Encoder position calibration method for synchronous motor

Abstract

The invention relates to an encoder position calibration method for a synchronous motor. The encoder position calibration method comprises the following steps: determining an initial deviation angle by adopting a current control shaft; determining a final deviation angle by adopting D-axis voltage reference measurement; and checking the deviation angle of the encoder. The method has the advantages that the magnetic pole position of the synchronous motor rotor is determined through open-loop turning, the deviation between the encoder position and the magnetic field position of the motor rotor is determined through closed-loop turning, the deviation between the encoder position and the magnetic field position is corrected, and finally the initial position of the encoder is obtained. The detection position is inconsistent with the actual position of the motor rotor; through a mode of determining the rotor magnetic pole position of the synchronous motor through low-speed open-loop turning, the problems of galloping caused by zero crossing of an encoder position due to direct closed-loop turning and confused data calculation are avoided, and the problem of confused data calculation caused by zero crossing of an encoder position detection value is avoided; the method optimizes the steps and flow of the initial position calibration of the encoder, and saves the installation and debugging time of equipment.

Description

Technical Field

[0001] The present invention relates to the field of motor control, and in particular to a method for calibrating the position of an encoder for a synchronous motor. Background Art

[0002] Synchronous motors, with their high power density, high efficiency, and fast dynamic response, are widely used in various high-performance drive systems. Detecting the initial magnetic pole position is a crucial factor in ensuring a smooth synchronous motor startup. Position encoders are typically used to monitor rotor position. However, during initial installation or when the relative mechanical position changes, or at the instant the synchronous motor starts, the position encoder cannot accurately identify and track the rotating magnetic field. This can lead to speed loss, overcurrent, and runaway accidents, necessitating urgent improvements. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for calibrating the position of an encoder for a synchronous motor. When the position encoder is initially installed or replaced, the encoder zero position is calibrated, thereby improving the measurement accuracy of the synchronous motor rotor position and preventing overcurrent and runaway accidents.

[0004] To achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A method for calibrating the position of an encoder for a synchronous motor, comprising:

[0006] S1, using the current control axis to determine the initial offset angle;

[0007] S2, using the D-axis voltage reference measurement to determine the final offset angle;

[0008] S3. Encoder offset angle calibration.

[0009] In S1, the synchronous motor rotates at a low speed in open-loop mode. When a constant current passes through the excitation circuit and armature circuit of the synchronous motor, the current-controlled shaft rotates at a low speed, and the magnetic shaft of the synchronous motor also rotates accordingly. It stops after rotating 360 degrees. At this time, the angle between the current-controlled shaft and the encoder position is the initial offset angle.

[0010] In S2, based on the determined initial offset angle, the D-axis voltage reference is applied, causing the synchronous motor to rotate at high speed in both directions at 85% of the rated speed. When the synchronous motor speed approaches the base speed, the PLC moves the offset angle according to pre-set instructions to retrieve the initial magnetic pole position of the motor rotor. The offset angle at this time is the final offset angle, and the value of this final offset angle is stored in the frequency conversion program.

[0011] In S3, the synchronous motor switches to closed-loop mode and uses an encoder to control the motor speed:

[0012] During closed-loop rotation, observe the encoder position curve and the motor rotor magnetic field position curve to obtain the difference between the two; then subtract the position value detected by the encoder from the motor rotor magnetic field position value to verify the accuracy of the offset angle.

[0013] The synchronous motor is driven by an inverter.

[0014] The current control axis is used to determine the electrical angle of the motor rotor. The current of the three-phase AC power is a vector with a phase difference of 120 degrees. The position of the current control axis is obtained through vector transformation.

[0015] The encoder is mounted directly on the shaft of the synchronous motor.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. An open-loop turntable is used to determine the synchronous motor rotor magnetic pole position, and a closed-loop turntable is used to determine the deviation between the encoder position and the motor rotor magnetic field position. The deviation between the two is corrected to finally obtain the encoder's initial position. This solves the problem of inconsistency between the detected position and the actual position of the motor rotor during the initial installation of the position encoder and after mechanical position changes.

[0018] 2. The method of first determining the synchronous motor rotor pole position by low-speed open-loop rotation avoids the problem of encoder position crossing zero and causing runaway and data calculation confusion caused by direct closed-loop rotation, and avoids the problem of data calculation confusion caused by encoder position detection value crossing zero;

[0019] 3. The steps and processes for encoder initial position calibration have been optimized, saving time for equipment installation and debugging. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the offset angle between the current control axis and the encoder position detection axis.

[0021] Figure 2 This is a schematic diagram of the offset angle between the current control axis and the encoder position detection axis detected after the encoder was replaced;

[0022] Figure 3 This is a schematic diagram of the final measured encoder position offset angle.

[0023] Figure 4 This is the encoder position calibration flow chart.

[0024] Figure 5 This is a schematic diagram of encoder position calibration data tracking.

[0025] Figure 6 It is the encoder position calibration curve analysis.

[0026] Figure 7This is the encoder position calibration control block diagram. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0028] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0029] [Example 1]

[0030] The synchronous motor is driven by an inverter. The encoder is directly mounted on the shaft of the synchronous motor to ensure that the center of the encoder is on the same axis as the axis of the motor shaft, thereby improving the measurement accuracy of the encoder. A method for calibrating the encoder position of a synchronous motor is provided. Figure 4 , the steps are as follows:

[0031] S1, using current control axis to determine the initial offset angle

[0032] The synchronous motor rotates at a low speed in an open-loop mode. When a constant current passes through the excitation circuit and the armature circuit of the synchronous motor, the current-controlled shaft rotates at a low speed, and the magnetic shaft of the synchronous motor also rotates accordingly. It stops after rotating 360 degrees. At this time, the angle between the current-controlled shaft and the encoder position is the initial offset angle, which serves as the reference value for the D-axis voltage reference measurement in step S2. The current-controlled shaft is used to determine the electrical angle of the motor rotor. The current of the three-phase alternating current is a vector with a phase difference of 120 degrees. The position of the current-controlled shaft is obtained through vector transformation.

[0033] S2. Use D-axis voltage reference measurement to determine the final offset angle

[0034] Based on the determined initial offset angle, by applying the D-axis voltage reference, the synchronous motor rotates at high speed in both directions at 85% of the rated speed. When the synchronous motor speed approaches the base speed, the PLC issues a command to move the offset angle to obtain the initial magnetic pole position of the synchronous motor rotor. The offset angle at this time is the final offset angle, and the value of this final offset angle is stored in the frequency conversion program.

[0035] S3, encoder offset angle calibration

[0036] The synchronous motor is switched to closed-loop mode, with an encoder controlling the motor speed. During closed-loop rotation, a real-time trend acquisition tool is used to observe the encoder position curve and the motor rotor magnetic field position curve, calculating the difference between the two. The encoder position value is then subtracted from the synchronous motor rotor magnetic field position value to verify the accuracy of the offset angle.

[0037] See Figure 5 The encoder speed and simulated speed are simultaneously input into the PLC module. The PLC issues a rotation angle command, causing the system to rotate at 60 degrees per second and collect operating curves. This curve analysis sends the results to the speed regulator and also generates the motor electrical speed, motor angle feedback, and motor speed feedback values, which serve as the basic data for encoder position calibration.

[0038] See Figure 6 ,The curve collects the encoder position and the encoder position offset in real time,,providing a basis for the next step of calculating the encoder initial position.

[0039] [Example 2]

[0040] In this embodiment, a method for calibrating the position of an encoder for a synchronous motor is the same as that in embodiment 1, with an additional encoder position calibration process.

[0041] See Figure 1-Figure 7 Synchronous motor control uses the motor's magnetic axis position as the motor's current control axis, while the position detection axis is derived from the position information detected by the position encoder from the magnetic pole installed on the resolver. Since it is impossible to ensure that the current control axis and the position detection axis completely overlap during mechanical installation, there will be an offset angle. If the vehicle is turned when the offset angle is too large, the control torque of the synchronous motor will be unbalanced, and even the motor speed will be out of control. First, the initial offset angle is determined by the current control axis, and then the final offset angle is determined by measuring the D-axis voltage reference. Finally, the parameters in the system application are modified, and a closed-loop turn is implemented to verify the accuracy of the offset angle: During closed-loop turn, the encoder position curve and the motor rotor magnetic field position curve are observed using a real-time trend acquisition tool to obtain the difference between the two. The encoder position value is then subtracted from the motor rotor magnetic field position value to verify the accuracy of the offset angle, which is then stored in the program to complete the encoder position calibration.

[0042] [Example 3]

[0043] In this embodiment, a method for calibrating an encoder position for a synchronous motor is the same as that in Example 1. A data calculation process for detecting zero crossing of the encoder position is added on the basis of Example 1 and / or Example 2 to avoid the problem of data calculation confusion caused by zero crossing of the encoder position detection value. The content is as follows:

[0044] ⑴ Before open-loop transfer, first check whether the parameter values ​​in the transmission file are correct, especially the open-loop angle value, transmission closing, and MD side selection to LOCAL control mode.

[0045] ⑵ Take the real-time trend chart and collect the two curves of Rtr Posn and Tach Posn.

[0046] ⑶Change the ol Id Ref value to 0.3.

[0047] (4) Select Enable open loop in ol cmd sw.

[0048] ⑸Send transfer command: Press ① on the operation panel.

[0049] ⑹ After an estimated one week of transfer, change the ol Id Ref value to 0.

[0050] ⑺Issue a stop command: Press O on the operation panel.

[0051] ⑻Select Disble open loop for ol cmd sw.

[0052] ⑼Observe the trend chart, place the cursor on the same period of the curve, subtract Tach Posn from Rtr Posn, add the marker offset value to the obtained arithmetic value, and send it to the drive.

[0053] (10) When (Rtr Posn-Tach Posn+marker offset)≧360°, it means that the encoder position detection has crossed zero. It is necessary to subtract 360° first and then send the final difference to the transmission.

[0054] The frequency converter adopts the innovation series frequency converter from GE of the United States.

[0055] The present invention adopts an open-loop turntable to determine the magnetic pole position of the synchronous motor rotor, and a closed-loop turntable to determine the deviation between the encoder position and the magnetic field position of the motor rotor, corrects the deviation between the two, and finally obtains the initial position of the encoder, thereby solving the problem of inconsistency between the detected position and the actual position of the motor rotor after the position encoder is initially installed and the mechanical position is changed; by first determining the magnetic pole position of the synchronous motor rotor with a low-speed open-loop turntable, the problem of encoder position zero crossing and runaway, resulting in data calculation confusion, is avoided due to direct closed-loop turntable, and the problem of data calculation confusion caused by the encoder position detection value crossing zero is avoided; the steps and processes of the encoder initial position calibration are optimized, saving the time of equipment installation and debugging.

Claims

1. A method for calibrating the position of an encoder for a synchronous motor, characterized in that: include: S1, using the current control axis to determine the initial offset angle; S2, using the D-axis voltage reference measurement to determine the final offset angle; S3. Encoder offset angle calibration.

2. The method for calibrating the encoder position of a synchronous motor according to claim 1, wherein: In S1, the synchronous motor rotates at a low speed in open-loop mode. When a constant current passes through the excitation circuit and armature circuit of the synchronous motor, the current-controlled shaft rotates at a low speed, and the magnetic shaft of the synchronous motor also rotates accordingly. It stops after rotating 360 degrees. At this time, the angle between the current-controlled shaft and the encoder position is the initial offset angle.

3. The method for calibrating the encoder position of a synchronous motor according to claim 1, wherein: In S2, according to the determined initial offset angle, by applying the D-axis voltage reference, the synchronous motor rotates at high speed in the forward and reverse directions at ()85% of the rated speed. When the speed of the synchronous motor is close to the base speed, the PLC moves the offset angle according to the pre-set instructions to obtain the initial magnetic pole position of the motor rotor. The offset angle at this time is the final offset angle, and the value of this final offset angle is stored in the frequency conversion program.

4. The method for calibrating the position of an encoder for a synchronous motor according to claim 1, wherein: In S3, the synchronous motor switches to closed-loop mode and uses an encoder to control the motor speed: During closed-loop rotation, observe the encoder position curve and the motor rotor magnetic field position curve to obtain the difference between the two; then subtract the position value detected by the encoder from the motor rotor magnetic field position value to verify the accuracy of the offset angle.

5. The method for calibrating the position of an encoder for a synchronous motor according to claim 1, wherein: The synchronous motor is driven by an inverter.

6. The method for calibrating the position of an encoder for a synchronous motor according to claim 1, wherein: The current control axis is used to determine the electrical angle of the motor rotor. The current of the three-phase alternating current is a vector with a phase difference of 120 degrees. The position of the current control axis is obtained through vector transformation.

7. The method for calibrating the position of an encoder for a synchronous motor according to claim 2, wherein: The encoder is directly mounted on the rotating shaft of the synchronous motor.

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