Method and system for acquiring initial position of permanent magnet motor

Abstract

The invention discloses a permanent magnet motor initial position obtaining method and system, and relates to the technical field of permanent magnet motor control, and the method comprises the following steps: collecting a three-phase current of a permanent magnet motor in a state of injecting a high-frequency square wave voltage signal, converting the three-phase current through a CLARK coordinate conversion method, and extracting a high-frequency response current based on the difference of adjacent sampling points; outputting an envelope signal of the high-frequency response current according to the high-frequency square wave voltage signal and the high-frequency response current; processing the envelope signal through an LTI-EPLL differential equation, outputting an estimated position and an estimated amplitude of a high-frequency response current, and identifying NS polarity; according to the NS polarity discrimination result, the estimated position is corrected, and final rotor position information is output; according to the invention, through the high-frequency injection and LTI-EPLL method, the initial position identification precision and polarity discrimination of the permanent magnet motor are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of permanent magnet motor control, in particular to a permanent magnet motor initial position acquisition method and system. BACKGROUND

[0002] The position sensorless control as an advanced control strategy, with small size, low cost and high reliability, shows broad application prospects in the scene of robot joint module. In the position sensorless control technology, the algorithm research on improving the motor starting process and low-speed running performance has become the current hot spot. Good starting performance requires the motor to start smoothly and reliably, without reverse vibration, low starting current and high energy efficiency; and excellent low-speed running performance requires the motor to run smoothly and reliably at low speed, with minimum rotor vibration. The key to achieving the above performance lies in the accurate estimation of the rotor position. If the position estimation is not accurate, the current required to drive the motor will increase, resulting in a decrease in energy efficiency, which is particularly important in precise control scenes such as robot joint modules.

[0003] For example, the application patent with the publication number CN104022714B discloses a kind of permanent magnet synchronous motor rotor initial position angle acquisition method and device, comprising: the three-phase current ia, ib and ic collected are equal to transform, obtain the current ialfa and ibeta in two-phase αβ coordinate system;Obtain current α-axis reference current ialfa_ref and β-axis reference current ibeta_ref, obtain α-axis reference voltage ualfa_ref and β-axis reference voltage ubeta_ref by PI control, update α-axis reference current ialfa_ref according to step length;According to the current α-axis reference voltage ualfa_ref and the β-axis reference voltage ubeta_ref, obtain PWM control signal, drive the permanent magnet synchronous motor;Again execute the foregoing step, until detecting that the motor stops rotating;Collect the current position angle and the rotating direction of the time when motor stops rotating, obtain the initial position angle. By the method and device, the initial position angle of motor rotor can be accurately obtained, and the accuracy and reliability of motor control are improved.

[0004] For example, the invention patent with publication number CN110138302A discloses a method and apparatus for obtaining the initial position angle of the rotor of a permanent magnet synchronous motor. The method includes: obtaining a first current response value corresponding to the first voltage excitation applied between the first phase and the second phase of the permanent magnet synchronous motor; obtaining a first angle and a second angle between the N-stage of the rotor and the first phase of the permanent magnet synchronous motor based on the voltage value and angular frequency corresponding to the first voltage excitation and the first current response value; if the first angle and the second angle are not the same, obtaining a second current response value after applying a second voltage excitation between the first phase and the third phase of the permanent magnet synchronous motor, obtaining a third current response value after applying a third voltage excitation between the second phase and the third phase of the permanent magnet synchronous motor; and determining the initial position angle of the rotor of the permanent magnet synchronous motor from the first angle and the second angle based on the magnitude of the second current response value and the third current response value.

[0005] The above-disclosed technical solutions have at least the following technical problems: Traditional identification of N / S polarity requires the injection of a pulse signal in addition to a square wave signal. This not only increases the complexity of the system, but also affects the accuracy of position estimation due to the additional pulse injection.

[0006] To address the above problems, this invention proposes a solution. Summary of the Invention

[0007] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a method and system for obtaining the initial position of a permanent magnet motor, which solves the problems of initial position recognition accuracy and polarity discrimination of permanent magnet motors through high-frequency injection and LTI-EPLL method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for obtaining the initial position of a permanent magnet motor includes: acquiring the three-phase current of the permanent magnet motor under the condition of injecting a high-frequency square wave voltage signal; converting the three-phase current using the CLARK coordinate transformation method; and extracting the high-frequency response current based on the difference between adjacent sampling points; outputting the envelope signal of the high-frequency response current according to the high-frequency square wave voltage signal and the high-frequency response current; processing the envelope signal using the LTI-EPLL differential equation to output the estimated position and estimated amplitude of the high-frequency response current, and identifying the NS polarity; correcting the estimated position according to the NS polarity discrimination result, and outputting the final rotor position information.

[0009] In a preferred embodiment, the three-phase current of the permanent magnet motor under the injected high-frequency square wave voltage signal is collected, and the three-phase current is transformed using the Clarke coordinate transformation method. The high-frequency response current is extracted based on the difference between adjacent sampling points, specifically as follows: Permanent magnet motor parameters and control constraints are acquired, and the target injected current amplitude is set; the electrical cutoff frequency is calculated based on the permanent magnet motor impedance, and the injection frequency is selected; the fundamental voltage and square wave peak voltage are calculated based on the target injected current amplitude and motor impedance to obtain the injected high-frequency square wave voltage signal; the high-frequency square wave voltage signal is injected into the permanent magnet motor, and the three-phase current is collected synchronously; after bias removal and zero-sequence component elimination of the collected three-phase current, the α and β axis currents are obtained through Clarke coordinate transformation; the current sampled value of the α and β axis currents is subtracted from the previous sampled value to obtain the high-frequency response currents of the α and β axes, respectively.

[0010] In a preferred embodiment, the step of outputting the envelope signal of the high-frequency response current based on the high-frequency square wave voltage signal and the high-frequency response current is specifically as follows: obtaining the voltage signal injected by the high-frequency square wave along the d-axis and the corresponding high-frequency response current; multiplying the high-frequency response current and the voltage signal injected by the high-frequency square wave along the d-axis by combining the sign function to obtain the envelope signals of the α-axis and β-axis.

[0011] In a preferred embodiment, the process of processing the envelope signal using the LTI-EPLL differential equation to output the estimated position and amplitude of the high-frequency response current and identify the N / S polarity is as follows: A differential equation model of the LTI-EPLL is constructed to output the estimated amplitude and estimated position, and the input signal is processed to give it periodic variation characteristics; based on the estimated amplitude and estimated position, the tracking error is output; the amplitude and phase of the input signal are extracted using the LTI-EPLL, and the estimated position and estimated amplitude of the rotor are obtained by back-calculating the tracking error using the formula based on the angular frequency of the injected signal; the current amplitude and position of the rotor are obtained, and the differential of the estimated residual is output based on the estimated position and estimated amplitude; the differential of the estimated residual is substituted into the differential equation model of the LTI-EPLL to output the error of the estimated amplitude of the rotor; the estimated position and estimated amplitude are determined to be converged based on the error of the estimated amplitude; if the estimated position and estimated amplitude are converged, the N / S polarity is identified based on the bidirectional convergence characteristic of the LTI-EPLL.

[0012] In a preferred embodiment, if the estimated position and the estimated amplitude converge, the N / S polarity is identified based on the bidirectional convergence characteristic of LTI-EPLL, specifically as follows: According to the bidirectional convergence characteristic of LTI-EPLL, two convergence points, namely P+ and P-, are extracted; when converged at point P+, the amplitude is positive and the phase error tends to 0; when converged at point P-, the amplitude is negative and the phase error tends to π radians; the N / S polarity of the rotor magnetic pole is determined according to the sign of the amplitude; if the amplitude > 0, the rotor is determined to be in the N pole position; if the amplitude < 0, the rotor is determined to be in the S pole position.

[0013] A system for obtaining the initial position of a permanent magnet motor is characterized by comprising an extraction module, an envelope signal module, an N / S polarity identification module, and a correction module, with interconnections between the modules. The extraction module collects the three-phase current of the permanent magnet motor under the injected high-frequency square wave voltage signal, transforms the three-phase current using the Clark coordinate transformation method, and extracts the high-frequency response current based on the difference between adjacent sampling points. The envelope signal module outputs the envelope signal of the high-frequency response current based on the high-frequency square wave voltage signal and the high-frequency response current. The N / S polarity identification module processes the envelope signal using the LTI-EPLL differential equation, outputs the estimated position and estimated amplitude of the high-frequency response current, and identifies the N / S polarity. The correction module corrects the estimated position based on the N / S polarity determination result and outputs the final rotor position information.

[0014] The technical effects and advantages of the method and system for obtaining the initial position of a permanent magnet motor according to the present invention are as follows: 1. This invention constructs a model of a high-frequency square wave injection method and extracts the high-frequency response current. Then, it uses an LTI-EPLL instead of a traditional QPLL to extract the initial position. Finally, utilizing the bidirectional convergence characteristic of the LTI-EPLL, the phase and amplitude of the high-frequency response current can be obtained simultaneously, where the phase corresponds to the rotor's initial position, and the positive and negative amplitudes correspond to the N / S polarity, thus achieving simultaneous acquisition of the rotor's initial position and N / S polarity.

[0015] 2. In the N / S polarity discrimination and position correction stages, this invention fully utilizes the bidirectional convergence characteristic of LTI-EPLL: when the system converges to point P+, the amplitude is positive and the phase error tends to zero; when the system converges to point P-, the amplitude is negative and the phase error tends to π. By judging the sign of the amplitude, the N and S poles of the rotor magnetic poles can be accurately distinguished. Based on this result, the correction module can perform polarity compensation on the estimated position and output the final rotor position information. This design not only ensures the correctness of the method in N / S polarity discrimination but also eliminates the ambiguity problem caused by symmetry, thereby achieving a globally unique solution for the initial position. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the process for obtaining the initial position of a permanent magnet motor according to the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of a permanent magnet motor initial position acquisition system according to the present invention. Detailed Implementation

[0018] 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.

[0019] Example 1, Figure 1 The present invention provides a method for obtaining the initial position of a permanent magnet motor, comprising the following steps: S1: Collect the three-phase current of the permanent magnet motor under the condition of injecting a high-frequency square wave voltage signal, convert the three-phase current through the CLARK coordinate transformation method, and extract the high-frequency response current based on the difference between adjacent sampling points. In this embodiment, the three-phase current of the permanent magnet motor is acquired under the condition of injecting a high-frequency square wave voltage signal. The three-phase current is transformed using the Clark coordinate transformation method, and the high-frequency response current is extracted based on the difference between adjacent sampling points, as detailed below: Obtain the parameters and control constraints of the permanent magnet motor, and set the target injection current amplitude, wherein the current amplitude is 0.5% to 5% of the rated current; The electrical cutoff frequency is calculated based on the impedance of the permanent magnet motor, and the injection frequency is selected to be greater than the control bandwidth and the electrical cutoff frequency, while avoiding the inverter switching frequency. Based on the target injected current amplitude and the motor impedance, the fundamental voltage and the square wave peak voltage are calculated to obtain the injected high-frequency square wave voltage signal. A high-frequency square wave voltage signal is injected into the permanent magnet motor, and the three-phase current is collected simultaneously. After removing the offset and eliminating the zero-sequence component of the collected three-phase current, the α and β axis currents are obtained through Clarke coordinate transformation; Subtract the previous sample value from the current sample value of the α-axis and β-axis currents to obtain the high-frequency response currents of the α-axis and β-axis, respectively.

[0020] The calculation formula for the high-frequency voltage signal is as follows:

[0021] The three-phase current conversion using the Clark coordinate transformation method is as follows:

[0022] The formula for calculating the high-frequency response current is as follows:

[0023] In the formula: U inj This represents the amplitude of the square wave voltage signal; k is related to the injection frequency of the high-frequency voltage signal, and its value varies between 1 and -1. Each variation changes the sign of the injected signal to generate the square wave. Its angular frequency is expressed as... To indicate, Injecting a high-frequency voltage signal along the d-axis. These are the q-axis high-frequency injected voltage signals, respectively. i α It is the α-axis current. i β It is the β-axis current. i a , i b and i c It is a three-phase current.

[0024] S2, based on the high-frequency square wave voltage signal and the high-frequency response current, outputs the envelope signal of the high-frequency response current; In this embodiment, based on the high-frequency square wave voltage signal and the high-frequency response current, the envelope signal of the high-frequency response current is output, as follows: Obtain the voltage signal injected by the high-frequency square wave along the d-axis and the corresponding high-frequency response current; Based on the high-frequency response current and the voltage signal injected by the high-frequency square wave along the d-axis, the envelope signals of the α-axis and β-axis are obtained by multiplying the high-frequency response current and the voltage signal injected by the high-frequency square wave along the d-axis using a sign function.

[0025] The envelope signal is as follows:

[0026] In the formula: I αh It is the envelope signal of the α axis. ，I βh It is the envelope signal along the β axis. Injecting a high-frequency voltage signal along the d-axis. These are the q-axis high-frequency injected voltage signals, respectively. i αh This represents the high-frequency response current along the α-axis. i βh This is the high-frequency response current along the β axis.

[0027] S3 processes the envelope signal using the LTI-EPLL differential equation, outputs the estimated location and amplitude of the high-frequency response current, and identifies the N and S polarities. In this embodiment, the envelope signal is processed using the LTI-EPLL differential equation to output the estimated location and amplitude of the high-frequency response current, and the N-S polarity is identified, as follows: Construct a differential equation model for LTI-EPLL, output the estimated amplitude and estimated position, and process the input signal to make the input signal have periodic variation characteristics; Based on the estimated amplitude and estimated position, the tracking error is output, which is the error between the actual input signal and the estimated value of the input signal. The amplitude and phase of the input signal are extracted by LTI-EPLL, and the estimated position and amplitude of the rotor are obtained by back-calculating the tracking error using the formula of the angular frequency of the injected signal. Obtain the current rotor amplitude and position, and output the derivative of the estimated residual based on the estimated position and estimated amplitude; Substituting the differential of the estimated residual into the differential equation model of LTI-EPLL, the error of the estimated rotor amplitude and the error of the estimated amplitude are output. Determine whether the estimated position and the estimated amplitude converge based on the error of the estimated amplitude; If the estimated position and the estimated magnitude converge, the polarity of NS can be identified based on the bidirectional convergence characteristic of LTI-EPLL.

[0028] The differential equation model of the LTI-EPLL is as follows:

[0029] The tracking error is as follows:

[0030] The differential of the estimated residual is as follows:

[0031] When the estimated location converges to Furthermore, when the estimated amplitude converges to A, the two frequency harmonics will partially cancel each other out, and the differential of the estimated residual will simplify to:

[0032] In the formula: For input signal, To track errors, The angular frequency of the injected signal, To estimate the location, The phase of the input signal, which contains rotor position information. To estimate the phase, To estimate the differential of the phase, To estimate the amplitude, To estimate the differential of the amplitude, and To ensure system stability and for the purpose of design gain, its value needs to be set to 120% of the electrical angular velocity. This represents the actual position of the rotor.

[0033] The input signal is processed to give it periodic variation characteristics, as detailed below:

[0034] In the formula: I αh It is the envelope signal of the α axis. ，I βh It is the envelope signal along the β axis. For input signal, For amplitude, Let ω be the angular frequency of the injected signal, and t be time. The phase of the input signal.

[0035] In this embodiment, if the estimated position and estimated amplitude converge, the NS polarity is identified based on the bidirectional convergence characteristic of LTI-EPLL, as follows: Based on the bidirectional convergence characteristics of LTI-EPLL, two convergence points are extracted, namely P+: (A, ε)=(U, 0) and P-: (A, ε)=(-U, π). When it converges to point P+, the amplitude A is positive and the phase error ε approaches 0; When it converges to point P-, the amplitude A is negative and the phase error ε tends to π radians; The polarity of the rotor magnetic poles (NS) is determined by the sign of the amplitude A. If A > 0, then the rotor is determined to be in the N-pole position; If A < 0, then the rotor is determined to be in the S pole position.

[0036] S4, Based on the determination result of NS polarity, the estimated position is corrected and the final rotor position information is output; In this embodiment, the estimated position is corrected based on the N / S polarity determination result, and the final rotor position information is output as follows: Based on the discrimination results of NS polarity, the NS polarity identification correction amount is obtained; Based on the NS polarity identification correction amount, the estimated position is corrected to obtain the initial position for starting the permanent magnet motor.

[0037] The NS polarity identification correction amount is obtained based on the NS polarity discrimination result, as follows:

[0038] The initial position is as follows:

[0039] In the formula: This is the correction amount for NS polarity identification. For amplitude, Pi The final position information of the input closed-loop system is used, which is the initial position of the permanent magnet motor when it starts.

[0040] Example 2, Figure 2 The present invention provides a system for obtaining the initial position of a permanent magnet motor, comprising an extraction module, an envelope signal module, an N / S polarity identification module, and a correction module, wherein the modules are interconnected. The extraction module is used to collect the three-phase current of the permanent magnet motor under the condition of injecting a high-frequency square wave voltage signal, convert the three-phase current through the CLARK coordinate transformation method, and extract the high-frequency response current based on the difference between adjacent sampling points. The envelope signal module is used to output the envelope signal of the high-frequency response current based on the high-frequency square wave voltage signal and the high-frequency response current. The NS polarity identification module is used to process the envelope signal through the LTI-EPLL differential equation, output the estimated position and estimated amplitude of the high-frequency response current, and identify the NS polarity. The correction module is used to correct the estimated position based on the determination result of the N and S polarities and output the final rotor position information.

[0041] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0042] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0043] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0044] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0045] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0046] 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 method for obtaining the initial position of a permanent magnet motor, characterized in that, include: The three-phase current of the permanent magnet motor under the condition of injecting a high-frequency square wave voltage signal is collected, the three-phase current is transformed by the CLARK coordinate transformation method, and the high-frequency response current is extracted based on the difference between adjacent sampling points. Based on the high-frequency square wave voltage signal and the high-frequency response current, the envelope signal of the high-frequency response current is output. The envelope signal is processed by the LTI-EPLL differential equation to output the estimated location and amplitude of the high-frequency response current, and the N-S polarity is identified. Based on the determination of NS polarity, the estimated position is corrected, and the final rotor position information is output.

2. The method for obtaining the initial position of a permanent magnet motor according to claim 1, characterized in that, The process involves acquiring the three-phase current of the permanent magnet motor under the injected high-frequency square wave voltage signal, transforming the three-phase current using the Clark coordinate transformation method, and extracting the high-frequency response current based on the difference between adjacent sampling points, as detailed below: Obtain permanent magnet motor parameters and control constraints, and set the target injection current amplitude; Calculate the electrical cutoff frequency based on the impedance of the permanent magnet motor, and select the injection frequency; Based on the target injected current amplitude and the motor impedance, the fundamental voltage and the square wave peak voltage are calculated to obtain the injected high-frequency square wave voltage signal. A high-frequency square wave voltage signal is injected into the permanent magnet motor, and the three-phase current is collected simultaneously. After removing the offset and eliminating the zero-sequence component of the collected three-phase current, the α and β axis currents are obtained through Clarke coordinate transformation; Subtract the previous sample value from the current sample value of the α-axis and β-axis currents to obtain the high-frequency response currents of the α-axis and β-axis, respectively.

3. The method for obtaining the initial position of a permanent magnet motor according to claim 2, characterized in that, The process of outputting the envelope signal of the high-frequency response current based on the high-frequency square wave voltage signal and the high-frequency response current is as follows: Obtain the voltage signal injected by the high-frequency square wave along the d-axis and the corresponding high-frequency response current; Based on the high-frequency response current and the voltage signal injected by the high-frequency square wave along the d-axis, the envelope signals of the α-axis and β-axis are obtained by multiplying the high-frequency response current and the voltage signal injected by the high-frequency square wave along the d-axis using a sign function.

4. The method for obtaining the initial position of a permanent magnet motor according to claim 3, characterized in that, The envelope signal is processed using the LTI-EPLL differential equation to output the estimated location and amplitude of the high-frequency response current, and the N-S polarity is identified, as follows: Construct a differential equation model for LTI-EPLL, output the estimated amplitude and estimated position, and process the input signal to make the input signal have periodic variation characteristics; Based on the estimated amplitude and estimated position, the tracking error is output; The amplitude and phase of the input signal are extracted by LTI-EPLL, and the estimated position and amplitude of the rotor are obtained by back-calculating the tracking error using the formula of the angular frequency of the injected signal. Obtain the current rotor amplitude and position, and output the derivative of the estimated residual based on the estimated position and estimated amplitude; Substituting the differential of the estimated residual into the differential equation model of LTI-EPLL, the error of the estimated rotor amplitude and the error of the estimated amplitude are output. Determine whether the estimated position and the estimated amplitude converge based on the error of the estimated amplitude; If the estimated position and the estimated magnitude converge, the polarity of NS can be identified based on the bidirectional convergence characteristic of LTI-EPLL.

5. The method for obtaining the initial position of a permanent magnet motor according to claim 4, characterized in that, If the estimated position and estimated magnitude converge, the polarity of NS is identified based on the bidirectional convergence characteristic of LTI-EPLL, as follows: Based on the bidirectional convergence characteristics of LTI-EPLL, two convergence points are extracted, namely P+ and P-. When it converges to point P+, the amplitude is positive and the phase error tends to 0; When it converges to point P-, the amplitude is negative and the phase error tends to π radians; The polarity of the rotor magnetic poles (NS) is determined by the sign of the amplitude. If the amplitude is greater than 0, the rotor is determined to be in the N-pole position; If the amplitude is less than 0, the rotor is determined to be in the S pole position.

6. The method for obtaining the initial position of a permanent magnet motor according to claim 5, characterized in that, The estimated position is corrected based on the N / S polarity discrimination result, and the final rotor position information is output as follows: Based on the discrimination results of NS polarity, the NS polarity identification correction amount is obtained; Based on the NS polarity identification correction amount, the estimated position is corrected to obtain the initial position for starting the permanent magnet motor.

7. A system using the method for obtaining the initial position of a permanent magnet motor as described in any one of claims 1-6, characterized in that, It includes an extraction module, an envelope signal module, an N / S polarity identification module, and a correction module, and the modules are interconnected. The extraction module is used to collect the three-phase current of the permanent magnet motor under the condition of injecting a high-frequency square wave voltage signal, convert the three-phase current through the CLARK coordinate transformation method, and extract the high-frequency response current based on the difference between adjacent sampling points. The envelope signal module is used to output the envelope signal of the high-frequency response current based on the high-frequency square wave voltage signal and the high-frequency response current. The NS polarity identification module is used to process the envelope signal through the LTI-EPLL differential equation, output the estimated position and estimated amplitude of the high-frequency response current, and identify the NS polarity. The correction module is used to correct the estimated position based on the determination result of the N and S polarities and output the final rotor position information.

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