PMSM position sensorless control method based on stator winding neutral point voltage

Abstract

The invention relates to a permanent magnet synchronous motor (PMSM) position sensorless control method based on stator winding neutral point voltage, which is characterized in that three symmetrical resistors are connected in parallel to reconstruct a virtual neutral point of a PMSM, third harmonic is obtained by measuring the voltage difference between the stator winding neutral point and the virtual neutral point, and rotor position information is extracted by using an SOGI-FLL-WPF technology. The manufacturing cost is low, extra high-frequency signals do not need to be injected, motor parameters do not need to be depended on, and only the motor is required to be provided with the star-connected stator windings.

Description

Technical Field

[0001] The invention relates to a PMSM position sensorless control method based on a stator winding neutral point voltage, belongs to the field of permanent magnet synchronous motor (PMSM) position sensorless control, and particularly relates to a position sensorless control method based on a voltage difference between a stator winding neutral point and a virtual neutral point and a second-order generalized integrator-based frequency-locked loop with prefilter (SOGI-FLL-WPF) technology. Background Art

[0002] Permanent magnet synchronous motors are widely used in aerospace, electric vehicles, household appliances and other fields due to their simple structure, high power density and good reliability. The classic control method of PMSM is field-oriented control (FOC), but this method requires accurate rotor position and speed information, and usually requires the installation of position sensors such as Hall sensors and orthogonal encoders, which increases the cost, volume and weight of the system and reduces its reliability.

[0003] In order to reduce the cost of permanent magnet synchronous motor drive systems and improve the reliability of the system, position sensorless control methods have been widely used. These methods can be roughly divided into two categories: rotor saliency-based and model-based control methods. However, the rotor saliency-based control method requires the injection of high-frequency signals, which generates electromagnetic noise. In addition, the high-frequency injection method is difficult to apply to medium and high-speed applications because the bus voltage limits the amplitude of the injected voltage; the model-based method has high position estimation accuracy at medium and high speeds, but it is easily affected by internal and external disturbances. The internal disturbances are mainly changes in motor parameters, and the external disturbances are mainly loads, inverter nonlinearities, sampling deviations, and harmonics. As the motor speed decreases, these disturbances seriously deteriorate the position estimation accuracy. Summary of the invention

[0004] In response to the problem of position sensorless control of the above-mentioned permanent magnet synchronous motor, the present invention proposes a position sensorless control method based on the neutral point voltage of the stator winding. The method does not need to inject additional high-frequency signals and rely on motor parameters. It directly detects the voltage difference between the neutral point and the virtual neutral point, and then uses the second-order generalized integrator-based frequency-locked loop with prefilter (Second-Order Generalized Integrator-Based Frequency-Locked Loop WithPrefilter, SOGI-FLL-WPF) technology to extract the rotor position information, thereby realizing sensorless control.

[0005] The PMSM position sensorless control method based on the stator winding neutral point voltage comprises the following steps:

[0006] Step 1: Rotor pre-positioning: setting current A fixed voltage vector is output through the current loop PI controller to align the rotor d-axis with the permanent magnet synchronous motor winding a phase, avoiding the If control open-loop start failure and reversal problem;

[0007] Step 2: If open-loop control, the control is current closed-loop control, and a uniform acceleration start strategy is adopted to accelerate the motor speed to the target set speed; the relationship between the virtual synchronous coordinate system of the If open-loop control and the actual rotor dq axis coordinate system is: the virtual coordinate system leads the actual coordinate system by π / 2,

[0008] Step 3: When the If open-loop control is stable, the third harmonic back electromotive force e3 is extracted by directly detecting the voltage difference between the neutral point and the virtual neutral point of the stator winding of the permanent magnet synchronous motor; the third harmonic back electromotive force is extracted by introducing a virtual neutral point and then directly detecting the voltage difference between the neutral point and the virtual neutral point;

[0009] Obtain the third harmonic back EMF. Since the flux density distribution of the rotor permanent magnet in the air gap around the motor is a non-ideal sine wave, the air gap flux contains integer multiples of the third harmonic, of which the third harmonic accounts for the largest proportion of the total harmonics. The third harmonic of the flux will generate a third harmonic back EMF at the neutral point of the stator winding. To this end, we use three symmetrical resistors in parallel on the motor phase line to reconstruct the virtual neutral point of the PMSM. By directly detecting the voltage difference between the neutral point and the virtual neutral point of the permanent magnet synchronous motor, the third harmonic back EMF can be effectively extracted.

[0010] Step 4: The third harmonic back-EMF signal is filtered through a pre-filter, which is a frequency adaptive bandpass filter. This enables the SOGI-FLL-WPF technology to achieve a better trade-off between speed and accuracy than the standard SOGI-FLL. It is also a SOGI-based orthogonal signal generator, but only uses the output of the α axis.

[0011] Step 5: The signal obtained by filtering in step 4 and its orthogonal signal are constructed through the SOGI module, and the electrical angular frequency of the signal is tracked using the FLL technology;

[0012] The filtered third harmonic back electromotive force e′3 is obtained, but the rotor position cannot be directly calculated from a single signal, so its orthogonal signal needs to be constructed. In addition, the electrical angular frequency needs to be tracked in real time to match the speed change. Therefore, the filtered signal is passed through the SOGI module to obtain the estimated Signal and its orthogonal signal At the same time, the frequency-locked loop FLL is used to track the estimated signal to obtain three times the electrical angle frequency. When the SOGI-FLL module is in steady state, the estimated electrical angular frequency Equal to the actual ω 3e ,so and The transfer function between and e′3 can be expressed as:

[0013]

[0014] Wherein, k2 is the gain coefficient of the SOGI-FLL module.

[0015] Step 6: normalize the two orthogonal signals obtained in step 5, obtain the estimated electrical angle value through the inverse tangent function, and perform frequency conversion;

[0016] Then and After unitization, we get and Finally, the estimated electrical angle is calculated by the arctan function Since the rotor position information is extracted from the third harmonic back EMF, the angle is three times the actual electrical angle frequency. Converted into actual electrical angle θ e ;

[0017] Step 7: Replace the angle generated by the If open-loop control with the electrical angle value of step 6, obtain the actual motor speed through differential calculation, and introduce the speed loop to realize position sensorless control.

[0018] The rotor position θ obtained in step 6e Replace the angle generated in the If open-loop control in step 2 Through θ e Calculate the speed and will The speed loop is introduced to perform speed closed-loop control.

[0019] The step 2 specifically includes:

[0020] Adopt uniform acceleration start strategy and set the d-axis current to remain at i d =0, the q-axis current is a constant starting current, and the current angular velocity ω is given e And integrate to get the position angle of the motor control To achieve position setting, a coordinate axis d′q′ leading the actual coordinate system by π / 2 is given in the initial stage as a virtual synchronous coordinate system. The PMSM torque equation and motion equation are rewritten as:

[0021]

[0022] In formulas (1) and (2): T e is the electromagnetic torque, n p is the pole pair number, ψ f is the permanent magnet flux, θ γ is the angular error between the coordinate systems, J is the moment of inertia, ω r is the mechanical angular velocity, T l is the load torque and B is the friction coefficient.

[0023] The step 4 specifically includes:

[0024] After a frequency adaptive bandpass filter, is a constant, and the transfer function between e′3 extracted by the prefilter and the input signal e3 can be expressed as:

[0025]

[0026] Where k1 is the gain coefficient of the pre-filter, is the electrical angular frequency of the signal, is the best choice corresponding to the damping coefficient Ensure that the pre-filter achieves the best balance between overshoot and settling time when extracting the signal.

[0027] The step five specifically includes:

[0028] The parameter selection in SOGI is done by linearizing the SOGI model:

[0029]

[0030] The poles of the closed-loop transfer function are all real numbers, corresponding to the case where the damping coefficient is equal to or greater than 1. When the damping coefficient is greater than 1, the response speed is too slow. The damping coefficient is selected to be equal to the unit damping factor, corresponding to the transfer function having the same poles, so k1=k2, and the characteristic polynomial of equation (8) is:

[0031]

[0032] Since equation (10) is a third-order polynomial with at least one real pole, it can also be expressed as:

[0033]

[0034] Among them, ζ and ω n denote the damping factor and natural frequency respectively, γ is the factor that determines the position of the real poles, according to equation (11), the coefficients of the same order s on both sides are equal, and let Then the gain λ of FLL can be expressed as:

[0035]

[0036] From equations (11) and (12), we can see that γ can be expressed as:

[0037]

[0038] The step six specifically includes:

[0039] The two orthogonal signals generated by the SOGI module are normalized and the rotor electrical angle is obtained by the inverse tangent function. When rotating counterclockwise, 2π / 3 and 4π / 3 are added to the second and third cycles of the triple electrical angular frequency respectively; when rotating clockwise, 4π / 3 and 2π / 3 are added to the first and second cycles respectively. The mathematical expression of the frequency conversion is shown in formula (14):

[0040]

[0041] Among them, D ir D is the direction symbol. When rotating counterclockwise, ir is 0; when rotating clockwise, D ir =1,ω f The electrical angle period.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention uses three symmetrical resistors in parallel to reconstruct the virtual neutral point of the PMSM, obtains the third harmonic by measuring the voltage difference between the neutral point of the stator winding and the virtual neutral point, and extracts the rotor position information by using the SOGI-FLL-WPF technology. First, the third harmonic signal is pre-filtered. Since the rotor position cannot be directly calculated by a single signal, its orthogonal signal is constructed by the SOGI module. In addition, the electrical angular frequency is tracked in real time by the FLL module to match the change of speed. Then, the two orthogonal signals are normalized and the rotor position information is obtained by the inverse tangent function. Since it is an angle obtained from the third harmonic, the electrical angular frequency obtained is three times the actual electrical angular frequency, and this electrical angle is converted into an actual electrical angle. Finally, the angle is replaced by If to control the given angle, and the motor speed is calculated by using the angle, and is incorporated into the speed loop, thereby realizing position sensorless control. The present invention has low manufacturing cost, does not need to inject additional high-frequency signals and rely on motor parameters, only requires the motor to have a star-connected stator winding, and the sensor part only uses the basic circuit without installing a position sensor, such as a Hall sensor and an orthogonal encoder, and has low manufacturing cost.

[0044] The present invention proposes a novel position sensorless control method based on a permanent magnet synchronous motor neutral point voltage and a second-order generalized integrator-based frequency-locked loop with prefilter (SOGI-FLL-WPF). BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 It is a rotor coordinate system diagram of the PMSM position sensorless control method based on the stator winding neutral point voltage of the present invention.

[0048] Figure 2 The block diagram of SOGI-FLL-WPF of the PMSM position sensorless control method based on the neutral point voltage of the stator winding of the present invention;

[0049] Figure 3 It is a sensorless control structure block diagram of the PMSM position sensorless control method based on the stator winding neutral point voltage of the present invention;

[0050] Figure 4 It is a schematic diagram of triple electrical angle frequency conversion of the PMSM position sensorless control method based on the stator winding neutral point voltage of the present invention;

[0051] Figure 5 This is a simulation result diagram of the non-sensing control loading of the PMSM position sensorless control method based on the stator winding neutral point voltage of the present invention;

[0052] Figure 6 This is a simulation result diagram of the non-sensing control speed increase of the PMSM position sensorless control method based on the stator winding neutral point voltage of the present invention;

[0053] Figure 5 (a) and Figure 6 (a) is the speed waveform, Figure 5 (b) and Figure 6 (b) is the electromagnetic torque waveform, Figure 5 (c) and Figure 6 (c) is the third harmonic back EMF waveform, Figure 5 (d) and Figure 6 (d) is the electrical angle waveform. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Reference Figure 3 The structural block diagram of the present invention is shown in FIG. It includes five modules: input, control, drive, permanent magnet synchronous motor and DC power supply. The input module includes a mechanical reference speed and the open loop reference current The control module includes open-loop If control and closed-loop FOC control; the drive module includes PWM output, Inverter, Amplifier and AD conversion.

[0056] The PMSM position sensorless control method based on the stator winding neutral point voltage comprises the following steps:

[0057] Step 1: Rotor pre-positioning: setting current A fixed voltage vector is output through the current loop PI controller to align the rotor d-axis with the permanent magnet synchronous motor winding a phase, avoiding the If control open-loop start failure and reversal problem;

[0058] Step 2: If open-loop control is used, set the open-loop target speed to 600r / min and the acceleration to 4000r / min, convert the speed into electrical angular velocity and integrate it to get the position angle of the motor control, then add the obtained electrical angle to establish a coordinate axis leading the actual coordinate system, set, perform current closed-loop and speed open-loop control, and force the motor open-loop to the set speed.

[0059] Step 3: When the If open-loop control is stable, the third harmonic back electromotive force e3 is extracted by directly detecting the voltage difference between the neutral point and the virtual neutral point of the stator winding of the permanent magnet synchronous motor; the third harmonic back electromotive force is extracted by introducing a virtual neutral point and then directly detecting the voltage difference between the neutral point and the virtual neutral point;

[0060] Obtain the third harmonic back EMF. Since the flux density distribution of the rotor permanent magnet in the air gap around the motor is a non-ideal sine wave, the air gap flux contains integer multiples of the third harmonic, of which the third harmonic accounts for the largest proportion of the total harmonics. The third harmonic of the flux will generate a third harmonic back EMF at the neutral point of the stator winding. To this end, we use three symmetrical resistors in parallel on the motor phase line to reconstruct the virtual neutral point of the PMSM. By directly detecting the voltage difference between the neutral point and the virtual neutral point of the permanent magnet synchronous motor, the third harmonic back EMF can be effectively extracted.

[0061] Step 4: The third harmonic back-EMF signal is filtered through a pre-filter, which is a frequency adaptive bandpass filter. This enables the SOGI-FLL-WPF technology to achieve a better trade-off between speed and accuracy than the standard SOGI-FLL. It is also a SOGI-based orthogonal signal generator, but only uses the output of the α axis.

[0062] Step 5: The signal obtained by filtering in step 4 and its orthogonal signal are constructed through the SOGI module, and the electrical angular frequency of the signal is tracked using the FLL technology;

[0063] The filtered third harmonic back electromotive force e′3 is obtained, but the rotor position cannot be directly calculated from a single signal, so its orthogonal signal needs to be constructed. In addition, the electrical angular frequency needs to be tracked in real time to match the speed change. Therefore, the filtered signal is passed through the SOGI module to obtain the estimated Signal and its orthogonal signal At the same time, the frequency-locked loop FLL is used to track the estimated signal to obtain three times the electrical angle frequency. When the SOGI-FLL module is in steady state, the estimated electrical angular frequency Equal to the actual ω 3e ,so and The transfer function between and e′3 can be expressed as:

[0064]

[0065] Wherein, k2 is the gain coefficient of the SOGI-FLL module.

[0066] Step 6: normalize the two orthogonal signals obtained in step 5, obtain the estimated electrical angle value through the inverse tangent function, and perform frequency conversion;

[0067] Then and After unitization, we get and Finally, the estimated electrical angle is calculated by the arctan function Since the rotor position information is extracted from the third harmonic back EMF, the angle is three times the actual electrical angle frequency. Converted into actual electrical angle θ e ;

[0068] Step 7: Replace the angle generated by the If open-loop control with the electrical angle value of step 6, obtain the actual motor speed through differential calculation, and introduce the speed loop to realize position sensorless control.

[0069] The rotor position θ obtained in step 6 e Replace the angle generated in the If open-loop control in step 2 Through θ e Calculate the speed and will The speed loop is introduced to perform speed closed-loop control.

[0070] The step 2 specifically includes:

[0071] Adopt uniform acceleration start strategy and set the d-axis current to remain at i d =0, the q-axis current is a constant starting current, and the current angular velocity ω is given e And integrate to get the position angle of the motor control To achieve position setting, a coordinate axis d′q′ leading the actual coordinate system by π / 2 is given in the initial stage as a virtual synchronous coordinate system. The PMSM torque equation and motion equation are rewritten as:

[0072]

[0073] In formulas (1) and (2): T e is the electromagnetic torque, n p is the pole pair number, ψ f is the permanent magnet flux, θ γ is the angular error between the coordinate systems, J is the moment of inertia, ω ris the mechanical angular velocity, T l is the load torque and B is the friction coefficient.

[0074] The step 4 specifically includes:

[0075] After a frequency adaptive bandpass filter, is a constant, and the transfer function between e′3 extracted by the prefilter and the input signal e3 can be expressed as:

[0076]

[0077] Where k1 is the gain coefficient of the pre-filter, is the electrical angular frequency of the signal, is the best choice corresponding to the damping coefficient Ensure that the pre-filter achieves the best balance between overshoot and settling time when extracting the signal.

[0078] The step five specifically includes:

[0079] get and The transfer function of SOGI-FLL-WPF cannot reflect the tracking characteristics of frequency and angle. Figure 2 To linearize, and It can be expressed as:

[0080]

[0081] Since the poles of the closed-loop transfer function (8) are all real numbers, this corresponds to the case where the damping coefficient is equal to or greater than 1. However, when the damping coefficient is greater than 1, the dynamic response of the transfer function (8) is overdamped and the response speed is too slow. Therefore, the damping coefficient is selected to be equal to the unit damping factor, which corresponds to the transfer function (8) having the same poles, so k1 = k2. The characteristic polynomials of equations (8) and (9) are:

[0082]

[0083] Since equation (10) is a third-order polynomial with at least one real pole, it can also be expressed as:

[0084]

[0085] Among them, ζ and ω n denote the damping factor and natural frequency respectively, γ is the factor that determines the position of the real poles, according to equation (11), the coefficients of the same order s on both sides are equal, and let Then the gain λ of FLL can be expressed as:

[0086]

[0087] From equations (11) and (12), we can see that γ can be expressed as:

[0088]

[0089] The step six specifically includes:

[0090] The two orthogonal signals generated by the SOGI module are normalized, and then the rotor electrical angle is obtained through the inverse tangent function. Figure 4 In order to convert this angle into an actual electrical angle diagram, the figure includes two cases of counterclockwise and clockwise rotation of the motor. When rotating counterclockwise, 2π / 3 and 4π / 3 are added to the second and third cycles of the triple electrical angle frequency respectively; when rotating clockwise, 4π / 3 and 2π / 3 are added to the first and second cycles respectively. The mathematical expression of this frequency conversion is shown in the formula:

[0091]

[0092] Among them, D ir D is the direction symbol. When rotating counterclockwise, ir is 0; when rotating clockwise, D ir =1,ω f The electrical angle period.

[0093] The step seven specifically includes:

[0094] Closed-loop FOC control. When the motor speed reaches the reference speed set by the open loop and remains stable, the switch S w1 and S w2 The state of is set to 1 to switch from open-loop control to closed-loop control, that is, to use the estimated electrical angle replace And the mechanical speed Introduced into the speed loop as speed feedback.

[0095] In order to verify the control performance of the PMSM position sensorless control method based on the neutral point voltage of the stator winding when the motor is suddenly loaded and the speed changes, simulation tests were carried out under the conditions of increasing the load to 0.1 at 1.4s and increasing the motor speed from 1500r / min to 1700r / min at 1.8s. The simulation results are shown in Figure 2. Figure 5 and Figure 6 As shown, it includes speed tracking, electromagnetic torque change, third harmonic back EMF tracking and rotor position error waveform.

[0096] Table 1 Permanent magnet synchronous motor parameters

[0097] parameter Numeric parameter Numeric Pole pairs 2 Bus voltage 24V Magnet Link 0.0124Wb Rated current 5.5A D-axis inductance 2.5e-4H Rated torque 0.2N·m Q-axis inductance 3.5e-4H Rated speed 3900r / min

[0098] Figure 5 The simulation waveform is shown when the motor speed increases from no-load to load 0.1 at 1500r / min. Figure 5 (a) It can be seen that when the load increases to 0.1, the actual motor speed drops to 1542r / min briefly and returns to the reference speed after 0.135 seconds, indicating that this method has good anti-interference performance. Figure 5 (c) It can be seen that the output signal of the SOGI-FLL-WPF module can quickly track the third harmonic back-EMF signal, indicating that this technology has a good dynamic tracking effect on the third harmonic back-EMF signal, so that the error between the estimated rotor position and the actual rotor position is almost zero when the motor is in steady state.

[0099] Figure 6 The simulation waveform is shown when the reference speed is increased to 1700r / min. Figure 6 (a) It can be seen that the actual speed of the motor can quickly track the reference speed, and the adjustment time is 0.2s. Figure 6 (c) It can be seen that the output signal of the SOGI-FLL-WPF module can also dynamically track the third harmonic back-EMF signal well.

[0100] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. A PMSM position sensorless control method based on the neutral point voltage of the stator winding, characterized in that: The following steps are involved: Step 1: Rotor pre-positioning: setting current A fixed voltage vector is output through the current loop PI controller to align the rotor d-axis with the permanent magnet synchronous motor winding A phase; Step 2: If open-loop control, the control is current closed-loop control, and a uniform acceleration starting strategy is adopted to accelerate the motor speed to the target set speed; Step 3: When the If open-loop control is stable, the voltage difference between the neutral point of the stator winding of the permanent magnet synchronous motor and the virtual neutral point is directly detected to extract the third harmonic back electromotive force e3; Step 4: Filter the third harmonic back EMF signal through a pre-filter; Step 5: The signal obtained by filtering in step 4 and its orthogonal signal are constructed through the SOGI module, and the electrical angular frequency of the signal is tracked using the FLL technology; Step 6: normalize the two orthogonal signals obtained in step 5, obtain the estimated electrical angle value through the inverse tangent function, and perform frequency conversion; Step 7: Replace the angle generated by the If open-loop control with the electrical angle value of step 6, obtain the actual motor speed through differential calculation, and introduce the speed loop to realize position sensorless control.

2. The PMSM position sensorless control method based on the stator winding neutral point voltage according to claim 1, characterized in that: The step 2 specifically includes: Adopt uniform acceleration start strategy and set the d-axis current to remain at i d =0, the q-axis current is a constant starting current, and the current angular velocity ω is given e And integrate to get the position angle of the motor control To achieve position setting, a coordinate axis d′q′ leading the actual coordinate system by π / 2 is given in the initial stage as a virtual synchronous coordinate system. The PMSM torque equation and motion equation are rewritten as: In formulas (1) and (2): T e is the electromagnetic torque, n p is the pole pair number, ψ f is the permanent magnet flux, θ γ is the angular error between the coordinate systems, J is the moment of inertia, ω r is the mechanical angular velocity, T l is the load torque and B is the friction coefficient.

3. The PMSM position sensorless control method based on stator winding neutral point voltage according to claim 1, characterized in that: The step 4 specifically includes: After a frequency adaptive bandpass filter, is a constant, and the transfer function between e′3 extracted by the prefilter and the input signal e3 can be expressed as: Where k1 is the gain coefficient of the pre-filter, is the electrical angular frequency of the signal, is the best choice corresponding to the damping coefficient Ensure that the pre-filter achieves the best balance between overshoot and settling time when extracting the signal.

4. The PMSM position sensorless control method based on stator winding neutral point voltage according to claim 1, characterized in that: The step five specifically includes: The parameter selection in SOGI is done by linearizing the SOGI model: The poles of the closed-loop transfer function are all real numbers, corresponding to the case where the damping coefficient is equal to or greater than 1. When the damping coefficient is greater than 1, the response speed is too slow. The damping coefficient is selected to be equal to the unit damping factor, corresponding to the transfer function having the same poles, so k1=k2, and the characteristic polynomial of equation (8) is: Since equation (10) is a third-order polynomial with at least one real pole, it can also be expressed as: Among them, ζ and ω n denote the damping factor and natural frequency respectively, γ is the factor that determines the position of the real poles, according to equation (11), the coefficients of the same order s on both sides are equal, and let Then the gain λ of FLL can be expressed as: From equations (11) and (12), we can see that γ can be expressed as:

5. The PMSM position sensorless control method based on stator winding neutral point voltage according to claim 1, characterized in that: The step six specifically includes: The two orthogonal signals generated by the SOGI module are normalized and the rotor electrical angle is obtained by the inverse tangent function. When rotating counterclockwise, 2π / 3 and 4π / 3 are added to the second and third cycles of the triple electrical angular frequency respectively; when rotating clockwise, 4π / 3 and 2π / 3 are added to the first and second cycles respectively. The mathematical expression of the frequency conversion is shown in formula (14): Among them, D ir D is the direction symbol. When rotating counterclockwise, ir is 0; when rotating clockwise, D ir =1,ω f The electrical angle period.

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