CN114640293A - Control method and system for linear induction motor driven by three-level inverter - Google Patents

Control method and system for linear induction motor driven by three-level inverter Download PDF

Info

Publication number
CN114640293A
CN114640293A CN202210269027.5A CN202210269027A CN114640293A CN 114640293 A CN114640293 A CN 114640293A CN 202210269027 A CN202210269027 A CN 202210269027A CN 114640293 A CN114640293 A CN 114640293A
Authority
CN
China
Prior art keywords
vector
voltage vector
current
evaluated
reference voltage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202210269027.5A
Other languages
Chinese (zh)
Inventor
徐伟
唐一融
董定昊
刘毅
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Huazhong University of Science and Technology
Original Assignee
Huazhong University of Science and Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Huazhong University of Science and Technology filed Critical Huazhong University of Science and Technology
Priority to CN202210269027.5A priority Critical patent/CN114640293A/en
Publication of CN114640293A publication Critical patent/CN114640293A/en
Pending legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
    • H02P25/06—Linear motors
    • H02P25/062—Linear motors of the induction type
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/14—Estimation or adaptation of machine parameters, e.g. flux, current or voltage

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Ac Motors In General (AREA)

Abstract

The invention provides a control method and a system for a linear induction motor driven by a three-level inverter, belonging to the technical field of linear motor control, wherein the method comprises the following steps: constructing a secondary flux linkage observer to observe a secondary flux linkage of the motor at the current moment; calculating the current of the motor at the next moment by combining a mathematical model of the linear induction motor; judging whether the inverter midpoint voltage exceeds a preset threshold value, and determining a value function and a reference voltage vector by combining the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage; determining a voltage vector to be evaluated according to the position of the reference voltage vector, substituting the voltage vector to be evaluated into a cost function, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as an optimal voltage vector; and generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize control of the linear induction motor. The invention can reduce the number of the evaluated voltage vectors and reduce the control complexity of the linear induction motor.

Description

Control method and system for linear induction motor driven by three-level inverter
Technical Field
The invention belongs to the technical field of linear motor control, and particularly relates to a control method and a control system of a linear induction motor driven by a three-level inverter.
Background
The linear induction motor can directly generate linear motion without a transmission mechanism such as a gear box and the like, and has wide application prospect in urban rail traffic driving systems such as subways, light rails and the like. Compared with a rotary induction motor driven rail transit system, the linear induction motor driven system has the advantages of stronger climbing capacity, smaller turning radius and smaller sectional area. However, the linear induction motor generates an edge effect due to the disconnection of the primary iron core, so that the mutual inductance change is severe during the operation of the motor, and the influence caused by the edge effect cannot be well considered in the conventional control methods such as vector control and direct torque control, so that the operation performance of the motor is not ideal. The model prediction control adopts a value function online optimization mode to select an optimal voltage vector and act on the inverter, and the influence of the side end effect of the linear induction motor can be effectively coped with by combining an equivalent circuit of the linear induction motor, so that the method has great development potential in a linear induction motor driving system.
On the other hand, the Neutral Point Clamped (NPC) type three-level inverter becomes the most widely used multi-level topological structure due to the advantages of simple structure, small voltage stress of a single power device, low switching frequency, small harmonic content and the like. For a motor control system driven by an NPC type three-level inverter, a traditional model predictive control algorithm has to evaluate 27 voltage vectors to obtain an optimal voltage vector, so that a large calculation load is brought. Meanwhile, besides general control requirements of motor driving, the model predictive control also fully considers inherent characteristics of the NPC type three-level inverter topological structure, such as neutral point voltage balance and smooth switching of voltage vectors; when the targets are introduced into model predictive control as additional constraints, the traditional method inevitably needs to introduce more weight coefficients into the cost function, and further brings about a complicated weight coefficient setting problem.
In the traditional single vector model prediction control, a tracking error exists between a selectable voltage vector and an expected optimal voltage vector, and the error becomes larger along with the increase of the voltage of a direct current bus, so that the current and thrust control performance of a high-power linear induction motor driving system is influenced. Relevant researches show that under the same switching frequency, the predicted track in a period of time in the future can be optimized by increasing the prediction step length, and the current quality is effectively improved. Therefore, the multi-step long-model predictive control becomes an effective method for further optimizing the relationship between the motor steady-state control performance (such as current THD and thrust ripple) and the switching frequency. However, the increase of the prediction step length also causes the exponential increase of the voltage vector which needs to be evaluated by the algorithm, so that the traditional multi-step long model prediction method cannot be directly applied to a motor control system to improve the performance of the motor control system.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a control method and a control system for a linear induction motor driven by a three-level inverter, and aims to solve the problems that the algorithm operation amount is large and a weight coefficient needs to be additionally introduced for midpoint voltage control when the traditional multi-step model predictive control method is applied to a linear induction motor driven by an NPC type three-level inverter.
To achieve the above object, in one aspect, the present invention provides a method for controlling a linear induction motor driven by a three-level inverter, including the steps of:
according to the phase current of the motor, the secondary angular velocity and the observed flux linkage at the previous moment, a secondary flux linkage observer is adopted to observe the secondary flux linkage of the motor at the current moment;
calculating the current of the motor at the next moment based on the secondary flux linkage at the current moment and by combining a mathematical model of the linear induction motor;
judging whether the inverter midpoint voltage exceeds a preset threshold, if not, determining a value function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current and the switching frequency as control targets; otherwise, determining a value function by taking the difference value between the current at the next moment and the reference current, the inverter midpoint voltage and the switching frequency as a control target and solving a reference voltage vector;
the neutral point voltage of the inverter is the potential difference of two capacitors in the NPC type three-level inverter;
determining a voltage vector to be evaluated according to the position of the reference voltage vector, respectively substituting the voltage vector to be evaluated into a cost function, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as an optimal voltage vector;
the voltage vector set to be evaluated is composed of all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined;
and generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize the control of the linear induction motor.
Further preferably, the method for determining a voltage vector to be evaluated according to the position of the reference voltage vector comprises the following steps:
dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a The medium vector magnitude is
Figure BDA0003553779140000034
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a plane formed by a voltage vector set to be evaluated into six sectors by adopting large vectors; making a perpendicular bisector for connecting lines of small vectors and zero vectors, small vectors and medium vectors, and small vectors and large vectors in the same sector, and dividing each sector into three subregions; the sub-region where the zero vector is located is a region R1, and the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
Further preferably, when the inverter midpoint voltage does not exceed a preset threshold, setting a difference value between the current at the next moment and the reference current and a switching frequency as a control target, setting N step lengths to determine a cost function, and solving a reference voltage vector; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage as control targets; the N step lengths are N control periods in the future which are predicted simultaneously in one control period of the motor; wherein N is more than or equal to 1;
the single step long value function is:
Figure BDA0003553779140000031
Figure BDA0003553779140000032
the N step size cost function is:
Figure BDA0003553779140000033
wherein the coefficient KiSatisfies the following conditions: k is1>K2>…>KN；
Figure BDA0003553779140000041
Is a reference voltage vector under N steps;
Figure BDA0003553779140000042
the optimal voltage vector determined for the last moment, namely the voltage vector acting on the inverter in the control period;
Figure BDA0003553779140000043
for the elements in the set of voltage vectors to be evaluated, i≥1；
Figure BDA0003553779140000044
Is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure BDA0003553779140000045
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l ismeqThe equivalent excitation inductance of the motor after considering the side effect is obtained; t issIs a control period; the lower subscript k + i represents the time k + i.
In another aspect, the present invention provides a linear induction motor control system driven by a three-level inverter, including:
the secondary flux linkage observation module is used for constructing a secondary flux linkage observer to observe a secondary flux linkage of the motor at the current moment according to the phase current of the motor, the secondary angular velocity and the observed flux linkage at the previous moment;
the motor current prediction module is used for calculating the motor current at the next moment based on the secondary flux linkage at the current moment and by combining a mathematical model of the linear induction motor;
the value function determining module is used for judging whether the midpoint voltage of the inverter exceeds a preset threshold value, determining a value function and solving a reference voltage vector by combining the difference value of the current and the reference current at the next moment, the switching frequency and the midpoint voltage of the inverter; the neutral point voltage of the inverter is the potential difference of two capacitors in the NPC type three-level inverter;
the optimal voltage vector selection module is used for determining a voltage vector to be evaluated according to the position of the reference voltage vector, substituting the voltage vector to be evaluated into the cost function respectively, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as the optimal voltage vector;
the voltage vector set to be evaluated is composed of all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined;
and the pulse sequence control module is used for generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize the control of the linear induction motor.
Further preferably, the specific step of the optimal voltage vector selection module determining the voltage vector to be evaluated according to the position of the reference voltage vector is as follows:
dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a The medium vector magnitude is
Figure BDA0003553779140000055
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a voltage vector set to be evaluated into six sectors by adopting large vectors;
making perpendicular bisectors for connecting lines of small vectors and zero vectors, small vectors and medium vectors and small vectors and large vectors in the same sector, and dividing each sector into three subregions;
wherein, the sub-region where the zero vector is located is a region R1; the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
Further preferably, the specific process of determining the cost function and solving the reference voltage vector by the cost function determination module is as follows:
when the inverter midpoint voltage does not exceed a preset threshold, setting a difference value between the current at the next moment and the reference current and a switching frequency as a control target, setting N step lengths to determine a cost function and solving a reference voltage vector; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage as control targets; n step lengths are N control periods in the future which are predicted simultaneously in one control period of the motor, and N is larger than or equal to 1.
Further preferably, the single step growth value function is:
Figure BDA0003553779140000051
Figure BDA0003553779140000052
the N step size cost function is:
Figure BDA0003553779140000053
wherein the coefficient KiSatisfies the following conditions: k1>K2>…>KN；
Figure BDA0003553779140000054
Is a reference voltage vector under N steps;
Figure BDA0003553779140000061
an optimal voltage vector determined for a previous time instant;
Figure BDA0003553779140000062
i is more than or equal to 1 and is an element in the voltage vector set to be evaluated;
Figure BDA0003553779140000063
is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure BDA0003553779140000064
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l ismeqThe equivalent excitation inductance of the motor after considering the side end effect is obtained; t issIs a control period; the corner mark k + i represents the time instant k + i.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
the invention provides a control method of a linear induction motor driven by a three-level inverter, which determines different value functions and reference voltage vectors by judging whether the midpoint voltage of the inverter exceeds a preset threshold value; all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined form a voltage vector set to be evaluated, and sectors are divided into the voltage vector set to be evaluated according to the amplitudes of elements in the voltage vector set to be evaluated; the simplified vector search method is provided based on the sector division of the reference voltage vector and the voltage vector set to be evaluated, the number of voltage vectors to be evaluated can be greatly reduced, and the complexity of the multi-step model predictive control of the linear induction motor is effectively reduced.
The invention provides a control method of a linear induction motor driven by a three-level inverter, wherein when the midpoint voltage of the inverter does not exceed a preset threshold, a difference value and switching frequency between current and reference current at the next moment are used as control targets, N step lengths are set to determine a cost function, and a reference voltage vector is solved; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage as control targets; the cascade optimization method is adopted for the neutral point voltage balance of the three-level inverter, the stability of the neutral point voltage can be well controlled while the current control performance is ensured, and weight coefficients introduced by different dimension control quantities in a cost function can be omitted; meanwhile, the multi-step prediction control method is applied to a linear induction motor control system and can effectively improve the steady-state performance under the same switching frequency.
Drawings
FIG. 1 is a flow chart of a control method of a linear induction motor driven by an NPC type three-level inverter provided by the invention;
fig. 2 is a T-type equivalent circuit diagram of a linear induction motor according to an embodiment of the present invention;
fig. 3 is a topology diagram of an NPC type three-level inverter provided by an embodiment of the present invention;
fig. 4 is a space voltage vector distribution diagram of an NPC type three-level inverter according to an embodiment of the present invention;
FIG. 5(a) is a diagram of a method for performing a first step of prediction according to a reference voltage according to an embodiment of the present invention
Figure BDA0003553779140000071
Selecting a schematic diagram of voltage vectors to be selected in the same sector;
FIG. 5(b) is a diagram of the second step of prediction according to the reference voltage according to the embodiment of the present invention
Figure BDA0003553779140000072
Selecting a to-be-selected voltage vector schematic diagram;
FIG. 5(c) is a diagram of the embodiment of the present invention for providing a reference voltage according to the third step of prediction
Figure BDA0003553779140000073
Selecting a to-be-selected voltage vector schematic diagram;
FIG. 6 is a schematic diagram of a reference voltage vector position transformation provided by an embodiment of the present invention;
fig. 7 is a block diagram of the overall control method of the linear induction motor according to the embodiment of the present invention;
fig. 8 is a control system architecture diagram of a linear induction motor according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
On one hand, the flow chart of the control method of the linear induction motor driven by the NPC type three-level inverter provided by the invention, as shown in fig. 1, specifically comprises the following steps:
s1: acquiring state parameters of a linear induction motor control system driven by the NPC type three-level inverter in real time; according to the phase current of the motor, the secondary angular velocity and the observation flux linkage at the last moment, the secondary flux linkage at the current moment of the motor is observed through a secondary flux linkage observer; the state parameters comprise motor phase current, secondary angular speed and inverter midpoint voltage;
s2: calculating the current of the motor at the next moment according to the secondary flux linkage at the current moment and by combining a mathematical model of the linear induction motor;
s3: judging whether the midpoint voltage of the inverter exceeds a set threshold value or not; if the current does not exceed the set threshold, determining a cost function and solving a reference voltage vector sequence by taking the difference value between the current at the next moment and the reference current and the switching frequency as control targets and combining the step size; if the current exceeds the set threshold, determining a single-step cost function for the control target by using the difference value between the current at the next moment and the reference current, the inverter midpoint voltage and the switching frequency, and solving a reference voltage vector;
s4: determining a voltage vector to be evaluated according to the position of the calculated reference voltage vector, substituting the voltage vector to be evaluated into a corresponding cost function, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as an optimal voltage vector;
s5: generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the inverter to realize control over the linear induction motor;
n step length: the future N control cycles can be predicted simultaneously in one control cycle.
Further preferably, the method for determining the voltage vector to be evaluated according to the position of the reference voltage vector comprises the following steps:
dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a The medium vector magnitude is
Figure BDA0003553779140000081
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a voltage vector set to be evaluated into six sectors by adopting large vectors; making a perpendicular bisector for connecting lines of small vectors and zero vectors, small vectors and medium vectors, and small vectors and large vectors in the same sector, and dividing each sector into three subregions; wherein, the sub-region where the zero vector is located is a region R1, and the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
Further preferably, when the inverter midpoint voltage does not exceed a preset threshold, setting a difference value between the current at the next moment and the reference current and a switching frequency as a control target, setting N step lengths to determine a cost function, and solving a reference voltage vector; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current, the switching frequency and the midpoint voltage of the inverter as control targets; n step lengths are N control periods in the future predicted at the same time in one control period of the motor, and N is larger than or equal to 1;
the single step long value function is:
Figure BDA0003553779140000091
Figure BDA0003553779140000092
the N step size cost function is:
Figure BDA0003553779140000093
wherein the coefficient KiSatisfies the following conditions: k1>K2>…>KN；
Figure BDA0003553779140000094
Is a reference voltage vector under N steps;
Figure BDA0003553779140000095
an optimal voltage vector determined for a previous time instant;
Figure BDA0003553779140000096
i is more than or equal to 1 and is an element in the voltage vector set to be evaluated;
Figure BDA0003553779140000097
is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure BDA0003553779140000098
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l is a radical of an alcoholmeqThe equivalent excitation inductance of the motor after considering the side end effect is obtained; t issIs a control period; the lower subscript k + i represents the time k + i.
In another aspect, the present invention provides a linear induction motor control system driven by a three-level inverter, including:
the secondary flux linkage observation module is used for constructing a secondary flux linkage observer to observe a secondary flux linkage of the motor at the current moment according to the phase current of the motor, the secondary angular velocity and the observed flux linkage at the previous moment;
the motor current prediction module is used for calculating the motor current at the next moment based on the secondary flux linkage at the current moment by combining a linear induction motor mathematical model;
the value function determining module is used for judging whether the midpoint voltage of the inverter exceeds a preset threshold value, determining a value function and solving a reference voltage vector by combining the difference value of the current and the reference current at the next moment, the switching frequency and the midpoint voltage of the inverter; the neutral point voltage of the inverter is the potential difference of two capacitors in the NPC type three-level inverter;
the optimal voltage vector selection module is used for determining a voltage vector to be evaluated according to the position of the reference voltage vector, substituting the voltage vector to be evaluated into the cost function respectively, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as the optimal voltage vector;
the voltage vector set to be evaluated is composed of all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined;
and the pulse sequence control module is used for generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize the control of the linear induction motor.
Further preferably, the specific step of determining the voltage vector to be evaluated by the optimal voltage vector selection module according to the position of the reference voltage vector is as follows: dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a The medium vector has a magnitude of
Figure BDA0003553779140000101
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a voltage vector set to be evaluated into six sectors by adopting large vectors;
making perpendicular bisector for the connecting lines of the small vector and the zero vector, the small vector and the medium vector and the small vector and the large vector in the same sector, and dividing each sector into three subregions;
wherein, the sub-region where the zero vector is located is a region R1; the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
Further preferably, the specific process of determining the cost function and solving the reference voltage vector by the cost function determination module is as follows:
when the neutral point voltage of the inverter does not exceed a preset threshold, setting N step lengths to determine a cost function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current and the switching frequency as control targets; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage as control targets; n step lengths are N control periods in the future which are predicted simultaneously in one control period of the motor, and N is larger than or equal to 1.
Further preferably, the single step growth value function is:
Figure BDA0003553779140000111
Figure BDA0003553779140000112
the N step size cost function is:
Figure BDA0003553779140000113
wherein the coefficient KiSatisfies the following conditions: k1>K2>…>KN；
Figure BDA0003553779140000114
A reference voltage vector under N step lengths;
Figure BDA0003553779140000115
an optimal voltage vector determined for a previous time instant;
Figure BDA0003553779140000116
i is more than or equal to 1 and is an element in the voltage vector set to be evaluated;
Figure BDA0003553779140000117
is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure BDA0003553779140000118
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l is a radical of an alcoholmeqThe equivalent excitation inductance of the motor after considering the side end effect is obtained; t issIs a control period; the corner mark k + i represents the time instant k + i.
Examples
The embodiment of the invention provides a linear induction motor multi-step model prediction control method driven by an NPC type three-level inverter, which comprises the following steps:
s1: respectively sampling motor phase current, inverter midpoint voltage and motor speed signals by using a current sensor, a voltage sensor and a speed sensor; calculating a secondary flux linkage according to the phase current and the speed of the motor based on a flux linkage observer, and compensating the controller delay of the NPC type three-level inverter by combining a linear induction motor mathematical model;
specifically, the construction process of the flux linkage observer comprises the following steps:
fig. 2 shows a T-type equivalent circuit of a linear induction motor, compared with a rotary induction motor, due to a primary core breaking structure, a side end effect is generated, so that an excitation inductance changes during the motor operation, and in order to quantitatively describe the mutual inductance change, a function f (q):
Figure BDA0003553779140000119
wherein: q ═ lR2/v2(Lm+Ll2) (ii) a l is the initial length of the motor; v. of2Is the linear velocity of the motor; r2Is a motor secondary resistance; l isl2Is the motor secondary leakage inductance; l ismThe excitation inductor is used for exciting the motor when the motor is static;
according to the equivalent circuit shown in fig. 2, the mathematical model of the linear induction motor can be expressed as:
Figure BDA0003553779140000121
wherein u is1＝u1α+ju1βAnd u2＝u2α+ju2βPrimary and secondary voltage vectors, respectively; i.e. i1＝i1α+ji1βAnd i2＝i2α+ji2βPrimary and secondary current vectors; psi1＝ψ1α+jψ1βAnd psi2＝ψ2α+jψ2βPrimary and secondary flux linkage vectors; l is1＝Lmeq+Ll1And L2＝Lmeq+Ll2Primary and secondary inductors; r1And R2Primary and secondary resistances of the motor; omega2To secondary angular velocity, FeIs electromagnetic thrust, and tau is motor polar distance; l ismeqTo consider the equivalent excitation inductance after the side-end effect, it can be expressed as:
Lmeq＝Lm(1-f(Q)) (3)
based on the mathematical model in equation (2), a secondary flux linkage observer can be constructed:
Figure BDA0003553779140000122
whereinK and k-1 represent motor state variables at the time of k and k-1, respectively, the superscript ^ represents observed quantity, TsIs a control period; based on the formula (4), the flux linkage observed quantity at the current moment can be obtained according to the sampling current, the secondary angular velocity and the observed flux linkage at the previous moment;
further specifically, the primary current vector i may be established based on the mathematical model in equation (2)1And secondary flux linkage psi2Equation of state for the state variables:
Figure BDA0003553779140000123
wherein the content of the first and second substances,
Figure BDA0003553779140000124
aiming at the delay caused by the calculation time of an actual control system, a motor mathematical model is required to be further combined to compensate the influence of the delay; predicting the k +1 moment through the sampling and observation value of the current k moment, wherein the prediction expression can be obtained by performing first-order Euler discretization through a formula (5):
Figure BDA0003553779140000131
wherein the content of the first and second substances,
Figure BDA0003553779140000132
M＝1-RsrTs/(σL1)，H＝Ts/(σL1)；
FIG. 3 is a topology of an NPC three-level inverter, where each phase of the motor can be connected to the positive (P), negative (N) or neutral point (O) of the DC bus in different switching states; therefore, 27 voltage vector elements to be evaluated can be generated by combining the three phases, so as to form a voltage vector set to be evaluated, and the distribution of the voltage vectors in the α β plane is shown in fig. 4; in fig. 4, the voltages can be classified into four categories according to magnitude: large, medium, small, zero vectors; table 1 lists the 27 voltages output by the NPC type three-level inverterVoltage vectors, vector amplitudes and vector categories corresponding to the vectors; wherein u isdcIs the dc bus voltage.
TABLE 1
Figure BDA0003553779140000133
Compared with a two-level inverter, the NPC type three-level inverter has the following advantages that because a neutral point is led out, the neutral point voltage of the inverter changes along with the change of current flowing through the neutral point in the running process of the motor, and the fluctuation of the current and the thrust is caused by the larger neutral point voltage deviation of the inverter, so that the neutral point voltage needs to be controlled to ensure the control performance of a motor driving system, and the neutral point voltage of the inverter is defined as:
ΔUc12＝Udc1-Udc2 (7)
wherein, Udc1And Udc2Are respectively a capacitor C1And C2Voltage on, as shown in fig. 3; based on kirchhoff's current law and the circuit topology shown in fig. 3, the following relationship exists between the currents:
Figure BDA0003553779140000141
wherein ic1And ic2Is flowed through a capacitor C1And C2A current on the substrate; i.e. i0Is the current flowing through the inverter midpoint; i.e. ia、ib、icThe three-phase current of the motor is obtained; sa、SbAnd ScThe switching states P, O and N are represented by numbers "1", "0", and "-1", respectively, for the switching states of the bridge arms of each phase;
by combining the equations (7) and (8) and discretizing, the midpoint voltage prediction expression at the time k +1 can be obtained:
Figure BDA0003553779140000142
wherein C ═ C1＝C2；
S2: judging whether the inverter midpoint voltage exceeds a set threshold, if not, determining a cost function by taking the difference value between the current at the next moment and the reference current and the switching frequency as a control target and solving a reference voltage vector; if the current exceeds the set threshold, determining a cost function for a control target by using the difference value between the current at the next moment and the reference current, the inverter midpoint voltage and the switching frequency, and solving a reference voltage vector;
in order to more clearly illustrate the implementation process of multi-step model predictive control, firstly, a method for deducing a cost function and a reference voltage vector of single-step model predictive control is provided, and after delay compensation is carried out on calculation delay brought by an actual microprocessor, the cost function of single-step model predictive control can be designed as follows:
Figure BDA0003553779140000143
wherein the content of the first and second substances,
Figure BDA0003553779140000144
is a reference current; the first term in the formula (10) is used for controlling the tracking performance of the current, and the second term is used for controlling the switching times of the inverter, namely the switching frequency; k is a radical offThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter; for subsequent derivation convenience, the difference value of the selected voltage vectors at adjacent moments is used as an evaluation standard of the switching times of the inverter; according to the formula (6), the predicted value of the current at the time k +2 can be further obtained:
Figure BDA0003553779140000151
substituting equation (11) into equation (10) can result in:
Figure BDA0003553779140000152
wherein λ ═ kf(σL1/Ts)2，
Figure BDA0003553779140000153
Is a reference voltage vector obtained based on the dead-beat control idea only considering the current tracking performance, i.e. when
Figure BDA0003553779140000154
After a control period the current will reach the reference current,
Figure BDA0003553779140000155
can be expressed as:
Figure BDA0003553779140000156
further, based on the following equation:
Figure BDA0003553779140000157
according to equation (14), assume that m1＝1，m2＝λ，
Figure BDA0003553779140000158
Equation (12) can be simplified to:
Figure BDA0003553779140000159
the last term in the formula (15) does not change with the change of the voltage vector to be evaluated and is a constant; therefore, in the single-step model predictive control, the cost function can be further simplified as:
Figure BDA00035537791400001510
equation (16) shows that if the voltage vector applied at the next moment satisfies
Figure BDA00035537791400001511
The cost function will have a minimum value at which the desired optimal control effect will be achieved and, therefore, will be
Figure BDA00035537791400001512
Referred to as reference voltage vectors; as can be seen from the voltage vector distribution diagram of the three-level inverter provided in fig. 4, the voltage vectors that can actually act are discrete, and the voltage vector closest to the reference voltage vector minimizes the value of the cost function, thereby producing the optimal control effect; therefore, the optimal voltage vector is selected based on the reference voltage vector guidance, so that repeated calculation and comparison of substituting each voltage vector into the cost function can be effectively avoided, and the algorithm complexity is further reduced;
furthermore, the value function deduced in the single-step model predictive control can be popularized to the occasions with multiple steps; the invention takes three steps as an example to specifically explain in consideration of the operational capability of an actual microprocessor and the improvement of the control performance by increasing one prediction step; the cost function of equation (12) is further generalized to three-step predictive control, which can be expressed as:
Figure BDA0003553779140000161
an assumption may be made that the secondary time constant is much larger than the sampling period, while the dynamic process of the secondary flux linkage is slower than the primary flux linkage
Figure BDA0003553779140000162
With reference to equation (13), in equation (17)
Figure BDA0003553779140000163
Can be expressed as:
Figure BDA0003553779140000164
in conjunction with equation (6), equation (14), and equation (18), equation (17) can be further simplified as:
Figure BDA0003553779140000165
wherein, the variable Ki，
Figure BDA0003553779140000166
And
Figure BDA0003553779140000167
the expression of (a) is:
Figure BDA0003553779140000168
Figure BDA0003553779140000169
Figure BDA00035537791400001610
wherein:
Figure BDA0003553779140000171
Figure BDA0003553779140000172
the last term in equation (19) also does not change with the change of the voltage vector to be evaluated, and is a constant, so equation (19) can be further simplified as:
Figure BDA0003553779140000173
analogy with the same theoryIn the single step model prediction control, the vector sequence can be based on the reference voltage
Figure BDA0003553779140000174
Figure BDA0003553779140000175
The selection of the optimal voltage vector sequence is controlled by guiding the multi-step model prediction;
further, the derived cost function can be generalized to the case of N steps:
Figure BDA0003553779140000176
wherein, the variable KiAnd reference voltage vector
Figure BDA0003553779140000177
The recurrence relation of (c) is as follows:
Figure BDA0003553779140000178
Figure BDA0003553779140000179
wherein the content of the first and second substances,
Figure BDA00035537791400001710
variable ki，KhV，KhI，KhG，KhLThe expression of (c) is as follows:
Figure BDA00035537791400001711
Figure BDA0003553779140000181
Figure BDA0003553779140000182
Figure BDA0003553779140000183
Figure BDA0003553779140000184
further, a cascade optimization method is adopted to simultaneously control the balance of the point voltage of the inverter and ensure the tracking effect of the current, and the whole optimization strategy can be realized by the following two steps by combining the solution of the value function and the reference voltage vector under the single step length and the multiple step lengths:
(1) judging whether the midpoint voltage of the inverter exceeds a set threshold value or not; if the set threshold is not exceeded, only the current and switching frequency are taken as control targets, formula (23) is taken as a cost function, and
Figure BDA0003553779140000185
Figure BDA0003553779140000186
as a sequence of reference voltage vectors; if the threshold value is exceeded, executing the step (2);
(2) when the inverter midpoint voltage exceeds a set threshold, the current, the inverter midpoint voltage and the switching frequency are taken as control targets, and the value function determined for the control targets is as follows:
Figure BDA0003553779140000191
Figure BDA0003553779140000192
wherein equation (24) is associated with a control target that takes into account current and switching frequency at a single step lengthIn agreement, equation (25) is used to ensure the stability of the inverter midpoint voltage; at this time, in
Figure BDA0003553779140000193
As a reference voltage vector;
s3: determining the specific position of the calculated reference voltage vector, determining a voltage vector to be evaluated according to a simplified search method, respectively substituting the voltage vector to be evaluated into corresponding cost functions, and selecting the voltage vector to be evaluated with the minimum cost function as an optimal voltage vector;
equation (16) shows that the single step model predicts the control cost function J1The magnitude of' can be equivalent to the voltage vector to be evaluated
Figure BDA0003553779140000194
And reference voltage vector
Figure BDA0003553779140000195
The smaller the distance between the two is, the smaller the value of the value function is; therefore, the process of solving the optimal cost function can be equivalent to the process of searching the voltage vector to be evaluated with the minimum distance from the reference voltage vector; in order to determine the distance relationship between the voltage vector to be evaluated and the reference voltage vector, the voltage vector shown in fig. 4 (the voltage vector to be evaluated and the reference voltage vector) may be further divided, a perpendicular bisector may be respectively made for the connecting lines of the small vector and the zero vector, the small vector and the medium vector, and the small vector and the large vector in the same sector, and each large sector may be further divided into 3 regions R1 to R3, as shown in fig. 5(a) to 5(c), at this time, the boundaries of adjacent sectors are all side lengths of side length
Figure BDA0003553779140000196
And the distance from a point on the boundary to a certain two voltage vectors is equal, which is a critical point; on the basis of the sector division, when the reference voltage vector is positioned in the region R1, the zero vector is the vector to be evaluated which is closest to the reference voltage vector, and the value of the cost function is also the minimum, so that the zero vector is taken as the optimal zero vector at the momentA voltage vector; when the reference voltage vector is located in the region R2, the distance between the two small vectors in the sector is smaller than that between the other voltage vectors, so that the optimal voltage vector can be selected by substituting the two small vectors into the formula (16) for further evaluation; similarly, when the reference voltage vector is located in the region R3, the distance between the two medium vectors and one large vector in the same sector is smaller than that between the other voltage vectors, so that the optimal voltage vector can be selected only by substituting the three voltage vectors into the formula (16) for further evaluation; by the simplified search method based on the reference voltage vector, 27 voltage vectors can be evaluated and converted into only 3 voltage vectors at most;
to avoid considering the judgment conditions in all sectors, the reference voltage vector may be first transformed into the first sector by the following transformation formula:
Figure BDA0003553779140000201
wherein n represents a sector in which the reference voltage vector is located; the transformation process of the voltage vector is shown in fig. 6, and at this time, only the situation in the first sector needs to be considered; to further determine whether the reference voltage vector is in the upper half or the lower half of the first sector, a variable is defined:
Figure BDA0003553779140000202
when Y is larger than 0, the converted voltage vector is positioned in the upper half part of the first sector, so that the reference voltage vector before conversion is also positioned in the upper half part of the positioned sector; otherwise, the reference voltage vector before transformation is positioned at the lower half part of the sector;
further, this sectorization and simplified search method can be generalized to the case of multiple step lengths. When the inverter midpoint voltage does not exceed the set threshold, based on the reference voltage vector sequence determined in S2
Figure BDA0003553779140000203
Figure BDA0003553779140000204
Guiding the selection of a voltage vector to be evaluated; slightly different from the simplified search method with single step length, the voltage vector to be evaluated determined by each step of prediction influences the reference voltage vector calculation of the next step of prediction under the condition of multiple step lengths, and meanwhile, the coefficient K in the formula (23)iSatisfies the following conditions: k1>K2>K3(ii) a Therefore, the more advanced prediction step has larger weight, and the determined candidate voltage vector also has larger influence on the value of the whole cost function; therefore, in the first step of prediction, the vector of the reference voltage is used as the reference
Figure BDA0003553779140000205
Selecting 5 voltage vectors of the same sector as the voltage vector to be selected, as shown in fig. 5 (a); in the second and third prediction steps, the same search method as that of the single vector is still adopted, as shown in fig. 5(b) and 5 (c); after the voltage vector sequences to be selected are determined, each voltage vector sequence to be selected needs to be substituted into a cost function (formula (23)), and the voltage vector sequence with the minimum cost function value is selected as an optimal voltage vector sequence; the multi-step model predictive control does not apply all the solved optimal voltage vector sequence to an actual control system, and only selects and outputs the first voltage vector in the optimal voltage vector sequence; in the next sampling period, the previous solving process is repeated, which is equivalent to a continuous rolling forward optimization process; tables 2 and 3 show voltage vectors to be evaluated selected according to the reference voltage vectors under different conditions; table 2 shows the voltage vector selection to be evaluated under the condition that the reference voltage vectors are different in the first-step prediction; table 3 shows the selection of the voltage vector to be evaluated under the condition that the reference voltage vectors are different in the second and third prediction steps;
TABLE 2
Figure BDA0003553779140000211
TABLE 3
Figure BDA0003553779140000212
When the inverter midpoint voltage exceeds a set threshold, the value of a cost function (formula (24) and formula (25)) needs to be considered at the same time; first, a reference voltage vector considering the current and switching frequency control performance is determined according to a cost function (formula (24))
Figure BDA0003553779140000213
And determine
Figure BDA0003553779140000214
The sector to which the sector belongs; because only the medium vector and the small vector can influence the midpoint voltage, the optimal voltage vector can be selected only by selecting the medium vector and the small vector in the same sector as a value function (formula (25)) for further evaluation of the voltage vector to be selected; the sequential cascade optimization method effectively reduces the number of voltage vectors to be evaluated while ensuring the control effect; table 4 shows the selection of the candidate voltage vector of the reference voltage vector under different conditions when the midpoint voltage of the inverter needs to be controlled; after the candidate voltage vectors are determined, each candidate voltage vector needs to be substituted into a cost function (formula (25)), and the voltage vector which enables the value of the cost function to be minimum is selected as an optimal voltage vector;
TABLE 4
Figure BDA0003553779140000221
S4: generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the inverter to realize control over the linear induction motor;
specifically, after the optimal voltage vector is determined, the model predictive control does not need a modulation link, and the determined voltage vector can be converted into corresponding 12 paths of pulse signals, which are directly applied to 12 IGBTs of the three-level inverter to complete the control of the linear induction motor, wherein the overall control block diagram of the embodiment is shown in fig. 7;
fig. 8 is an architecture diagram of a multi-step model predictive control system of a linear induction motor driven by an NPC three-level inverter, which includes: the current-time secondary flux linkage observation module 100, the motor current prediction module 200, the cost function determination module 300, the optimal voltage vector selection module 400 and the pulse sequence control module 500;
the current-time secondary flux linkage observation module 100 is used for acquiring real-time acquired state parameters of the linear induction motor control system; observing a secondary flux linkage of the motor at the current moment through a pre-constructed secondary flux linkage observer according to the state parameters; wherein the state parameters include: motor phase current, speed and inverter midpoint voltage;
the motor current prediction module 200 is configured to calculate a motor current at a next moment based on a secondary flux linkage at a current moment and in combination with a mathematical model of the linear induction motor;
the cost function determining module 300 is configured to determine whether the midpoint voltage needs to be controlled according to the collected midpoint voltage of the inverter, determine a corresponding cost function according to different control targets, and calculate a reference voltage vector by combining parameters such as current and secondary flux linkage;
the optimal voltage vector selection module 400 is configured to determine a voltage vector to be evaluated according to the calculated reference voltage vector and a simplified search method, and further determine an optimal voltage vector in combination with a cost function;
the pulse sequence control module 500 is configured to generate a three-phase bridge arm pulse sequence of the inverter according to the determined optimal voltage vector, so as to control the linear induction motor.
Specifically, the functions of each module in the NPC type three-level inverter-driven linear induction motor multi-step model predictive control system provided by the present invention may refer to the detailed description of the above method embodiments, and are not described herein again.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A control method of a linear induction motor driven by a three-level inverter is characterized by comprising the following steps:
constructing a secondary flux linkage observer to observe a current-time secondary flux linkage of the motor according to the phase current of the motor, the secondary angular velocity and the observed flux linkage at the previous time;
calculating the current of the motor at the next moment based on the secondary flux linkage at the current moment and by combining a mathematical model of the linear induction motor;
judging whether the inverter midpoint voltage exceeds a preset threshold value, determining a value function and solving a reference voltage vector by combining the difference value of the current at the next moment and the reference current, the switching frequency and the inverter midpoint voltage;
the neutral point voltage of the inverter is the potential difference of two capacitors in the NPC type three-level inverter;
determining a voltage vector to be evaluated according to the position of the reference voltage vector, respectively substituting the voltage vector to be evaluated into a cost function, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as an optimal voltage vector;
the voltage vector set to be evaluated is composed of all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined;
and generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize the control of the linear induction motor.
2. The method for controlling a linear induction motor according to claim 1, wherein the method for determining the voltage vector to be evaluated based on the position of the reference voltage vector comprises the steps of:
dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a The medium vector magnitude is
Figure FDA0003553779130000011
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a voltage vector set to be evaluated into six sectors by adopting large vectors;
making perpendicular bisectors for connecting lines of small vectors and zero vectors, small vectors and medium vectors and small vectors and large vectors in the same sector, and dividing each sector into three subregions;
wherein, the sub-region where the zero vector is located is a region R1; the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
3. The method of linear inductor motor control of claim 2, wherein determining the cost function and solving for the reference voltage vector is by:
when the neutral point voltage of the inverter does not exceed a preset threshold, setting N step lengths to determine a cost function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current and the switching frequency as control targets; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage as control targets; n step lengths are N control periods in the future which are predicted simultaneously in one control period of the motor, and N is larger than or equal to 1.
4. The linear inductor motor control method of claim 3, wherein the single step long value function is:
Figure FDA0003553779130000021
Figure FDA0003553779130000022
the N step size cost function is:
Figure FDA0003553779130000023
wherein the coefficient KiSatisfies the following conditions: k1>K2>…>KN；
Figure FDA0003553779130000024
A reference voltage vector under N step lengths;
Figure FDA0003553779130000025
an optimal voltage vector determined for a previous time instant;
Figure FDA0003553779130000026
i is more than or equal to 1 and is an element in the voltage vector set to be evaluated;
Figure FDA0003553779130000027
is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure FDA0003553779130000028
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l is a radical of an alcoholmeqThe equivalent excitation inductance of the motor after considering the side end effect is obtained; t is a unit ofsIs a control period; when the corner mark k + i represents k + iAnd (6) engraving.
5. A three-level inverter driven linear induction motor control system, comprising:
the secondary flux linkage observation module is used for constructing a secondary flux linkage observer to observe a secondary flux linkage of the motor at the current moment according to the phase current of the motor, the secondary angular velocity and the observed flux linkage at the previous moment;
the motor current prediction module is used for calculating the motor current at the next moment based on the secondary flux linkage at the current moment by combining a linear induction motor mathematical model;
the value function determining module is used for judging whether the inverter midpoint voltage exceeds a preset threshold value, determining a value function and solving a reference voltage vector by combining the difference value of the current and the reference current at the next moment, the switching frequency and the inverter midpoint voltage; the neutral point voltage of the inverter is the potential difference of two capacitors in the NPC type three-level inverter;
the optimal voltage vector selection module is used for determining a voltage vector to be evaluated according to the position of the reference voltage vector, substituting the voltage vector to be evaluated into the cost function respectively, and selecting the voltage vector to be evaluated, which enables the cost function to be minimum, as the optimal voltage vector;
the voltage vector set to be evaluated is composed of all voltage vectors which can be generated after corresponding switch states of bridge arms of each phase of the NPC type three-level inverter are combined;
and the pulse sequence control module is used for generating three-phase bridge arm pulses according to the optimal voltage vector and acting on corresponding bridge arms of the NPC type three-level inverter to realize the control of the linear induction motor.
6. The linear induction motor control system of claim 5, wherein the optimal voltage vector selection module determines the voltage vector to be evaluated according to the position of the reference voltage vector by the specific steps of:
dividing each element in the voltage vector set to be evaluated into a large vector, a medium vector, a small vector and a zero vector according to the magnitude; wherein the large vector magnitude is 2/3 times udc(ii) a InThe vector magnitude is
Figure FDA0003553779130000031
Multiple of udc(ii) a Small vector magnitude of 1/3 times udc；udcIs a dc bus voltage;
dividing a voltage vector set to be evaluated into six sectors by adopting large vectors;
making perpendicular bisectors for connecting lines of small vectors and zero vectors, small vectors and medium vectors and small vectors and large vectors in the same sector, and dividing each sector into three subregions;
wherein, the sub-region where the zero vector is located is a region R1; the region where the small vector is located is a region R2; the region where the medium vector and the large vector are located is a region R3;
when the reference voltage vector is located in the region R1, the zero vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R2, the small vector of the sector where the reference voltage vector is located is used as a vector to be evaluated; when the reference voltage vector is located in the region R3, the medium vector and the large vector of the sector in which the reference voltage vector is located are used as the vectors to be evaluated.
7. The linear inductor motor control system of claim 6, wherein the cost function determination module determines the cost function and solves the reference voltage vector by:
when the neutral point voltage of the inverter does not exceed a preset threshold, setting N step lengths to determine a cost function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current and the switching frequency as control targets; otherwise, determining a single-step long value function and solving a reference voltage vector by taking the difference value between the current at the next moment and the reference current, the switching frequency and the midpoint voltage of the inverter as control targets; wherein, N step length is N control periods in the future which are simultaneously controlled in one control period of the motor, and N is more than or equal to 1.
8. The linear inductor motor control system of claim 7, wherein the single step cost function is:
Figure FDA0003553779130000041
Figure FDA0003553779130000042
the N step size cost function is:
Figure FDA0003553779130000043
wherein the coefficient KiSatisfies the following conditions: k1>K2>…>KN；
Figure FDA0003553779130000044
Is a reference voltage vector under N steps;
Figure FDA0003553779130000045
an optimal voltage vector determined for a previous time instant;
Figure FDA0003553779130000046
i is more than or equal to 1 and is an element in the voltage vector set to be evaluated;
Figure FDA0003553779130000047
is a reference voltage vector under single step length; k isf(σL1/Ts)2，kfThe weight coefficient is used for adjusting the control weight between the current tracking performance and the switching times of the inverter;
Figure FDA0003553779130000051
L1＝Lmeq+Ll1and L2＝Lmeq+Ll2Primary and secondary inductances of the motor respectively; l ismeqTo consider the edge endThe motor after effect is equivalent to an excitation inductor; t issIs a control period; the corner mark k + i represents the time instant k + i.
CN202210269027.5A 2022-03-18 2022-03-18 Control method and system for linear induction motor driven by three-level inverter Pending CN114640293A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210269027.5A CN114640293A (en) 2022-03-18 2022-03-18 Control method and system for linear induction motor driven by three-level inverter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210269027.5A CN114640293A (en) 2022-03-18 2022-03-18 Control method and system for linear induction motor driven by three-level inverter

Publications (1)

Publication Number Publication Date
CN114640293A true CN114640293A (en) 2022-06-17

Family

ID=81950522

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202210269027.5A Pending CN114640293A (en) 2022-03-18 2022-03-18 Control method and system for linear induction motor driven by three-level inverter

Country Status (1)

Country Link
CN (1) CN114640293A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115622465A (en) * 2022-11-18 2023-01-17 西南交通大学 Multi-level converter weightless factor model prediction control method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115622465A (en) * 2022-11-18 2023-01-17 西南交通大学 Multi-level converter weightless factor model prediction control method

Similar Documents

Publication Publication Date Title
CN108028599B (en) Controlling a three-phase power converter
CN110557074B (en) Prediction current control method for permanent magnet motor system of cascaded H-bridge inverter
CN109728757B (en) Method and system for controlling prediction thrust of linear induction motor by using arbitrary double-vector model
CN110829908B (en) Permanent magnet traction motor control method based on hybrid multi-level inverter
CN111541411B (en) Double-three-level inverter open winding motor model control method
CN110971162B (en) Model prediction torque control method of NPC three-level converter-PMSM system
CN107565865A (en) A kind of fault-tolerant double vector prediction control method and device of six-phase permanent-magnet motor
WO2022151609A1 (en) Dual three-phase permanent magnet synchronous motor control method for alternately executing sampling and control program
CN109600085B (en) Permanent magnet synchronous motor direct prediction duty ratio control method based on variable control set
CN113708688B (en) Permanent magnet motor vector-reduction model predictive control method
CN104779830A (en) Variable-dead-time inversion control method
CN106712555A (en) Common-mode voltage satisfactory decision-based FCS-MPC (Finite Control Set Model Predictive Control) method
Liu et al. An optimal model predictive control method for five-level active NPC inverter
CN112217437A (en) Permanent magnet synchronous motor three-vector model prediction current control circuit and method
CN114640293A (en) Control method and system for linear induction motor driven by three-level inverter
CN115833671A (en) Double three-phase motor high-precision model prediction current control system and control method
CN111817627A (en) Discrete modeling and control method of double three-phase induction motor under low switching frequency
CN110620539A (en) Direct torque control optimization method for open-winding motor under variable bus voltage working condition
CN114157171A (en) Improved model prediction current control method based on thermal management
CN109617438B (en) Control method of pure electric vehicle modular multilevel converter
CN117097189A (en) Control method of photovoltaic inverter
CN108400616B (en) MPDPC-based dynamic performance optimization method for photovoltaic grid-connected inverter
CN113676097B (en) Linear motor model prediction control method and system based on optimal reference flux linkage
CN113904578B (en) Weight coefficient-free model predictive control method for single-phase cascade H-bridge converter
González et al. Comparative assessment of model predictive current control strategies applied to six-phase induction machines

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination