Vector control method of synchronous motor, recording medium and system

Abstract

The invention belongs to the technical field of motor control, and particularly relates to a vector control method of a synchronous motor, which comprises the following steps of: obtaining a relationship between virtual current deviation and virtual voltage deviation in a vector control intermediate process; finding a voltage vector deviation closest to the virtual voltage deviation from all probabilities of the voltage vector deviation of the current period relative to the voltage vector deviation of the previous period, performing sum operation on the voltage vector deviation and a reference value of the voltage vector of the previous period to obtain a reference value of the voltage vector of the current period, acting the reference value on a bridge arm of a motor inverter, and changing the on-off state of the inverter. Vector control over the motor is achieved, and the dependence of an algorithm on motor parameters is reduced by circularly using the current of the previous period. The method can greatly reduce the amount of data needing to be calculated, improves the control efficiency and precision, and is suitable for speed regulation of the synchronous motor. The invention also provides a non-transitory readable recording medium storing the program of the method and a system comprising the medium, and the program can be called through a processing circuit to execute the method.

Description

Technical Field

[0001] The invention belongs to the technical field of motor control and discloses a vector control method, recording medium and system for a synchronous motor. Background Art

[0002] Permanent magnet linear synchronous motor (PMLSM) has been widely used in various motion control applications, such as computer numerical control machine tools, electric vehicles and other industrial machines due to its outstanding advantages of high speed, high dynamics and high precision.

[0003] In recent years, due to its good dynamic response and flexible multivariable control, model predictive control is considered to be a promising control strategy for power electronic converters, including finite control set and continuous control set. Finite control set model predictive control generates continuous control signals and obtains the optimal vector by minimizing the cost function. Compared with finite control set model prediction, discrete control set model prediction uses non-fixed switching frequency and does not require a modulator, which has attracted widespread attention from researchers. Discrete control set model prediction can be divided into model predictive current control, model predictive torque control and model predictive speed control. Compared with other methods, model predictive current control (MPCC) uses current as the control variable. On the one hand, the current is easy to measure, and on the other hand, the adjustment of weight factors can be omitted. However, the key problem of applying model predictive current control to motor control systems is the large amount of calculation and high dependence on motor parameters. The high dependence on motor parameters increases the amount of calculation from another perspective, which leads to low control efficiency and accuracy.

[0004] In 1992, Kandel of the University of South Florida proposed combining recurrent neural network (RNN) with robot control. The adaptive method provides a certain degree of robustness by compensating for small changes in neuron characteristics. In 2023, PRBana of the Norwegian University of Science and Technology used artificial neural networks as internal current controllers and PI and MPC schemes as monitoring controllers for voltage source converters. The above studies use artificial neural networks as observers to achieve parameter identification and solve control system problems. However, the model predictive current control algorithm and the recurrent neural network algorithm are not closely combined in essence. How to transplant the adaptive method in the principle of artificial neural network algorithm into the predictive current control model to solve the problem of high dependence on motor parameters and reduce the amount of calculation is a problem that technicians in this field are considering. Summary of the invention

[0005] In view of the above problems, the present invention provides a vector control method for a synchronous motor, comprising the following steps:

[0006] Based on the traditional motor mathematical model, the state equation of the small signal model is established through the difference between the motor voltage and current parameters in the instantaneous and steady states. The relationship between the virtual current deviation and the virtual voltage deviation in the intermediate process of vector control is obtained by Laplace transforming the state equation.

[0007] The reference value of the voltage vector of the previous cycle is used to participate in the motor control of the current cycle. The difference between the instantaneous predicted current generated by the state equation of the small signal model and the reference current output by the PI control of the previous cycle is used as the virtual current deviation. According to the relationship between the virtual current deviation and the virtual voltage deviation, the virtual voltage deviation is obtained. The voltage vector deviation closest to the virtual voltage deviation is found from all possible voltage vector deviations of the current cycle relative to the previous cycle. The voltage vector deviation is vector summed with the reference value of the voltage vector of the previous cycle to obtain the reference value of the voltage vector of the current cycle. The reference value of the voltage vector is applied to the bridge arm of the motor inverter to change the switching state of the inverter. The state quantity determined by the reference value of the voltage vector of the current cycle is substituted into the state equation to calculate the instantaneous predicted current of the next cycle, and the operation of the next cycle is started. The loop is iterated until the virtual current deviation meets the set threshold value to complete the vector control of the motor.

[0008] Preferably, the coordinate system of the vector control is a DQ coordinate system after Park transformation.

[0009] Preferably, obtaining the relationship between the virtual current deviation and the virtual voltage deviation in the intermediate process of vector control comprises the following steps:

[0010] Under steady-state conditions, it is approximately assumed that the current remains constant in each control cycle;

[0011]

[0012] Among them U d , U q , I d ,I q are the steady-state voltage and current components respectively;

[0013] R s is the rotor winding resistance; V is the rotor speed of the motor; ψ d , q is the permanent magnet dq axis flux; τ is the motor pole pitch;

[0014] Subtract it from the traditional motor mathematical model and convert it into the state equation form of a small signal model;

[0015]

[0016] Among them, the state variable matrix A and the input matrix B are:

[0017]

[0018] τ d and τ q is the electrical time constant, L d , L q are the inductance of the direct axis and quadrature axis respectively; the state variable is X=[δi d ,δi q ] Τ , the input variable is U=[δU d ,δU q ],δi d and δi q represents a small deviation between the instantaneous current and the steady-state value; Laplace transform of the state equation yields:

[0019]

[0020] in,

[0021] According to the initial value theorem, the Laplace transform of the state variable X(t) is:

[0022]

[0023] Virtual voltage deviation △U dq The relationship between the virtual current deviation △X is expressed as:

[0024]

[0025] Preferably, the method for finding the voltage vector deviation that is closest to the virtual voltage deviation is: setting all possible vector starting points of the voltage vector deviation at the origin of the DQ coordinate system, the vector vertices constitute the vertices and center of a regular hexagon, and at least one vector distributed on the sides or symmetry axes of the regular hexagon coincides with the horizontal coordinate axis; dividing the regular hexagon into 4 equal parts in the horizontal direction and 2 equal parts in the vertical direction to form 8 areas, each area edge includes 2 vector vertices of the voltage vector deviation; first determine the area where the vector vertex of the virtual voltage deviation is located, and then find a point closest to the vector vertex of the virtual voltage deviation from the 2 vector vertices of the voltage vector deviation included in the edge of the area, and the voltage vector deviation corresponding to the point is the voltage vector deviation closest to the virtual voltage deviation.

[0026] Another embodiment of the present invention is to provide a non-transitory readable recording medium for storing one or more programs including a plurality of instructions. When the instructions are executed, the processing circuit will execute the above-mentioned vector control method for a synchronous motor.

[0027] Another embodiment of the present invention is to provide a vector control system for a synchronous motor, including a processing circuit and a memory electrically coupled thereto, wherein the memory is configured to store at least one program, wherein the program includes a plurality of instructions, and the processing circuit runs the program to execute the above-mentioned vector control method for a synchronous motor.

[0028] Compared with the prior art, the vector control method, recording medium and system of a synchronous motor provided by the present invention have the following beneficial effects:

[0029] By using the idea of ​​cyclic iteration, the sampled current of multiple cycles is predicted to obtain the change of current. By recycling the current at the previous moment, the motor motion state is reflected in real time, reducing the algorithm's dependence on motor parameters.

[0030] By dividing the area to be selected in the stationary reference coordinate system into 8 small areas, comparing the horizontal and vertical coordinates, and finally selecting the optimal virtual voltage vector from only 2 possible virtual voltage vectors, the amount of data processing is effectively reduced. Experimental results show that compared with the traditional MPCC method, this method can achieve smaller current harmonics and has stronger robustness to parameter mismatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the prediction process of the MPCC algorithm of PMLSM proposed in the embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of a virtual voltage vector deviation under a specific voltage vector in an embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of all possible virtual voltage vector deviations in an embodiment of the present invention;

[0034] Figure 4 This is the division and selection of the optimal virtual voltage vector region in the embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making innovative efforts are within the scope of protection of the present invention.

[0036] like Figure 1-4 As shown, a vector control method embodiment of a synchronous motor provided by the present invention includes the following steps:

[0037] Under steady-state conditions, since the mechanical time constant is much larger than the electrical time constant, it can be approximately assumed that the current remains constant in each control cycle, such as Figure 1 As shown. At this time, the steady-state voltage equation is:

[0038]

[0039] Among them U d , U q , I d ,I q are steady-state voltage and current components respectively; R s is the rotor winding resistance; V is the rotor speed of the motor; ψ d , q is the permanent magnet dq-axis magnetic flux; τ is the motor pole pitch.

[0040] Subtracting the traditional motor equation from the steady-state voltage equation gives the state equation form of the PMLSM small signal model. The small signal model of the permanent magnet synchronous motor is established in the form of the state equation:

[0041]

[0042] Among them, the state variable is X = [δi d ,δi q ] Τ , the input variable is U=[δU d ,δU q ], where δi d =i d -I d ,δi q =i q -I q , δU d =u d -U d , δU q =u q -U q , τ d =L d / R,τ q =L q / R,δi d ,δi q Indicates the small deviation between the instantaneous current and the steady-state value, δU d and δU q represents a small deviation of the instantaneous voltage from the steady-state value,

[0043] The state variable matrix A and input matrix B are:

[0044] τ d and τ qis the electrical time constant.

[0045] The Laplace equation of state can be obtained:

[0046]

[0047] in,

[0048] According to the initial value theorem, the Laplace transformation of the state variable X(t) can be:

[0049]

[0050] The virtual current deviation and virtual voltage deviation can be expressed as:

[0051]

[0052] ΔU dq is the virtual voltage deviation, and ΔX is the virtual current deviation.

[0053] Using the mover position, the voltage deviation can be projected from the rotating reference frame to the stationary reference frame:

[0054]

[0055] The idea of ​​loop iteration is applied to MPCC to reduce the dependence on the motor model.

[0056] The discrete state equation of the permanent magnet synchronous linear motor is set as follows. That is, in order to obtain the expression of the predicted state variable for each time period, the previous predicted state variable is used:

[0057]

[0058] Among them, X(k) is the current state vector, X(k-1) is the previous current state vector, U(k) is the input vector, Y(k) is the output voltage vector, and N is the prediction step size.

[0059] Define the following vector:

[0060]

[0061] The voltage vector deviation It consists of real and imaginary parts. The reference voltage vector of the next control cycle is:

[0062]

[0063] if Due to the limitations of the two-level inverter topology, is the effective voltage vector predicted at the next moment, including

[0064]

[0065] Figure 2 The present invention is based on the situation Take the example of all possible virtual voltage vector deviation diagrams. In order to better describe the voltage deviation vector, the coordinates [γ, L] are converted to α and β axes, where γ represents the angle of the vector and L represents the length of the vector. If the voltage vectors of the next cycle are:

[0066] Then the virtual voltage vector deviations are:

[0067]

[0068] Figure 3 is the deviation diagram of all possible virtual voltage vectors analyzed by the present invention according to the above method. L, γ in all processes can be obtained:

[0069]

[0070]

[0071] The variable i represents the serial number of the voltage vector in the previous control cycle, and the variable j represents the serial number of the predicted voltage vector. According to the above formula, all virtual voltage vector spaces are obtained. Different vectors in the previous control cycle correspond to different hexagonal vectors in the next control cycle, thereby constructing a larger vector hexagon. In the case of , the candidate voltage vector deviations of the next control cycle form space 1, space 2, space 3, space 4, space 5, and space 6 respectively.

[0072] Figure 4 The present invention proposes the selection and application of the optimal virtual voltage vector based on Cartesian distance minimization. In order to select the optimal voltage vector and solve the problem of large amount of calculation, the algorithm proposed by the present invention divides the corresponding small hexagon into 1-8 areas. With point O as the origin, In the positive direction, the small hexagon can be divided into 8 areas according to the horizontal and vertical coordinates, as shown in the following formula:

[0073]

[0074] Where m and n represent the horizontal and vertical coordinates of the vector distance zero point, respectively. In this case, point 0 is the zero point and the OC direction is the positive direction. It can be assumed that the positions of the two points M and N are (x1, y1) and (x2, y2) respectively. The Cartesian distance Distance between the two points can be expressed as:

[0075] Distance 2 =(x1-x2) 2 +(y1-y2) 2 (14)

[0076] Assume that point A is the reference virtual voltage vector deviation. By comparing the horizontal and vertical coordinates of point A, it can be found that point A is located in area 3. In area 3, there are two voltage vectors and They are the two voltage vectors closest to point A. According to the Cartesian distance formula, we can calculate |AB| 2 and |AG| 2 , and compare them to obtain the optimal virtual voltage deviation vector; perform vector sum operation on the voltage vector deviation and the reference value of the voltage vector of the previous cycle to obtain the reference value of the voltage vector of the current cycle, and apply the reference value of the voltage vector to the bridge arm of the motor inverter to change the switching state of the inverter; substitute the state quantity determined by the reference value of the voltage vector of the current cycle into the state equation to calculate the instantaneous predicted current of the next cycle, start the operation of the next cycle, and iterate until the virtual current deviation meets the set threshold, thus completing the vector control of the motor.

[0077] Compiling the above method steps into a program and then storing it on a hard disk or other non-transitory storage medium constitutes an embodiment of "a non-transitory readable recording medium" of the present invention; and electrically connecting the storage medium to a computer processor and completing vector control of the synchronous motor through data processing constitutes an embodiment of "a vector control system of a synchronous motor" of the present invention.

[0078] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computers, available storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0079] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0080] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0081] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0082] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A vector control method for a synchronous motor, characterized in that: The following steps are involved: Based on the traditional motor mathematical model, the state equation of the small signal model is established through the difference between the motor voltage and current parameters in the instantaneous and steady states. The relationship between the virtual current deviation and the virtual voltage deviation in the intermediate process of vector control is obtained by Laplace transforming the state equation. The reference value of the voltage vector of the previous cycle is used to participate in the motor control of the current cycle. The difference between the instantaneous predicted current generated by the state equation of the small signal model and the reference current output by the PI control of the previous cycle is used as the virtual current deviation. According to the relationship between the virtual current deviation and the virtual voltage deviation, the virtual voltage deviation is obtained. The voltage vector deviation closest to the virtual voltage deviation is found from all possible voltage vector deviations of the current cycle relative to the previous cycle. The voltage vector deviation is vector summed with the reference value of the voltage vector of the previous cycle to obtain the reference value of the voltage vector of the current cycle. The reference value of the voltage vector is applied to the bridge arm of the motor inverter to change the switching state of the inverter. The state quantity determined by the reference value of the voltage vector of the current cycle is substituted into the state equation to calculate the instantaneous predicted current of the next cycle, and the operation of the next cycle is started. The loop is iterated until the virtual current deviation meets the set threshold value to complete the vector control of the motor.

2. A vector control method for a synchronous motor according to claim 1, characterized in that: The coordinate system of the vector control is the DQ coordinate system after Park transformation.

3. A vector control method for a synchronous motor according to claim 2, characterized in that: Obtaining the relationship between the virtual current deviation and the virtual voltage deviation in the intermediate process of vector control includes the following steps: Under steady-state conditions, it is approximately assumed that the current remains constant in each control cycle; Among them U d , U q , I d ,I q are the steady-state voltage and current components respectively; R s is the rotor winding resistance; V is the rotor speed of the motor; ψ d , q is the permanent magnet dq axis flux; τ is the motor pole pitch; Subtract it from the traditional motor mathematical model and convert it into the state equation form of a small signal model; Among them, the state variable matrix A and the input matrix B are: τ d and τ q is the electrical time constant, L d , L q are the inductance of the direct axis and quadrature axis respectively; the state variable is X=[δi d ,δi q ] Τ , the input variable is U=[δU d ,δU q ],δi d and δi q represents a small deviation between the instantaneous current and the steady-state value; Laplace transform of the state equation yields: in, According to the initial value theorem, the Laplace transform of the state variable X(t) is: Virtual voltage deviation △U dq The relationship between the virtual current deviation △X is expressed as:

4. A vector control method for a synchronous motor according to claim 3, characterized in that: The method for finding the voltage vector deviation closest to the virtual voltage deviation is as follows: all possible vector starting points of the voltage vector deviation are set at the origin of the DQ coordinate system, the vector vertices constitute the vertices and center of a regular hexagon, and at least one vector distributed on the sides or symmetry axes of the regular hexagon coincides with the horizontal coordinate axis; the regular hexagon is equally divided into 4 parts in the horizontal direction and 2 parts in the vertical direction to form 8 areas, and the edge of each area includes 2 vector vertices of the voltage vector deviation; first determine the area where the vector vertex of the virtual voltage deviation is located, and then find a point closest to the vector vertex of the virtual voltage deviation from the two vector vertices of the voltage vector deviation included in the edge of the area, and the voltage vector deviation corresponding to the point is the voltage vector deviation closest to the virtual voltage deviation.

5. A non-transitory readable recording medium for storing one or more programs including a plurality of instructions, characterized in that: When the instruction is executed, the processing circuit will be caused to execute the vector control method for a synchronous motor according to any one of claims 1 to 4.

6. A vector control system for a synchronous motor, comprising a processing circuit and a memory electrically coupled thereto, characterized in that: The memory configuration stores at least one program, wherein the program includes a plurality of instructions, and the processing circuit runs the program to execute a vector control method for a synchronous motor as described in any one of claims 1-4.

Images