfy the minimum path switching principle (i.e., only one phase is allowed to change a level each time) and to ensure the closure of the switching path, utilizes the switching state vector corresponding to the basic vector for switching, employing a seven-segment modulation method. The specific details are as follows:

[0171] As attached Figure 2 As shown,

[0172] 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 state vector switching path is t0 / 4→t1 / 2→t6 / 2→t0 / 2→t6 / 2→t1 / 2→t0 / 4;

[0173] 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;

[0174] 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;

[0175] 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;

[0176] 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;

[0177] 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.

[0178] Feasibility verification

[0179] 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.

[0180] The method of the present invention is used to control it, and the specific method is as follows:

[0181] 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.

[0182] 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 s After the reference voltage sampling frequency (f is the reference voltage frequency), the phase-shifted PWM is used as the left half-bridge PWM control signal corresponding to the second-level unit H-bridge; similarly, after the right half-bridge PWM control signal of the first-level unit H-bridge is phase-shifted by π / 3k, the phase-shifted PWM is used as the right half-bridge PWM control signal corresponding to the second-level unit H-bridge.

[0183] The control signals for each H-bridge in the third-level unit are allocated as follows: the PWM control signal of the left half-bridge of the H-bridge in the first-level unit is shifted by 2π / 3k, and the shifted PWM signal is used as the corresponding left half-bridge PWM control signal for the H-bridge in the third-level unit. Similarly, the PWM control signal of the right half-bridge of the H-bridge in the first-level unit is shifted by 2π / 3k, and the shifted PWM signal is used as the corresponding right half-bridge PWM control signal for the H-bridge in the third-level unit.

[0184] like Figure 4 The figure shows the simulated phase voltage waveforms of the inverters with three cascaded H-bridges controlled by the phase-shifted space vector modulation method in the pq coordinate system. From the simulated waveforms, the three phase voltages are completely symmetrical, which demonstrates the correctness of the present invention.

[0185] like Figure 5 The diagram shown is a topology diagram of an inverter with n cascaded H-bridges. The phase-shifting modulation method of this invention is still applicable to inverters with n cascaded H-bridges. The specific control method is as follows:

[0186] The control signal allocation for each H-bridge in the first-level unit is the same as that for the first-level unit of an inverter with three cascaded H-bridges.

[0187] 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 / nk (n is the number of H-bridges cascaded in each phase), and the phase-shifted PWM is used as the corresponding left half-bridge PWM control signal of the H-bridge in the second-level unit; similarly, the PWM control signal of the right half-bridge of the H-bridge in the first-level unit is shifted by π / nk, and the phase-shifted PWM is used as the corresponding right half-bridge PWM control signal of the H-bridge in the second-level unit.

[0188] The control signals for each H-bridge in the i-th level unit are allocated as follows: the PWM control signal of the left half-bridge of the H-bridge in the first level unit is shifted by (i-1)π / nk, and the shifted PWM signal is used as the corresponding left half-bridge PWM control signal of the H-bridge in the i-th level unit; similarly, the PWM control signal of the right half-bridge of the H-bridge in the first level unit is shifted by (i-1)π / nk, and the shifted PWM signal is used as the corresponding right half-bridge PWM control signal of the H-bridge in the i-th level unit.

[0189] The control signals for each H-bridge in the nth-level unit are allocated as follows: the PWM control signal of the left half-bridge of the H-bridge in the first-level unit is shifted by (n-1)π / nk, and the shifted PWM signal is used as the corresponding left half-bridge PWM control signal for the H-bridge in the nth-level unit. Similarly, the PWM control signal of the right half-bridge of the H-bridge in the first-level unit is shifted by (n-1)π / nk, and the shifted PWM signal is used as the corresponding right half-bridge PWM control signal for the H-bridge in the nth-level unit.

Claims

1. An H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation, characterized in that: It includes an inverter body and a controller; the controller is used to send PWM signals to the switching transistors in the inverter body; the inverter body consists of three phases A, B and C, and each phase is composed of n cascaded H-bridges. Each H-bridge consists of four switching transistors and a DC power supply connected in parallel. The H-bridge has two AC output terminals. The four switching transistors are connected in series with two transistors and then connected in parallel. Each H-bridge has an independent DC power supply. The cascading of n H-bridges in each phase is specifically formed by connecting the AC output ends of the n H-bridges one after the other. The switching transistor is driven by a PWM signal; The modulation method executed by the controller is a phase-shift space vector modulation method; The modulation method includes the following steps. 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; 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 r Let q be the x-coordinate of the reference vector. r The ordinate of the reference vector; S3. Determine the reference vector V r (p r q r The sector where V is located. r (p r q r )for S4. Calculate the basic vector action time of the composite reference vector: Determine the sector where the reference vector is located, determine the basic vector based on the sector where the reference vector is located, and calculate the basic vector action time using the volt-second balance principle. S5. The switching path of the basic vector for allocating the composite reference vector: switching is performed using the switch state vector corresponding to the basic vector; The conversion from the α-β coordinate system to the pq coordinate system described in S1 is as follows. The basic vector expression for the two-level space vector modulation method in the S1.1, α-β coordinate system is: In equation (1), α and β are the abscissa and ordinate of the α-β coordinate system, respectively, and a, b, and c are the number of half-bridge three-phase output levels of each H-bridge of the inverter, which are integers and can only be 0 and 1. S1.2, Stretch the α coordinate in the α-β coordinate system to three times its original value, and stretch the β coordinate back to its original value. After multiplying, the pq coordinate system is obtained as follows: In equation (2), p and q are the abscissa and ordinate in the pq coordinate system, respectively; S1.3 From equation (2), we can obtain six non-zero basic vectors V1(2,0), V2(1,1), V3(-1,1), V4(-2,0), V5(-1,-1), V6(1,-1), and one zero vector V0(0,0); S1.

4. Six sectors are constructed based on non-zero and zero vectors. Each sector is an isosceles right triangle, as follows: V0, V1, and V6 constitute the first sector, i.e., sector I. V0, V1, and V2 constitute the second sector, namely sector II; V0, V2, and V3 constitute the third sector, namely sector III; V0, V3, and V4 constitute the fourth sector, namely sector IV; V0, V4, and V5 constitute the fifth sector, namely sector V; V0, V5, and V6 constitute the sixth sector, namely sector VI. S1.

5. Define (a,b,c) that satisfies equation (2) as the basic vector V(p,q) switch state vector; There are six non-zero basic vectors and only one switch state vector, namely: S1(1,0,0), S2(1,1,0), S3(0,1,0), S4(0,1,1), S5(0,0,1), S6(1,0,1); The zero fundamental vector V0(0,0) corresponds to two switch state vectors, namely: S0(0,0,0) and S7(1,1,1); The reference vector V mentioned in S3 r (p r q r The sector containing the information is as follows: If p r ≥0&q r ≤0&|p r |≥|q r |, then the reference vector V r Located in the first sector; If p r >0&q r >0&|p r |>|q r |, then the reference vector V r Located in the second sector; 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; If p r <0&q r >0&|p r |>|q r |, then the reference vector V r Located in the fourth sector; If p r <0&q r <0&|p r |>|q r |, then the reference vector V r Located in the fifth sector; 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 sector six.

2. The H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation method according to claim 1, characterized in that, 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: S2.

1. Let the mathematical model of an ideal three-phase sinusoidal voltage be: 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; S2.2 Substituting equation (3) into equation (1), we obtain the reference voltage vector U in the α-β coordinate system. r for: 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 ; S2.

3. Dividing equation (4) by E to normalize it yields the reference vector V. r (α r ,β r )for: In equation (5), Defined as reference vector V r The radius of the trajectory, E is the supply voltage for each cascaded H-bridge; S2.4, combining equations (1) and (5), we obtain the reference vector V. r Maximum radius of trajectory 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: S2.6, From equation (6) we get Substituting into equation (5), we obtain the reference vector V. r (α r ,β r )for: 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: 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:

3. The H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation method according to claim 1, characterized in that, The calculation of the basic vector action time of the composite reference vector described in S4 is as follows: S4.1, with reference vector V r Taking the first sector as an example, the basic vectors are V0, V1, and V6. The reference vector V is synthesized using the basic vectors. r ,have to: S4.

2. Based on the coordinate values ​​of the basic vector and the reference vector, the following formula can be derived: S4.3, Solving equation (11) yields the action time of the basic vector of sector I: S4.4 Similarly, the action time of the basic vectors in other sectors is as follows: Sector II: t2=q r *T s ; Sector III: t0 = (1-q) r )*T s , Sector IV: t3 = q r *T s , Sector V: t5 = -q r *T s ; Sector VI: t0 = (1 + q) r )*T s , Where t0, t1, t2, t3, t4, t5, and t6 represent the durations of action of the basic vectors V0, V1, V2, V3, V4, V5, and V6, respectively, and T s This indicates the sampling period of the reference vector.

4. The H-bridge cascaded multilevel inverter based on phase-shifted space vector modulation method according to claim 3, characterized in that, The switching path of the basic vector for allocating and synthesizing the reference vector, as described in S5, employs a seven-segment modulation method, specifically as follows: 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 state vector switching path is t0 / 4→t1 / 2→t6 / 2→t0 / 2→t6 / 2→t1 / 2→t0 / 4; 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; 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; 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; 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; 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.

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