阅读说明：本技术 一种准z源网络直接矩阵变换器的双空间矢量控制方法 (Double-space vector control method of quasi-Z-source network direct matrix converter ) 是由 郭有贵 邹博维 于 2020-06-04 设计创作，主要内容包括：本发明设计一种准Z源网络直接矩阵变换器的双空间矢量调制方法。包括以下步骤：1、釆集准Z源直接矩阵变换器的三相输入电压U<Sub>a</Sub>、U<Sub>b</Sub>、U<Sub>c</Sub>和三相输出电流i<Sub>A</Sub>、i<Sub>B</Sub>、i<Sub>C</Sub>；2、将准Z源网络直接矩阵变换器等效为虚拟整流级和虚拟逆变级的串联电路模型；3、通过分析QZS-DMC的开关状态,找出全部的直通零矢量；4、进行空间矢量调制,通过扇区的组合选取,与27个基本空间矢量进行有效结合；5、对电压传输比进行分析；6、分析开关时序,调整矢量作用顺序及作用时间。最后在保证双向开关最低切换次数的基础上形成本发明提出的双空间矢量调制方法。与现有技术相比,本发明具有提高输出性能、降低开关频率、减少开关损耗,并提高输入输出波形质量等优点。(The invention designs a double-space vector modulation method of a quasi-Z source network direct matrix converter. The method comprises the following steps: 1. three-phase input voltage U integrated with Z-source direct matrix converter a 、U b 、U c And three-phase output current i A 、i B 、i C (ii) a 2. The quasi-Z source network direct matrix converter is equivalent to a series circuit model of a virtual rectification stage and a virtual inversion stage; 3. all straight-through zero vectors are found out by analyzing the switching state of the QZS-DMC; 4. performing space vector modulation, and effectively combining the space vector modulation with 27 basic space vectors through combination selection of sectors; 5. analyzing the voltage transmission ratio; 6. and analyzing the switching time sequence, and adjusting the vector action sequence and action time. And finally, forming the double-space vector modulation method provided by the invention on the basis of ensuring the minimum switching times of the bidirectional switch. Compared with the prior art, the invention has the advantage of improving the outputThe switching frequency can be reduced, the switching loss is reduced, the input and output waveform quality is improved, and the like.)

1. A double space vector control method of a quasi Z source network direct matrix converter is used for determining switching signals of 12 bidirectional switches in the quasi Z source-direct matrix converter, and is characterized in that the modulation method comprises the following steps:

s1 three-phase input voltage U of multiple-source Z-source double-stage matrix converter_a、U_b、U_cAnd three-phase output current i_A、i_B、i_C；

S2, the direct matrix converter based on the improved quasi-Z source network is equivalent to a series circuit model of a virtual rectification stage and a virtual inversion stage;

s3, finding out all through zero vectors by analyzing the switch state of the QZS-DMC;

s4, space vector modulation is carried out, and effective combination is carried out on the space vector modulation and 27 basic space vectors through combination selection of sectors;

s5, analyzing the voltage transmission ratio to obtain the relation between the transmission ratio of the whole circuit and the through duty ratio D;

and S6, analyzing the switch time sequence, and adjusting the action sequence and the action time of the vector. And finally, forming an improved direct space vector modulation strategy with a direct-through zero vector on the basis of ensuring the minimum switching times of the bidirectional switch.

2. The method as claimed in claim 1, wherein the step S1 requires a sampling instrument to collect the three-phase input voltage U of the direct matrix converter based on the quasi-Z source network_a、U_b、U_cAnd three-phase output current i_A、i_B、i_C。

3. The method of claim 1, wherein the double space vector modulation method of the direct matrix converter based on the quasi-Z source network corresponds to two parts of virtual rectification modulation and virtual inverter modulation for the direct matrix converter in step S2. The virtual rectification modulation is input current space vector modulation. A total of 9 switch states correspond to 9 current space vectors, including 6 non-zero vectors and 3 zero vectors. The virtual inverter is modulated as an output voltage space vector modulation. According to the principle that the upper and lower same bridge arms cannot be conducted simultaneously and the output cannot be short-circuited, 8 switch states correspond to 8 voltage space vectors which comprise 6 effective vectors and 2 zero vectors.

4. The dual space vector modulation method of the direct matrix converter based on the quasi-Z source network as claimed in claim 1, wherein the step S3 specifically includes the following steps:

the switching states of a conventional direct matrix converter strictly follow two constraints: any two phases in the three-phase input can not be short-circuited, and any one phase in the three-phase output can not be open-circuited. After the introduction of the quasi-Z source network, the three-phase input side can be short-circuited at the same time. For better distinction, four switch states can be distinguished according to the working modes in the through state and the non-through state. When the quasi-Z source direct matrix converter actually operates in a non-direct state, the quasi-Z source direct matrix converter is the same as the traditional direct matrix converter in working state, two constraint conditions are met, 27 switching states exist, and all direct zero vectors are found out.

5. The dual space vector modulation method of the direct matrix converter based on the quasi-Z source network as claimed in claim 1, wherein the step S4 specifically includes the following steps:

after the switching states of the QZS-DMC in the direct-connection state and the non-direct-connection state are analyzed, different switching states correspond to different space vectors according to the concept of the vectors;

the voltage vector is defined as follows:

the current vectors are as follows:

first, it needs to calculateReferencing sector angle θ of output phase voltage vector and input current vector_vAnd theta_iDetermining the distribution sector, decomposing the reference vector in respective space, selecting basic voltage and current vectors for synthesis, selecting proper through zero vector according to the basic vector, calculating the action time of each switch state, determining the action sequence of the vectors and completing the whole modulation.

6. The dual space vector modulation method of the direct matrix converter based on the quasi-Z source network as claimed in claim 1, wherein the step S5 specifically includes the following steps:

let u_pFor outputting the phase voltage u of QZS-DMC_iFor the input phase voltage u_oInputting a reference voltage phase angle for an alternating current bus voltage, M being a modulation degree of an SVMPhase angle of input reference currentInitial phase theta of output voltage_oInitial phase of input current theta_iThen, the following relationship is given:

the method is simplified and can be obtained:

the voltage transfer ratio G of the whole circuit is:

7. the dual space vector modulation method of the direct matrix converter based on the quasi-Z source network as claimed in claim 1, wherein the step S6 specifically includes the following steps:

for SVM modulation, the arrangement of vector action sequence and action time is particularly important, and reasonable switching time sequence can effectively reduce the loss of a switching tube and improve the quality of the output waveform of the converter. The vector arrangement principle mainly reduces the switching times of switches as much as possible, wherein the reasonable selection of the through zero vector is very critical while the reasonable selection of the zero vector is considered;

the through state is generated along with the switching of the switching tube, and different bridge arms are alternately through, so that the switching times of the switching tube are reduced; the action time of the head zero vector and the tail zero vector is shortened, the action time of the middle zero vector is prolonged, and the maximum utilization rate of the direct zero vector to the traditional zero vector is ensured.

Technical Field

The invention relates to a control method of a quasi-Z source network direct matrix converter, in particular to a double-space vector modulation method of the quasi-Z source network direct matrix converter.

Background

The traditional AC-DC-AC method has many defects: (1) the AC-DC-AC frequency converter comprises a large capacitor or a large inductor as a DC energy storage link, so that the AC-DC-AC frequency converter is large in size and heavy in weight, causes inconvenience in installation and use of the frequency conversion device, and is difficult to maintain, particularly for a large electrolytic capacitor, and the service life of the frequency converter is seriously influenced due to volatilization of electrolyte; (2) the rectification side of most of the AC-DC-AC frequency converters adopts diode full-bridge rectification, so that the power factor of the input side is lower, and the harmonic pollution to a power grid is serious; (3) in the industrial application occasions of locomotive traction, elevators and the like which need continuous electric operation and continuous power generation and braking, when an AC-DC-AC frequency converter-motor is in braking operation, energy is generally consumed on a braking resistor and is not fed back to a power grid, so that the energy is not saved; (4) in industrial places such as alcohol plants, chemical plants and the like for producing dangerous goods, a large-capacity braking resistor in the PWM frequency converter can cause fire, and is a potential factor influencing safe production.

The Matrix Converter (MC) is a unidirectional forced AC/AC conversion system and can realize frequency modulation and voltage regulation; energy can flow in two directions, and four-quadrant operation is realized; no energy storage element is arranged in the middle; having a sinusoidal input current and an output voltage; and a controllable input power factor. Compared with the traditional AC-DC converter, the MC has higher reliability and smaller volume due to the lack of energy storage elements. With the rapid development of locomotive traction systems and distributed energy systems in industrial applications, the development of high performance power converters has been reluctant. The traditional Direct Matrix Converter (DMC) has lower voltage transmission ratio (maximum value is 0.866), poor interference resistance and complex commutation strategy. These drawbacks severely limit their application in the relevant industrial fields.

Disclosure of Invention

The present invention aims to overcome the defects of the prior art and provide a double space vector control method for a quasi-Z source network direct matrix converter.

The purpose of the invention can be realized by the following technical scheme:

a double space vector control method of a quasi Z source network direct matrix converter is used for determining switching signals of 12 bidirectional switches in the quasi Z source-direct matrix converter, and the modulation method comprises the following steps:

1) three-phase input voltage U integrated with Z-source direct matrix converter_a、U_b、U_cAnd three-phase output current i_A、i_B、i_C；

2) The quasi-Z source network direct matrix converter is equivalent to a series circuit model of a virtual rectification stage and a virtual inversion stage;

3) all straight-through zero vectors are found out by analyzing the switching state of the QZS-DMC;

4) performing space vector modulation, and effectively combining the space vector modulation with 27 basic space vectors through combination selection of sectors;

5) and analyzing the voltage transmission ratio to obtain the relationship between the transmission ratio of the whole circuit and the through duty ratio D.

6) And analyzing the switching time sequence, and adjusting the vector action sequence and action time. And finally, forming a double-space vector control method of the quasi-Z source network direct matrix converter on the basis of ensuring the minimum switching times of the bidirectional switch.

Drawings

FIG. 1 is a diagram of the connection of QZS-DMC;

FIG. 2 is a QZS-DMC space vector diagram;

FIG. 3 is a QZS-DMC space vector synthesis diagram;

FIG. 4 is a graph of QZS-DMC voltage transfer ratio variation;

FIG. 5 is a graph of QZS-DMC vector action sequence versus time;

FIG. 6 is a QZS-DMCPWM switch timing diagram.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The method comprises the following specific steps of 1: analyzing QZS-DMC switch states

The switching states of a conventional direct matrix converter strictly follow two constraints: any two phases in the three-phase input can not be short-circuited, and any one phase in the three-phase output can not be open-circuited. After the introduction of the quasi-Z source network, the three-phase input side can be short-circuited at the same time. For better distinction, four switch states can be distinguished, as shown in fig. 1, depending on the mode of operation in the through state and in the non-through state.

In fig. 1, (a) the output phases are respectively connected to different input phases, (b) any two of the output phases are connected to the same input phase, (c) the three-phase output is connected to the same input phase, and (d) the output phases are in a through state, that is: the three-phase input is connected with any same output phase to form a bridge arm straight-through.

Defining a switching function S of a quasi-Z-source matrix converter_ijThe following were used:

when the quasi-Z-source direct matrix converter actually operates in a non-direct state, the working state of the quasi-Z-source direct matrix converter is the same as that of the traditional direct matrix converter, two constraint conditions are met, and 27 switching states exist, which is shown in Table 1. The 27 switch states are divided into three groups, which correspond to three connection modes (a), (b) and (c) in fig. 1, wherein the connection mode (b) comprises 18 switch states, which are respectively B, C two outputs connected with the same phase, A, C two outputs connected with the same phase, and A, B two outputs connected with the same phase. When the quasi-Z source direct matrix converter operates in the through state, the switch states are as shown in Table 2, where S is_tThe phase-through state is divided into three groups, namely an A-phase through state, a B-phase through state and a C-phase through state. In fact, there are also any two-leg through and three-leg simultaneous through states that the present invention does not consider in view of reducing switching losses and in combination with conventional switching states.

TABLE 1 QZS-DMC ON-OFF STATE IN NON-DIRECT CONDITION

TABLE 2 through zero vector switch state table

The concrete step two: space vector modulation is performed.

In the first step, the switching states of the QZS-DMC in the direct-connection state and the non-direct-connection state are analyzed, and different switching states correspond to different space vectors according to the concept of vectors.

The voltage vector is defined as follows:

the current vectors are as follows:

in 27 switch states in the non-through mode, each of the 27 switch states corresponds to two space vectors: the output phase voltage space vector and the input phase current space vector are detailed in table 3. Table 1(a) the phases of two vectors corresponding to the switching states included in the group connection mode change constantly in space, have no fixed direction, and cannot be effectively used, which is called as "null vector"; (b) voltage and current vectors corresponding to 18 switch states included in the group connection mode have fixed directions and are irrelevant to input voltage phases and output current phases, so that the voltage and current vectors are effective vectors and can be fully utilized; (c) vectors corresponding to three switch states included in the group connection mode are called zero vectors; (d) the connection mode is a through switch state, the three types of the connection modes are totally 27, the corresponding vectors are similar to a zero vector, and the phase and the amplitude are zero, so the connection mode is called a through zero vector and is used for a boosting mode.

As can be seen from table 3, the output voltage vectors corresponding to the 18 effective vectors are uniformly distributed in the space, each 60-degree angle is a gradient, and a total of 6 sectors form a regular hexagon; similarly, the input current vectors are uniformly distributed, each 60-degree angle is a gradient, and the total number of the input current vectors is 6 sectors, so that a regular hexagon is formed, and the specific vector distribution is shown in fig. 2.

TABLE 3 QZS-DMC vector Table

The three-phase output reference phase voltages are set as follows:

the input reference phase currents are as follows:

after the switch state is analyzed in combination with the vector, the selection of the switch state and the calculation of the action time are performed as follows. Firstly, the sector angle theta of a reference output phase voltage vector and an input current vector is calculated_vAnd theta_iDetermining the distribution sector, decomposing the reference vector in respective space, selecting basic voltage and current vectors for synthesis, selecting proper through zero vector according to the basic vector, calculating the action time of each switch state, determining the action sequence of the vectors and completing the whole modulation.

Assume a current output phase voltage vector U_oAnd the input current vector I_iAre located in the first sector, and the basic voltage vectors in the corresponding sectors are + -1, + -2, + -3 and + -7, + -8, + -9 and + -1, + -4, + -7 and + -3, + -6, + -9. The principle of selecting the vectors is to combine the output phase voltage vector and the input current vector, at the moment, four basic vectors of +/-1, +/-3, +/-7 and +/-9 are selected, and S is selected according to the basic vectors_t1、S_t3Two kinds of straight-through vectors. The same can be deduced from the vector combinations selected by other sectors, see table 4. Vector synthesis process referring to output phase voltage vector U as shown in fig. 3_oCan be decomposed into U_o1And U_o2Wherein U is_o1Synthesized from basic voltage vectors + -9, + -7, U_o2Synthesized by +/-3 and +/-1 and input current vector I_iSynthesis of (2) and U_oThe same is true. This method is applicable to any other sector.

TABLE 4 QZS-DMC output Voltage, input Current sector combination vector selection Table

Let d₁、d₂、d₃、d₄、d_stFour basic vectors and a straight-through zero vector are in one orderThe action time within one switching period, according to the space vector modulation principle, is calculated as follows:

wherein M is a QZS-DMC modulation degree and satisfies M ∈ [0, 1%]，Is the power factor angle.

The concrete steps are as follows: the voltage transfer ratio was analyzed.

Let u_pFor outputting the phase voltage u of QZS-DMC_iFor the input phase voltage u_oInputting a reference voltage phase angle for an alternating current bus voltage, M being a modulation degree of an SVMPhase angle of input reference currentInitial phase theta of output voltage_oInitial phase of input current theta_iThen, the following relationship is given:

the method is simplified and can be obtained:

the voltage transfer ratio G of the whole circuit is:

if the input current and the output voltage are standard three-phase sine, the voltage transmission ratio G of the whole circuit is as follows:

for better intuition, the variation characteristics of the voltage transfer ratio G are compared under different through duty ratios D and different modulation degrees M, and a detailed comparison curve is shown in fig. 4 below, from which it is apparent that QZS-DMC has a higher voltage transfer ratio and the influence of D and M on the voltage transfer ratio.

The concrete steps are as follows: the switching sequences are analyzed.

For SVM modulation, the arrangement of vector action sequence and action time is particularly important, and reasonable switching time sequence can effectively reduce the loss of a switching tube and improve the quality of the output waveform of the converter. The vector arrangement principle mainly reduces the switching times of the switches as much as possible, wherein the reasonable selection of the through zero vector is very critical while the reasonable selection of the zero vector is considered. The following description will be given taking an example in which the current vector is located in the first sector and the voltage vector is located in the third sector. As shown in fig. 5, in one PWM switching period, the basic voltage vectors are symmetrically distributed with the middle zero vector as the reference, and the zero vectors are respectively added from the beginning to the end. The through zero vector adopts a uniform insertion principle, in order to not influence the working state of the QZS-DMC in a non-through state, the through time occupies zero vector action time, the through time is equally divided into ten parts and respectively inserted between the zero vector and the basic voltage vector and between the action time of two adjacent basic voltage vectors, and the corresponding through zero vector is selected according to the switching state of the front and rear vectors. Within a half period, according to the time sequence, the vector action sequence is bbb and S_tbb、abb、abS_t、aba、aS_ta、aca、acS_t、acc、S_tcc. ccc, when the switch state of a certain output bridge arm is about to be switched, a through state is generated. The specific PWM switching time sequence is shown in FIG. 6, and it can be seen that a through state is generated along with the switching of the switching tube, and different bridge arms are alternately through, so that the switching times of the switching tube are reduced; the action time of the head zero vector and the tail zero vector is shortened, the action time of the middle zero vector is prolonged, and the maximum utilization rate of the direct zero vector to the traditional zero vector is ensured.