A sensorless controller for a permanent magnet synchronous motor of an air compressor

Abstract

The application discloses a kind of air compressor permanent magnet synchronous motor sensorless controller, specifically relates to air compressor motor control technical field, including controller shell, signal acquisition unit, signal processing unit, rotor state estimation unit, starting control unit, current control unit, modulation output unit, parameter adaptive unit, fault protection unit and control communication unit, the controller shell both ends are respectively provided with back cover and front cover.The application does not need to set rotor position and speed sensor, reduces the assembly components and failure point of air compressor motor, reduces manufacturing and maintenance cost.Through initial position identification, open-loop starting, closed-loop smooth switching and rotor state estimation, improve the starting success rate and operating stability of motor under the condition of residual pressure and load mutation.Through parameter adaptation, confidence evaluation and hierarchical protection, improve control accuracy, safety and reliability under low speed, high temperature and complex working conditions.

Description

Technical Field

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

[0002] Permanent magnet synchronous motors are characterized by high power density, high operating efficiency and good speed regulation performance. They are widely used in screw air compressors, scroll air compressors and other variable frequency compression equipment. Existing permanent magnet synchronous motors usually obtain rotor position and speed information through encoders, Hall sensors or rotary transformers to achieve closed-loop control.

[0003] However, air compressors typically contain complex factors such as oil and gas, dust, vibration, temperature changes, and electromagnetic interference. Rotor position sensors and their connecting lines are prone to aging, loosening, moisture, or signal abnormalities, increasing system costs and assembly difficulty, and reducing equipment reliability. In addition, traditional sensorless control methods have weak back electromotive force when the motor is stationary, starting at low speed, or experiencing sudden load changes, making it difficult to accurately estimate rotor position and speed. This can easily lead to problems such as reverse startup, loss of synchronization, current surges, torque fluctuations, and abnormal compressor shutdowns.

[0004] Therefore, there is an urgent need for a sensorless controller for permanent magnet synchronous motors used in air compressors 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 controller for a permanent magnet synchronous motor in an air compressor. By incorporating a parameter adaptive unit, a fault protection unit, and a control communication unit, the present invention eliminates the need for rotor position and speed sensors, reducing the manufacturing, assembly, and maintenance costs of the air compressor motor system. Through rotor initial position identification, orientation positioning, open-loop speed-up, and closed-loop smooth switching, the invention improves the motor's start-up success rate and reduces reverse rotation, step loss, and current surges. By integrating voltage, current, bus voltage, and air compressor operating status, and employing parameter adaptation and estimation confidence evaluation, the invention enhances control accuracy and stability under low-speed, variable load, and high-temperature environments. Furthermore, through fault identification, current limiting, load reduction, and shutdown protection, the invention improves the air compressor's operational safety and the controller's reliability, 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 controller for a permanent magnet synchronous motor in an air compressor, comprising a controller housing, a signal acquisition unit, a signal processing unit, a rotor state estimation unit, a start control unit, a current control unit, a modulation output unit, a parameter adaptive unit, a fault protection unit, and a control communication unit. The controller housing has a rear cover and a front cover at both ends, respectively. Mounting screws are provided between the rear cover and the front cover and the controller housing, and the rear cover and the front cover are fixedly connected to the controller housing by the mounting screws. A terminal block is provided on the front cover. Mounting flanges are provided at the bottom of both the rear cover and the front cover, and mounting holes are provided through both sides of the mounting flanges. Heat dissipation fins are provided on the outer side of the controller housing.

[0007] The signal acquisition unit is used to acquire phase current, phase voltage, DC bus voltage, power module temperature, and air compressor operating status signals of the permanent magnet synchronous motor.

[0008] The signal processing unit is used to filter, bias correct, outlier remove, and perform analog-to-digital conversion on the signal output by the signal acquisition unit.

[0009] The rotor state estimation unit is used to estimate the rotor position, speed, back electromotive force and load state of the permanent magnet synchronous motor based on the motor voltage, current and motor mathematical model.

[0010] The start control unit is used to perform rotor initial position identification, orientation positioning, open-loop speed increase and closed-loop switching control when the permanent magnet synchronous motor is stationary or at low speed.

[0011] The current control unit is used to decouple the excitation current and torque current of the permanent magnet synchronous motor based on the rotor state estimation results.

[0012] The modulation output unit is used to generate a pulse width modulation signal according to the voltage command output by the current control unit, and control the power switching device to drive the permanent magnet synchronous motor to run.

[0013] The parameter adaptive unit is used to correct the control parameters based on motor speed, load changes, estimation errors and operating temperature.

[0014] The fault protection unit is used to perform current limiting, load reduction, shutdown or fault alarm based on detected overcurrent, overvoltage, undervoltage, overtemperature, stall, loss of synchronization, estimation abnormality and communication abnormality.

[0015] The intelligent control module obtains rotor position and speed information through the rotor state estimation unit during the operation of the permanent magnet synchronous motor.

[0016] The control communication unit is used to interact with the air compressor main controller, pressure sensor, temperature sensor or host computer, receive start / stop commands, target pressure, target speed and operating mode commands, and output actual speed, output power, motor temperature, estimated confidence level, fault status and protection status.

[0017] In a preferred embodiment, the signal acquisition unit includes a DC bus voltage acquisition channel located on the inverter input side, at least two phase current acquisition channels located on the inverter output side, and a temperature acquisition channel for acquiring the power module temperature; the signal acquisition unit is also used to acquire status signals such as the air compressor start / stop command, target pressure, actual pressure, exhaust temperature, oil and gas temperature, and operating mode.

[0018] In a preferred embodiment, the rotor state estimation unit includes a stationary coordinate system voltage-current transformation module, a flux linkage observation module, a back electromotive force (EMF) calculation module, a rotor position calculation module, a speed calculation module, and an error correction module. The stationary coordinate system voltage-current transformation module converts the acquired three-phase voltage and three-phase current into two-phase stationary coordinate system voltage and current. The flux linkage observation module estimates the stator flux linkage based on a voltage model, a current model, or a voltage-current hybrid model. The back EMF calculation module calculates the back EMF based on the stator flux linkage and current changes. The rotor position calculation module calculates the rotor position based on the back EMF, flux linkage direction, or high-frequency response characteristics. The speed calculation module calculates the rotor speed based on the rotor position changes in adjacent control cycles. The error correction module corrects the estimation results based on current observation errors, back EMF residuals, and the consistency of speed changes.

[0019] In a preferred embodiment, the start-up control unit includes a rotor initial position identification module, a rotor positioning module, an open-loop speed-up module, and a closed-loop switching module. The rotor initial position identification module is used to apply a test voltage vector with a preset direction and amplitude to the permanent magnet synchronous motor and identify the initial position of the rotor magnetic poles based on the difference in current response. The rotor positioning module is used to orient the stator magnetic field to the identified rotor initial position so that the rotor is kept within a preset electrical angle range. The open-loop speed-up module is used to drive the motor to speed up according to a preset frequency curve and voltage amplitude curve. The closed-loop switching module is used to switch the open-loop control to closed-loop control based on the estimated rotor position when the back electromotive force is effective, the estimation error is less than a preset threshold, and the speed reaches the switching speed.

[0020] In a preferred embodiment, the start control unit determines the start current, rotor positioning time, open-loop acceleration slope, and closed-loop switching speed based on at least one of the following parameters: air compressor downtime, exhaust pressure, compression chamber pressure, target speed, ambient temperature, and motor temperature.

[0021] In a preferred embodiment, the current control unit includes a coordinate transformation module, a torque current controller, an excitation current controller, a voltage feedforward module, and a current limiting module. The coordinate transformation module converts the motor current into excitation current and torque current based on the estimated rotor position. The torque current controller generates a target torque current based on the difference between the target speed and the estimated speed. The excitation current controller generates a target excitation current based on the motor operating speed, bus voltage, and load status. The current limiting module limits the target excitation current and target torque current based on the motor rated current, power module temperature, bus voltage, and air compressor load.

[0022] In a preferred embodiment, the parameter adaptive unit corrects the control parameters online based on data such as the estimated values ​​of motor stator resistance, motor inductance, permanent magnet flux linkage, speed estimation error, current loop tracking error, and motor and power module temperatures. The control parameters include the current loop proportional coefficient, current loop integral coefficient, observer gain, speed loop gain, back EMF filter coefficient, start-up acceleration slope, and closed-loop switching threshold.

[0023] In a preferred embodiment, the fault protection unit judges changes in current, bus voltage, temperature, estimation error, and speed through multiple consecutive control cycles to distinguish between instantaneous disturbances, general abnormalities, and serious faults. When an instantaneous overcurrent or short-term estimation error is detected, the fault protection unit reduces the torque current command or temporarily freezes map parameter updates. When a continuous overcurrent, bus overvoltage, power module overtemperature, rotor step loss, or stall is detected, the fault protection unit stops the pulse width modulation signal output and generates a corresponding fault code.

[0024] In a preferred embodiment, the rotor state estimation unit is provided with an estimation confidence evaluation module. The estimation confidence evaluation module calculates the positioning confidence based on at least two of the following: back EMF amplitude, dot product residual, flux change rate, current tracking error, estimated speed continuity, and voltage utilization rate. When the positioning confidence is higher than a first threshold, closed-loop control is performed using the back EMF observation results. When the positioning confidence is between the first and second thresholds, the weights of the inertial model, speed smoothing model, or current model are increased. When the positioning confidence is lower than the second threshold, load reduction control, re-estimation, open-loop auxiliary control, or shutdown protection are executed.

[0025] The technical effects and advantages of this invention are as follows:

[0026] This invention, by incorporating a parameter adaptive unit, a fault protection unit, and a control communication unit, eliminates the need for rotor position and speed sensors, thereby reducing the manufacturing, assembly, and maintenance costs of the air compressor motor system. Through rotor initial position identification, orientation positioning, open-loop speed increase, and closed-loop smooth switching, it improves the motor's start-up success rate and reduces reverse rotation, step loss, and current surges. By integrating voltage, current, bus voltage, and air compressor operating status, and employing parameter adaptation and estimation confidence evaluation, it enhances control accuracy and stability under low-speed, variable load, and high-temperature environments. Furthermore, through fault identification, current limiting, load reduction, and shutdown protection, it improves the air compressor's operational safety and the controller's reliability. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0028] Figure 2 This is a schematic diagram of the system of the present invention.

[0029] The attached diagram is labeled as follows: 1. Controller housing; 2. Rear cover; 3. Front cover; 4. Mounting screw; 5. Terminal block; 6. Mounting flange; 7. Mounting hole; 8. Heat sink fins. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0031] As attached Figure 1 and attached Figure 2 As shown, the present invention provides a sensorless controller for a permanent magnet synchronous motor for an air compressor, comprising a controller housing 1, a signal acquisition unit, a signal processing unit, a rotor state estimation unit, a start control unit, a current control unit, a modulation output unit, a parameter adaptive unit, a fault protection unit, and a control communication unit. The controller housing 1 has a rear cover 2 and a front cover 3 at both ends, respectively. Mounting screws 4 are provided between the rear cover 2 and the front cover 3 and the controller housing 1, and the rear cover 2 and the front cover 3 are fixedly connected to the controller housing 1 by the mounting screws 4. A terminal block 5 is provided on the front cover 3. Mounting flanges 6 are provided at the bottom of both the rear cover 2 and the front cover 3. Mounting holes 7 are provided through both sides of the mounting flanges 6. Heat dissipation fins 8 are provided on the outer side of the controller housing 1.

[0032] The signal acquisition unit is used to acquire phase current, phase voltage, DC bus voltage, power module temperature, and air compressor operating status signals of the permanent magnet synchronous motor.

[0033] The signal processing unit is used to filter, bias correct, outlier remove, and perform analog-to-digital conversion on the signal output by the signal acquisition unit.

[0034] The rotor state estimation unit is used to estimate the rotor position, speed, back electromotive force and load state of the permanent magnet synchronous motor based on the motor voltage, current and motor mathematical model.

[0035] The start control unit is used to perform rotor initial position identification, orientation positioning, open-loop speed increase and closed-loop switching control when the permanent magnet synchronous motor is stationary or at low speed.

[0036] The current control unit is used to decouple the excitation current and torque current of the permanent magnet synchronous motor based on the rotor state estimation results.

[0037] The modulation output unit is used to generate a pulse width modulation signal according to the voltage command output by the current control unit, and control the power switching device to drive the permanent magnet synchronous motor to run.

[0038] The parameter adaptive unit is used to correct the control parameters based on motor speed, load changes, estimation errors and operating temperature.

[0039] The fault protection unit is used to perform current limiting, load reduction, shutdown or fault alarm based on detected overcurrent, overvoltage, undervoltage, overtemperature, stall, loss of synchronization, estimation abnormality and communication abnormality.

[0040] The intelligent control module obtains rotor position and speed information through the rotor state estimation unit during the operation of the permanent magnet synchronous motor.

[0041] The control communication unit is used to interact with the air compressor main controller, pressure sensor, temperature sensor or host computer, receive start / stop commands, target pressure, target speed and operating mode commands, and output actual speed, output power, motor temperature, estimated confidence level, fault status and protection status.

[0042] The signal acquisition unit includes a DC bus voltage acquisition channel located on the inverter input side, at least two phase current acquisition channels located on the inverter output side, and a temperature acquisition channel for acquiring the power module temperature; the signal acquisition unit is also used to acquire status signals such as the air compressor start / stop command, target pressure, actual pressure, exhaust temperature, oil and gas temperature, and operating mode.

[0043] The rotor state estimation unit includes a stationary coordinate system voltage-current transformation module, a flux linkage observation module, a back electromotive force (EMF) calculation module, a rotor position calculation module, a speed calculation module, and an error correction module. The stationary coordinate system voltage-current transformation module converts the collected three-phase voltage and three-phase current into two-phase stationary coordinate system voltage and current. The flux linkage observation module estimates the stator flux linkage based on a voltage model, a current model, or a voltage-current hybrid model. The back EMF calculation module calculates the back EMF based on the stator flux linkage and current changes. The rotor position calculation module calculates the rotor position based on the back EMF, flux linkage direction, or high-frequency response characteristics. The speed calculation module calculates the rotor speed based on the rotor position changes in adjacent control cycles. The error correction module corrects the estimation results based on current observation errors, back EMF residuals, and the consistency of speed changes.

[0044] The start-up control unit includes a rotor initial position identification module, a rotor positioning module, an open-loop speed-up module, and a closed-loop switching module. The rotor initial position identification module is used to apply a test voltage vector with a preset direction and amplitude to the permanent magnet synchronous motor and identify the initial position of the rotor magnetic poles based on the difference in current response. The rotor positioning module is used to orient the stator magnetic field to the identified rotor initial position so that the rotor is kept within a preset electrical angle range. The open-loop speed-up module is used to drive the motor to speed up according to a preset frequency curve and voltage amplitude curve. The closed-loop switching module is used to switch the open-loop control to closed-loop control based on the estimated rotor position when the back electromotive force is effective, the estimation error is less than a preset threshold, and the speed reaches the switching speed.

[0045] The start-up control unit determines the start-up current, rotor positioning time, open-loop acceleration slope, and closed-loop switching speed based on at least one of the following parameters: air compressor downtime, exhaust pressure, compression chamber pressure, target speed, ambient temperature, and motor temperature.

[0046] The current control unit includes a coordinate transformation module, a torque current controller, an excitation current controller, a voltage feedforward module, and a current limiting module. The coordinate transformation module converts the motor current into excitation current and torque current based on the estimated rotor position. The torque current controller generates a target torque current based on the difference between the target speed and the estimated speed. The excitation current controller generates a target excitation current based on the motor operating speed, bus voltage, and load status. The current limiting module limits the target excitation current and target torque current based on the motor rated current, power module temperature, bus voltage, and air compressor load.

[0047] The parameter adaptive unit corrects the control parameters online based on data such as the estimated values ​​of motor stator resistance, motor inductance, permanent magnet flux linkage, speed estimation error, current loop tracking error, and motor and power module temperatures. The control parameters include the current loop proportional coefficient, current loop integral coefficient, observer gain, speed loop gain, back EMF filter coefficient, start-up acceleration slope, and closed-loop switching threshold.

[0048] The fault protection unit judges changes in current, bus voltage, temperature, estimation error, and speed through multiple consecutive control cycles to distinguish between instantaneous disturbances, general abnormalities, and serious faults. When an instantaneous overcurrent or short-term estimation error is detected, the fault protection unit reduces the torque current command or temporarily freezes map parameter updates. When a continuous overcurrent, bus overvoltage, power module overtemperature, rotor step loss, or stall is detected, the fault protection unit stops the pulse width modulation signal output and generates a corresponding fault code.

[0049] The rotor state estimation unit is equipped with an estimation confidence evaluation module. The estimation confidence evaluation module calculates the positioning confidence based on at least two of the following: back EMF amplitude, dot product residual, flux change rate, current tracking error, estimated speed continuity, and voltage utilization rate. When the positioning confidence is higher than a first threshold, closed-loop control is performed using the back EMF observation results. When the positioning confidence is between the first and second thresholds, the weights of the inertial model, speed smoothing model, or current model are increased. When the positioning confidence is lower than the second threshold, load reduction control, re-estimation, open-loop auxiliary control, or shutdown protection are executed.

[0050] The specific implementation method is as follows: When using this invention, the control module can be implemented using a microcontroller, digital signal processor, field-programmable gate array, or processor with real-time computing capabilities, and is connected to the inverter power module through a drive interface. After the control module starts, it first reads the motor nameplate parameters, air compressor operating parameters, and preset control parameters. The motor parameters include rated current, rated speed, number of pole pairs, stator resistance, inductance parameters, and permanent magnet flux linkage parameters. The air compressor operating parameters include target pressure, actual pressure, exhaust temperature, oil-gas temperature, start-up mode, and shutdown time. The signal acquisition unit acquires the motor phase current, DC bus voltage, power module temperature, and air compressor temperature according to a preset sampling period. Pressure and temperature signals are collected, filtered, zero-point calibrated, and anomaly detected before being sent to the rotor state estimation unit and current control unit. The control module synchronizes various signals according to the sampling timestamp to avoid rotor position estimation errors caused by sampling delays. When the air compressor starts, the control module first determines whether the motor is stationary and, based on the shutdown time and pressure status, determines whether there is significant starting resistance in the compressor. Subsequently, the start control unit applies a test voltage vector of a predetermined amplitude to the motor, causing a test current to be generated in the stator winding. Due to different rotor magnetic pole positions, the motor exhibits different current responses under different voltage vectors. The control module compares the current amplitudes corresponding to multiple test voltage vectors. The initial rotor position is determined by the response slope or current change. After initial position identification, the control module applies a directional current to stabilize the rotor near the preset initial electrical angle. The directional time is adjusted according to the starting load, compression chamber pressure, and motor temperature. When the starting load is large, the directional current is increased or the directional time is extended; when the starting load is small, the directional current is reduced to minimize unnecessary energy loss. After rotor positioning is complete, the open-loop speed-up module outputs a rotating voltage vector according to the preset electrical angle frequency curve. During speed-up, the control module limits the output voltage and torque current based on the motor current and bus voltage to prevent overcurrent due to excessive starting resistance of the air compressor. The open-loop speed-up slope is adjusted according to the actual pressure. The temperature and current response are adjusted. When the motor speed reaches the preset range and the back EMF amplitude, dot product residual and current tracking error meet the closed-loop switching conditions, the closed-loop switching module transfers the control to the rotor state estimation unit. During the switching process, the phase correction between the open-loop angle and the estimated angle is performed, and the control switching is completed by gradually changing the angle and speed to avoid torque impact caused by sudden angle changes. During normal operation, the rotor state estimation unit estimates the stator flux and back EMF based on the motor voltage equation, current equation and permanent magnet synchronous motor mathematical model, and calculates the rotor position from the direction of the back EMF. In the low-speed region, the back EMF is weak, and the control module increases the weight of the current model and motion model.For medium- and high-speed regions, the weight of the back EMF observation model is increased. By fusing models from different operating ranges, continuous rotor position and speed estimation results are obtained. The current control unit converts the three-phase current into excitation current and torque current, and calculates the target torque current based on the deviation between the target speed and the estimated speed. For the constant pressure operation mode of the air compressor, the control module adjusts the target speed according to the deviation between the actual pressure and the target pressure; when the actual pressure reaches the target pressure, the motor speed is reduced; when the pressure drops, the motor speed is increased. The current limiting module limits the current command based on the motor rated current, power module temperature, and DC bus voltage. The parameter adaptive unit continuously analyzes the current loop. The system monitors tracking errors, estimated speed errors, and motor temperature changes. When the motor temperature rises and causes a change in stator resistance, the stator resistance parameters in the voltage model are corrected. When the operating status indicates a deviation in the inductance or permanent magnet flux linkage, the corresponding model parameters are corrected. When the estimation error continuously increases, the observer gain and filter coefficient are adjusted to improve the stability of rotor position estimation. The fault protection unit continuously monitors the motor operating status. When a short-term overcurrent or sudden load increase is detected, the target torque current is first reduced and acceleration is limited. When a continuous overcurrent, bus overvoltage, power module overtemperature, stalled rotor, or rotor loss of synchronism is detected, the pulse width modulation signal output is stopped, and a signal is sent to the air compressor main controller. Fault codes indicate that once the fault is cleared and restart conditions are met, the control module re-executes the rotor initial position identification and startup process. The control communication unit can connect to the air compressor main controller via serial communication, CAN communication, RS485 communication, or other industrial communication interfaces. The control module transmits estimated speed, output current, output power, temperature, positioning accuracy, and fault status to the main controller. The main controller sends start / stop commands, target pressure, target speed, and operating mode commands to the control module. Through this structure and control process, the control module achieves reliable startup, smooth speed regulation, state estimation, and parameter adjustment of the permanent magnet synchronous motor without the need for a rotor position sensor. This invention provides fault protection and is applicable to air compressor systems of different capacities and compressor structures. It eliminates the need for rotor position and speed sensors, reducing manufacturing, assembly, and maintenance costs for the air compressor motor system. Through rotor initial position identification, orientation positioning, open-loop speed increase, and closed-loop smooth switching, it improves motor start-up success rate and reduces reverse rotation, step loss, and current surges. By integrating voltage, current, bus voltage, and air compressor operating status, and employing parameter adaptation and estimation confidence evaluation, it improves control accuracy and stability under low-speed, variable load, and high-temperature environments. Through fault identification, current limiting, load reduction, and shutdown protection, it enhances air compressor operational safety and controller reliability.

[0051] Working principle of this invention:

[0052] Refer to the instruction manual appendix Figure 1 and attached Figure 2When using this invention, the inclusion of a parameter adaptive unit, a fault protection unit, and a control communication unit eliminates the need for rotor position and speed sensors, reducing the manufacturing, assembly, and maintenance costs of the air compressor motor system. Through rotor initial position identification, orientation positioning, open-loop speed increase, and closed-loop smooth switching, the invention improves motor start-up success rate and reduces reverse rotation, step loss, and current surges. By integrating voltage, current, bus voltage, and air compressor operating status, and employing parameter adaptation and estimation confidence evaluation, the invention enhances control accuracy and stability under low speed, variable load, and high temperature environments. Furthermore, through fault identification, current limiting, load reduction, and shutdown protection, the invention improves air compressor operating safety and controller reliability.

[0053] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0054] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0055] 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 controller for a permanent magnet synchronous motor used in an air compressor, characterized in that: The controller includes a controller housing (1), a signal acquisition unit, a signal processing unit, a rotor state estimation unit, a start control unit, a current control unit, a modulation output unit, a parameter adaptive unit, a fault protection unit, and a control communication unit. The controller housing (1) is provided with a rear cover (2) and a front cover (3) at both ends. The rear cover (2) and the front cover (3) are provided with mounting screws (4) between them and the controller housing (1). The rear cover (2) and the front cover (3) are fixedly connected to the controller housing (1) by the mounting screws (4). The front cover (3) is provided with a terminal block (5). The bottom of the rear cover (2) and the front cover (3) are provided with mounting flanges (6). Mounting holes (7) are provided through both sides of the mounting flanges (6). Heat dissipation fins (8) are provided on the outside of the controller housing (1). The signal acquisition unit is used to acquire phase current, phase voltage, DC bus voltage, power module temperature, and air compressor operating status signals of the permanent magnet synchronous motor. The signal processing unit is used to filter, bias correct, outlier remove, and perform analog-to-digital conversion on the signal output by the signal acquisition unit. The rotor state estimation unit is used to estimate the rotor position, speed, back electromotive force and load state of the permanent magnet synchronous motor based on the motor voltage, current and motor mathematical model. The start control unit is used to perform rotor initial position identification, orientation positioning, open-loop speed increase and closed-loop switching control when the permanent magnet synchronous motor is stationary or at low speed. The current control unit is used to decouple the excitation current and torque current of the permanent magnet synchronous motor based on the rotor state estimation results. The modulation output unit is used to generate a pulse width modulation signal according to the voltage command output by the current control unit, and control the power switching device to drive the permanent magnet synchronous motor to run. The parameter adaptive unit is used to correct the control parameters based on motor speed, load changes, estimation errors and operating temperature. The fault protection unit is used to perform current limiting, load reduction, shutdown or fault alarm based on detected overcurrent, overvoltage, undervoltage, overtemperature, stall, loss of synchronization, estimation abnormality and communication abnormality.

2. The intelligent control module obtains rotor position and speed information through the rotor state estimation unit during the operation of the permanent magnet synchronous motor; The control communication unit is used to interact with the air compressor main controller, pressure sensor, temperature sensor or host computer, receive start / stop commands, target pressure, target speed and operating mode commands, and output actual speed, output power, motor temperature, estimated confidence level, fault status and protection status.

3. The sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The signal acquisition unit includes a DC bus voltage acquisition channel located on the inverter input side, at least two phase current acquisition channels located on the inverter output side, and a temperature acquisition channel for acquiring the power module temperature; the signal acquisition unit is also used to acquire status signals such as the air compressor start / stop command, target pressure, actual pressure, exhaust temperature, oil and gas temperature, and operating mode.

4. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The rotor state estimation unit includes a stationary coordinate system voltage-current transformation module, a flux linkage observation module, a back electromotive force (EMF) calculation module, a rotor position calculation module, a speed calculation module, and an error correction module. The stationary coordinate system voltage-current transformation module converts the collected three-phase voltage and three-phase current into two-phase stationary coordinate system voltage and current. The flux linkage observation module estimates the stator flux linkage based on a voltage model, a current model, or a voltage-current hybrid model. The back EMF calculation module calculates the back EMF based on the stator flux linkage and current changes. The rotor position calculation module calculates the rotor position based on the back EMF, flux linkage direction, or high-frequency response characteristics. The speed calculation module calculates the rotor speed based on the rotor position changes in adjacent control cycles. The error correction module corrects the estimation results based on current observation errors, back EMF residuals, and the consistency of speed changes.

5. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The start-up control unit includes a rotor initial position identification module, a rotor positioning module, an open-loop speed-up module, and a closed-loop switching module. The rotor initial position identification module is used to apply a test voltage vector with a preset direction and amplitude to the permanent magnet synchronous motor and identify the initial position of the rotor magnetic poles based on the difference in current response. The rotor positioning module is used to orient the stator magnetic field to the identified rotor initial position so that the rotor is kept within a preset electrical angle range. The open-loop speed-up module is used to drive the motor to speed up according to a preset frequency curve and voltage amplitude curve. The closed-loop switching module is used to switch the open-loop control to closed-loop control based on the estimated rotor position when the back electromotive force is effective, the estimation error is less than a preset threshold, and the speed reaches the switching speed.

6. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The start-up control unit determines the start-up current, rotor positioning time, open-loop acceleration slope, and closed-loop switching speed based on at least one of the following parameters: air compressor downtime, exhaust pressure, compression chamber pressure, target speed, ambient temperature, and motor temperature.

7. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The current control unit includes a coordinate transformation module, a torque current controller, an excitation current controller, a voltage feedforward module, and a current limiting module. The coordinate transformation module converts the motor current into excitation current and torque current based on the estimated rotor position. The torque current controller generates a target torque current based on the difference between the target speed and the estimated speed. The excitation current controller generates a target excitation current based on the motor operating speed, bus voltage, and load status. The current limiting module limits the target excitation current and target torque current based on the motor rated current, power module temperature, bus voltage, and air compressor load.

8. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The parameter adaptive unit corrects the control parameters online based on data such as the estimated values ​​of motor stator resistance, motor inductance, permanent magnet flux linkage, speed estimation error, current loop tracking error, and motor and power module temperatures. The control parameters include the current loop proportional coefficient, current loop integral coefficient, observer gain, speed loop gain, back EMF filter coefficient, start-up acceleration slope, and closed-loop switching threshold.

9. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The fault protection unit judges changes in current, bus voltage, temperature, estimation error, and speed through multiple consecutive control cycles to distinguish between instantaneous disturbances, general abnormalities, and serious faults. When an instantaneous overcurrent or short-term estimation error is detected, the fault protection unit reduces the torque current command or temporarily freezes map parameter updates. When a continuous overcurrent, bus overvoltage, power module overtemperature, rotor step loss, or stall is detected, the fault protection unit stops the pulse width modulation signal output and generates a corresponding fault code.

10. A sensorless controller for a permanent magnet synchronous motor in an air compressor according to claim 1, characterized in that: The rotor state estimation unit is equipped with an estimation confidence evaluation module. The estimation confidence evaluation module calculates the positioning confidence based on at least two of the following: back EMF amplitude, dot product residual, flux change rate, current tracking error, estimated speed continuity, and voltage utilization rate. When the positioning confidence is higher than a first threshold, closed-loop control is performed using the back EMF observation results. When the positioning confidence is between the first and second thresholds, the weights of the inertial model, speed smoothing model, or current model are increased. When the positioning confidence is lower than the second threshold, load reduction control, re-estimation, open-loop auxiliary control, or shutdown protection are executed.

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