A high-frequency injection positionless control method for a cascade H-bridge power supply permanent magnet motor

Abstract

The application discloses a high-frequency injection positionless control method for a cascade H-bridge power supply permanent magnet motor, which separately configures one H-bridge module of each phase of a cascade H-bridge converter into a square wave output mode, configures the remaining H-bridge modules of each phase of the cascade H-bridge converter into a conventional modulation mode of carrier phase shift, uses rotation transformation to extract motor rotor position information and position bias information, designs a moving average filtering algorithm based on the characteristics of high sampling rate of the cascade H-bridge to eliminate the influence of harmonic voltage in the injected square wave signal, and then uses a phase-locked loop technology to obtain motor rotor position observation results, so as to realize positionless control. The application raises the upper limit of the signal injection frequency of the cascade H-bridge motor system from half of the switching frequency to the switching frequency, is helpful for the signal separation link involved in the positionless control, can reduce the disturbance caused by the injected high-frequency signal, improve the signal-to-noise ratio and accuracy of the motor rotor position observation, and improve the operation performance of the positionless control.

Description

TECHNICAL FIELD

[0001] The application relates to a motor system, and particularly discloses a high-frequency injection positionless control method for a cascade H-bridge powered permanent magnet motor. BACKGROUND

[0002] Permanent magnet synchronous motors are widely used in high-power applications such as energy exploration due to their simple structure and high power density. To improve the reliable operation of the permanent magnet electric drive system and reduce the cost, a positionless control method is usually used to observe the motor rotor position online for vector control to avoid using a position sensor. In the high-speed region, the motor rotor position is usually observed online based on the motor model to obtain the motor extended back electromotive force, while in the low-speed region, the high-frequency signal injection method is used to observe the motor rotor position due to the extremely low signal-to-noise ratio. In order to facilitate signal separation, the frequency of the injected signal should be as high as possible. On the other hand, in order to improve the single-machine capacity of the electric drive equipment, the industry uses a cascade H-bridge topology to power the motor system to improve the voltage level and power level of the motor system. However, in high-power applications, the switching frequency of the power device of the converter is at a low level due to the capacity of the heat sink. The signal injection frequency of the existing standard cascade H-bridge converter powered permanent magnet motor system orthogonal square wave injection positionless control can only reach half of the switching frequency, resulting in a too low final signal injection frequency, which limits the improvement of the positionless control performance of the motor system. SUMMARY

[0003] The application aims to solve the technical problem of the prior art that the signal injection frequency of the high-frequency injection positionless control method can only reach half of the switching frequency, thereby causing the positionless control performance to decline, and achieve the purpose of improving the positionless control performance of the cascade H-bridge powered permanent magnet synchronous motor system.

[0004] The cascade H-bridge powered permanent magnet motor high-frequency injection positionless control method comprises the following steps:

[0005] Step 1: One H-bridge module of each phase of the cascade H-bridge converter is configured as a square wave output mode. The modulation wave signal of the H-bridge module does not contain the reference voltage signal given by the motor controller, the frequency of the square wave signal reaches the switching frequency of the power device, and the adjustment of the amplitude of the fundamental wave of the output square wave signal is realized by adjusting the phase shift angle of the square waves of the two bridge arms of the H-bridge module, and the high-frequency signal is in the form of a square wave; the number of H-bridge modules of each phase of the cascade H-bridge converter is greater than or equal to 2; the phase shift angle of the square wave signals of the three-phase output of the cascade H-bridge converter is set to 240 degrees, that is, the A-phase output square wave signal leads the B-phase signal by 2 / 3 square wave periods and leads the C-phase signal by 4 / 3 square wave periods;

[0006] Step 2: Based on the high-frequency signal injection in Step 1, configure the remaining H-bridge modules in each phase of the cascaded H-bridge converter into the carrier phase-shifted conventional modulation mode, with the reference voltage as the modulation target output voltage, and complete the motor vector control while implementing high-frequency signal injection in Step 1;

[0007] Step 3: Based on the high-frequency signal injection and motor vector control achieved in Steps 1 and 2, use current sensors to sample the motor stator phase currents, use high-pass filters to extract the high-frequency components of the phase currents, and use rotation transformation to extract the rotor position information superimposed with high-frequency signals and the rotor position offset information superimposed with high-frequency signals, respectively;

[0008] Step 4: Use a moving average filtering algorithm to filter out the high-frequency signals contained in the rotor position information superimposed with high-frequency signals and the rotor position offset information superimposed with high-frequency signals in Step 3, obtaining the rotor position information and the rotor position offset information, wherein the window length of the moving average filtering is set to the ratio of the sampling frequency to the frequency of the injected high-frequency signals;

[0009] Step 5: According to the rotor position information and the rotor position offset information obtained in Step 4, calculate the normalized sine and cosine values of the permanent magnet motor rotor position angle, and further use phase-locked loop technology to calculate the motor rotor position, achieving position control-free.

[0010] Wherein:

[0011] In Step 1, one H-bridge module in each phase of the three-phase output of the cascaded H-bridge converter is individually configured into square wave output mode, and the output voltage of bridge arm 1 in the H-bridge module defined in square wave output mode is , the output voltage of bridge arm 2 is , and the output voltage of the H-bridge module is , the bridge arm 1 and the bridge arm 2 are configured to output square wave voltages with a duty cycle of 50%, and the phase shift angle of the two bridge arms is adjusted to to achieve the goal of adjustable fundamental amplitude of the H-bridge module output square wave voltage.

[0012] In Step 2, the modulation is configured according to the number of remaining H-bridge modules, specifically, if carrier phase-shifted modulation is used, the carrier phase-shifted angle depends on the number of remaining H-bridge modules in each phase, and if carrier layering modulation is used, the number of layered carriers also depends on the number of remaining H-bridge modules in each phase, to ensure decoupled operation of the H-bridge module configured into square wave output mode and other H-bridge modules.

[0013] In Step 3, the high-frequency component of the phase current is extracted using a high-pass filter , and the discrete sampling value is expressed as

[0014] ,

[0015] where and are the average inductance and the differential inductance of the permanent magnet motor, respectively, and their expressions are and are the d-axis and q-axis inductances of the motor, respectively, is the phase lag angle caused by the digitalization and modulation delay of the voltage signal, is the phase lead angle introduced by the high-pass filter, θ e is the electrical angle of the rotor position of the motor; A 1 is the high-frequency current amplitude coefficient, and its expression is , ω h is the angular frequency of the injected signal, V 1 is the amplitude of the injected signal, denotes the sampling result of the variable at time, T s is the switching period, is the switching period, is a positive integer;

[0016] the rotation transformation is used to extract the rotor position information superimposed with the high-frequency signal from the high-frequency current response result Expression: the rotation transformation is used to extract the rotor position bias information superimposed with the high-frequency signal from the high-frequency current response result Expression: .

[0017] In step 4, the high-frequency signal contained in the rotor position information and the rotor position bias information in step 3 is filtered out using the moving average filtering algorithm, and and the expressions after filtering out the high-frequency signal are: , wherein, and are the rotor position information and the rotor position bias information, respectively; is the window length of the moving average filtering, which is set to be the ratio of the sampling frequency and the frequency of the injected high-frequency signal, is a positive integer, indicating the discrete sampling result, corresponding to time; is a non-negative integer, indicating the serial number of the data in the moving average filtering window.

[0018] ​In step 5, the unitized cosine value of the permanent magnet motor rotor position angle is obtained, and the expression is: .

[0019] Beneficial effects: the cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control method provided by the application has the following advantages:

[0020] (1) In the application, one H-bridge module of each phase of the cascade H-bridge converter is configured as a square wave signal injection mode, and other modules are configured as a reference voltage modulation mode, the decoupling modulation of the high-frequency injection signal and the reference voltage signal is realized, the frequency of the high-frequency signal required for motor rotor position observation is increased from half of the switching frequency of the power device to the switching frequency, the motor fundamental frequency signal and the high-frequency response signal are separated, the modulation performance of the cascade H-bridge topology is not affected, and the rotor position observation accuracy is improved.

[0021] (2) The moving average filter algorithm used in the application can not only eliminate the influence of high-frequency signals in the rotor position information and rotor position offset information extraction process, but also eliminate the influence of high-frequency current harmonics caused by voltage harmonics in the injected high-frequency square wave signal on rotor position observation, and improve the signal-to-noise ratio of motor position observation.

[0022] (3) By increasing the injection signal frequency and eliminating the influence of the injection signal harmonic component, the signal-to-noise ratio of motor rotor position observation is improved, and the high-frequency current disturbance caused by high-frequency signal injection is reduced, so that the cascade H-bridge power supply permanent magnet synchronous motor system has better rotor position observation performance and positionless control performance. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is the cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control flowchart provided by the application.

[0024] Figure 2 It is the signal injection implementation schematic diagram of the existing standard cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control.

[0025] Figure 3 It is the signal processing flowchart of the existing standard cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control.

[0026] Figure 4 It is the signal injection implementation schematic diagram of the cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control provided by the application.

[0027] Figure 5 It is the signal processing flowchart of the cascade H-bridge power supply permanent magnet motor high-frequency injection positionless control provided by the application.

[0028] Figure 6is the experimental result of rotor position information extraction of the existing standard cascaded H-bridge power supply permanent magnet motor high-frequency injection positionless control.

[0029] Figure 7 is the experimental result of rotor position information extraction of the cascaded H-bridge power supply permanent magnet motor high-frequency injection positionless control provided by the application.

[0030] Figure 8 is the experimental result of rotor position observation error of the existing standard cascaded H-bridge power supply permanent magnet motor high-frequency injection positionless control.

[0031] Figure 9 is the experimental result of rotor position observation error of the cascaded H-bridge power supply permanent magnet motor high-frequency injection positionless control provided by the application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person skilled in the art without creative work fall within the protection scope of the application.

[0033] As shown in the flow chart of the cascaded H-bridge power supply permanent magnet motor high-frequency injection positionless control provided by the application, the method comprises the following steps. Figure 1 Step 1: Each H-bridge module of the cascaded H-bridge converter is configured as a square wave output mode, the H-bridge module modulation wave signal does not contain the reference voltage signal given by the motor controller, the square wave signal frequency reaches the switching frequency of the power device, and the adjustment of the output square wave signal fundamental wave amplitude is realized by adjusting the phase shift angle of the square wave of the two bridge arms of the H-bridge module, and the high-frequency signal injection is completed, wherein the high-frequency signal is in the form of a square wave; the number of H-bridge modules of each phase of the cascaded H-bridge converter is greater than or equal to 2; the phase shift angle of the square wave signals of the three-phase output of the cascaded H-bridge converter is set to 240 degrees, that is, the A-phase output square wave signal leads the B-phase signal by 2 / 3 square wave periods and leads the C-phase signal by 4 / 3 square wave periods;

[0034] Step 2: Based on the high-frequency signal injection of step 1, the remaining H-bridge modules of each phase of the cascaded H-bridge converter are configured as a conventional modulation mode with carrier phase shift, and the reference voltage is used as the modulation target output voltage. The high-frequency signal injection of step 1 is implemented at the same time to complete the motor vector control.

[0035] Step 3: On the basis of the high-frequency signal injection and motor vector control of steps 1 and 2, the motor stator phase current is sampled using a current sensor, the high-frequency component of the phase current is extracted using a high-pass filter, and the rotor position information superimposed with the high-frequency signal and the rotor position bias information superimposed with the high-frequency signal are extracted using a rotation transformation, respectively.

[0036] Step 4: Use a moving average filtering algorithm to filter out the high-frequency signal contained in the rotor position information superimposed with the high-frequency signal and the rotor position bias information superimposed with the high-frequency signal in step 3, to obtain the rotor position information and the rotor position bias information, wherein the window length of the moving average filtering is set to the ratio of the sampling frequency to the frequency of the injected high-frequency signal;

[0037] Step 5: Based on the rotor position information and rotor position offset information obtained in step 4, the normalized sine and cosine values ​​of the permanent magnet motor rotor position angle are calculated. The motor rotor position is further calculated using phase-locked loop technology to achieve position-free control.

[0038] like Figure 2 The schematic diagram of the implementation of high-frequency injection without position control signal injection for the existing standard cascade H-bridge powered permanent magnet motor is shown in FIG. is the amplitude of the injected square wave signal, and The injected α Axis and β Shaft high frequency square wave voltage signal, and are the α-axis and β-axis voltage reference values ​​output by the motor controller respectively. V dc is the DC bus voltage of the H-bridge module. T s1 Each H-bridge module in each phase performs reference voltage modulation and high-frequency signal injection simultaneously, so the final voltage modulation signal of each phase is and satisfy , written in complex vector form: .from Figure 2 It can be seen that in the existing standard cascade H-bridge powered permanent magnet synchronous motor high-frequency signal injection position-free control, the modulation of the high-frequency signal and the modulation of the reference voltage are performed simultaneously in the H-bridge module, which results in the injection frequency of the orthogonal square wave signal being limited to half the carrier frequency, restricting the improvement of the permanent magnet motor high-frequency injection position observation performance and position-free control performance.

[0039] like Figure 3 The flowchart of the existing standard cascade H-bridge powered permanent magnet motor high frequency injection position-free control signal processing is shown in FIG. is the motor phase current complex vector in the stationary αβ coordinate system, Represents the high-frequency component of the motor phase current obtained through the high-pass filter, and They are respectively Use rotation transformation separately and The rotor position information superimposed with the high-frequency signal and the position offset information. θ e is the rotor position, and are the average inductance and the differential inductance of the permanent magnet motor, respectively, and their expressions are . and are the d-axis and q-axis inductances of the motor, respectively. is the phase lag angle caused by the digitization of the voltage signal and the modulation delay, is the phase lead angle introduced by the high-pass filter, ω h is the angular frequency of the injected signal. is the amplitude coefficient of the current response generated by the high-frequency signal injected by the existing injection method, and its expression is , represents the discrete sampling result at the moment. According to Figure 2 and Figure 3 introduce the existing standard cascaded H-bridge high-frequency injection positionless control position observation principle, and the expression of the fundamental component of the injected high-frequency square wave voltage signal is:

[0040] (1)

[0041] The current response component caused by this voltage component is:

[0042] (2)

[0043] Further, in the existing standard high-frequency injection positionless control, the sampling of the signal is performed at the peak and trough positions of the carrier, and the sampling period is T s1 , as shown in Figure 2 . On the other hand, the frequency of the injected high-frequency signal is half of the carrier frequency, so there is . From this, the high-frequency current response result obtained by the discrete sampling and the high-pass filtering can be calculated:

[0044] (3)

[0045] Further, using the rotation transformation and on the high-frequency current response, we can obtain and , which are the rotor position information superimposed with the high-frequency signal and the position offset information, respectively. Further, since the high-frequency signal has a phase difference of 180 degrees between adjacent two discrete samplings, the high-frequency signal in and can be eliminated by calculating the average of adjacent two discrete values, and thus and , further through complex multiplication and normalization operation, the positive and negative cosine complex vectors of the rotor position angle can be obtained . Finally, the rotor position angle of the motor can be obtained by using the phase-locked loop technology. Further, the limitations of the existing standard high-frequency injection method are analyzed: since the injected square wave voltage signal frequency reaches half of the carrier frequency and needs to be synchronized with the carrier, the high-frequency square wave signal is usually superimposed in the modulation wave of a single H-bridge module. However, this will affect the modulation performance of the cascaded H-bridge converter topology and introduce new current harmonics. For example, the H-bridge module injecting the square wave voltage signal breaks the balance of the carrier frequency sub-harmonic of each H-bridge module in the carrier phase shift strategy, introduces the carrier frequency current harmonic, and the current harmonic of the H-bridge module injecting the square wave voltage signal is twice the carrier angular frequency 2 ω c For example, the corresponding current harmonic expression is:

[0046] (4)

[0047] wherein p and n represent the positive and negative sequence components, respectively. The subscript c 2 indicates that the frequency of the variable is twice the carrier frequency. γ is the phase of the corresponding current harmonic. After the rotation transformation and , it becomes:

[0048] (5)

[0049] After the operation of averaging the adjacent two discrete sampling values, the following can be obtained:

[0050] (6)

[0051] It can be seen that this additional harmonic cannot be eliminated by the adjacent sampling value averaging link, and finally it will mix into the extracted rotor position angle positive and negative cosine components, resulting in the decrease of the signal-to-noise ratio of the position observation.

[0052] As shown in Figure 4 , the high-frequency injection positionless control signal injection implementation schematic diagram of the cascaded H-bridge power supply permanent magnet motor provided by the application is provided, wherein is the output voltage of the bridge arm 1 in the square wave output mode H-bridge module, is the output voltage of the bridge arm 2, and is the output voltage of the square wave mode H-bridge module. The bridge arm 1 and the bridge arm 2 are configured to output square wave voltages with a duty cycle of 50% and an amplitude of V dc / 2, and and the square waves have a numerical value of the phase shift angle, wherein V dc is the DC voltage value of the H-bridge module. Thus the output voltage of the H-bridge module is a three-level signal with a period equal to the period of the square wave signal, and the fundamental amplitude can be set by modifying the phase shift angle . At this time, the frequency of the square wave signal is equal to the switching frequency of the power device, and the technical goal of increasing the signal injection frequency to the switching frequency is achieved. The fundamental component of the injected high-frequency voltage signal can be expressed using a complex vector as , wherein V 1 is the fundamental amplitude of the injected signal, ω h is the angular frequency of the injected signal. The difference between the high-frequency signal injection method of the present application and the existing standard high-frequency signal injection method is that the H-bridge module in the square wave injection mode of the present application does not participate in the synthesis of the motor control reference voltage, i.e. by separately configuring the H-bridge to be in the high-frequency square wave output mode to achieve decoupled modulation of the injected signal and the low-frequency control signal. After using the method of the present application, the upper limit of the square wave signal injection frequency is increased from half the switching frequency to the switching frequency.

[0053] As Figure 5 shown, the present application provides a cascade H-bridge powered permanent magnet motor high-frequency injection positionless control signal processing flowchart, wherein A 1 is the amplitude coefficient of the injected high-frequency signal current response, expressed as , V 1 is the fundamental amplitude of the injected high-frequency square wave voltage signal. is the window length of the moving average filter, set as the ratio of the sampling frequency and the injected high-frequency signal frequency. Without loss of generality, when the sampling frequency is set to 12 kHz and the switching frequency / signal injection frequency is set to 500 Hz, = 24. According to Figure 2 and Figure 3 introduce the existing standard cascade H-bridge high-frequency injection positionless control position observation principle, the expression of the injected high-frequency square wave voltage signal is:

[0054] (7)

[0055] Further, the expression of the high-frequency current response is:

[0056] (8)

[0057] Further, the expression of the high-frequency current discrete sampling value after discrete sampling and high-pass filtering is:

[0058] (9)

[0059] Furthermore, a rotation transformation is used for the high frequency current response and Available and , which are the rotor position information and position offset information superimposed with high-frequency signals. Further, the moving average filtering algorithm is used to eliminate the high-frequency components in the high-frequency current response signal to obtain and , further through complex multiplication and per-unit operation, the sine and cosine complex vectors of the rotor position angle can be obtained Finally, the phase-locked loop technology is used to obtain the rotor position angle of the motor. Furthermore, the moving average filtering algorithm provided by the present invention can eliminate the influence of harmonic voltage in the injected high-frequency square wave voltage signal. The main harmonic order of the square wave voltage signal is 6 n ±1 time, n is a positive integer, Subvoltage harmonics For example, the expression is:

[0060] (10)

[0061] in yes The amplitude of the sub-voltage harmonic. Furthermore, the high-frequency current response caused by the harmonic voltage signal is:

[0062] (11)

[0063] This current component passes through the signal Figure 5 Rotation Transformation and The expression after the action is:

[0064] (12)

[0065] It can be seen that The harmonic voltage signal of the order of the current harmonic is 6. n Second and times, which are all integer multiples of the fundamental period of the injected signal. Using a moving average filtering algorithm with a window length equal to the ratio of the fundamental period to the sampling frequency can eliminate the influence of harmonic voltages in the injected voltage signal, that is, satisfying:

[0066] (13)

[0067] Therefore, the high-frequency injection positionless control method provided by the application can not only improve the signal injection frequency and facilitate signal separation and extraction of rotor position information, but also better eliminate the influence of harmonic components in the injected voltage signal without affecting the normal modulation performance of the cascaded H-bridge converter, so that a higher signal-to-noise ratio of the rotor position information is obtained, and better motor rotor position observation effect can be achieved under the premise of lower high-frequency current harmonic disturbance.

[0068] As shown in Figure 6 and Figure 7 , the experimental results of extracting rotor position information by using the high-frequency injection positionless control of the cascaded H-bridge power supply permanent magnet motor are shown in the figures, wherein Figure 6 the existing standard high-frequency injection method is used, Figure 7 and the high-frequency injection method provided by the application is used. The experiment is completed on a laboratory prototype, each phase of the cascaded H-bridge converter contains 3 cascaded H-bridge modules, power devices use IGBT, and the switching frequency is limited to 500 Hz. The square wave signal frequency of the existing standard high-frequency injection method is 250 Hz, and has reached the upper limit of the frequency, while the square wave signal frequency of the high-frequency injection method provided by the application is increased to 500 Hz. and are the high-frequency current waveforms of the α-axis and the β-axis extracted by the high-pass filter respectively, θ α and θ β are the normalized cosine value and the sine value of the rotor position angle respectively. It can be seen that the rotor position angle cosine and sine values obtained by using the existing standard high-frequency injection positionless control of the cascaded H-bridge power supply permanent magnet synchronous motor have a large amount of harmonic interference, while the high-frequency injection positionless control provided by the application can extract smooth rotor position angle cosine and sine values, and the signal-to-noise ratio of the rotor position observation is obviously improved. Moreover, due to the higher signal injection frequency, the high-frequency current disturbance amplitude caused by the high-frequency injection positionless control provided by the application is lower than that of the existing standard high-frequency injection method.

[0069] As shown in Figure 8 and Figure 9 , the experimental results of rotor position observation error of the cascaded H-bridge power supply permanent magnet motor by using the high-frequency injection positionless control are shown in the figures, wherein Figure 8 the existing standard high-frequency injection method is used, Figure 9 and the high-frequency injection method provided by the application is used. The superscript “^” represents the observed variable, and the superscript “~” represents the observation error of the variable. From Figure 8 and Figure 9 it can be seen that the maximum observation error of the motor rotor position by using the existing standard high-frequency injection method is about 47°, while the maximum observation error of the motor rotor position by using the high-frequency injection method provided by the application is about 6°. Therefore, Figure 6~Figure 9The experimental results verify that the application can improve the signal-to-noise ratio and accuracy of rotor position observation of the cascade H-bridge power supply permanent magnet synchronous motor under the premise of reducing high-frequency current disturbance.

[0070] The above shows and describes the basic principles, main features and advantages of the application. Those skilled in the art should understand that the application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the application. Without departing from the spirit and scope of the application, various changes and improvements can be made to the application, and these changes and improvements all fall within the scope of the claimed application.

Claims

1. A method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor, characterized in that: The method comprises the following steps: Step 1: Configure one H-bridge module per phase of the cascaded H-bridge converter to a square wave output mode. The modulation wave signal of this type of H-bridge module does not include a reference voltage signal provided by the motor controller. The frequency of the square wave signal reaches the switching frequency of the power device. The fundamental amplitude of the output square wave signal is adjusted by adjusting the phase shift angle of the square waves of the two bridge arms of the H-bridge module to complete high-frequency signal injection, wherein the high-frequency signal is in square wave form. The number of H-bridge modules per phase of the cascaded H-bridge converter is greater than or equal to 2. The phase shift angle of the square wave signal output by the three-phase cascaded H-bridge converter is set to 240 degrees, that is, the square wave signal output by phase A leads the square wave signal by 2 / 3 of the square wave period of the phase B signal and leads the square wave signal by 4 / 3 of the square wave period of the phase C signal. Step 2: Based on the high-frequency signal injection in step 1, the remaining H-bridge modules in each phase of the cascaded H-bridge converter are configured in a conventional modulation mode with carrier phase shifting, with the reference voltage as the modulated target output voltage. The motor vector control is performed while the high-frequency signal injection is performed in step 1. Step 3: Based on the high-frequency signal injection and motor vector control implemented in steps 1 and 2, a current sensor is used to sample the motor stator phase current, a high-pass filter is used to extract the high-frequency component of the phase current, and a rotational transformation is used to extract the rotor position information superimposed with the high-frequency signal and the rotor position offset information superimposed with the high-frequency signal; Step 4: Use a moving average filtering algorithm to filter out the high-frequency signal contained in the rotor position information superimposed with the high-frequency signal and the rotor position bias information superimposed with the high-frequency signal in step 3, to obtain the rotor position information and the rotor position bias information, wherein the window length of the moving average filtering is set to the ratio of the sampling frequency to the frequency of the injected high-frequency signal; Step 5: Based on the rotor position information and rotor position offset information obtained in step 4, the normalized sine and cosine values ​​of the permanent magnet motor rotor position angle are calculated. The motor rotor position is further calculated using phase-locked loop technology to achieve position-free control.

2. A method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor according to claim 1, characterized in that: In step 1, an H-bridge module of each phase of the three-phase output of the cascaded H-bridge converter is separately configured as a square wave output mode, and the output voltage of the bridge arm 1 in the H-bridge module in the square wave output mode is defined as , the output voltage of bridge arm 2 is , then the output voltage of the H-bridge module is , configure bridge arm 1 and bridge arm 2 to output a square wave voltage with a duty cycle of 50%, and adjust the phase shift angle of the two bridge arm square waves The goal of achieving adjustable amplitude of the fundamental wave of the square wave voltage output by the H-bridge module is achieved.

3. The method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor according to claim 2, characterized in that: In step 2, the modulation is configured according to the number of remaining H-bridge modules. Specifically, if carrier phase shift modulation is used, the carrier phase shift angle depends on the number of remaining H-bridge modules in each phase. If carrier stacking modulation is used, the number of stacked carriers also depends on the number of remaining H-bridge modules in each phase, so as to ensure the decoupling operation of the H-bridge module configured in square wave output mode and other H-bridge modules.

4. A method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor according to claim 3, characterized in that: In step 3, the high-pass filter is used to extract the high-frequency component of the phase current. , whose discrete sampling values The expression is ， in and are the average inductance and differential inductance of the permanent magnet motor, respectively, and their expressions are ; and are the motor d-axis and q-axis inductances, It is the phase lag angle caused by the voltage signal digital and modulation delay. is the phase advance angle introduced by the high-pass filter, θ e is the motor rotor position in electrical degrees; A 1 is the high-frequency current amplitude coefficient, and its expression is , ω h is the angular frequency of the injected signal, V 1 is the amplitude of the injected signal, Indicates that the variable is The sampling results at the moment, T s is the switching period, It is switching cycles, is a positive integer; Using Rotation Transformations Extract the rotor position information superimposed with the high-frequency signal from the high-frequency current response results expression: ; Use rotation transformation Extract rotor position bias information superimposed with high-frequency signals from high-frequency current response results expression: .

5. A method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor according to claim 4, characterized in that: In step 4, a moving average filtering algorithm is used to filter out the high-frequency signals contained in the rotor position information and the rotor position bias information in step 3. and The expression after filtering out high-frequency signals is: , ,in, and They are motor rotor position information and rotor position offset information respectively; is the window length of the moving average filter, which is set to the ratio of the sampling frequency to the frequency of the injected high-frequency signal. Is a positive integer, indicating the The discrete sampling results correspond to time; It is a non-negative integer, representing the sequence number of the data in the moving average filter window.

6. A method for high-frequency injection position-free control of a cascaded H-bridge powered permanent magnet motor according to claim 5, characterized in that: In step 5, the normalized sine and cosine values ​​of the permanent magnet motor rotor position angle are obtained, and the expression is: .

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