CN114303472B

CN114303472B - AC linear motor sectional power supply method

Info

Publication number: CN114303472B
Application number: CN200910125309.2A
Authority: CN
Inventors: 张明元; 许金; 沈建清; 李维波; 马名中; 饶金; 马伟明; 鲁军勇
Original assignee: Naval University of Engineering PLA
Current assignee: Naval University of Engineering PLA
Filing date: 2009-12-31
Publication date: 2012-11-21
Anticipated expiration: 2029-12-31

Abstract

The invention discloses a method for sectionally supplying power to an alternating current linear motor, which comprises the following steps: when the secondary of the motor is in an initial position, n segments of primary 1, 2, … … and n are electrified in series, and the secondary starts to move; when the secondary side just completely leaves the primary side of the 1 st section, the three-phase winding of the motor is sequentially switched to the primary sides of the 2 nd, 3 rd, … … th and n +1 st sections to be electrified in series based on the phase current zero-crossing point; thirdly, when the secondary side just leaves the primary side of the 2 nd, 3 rd and … … th sections completely, the sectional power supply switching method is the same as the 2 nd step; and fourthly, cutting off the power supply of all primary sections when the secondary section stops moving through braking. The segmented power supply method is based on series power supply of electrified primary, can ensure equal current and consistent power density in each segment of primary, is favorable for reducing the volume weight of the motor and reducing the complexity of motor control, avoids large fluctuation of electromagnetic force during power supply switching due to the adoption of a current zero-crossing switching strategy, and is particularly suitable for high-speed and high-power alternating current linear motors.

Description

AC linear motor sectional power supply method

Technical Field

The invention belongs to the field of linear motors, and particularly relates to a primary segmented linear motor and a method for realizing switching power supply between segments. The invention is suitable for the alternating current linear motor (comprising a linear induction motor and a linear synchronous motor) with a long primary and short secondary structure, and is particularly suitable for the high-speed and high-power linear motor for electromagnetic emission.

State of the art

With the continuous maturity of the theory and design technology of linear motors and the continuous deep development of power electronic technology, linear motors are being widely applied. At present, an electromagnetic launching device taking a linear motor technology as a core is a hot subject of research of military and strong countries in the west, such as an electromagnetic catapult, an electromagnetic rail gun and the like. However, for high power long primary ac linear motors used in devices such as electromagnetic ejectors: firstly, the existing power supply is difficult to or cannot meet the requirement of full primary whole-course power-on; secondly, when the primary and secondary non-coupling parts are electrified in the whole process, the non-coupling parts do not work, so that the motor efficiency is low and the energy waste is serious. To solve these problems, it is an effective method for engineering to perform segmented power supply on the primary side.

At present, a few documents have made preliminary studies on the sectional power supply technology for the long primary ac linear motor, such as a vertical hoisting machine described in "vertical hoisting system driven by multi-section primary permanent magnet linear synchronous motor" (chinese motor engineering, No. 18 in 2007), a logistics transmission device described in "transmission system driven by long stator linear motor" (micromotor, No. 4 in 2002), and so on. But because of low speed and low power, the methods adopt a method of supplying power to the electrified primary in parallel. The primary parallel power supply has two main disadvantages: when the power supply voltage is not changed, the current in each section of electrified primary changes along with the movement of the secondary, so that the power density of each section of primary is unequal, the primary cannot be used as far as possible, and the reduction of the volume and the weight of the motor is not facilitated; secondly, the currents in the primary stages are unequal, so that the difficulty of performing accurate closed-loop control on the secondary motion through current feedback is increased. The two defects are difficult to tolerate in occasions with high power and high precision, such as plane ejection.

In addition, the magnetic suspension train adopting long primary drive also widely adopts the sectional power supply technology. The sectional power supply method of the magnetic suspension train mainly comprises a frog-leaping method, a two-step method, a three-step method and the like, but the essence of all the methods is that the sectional power supply is based on the parallel connection of the sections, so that the requirements of stable state operation can be met, but the requirements of certain special application occasions such as electromagnetic emission and the like cannot be met. The electromagnetic transmitting device generally adopts a pulse intermittent working mode, has short working time, large transient power and large current, and has strict requirements on the fluctuation of electromagnetic force, so the electromagnetic transmitting device must seek a reliable segmented power supply switching method with small electromagnetic force fluctuation, but related information cannot be found in the published documents temporarily.

Disclosure of Invention

The invention aims to adapt to the special requirements of an electromagnetic transmitting device of a linear motor with a long primary, and adopts a method for supplying power to the primary in a segmented manner. The method can ensure that the currents in the electrified primary stages of all the sections are equal on the premise of keeping the power supply voltage unchanged, thereby fundamentally solving the defects existing in the parallel power supply of the primary stages; meanwhile, the method also avoids the defect of overlarge electromagnetic force fluctuation during power supply switching.

The invention provides a method for sectionally supplying power to an alternating current linear motor, which comprises the following steps:

step 1, when the motor secondary is at the initial position, the 1 st, 2 nd, … … th and n th primary sections are electrified in series, and the secondary starts to move;

step 2, when the secondary just leaves the primary of the 1 st section completely, judging whether each phase current crosses zero or not by detecting A, B, C three-phase currents in the primary, removing power supply from the phase of the primary of the 1 st section as long as a certain phase current crosses zero, simultaneously connecting the phases of the primary of the n +1 th section, enabling the three-phase currents to cross zero in sequence in a phase angle of 120-180 degrees, and enabling the motor to be electrified from the primary of the 1 st, 2 nd, … … th and n th sections in series within the period of time, and completely switching to the primary of the 2 nd, 3 rd, … … th and n +1 th sections in series;

step 3, when the secondary just leaves the 2 nd, 3 rd, … … th and N-N segment primary completely (N is the total segment number of the primary), the method for switching the segmented power supply is the same as the step 2;

and step 4, cutting off the power supply of all primary sections when the secondary stops moving through braking.

The method provided by the invention can be suitable for various primary segmented alternating current linear motors, and particularly has a remarkable technical effect for high-speed and high-power linear motors, and the method is specifically described as follows:

(1) because the method of the power supply of the primary series of the electrifying section is adopted, the equal current and the consistent power density in each section of primary can be ensured, the volume weight of the motor can be reduced, and the material performance can be close to the maximum;

(2) because all the primary power supply sections share one power supply to supply power in series, the complexity of motor control can be greatly reduced, and the accurate closed-loop control of secondary motion through current feedback is facilitated;

(3) because the method of switching power supply when the current crosses zero is adopted, the fluctuation of the current during power supply switching can be obviously reduced, thereby being beneficial to reducing the fluctuation of electromagnetic force.

Drawings

FIG. 1 is a schematic diagram of a linear motor with a gapless structure between primary sections and sections of the invention adopting a series segmented power supply method;

FIG. 2 is a schematic diagram of different timing sequences of the primary A, B, C three-phase switching power supply of the present invention;

fig. 3 is a schematic diagram of a linear motor with a gap structure between primary stages and stages according to the present invention, which adopts a series segmented power supply method.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

The long primary alternating current linear motor aimed by the method needs to meet the following conditions: the primary is divided into several sections, the primary specification of each section is the same, the three-phase (or multi-phase) windings are independent, no middle point connection is provided, and each phase of each primary section is provided with an independent power supply switch.

Let n be the number of primary stages energized simultaneously. In the case of a linear motor having such a structure that the primary sections are closely connected to each other, the length of the secondary section is generally designed to be slightly smaller than the total length of the primary section of the n-1 sections in order to reduce the weight of the secondary section. This power supply switching method will be described in detail below with an example of n ═ 2.

As shown in fig. 1, a segment of primary length L₁A secondary length of L₂，L₃Is the length reserved for the segmented power supply switch. In general, L₃＝(n-1)L₁-L₂In FIG. 1, n is 2, so L₃＝L₁-L₂。

The kth primary stage and the (k + 1) th primary stage realize series power supply through a power supply network, and the secondary stage moves forwards under the action of electromagnetic force. When the secondary terminal B just leaves the kth primary terminal, switching power supply is started. Since A, B, C three-phase current can be very large (up to 10000A or more), if the k +2 th primary is turned on and the k-th primary is turned off according to the secondary position only, regardless of whether the phase current is zero-crossing, current surge will be caused, which is very disadvantageous to the motor body and system control. The method adopted by the invention is that the zero crossing point of the three-phase current is detected, and the phase current leaves from the kth primary stage from the B end of the secondary stage, and the phase current crosses zero, so that the power supply switch of the phase of the kth +2 primary stage is switched on, and the power supply switch of the phase of the kth primary stage is switched off, and the other two phases are the same in the same way until the three-phase is switched over.

As shown in fig. 2, according to the secondary B-terminal leaving the firstPhase of phase A current in k-segment primary phase

A, B, C the timing of the three-phase switching power supply has three cases, namely:

(1) when in use

Or

The switching time sequence is C phase, B phase and A phase, the switching time of the B phase lags behind the 1/6 cycles of the C phase, and the switching time of the A phase lags behind the 1/3 cycles of the C phase;

(2) when in use

Or

The switching time sequence is B phase, A phase and C phase, the switching time of the A phase lags behind 1/6 cycles of the B phase, and the switching time of the C phase lags behind 1/3 cycles of the B phase;

(3) when in use

Or

The switching time sequence is A phase, C phase and B phase, the switching time of the C phase lags behind 1/6 cycles of the A phase, and the switching time of the B phase lags behind 1/3 cycles of the A phase;

in fig. 2, it can also be seen that, in any of the three cases, the switching from the secondary side B to the kth primary side is completed, and the time required for switching to the three phases is 1/3 cycles at the shortest and 1/2 cycles at the longest.

It must be ensured that the three phases of the primary of the (k + 2) th section are completely electrified before the secondary A end enters the primary of the (k + 2) th section. The following description is divided into two cases of a synchronous linear motor and an induction linear motor.

For a synchronous linear motor, the secondary speed is denoted as V, the current frequency is f, the period is T, and the pole pitch is τ. According to the principle of the synchronous linear motor, if V is 2 τ f, the time from the B end to the a end to the k +2 th primary end is:

according to the design principle of linear motors, L₃When the integral multiple of tau is positive, the fluctuation of electromagnetic force is minimum. From the above discussion, the time required for the three phases to switch over is between T/3 and T/2, thus even in the worst case, namely L₃T is T/2 as known from formula (1), and it is also ensured that the three phases of the primary stage of the (k + 2) th stage are completely electrified before the end a enters the primary stage of the (k + 2) th stage.

In order to improve the efficiency of the linear motor as much as possible in engineering, L is required₃The smaller the better. L is₃Minimum (i.e. L)₃τ) still meets the time required for switching the power supply, which is also one of the advantages of the present invention.

For an induction linear motor, the secondary speed is denoted as V, the current frequency is f, the period is T, and the slip frequency is denoted as f_sAnd the pole pitch is tau. Based on the principle of induction linear motors, V is 2 τ (f-f)_s) Then, the time from the B end to the a end to the k +2 th primary end is:

(2) as can be seen from comparison of the formula with the formula (1), the induction linear motor has a larger time margin for switching power supply than the synchronous linear motor. Therefore, the synchronous linear motor can meet the requirement that the induction linear motor can be used when the three phases of the primary of the (k + 2) th section are completely electrified before the secondary A end enters the primary of the (k + 2) th section.

The above description is directed to a linear motor having no gap structure between the primary stages, but the present invention is also applicable to an ac linear motor having a gap structure between the primary stages. This is explained below with reference to fig. 3.

As shown in FIG. 3, a primary length is designated L₁And the secondary length is denoted as L₂And the interval between segments is denoted as L₃. When the number of the segments of the primary and secondary simultaneously electrified is n, L is L in order to ensure that the length of the coupling between the primary and the secondary is not changed when the secondary moves₂＝(n-1)L₁+L₃. In FIG. 3, n is 2, so L₂＝L₁+L₃。

The power supply switching method when the interval exists between the primary sections is the same as that when the interval does not exist between the primary sections, and the segmented power supply switching is also carried out according to two conditions of the secondary position and the zero crossing point of the three-phase current. Specifically, by detecting the zero crossing point of three-phase current, which phase current leaves from the kth primary stage from the secondary B end and crosses zero, the power supply switch of the phase at the kth +2 primary stage is switched on, and the power supply switch of the phase at the kth primary stage is switched off at the same time, and the other two phases are the same until the three phases are switched over. The time sequence and the required time of three-phase switching are the same as the condition that no interval exists between the primary section and the primary section.

Interval L between primary sections₃It must be a positive integer multiple of the pole pitch τ to minimize the fluctuation of the electromagnetic force. Taking L as the same as the derivation method when no interval exists between the primary section and the section₃Before the terminal a enters the section k +2 primary stage, the three phases of the section k +2 primary stage are all powered on, and details are not repeated here.

Claims

1. A method for sectionally supplying power to an alternating current linear motor comprises the following steps:

2. The ac linear motor segment power supply method according to claim 1, wherein: the multiphase windings of each primary section are independent, the midpoints are not connected, and an independent power supply switch is arranged for each phase.

3. The ac linear motor segment power supply method according to claim 1, wherein: each phase of the n primary stages which are simultaneously energized is supplied in series.

4. The ac linear motor segment power supply method according to claim 1, wherein: and the multiphase winding is switched to supply power on the basis of two conditions of a secondary position and a phase current zero crossing point.