A direct torque control system and method for a switched reluctance motor

Abstract

The present invention discloses a direct torque control system and method for a switched reluctance motor, and relates to the field of direct torque control of motors. The present invention aims to solve the problem of low control accuracy in the direct torque control of a switched reluctance motor in the prior art; the present invention establishes 12 voltage sectors consisting of 12 voltage vectors, determines the sector where the flux is located according to the flux and flux angle, and determines the voltage vector at the current moment through the sector; predicts the flux prediction value and torque prediction value corresponding to the voltage vector at the next moment according to the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment; determines the optimal voltage vector according to the flux given value, torque given value, flux prediction value and torque prediction value. The present invention can effectively suppress the torque pulsation of the switched reluctance motor and achieve a higher-precision torque output of the switched reluctance motor.

Description

Technical Field

[0001] The present invention relates to the field of direct torque control of motors, and in particular to a direct torque control system and method for a switched reluctance motor. Background Art

[0002] With the rapid development of motor theory, power electronics technology and microcomputer technology, the development of the switched reluctance motor speed control system has become increasingly mature. The switched reluctance motor rotor is made of laminated silicon steel sheets. This special structure determines that the switched reluctance motor can work reliably in some harsh environments. It has a simple structure, a wide speed regulation range, and a large starting torque. It has been widely used in aerospace, automobile, textile industry, household appliances and other fields. Due to the double salient pole structure and special operation mode of the switched reluctance motor, it has a high degree of nonlinearity, which is reflected in the fact that the torque is a nonlinear function of the current and the rotor position. Therefore, the torque pulsation problem is more serious during operation, which also limits the application and promotion of the switched reluctance motor. Applying direct torque control to the switched reluctance motor does not rely on the accurate switched reluctance motor model. It only needs the parameters on the stator side of the motor. Under the static stator coordinates, by changing the flux and torque, it can be controlled within the hysteresis loop width, thereby reducing the torque pulsation of the switched reluctance motor.

[0003] Although the direct torque control of the switched reluctance motor in the prior art has improved the problem of torque pulsation to a certain extent, the operation of the switched reluctance motor is maintained by phase switching. The sum of the superposition of the torques of each phase is the total electromagnetic torque output by the switched reluctance motor. In the process of phase switching, since the current in the winding cannot change suddenly, there is a certain phase switching time, and it cannot be completed instantaneously. The current of the off-phase gradually decreases, and the current of the on-phase gradually increases, that is, there is a phase switching delay. In the process of phase switching, the electromagnetic torque of the off-phase is reduced, which is greater than the electromagnetic torque of the on-phase. Therefore, after superposition, the total electromagnetic torque shows a downward trend, making the torque pulsation problem still very prominent. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a direct torque control system and method for a switched reluctance motor, which can effectively suppress the torque pulsation of the switched reluctance motor and achieve higher-precision torque output of the switched reluctance motor.

[0005] A first aspect of the present invention provides a direct torque control system of a switched reluctance motor, comprising:

[0006] The sampling module is used to sample the current, voltage and rotor position angle at the current moment, and then obtain the flux and flux angle;

[0007] A sector determination module is used to establish 12 voltage sectors consisting of 12 voltage vectors, determine the sector where the flux is located according to the flux and the flux angle, and determine the voltage vector at the current moment through the sector;

[0008] The prediction module is used to predict the flux prediction value ψ(k+1) and torque prediction value T corresponding to the voltage vector at the next moment according to the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment. e (k+1);

[0009] Evaluation module, used to determine the given value ψ according to the flux linkage * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e (k+1) Determine the optimal voltage vector.

[0010] A second aspect of the present invention provides a direct torque control method for a switched reluctance motor, comprising:

[0011] S1, sampling the current, voltage and rotor position angle at the current moment, and then obtaining the flux and flux angle;

[0012] S2, establishing 12 voltage sectors consisting of 12 voltage vectors, determining the sectors where the flux is located according to the flux and the flux angle, and determining the voltage vector through the sectors;

[0013] S3, predict the flux prediction value ψ(k+1) and torque prediction value T corresponding to the voltage vector at the next moment according to the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment e (k+1);

[0014] S4, used to set the value ψ according to the flux linkage * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e (k+1) Determine the optimal voltage vector.

[0015] Furthermore, the corresponding relationship between the sector angle δ and the sector number N in the 12 voltage sectors is:

[0016] When sector N=1, the sector angle δ is [0, π / 6); when sector N=2, the sector angle δ is [π / 6, π / 3); when sector N=3, the sector angle δ is [π / 3, π / 2); when sector N=4, the sector angle δ is [π2, 2π3); when sector N=5, the sector angle δ is [2π / 3, 5π / 6); when sector N=6, the sector angle δ is [5π / 6, π); when sector N=7, the sector angle δ is [π / 3, π / 2]; when sector N=4, the sector angle δ is [π2, 2π3]; when sector N=5, the sector angle δ is [2π / 3, 5π / 6]; when sector N=6, the sector angle δ is [5π / 6, π]; when sector N=7, the sector angle δ is [π / 3, π / 2]; when sector N=8, the sector angle δ is [π / 3, π / 2]; when sector N=9, the sector angle δ is [π / 3, π / 2]; when sector N=10, the sector angle δ is [π / 3, π / 2]; when sector N=11, the sector angle δ is [π / 3, π / 2]; when sector N=12, the sector angle δ is [π / 3, 2π3]; when sector N=13, the sector angle δ is [π / 3, 2π3]; when sector N=14, the sector angle δ is [π / 3, 2π3] When sector N=8, the sector angle δ is [-5π / 6, -2π / 3); when sector N=9, the sector angle δ is [-2π / 3, -π / 2); when sector N=10, the sector angle δ is [-π / 2, -π / 3); when sector N=11, the sector angle δ is [-π / 3, -π / 6); when sector N=12, the sector angle δ is [-π / 6, 0).

[0017] Furthermore, the flux prediction value ψ(k+1) and the torque prediction value T e (k+1) are:

[0018]

[0019]

[0020] in, θ k+1 =θ k +ωΔT.

[0021] Further, step S4 includes:

[0022] S41. Establish evaluation function:

[0023]

[0024] S42, set the magnetic flux to a given value ψ * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e Among the (k+1) input evaluation functions, the set of voltage vectors with the smallest error is the optimal voltage vector.

[0025] Furthermore, the torque setting The method to obtain is:

[0026] The torque setting value is obtained by subtracting the rotor speed from the rotor speed setting value and adjusting it through PI.

[0027] As described above, the present invention has the following effects:

[0028] 1. The present invention re-divides the sectors, and re-divides the 6 sectors in the prior art into 12 sectors, so as to avoid the problem of reducing the control accuracy due to the early error of selecting the optimal vector due to too few voltage vectors in the 6 sectors;

[0029] 2. The present invention combines improved direct torque control with a model prediction method, and uses the model to predict the corresponding flux prediction value and torque prediction value under a preselected voltage vector. The flux prediction value and the torque prediction value are combined with the flux given value and the torque given value to screen out the optimal voltage vector as the output through a prediction function, thereby reducing and suppressing the torque pulsation of the switched reluctance motor and achieving higher-precision torque output of the switched reluctance motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a direct torque control system of a switched reluctance motor according to a specific embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the expansion of voltage vectors and sectors according to a specific embodiment of the present invention;

[0032] Figure 3 This is a main program flow chart of a specific embodiment of the present invention. Figure 3 a is the main program flow chart, Figure 3 b is the initialization subroutine flow chart.

[0033] Figure 4 A terminal subroutine flow chart of a specific embodiment of the present invention;

[0034] Figure 5 A torque waveform diagram of a switched reluctance motor according to a specific embodiment of the present invention using the direct torque control of the present application;

[0035] Figure 6 The waveform diagram of torque ripple coefficient at different speeds when the switched reluctance motor of a specific embodiment of the present invention adopts the direct torque control of the present application and the traditional direct torque control. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0037] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0038] like Figure 1 As shown, a direct torque control system of a switched reluctance motor in this embodiment includes:

[0039] The sampling module is used to sample the current, voltage and rotor position angle at the current moment, and then obtain the flux and flux angle;

[0040] A sector determination module is used to establish 12 voltage sectors consisting of 12 voltage vectors, determine the sector where the flux is located according to the flux and the flux angle, and determine the voltage vector at the current moment through the sector;

[0041] The prediction module is used to predict the flux prediction value ψ(k+1) and torque prediction value T corresponding to the voltage vector at the next moment according to the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment. e (k+1);

[0042] Evaluation module, used to determine the given value ψ according to the flux linkage * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e (k+1) Determine the optimal voltage vector.

[0043] The outer loop of the direct torque control system of the switched reluctance motor of this embodiment is speed and PI control, and the inner loop adopts a control strategy of model prediction direct torque.

[0044] In a specific embodiment, a control method based on the direct torque control of the switched reluctance motor includes the following steps:

[0045] S1, sampling the current i, voltage V and rotor position angle θ at the current moment, and then obtaining the flux and flux angle;

[0046] S2, establishing 12 voltage sectors consisting of 12 voltage vectors, determining the sectors where the flux is located according to the flux and the flux angle, and determining the voltage vector through the sectors;

[0047] During the operation of the switched reluctance motor, due to the double salient pole structure of the motor body and the nonlinear saturation of the magnetic circuit, the torque pulsation phenomenon is more significant than that of other motors. Although the direct torque control of the switched reluctance motor has improved the torque pulsation problem to a certain extent, the torque pulsation problem is still very prominent, mainly because the negative torque is introduced in the switching area of ​​the switched reluctance motor, which reduces the total torque of the three-phase superposition. In traditional direct torque control, due to the small number of selectable voltage vectors, the selected voltage vector may not be the optimal vector, but only the voltage vector closest to the optimal solution among the six voltage vectors, resulting in too low control accuracy. Therefore, this embodiment improves the traditional direct torque control by redividing the sectors and adding voltage vectors. By determining the sector where the magnetic flux is located, the corresponding voltage vector is pre-selected to avoid the introduction of negative torque in the switching area. The optimal vector is selected from the pre-selected voltage vectors as the output through model prediction, thereby suppressing the SRM torque pulsation and achieving a higher precision torque output of the SRM. The corresponding relationship between the angle δ of each sector in the 12 voltage sectors described in this embodiment and the sector number N is:

[0048] When sector N=1, the sector angle δ is [0, π / 6); when sector N=2, the sector angle δ is [π / 6, π / 3); when sector N=3, the sector angle δ is [π / 3, π / 2); when sector N=4, the sector angle δ is [π2, 2π3); when sector N=5, the sector angle δ is [2π / 3, 5π / 6); when sector N=6, the sector angle δ is [5π / 6, π); when sector N=7, the sector angle δ is [π / 3, π / 2]; when sector N=4, the sector angle δ is [π2, 2π3]; when sector N=5, the sector angle δ is [2π / 3, 5π / 6]; when sector N=6, the sector angle δ is [5π / 6, π]; when sector N=7, the sector angle δ is [π / 3, π / 2]; when sector N=8, the sector angle δ is [π / 3, π / 2]; when sector N=9, the sector angle δ is [π / 3, π / 2]; when sector N=10, the sector angle δ is [π / 3, π / 2]; when sector N=11, the sector angle δ is [π / 3, π / 2]; when sector N=12, the sector angle δ is [π / 3, 2π3]; when sector N=13, the sector angle δ is [π / 3, 2π3]; when sector N=14, the sector angle δ is [π / 3, 2π3] When sector N=8, the sector angle δ is [-5π / 6, -2π / 3); when sector N=9, the sector angle δ is [-2π / 3, -π / 2); when sector N=10, the sector angle δ is [-π / 2, -π / 3); when sector N=11, the sector angle δ is [-π / 3, -π / 6); when sector N=12, the sector angle δ is [-π / 6, 0).

[0049] S3, predict the flux prediction value ψ(k+1) and torque prediction value T corresponding to the voltage vector at the next moment according to the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment e (k+1); specifically includes the following steps:

[0050] When the flux is in the non-commutation sector, according to the traditional direct torque control principle, the optimal solution can be selected from the corresponding eight voltage vectors. When the flux is in the commutation sector, if the torque needs to be increased, the relevant inductance in the decreasing state needs to be closed to avoid the introduction of negative torque; when the torque needs to be reduced, the relevant inductance in the increasing state needs to be closed so that the total torque meets the torque reduction requirement. Based on the above analysis, when the flux is in the commutation sector, the optimal vector will be selected from the corresponding four voltage vectors.

[0051] S31. According to the SRM flux and current curves, the P-phase flux expression of the stator and rotor non-aligned position is:

[0052] ψ p =L q i p ;

[0053] Where: L q is the unsaturated inductance of the magnetic circuit, i p is the current of phase P.

[0054] When the stator and rotor are aligned, considering the flux saturation characteristics, the flux expression is:

[0055]

[0056] Where: L d is the inductance before the magnetic circuit is saturated, L dsat is the saturation inductance coefficient; I m is the same as ψ m The maximum rated current that matches the current; A and B are the calculated flux linkage ψ p The reference coefficient of .

[0057] S32, selecting an interpolation function to perform interpolation calculation between its position and the extreme position between the non-aligned position, and then the angle correction expression is:

[0058]

[0059] Therefore, the flux characteristics of the switched reluctance motor can be obtained as:

[0060]

[0061] Where: θ p is the rotor position angle of phase P, L q is the unsaturated inductance of the magnetic circuit, f(θ p ) is the modified angle expression.

[0062] Combining the electromechanical connection equation of the switched reluctance motor, the electromagnetic torque is obtained as follows:

[0063]

[0064] Combining the electromagnetic torque equation of the switched reluctance motor, the torque expression can be obtained:

[0065]

[0066] S33. According to the differential equation of switched reluctance motor, the Cody current expression is:

[0067]

[0068] Where: ω is the rotor angular velocity, R is the P-phase winding resistance.

[0069] S34. Within one sampling time, the torque, flux and current expressions are discretized by Euler equations to obtain the flux prediction value ψ(k+1) and the torque prediction value T e (k+1) are:

[0070]

[0071]

[0072] in, θ k+1 =θ k +ωΔT.

[0073] S4, used to set the value ψ according to the flux linkage * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e (k+1) Determine the optimal voltage vector, specifically including:

[0074] S41, establishing an evaluation function;

[0075] The evaluation function reflects the difference between the flux, torque and the set value. MPC selects the optimal voltage vector based on the evaluation function, so the selection of the evaluation function determines the control performance of the entire system. Since torque and flux are of different dimensions, a weight coefficient needs to be introduced. The evaluation function is defined as:

[0076]

[0077] In order to eliminate the weight coefficient, the present invention converts the torque and flux linkage errors into torque and flux linkage error rates, making them physical quantities in the same dimension, and the evaluation function can be obtained as follows:

[0078]

[0079] S42, set the magnetic flux to a given value ψ * , torque given value Flux prediction value ψ(k+1) and torque prediction value T e Among the (k+1) input evaluation functions, the set of voltage vectors with the smallest error is the optimal voltage vector.

[0080] The torque given value is The method to obtain is:

[0081] The torque setting value is obtained by subtracting the rotor speed from the rotor speed setting value and adjusting it through PI.

[0082] In a specific embodiment, the switched reluctance motor is a three-phase 12 / 8 switched reluctance motor; Figure 2 As can be seen from the voltage vector and sector expansion diagram, after the expansion of 12 sectors, the corresponding voltage vectors also increase from 6 to 12, which can achieve more precise control.

[0083] By determining the sector where the flux is located, the corresponding voltage vector direct torque control is selected. As shown in Table 1, the corresponding table of sector numbers and voltage vectors, when the flux is located in sector N = 1, the voltage vectors V1, V2, V3, and V4 can all increase the torque, and the voltage vectors V9, V 10 、V 11 、V 12 The torque can be reduced, so the optimal vector is selected from these eight voltage vectors. When the stator flux is in the N = 2 sector, theoretically, the voltage vectors V2, V3, V4, and V5 can all increase the torque. 12 、V 11 、V 10 The torque can be reduced. However, when the phase change area is entered and the torque needs to be increased, the voltage vectors V2 and V3 will turn on phase A or continue to flow, thereby introducing negative torque. Therefore, you can choose from the voltage vectors V4 and V5. When the torque needs to be reduced, phase B should be turned off, and phases A and C can generate negative torque to meet the torque reduction requirement. At this time, you can choose from the voltage vectors V 11 、V 10 The pre-selected voltage vector is selected by the evaluation function, and the increase or decrease of the torque does not need to be considered. It is just to select the voltage vector corresponding to the torque closest to the set torque value. This will be explained in detail below. Therefore, when the flux linkage is in sector 2, it can be selected from V4, V5, V 11 、V 10 The preferred voltage vector is selected among these four sectors. Similarly, the voltage vector selected when the flux linkage is in other sectors can be obtained.

[0084] Table 1

[0085]

[0086] Figure 3 a is the main program flow chart of the present invention. The main program is the main body of a program. The task allocation and management are performed through the task scheduler, covering all functions of the control system, including system initialization, motor start and stop, interrupt service, rotor position judgment and speed calculation, etc. Figure 3 b is the initialization subroutine flow chart. When the DSP is powered on, each module must be initialized to enable the system to run. Initialization mainly includes assigning values ​​to defined variables, configuring I / O, configuring digital / analog conversion registers, configuring PWM registers, and establishing an interrupt vector table.

[0087] Figure 4 It is the interrupt subroutine flow chart of the present invention, which consists of current, voltage sampling, PI, MPC and other links. By sampling the current voltage, current value and rotor position information of the system, the flux value at the current moment is estimated, and the sector position of the flux at this time is judged by synthesizing the amplitude and angle of the flux to select the corresponding voltage vector, and then the flux, sector position and other information are used to predict the flux and torque values ​​corresponding to the pre-selected voltage vector through the model prediction module, and the optimal voltage vector is selected through the evaluation function, and finally the interrupt flag is cleared, and the main program is returned to wait for the next interrupt instruction.

[0088] The switched reluctance motor adopts the improved direct torque control described in this embodiment, and its torque waveform is as follows: Figure 5 As shown, the torque ripple coefficient waveforms at different speeds obtained by using the traditional torque control method of the switched reluctance motor and the improved direct torque control method of this embodiment are shown in FIG. Figure 6 As shown, through the comparison of the torque pulsation coefficient waveforms, it can be seen that due to the large pulsation of the torque in the commutation zone of the traditional DTC, the overall torque pulsation coefficient is large, and the improved torque pulsation control method of the present embodiment shuts off the inductance reduction phase in the commutation zone in advance, thereby increasing the torque value in the commutation zone, so the overall torque pulsation coefficient is significantly reduced compared with the traditional DTC.

[0089] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A direct torque control method for a switched reluctance motor, characterized in that: include: S1, sampling the current, voltage and rotor position angle at the current moment, and then obtaining the flux and flux angle; S2. 12 voltage sectors consisting of 12 voltage vectors are established. The sectors where the flux is located are determined according to the flux and the flux angle, and the voltage vector is determined by the sectors. The corresponding relationship between the angle δ of each sector in the 12 voltage sectors and the sector number N is: When sector N=1, the sector angle δ is [0, π / 6); when sector N=2, the sector angle δ is [π / 6, π / 3); when sector N=3, the sector angle δ is [π / 3, π / 2); when sector N=4, the sector angle δ is [π / 2, 2π / 3); when sector N=5, the sector angle δ is [2π / 3, 5π / 6); when sector N=6, the sector angle δ is [5π / 6, π); when sector N=7, The sector angle δ is [-π, -5π / 6); when sector N=8, the sector angle δ is [-5π / 6, -2π / 3); when sector N=9, the sector angle δ is [-2π / 3, -π / 2); when sector N=10, the sector angle δ is [-π / 2, -π / 3); when sector N=11, the sector angle δ is [-π / 3, -π / 6); when sector N=12, the sector angle δ is [-π / 6, 0); S3: predict the flux value corresponding to the voltage vector at the next moment based on the flux, rotor position angle, current and sector information corresponding to the voltage vector at the current moment ψ (k+1) and torque prediction value T e (k+1); the magnetic flux prediction value ψ (k+1) and torque prediction value T e (k+1) are: ； ； in, ,θ k+1 =θ k +ωΔT;L q is the unsaturated inductance of the magnetic circuit; i p is the current of phase P; L dsat is the saturation inductance; A and B are the calculated flux linkage ψ p Reference coefficient; f(θ k+1 ) is the correction angle; ω is the rotor angular velocity; R is the P-phase winding resistance; S4, used to set the value ψ according to the flux linkage * , torque given value T e * , magnetic flux prediction value ψ (k+1) and torque prediction value T e (k+1) Determine the optimal voltage vector, including: S41. Establish evaluation function: ； S42, set the magnetic flux to a given value ψ * , torque given value T e * , magnetic flux prediction value ψ (k+1) and torque prediction value T e Among the (k+1) input evaluation functions, the set of voltage vectors with the smallest error is the optimal voltage vector.

2. The direct torque control method of a switched reluctance motor according to claim 1, characterized in that: Torque setting value T e * The method to obtain is: The rotor speed is subtracted from the rotor speed given value and then adjusted by PI to obtain the torque given value T e * .

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