A SRM direct torque control method and system based on minimum voltage vector deviation

Abstract

The invention discloses a direct torque control method and system based on minimum voltage vector deviation SRM, which relates to the field of motor direct torque control. The invention calculates the stator flux phase angle ∠ψ according to the torque reference value #imgabs0# s Get the stator flux reference value phase angle #imgabs1# and then determine the voltage vector reference value u ref ; According to the phase angle δ ref , the sector where the voltage vector reference value is located and the relationship between the non-zero voltage vector determine the non-zero voltage vector u that needs to be acted on n ; By calculating the voltage vector reference value u ref and non-zero voltage vector Du n The minimum deviation between them determines the duty cycle D. The present invention solves the problem of large torque pulsation caused by single voltage vector operation and realizes high-precision output of torque.

Description

Technical Field

[0001] The present invention relates to the field of direct torque control of electric motors, and more specifically, discloses a method and system for direct torque control of a switched reluctance motor (SRM) based on minimum voltage vector deviation. Background Art

[0002] Switched reluctance motor (SRM) has many competitive advantages. It has a simple mechanical structure, low price, strong reliability and high fault tolerance. In addition, it has many control parameters, flexible control methods, and fast speed adjustment. The products are involved in aviation power manufacturing, distributed energy storage and power generation, automobile drive, daily household appliances and other fields. SRM is a speed regulating motor with great application value developed after permanent magnet synchronous motor and AC induction motor, and has become one of the hot research objects of many scholars.

[0003] The noise and torque pulsation problems of SRM itself are the main reasons why it cannot be used in large quantities. Therefore, current research mainly focuses on reducing torque pulsation. This problem is studied from two aspects: improvement of motor structure and improvement of control strategy. As for the improvement of motor structure, it is mainly from the perspective of adjusting the shape, outer diameter and number of turns of the stator and rotor; in terms of control strategy, not only the traditional theoretical methods are being optimized and improved, but new theoretical methods are also constantly emerging, such as vector control, torque distribution control, predictive control and fault-tolerant control, which all reduce torque pulsation.

[0004] DTC control strategy is widely used in AC speed regulation system. It uses feedback from torque loop and flux loop to control the on and off of switch tube. There is no complex mathematical model in the system structure, and the control performance is excellent, which can be completed by digitalization. For SRM motor, by analyzing the source of its torque pulsation, it can be known that it uses pulsed power supply during operation, and there is a phase change process between each phase. During the phase change process, the increase and decrease of torque are inconsistent, which will produce torque pulsation: Traditional direct torque control uses basic voltage vector in the fixed working cycle of the switch tube, and the action time of the vector is certain, which will cause excessive increase or decrease of torque in the control process, so it will cause large torque and flux fluctuations, which is difficult to meet the phase change requirements of SRM.

[0005] Therefore, those skilled in the art are committed to developing a switched reluctance motor (SRM) direct torque control method based on minimum voltage vector deviation. Summary of the invention

[0006] To achieve the above objectives, the present invention provides an SRM direct torque control method and system based on minimum voltage vector deviation, which solves the problem of large torque pulsation caused by single voltage vector operation, thereby achieving high-precision torque output.

[0007] A first aspect of the present invention provides a SRM direct torque control method based on minimum voltage vector deviation, comprising the following steps:

[0008] S1, according to the torque reference value Stator flux phase angle ∠ψ s Get the stator flux reference value phase angle Then determine the voltage vector reference value u ref ;

[0009] S2, according to the phase angle δ ref , the sector where the voltage vector reference value is located and the relationship between the non-zero voltage vector determine the non-zero voltage vector u that needs to be acted on n ;

[0010] S3, by calculating the voltage vector reference value u ref and non-zero voltage vector Du n The minimum deviation between them determines the duty cycle D.

[0011] Furthermore, the voltage vector reference value u ref Methods for determination include:

[0012] S11, speed reference value n ref The torque reference value is generated by PI regulation with the actual speed n

[0013] S12, the torque reference value and the actual torque T e After PI adjustment, the phase angle ∠ψ with the stator flux s Add together to get the stator flux reference value phase angle for:

[0014]

[0015] Among them, k p and k i are proportional coefficient and integral coefficient respectively, S represents the integral operator, is the torque reference value, ∠ψ s is the stator flux phase angle;

[0016] S13. Obtain the stator flux vector reference value by the following formula:

[0017]

[0018] Among them, |ψ s | ref is the reference value of the stator flux amplitude, |ψ s | is the stator flux amplitude;

[0019] S14, according to the stator flux ψ s and the stator flux reference value phase angle Get the voltage vector reference value u ref ,for:

[0020]

[0021] Furthermore, the stator flux phase angle ∠ψ s for:

[0022]

[0023] Among them, ψ α , β To obtain the α and β components of the stator flux vector in real time, coordinate transformation is performed.

[0024] Furthermore, the phase angle δ ref , the relationship between the sector where the voltage vector reference value is located and the non-zero voltage vector is:

[0025] When δ=[0,5π / 18), the corresponding sector number N=1;

[0026] When δ=[13π / 45,2π / 3), the corresponding sector number N=2;

[0027] When δ=[2π / 3,17π / 18), the corresponding sector number N=3;

[0028] When δ=[43π / 45,-2π / 3), the corresponding sector number N=4;

[0029] When δ=[-2π / 3,-7π / 18), the corresponding sector number N=5;

[0030] When δ=[-17π / 45,0), the corresponding sector number N=6;

[0031] When δ=[5π / 18,13π / 45), the corresponding sector number N=7;

[0032] When δ=[17π / 18,43π / 45), the corresponding sector number N=8;

[0033] When δ=[-7π / 18,-17π / 45), the corresponding sector number N=9.

[0034] Furthermore, the non-zero voltage vector includes:

[0035] u1(1,0,-1), u2(0,1,-1), u3(-1,1,0), u4(-1,0,1), u5(0,-1,1), u6(1,-1,0), u7(1,1,-1), u8(-1,1,1), u9(1,-1,1).

[0036] Furthermore, the phase angle δ ref The calculation method is:

[0037]

[0038] Further, the voltage vector reference value u is calculated ref and non-zero voltage vector Du n Deviation between ε Methods for finding the minimum value include:

[0039] S31, establish deviation |u ε The square equation of | is:

[0040]

[0041] in, and Respectively represent u ref Components on the α and β axes; u nα and u nβ Respectively represent u n Components on the α-axis and the β-axis;

[0042] S32. Solve the duty cycle D according to the following formula to obtain the duty cycle of the non-zero voltage vector in the non-commutation region as D1 and the duty cycle of the non-zero voltage vector in the non-commutation region as D2:

[0043]

[0044] The duty cycle of the non-zero voltage vector in the non-commutation region is D:

[0045]

[0046] The duty cycle of the non-zero voltage vector in the commutation region is D:

[0047]

[0048] A second aspect of the present invention provides an SRM direct torque control system based on minimum voltage vector deviation, comprising:

[0049] The first PI controller is used to adjust the speed reference value n ref And the actual speed n get the torque reference value

[0050] Voltage vector reference value acquisition module, according to the torque reference value and the actual torque T e The phase angle ∠ψ of the stator flux is adjusted by PI s Add together to get the stator flux reference value phase angle According to the stator flux ψ s and the stator flux reference value phase angle Get the voltage vector reference value u ref ;

[0051] Vector selection module, used to select the phase angle δ ref , the sector where the voltage vector reference value is located and the non-zero voltage vector relationship determine the sector, and then determine the non-zero voltage vector u that needs to be applied n ;

[0052] A duty cycle optimization module is used to calculate the voltage vector reference value u ref and non-zero voltage vector Du n The minimum deviation between them determines the duty cycle D.

[0053] Compared with the prior art, the present invention has the following technical effects:

[0054] 1. The DTC control method based on the minimum voltage vector deviation is adopted to optimize the duty cycle of all voltage vectors acting on the SRM motor, so that the torque and flux of the motor are adjusted through the interaction of a non-zero vector and a zero vector for maintaining torque. The problem of large torque pulsation caused by single voltage vector operation is solved, which can not only reduce the torque pulsation in the non-commutation area, but also suppress the change of the torque of the two conducting phases in the commutation area to meet the system requirements of increasing the torque in the commutation area.

[0055] 2. In the present invention, a voltage vector is added to each commutation zone position, that is, voltage vectors u7 (1, 1, -1), u8 (-1, 1, 1), and u9 (1, -1, 1) are added in the commutation zones between AB, BC, and CA, respectively. The added voltage vectors make the commutation zone not a single phase turned on but two phases turned on simultaneously, so as to increase the output torque of the commutation zone and reduce the torque pulsation amplitude of the commutation zone.

[0056] 3. At the beginning of commutation, the conduction phase current is in the initial establishment stage, the inductance slope is small at this time, and the generated torque is also low. The previous phase has a stronger ability to provide torque at this time, so the total torque is mainly provided by the previous phase. In order to solve the problem that the previous phase torque decreases too quickly and the next conduction phase torque increases too slowly, resulting in a reduction in total output torque, the present invention allows the adjacent phase to be turned on at this moment before the off-phase current disappears, and the next phase torque rises in advance to increase the system torque. This can increase the torque in the commutation zone, reduce the torque fluctuation of the system, and make the motor run more stably.

[0057] 4. The present invention optimizes the duty cycle of all voltage vectors of the SRM motor so that the motor interacts with a non-zero vector and a zero vector for maintaining torque, so that the deviation between the actual action vector of the torque and the reference value of the voltage vector is minimized, and the torque and flux of the motor are adjusted.

[0058] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A system structure diagram of a switched reluctance motor direct torque control based on minimum voltage vector deviation according to an embodiment of the present invention;

[0060] Figure 2 A program flow chart of a switched reluctance motor direct torque control method based on minimum voltage vector deviation according to an embodiment of the present invention;

[0061] Figure 3 It is the basic spatial voltage vector diagram of the traditional three-phase SRM;

[0062] Figure 4 A schematic diagram of a commutation region according to an embodiment of the present invention;

[0063] Figure 5 A coordinate transformation diagram of a reference voltage vector according to an embodiment of the present invention;

[0064] Figure 6 A distribution diagram of sectors and non-zero voltage vectors according to an embodiment of the present invention;

[0065] Figure 7 A vector action time calculation diagram according to an embodiment of the present invention;

[0066] Figure 8 It is a speed waveform diagram when a conventional DTC control method and a voltage vector improved DTC control method are used under no-load starting of an embodiment of the present invention;

[0067] Fig. 9The current and torque waveforms of the conventional DTC control method and the voltage vector improved DTC control method during low speed operation in one embodiment of the present invention are shown as follows: Fig. 9 a is the current waveform when the traditional DTC control method is used. Fig. 9 b is the torque waveform when the traditional DTC control method is used. Fig. 9 c is the current waveform when the voltage vector improved DTC control method is adopted. Fig. 9 d is the torque waveform of the improved DTC control method using voltage vector;

[0068] Fig.10 The current and torque waveforms of the conventional DTC control method and the voltage vector improved DTC control method during high-speed operation in one embodiment of the present invention are shown as follows: Fig.10 a is the current waveform when the traditional DTC control method is used. Fig.10 b is the torque waveform when the traditional DTC control method is used. Fig.10 c is the current waveform when the voltage vector improved DTC control method is adopted. Fig.10 d is the torque waveform of the improved DTC control method using voltage vector;

[0069] Fig.11 for Fig.10 The enlarged waveform of the middle Fig.11 a is Fig.10 A magnified waveform of a. Fig.11 b is Fig.10 b is the enlarged waveform. Fig.11 c is Fig.10 c is the enlarged waveform of Fig.11 d is Fig.10 d is the enlarged waveform;

[0070] Fig.12 The speed and torque waveforms of the voltage vector improved DTC control method under the condition of a sudden speed change in one embodiment of the present invention are as follows: Fig.12 a is the speed waveform when the speed suddenly changes. Fig.12 b is the torque waveform under the condition of sudden speed change;

[0071] Fig.13 In one embodiment of the present invention, the speed and torque waveforms of the conventional DTC control method are shown in the case of a sudden speed change. Fig.13 a is the speed waveform when the speed suddenly changes. Fig.13 b is the torque waveform under the condition of sudden speed change;

[0072] Fig.14 The speed and torque waveforms of the voltage vector improved DTC control method under the condition of torque mutation in one embodiment of the present invention are as follows: Fig.14 a is the speed waveform when the speed suddenly changes. Fig.14 b is the torque waveform under the condition of sudden speed change;

[0073] Fig.15 In one embodiment of the present invention, the speed and torque waveforms of the conventional DTC control method are shown in the case of a torque mutation. Fig.15 a is the speed waveform when the speed suddenly changes. Fig.15 b is the torque waveform under the condition of sudden speed change;

[0074] Fig.16 It is a speed waveform diagram when a conventional DTC control method with a minimum voltage vector deviation and an improved DTC control method with a minimum voltage vector deviation are used under no-load starting according to an embodiment of the present invention;

[0075] Fig.17 The current and torque waveforms of the conventional DTC control method using the minimum voltage vector deviation and the improved DTC control method using the minimum voltage vector deviation during low-speed operation in one embodiment of the present invention are shown in FIG. Fig.17 a is the current waveform when the traditional DTC control method with minimum voltage vector deviation is used. Fig.17 b is the torque waveform when the traditional DTC control method with minimum voltage vector deviation is used. Fig.17 c is the current waveform when the improved DTC control method with minimum voltage vector deviation is adopted. Fig.17 d is the torque waveform of the improved DTC control method using the minimum voltage vector deviation;

[0076] Fig.18 The current and torque waveforms of the conventional DTC control method using the minimum voltage vector deviation and the improved DTC control method using the minimum voltage vector deviation during high-speed operation in one embodiment of the present invention are shown in FIG. Fig.18 a is the current waveform when the traditional DTC control method with minimum voltage vector deviation is used. Fig.18 b is the torque waveform when the traditional DTC control method with minimum voltage vector deviation is used. Fig.18 c is the current waveform when the improved DTC control method with minimum voltage vector deviation is adopted. Fig.18 d is the torque waveform of the improved DTC control method using the minimum voltage vector deviation;

[0077] Fig.19 It is a speed waveform diagram when a conventional DTC control method with a minimum voltage vector deviation and an improved DTC control method with a minimum voltage vector deviation are used under a sudden speed change according to an embodiment of the present invention;

[0078] Fig. 201 is a torque waveform diagram of a conventional DTC control method for a minimum voltage vector deviation and an improved DTC control method for a minimum voltage vector deviation under a torque mutation condition in one embodiment of the present invention. Fig.15 a is the speed waveform when the speed suddenly changes. Fig.15 b is the torque waveform when the speed changes suddenly. DETAILED DESCRIPTION

[0079] 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.

[0080] 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.

[0081] While some exemplary embodiments of the present invention have been described for the purpose of illustration, it should be understood that the present invention may be implemented in other ways not specifically shown in the drawings.

[0082] like Figure 1 As shown, in a specific embodiment, a SRM direct torque control system based on minimum voltage vector deviation is provided, comprising:

[0083] The first PI controller is used to adjust the speed reference value n ref And the actual speed n get the torque reference value

[0084] Voltage vector reference value acquisition module, according to the torque reference value and the actual torque T e The phase angle ∠ψ of the stator flux is adjusted by PI s Add together to get the stator flux reference value phase angle According to the stator flux ψ s and the stator flux reference value phase angle Get the voltage vector reference value u ref ;

[0085] Vector selection module, used to select the phase angle δ ref, the sector where the voltage vector reference value is located and the non-zero voltage vector relationship determine the sector, and then determine the non-zero voltage vector u that needs to be applied n ;

[0086] A duty cycle optimization module is used to calculate the voltage vector reference value u ref and non-zero voltage vector Du n The minimum deviation between them determines the duty cycle D.

[0087] Based on the SRM direct torque control control device based on minimum voltage vector deviation described in the above embodiment, a SRM direct torque control control method based on minimum voltage vector deviation is provided. Figure 2 As shown, the following steps are included:

[0088] S1, according to the torque reference value Stator flux reference value phase angle Get the stator flux vector reference value Then determine the voltage vector reference value u ref ;

[0089] There are four ways to express the electromagnetic and energy relationship of SRM during operation. The voltage equation is used to calculate the voltage of each phase; the flux equation is used to calculate the electromotive force and back electromotive force; the mechanical equation reflects the relationship between the rotor position angle and the mechanical angular velocity; and the electromechanical connection equation obtains the relationship between torque and flux.

[0090] The voltage equation for the jth phase of the SRM is:

[0091]

[0092] In the formula, ψ j is the flux linkage of the jth phase, R j is the resistance of the jth phase, i j is the current through the j-phase winding, u j is the terminal voltage of the j-th phase winding.

[0093] The equation for the j-phase flux is:

[0094] ψ j =L j (i j ,θ)·i j ;

[0095] Among them, L j (i j ,θ) is the inductance of the j-th phase winding.

[0096] The mechanical equation is:

[0097]

[0098]

[0099] Where J is the moment of inertia, ω is the rotor mechanical angular velocity, T L represents the j-phase load torque of the rotor, B represents the viscous friction coefficient, T j The rotor j-phase electromagnetic torque and θ is the rotor position angle.

[0100] The electrical energy in the motor winding is W e , the magnetic energy stored in the inductor can be expressed as W f , the load itself has a magnetic energy W c , magnetic energy constitutes the other two energies:

[0101] dW e =dW f +dW c ;

[0102]

[0103]

[0104] When the motor rotor position is a small angle Δθ, the magnitude of the magnetic energy will also change with the change of the rotor. During the change of Δθ, the amount of magnetic energy storage changing with Δθ and the amount of change in the electric energy in the winding are shown in the following formulas:

[0105]

[0106]

[0107] Then we get ΔW c =ΔW e -ΔW f =S ABCD -(S OBC -S OAD )=S OAB .

[0108] According to the principle of conservation of energy, the partial change in mechanical energy is the product of torque and angle change, ΔW m =T e Δθ. And ΔW c =ΔW m , and when Δθ is very small, the current is considered constant, and the electromagnetic torque T e :

[0109]

[0110] The instantaneous torque of the SRM is obtained according to the voltage equation of the jth phase of the SRM:

[0111]

[0112] The power generated by the power supply is expressed as P:

[0113]

[0114] Ri 2 is the energy consumed when the current passes through the winding, P e It is the difference between the power generated by the power supply and the energy consumed by the winding, that is, the active power P consumed by the winding magnetic field e for:

[0115]

[0116] Magnetic energy W e =P e dt, represents the active power P of the winding group magnetic field e The energy generated per unit time dt, part of which is responsible for the load torque, becomes mechanical energy W m ; Part of it is used as reserve energy W f Still exists in the magnetic field, that is:

[0117]

[0118] During the closing process of the power tube, the current i is usually considered to be constant, and the real-time torque can be expressed as:

[0119]

[0120] After SRM reaches the magnetic circuit saturation range, the magnetic storage energy W f It does not change with the change of θ, and the relationship between the change of magnetic storage energy and angle can be ignored. It can be simplified to:

[0121]

[0122] The rotation direction of the SRM is determined by the current input direction. The conduction current has no negative value, so i does not affect the positive and negative changes of the torque. The sign of the torque T is determined by Decide. When , the phase of the flux linkage value ψ is ahead of θ, T is positive and plays a driving role, and the SRM accelerates at this time; When the flux phase ψ lags behind θ, T is a negative value and acts as a brake. At this time, the SRM decelerates. Therefore, by adjusting the position of θ, a different phase relationship with the flux ψ is achieved to adjust the motor speed.

[0123] In order to more intuitively reflect the torque ripple of the switched reluctance motor, the torque ripple coefficient k is introduced:

[0124]

[0125] Tmax represents the torque ripple coefficient; Tmax is the maximum torque value when the motor is working smoothly; Tmin is the minimum torque value when the motor is working smoothly; Ταv is the average torque value when the motor is working smoothly.

[0126] In this embodiment, the real-time voltage, real-time current and real-time position of the motor are collected to obtain the real-time speed n and torque T of the motor. e and magnetic flux ψ s ; Voltage vector reference value u ref Methods for determining include:

[0127] S11, speed reference value n ref The torque reference value is generated by PI regulation with the actual speed n

[0128] S12, the torque reference value and the actual torque T e After PI adjustment, the phase angle ∠ψ with the stator flux s Add together to get the stator flux reference value phase angle for:

[0129]

[0130] Among them, ∠ψ s is the stator flux phase angle, k p and k i are proportional coefficient and integral coefficient respectively, S represents the integral operator, is the torque reference, usually the output of the speed controller;

[0131] The stator flux phase angle ∠ψ s By acquiring the stator flux vector in real time and performing coordinate transformation, ψ α , β Component, that is, the stator flux phase angle ∠ψ s Obtained by the following formula:

[0132]

[0133] S13. Obtain the stator flux vector reference value by the following formula:

[0134]

[0135] Among them, |ψ s | ref is the reference value of the stator flux amplitude, |ψ s | is the stator flux amplitude;

[0136] S14, according to the stator flux ψs and the stator flux reference value phase angle Get the voltage vector reference value u ref ,for:

[0137]

[0138] S2, according to the phase angle δ ref , the sector where the voltage vector reference value is located and the relationship between the non-zero voltage vector determine the non-zero voltage vector u that needs to be acted on n ;

[0139] Traditional direct torque control includes six basic space voltage vectors V1~V6, such as Figure 3 As shown, V1~V6 are formed by combining phase voltage vectors. According to the voltage generated by the three-phase winding, Va, Vb, and Vc are established in a counterclockwise direction at a distance of 120°; then, vectors -Va, -Vb, and -Vc in the opposite direction are established in a symmetrical position; after superposition and combination, vectors V1~V6 can be determined. Taking the generation of V1 as an example, V1=Va-Vc=1×Va+0×Vb+(-1)×Vc, indicating the conduction state of phase a winding, the continuous flow state of phase b, and the disconnection state of phase c. (1,0,-1) represents V1, and the representation method of V2~V6 is similar to that of V1. The voltage vectors represented by the six fixed power tube states divide the plane area into six sectors, each occupying 60°. V2~V6 can be expressed as V2(0,1,-1), V3(-1,1,0), V4(-1,0,1), V5(0,-1,1), and V6(1,-1,0).

[0140] The SRM commutation area will produce large torque pulsation due to inconsistent torque increase and decrease. In order to solve this problem, in the sector determined by the six voltage vectors of direct torque control, an improved voltage vector for simultaneous conduction of two phases is added in the commutation area of ​​adjacent voltage vectors, such as Figure 4 As shown. Since it is a three-phase SRM, there is a commutation zone for every two phases, and there are three commutation zones in total. Three improved voltage vectors are added, namely u7 (1, 1, -1), u8 (-1, 1, 1) and u9 (1, -1, 1), and sectors 7, 8 and 9 are added. That is, in this embodiment, there are nine non-zero voltage vectors, namely: u1 (1, 0, -1), u2 (0, 1, -1), u3 (-1, 1, 0), u4 (-1, 0, 1), u5 (0, -1, 1), u6 (1, -1, 0), u7 (1, 1, -1), u8 (-1, 1, 1), u9 (1, -1, 1), including nine sectors, as shown in detail. Figure 4 shown.

[0141] The original voltage vector amplitude is 2u dc / 3, improved voltage vector amplitude The increased voltage vector makes the commutation area not a single phase conduction, but two phases conduction at the same time to increase the torque. Before the off phase current disappears, let the adjacent phase open at this moment, and the next phase

[0142] The torque rises in advance to increase the system torque, which can increase the torque in the commutation area, reduce the torque fluctuation of the system, and make the motor run more stably.

[0143] Take the commutation process of phase A and phase B as an example. During the operation of the motor, when the torque and magnetic flux need to increase during the change process, the voltage vector state of the phase in the commutation zone changes from u1 (1, 0, -1) to u2 (0, 1, -1). In this process, the current of phase C is still in the demagnetization state, the current of phase B increases for the current, the current of phase A disappears, and the thyristor is used for continuous current. In this commutation process, the current of phase A and phase B is turned on at the same time to increase the number of conducting phases, that is, there is 1×u a +1×u b +(-1)×u c , represented by u7(1,1,-1). Combined Figure 4 After adding u7, the voltage vector change in the commutation zone changes from u1 (1, 0, -1) to u7 (1, 1, -1) without passing through u2. Phase B changes from being off to being excited by current. During this process, phases A and B are excited at the same time. The effect produced is: the torque of phase A remains the same, the torque of phase C also remains the same, and phase B is opened in advance to provide increased torque, so that the total torque in the commutation zone is increased, the torque reduction in the commutation process of u1 and u2 is avoided, and the torque pulsation in the commutation zone is eliminated.

[0144] Similarly, during the operation of the motor, the two-phase commutation zone is also the same. When the B phase and the C phase are commutated, the current is passed through the C phase in advance, and the vector u8 (-1, 1, 1) is added in the commutation zone; when the C phase and the A phase are commutated, the current is passed through the A phase in advance, and the vector u9 (1, -1, 1) is added in the commutation zone. However, in this process, the positive torque generated in advance by the next phase increases faster, resulting in a small range of torque increase. At the same time, the torque reduction of the previous phase is relatively small relative to the increase, which will also cause a significant increase in the total torque. Therefore, it is necessary to make the torque increment in the commutation zone smooth and use the minimum voltage vector for control. First, a non-zero voltage vector is output to increase the torque in advance, compensate for the negative torque generated by the previous phase interruption, and eliminate the redundant torque error. The zero voltage vector is output for the remaining time to maintain the torque in the commutation zone unchanged to reduce the output torque fluctuation.

[0145] The reference voltage vector is determined by the corresponding phase angle to exist in different sectors of the plane. The non-zero voltage vector needs to determine the sector where the reference voltage is located. The non-zero voltage vector is selected according to the sector position. The commonly used coordinate transformation is used for the reference voltage vector, and the voltage vector is decomposed to determine the corresponding amplitude and phase angle. Then the sector is determined, such as Figure 5 The coordinate transformation diagram shown in the figure shows the set relationship, and the reference voltage vector is transformed as follows:

[0146]

[0147] Get the reference voltage amplitude |u ref | and the phase angle δ ref for:

[0148]

[0149] Among them, δ ref The four-quadrant inverse tangent function arctant2 is used, and its range is the same as that of direct torque control, which is [-π, π]; according to the angle δ ref It can correspond to the sector of the reference voltage vector.

[0150] Table 1 gives the angle δ ref The relationship table between the reference voltage sector and the non-zero voltage vector. After determining the sector, the non-zero voltage vector u that needs to be applied can be further determined. n , as shown in Table 1, the sectors and non-zero voltage vectors are distributed as Figure 6 shown.

[0151] Table 1 Angle δ ref Table of relationship between reference voltage sector and non-zero voltage vector

[0152]

[0153] The size of the commutation area determines the working state of the motor. If the commutation area is too large, the current of the off-phase winding will continue to decrease, and the negative torque generated will increase, which is not conducive to the operation of the motor. Here, an electrical angle of 2° is selected to achieve fast commutation of the motor.

[0154] S3, by calculating the voltage vector reference value u ref and non-zero voltage vector Du n The minimum deviation between them determines the duty cycle D.

[0155] Non-zero voltage vector u nThe action time of the voltage vector varies with the duty cycle, and the effect is also different. When the duty cycle is 1, only the non-zero voltage vector acts in the entire control cycle, which will cause the torque to increase rapidly, and it is easy to cause the actual torque to be greater than the reference torque. In order to avoid this situation, when the actual torque is close to the reference torque, the zero voltage vector can be used to act on the remaining control cycle to slow down or stabilize the torque growth rate. Therefore, it is necessary to optimize the duty cycle. The method based on the minimum voltage vector deviation can be used to calculate the duty cycle. The calculation method is as follows: Figure 7 shown.

[0156] will u ref He Du n The deviation is defined as u ε , only when u ε Perpendicular to Du n When ε The amplitude will be minimized.

[0157] In order to avoid calculating u ref The amplitude and angle δ of |u ε The square of | is used to establish the deviation |u ε The square equation of | is:

[0158]

[0159] in, and Respectively represent u ref Components on the α and β axes; u nα and u nβ Respectively represent u n Components on the α-axis and the β-axis;

[0160] Solve the duty cycle D according to the following formula, and get the duty cycle of the non-zero voltage vector in the non-commutation region as D1 and the duty cycle of the non-zero voltage vector in the non-commutation region as D2:

[0161]

[0162] The duty cycle of the non-zero voltage vector in the non-commutation region is D:

[0163]

[0164] The duty cycle of the non-zero voltage vector in the commutation region is D:

[0165]

[0166] In order to further verify the present invention, Figure 1The conventional DTC simulation based on the minimum voltage vector deviation and the improved DTC simulation based on the minimum voltage vector deviation are compared to verify the feasibility and superiority of the proposed method.

[0167] In a specific embodiment, the simulation parameter variables used for the SRM experiment are: the internal resistance of the winding is mainly determined by the material of the winding, so the internal resistance of each phase winding is set to 0.15Ω, and the rotational inertia of the motor is set to 0.008kg·m under stable operation with low resistance. 2 , Similarly, the damping coefficient is set to 0.008N·m·s, the system is loaded with a load torque of 10N·m for motor operation, a 310V power supply is used for inverter voltage conversion, and the magnetic flux for control is set to 0.45Wb.

[0168] Firstly, a simulation comparison between the improved direct torque control of the present invention and the traditional direct torque control is carried out, including a no-load starting experiment, a low-speed operation experiment, a high-speed operation experiment, a speed mutation experiment and a torque mutation experiment.

[0169] In the no-load process experiment, the speed setting value of the two control methods is 500r / min, and the commonly used traditional DTC control and the improved DTC control technology with added voltage vector are simulated and compared. Figure 6 As shown. From the waveform of no-load startup, it can be seen that there is little difference between the two in motor startup. The improved DTC can complete the startup process in about 0.13s, and the startup process is smooth. The startup time of the traditional DTC is about 0.17s, and then the startup process is completed stably. Compared with the traditional DTC control, the improved DTC is faster in startup and has a faster response speed.

[0170] In the low-speed operation experiment, the current and torque of the two control algorithms are compared and analyzed, where the speed is set to 500r / min, and the speed loop adopts PI control. The difference between the two algorithms is judged by the comparison method to judge the advantages of the corresponding control algorithm. Fig. 9 As can be seen from the figure, the phase currents of the traditional DTC and the improved DTC change in stages over time, and the currents fluctuate within the corresponding driving range. The difference between the two is only in the shape. The current waveforms are similar and they play the same driving role on the motor. Fig. 9From the torque control waveform, it can be seen that both algorithms are relatively stable. The torque of the improved DTC is in a stable state 0.06s after starting. The torque difference range is large but the torque is relatively smooth, and the value is maintained at around 10N·m. The torque difference is basically around 1.9N·m, without range fluctuations, and the torque fluctuation coefficient is 0.19. The torque pulsation does not affect the normal operation of the motor. The torque of the traditional DTC fluctuates in the range, which is mainly reflected in the commutation zone of the two phases of the SRM. At this time, the torque fluctuation suddenly increases, and the torque fluctuation coefficient is 0.3. Due to the torque pulsation in the commutation zone, its torque pulsation coefficient is larger than that of the improved DTC. After precise calculation and comparative analysis of the torque pulsation coefficient, under low-speed conditions, the improved DTC can better control the torque pulsation during the motor adjustment process compared with the traditional DTC.

[0171] In the high-speed operation experiment, the current and torque of the two control algorithms are compared and analyzed, and the following results are obtained: Fig.10 The simulation comparison waveform shown in the figure shows that the speed is set to 1000r / min and the speed loop adopts PI control. By comparing the experimental quantity under high speed, the effectiveness and practicality of the reaction control algorithm are verified. Fig.11 The amplified waveforms of current and torque at high speed are analyzed. Under the high-speed operation condition with increased speed, unlike the traditional DTC technology with interval fluctuations, the improved DTC reduces the torque pulsation in the commutation zone, and the torque fluctuation is small throughout the process, eliminating the torque fluctuation existing in the commutation zone of the traditional DTC technology, making the motor run more smoothly; by comparing and analyzing the amplified images, under the condition of high-speed operation of the motor, the overall torque pulsation of different control methods is slightly reduced due to the increase in speed. In the traditional DTC technology, the torque drop of the previous phase in the commutation zone is greater than the torque increase of the next phase, which leads to a decrease in the torque in the commutation zone, resulting in a torque pulsation of 2.6N·m, and a torque pulsation coefficient of 0.26. The entire process of the improved DTC is relatively smooth, there is no torque pulsation in the commutation zone, and its torque pulsation coefficient is 0.16; after simulation analysis and comparison, it can be seen that the improved DTC can effectively reduce the torque pulsation in the commutation zone regardless of high or low speed.

[0172] In the speed mutation test, the mutation of the improved DTC is as follows Fig.12 As shown, the mutation of traditional DTC is as follows Fig.13 As shown. Fig.12 and Fig.13Comparative analysis shows that when a sudden change command is issued to the speed at 0.3s, the improved DTC completes the speed change in 0.05s, changing the speed from 500r / min to 1000r / min, while the traditional DTC completes the speed change after 0.07s. Both control methods can maintain a stable speed. However, the traditional DTC responds slower than the improved DTC. Comparing the torque of the two control methods, the torque of the improved DTC changes to 30N·m during the sudden change process and remains stable after 0.05s. The torque of the traditional DTC suddenly changes to 38N·m and recovers after a long time of 0.07s. By comparison, it can be seen that the speed response of the improved DTC is faster and more stable in the face of fluctuations.

[0173] Under the torque mutation test, the mutation of the improved DTC is as follows Fig.14 As shown, the mutation of traditional DTC is as follows Fig.15 As shown. Fig.14 and Fig.15 A comparative analysis shows that the torque suddenly changes at 0.2s, with a sudden increase of 10N·m, and then the added torque is removed at 0.4s. The speed of both the improved DTC and the traditional DTC returns to normal after 0.35s. After the sudden change, the torque of the improved DTC will gradually maintain at 10N·m, and disappear quickly after the added torque is removed at 0.4s. The torque of the traditional DTC will fluctuate greatly at 0.2s, and cannot be smoothly maintained at 10N·m. The torque disappearance process at 0.4s is also relatively slow. By comparison, it can be seen that the improved DTC is more stable in the face of torque mutations, responds quickly to torque, and can control torque well.

[0174] A comparative analysis was conducted between the traditional DTC control with minimum voltage vector deviation and the improved DTC control with minimum voltage vector deviation, including no-load starting experiments, low-speed operation experiments, high-speed operation experiments, speed mutation experiments and torque mutation experiments.

[0175] In the no-load starting experiment, the motor is started without load, and the superiority of the algorithm is compared by judging the fluctuation of the speed. The simulation comparison diagram of the traditional DTC control with minimum voltage vector deviation and the improved DTC control with minimum voltage vector deviation is shown in the figure. Fig.16 As shown in the figure, the start time of the improved DTC with minimum voltage vector deviation is about 0.14s, and the start time of the traditional DTC with minimum voltage vector deviation is about 0.19s. Therefore, compared with the traditional DTC with minimum voltage vector deviation, the improved DTC with minimum voltage vector deviation has a faster response speed, which is consistent with Figure 8 Compared with traditional DTC and improved DTC, the control method of minimum voltage vector deviation has less influence on the response speed.

[0176] In the low-speed running experiment, the traditional DTC with minimum voltage vector deviation and the improved DTC with minimum voltage vector deviation are compared and analyzed. At this time, the speed setting value is 500r / min. The simulation comparison diagram is as follows: Fig.17 As shown, Figures a and b are traditional DTC simulation waveforms of minimum voltage vector deviation, and Figures c and d are improved DTC simulation waveforms of minimum voltage vector deviation; Fig.17 It can be seen from the current waveform that the conventional and improved DTC with increased minimum voltage vector deviation are Fig. 9 The original phase currents all show periodic changes and similar shapes; however, the control method with increased voltage vector deviation has relatively small torque fluctuations, which are around 2N·m and 1.1N·m respectively, and the torque pulsation coefficients are 0.2 and 0.11, which is smaller than the original control method. The overall torque pulsation of the improved DTC with minimum voltage vector deviation is more stable; the traditional DTC with minimum voltage vector deviation still has torque pulsation in the commutation area. It can be seen that the control method with minimum voltage vector deviation is conducive to reducing the overall torque pulsation of the system, and the improved DTC is more effective in suppressing the torque pulsation in the SRM commutation area.

[0177] In the high-speed operation experiment, under high-speed operation conditions, the traditional DTC technology with minimum voltage vector deviation and the improved DTC technology with minimum voltage vector deviation are compared and analyzed, and the speed setting value is 1000r / min. Fig.18 a, b are the traditional DTC simulation waveforms of minimum voltage vector deviation; c, d are the improved DTC simulation waveforms of minimum voltage vector deviation; Fig.18 It can be seen from the figure that under high-speed operation, the currents of the traditional DTC with minimum voltage vector deviation and the improved DTC with minimum voltage vector deviation both show periodic changes. The traditional DTC with minimum voltage vector deviation has slight torque fluctuations in the commutation zone, and the torque pulsation coefficient is 0.14; while the improved DTC with minimum voltage vector deviation has a smoother torque waveform, and the torque pulsation coefficient is 0.08. The system torque pulsation at high speed is lower than that at low speed. The control method with increased voltage vector deviation can reduce the torque pulsation of the system. Through the above comparative analysis with the traditional control method, it can be seen that the improved DTC with minimum voltage vector deviation can better control the torque pulsation under both high-speed and low-speed conditions.

[0178] Under the speed mutation experiment, the control performance of different control algorithms is analyzed. The comparison of the simulation waveforms of the traditional DTC control with minimum voltage vector deviation and the improved DTC with minimum voltage vector deviation is shown in the figure below. Fig.19 As shown. Fig.19It can be seen that at 0.35s, the speed changes from 500r / min to 1000r / min, and the time taken by the improved DTC control with the minimum voltage vector deviation to reach the latest given value is about 0.1s, and the time taken by the traditional DTC with the minimum voltage vector deviation is about 0.12s. It can be seen that compared with the traditional DTC control with the minimum voltage vector deviation, the control method with increased voltage vector has better speed response performance.

[0179] In the torque mutation test, the torque suddenly increased from 3N·m to 12N·m at 0.2s, and then decreased from 12N·m to 3N·m at 0.4s. Fig. 20 By comparison, it can be seen that the torque waveform of the traditional DTC with minimum voltage vector deviation is unstable during the torque increase and decrease process, and its size change is about 3.5N·m, while the torque size change of the improved DTC with minimum voltage vector deviation is about 2.1N·m. According to the above analysis, the dynamic characteristics of the improved DTC with minimum voltage vector deviation are better than the traditional DTC control method with minimum voltage vector deviation in the case of torque mutation, which reduces the torque variation range during the mutation process.

[0180] 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 SRM direct torque control method based on minimum voltage vector deviation, characterized in that: The steps include: S1, according to the torque reference value , stator flux phase angle Get the stator flux reference value phase angle , and then determine the voltage vector reference value ; S2, according to the phase angle , the sector where the voltage vector reference value is located and the relationship between the non-zero voltage vector determine the non-zero voltage vector that needs to be acted on , the phase angle , the relationship between the sector where the voltage vector reference value is located and the non-zero voltage vector is: when When , the corresponding sector number N=1; when When , the corresponding sector number N=2; when When , the corresponding sector number N=3; when When , the corresponding sector number N=4; when When , the corresponding sector number N=5; when When , the corresponding sector number N=6; when When , the corresponding sector number N=7; when When , the corresponding sector number N=8; when When , the corresponding sector number N=9; S3, by calculating the voltage vector reference value and non-zero voltage vector D The minimum deviation between them determines the duty cycle D, including: S31. Establish deviation The square equation of is: ； in, and Respectively exist Axis and The weight of the axis; and Respectively exist Axis and The weight of the axis; S32. Calculate the duty cycle D according to the following formula: ； The duty cycle D1 of the non-zero voltage vector in the non-commutation region is obtained as: ； The duty cycle D2 of the non-zero voltage vector in the commutation region is obtained as: 。 2. The SRM direct torque control method based on minimum voltage vector deviation according to claim 1, characterized in that: The voltage vector reference value Methods for determining include: S11, speed reference value The torque reference value is generated by PI regulation with the actual speed n ; S12, the torque reference value and actual torque Phase angle with stator flux after PI adjustment Add together to get the stator flux reference value phase angle ,for: ； in, and are proportional coefficient and integral coefficient respectively, S represents the integral operator, is the torque reference value, is the stator flux phase angle; S13. Obtain the stator flux vector reference value through the following formula : ； in, is the reference value of the stator flux amplitude, is the stator flux amplitude; S14, according to the stator flux and the stator flux reference value phase angle Get the voltage vector reference value ,for: 。 3. The SRM direct torque control method based on minimum voltage vector deviation according to claim 2 is characterized in that: The stator flux phase angle for: ； in, To obtain the α and β components of the stator flux vector in real time, coordinate transformation is performed.

4. The SRM direct torque control method based on minimum voltage vector deviation according to claim 1, characterized in that: The non-zero voltage vector includes: 、 、 、 、 、 、 、 、 。 5. The SRM direct torque control method based on minimum voltage vector deviation according to claim 1, characterized in that: The phase angle The calculation method is: 。 6. A SRM direct torque control system based on minimum voltage vector deviation, comprising: The first PI controller is used to adjust the speed reference value And the actual speed n get the torque reference value ; Voltage vector reference value acquisition module, according to the torque reference value and actual torque The phase angle of stator flux is adjusted by PI Add together to get the stator flux reference value phase angle ; According to the stator flux and the stator flux reference value phase angle Get the voltage vector reference value ; Vector selection module, used to select , the sector where the voltage vector reference value is located and the non-zero voltage vector relationship determine the sector, and then determine the non-zero voltage vector that needs to be acted on , the phase angle , the relationship between the sector where the voltage vector reference value is located and the non-zero voltage vector is: when When , the corresponding sector number N=1; when When , the corresponding sector number N=2; when When , the corresponding sector number N=3; when When , the corresponding sector number N=4; when When , the corresponding sector number N=5; when When , the corresponding sector number N=6; when When , the corresponding sector number N=7; when When , the corresponding sector number N=8; when When , the corresponding sector number N=9; A duty cycle optimization module is used to calculate the voltage vector reference value and non-zero voltage vector D Deviation The minimum value determines the duty cycle D; The deviation The square equation of is: ； in, and Respectively exist Axis and The weight of the axis; and Respectively exist Axis and The weight of the axis; The duty cycle D is solved according to the following formula: ； Then the duty cycle of the non-zero voltage vector in the non-commutation region is obtained as D1: ； The duty cycle of the non-zero voltage vector in the commutation region is obtained as D2: 。

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