Permanent magnet synchronous motor position estimation method based on second harmonic tracking

Abstract

The application discloses a permanent magnet synchronous motor position estimation method based on secondary harmonic tracking. When the permanent magnet synchronous motor is in zero speed and low speed state, a high-frequency sinusoidal pulse voltage signal is injected into the estimated d-axis of the motor. The secondary harmonic current response signal is extracted, and the amplitude thereof is obtained through heterodyne and low-pass filtering processing. The system is converged to the minimum point of the current secondary harmonic amplitude through the minimum value gradient tracking method, so that the effective detection of the zero speed and low speed position of the permanent magnet synchronous motor is realized. The application can realize the unique position convergence point in the whole error range, so as to improve the estimation performance and robustness of the system in the zero speed and low speed interval.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a position estimation method for permanent magnet synchronous motors based on second harmonic tracking. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are widely used in electric vehicles, aerospace electric drives, industrial robots, and servo control due to their high power density, high efficiency, and excellent dynamic response performance. In vector control frameworks, motor performance is highly dependent on the accurate acquisition of rotor position. Traditionally, position information is obtained in real time through mechanical position sensors. However, these sensors may face problems such as high cost, large size, insufficient anti-interference capability, and decreased reliability in complex environments, limiting the application requirements of systems in high-integration, miniaturized, and high-reliability scenarios. Therefore, various sensorless control methods have gradually become an important research direction for permanent magnet synchronous motors.

[0003] Existing sensorless methods are mainly divided into two categories: low-frequency model methods based on back EMF observation and high-frequency methods based on signal injection. Back EMF-based observation algorithms, such as sliding mode observers and extended Kalman filters, can achieve high estimation accuracy in the medium-to-high speed range. However, because the amplitude of the motor's back EMF is close to zero at low speeds and zero speeds, these methods are prone to problems such as amplified estimation errors and unstable responses in the low-speed range, making it difficult to meet the high-precision detection requirements for initial position and low-speed segments.

[0004] To address the challenges of zero-speed and low-speed estimation, high-frequency signal injection methods have become a research hotspot. These methods inject high-frequency voltage or current signals into the stator windings of a permanent magnet synchronous motor (PMSM) to construct a position-dependent high-frequency response model, utilizing the salient pole effect or saturation nonlinearity of the PMSM, and then calculate the position estimation result. Existing high-frequency injection methods typically extract position error information using injected subharmonic signals. However, since the injected subharmonic model often exhibits bipolar characteristics, with two symmetrical convergence points within the same error period, the system needs additional polarity determination to determine the correct convergence direction. Under conditions such as load disturbances, motor parameter mismatches, or high noise levels, polarity determination is prone to misjudgment, leading to incorrect system convergence or even requiring repeated corrections, complicating the position estimation process and affecting the stability of low-speed operation.

[0005] Therefore, how to construct a position detection method for permanent magnet synchronous motors that does not require polarity discrimination, has unique convergence, stable estimation, and is applicable to zero speed and low speed has become a key technical problem in the field of sensorless control. Summary of the Invention

[0006] Purpose of the invention: This invention provides a position estimation method for permanent magnet synchronous motors based on second harmonic tracking, which achieves a unique position convergence point within the entire error range, thereby improving the estimation performance and robustness of the system in the zero-speed and low-speed ranges.

[0007] Technical solution: The position estimation method for permanent magnet synchronous motors based on second harmonic tracking described in this invention includes the following steps:

[0008] When the permanent magnet synchronous motor is in a zero-speed or low-speed state, a high-frequency sinusoidal pulsating voltage signal is injected into the estimated d-axis of the motor.

[0009] The second harmonic current response signal is extracted and its amplitude is obtained by heterodyne and low-pass filtering.

[0010] By using the minimum gradient tracking method, the system converges to the minimum point of the second harmonic amplitude of the current, thus achieving effective detection of the zero-speed and low-speed positions of the permanent magnet synchronous motor.

[0011] Furthermore, the estimated d-axis voltage signal of the motor after injection of a high-frequency sinusoidal pulsating voltage signal is expressed as:

[0012]

[0013] In the formula, This is the reference value for the d-axis voltage output of the system current loop. The amplitude of the injected high-frequency voltage, The angular frequency of the injected high-frequency voltage.

[0014] Furthermore, the current response signal is represented as:

[0015]

[0016] In the formula, The difference between the actual location and the estimated location. It is a q-axis high-frequency inductor. This refers to the high-frequency d-axis inductance corresponding to the positive half-cycle of the injected voltage. This refers to the high-frequency d-axis inductance corresponding to the negative half-cycle of the injected voltage.

[0017] Furthermore, the value of the high-frequency d-axis inductance is expressed as follows:

[0018]

[0019] In the formula, The d-axis high-frequency inductance at saturation This is the d-axis high-frequency inductance when it is not saturated, and it has... .

[0020] Furthermore, the second harmonic current response signal is extracted, and its amplitude is obtained by heterodyne and low-pass filtering. A band-pass filter is then used to extract the high-frequency current response signal at twice the injection frequency, as shown below:

[0021]

[0022] After heterodyne processing, the amplitude is obtained using a low-pass filter, and expressed as follows:

[0023] .

[0024] Furthermore, the minimum gradient pursuit method is used to converge the system to the minimum point of the second harmonic amplitude of the current. A gradient is constructed based on the change in the amplitude of the second harmonic of the high-frequency current response signal relative to the position error, and the convergence position of the negative gradient is used as the estimated position. The constructed gradient is expressed as:

[0025]

[0026] In the formula, This represents the current state of the control cycle. Given the state of the previous control cycle, the estimated position is represented by the gradient as follows:

[0027]

[0028] The gradient constructed using the second harmonic amplitude has only a single convergence result within one error cycle.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The amplitude of the second harmonic constructed by the present invention exhibits a single-peak unique minimum characteristic with respect to the position error, so that the system has only one stable convergence point in the entire error range, without the need for an additional polarity judgment process, fundamentally avoiding the problem of erroneous convergence and reconvergence caused by polarity misjudgment, and improving the robustness and reliability of position estimation; (2) The present invention extracts the second harmonic of the high-frequency injected current response, which is more clearly distinguished from the frequency of the fundamental current in the zero and low speed stages of the motor, expanding the usable speed range of the zero and low speed sensorless method; (3) The present invention adopts The second harmonic amplitude is extracted by combining heterodyne and low-pass filtering, which effectively suppresses the interference of high-frequency noise and inverter switching harmonics, making the extracted position signal smoother and more stable. Combined with the gradient tracking algorithm based on the second harmonic amplitude, the system can still maintain reliable convergence characteristics under complex working conditions such as load disturbance, motor parameter changes and measurement noise. (4) This invention only needs to construct a simple gradient direction for the second harmonic amplitude and update the estimated position in an incremental way. There is no need to solve complex optimization problems, the computational burden is small, and it can be directly embedded in conventional microcontrollers. It has low cost, strong applicability, and good engineering promotion value. Attached Figure Description

[0030] Figure 1 This is a block diagram of the permanent magnet synchronous motor position estimation method based on second harmonic tracking in this invention.

[0031] Figure 2 This is a schematic diagram of the amplitude trajectories of the second and third harmonics injected in the high-frequency current response described in this invention.

[0032] Figure 3 The figures show the simulation results of the estimated position, actual position, and position estimation error of the permanent magnet synchronous motor initial position direct detection system in different convergence intervals in the method of this invention. Detailed Implementation

[0033] like Figure 1 As shown, a position estimation method for a permanent magnet synchronous motor based on second harmonic tracking includes the following steps:

[0034] The permanent magnet synchronous motor is powered by a three-phase bridge inverter. The main control structure of this invention is the injection of a high-frequency voltage signal and the acquisition of the current response. A high-frequency pulsating voltage signal is injected into the estimated d-axis direction of the motor, and a high-frequency current response is acquired. By demodulating the second harmonic of the current response, the initial position of the motor rotor can be accurately determined.

[0035] First, a high-frequency sinusoidal pulse voltage is injected into the estimated d-axis of the motor. The estimated d-axis voltage after injection can be expressed as:

[0036]

[0037] In the formula, This is the reference value for the d-axis voltage output of the system current loop. The angular frequency of the injected high-frequency voltage, Let represent the amplitude of the injected high-frequency voltage. When the estimated position is close to the actual position of the motor, the positive half-cycle of the injected sinusoidal voltage is in the direction of magnetization, which will cause saturation of the d-axis magnetic circuit and a decrease in the d-axis high-frequency inductance; while the negative half-cycle of the injected sinusoidal voltage is in the direction of demagnetization, which will cause the d-axis magnetic circuit to exit saturation, and the d-axis high-frequency inductance to rise and recover. The high-frequency current response induced by the injected pulsating voltage in the windings of the permanent magnet synchronous motor can be expressed as:

[0038]

[0039] In the formula, The difference between the actual location and the estimated location. It is a q-axis high-frequency inductor. This refers to the high-frequency d-axis inductance corresponding to the positive half-cycle of the injected voltage. Let be the high-frequency d-axis inductance corresponding to the negative half-cycle of the injected voltage. The value of the high-frequency d-axis inductance can then be expressed as:

[0040]

[0041] In the formula, The d-axis high-frequency inductance at saturation This is the d-axis high-frequency inductance when it is not saturated, and it has... Subsequently, the second harmonic current response signal is extracted, and its amplitude is obtained by heterodyne and low-pass filtering. A band-pass filter is then used to extract the high-frequency current response signal at twice the injection frequency, which can be expressed as:

[0042]

[0043] After heterodyne processing, its amplitude is extracted using a low-pass filter, and can be expressed as:

[0044]

[0045] like Figure 2 As shown, the amplitude trajectory of the conventionally injected sub-high frequency current exhibits symmetry, and there are inevitably two convergence points when using PI control. However, the second harmonic current response amplitude trajectory extracted in the above steps has an asymmetric characteristic on the d-axis, where the positive direction of the d-axis corresponds to the minimum amplitude point. Therefore, the minimum gradient pursuit method is used to converge the system to the minimum point of the second harmonic current amplitude. A gradient is constructed based on the change in the amplitude of the second harmonic of the high-frequency current response signal relative to the position error, and the convergence point of the negative gradient is used as the estimated position. The constructed gradient can be expressed as:

[0046]

[0047] In the formula, This represents the current state of the control cycle. Given the state of the previous control cycle, the estimated position can be represented by the gradient as follows:

[0048]

[0049] The gradient constructed using the second harmonic amplitude has only a single convergence result within one error cycle, avoiding the polarity ambiguity of the convergence result in traditional methods, thus making the position estimation of permanent magnet synchronous motors more accurate and effective.

[0050] To verify this method, a model was built for simulation verification. The simulation conditions were as follows: the permanent magnet synchronous motor rotor initial position was in different convergence intervals, and the permanent magnet synchronous motor position estimation method based on second harmonic tracking described in this invention was implemented. The initial position convergence and subsequent start-up were observed. The simulation results are as follows. Figure 3 As shown, when the motor rotor is in , , , The actual locations are as follows for four different convergence intervals: , , , The initial position converges without polarity determination, and the convergence result is fast and accurate, subsequently completing the startup process of the permanent magnet synchronous motor. This demonstrates that the position estimation method for permanent magnet synchronous motors based on second harmonic tracking can effectively detect a single convergence point of the initial position when the motor rotor is in any position, and can be extended to the low-speed position tracking stage after startup, indicating the feasibility of this invention.

Claims

1. A position estimation method for a permanent magnet synchronous motor based on second harmonic tracking, characterized in that, Includes the following steps: When the permanent magnet synchronous motor is in a zero-speed or low-speed state, a high-frequency sinusoidal pulsating voltage signal is injected into the estimated d-axis of the motor. The second harmonic current response signal is extracted and its amplitude is obtained by heterodyne and low-pass filtering. By using the minimum gradient tracking method, the system converges to the minimum point of the second harmonic amplitude of the current, thus achieving effective detection of the zero-speed and low-speed positions of the permanent magnet synchronous motor.

2. The position estimation method for permanent magnet synchronous motors based on second harmonic tracking as described in claim 1, characterized in that, The estimated d-axis voltage signal of the motor after injection of a high-frequency sinusoidal pulsating voltage signal is expressed as: In the formula, This is the reference value for the d-axis voltage output of the system current loop. The amplitude of the injected high-frequency voltage, The angular frequency of the injected high-frequency voltage.

3. The position estimation method for permanent magnet synchronous motors based on second harmonic tracking as described in claim 1, characterized in that, The current response signal is represented as: In the formula, The difference between the actual location and the estimated location. It is a q-axis high-frequency inductor. This refers to the high-frequency d-axis inductance corresponding to the positive half-cycle of the injected voltage. This refers to the high-frequency d-axis inductance corresponding to the negative half-cycle of the injected voltage.

4. The position estimation method for permanent magnet synchronous motors based on second harmonic tracking as described in claim 3, characterized in that, The value of the high-frequency d-axis inductance is expressed as: In the formula, The d-axis high-frequency inductance at saturation This is the d-axis high-frequency inductance when it is not saturated, and it has... .

5. The position estimation method for permanent magnet synchronous motors based on second harmonic tracking as described in claim 1, characterized in that, The second harmonic current response signal is extracted, and its amplitude is obtained by heterodyne and low-pass filtering. A band-pass filter is then used to extract the high-frequency current response signal at twice the injection frequency, as shown below: After heterodyne processing, the amplitude is obtained using a low-pass filter, and expressed as follows: 。 6. The position estimation method for permanent magnet synchronous motors based on second harmonic tracking as described in claim 1, characterized in that, The minimum gradient pursuit method is used to converge the system to the minimum point of the second harmonic amplitude of the current. A gradient is constructed based on the change in the amplitude of the second harmonic of the high-frequency current response signal relative to the position error, and the convergence position of the negative gradient is used as the estimated position. The constructed gradient is expressed as: In the formula, This represents the current state of the control cycle. Given the state of the previous control cycle, the estimated position is represented by the gradient as follows: The gradient constructed using the second harmonic amplitude has only a single convergence result within one error cycle.

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