阅读说明：本技术 减少稳态跟踪误差的两矢量模型预测控制方法 (Two-vector model prediction control method for reducing steady-state tracking error ) 是由 刘永露 杨正茂 王辉 粟梅 但汉兵 孙尧 熊文静 陈希达 于 2019-12-17 设计创作，主要内容包括：本发明提供了一种减少稳态跟踪误差的两矢量模型预测控制方法,包括：采集逆变器三相并网电压和三相并网电流的实际值,利用克拉克变换得到两相静止坐标系下的电压值和电流值；根据获取到的电压值和电流值计算出三相逆变器的输出参考电压矢量,并计算所述输出参考电压矢量的幅值和相角；判断所述输出参考电压矢量所在的大扇区及具体位于大扇区中的具体区间；根据最短距离确定最优矢量组合和各矢量的占空比；确定每个逆变器基础电压矢量的占空比；采用脉宽调制技术,实现对系统的控制。本发明的方法增加了两个备选矢量组合,减少了参考电压矢量与合成矢量之间的误差,有效地提高了系统的电流稳态跟踪性能。(The invention provides a two-vector model prediction control method for reducing steady-state tracking error, which comprises the following steps: acquiring actual values of three-phase grid-connected voltage and three-phase grid-connected current of the inverter, and obtaining a voltage value and a current value under a two-phase static coordinate system by using Clark transformation; calculating an output reference voltage vector of the three-phase inverter according to the acquired voltage value and current value, and calculating the amplitude and phase angle of the output reference voltage vector; judging a large sector where the output reference voltage vector is located and a specific interval specifically located in the large sector; determining an optimal vector combination and the duty ratio of each vector according to the shortest distance; determining a duty cycle of each inverter base voltage vector; and the control of the system is realized by adopting a pulse width modulation technology. The method of the invention adds two alternative vector combinations, reduces the error between the reference voltage vector and the synthesized vector, and effectively improves the current steady-state tracking performance of the system.)

1. A two-vector model predictive control method for reducing steady-state tracking errors, comprising:

step 1, collecting actual values of three-phase grid-connected voltage and three-phase grid-connected current of an inverter, and obtaining a voltage value and a current value under a two-phase static coordinate system by using Clark transformation;

step 2, calculating an output reference voltage vector of the three-phase inverter according to the obtained voltage value and current value, and calculating the amplitude and phase angle of the output reference voltage vector;

step 3, judging a large sector where the output reference voltage vector is located and a specific interval specifically located in the large sector according to the amplitude and the phase angle;

step 4, calculating the distance between the output reference voltage vector and a straight line formed by two adjacent basic voltage vector end points, and determining the optimal vector combination and the duty ratio of each vector according to the shortest distance;

step 5, determining the duty ratio of the basic voltage vector of each inverter according to the condition of the large sector to which the output reference voltage vector belongs;

and 6, controlling the system by adopting a pulse width modulation technology.

2. The two-vector model predictive control method for reducing steady-state tracking error according to claim 1, wherein the step 1 specifically comprises:

collecting three-phase grid-connected voltage v_a、v_b、v_cAnd three-phase grid-connected current i_a、i_b、i_cAnd converting the three-phase voltage on the output side to αβ rotation coordinate system by using Clark conversion:

the output side three-phase current is converted to αβ rotation coordinate system by using Clark conversion:

output side reference three-phase current i by using Clark conversion_{a_ref}、i_{b_ref}、i_{c_ref}And the inverter output voltage v_A、v_B、v_CConversion to αβ rotational coordinate system:

3. the two-vector model predictive control method for reducing steady-state tracking error according to claim 2, wherein the step 2 specifically comprises:

and obtaining αβ a differential equation under a rotating coordinate system according to the mathematical model of the output state of the inverter:

the above equation is rewritten using the forward difference equation as:

wherein L is_fIndicating the inductance value, T, of the output side_sWhich represents the period of the sampling,

outputting a reference value i of the current according to the k +2 moment_{α_ref}(k+2)，i_{β_ref}(k +2) obtaining the voltage v needed to be synthesized and output by the inverter at the moment of k +1_oα(k+1)，v_oβ(k+1)：

According to the formula, the reference vector of the voltage vector output by the inverter can be calculated as follows:

V_ref＝V∠θ

wherein the content of the first and second substances,

4. the two-vector model predictive control method of reducing steady-state tracking error according to claim 3, wherein said step 3 specifically comprises:

step 31, if the phase angle theta is greater than 0 and the quotient of theta divided by pi/3 is 0, then the voltage vector V is referenced_refThe large sector 1; quotient 1, reference voltage vector V_refThe large sector 2; quotient 2, reference voltage vector V_refThe large sector 3;

if the phase angle θ is less than 0, (θ +2 π) divided by π/3, the reference voltage vector V is 3_refThe large sector 4; quotient 4, reference voltage vector V_refThe large sector 5; quotient 5, reference voltage vector V_refThe large sector 6;

absolute angle theta of phase angle theta_jThe remainder of dividing theta by pi/3 when theta is larger than 0, and the remainder of dividing (theta +2 pi) by pi/3 when theta is smaller than 0;

step 32, judging the specific position of the reference vector in the large sector;

if theta is greater than theta_jE.g. [0, π/6) and

if theta is greater than theta_jE.g. [0, π/6) and

if theta is greater than theta_jE.g. [0, π/6) and

if theta is greater than theta_jE.g. [0, π/6) and

if theta is greater than theta_j∈(π/6,π/3]And is

if theta is greater than theta_j∈(π/6,π/3]And isThen the reference voltage vector V_refInterval v located in the large sector;

if theta is greater than theta_j∈(π/6,π/3]And is

if theta is greater than theta_j∈(π/6,π/3]And is

5. The two-vector model predictive control method of reducing steady-state tracking error of claim 4, wherein step 4 specifically comprises:

suppose a reference voltage vector V_refLocated in the interval I, calculating the distance L₁＝V_refsin(θ)，

Suppose a reference voltage vector V_refLocated in interval II, calculating distance L₁＝V_refsin(θ)，

Suppose a reference voltage vector V_refLocated in interval III, calculating distance

Suppose a reference voltage vector V_refLocated in the interval IV, calculating the distance L₁＝V_refsin(π/3-θ)，

Suppose a reference voltage vector V_refLocated in the interval V, and calculating the distance L₁＝V_refsin(π/3-θ)，

Suppose a reference voltage vector V_refLocated in the interval VI, calculating the distance If L is₁≤L₂(ii) a The duty cycle d₀＝0，d₁＝0，d₂＝1-d6，d₃＝0，d₄＝0，d₅＝0，

Suppose a reference voltage vector V_refLocated in the interval VII-1, calculating the distance

Suppose a reference voltage vector V_refLocated in the interval VII-2, calculating the distance

6. The two-vector model predictive control method of reducing steady-state tracking error of claim 5, wherein said step 5 specifically comprises:

7 basic vectors can be output according to the switching state of a three-phase inverter switching tube: zero vector V₀(0, 0) and V₇(1,1,1) and a valid vector V₁＝(1,0,0)，V₂＝(1,1,0)，V₃＝(0,1,0)，V₄＝(0,1,1)，V₅＝(0,0,1)，V₆(1,0, 1); in each switching period, the zero vector duty ratio is counted as d_v0Effective vector duty ratio of d_v1、d_v2、d_v3、d_v4、d_v5、d_v6(ii) a According to a reference voltage vector V_refDetermining the duty ratio of a basic voltage vector of each inverter under the condition of the large sector;

therein, step 51, reference voltage vector V_refLocated in the 1 st large sector, d_v0＝d₀，d_v1＝d₁，d_v2＝d₂，d_v3＝d₃，d_v4＝d₄，d_v5＝d₅，d_v6＝d₆；

Step 52, reference voltage vector V_refLocated in the 2 nd large sector, d_v0＝d₀，d_v1＝d₆，d_v2＝d₁，d_v3＝d₂，d_v4＝d₃，d_v5＝d₄，d_v6＝d₅；

Step 53, reference voltage vector V_refLocated in the 3 rd large sector, d_v0＝d₀，d_v1＝d₅，d_v2＝d₆，d_v3＝d₁，d_v4＝d₂，d_v5＝d₃，d_v6＝d₄；

Step 54, reference voltage vector V_refLocated in the 4 th large sector, d_v0＝d₀，d_v1＝d₄，d_v2＝d₅，d_v3＝d₆，d_v4＝d₁，d_v5＝d₂，d_v6＝d₃；

Step 55, reference voltage vector V_refLocated in the 5 th large sector, d_v0＝d₀，d_v1＝d₃，d_v2＝d₄，d_v3＝d₅，d_v4＝d₆，d_v5＝d₁，d_v6＝d₂；

Step 56, reference voltage vector V_refLocated in the 6 th large sector, d_v0＝d₀，d_v1＝d₂，d_v2＝d₃，d_v3＝d₄，d_v4＝d₅，d_v5＝d₆，d_v6＝d₁。

Technical Field

The invention relates to the technical field of power electronic conversion and the control field, in particular to a two-vector model prediction control method for reducing steady-state tracking errors.

Background

The traditional prediction control method only has single vector action in one control period, and the steady-state performance of the system is poor. Numerous studies have shown that the use of multiple vectors in a single sampling period can effectively improve the steady state performance of the system. Common methods are voltage space vector modulation and two vector predictive control. The former has better steady-state performance, but the modulation process is more complex, the calculated amount of the system is larger, the requirement on a CPU is higher, and the requirement on the switching frequency is also higher. The two-vector predictive control can effectively improve the steady-state performance of the system, and the specific method comprises the steps of firstly selecting an effective vector, then selecting a zero vector, finally calculating the duty ratio of each vector, and then adopting a PWM (pulse width modulation) technology to realize the control of the system. According to the method, only the combination of vectors in the same sector is considered, the output vector is a local optimal value and is not global optimal, a large current tracking error is easily caused, and the steady-state performance of the system is not optimal.

Disclosure of Invention

The invention provides a two-vector model prediction control method for reducing steady-state tracking errors, and aims to improve the steady-state tracking performance of a system.

In order to achieve the above object, an embodiment of the present invention provides a two-vector model predictive control method for reducing steady-state tracking error, including:

step 1, collecting actual values of three-phase grid-connected voltage and three-phase grid-connected current of an inverter, and obtaining a voltage value and a current value under a two-phase static coordinate system by using Clark transformation;

step 2, calculating an output reference voltage vector of the three-phase inverter according to the obtained voltage value and current value, and calculating the amplitude and phase angle of the output reference voltage vector;

step 3, judging a large sector where the output reference voltage vector is located and a specific interval specifically located in the large sector according to the amplitude and the phase angle;

step 4, calculating the distance between the output reference voltage vector and a straight line formed by two adjacent basic voltage vector end points, and determining the optimal vector combination and the duty ratio of each vector according to the shortest distance;

step 5, determining the duty ratio of the basic voltage vector of each inverter according to the condition of the large sector to which the output reference voltage vector belongs;

and 6, controlling the system by adopting a pulse width modulation technology.

The scheme of the invention has the following beneficial effects:

the two-vector model prediction control method for reducing the steady-state tracking error increases the combination of two alternative vectors, reduces the error between the reference voltage vector and the synthetic vector, and effectively improves the steady-state tracking performance of the system.

Drawings

FIG. 1 is a schematic flow chart of a two vector model predictive control method for reducing steady state tracking error in accordance with the present invention;

FIG. 2 is a schematic diagram of a three-phase inverter control circuit;

FIG. 3 is a schematic diagram of the division of sectors in the αβ coordinate system;

FIG. 4 is a schematic diagram illustrating the selection of the optimal vector combination with the reference vector located in the interval I;

FIG. 5 is a schematic diagram illustrating the selection of the optimal vector combination with the reference vector located in the interval II;

FIG. 6 is a schematic diagram of selecting the optimal vector combination in the interval III with the reference vector;

FIG. 7 is a diagram illustrating the selection of the optimal vector combination in the interval IV with reference vectors;

FIG. 8 is a diagram illustrating the selection of the optimal vector combination with the reference vector located in the interval V;

FIG. 9 is a schematic diagram illustrating the selection of the optimal vector combination for the interval VI where the reference vector is located;

FIG. 10 is a diagram illustrating the selection of the optimal vector combination with the reference vector located in the interval VII-1;

FIG. 11 is a diagram illustrating the selection of the optimal vector combination with the reference vector located in the interval VII-2;

FIG. 12 is a graph of experimental output current waveforms for a three-phase inverter circuit in which the method of the present invention is applied;

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1 and fig. 2, an embodiment of the present invention provides a two-vector model predictive control method for reducing steady-state tracking error, including:

step 1, collecting actual values of three-phase grid-connected voltage and three-phase grid-connected current of an inverter, and obtaining a voltage value and a current value under a two-phase static coordinate system by using Clark transformation;

step 2, calculating an output reference voltage vector of the three-phase inverter according to the obtained voltage value and current value, and calculating the amplitude and phase angle of the output reference voltage vector;

step 3, judging a large sector where the output reference voltage vector is located and a specific interval specifically located in the large sector according to the amplitude and the phase angle;

step 4, calculating the distance between the output reference voltage vector and a straight line formed by two adjacent basic voltage vector end points, and determining the optimal vector combination and the duty ratio of each vector according to the shortest distance;

step 5, determining the duty ratio of the basic voltage vector of each inverter according to the condition of the large sector to which the output reference voltage vector belongs;

and 6, controlling the system by adopting a pulse width modulation technology.

Wherein, the step 1 specifically comprises:

collecting three-phase grid-connected voltage v_a、v_b、v_cAnd three-phase grid-connected current i_a、i_b、i_c. Three phases at the output side by using Clark conversionThe voltage is converted to αβ under a rotating coordinate system:

the output side three-phase current is converted to αβ rotation coordinate system by using Clark conversion:

output side reference three-phase current i by using Clark conversion_{a_ref}、i_{b_ref}、i_{c_ref}And the inverter output voltage v_A、v_B、v_CConversion to αβ rotational coordinate system:

wherein, the step 2 specifically comprises:

and obtaining αβ a differential equation under a rotating coordinate system according to the mathematical model of the output state of the inverter:

the above equation is rewritten using the forward difference equation as:

wherein L is_fIndicating the inductance value, T, of the output side_sRepresenting the sampling period.

Outputting a reference value i of the current according to the k +2 moment_{α_ref(k+2)}，i_{β_ref(k+2)}Obtaining the voltage v of the inverter output needed to be synthesized at the moment of k +1_oα(k+1)，v_oβ(k+1),

According to the formula, the reference vector of the voltage vector output by the inverter can be calculated as follows:

V_ref＝V∠θ

wherein the content of the first and second substances,

as shown in fig. 3, the step 3 specifically includes:

step 31, if the phase angle theta is greater than 0 and the quotient of theta divided by pi/3 is 0, then the voltage vector V is referenced_refThe large sector 1; quotient 1, reference voltage vector V_refThe large sector 2; quotient 2, reference voltage vector V_refThe large sector 3;

if the phase angle θ is less than 0, (θ +2 π) divided by π/3, the reference voltage vector V is 3_refThe large sector 4; quotient 4, reference voltage vector V_refThe large sector 5; quotient 5, reference voltage vector V_refThe large sector 6;

absolute angle theta of phase angle theta_jThe remainder of dividing theta by pi/3 when theta is larger than 0, and the remainder of dividing (theta +2 pi) by pi/3 when theta is smaller than 0;

step 32, determining the specific position of the reference vector in the large sector, where the determination criteria are shown in table 1:

if theta is greater than theta_jE.g. [0, π/6) and

then the reference voltage vector V_refIs located at the largeInterval I in the sector;

if theta is greater than theta_jE.g. [0, π/6) and

then the reference voltage vector V_refAn interval II located in the large sector;

if theta is greater than theta_jE.g. [0, π/6) and

then the reference voltage vector V_refAn interval III located in the large sector;

if theta is greater than theta_jE.g. [0, π/6) and

then the reference voltage vector V_refAn interval VII-1 located in the large sector;

if theta is greater than theta_j∈(π/6,π/3]And is

Then the reference voltage vector V_refAn interval IV in the large sector;

if theta is greater than theta_j∈(π/6,π/3]And is

Then the reference voltage vector V_refInterval v located in the large sector;

if theta is greater than theta_j∈(π/6,π/3]And is

Then the reference voltage vector V_refAn interval VI located in the large sector;

if theta is greater than theta_j∈(π/6,π/3]And is

Then the reference voltage vector V_refThe interval VII-2 located in the large sector.

Wherein, step 4 specifically includes:

as shown in fig. 4, falseSuch as reference voltage vector V_refLocated in the interval I, calculating the distance L₁＝V_refsin(θ)，

If L is₁≤L₂Then, the duty ratio d₀＝1-d₁，I₁＝V_refcos(θ)/V，d₂＝0，d₃＝0，d₄＝0，d₅＝0，d ₆0; if L is₁＞L₂Then, the duty ratio d₀＝0，d₁＝0，d₃＝0，d₄＝0，d₅＝0，d₆＝1-d₂；

As shown in FIG. 5, suppose that the reference voltage vector V_refLocated in interval II, calculating distance L₁＝V_refsin(θ)，

If L is₁＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝1-d₁，

d₂＝0，d₃＝0，d₄＝0，d₅＝0，d ₆0; if L is₂＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝0，d₁＝0，d₃＝0，d₄＝0，d₅＝0，d₆＝1-d₂(ii) a If L is₃＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝0，d₁＝1-d₃，d₂＝0，

d₄＝0，d₅＝0，d₆＝0；

As shown in FIG. 6, suppose that the reference voltage vector V_refLocated in interval III, calculating distance L₁＝

If L is₁≤L₂Then, the duty ratio d₀＝0，d₁＝1-d₃，d₂＝0，

d₄＝0，d₅＝0，d ₆0; if L is₁＞L₂Then, the duty ratio d₀＝0，

d₂＝1-d₁，d₃＝0，d₄＝0，d₅＝0，d₆＝0；

As shown in FIG. 7, suppose that the reference voltage vector V_refLocated in the interval IV, calculating the distance L₁＝V_refsin(π/3-θ)，

If L is₁≤L₂Then, the duty ratio d₀＝1-d₂，d₁＝0，d₂＝V_refcos(π/3-θ)/V，d₃＝0，d₄＝0，d₅＝0，d ₆0; if L is₁＞L₂Then, the duty ratio d₀＝0，d₁＝1-d₃，d₂＝0，

d₄＝0，d₅＝0，d₆＝0；

As shown in FIG. 8, suppose that the reference voltage vector V_refLocated in the interval V, and calculating the distance L₁＝V_refsin(π/3-θ)，

If L is₁＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝1-d₁，d₁＝0，d₂＝V_refcos(π/3-θ)/V，d₃＝0，d₄＝0，d₅＝0，d ₆0; if L is₂＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝0，d₁＝1-d₃，d₂＝0，

d₄＝0，d₅＝0，d ₆0; if L is₃＝min(L₁,L₂,L₃) Then, the duty ratio d₀＝0，d₁＝0，d₂＝1-d₆，d₃＝0，d₄＝0，d₅＝0，

As shown in FIG. 9, suppose that the reference voltage vector V_refLocated in the interval VI, calculating the distance

If L is₁≤L₂(ii) a The duty cycle d₀＝0，d₁＝0，d₂＝1-d6，d₃＝0，d₄＝0，d₅＝0，

If L is₁＞L₂Then, the duty ratio d₀＝0，

d₂＝1-d₁，d₃＝0，d₄＝0，d₅＝0，d₆＝0；

As shown in FIG. 10, suppose that the reference voltage vector V_refLocated in the interval VII-1, calculating the distance

The duty cycle d₀＝0，d₁＝1-d₂，

d₃＝0，d₄＝0，d₅＝0，d₆＝0；

As shown in FIG. 11, suppose that the reference voltage vector V_refLocated in the interval VII-2, calculating the distance

The duty cycle d₀＝0，

d₂＝1-d₁，d₃＝0，d₄＝0，d₅＝0，d₆＝0。

Wherein, the step 5 specifically comprises:

7 basic vectors can be output according to the switching state of a three-phase inverter switching tube: zero vector V₀(0, 0) and V₇(1,1,1) and a valid vector V₁＝(1,0,0)，V₂＝(1,1,0)，V₃＝(0,1,0)，V₄＝(0,1,1)，V₅＝(0,0,1)，V₆(1,0, 1); in each switching period, the zero vector duty ratio is counted as d_v0Effective vector duty ratio of d_v1、d_v2、d_v3、d_v4、d_v5、d_v6(ii) a According to a reference voltage vector V_refDetermining the duty ratio of a basic voltage vector of each inverter under the condition of the large sector; the correspondence between the specific execution vector and its duty cycle is shown in table 2:

TABLE 2

Therein, step 51, reference voltage vector V_refLocated in the 1 st large sector, d_v0＝d₀，d_v1＝d₁，d_v2＝d₂，d_v3＝d₃，d_v4＝d₄，d_v5＝d₅，d_v6＝d₆；

Step 52, reference voltage vector V_refLocated in the 2 nd large sector, d_v0＝d₀，d_v1＝d₆，d_v2＝d₁，d_v3＝d₂，d_v4＝d₃，d_v5＝d₄，d_v6＝d₅；

Step 53, reference voltage vector V_refLocated in the 3 rd large sector, d_v0＝d₀，d_v1＝d₅，d_v2＝d₆，d_v3＝d₁，d_v4＝d₂，d_v5＝d₃，d_v6＝d₄；

Step 54, reference voltage vector V_refLocated in the 4 th large sector, d_v0＝d₀，d_v1＝d₄，d_v2＝d₅，d_v3＝d₆，d_v4＝d₁，d_v5＝d₂，d_v6＝d₃；

Step 55, reference voltage vector V_refLocated in the 5 th large sector, d_v0＝d₀，d_v1＝d₃，d_v2＝d₄，d_v3＝d₅，d_v4＝d₆，d_v5＝d₁，d_v6＝d₂；

Step 56, reference voltage vector V_refLocated in the 6 th large sector, d_v0＝d₀，d_v1＝d₂，d_v2＝d₃，d_v3＝d₄，d_v4＝d₅，d_v5＝d₆，d_v6＝d₁。

After the optimal vector combination and the duty ratio of each vector are determined according to the steps, the switch combination corresponding to the optimal voltage vector is acted on the three-phase inverter control circuit, as shown in fig. 12, the output current waveform diagram is obtained by adopting the method of the invention and carrying out experiments according to the circuit shown in fig. 2, and the specific experimental parameters are shown in table 3:

TABLE 3

Simulation parameters	Parameter(s)
		Voltage V at DC sidedc	90V
Ac voltage (peak value) v	50V
		Filter inductance L	10mH
Sampling frequency f	10kHz

The algorithm is realized by using a DSP, and the output current of the three-phase inverter circuit shown in fig. 2 is controlled, so that the output current waveform of the three-phase inverter is good in a steady state, the ripple wave is small, and the steady-state tracking effect of the current is good.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.