A sensorless control method for a permanent magnet synchronous motor for a press

Abstract

The application discloses a kind of press permanent magnet synchronous motor sensorless control method, specifically relates to motor control technical field, comprising the following steps: step 1: acquisition permanent magnet synchronous motor three-phase current, bus voltage, motor driving state and press operating state;Step 2: the three-phase current of acquisition is carried out coordinate transformation, obtains d-axis current and q-axis current under the rotating coordinate system.The application does not need to configure rotor position sensor, can reduce the manufacturing cost of press system, assembly difficulty and sensor failure risk.Through rotor pre-positioning, open-loop speed-up, back electromotive force observation and closed-loop smooth switching, the stability of motor starting and low-speed operation is improved, and the starting out of step, current impact and torque fluctuation are reduced.According to press load, speed and position estimation error adaptive adjustment control parameter, the operating efficiency, control accuracy and reliability of motor in wide speed range are improved, and the press operation safety is improved through abnormal detection and protection control.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and more specifically, to a sensorless control method for a permanent magnet synchronous motor used in a press. Background Technology

[0002] Presses typically use permanent magnet synchronous motors as drive devices to improve operating efficiency, reduce noise, and reduce equipment size. Existing permanent magnet synchronous motor control methods usually use encoders, rotary transformers, or Hall sensors to obtain rotor position and speed information. However, position sensors increase the manufacturing cost, assembly difficulty, and potential failure points of the press. In environments with high temperature, vibration, oil mist, and electromagnetic interference, sensors may also experience signal drift, failure, or connection failure, affecting the stable operation of the press.

[0003] Existing sensorless control methods mostly rely on back EMF to estimate rotor position. However, the back EMF is weak during compressor startup, low-speed operation, and sudden load changes, which can easily lead to position estimation errors, resulting in startup failure, torque fluctuations, current surges, or loss of synchronization.

[0004] Therefore, there is an urgent need for a sensorless control method for permanent magnet synchronous motors used in presses to solve the above problems. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a sensorless control method for a permanent magnet synchronous motor used in a press. This invention eliminates the need for position sensors, reducing press manufacturing costs, assembly complexity, and sensor failure risks. By combining pre-positioning, open-loop speed increase, back EMF observation, and closed-loop smooth switching, it improves the reliability of position estimation during startup and low-speed phases of the permanent magnet synchronous motor, reducing current surges, torque fluctuations, and startup step loss. By adaptively adjusting the current setpoint and observer parameters based on press load, speed, and estimation error, it improves the press's operational stability, control accuracy, and energy efficiency over load fluctuations and a wide speed range. Furthermore, by establishing an anomaly detection and protection control mechanism, it enhances the safety and reliability of the press system, thereby addressing the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a sensorless control method for a permanent magnet synchronous motor used in a press, comprising the following steps:

[0007] Step 1: Collect the three-phase current, bus voltage, motor drive status, and compressor operating status of the permanent magnet synchronous motor;

[0008] Step 2: Perform coordinate transformation on the collected three-phase currents to obtain the d-axis current and q-axis current in the rotating coordinate system;

[0009] Step 3: During the start-up phase of the permanent magnet synchronous motor, rotor prepositioning control and open-loop speed-up control are used to generate the initial electrical angle and initial electrical angular velocity.

[0010] Step 4: During the open-loop acceleration process, calculate the back EMF estimate based on the motor voltage, current and motor parameters, and use a back EMF observer to obtain the estimated rotor position and estimated rotor speed.

[0011] Step 5: Determine the sensorless closed-loop switching conditions based on the rotor estimated speed, back EMF estimated quantity, and position estimation error;

[0012] Step 6: When the sensorless closed-loop switching condition is met, the control angle is smoothly switched from the open-loop electrical angle to the rotor estimated position, and the permanent magnet synchronous motor is driven by current closed-loop control and speed closed-loop control.

[0013] Step 7: During the sensorless closed-loop operation, the d-axis current setpoint, q-axis current setpoint, and observer parameters are adaptively adjusted based on changes in compressor load, motor speed, and position estimation error.

[0014] Step 8: When an out-of-step, abnormal current, abnormal bus voltage, abnormal speed, or abnormal compressor operation is detected, the system enters the protection control state.

[0015] In a preferred embodiment, the compressor operating status in step 1 includes compressor start / stop status, target speed, exhaust pressure, intake pressure, ambient temperature, operating time, and load level.

[0016] In a preferred embodiment, the rotor pre-positioning control includes applying a d-axis current in a preset direction to the permanent magnet synchronous motor to align the rotor magnetic poles to a preset electrical angle; after the pre-positioning time reaches a preset time threshold, maintaining the preset electrical angle or entering open-loop speed-up control.

[0017] In a preferred embodiment, the open-loop acceleration control includes generating an open-loop electrical angular velocity and an open-loop electrical angle based on a preset start-up curve; adjusting the acceleration of the start-up curve based on the compressor load level, bus voltage, and three-phase current; and reducing the open-loop acceleration or maintaining the current open-loop electrical angular velocity when the q-axis current exceeds a preset current threshold.

[0018] In a preferred embodiment, the back EMF observer calculates the back EMF estimate based on the stator voltage, motor phase current, stator resistance, d-axis inductance, and q-axis inductance, and performs phase tracking of the back EMF estimate through a phase-locked loop to obtain the rotor estimated position and rotor estimated speed.

[0019] In a preferred embodiment, the sensorless closed-loop switching conditions include the rotor estimated speed being greater than a preset switching speed threshold, the back EMF estimated amount being greater than a preset back EMF threshold, the position estimation error being less than a preset error threshold, and the duration of the conditions being greater than a preset stabilization time threshold.

[0020] In a preferred embodiment, the smooth switching includes weighted fusion of the open-loop electrical angle and the estimated rotor position according to a preset transition time; and gradually decreasing the weight of the open-loop electrical angle and gradually increasing the weight of the estimated rotor position during the transition time to generate a control electrical angle.

[0021] In a preferred embodiment, the adaptive adjustment includes adjusting the q-axis current setpoint according to changes in the compressor load to control the motor output torque; adjusting the d-axis current setpoint according to the motor speed and bus voltage to perform field weakening control; and adjusting the gain parameter of the back EMF observer according to the position estimation error and speed fluctuation.

[0022] In a preferred embodiment, the protection control states include speed reduction operation, current limiting operation, shutdown operation, and fault restart; wherein, when the position estimation error continues to exceed the preset step loss threshold, the sensorless closed-loop control is stopped, and the rotor prepositioning control and open-loop speed-up control are re-executed.

[0023] In a preferred embodiment, the current closed-loop control uses a d-axis current regulator and a q-axis current regulator to generate d-axis voltage commands and q-axis voltage commands respectively, and outputs the d-axis voltage commands and q-axis voltage commands to the inverter after coordinate inverse transformation and pulse width modulation to drive the permanent magnet synchronous motor.

[0024] The technical effects and advantages of this invention are as follows:

[0025] This invention eliminates the need for position sensors, reducing manufacturing costs, assembly complexity, and sensor failure risks associated with the press. By combining pre-positioning, open-loop speed increase, back EMF observation, and closed-loop smooth switching, it improves the reliability of position estimation for permanent magnet synchronous motors during startup and low-speed phases, reducing current surges, torque fluctuations, and startup step loss. By adaptively adjusting the current setpoint and observer parameters based on press load, speed, and estimation errors, it enhances the press's operational stability, control accuracy, and energy efficiency across load fluctuations and a wide speed range. Furthermore, by implementing an anomaly detection and protection control mechanism, it improves the safety and reliability of the press system. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a sensorless control method for a permanent magnet synchronous motor used in a press, comprising the following steps:

[0028] Step 1: Collect the three-phase current, bus voltage, motor drive status, and compressor operating status of the permanent magnet synchronous motor;

[0029] Step 2: Perform coordinate transformation on the collected three-phase currents to obtain the d-axis current and q-axis current in the rotating coordinate system;

[0030] Step 3: During the start-up phase of the permanent magnet synchronous motor, rotor prepositioning control and open-loop speed-up control are used to generate the initial electrical angle and initial electrical angular velocity.

[0031] Step 4: During the open-loop acceleration process, calculate the back EMF estimate based on the motor voltage, current and motor parameters, and use a back EMF observer to obtain the estimated rotor position and estimated rotor speed.

[0032] Step 5: Determine the sensorless closed-loop switching conditions based on the rotor estimated speed, back EMF estimated quantity, and position estimation error;

[0033] Step 6: When the sensorless closed-loop switching condition is met, the control angle is smoothly switched from the open-loop electrical angle to the rotor estimated position, and the permanent magnet synchronous motor is driven by current closed-loop control and speed closed-loop control.

[0034] Step 7: During the sensorless closed-loop operation, the d-axis current setpoint, q-axis current setpoint, and observer parameters are adaptively adjusted based on changes in compressor load, motor speed, and position estimation error.

[0035] Step 8: When an out-of-step, abnormal current, abnormal bus voltage, abnormal speed, or abnormal compressor operation is detected, the system enters the protection control state.

[0036] The compressor operating status in step 1 includes compressor start / stop status, target speed, exhaust pressure, intake pressure, ambient temperature, operating time, and load level.

[0037] The rotor pre-positioning control includes applying a d-axis current in a preset direction to the permanent magnet synchronous motor to align the rotor magnetic poles to a preset electrical angle; after the pre-positioning time reaches a preset time threshold, maintaining the preset electrical angle or entering open-loop speed-up control.

[0038] The open-loop acceleration control includes generating an open-loop electrical angular velocity and an open-loop electrical angle based on a preset start-up curve; adjusting the acceleration of the start-up curve based on the compressor load level, bus voltage, and three-phase current; and reducing the open-loop acceleration or maintaining the current open-loop electrical angular velocity when the q-axis current exceeds a preset current threshold.

[0039] The back EMF observer calculates the back EMF estimate based on the stator voltage, motor phase current, stator resistance, d-axis inductance, and q-axis inductance, and performs phase tracking of the back EMF estimate through a phase-locked loop to obtain the rotor estimated position and rotor estimated speed.

[0040] The sensorless closed-loop switching conditions include the rotor estimated speed being greater than a preset switching speed threshold, the back EMF estimated amount being greater than a preset back EMF threshold, the position estimation error being less than a preset error threshold, and the duration of the conditions being greater than a preset stabilization time threshold.

[0041] The smooth switching includes weighted fusion of the open-loop electrical angle and the estimated rotor position according to a preset transition time; and gradually reducing the weight of the open-loop electrical angle and gradually increasing the weight of the estimated rotor position during the transition time to generate the control electrical angle.

[0042] The adaptive adjustment includes adjusting the q-axis current setpoint according to the compressor load change to control the motor output torque; adjusting the d-axis current setpoint according to the motor speed and bus voltage to perform field weakening control; and adjusting the gain parameter of the back EMF observer according to the position estimation error and speed fluctuation.

[0043] The protection and control states include speed reduction operation, current limiting operation, shutdown operation, and fault restart; among them, when the position estimation error continues to exceed the preset step loss threshold, the sensorless closed-loop control is stopped, and the rotor prepositioning control and open-loop speed-up control are re-executed.

[0044] The current closed-loop control uses a d-axis current regulator and a q-axis current regulator to generate d-axis voltage commands and q-axis voltage commands respectively. The d-axis voltage commands and q-axis voltage commands are then output to the inverter after coordinate inverse transformation and pulse width modulation to drive the permanent magnet synchronous motor.

[0045] Example

[0046] Taking a refrigeration compressor as an example, the compressor consists of a three-phase permanent magnet synchronous motor, a three-phase inverter, a controller, a current sampling circuit, a bus voltage sampling circuit, and a compressor status acquisition circuit. The controller can be a digital signal processor, a microcontroller, or an integrated control chip with motor control functions.

[0047] After receiving the start command, the controller first checks the bus voltage, inverter status, three-phase current sampling status, and compressor fault status. If the bus voltage is within the allowable range and no overcurrent or overtemperature fault is detected, the controller enters the motor start-up process.

[0048] During the pre-positioning phase, the controller sets the d-axis current setpoint to the pre-positioning current value, sets the q-axis current setpoint to zero, and outputs the corresponding voltage vector to the inverter. This voltage vector is maintained for a preset time, such as 100ms to 1000ms, to align the permanent magnet synchronous motor rotor poles to the preset initial electrical angle. The pre-positioning current value can be set according to the motor's rated current, the compressor load, and the ambient temperature to avoid excessive current causing motor overheating or compressor mechanical shock.

[0049] After pre-positioning, the controller enters the open-loop acceleration phase. The controller generates open-loop electrical angular velocity and open-loop electrical angle according to a preset start-up curve, gradually increasing the open-loop electrical angular velocity from zero to a preset switching speed. The start-up curve can be a linear acceleration curve, a piecewise acceleration curve, or an S-shaped acceleration curve. During acceleration, the controller collects three-phase current in real time. When the q-axis current exceeds a preset threshold, it indicates a large start-up load on the compressor. The controller then reduces the acceleration or maintains the current speed to prevent the motor from losing synchronization.

[0050] The controller performs Clark and Park transformations on the collected three-phase currents to obtain the d-axis and q-axis currents. Simultaneously, it calculates the back electromotive force (EMF) estimate based on the bus voltage, pulse width modulation duty cycle, motor phase current, stator resistance, and inductance parameters. The back EMF observer filters and performs phase tracking on the estimate, and outputs the estimated rotor position and speed via a phase-locked loop.

[0051] When the rotor's estimated speed reaches the preset switching speed, such as 5% to 15% of the rated speed, and the estimated back EMF is greater than the preset threshold, the position estimation error is within the allowable range, and this condition is maintained for a preset time, the controller determines that the sensorless closed-loop switching conditions are met. The controller does not directly switch the control angle to the estimated angle, but instead performs angle fusion within a preset transition time.

[0052] The control electrical angle can be calculated using the following formula:

[0053] Control electrical angle = (1-k) × open-loop electrical angle + k × estimated rotor position;

[0054] Where k is the switching weight, which gradually increases from 0 to 1 during the transition time. In this way, the control angle continuously transitions from the open-loop electrical angle to the estimated rotor position, reducing current fluctuations and torque abrupt changes during switching.

[0055] After the switch is completed, the controller operates in a sensorless vector control mode. The speed loop generates the q-axis current setpoint based on the difference between the target speed and the estimated rotor speed. The q-axis current is used to adjust the motor output torque. The d-axis current setpoint is usually set to zero or a slightly negative value below the base speed; when the speed is higher than the base speed and the bus voltage is close to the voltage limit, the controller outputs a negative d-axis current to achieve field weakening speed control.

[0056] During stable operation of the press, the controller adjusts the target speed and q-axis current setpoint based on the exhaust pressure, intake pressure, or press load level. When the press load increases, the q-axis current setpoint is increased; when a drop in bus voltage, current approaching the limit, or motor temperature rise is detected, the target speed is decreased or the q-axis current setpoint is limited. Simultaneously, the controller automatically adjusts the phase-locked loop bandwidth, observer gain, or filter parameters based on position estimation errors and speed fluctuations to improve position estimation stability across different speed ranges.

[0057] When the controller detects that the three-phase current exceeds the overcurrent threshold, the bus voltage is abnormal, the deviation between the rotor estimated speed and the commanded speed is continuously too large, the position estimation error exceeds the step loss threshold, or the compressor experiences abnormal exhaust pressure or temperature, it enters the protection control state. The protection control state may include limiting the output torque, reducing the speed, stopping the pulse width modulation output, or re-executing the pre-positioning and startup process after shutdown.

[0058] Through the above control methods, the permanent magnet synchronous motor for the press can achieve start-up, speed increase, stable operation, field weakening speed increase and fault protection without the need for encoders, rotary transformers or Hall position sensors, thereby improving the reliability and economy of the press drive system.

[0059] This invention eliminates the need for position sensors, reducing manufacturing costs, assembly complexity, and sensor failure risks associated with the press. By combining pre-positioning, open-loop speed increase, back EMF observation, and closed-loop smooth switching, it improves the reliability of position estimation for permanent magnet synchronous motors during startup and low-speed phases, reducing current surges, torque fluctuations, and startup step loss. By adaptively adjusting the current setpoint and observer parameters based on press load, speed, and estimation errors, it enhances the press's operational stability, control accuracy, and energy efficiency across load fluctuations and a wide speed range. Furthermore, by implementing an anomaly detection and protection control mechanism, it improves the safety and reliability of the press system.

[0060] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sensorless control method for a permanent magnet synchronous motor used in a press, characterized in that, Includes the following steps: Step 1: Collect the three-phase current, bus voltage, motor drive status, and compressor operating status of the permanent magnet synchronous motor; Step 2: Perform coordinate transformation on the collected three-phase currents to obtain the d-axis current and q-axis current in the rotating coordinate system; Step 3: During the start-up phase of the permanent magnet synchronous motor, rotor prepositioning control and open-loop speed-up control are used to generate the initial electrical angle and initial electrical angular velocity. Step 4: During the open-loop acceleration process, calculate the back EMF estimate based on the motor voltage, current and motor parameters, and use a back EMF observer to obtain the estimated rotor position and estimated rotor speed. Step 5: Determine the sensorless closed-loop switching conditions based on the rotor estimated speed, back EMF estimated quantity, and position estimation error; Step 6: When the sensorless closed-loop switching condition is met, the control angle is smoothly switched from the open-loop electrical angle to the rotor estimated position, and the permanent magnet synchronous motor is driven by current closed-loop control and speed closed-loop control. Step 7: During the sensorless closed-loop operation, the d-axis current setpoint, q-axis current setpoint, and observer parameters are adaptively adjusted based on changes in compressor load, motor speed, and position estimation error. Step 8: When an out-of-step, abnormal current, abnormal bus voltage, abnormal speed, or abnormal compressor operation is detected, the system enters the protection control state.

2. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The compressor operating status in step 1 includes compressor start / stop status, target speed, exhaust pressure, intake pressure, ambient temperature, operating time, and load level.

3. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The rotor pre-positioning control includes applying a d-axis current in a preset direction to the permanent magnet synchronous motor to align the rotor magnetic poles to a preset electrical angle; after the pre-positioning time reaches a preset time threshold, maintaining the preset electrical angle or entering open-loop speed-up control.

4. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The open-loop acceleration control includes generating an open-loop electrical angular velocity and an open-loop electrical angle based on a preset start-up curve; adjusting the acceleration of the start-up curve based on the compressor load level, bus voltage, and three-phase current; and reducing the open-loop acceleration or maintaining the current open-loop electrical angular velocity when the q-axis current exceeds a preset current threshold.

5. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The back EMF observer calculates the back EMF estimate based on the stator voltage, motor phase current, stator resistance, d-axis inductance, and q-axis inductance, and performs phase tracking of the back EMF estimate through a phase-locked loop to obtain the rotor estimated position and rotor estimated speed.

6. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The sensorless closed-loop switching conditions include the rotor estimated speed being greater than a preset switching speed threshold, the back EMF estimated amount being greater than a preset back EMF threshold, the position estimation error being less than a preset error threshold, and the duration of the conditions being greater than a preset stabilization time threshold.

7. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The smooth switching includes weighted fusion of the open-loop electrical angle and the estimated rotor position according to a preset transition time; and gradually reducing the weight of the open-loop electrical angle and gradually increasing the weight of the estimated rotor position during the transition time to generate the control electrical angle.

8. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The adaptive adjustment includes adjusting the q-axis current setpoint according to the compressor load change to control the motor output torque; adjusting the d-axis current setpoint according to the motor speed and bus voltage to perform field weakening control; and adjusting the gain parameter of the back EMF observer according to the position estimation error and speed fluctuation.

9. The sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The protection and control states include speed reduction operation, current limiting operation, shutdown operation, and fault restart; among them, when the position estimation error continues to exceed the preset step loss threshold, the sensorless closed-loop control is stopped, and the rotor prepositioning control and open-loop speed-up control are re-executed.

10. A sensorless control method for a permanent magnet synchronous motor for a press according to claim 1, characterized in that: The current closed-loop control uses a d-axis current regulator and a q-axis current regulator to generate d-axis voltage commands and q-axis voltage commands respectively. The d-axis voltage commands and q-axis voltage commands are then output to the inverter after coordinate inverse transformation and pulse width modulation to drive the permanent magnet synchronous motor.