CN103346721A - Thrust ripple suppressing method of primary permanent magnet linear motor - Google Patents

Abstract

The invention discloses a thrust fluctuation suppression method of a primary permanent magnet linear motor. The positioning force of the primary permanent magnet linear motor is obtained through finite element simulation or actual measurement of a torque tester, and the harmonic spectrum analysis is performed on the waveform of the positioning force to determine The fundamental wave and main high-order harmonic components in the positioning force; the no-load back EMF waveform of the motor is simulated by finite element method, and the three-phase current component used to offset the harmonic component of the positioning force is calculated, so that the additional electromagnetic push and the positioning force The amplitude of the fundamental wave and the main high-order harmonic components are equal and the phases are opposite. The three-phase harmonic current is injected into the current hysteresis vector control system to suppress the thrust fluctuation of the permanent magnet linear motor; there is no need to modify the motor body, It can be realized through the control strategy, which can significantly suppress the thrust fluctuation of the motor, reduce the noise during the operation of the motor, and at the same time keep the characteristics of the motor's no-load magnetic potential and thrust output capability unchanged.

Description

Thrust fluctuation suppression method for primary permanent magnet linear motor

technical field

The invention relates to a primary permanent magnet linear motor technology, in particular to a control method for suppressing thrust fluctuations of a primary permanent magnet linear motor, belongs to the technical field of motor drive and control, and is suitable for urban rail transit and other application occasions.

Background technique

With the continuous improvement of the performance of permanent magnet materials and the continuous improvement of the design and manufacturing technology of permanent magnet linear motors, permanent magnet linear motors have been widely used in industrial automation and rail transportation because of their high performance, high stability, low noise and high efficiency. widely used. The primary permanent magnet linear motor is a new type of permanent magnet brushless linear motor. Its structural feature is that the permanent magnet and armature winding are placed on the primary mover, and the secondary structure is simple. It is only composed of a magnetic core and integrates a linear motor. The induction motor has the advantages of simple structure, low cost and high power density of permanent magnet linear synchronous motor, especially suitable for long stator applications. However, in the primary permanent magnet linear motor, the interaction between the permanent magnet and the doubly salient pole structure produces a large positioning force, which causes the thrust fluctuation during the operation of the motor, which directly affects the low-speed performance of the motor in the speed control system. and high-precision positioning in position control systems.

At present, the methods for suppressing the thrust fluctuation of the primary permanent magnet linear motor mainly focus on the optimal design of the motor body structure, such as adding auxiliary teeth at both ends of the mover, optimizing the length of the stator, opening auxiliary slots on the stator and rotor, and so on. This type of method is applicable to the design stage of the motor body structure. Generally, the finite element model of the motor is established through computer software, and then the structural parameters of the motor are adjusted according to a specific optimization strategy to achieve the effect of reducing thrust fluctuations. However, because the structure optimization method is usually restricted by different types of motor structures, the effect of suppressing thrust fluctuations is limited; in addition, due to the modification of the motor structure, it will inevitably affect the no-load back EMF and power output capability of the motor, and at the same time It also increases the manufacturing cost, so that this kind of optimization method for the structure of the motor body has certain limitations in the actual industrialization process.

Contents of the invention

The purpose of the present invention is to propose a thrust fluctuation suppression method for primary permanent magnet linear motors, without modifying the motor body, only need to modify the relevant control software, and offset the positioning force of the motor through the control strategy, so as to suppress the thrust of the motor The wave effect improves the dynamic performance of the motor.

The technical scheme that the present invention adopts is: adopt conventional current hysteresis loop vector control system, comprise the following steps:

，利用傅里叶级数逼近法对定位力的波形进行谐波频谱分析，确定定位力中基波与主要高次谐波分量；A _k 为k次定位力谐波分量的幅值，φ _k 为k次定位力谐波分量的相位角，

，τ _s 为电机初级动子极距，x是初级动子位移。 (1) The positioning force of the primary permanent magnet linear motor is obtained through finite element simulation or actual measurement of the torque tester

, use the Fourier series approximation method to analyze the harmonic spectrum of the waveform of the positioning force, and determine the fundamental wave and main high-order harmonic components in the positioning force; A _k is the amplitude of the k -th harmonic component of the positioning force, φ _k is the phase angle of the kth harmonic component of the positioning force,

, τ _s is the pole distance of the primary mover of the motor, and x is the displacement of the primary mover.

，E _m 为反电势幅值。 (2) Use finite element simulation to simulate the no-load back EMF waveform of the primary permanent magnet linear motor to determine the no-load back EMF

, Em _is the magnitude of the back EMF.

以及附加电磁推力F′ _PMk 与定位力中的基波与主要高次谐波分量的幅值相等且相位相反，

，计算出用于抵消k次定位力谐波分量的三相电流分量i _ak (x)、i _bk (x)、i _ck (x)： (3) According to the additional electromagnetic thrust

And the amplitude of the additional electromagnetic thrust F′ _PMk and the fundamental wave in the positioning force and the main higher harmonic components are equal and the phases are opposite,

, calculate the three-phase current components i _ak (x) , i _bk (x) , i _ck (x) used to offset the k -order positioning force harmonic components:

，

,

v is the speed of the measured motor, I _mk is the amplitude of the current component, μ _k is the harmonic order of the current component, and θ _k is the phase angle of the current component.

，对永磁型直线电机的推力波动进行抑制。  (4) Inject three-phase harmonic current into the current hysteresis vector control system

, to suppress the thrust fluctuation of the permanent magnet linear motor.

The present invention has following beneficial effect after adopting above-mentioned technical scheme:

1. On the basis of the commonly used current hysteresis vector control drive system, the present invention proposes a control method for injecting current harmonics to offset the positioning force of the primary permanent magnet linear motor, so that the additional electromagnetic thrust generated and the fundamental wave in the positioning force The main high-order harmonic components are equal in amplitude and opposite in phase, and can cancel each other out, thereby achieving the purpose of suppressing thrust fluctuations, which is easy to implement.

2. The present invention does not need to modify the motor body, and can be realized through the control strategy. It only needs to modify the relevant control software, which can significantly suppress the thrust fluctuation of the motor, reduce the noise during the operation of the motor, and maintain the no-load magnetic field of the motor at the same time. The characteristics such as potential and thrust output capability remain unchanged.

Description of drawings

Figure 1 is the positioning force waveform of the primary permanent magnet linear motor;

Fig. 2 is the positioning force waveform harmonic analysis of Fig. 1;

Figure 3 is the no-load back EMF waveform of the primary permanent magnet linear motor;

Fig. 4 is the control system block diagram that the present invention adopts current hysteresis vector control to suppress the thrust fluctuation of primary permanent magnet type linear motor;

Figure 5 is the thrust and current waveforms of the control system in Figure 4 before harmonic current injection;

Figure 6 is the thrust and current waveforms of the control system in Figure 4 after harmonic current injection.

Detailed ways

，A _k 为定位力的k次基波与主要高次谐波分量的幅值，φ _k 为k次基波与主要高次谐波分量的相位角，

，τ _s 为电机初级动子极距，x是初级动子位移。 The present invention is based on a conventional current hysteresis vector control primary permanent magnet linear motor drive control system. Firstly, the positioning force data of the primary permanent magnet linear motor is obtained through the finite element simulation or the actual measurement of the torque tester, and the harmonic spectrum analysis is performed on the positioning force waveform by using the Fourier series approximation method to determine the kth fundamental wave in the positioning force Compared with the main high-order harmonic component, the determination standard of the main high-order harmonic component is to compare the amplitude of the harmonic component with the amplitude of the fundamental wave, and the harmonic component whose ratio is large and cannot be ignored is determined as the main high-order harmonic component . Positioning Force of Primary Permanent Magnet Linear Motor ,

, A _k is the amplitude of the k -order fundamental wave and the main higher-order harmonic component of the positioning force, φ _k is the phase angle between the k -order fundamental wave and the main higher-order harmonic component,

, τ _s is the pole distance of the primary mover of the motor, and x is the displacement of the primary mover.

，E _m 为反电势幅值。 Secondly, the no-load back EMF waveform of the primary permanent magnet linear motor is simulated by finite element analysis, the back EMF waveform of the primary permanent magnet linear motor is analyzed, and the corresponding no-load back EMF mathematical expression is written, the no-load back EMF

, Em _is the magnitude of the back EMF.

The no-load back EMF waveform of the primary permanent magnet linear motor is sinusoidally distributed, except for the fundamental wave of the no-load back EMF, the harmonic content of the rest of the back EMF is negligible.

Then, according to the mutual coupling between the harmonic current component and the fundamental wave component of the permanent magnet back EMF to generate an additional electromagnetic thrust component, the corresponding harmonic current component is calculated, so that the fundamental wave in the additional electromagnetic thrust and the positioning force is the same as the main The higher harmonic components have equal amplitudes and opposite phases, that is, the additional electromagnetic thrust component and the positioning force can roughly cancel each other out, so as to achieve the purpose of suppressing thrust fluctuations.

，v为实测电机的速度，、

、

是用于抵消k次定位力谐波分量的三相电流分量。 Additional Electromagnetic Thrust

, v is the speed of the measured motor, ,

,

is the three-phase current component used to offset the harmonic component of the k -order positioning force.

，可以计算出用于抵消k次定位力谐波分量的三相电流分量

、、 ： The amplitude of the additional electromagnetic thrust F′ _PMk and the fundamental wave in the positioning force and the main high-order harmonic components are equal and opposite in phase, that is,

, the three-phase current component used to offset the harmonic component of the k -order positioning force can be calculated

, , :

，

,

I _mk is the magnitude of the current component, μ _k is the harmonic order of the current component, and θ _k is the phase angle of the current component.

Injecting three-phase harmonic current into current hysteresis vector control system , offset the positioning force, and suppress the thrust fluctuation of the permanent magnet linear motor.

The present invention will be further described below by taking a three-phase magnetic flux switching primary permanent magnet linear motor as an example.

Example

Figure 1 is the positioning force waveform of the three-phase flux switching primary permanent magnet linear motor obtained by finite element simulation. It can be seen from Figure 1 that the positioning force amplitude of the three-phase flux switching primary permanent magnet linear motor is relatively large, and its peak-to-peak fluctuation exceeds 330N. The positioning force waveform contains high-order harmonic components, which need to be analyzed. Harmonic analysis is used to establish the mathematical expression of the positioning force, and the analysis results are shown in Figure 2.

Table 1 below presents the results of the positioning force harmonic analysis:

Table 1 Harmonic analysis of positioning force

 

It can be seen from the amplitude of the main harmonic components in Table 1, the ratio to the fundamental component and the phase angle, the harmonic components of the positioning force are very large, and the amplitudes of the 2nd, 5th and 6th harmonics are relatively large, which are different from the fundamental The wave amplitude ratios reached 15.45%, 9.78%, and 13.75% respectively, while the amplitude ratios of the remaining high-order harmonics to the fundamental wave were all less than 5%, so it can be considered that the 2nd, 5th, and 6th harmonics are the main Higher harmonic components, the rest of the higher harmonics can be ignored. The main high-order harmonic component here refers to the main high-order harmonic component whose amplitude is larger than that of the fundamental wave and cannot be ignored.

Therefore, the positioning force of the flux switching primary permanent magnet linear motor can be approximately expressed as:

                                          （1）

(1)

Among them, τ _s is the pole distance of the mover, A _k and φ _k are the amplitude and phase angle of the k -order harmonic component, and x is the displacement of the mover relative to the initial position.

Figure 3 is the no-load back EMF waveform obtained by finite element simulation. Using wavestar software to analyze its harmonics, it can be obtained that its total harmonic distortion (THD) is only 2.914%, and the harmonic components are very small, so no-load The mathematical expression of back EMF can be expressed as:

                                               （2）

(2)

Where E _m is the magnitude of the back EMF.

According to the mutual coupling between the harmonic current component and the fundamental wave component of the permanent magnet magnetic potential to generate additional electromagnetic thrust components, the corresponding harmonic current components are calculated, so that the fundamental wave and main high-order components in the additional electromagnetic thrust and positioning force generated The harmonic components have equal amplitudes and opposite phases, and can cancel each other out, thereby achieving the purpose of suppressing thrust fluctuations. details as follows:

The additional electromagnetic thrust F′ _PMk used to offset the harmonic component of the positioning force k times:

(3)

Among them, F′ _PMk is the additional electromagnetic thrust used to _cancel the harmonic component of the k -order positioning force, i _ak (x) , i _bk (x) and ick (x) are the additional electromagnetic thrust used to cancel the harmonic component of the k -order positioning force The three-phase current components, v is the speed of the measured motor , and the three-phase current components i _ak (x) , i _bk (x) and i _ck (x) used to offset the harmonic component of the k -order positioning force are:

                                          （4）

(4)

Among them, I _mk is the amplitude of the current component, μ _k is the harmonic order of the current component, and θ _k is the phase angle of the current component.

Substituting formula (2) and (4) into formula (3) can get:

                                   （5）

(5)

Therefore, the three-phase injected harmonic current can be expressed as:

                                                      （6）

(6)

Injecting the three-phase harmonic current into the current hysteresis vector control system can suppress the thrust fluctuation of the permanent magnet linear motor.

The simulation application example of the present invention is provided below, thus can know effect of the present invention:

As shown in Figure 4, on the basis of the magnetic flux switching permanent magnet linear motor drive system controlled by the current hysteresis vector control, combined with the above-mentioned harmonic current injection method, the corresponding primary permanent magnet that inhibits magnetic flux switching can be obtained as shown in Figure 4 Type linear motor thrust fluctuation control system, the control system includes PI speed regulator 1, thrust-current conversion module 2, 2r/3s conversion (rotor rotating two-phase/stator stationary three-phase conversion) module 3, summation module 4, Current hysteresis PWM module 5, inverter 6, LFSPM motor 7 (primary permanent magnet linear motor 7), photoelectric encoder 8, motor speed and position detection module 9, harmonic current solution module 10. According to the speed v of the measured motor and the specified speed v ^* , the speed difference v(n) is obtained; the speed difference is passed through the PI speed regulator 1 to obtain the required electromagnetic thrust command value F _e ^* ; using I _d =0 control, Through the thrust-current conversion module 2, the corresponding reference values of the orthogonal and direct axis currents i _d ^* and i _q ^* are obtained from F _e ^* ; using the feedback position angle θ _e of the mover, the 2r/3s transformation is performed through the module 3 to obtain the static state of the stator The three-phase winding currents ia , ib _, ic in the coordinate system; this current, _together with _the harmonic currents ia _' ^, ib _' ^, ic _' obtained by the harmonic current solution module 10 ^, passes through the summation module 4 Calculate and obtain the required three-phase winding current reference value i _a ^* , i _b ^* , i _c ^* ; the reference current i _a ^* , i _b ^* , i _c ^* and the three-phase winding real-time current feedback value i _a1 , i _b1 and i _c1 go through the current hysteresis PWM module 5 for hysteresis comparison, and get the PWM on-off signal of the power electronic device in the inverter 6, so as to control the current in the winding to follow the command current value; Obtain the pulse signal of the LFSPM motor 7, and then calculate the real-time feedback speed v of the motor and the mover position angle θ _e through the motor speed and position detection module 9, which are used for the closed-loop control of the speed loop and corresponding calculations. Establish the Matlab/Simulink simulation model according to the block diagram in Figure 4. Figure 5 shows the thrust and current waveforms before harmonic current injection, and Figure 6 shows the thrust and current waveforms after harmonic current injection. It can be seen from Figure 5 and Figure 6 that: before the harmonic current injection, the peak-to-peak value of the thrust pulsation reaches 386N, and the current of each phase presents a good sinusoid; A certain harmonic component, the electromagnetic thrust generated by the harmonic component just offsets the positioning force of the flux switching permanent magnet linear motor. The simulation results prove that the control strategy proposed by the present invention significantly suppresses the thrust fluctuation of the primary permanent magnet motor, while keeping the thrust output capability of the motor unchanged.

Claims (1)

1. the force oscillation inhibition method of a primary permanent magnet type linear motor adopts conventional current hysteresis ring vector control system, it is characterized in that may further comprise the steps:

(1) surveys the detent force that obtains primary permanent magnet type linear motor by finite element simulation or torque tester

, utilize the Fourier series approximatioss that the waveform of detent force is carried out the harmonic spectrum analysis, determine first-harmonic and main higher harmonic components in the detent force; A _k For kThe amplitude of inferior detent force harmonic component, φ _k For kThe phase angle of inferior detent force harmonic component,

, τ _s Be electric motor primary mover pole span, xIt is elementary mover displacement;

(2) the unloaded counter potential waveform of employing finite element simulation primary permanent magnet type linear motor is determined unloaded back-emf , E _m Be the back-emf amplitude;

(3) according to additional electromagnetic thrust And additional electromagnetic thrust F ' _PMk Equate with the amplitude of main higher harmonic components with first-harmonic in the detent force and phase place opposite,

, calculate for counteracting kThe three-phase current component of inferior detent force harmonic component i _Ak (x), i _Bk (x), i _Ck (x):

，

vBe the speed of actual measurement motor, I _Mk Be the amplitude of current component, μ _k Be the harmonic number of current component, θ _k Phase angle for current component;

(4) current hysteresis ring vector control system is injected the three phase harmonic electric current

, the force oscillation of permanent magnet type linear motor is suppressed.

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