Low-speed area sensorless control method and system

Abstract

The invention belongs to the field of permanent magnet synchronous motor control, and discloses a low-speed region position sensorless control method and system, and the method comprises the steps: obtaining the high-frequency current response of a quadrature axis in a controlled motor; the high-frequency current response is a high-frequency current response of a quadrature axis in the collected motor after high-frequency square wave voltage is injected into a direct axis of the controlled motor, and the variable quantity of the high-frequency current response is calculated according to the high-frequency current response; calculating an angle error by using the injected high-frequency square wave voltage, the stator inductance difference, the variable quantity of the high-frequency current response and the sampling period of the current; and integrating the angle error, using an integral result to update the rotor position estimation value, and continuously correcting the angle error through feedback until the angle error tends to zero to obtain the rotor estimation position. Accurate control over the motor without the position sensor in the low-speed area is achieved.

Description

Technical Field

[0001] This application belongs to the field of permanent magnet synchronous motor control, and particularly relates to a sensorless control method and system in the low-speed region. Background Art

[0002] A permanent magnet synchronous motor (PMSM) is a motor in which a rotor excited by a permanent magnet rotates synchronously with a stator spatial magnetic field. Due to its excellent performance, the permanent magnet synchronous motor is widely used in various fields. High-precision control of modern permanent magnet motors usually requires feedback of the rotor position. In order to reduce system cost, reduce the volume of the motor, improve system stability, and ensure that the motor can operate stably in a complex environment, the PMSM sensorless control scheme has been widely applied. In the sensorless control system of the permanent magnet synchronous motor, the sensorless control system of the PMSM in the low-speed operation state has poor observation effects on the rotational speed and rotor position. Therefore, considering that when the motor operates at low speed, the useful signal-to-noise ratio is very low, resulting in a large error in the calculated back electromotive force, and the detection of the rotor speed and position fails when operating in the low-speed range, how to achieve sensorless control of the PMSM in the low-speed region has become one of the research hotspots in the current motor control field. Summary of the Invention

[0003] An embodiment of this application provides a sensorless control method in the low-speed region based on high-frequency square wave injection, which solves the problem that when the motor operates at low speed, the useful signal-to-noise ratio is very low, resulting in a large error in the calculated back electromotive force, and the detection of the rotor speed and position fails when operating in the low-speed range.

[0004] A first aspect of an embodiment of this application provides a sensorless control method in the low-speed region, including: Obtain the high-frequency current response of the quadrature axis in the controlled motor, where the high-frequency current response is the high-frequency current response of the quadrature axis in the collected motor after injecting a high-frequency square wave voltage into the direct axis of the controlled motor, and calculate the change amount of the high-frequency current response according to the high-frequency current response; Calculate the angle error by using the injected high-frequency square wave voltage, the difference in stator inductance, the change amount of the high-frequency current response, and the current sampling period; Integrate the angle error, use the result of the integration to update the rotor position estimate value, and continuously correct the angle error through feedback until the angle error tends to zero to obtain the rotor estimated position.

[0005] In one embodiment, calculating the angle error by using the injected high-frequency square wave voltage, the difference in stator inductance, the change amount of the high-frequency current response, and the current sampling period includes: The angle error is calculated using a rotor estimated error angle equation including a high-frequency square wave voltage, a stator inductance difference, a change in a high-frequency current response, and a current sampling period. The rotor estimated error angle equation is: , in, is the change in high-frequency current response, is the current sampling period, is the injected high frequency square wave voltage, for In the actual synchronous rotating coordinate system Shaft stator inductance, for In the actual synchronous rotating coordinate system Shaft stator inductance.

[0006] In one embodiment, obtaining a high-frequency current response generated in the controlled motor, wherein the high-frequency current response is a high-frequency current response generated in the motor after a high-frequency square wave voltage is injected into a direct axis of the controlled motor, and calculating a change amount of the high-frequency current response according to the high-frequency current response includes: exist Injecting a first high-frequency square wave voltage signal into the direct axis of the motor in an estimated synchronous rotating coordinate system, wherein the first high-frequency square wave voltage signal is a high-frequency square wave voltage signal represented by a high-frequency square wave voltage signal equation; Will It is estimated that the first high-frequency square wave voltage signal injected into the motor direct axis in the synchronous rotating coordinate system is converted to The actual synchronous rotating coordinate system obtains a second high-frequency square wave voltage signal, which is obtained by using A second high-frequency square wave voltage signal represented by a high-frequency square wave voltage signal equation in an actual synchronous rotating coordinate system; The high frequency model of the motor is combined with The high-frequency square wave voltage signal equation in the actual synchronous rotating coordinate system is combined to obtain a first high-frequency current signal equation representing the third high-frequency current signal; Convert the first high-frequency current signal equation to The second high-frequency current signal equation is obtained in the synchronous rotating coordinate system. The second high-frequency current signal equation is expressed as Estimate high-frequency current signals in a synchronously rotating coordinate system; The current dynamic response equation is obtained by discretizing the second high-frequency current signal equation, and the change amount of the high-frequency current response is calculated through the current dynamic response equation.

[0007] In one embodiment, the high-frequency square wave voltage signal equation is: , Among them, and are respectively the estimated direct-axis high-frequency injection voltage component and quadrature-axis high-frequency injection voltage component in the synchronous rotating coordinate system, is the polarity switching factor of the square-wave voltage, and

[0008] In one embodiment, the conversion relationship between the actual synchronous rotating coordinate system and the estimated synchronous rotating coordinate system is expressed as: , where and and are respectively the voltage and current in the actual synchronous rotating coordinate system, where is the direct-axis voltage in the actual synchronous rotating coordinate system, is in the actual synchronous rotating coordinate system, is, is the quadrature-axis current in the actual synchronous rotating coordinate system; and and are respectively the voltage and current in the estimated synchronous rotating coordinate system, where is the direct-axis voltage in the estimated synchronous rotating coordinate system, is in the estimated synchronous rotating coordinate system, axis voltage; is the difference between the actual rotor position angle and the estimated rotor position angle , = .

[0009] In one embodiment, the high-frequency square-wave voltage signal equation is: .

[0010] In one embodiment, the high-frequency model of the motor is: , where is the direct-axis stator inductance in the actual synchronous rotating coordinate system, is the quadrature-axis stator inductance in the actual synchronous rotating coordinate system, is The direct-axis high-frequency voltage signal in the actual synchronous rotating coordinate system, is the quadrature-axis high-frequency voltage signal in the actual synchronous rotating coordinate system, 、 is the direct-axis high-frequency current signal in the actual synchronous rotating coordinate system, is the quadrature-axis high-frequency current signal in the actual synchronous rotating coordinate system.

[0011] In one embodiment, the first high-frequency current signal equation is: = .

[0012] In one embodiment, the second high-frequency current signal equation is: = , wherein, is the sampling period of the current.

[0013] In the second aspect of the embodiments of the present application, a sensorless control system in the low-speed region is provided, including: a processor and a three-phase inverter. The processor uses a current sensor to obtain the high-frequency current response generated in the controlled motor. The high-frequency current response is obtained by setting the direct-axis current to zero, setting the quadrature-axis current to the target current, injecting a high-frequency square-wave voltage into the direct axis of the controlled motor after passing through a PI regulator, and then outputting a high-frequency current response in the motor through pulse width modulation of the SVPWM module after PARK inverse transformation and passing through the three-phase inverter. The change amount of the high-frequency current response is calculated according to the high-frequency current response; The processor injects a high-frequency square-wave voltage into the phase-locked loop position observer, and calculates the angle error by using the injected high-frequency square-wave voltage, the difference in stator inductance, the change amount of the high-frequency current response, and the sampling period of the current; The processor integrates the angle error, uses the result of the integration to update the rotor position estimate value, and continuously corrects the angle error through feedback until the angle error tends to zero to obtain the rotor estimated position.

[0014] The technical solution provided by the embodiments of the present application has at least the following beneficial effects compared with the prior art: In the present application, by injecting a high-frequency square-wave voltage into the direct axis, calculating the angle error through the change amount of the high-frequency current response of the motor and the sampling period of the current; and continuously correcting the angle error through feedback until the angle error tends to zero to obtain the rotor estimated position. Precise control of the sensorless motor in the low-speed region is achieved. Description of the Drawings

[0015] Figure 1It is a flowchart of a sensorless control method for the low-speed region provided by an embodiment of the present application; Figure 2 It is a relationship diagram between the actual rotor and the estimated rotor synchronous rotation coordinate system provided by an embodiment of the present application; Figure 3 It is a data processing logic diagram of a phase-locked loop position observer provided by an embodiment of the present application; Figure 4 It is a schematic structural diagram of a sensorless control system for the low-speed region provided by an embodiment of the present application; Figure 5 It is a simulation waveform diagram of the rotor speed during load change operation provided by an embodiment of the present application. Detailed implementation manners

[0016] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0017] The embodiment of the present application belongs to a sensorless control scheme for PMSM, and is used to solve the problem of sensorless control of PMSM in the low-speed region. The PMSM sensorless control system may include a controller, a drive circuit, a three-phase inverter, and a sensor for detecting the position and speed of the PMSM and feeding back this information to the controller. And a feedback loop for feeding back the position and speed information of the PMSM to the controller for realizing closed-loop control. The embodiment of the present application is an improvement based on the existing PMSM sensorless control system. Considering that when the motor runs at a low speed, the useful signal-to-noise ratio is very low, resulting in a large error in the calculated back electromotive force, and the detection of the rotor speed and position fails during operation in the low-speed range, so as to realize sensorless control of PMSM in the low-speed region.

[0018] In the embodiment of the present application, as Figure 1 shown in a flowchart of a sensorless control method for the low-speed region, a sensorless control method for the low-speed region of the present application includes: S101 Obtain the high-frequency current response of the quadrature axis in the controlled motor. The high-frequency current response is the high-frequency current response of the quadrature axis in the collected motor after injecting a high-frequency square wave voltage into the direct axis of the controlled motor, and calculate the change amount of the high-frequency current response according to the high-frequency current response; The motor mentioned here refers to a permanent magnet synchronous motor. A permanent magnet synchronous motor is a motor in which the rotor excited by permanent magnets rotates synchronously with the stator spatial magnetic field. The control of a permanent magnet synchronous motor can be sensorless or with a position sensor. In the sensorless control scheme, the position and speed of the motor are estimated through the electrical signals of the motor (such as voltage and current), so as to achieve the control of the motor. Generally, the electrical signals of the motor, that is, the current response, do not contain high-frequency current response. After injecting a high-frequency square wave voltage into the direct axis of the controlled motor, a high-frequency current response will be generated in the motor. The high-frequency current response is obtained through a current sensor, and the change amount of the high-frequency current response can be obtained in the current sampling period according to the high-frequency current response.

[0019] The high-frequency square wave voltage refers to that the high-frequency square wave frequency of high-frequency injection is much greater than the fundamental frequency of the stator current of the motor. Therefore, the fundamental current remains basically unchanged within one switching period of the fundamental frequency current. Since the high-frequency square wave voltage injected into the direct axis has the characteristic of equal amplitude and opposite directions, the amplitudes of the high-frequency currents at two adjacent sampling points are almost the same. The quadrature-axis fundamental current can be extracted through the mathematical relationship between two consecutive current sampling values, so that a filter is not needed.

[0020] S102 calculates the angle error by using the injected high-frequency square wave voltage, the difference in stator inductance, the change amount of the high-frequency current response, and the current sampling period; In one embodiment, the rotor estimated error angle equation including the high-frequency square wave voltage, the difference in stator inductance, the change amount of the high-frequency current response, and the current sampling period is used to calculate the angle error. The rotor estimated error angle equation adopts the following form: , where, is the change amount of the high-frequency current response, is the current sampling period, is the injected high-frequency square wave voltage, is the stator inductance of the axis in the actual synchronous rotating coordinate system, is the stator inductance of the axis in the actual synchronous rotating coordinate system.

[0021] The angle error refers to the error between the estimated rotor position and the actual rotor position. In this embodiment, through the established rotor estimated error angle equation, the angle error is calculated by using the injected high-frequency square wave voltage in combination with the difference in inductance, the change amount of the high-frequency current response, and the current sampling period. More accurate calculation of the angle error can be achieved.

[0022] S103 integrates the angular error, uses the result of the integration to update the estimated rotor position value, and continuously corrects the angular error through feedback until the angular error tends to zero, thereby obtaining the estimated rotor position.

[0023] It can be understood that integrating the angular error is to convert the instantaneous error into a cumulative error for calculating the estimated rotor position value. By continuously performing feedback to calculate the angular error through step S102 and correcting the angular error, until the angular error tends to zero, at which point the estimated rotor position is obtained.

[0024] In one embodiment, after injecting a high-frequency square-wave voltage into the direct axis of the controlled motor, the high-frequency current response generated in the motor is used to calculate the change in the high-frequency current response, including: At Estimate the first high-frequency square-wave voltage signal injected into the direct axis of the motor in the synchronous rotating coordinate system. The first high-frequency square-wave voltage signal is a high-frequency square-wave voltage signal represented by the high-frequency square-wave voltage signal equation; It can be understood that The estimated synchronous rotating coordinate system is the coordinate system in which the estimated current is located. Relative to the estimated synchronous rotating coordinate system, the coordinate system in which the actual current is located is The actual synchronous rotating coordinate system, and there is a conversion relationship between the two.

[0025] See Figure 2 As shown, in one embodiment, The actual synchronous rotating coordinate system and The conversion relationship of the estimated synchronous rotating coordinate system is: , Wherein, , , Are respectively The voltage and current in the actual synchronous rotating coordinate system, where Is The Axis voltage in the actual synchronous rotating coordinate system, Is In the actual synchronous rotating coordinate system, Is, Is The Axis current in the actual synchronous rotating coordinate system; , , Are respectively The voltage and current in the estimated synchronous rotating coordinate system, where Is The Axis voltage in the estimated synchronous rotating coordinate system, To estimate the axis voltage in the synchronous rotating coordinate system; is the actual rotor position angle and the estimated rotor position angle The difference between them, = .

[0026] The high-frequency square-wave voltage signal injected into the direct axis of the motor is denoted as the first high-frequency square-wave voltage signal for distinction from other steps. The first high-frequency square-wave voltage signal is the high-frequency square-wave voltage signal represented by the high-frequency square-wave voltage signal equation, and the high-frequency square-wave voltage signal equation is: , wherein, , are respectively the direct-axis (d-axis) high-frequency injection voltage component and the quadrature-axis (q-axis) high-frequency injection voltage component in the estimated synchronous rotating coordinate system, is the polarity switching factor of the square-wave voltage, is the peak value of the high-frequency injection voltage.

[0027] It can be understood that in the estimated synchronous rotating coordinate system, there is a direct-axis (d-axis) high-frequency injection voltage component, while the quadrature-axis (q-axis) high-frequency injection voltage component is zero.

[0028] Convert the first high-frequency square-wave voltage signal injected into the direct axis of the motor in the estimated synchronous rotating coordinate system to the actual synchronous rotating coordinate system to obtain a second high-frequency square-wave voltage signal, and the second high-frequency square-wave voltage signal is the second high-frequency square-wave voltage signal represented by the high-frequency square-wave voltage signal equation in the actual synchronous rotating coordinate system; Using the conversion relationship between the estimated synchronous rotating coordinate system and the actual synchronous rotating coordinate system to perform the conversion between the first high-frequency square-wave voltage signal and the second high-frequency square-wave voltage signal. It can be understood that the conversion process can be achieved by converting the high-frequency square-wave voltage signal equation representing the first high-frequency square-wave voltage signal to the high-frequency square-wave voltage signal equation in the actual synchronous rotating coordinate system representing the second high-frequency square-wave voltage signal.

[0029] Obtain the high-frequency square-wave voltage signal equation in the actual synchronous rotating coordinate system as: , The high-frequency model of the motor and The high-frequency square wave voltage signal equation in the actual synchronous rotating coordinate system is combined to obtain a first high-frequency current signal equation representing the third high-frequency current signal; The high-frequency model of the motor refers to the stator inductance-related inductance generated in the motor when the PMSM is excited by a high-frequency square wave. High-frequency voltage signal in the actual synchronous rotating coordinate system.

[0030] It is expressed as: , in, for The direct-axis stator inductance in the actual synchronous rotating coordinate system is: for The quadrature-axis stator inductance in the actual synchronous rotating coordinate system is: for Direct axis high frequency voltage signal in actual synchronous rotating coordinate system, for The quadrature axis high frequency voltage signal in the actual synchronous rotating coordinate system, , for Direct axis high frequency current signal in actual synchronous rotating coordinate system, for The quadrature-axis high-frequency current signal in the actual synchronous rotating coordinate system.

[0031] The left side of the high frequency model of the motor is The left side of the high-frequency square wave voltage signal equation in the actual synchronous rotating coordinate system is consistent. The high-frequency square wave voltage signal equation in the actual synchronous rotating coordinate system is eliminated by simultaneously eliminating the high-frequency voltage signal represented by the left-hand term, and only the high-frequency voltage signal, stator inductance, and actual rotor position angle are obtained. Estimated rotor position angle The difference between and the peak value of the high-frequency injection voltage are used to represent the first high-frequency current signal equation of the third high-frequency current signal.

[0032] The first high-frequency current signal equation obtained is: = .

[0033] It can be understood that the first high frequency current signal equation is In actual synchronous rotating coordinate system.

[0034] Convert the first high-frequency current signal equation to The second high-frequency current signal equation is obtained in the synchronous rotating coordinate system. The second high-frequency current signal equation is expressed as Estimate high-frequency current signals in a synchronously rotating coordinate system; The second high-frequency current signal equation is obtained as follows: = , where and are respectively the estimated direct-axis high-frequency injection current component and quadrature-axis high-frequency injection current component of the current in the synchronous rotating coordinate system.

[0035] The current dynamic response equation is obtained by discretizing the second high-frequency current signal equation, and the change amount of the high-frequency current response is calculated through the current dynamic response equation.

[0036] By discretizing the second high-frequency current signal equation, that is, converting the high-frequency current signal equation in continuous time into a discrete-time form, it can be understood that there is no limitation on the discretization method. After discretization, the second high-frequency current signal equation that does not reflect the sampling period of the current is converted into a current dynamic response equation related to the sampling period of the current and related to the change amount of the high-frequency current signal. That is, it can be expressed as: = , where is the sampling period of the current.

[0037] where, when the rotor estimation error angle is small enough, = From the current dynamic response equation, the rotor estimation error angle equation can be obtained, and the equation is: , where is the change amount of the high-frequency current response.

[0038] See Figure 3 Combined with Figure 4 shown in, a sensorless control system in a low-speed area disclosed in an embodiment of the present application includes: It includes a processor and a three-phase inverter. The processor uses a current sensor to obtain the high-frequency current response generated in the controlled motor. The high-frequency current response is that the processor sets the direct-axis current to zero, sets the quadrature-axis current to the target current, injects a high-frequency square-wave voltage into the direct axis of the controlled motor after passing through a PI regulator, and after PARK inverse transformation and pulse width modulation by the SVPWM module, outputs through the three-phase inverter to generate a high-frequency current response in the quadrature axis of the motor, and calculates the change amount of the high-frequency current response according to the high-frequency current response; generating a high-frequency current response in the quadrature axis means Figure 4The current signals in the three-phase stationary coordinate system (ABC coordinate system) collected by the current sensor therein are subjected to the CLARK transformation: the currents in the three-phase stationary coordinate system (ABC coordinate system) are converted into the two-phase stationary coordinate system (α-β coordinate system) for the convenience of control and observation, and the direct-axis and quadrature-axis currents are converted into the actual synchronous rotating coordinate system through the PARK transformation, where the high-frequency current response of the quadrature axis participates in the calculation of the angle error, and the current signal of the direct axis is used for the judgment of the direct-axis direction.

[0039] The processor calculates the angle error by using the phase-locked loop position observer. The parameters included in the calculation of the angle error are: the injected high-frequency square-wave voltage, the difference in stator inductance, the change in the high-frequency current response, and the current sampling period, and calculates the angle error; The processor integrates the angle error, uses the result of the integration to update the rotor position estimate, and continuously corrects the angle error through feedback until the angle error tends to zero to obtain the rotor estimated position.

[0040] The processor here belongs to a microprocessor, the PI regulator is implemented by a hardware circuit, and the phase-locked loop position observer in the processor is excited by the direct-axis high-frequency square-wave voltage ( ) to extract the change in the high-frequency current response , combines the stator inductance parameters 、 to calculate the angle error . The rotor angle estimate is corrected in a closed loop through integration and polarity judgment to achieve low-speed high-precision control without an encoder.

[0041] In one embodiment, as shown by Figure 3 , the phase-locked loop position observer uses the injected high-frequency square-wave voltage to generate a high-frequency current response in the motor , combines the inductance difference and the change in the high-frequency current response , combines the current sampling period to calculate the angle error , After being processed by the PI regulator, the rotor position estimate is obtained through integration , and the error is continuously corrected through feedback until →0, wherein, the estimate of the rotor position is .

[0042] Figure 5As shown, the motor starts with no load, and the given speed is 200 r / min. At t = 0.45 s, a load of 8 N·m is suddenly applied, and at t = 0.7 s, the load is suddenly reduced to 5 N·m. It can be seen that the estimated speed during load change operation can track the actual speed in real time. This proves that the method adopted in this application can still maintain good operating performance when the motor load changes, showing high stability, and the sensorless control method based on high-frequency square wave injection in the low-speed region is effective.

[0043] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A low-speed zone position sensorless control method, characterized in that: include: Obtaining a high-frequency current response of the quadrature axis of the controlled motor, wherein the high-frequency current response is a high-frequency current response of the quadrature axis of the motor acquired after a high-frequency square wave voltage is injected into the direct axis of the controlled motor, and calculating a change in the high-frequency current response according to the high-frequency current response; The angle error is calculated using the injected high-frequency square wave voltage, the stator inductance difference, the change in the high-frequency current response, and the current sampling period; The angle error is integrated and the result of the integration is used to update the estimated value of the rotor position. The angle error is continuously corrected through feedback until the angle error approaches zero, and the estimated rotor position is obtained.

2. The low speed area position sensorless control method according to claim 1, characterized in that: The angle error is calculated using the injected high-frequency square wave voltage, the stator inductance difference, the change in the high-frequency current response, and the current sampling period, including: The angle error is calculated using a rotor estimated error angle equation including a high-frequency square wave voltage, a stator inductance difference, a change in a high-frequency current response, and a current sampling period. The rotor estimated error angle equation is: ， in, is the change in high-frequency current response, is the current sampling period, is the injected high frequency square wave voltage, for In the actual synchronous rotating coordinate system Shaft stator inductance, for In the actual synchronous rotating coordinate system Shaft stator inductance.

3. The low speed area position sensorless control method according to claim 1, characterized in that: Obtaining a high-frequency current response generated in the controlled motor, wherein the high-frequency current response is a high-frequency current response generated in the motor after a high-frequency square wave voltage is injected into the direct axis of the controlled motor, and calculating a change amount of the high-frequency current response according to the high-frequency current response, including: exist Injecting a first high-frequency square wave voltage signal into the direct axis of the motor in an estimated synchronous rotating coordinate system, wherein the first high-frequency square wave voltage signal is a high-frequency square wave voltage signal represented by a high-frequency square wave voltage signal equation; Will It is estimated that the first high-frequency square wave voltage signal injected into the motor direct axis in the synchronous rotating coordinate system is converted to The actual synchronous rotating coordinate system obtains a second high-frequency square wave voltage signal, which is obtained by using A second high-frequency square wave voltage signal represented by a high-frequency square wave voltage signal equation in an actual synchronous rotating coordinate system; The high frequency model of the motor is combined with The high-frequency square wave voltage signal equation in the actual synchronous rotating coordinate system is combined to obtain a first high-frequency current signal equation representing the third high-frequency current signal; Convert the first high-frequency current signal equation to The second high-frequency current signal equation is obtained in the synchronous rotating coordinate system. The second high-frequency current signal equation is expressed as Estimate high-frequency current signals in a synchronously rotating coordinate system; The current dynamic response equation is obtained by discretizing the second high-frequency current signal equation, and the change amount of the high-frequency current response is calculated through the current dynamic response equation.

4. The low speed area position sensorless control method according to claim 3, characterized in that: The high-frequency square wave voltage signal equation is: ， in, , They are Estimate the direct-axis high-frequency injection voltage component and the quadrature-axis high-frequency injection voltage component in the synchronous rotating coordinate system. is the polarity switching factor of the square wave voltage, is the peak value of the high frequency injected voltage.

5. The low speed area position sensorless control method according to claim 3, characterized in that: The actual synchronous rotation coordinate system and The estimated transformation relationship of the synchronous rotating coordinate system is expressed as: , in, , , They are The voltage and current in the actual synchronous rotating coordinate system are: for The direct axis voltage in the actual synchronous rotating coordinate system, for In the actual synchronous rotating coordinate system, for, for The quadrature axis current in the actual synchronous rotating coordinate system; , , They are Estimate the voltage and current in the synchronously rotating coordinate system, where for Estimate the direct axis voltage in the synchronously rotating coordinate system, for Estimate the synchronously rotating coordinate system Shaft voltage; is the actual rotor position angle Estimated rotor position angle The difference between = .

6. The low speed area position sensorless control method according to claim 5, characterized in that: The high-frequency square wave voltage signal equation is: 。 7. The low speed area position sensorless control method according to claim 5, characterized in that: The high frequency model of the motor is: ， in, for The direct-axis stator inductance in the actual synchronous rotating coordinate system is: for The quadrature-axis stator inductance in the actual synchronous rotating coordinate system is: for Direct axis high frequency voltage signal in actual synchronous rotating coordinate system, for The quadrature axis high frequency voltage signal in the actual synchronous rotating coordinate system, , for Direct axis high frequency current signal in actual synchronous rotating coordinate system, for The quadrature-axis high-frequency current signal in the actual synchronous rotating coordinate system.

8. The low speed area position sensorless control method according to claim 7, characterized in that: The first high-frequency current signal equation is: = 。 9. The low speed area position sensorless control method according to claim 5, characterized in that: The second high-frequency current signal equation is: = , in, is the current sampling period.

10. A low-speed zone position sensorless control system, characterized in that: The invention comprises a processor and a three-phase inverter, wherein the processor uses a current sensor to obtain a high-frequency current response generated in the controlled motor, wherein the high-frequency current response is that the processor sets the direct-axis current to zero and the quadrature-axis current to a target current, injects a high-frequency square wave voltage into the direct-axis of the controlled motor after passing through a PI regulator, and then generates a high-frequency current response in the quadrature-axis of the motor through a PARK inverse transformation and pulse width modulation of an SVPWM module through a three-phase inverter output, and calculates a change amount of the high-frequency current response according to the high-frequency current response; The processor injects a high-frequency square wave voltage into the phase-locked loop position observer, and calculates the angle error by using the injected high-frequency square wave voltage, the stator inductance difference, the change in the high-frequency current response, and the current sampling period; The processor integrates the angle error, uses the result of the integration to update the estimated value of the rotor position, and continuously corrects the angle error through feedback until the angle error approaches zero, thereby obtaining the estimated rotor position.

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