Speed sensorless induction motor wide-speed-range stable operation system and method

Abstract

The present invention relates to a speed sensorless induction motor wide-speed-range stable operation system and a method. According to the system, orthogonal characteristics of a rotor flux linkage are used to correct a voltage model of an induction motor, a rotor flux linkage observer and a stator current extended state observer are established, and a motor observation model is reconstructed; an extended state variable is taken as a feedback item to ensure the stability of rotor flux linkage estimation; and speed information is extracted from the rotor flux linkage estimation by means of phase-locked loop, thereby implementing induction motor sensorless control. The present invention involves a reasonable design, can effectively improve the operation stability of a speed sensorless induction motor in a low-speed power generation mode and a high-speed range, and achieves wide-speed-range sensorless stable control.

Description

System and method for stable operation of speed sensorless induction motor with wide speed regulation range Technical Field

[0001] The present invention belongs to the technical field of motor control, and in particular to a system and method for stable operation of a speed sensorless induction motor with a wide speed regulation range. Background Art

[0002] Sensorless induction motor drive control methods based on motor mathematical models have been successfully implemented in real industrial applications, improving operational reliability in the event of an induction motor speed sensor failure. To meet the evolving needs of induction motor applications, methods for improving sensorless control performance have attracted extensive research interest in recent years. Currently, sensorless induction motors face the following two main challenges:

[0003] (1) Operation stability in the low-speed zone. In the low-speed zone, different sensorless control methods have different stability problems. For the method using the voltage model to estimate the rotor flux, the critical stability of pure integration leads to the integral drift problem. The traditional low-pass filter will cause instability problems when the synchronization frequency is lower than the filter cutoff frequency. For the method that combines the voltage and current models (such as adaptive full-order observers, reduced-order observers, model reference adaptive systems based on stator current, etc.), the instability range is in the low-speed power generation mode. In order to ensure the stability of sensorless control in the low-speed range, it is necessary to study the designed observer structure in the continuous domain / frequency domain to ensure the stability of the observer at different operating points;

[0004] (2) High-speed operational stability. Instability in the high-speed region is often caused by the increase in the imaginary pole of the observer as the induction motor speed increases. This pole may exceed the unit circle in the discrete domain, leading to instability. To ensure the stability of sensorless control in the high-speed range, the designed observer structure needs to ensure its stability in the discrete domain.

[0005] As the demand for sensorless performance in practical industrial applications continues to increase, existing sensorless methods designed only for the rated speed range are not suitable for induction motor applications operating over a wide speed range (for example, induction motors used in cranes or subway traction).

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a speed sensorless induction motor wide speed regulation range stable operation system and method, which can solve the instability problem of the sensorless induction motor in the low speed power generation operation range and the high speed operation range.

[0008] The present invention solves the technical problem by adopting the following technical solutions:

[0009] A speed sensorless induction motor wide speed regulation range stable operation system includes a flux weakening controller, a current controller, a flux observer and a phase-locked loop speed estimator, wherein the flux observer, the phase-locked loop speed estimator, the flux weakening controller and the current controller are connected in sequence, wherein the flux weakening controller adopts a voltage closed-loop flux weakening control strategy to ensure the operation capability of the induction motor in a high-speed flux weakening region, the current controller adopts a proportional integral PI regulator, the flux observer is used to obtain rotor flux, and the phase-locked loop speed estimator is used to extract speed information from the rotor flux estimation to perform sensorless control of the induction motor.

[0010] A method for controlling a speed sensorless induction motor stable operation system with a wide speed regulation range comprises the following steps:

[0011] Step 1: Correct the voltage model in the induction motor mathematical model by using the orthogonal characteristics of the flux linkage;

[0012] Step 2: Based on the motor mathematical model with the corrected orthogonal characteristics, a rotor flux observer and a stator current expansion state observer are constructed, and the control gains of the observers are constructed to obtain the rotor flux;

[0013] Step 3: Extract the speed information from the rotor flux through the phase-locked loop speed estimator, and input the rotor speed information into the field weakening controller and the current controller in sequence to perform sensorless control of the induction motor.

[0014] Moreover, the specific implementation method of step 1 is:

[0015] Among them, i s is the stator current of the induction motor, u s is the stator voltage of the induction motor, R s and R r are the stator and rotor resistances respectively; L s , L r and L m are the self-inductance and mutual inductance of the stator and rotor respectively; λ r is the rotor flux; ω e is the synchronous angular velocity; is the leakage inductance coefficient, and j represents the imaginary part of the complex vector.

[0016] Moreover, the rotor flux observer and the stator current expansion state observer in step 2 are:

[0017] in, is the observer’s estimate of the stator current, is the error value of stator current estimation, f is the expanded state variable of the observer, is the estimated value of the rotor flux, is the estimated value of the synchronous speed, k1, k2 and k3 are the control gains of the observer.

[0018] Moreover, the control gains k1 and k2 of the observer are:

[0019] Where α is the bandwidth of the observer, 1 / T s is the sampling frequency of the system, T s is the sampling time of the system; the gain k3 is:

[0020] Where β is the gain coefficient, ω n is the rated angular velocity of the motor.

[0021] Furthermore, the specific implementation method of step 3 of extracting the speed information from the rotor flux through the phase-locked loop speed estimator is as follows:

[0022] in, is the estimated value of synchronous speed, Δθ is the angle error, ω r is the motor speed, ω sl For slip, is the estimated value of motor speed, i sq is the q-axis current in the synchronous rotating coordinate system, λ rd is the amplitude of the rotor flux.

[0023] The advantages and positive effects of the present invention are:

[0024] This invention utilizes the orthogonal characteristics of the rotor flux to modify the induction motor voltage model, establish a rotor flux observer and a stator current extended state observer, and reconstruct the motor observation model. The extended state variable is used as a feedback term to ensure the stability of the rotor flux estimation. Speed ​​information is extracted from the rotor flux estimate via a phase-locked loop (PLL), enabling sensorless control of the induction motor. This method effectively improves the stability of sensorless induction motors operating in both low-speed power generation mode and high-speed ranges, achieving stable sensorless control over a wide speed range. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a control block diagram of a speed sensorless induction motor stable operation system with a wide speed regulation range according to the present invention;

[0026] FIG2 is a schematic diagram showing the principle of speed estimation using a phase-locked loop according to the present invention;

[0027] FIG3 is an experimental waveform diagram of an existing full-order flux observer method in a low-speed power generation mode according to an embodiment of the present invention;

[0028] FIG4 is a waveform diagram of experimental results of the present invention using the present invention in a low-speed power generation mode according to an embodiment of the present invention;

[0029] FIG5 is a waveform diagram of experimental results using an existing full-order flux observer method in a high-speed operation mode according to an embodiment of the present invention;

[0030] FIG6 is a waveform diagram of experimental results of the present invention in the high-speed operation mode according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with the accompanying drawings.

[0032] The speed sensorless induction motor wide speed regulation range stable operation system, as shown in Figure 1, includes a flux weakening controller, a current controller, a flux observer and a phase-locked loop speed estimator, wherein the flux observer, the phase-locked loop speed estimator, the flux weakening controller and the current controller are connected in sequence. The flux weakening controller adopts a voltage closed-loop flux weakening control strategy to ensure the operation capability of the induction motor in the high-speed flux weakening area. The current controller adopts a proportional integral PI regulator. The flux observer is used to obtain the rotor flux. The phase-locked loop speed estimator uses the PI link to estimate the synchronous speed, and then subtracts the calculated value of the slip speed to obtain the rotor speed.

[0033] A method for controlling a speed sensorless induction motor stable operation system with a wide speed regulation range comprises the following steps:

[0034] Step 1: Modify the voltage model in the induction motor mathematical model through the orthogonal characteristics of the flux linkage.

[0035] The mathematical model expression of the traditional induction motor in the stationary α-β coordinate system is:

[0036] Where i s is the stator current of the induction motor, u s is the stator voltage of the induction motor, R s and R r are the stator and rotor resistances respectively; L s 、L r and L m are the self-inductance and mutual inductance of the stator and rotor respectively; λ r is the rotor flux; ω r is the rotor angular velocity; T r =L r / R r is the rotor time constant, is the leakage inductance coefficient, and j represents the imaginary part.

[0037] The first line of equation (1) represents the voltage model (VM) of the induction motor. In traditional VM-based design methods, the integral drift problem caused by pure integration is common. The second line of equation (1) represents the current model (CM) of the induction motor. In traditional design methods based on the combination of VM and CM, the instability problem of low-speed power generation mode is common. The present invention utilizes the orthogonal characteristics of magnetic flux:

[0038] By improving formula (1), we can get:

[0039] Step 2: Based on the motor mathematical model with the corrected orthogonal characteristics, a rotor flux observer and a stator current expansion state observer are constructed, and the control gain of the observer is constructed to obtain the rotor flux.

[0040] The rotor flux observer and stator current expansion state observer are:

[0041] in, is the observer’s estimate of the stator current, is the error value of stator current estimation, f is the expanded state variable of the observer, is the estimated value of the rotor flux, is the estimated value of the synchronous speed, k1, k2 and k3 are the control gains of the observer.

[0042] The control gains k1 and k2 of the observer are:

[0043] Where α is the bandwidth of the observer, which is selected by the sampling frequency of the system: α = 1 / (20T s ). Among them, 1 / T s represents the sampling frequency of the system, and T s Represents the sampling time of the system.

[0044] The gain k3 is:

[0045] Where β is the gain coefficient, ω n is the rated angular velocity of the motor. β=1.2,ω n =50πrad / s.

[0046] Finally, the forward Euler method is used to discretize Equation (4) to obtain the specific expression applied to discrete control systems:

[0047] Where a = R s / σL s , b=1 / σL s , c=L m / σL s L r ; The subscript (k) represents the kth sampling time, T s Represents the sampling time of the system.

[0048] Step 3: Extract the speed information from the rotor flux through the phase-locked loop speed estimator, and input the rotor speed information into the field weakening controller and the current controller in sequence to perform sensorless control of the induction motor.

[0049] As shown in Figure 2, the amplitude normalization is expressed as:

[0050] The angular error is obtained by linearization of small signals:

[0051] Then use the PI link as a phase-locked loop to make the angle estimation track the angle of the magnetic flux. When Δθ = 0, synchronous speed estimation can be achieved.

[0052] Finally, the rotor speed is obtained by subtracting the calculated value of slip speed from the synchronous speed:

[0053] Among them, i sq is the q-axis current in the synchronous rotating coordinate system, λ rd is the amplitude of the rotor flux. r is the motor speed, ω sl For the slip, is the estimated value of the motor speed.

[0054] According to the above-mentioned speed sensorless induction motor wide speed regulation range stable operation system and method, comparative experiments of the present invention and the traditional method are carried out in low-speed power generation mode and high-speed mode to illustrate the advantages and effects of the present invention.

[0055] Figures 3 and 4 show experimental comparisons of the method of the present invention and the conventional method in a low-speed power generation mode. In the figures, the reference value of the rotor frequency is set to 2 Hz (60 r / min).

[0056] First, a -50% rated load is applied at 4 seconds, and the induction motor operates in sensorless low-speed generating mode. The load torque is then reduced by 10% of the rated load, and the induction motor approaches zero stator frequency with each torque reduction.

[0057] In Figure 3, an existing full-order flux observer method is used. This observer loses stability when the load torque drops to -90% of the rated load.

[0058] In Figure 4, the induction motor is stable at -90% of rated load using the sensorless control method proposed in the present invention. Therefore, compared with existing methods, the method of the present invention has better stability and can extend the stable operating point closer to zero stator frequency.

[0059] Figures 5 and 6 show experimental comparisons of the present invention's method and conventional methods in high-speed operation. In the figures, the rotor frequency reference value is set to 5 Hz (150 rpm). The induction motor's reference frequency is set to 50 Hz at 2 seconds, 100 Hz at 8 seconds, and 150 Hz (three times the rated speed) at 14 seconds.

[0060] Figure 5 shows an existing full-order flux observer method. Judging from the speed estimation waveform, the existing method cannot guarantee the stability of the sensorless system at 150 Hz. Judging from the current estimation waveform, the existing method has poor current estimation accuracy in the high-speed range.

[0061] In Figure 6, the proposed method ensures the stability of the sensorless system at high speeds and significantly improves the current estimation accuracy. More importantly, the proposed observer is implemented using the forward Euler method, avoiding increased complexity.

[0062] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. Speed ​​sensorless induction motor wide speed range stable operation system, characterized by: The invention comprises a flux weakening controller, a current controller, a flux observer and a phase-locked loop speed estimator, wherein the flux observer, the phase-locked loop speed estimator, the flux weakening controller and the current controller are connected in sequence, wherein the flux weakening controller adopts a voltage closed-loop flux weakening control strategy to ensure the operation capability of the induction motor in a high-speed flux weakening area, the current controller adopts a proportional integral PI regulator, the flux observer is used to obtain the rotor flux, and the phase-locked loop speed estimator is used to extract the speed information from the rotor flux estimation to perform sensorless control of the induction motor.

2. A control method for a speed sensorless induction motor wide speed regulation range stable operation system as claimed in claim 1, characterized in that: The following steps are involved: Step 1, modifying the voltage model in the mathematical model of the induction motor by using the orthogonal characteristics of the flux linkage; Step 2: According to the motor mathematical model of the corrected orthogonal characteristics, a rotor flux observer and a stator current expansion state observer are constructed, and the control gain of the observer is constructed to obtain the rotor flux; Step 3: Extract the speed information from the rotor flux through the phase-locked loop speed estimator, and input the rotor speed information into the weak magnetic controller and the current controller in sequence to perform sensorless control of the induction motor.

3. The control method of the speed sensorless induction motor wide speed regulation range stable operation system according to claim 2, characterized in that: The voltage model used in step 1 is: Among them, i s is the stator current of the induction motor, u s is the stator voltage of the induction motor, R s and R r are the stator and rotor resistances respectively; L s , L r and L m are the self-inductance and mutual inductance of the stator and rotor respectively; λ r is the rotor flux; ω e is the synchronous angular velocity; is the leakage inductance coefficient, and j represents the imaginary part of the complex vector.

4. The control method of the speed sensorless induction motor wide speed regulation range stable operation system according to claim 2, characterized in that: The rotor flux observer and the stator current expansion state observer in step 2 are: in, is the observer’s estimate of the stator current, is the error value of stator current estimation, f is the expanded state variable of the observer, is the estimated value of the rotor flux, is the estimated value of the synchronous speed, k1, k2 and k3 are the control gains of the observer.

5. The control method of the speed sensorless induction motor wide speed regulation range stable operation system according to claim 4, characterized in that: The control gains k1 and k2 of the observer are: Where α is the bandwidth of the observer, 1 / T s is the sampling frequency of the system, T s is the sampling time of the system; The gain k3 is: Where β is the gain coefficient, ω n is the rated angular velocity of the motor.

6. The control method of the speed sensorless induction motor wide speed regulation range stable operation system according to claim 2, characterized in that: The specific implementation method of step 3 of extracting the speed information from the rotor flux through the phase-locked loop speed estimator is: in, is the estimated value of synchronous speed, Δθ is the angle error, ω r is the motor speed, ω sl For the slip, is the estimated value of motor speed, i sq is the q-axis current in the synchronously rotating coordinate system, λ rd is the rotor flux The amplitude of .

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