CN104092421A - Method for selecting capacity of current transformer for driving long stator linear synchronous motor - Google Patents

Abstract

The invention relates to a method for selecting the capacity of a current transformer for driving a long stator linear synchronous motor. The method for selecting the capacity of the current transformer for driving the long stator linear synchronous motor comprises the steps that (1) boundary conditions are obtained according to the overall requirements of a current high-speed magnetic-levitation project; (2) the expected acceleration mileage Sm of a train, the traction Fx existing when the train travels at the highest speed and the stator current Isvm and the stator voltage Usm which are required when the train travels at the highest speed are calculated based on the boundary conditions; (3) assuming that the maximum current output by the current transformer is Ism0=Isvm, a velocity curve existing when the train is accelerated is calculated according to a mathematic model, and the current acceleration mileage S*m of the train is obtained; (4) the current acceleration mileage S*m is compared with the expected acceleration mileage Sm so that the limiting value I*sm of the stator current can be obtained; (6) the capacity of the current transformer is obtained by means of the voltage Usm calculated in the step (2) and the current I*sm calculated in the step (5). Compared with the prior art, the method for selecting the capacity of the current transformer for driving the long stator linear synchronous motor has the advantages that calculation is flexible, and the matching degree of calculation results is high.

Description

A kind of long stator synchronous linear motor drives uses Converter Capacity system of selection

Technical field

The present invention relates to high-speed magnetic floating technical field, especially relate to a kind of long stator synchronous linear motor driving Converter Capacity system of selection.

Background technology

Along with the development of domestic industry technical merit and the raising of the high-power converter design level of production, the use of other high-voltage high-power converter of megavolt-ampere level is more and more common.For long stator synchronous linear motor, drive, the demand of the high-power converter that particularly high-speed maglev train drives also will get more and more.Drop at present other Converter Capacity of megavolt-ampere level that high-speed magnetic floating commercial operation uses and only had 15MVA and two kinds of ranks of 7.5MVA.Along with often leading the development of high speed Maglev, according to the demand of different engineering projects, probably requiring has the current transformer of more power grades available.And along with the increase of power grade, expansion is also needed in the standardized work of high-power converter power grade that is applied to high speed Maglev badly.So, in concrete engineering project, need the current transformer of which kind of capacity just suitable? in following equipment standard is formulated, should how to formulate again the capacitance grade of high-power converter to meet the needs of engineering project?

The Capacity Selection of general high-power converter is divided into 3 steps:

(1) understand load characteristic and Changing Pattern, calculate the size of load current or make load current figure I=f (t).

The selected process of Converter Capacity, is actually the optimum Match process of current transformer and motor.For the motor of different loads characteristic, adopt diverse ways computational load electric current:

The calculating of Converter Capacity when-constant load is moved continuously: generally consider electric motor starting mode, according to the starting current of motor or rated current, determine load current, then the capacity of preliminary election current transformer.

The calculating of Converter Capacity when-cyclic variation load moves continuously: first make motor load map of current n=Φ (t) and I=f (t), then obtain average load current, then the capacity of preliminary election current transformer.

The calculating of Converter Capacity when-aperiodicity varying duty moves continuously: generally by the rated current of motor Current calculation current transformer during breakdown torque in output.

(2) according to the capacitance grade preliminary election Converter Capacity of existing current transformer;

(3) according to overload and startup capability check preliminary election current transformer.

Commercial off-the-shelf is often led high speed Maglev trailer system and is a powerful long stator synchronous linear motor system at present, and its stator is positioned on track, and rotor is the magnetic-levitation train of high-speed cruising, but and is not suitable for above-mentioned universal method.This is because the above-mentioned first step---calculate current transformer load current for be ripe motor product.These motor products have corresponding standard termination characteristic, can be calculated or be inquired about by standard or standard.And the linear synchronous motor that high-speed magnetic floating technology adopts not is general ripe motor product.Because the circuit of putting into commercial operation at present only has Shanghai demonstration line, the load characteristic of the linear electric motors that it adopts is only applicable to this engineering project of Shanghai line.When linear electric motors output breakdown torque, train startup stage, its output voltage is lower.And the required maximum output voltage of motor depends on and the requirement of maximum speed, line condition and departure interval etc. that train must reach will make a big difference between different engineering projects.For following engineering project, the possible difference because of project demands, and make motor load characteristic different.

In addition, the current transformer of putting into commercial operation at present, be applicable to high speed Maglev only has 15MVA and two kinds of standards of 7.5MVA, and not only the leeway of preliminary election is limited, and the result of carrying out verification according to this alternative capacity can not guarantee accurately.If be not limited to existing capacity, but suppose that a certain capacitance grade and parameter carry out tentative calculation verification, the optional combination of hypothesis is too many, will cause amount of calculation larger, and efficiency is low, and can not guarantee to obtain optimal result.

Summary of the invention

Object of the present invention is exactly the defect existing in order to overcome above-mentioned prior art, angle from high-speed magnetic floating project demands, the Mathematical Modeling of linear synchronous generator of take is basis, the long stator synchronous linear motor that has proposed a kind ofly to calculate flexibly, result of calculation matching degree is high drives uses Converter Capacity system of selection, is applicable to high-speed magnetic floating project.The method not only can obtain reasonably, be applicable to the key characteristic parameters such as the required entries object Converter Capacity and voltage, electric current in concrete high-speed magnetic floating project, and also can bring into play booster action in the formulation process of production domesticization high-power converter capacitance grade.

Object of the present invention can be achieved through the following technical solutions:

Long stator synchronous linear motor drives and uses a Converter Capacity system of selection, comprises the steps:

(1) according to the overall project demands of current high-speed magnetic floating project, obtain boundary condition, comprise speed target value v _m, Holding acceleration a _b, train maximum marshalling number n and train be at the average acceleration a of accelerating sections;

(2), based on described boundary condition, according to the Mathematical Modeling of Newton's second law and long stator synchronous linear motor, calculate the expectation of train and accelerate mileage s _m, the tractive effort F of train while being about to arrive maximum speed _xand required stator current I now _svmand voltage U _sm;

(3) suppose that current transformer output maximum current is I _sm0=I _svm, with I _sm0and U _smas the limit value of long stator linear synchronous motor stator current, voltage, the Mathematical Modeling of substitution long stator synchronous linear motor, obtain train when preacceleration mileage

(4) relatively more described when preacceleration mileage accelerate mileage s with expectation _msize, if be greater than increase stator current limit value otherwise reduce stator current limit value the current increment of Δ I for setting;

(5) order repeating step (3), until equal s _mtill, the stator current limit value now obtaining be needed current transformer maximum output current;

(6) by step (2), calculate gained voltage U _smand step (5) is calculated gained electric current obtain the capacity of required current transformer, expression formula is:

$S={3U}_{\mathrm{sm}}{I}_{\mathrm{sm}}^{*}$

Wherein, U _sm, be respectively the effective value of phase voltage, phase current.

Described overall project demands comprises minimum departure interval of train, highest running speed of train, the capacity of train and the climbing capacity of train.

From operation principle, say, the long stator synchronous linear motor that high-speed magnetic floating adopts, its traction control and general linear synchronized motor are similar.According to traditional synchronous motor principle, the dq Mathematical Modeling of long stator linear synchronous motor in the time of can obtaining stable state.Under rotor field-oriented control strategy, in order to reach the object with suspension magnetic decoupling zero, the d shaft current of linear synchronous generator is approximate is controlled as zero, and therefore the Mathematical Modeling of described long stator synchronous linear motor comprises following equation:

Voltage equation

$\left\{\begin{array}{c}{u}_d=-\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{\mathrm{vL}}_q{i}_q\\ u_q={\mathrm{Ri}}_q+\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{\mathrm{vL}}_{\mathrm{sm}}{i}_m\end{array}\right.---\left(1\right)$

$u_d^2+u_q^2=U_s^2---\left(2\right)$

Thrust equation

$F_x=\frac{3}{2}\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{L}_{\mathrm{sm}}{i}_m{i}_q---\left(3\right)$

Power

$P=\frac{3}{2}{u}_q{i}_q---\left(4\right)$

Motor stator electric current

$I_s=i_q/\sqrt{2}=\frac{-2v\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{\mathrm{RL}}_{\mathrm{sm}}{i}_m+\sqrt{{\left(2v\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{\mathrm{RL}}_{\mathrm{sm}}{i}_m\right)}^2-4(R^2+{\left(v\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{L}_q\right)}^2)({\left(v\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{L}_{\mathrm{sm}}{i}_m\right)}^2-U_s^2)}}{2\sqrt{2}(R^2+{\left(v\frac{\mathrm{\π}}{{\mathrm{\τ}}_s}{L}_q\right)}^2)}---\left(5\right)$

U in above-mentioned equation _d, u _qfor d, the q shaft voltage component of current transformer output, U _sfor linear motor stator electric end input voltage, L _qfor linear electric motors q axle inductance, L _smfor the mutual inductance of linear motor stator electric winding and excitation winding, i _qfor linear electric motors q shaft current, i _mfor exciting current, τ _sfor the pole span of linear electric motors, v is train speed, F _xfor tractive force of train, P is the active power that linear electric motors consume, and R is the resistance of linear motor stator electric winding.

According to the Mathematical Modeling of described long stator synchronous linear motor, the ceiling voltage U of the required output of current transformer _smcomputational process, specific as follows:

A) Negotiation speed desired value v _mwith Holding acceleration a _b, calculate train be about to reach before maximum speed must tractive effort F _x=F _z(v _m)+ma _b, F wherein _z(v _m) represent that train is in speed v _munder resistance, the quality that m is train, is calculated by the drag characteristic of speed and train;

B) according to formula (5), obtain train and reach the stator current before maximum speed

C) according to average acceleration a and speed target value v _mobtain the actual acceleration distance of train

D) by I _svmand s _mcan calculate the pressure drop u on feeder cable and stator cable _σ;

E) by speed target value v _mwith train marshalling list n, can calculate the back-emf u of train under maximum speed _dpand u _qp;

F) by u _σ, u _dpand u _qpcan obtain the train voltage U that current transformer is exported when reaching maximum speed _sm.

Calculate the rate curve of train when accelerating in described step (3), obtain train when preacceleration mileage be specially:

A) according to the basic data initialization linear electric motors parameter of project, and and I _sm0, U _smand s _mtogether as input data;

B) according to formula (5), calculate motor stator electric current I _s;

C) if motor stator electric current I _s>=I _sm0, get I _sm0as stator current, calculate;

D) according to formula (2), calculate motor thrust F _x;

E) according to Newton's second law, calculate train current acceleration a _x, speed v _xwith displacement s _x;

F) if present speed v _x<v _m, according to current displacement and speed, upgrade linear electric motors parameter, return to step a);

G) if present speed v _x>=v _m, export accelerating sections displacement

Described basic data comprises circuit line style data, station and electric substation's position data.

Compared with prior art, the present invention has the following advantages:

(1) be not subject to the restriction of existing Converter Capacity, but according to the actual demand of engineering project, obtain the boundary condition of calculating.

(2) take the demand of actual items is starting point, and the matching of result of calculation and project is high.

(3) take the Mathematical Modeling of long stator synchronous linear motor carries out iterative computation as basis, and computational efficiency is high, and result of calculation is accurate.

(4) computational methods are flexible, are applicable to various high-speed magnetic floating projects.Therefore in the Standardization Research process of the high-power converter driving for long stator synchronous linear motor, can be used as strong aid.

Accompanying drawing explanation

Fig. 1 is linear synchronized motor steady operation polar plot;

Fig. 2 is schematic flow sheet of the present invention;

Fig. 3 is train accelerating sections rate curve calculation process;

Fig. 4 is the schematic diagram that is related to of Holding acceleration and the gradient;

Fig. 5 is speed, the accelerating curve of embodiment 1;

Fig. 6 is the current transformer power curve of embodiment 1;

Fig. 7 is current transformer voltage, the current curve of embodiment 1.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.The present embodiment be take technical solution of the present invention and is implemented as prerequisite, provided detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

The one section of virtual circuit of take is below example, calculates in this section of circuit according to different engineering project index requests, the capacitance grade of the current transformer that should adopt respectively.Wherein, linear electric machine traction adopts two-step method both end power supplying, traction minute head of district 40km, stator segment average length 1200m, 5 marshallings of train, parameter and the resistance model of employing Shanghai Maglev.Average load (80% is fully loaded) is considered in the load of vehicle.All the other hypothesis are as follows:

1) cable limit value:

In calculating, the stator current of gained can not be greater than the threshold value of cable overcurrent protection, the highest voltage withstand class that can not surpass stator cable of stator terminal voltage.The cable model that actual threshold value and voltage withstand class should adopt according to detailed programs is determined.In following embodiment, suppose that stator current overcurrent protection threshold value is 2000A, withstand voltage is 20kV line voltage.

2) train reaches the Holding acceleration before maximal rate:

Consider the acceleration capacity that high-speed maglev train is stronger, here the Holding acceleration that adopted calculates the value of defined in rules > > with reference to < < train traction, get temporarily 0.15m/s ²and 0.2m/s ²calculate respectively.

The value of Holding acceleration is directly related in the climbing capacity under highest running speed with train.As shown in Figure 4, suppose a _bfor Holding acceleration, the quality of train is m, and the gradient of circuit is θ, and acceleration of gravity is g, and F is that train overcomes the free tractive force after resistance on level tangent track, has F=ma _b.When the weight component mg θ when the F of train goes up a slope with train equates, can guarantee that train keeps highest running speed operation on this ramp.Now have

${\mathrm{ma}}_b=\mathrm{mg\&theta;}\&DoubleRightArrow;a_b=\mathrm{g\&theta;}$

From the known Holding acceleration a of above formula _bthe ruling grade θ that can guarantee highest running speed to train is directly proportional, and differs g doubly.

3) average acceleration of accelerating sections: 0.4m/s ²and 0.5m/s ².

4) target velocity grade: 400km/h, 500km/h.

According to above-mentioned hypothesis, below will calculate according to three kinds of situations shown in table 1 table.

The input parameter of table 1 embodiment

(1) embodiment 1:

1), according to target velocity, average acceleration and step as shown in Figure 2, calculate the acceleration mileage s of train _m=15432m, tractive effort F when train is about to arrive maximum speed _x≈ 142256N, and required stator current I now _svm=590A.

2) be illustrated in figure 1 linear synchronized motor steady operation polar plot, wherein, when the stator terminal of linear electric motors applies cosine voltage U _stime, phase angle is β, d, q shaft voltage can be expressed as

$\left\{\begin{array}{c}{u}_d={-U}_s\sin \mathrm{\&beta;}\\ u_q=U_s\cos \mathrm{\&beta;}\end{array}\right.$

Voltage when therefore, calculating train is about to arrive target velocity wherein, u _d=-4.78kV, u _q=6.71kV, U _smfor phase voltage effective value.

3) by above-mentioned I _svm, U _smand s _mflow process shown in substitution Fig. 3 is calculated train and is accelerated mileage, by result of calculation with s _mcompare.When time, can obtain speed and accelerating curve as shown in Figure 5, now $I_{\mathrm{sm}}^{*}=0.625\mathrm{kA}.$

The result of calculation of embodiment 1 gathers to table 2, and in table, Converter Capacity is by formula calculate.Result of calculation shows, in the engineering project of embodiment 1, as long as the current transformer that employing capacity is 11MVA can meet engineering demand.Now the highest phase voltage of current transformer output is no more than 6kV.According to this result of calculation, in concrete engineering, can adopt corresponding cable and equipment, be conducive to cost saving.

Table 2 embodiment 1 Converter Capacity result of calculation

Fig. 5 is speed, the acceleration-position curve of embodiment 1.Wherein, solid line is rate curve, and dotted line is accelerating curve.Visible, when speed is lower, the acceleration peak of train can reach 0.74m/s ², in the moment that is about to arrive target velocity 400km/h, acceleration still has 0.15m/s ²(meeting Holding acceleration is 0.15m/s ²condition).

Fig. 6 is the active power curve of current transformer output in embodiment 1.Owing to having adopted both end power supplying, at the two ends of subregion, be respectively provided with a traction substation, Mei Zuo electric substation respectively configures one group of current transformer to this switched-mode power supply.Therefore in Fig. 5, have two power curve, wherein solid line represents that dotted line represents the power (power of standing afterwards) that traction becomes near terminal near the power (next stop power) of the traction change of starting point, and Grey curves is train speed.In figure, the maximum power of two traction changes appears at different mileage positions, and this is the method for distributing electric current by mileage owing to having adopted.In Fig. 6, maximum power does not appear at train and is about to reach before maximum speed, not waste of the Converter Capacity that this explanation calculates by methods described herein.If the surplus of Converter Capacity is larger, the peak value of power will appear at more close train and reach the position of maximum speed.

Figure 7 shows that current transformer voltage, current curve after embodiment 1 calculates.Wherein electric current is the q shaft current after dq conversion, corresponding with the peak value of actual stator electric current.As we know from the figure, before reaching target velocity, in a flash, the voltage of both-end current transformer has all reached peak value 5.83kV, and both-end electric current sum is I _svm=590A (effective value).But both-end electric current is different, distance train is large compared with near next stop output current of converter, and distance train is little compared with rear station output current of converter far away, and this is also owing to distributing the control method of electric current to cause by mileage.In addition, as can be seen from Figure 7, when train is about to arrive target velocity, be not that current transformer is exported in maximum current.This is also why to need to carry out iterative computation reason.

(2) embodiment 2 and embodiment 3:

The Converter Capacity result of calculation that meets embodiment 2 and embodiment 3 is as shown in table 1.Concrete simulation curve and Fig. 5～Fig. 7 are similar, repeat no more here.As known from Table 1, adopt 15MVA high power current transformer substantially can meet the requirement of embodiment 2.If but wish to improve the acceleration capacity of train and the level that climbing capacity arrives embodiment 3, need the more current transformer of high power capacity grade, about 21MVA.This is because the increase of acceleration capacity requires the electric current fan-out capability of current transformer also to want corresponding increase.Adopt the current transformer of embodiment 3 that shortened to approximately 20 second than employing embodiment 2 running time that makes train.

Table 1 embodiment 2 and 3 Converter Capacity result of calculation

Claims (5)

1. long stator synchronous linear motor drives and uses a Converter Capacity system of selection, it is characterized in that, comprises the steps:

(1) according to the overall project demands of current high-speed magnetic floating project, obtain boundary condition, comprise speed target value v _m, Holding acceleration a _b, train maximum marshalling number n and train be in the average acceleration of accelerating sections

(2), based on described boundary condition, according to the Mathematical Modeling of Newton's second law and long stator synchronous linear motor, calculate the expectation of train and accelerate mileage s _m, the tractive effort F of train while being about to arrive maximum speed _xand required stator current I now _svmand voltage U _sm;

(3) suppose that current transformer output maximum current is I _sm0=I _svm, with I _sm0and U _smas the limit value of long stator linear synchronous motor stator current, voltage, the rate curve of the calculated with mathematical model train of substitution long stator synchronous linear motor when accelerating, obtain train when preacceleration mileage

(4) relatively more described when preacceleration mileage accelerate mileage s with expectation _msize, if be greater than increase stator current limit value otherwise reduce stator current limit value the current increment of Δ I for setting;

(5) order repeating step (3), until equal s _mtill, the stator current limit value now obtaining be needed current transformer maximum output current;

(6) by step (2), calculate gained voltage U _smand step (5) is calculated gained electric current obtain the capacity of required current transformer, expression formula is:

Wherein, U _sm, be respectively the effective value of phase voltage, phase current.

2. a kind of long stator synchronous linear motor according to claim 1 drives and uses Converter Capacity system of selection, it is characterized in that, described overall project demands comprises minimum departure interval of train, highest running speed of train, the capacity of train and the climbing capacity of train.

3. a kind of long stator synchronous linear motor according to claim 1 drives and uses Converter Capacity system of selection, it is characterized in that, the Mathematical Modeling of described long stator synchronous linear motor comprises following equation:

Voltage equation

Thrust equation

Power

Motor stator electric current

U in above-mentioned equation _d, u _qfor d, the q shaft voltage component of current transformer output, U _sfor linear motor stator electric end input voltage, L _qfor linear electric motors q axle inductance, L _smfor the mutual inductance of linear motor stator electric winding and excitation winding, i _qfor linear electric motors q shaft current, i _mfor exciting current, τ _sfor the pole span of linear electric motors, v is train speed, F _xfor tractive force of train, P is the active power that linear electric motors consume, and R is the resistance of linear motor stator electric winding.

4. a kind of long stator synchronous linear motor according to claim 3 drives and use Converter Capacity system of selection, it is characterized in that, calculates the rate curve of train when accelerating in described step (3), and what obtain train works as preacceleration mileage be specially:

A) according to the basic data initialization linear electric motors parameter of project, and and I _sm0, U _smand s _mtogether as input data;

B) calculate motor stator electric current I _s;

C) if motor stator electric current I _s>=I _sm0, get I _sm0as stator current, calculate;

D) calculate motor thrust F _x;

E) according to Newton's second law, calculate train current acceleration a _x, speed v _xwith displacement s _x;

F) if present speed v _x<v _m, according to current displacement and speed, upgrade linear electric motors parameter, return to step a);

G) if present speed v _x>=v _m, export accelerating sections displacement

5. a kind of long stator synchronous linear motor according to claim 4 drives and uses Converter Capacity system of selection, it is characterized in that, described basic data comprises circuit line style data, station and electric substation's position data.