Asynchronous motor rotor resistance online correction method

Abstract

The invention relates to an asynchronous motor rotor resistance on-line correction method. The method comprises the following steps: firstly, calculating slip frequency of a voltage model and a current model; judging whether a rotor resistance correction coefficient is updated or not according to the motor synchronous frequency omegasgt, the voltage model threshold omegath and the motor torque current iphi2gt and the threshold Ith; if yes, a correction coefficient is calculated according to the slip frequency of the voltage model and the current model, and otherwise, the coefficient stored in the last period is adopted; updating the rotor resistance according to the correction coefficient, and storing the current period coefficient; and updating a current model according to the corrected rotor resistance, and performing motor vector control. The characteristic that the orientation of the voltage model in the high-speed area is accurate is utilized, the slip frequency calculated by the voltage model and the slip frequency calculated by the current model are compared to obtain the rotor resistance correction coefficient, online correction of the rotor resistance is achieved, the high torque control precision requirement of the current model area and the torque calculation consistency of the current model and the voltage model are guaranteed, and the reliability of the rotor resistance is improved. And torque fluctuation caused by model switching is reduced.

Description

Technical Field

[0001] This invention belongs to the field of motor control technology, and in particular to a method for online correction of rotor resistance of an asynchronous motor. Background Technology

[0002] With the development of industrial applications, the requirements for the control performance of asynchronous motors are becoming increasingly stringent. Indirect vector control is a widely used vector control method for asynchronous motors. However, it uses a current model in the low-speed range, making its torque control accuracy susceptible to the influence of rotor resistance.

[0003] Rotor resistance is typically obtained using offline identification methods. In practical applications, rotor resistance is easily affected by temperature changes and the skin effect. If the rotor resistance is not corrected, it will lead to errors in slip calculation, which in turn will cause deviations in the magnetic field positioning angle, affecting the accuracy of torque output.

[0004] There are many methods for online rotor resistance correction, mainly including: 1) Parameter adaptive method, which is further divided into torque method, reactive power method, voltage method, etc. The main drawback is that the compensation effect varies greatly under different load conditions; 2) Some literature proposes the Kalman filter observer method to achieve adaptive observation of rotor time constant. This method has strong anti-noise performance, but the amount of calculation is large and it is difficult to implement.

[0005] Therefore, those skilled in the art urgently need a method for identifying the rotor resistance of asynchronous motors to solve the problems of poor accuracy and high complexity in online identification. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and propose an online correction method for the rotor resistance of an asynchronous motor, which is easy to implement in industrial applications and has high accuracy.

[0007] The technical problem solved by this invention is achieved through the following technical solution: A method for online correction of rotor resistance of an asynchronous motor includes the following steps: Step 1: Obtain the voltage model slip angular frequency based on the voltage model back EMF regulator; calculate the current model slip angular frequency. Step 2: Determine the real-time operating status. If the motor synchronization frequency is met... oh s Voltage model threshold oh th and motor torque current i Ф2 Motor torque and current threshold I th If so, then the current state is under voltage model load conditions; Step 3: If the conditions in Step 2 are met, calculate the rotor resistance correction coefficient.k = / If step 2 is not satisfied, then the rotor resistance correction coefficient k adopts the value of the previous period. k prev； Step 4: Calculate the rotor resistance correction value R r ′= k ⋅ R r0 And save the rotor correction coefficients. k prev =k ; Step 5: Perform vector control of the asynchronous motor based on the newly calculated rotor resistance.

[0008] Furthermore, the specific implementation method of step 1 is as follows: using the back electromotive force Ф1 axis component. Perform PI control to obtain the voltage model slip angular frequency. The synchronous frequency of the motor was calculated. oh s =Δ oh UM +ω r in, oh s Δ is the synchronous frequency of the motor. oh UM slip angular frequency, oh r Motor encoder speed; Calculate the back electromotive force:

[0009]

[0010] in, and These are the α and β axis components of the stationary coordinate system for the back electromotive force, respectively; and These are the stationary coordinate system components α and β of the output motor voltage, respectively. and Let α and β be the stationary coordinate system components of the stator current, respectively; Lo is the leakage inductance value; R s Stator resistance value, rotor flux linkage In space at synchronous frequency Rotation, with an angle of α with the stator α axis f s.UM1 The Ф1 axis is oriented in the rotor flux linkage superior, f s.UM1 The calculation method is as follows:

[0011]

[0012] in, and These are the back electromotive force components along the Ф1 and Ф2 axes, respectively. For rotor flux linkage, when the reference vector is directed to the rotor flux linkage, the back electromotive force is... =0, construct the closed-loop regulator of the phase-locked loop (PLL), and input the actual value of the back electromotive force to the regulator. With the back EMF set to 0, the regulator output serves as the slip frequency. The regulator adjusts its output value according to the direction of the actual synchronous frequency, ensuring that the actual flux linkage is aligned with the rotor flux linkage when the rotational speed is in the forward and reverse directions, thus obtaining an accurate slip angular frequency. .

[0013] Slip angular frequency of the current model The calculation formula is as follows:

[0014] Among them, △ The slip angular frequency, For mutual inductance, R r For rotor resistance, For rotor inductance, For rotor flux linkage, Torque current Furthermore, the specific implementation method of step 2 is as follows: determine the real-time operating status, and if the motor synchronization frequency is satisfied... oh s Voltage model threshold oh th and motor torque current i Ф2 Motor torque and current threshold I th .

[0015] Furthermore, the specific implementation method of step 3 is as follows: the voltage model slip angular frequency is... With current model slip angular frequency The ratio is used as the rotor correction coefficient k: k = /

[0016] Furthermore, the specific implementation method of step 4 is as follows: the corrected rotor resistance R r ′= k ⋅ Rr0 ; in, R r0 This is the initial nominal rotor resistance value.

[0017] Rotor resistance correction coefficient k Save to k prev Furthermore, the specific implementation method of step 5 is as follows: The corrected... Rr Substitute the slip calculation formula into the current model and recalculate the slip angular frequency. and magnetic field orientation control: ,in L m Main inductor, L r This is the total rotor inductance.

[0018] The advantages and positive effects of this invention are: 1. This invention calculates the slip angular frequency of the voltage model; determines the real-time operating conditions, and if the motor synchronization frequency is satisfied... oh s Voltage model threshold oh th and motor torque current i Ф2 Motor torque and current threshold I th If the rotor resistance correction coefficient is not satisfied, the current model is updated based on the rotor resistance correction coefficient, and vector control of the asynchronous motor is performed. If the storage of historical data is not satisfied, the correction coefficient of the previous cycle is saved. k prev The current model is updated for asynchronous motor vector control. This invention utilizes the relatively accurate orientation of the voltage model in the high-speed region, comparing the slip calculated by the voltage model with that calculated by the current model to obtain the rotor resistance correction coefficient, thus achieving online correction of the rotor resistance. R r This ensures high torque control accuracy in the current model region and guarantees consistency between the torque calculations of the current model and the voltage model, reducing torque fluctuations caused by model switching.

[0019] 2. This invention updates the rotor resistance correction coefficient only under high-confidence operating conditions (high-speed heavy load, i.e., when the synchronous frequency is determined to be in the voltage model and the torque current is greater than the threshold value). k This avoids noise interference from the voltage model at low speeds or low torque, making the correction coefficients more accurate.

[0020] 3. This invention uses the real-time operating condition as the current rotor resistance update condition and uses the comparison between the voltage model and the current model to correct the rotor resistance. It can be directly embedded into the existing vector control system, with low computational load and easy implementation. Attached Figure Description

[0021] Figure 1 This is a flowchart of the online rotor resistance correction process of the present invention; Figure 2 This is a schematic diagram illustrating the principle of calculating the slip angular frequency of the voltage model in this invention. Figure 3 This is a vector diagram of the motor model of the present invention; Figure 4 This is a schematic diagram illustrating the calculation of torque values ​​using the current and voltage models of this invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] An online correction method for the rotor resistance of an asynchronous motor, such as Figure 1 As shown, it includes the following steps: Step 1: Obtain the voltage model slip angular frequency based on the voltage model back EMF regulator; calculate the current model slip angular frequency.

[0024] Using the back electromotive force Ф1 axis component Perform PI control to obtain the voltage model slip angular frequency. The synchronous frequency of the motor was calculated. oh s =Δ oh UM +ω r in, oh s Δ is the synchronous frequency of the motor. oh UM slip angular frequency, oh r Motor encoder speed; Calculate the back electromotive force:

[0025]

[0026] in, and These are the α and β axis components of the stationary coordinate system for the back electromotive force, respectively; and These are the stationary coordinate system components α and β of the output motor voltage, respectively. and Let α and β be the stationary coordinate system components of the stator current, respectively; Lo is the leakage inductance value; R s Stator resistance value, rotor flux linkage In space at synchronous frequency Rotation, with an angle of α with the stator α axis f s.UM1 The Ф1 axis is oriented in the rotor flux linkage superior, f s.UM1 The calculation method is as follows:

[0027]

[0028] in, and These are the back electromotive force components along the Ф1 and Ф2 axes, respectively. For rotor flux linkage, when the reference vector is directed to the rotor flux linkage, the back electromotive force is... =0, construct the closed-loop regulator of the phase-locked loop (PLL), and input the actual value of the back electromotive force to the regulator. With the back electromotive force set to 0, the regulator output is used as the slip frequency; for example... Figure 2 As shown, the regulator adjusts its output value according to the positive and negative directions of the actual synchronous frequency, thereby ensuring that the actual magnetic flux is aligned with the rotor magnetic flux when the speed is in the forward and reverse directions, thus obtaining an accurate slip angular frequency. .

[0029] Slip angular frequency of the current model The calculation formula is as follows:

[0030] Among them, △ The slip angular frequency, For mutual inductance, R r For rotor resistance, For rotor inductance, For rotor flux linkage, Torque current Among the above parameters L m and L r It can be obtained using offline identification methods and is less affected by temperature; It can be obtained by sampling the current and then performing a vector rotation.

[0031] Step 2: Determine the real-time operating status. If the motor synchronization frequency is met... oh s Voltage model threshold oh th and motor torque currenti Ф2 Motor torque and current threshold I th Then it is the voltage model load mode.

[0032] Condition 1: Motor synchronization frequency oh s > oh th ( oh th For the voltage model threshold, take oh th =10% oh n ,in oh n (Rated frequency of the motor); Condition 2: Motor torque current i Ф2 > I th ( i Ф2 This is the actual value. I th As the threshold, take I th =10% I n， in I n (This refers to the motor's rated current).

[0033] The conditions for updating the rotor resistance correction coefficient are considered met only if both conditions 1 and 2 are satisfied.

[0034] Step 3: Calculate the rotor resistance correction coefficient.

[0035] If the conditions in step 2 are met, then the slip angular frequency of the voltage model will be... With current model slip angular frequency The ratio is used as the rotor correction coefficient k: k = /

[0036] If the conditions in step 2 are not met, then adopt... k = k prev Step 4, Corrected rotor resistance R r ′= k ⋅ R r0 ;in, R r0 This is the initial nominal rotor resistance value.

[0037] And save the correction coefficients. k prev = k Step 5: Update the current model based on the rotor resistance correction coefficient and perform vector control of the asynchronous motor.

[0038] Corrected Rr Substitute the slip calculation formula into the current model and recalculate the slip angular frequency. and magnetic field orientation control: ,in L m Main inductor, L r This is the total rotor inductance.

[0039] This invention is based on the fact that both the current model and the voltage range satisfy the relationship that the motor synchronous frequency = rotor speed + slip speed.

[0040] This method employs a current model for motor control at low speeds, calculating slip based on rotor resistance and incorporating it into the magnetic field angle orientation calculation. At high speeds, a voltage model is used for motor control calculations, calculating the slip angular frequency by constructing a phase-locked loop-like adjustment system, which also contributes to the magnetic field angle orientation. Simultaneously, the current model is run in real-time at high speeds to calculate slip, and the slip calculated using both the voltage and current models is compared to calculate the rotor resistance correction coefficient. k The final coefficient is adopted. k Online correction of rotor resistance R r .

[0041] The slip angular frequency of the current model described in step 1 The calculation formula is as follows:

[0042] Among them, △ The slip angular frequency, For mutual inductance, R r For rotor resistance, For rotor inductance, For rotor flux linkage, Torque current Among the above parameters L m and L r It can be obtained using offline identification methods and is less affected by temperature; It can be obtained by sampling the current and then performing a vector rotation.

[0043] It can be calculated based on the current and the motor, where the rotor flux linkage calculation formula is as follows:

[0044] The voltage model calculation slip described in step 1 The derivation of the calculation formula is as follows: In the voltage model range The calculation formula is as follows:

[0045] in, The Ф2-axis component of the back electromotive force. This is the synchronization frequency.

[0046] The formula for calculating back electromotive force is as follows:

[0047]

[0048] in, and These are the α and β axis components of the stationary coordinate system for the back electromotive force, respectively; and These are the stationary coordinate system components α and β of the output motor voltage, respectively. and These are the α and β axis components of the stator current in the stationary coordinate system, respectively. This is the leakage inductance value.

[0049] Rotor flux In space at synchronous frequency Rotation, with an angle of α with the stator α axis f s From vector Figure 3 It is concluded that, due to the orientation of the Ф1 axis in Above, therefore there is

[0050]

[0051] Within the voltage model range, to ensure controlled flux linkage, a vector control system oriented according to rotor flux linkage is employed. This is based on the back electromotive force calculation formula and vector... Figure 3 It can be seen that when the reference vector is oriented onto the rotor flux linkage, =0. Therefore, by constructing a closed-loop PI controller similar to a phase-locked loop (PLL), the regulation is achieved. =0 achieves rotor flux orientation, and the regulator output serves as the slip angular frequency, such as Figure 2 As shown.

[0052] according to Figure 2 and Figure 3As shown, when When the value is greater than 0, it indicates that the actual magnetic flux linkage of the motor leads the rotor magnetic flux linkage, and that the synchronous frequency ω is greater than 0. s Faster, thus causing angle φ s Leading, when the synchronization frequency ω s When the value is greater than 0, the regulator input is negative, reducing the positive slip value; when the synchronization frequency ω s When the value is less than 0, the regulator input is positive, reducing the negative slip value. Through this adjustment, the synchronization frequency ω is adjusted. s Slowing down, thus the actual flux linkage value moves closer to the rotor flux linkage, and the actual angle moves towards... f s The reference vector is moved closer until it is aligned with the rotor flux linkage. Conversely, it is moved further away. By properly setting the PI parameters of the regulator, the reference vector can be quickly positioned onto the rotor flux linkage, ensuring the accuracy of the magnetic field orientation angle and the accuracy of the voltage model slip calculation.

[0053] The selection of the judgment conditions in step 2 mainly considers the following factors: (The above derivation includes...) , , and Leakage inductance can be obtained through sampling and static coordinate system transformation; L o The changes in the motor's operating conditions over a long period of time are almost negligible; R s The stator resistance changes with temperature. As can be seen from the above calculation formula, in the medium and high speed range, the stator resistance... R s The reduced proportion of the voltage drop component has a negligible impact on the calculated back electromotive force. Therefore, to ensure accurate magnetic field orientation, the voltage model must be enabled only after reaching a certain speed threshold, thus minimizing the influence of stator resistance variations on orientation. Based on the analysis of error influencing factors in both the current and voltage models, a general approach is taken... oh th =10% oh n This serves as a switching point between the two models.

[0054] At low torque, noise in the sampled current can cause significant fluctuations in the slip values ​​of both the voltage and current models. Therefore, rotor resistance correction is only initiated after the torque current exceeds a certain value. Considering that the calculated slip value is very small, typically less than 3%, even a small current error can lead to a large slip calculation error. Therefore, taking into account factors such as the accuracy of slip calculation and the applicability of rotor resistance under light loads, a torque current threshold I can be set. th 10%I n (I n (Rated current).

[0055] Steps 3 and 4 are implemented with the following considerations: When the motor is running in the voltage model range, the rotor resistance correction coefficient is obtained in real time by comparing the slip calculated by the voltage model and the slip calculated by the current model. When the motor runs in the low-speed current model range, the rotor correction coefficient is latched and the rotor resistance is corrected using the latched value. The corrected rotor resistance is then applied to the low-speed current model region, thereby ensuring the accuracy of slip and torque calculation in the low-speed current model region, as well as the smoothness of torque switching between the current model region and the voltage model region, and preventing torque fluctuations.

[0056] Experimental verification was conducted on the trailer unit in the laboratory. The trailer unit consisted of two motors connected by a coupling, with a torque sensor installed in between. The motor under test operated in torque control mode, while the auxiliary motor drove it to operate within the current model and voltage model ranges. The consistency of torque between the two model regions was observed. The unit was run for an extended period, and the torque consistency between the two model regions was also observed under both cold and hot motor conditions. The experimental results are as follows: Figure 4 As shown in the experimental comparison, after long-term operation using the rotor resistance value identified offline, the torque in the current model and voltage model regions will have a difference. After the rotor resistance is corrected online using this method, the torque in the current model and voltage model are basically consistent, ensuring the smoothness of torque changes during acceleration / deceleration.

[0057] It should be emphasized that the embodiments described in this invention are illustrative and not limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementation methods derived by those skilled in the art based on the technical solutions of this invention also fall within the scope of protection of this invention.

Claims

1. A method for online correction of rotor resistance of an asynchronous motor, characterized in that: Includes the following steps: Step 1: Obtain the voltage model slip angular frequency Δ based on the output of the voltage model back EMF regulator. ω UM And calculate the slip angular frequency Δ of the current model. ω IM ; Step 2: Determine the motor's operating status and synchronous frequency. ω s Voltage model threshold ω th and motor torque current i Ф2 Motor torque and current threshold I th Then the voltage model load condition is satisfied; Step 3: If the conditions in Step 2 are met, calculate the rotor resistance correction coefficient. k = / If step 2 is not satisfied, then the rotor resistance correction coefficient k adopts the value of the previous period. k prev ; Step 4: Calculate the rotor resistance correction value R r ′= k ⋅ R r0 And save the rotor correction coefficients. k prev =k ; Step 5: Perform vector control of the asynchronous motor based on the newly calculated rotor resistance.

2. The method for online correction of rotor resistance of an asynchronous motor according to claim 1, characterized in that: The specific implementation method of step 1 is as follows: using the back electromotive force Ф1 axis component. Perform PI control to obtain the voltage model slip angular frequency. The synchronous frequency of the motor was calculated. ω s =D ω UM +oh r in, ω s Δ is the synchronous frequency of the motor. ω UM slip angular frequency, ω r Motor encoder speed; Calculate the back electromotive force: ； ； in, and These are the α and β axis components of the stationary coordinate system for the back electromotive force, respectively; and These are the stationary coordinate system components α and β of the output motor voltage, respectively. and Let α and β be the stationary coordinate system components of the stator current, respectively; Lo is the leakage inductance value; R s Stator resistance value, rotor flux linkage In space at synchronous frequency Rotation, with an angle of α with the stator α axis φ s.UM1 The Ф1 axis is oriented in the rotor flux linkage superior, φ s.UM1 The calculation method is as follows: ； ； in, and These are the back electromotive force components along the Ф1 and Ф2 axes, respectively. For rotor flux linkage, when the reference vector is directed to the rotor flux linkage, the back electromotive force is... =0, construct the closed-loop regulator of the phase-locked loop (PLL), and input the actual value of the back electromotive force to the regulator. With the back EMF set to 0, the regulator output serves as the slip frequency. The regulator adjusts its output value according to the direction of the actual synchronous frequency, ensuring that the actual flux linkage is aligned with the rotor flux linkage when the rotational speed is in the forward and reverse directions, thus obtaining an accurate slip angular frequency. .

3. The method for online correction of rotor resistance of an asynchronous motor according to claim 1, characterized in that: The specific implementation method of step 3 is as follows: if the operating state judgment condition of step 2 is met, then the voltage model slip angular frequency is... With current model slip angular frequency The ratio is used as the rotor correction coefficient k: k = / ； Corrected rotor resistance R r ′= k ⋅ R r0 ; in, R r0 The initial nominal rotor resistance value is used. If the operating status judgment condition in step 2 is not met, the value recorded when the condition was met in the previous cycle will be used instead. k prev Assign to k。 4. The method for online correction of rotor resistance of an asynchronous motor according to claim 1, characterized in that: The specific implementation method of step 4 is as follows: the corrected rotor resistance R r ′= k ⋅ R r0 ,in R r0 This is the initial nominal rotor resistance value; Rotor resistance correction coefficient k Save to k prev ,Right now k = k prev .

5. The method for online correction of rotor resistance of an asynchronous motor according to claim 1, characterized in that: The specific implementation method of step 5 is as follows: The corrected... Rr Substitute the slip calculation formula into the current model and recalculate the slip angular frequency. and magnetic field orientation control: ,in L m Main inductor, L r This is the total rotor inductance.

Images