Improved pulsating high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control strategy based on three-parameter notch filter

Abstract

The invention belongs to a permanent magnet synchronous motor control technology. The invention relates to an improved pulsating high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control strategy based on a three-parameter notch filter. The strategy comprises the following steps: selecting the frequency and amplitude of injection voltage based on a mathematical model under the permanent magnet synchronous motor low-speed domain and pulsating high-frequency voltage injection conditions; according to the frequency of the selected injection voltage and the frequency of the fundamental wave voltage in the system, selecting a proper three-parameter filter TPNF filtering parameter to form a current loop structure of the novel permanent magnet synchronous motor control system; and forming an improved pulsating high-frequency voltage injection position demodulation strategy according to the TPNF filtering parameters in combination with a fourth-order generalized integrator, and constructing a TPNF-based improved pulsating high-frequency voltage injection sensorless control strategy based on the demodulation strategy. The purpose of improving the precision of a position observation result is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet synchronous motor control, and in particular relates to a sensorless control strategy for permanent magnet synchronous motors in the low-speed range based on the improvement of a three-parameter notch filter for pulsating high-frequency voltage injection. Background Art

[0002] Under the background of promoting the development goals of "carbon peak and carbon neutrality", the wide application of electric vehicles provides important support for China's automotive industry to achieve emission reduction goals. Thanks to policy support and the growth of market demand, the production of new energy vehicles in China reached 7.058 million in 2022, and the sales volume was 6.887 million, with year-on-year growth rates of 96.9% and 93.4% respectively. The market penetration rate rose to 25.6%, an increase of 12.1 percentage points compared with 2021. In order to enable more vehicles using green energy to drive on future roads, the development of sensorless control technology for permanent magnet synchronous motors has become one of the effective means to improve the motor control performance of electric vehicles and achieve emission reduction goals.

[0003] In the research of sensorless control technology for permanent magnet synchronous motors, the function of physical position sensors is mainly replaced by designing rotor position estimation algorithms. Such technologies can be roughly divided into two types: model methods and injection methods. The model method relies on the parameters and mathematical model of the permanent magnet synchronous motor itself, and obtains the rotor position information by detecting the back electromotive force. However, at low speeds, due to the low back electromotive force, it is difficult to achieve accurate position estimation based on the motor model. Therefore, this type of method is usually only applicable to medium and high-speed operation conditions. In contrast, the high-frequency injection method observes the rotor position by applying a high-frequency signal to the motor, showing a higher signal-to-noise ratio in the low-speed state, and is particularly suitable for sensorless control of permanent magnet synchronous motors in the low-speed range. Especially the pulsating high-frequency injection technology, by applying a high-frequency voltage on the D-axis of the estimated synchronous rotating coordinate system, triggers the saturation salient pole effect of the permanent magnet, thus generating an obvious salient pole phenomenon. This technology shows good applicability in both interior permanent magnet synchronous motors (IPMSM) and surface-mounted permanent magnet synchronous motors (SPMSM), especially meeting the requirements of sensorless control when electric vehicles are driving at low speeds. However, the traditional pulsating high-frequency injection method does not fully consider the group delay effect of the filter during position observation, resulting in a large error in the position observation result. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a sensorless control strategy for permanent magnet synchronous motors in the low-speed range based on the improvement of a three-parameter notch filter for pulsating high-frequency voltage injection, which at least partially solves the problem of large errors in position observation results existing in the prior art.

[0005] An embodiment of the present invention provides a sensorless control strategy for a permanent magnet synchronous motor in the low-speed range based on the improvement of a three-parameter notch filter, including:

[0006] Step 1, select appropriate filtering parameters of the three-parameter notch filter according to the frequency of the injected voltage and the frequency of the fundamental voltage in the system, and form an improved current loop structure in the new permanent magnet synchronous motor control system;

[0007] Step 2, according to the filtering parameters of the three-parameter notch filter and combined with a fourth-order generalized integrator, form an improved position demodulation strategy for pulsating high-frequency voltage injection, and form an improved speed loop structure in the new permanent magnet synchronous motor control system;

[0008] Step 3, jointly form a sensorless control system for a permanent magnet synchronous motor in the low-speed range based on the improvement of pulsating high-frequency voltage injection by the improved current loop and speed loop in series.

[0009] Optionally; in Step 1, an improved current loop control structure based on a three-parameter notch filter is established; first, analyze the working characteristics and operation process of the permanent magnet synchronous motor under the condition of pulsating high-frequency voltage injection in the low-speed range, so as to determine the mathematical model of the permanent magnet synchronous motor under the conditions of the low-speed range and pulsating high-frequency voltage injection, and select the frequency and amplitude of the injected voltage based on the mathematical model; secondly, design the filtering parameters of the three-parameter notch filter, and the parameter design process includes determining the filtering parameters of the three-parameter notch filter based on the transfer function of the three-parameter notch filter;

[0010] The transfer function of the three-parameter notch filter is:

[0011] In the formula , ω b is the difference between the notch bandwidth of the notch filter and the frequency when the amplitude attenuation reaches -3dB, δ p is the notch depth, ω n is the center frequency of the notch filter and the pulsating high-frequency voltage injection frequency, s is a complex variable; set the center frequency, notch depth, and notch bandwidth of the notch filter according to the injection frequency and the requirements of the system dynamic performance; finally, replace the low-pass filter on the traditional pulsating high-frequency voltage injection current loop structure with a three-parameter notch filter to form an improved current loop structure in the new permanent magnet synchronous motor control system.

[0012] Optional; in Step 2, a speed loop control structure improved based on a three-parameter notch filter and a fourth-order generalized integrator is established. First, according to the mathematical model of the permanent magnet synchronous motor under the condition of pulsating high-frequency voltage injection in the low-speed range and the frequency and amplitude of the injected voltage, the parameters of the fourth-order generalized integrator are set. The parameter design process includes setting parameters according to the fourth-order generalized integration transfer function and the characteristic equation.

[0013] The transfer function of the fourth-order generalized integrator is:

[0014] The characteristic equation of the fourth-order generalized integrator is:

[0015] The fourth-order standard characteristic equation is:

[0016] In the transfer function of the fourth-order generalized integrator, k 1 and k 2 are the filtering parameters of the fourth-order generalized integrator, which determine the filtering bandwidth, and ω is the filtering center frequency of the filter; in the standard fourth-order characteristic equation, ξ = 0.707; ωn1, ω n2 , ω n3 are the natural frequencies of oscillation of each pole of the standard characteristic equation; c 1 , c 2 , c 3 are constants. To simplify the parameter tuning process, let c 1 = c 2 = 1, c 3 = 0.05. Assume that the oscillation frequency of all poles is . The center frequency ω is set to the frequency of the pulsating high-frequency voltage signal; compare the characteristic equation of the fourth-order generalized integrator with the fourth-order standard characteristic equation as shown above to obtain the optimal k 1 , k 2 The parameters are k1 = 0.48 and k2 = 1.1; secondly, set the filtering parameters of the three-parameter notch filter used for the position feedback information according to the method described in Step 1; finally, replace the band-pass filter used in the traditional position feedback with the fourth-order generalized integrator, and replace the low-pass filter used in the position feedback with the three-parameter notch filter to form an improved speed loop structure in the new permanent magnet synchronous motor control system.

[0017] Optional; in Step 3, an improved current loop and speed loop are connected in series to jointly form a sensorless control system for the low-speed range of a permanent magnet synchronous motor with pulsating high-frequency voltage injection improved based on a three-parameter notch filter; connect the current loop in the improved permanent magnet synchronous motor control system in Step 2 in series with the speed loop in the improved permanent magnet synchronous motor control system to form a sensorless control system for the low-speed range of a permanent magnet synchronous motor with pulsating high-frequency voltage injection improved based on a three-parameter notch filter.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention fully considers the problems of poor system dynamic performance and low position estimation accuracy caused by the amplitude attenuation and phase delay characteristics of the low-pass filter and band-pass filter in traditional pulsating high-frequency voltage injection. A three-parameter notch filter with no filtering delay, no amplitude attenuation, and completely decoupled filtering characteristics is used to replace the low-pass filter to filter out the high-frequency current components on the current loop, solving the problems of serious signal amplitude attenuation and phase delay caused by the L low-pass filter in traditional pulsating high-frequency voltage injection, and improving the dynamic performance with the increased current loop bandwidth. A fourth-order generalized integrator without filtering delay is used to replace the band-pass filter used in the position feedback after reasonable parameter design to extract the high-frequency signal containing position information. The high-frequency signal and the demodulation signal are passed through the three-parameter notch filter to obtain the position estimation information, solving the problem of low position observation accuracy in the existing methods. Description of the Drawings

[0020] By describing the exemplary embodiments of the present invention in more detail in conjunction with the drawings, the above and other objects, features, and advantages of the present invention will become more obvious. Among them, in the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0021] Figure 1 Schematic diagrams of the two-phase stationary coordinate system, two-phase rotating coordinate system, and estimated two-phase rotating coordinate system provided for this embodiment;

[0022] Figure 2 Block diagram of the improved current loop structure provided for this embodiment;

[0023] Figure 3 Block diagram of the improved position error signal demodulation strategy structure provided for this embodiment;

[0024] Figure 4 Block diagram of the sensorless control strategy system for permanent magnet synchronous motors at low speed ranges based on pulsating high-frequency voltage injection improved by a three-parameter notch filter provided for this embodiment. Detailed Embodiments

[0025] The embodiments of the present invention will be described in detail below in conjunction with the drawings.

[0026] It should be clear that the following uses specific specific examples to illustrate the implementation modes of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The present invention can also be implemented or applied through other different specific implementation modes. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0027] It should also be noted that the following describes various aspects of embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Those skilled in the art to which the present invention pertains should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement a device and / or practice a method. Additionally, this device and / or method can be implemented using other structures and / or functions in addition to one or more of the aspects described herein.

[0028] It further needs to be explained that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. The diagrams only show the components related to the present invention, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in its actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0029] In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0030] A sensorless control strategy for a permanent magnet synchronous motor based on pulsating high-frequency voltage injection with an improved three-parameter notch filter includes the following steps:

[0031] Step 1: First, analyze the working characteristics and operating process of the permanent magnet synchronous motor under the condition of pulsating high-frequency voltage injection in the low-speed range, determine the mathematical model of the permanent magnet synchronous motor under the low-speed range and the condition of pulsating high-frequency voltage injection, and select appropriate frequencies and amplitudes of the injected voltage, specifically as follows:

[0032] Analyze the mathematical model of a permanent magnet synchronous motor (PMSM) under the condition of pulsating high-frequency voltage injection in the low-speed range, and establish the relationship between the rotor position estimation error information and the injection voltage frequency and injection voltage amplitude through the mathematical model.

[0033] The voltage equation of the PMSM in the synchronous rotating coordinate system is:

[0034] ,

[0035] where: u s , i s , L s (s is d, q) are the voltage, current, and inductance of the axis; R s , ω e , are the stator resistance, rotor electrical angular velocity, and permanent magnet flux linkage respectively.

[0036] When the motor operates in the low-speed stage, the frequency of the injected voltage is much higher than the rotor electrical angular velocity. Therefore, the terms containing ω e and the stator resistance voltage drop in the voltage equation can be ignored, and the high-frequency voltage equation can be simplified to:

[0037] ,

[0038] where: h represents the high-frequency characteristic.

[0039] The rotor position estimation error △θ is defined as:

[0040] ,

[0041] where: θ and are the actual and estimated rotor positions respectively.

[0042] The two-phase stationary coordinate system, the two-phase rotating coordinate system, and the estimated two-phase rotating coordinate system are as Figure 1 shown, The coordinate system corresponds to the estimated two-phase rotating coordinate system. From the coordinate relationship diagram, the voltage and current in the coordinate system can be expressed as the voltage and current forms in the coordinate system as follows:

[0043] ,

[0044] where: corresponds to the voltage component in the coordinate system , corresponds to the current component in the coordinate system.

[0045] A high-frequency sinusoidal voltage signal is injected into the d-axis of the estimated coordinate system as shown in the following equation.

[0046] ,

[0047] where: U mh and ω h are the amplitude and angular frequency of the injected high-frequency voltage, respectively.

[0048] Combining the above, the high-frequency current response in the estimated rotating coordinate system can be expressed as:

[0049] ,

[0050] where: , are the high-frequency current components in the estimated coordinate system, , are the average inductance and half-difference inductance, respectively. To obtain a better rotor position estimation value, according to the parameters of the actual motor selected by the system, the inverter power supply, and the performance of the inverter switching devices, the optimal injection voltage frequency and injection voltage amplitude are calculated through the above mathematical model.

[0051] It can be seen from the above equation that the rotor position estimation error can be adjusted from the estimated quadrature-axis high-frequency current component . First, the high-frequency component is extracted from the current using a BPF, then multiplied by the synchronous amplitude modulation signal 2sin(ω h t), and the multiplied signal is filtered using an LPF to obtain the position error signal

[0052] information , The expression is as follows:

[0053] ,

[0054] where: is the rotor position error estimation coefficient,

[0055] When the rotor position estimation error is very small, sin2△θ≈2△θ, and at this time , the extracted is adjusted to 0 using a PI regulator, and the rotor position estimation value can be obtained. Integrating it can obtain the rotor position estimation value .

[0056] Step 2: Select appropriate TPNF filtering parameters according to the frequency of the injected voltage and the fundamental voltage frequency in the system, replace the LPF used in the traditional algorithm, and form the current loop structure of the new permanent magnet synchronous motor control system, as follows:

[0057] First, calculate the optimal TPNF filtering parameters according to the requirements of the usage environment. The TPNF transfer function is:

[0058] ,

[0059] where: , . ω b is the difference between the notch bandwidth of the notch filter and the frequency when the amplitude attenuation reaches -3 dB. δ p is the notch depth. As decreases, the attenuation at the center frequency of the notch filter gradually increases and is equal to 20lg|δ p |. ω n is the center frequency of the notch filter and the pulsating high-frequency voltage injection frequency. The TPNF takes the optimal notch bandwidth of 40 Hz; the optimal notch depth of -40 dB; and the center frequency is the frequency of the injected voltage signal.

[0060] Secondly, replace the LPF in the traditional pulsating high-frequency voltage injection current loop with the TPNF after reasonable parameter design. The improved current loop structure diagram is as shown in Figure 2 . The purposes of reducing the filtering delay of the signal, increasing the current loop control bandwidth, and ensuring the current loop control performance are achieved.

[0061] Step 3: According to the selected TPNF filtering parameters above, match the FOGI after reasonable parameter design to form an improved pulsating high-frequency voltage injection position demodulation strategy, complete the position feedback of the new control system, and construct the mathematical model of the permanent magnet synchronous motor sensorless control system based on the improved three-parameter notch filter pulsating high-frequency voltage injection as follows:

[0062] First, calculate the optimal FOGI filtering parameters according to the requirements of the usage environment.

[0063] The FOGI transfer function is:

[0064] The FOGI characteristic equation is:

[0065] The standard fourth-order characteristic equation is:

[0066] In the standard fourth-order characteristic equation, ξ = 0.707; ω n1 , ω n2 , ω n3is the natural frequency of oscillation of each pole of the standard characteristic equation; c 1 、c 2 、c 3 are constants. To simplify the parameter tuning process, let c 1 = c 2 = 1, c 3 = 0.05. Assume that the oscillation frequency of all poles is , and the center frequency ω is set to the frequency of the injected pulsating high-frequency voltage signal. Comparing the characteristic equation of the fourth-order generalized integrator with the fourth-order standard characteristic equation to obtain the optimal k 1 、k 2 parameters. Finally, the parameters of the fourth-order generalized integrator are tuned to: k 1 = 0.48, k 2 = 1.1.

[0067] Secondly, when the q-axis response current of the motor passes through the newly designed position signal modulation strategy based on the fourth-order generalized integrator, the position error signal containing position information can be obtained as shown below. In the formula, the TPNF filter center frequency is set to 2 times the injected voltage frequency; the notch bandwidth is set to 40 Hz; the notch depth is -40 dB. The new position signal adjustment structure is formed as Figure 3 shown.

[0068] ,

[0069] Finally, replacing the BPF+LPF position signal adjustment strategy in the traditional method with the newly formed TPNF+FOGI pulsating high-frequency voltage injection position signal demodulation strategy to complete the position feedback of the new control system, and constructing the mathematical model of the sensorless control system of the permanent magnet synchronous motor with pulsating high-frequency voltage injection based on the improved three-parameter notch filter. Its system structure block diagram is as Figure 4 shown.

[0070] Step 4. Finally, form a software program that can be used in practice according to the results of the mathematical model operation.

[0071] Using a three-parameter notch filter (TPNF) to replace the low-pass filter (LPF) in the traditional pulsating high-frequency voltage injection method and applying it to the current loop feedback can effectively improve the delay problem of the current loop signal feedback and maintain the control performance of the system. In addition, by using a fourth-order generalized integrator (FOGI) with optimized parameter design to replace the band-pass filter (BPF) in the traditional method, the required high-frequency voltage signal can be obtained when demodulating the position information, thus avoiding the phase delay problem that occurs when extracting the high-frequency signal containing position information and effectively solving the problems such as delayed extraction of position information and low signal-to-noise ratio existing in the traditional method.

[0072] By analyzing the operating characteristics of a permanent magnet synchronous motor in the low-speed range under the condition of pulsating high-frequency voltage injection, selecting appropriate TPNF filtering parameters according to the frequency of the injected voltage and the frequency of the fundamental voltage in the system, introducing a fourth-order generalized integrator (FOGI), adopting a TPNF+FOGI position information demodulation strategy to demodulate the signal containing position information, constructing a mathematical model of a sensorless control system for a permanent magnet synchronous motor with pulsating high-frequency voltage injection based on an improved three-parameter notch filter, and finally generating a practical software program according to the results of the mathematical model operation. The sensorless control strategy for a permanent magnet synchronous motor in the low-speed range based on pulsating high-frequency voltage injection based on an improved three-parameter notch filter can greatly improve the control performance of the permanent magnet synchronous motor in the low-speed range and enhance the reliability of the entire motor control system.

[0073] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present invention. In addition, the above-disclosed specific details are only for illustrative and easy-to-understand purposes, rather than limitations, and the above details do not limit the present invention to necessarily adopt the above specific details for implementation.

[0074] In the present invention, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Words such as "including", "comprising", "having", etc. are open-ended terms, meaning "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used herein refer to the word "and / or" and can be used interchangeably with it, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to" and can be used interchangeably with it.

[0075] In addition, as used herein, "or" in the listing of items starting with "at least one" indicates a separate listing, so that for example, the listing of "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the term "exemplary" does not mean that the described examples are preferred or better than other examples.

[0076] It should also be noted that in the systems and methods of the present invention, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent solutions of the present invention.

[0077] Various changes, substitutions, and alterations to the technology described herein can be made without departing from the teachings defined by the appended claims. Additionally, the scope of the claims of the present invention is not limited to the specific aspects of the processes, machines, manufactures, compositions of events, means, methods, and acts described above. Processes, machines, manufactures, compositions of events, means, methods, or acts that are currently existing or later to be developed and that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein can be utilized. Accordingly, the appended claims include such processes, machines, manufactures, compositions of events, means, methods, or acts within their scope.

[0078] The foregoing description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the present invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0079] The foregoing description has been presented for purposes of illustration and description. Additionally, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although numerous example aspects and embodiments have been discussed above, those skilled in the art will recognize some of their variations, modifications, alterations, additions, and subcombinations.

Claims

1. A low-speed sensorless control strategy for permanent magnet synchronous motor with pulse high-frequency voltage injection based on an improved three-parameter notch filter, characterized in that: include: Step 1, selecting appropriate three-parameter notch filter filter parameters according to the selected injection voltage frequency and the frequency of the fundamental voltage in the system to form an improved current loop structure in the novel permanent magnet synchronous motor control system; Step 2: Based on the three-parameter notch filter parameters and in combination with a fourth-order generalized integrator, an improved position demodulation strategy for pulse high-frequency voltage injection is formed to form an improved speed loop structure in a novel permanent magnet synchronous motor control system; Step three, the improved current loop and speed loop are connected in series to form a low-speed position sensorless control system for the permanent magnet synchronous motor based on an improved three-parameter notch filter and a pulsating high-frequency voltage injection.

2. The improved pulse high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control strategy based on three-parameter notch filter according to claim 1 is characterized in that: The step 1 is to establish a current loop control structure improved based on a three-parameter notch filter; first, the working characteristics and operation process of the permanent magnet synchronous motor under the condition of pulse high-frequency voltage injection in the low-speed domain are analyzed, so as to determine the mathematical model of the permanent magnet synchronous motor under the conditions of low-speed domain and pulse high-frequency voltage injection, and the frequency and amplitude of the injection voltage are selected based on the mathematical model; Secondly, the filtering parameters of the three-parameter notch filter are designed, and the parameter design process includes determining the filtering parameters of the three-parameter notch filter based on the transfer function of the three-parameter notch filter; The three-parameter notch filter transfer function is: In the formula , ω b is the difference between the notch bandwidth of the notch filter and the frequency when the amplitude is attenuated to -3dB, δ p is the notch depth, ω n are the center frequency of the notch filter and the pulse high-frequency voltage injection frequency, and s is a complex variable; the notch filter center frequency, notch depth and notch bandwidth are set according to the injection frequency and the requirements of the system dynamic performance; finally, the low-pass filter on the traditional pulse high-frequency voltage injection current loop structure is replaced by a three-parameter notch filter to form an improved current loop structure in the new permanent magnet synchronous motor control system.

3. The improved pulse high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control strategy based on three-parameter notch filter according to claim 1 is characterized in that: The second step is to establish a speed loop control structure based on a three-parameter notch filter and a fourth-order generalized integrator. First, the fourth-order generalized integrator parameters are set according to the mathematical model of the permanent magnet synchronous motor under the condition of pulse high-frequency voltage injection in the low-speed domain and the frequency and amplitude of the injected voltage. The parameter design process includes setting the parameters according to the fourth-order generalized integral transfer function and the characteristic equation. The transfer function of the fourth-order generalized integrator is: The characteristic equation of the fourth-order generalized integrator is: The fourth-order standard characteristic equation is In the standard fourth-order characteristic equation, ξ=0.707; ω n1 ,ω n2 ,ω n3 is the natural frequency of oscillation of each pole of the standard characteristic equation; c1, c2, c3 are constants; in order to simplify the parameter setting process, let c1=c2=1, c3=0.05 and assume that the oscillation frequency of all poles is , the center frequency ω is set to the frequency of the pulsating high-frequency voltage signal; in the transfer function of the fourth-order generalized integrator, k1 and k2 determine the filter bandwidth, and ω is the filter center frequency of the filter; the fourth-order generalized integrator characteristic equation is compared with the fourth-order standard characteristic equation as shown above, and the optimal k1 and k2 parameters k1=0.48 k2=1.1 are obtained; secondly, the filter parameters of the three-parameter notch filter used for position feedback information are set according to the method described in step 1; finally, the fourth-order generalized integrator replaces the bandpass filter used in the traditional position feedback, and the three-parameter notch filter replaces the low-pass filter used in the position feedback, forming an improved speed loop structure in the new permanent magnet synchronous motor control system.

4. The improved pulse high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control strategy based on three-parameter notch filter according to claim 1 is characterized in that: The step three establishes an improved current loop and a speed loop in series to form a pulse high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control system based on an improved three-parameter notch filter; the current loop in the improved permanent magnet synchronous motor control system in step two is connected in series with the speed loop in the improved permanent magnet synchronous motor control system to form a pulse high-frequency voltage injection permanent magnet synchronous motor low-speed domain position sensorless control system based on an improved three-parameter notch filter.

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