A permanent magnet synchronous motor starting method and system

Abstract

The invention discloses a permanent magnet synchronous motor starting method and system, and relates to the technical field of motor control. The method is based on a mathematical model of the permanent magnet synchronous motor in a d-q coordinate system, and detects the initial rotor position by injecting a high-frequency detection pulse into a stator winding; based on the detected position information, applies a pre-magnetization current of a predetermined frequency; uses an S-shaped acceleration curve to gradually increase the voltage frequency and amplitude until the rated speed is reached; in the starting process, the stator current and the rotor position deviation are monitored and adjusted in real time, and a fault protection mechanism is set; the method of the invention can realize the smooth and reliable starting of the permanent magnet synchronous motor, and has strong practicality.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a permanent magnet synchronous motor starting method and system. Background Art

[0002] Permanent magnet synchronous motors have the advantages of high efficiency, high power density and good speed regulation performance, and are widely used in industrial automation, new energy vehicles and other fields. However, since permanent magnets are installed on the rotor of permanent magnet synchronous motors, torque pulsation and unstable starting are prone to occur during the starting process.

[0003] The existing starting methods mainly include V / f open-loop starting and vector control starting. The V / f open-loop starting method is simple to implement, but the starting performance is poor and it is easy to lose steps. The vector control starting method has better performance, but it requires accurate knowledge of the initial position of the rotor and the control algorithm is complex. In addition, the existing starting methods generally lack effective protection mechanisms, which may cause motor damage under abnormal conditions.

[0004] Therefore, it is urgent to develop a permanent magnet synchronous motor starting method that has both reliability and performance. Summary of the invention

[0005] The purpose of the present invention is to solve the problems in the prior art that permanent magnet synchronous motors are unstable in starting, easy to lose step and lack protection mechanisms. Based on the mathematical model of the permanent magnet synchronous motor, a high-frequency signal injection method is used to accurately detect the initial position, and a control strategy combining pre-magnetization and S-shaped acceleration curve is adopted, so as to achieve the purpose of smooth and reliable starting of the permanent magnet synchronous motor.

[0006] In order to achieve the above-mentioned purpose of the present invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for starting a permanent magnet synchronous motor, wherein the permanent magnet synchronous motor comprises a stator and a rotor, wherein the stator has a three-phase winding, and a permanent magnet is arranged on the rotor.

[0008] The mathematical model of the permanent magnet synchronous motor is expressed in the dq coordinate system as follows:

[0009] ;

[0010] ;

[0011] in, , are the d-axis and q-axis voltages, respectively, , are the d-axis and q-axis currents, respectively. , are the d-axis and q-axis inductances, is the stator resistance, is the electrical angular velocity, is the permanent magnet flux, is the start time;

[0012] The starting method controls the current of the d-axis and the q-axis in real time based on the mathematical model, and the starting method comprises the following steps:

[0013] Step S1, detecting the initial rotor position of the permanent magnet synchronous motor;

[0014] Step S2, based on the detected initial rotor position, applying a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency;

[0015] Step S3, after pre-magnetization is completed, gradually increase the frequency and amplitude of the voltage applied to the three-phase winding of the stator according to a preset acceleration curve until the motor reaches the rated speed.

[0016] Furthermore, the detecting the initial rotor position of the permanent magnet synchronous motor includes:

[0017] Step S11, applying high-frequency detection pulses to any two phases of the stator three-phase winding in sequence, the mathematical expression of which is:

[0018] ,in, is the applied high frequency detection pulse, is the pulse amplitude, ranging from 0.1 to 0.5 times the rated voltage, is the high frequency angular frequency, and its value range is rad / s;

[0019] Step S12, collecting the corresponding current response ;

[0020] Step S13, calculating the initial rotor position angle based on the amplitude difference of the current response;

[0021] Based on the amplitude difference of the current response, the initial rotor position angle is calculated by the following formula : ;in, , is the current response amplitude of any two phases.

[0022] Furthermore, the frequency of the pre-magnetization current is 10-100 Hz and the duration is 50-200 ms;

[0023] The pre-magnetization current Take the following expression: ;

[0024] in, is the pre-magnetization current amplitude, ranging from 0.3 to 0.6 times the rated current, is the pre-magnetization frequency, is the pre-magnetization time, and its value range is 50-200ms.

[0025] Furthermore, the stator current is monitored in real time during the pre-magnetization stage. , , when the stator current is detected to exceed the preset threshold , automatically adjust the amplitude of the pre-magnetization current: , and are the pre-magnetization current amplitudes before and after adjustment respectively.

[0026] Furthermore, the preset acceleration curve adopts an S-shaped curve ,

[0027] is the rated angular velocity, is the start time, is the total startup time; a and b are curve coefficients, which are solved by the following equations:

[0028] ; ; ;

[0029] The solution is: .

[0030] Furthermore, the actual rotor position is continuously monitored during the startup process. and theoretical position ;

[0031] When position deviation is detected Exceeding the preset range When the stator current phase angle is adjusted according to the following formula :

[0032] ;in, , is the proportional coefficient, the value range is 0.5-2, is the integral coefficient, and its value range is 0.1-0.5.

[0033] Furthermore, the startup method also includes a fault protection step:

[0034] Real-time monitoring of motor speed during startup , stator current and position deviation ; When any of the following situations occurs, the protection operation is executed:

[0035] The speed ω exceeds 1.2 times the rated speed; the stator current Exceeding 1.5 times of rated current; Position deviation Exceeding ±30° of electrical angle;

[0036] The protection operation includes: cutting off the input voltage and applying a braking current to the stator winding, wherein the amplitude of the braking current does not exceed 0.8 times of the rated current.

[0037] In a second aspect, the present invention provides a permanent magnet synchronous motor starting system, which is used in the method of the first aspect, and the system includes a position detection unit, a pre-magnetization control unit and an acceleration control unit connected in sequence:

[0038] The position detection unit is used to detect the initial rotor position of the permanent magnet synchronous motor;

[0039] The pre-magnetization control unit is used to apply a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency based on the detected initial rotor position;

[0040] The acceleration control unit is used to gradually increase the voltage frequency and amplitude applied to the stator three-phase winding according to a preset acceleration curve after pre-magnetization is completed, until the motor reaches the rated speed.

[0041] Furthermore, the system also includes a current monitoring unit and a current regulating unit:

[0042] The current monitoring unit is used to monitor the stator current in real time. ;

[0043] The current regulating unit is used to adjust the current when the stator current exceeds a preset threshold When the pre-magnetization current amplitude is automatically adjusted, the preset threshold 1.2 times the rated current of the motor.

[0044] Furthermore, the system also includes: a position deviation monitoring unit for continuously monitoring the deviation between the actual position and the theoretical position of the rotor;

[0045] The phase adjustment unit is used to adjust the stator current phase angle when the position deviation exceeds a preset range, wherein the position deviation preset range ±5° of electrical angle.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention adopts a high-frequency signal injection method to detect the initial position, avoiding the disadvantage of adding a position sensor in the traditional method and improving the reliability and economy of the system; a stable magnetic field is established through a pre-magnetization process, combined with a speed control strategy of an S-shaped acceleration curve, which significantly improves the smoothness of the starting process and effectively suppresses torque pulsation; the control method is based on the mathematical model of the permanent magnet synchronous motor, has strong versatility, and can be applied to permanent magnet synchronous motors of different types and specifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flow chart of a method for starting a permanent magnet synchronous motor according to the present invention;

[0049] Figure 2 The figure is a schematic diagram of the composition of a permanent magnet synchronous motor starting system of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] like Figure 1 As shown in FIG. 1 , a flow chart of a method for starting a permanent magnet synchronous motor of the present invention is shown. The permanent magnet synchronous motor comprises a stator and a rotor. The stator has a three-phase winding. A permanent magnet is arranged on the rotor. The mathematical model of the permanent magnet synchronous motor is expressed as follows in the dq coordinate system:

[0053] ;

[0054] ;

[0055] in, , are the d-axis and q-axis voltages, respectively, , are the d-axis and q-axis currents, respectively. , are the d-axis and q-axis inductances, is the stator resistance, is the electrical angular velocity, is the permanent magnet flux, For the startup time.

[0056] The dq coordinate system in this embodiment is a rotating coordinate system, in which the d-axis is consistent with the direction of the rotor magnetic field, and the q-axis leads the d-axis by 90 degrees. This coordinate transformation can convert three-phase AC quantities into two-phase DC quantities, greatly simplifying the design of the control system. In practical applications, the d-axis current is mainly used to adjust the excitation flux, and the q-axis current is mainly used to control the torque. By reasonably configuring the ratio of the d-axis and q-axis currents, different control objectives can be achieved, such as maximum torque control, maximum power factor control, etc.

[0057] The starting method controls the current of the d-axis and the q-axis in real time based on the mathematical model, and the starting method comprises the following steps:

[0058] Step S1, detecting the initial rotor position of the permanent magnet synchronous motor;

[0059] Step S2, based on the detected initial rotor position, applying a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency;

[0060] Step S3, after pre-magnetization is completed, gradually increase the frequency and amplitude of the voltage applied to the three-phase winding of the stator according to a preset acceleration curve until the motor reaches the rated speed.

[0061] The detecting of the initial rotor position of the permanent magnet synchronous motor comprises:

[0062] Step S11, applying high-frequency detection pulses to any two phases of the three-phase stator winding in sequence.

[0063] The frequency selection of high-frequency detection pulses needs to consider the electrical time constant of the motor itself. If the frequency is too low, the detection time will be too long, and if the frequency is too high, the detection signal may be attenuated due to the inductive reactance characteristics of the motor winding. After experimental verification, the best detection effect can be obtained at a frequency of about 2π·1500rad / s. For example, for a permanent magnet synchronous motor with a rated power of 5kW, 0.3 times the rated voltage (about 80V) is selected as the pulse amplitude. When the detection frequency is 1500Hz, the initial position detection can be completed within 20ms, and the position error is less than 3 degrees.

[0064] Its mathematical expression is: ,in, is the applied high frequency detection pulse, is the pulse amplitude, ranging from 0.1 to 0.5 times the rated voltage, is the high frequency angular frequency, and its value range is rad / s.

[0065] Step S12, collecting the corresponding current response ;

[0066] Step S13, calculating the initial rotor position angle based on the amplitude difference of the current response;

[0067] Based on the amplitude difference of the current response, the initial rotor position angle is calculated by the following formula : ;in, , is the current response amplitude of any two phases.

[0068] The frequency of the pre-magnetization current is 10-100 Hz, and the duration is 50-200 ms;

[0069] The pre-magnetization current Take the following expression: ;

[0070] in, is the pre-magnetization current amplitude, ranging from 0.3 to 0.6 times the rated current, is the pre-magnetization frequency, is the pre-magnetization time, and its value range is 50-200ms.

[0071] Real-time monitoring of stator current during the pre-magnetization phase , , when the stator current is detected to exceed the preset threshold , automatically adjust the amplitude of the pre-magnetization current: , and are the pre-magnetization current amplitudes before and after adjustment respectively.

[0072] The core purpose of the pre-magnetization process is to establish a stable magnetic field before starting to prevent the loss of step during the starting process; the selection of the pre-magnetization frequency needs to balance the starting time and the pre-magnetization effect: too low a frequency will extend the starting time, and too high a frequency may result in insufficient magnetic field establishment.

[0073] Analysis of a large amount of experimental data shows that a better pre-magnetization effect can be obtained when the pre-magnetization frequency is selected at around 50Hz and the duration is 100ms; taking a permanent magnet synchronous motor with a rated speed of 3000rpm as an example, using 0.4 times the rated current (about 4A) as the pre-magnetization current amplitude can smoothly establish the stator magnetic field and effectively suppress the torque pulsation during the startup process. The torque fluctuation during the startup process is reduced by about 40%.

[0074] The preset acceleration curve adopts an S-shaped curve , is the rated angular velocity, is the start time, is the total startup time; a and b are curve coefficients, which are solved by the following equations:

[0075] ; ; ;

[0076] The solution is: .

[0077] The design of the S-shaped acceleration curve fully considers the dynamic characteristics of the motor system. By using smaller acceleration at the beginning and end of the acceleration and larger acceleration in the middle, smooth control of the startup process is achieved. The solution process of the curve coefficients a and b takes into account three constraints: the terminal speed condition, the terminal acceleration zero condition, and the midpoint acceleration maximum condition. This curve characteristic makes the speed and acceleration changes very smoothly during the startup process, which can effectively reduce mechanical shock; in practical applications, the startup time T can be adjusted according to the specific parameters of the motor.

[0078] For example, for a permanent magnet synchronous motor with a rated power of 10kW, when the total starting time T=2s is selected, the maximum acceleration of the entire starting process does not exceed 30% of the rated speed per second, which effectively reduces the starting impact.

[0079] Continuous monitoring of the actual rotor position during startup and theoretical position ;

[0080] When position deviation is detected Exceeding the preset range When the stator current phase angle is adjusted according to the following formula :

[0081] ;in, , is the proportional coefficient, the value range is 0.5-2, is the integral coefficient, and its value range is 0.1-0.5.

[0082] The startup method also includes a fault protection step:

[0083] Real-time monitoring of motor speed during startup , stator current and position deviation ; When any of the following situations occurs, the protection operation is executed:

[0084] The speed ω exceeds 1.2 times the rated speed; the stator current Exceeding 1.5 times of rated current; Position deviation Exceeds ±30° of electrical angle.

[0085] The protection operation includes: cutting off the input voltage and applying a braking current to the stator winding, wherein the amplitude of the braking current does not exceed 0.8 times of the rated current.

[0086] In addition, for more precise control, the starting method also includes an adaptive starting control strategy based on load torque: ;in, is the actual acceleration time, is the benchmark acceleration time, is the adaptive coefficient, the value range is 0.5-2, To estimate the load torque, is the rated torque.

[0087] At the same time, the following constraints are met: ; ; ;in: is the minimum permissible acceleration time; is the maximum allowable acceleration time; is the maximum permissible angular acceleration.

[0088] Example 2

[0089] A permanent magnet synchronous motor starting system, used to execute the method of embodiment 1, such as Figure 2 As shown, it is a schematic diagram of the composition of a permanent magnet synchronous motor starting system of the present invention; the system includes a position detection unit, a pre-magnetization control unit and an acceleration control unit connected in sequence.

[0090] The position detection unit is used to detect the initial rotor position of the permanent magnet synchronous motor.

[0091] The pre-magnetization control unit is used to apply a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency based on the detected initial rotor position.

[0092] The acceleration control unit is used to gradually increase the voltage frequency and amplitude applied to the stator three-phase winding according to a preset acceleration curve after pre-magnetization is completed, until the motor reaches the rated speed.

[0093] This system adopts modular design concept, and each functional unit is connected through a standardized interface, which has strong scalability and maintainability. The position detection unit uses a high-performance DSP as the core processor, which has high-speed sampling and real-time processing capabilities and can complete a position calculation within 0.1ms.

[0094] The pre-magnetization control unit and the acceleration control unit are implemented using FPGA, which can realize complex PWM modulation strategies. The PWM carrier frequency can reach 20kHz, greatly improving the accuracy of current control.

[0095] The current monitoring unit uses a Hall sensor for current sampling, with a sampling accuracy better than 0.1% and a sampling frequency of up to 100kHz.

[0096] The system also includes a current monitoring unit and a current regulating unit; the current monitoring unit is used to monitor the stator current in real time. The current regulating unit is used to adjust the current when the stator current exceeds the preset threshold When the pre-magnetization current amplitude is automatically adjusted, the preset threshold 1.2 times the rated current of the motor.

[0097] The system also includes: a position deviation monitoring unit for continuously monitoring the deviation between the actual rotor position and the theoretical position; a phase adjustment unit for adjusting the stator current phase angle when the position deviation exceeds a preset range, wherein the position deviation preset range ±5° of electrical angle.

[0098] The technical effect of the present invention is illustrated below with a practical application case: In a new energy vehicle drive motor project, the starting method of the present invention is used to control a permanent magnet synchronous motor with a rated power of 30kW and a rated speed of 6000rpm. The motor has the following parameters: stator resistance Rs=0.1Ω, d-axis inductance Ld=2mH, q-axis inductance Lq=3mH, permanent magnet flux ψf=0.175Wb.

[0099] By adopting the method of the present invention, during the entire starting process: the initial position detection time only takes 25 ms, and the position detection error is less than 2 degrees; the pre-magnetization stage adopts a 50 Hz frequency, 0.5 times the rated current, and lasts for 150 ms to successfully establish a stable magnetic field; the acceleration process adopts an S-shaped curve with a total time T=3s, and the maximum torque fluctuation does not exceed 5%, which is 65% lower than the traditional V / f starting method; during the entire starting process, the stator current is always kept below the rated value, the maximum position deviation does not exceed 3 degrees, and the protection mechanism is not triggered.

[0100] This method has been verified on 100 motors of the same model, with a startup success rate of 99.9%, demonstrating extremely high reliability.

[0101] Compared with the traditional V / f starting method, the starting method of the present invention has obvious advantages: the starting time is shortened by about 40%, the torque pulsation is reduced by 65%, and the stator current peak is reduced by about 35%. These improvements significantly improve the dynamic performance and reliability of the motor system and provide an effective solution for the optimization of the new energy vehicle drive system.

[0102] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for starting a permanent magnet synchronous motor, wherein the permanent magnet synchronous motor comprises a stator and a rotor, wherein the stator has a three-phase winding and a permanent magnet is arranged on the rotor, wherein: The mathematical model of the permanent magnet synchronous motor is expressed in the dq coordinate system as follows: ； ； in, , are the d-axis and q-axis voltages, respectively, , are the d-axis and q-axis currents, respectively. , are the d-axis and q-axis inductances, is the stator resistance, is the electrical angular velocity, is the permanent magnet flux, is the start time; The starting method controls the current of the d-axis and the q-axis in real time based on the mathematical model, and the starting method comprises the following steps: Step S1, detecting the initial rotor position of the permanent magnet synchronous motor; Step S2, based on the detected initial rotor position, applying a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency; Step S3, after the pre-magnetization is completed, gradually increasing the voltage frequency and amplitude applied to the stator three-phase winding according to a preset acceleration curve until the motor reaches the rated speed; Continuous monitoring of the actual rotor position during startup and theoretical position ; When position deviation is detected Exceeding the preset range When the stator current phase angle is adjusted according to the following formula : ;in, , is the proportional coefficient, the value range is 0.5-2, is the integral coefficient, and its value range is 0.1-0.

5.

2. A permanent magnet synchronous motor starting method according to claim 1, characterized in that: The detecting of the initial rotor position of the permanent magnet synchronous motor comprises: Step S11, applying high-frequency detection pulses to any two phases of the stator three-phase winding in sequence, the mathematical expression of which is: ,in, is the applied high frequency detection pulse, is the pulse amplitude, ranging from 0.1 to 0.5 times the rated voltage, is the high frequency angular frequency, and its value range is rad / s; Step S12, collecting the corresponding current response ; Step S13, calculating the initial rotor position angle based on the amplitude difference of the current response; Based on the amplitude difference of the current response, the initial rotor position angle is calculated by the following formula : ;in, , is the current response amplitude of any two phases.

3. A permanent magnet synchronous motor starting method according to claim 1, characterized in that: The frequency of the pre-magnetization current is 10-100 Hz, and the duration is 50-200 ms; The pre-magnetization current Take the following expression: ; in, is the pre-magnetization current amplitude, ranging from 0.3 to 0.6 times the rated current, is the pre-magnetization frequency, is the pre-magnetization time, and its value range is 50-200ms.

4. A permanent magnet synchronous motor starting method according to claim 1, characterized in that: Real-time monitoring of stator current during the pre-magnetization phase , , when the stator current is detected to exceed the preset threshold , automatically adjust the amplitude of the pre-magnetization current: , and are the pre-magnetization current amplitudes before and after adjustment respectively.

5. A permanent magnet synchronous motor starting method according to claim 4, characterized in that: The preset acceleration curve adopts an S-shaped curve , is the rated angular velocity, is the start time, is the total start-up time; a and b are curve coefficients.

6. A permanent magnet synchronous motor starting method according to claim 5, characterized in that: The startup method also includes a fault protection step: Real-time monitoring of motor speed during startup , stator current and position deviation ; When any of the following situations occurs, the protection operation is executed: The speed ω exceeds 1.2 times the rated speed; the stator current Exceeding 1.5 times of the rated current; Position deviation Exceeding ±30° of electrical angle; The protection operation includes: cutting off the input voltage and applying a braking current to the stator winding, wherein the amplitude of the braking current does not exceed 0.8 times of the rated current.

7. A permanent magnet synchronous motor starting system, used to execute the method according to any one of claims 1 to 6, characterized in that: The system comprises a position detection unit, a pre-magnetization control unit and an acceleration control unit connected in sequence: The position detection unit is used to detect the initial rotor position of the permanent magnet synchronous motor; The pre-magnetization control unit is used to apply a pre-magnetization current to the stator three-phase winding using a pulse width modulation signal of a predetermined frequency based on the detected initial rotor position; The acceleration control unit is used to gradually increase the voltage frequency and amplitude applied to the stator three-phase winding according to a preset acceleration curve after pre-magnetization is completed, until the motor reaches the rated speed.

8. A permanent magnet synchronous motor starting system according to claim 7, characterized in that: The system also includes a current monitoring unit and a current regulating unit: The current monitoring unit is used to monitor the stator current in real time. ; The current regulating unit is used to adjust the current when the stator current exceeds a preset threshold When the pre-magnetization current amplitude is automatically adjusted, the preset threshold 1.2 times the rated current of the motor.

9. A permanent magnet synchronous motor starting system according to claim 8, characterized in that: The system further comprises: a position deviation monitoring unit for continuously monitoring the deviation between the actual position and the theoretical position of the rotor; The phase adjustment unit is used to adjust the stator current phase angle when the position deviation exceeds a preset range, wherein the position deviation preset range ±5° of electrical angle.

Images