阅读说明：本技术 一种感应电机多步模型预测控制方法 (Induction motor multi-step model prediction control method ) 是由 张延庆 尹忠刚 杜超 高峰涛 于 2019-11-21 设计创作，主要内容包括：本发明一种感应电机多步模型预测控制方法,通过对最优电压矢量和次优电压矢量为基础的模型进行第二拍预测,根据k+2时刻以最优电压矢量和次优电压矢量为基础的预测值进行比较,选择出最终作用于逆变器的电压矢量,由于仅对以最优电压矢量和次优电压矢量为基础的模型进行多步预测,从而显著降低了算法的计算量,提高了多步模型预测控制的实用性。本发明解决了现有技术中存在的多步模型预测控制计算量大的问题。(According to the multi-step model prediction control method for the induction motor, second beat prediction is carried out on a model based on the optimal voltage vector and the suboptimal voltage vector, the predicted values based on the optimal voltage vector and the suboptimal voltage vector are compared according to the k +2 moment, the voltage vector which finally acts on the inverter is selected, and due to the fact that multi-step prediction is only carried out on the model based on the optimal voltage vector and the suboptimal voltage vector, the calculated amount of an algorithm is remarkably reduced, and the practicability of multi-step model prediction control is improved. The invention solves the problem of large calculation amount of multi-step model predictive control in the prior art.)

1. The multi-step model predictive control method of the induction motor is characterized by being implemented according to the following steps:

step 1: establishing a mathematical model of the induction motor under a two-phase static coordinate system by taking the stator current and the stator flux linkage of the induction motor as state variables;

step 2: based on the mathematical model of the induction motor in the two-phase static coordinate system obtained in the step 1, predicting the stator flux linkage and the electromagnetic torque at the moment k +1 to obtain a predicted value of the stator flux linkage and a predicted value of the electromagnetic torque, assuming that the current moment is the moment k;

and step 3: designing a cost function, and calculating the cost function according to the stator flux linkage at the k +1 moment and the predicted value of the electromagnetic torque obtained in the step 2, so that the voltage vector with the minimum cost function value is the optimal voltage vector at the k +1 moment, and the corresponding cost function value is G_min1(k + 1); making the value of the cost function only greater than G_min1The voltage vector of (k +1) is the suboptimal voltage vector u at the moment of k +1_sub(k +1) having a corresponding cost function value of G_min2(k +1), based on the steps, obtaining an optimal voltage vector and a suboptimal voltage vector at the moment of k + 1;

and 4, step 4: and (3) for the optimal voltage vector and the suboptimal voltage vector obtained in the step (3), combining the mathematical model of the induction motor under the two-phase static coordinate system established in the step (1), and calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 on the basis of the optimal voltage vector at the moment k +1 to be min { G }, wherein the minimum value is represented by_min1(k +2) }, calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 to be expressed as min { G { on the basis of the suboptimal voltage vector at the moment k +1_min2(k +2) }, if G_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter; if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_sub(k +1) is used as the output of the inverter, and according to the steps, the multi-step prediction is only carried out on the model based on the optimal voltage vector and the suboptimal voltage vector, so that the calculation amount of the algorithm is obviously reduced, and the practicability of the multi-step model prediction control is improved.

2. The multi-step model predictive control method for the induction motor as claimed in claim 1, wherein the mathematical model of the induction motor in the step 1 under the two-phase static coordinate system is

Dx＝Ax+Bu (1)

Wherein D represents a differential operator,

x＝[i_sψ_s]^T＝[i_sαi_sβψ_sαψ_sβ]^T，

u＝u_s＝[u_sαu_sβ]^T，

electromagnetic torque T of induction motor_eThe expression is as follows:

wherein the content of the first and second substances,

R_s、R_rrepresenting the resistance of a motor stator and the resistance of a motor rotor;

ψ_srepresenting stator flux linkage vector, #_sα、ψ_sβRepresenting the stator flux linkage component under the α axis, the stator flux linkage component under the β axis;

L_s、L_r、L_mrepresenting the inductance of the stator, the inductance of the rotor and the mutual inductance of the motor;

ω_rrepresenting the motor rotor speed;

u_srepresenting stator voltage vector, u_sα、u_sβRepresenting α an off-axis stator voltage component, β an off-axis stator voltage component;

n_prepresenting the number of pole pairs of the motor;

i_srepresenting stator current vector, i_sα、i_sβRepresenting α shaft lower stator current component, β shaft lower stator current component;

3. The multi-step model predictive control method of the induction motor according to claim 1, wherein the step 2 is implemented according to the following steps:

step 2.1: the stator flux linkage equation of the induction motor under the two-phase static coordinate system obtained according to the formula (1) is shown in formulas (3) to (4), and the stator current equation is shown in formulas (5) to (6):

Dψ_sα＝u_sα-R_si_sα(3)

Dψ_sβ＝u_sβ-R_si_sβ(4)

Di_sα＝-λ(R_sL_r+R_rL_s)i_sα-ω_ri_sβ+λR_rψ_sα+λL_rω_rψ_sβ+λL_ru_sα(5)

Di_sβ＝ω_ri_sα-λ(R_sL_r+R_rL_s)i_sβ-λL_rω_rψ_sα+λR_rψ_sβ+λL_ru_sβ(6)

step 2.2: based on a forward Euler discretization formula, discretizing formulas (3) to (6) to obtain stator flux linkage predicted values at the moment k +1 in the model predictive control method as shown in formulas (7) to (8), and stator current predicted values as shown in formulas (9) to (10):

wherein, T_sIs a sampling period;

step 2.3: according to the predicted value of the stator flux linkage and the predicted value of the stator current at the moment k +1, obtaining the predicted value of the electromagnetic torque at the moment k +1 as

4. The multi-step model predictive control method of the induction motor according to claim 3, wherein the step 3 is implemented according to the following steps:

step 3.1: for an induction motor drive system, the cost function is expressed as:

wherein the content of the first and second substances,

step 3.2: for a two-level voltage source inverter, there are 8 voltage vectors u in one control period_iI is 0,1,2,3,4,5,6,7, and the 8 voltage vectors are respectively substituted into the formula (12) to obtain the corresponding cost function torque component value G_i(k +1), i is 0,1,2,3,4,5,6,7, and the voltage with the smallest cost function value is selected according to the selection principle of minimizing the cost function valueThe vector is used as the optimal voltage vector u at the moment k +1_opt(k +1) having a corresponding cost function value of G_min1(k + 1); selecting a voltage vector having a cost function value greater than a minimum value as the suboptimal voltage vector u at the time k +1_sub(k +1) having a corresponding cost function value of G_min2(k+1)。

5. The multi-step model predictive control method of the induction motor according to claim 4, wherein the step 4 is implemented according to the following steps:

step 4.1: combining the formulas (7) to (10), based on the forward Euler discretization formula, selecting the optimal voltage vector u at the moment k +1_optOn the basis of (k +1), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the optimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_opt(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min1(k +2) }; meanwhile, combining the formulas (7) to (10), based on the forward Euler discretization formula, the sub-voltage vector u selected at the moment k +1_optOn the basis of (k +1), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the suboptimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_sub(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min2(k+2)}；

Step 4.2: comprehensively considering and selecting the output of the inverter according to the cost function values at the k +1 moment and the k +2 moment;

step 4.3: if the optimum voltage vector finally selected as the inverter output is a zero vector, i.e. u₀Or u₇Then u is selected according to the principle of minimum switch switching₀Or u₇Therefore, the switching state only needs to be switched once, and the reduction of the switching loss is facilitated.

6. The multi-step model predictive control method of the induction machine according to claim 5, characterized in that the step 4.2 is implemented as follows:

1) if G is_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter;

2) if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_sub(k +1) as the output of the inverter.

Technical Field

The invention belongs to the technical field of speed regulation control of high-performance induction motors, and particularly relates to a multi-step model prediction control method for an induction motor.

Background

The induction motor has a series of advantages of low manufacturing cost, firmness and durability, reliable operation, low price and the like, so the induction motor is widely applied to various aspects of national economy such as the industrial field, transportation, national defense and military equipment, electric power, coal, metallurgy, plastic, petrifaction, food, textile industry and the like. However, the induction motor is a complex object with characteristics of nonlinearity, multivariable, strong coupling, parameter time variation and large interference, and an advanced control algorithm is required to perform high-performance control on the induction motor so as to further improve the control performance of the induction motor.

The model predictive control has recently gained wide attention as a novel control method in the field of power electronics, and the method has the advantages of good dynamic characteristics, high flexibility, easy processing of multivariable control problems including constraint conditions and the like. The basic principle of model predictive control provides a distinctive method of energy management that treats a power converter as a non-linear, discrete actuator. In a model predictive control system, the control action is implemented by a single controller, while the controller's action is obtained by taking from all possible states, and the final optimal action is obtained by minimizing the cost function. In the model predictive control algorithm, a one-step prediction mode is usually adopted for reducing the overall calculated amount, and if the control behavior of the motor in multiple steps in the future can be evaluated, the switching frequency of the inverter can be effectively reduced while the motor has good dynamic and static performances, so that the method has important practical significance in medium-high voltage high-power and multi-level driving occasions. However, in the implementation process of the "multi-step strategy", the computation complexity of the classical prediction model is high, and the exhaustive optimization time required by the finite set model prediction control is exponentially and rapidly increased along with the increase of the prediction step length, so that the "multi-step strategy" is difficult to implement in a short discrete control period.

Disclosure of Invention

The invention aims to provide a multi-step model predictive control method for an induction motor, which solves the problem of large calculated amount of multi-step model predictive control in the prior art.

The technical scheme adopted by the invention is that the multi-step model predictive control method of the induction motor is implemented according to the following steps:

step 1: establishing a mathematical model of the induction motor under a two-phase static coordinate system by taking the stator current and the stator flux linkage of the induction motor as state variables;

step 2: based on the mathematical model of the induction motor in the two-phase static coordinate system obtained in the step 1, predicting the stator flux linkage and the electromagnetic torque at the moment k +1 to obtain a predicted value of the stator flux linkage and a predicted value of the electromagnetic torque, assuming that the current moment is the moment k;

and step 3: designing a cost function, and calculating the cost function according to the stator flux linkage at the k +1 moment and the predicted value of the electromagnetic torque obtained in the step 2, so that the voltage vector with the minimum cost function value is the optimal voltage vector at the k +1 moment, and the corresponding cost function value is G_min1(k + 1); making the value of the cost function only greater than G_min1The voltage vector of (k +1) is the suboptimal voltage vector u at the moment of k +1_sub(k +1) having a corresponding cost function value of G_min2(k +1), based on the above steps, the optimal voltage vector and the suboptimal voltage vector at the time of k +1 can be obtained.

And 4, step 4: and (3) for the optimal voltage vector and the suboptimal voltage vector obtained in the step (3), combining the mathematical model of the induction motor under the two-phase static coordinate system established in the step (1), and calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 on the basis of the optimal voltage vector at the moment k +1 to be min { G }, wherein the minimum value is represented by_min1(k +2) }, calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 to be expressed as min { G { on the basis of the suboptimal voltage vector at the moment k +1_min2(k +2) }, if G_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter; if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_subAnd (k +1) is used as the output of the inverter, and according to the steps, the multi-step prediction is only carried out on the model based on the optimal voltage vector and the suboptimal voltage vector, so that the calculation amount of the algorithm is obviously reduced, and the practicability of the multi-step model prediction control is improved.

The present invention is also characterized in that,

the mathematical model of the induction motor in the two-phase static coordinate system in the step 1 is

Dx＝Ax+Bu (1)

Wherein D represents a differential operator,

x＝[i_sψ_s]^T＝[i_sαi_sβψ_sαψ_sβ]^T，

u＝u_s＝[u_sαu_sβ]^T，

electromagnetic torque T of induction motor_eThe expression is as follows:

wherein the content of the first and second substances,

R_s、R_rrepresenting the resistance of a motor stator and the resistance of a motor rotor;

ψ_srepresenting stator flux linkage vector, #_sα、ψ_sβRepresenting the stator flux linkage component under the α axis, the stator flux linkage component under the β axis;

L_s、L_r、L_mrepresenting the inductance of the stator, the inductance of the rotor and the mutual inductance of the motor;

ω_rrepresenting the motor rotor speed;

u_srepresenting stator voltage vector, u_sα、u_sβRepresenting α an off-axis stator voltage component, β an off-axis stator voltage component;

n_prepresenting the number of pole pairs of the motor;

i_srepresenting stator current vector, i_sα、i_sβRepresenting α shaft lower stator current component, β shaft lower stator current component;

representing the cross product.

The step 2 is implemented according to the following steps:

step 2.1: the stator flux linkage equation of the induction motor under the two-phase static coordinate system obtained according to the formula (1) is shown in formulas (3) to (4), and the stator current equation is shown in formulas (5) to (6).

Dψ_sα＝u_sα-R_si_sα(3)

Dψ_sβ＝u_sβ-R_si_sβ(4)

Di_sα＝-λ(R_sL_r+R_rL_s)i_sα-ω_ri_sβ+λR_rψ_sα+λL_rω_rψ_sβ+λL_ru_sα(5)

Di_sβ＝ω_ri_sα-λ(R_sL_r+R_rL_s)i_sβ-λL_rω_rψ_sα+λR_rψ_sβ+λL_ru_sβ(6)

Step 2.2: based on a forward Euler discretization formula, discretizing formulas (3) to (6) to obtain stator flux linkage predicted values at the moment k +1 in the model predictive control method as shown in formulas (7) to (8), and stator current predicted values as shown in formulas (9) to (10):

wherein, T_sIs a sampling period;

step 2.3: according to the predicted value of the stator flux linkage and the predicted value of the stator current at the moment k +1, obtaining the predicted value of the electromagnetic torque at the moment k +1 as

Step 3 is specifically implemented according to the following steps:

step 3.1: for an induction motor drive system, the cost function is expressed as:

wherein the content of the first and second substances,

representing the reference torque generated by the speed loop through the proportional integral regulator, k being a weight coefficient, representing the relative importance of the electromagnetic torque and flux linkage,

giving a stator flux linkage amplitude;

step 3.2: for a two-level voltage source inverter, there are 8 voltage vectors u in one control period_iI is 0,1,2,3,4,5,6,7, and the 8 voltage vectors are respectively substituted into the formula (12) to obtain the corresponding cost function torque component value G_i(k +1), i is 0,1,2,3,4,5,6,7, and according to the selection principle of minimizing the cost function value, the voltage vector which minimizes the cost function value is selected as the optimal voltage vector u at the moment of k +1_opt(k +1) having a corresponding cost function value of G_min1(k + 1); selecting a voltage vector having a cost function value greater than a minimum value as the suboptimal voltage vector u at the time k +1_sub(k +1) having a corresponding cost function value of G_min2(k+1)。

Step 4 is specifically implemented according to the following steps:

step 4.1: combining the formulas (7) to (10), based on the forward Euler discretization formula, selecting the optimal voltage vector u at the moment k +1_optOn the basis of (k +1), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the optimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_opt(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min1(k +2) }; meanwhile, combining the formulas (7) to (10), based on the forward Euler discretization formula, the sub-voltage vector u selected at the moment k +1_optOn the basis of (k +1), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the suboptimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_sub(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min2(k+2)}；

Step 4.2: comprehensively considering and selecting the output of the inverter according to the cost function values at the k +1 moment and the k +2 moment;

step 4.3: as a special case, if the optimal voltage vector finally selected as the inverter output is a zero vector, i.e. u₀Or u₇Then u is selected according to the principle of minimum switch switching₀Or u₇Therefore, the switching state only needs to be switched once, and the reduction of the switching loss is facilitated.

Step 4.2 is specifically as follows:

1) if G is_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter;

2) if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_sub(k +1) as the output of the inverter.

The multi-step model prediction control method has the advantages that the model based on the optimal voltage vector and the suboptimal voltage vector is subjected to second beat prediction, the predicted values based on the optimal voltage vector and the suboptimal voltage vector at the k +2 moment are compared, and the voltage vector finally acting on the inverter is selected.

Drawings

FIG. 1 is a block diagram of the multi-step model predictive control method of an induction motor according to the present invention;

FIG. 2 is a circuit diagram of a two-level voltage source inverter of the present invention;

fig. 3 is a voltage vector of the two-level voltage source inverter of the present invention.

Detailed Description

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

The invention discloses a multi-step model prediction control method of an induction motor, which is implemented according to the following steps as shown in figure 1:

step 1: establishing a mathematical model of the induction motor under a two-phase static coordinate system by taking the stator current and the stator flux linkage of the induction motor as state variables;

the mathematical model of the induction motor in the two-phase static coordinate system in the step 1 is

Dx＝Ax+Bu (1)

Wherein D represents a differential operator,

x＝[i_sψ_s]^T＝[i_sαi_sβψ_sαψ_sβ]^T，

u＝u_s＝[u_sαu_sβ]^T，

electromagnetic torque T of induction motor_eThe expression is as follows:

wherein the content of the first and second substances,

R_s、R_rrepresenting the resistance of a motor stator and the resistance of a motor rotor;

ψ_srepresenting stator flux linkage vector, #_sα、ψ_sβRepresenting the stator flux linkage component under the α axis, the stator flux linkage component under the β axis;

L_s、L_r、L_mrepresenting the inductance of the stator, the inductance of the rotor and the mutual inductance of the motor;

ω_rrepresenting the motor rotor speed;

u_srepresenting stator voltage vector, u_sα、u_sβRepresenting α an off-axis stator voltage component, β an off-axis stator voltage component;

n_prepresenting the number of pole pairs of the motor;

i_srepresenting stator current vector, i_sα、i_sβRepresenting α shaft lower stator current component, β shaft lower stator current component;

representing the cross product.

Step 2: based on the mathematical model of the induction motor in the two-phase static coordinate system obtained in the step 1, predicting the stator flux linkage and the electromagnetic torque at the moment k +1 to obtain a predicted value of the stator flux linkage and a predicted value of the electromagnetic torque, assuming that the current moment is the moment k;

the step 2 is implemented according to the following steps:

step 2.1: the stator flux linkage equation of the induction motor under the two-phase static coordinate system obtained according to the formula (1) is shown in formulas (3) to (4), and the stator current equation is shown in formulas (5) to (6).

Dψ_sα＝u_sα-R_si_sα(3)

Dψ_sβ＝u_sβ-R_si_sβ(4)

Di_sα＝-λ(R_sL_r+R_rL_s)i_sα-ω_ri_sβ+λR_rψ_sα+λL_rω_rψ_sβ+λL_ru_sα(5)

Di_sβ＝ω_ri_sα-λ(R_sL_r+R_rL_s)i_sβ-λL_rω_rψ_sα+λR_rψ_sβ+λL_ru_sβ(6)

Step 2.2: based on a forward Euler discretization formula, discretizing formulas (3) to (6) to obtain stator flux linkage predicted values at the moment k +1 in the model predictive control method as shown in formulas (7) to (8), and stator current predicted values as shown in formulas (9) to (10):

wherein, T_sIs a sampling period;

step 2.3: according to the predicted value of the stator flux linkage and the predicted value of the stator current at the moment k +1, obtaining the predicted value of the electromagnetic torque at the moment k +1 as

And step 3: designing a cost function, and calculating the cost function according to the stator flux linkage at the k +1 moment and the predicted value of the electromagnetic torque obtained in the step 2, so that the voltage vector with the minimum cost function value is the optimal voltage vector at the k +1 moment, and the corresponding cost function value is G_min1(k + 1); making the value of the cost function only greater than G_min1The voltage vector of (k +1) is the suboptimal voltage vector u at the moment of k +1_sub(k +1) having a corresponding cost function value of G_min2(k +1), based on the above steps, the optimal voltage vector and the suboptimal voltage vector at the time of k +1 can be obtained.

Step 3 is specifically implemented according to the following steps:

step 3.1: for an induction motor drive system, the cost function is expressed as:

wherein the content of the first and second substances,

representing the reference torque generated by the speed loop through the proportional integral regulator, k being a weight coefficient, representing the relative importance of the electromagnetic torque and flux linkage,

for a given stator flux linkage amplitude;

step 3.2: for a two-level voltage source inverter, there are 8 voltage vectors u in one control period_iI is 0,1,2,3,4,5,6,7, and the 8 voltage vectors are respectively substituted into the formula (12) to obtain the corresponding cost function torque component value G_i(k +1), i is 0,1,2,3,4,5,6,7, and according to the selection principle of minimizing the cost function value, the voltage vector which minimizes the cost function value is selected as the optimal voltage vector u at the moment of k +1_opt(k +1) having a corresponding cost function value of G_min1(k + 1); selecting a voltage vector having a cost function value greater than a minimum value as the suboptimal voltage vector u at the time k +1_sub(k +1) having a corresponding cost function value of G_min2(k+1)。

And 4, step 4: and (3) for the optimal voltage vector and the suboptimal voltage vector obtained in the step (3), combining the mathematical model of the induction motor under the two-phase static coordinate system established in the step (1), and calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 on the basis of the optimal voltage vector at the moment k +1 to be min { G }, wherein the minimum value is represented by_min1(k +2) }, calculating the minimum value of the cost function of 8 voltage vectors at the moment k +2 to be expressed as min { G { on the basis of the suboptimal voltage vector at the moment k +1_min2(k +2) }, if G_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter; if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_sub(k +1) is used as the output of the inverter, and according to the steps, the multi-step prediction is only carried out on the model based on the optimal voltage vector and the suboptimal voltage vector, so that the calculation amount of the algorithm is obviously reduced, and the practicability of the multi-step model prediction control is improved.

Step 4 is specifically implemented according to the following steps:

step 4.1: combining the formulas (7) to (10), based on the forward Euler discretization formula, selecting the optimal voltage vector u at the moment k +1_optOn the basis of (k +1), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the optimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_opt(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min1(k +2) }; meanwhile, combining the formulas (7) to (10), based on the forward Euler discretization formula, the sub-voltage vector u selected at the moment k +1_optOn the basis of (k +2), 8 voltage vectors are substituted again to carry out second-step prediction, namely the state of the k +2 moment is predicted, and the suboptimal voltage vector u of the 8 voltage vectors at the k +1 moment at the k +2 moment is calculated_sub(k +1) based individual cost function values, wherein the minimum cost function value is expressed as min { G }_min2(k+2)}；

Step 4.2: comprehensively considering and selecting the output of the inverter according to the cost function values at the k +1 moment and the k +2 moment;

step 4.2 is specifically as follows:

1) if G is_min1(k+1)+min{G_min1(k+2)}≤G_min2(k+1)+min{G_min2(k +2) }, the optimal voltage vector u at the moment of k +1 is adopted_opt(k +1) as the output of the inverter;

2) if G is_min1(k+1)+min{G_min1(k+2)}>G_min2(k+1)+min{G_min2(k +2) }, the suboptimal voltage vector u at the moment of k +1 is adopted_sub(k +1) as the output of the inverter.

Step 4.3: as a special case, if the optimal voltage vector finally selected as the inverter output is a zero vector, i.e. u₀Or u₇Then u is selected according to the principle of minimum switch switching₀Or u₇Therefore, the switching state only needs to be switched once, and the reduction of the switching loss is facilitated.

The invention relates to a multi-step model predictive control method for an induction motor, which solves the problem of large calculated amount of multi-step model predictive control, and selects a voltage vector finally acting on an inverter by carrying out second beat prediction on a model based on an optimal voltage vector and a suboptimum voltage vector, comparing predicted values based on the optimal voltage vector and the suboptimum voltage vector according to k +2 moments, wherein the calculated amount of an algorithm is obviously reduced and the practicability of multi-step model predictive control is improved because the multi-step prediction is only carried out on the model based on the optimal voltage vector and the suboptimum voltage vector.