阅读说明：本技术 一种基于占空比调制的磁通切换型永磁直线电机直接推力控制方法 (Direct thrust control method of flux switching type permanent magnet linear motor based on duty ratio modulation ) 是由 曹瑞武 蒋宁 王凯 于 2019-11-01 设计创作，主要内容包括：本发明公开了一种基于占空比调制的磁通切换型永磁直线电机直接推力控制方法,包括以下步骤：通过设计的磁链观测器对电机的定子磁链进行估算,并计算出定子磁链位置角；通过磁链、推力的估算值和给定值之间的差值计算占空比,并选择有效的电压矢量；通过逆变器实现一个周期内同时采用非零矢量和零矢量,从而更稳定地控制电机运行。相比于传统的直接推力控制,可以在保持结构简单和动态性能不变的基础上,降低对电机参数的依赖性,有效减小电机的推力和磁链波动,提高系统的稳定性和鲁棒性。(The invention discloses a direct thrust control method of a flux switching type permanent magnet linear motor based on duty ratio modulation, which comprises the following steps of: estimating the stator flux linkage of the motor through a designed flux linkage observer, and calculating a stator flux linkage position angle; calculating a duty ratio through a flux linkage, a difference value between an estimated value of the thrust and a given value, and selecting an effective voltage vector; the inverter is used for realizing that a non-zero vector and a zero vector are simultaneously adopted in one period, so that the motor is controlled to operate more stably. Compared with the traditional direct thrust control, the method has the advantages that on the basis of keeping the structure simple and the dynamic performance unchanged, the dependence on motor parameters is reduced, the thrust and flux linkage fluctuation of the motor are effectively reduced, and the stability and the robustness of the system are improved.)

1. A direct thrust control method of a magnetic flux switching type permanent magnet linear motor based on duty ratio modulation is characterized by comprising the following specific steps of:

step 1: three-phase current i for detecting magnetic flux switching type permanent magnet linear motor_a、i_b、i_cAnd obtaining the current i under a two-phase static coordinate system through 3s/2s (Clarke) conversion_αAnd i_βDetecting the bus voltage and the inverter switching state S_a、S_b、S_cThen obtaining the voltage u under the two-phase static coordinate system through 3s/2s (Clarke) conversion_αAnd u_β；

Step 2: obtaining the actual speed V of the LFSPM motor according to the grating ruler and the given speed V_refObtaining a reference thrust F by means of a PI controller_ref；

And step 3: according to the current signal i obtained in the step 1_α、i_βSum voltage signal u_α、u_βFlux linkage estimation is performed by an observer and then by psi_α、ψ_βPerforming arc tangent calculation to obtain stator flux linkage position angle theta_sAnd estimating the motor thrust, wherein the specific expression is as follows:

in the formula tau_sThe pole pitch of the motor stator;

and 4, step 4: calculating a duty ratio d according to the estimated flux linkage value, the given thrust and the difference value of the estimated thrust; flux linkage, difference in thrust, and stator flux linkage position angle θ_sThen, a selection signal is output to the voltage vector switch table through the hysteresis regulator to select an effective voltage vector u_k；

And 5: according to the duty ratio d and the voltage vector u obtained in the step 4_kThe obtained modulation signal is output to an inverter, so that the accurate control of the motor thrust and flux linkage is realized.

2. The magnetic flux switching type permanent magnet linear motor position sensorless control based on the novel sliding-mode observer method is characterized in that: in step 3, the transfer function of the flux linkage observer is:

wherein D represents a linear compensator, i.e. a PI controller in a flux linkage observer; and R is the motor stator resistance.

3. The magnetic flux switching type permanent magnet linear motor position sensorless control based on the novel sliding-mode observer method according to claim 1 is characterized in that: in the step 4, the duty ratio is calculated by using the flux linkage, the difference between the estimated value of the thrust and the given value, and the specific expression is as follows:

in the formula (d)_FAnd d_ψThe duty cycle of the thrust and flux linkage, respectively, F_refAnd psi_refReference values of electromagnetic thrust and flux linkage, F, of the (k-1) th cycle, respectively₀And psi₀The initial values of the electromagnetic thrust and the flux linkage of the (k-1) th cycle are respectively, and the absolute values of the initial values are removed to ensure that the duty ratio is larger than zero.

Technical Field

The invention relates to a direct thrust control (DTFC) method of a flux switching permanent magnet linear motor based on duty ratio modulation, which is suitable for the field of long-stroke driving systems of rail transit with high position sensor cost.

Background

At present, linear induction motors are used in urban rail transit systems such as Guangzhou subways and capital international airports, but have the problems of low efficiency and high cost. The permanent magnet and armature winding of the magnetic flux switching permanent magnet linear motor (LFSPM) are both arranged on the primary short rotor, and the secondary long stator is only made of magnetic conductive materials. Compared with a linear induction motor and a permanent magnet synchronous linear motor, the LFSPM motor has the advantages of low cost, high efficiency and high thrust density, and has a non-reduced wide application prospect in the field of rail transit driving systems. Accurate position and speed information is required for controlling a high-performance flux-switching permanent magnet linear motor, but the cost of the whole driving system is increased and the reliability is reduced due to expensive position sensors such as a grating ruler. Therefore, the position ring can be omitted by adopting direct thrust control, so that the installation of a position sensor is avoided, and only a low-cost speed sensor for rail transit is required to be installed.

Direct Torque Control (DTC) is a control strategy developed after vector control, has the advantages of fast dynamic response, simple structure, no need of position signals and the like, and is mainly applied to induction motors and permanent magnet synchronous motors. This control strategy is applied to linear motors in the future, and gradually evolves to direct thrust control (DTFC).

In the traditional DTFC, a voltage vector is generally selected by two hysteresis comparators and a voltage vector switch table, only a single voltage vector can be acted in one period, and the problems of large thrust, large flux linkage fluctuation, unfixed inverter switching frequency and the like exist. In order to solve the problem of large thrust fluctuation of the motor, a plurality of level inverters are adopted by a student to increase the number of selectable voltage vectors so as to reduce the thrust fluctuation, but the cost and complexity of system hardware are increased. In addition, the scholars suppress the thrust fluctuation by introducing a zero vector, but the effect is not obvious. Scholars at home and abroad select the optimal voltage vector of the next period by introducing model predictive control, so that the thrust fluctuation is effectively reduced, but the method greatly increases the complexity of the system, is difficult to apply to practical engineering and does not conform to the characteristic of simple structure of direct thrust control.

Because the LFSPM motor has the characteristics of small inductance, small magnetic linkage and small stator pole distance, the adoption of the traditional DTFC control can generate quite obvious thrust and magnetic linkage fluctuation. Aiming at the problem, the invention provides a direct thrust control method of a flux switching type permanent magnet linear motor based on duty ratio modulation, which reduces the dependence on motor parameters, effectively reduces the electromagnetic thrust and flux linkage fluctuation of the motor and improves the stability and robustness of a system on the basis of keeping the simple structure and the dynamic performance of the traditional DTFC.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a direct thrust control strategy suitable for a flux switching permanent magnet linear motor, so that the problems of large flux linkage and large thrust fluctuation caused by the adoption of a traditional DTFC control strategy are solved.

The solution adopted in the invention is as follows: on the basis of the traditional DTFC, introducing duty ratio modulation to simultaneously act by adopting a non-zero vector and a zero vector in one period, thereby adjusting the action amplitude of an effective voltage vector; and meanwhile, a novel flux linkage observer is adopted to improve flux linkage estimation precision. Through simulation and experiments, the invention can effectively reduce the thrust and flux linkage fluctuation of the motor on the premise of keeping the characteristic of simple structure of the traditional DTFC.

The direct thrust control method of the flux switching type permanent magnet linear motor based on duty ratio modulation comprises the following steps of:

step 1: three-phase current i for detecting magnetic flux switching type permanent magnet linear motor_a、i_b、i_cAnd obtaining the current i under a two-phase static coordinate system through 3s/2s (Clarke) conversion_αAnd i_βDetecting the bus voltage and the inverter switching state S_a、S_b、S_cThen obtaining the voltage u under the two-phase static coordinate system through 3s/2s (Clarke) conversion_αAnd u_β；

Step 2: obtaining the actual speed V of the LFSPM motor according to the grating ruler and the given speed V_refObtaining a reference thrust F by means of a PI controller_ref；

And step 3: according to the current signal i obtained in the step 1_α、i_βSum voltage signal u_α、u_βEstimating flux linkage by flux linkage observer, and performing flux linkage estimation by psi_α、ψ_βPerforming arc tangent calculation to obtain stator flux linkage position angle theta_s(ii) a At two sidesIn the stationary coordinate system, through psi_α、ψ_βAnd i_α、i_βCalculating to obtain an estimated motor thrust F, wherein the specific expression is as follows:

in the formula tau_sThe pole pitch of the motor stator;

and 4, step 4: calculating a duty ratio d according to the estimated flux linkage value, the given thrust and the difference value of the estimated thrust; flux linkage, difference in thrust, and stator flux linkage position angle θ_sAnd then a selection signal is output to the voltage vector switch table through the hysteresis regulator to select a voltage vector u_k；

And 5: according to the duty ratio d and the voltage vector u obtained in the step 4_kThe obtained modulation signal is output to an inverter, so that the accurate control of the motor thrust and flux linkage is realized.

The invention has the following beneficial effects:

1) by a simple duty ratio calculation method, a single voltage vector is not adopted in one period, the thrust fluctuation of the motor is effectively reduced, and the dependency on motor parameters is reduced.

2) The novel flux linkage observer is adopted to estimate the flux linkage of the motor, the advantages of the voltage type flux linkage observer and the current type flux linkage observer are combined, the flux linkage estimation accuracy is improved, and the thrust fluctuation of the motor is further reduced.

3) The invention is also applicable to other linear permanent magnet motors.

Drawings

The invention is further illustrated with reference to the following figures and examples:

fig. 1 is a block diagram of direct thrust control of a flux switching permanent magnet linear motor based on duty cycle modulation;

fig. 2 is a cross-sectional view of a flux switching permanent magnet linear motor;

FIG. 3 is F₀＜F_refCalculating a schematic diagram of the time duty ratio;

FIG. 4 is F₀＞F_refCalculating a schematic diagram of the time duty ratio;

FIG. 5 is a block diagram of a flux linkage observer;

FIG. 6 is a DTFC loading simulation comparison waveform; wherein fig. 6(a) is a conventional DTFC;

fig. 6(b) is a DTFC based on duty cycle modulation;

FIG. 7 is an experimental waveform of the DTFC speed dynamic response of the present invention under no load conditions;

FIG. 8 is an experimental waveform of the DTFC flux linkage of the present invention under no-load conditions;

fig. 9 is an experimental waveform diagram of the DTFC of the present invention under a load of 50N.

Detailed Description

The invention provides a direct thrust control method of a flux switching type permanent magnet linear motor based on duty ratio modulation, which aims to make the purpose, technical scheme and effect of the invention clearer and further describes the invention in detail by referring to the attached drawings and taking examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention relates to a direct thrust control scheme of a flux switching permanent magnet linear motor based on duty ratio modulation, and a specific control block diagram is shown in figure 1. Given speed V_refThe difference value between the actual speed V and the given thrust F is obtained through a PI controller_refAnd the estimated difference value between the flux linkage and the thrust and a given value is used for calculating a duty ratio d, and then a selection signal is output to a switch table through a hysteresis regulator to select an effective voltage vector u_kAnd finally, the magnetic flux linkage and the thrust of the motor are accurately controlled.

Fig. 2 is a cross-sectional view of a flux switching permanent magnet linear motor. It can be known from the figure that the primary short rotor of the motor is composed of an armature winding and a permanent magnet, while the secondary long stator is very simple in structure and only composed of a magnetic conduction iron core, and has the advantages of reliability and low cost. Therefore, compared with a linear induction motor and a permanent magnet synchronous linear motor, the LFSPM motor has the advantages of low cost, high efficiency and high thrust density, and has a very wide application prospect in the field of rail transit driving systems.