Method for estimating rotor position of multi-stage motor in low speed range based on excitation system

Abstract

The application relates to a multi-stage motor low-speed rotor position estimation method based on an excitation system, which is applied to a multi-stage brushless synchronous motor, the multi-stage brushless synchronous motor comprising a main motor and a two-phase excitation motor coaxially installed, and the rotor position of the multi-stage brushless synchronous motor referring to the rotor position of the main motor in the multi-stage brushless synchronous motor. Steps 1-5 are respectively implemented in the original non-rotating state and the low-speed rotating state of the motor to obtain the rotor position theta e of the excitation motor and the initial rotor position theta e0 of the excitation motor, calculate the rotor position increment of the excitation motor, and determine the rotor position of the main motor according to the rotor position increment of the excitation motor and the initial rotor position of the main motor, that is, the rotor position of the multi-stage brushless synchronous motor. When the signal is extracted, the application replaces the complex mathematical operation in the signal injection-demodulation-extraction process with simple trigonometric function operation and a low-pass filter, and the application has a lower requirement on the processor performance, and the current common processor can meet the requirement.

Description

Technical Field

[0001] This invention belongs to the field of synchronous motor rotor position estimation technology, and relates to a method for estimating the rotor position of a multi-stage motor in the low-speed section based on the excitation system. Specifically, it relates to a method for estimating the rotor position of a multi-stage brushless synchronous motor in the low-speed section based on the exciter rotor current estimation and unaffected by the main motor operating conditions. Background Technology

[0002] Three-stage brushless synchronous motors offer advantages such as high power quality and reliability, and are widely used as generators in aircraft power systems. By operating the three-stage brushless synchronous motor in electric mode to start the aircraft engine, and then having the engine drive it in generator mode to supply power to onboard electrical equipment after starting, the three-stage brushless synchronous motor achieves integrated starting and generating. This eliminates the need for a dedicated engine starter, reduces system size and weight, and increases integration, which is of great significance to aircraft power systems.

[0003] When a three-stage brushless synchronous motor operates in electric mode to start an aero engine, accurate rotor position information is required. Traditional mechanical position sensors for obtaining rotor position suffer from low reliability and increased system size and weight. Online rotor position estimation for a three-stage brushless synchronous motor can eliminate the need for mechanical position sensors, enabling sensorless start-up control, improving system reliability, and reducing size and weight.

[0004] A three-stage brushless synchronous motor consists of a coaxially mounted permanent magnet auxiliary exciter, an exciter, and a main motor. Its structural diagram is shown below. Figure 1 As shown. In some applications, the permanent magnet auxiliary exciter can be omitted, forming a two-stage brushless synchronous motor. Since the core components and operating principles are basically the same, three-stage and two-stage brushless synchronous motors are collectively referred to as multi-stage brushless synchronous motors.

[0005] Traditional rotor position estimation methods for low-speed multi-stage brushless synchronous motors largely rely on the salient polarity of the main motor. However, when a multi-stage brushless synchronous motor operates in electric mode to start an aero-engine, the salient polarity of the main motor changes, causing traditional methods to fail. Rotor position estimation methods based on "main motor injection - exciter detection" do not depend on the salient polarity of the main motor, but require injecting high-frequency or low-frequency signals into the stator side of the main motor, which can lead to problems such as vibration and increased losses. Rotor position estimation methods based on "main exciter injection - main motor detection" also do not depend on the salient polarity of the main motor, but signal extraction from the stator side is easily affected by the operating conditions of the main motor. Currently, there are rotor position estimation methods without high-frequency signal injection, including the exciter current harmonic method and the exciter rotor current trajectory method, which avoid additional signal injection and the influence of the main motor's operating conditions. However, these methods are more complex, computationally intensive, and require higher processing power from the controller. Summary of the Invention

[0006] Technical problems to be solved

[0007] To avoid the shortcomings of existing technologies, this invention proposes a method for estimating the rotor position of a multi-stage motor in the low-speed section based on the excitation system. This method overcomes the problems of dependence on motor salient polarity, vibration and loss caused by additional signal injection, and complex estimation methods in existing technologies. This invention does not depend on motor salient polarity, does not require additional signal injection, and is not affected by the operating state of the main motor.

[0008] Technical solution

[0009] A method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system is characterized by including a coaxially mounted main motor and a two-phase exciter. The rotor position refers to the rotor position of the main motor in the multi-stage brushless synchronous motor. The estimation steps are as follows:

[0010] Steps 1 through 5 are performed respectively in the motor's initial stationary state and low-speed rotating state to obtain the exciter rotor position θ. e and the initial position θ of the exciter rotor e0 ;

[0011] Step 1: Apply a two-phase symmetrical voltage u to the stator winding of the two-phase exciter. esα and u esβ The two-phase voltage u of the stator α-phase and β-phase currents of the two-phase exciter is collected. esd u esq and current i esα i esβ ;

[0012] Step 2: Calculate the dq-axis voltage u of the exciter stator. esd and u esq Current iesd and i esq ;

[0013] Step 2: Estimate the dq axis current of the exciter rotor;

[0014]

[0015] Where: R es and L es These are the exciter stator winding resistance and self-inductance, respectively, M em For the maximum mutual inductance between the exciter stator and rotor, ψ d and ψ q The air gap flux linkage of the dq axis obtained through iteration;

[0016] Step 3: Perform coordinate transformation on the dq-axis current of the exciter rotor sequentially. After the coordinate transformation, perform low-pass filtering to obtain the cosine and sinine signals related to the position of the exciter rotor, denoted as f. cos and f sin ;

[0017] The coordinate transformation is as follows:

[0018]

[0019] i erd1 and i erq1 The exciter's two-phase currents after coordinate transformation; Let be the coordinate transformation matrix, where θ is the coordinate transformation angle, and:

[0020] When the excitation magnetic field of the exciter rotates in the same direction as the motor, i.e., when the excitation is in the same direction, θ = 6ω esf t;

[0021] When the excitation magnetic field of the exciter rotates in the opposite direction to the rotation of the motor, i.e., when it is reverse excitation, θ=-6ω esf t;

[0022] Step 4: For f cos and f sin After performing phase-locked loop processing, the electrical angle θ of the exciter rotor position is obtained as 6 times the angle. 6e , that is, θ 6e =6θ e , where θ e The electric angle of the exciter rotor position is θ, which is the exciter rotor position when the motor is rotating at low speed. e The initial position θ of the exciter rotor is when the motor is not rotating. e0 ;

[0023] Step 5: Calculate the exciter rotor position increment Δθ e =θ e-θ e0 ;

[0024] Step 6: Using the electric angle increment value Δθ of the exciter rotor position e Divide by the number of pole pairs of the exciter to obtain the mechanical angle increment of the exciter rotor position, then multiply by the number of pole pairs of the main motor to obtain the electrical angle increment of the main motor rotor position, and finally add the initial electrical angle of the main motor rotor position to obtain the main motor rotor position, which is the rotor position of the multi-stage brushless synchronous motor.

[0025] The two symmetrical voltage signals are:

[0026]

[0027] U esf and ω esf These represent the voltage amplitude and the electric angular velocity, θ. esf =ω esf t represents the voltage phase.

[0028] The exciter stator dq axis current i esd and i esq for:

[0029]

[0030] The exciter stator dq axis voltage u esd and u esq for:

[0031]

[0032] The dq-axis air gap flux ψ d and ψ q for:

[0033]

[0034] The low-pass filter is:

[0035]

[0036] Here, LPF represents low-pass filtering.

[0037] The low speed of the multi-stage motor refers to the mechanical speed between 0-240 rpm.

[0038] Beneficial effects

[0039] This invention proposes a method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system. This method is applied to multi-stage brushless synchronous motors, which include a coaxially mounted main motor and a two-phase exciter. The rotor position of the multi-stage brushless synchronous motor refers to the rotor position of the main motor. Steps 1 to 5 are performed in both the initial stationary state and the low-speed rotating state of the motor to obtain the exciter rotor position θ. e and the initial position θ of the exciter rotor e0 Calculate the exciter rotor position increment, and determine the main motor rotor position based on the exciter rotor position increment and the initial position of the main motor rotor, which is the rotor position of the multi-stage brushless synchronous motor.

[0040] The beneficial effects of this invention include: 1) Because the inherent signal of the exciter itself is used as the effective signal for rotor position estimation, compared with the traditional rotor position estimation method based on additional signal injection, which introduces torque ripple, this invention reduces torque ripple and also reduces high-frequency harmonic losses caused by additional signal injection; 2) Because the order of magnitude of the excitation system current is much smaller than that of the main motor current during startup, and the order of magnitude does not change significantly during low-speed startup, compared with the traditional rotor position estimation method based on high-frequency signal injection from the main motor stator winding, the signal-to-noise ratio is higher and it is not affected by changes in the main motor's operating state, such as salient polarity and load changes, effectively improving the accuracy of rotor position estimation. In actual operation, during startup with a load of 45 N·m from 0 rpm to 240 rpm, the estimation error does not exceed 5°. Figure 8 As shown, curves A, B, C, and D represent the actual position, estimated position, estimation error, and estimated rotational speed, respectively. In existing literature, when using other methods for position estimation, the maximum load is 30 N·m, and the estimation error is within 10°. 3) When extracting signals, this invention only uses simple trigonometric function operations and low-pass filters. Compared with the complex mathematical operations used in the signal injection-demodulation-extraction process in existing methods, this invention has lower requirements for processor performance, and most common processors can meet the requirements. Attached Figure Description

[0041] Figure 1 Schematic diagram of a three-stage brushless synchronous motor

[0042] Figure 2 The flowchart below shows the rotor position estimation method for the low-speed section of the multi-stage brushless synchronous motor proposed in this invention.

[0043] Figure 3 Estimate the current waveform for the dq axis of the exciter rotor.

[0044] Figure 4 Estimate the waveform of the current along the dq axis of the exciter rotor after coordinate transformation.

[0045] Figure 5 The waveform after passing through a low-pass filter (i.e., the cosine and sinine signals related to the exciter rotor position).

[0046] Figure 6 To estimate θ 6e θ e and rotor position increment Δθ e

[0047] Figure 7 Estimated value, actual value and estimation error of the main motor rotor position

[0048] Figure 8 Experimental results of starting with a load of 45 N·m from 0 rpm to 240 rpm Detailed Implementation

[0049] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0050] Step 1: Apply two-phase symmetrical voltages to the stator windings of the two-phase exciter and collect the two-phase stator currents of the two-phase exciter;

[0051] Step 2: Based on the two-phase symmetrical voltage signals and their phase information, the stator dq-axis voltage and stator dq-axis current are obtained from the acquired stator two-phase current information, and then the exciter rotor dq-axis current is estimated.

[0052] Step 3: Perform coordinate transformation and low-pass filtering on the estimated exciter rotor dq axis currents in sequence to obtain the cos and sin signals related to the exciter rotor position;

[0053] Step 4: Obtain the exciter rotor position based on the cos and sin signals related to the exciter rotor position;

[0054] Step 5: Obtain the exciter rotor position increment based on the exciter rotor position and the exciter rotor initial position. The exciter rotor initial position is the exciter rotor position obtained from Steps 1 to 4 above when the system is stationary.

[0055] Step 6: Determine the position of the main motor rotor based on the exciter rotor position increment and the initial position of the main motor rotor, which is the rotor position of the multi-stage brushless synchronous motor.

[0056] In this embodiment, the exciter of the multi-stage brushless synchronous motor is a two-phase exciter, meaning the exciter stator windings are two-phase windings with a 90° electrical angle difference. The exciter has 6 pole pairs, and the main motor has 3 pole pairs. The following detailed explanation uses the motor starting from 0 rpm to 240 rpm as an example.

[0057] 1. Apply two-phase symmetrical voltages u to the two-phase windings of the exciter stator (denoted as the α-phase winding and the β-phase winding, respectively). esα and u esβ Excitation voltage amplitude U esf =200V, electric angular velocity ω esf =200*2πrad / s, and the direction of rotation of the excitation magnetic field is opposite to the direction of rotation of the motor. The two-phase stator currents of the two-phase exciter are collected and denoted as i... esα and i esβ The current along the dq axis of the exciter rotor is estimated and denoted as i. erd and i esq ,like Figure 3 As shown.

[0058] 2. For the estimated exciter rotor dq-axis current i erd and i esq Perform the following coordinate transformation to obtain i erd1 and i esq1 .

[0059]

[0060] Where, ω esf It is the excitation angular frequency of the exciter stator, ω. esf = 200 * 2π rad / s, where t represents time.

[0061] The two-phase current waveform of the exciter stator after coordinate transformation (i.e., i) erd1 and i erq1 )like Figure 4 As shown.

[0062] 3. The exciter rotor dq-axis current i after coordinate transformation erd1 and i erq1 The signal is filtered by a Butterworth low-pass filter with a cutoff frequency of 300Hz. After low-pass filtering, the cosine signal related to the exciter rotor position (denoted as f) is obtained. cos ) and sin signal (denoted as f) sin ),like Figure 5 As shown.

[0063] 4. Regarding the above f cos and f sin After processing with a phase-locked loop, the electrical angle θ of the exciter rotor position is obtained as 6 times the angle θ. 6e ,like Figure 6 As shown. Figure 6 Dividing the angle shown by 6 yields the electrical angle θ of the exciter rotor position. e .

[0064] 5. Subtract the initial value of the exciter rotor position electrical angle from the obtained exciter rotor position electrical angle to obtain the increment value of the exciter rotor position electrical angle (denoted as Δθ). e ), that is, Δθ e =θ e -θ e0 Where θ e0 The initial electrical angle value of the exciter rotor position is the exciter rotor position obtained by the steps described above when the system is stationary.

[0065] 6. Divide the obtained electrical angle increment of the exciter rotor position by the number of pole pairs (6) to obtain the mechanical angle increment of the exciter rotor position. Since the exciter and the main motor are coaxially mounted, the mechanical angle increment of the exciter rotor position is also the mechanical angle increment of the main motor rotor position. Multiply the obtained mechanical angle increment of the main motor rotor position by the number of pole pairs of the main motor to obtain the electrical angle increment of the main motor rotor position. Finally, add the initial electrical angle value of the main motor rotor position to obtain the main motor rotor position, which is the rotor position of the multi-stage brushless synchronous motor. Figure 7 The figure shows the final estimated position of the main motor rotor, the actual rotor position, and the estimation error.

Claims

1. A method for estimating the rotor position in the low-speed section of a multi-stage motor based on an excitation system, characterized in that... This includes the coaxially mounted main motor and the two-phase exciter. The rotor position refers to the rotor position of the main motor in a multi-stage brushless synchronous motor. The estimation steps are as follows: Steps 1 through 5 are performed respectively in the motor's initial stationary state and low-speed rotating state to obtain the exciter rotor position θ. e and the initial position θ of the exciter rotor e0 ; Step 1: Apply a two-phase symmetrical voltage u to the stator winding of the two-phase exciter. esα and u esβ The two-phase voltage u of the stator α-phase and β-phase currents of the two-phase exciter is collected. esd u esq and current i esα i esβ ; Step 2: Calculate the dq-axis voltage u of the exciter stator. esd and u esq Current i esd and i esq ; Step 2: Estimate the dq axis current of the exciter rotor; Where: R es and L es These are the exciter stator winding resistance and self-inductance, respectively, M em For the maximum mutual inductance between the exciter stator and rotor, ψ d and ψ q The air gap flux linkage of the dq axis obtained through iteration; Step 3: Perform coordinate transformation on the dq-axis current of the exciter rotor sequentially. After the coordinate transformation, perform low-pass filtering to obtain the cosine and sinine signals related to the position of the exciter rotor, denoted as f. cos and f sin ; The coordinate transformation is as follows: i erd1 and i erq1 The exciter's two-phase currents after coordinate transformation; Let be the coordinate transformation matrix, where θ is the coordinate transformation angle, and: When the excitation magnetic field of the exciter rotates in the same direction as the motor, i.e., when the excitation is in the same direction, θ = 6ω esf t; When the excitation magnetic field of the exciter rotates in the opposite direction to the rotation of the motor, i.e., when it is reverse excitation, θ=-6ω esf t; Step 4: For f cos and f sin After performing phase-locked loop processing, the electrical angle θ of the exciter rotor position is obtained as 6 times the angle. 6e , that is, θ 6e =6θ e , where θ e The electric angle of the exciter rotor position is θ, which is the exciter rotor position when the motor is rotating at low speed. e The initial position θ of the exciter rotor is when the motor is not rotating. e0 ; Step 5: Calculate the exciter rotor position increment Δθ e =θ e -θ e0 ; Step 6: Using the electric angle increment value Δθ of the exciter rotor position e Divide by the number of pole pairs of the exciter to obtain the mechanical angle increment of the exciter rotor position, then multiply by the number of pole pairs of the main motor to obtain the electrical angle increment of the main motor rotor position, and finally add the initial electrical angle of the main motor rotor position to obtain the main motor rotor position, which is the rotor position of the multi-stage brushless synchronous motor.

2. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The two symmetrical voltage signals are: Among them U esf and ω esf These represent the voltage amplitude and the electric angular velocity, θ, respectively. esf =ω esf t represents the voltage phase.

3. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The exciter stator dq axis current i esd and i esq for: 。 4. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The exciter stator dq axis voltage u esd and u esq for: 。 5. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The dq-axis air gap flux ψ d and ψ q for: 。 6. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The low-pass filter is: Here, LPF represents low-pass filtering.

7. The method for estimating the rotor position of a multi-stage motor in the low-speed range based on an excitation system according to claim 1, characterized in that: The low speed of the multi-stage motor refers to the mechanical speed between 0-240 rpm.

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