A control method for asynchronous motor at zero synchronous speed

Abstract

The control method of an asynchronous motor under zero synchronous speed provided by the present invention compares the synchronous speed of the asynchronous motor with the boundary synchronous speed, and adopts a composite control scheme of vector control and torque current correction control according to the comparison result, thereby avoiding the low-speed unobservable problem caused by single vector control; by adjusting the torque current, the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, and crosses the zero synchronous speed area to ensure that the full speed range of the rotor speed during the forward and reverse switching of the asynchronous motor speed is observable; through a reasonable synchronous speed limit value, it is ensured that the asynchronous motor operating condition point will not suddenly change to the reverse electric working condition after actively crossing the zero synchronous speed area; by correcting the torque current signal again after the asynchronous motor operating condition point actively crosses the zero synchronous speed area, so as to restore it to the initial value before the speed switching, it is avoided that the motor is damaged by running at a non-initial torque current for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of asynchronous motor control, and in particular to a control method of an asynchronous motor at zero synchronous speed. Background Art

[0002] At present, with the continuous application of asynchronous motors in various industries, it is very important for the vector control system of asynchronous motors to obtain accurate rotor speed information in order to ensure the stability of asynchronous motor operation. The early asynchronous motor vector control method required the installation of a speed sensor at the motor shaft end to obtain the rotor speed, but the sensor-based vector control system is expensive, has poor reliability, and has high maintenance costs in the later stage, so sensorless control technology came into being.

[0003] The asynchronous motor speed sensorless vector control system has the advantages of low cost, high reliability, and low maintenance rate because it does not use speed sensors. Since the adaptive full-order observer used in the existing system cannot work normally when the synchronous speed is zero, the rotor speed of the asynchronous motor at zero synchronous speed is unobservable, which makes it difficult for the asynchronous motor speed sensorless drive system to operate stably with load at zero synchronous speed; specifically, the asynchronous motor is used in industrial fields such as lifting with gravity loads or power generation, where the rotor speed needs to be frequently switched between forward and reverse, and the asynchronous motor cannot observe the rotor speed at zero synchronous speed;

[0004] The existing speed sensorless driven asynchronous motor control method adopts a fixed coefficient virtual voltage injection technology in the low-speed power generation mode and zero current frequency to solve the problem of asynchronous motor zero frequency being unobservable, and realize the zero-frequency stability of the motor. However, due to the difference between the observer input voltage and the actual voltage of the motor, the rotor speed control accuracy of the motor is insufficient at medium and high speeds, and the method requires a larger flux current at low speed and load, resulting in large losses; or a restriction method is adopted to make the motor operating condition point avoid the zero synchronous speed condition, but the application problem in the field of complex working conditions is not fundamentally solved; or an additional error injection method is adopted to realize "pseudo stator current zero frequency", etc. Although this method can make the speed sensorless vector control system of the asynchronous motor remain stable at zero synchronous speed, due to the additional injection of a rotor speed error term, when the rotor speed is observed under low speed and zero speed conditions, there will be a large error between the rotor speed observation value and the rotor speed actual value, which means that this method will sacrifice the accuracy of observation and fail to meet the accuracy requirements of engineering applications.

[0005] Therefore, how to ensure the speed observability of the asynchronous motor speed vector-free control system during the forward and reverse speed switching process becomes an urgent problem to be solved. Summary of the invention

[0006] The present invention provides a control method for an asynchronous motor at zero synchronous speed. Since the current asynchronous motor speed sensorless vector control system reverses the asynchronous motor rotor after the speed switching command is issued, the rotor speed will continue to decrease, and the synchronous speed will gradually approach zero frequency. The traditional sensorless vector control system with a feedback matrix cannot solve the problem of speed observation failure near zero synchronous speed. Based on this, the present invention adopts vector control under normal working conditions, adopts torque current correction control when the synchronous speed is less than or equal to the boundary value of the unstable area, and adopts issuing an active crossing command when the synchronous speed reaches the limit value, so that the asynchronous motor actively crosses the zero synchronous speed area, ensuring the global stability of the system and the observability of the rotor speed in the full speed range, thereby solving the defects of the above-mentioned prior art.

[0007] The present invention provides a control method for an asynchronous motor at zero synchronous speed, comprising the steps of:

[0008] S1 builds a speed sensorless vector control system for asynchronous motors;

[0009] S2 obtains the boundary synchronous speed corresponding to the unstable boundary of the vector control system based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system;

[0010] S3 compares the synchronous speed of the asynchronous motor with the boundary synchronous speed, and if the synchronous speed is greater than the boundary synchronous speed, uses vector control;

[0011] If the synchronous speed is less than or equal to the boundary synchronous speed, adjusting the torque current so that the synchronous speed of the asynchronous motor converges to the synchronous speed limit value;

[0012] S4 sends an active crossing instruction to the asynchronous motor after the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, so that the synchronous speed suddenly changes from the synchronous speed limit value to a synchronous speed with an equal value and opposite direction.

[0013] Further, in step S1, an asynchronous motor speed sensorless vector control system is constructed, including:

[0014] S101 establishes a mathematical model of an asynchronous motor in a two-phase stationary coordinate system;

[0015] S102, based on the mathematical model, taking the stator current and rotor flux of the asynchronous motor as state variables and the stator current as an output variable, obtaining a state space expression of the asynchronous motor;

[0016] S103 establishes an adaptive full-order observer model of the asynchronous motor based on the state space expression.

[0017] In step S2, based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system, obtaining the boundary synchronous speed corresponding to the unstable boundary of the vector control system includes:

[0018] S201, based on the adaptive full-order observer model, obtaining the error vector of the asynchronous motor and obtaining the error coefficient matrix E;

[0019] S202 obtains the boundary condition as det(E)=0 according to the error coefficient matrix E, and the synchronous speed boundary of the unstable area of ​​the asynchronous motor speed sensorless vector control system under the low-speed power generation condition is:

[0020]

[0021] in, is the intermediate parameter;

[0022] The synchronous speed limit value is obtained as ω uns =θ|ω r |;

[0023] Among them, L s is the stator inductance of the asynchronous motor, R s is the stator resistance of the asynchronous motor, is the asynchronous motor rotor time constant, R r is the asynchronous motor rotor resistance, L r is the asynchronous motor rotor inductance, ω r is the rotor speed of the asynchronous motor, ω e is the synchronous speed of the asynchronous motor.

[0024] In step S3, when the synchronous speed is equal to the boundary synchronous speed, the asynchronous motor adjusts the torque current to decelerate, including:

[0025] S301 obtains the torque current, slip speed and rotor speed at the moment, obtains the difference of slip speed in the process of synchronous speed decelerating from the boundary synchronous speed to the synchronous speed limit value; obtains the quantitative relationship between the d-axis component and the q-axis component of the stator current increment, and calculates the torque current change Δi sq include:

[0026]

[0027] S302 further obtains the torque current command value The slip speed of the asynchronous motor is adjusted by the torque current command value, thereby adjusting the synchronous speed of the asynchronous motor:

[0028]

[0029] in, is the initial value of the torque current when the synchronous speed is equal to the boundary synchronous speed, Δω s is the difference in slip speed during the process of the synchronous speed being decelerated from the boundary synchronous speed to the synchronous speed limit value, f s is the discrete system sampling frequency; i sd is the d-axis component of the stator current; i sq is the q-axis component of the stator current.

[0030] Preferably, the synchronous speed limit value ω lim for:

[0031]

[0032] Among them, n p is the number of pole pairs of the asynchronous motor, T L is the load torque, J is the moment of inertia of the asynchronous motor, L m is the mutual inductance between the stator winding and the rotor winding, ω ini is the initial rotor speed at the moment when the synchronous speed is equal to the boundary synchronous speed, It is the total time of the process of decelerating the synchronous speed of the asynchronous motor from the boundary synchronous speed to the synchronous speed limit value.

[0033] After step S4, the method further includes:

[0034] S5 is at synchronous speed by ω lim Transform to -ω lim After that, the torque current is adjusted again to restore the torque current to the initial torque current before the synchronous speed is reduced to the boundary synchronous speed.

[0035] The present invention also provides an asynchronous motor, which is controlled by the steps of the control method of the asynchronous motor at zero synchronous speed as described in any one of the above items.

[0036] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the control method of the asynchronous motor at zero synchronous speed as described in any one of the above are implemented.

[0037] The control method of the asynchronous motor at zero synchronous speed provided by the present invention has the following technical effects:

[0038] (1) By comparing the synchronous speed of the asynchronous motor with the boundary synchronous speed, a composite control scheme of vector control and torque current correction control is adopted according to the comparison result. The reasonable switching of the two control methods avoids the low-speed unobservable problem caused by single vector control;

[0039] (2) by adjusting the torque current, the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, and crosses the zero synchronous speed region to ensure that the full speed range of the rotor speed during the forward and reverse switching process of the asynchronous motor speed is observable;

[0040] (3) Use a reasonable synchronous speed limit value to ensure that the asynchronous motor operating condition point will not suddenly change to the reverse motoring condition after actively crossing the zero synchronous speed area;

[0041] (4) After the asynchronous motor actively crosses the zero synchronous speed region at the operating point, the torque current signal is corrected again so that the torque current is restored to the initial value before the speed switching, thereby avoiding damage to the asynchronous motor caused by the motor running at a non-initial torque current for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a schematic diagram of the principle of the control method of the asynchronous motor at zero synchronous speed provided by the present invention;

[0044] Figure 2 It is a flow chart of a control method of an asynchronous motor at zero synchronous speed provided by the present invention;

[0045] Figure 3 It is one of the synchronous speed limit value schematic diagrams of the control method of the asynchronous motor at zero synchronous speed provided by the present invention;

[0046] Figure 4 A second schematic diagram of the synchronous speed limit value of the control method for the asynchronous motor at zero synchronous speed provided by the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] In one embodiment, Figure 1The figure shows a schematic diagram of a control method for an asynchronous motor at zero synchronous speed provided by the present invention, wherein a suitable excitation current (i.e., d-axis current) instruction is preset (generally set to 30%-60% of the rated value of the stator current of the asynchronous motor);

[0049] Under the condition of rotor speed reversal, the composite control scheme gives a rotor speed reversal command (such as the rotor speed command changes from 150rpm to -150rpm at a constant acceleration). The difference between the rotor speed command and the observed speed output by the speed adaptive law is input to the speed loop proportional integral controller to generate the initial value of the torque current command (i.e., the q-axis current command);

[0050] The initial value of the torque current command plus the modified torque current signal enabled by the composite control scheme constitutes the torque current command value. The difference between the torque current command value and the actual torque current generates the q-axis voltage command through the current loop proportional-integral controller. At the same time, the difference between the excitation current command value and the actual excitation current generates the d-axis voltage command through the current loop proportional-integral controller. The d- and q-axis voltage commands are calculated by the inverse Park transform to output the voltage commands in the two-phase stationary coordinate system;

[0051] The voltage command in the two-phase stationary coordinate system outputs a switching signal through voltage space vector pulse width modulation. The switching signal acts on the DC power output from the AC power supply and the rectifier circuit to the drive and power switch circuit, and the AC voltage applied to the asynchronous motor end can be obtained. At this time, by sampling the three-phase current of the asynchronous motor and performing Clarke transformation and Park transformation on it, the actual values ​​of the d and q axis currents can be obtained, forming a current loop closed-loop control;

[0052] In the composite control scheme, the voltage command is input into the adaptive full-order observer, and the synchronous speed of the asynchronous motor is obtained by calculating the rotor position angle and integrating it. The synchronous speed of the asynchronous motor is compared with the boundary value of the unstable region in real time online. When the synchronous speed is less than the boundary value of the unstable region, the torque current correction control is started to correct the torque current. First, the adaptive convergence of the synchronous speed is completed, and then the operating condition point of the asynchronous motor actively crosses the zero synchronous speed region, ensuring that the full speed range of the rotor speed can be observed during the forward and reverse switching process of the asynchronous motor speed.

[0053] In one embodiment, Figure 2 As shown, the control method of the asynchronous motor at zero synchronous speed provided by the present invention comprises the steps of:

[0054] S1 builds a speed sensorless vector control system for asynchronous motors;

[0055] S2 obtains the boundary synchronous speed corresponding to the unstable boundary of the vector control system based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system;

[0056] S3 compares the synchronous speed of the asynchronous motor with the boundary synchronous speed, and if the synchronous speed is greater than the boundary synchronous speed, uses vector control;

[0057] If the synchronous speed is less than or equal to the boundary synchronous speed, adjusting the torque current so that the synchronous speed of the asynchronous motor converges to the synchronous speed limit value;

[0058] S4 sends an active crossing instruction to the asynchronous motor after the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, so that the synchronous speed suddenly changes from the synchronous speed limit value to a synchronous speed with an equal value and opposite direction.

[0059] Wherein, step S1 specifically includes:

[0060] The rotor adaptive law is adopted to establish an adaptive full-order observer to form an asynchronous motor speed sensorless vector control system:

[0061] S101 establishes the mathematical model of the asynchronous motor in a two-phase stationary coordinate system, including:

[0062]

[0063] Among them, i s =[i sα i sβ ] T is the stator current column vector, ψ r =[ψ rα ψ rβ ] T is the rotor flux column vector, u s =[u sα u sβ ] T is the stator voltage column vector, subscripts α and β represent the α-axis component and β-axis component in the two-phase stationary coordinate system respectively;

[0064] A 11 , A 12 , A 21 , A 22 , B are the matrix coefficients in the asynchronous motor state equation, a, b, c, d are the intermediate parameters related to the motor parameters, where A 11 =aI, A 12 =cI-cω r τ r J, A 21 =dI, B=[bI0] T ,

[0065] Among them, R s is the stator resistance of the asynchronous motor, R r is the asynchronous motor rotor resistance, L s is the stator inductance of the asynchronous motor, L r is the asynchronous motor rotor inductance, L m It is the mutual inductance between the stator and rotor of the asynchronous motor. is the asynchronous motor rotor time constant, is the leakage inductance coefficient of the asynchronous motor, ω r is the rotor speed value of the asynchronous motor; represents the time differential operator.

[0066] S102 is based on the mathematical model, takes the stator current and rotor flux of the asynchronous motor as state variables, takes the stator current as output variable, and obtains the state space expression of the asynchronous motor, which is:

[0067]

[0068] Among them, C is the matrix coefficient of the asynchronous motor output equation:

[0069]

[0070] Furthermore, an adaptive full-order observer is used to estimate the rotor speed of the asynchronous motor. Substitute the actual rotor speed ω of the asynchronous motor in equation (2) r , the adaptive full-order observer model of the asynchronous motor used is obtained as:

[0071]

[0072] Among them, A 12 and A 22 is the matrix coefficient in the full-order observer:

[0073]

[0074] and They are column vectors composed of stator current and rotor flux estimation values ​​in the speed sensorless vector control system of asynchronous motor;

[0075] S103 establishes an adaptive full-order observer model of the asynchronous motor based on the state space expression, specifically including:

[0076] Using Popov's hyperstability theory, the adaptive law of the estimated value of the asynchronous motor rotor speed in equation (3) can be obtained as:

[0077]

[0078] Among them, K P is the proportional adjustment coefficient of the speed adaptive law, K I is the integral time constant of the speed adaptive law, is the current error.

[0079] Further, in step S2, based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system, obtaining the boundary synchronous speed corresponding to the unstable boundary of the vector control system includes:

[0080] S201 obtains the error vector of the asynchronous motor and the error coefficient matrix E based on the adaptive full-order observer model, specifically including the steps of:

[0081] In practical engineering applications, in order to reduce the unstable area of ​​the asynchronous motor speed sensorless vector control system under low-speed power generation conditions, it is necessary to add a feedback matrix to the adaptive full-order observer, and then the equation (3) in step S1 becomes:

[0082]

[0083] Where G = [g1I-g2J g3I-g4J] T is the feedback matrix, g1, g2, g3, g4 are independent parameters in the feedback matrix.

[0084] Specifically, the feedback matrix in equation (5) can be taken as

[0085]

[0086] Combined with the state equation expression of the asynchronous motor in step S1, subtracting equation (5) from equation (1) yields the error vector equation:

[0087]

[0088] in, is the current error, is the flux error, ΔA 12 =-cΔω r τ r J, is the speed error;

[0089] In order to analyze the stability of the observer and the speed estimation, the error vector is redefined as:

[0090] e=[e i e ψ Δω r ] T (8)

[0091] Furthermore, in the two-phase synchronous rotating coordinate system, using the small signal linearization principle, the error vector is expressed as:

[0092] Δe=EΔe+ΔEe (9)

[0093] Among them, E is the fifth-order error coefficient matrix, which is expressed as follows:

[0094]

[0095] Among them, ω e is the synchronous speed of the asynchronous motor, ω s is the slip speed of the asynchronous motor;

[0096] a 51 ~a 55 All of them are intermediate parameters related to the motor's operating status or its own parameters, among which:

[0097] a 51 =-K P (ω e +g2)ψ rd ;

[0098] a 52 =[K P (a-g1)+K I ]ψ rd ;

[0099] a 53 =-K P Cτ r ω r ψ rd ;

[0100] a 54 =K P cψ rd ;

[0101]

[0102] The boundary conditions for the stability of the asynchronous motor speed sensorless vector control system are:

[0103] det(E)=0 (11)

[0104] Further, in step S202, according to formula (11), the synchronous speed boundary of the unstable area of ​​the asynchronous motor speed sensorless vector control system under the low-speed power generation condition is:

[0105]

[0106] in, is the intermediate parameter;

[0107] If there is no feedback matrix, the synchronous speed value of the asynchronous motor when it reaches the boundary of the unstable region is ω uns , then:

[0108] ω uns =θ|ω r | (13)

[0109] If the motor operating condition is Figure 3-Figure 4 The normal electric operation in the first quadrant shown gradually decelerates to the electromagnetic braking operation in the second quadrant, with:

[0110] ω uns =-θω r (14)

[0111] The resulting synchronous speed limit value is ω uns =θ|ω r |;

[0112] Further, in step S3, at the moment when the synchronous speed is equal to the boundary synchronous speed, the asynchronous motor adjusts the torque current to decelerate, and on the premise of ensuring that the rotor speed of the asynchronous motor is observable, the synchronous speed of the asynchronous motor is reduced to a prescribed limit value, in preparation for active crossing, specifically including the following steps:

[0113] S301 obtains the torque current, slip speed and rotor speed at the moment, and obtains the slip speed difference in the process of the synchronous speed being decelerated from the boundary synchronous speed to the synchronous speed limit value, including:

[0114] Assume that the asynchronous motor operates in a steady state under medium and low speed electric working conditions, and a speed switching command is given at the initial time t0 to decelerate from the boundary synchronous speed to the synchronous speed limit value. According to the motion equation of the asynchronous motor:

[0115]

[0116] Where, J is the moment of inertia of the asynchronous motor, n p is the number of pole pairs of the asynchronous motor, T e is the electromagnetic torque of the asynchronous motor, T L It is the load torque of the asynchronous motor.

[0117] After the speed switching command is given, the asynchronous motor decelerates according to the predetermined acceleration until the speed switching process is completed. This process satisfies formula (16):

[0118]

[0119] Among them, ±ω ini is the steady-state speed before and after the speed switching, is the total time of the process in which the synchronous speed of the asynchronous motor is decelerated from the boundary synchronous speed to the synchronous speed limit value;

[0120] By correcting the torque current command value of the asynchronous motor, the synchronous speed of the asynchronous motor is adjusted so that the synchronous speed of the asynchronous motor adaptively converges to the synchronous speed limit value. The torque current command value of the asynchronous motor can be expressed as:

[0121]

[0122] in, is the actual torque current command value, is the torque current command value before the composite control scheme of the present invention is started, Δi sq It is the torque current correction signal corresponding to each running time step of the asynchronous motor in the synchronous speed adaptive convergence stage, that is, the torque current change;

[0123] Based on formula (14), and the asynchronous motor synchronous speed ω e , slip speed ω s , rotor speed ω r The relationship between:

[0124] ω e =ω s +ω r (18)

[0125] When the synchronous speed of the asynchronous motor reaches the unstable boundary ω uns When the rotor speed is:

[0126] (1+θ)ω r =-ω s (19)

[0127] The relationship between the electromagnetic torque and torque current of an asynchronous motor is:

[0128]

[0129] Combining equations (15), (16) and (20), at time t1, the synchronous speed of the asynchronous motor reaches the unstable boundary ω uns When , the torque current is:

[0130]

[0131] The slip speed is:

[0132]

[0133] Among them, t1 is the time when the asynchronous motor synchronous speed reaches the unstable boundary ω uns moment.

[0134] According to formula (20), the rotor speed at this time is:

[0135]

[0136] Combined with the attached pictures Figure 3 As shown, in the adaptive convergence stage of the asynchronous motor synchronous speed, from ω uns Adjust to ω lim In the process, the slip speed of the asynchronous motor should satisfy the following relationship:

[0137]

[0138] Further, in conjunction with the accompanying drawings Figure 3 As shown, in order to make the asynchronous motor work under the condition of crossing the synchronous speed boundary (ω lim , -ω lim ) interval, the operating condition point of the asynchronous motor does not fall into the third quadrant, that is, the asynchronous motor does not enter the reverse motoring condition, and its slip speed and synchronous speed limit value should satisfy the following relationship:

[0139] ω s (t1)-Δω s >2ω lim (25)

[0140] The synchronous speed limit value ω can be obtained from this lim for:

[0141]

[0142] Thus, the steady-state speed ω before any speed switching ini The total time of the speed switching process Synchronous speed limit valueω lim They can all be adaptively valued according to actual working conditions to ensure the speed observability of the asynchronous motor speed sensorless vector control system.

[0143] Furthermore, in step S301, the quantitative relationship between the d-axis component and the q-axis component of the stator current increment is obtained, and the torque current change Δi is calculated. sq include:

[0144] Assume that the discrete sampling frequency of the asynchronous motor speed sensorless vector control system is f s , then in one running step of the discrete system, it should satisfy

[0145] ΔT e ≈0 (27)

[0146] Right now

[0147]

[0148] Among them, Δi sd is the difference in the stator d-axis current of the asynchronous motor between two adjacent operating steps of the discrete system; Δi sq It is the difference of the stator q-axis current of the asynchronous motor between two adjacent running steps of the discrete system, and is also the torque current change or correction signal corresponding to each running step in the synchronous speed adaptive convergence stage, that is, the value of the torque current actively corrected and adjusted in the synchronous speed adaptive convergence stage;

[0149] According to formula (28), the relationship between the stator current and the current correction signal can be obtained as follows:

[0150] i sd Δi sq +i sq Δi sd =0 (29)

[0151] Therefore, in each running step during the phase of synchronous speed adaptive convergence, we have:

[0152]

[0153] In the formula, f s is the operating frequency of the discrete system.

[0154] Substituting equation (29) into (30), it can be deduced that in the synchronous speed adaptive convergence stage, the torque current correction signal expression for each operating step is:

[0155]

[0156] S302 further obtains the torque current command value The slip speed of the asynchronous motor is adjusted by the torque current command value, thereby adjusting the synchronous speed of the asynchronous motor; when the synchronous speed of the asynchronous motor reaches the unstable boundary ω uns When the torque current command value is changed according to the torque current correction signal of formula (31), the synchronous speed reaches the specified limit value ω lim ,The composite control scheme gives active crossing instructions and actively completes the zero speed crossing of the synchronous speed of the asynchronous motor, ensuring that the speed of the whole process is observable.

[0157] Preferably, after step S4, after the asynchronous motor completes the active crossing described in step 3, step S5 is further included, when the synchronous speed is changed from ω lim Transform to -ω lim After that, the torque current is adjusted again to restore the torque current to the initial torque current before the synchronous speed is reduced to the boundary synchronous speed.

[0158] Preferably, in the adaptive convergence stage of the synchronous speed and the initial torque current recovery stage, it is necessary to clarify the operating trajectory of the operating point of the asynchronous motor, which specifically includes the following steps:

[0159] When the composite control scheme gives an active crossing command, the asynchronous motor synchronous speed zero speed crossing is completed, that is, the synchronous speed changes from ω lim Mutation to -ω lim After the zero-speed crossing is completed, the torque current correction command is given again to restore the initial torque current. This process also uses the torque current correction command shown in formula (31). The motor operating condition point is as follows: Figure 4 As shown, the asynchronous motor is prevented from being damaged by running at a non-initial torque current for a long time.

[0160] It should be noted that, in combination with the requirements and goals of the asynchronous motor speed sensorless vector control system to be controllable over the full speed range, it is necessary to derive its actual operating point trajectory based on the motion equation of the asynchronous motor. After the synchronous speed adaptive convergence phase is completed, the synchronous speed of the asynchronous motor reaches the limit value ω lim Ideally, the motor operating conditions at this stage are as follows: Figure 4 As shown by the middle line l2, it does not conform to the actual operating conditions.

[0161] Furthermore, according to formula (15), when the torque current of the asynchronous motor changes, its rotor speed changes accordingly, and the relationship is integral. Therefore, the actual operating condition point trajectory cannot be the same as Figure 4 The middle l2 line is consistent;

[0162] Further obtaining the running trajectory of the operating condition point of the asynchronous motor includes the following steps:

[0163] Assume that the total time for synchronous speed adaptive convergence is t ad In this stage, the torque current is continuously corrected so that the slip speed of the asynchronous motor is a linear function of time:

[0164]

[0165] Then from time t1 to time t, the rotor speed is:

[0166]

[0167] The expression of electromagnetic torque is:

[0168]

[0169] Combining equations (15), (16) and (20), the electromagnetic torque at time t1 can be obtained as

[0170]

[0171] Combining equations (32), (33) with equations (34) and (35), the expression of the rotor speed changing with time during the synchronous speed adaptive convergence process can be obtained as follows:

[0172] ω r (t) = xt 2 +yt+z (36)

[0173] Further:

[0174]

[0175] It can be seen from formula (36) that the rotor speed is a quadratic function of time during the synchronous speed adaptive convergence process. As shown in formula (32), the rotor speed of the asynchronous motor and the slip speed are in a quadratic function relationship during the synchronous speed adaptive convergence process, as shown in Figure 4 Similarly, in the initial torque current recovery stage, the rotor speed and slip speed of the asynchronous motor also present a quadratic function relationship, as shown in Figure 1. Figure 4 Shown by line l5.

[0176] On the other hand, the present invention further provides an asynchronous motor, wherein the asynchronous motor is controlled by the steps of the control method of the asynchronous motor at zero synchronous speed as described in any one of the above items, specifically comprising:

[0177] S1 builds a speed sensorless vector control system for asynchronous motors;

[0178] S2 obtains the boundary synchronous speed corresponding to the unstable boundary of the vector control system based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system;

[0179] S3 compares the synchronous speed of the asynchronous motor with the boundary synchronous speed, and if the synchronous speed is greater than the boundary synchronous speed, uses vector control;

[0180] If the synchronous speed is less than or equal to the boundary synchronous speed, adjusting the torque current so that the synchronous speed of the asynchronous motor converges to the synchronous speed limit value;

[0181] S4 sends an active crossing instruction to the asynchronous motor after the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, so that the synchronous speed suddenly changes from the synchronous speed limit value to a synchronous speed with an equal value and opposite direction.

[0182] On the other hand, the present invention further provides a computer program product, the computer program product includes a computer program stored on a non-transitory computer-readable storage medium, the computer program includes program instructions, when the program instructions are executed by a computer, the computer can execute the control method of the asynchronous motor at zero synchronous speed provided by the above methods, the method comprising: S1 constructing a speed sensorless vector control system of the asynchronous motor; S2 obtaining a boundary synchronous speed corresponding to an unstable boundary of the vector control system based on a stable boundary condition of the speed sensorless vector control system of the asynchronous motor; S3 comparing the synchronous speed of the asynchronous motor with the boundary synchronous speed, if the synchronous speed is greater than the boundary synchronous speed, using vector control;

[0183] If the synchronous speed is less than or equal to the boundary synchronous speed, the torque current is adjusted so that the synchronous speed of the asynchronous motor converges to the synchronous speed limit value; S4 after the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, an active crossing command is issued to the asynchronous motor so that the synchronous speed suddenly changes from the synchronous speed limit value to a synchronous speed with an equal value and opposite direction.

[0184] On the other hand, the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon, which is implemented when the computer program is executed by a processor to execute the above-mentioned control method of the asynchronous motor at zero synchronous speed.

[0185] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0186] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for an asynchronous motor at zero synchronous speed, characterized in that: include: S1 builds asynchronous motor speed sensorless vector control system, including: S101 establishes a mathematical model of an asynchronous motor in a two-phase stationary coordinate system; S102, based on the mathematical model, taking the stator current and rotor flux of the asynchronous motor as state variables and the stator current as an output variable, obtaining a state space expression of the asynchronous motor; S103, establishing an adaptive full-order observer model of the asynchronous motor based on the state space expression; S2 obtains the boundary synchronous speed corresponding to the unstable boundary of the vector control system based on the stable boundary conditions of the asynchronous motor speed sensorless vector control system, including: S201: Based on the adaptive full-order observer model, obtain the error vector of the asynchronous motor and obtain the error coefficient matrix ; S202 According to the error coefficient matrix The boundary condition is The synchronous speed boundary of the asynchronous motor speed sensorless vector control system in the unstable area under low-speed power generation conditions is: in, is the intermediate parameter; The synchronous speed limit value is ; in, is the stator inductance of the asynchronous motor, is the stator resistance of the asynchronous motor, is the asynchronous motor rotor time constant, is the asynchronous motor rotor resistance, is the asynchronous motor rotor inductance, is the rotor speed of the asynchronous motor, is the synchronous speed of the asynchronous motor; S3 compares the synchronous speed of the asynchronous motor with the boundary synchronous speed, and if the synchronous speed is greater than the boundary synchronous speed, uses vector control; If the synchronous speed is less than or equal to the boundary synchronous speed, adjusting the torque current so that the synchronous speed of the asynchronous motor converges to the synchronous speed limit value; S4 sends an active crossing instruction to the asynchronous motor after the synchronous speed of the asynchronous motor converges to the synchronous speed limit value, so that the synchronous speed suddenly changes from the synchronous speed limit value to a synchronous speed with an equal value and opposite direction.

2. The control method of an asynchronous motor at zero synchronous speed according to claim 1, characterized in that: In step S3, when the synchronous speed is equal to the boundary synchronous speed, the asynchronous motor adjusts the torque current to decelerate, including the steps of: S301 obtains the torque current, slip speed and rotor speed at the moment, obtains the slip speed difference in the process of the synchronous speed being decelerated from the boundary synchronous speed to the synchronous speed limit value; obtains the stator current increment Axis components and Quantitative relationship between axis components, calculation of torque current change include: ； S302 further obtains the torque current command value , adjusting the slip speed of the asynchronous motor by the torque current command value, and then adjusting the synchronous speed of the asynchronous motor: ； in, is the initial value of the torque current at the moment when the synchronous speed is equal to the boundary synchronous speed, is the difference in slip speed during the process of the synchronous speed being decelerated from the boundary synchronous speed to the synchronous speed limit value, is the discrete system sampling frequency; is the stator current Axis component; is the stator current Axis component.

3. The control method of an asynchronous motor at zero synchronous speed according to claim 2, characterized in that: The synchronous speed limit value for: ； in, is the number of pole pairs of the asynchronous motor, is the load torque, is the moment of inertia of the asynchronous motor, is the mutual inductance between the stator and rotor windings, is the initial rotor speed at the moment when the synchronous speed is equal to the boundary synchronous speed, It is the total time of the process of decelerating the synchronous speed of the asynchronous motor from the boundary synchronous speed to the synchronous speed limit value.

4. The control method of an asynchronous motor at zero synchronous speed according to claim 3, characterized in that: After step S4, the method further comprises the following steps: S5 is at synchronous speed Transform to After that, the torque current is adjusted again to restore the torque current to the initial torque current before the synchronous speed is reduced to the boundary synchronous speed.

5. An asynchronous motor, characterized in that: The asynchronous motor is controlled by the steps of the control method of the asynchronous motor at zero synchronous speed as claimed in any one of claims 1 to 4.

6. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the control method of the asynchronous motor at zero synchronous speed as claimed in any one of claims 1 to 4 are implemented.

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