阅读说明：本技术 一种基于改进svpwm算法的npc三电平逆变器设计方法 (NPC three-level inverter design method based on improved SVPWM algorithm ) 是由 骆子溥 陈明华 刘凤龙 于 2020-11-30 设计创作，主要内容包括：本发明属于电子技术领域,具体涉及一基于改进SVPWM算法的NPC三电平逆变器设计方法,包括：1)对直角坐标系进行分区；2)将坐标系直角坐标系变换为60°坐标系；3)对坐标系进行分区,并进行扇区判定；4)计算基本矢量作用时间。本发明应用60°坐标系,以适应空间电压矢量的夹角θ通常为60°的倍数的情况。在60°坐标系下的SVPWM算法不包含三角函数,与直角坐标系下的算法相比大大减少了计算流程,有效提高系统效率。(The invention belongs to the technical field of electronics, and particularly relates to an NPC three-level inverter design method based on an improved SVPWM algorithm, which comprises the following steps: 1) partitioning the rectangular coordinate system; 2) transforming the rectangular coordinate system of the coordinate system into a 60-degree coordinate system; 3) partitioning the coordinate system and judging the sector; 4) the base vector action time is calculated. The invention applies a 60 ° coordinate system to accommodate the situation where the angle θ of the space voltage vector is typically a multiple of 60 °. The SVPWM algorithm under the 60-degree coordinate system does not contain a trigonometric function, so that the calculation process is greatly reduced compared with the algorithm under the rectangular coordinate system, and the system efficiency is effectively improved.)

1. An NPC three-level inverter design method based on an improved SVPWM algorithm is characterized by comprising the following steps:

step 1, partitioning an orthogonal coordinate system:

step 1.1, setting an original rectangular coordinate system as an alpha-beta coordinate system, and drawing a basic space voltage vector in the alpha-beta coordinate system;

step 1.2, define reference voltage vector U_ref：

U_ref＝U_ref·e^jθ (1)

Wherein, U_refIs a reference voltage vector U_refTheta is a reference voltage vector U_refThe spatial angle of (d);

reference voltage vector U_refThe magnitude of the component on the coordinate axis alpha, beta is respectively U_α、U_βRepresents, U_α、U_βAnd reference voltage vector U_refThe derived relationship of (a) is:

step 2, transforming the rectangular coordinate system of the coordinate system into a 60-degree coordinate system:

step 2.1, establishing a 60-degree coordinate system g-h on the rectangular coordinate system alpha-beta, as shown in FIG. 4;reference voltage vector U_refThe calculation formula for transforming from the rectangular coordinate system alpha-beta to the 60-degree coordinate system g-h is as follows:

wherein, U_g、U_hIs a reference voltage vector U_refThe amplitude of the component on the coordinate axis g, h;

according to Clark transformation, the transformation relation between the three-phase rotating coordinate system a-b-c and the rectangular coordinate system alpha-beta can be obtained as follows:

wherein, U_a、U_b、U_cThree-phase voltage;

the formula (3) and the formula (4) are combined to obtain the transformation relation between the three-phase rotating coordinate system a-b-c and the 60-degree coordinate system g-h:

step 2.2, reference voltage vector U_refCalculating per unit value to obtain U_g、U_hPer unit value ofMaking per unit value U of reference voltage vector^* _refFalling within a 60 DEG coordinate system g-h;

step 3, partitioning the coordinate system, and judging the sectors:

step 3.1, dividing each 60-degree vector space range in a 60-degree coordinate system g-h into a large area, sequentially partitioning the large area in the anticlockwise direction from a coordinate axis g to obtain six large sectors N with numbers I-VI, and dividing each large sector into six small sectors N with numbers 1-6;

step 3.2, the per unit value obtained in the step 2Is compared with 0 to determine a reference voltage vector U_refThe large sector in which it is located;

step 3.3, in the judgment process of the small reference vector sector, the reference voltage vector which is not in the large sector I needs to be rotated clockwise (N-1) by 60 degrees and then placed in the large sector I; the reference voltage vector before rotation can be calculated by the geometric relation of the triangleThe transformation formula is as follows:

wherein the content of the first and second substances,as a reference voltage vector before rotationThe magnitude of the component on the coordinate axes g, h, N representing the reference voltage vector before rotationThe position of the large sector;

step 3.4, obtaining the judgment of the small sector to which the reference voltage vector belongs under a 60-degree coordinate system according to the transformation relation obtained by the formula (10);

step 4, calculating the action time of the basic vector:

from the relationship between the rectangular coordinate system and the 60 ° coordinate system shown in fig. 4, the reference voltage vector U_refThe coordinates in the 60 ° coordinate system can be expressed as:

wherein M is defined as the modulation ratio, and

converting the action time of the basic vector obtained under the traditional rectangular coordinate system by a formula 11 to obtain the action time T of the basic vector under the coordinate system of 60 degrees_a、T_b、T_c。

2. The NPC three-level inverter design method based on the improved SVPWM algorithm as claimed in claim 1, wherein said step 2.2 specifically comprises:

setting the maximum vector modulus of a 60-degree coordinate system g-h as U_maxTo U with_maxThe/2 is taken as a reference quantity so as to realize the per unit value calculation of the reference voltage vector, namely:

three-phase voltage U_a、U_b、U_cExpressed as:

get the reference value U_BComprises the following steps:

according to the formula (7), whenWhen the temperature of the water is higher than the set temperature,at most 1, at this timeSo the per-unit transformation is expressed as:

wherein the content of the first and second substances,is U_g、U_hPer unit value of;

reference voltage vector U according to equation (9)_refAnd performing per-unit processing to obtain the vector distribution of the reference voltage under a 60-degree coordinate system g-h.

3. The NPC three-level inverter design method based on the improved SVPWM algorithm as claimed in claim 1, wherein said step 3.2 is to calculate the per unit value obtained in step 2Is compared with 0 to determine a reference voltage vector U_refThe judgment basis of the large sector is as follows:

when in useAnd isTime reference voltage vector U_refLocated in large sector ii;

when in useAnd isTime reference voltage vector U_refLocated in large sector iii;

when in useTime reference voltage vector U_refLocated in a large sector iv;

when in useAnd isTime reference voltage vector U_refLocated in large sector v;

when in useAnd isTime reference voltage vector U_refLocated in a large sector vi.

4. The NPC three-level inverter design method based on the improved SVPWM algorithm as claimed in claim 1, wherein the step 3.4 obtains the determination of the small sector to which the reference voltage vector belongs in the 60 ° coordinate system according to the transformation relationship obtained by the formula (10), and the determination is based on:

when in useAnd isTime reference voltage vector U_refLocated in small sector 1;

when in useAnd isTime reference voltage vector U_refLocated in small sector 2;

when in useAnd isTime reference voltage vector U_refLocated in small sector 3;

when in useAnd isTime reference voltage vector U_refLocated in small sector 4;

when in useAnd isTime reference voltage vector U_refLocated in small sector 5;

when in useAnd isTime reference voltage vector U_refLocated in small sector 6.

5. The NPC three-level inverter design method based on the improved SVPWM algorithm as claimed in claim 1, wherein said step 4, 60 ° coordinate system is characterized in that action time T of each basic vector of reference voltage vector in large sector I_a、T_b、T_cRespectively as follows:

in the small sectors 1, 2,

in the small sectors 3, 4,

in the small sector 5 of the area to be covered,

in the small sector 6 of the area to be covered,

wherein, T_sIs the sampling period.

Technical Field

The invention belongs to the technical field of electronics, and particularly relates to an NPC three-level inverter design method based on an improved SVPWM algorithm.

Background

In recent years, due to the rapid progress of power electronic technology in China, inverters have high heat in many fields. The multi-level inverter does not need a high voltage-resistant device, but has a higher switching frequency and a lower output harmonic amount. Among various multi-level inverters, a Neutral Point Clamped (NPC) three-level inverter has the advantages of simple circuit structure, digital modulation method, high direct-current side voltage utilization rate and the like, and keeps extremely high research heat in people.

Currently, there are three main modulation methods for a three-level inverter: carrier modulation, low harmonic cancellation modulation (SHEPWM), and space voltage vector modulation (SVPWM). The SVPWM modulation of the three types of modulation has wide application range and has the advantages that: the method has relatively good performance in a wide modulation ratio, high direct-current side voltage utilization rate and avoids the trouble of needing a large amount of angle data.

The traditional SVPWM algorithm based on a rectangular coordinate system is applied at present, however, the included angle theta of the basic space voltage vector is usually a multiple of 60 degrees, so that the operation amount of a trigonometric function in sector judgment and calculation of the acting time of the basic vector is increased, and the complexity of the control algorithm is greatly increased.

Disclosure of Invention

Aiming at the technical problems, the invention provides an NPC three-level inverter design method based on an improved SVPWM algorithm, which comprises the following steps:

step 1, partitioning an orthogonal coordinate system:

step 1.1, setting an original rectangular coordinate system as an alpha-beta coordinate system, and drawing a basic space voltage vector in the alpha-beta coordinate system;

step 1.2, define reference voltage vector U_ref：

U_ref＝U_ref·e^jθ (1)

Wherein, U_refIs a reference voltage vector U_refTheta is a reference voltage vector U_refThe spatial angle of (d);

reference voltage vector U_refThe magnitude of the component on the coordinate axis alpha, beta is respectively U_α、U_βRepresents, U_α、U_βAnd reference voltage vector U_refThe derived relationship of (a) is:

step 2, transforming the rectangular coordinate system of the coordinate system into a 60-degree coordinate system:

step 2.1, establishing a 60-degree coordinate system g-h on the rectangular coordinate system alpha-beta, as shown in FIG. 4; reference voltage vector U_refThe calculation formula for transforming from the rectangular coordinate system alpha-beta to the 60-degree coordinate system g-h is as follows:

wherein, U_g、U_hIs a reference voltage vector U_refThe amplitude of the component on the coordinate axis g, h;

according to Clark transformation, the transformation relation between the three-phase rotating coordinate system a-b-c and the rectangular coordinate system alpha-beta can be obtained as follows:

wherein, U_a、U_b、U_cThree-phase voltage;

the formula (3) and the formula (4) are combined to obtain the transformation relation between the three-phase rotating coordinate system a-b-c and the 60-degree coordinate system g-h:

step 2.2, reference voltage vector U_refCalculating per unit value to obtain U_g、U_hPer unit value ofMaking per unit value U of reference voltage vector^* _refFalling within a 60 DEG coordinate system g-h;

step 3, partitioning the coordinate system, and judging the sectors:

step 3.1, dividing each 60-degree vector space range in a 60-degree coordinate system g-h into a large area, sequentially partitioning the large area in the anticlockwise direction from a coordinate axis g to obtain six large sectors N with numbers I-VI, and dividing each large sector into six small sectors N with numbers 1-6;

step 3.2, the per unit value obtained in the step 2Is compared with 0 to determine a reference voltage vector U_refThe large sector in which it is located;

step 3.3, in the judgment process of the small reference vector sector, the reference voltage vector which is not in the large sector I needs to be rotated clockwise (N-1) by 60 degrees and then placed in the large sector I; the reference voltage vector before rotation can be calculated by the geometric relation of the triangleThe transformation formula is as follows:

wherein the content of the first and second substances,as a reference voltage vector before rotationThe magnitude of the component on the coordinate axes g, h, N representing the reference voltage vector before rotationThe position of the large sector;

step 3.4, obtaining the judgment of the small sector to which the reference voltage vector belongs under a 60-degree coordinate system according to the transformation relation obtained by the formula (10);

step 4, calculating the action time of the basic vector:

from the relationship between the rectangular coordinate system and the 60 ° coordinate system shown in fig. 4, the reference voltage vector U_refThe coordinates in the 60 ° coordinate system can be expressed as:

wherein M is defined as the modulation ratio, and

converting the action time of the basic vector obtained under the traditional rectangular coordinate system by a formula 11 to obtain the action time T of the basic vector under the coordinate system of 60 degrees_a、T_b、T_c。

The step 2.2 specifically comprises:

setting the maximum vector modulus of a 60-degree coordinate system g-h as U_maxTo U with_maxThe/2 is taken as a reference quantity so as to realize the per unit value calculation of the reference voltage vector, namely:

three-phase voltage U_a、U_b、U_cExpressed as:

get the reference value U_BComprises the following steps:

according to the formula (7), whenWhen the temperature of the water is higher than the set temperature,at most 1, at this timeSo the per-unit transformation is expressed as:

wherein the content of the first and second substances,is U_g、U_hPer unit value of;

reference voltage vector U according to equation (9)_refAnd performing per-unit processing to obtain the vector distribution of the reference voltage under a 60-degree coordinate system g-h.

Step 3.2, the per unit value obtained in step 2Is compared with 0 to determine a reference voltage vector U_refThe judgment basis of the large sector is as follows:

when in useAnd isTime reference voltage vector U_refLocated in large sector ii;

when in useAnd isTime reference voltage vector U_refLocated in large sector iii;

when in useTime reference voltage vector U_refLocated in a large sector iv;

when in useAnd isTime reference voltage vector U_refLocated in large sector v;

when in useAnd isTime reference voltage vector U_refLocated in a large sector vi.

In step 3.4, the small sector to which the reference voltage vector belongs is determined according to the transformation relationship obtained by the formula (10) in a 60 ° coordinate system, and the determination basis is as follows:

when in useAnd isTime reference voltage vector U_refLocated in small sector 1;

when in useAnd isTime reference voltage vector U_refLocated in small sector 2;

when in useAnd isTime reference voltage vector U_refLocated in small sector 3;

when in useAnd isTime reference voltage vector U_refLocated in small sector 4;

when in useAnd isTime reference voltage vector U_refLocated in small sector 5;

when in useAnd isTime reference voltage vector U_refLocated in small sector 6.

In the step 4, the action time T of each basic vector of the reference voltage vector in the large sector I under the coordinate system of 60 degrees_a、T_b、 T_cRespectively as follows:

in the small sectors 1, 2,

in the small sectors 3, 4,

in the small sector 5 of the area to be covered,

in the small sector 6 of the area to be covered,

wherein, T_sIs the sampling period.

The invention has the beneficial effects that:

the invention provides an NPC three-level inverter design method based on an improved SVPWM algorithm, which applies a 60-degree coordinate system to adapt to the condition that the included angle theta of a space voltage vector is usually a multiple of 60 degrees. The SVPWM algorithm under the 60-degree coordinate system does not contain a trigonometric function, so that the calculation process is greatly reduced compared with the algorithm under the rectangular coordinate system, and the system efficiency is effectively improved.

The invention has reasonable design, easy realization and good practical value.

Drawings

Fig. 1 is a flowchart of an NPC three-level inverter design method based on an improved SVPWM algorithm according to an embodiment of the present invention;

FIG. 2 is a complex plane distribution diagram of reference voltage vectors in the rectangular coordinate system according to an embodiment of the present invention;

FIG. 3 is a diagram comparing the rectangular coordinate system and the 60 coordinate system according to the embodiment of the present invention;

FIG. 4 is a complex plane distribution diagram of the reference voltage vector in the 60 ° coordinate system according to the embodiment of the present invention;

fig. 5 is a schematic diagram illustrating the division of the large and small sectors according to the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

At present, the traditional SVPWM algorithm of the NPC three-level inverter is based on a rectangular coordinate system, however, the included angle of the reference voltage vector is usually a multiple of 60 degrees, so that the operation amount of a trigonometric function in sector judgment and calculation of the action time of a basic vector is increased, and the complexity of the control algorithm is greatly increased.

The invention provides an NPC three-level inverter design method based on an improved SVPWM algorithm, which is characterized in that the traditional SVPWM algorithm based on a rectangular coordinate system is improved to obtain the SVPWM algorithm under a 60-degree coordinate system, so that the use of trigonometric functions can be effectively reduced, the operation flow is simplified, and the specific improvement content comprises the following steps, as shown in FIG. 1:

step 1, partitioning an orthogonal coordinate system:

step 1.1, setting the original rectangular coordinate system as an alpha-beta coordinate system, and drawing the basic reference voltage vector in the alpha-beta coordinate system as shown in figure 2, wherein V_oooThe vector with an arrow is a state vector of the basic reference voltage vector, wherein 0 is a zero vector;

step 1.2, define reference voltage vector U_ref：

U_ref＝U_ref·e^jθ (1)

Wherein, U_refIs a reference voltage vector U_refTheta is a reference voltage vector U_refThe spatial angle of (d);

reference voltage vector U_refThe magnitude of the component on the coordinate axis alpha, beta is respectively U_α、U_βRepresents, U_α、U_βAnd reference voltage vector U_refThe derived relationship of (a) is:

step 2, transforming the rectangular coordinate system of the coordinate system into a 60-degree coordinate system:

step 2.1, establishing a 60-degree coordinate system g-h on the rectangular coordinate system alpha-beta, as shown in FIG. 3; reference voltage vector U_refThe calculation formula for transforming from the rectangular coordinate system alpha-beta to the 60-degree coordinate system g-h is as follows:

wherein, U_g、U_hIs a reference voltage vector U_refThe amplitude of the component on the coordinate axis g, h;

according to Clark transformation, the transformation relation between the three-phase rotating coordinate system a-b-c and the rectangular coordinate system alpha-beta can be obtained as follows:

wherein, U_a、U_b、U_cThree-phase voltage;

the formula (3) and the formula (4) are combined to obtain the transformation relation between the three-phase rotating coordinate system a-b-c and the 60-degree coordinate system g-h:

step 2.2, reference voltage vector U_refCalculating per unit value to obtain U_g、U_hPer unit value ofMaking per unit value U of reference voltage vector^* _refFalling within a 60 DEG coordinate system g-h;

setting the maximum vector modulus of a 60-degree coordinate system g-h as U_maxTo U with_maxThe/2 is taken as a reference quantity so as to realize the per unit value calculation of the reference voltage vector, namely:

three-phase voltage U_a、U_b、U_cExpressed as:

get the reference value U_BComprises the following steps:

according to the formula (7), whenWhen the temperature of the water is higher than the set temperature,at most 1, at this timeSo the per-unit transformation is expressed as:

wherein the content of the first and second substances,is U_g、U_hPer unit value of;

reference voltage vector U according to equation (9)_refPer unit processing is carried out, so that the reference voltage vector distribution under a 60-degree coordinate system g-h is obtained, as shown in FIG. 4;

step 3, partitioning the coordinate system, and judging the sectors:

step 3.1, dividing each 60-degree vector space range in a 60-degree coordinate system g-h into a large area, sequentially partitioning the large area in the anticlockwise direction from a coordinate axis g to obtain six large sectors N with numbers I-VI, and dividing each large sector into six small sectors N with numbers 1-6, as shown in FIG. 5;

step 3.2, the per unit value obtained in the step 2Is compared with 0 to determine a reference voltage vector U_refThe large sector is located according to the judgment shown in table 1, wherein "+" represents greater than 0 and "-" represents less than 0;

large sector judgment basis in 160 degree coordinate system of table

Step 3.3, in the judgment process of the small reference vector sector, the reference voltage vector which is not in the large sector I needs to be rotated clockwise (N-1) by 60 degrees and then placed in the large sector I; the reference voltage vector before rotation can be calculated by the geometric relation of the triangleThe transformation formula is as follows:

wherein the content of the first and second substances,as a reference voltage vector before rotationThe magnitude of the component on the coordinate axes g, h, N representing the reference voltage vector before rotationThe position of the large sector;

step 3.4, obtaining the judgment of the small sector to which the reference voltage vector belongs under a 60-degree coordinate system according to the transformation relation obtained by the formula (10), wherein the judgment is according to the judgment shown in table 2, wherein "+" represents more than 0, and "-" represents less than 0; compared with the small sector judgment under a rectangular coordinate system, the judgment of the small sector n under the coordinate system of 60 degrees is simpler;

judgment basis of small sector n in 260-degree coordinate system of table

Step 4, calculating the action time of the basic vector:

similar to the SVPWM calculation of the conventional NPC three-level inverter, the reference voltage vector U can be obtained from the relationship between the rectangular coordinate system and the 60 ° coordinate system shown in fig. 3_refThe coordinates in the 60 ° coordinate system can be expressed as:

wherein M is defined as the modulation ratio, and

converting the action time of the basic vector obtained under the traditional rectangular coordinate system by a formula 11 to obtain the action time T of the basic vector under the coordinate system of 60 degrees_a、T_b、T_c(ii) a Table 3 shows the action time of each basic vector of the reference voltage vector in the large sector i under the coordinate system of 60 °;

TABLE 3 base vector action time

Wherein, T_sIs the sampling period.

It is apparent from table 3 that the SVPWM algorithm under the 60 ° coordinate system does not include a trigonometric function, and the calculation flow is greatly reduced compared with the algorithm under the rectangular coordinate system.

And a seven-segment symmetrical SVPWM modulation method is adopted for the action time sequence of each basic vector, and the implementation requirement is the same as that of the traditional SVPWM algorithm based on a rectangular coordinate system.