BLDC coupled high frequency injection method gradient phase-locked loop control method

Abstract

The application discloses a BLDC coupled high-frequency injection method gradient phase-locked loop control method, and belongs to the technical field of brushless direct current motor control. The method comprises the following steps: constructing a hardware topology: adopting a three-phase inverter to drive a BLDC, and connecting a high-frequency coupling branch composed of a coupling capacitor and a sampling resistor in series in parallel between the end of a three-phase winding and the ground; generating a high-frequency sinusoidal voltage signal through a signal generator, injecting the signal into the stator winding of the motor through the coupling capacitor, and selecting the injection phase according to the sector in which the rotor is located; signal extraction: during the period when two phases are conducted and one phase is suspended, collecting the high-frequency response signal of the terminal voltage of the two conducted phases, detecting the amplitude of the collected signal, and obtaining the voltage amplitude; differential processing: constructing the differential signal of the two conducted phases, eliminating the direct current component through differential operation, and retaining the 2 times frequency component related to the rotor position; normalization processing: constructing a gradient orthogonal signal; and performing coordinate transformation and phase-locked loop position estimation. The application significantly improves the running performance of the BLDC motor under a low-speed heavy-load working condition.

Description

Technical Field

[0001] This invention belongs to the field of brushless DC motor control technology, specifically relating to a gradient phase-locked loop control method using BLDC coupled high-frequency injection. Background Technology

[0002] Currently, sensorless control technology is mainly divided into two categories: high-speed detection methods based on back electromotive force and low-speed / zero-speed detection methods based on salient pole effect. For low-speed and zero-speed operating conditions, high-frequency signal injection is the mainstream solution. Among them, coupled high-frequency signal injection injects high-frequency voltage through capacitive coupling, effectively isolating the DC bus voltage and avoiding the influence of inverter nonlinear dead zone, thus having advantages in hardware topology.

[0003] In aerospace (e.g., generators) and industrial drive applications, BLDC (brushless DC motors) often require direct heavy-load starting under low-speed or even zero-speed conditions. However, there is currently no ideal sensorless control method to address the rotor position estimation accuracy and starting performance under such low-speed, heavy-load conditions. Existing signal processing and position calculation methods for coupled high-frequency injection still have the following shortcomings:

[0004] 1. Inductor parameter drift under heavy load leads to estimation errors: Traditional back EMF-based methods fail at low speeds, while mainstream high-frequency signal injection methods typically rely on ideal inductor models. However, during heavy-load startup, the motor stator current is extremely high, causing varying degrees of magnetic circuit saturation, and the inductor parameters change drastically with the load current. Existing technologies mostly use fixed-parameter models or simple arctangent calculations, which cannot adapt to this parameter drift, resulting in significant errors in the calculated rotor position, which can seriously cause motor reversal or startup failure.

[0005] 2. Noise sensitivity: The traditional arctangent calculation method is not only computationally intensive, but also extremely sensitive to high-frequency sampling noise. Directly differentiating to calculate the rotational speed will introduce a great deal of noise interference.

[0006] 3. The disconnect between lookup table method and observer: Although the simple lookup table method can handle nonlinear mapping, it is a static mapping and cannot provide smooth speed estimation. It is also easily affected by the jump of sampling point. Although the simple PLL method is smooth, it is difficult to adapt to the complex nonlinear characteristics of motor magnetic circuit.

[0007] In summary, existing control schemes struggle to simultaneously address the parametric nonlinearity caused by heavy-load magnetic saturation and the high-dynamic tracking problem during startup. Therefore, a control scheme that combines the nonlinear mapping capability of lookup tables with the filtering and tracking capability of phase-locked loops is urgently needed to achieve high-precision, robust position detection across the entire angular range. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the prior art by proposing a BLDC coupled high-frequency injection gradient phase-locked loop control method, specifically a sensorless control method for BLDC motors based on an offline lookup table linearized phase-locked loop.

[0009] This invention aims to normalize the position error signal by establishing a "voltage-angle-gradient" mapping relationship, thereby eliminating the nonlinear gain effect caused by the salient pole effect of the motor. This allows the phase-locked loop to maintain a constant loop bandwidth and damping characteristics under any rotor angle, thus significantly improving the rotor position estimation accuracy and dynamic tracking performance under low-speed heavy-load conditions. It provides a reliable sensorless control method for brushless DC motors under low-speed heavy-load conditions.

[0010] This invention proposes a gradient phase-locked loop (PLL) control method using BLDC coupling high-frequency injection. Its core lies in injecting a high-frequency sinusoidal voltage through a coupling capacitor and calculating the position using a closed-loop structure of offline table lookup and PLL.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A gradient phase-locked loop control method using BLDC coupled high-frequency injection, the control method comprising the following steps:

[0013] S1: Hardware Topology Construction: A three-phase inverter drives a BLDC motor. High-frequency coupling branches consisting of coupling capacitors and sampling resistors connected in parallel between the ends of the three-phase windings and ground are used to generate high-frequency sinusoidal voltage signals through a signal generator, which are then injected into the motor stator windings through the coupling capacitors. The input of the high-frequency signal processing unit is connected to the high-frequency coupling branches to extract and process the high-frequency response signals generated by the motor windings. The high-frequency signal processing unit consists of a bandpass filter and an amplitude detection circuit. The amplitude detection circuit consists of an absolute value circuit, a low-pass filter circuit, and a voltage comparator connected in series.

[0014] S2: Signal extraction: Based on step S1, during the period when two phases are conducting and one phase is floating, the high-frequency response signal of the voltage at the two conducting phase terminals is collected, and the amplitude of the collected signal is detected to obtain the voltage amplitude.

[0015] S3: Differential processing: Based on step S2, construct a differential signal for the two conducting phases, eliminate the DC component through differential operation, and retain the 2nd harmonic component related to the rotor position;

[0016] S4: Normalization: Calculate the ratio of line voltage to injected high-frequency voltage, and simplify by substituting the equivalent inductance expression; during the simplification process, fully consider... and conditions;

[0017] in, It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. Given the rotor position angle, taking a first-order approximation of the above equation and ignoring the fourth harmonic component, we obtain the normalized position-dependent voltage signal. ;

[0018] S5: Construct the voltage signal by offline table lookup. The gradient of is used as an orthogonal signal;

[0019] S6: Based on step S5, perform coordinate transformation and phase-locked loop position estimation.

[0020] Furthermore, in step S1, capacitors C1, C2, and C3 constitute a high-frequency signal coupling circuit, which is connected in series between the high-frequency signal generation circuit and the motor winding. The high-frequency signal coupling circuit is used to couple the high-frequency detection signal emitted by the high-frequency signal generation circuit to the motor winding. By selecting a capacitance value of 1μF, the high-frequency signal coupling circuit transmits high-frequency signals and blocks low-frequency signals, thereby preventing low-frequency drive voltage from reaching the high-frequency signal generation circuit side and protecting the external high-frequency signal generation circuit.

[0021] Furthermore, in step S2, during the period when phases B and C are conducting and phase A is floating, the high-frequency response signals of the terminal voltages of phases B and C are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ub and Uc.

[0022] During the period when phases CA are conducting and phase B is floating, high-frequency response signals of the voltage at the terminals of phases C and A are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Uc and Ua.

[0023] During the period when phases A and B are conducting and phase C is floating, high-frequency response signals of the voltage at the terminals of phases A and B are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ua and Ub.

[0024] Furthermore, in step S3, when phases BC are conducting, the differential signal Ud = Ub - Uc;

[0025] When both phases of CA are conducting, the differential signal Ud = Uc - Ua;

[0026] When phases A and B are conducting, the differential signal Ud = Ua - Ub.

[0027] Furthermore, in step S4, the normalized position-related voltage signal is obtained. The process is as follows:

[0028] , , This is the inductance of the three-phase decoupling equivalent circuit, neglecting leakage flux. It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. It is the direct-axis inductance of a permanent magnet motor. It is the quadrature-axis inductance of the permanent magnet motor; and it has the following relationship:

[0029]

[0030]

[0031] Assuming BC is conducting, , The amplitude of the injected high-frequency sinusoidal voltage excitation signal is calculated similarly during the conduction periods of CA and AB, requiring only the addition of a sector compensation angle. That's all;

[0032]

[0033]

[0034]

[0035] The above equation can be approximated by a first order as follows:

[0036]

[0037] in, Equivalent inductance The voltage division of the inductor, similarly:

[0038]

[0039] in, Equivalent inductance Inductive voltage divider;

[0040] Ignoring the 4th harmonic component,

[0041]

[0042] When BC is on, =0°; When CA is on =120°; When AB is conducting =-120°.

[0043] Furthermore, in step S5, the voltage signal is constructed by offline table lookup. The gradient of is used as an orthogonal signal; the specific construction process is as follows:

[0044] (9)

[0045]

[0046] make

[0047] in, , It is the voltage vector formed by voltage and voltage gradient in the α-β coordinate system.

[0048] Furthermore, in step S6, the coordinate transformation and phase-locked loop position estimation are as follows:

[0049] Construct the observer coordinate system MT and estimate the observer coordinate system M'T';

[0050]

[0051] in, This is the sector compensation angle, which corresponds to the initial phase offset for different conduction phase sequences;

[0052] Will Transforming to the MT coordinate system yields:

[0053]

[0054] Transforming back to the M'T' coordinate system, we get:

[0055]

[0056]

[0057]

[0058] Error Gain .

[0059] The advantages of this invention compared to existing technologies are as follows: This invention proposes a BLDC coupled high-frequency injection gradient phase-locked loop (PLL) control method, specifically a sensorless control method based on a gradient lookup table-linearized PLL. This method significantly improves the operating performance of BLDC motors under low-speed, heavy-load conditions. By introducing an offline lookup table mechanism of voltage-angle-gradient, this invention can compensate for the nonlinear error gain caused by inductor parameter drift and salient pole effect in real time, ensuring that the PLL maintains a constant loop bandwidth and optimal damping state throughout the entire angle range. This solves the problems of easy oscillation and lockout during heavy-load startup of traditional methods. Simultaneously, combined with input limiting protection and a second-order closed-loop observation structure, the BLDC coupled high-frequency injection system not only possesses strong robustness against load disturbances but also outputs smooth speed and position signals, achieving reliable startup of the motor with high dynamics and high stability. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of a BLDC-coupled high-frequency injection system.

[0061] Figure 2 This is a schematic diagram of the coordinate system definition.

[0062] Figure 3 This is a schematic diagram of a phase-locked loop (PLL) with inductive voltage division and its gradient.

[0063] The component names and reference numerals in the above figures are as follows: Detailed Implementation

[0064] like Figures 1-3 As shown, this embodiment describes a gradient phase-locked loop control method using BLDC coupled high-frequency injection, the control method comprising the following steps:

[0065] S1: Hardware Topology Construction: A three-phase inverter drives a BLDC motor. High-frequency coupling branches, consisting of coupling capacitors and sampling resistors connected in series, are connected in parallel between the ends of the three-phase windings and ground. A high-frequency sinusoidal voltage signal is generated by a signal generator and injected into the motor stator windings via the coupling capacitors. The input of the high-frequency signal processing unit is connected to the high-frequency coupling branches to extract and process the high-frequency response signal generated by the motor windings. The high-frequency signal processing unit consists of a bandpass filter and an amplitude detection circuit. The amplitude detection circuit is composed of an absolute value circuit, a low-pass filter circuit, and a voltage comparator connected in series (see...). Figure 1 (Amplitude detection circuit within the dashed box)

[0066] S2: Signal extraction: Based on step S1, during the period when two phases are conducting and one phase is floating, the high-frequency response signal of the voltage at the two conducting phase terminals is collected, and the amplitude of the collected signal is detected to obtain the voltage amplitude.

[0067] S3: Differential processing: Based on step S2, construct a differential signal for the two conducting phases, eliminate the DC component through differential operation, and retain the 2nd harmonic component related to the rotor position;

[0068] S4: Normalization: Calculate the ratio of line voltage to injected high-frequency voltage, and simplify by substituting the equivalent inductance expression; during the simplification process, fully consider... and conditions;

[0069] in, It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. Given the rotor position angle, taking a first-order approximation of the above equation and ignoring the fourth harmonic component, we obtain the normalized position-dependent voltage signal. ;

[0070] S5: Construct the voltage signal by offline table lookup. The gradient of is used as an orthogonal signal;

[0071] S6: Based on step S5, perform coordinate transformation and phase-locked loop position estimation.

[0072] Furthermore, in step S1, capacitors C1, C2, and C3 constitute a high-frequency signal coupling circuit, which is connected in series between the high-frequency signal generation circuit and the motor winding. The high-frequency signal coupling circuit is used to couple the high-frequency detection signal emitted by the high-frequency signal generation circuit to the motor winding. By selecting a capacitance value of 1μF, the high-frequency signal coupling circuit transmits high-frequency signals and blocks low-frequency signals, thereby preventing low-frequency drive voltage from reaching the high-frequency signal generation circuit side and protecting the external high-frequency signal generation circuit.

[0073] Furthermore, in step S2, during the period when phases B and C are conducting and phase A is floating, the high-frequency response signals of the terminal voltages of phases B and C are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ub and Uc.

[0074] During the period when phases CA are conducting and phase B is floating, high-frequency response signals of the voltage at the terminals of phases C and A are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Uc and Ua.

[0075] During the period when phases A and B are conducting and phase C is floating, high-frequency response signals of the voltage at the terminals of phases A and B are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ua and Ub.

[0076] Furthermore, in step S3, when phases BC are conducting, the differential signal Ud = Ub - Uc;

[0077] When both phases of CA are conducting, the differential signal Ud = Uc - Ua;

[0078] When phases A and B are conducting, the differential signal Ud = Ua - Ub.

[0079] Furthermore, in step S4, the normalized position-related voltage signal is obtained. The process is as follows:

[0080] , , This is the inductance of the three-phase decoupling equivalent circuit, neglecting leakage flux. It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. It is the direct-axis inductance of a permanent magnet motor. It is the quadrature-axis inductance of the permanent magnet motor; and it has the following relationship:

[0081]

[0082]

[0083] Assuming BC is conducting, , The amplitude of the injected high-frequency sinusoidal voltage excitation signal is calculated similarly during the conduction periods of CA and AB, requiring only the addition of a sector compensation angle. That's all;

[0084]

[0085]

[0086]

[0087] The above equation can be approximated by a first order as follows:

[0088]

[0089] in, Equivalent inductance The voltage division of the inductor, similarly:

[0090]

[0091] in, Equivalent inductance Inductive voltage divider;

[0092] Ignoring the 4th harmonic component,

[0093]

[0094] When BC is on, =0°; When CA is on =120°; When AB is conducting =-120°.

[0095] Furthermore, in step S5, the voltage signal is constructed by offline table lookup. The gradient of is used as an orthogonal signal; the specific construction process is as follows:

[0096] (9)

[0097]

[0098] make

[0099] in, , It is the voltage vector formed by voltage and voltage gradient in the α-β coordinate system.

[0100] Furthermore, in step S6, the coordinate transformation and phase-locked loop position estimation are as follows:

[0101] Construct the observer coordinate system MT and estimate the observer coordinate system M'T';

[0102]

[0103] in, This is the sector compensation angle, which corresponds to the initial phase offset for different conduction phase sequences;

[0104] Will Transforming to the MT coordinate system yields:

[0105]

[0106] Transforming back to the M'T' coordinate system, we get:

[0107]

[0108]

[0109]

[0110] Error Gain .

[0111] The first key technical point of this invention: assuming that during the BC conduction period, ,in, The rotor position angle is assumed to be based on the actual operation of the motor and the conduction logic. This assumption limits the range of rotor position angles during a specific conduction phase, avoids complex full-angle range analysis, reduces computational complexity, and ensures the accuracy and reliability of the analysis within a specific conduction phase.

[0112] The second key technical point of this invention: calculating the ratio of line voltage to input voltage, for example, taking phase B, calculating... ,in, , , The equivalent inductance of the three-phase decoupling circuit is given by formula (2). Substituting this into the above formula simplifies the process. During simplification, full consideration is given to… and conditions, It is the constant term of the inductance. To approximate the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit, a first-order approximation is taken for the above formula to reduce the computational complexity. The approximated expression is multiplied by the relevant equivalent inductance expression and expanded, and simplified using trigonometric function formulas. Ignore irrelevant or interfering components of the fourth harmonic component, as shown in formulas (4)-(8).

[0113] The third key technical point of this invention: clearly defining the BC conduction time. ,but Analyzing the monotonicity of the voltage response within this interval yields the following results: The conclusion of monotonically increasing, among which, Equivalent inductance Inductive voltage divider Equivalent inductance Inductive voltage divider;

[0114] Based on this, orthogonal signals are constructed through offline table lookup and then fed into a scalar gradient phase-locked loop.

[0115] The fourth key technical point of this invention is the amplitude limiting protection mechanism; the amplitude of the input signal is monitored before the table lookup. If the measured voltage amplitude exceeds the theoretical boundary of the monotonic interval, the input value is forcibly clamped at the boundary value to prevent mathematical overflow, and the boundary information is used to quickly correct large angle deviations.

[0116] Example:

[0117] This embodiment discloses a gradient phase-locked loop control method using BLDC coupled high-frequency injection, the method comprising the following steps:

[0118] S1 Hardware Topology: A three-phase inverter drives a BLDC motor. High-frequency coupling branches are connected in parallel between the ends of the three-phase windings and ground, consisting of capacitors and sampling resistors connected in series. A signal generator produces a high-frequency sinusoidal voltage signal, which is injected into the motor stator windings through the coupling capacitors. Figure 1 In this circuit, the high-frequency detection signal injection unit consists of a high-frequency signal generation circuit and a coupling circuit. The injection phase needs to be selected according to the sector where the rotor is located. Capacitors C1, C2, and C3 form a high-frequency signal coupling circuit, connected in series between the high-frequency signal generation circuit and the motor windings. This circuit is used to couple the high-frequency detection signal emitted by the high-frequency signal generation circuit to the motor windings. By selecting appropriate capacitor values, this circuit can transmit high-frequency signals and block low-frequency signals, thereby preventing low-frequency drive voltage from reaching the high-frequency signal generation circuit side and protecting the external high-frequency signal generation circuit. The high-frequency signal processing unit consists of a bandpass filter and an amplitude detection circuit. The amplitude detection circuit consists of an absolute value circuit, a low-pass filter circuit, and a voltage comparator connected in series (see...). Figure 1 The amplitude detection circuit within the dashed box works as follows: First, the line voltage is filtered by a bandpass filter to obtain its high-frequency components Uab, Ubc, and Uca. Then, |Uab|, |Ubc|, and |Uca| are obtained using an absolute value circuit. Next, the absolute value signals are low-pass filtered to obtain the amplitudes of the high-frequency line voltage components UabAMP, UbcAMP, and UcaAMP. According to the control principle, obtaining the amplitudes of the high-frequency line voltage components allows for comparison and determination of the relative inductance of the windings.

[0119] S2 signal extraction: During the period when phases B and C are conducting and phase A is floating, the high-frequency response signals of the voltages at the terminals of phases B and C are acquired. The amplitudes of the acquired signals are detected to obtain the voltage amplitudes Ub and Uc. The same procedure applies when CA and AB are conducting.

[0120] S3 Differential Processing: Construct a differential signal. Taking BC conduction as an example, Ud = Ub - Uc. The DC component of the voltage is eliminated through differential operation, retaining the second harmonic component related to the rotor position. The same applies to CA and AB conduction.

[0121] S4 normalization processing: , , This is the inductance of the three-phase decoupling equivalent circuit, neglecting leakage flux. It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. It is the direct-axis inductance of a permanent magnet motor. It is the quadrature-axis inductance of a permanent magnet motor. And it has the following relationship:

[0122]

[0123]

[0124] Assuming BC is conducting, , This represents the amplitude of the injected high-frequency sinusoidal voltage excitation signal. The same principle applies during the conduction periods of CA and AB; only a sector compensation angle needs to be added. That's all.

[0125]

[0126]

[0127]

[0128] The above equation can be approximated by a first order as follows:

[0129]

[0130] Similarly:

[0131]

[0132] Ignoring the 4th harmonic component,

[0133]

[0134] S4 constructs gradient orthogonal signals:

[0135] (9)

[0136]

[0137] make ;

[0138] S5 constructs the observer coordinate system MT and estimates the observer coordinate system M'T', as follows: Figure 2 As shown; This is the sector compensation angle, which corresponds to the initial phase offset for different conduction phase sequences. .

[0139]

[0140] Will Transforming to the MT coordinate system yields:

[0141]

[0142] Transforming back to the M'T' coordinate system, we get:

[0143]

[0144]

[0145]

[0146] Error Gain .

Claims

1. A gradient phase-locked loop control method using BLDC coupled high-frequency injection, characterized in that: The control method includes the following steps: S1: Hardware Topology Construction: A three-phase inverter drives a BLDC motor. High-frequency coupling branches consisting of coupling capacitors and sampling resistors connected in parallel between the ends of the three-phase windings and ground are used to generate high-frequency sinusoidal voltage signals through a signal generator, which are then injected into the motor stator windings through the coupling capacitors. The input of the high-frequency signal processing unit is connected to the high-frequency coupling branches to extract and process the high-frequency response signals generated by the motor windings. The high-frequency signal processing unit consists of a bandpass filter and an amplitude detection circuit. The amplitude detection circuit consists of an absolute value circuit, a low-pass filter circuit, and a voltage comparator connected in series. S2: Signal extraction: Based on step S1, during the period when two phases are conducting and one phase is floating, the high-frequency response signal of the voltage at the two conducting phase terminals is collected, and the amplitude of the collected signal is detected to obtain the voltage amplitude. S3: Differential processing: Based on step S2, construct a differential signal for the two conducting phases, eliminate the DC component through differential operation, and retain the 2nd harmonic component related to the rotor position; S4: Normalization: Calculate the ratio of line voltage to injected high-frequency voltage, and simplify by substituting the equivalent inductance expression; during the simplification process, fully consider... and conditions; in, It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. Given the rotor position angle, taking a first-order approximation of the above equation and ignoring the fourth harmonic component, we obtain the normalized position-dependent voltage signal. ; S5: Construct the voltage signal by offline table lookup. The gradient of is used as an orthogonal signal; S6: Based on step S5, perform coordinate transformation and phase-locked loop position estimation.

2. The control method according to claim 1, characterized in that: In step S1, capacitors C1, C2, and C3 form a high-frequency signal coupling circuit, which is connected in series between the high-frequency signal generation circuit and the motor winding. The high-frequency signal coupling circuit is used to couple the high-frequency detection signal emitted by the high-frequency signal generation circuit to the motor winding. By selecting a capacitance value of 1μF, the high-frequency signal coupling circuit transmits high-frequency signals and blocks low-frequency signals, thereby preventing low-frequency drive voltage from reaching the high-frequency signal generation circuit side and protecting the external high-frequency signal generation circuit.

3. The control method according to claim 2, characterized in that: In step S2, during the period when phases B and C are conducting and phase A is floating, high-frequency response signals of the voltage at the terminals of phases B and C are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ub and Uc. During the period when phases CA are conducting and phase B is floating, high-frequency response signals of the voltage at the terminals of phases C and A are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Uc and Ua. During the period when phases A and B are conducting and phase C is floating, high-frequency response signals of the voltage at the terminals of phases A and B are collected, and the amplitude of the collected signals is detected to obtain the voltage amplitudes Ua and Ub.

4. The control method according to claim 3, characterized in that: In step S3, when phases B and C are conducting, the differential signal Ud = Ub - Uc; When both phases of CA are conducting, the differential signal Ud = Uc - Ua; When phases A and B are conducting, the differential signal Ud = Ua - Ub.

5. The control method according to claim 4, characterized in that: In step S4, the normalized position-related voltage signal is obtained. The process is as follows: , , This is the inductance of the three-phase decoupling equivalent circuit, neglecting leakage flux. It is the constant term of the inductance. This represents the magnitude of the inductance change caused by the salient pole effect of the magnetic circuit. It is the direct-axis inductance of a permanent magnet motor. It is the quadrature-axis inductance of the permanent magnet motor; and it has the following relationship: Assuming BC is conducting, , For the amplitude of the injected high-frequency sinusoidal voltage excitation signal, the same applies during the conduction periods of CA and AB; only a sector compensation angle needs to be added. That's all; The above equation can be approximated by a first order as follows: in, Equivalent inductance The voltage division of the inductor, similarly: in, Equivalent inductance Inductive voltage divider; Ignoring the 4th harmonic component, When BC is on, =0°; When CA is on =120°; When AB is conducting =-120°.

6. The control method according to claim 5, characterized in that: In step S5, the voltage signal is constructed by offline table lookup. The gradient of is used as an orthogonal signal; the specific construction process is as follows: (9) make in, , It is the voltage vector formed by voltage and voltage gradient in the α-β coordinate system.

7. The control method according to claim 6, characterized in that: In step S6, the coordinate transformation and phase-locked loop position estimation are as follows: Construct the observer coordinate system MT and estimate the observer coordinate system M'T'; in, This is the sector compensation angle, which corresponds to the initial phase offset for different conduction phase sequences; Will Transforming to the MT coordinate system yields: Transforming back to the M'T' coordinate system, we get: Error Gain .

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