The bearingless motor is an AC motor with a novel structure. Two sets of windings, one torque winding and one suspension winding with different pole pairs are embedded in the stator. By controlling two sets of winding currents, not only electromagnetic torque is generated, but also the rotor is rotated. It can also produce magnetic levitation force to make the rotor levitate, achieving the non-contact, no lubrication and no mechanical friction rotation of the motor.
Due to its compact structure and high power density, the bearingless motor can achieve high speed and high power at the same time, which has become a research hotspot in the field of high-speed motor drives.
According to different rotor structures, bearingless motors can be classified into three types: induction, permanent magnet, and magnetoresistive. In order to achieve the decoupling of the torque and the suspension force, the induction type bearingless motor adopts the air gap magnetic field orientation control method, the permanent magnet type bearingless motor adopts the rotor field oriented control method,3, the magnetic resistance type bearingless motor adopts the stator field orientation. Method W. These high-performance control methods all need to detect the position and velocity of the rotor, obtain the precise spatial position of the magnetic flux required for magnetic field orientation, realize the decoupling control of the torque and the levitation force, and ensure the stable suspension operation of the rotor. Traditionally, the spatial position and speed of the rotor have been measured using mechanical sensors, which has problems such as installation, connection, and reliability. For bearingless motors, the use of mechanical position/speed sensors has greater limitations because the sensors themselves are mechanically difficult or impossible to implement at high speeds and speeds, which can severely limit the excellent high speed performance inherent to bearingless motors. Play.
The study of sensorless operation of bearingless motors has become a need for further development of bearingless motor technology, but no research propositions have yet been addressed. For a bearingless motor, there can be no radial displacement sensor operation. However, from the perspective of high-speed and full-featured bearingless motor characteristics, the study of positionless/speed sensor operation is more practical.
The sensorless operation in the AC drive of the China University of Electrical Engineering refers to the information about the electric quantity in the torque winding of the stator of the motor in the stationary a-0 coordinate system using the motor winding machine, and the position and speed of the rotor are estimated through appropriate processing. High-performance control without mechanical position/speed sensor. At present, many papers have proposed various rotor position and velocity detection methods, most of which are obtained by detecting the back-EMF of the fundamental wave to obtain the position information of the rotor. M. Although simple, these methods will be used at zero speed or low speed. The low-speed adaptability is poor because the back-EMF is too small or not detectable at all. In addition, because the fundamental wave voltage and current signals are used to calculate the rotor position fB speed, it is very sensitive to changes in the motor parameters and has poor robustness. Bearingless motors from stationary to floating, and from low to high speed rotors are the fundamental guarantee for the operation of the motor. This is largely influenced by the speed and position of the detection accuracy in the full speed range, so based on the fundamental information Position detection methods are difficult to meet the control needs of bearingless motors.
In order to obtain accurate rotor position information at any speed including zero speed, some rotor position self-detection methods for rotor salient pole tracking have been proposed. This method requires that the motor has a certain degree of saliency and needs to apply continuous high-frequency excitation, but it can achieve effective detection of the rotor position within the full speed range including zero speed. In addition, this method tracks the spatial salient pole effect of the rotor of the motor and is therefore insensitive to changes in the motor parameters and has good robustness. Because the bearingless motor generally must be specially designed, the saliency of the rotor can be guaranteed by the motor design. This actually realizes the integration of the sensor and the motor. Therefore, transplanting this kind of rotor position self-detection method has practical feasibility and important practical significance in the application of bearingless motor control.
This paper first introduces the principle of high-frequency voltage carrier injection method for tracing the rotor salient pole of the permanent magnet type bearingless motor, discusses the method of self-detection of the rotor position, and establishes the permanent magnet type bearingless motor without sensor. The operation control model was used to verify the rotor pole salient effect self-detection and sensorless operation simulation using Matlab. The dynamic and static performance of the rotor suspension operation was given. The correctness and feasibility of the proposed method were verified.
Symmetry, that is, shaft inductors of unequal size, provides the possibility of tracking rotor salient poles by injecting high frequency carrier signals. When using the salient pole effect to track the rotor position, the current response of the motor under high frequency voltage excitation needs to be analyzed. For this purpose, a permanent magnet type bearingless motor mathematical model under high frequency voltage excitation needs to be established.
(1) Mathematical model of permanent magnet type bearingless motor excited by high frequency The permanent magnet type bearingless motor is essentially a permanent magnet synchronous voltage equation and flux linkage equation can be expressed as /1, respectively, the voltage and current of the torque winding. , flux linkage, subscripts or, y represent the components in the coordinate system; torque resistance; 4 represents the rotor d-axis component of the flux generated by the permanent magnet in the torque winding; 1 = average inductance, = half Differential inductance, b is the self-inductance of the torque winding in the rotor synchronous speed coordinate system; it is the electrical angle between the a-axis and the d-axis, ie the spatial position angle of the rotor; D = d/d "in the voltage source inverter power supply Under the circumstances, the high-frequency voltage signal can be directly superimposed on the fundamental voltage excitation of the torque winding of the bearingless motor through the inverter, and the angular frequency of the high-frequency voltage signal is called, and the amplitude is 1, then it is at rest. The high-frequency voltage signal injected in the a-0 coordinate system can be expressed as the stator torque winding input total voltage. It can be expressed as the frequency of the high-frequency voltage signal injected is generally much higher than the fundamental frequency of the operation. In order to approximate the pure inductive reactance, the motor model of equations (1) and (2) can be Simplified to obtain the current response of the motor under high-frequency voltage excitation based on equations (3) and (5). As can be seen from the analysis formula (6), only the negative-phase-sequence current component contains the year-on-year, etc.: permanent magnet type bearingless motors The sensorless operation studies the location information of the k2IRN2N4 subunit, but it must be extracted with appropriate signal processing techniques to enable detection of the rotor position.
(2) Self-detection method for rotor position based on salient pole salvo tracking In order to extract the rotor position information contained in the phase angle of the negative phase sequence component of the high frequency current response signal, the fundamental current, carrier frequency current and high frequency response current must be filtered out. The positive sequence component in. The frequency of the high-frequency injection signal is much higher than the frequency of the fundamental wave, and the carrier frequency is much higher than the frequency of the high-frequency injection signal. Therefore, both the fundamental wave frequency and the carrier frequency signal can be filtered by a conventional band-pass filter (BPF). The high-frequency response current positive phase sequence component and the negative phase sequence component rotate in the opposite direction. Therefore, the high-frequency response current can be first converted into a coordinate system that rotates synchronously with the high-frequency injection voltage so that the positive phase sequence component of the high-frequency response current. It appears as a direct current and is filtered out by a high-pass filter to finally obtain the negative phase sequence component of the high-frequency response current signal. The high-frequency current signal filtering block diagram is shown.
After the high-frequency response current filtering process filters out irrelevant signals, the tracked signal will be a rotating current vector whose phase is modulated by the rotor or flux angle. The rotor position tracking observer can be used to realize the detection of its spatial position. The tracking observer uses a heterodyne method to demodulate the negative-sequence high-frequency current of the spatial salient-pole modulation. Through simple signal analysis, the vector angle error expression can be obtained as follows. By adjusting the vector angle error to zero, the rotor position estimation formula can be converged to the true value. By taking the time differential equation, the rotor angular velocity can be obtained.
3 Permanent-magnet type bearingless motor control model Permanent-magnet type bearingless motor control is divided into two parts of electromagnetic torque control and suspension force control, in which the torque control adopts the rotor field-oriented vector control mode with usually G=0; the suspension force control It is through the detection of the rotor radial displacement offset to calculate the suspension force, and then generate the input signal of the suspension winding to achieve control, so to obtain accurate, can be used for real-time calculation of the suspension force expression is the key to the control of the suspension winding.
The permanent magnet type bearingless motor suspension force in the synchronous speed rotation coordinate system can be expressed as "wide"
In the levitation force control, the levitation force value/Qiao can be generated by detecting the offset error of the rotor displacement, and then the value of the levitation winding current value ~h can be calculated by the following formula. From the formula (10), it can be seen that, for an internal device, Insert permanent magnet type bearing motor, A, A, as a constant, after obtaining the torque winding current Q, the suspension winding current can be obtained through the levitation force signal, so as to achieve the purpose of controlling the radial levitation force of the rotor.
A block diagram of a bearingless motor control system including torque control, suspension force control, and rotor position and speed self-test is given. Due to the adopted control strategy, sensorless operation of the permanent and permanent magnet type bearingless motors can be based on the control system after the derived spatial salient pole tracking rotor position self-detection method and the permanent magnet type bearingless motor suspension force analytical expression. The feasibility and correctness of sensorless operation of the permanent magnet type bearingless motor were verified by simulation. The parameters of the interpolated permanent magnet bearingless motor used in the simulation can be found in the appendix.
High-frequency response current vector space motion trajectory. This is an ellipse that rotates with the salient pole position of the rotor space. The major axis is (ip+Z), the minor axis is (/p-/), and the angle between the major axis and the a-axis is the rotor spatial position angle 怂. Because of the continuous rotation of the rotor, the rotor position angle is a function of time, and its increase direction is consistent with the rotation direction of the rotor, indicating the existence of the salient pole depending on the rotor position and the effectiveness of the rotor position detection method.
The practical application of the method in the permanent magnet type bearingless motor is compared with the running simulation of permanent magnet type bearingless motor with and without mechanical position/speed sensor under high speed and low speed. And respectively represents the motor 0-60r/min rpm and 0-6000r/min no-load starting process speed change and rotor 0 (vertical) direction displacement curve. The initial air gap eccentricity at rest is Aa=Ay0=O.3mm. It can be seen that there is no difference in the characteristics of the sensorless and non-sensor operating modes, indicating that the rotor position self-detection method based on the spatial salient pole tracking can be in the full speed range of low speed and high speed. The correct observation of the rotor position is obtained to ensure that the motor can achieve a successful start and stable suspension operation from standstill to a given speed. In order to further verify the self-detection of the rotor's spatial position as the ability to evaluate the anti-load perturbation of the sensorless operation control system of the bearingless motor, the simulation of sudden rated load under rated speed was carried out, and the torque, speed and radial displacement in P direction were simulated. The dynamic response to change is as shown. The comparison of simulation results shows that the position estimation method based on spatial salient pole tracking detection can effectively ensure the stable suspension of the bearingless motor rotor under the dynamic conditions of load disturbance and obtain the same good static and dynamic performance as the mechanical position sensor system. But at the same time, we must also see that due to the rotor position observation in the dynamic process, there will still be an estimation error, which will have a certain impact on the rotor levitation. Therefore, it is still necessary to further study the position of the rotor in space salient pole tracking, etc.: permanent magnet type bearingless motor Sensorless operation research bookmark6 In order to solve the limitations of the application of mechanical speed / position sensor in bearingless motors, this paper presents a rotor position self-detection method based on motor salient pole tracking. This method adopts high-frequency voltage signal injection technology to get rid of traditional fundamental wave information detection, parameter identification and other processing methods, thus it can effectively detect the spatial position of the rotor in the full speed range, and realize the stable suspension operation of the motor. The simulation results show that the rotor position self-detection method can achieve high rotor position observation accuracy in the embedded permanent magnet type bearingless motor with a higher salient pole, ensuring that the bearingless motor achieves electromagnetic torque and magnetic levitation. The effective decoupling of forces ensures good operating performance under a variety of operating conditions. This is a new idea for a sensorless speed control system that integrates a position/speed sensor inside a motor. It will be of great significance for the practical application of a bearingless motor.
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