CN111903225B - AC linear motor sectional power supply method - Google Patents

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

A segmental power supply method for an AC linear motor

technical field

The invention belongs to the field of linear motors, and in particular relates to a primary segmented linear motor and a method for realizing switching power supply between segments. The invention is suitable for AC linear motors with long primary and short secondary structures (including linear induction motors and linear synchronous motors), especially for high-speed and high-power linear motors for electromagnetic emission.

state of the art

With the continuous maturity of linear motor theory and design technology and the continuous development of power electronics technology, linear motors are being used more and more widely. At present, the electromagnetic launcher with the linear motor technology as the core is a hot topic in the research of various military powers in the West, such as electromagnetic catapults and electromagnetic rail guns. However, for the high-power long-primary AC linear motors used in devices such as electromagnetic catapults: first, the existing power supply is difficult or unable to meet the requirements of full primary full power; No work is done, resulting in low motor efficiency and serious energy waste. In order to solve these problems, it is an effective way to implement subsection power supply to the primary stage.

At present, there are a small number of literatures that have conducted preliminary research on the segmented power supply technology for long primary AC linear motors, such as the "Vertical Lifting System Driven by Multi-Segment Primary Permanent Magnet Linear Synchronous Motors" (Proceedings of the Chinese Society for Electrical Engineering, No. 18, 2007) The vertical elevator, the logistics transmission device described in "Transmission System Driven by Long Stator Linear Motor" (Micro Motor, No. 4, 2002), etc. However, due to the low speed and low power, they all adopt the method of parallel power supply to the energized primary. There are two major disadvantages in the primary parallel power supply: first, when the supply voltage remains unchanged, the current in each section of the electrified primary will change with the movement of the secondary, resulting in unequal primary power densities in each section, making it impossible for the primary Second, the current in each section of the electrified primary is not equal, which will increase the difficulty of precise closed-loop control of the secondary movement through current feedback. These two major disadvantages are unacceptable in occasions with high power and high precision such as aircraft ejection.

In addition, the segmented power supply technology is also widely used in maglev trains with long primary drives. The segmental power supply methods of maglev trains mainly include "leapfrog method", "two-step method", "three-step method", etc., but the essence of all these methods is still based on parallel power supply between segments, which can meet the requirements of steady-state work. However, it cannot meet the requirements of some special applications such as electromagnetic emission. Electromagnetic emission devices generally work in intermittent pulse mode, with short working time, large transient power, and large current, which have strict requirements on electromagnetic force fluctuations. Therefore, electromagnetic emission devices must seek a reliable and less electromagnetic force fluctuation Segment power supply switching method, but there is no relevant information in the open literature for the time being.

Contents of the invention

The purpose of the present invention is to adapt to the special requirements of the long-primary linear motor electromagnetic emission device, and adopt a method for implementing segmental power supply to the primary. This method can ensure that under the premise that the power supply voltage remains unchanged, the currents in the electrified primary stages of each section are equal, thus fundamentally solving the shortcomings of the primary parallel power supply; at the same time, this method also avoids electromagnetic force fluctuations when the power supply is switched. Excessive disadvantage.

The segmental power supply method of an AC linear motor provided by the present invention, the steps of which include:

Step 1 When the secondary of the motor is at the initial position, make the first, second, ..., n segments of n primary stages energized in series, and the secondary starts to move;

Step 2 When the secondary happens to completely leave the primary stage of the first stage, by detecting the three-phase currents of A, B, and C in the primary stage, it is judged whether the current of each phase has crossed zero. As long as the current of a certain phase crosses zero, the first stage will be turned off. The primary phase cuts off the power supply, and at the same time, the n+1th primary phase is energized, and the three-phase current will cross zero sequentially within the phase angle of 120° to 180°, and the motor will start from the 1st, 2nd,... , n stages of primary series energization, completely switch to the 2nd, 3rd, ..., n+1 primary series energization;

Step 3 When the secondary just completely leaves the 2nd, 3rd, ..., N-n stage primary (N is the total number of primary stages), the switching method of the segmental power supply is the same as the 2nd step;

Step 4 When the secondary is stopped by braking, remove power from all primary stages.

The method provided by the present invention can be applied to various primary segmented AC linear motors, especially for high-speed and high-power linear motors, the technical effect is particularly remarkable, and the specific description is as follows:

(1) Due to the adoption of the primary series power supply method in the energized section, it can ensure that the current in the primary section of each section is equal, and the power density is consistent, which is conducive to reducing the volume and weight of the motor, and is conducive to using the material performance to the extreme;

(2) Since all the primary stages of the energized section share a power supply in series, the complexity of motor control can be greatly reduced, which is conducive to the realization of precise closed-loop control of secondary motion through current feedback;

(3) Since the method of switching the power supply when the current crosses zero is adopted, the fluctuation of the current when the power supply is switched can be significantly reduced, thereby helping to reduce the fluctuation of the electromagnetic force.

Description of drawings

Fig. 1 is the schematic diagram of the linear motor with no gap structure between the primary section and the section of the present invention adopting the method of power supply in series;

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

Fig. 3 is a schematic diagram of the linear motor with a gap structure between the primary section and the section of the present invention adopting the method of power supply in series and section.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

The long primary AC linear motor targeted by this method needs to meet the following conditions: the primary is divided into several sections, the primary specifications of each section are the same, the three-phase (or multi-phase) windings are independent, there is no midpoint connection, and each phase of each primary section is set Independent power switch.

Let n be the number of primary stages that are energized at the same time. For a linear motor with a structure in which the primary section is closely connected, in order to reduce the secondary weight, the secondary length is usually designed to be slightly smaller than the total primary length of n-1 sections. The following takes n=2 as an example to describe this power supply switching method in detail.

As shown in FIG. 1 , a primary length is L ₁ , a secondary length is L ₂ , and L ₃ is a length reserved for segmental power supply switching. In general, L ₃ =(n-1)L ₁ -L ₂ , and FIG. 1 takes n=2 as an example, so L ₃ =L ₁ -L ₂ .

The kth primary and the k+1th primary are powered in series through the power supply network, and the secondary moves forward under the action of electromagnetic force. When the secondary B end just leaves the k-th primary, start switching power supply. Since the three-phase current of A, B, and C may be very large (up to 10000A or more), if only according to the position of the secondary, regardless of whether the phase current crosses zero, the k+2 primary stage is connected, and the primary stage of the second stage is disconnected at the same time. The k-stage primary will cause a current shock, which is very unfavorable to the motor body and system control. The method adopted in the present invention is to detect the zero-crossing point of the three-phase current, starting from the secondary B terminal leaving the kth section primary, which phase current is zero-crossing, just turn on the power supply switch of the phase of the k+2 section primary, and at the same time Turn off the power supply switch of the primary phase of the k-th section, and do the same for the other two until the three phases are switched.

的不同，A、B、C三相切换供电的时序有三种情况，即：As shown in Figure 2, according to the phase A current phase when the secondary B terminal leaves the kth primary

The timing of A, B, C three-phase switching power supply has three situations, namely:

或

时，切换的时序是C相、B相、A相，且B相切换时刻滞后C相1/6周期，A相切换时刻滞后C相1/3周期；(1) when

or

, the switching timing is phase C, phase B, and phase A, and the switching time of phase B lags behind phase C by 1/6 cycle, and the switching time of phase A lags phase C by 1/3 cycle;

或

时，切换的时序是B相、A相、C相，且A相切换时刻滞后B相1/6周期，C相切换时刻滞后B相1/3周期；(2) when

or

, the switching timing is phase B, phase A, and phase C, and the switching time of phase A lags behind phase B by 1/6 cycle, and the switching time of phase C lags behind phase B by 1/3 cycle;

或

时，切换的时序是A相、C相、B相，且C相切换时刻滞后A相1/6周期，B相切换时刻滞后A相1/3周期；(3) when

or

, the switching timing is phase A, phase C, and phase B, and the switching time of phase C lags behind phase A by 1/6 cycle, and the switching time of phase B lags behind phase A by 1/3 cycle;

It can also be seen from Figure 2 that no matter which of the above three cases is the case, the minimum time required is 1/3 cycle from the time when the secondary B terminal leaves the k-th primary stage and starts to switch, and the three phases are switched and powered. , up to 1/2 period.

It must be ensured that before the secondary A terminal enters the k+2 primary stage, all three phases of the k+2 primary stage are energized. The following is divided into two cases of synchronous linear motor and induction linear motor.

For synchronous linear motors, the secondary speed is recorded as V, the current frequency is f, the period is T, and the pole distance is τ. According to the principle of synchronous linear motor, V=2τf, then the time for the secondary to leave the k+2 primary from terminal B, and enter the k primary from terminal A is:

According to the design principles of linear motors, when L ₃ is taken as a positive integer multiple of τ, the fluctuation of electromagnetic force is the smallest. From the above discussion, the time required for the completion of the three-phase switching is between T/3 and T/2, so even according to the most unfavorable situation, that is, L ₃ =τ, it can be known from the formula (1) that t=T/2, It can also ensure that before the A terminal enters the primary stage of the k+2 stage, all three phases of the primary stage of the stage k+2 are energized.

In order to improve the efficiency of the linear motor as far as possible in engineering, it is required that the smaller the _L3 , the better. When L ₃ is the smallest (that is, L ₃ =τ), the time required for switching power supply is still satisfied, which is also one of the advantages of the present invention.

For the induction linear motor, the secondary speed is recorded as V, the current frequency is f, the period is T, the slip frequency is recorded as f _s , and the pole distance is τ. According to the principle of induction linear motor, V=2τ(ff _s ), then the time for the secondary to leave the k+2 primary stage from the B terminal and enter the kth primary stage from the A terminal is:

Comparing formula (2) with formula (1), it can be seen that the time margin for switching power supply of induction linear motor is larger than that of synchronous linear motor. Therefore, the synchronous linear motor can meet the requirement that all three phases of the primary stage of the k+2 stage are energized before the secondary A terminal enters the primary stage of the k+2 stage, and the induction linear motor can also do the same.

The above description is for the linear motor with no space between the primary section and the section, but the present invention is also applicable to the AC linear motor with the space between the primary section and the section. This will be described below with reference to FIG. 3 .

As shown in Figure 3, the primary length of a segment is denoted as L ₁ , the secondary length is denoted as L ₂ , and the interval between segments is denoted as L ₃ . When the number of stages that the primary is powered on at the same time is n, in order to ensure that the length of the coupling between the primary and secondary stages remains unchanged when the secondary is moving, then L ₂ =(n-1)L ₁ +L ₃ . Figure 3 takes n=2 as an example, so L ₂ =L ₁ +L ₃ .

The power supply switching method when there is an interval between the primary section and the section is the same as when there is no interval between the primary section and the section. It is also based on the two conditions of the secondary position and the zero-crossing point of the three-phase current to perform segmented power supply switching. Specifically, by detecting the zero-crossing point of the three-phase current, starting from the secondary B terminal leaving the k-th primary, which phase current crosses zero, the power supply switch of the k+2 primary phase of the phase is turned on, and at the same time it is turned off The power supply switch of the primary phase of the k-th section is the same as the other two until the three phases are switched. The timing and time required for three-phase switching are the same as the case where there is no interval between the primary stage and the stage.

The interval L ₃ between the primary segment and the segment must be a positive integer multiple of the pole distance τ in order to minimize the fluctuation of the electromagnetic force. The derivation method is exactly the same as when there is no interval between the primary section and the section. Taking L ₃ =τ, it can be satisfied that before the A terminal enters the k+2th primary stage, all the three phases of the k+2th primary stage are energized, and no longer repeat.

Claims (4)

1. A method for sectionally supplying power to an alternating current linear motor 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.

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.

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