阅读说明：本技术 一种异步电机容错控制方法及设备 (Fault-tolerant control method and device for asynchronous motor ) 是由 向超群 成庶 于天剑 欧阳泽铿 李卓鑫 于 2020-06-17 设计创作，主要内容包括：本说明书一个或多个实施例提供的一种异步电机容错控制方法及设备,包括：建立异步电机的动态模型,预测出下一时刻的定子磁链及下一时刻的电磁转矩；根据容错逆变器结构以及预测开关序列,确定逆变器下一时刻中点电压偏移量；根据下一时刻的定子磁链、下一时刻的电磁转矩及电压偏移量构建评价函数,确定评价函数最小时的定子电压矢量为最优电压矢量；根据最优电压矢量时转矩的变化率得到最优电压矢量时的占空比,根据占空比调控异步电机。本说明书一个或多个实施例在电机器件故障时通过占空比进行转矩的预测及控制,有利于减小转矩脉动,抑制电压偏移,降低输出电流谐波含量,整体提高电机在发生故障时的应对效果。(One or more embodiments of the present disclosure provide a fault-tolerant control method and apparatus for an asynchronous motor, including: establishing a dynamic model of the asynchronous motor, and predicting a stator flux linkage at the next moment and an electromagnetic torque at the next moment; determining the neutral point voltage offset of the inverter at the next moment according to the fault-tolerant inverter structure and the predicted switching sequence; constructing an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque and the voltage offset at the next moment, and determining a stator voltage vector when the evaluation function is minimum as an optimal voltage vector; and obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio. According to one or more embodiments of the present disclosure, when a motor device fails, torque is predicted and controlled through a duty ratio, which is beneficial to reducing torque ripple, suppressing voltage offset, reducing output current harmonic content, and integrally improving a response effect of the motor when the motor device fails.)

1. A fault-tolerant control method for an asynchronous motor is characterized by comprising the following steps:

establishing a dynamic model of the asynchronous motor, determining a rotor flux linkage according to the dynamic model, dispersing the dynamic model and the rotor flux linkage through a forward Euler method to obtain a stator flux linkage at the next moment, and predicting the electromagnetic torque at the next moment;

acquiring a switching sequence of an asynchronous motor, establishing a topological structure of a fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset;

calculating an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque at the next moment and the voltage offset, and determining the stator voltage vector when the evaluation function is minimum as an optimal voltage vector;

and obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio.

2. The method according to claim 1, characterized in that the establishing of the dynamic model of the asynchronous machine is in particular:

wherein psi_sIs a stator flux linkage vector, t is a unit time variable, u_sIs a stator voltage vector, i_sIs stator current vector, R_sIs stator resistance, R_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, ω_rAs to the electrical angular velocity of the rotor,is the leakage inductance coefficient of the motor, L_mFor mutual inductance, j is a mathematical symbol representing a complex number.

3. The method according to claim 1, wherein the stator flux linkage at the next time and the electromagnetic torque at the next time are specifically:

ψ_s(k+1)＝ψ_s(k)+T_s[u_s(k)-R_si_s(k)]

wherein psi_sIs a stator flux linkage vector, T_eIs an electromagnetic torque, k is a time variable, T_sTo control the period, u_sIs stator voltage vector, R_sIs stator resistance, i_sIs a stator current vector, p is a pole pair number of the motor,and Im is a mathematical sign representing an imaginary part for the complex conjugate of the stator flux linkage vector.

4. Method according to claim 1, characterized in that the stator voltage vector is, in particular:

wherein, U_sAs stator voltage vector, S_b、S_cRespectively a b-phase switching function and a c-phase switching function in a fault inverter topology structure, U_dcFor topological structure DC link voltage, U_C1、U_C2Respectively, a first capacitor voltage and a second capacitor voltage of the topological structure, and j is a mathematical symbol representing a complex number.

5. The method of claim 1, wherein discretizing the current and voltage relationship of the flapping structure capacitor to obtain a voltage offset comprises:

the relationship between the current and the voltage of the capacitor of the quenching structure is

Wherein i_C1、i_C2Respectively a first capacitor current and a second capacitor current of a topological structure, U_C1、U_C2Respectively a first capacitor voltage and a second capacitor voltage of a topological structure, C is a capacitance value of the topological structure, the capacitance values of the first capacitor and the second capacitor in the topological structure are the same, t is a unit time variable, i_a、i_b、i_cRespectively an A-phase load current, a B-phase load current and a C-phase load current in a topological structure, S_b、S_cRespectively a B-phase switching function and a C-phase switching function in a fault inverter topological structure;

the voltage offset is specifically as follows:

wherein, Delta U_cIs the voltage offset, k is a time variable, T_sIs a control cycle.

6. The method according to claim 1, characterized in that the evaluation function is, in particular:

wherein g is an evaluation function,

7. The method according to claim 1, wherein the duty cycle is in particular:

wherein, t_optIs a duty cycle that is a function of,for a given amount of electromagnetic torque, T_eFor electromagnetic torque, T_jFor the electromagnetic torque under the action of the optimal voltage vector, k is a time variable, S_jIs the rate of change of the optimum voltage vector, T_sFor controlling the period, S_{opt_T}Is the rate of change of torque, T, of the effective voltage vector_{e_opt}Is the electromagnetic torque under the action of the effective vector.

8. An asynchronous motor fault tolerant control apparatus comprising:

the dynamic model module is used for establishing a dynamic model of the asynchronous motor, determining a rotor flux linkage according to the dynamic model, dispersing the dynamic model and the rotor flux linkage through a forward Euler method to obtain a stator flux linkage at the next moment, and predicting the electromagnetic torque at the next moment;

the inverter module is used for acquiring a switching sequence of the asynchronous motor, establishing a topological structure of the fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset;

the determining module is used for calculating an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque at the next moment and the voltage offset, and determining the stator voltage vector when the evaluation function is minimum as an optimal voltage vector;

and the control module is used for obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector and regulating and controlling the asynchronous motor according to the duty ratio.

Technical Field

One or more embodiments of the present disclosure relate to the field of machine control technologies, and in particular, to a fault-tolerant control method and apparatus for an asynchronous motor.

Background

In an asynchronous motor, a switching device is one of important constituent elements, and an inverter is the core of the switching device. In the prior art, an inverter of an asynchronous motor is generally a three-level Neutral-Point-Clamped (NPC) inverter or a two-level inverter, and compared with the latter, the NPC has the advantages of lower voltage stress of a switching device, lower harmonic content, smaller voltage offset and the like. Meanwhile, the NPC inverter topology is more complex, switching devices are multiplied, the system fault rate is obviously increased, and the reliability is reduced.

If the switching device fails, fault-tolerant control is needed to ensure the system to continue to operate. In the existing software fault-tolerant control of the NPC inverter, although the vector is lacked, the voltage utilization rate is reduced by half when the fault-tolerant operation is carried out; however, the fluctuation of the midpoint voltage of the capacitor can be increased along with the increase of the load current, the fluctuation of the midpoint voltage can be increased due to the reduction of the output frequency, and the torque ripple and the secondary failure of the inverter can be caused due to the unbalance of the midpoint voltage.

Disclosure of Invention

In view of the above, an object of one or more embodiments of the present disclosure is to provide a fault-tolerant control method and apparatus for an asynchronous motor.

In view of the above object, one or more embodiments of the present specification provide a fault-tolerant control method for an asynchronous motor, including:

establishing a dynamic model of the asynchronous motor, determining a rotor flux linkage according to the dynamic model, dispersing the dynamic model and the rotor flux linkage through a forward Euler method to obtain a stator flux linkage at the next moment, and predicting the electromagnetic torque at the next moment;

acquiring a switching sequence of an asynchronous motor, establishing a topological structure of a fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset;

calculating an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque at the next moment and the voltage offset, and determining the stator voltage vector when the evaluation function is minimum as an optimal voltage vector;

and obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio.

In some embodiments, the establishing a dynamic model of the asynchronous machine specifically includes:

wherein psi_sIs a stator flux linkage vector, t is a unit time variable, u_sIs a stator voltage vector, i_sIs stator current vector, R_sIs stator resistance, R_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, ω_rAs to the electrical angular velocity of the rotor,is the leakage inductance coefficient of the motor, L_mFor mutual inductance, j is a mathematical symbol representing a complex number.

In some embodiments, the stator flux linkage at the next time and the electromagnetic torque at the next time are specifically:

ψ_s(k+1)＝ψ_s(k)+T_s[u_s(k)-R_si_s(k)]

wherein psi_sIs a stator flux linkage vector, T_eIs an electromagnetic torque, k is a time variable, T_sTo control the period, u_sIs stator voltage vector, R_sTo be fixedSub-resistance i_sIs a stator current vector, p is a pole pair number of the motor,

and Im is a mathematical sign representing an imaginary part for the complex conjugate of the stator flux linkage vector.

In some embodiments, the stator voltage vector is, in particular:

wherein, U_sAs stator voltage vector, S_b、S_cRespectively a b-phase switching function and a c-phase switching function in a fault inverter topology structure, U_dcFor topological structure DC link voltage, U_C1、U_C2Respectively, a first capacitor voltage and a second capacitor voltage of the topological structure, and j is a mathematical symbol representing a complex number.

In some embodiments, the discretizing the relationship between the current and the voltage of the capacitance of the flapping structure to obtain the voltage offset includes:

the relationship between the current and the voltage of the capacitor of the quenching structure is

Wherein i_C1、i_C2Respectively a first capacitor current and a second capacitor current of a topological structure, U_C1、U_C2Respectively a first capacitor voltage and a second capacitor voltage of a topological structure, C is a capacitance value of the topological structure, the capacitance values of the first capacitor and the second capacitor in the topological structure are the same, t is a unit time variable, i_a、i_b、i_cRespectively an A-phase load current, a B-phase load current and a C-phase load current in a topological structure, S_b、S_cRespectively a B-phase switching function and a C-phase switching function in a fault inverter topological structure;

the voltage offset is specifically as follows:

wherein, Delta U_cIs the voltage offset, k is a time variable, T_sIs a control cycle.

In some embodiments, the evaluation function is, in particular:

wherein g is an evaluation function,respectively given electromagnetic torque and stator flux linkage vector, T_e、ψ_s、ΔU_CRespectively electromagnetic torque, stator flux linkage vector and voltage offset, k is time variable, T_en、ψ_sn、U_dcRated torque, rated flux linkage and topological structure direct current link voltage, lambda_f、λ_dcWeight coefficients of flux linkage and voltage, I_mFor the maximum current, | x | | | is the mathematical operator, the absolute value of the orientation quantity modulus.

In some embodiments, the duty cycle is, in particular:

wherein, t_optIs a duty cycle that is a function of,

for a given amount of electromagnetic torque, T_eFor electromagnetic torque, T_jFor the electromagnetic torque under the action of the optimal voltage vector, k is a time variable, S_jIs the rate of change of the optimum voltage vector, T_sFor controlling the period, S_{opt_T}Is the rate of change of torque, T, of the effective voltage vector_{e_opt}Is the electromagnetic torque under the action of the effective vector.

Based on the same concept, one or more embodiments of the present specification further provide an asynchronous motor fault-tolerant control apparatus, including:

the dynamic model module is used for establishing a dynamic model of the asynchronous motor, determining a rotor flux linkage according to the dynamic model, dispersing the dynamic model and the rotor flux linkage through a forward Euler method to obtain a stator flux linkage at the next moment, and predicting the electromagnetic torque at the next moment;

the inverter module is used for acquiring a switching sequence of the asynchronous motor, establishing a topological structure of the fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset;

the determining module is used for calculating an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque at the next moment and the voltage offset, and determining the stator voltage vector when the evaluation function is minimum as an optimal voltage vector;

and the control module is used for obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector and regulating and controlling the asynchronous motor according to the duty ratio.

As can be seen from the above description, one or more embodiments of the present specification provide a fault-tolerant control method and apparatus for an asynchronous motor, including: establishing a dynamic model of the asynchronous motor, and predicting a stator flux linkage at the next moment and an electromagnetic torque at the next moment; determining the neutral point voltage offset of the inverter at the next moment according to the fault-tolerant inverter structure and the predicted switching sequence; constructing an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque and the voltage offset at the next moment, and determining a stator voltage vector when the evaluation function is minimum as an optimal voltage vector; and obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio. According to one or more embodiments of the present disclosure, when a motor device fails, torque is predicted and controlled through a duty ratio, which is beneficial to reducing torque ripple, suppressing voltage offset, reducing output current harmonic content, and integrally improving a response effect of the motor when the motor device fails.

Drawings

In order to more clearly illustrate one or more embodiments or prior art solutions of the present specification, the drawings that are needed in the description of the embodiments or prior art will be briefly described below, and it is obvious that the drawings in the following description are only one or more embodiments of the present specification, and that other drawings may be obtained by those skilled in the art without inventive effort from these drawings.

Fig. 1 is a schematic diagram of a fault tolerant inverter topology as set forth in one or more embodiments herein;

fig. 2 is a schematic flow chart of a fault-tolerant control method for an asynchronous motor according to one or more embodiments of the present disclosure;

fig. 3 is a schematic structural diagram of an asynchronous motor fault-tolerant control device according to one or more embodiments of the present disclosure.

Detailed Description

To make the objects, technical solutions and advantages of the present specification more apparent, the present specification is further described in detail below with reference to the accompanying drawings in combination with specific embodiments.

It should be noted that technical terms or scientific terms used in the embodiments of the present specification should have a general meaning as understood by those having ordinary skill in the art to which the present disclosure belongs, unless otherwise defined. The use of "first," "second," and similar terms in this disclosure is not intended to indicate any order, quantity, or importance, but rather is used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that a element, article, or method step that precedes the word, and includes the element, article, or method step that follows the word, and equivalents thereof, does not exclude other elements, articles, or method steps. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.

As described in the background section, if a switching device of an asynchronous motor fails, fault-tolerant control is required to be performed to ensure that the system continues to operate. The existing fault-tolerant control method can be divided into two types, one type is hardware fault tolerance, for example, redundant bridge arms are added; one is software fault tolerance, and after a fault, residual voltage vectors are utilized for fault tolerance control. Hardware fault-tolerant structures are complex, equipment cost is increased, most of existing fault-tolerant control adopts a software fault-tolerant mode, and as shown in fig. 1, the fault-tolerant control is a schematic diagram of a fault-tolerant control topological structure after a three-level NPC inverter fails. And when the A phase fails, the failed bridge arm is cut off from the main circuit, and meanwhile, the failed phase is connected with the midpoint of the direct-current bus to form an eight-switch three-phase inverter topology. Due to the lack of vectors, the voltage utilization rate is reduced by half during fault-tolerant operation. On the other hand, the fluctuation of the midpoint voltage of the capacitor can be increased along with the increase of the load current, the fluctuation of the midpoint voltage can be increased due to the reduction of the output frequency, and the torque ripple and the secondary failure of the inverter can be caused due to the unbalance of the midpoint voltage.

By combining the actual conditions, the fault-tolerant control scheme of the asynchronous motor carries out fault-tolerant control on the switching device through model predictive control, and the model predictive control has the advantages of visual concept, quick dynamic response, easiness in processing nonlinear constraint, multivariable control capability and the like, and is widely applied to the fields of power electronics and power transmission. Compared with direct torque control, Model Predictive Torque Control (MPTC) directly predicts changes in relevant variables such as electromagnetic torque and stator flux linkage at the next time using an accurate model. By predicting the voltage vector of the selected set, the voltage vector that minimizes the evaluation function is selected as the output at the next time, and therefore, MPTC is more accurate and efficient in vector selection than direct torque control.

Meanwhile, in order to improve the adverse effect caused by low sampling frequency, a higher sampling rate is adopted to improve the steady-state performance of the system, but a faster hardware platform needs to be equipped, and the cost of the system is increased. The virtual vector is synthesized by using the basic voltage vector, the freedom degree of voltage vector selection is increased, and the MPTC has greater control flexibility, so that satisfactory performance is obtained under a steady state. Although the number of selectable vectors increases, the amount of calculation at the evaluation function also increases in proportion to the number of vectors. Furthermore, a method of improving the performance of the conventional MPTC by the dead-beat duty cycle control is introduced, and an optimal voltage vector is first selected according to the principle that the evaluation function is minimized. And then, calculating the duty ratio of an optimal voltage vector and a zero vector according to the torque dead beat principle, and performing MPTC according to the duty ratio, thereby being beneficial to reducing torque pulsation, inhibiting midpoint voltage deviation and reducing the harmonic content of output current.

Hereinafter, the technical means of the present specification will be described in detail by specific examples.

Referring to fig. 2, a fault-tolerant control method for an asynchronous motor according to an embodiment of the present disclosure includes the following steps:

step 201, establishing a dynamic model of the asynchronous motor, determining a rotor flux linkage according to the dynamic model, dispersing the dynamic model and the rotor flux linkage through a forward Euler method to obtain a stator flux linkage at a next moment, and predicting an electromagnetic torque at the next moment.

The method comprises the steps of predicting the stator flux linkage and the electromagnetic torque at the next moment through an established dynamic model of the asynchronous motor. The asynchronous motor is an alternating current motor which is an asynchronous motor and is also called an induction motor, and electromagnetic torque is generated by interaction of an air gap rotating magnetic field and induction current of a rotor winding, so that electromechanical energy is converted into mechanical energy. Hereinafter, the next time is a time in the future of the current time, and may be a next minute, a next second or a set time interval according to a specific application scenario, and in the art, the current time is generally represented by k, and the next time is generally represented by k + 1.

With stator flux linkage and stator current as state variables, the mathematical model of an asynchronous induction machine can be expressed as:

wherein psi_sIs a stator flux linkage vector, t is a unit time variable, u_sIs a stator voltage vector, i_sIs stator current vector, R_sIs stator resistance, R_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, ω_rAs to the electrical angular velocity of the rotor,

is the leakage inductance coefficient of the motor, L_mFor mutual inductance, j is a mathematical symbol representing a complex number, and in an asynchronous induction motor, the data relating to the stator is generally distinguished from the data relating to the rotor by subscripts and r.

Thus, the electromagnetic torque can be observed from the stator flux linkage and the stator current

Wherein, T_eIs electromagnetic torque, p is the number of pole pairs of the motor,and Im is a mathematical sign representing an imaginary part for the complex conjugate of the stator flux linkage vector.

The rotor flux linkage can be expressed as

Wherein psi_rThe forward Euler method is used for discretizing the formulas (1) and (3) to eliminate the rotor current and the rotor flux linkage as a rotor flux linkage vector, the stator flux linkage and the stator current at the moment of k +1 are solved,

ψ_s(k+1)＝ψ_s(k)+T_s[u_s(k)-R_si_s(k)](4)

wherein, T_sTo control the period, τ_r＝L_r/R_r，τ_s＝L_s/R_s，k_r＝L_m/L_r，v_sThe electromagnetic torque at the moment k can be observed according to the stator flux linkage and the stator current at the moment k as a voltage vector,

meanwhile, the torque at the time k +1 can also be predicted.

Step 202, acquiring a switching sequence of the asynchronous motor, establishing a topological structure of the fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset.

The step aims to calculate the voltage offset through the acquired switching sequence and the established topological structure of the fault inverter.

The fault-tolerant structure of the three-level inverter after phase failure consists of two bridge arms, as shown in fig. 1, after the bridge arm of the failure phase A is cut off, the phase output is directly connected with the middle point of the direct-current link capacitor.

The output of the inverter is determined by the switching combination of each arm, and a switching function equation (8) of each phase is defined, where x represents one of the B-phase and the C-phase, that is, x is B, C.

Wherein S is_xFor the switching function of the x-phase, P, O, N is a code number, representing only the switching state, S_x1、S_x2、S_x3And S_x4Respectively representing the 1 st, 2 nd, 3 rd and 4 th switching functions of the x-phase bridge arm. As shown in fig. 1When S is_xWhen 2, the output voltage is U_C1When S is_xWhen 1, the output voltage is 0, when S_xWhen equal to 0, the output voltage is-U_C2Since the a-phase fails and the output voltage of the a-phase is 0, the output phase voltage of the inverter can be expressed as formula (9), where O is the dc side midpoint:

wherein, U_C1、U_C2Respectively, a first capacitor voltage and a second capacitor voltage of the topological structure.

From the relationship between the inverter output phase voltages and the load output phase voltages, assuming that the load voltages are balanced in three phases, the load phase voltages can be derived as shown in equation (10), where N is the load neutral point:

therefore, according to the definition of the space vector, the motor stator voltage vector can be obtained:

wherein, U_sIs the stator voltage vector.

Expressions (12) of the stator voltage vector and the phase switching function and the capacitor voltage can be obtained by substituting expressions (8) to (10) into expression (11).

Wherein, U_dcThe direct current link voltage is in a topological structure.

All voltage vectors of the eight-switch three-phase inverter can be obtained according to the formula (11), wherein the voltage vectors comprise 6 small vectors, 2 medium vectors and 1 zero vector, and only 6 small vectors and 1 zero vector are adopted to ensure a circular flux linkage. When the midpoint potential is balanced, U_C1＝U_C2＝U_dc/2。

Defining the potential offset amount delta U when the midpoint potential is offset_cCharacterizing the degree of shift of the midpoint potential, the amount of shift Δ U_c＝U_C1-U_C2. The voltage vector diagram of the inverter will also change with a corresponding offset.

Assuming that the capacitance values of the two capacitors on the DC side are the same, i.e. C₁＝C₂C is a uniform topological capacitance. i.e. i_c1，i_c2And i_NPThe currents flowing through the first capacitor C1, the second capacitor C2 and the midpoint O, respectively, can be obtained by applying kirchhoff's current law to the current at the midpoint O.

As can be seen from equation (13), the fluctuation of the midpoint potential is caused by the midpoint current, which is an accumulated effect of the midpoint current on time. Considering the load side in turn, the relationship of the midpoint current to the load current can be derived from the topology of the inverter.

i_NP＝i_a+|S_b-1|i_b+|S_c-1|i_c(14)

Wherein i_a、i_b、i_cRespectively, the A-phase load current, the B-phase load current and the C-phase load current in the topological structure.

For the inverter, the midpoint potential can be controlled to a certain extent by controlling only the output voltage vector of the inverter, but the magnitude and direction of the load current are not considered simultaneously, and the phenomenon that the output voltage vector aggravates the midpoint potential imbalance degree instead occurs.

Phase A is connected with the middle point O of the DC side capacitor, and load current flows through the capacitors C1 and C2 to cause the middle point voltage to fluctuate, so that U is enabled_C1≠U_C2。

Thus, the first capacitance current i_C1A second capacitance current i_C2And a first capacitor voltage U_C1Second capacitor voltage U_C2Can be expressed as:

discretizing the formula (15) to obtain U_C1(k +1) and U_C2(k +1) is:

by setting the equation (16), the voltage offset of the voltage generated by the voltage vector action at the time k +1 can be predicted.

And 203, calculating an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque at the next moment and the voltage offset, and determining the stator voltage vector when the evaluation function is minimum as an optimal voltage vector.

The step aims to calculate an evaluation function and determine an optimal voltage vector according to the evaluation function. Only two items of torque and flux linkage are needed in the traditional two-level MPTC evaluation function, and the midpoint capacitance is needed to be added in the fault-tolerant inverter in the scheme as an evaluation item, so that the evaluation function can be constructed:

wherein g is an evaluation function,

for a given quantity of the electron flux linkage and a given quantity of the stator flux linkage vector, T, respectively_e、ψ_s、ΔU_CRespectively electromagnetic torque, stator flux linkage vector and voltage offset, k is time variable, T_en、ψ_sn、U_dcRated torque, rated flux linkage and topological structure direct current link voltage, lambda_f、λ_dcRespectively, the weight coefficients of flux linkage and voltage, | | x | | is a mathematical operator, and the absolute of a vector module is takenAnd (6) comparing the values.

Taking into account the maximum current I_mThe constraint merit function may be expressed as:

wherein the maximum current I_mSatisfies the following conditions:

wherein, I_MAXIs the theoretical maximum current value.

The evaluation functions are calculated to finally obtain 7 evaluation functions g with different sizes, wherein the evaluation functions g respectively correspond to 7 stator voltage vectors, and the calculation process of the stator voltage vectors is as shown in a formula (12). The smallest stator voltage vector among the 7 stator voltage vectors is determined as the optimal voltage vector.

And 204, obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio.

The step aims to determine the corresponding duty ratio according to the optimal voltage vector, and regulate and control the asynchronous motor according to the duty ratio. In one cycle, the inverter can be duty-controlled with 6 active vectors and zero vectors (i.e. the 7 stator voltage vectors mentioned in the previous step), respectively. According to the dead beat control principle:

wherein, T_eIs the electromagnetic torque, k is a time variable,for a given amount of electromagnetic torque, S_optAnd S₀The rate of change of torque, t, when effective and zero vectors act, respectively_optIs duty ratio, T_sIs a control cycle.

Meanwhile, the rate of change of the electromagnetic torque may be expressed as:

T_j(k+1)-T_j(k)＝S_j·T_s(22)

wherein, T_j(k+1)、T_j(k)、S_jThe electromagnetic torque at the time k +1, the electromagnetic torque at the time k, and the change rate of the optimal voltage vector are obtained after the optimal voltage vector is applied.

Therefore, from equations (21) and (22), the duty cycle of the optimal voltage vector can be calculated as:

wherein, t_optIs a duty cycle that is a function of,for a given amount of electromagnetic torque, T_eFor electromagnetic torque, T_jFor the electromagnetic torque under the action of the optimal voltage vector, k is a time variable, S_jIs the rate of change of the optimum voltage vector, T_sFor controlling the period, S_{opt_T}Is the rate of change of torque, T, of the effective voltage vector_{e_opt}Is the electromagnetic torque under the action of the effective vector.

And finally, generating an adjusted switching sequence according to the duty ratio of the optimal voltage vector, controlling a switching device of the asynchronous motor through the newly generated switching sequence, and finally driving the asynchronous motor.

The fault-tolerant control method for the asynchronous motor, which is provided by applying one or more embodiments of the specification, comprises the following steps: establishing a dynamic model of the asynchronous motor, and predicting a stator flux linkage at the next moment and an electromagnetic torque at the next moment; determining the neutral point voltage offset of the inverter at the next moment according to the fault-tolerant inverter structure and the predicted switching sequence; constructing an evaluation function according to the stator flux linkage at the next moment, the electromagnetic torque and the voltage offset at the next moment, and determining a stator voltage vector when the evaluation function is minimum as an optimal voltage vector; and obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio. According to one or more embodiments of the present disclosure, when a motor device fails, torque is predicted and controlled through a duty ratio, which is beneficial to reducing torque ripple, suppressing voltage offset, reducing output current harmonic content, and integrally improving a response effect of the motor when the motor device fails.

In an optional embodiment of this specification, in order to accurately represent the dynamic performance of the asynchronous motor and make the calculation result more accurate to characterize each item of data of the motor, the establishing a dynamic model of the asynchronous motor specifically includes:

wherein psi_sIs a stator flux linkage vector, t is a unit time variable, u_sIs a stator voltage vector, i_sIs stator current vector, R_sIs stator resistance, R_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, ω_rAs to the electrical angular velocity of the rotor,

is the leakage inductance coefficient of the motor, L_mFor mutual inductance, j is a mathematical symbol representing a complex number.

In an optional embodiment of this specification, the stator flux linkage at the next time and the electromagnetic torque at the next time are specifically:

ψ_s(k+1)＝ψ_s(k)+T_s[u_s(k)-R_si_s(k)]

wherein psi_sIs a stator flux linkage vector, T_eIs an electromagnetic torque, k is a time variable, T_sTo control the period, u_sIs stator voltage vector, R_sIs stator resistance, i_sIs a stator current vector, p is a pole pair number of the motor,and Im is a mathematical sign representing an imaginary part for the complex conjugate of the stator flux linkage vector.

In an optional embodiment of this specification, the stator voltage vector specifically includes:

wherein, U_sAs stator voltage vector, S_b、S_cRespectively a b-phase switching function and a c-phase switching function in a fault inverter topology structure, U_dcFor topological structure DC link voltage, U_C1、U_C2Respectively, a first capacitor voltage and a second capacitor voltage of the topological structure, and j is a mathematical symbol representing a complex number.

In an optional embodiment of this specification, the discretizing the relationship between the current and the voltage of the capacitor of the flapping structure to obtain the voltage offset includes:

the relationship between the current and the voltage of the capacitor of the quenching structure is

Wherein i_C1、i_C2Respectively a first capacitor current and a second capacitor current of a topological structure, U_C1、U_C2Respectively a first capacitor voltage and a second capacitor voltage of a topological structure, C is a capacitance value of the topological structure, the capacitance values of the first capacitor and the second capacitor in the topological structure are the same, t is a unit time variable, i_a、i_b、i_cRespectively an A-phase load current, a B-phase load current and a C-phase load current in a topological structure, S_b、S_cRespectively a B-phase switching function and a C-phase switching function in a fault inverter topological structure;

the voltage offset is specifically as follows:

wherein, Delta U_cIs the voltage offset, k is a time variable, T_sIs a control cycle.

In an alternative embodiment of the present specification, the evaluation function specifically includes:

wherein g is an evaluation function,respectively given electromagnetic torque and stator flux linkage vector, T_e、ψ_s、ΔU_CRespectively electromagnetic torque, stator flux linkage vector and voltage offset, k is time variable, T_en、ψ_sn、U_dcRated torque, rated flux linkage and topological structure direct current link voltage, lambda_f、λ_dcWeight coefficients of flux linkage and voltage, I_mFor the maximum current, | x | | | is the mathematical operator, the absolute value of the orientation quantity modulus.

In an optional embodiment of this specification, the duty ratio is specifically:

wherein, t_optIs a duty cycle that is a function of,

for a given amount of electromagnetic torque, T_eFor electromagnetic torque, T_jFor the electromagnetic torque under the action of the optimal voltage vector, k is a time variable, S_jIs the rate of change of the optimum voltage vector, T_sFor controlling the period, S_{opt_T}Is the rate of change of torque, T, of the effective voltage vector_{e_opt}Is the electromagnetic torque under the action of the effective vector.

Based on the same concept, one or more embodiments of the present specification further provide an asynchronous motor fault-tolerant control apparatus, as shown in fig. 3, including:

the dynamic model module 301 is configured to establish a dynamic model of the asynchronous motor, determine a rotor flux linkage according to the dynamic model, discretize the dynamic model and the rotor flux linkage by a forward euler method to obtain a stator flux linkage at a next time, and predict an electromagnetic torque at the next time;

the inverter module 302 is used for acquiring a switching sequence of the asynchronous motor, establishing a topological structure of the fault inverter, determining a stator voltage vector and a topological structure capacitance current and voltage relation according to the topological structure and the switching sequence, and performing discretization treatment on the topological structure capacitance current and voltage relation to obtain a voltage offset;

the determining module 303 is configured to calculate an evaluation function according to the stator flux linkage at the next time, the electromagnetic torque at the next time, and the voltage offset, and determine that the stator voltage vector when the evaluation function is minimum is an optimal voltage vector;

and the control module 304 is used for obtaining the duty ratio of the optimal voltage vector according to the change rate of the torque of the optimal voltage vector, and regulating and controlling the asynchronous motor according to the duty ratio.

As an optional embodiment, the establishing a dynamic model of the asynchronous motor specifically includes:

wherein psi_sIs a stator flux linkage vector, t is a unit time variable, u_sIs a stator voltage vector, i_sIs stator current vector, R_sIs stator resistance, R_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, ω_rAs to the electrical angular velocity of the rotor,is the leakage inductance coefficient of the motor, L_mFor mutual inductance, j is a mathematical symbol representing a complex number.

As an optional embodiment, the stator flux linkage at the next time and the electromagnetic torque at the next time are specifically:

ψ_s(k+1)＝ψ_s(k)+T_s[u_s(k)-R_si_s(k)]

wherein psi_sIs a stator flux linkage vector, T_eIs an electromagnetic torque, k is a time variable, T_sTo control the period, u_sIs stator voltage vector, R_sIs stator resistance, i_sIs a stator current vector, p is a pole pair number of the motor,and Im is a mathematical sign representing an imaginary part for the complex conjugate of the stator flux linkage vector.

As an optional embodiment, the stator voltage vector specifically includes:

wherein, U_sAs stator voltage vector, S_b、S_cRespectively a b-phase switching function and a c-phase switching function in a fault inverter topology structure, U_dcFor topological structure DC link voltage, U_C1、U_C2Respectively, a first capacitor voltage and a second capacitor voltage of the topological structure, and j is a mathematical symbol representing a complex number.

As an optional embodiment, the discretizing the relationship between the current and the voltage of the capacitor of the flapping structure to obtain the voltage offset includes:

the relationship between the current and the voltage of the capacitor of the quenching structure is

Wherein i_C1、i_C2Respectively a first capacitor current and a second capacitor current of a topological structure, U_C1、U_C2Respectively a first capacitor voltage and a second capacitor voltage of a topological structure, C is a capacitance value of the topological structure, the capacitance values of the first capacitor and the second capacitor in the topological structure are the same, t is a unit time variable, i_a、i_b、i_cRespectively an A-phase load current, a B-phase load current and a C-phase load current in a topological structure, S_b、S_cRespectively a B-phase switching function and a C-phase switching function in a fault inverter topological structure;

the voltage offset is specifically as follows:

wherein, Delta U_cIs the voltage offset, k is a time variable, T_sIs a control cycle.

As an optional embodiment, the evaluation function specifically includes:

wherein g is an evaluation function,respectively given electromagnetic torque and stator flux linkage vector, T_e、ψ_s、ΔU_CRespectively electromagnetic torque, stator flux linkage vector and voltage offset, k is time variable, T_en、ψ_sn、U_dcRated torque, rated flux linkage and topological structure direct current link voltage, lambda_f、λ_dcWeight coefficients of flux linkage and voltage, I_mFor the maximum current, | x | | | is the mathematical operator, the absolute value of the orientation quantity modulus.

As an optional embodiment, the duty ratio specifically includes:

wherein, t_optIs a duty ratioThe ratio of the amount of the acid to the amount of the water,for a given amount of electromagnetic torque, T_eFor electromagnetic torque, T_jFor the electromagnetic torque under the action of the optimal voltage vector, k is a time variable, S_jIs the rate of change of the optimum voltage vector, T_sFor controlling the period, S_{opt_T}Is the rate of change of torque, T, of the effective voltage vector_{e_opt}Is the electromagnetic torque under the action of the effective vector.

The device of the foregoing embodiment is used to implement the corresponding method in the foregoing embodiment, and has the beneficial effects of the corresponding method embodiment, which are not described herein again.

Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these examples; within the spirit of the present disclosure, features from the above embodiments or from different embodiments may also be combined, steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present description as described above, which are not provided in detail for the sake of brevity.

In addition, well-known power/ground connections to Integrated Circuit (IC) chips and other components may or may not be shown in the provided figures, for simplicity of illustration and discussion, and so as not to obscure one or more embodiments of the disclosure. Further, devices may be shown in block diagram form in order to avoid obscuring the understanding of one or more embodiments of the present description, and this also takes into account the fact that specifics with respect to implementation of such block diagram devices are highly dependent upon the platform within which the one or more embodiments of the present description are to be implemented (i.e., such specifics should be well within purview of one skilled in the art). Where specific details (e.g., circuits) are set forth in order to describe example embodiments of the disclosure, it should be apparent to one skilled in the art that one or more embodiments of the disclosure can be practiced without, or with variation of, these specific details. Accordingly, the description is to be regarded as illustrative instead of restrictive.

While the present disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications, and variations of these embodiments will be apparent to those of ordinary skill in the art in light of the foregoing description. For example, other memory architectures (e.g., dynamic ram (dram)) may use the discussed embodiments.

It is intended that the one or more embodiments of the present specification embrace all such alternatives, modifications and variations as fall within the broad scope of the appended claims. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of one or more embodiments of the present disclosure are intended to be included within the scope of the present disclosure.