CN102739083A - Optimization modulation method of electric railway train traction rectifying system - Google Patents

Abstract

The invention relates to an optimization modulation method of an electric railway train traction rectifying system. The optimization modulation method comprises off-line calculation of an optimization switching angle and real-time control on a double-closed-loop PWM (pulse-width modulation) rectification algorithm. The off-line calculation method of the optimization switching angle comprises the following steps of: generating fixed switching numbers on each cyclic wave, changing the numerical value of the switching angle, and calculating the sum of harmonic waves of net side current, thus obtaining the optimal switching angle when the sum of the harmonic waves of the net side current is lowest. The real-time control method of the double-closed loop PWM rectification algorithm comprises the following steps of: obtaining the numerical value of the optimal switching angle of a rectification unit power device according to the phase and amplitude of set voltage; and driving a corresponding switching element to act by the output of a single-phase high-power rectifying system, thus carrying out the on-line real-time control.

Description

Electric railway train traction commutation system is optimized modulator approach

Technical field

The present invention relates to electric railway train traction system, particularly a kind of single-phase rectifier cells modulate method.

Background technology

Electrified railway power supply is provided by traction substation segmentation along the line, and circuit is long, capacity is big, load fluctuation is serious.In order to reduce the working loss of high pressure, high-current switch device, improve the current utilization rate and power performance level of switching device, the High power Traction commutation system of train employing is an a kind of single-phase rectifier system.This commutation system must adopt lower switching frequency; In the converter system of number MW class; Switching frequency is usually less than the hundreds of hertz, and the powered operation frequency is 50 hertz, and low carrier frequency ratio will make waveform harmonics content increase; Increase the possibility of supply network vibration, influenced safe operation when serious.

The PWM modulator approach of optimizing; Be different from sine pulse width modulation (PWM) (the SPWM Sinusoidal Pulse Width Modulation) modulation system that traditional comparator produces; According to voltage-phase and the fixing modulation system that produces switching angle of amplitude, be also referred to as programmable PWM modulator approach (ProgrammedPWM).Can be divided into two types, decide harmonic wave and eliminate pulse-width modulation (SHEPWM Selective Harmonic Elemination Pulse Width Modulation) and optimized PWM (OPWM optimized Pulse Width Modulation).The SHEPWM method proposes (Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters (1973)) principle for through setting the method at PWM Waveform switch angle by Hasmukh S.Patel and Richard G.Hoft the earliest, eliminates voltage harmonic specific time.This method is at first advanced fourier decomposition to the PWM voltage waveform, obtains the expression formula of first-harmonic and each time voltage harmonic component, makes fundametal compoment equal required voltage first-harmonic value then; Make that harmonic component is zero can eliminate certain subharmonic; Thereby obtain a set of equations group, after obtaining many groups of this Nonlinear System of Equations and separating, with switching angle according to sequence arrangement from small to large; And further optimize according to line polarity of voltage criterion etc. and to choose; Obtain the SHEPWM switching angle, according to needed voltage base value, the online switching angle formation voltage waveform that calls these calculated in advance is exported during modulation.The SHEPWM method can eliminate in the output voltage than the low order voltage harmonic; But the increase (D.G.Holmes that can cause higher harmonics content; And the electrical system high order harmonic component is easy to cause that railway power supply net vibration (hands over orthogonal electric traction influence of harmonic and improve electric railway 2010.3 T.A.Lipo.Pulse Width Modulation for Power Converters IEEE press2003); Electric railway traction load harmonic analysis railway society 2011.6 based on wavelet transformation).Method in these existing documents or the patent all is to the three-phase alternating current system, is optimized modulation in motor-driven inversion side, fails effectively to reduce single-phase rectifier element mesh side harmonic content.

Summary of the invention

The objective of the invention is to solve harmonic content problem of higher under the existing electric railway train traction commutation system low switching frequency working method, propose a kind of PWM rectification control method that adopts based on two closed loops.PWM modulator approach of the present invention produces link and feedforward compensation control through the switching angle of optimizing, and realizes high performance single-phase rectifier control, under low switching frequency, reduces the overall harmonic content of system, reduces influence and interference to the net supply network.

Optimized PWM modulation strategy of the present invention is applicable to and solves the harmonic content that reduces electric railroad train traction dynamical system rectification unit.Adopt the PWM switching angle computational methods of optimization aim function, calculate the PWM switching angle, obtain satisfied output voltage, current waveform, reduce total harmonic distortion (THD) content of voltage, electric current through optimizing according to the optimization criterion that total harmonic current is minimum.The present invention can reduce overall harmonic current content and harmonic power, thereby reduces electric railway train traction commutation system current on line side harmonic content.

Technical scheme of the present invention comprises that mainly the calculated off-line of optimal switching angle and the real-time control of two closed loop PWM rectification algorithms realize two parts:

The offline computing method of described optimal switching angle is: ripple produces fixing switch number weekly, under different voltage modulation ratios, changes the numerical value of switching angle, calculates the each harmonic sum of current on line side; The switching angle that obtains when the current on line side harmonic wave with when minimum is the optimized switching angle of asking for;

The real-time control method of described pair of closed loop PWM rectification algorithm is: according to the phase place and the amplitude of given voltage; Obtain the numerical value at the optimized switching angle of rectification unit power device; Controller output by single-phase power rectifier system drives corresponding switching device action, carries out online in real time control.

Its characteristic can specifically be divided into following six aspects:

1, in the calculated off-line of switching angle, the present invention adopts the multidimensional optimizing algorithm to single-phase power rectifier system power devices switch angle.Ripple produces fixing switch number weekly, under different voltage modulation ratios, changes the numerical value of switching angle, calculates the each harmonic sum of current on line side.The switching angle that obtains when the current on line side harmonic wave with when minimum is exactly the optimized switching angle of asking for.This searching process is actually the non-linear global optimizing problem under the constraint, adopts methods such as iterative method, climbing method, simplex method to calculate usually.

2, in the multidimensional optimizing is calculated, need avoid algorithm can't restrain and be absorbed in the situation of local optimum through rationally choosing initial value.The present invention adopts new method to confirm initial value, such as establishing different switching angle initial values according to certain intervals, setting up initial value perhaps according to the method for optimizing last time result as this optimizing initial value immediately.When guaranteeing optimizing efficient, improve Algorithm Convergence.Can calculate the optimal switching angle of complete modulation scope.

3, the present invention is directed to two level power topological structures adopts a plurality of rectification units that DC bus-bar voltage is provided jointly.The present invention is on the optimized calculation method basis of single rectification unit; To many rectification units working method; The new computational methods of optimal switching angle have been proposed; This method is an optimization aim with the synthetic net side total current harmonic wave minimum of two rectification units, the power device switching angle of each rectification unit is carried out the associating optimizing, the optimal switching angle of each rectification unit of calculated off-line.

When the real-time control of PWM rectification algorithm realized, the value storage of the optimal switching angle that single-phase power rectifier system calculates said off-line optimizing was in its controller.

The real-time control of PWM rectification algorithm of the present invention comprises the traditional outer voltage control of DC bus-bar voltage and the current inner loop of rectification unit are controlled; Be that outer shroud is controlled DC bus-bar voltage according to set-point; Interior ring carries out closed-loop control according to the definite given electric current of outer shroud output.The inventive method and the compensation of power feedforward link, whole pair of closed loop rectification control method of the common formation of electric voltage feed forward compensation tache.The invention is characterized in the pulse generation link, comprise switching angle correction and dead area compensation, further improve control performance.The real-time control of PWM rectification algorithm realizes comprising following content:

1, the power feedforward compensation is the present invention to the feedforward compensation of single-phase power rectifier system rectification power output; The electric voltage feed forward compensation is according to single-phase power rectifier system mathematic model prediction and calculation; Jointly control with the current tracking controlling unit; Improve the control ability and the dynamic characteristic of electric current loop; Overcome the influence of the big inertia electric traction of bullet train system output-power fluctuation, improve bullet train electric traction system dynamics response speed.

2, obtain voltage amplitude and phase place through above-mentioned power feedforward with the closed-loop control link, get into the pulse generation link.What be different from traditional sinusoidal or space vector modulation strategy is that according to the result of described optimal switching angle calculated off-line, output drives the rectifier work of commutation system to the trigger impulse of corresponding power device in the pulse generation link in the present invention.

3, when the trigger impulse of above-mentioned pulse generation link produced, the present invention further compensated power device dead band characteristic, introduced the pulsewidth compensation tache, and switching angle is revised, and further improved the output characteristic of system.

The present invention adopts the multidimensional optimizing algorithm; With current on line side harmonic content minimum is optimization aim; Semiconductor power device switching angle to trailer system single-phase rectifier power supply unit is optimized calculating; Under low switching frequency, the angle that adopts computation optimization to obtain is carried out the modulation of programming type to each rectification unit power device and is triggered.Through improving trigger impulse generation link, realize system stable operation.The present invention adopts the feed forward prediction control method, overcomes the influence of system power fluctuation, improves dynamic responding speed.The present invention can make total harmonic current content of electric railway train traction system net side input current minimum; Reduce the distortion of net side input voltage; Improve contact line power supply environment, reduce loss, reduce the contact line electric power system because harmonic excitation causes the risk of electrical network vibration and circulation.The present invention also is applicable in the power unit of other type power topological structure.

Description of drawings

Fig. 1 electric traction commutation system and control flow;

The PWM oscillogram of Fig. 2 first rectification unit 1;

The PWM oscillogram of Fig. 3 second rectification unit 2;

Fig. 4 optimizes angle result of calculation;

Fig. 5 rectification circuit model;

Fig. 6 rectification unit structure chart;

Fig. 7 switching mode sketch map;

Fig. 8 dead area compensation pattern 1 sketch map;

Fig. 9 dead area compensation pattern 2 sketch mapes;

Figure 10 dead area compensation mode 3 sketch map.

Embodiment

Further specify the present invention below in conjunction with accompanying drawing and embodiment.

Commutation system of the present invention is optimized modulator approach and may further comprise the steps:

1, calculates single rectification unit optimized PWM switching angle

The offline computing method of single rectification unit optimized PWM switching angle is following:

When the PWM waveform kept symmetry with every half cycles and 1/4th cycles respectively, promptly waveform was the symmetric points even symmetry with the pi/2, and when being the symmetric points odd symmetry with π, harmonic content is minimum.Like this, a demand goes out 0 ~ pi/2 optimal switching angle, carries out fourier coefficient when calculating, and only need calculate four/one-period to get final product.The present invention adopts the method for 7 pulse wave unipolarities modulation, promptly in the per quart cycle, and switch motion 7 times.The modulation waveform of single rectification unit is as shown in Figure 2.Among Fig. 2, α ₁, α ₂, α ₃, α ₄, α ₅, α ₆, α ₇For the switch motion moment, be called switching angle, U _dBe DC bus-bar voltage, suppose each switching angle sequence arrangement by size, calculate the fourier coefficient of different switching angles, obtain each time voltage harmonic content.

Each time voltage harmonic coefficient b _nComputing formula following, n is a harmonic number:

$b_n=\frac{{4U}_d}{\mathrm{n\π}}(\cos n{\mathrm{\α}}_1-\cos {\mathrm{n\α}}_2+\cos {\mathrm{n\α}}_3-\cos {\mathrm{n\α}}_4+\cos {\mathrm{n\α}}_5-\cos {\mathrm{n\α}}_6+\cos {\mathrm{n\α}}_7)---\left(1\right)$

Fig. 5 is the simplification circuit model of commutation system, and among the figure, Usk is a component of voltage of converting Circuit Fault on Secondary Transformer, l _σBe transformer leakage inductance, R is the winding internal resistance, and Ua is rectification side input voltage, and visible this loop is the series connection topology.After obtaining the voltage harmonic coefficient,, can obtain the nth harmonic current i according to circuit model shown in Figure 5 _nThe weighting expression formula do;

$i_n=\frac{u_n}{{\mathrm{nx}}_{\mathrm{\σ}}}=\frac{b_n}{{\mathrm{nx}}_{\mathrm{\σ}}}---\left(2\right)$

u _nBe the voltage harmonic component value that calculates according to formula (1), x _σBe the anti-coefficient of rectifier transformer leakage inductance.

Therefore, total harmonic current effective value I _DnFor

$I_{\mathrm{dn}}=\frac{1}{x_{\mathrm{\σ}}}\sqrt{\underset{n=2}{\overset{N}{\mathrm{\Σ}}}{\left(\frac{u_n}{n}\right)}^2}=\frac{1}{x_{\mathrm{\σ}}}\sqrt{\underset{n=2}{\overset{N}{\mathrm{\Σ}}}{\left(\frac{b_n}{n}\right)}^2}---\left(3\right)$

N is the calculating harmonic number upper limit of setting as required.x _σBe generally constant.

Foundation with the harmonic current be variable weighted optimization parameter WTHD as shown in the formula:

$\mathrm{WTHD}=\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\Σ}}}{\left(\frac{b_n}{n}\right)}^2}}{u_1}---\left(4\right)$

In the formula, u ₁Be the fundamental voltage coefficient, the total harmonic distortion coefficient of WTHD--weight.

Majorized function func is expressed as:

$\mathrm{func}=\min \left(\mathrm{WTHD}\right)=\min \left(\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\Σ}}}{\left(\frac{u_n}{n}\right)}^2}}{u_1}\right)=\min \left(\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\Σ}}}{\left(\frac{b_n}{n}\right)}^2}}{b_1}\right)---\left(5\right)$

Promptly ask for the minimum value of weighted optimization criterion (4).

Switching angle changes and difference with modulation ratio, needs to calculate the optimal switching angle under the different modulating ratio.In control, modulation ratio is carried out discretization, the present invention adopts perunit value; Modulation ratio from 0 to 1 is divided into 100 grades, and every grade differs 0.01, under every grade of modulation ratio; Change each switching angle; Calculate the commutation system harmonic current value under the different switching angles respectively, when total harmonic current hour, obtain the optimum switch angle.This problem belongs to conditional function multidimensional searching process.

2, confirm switching angle optimizing initial value

Formula (5) is a nonlinear function; Different modulating is the non-linear global optimizing mathematical problem of constraint than the searching process of following switching angle, and the optimizing initial value is very big to the influence of Optimization result, often finishes search owing to being absorbed in local optimum easily; Cause to obtain global optimum; Therefore, the present invention adopts three kinds of method synthesis to choose initial value, guarantees that optimizing finishes to obtain global optimum:

1) takes to confirm start angle according to the method for certain intervals division grid; Carry out repeatedly optimizing; With 7 switching angles is example, in 90 degree electrical degrees, divides grid according to the interval of 13,26,39,52,65,78,90 degree; The initial value of given each lattice is confirmed global optimum according to the majorized function value then.This method is used for confirming one group of initial switching angle;

When 2) gradually changing owing to modulation ratio, the variation at optimized switching angle is also comparatively slow, therefore can be with optimizing last time result; Initial value as optimizing next time; Therefore can be according to method 1) confirm first group of switching angle, the optimizing of constraint multidimensional is arranged then one by one, all optimized angle; But this method can cause error when optimizing when the angle segmentation distributes, and therefore can combine next method to use;

3) when switching angle more for a long time, the method for taking to produce start angle is at random carried out repeatedly optimizing, and then to each time optimizing result relatively, obtains the result of global optimum.

The above-mentioned three kinds of methods of integrated use, the present invention is in the 90 degree electrical degrees, and promptly the switching angle in 1/4 cycle is optimized, and result of calculation is as shown in Figure 4, and the voltage harmonic frequency n of calculating in the formula (1) is 25 to the maximum.

3, calculate many rectification units optimal switching angle

The method of calculating many rectification units optimal switching angle is following:

The power rectifier system adopts many rectification units parallel form, and the present invention proposes the power device switching angle of two rectification units is merged the method for optimizing.The switching angle that the method extends to a plurality of rectification units merges optimization.The switching waveform of first rectification unit is as shown in Figure 2, and the switching waveform of second rectification unit is as shown in Figure 3.α ₁, α ₂, α ₃, α ₄, α ₅, α ₆, α ₇Be the switching angle of first rectification unit, α ₈, α ₉, α ₁₀, α ₁₁, α ₁₂, α ₁₃, α ₁₄It is the switching angle of second rectification unit.Usually two groups of secondary winding parameters of rectifier transformer are identical, therefore can think, two groups of rectification units are identical to the net side input side function of current, can both additions be obtained total input current.The present invention carries out the associating optimizing to the switching angle of first rectification unit 1 and second rectification unit 2.The Harmonics Calculation formula of setting up first rectification unit 1 and second rectification unit 2 is following:

$\left\{\begin{array}{c}0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<{\mathrm{\&alpha;}}_3<{\mathrm{\&alpha;}}_4<{\mathrm{\&alpha;}}_5<{\mathrm{\&alpha;}}_6<{\mathrm{\&alpha;}}_7<\mathrm{\&pi;}/2\\ 0<{\mathrm{\&alpha;}}_8<{\mathrm{\&alpha;}}_9<{\mathrm{\&alpha;}}_{10}<{\mathrm{\&alpha;}}_{11}<{\mathrm{\&alpha;}}_{12}<{\mathrm{\&alpha;}}_{13}<{\mathrm{\&alpha;}}_{14}<\mathrm{\&pi;}/2\\ {\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="HDA00001853881400012.png,HDA00001853881400051.png"\; state="\{\{state\}\}">b</figure-callout>}}_{1\_1}=\frac{{4U}_d}{\mathrm{\&pi;}}(\cos {\mathrm{\&alpha;}}_1-\cos {\mathrm{\&alpha;}}_2+\cos {\mathrm{\&alpha;}}_3-\cos {\mathrm{\&alpha;}}_4+\cos {\mathrm{\&alpha;}}_5-\cos {\mathrm{\&alpha;}}_6+\cos {\mathrm{\&alpha;}}_7)\\ {\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="HDA00001853881400012.png,HDA00001853881400051.png"\; state="\{\{state\}\}">b</figure-callout>}}_{1\_2}=\frac{{4U}_d}{\mathrm{\&pi;}}({\cos \mathrm{\&alpha;}}_8-\cos {\mathrm{\&alpha;}}_9+\cos {\mathrm{\&alpha;}}_{10}-\cos {\mathrm{\&alpha;}}_{11}+\cos {\mathrm{\&alpha;}}_{12}-\cos {\mathrm{\&alpha;}}_{13}+\cos {\mathrm{\&alpha;}}_{14})\\ {\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="HDA00001853881400012.png,HDA00001853881400051.png"\; state="\{\{state\}\}">b</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="HDA00001853881400012.png,HDA00001853881400051.png"\; state="\{\{state\}\}">b</figure-callout>}}_{1\_1}+{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="HDA00001853881400012.png,HDA00001853881400051.png"\; state="\{\{state\}\}">b</figure-callout>}}_{1\_2}\\ b_n=\frac{{4U}_d}{\mathrm{n\&pi;}}(\cos n{\mathrm{\&alpha;}}_1-\cos n{\mathrm{\&alpha;}}_2+\cos n{\mathrm{\&alpha;}}_3-\cos n{\mathrm{\&alpha;}}_4+\cos n{\mathrm{\&alpha;}}_5-\cos n{\mathrm{\&alpha;}}_6+\cos {\mathrm{n\&alpha;}}_7\\ +\cos n{\mathrm{\&alpha;}}_8-\cos n{\mathrm{\&alpha;}}_9+\cos n{\mathrm{\&alpha;}}_{10}-\cos n{\mathrm{\&alpha;}}_{11}+\cos n{\mathrm{\&alpha;}}_{12}-\cos n{\mathrm{\&alpha;}}_{13}+\cos n{\mathrm{\&alpha;}}_{14})\end{array}\right.---\left(6\right)$

In the following formula, b _{1_1}Be the first-harmonic content of first rectification unit 1, b _{1_2}Be the first-harmonic content of second rectification unit 2, b ₁Be the first-harmonic content sum of first rectification unit 1 and second rectification unit 2, b _nIt is the nth harmonic content sum of two rectification units.

According to computing formula (6); Optimizing algorithm according to aforementioned single rectification unit; Calculate the numerical value at the optimized switching angle of rectification unit power device, described value storage in the pulse generation unit of controller, is tabled look-up according to the given voltage-phase of rectification unit and amplitude in control procedure and obtained switching angle; The controller output of single-phase power rectifier system drives corresponding switching device action, realizes optimizing modulation.

The present invention adopts traditional two closed loop control methods, and promptly outer voltage realizes that DC bus-bar voltage is stable, and current inner loop realizes power control and power factor controlling, adopts the feedforward compensation link, comprises new methods such as switching angle correction and dead area compensation algorithm and realizes.

1, feedforward compensation control method

The modulation of employing optimized PWM is a kind of pulse generating method of the type of programming, and comparatively speaking, the system dynamics response can descend to some extent.The present invention adopts the feedforward compensation method, and the control system flow process is optimized, and satisfies the requirement of dynamic response.Compensation method of the present invention comprises power back-off and voltage compensation, in outer voltage, through measuring the dc bus output voltage U _DcWith current i _Dc, both products can obtain power output P,

P＝U _dc×i _dc （7）

In the formula: U _DcDC bus-bar voltage, i _DcDc bus current;

Ignore the current transformer loss, can obtain importing active power, carry out unity power factor control, thus power P divided by the input voltage on line side, can feedover obtains the output valve of outer voltage, the set-point of current inner loop.When fluctuation takes place power, fast controlling unit is compensated.Satisfy dynamic need.

The present invention takes the electric voltage feed forward compensation in current inner loop.The rectification circuit structure is as shown in Figure 5, U _SkBe Transformer Winding voltage, l _σBe the winding leakage inductance, winding resistance R, set up dynamic math equation suc as formula (8):

$U_{\mathrm{sk}}=U_a+l_{\mathrm{\&delta;}}\frac{\mathrm{di}}{\mathrm{dt}}+\mathrm{Ri}---\left(8\right)$

During stable state,

U _sk＝U _a+jωl _δi+Ri （9）

ω is the system works frequency.

Gather input voltage on line side U _Sk, according to system features circuit parameter l _σWith R, calculate U according to mains frequency _a, the voltage of electric current loop output is compensated.

2, switching angle pulse generating method

Obtain voltage amplitude and phase place according to the closed-loop control link, through the online switching angle that searches, the trigger impulse by the controller of single-phase rectifier system output corresponding power device drives rectifier work.The present invention produces and the pulse generation mode through improving traditional switching angle; Rectification unit is optimized modulation: obtain voltage amplitude and phase place according to the closed-loop control link; Through the online switching angle that searches, the trigger impulse by the controller of single-phase rectifier system output corresponding power device drives rectifier work; Digital control delayed impact is eliminated in the adjustment compensation, realizes system stable operation.Obtain good optimized PWM generation effect.

3, dead area compensation algorithm

During high-power converter driving power device,, must carry out dead band generation and minimum pulse width control,, produce and distort the waveform generation influence for protecting device, preventing to mislead, even system oscillation.The present invention compensates the power device dead band in the single-phase power rectifier system of electric railway train traction system.What the present invention adopted is floatless switch angle triggering mode, according to the moment and the mode of switch triggering, in conjunction with current direction and switching tube state; Switching tube is controlled; Confirm the moment and the mode of switch triggering, realize the dead band is compensated, improve the dynamic responding speed of system.

Shown in Figure 6 is single rectification unit topological structure, DC bus-bar voltage U _DcAs shown in Figure 6 with the positive direction of input current i.The present invention adopts the bipolarity modulation; Two power devices carry out complementary modulation according to the output cycle on the arm path; Power device on another brachium pontis need carry out complementary modulation according to output waveform, and the modulation device switching signal of preceding half cycles and later half cycle is opposite.For ease of explanation, explain that with three pulse wave modes the dead band produces and removing method, trigger impulse and waveform are as shown in Figure 7.

Operating mode and compensation method that the dead band produces divide three kinds:

1, positive half cycles, T1 and T2 complementary drive, in both on off state interchange process, the current i direction is judged in the dead band that exists two pipes to turn-off simultaneously, when the electric current forward flow, has increased positive voltage pulse width Delta U ₁, at this moment, get into Dead Time at T1, T2, open the T3 pipe in advance, the short circuit input produces zero level, compensates; During reverse flow, because that T4 pipe is opened is clamped, electric current can not pass through the T2 reverse flow, and the input short circuit needn't compensate.The dead band produces with the compensation signal as shown in Figure 8.Among Fig. 8: a is the desired voltage waveform, has the dead band because T1 and T2 exchange in the opening process, causes voltage distortion, shown in waveform d.T3, T4 switch are carried out the Active Compensation control like waveform e and f, can obtain the desired voltage waveform.

2, negative half period ripple, T1 and T2 complementary drive, in both on off state interchange process, the current i direction is judged in the dead band that exists two pipes to turn-off simultaneously, when reverse direction current flow, has increased negative voltage pulse width Delta U ₂, at this moment, get into Dead Time at T1, T2, open the T4 pipe in advance, the short circuit input produces zero level, compensates; During forward flow, because that T3 pipe is opened is clamped, electric current can not pass through the T1 forward flow, and the input short circuit needn't compensate.The dead band produces with the compensation sketch map as shown in Figure 9.Among Fig. 9: a is the desired voltage waveform, has the dead band because T1 and T2 exchange in the opening process, causes voltage distortion, shown in waveform d.T3, T4 switch are carried out the Active Compensation control like waveform e and f, can obtain the desired voltage waveform.

3, during zero crossing, T1 and T3 complementary drive, in both on off state interchange process, the current i direction is judged in the dead band that exists two pipes to turn-off simultaneously, when the electric current forward flow, has increased positive voltage pulse width Delta U ₃, at this moment, get into Dead Time at T1, T3, open the T2 pipe in advance, the short circuit input produces zero level, compensates; During reverse flow, because that T2 pipe is opened is clamped, electric current can not pass through the T1 reverse flow, and the input short circuit needn't compensate.The dead band produces with the compensation signal shown in figure 10.Among Figure 10: a is the desired voltage waveform, has the dead band because T1 and T3 exchange in the opening process, causes voltage distortion, shown in waveform d.T2, T4 switch are carried out the Active Compensation control like waveform e and f, can obtain the desired voltage waveform.

It is following that commutation system of the present invention is optimized modulated process: according to given rectification unit output d-c bus voltage value

The d-c bus voltage value U that obtains with actual measurement _DcIt is poor to subtract each other, and sends into the constant voltage controlling unit, and suing for peace divided by the feedforward compensation amount of voltage effective value with power output P afterwards obtains current amplitude i _SmMeasure net side input ac voltage U simultaneously _s, obtain voltage-phase and voltage given amount through phase-locked loop (PLL), multiply each other with current amplitude, divided by 2 obtain rectification unit 1 Current Control link set-point

The rectification unit input current value i that obtains with actual measurement _S1It is poor to subtract each other, and sends into the current tracking controlling unit, and carries out voltage compensation.With voltage on line side value U _sProportionally after the subtraction calculations, obtain the given voltage of rectification

Send into the pulse generation unit, inquiry combines the dynamic response demand simultaneously according to the optimal switching angle that calculated off-line obtains; Carry out the pulsewidth compensation, the final synthetic switching angle that obtains power device is through the trigger impulse link; Produce trigger impulse 1, drive rectification unit 1 work.

Claims (7)

1. an electric railway train traction commutation system is optimized modulator approach, it is characterized in that described optimization modulator approach comprises the calculated off-line of optimal switching angle and the real-time control of two closed loop PWM rectification algorithms;

The offline computing method of described optimal switching angle is: ripple produces fixing switch number weekly, under different voltage modulation ratios, changes the numerical value of switching angle, calculates the each harmonic sum of current on line side; The switching angle that obtains when the current on line side harmonic wave with when minimum is the optimized switching angle of asking for;

The real-time control method of described pair of closed loop PWM rectification algorithm is: according to the phase place and the amplitude of given voltage; Obtain the numerical value at the optimized switching angle of rectification unit power device; Controller output by the single-phase rectifier system drives corresponding switching device action, carries out online in real time control.

2. electric railway train traction commutation system according to claim 1 is optimized modulator approach; It is characterized in that; The calculated off-line step of described optimal switching angle is: the initial value of at first establishing switching angle; Set up and optimize criterion and carry out the multidimensional optimizing of switching angle and calculate, when the current on line side harmonic content sum of calculating hour, promptly establish the switching angle of optimizing.

3. electric railway train traction commutation system according to claim 2 is optimized modulator approach, it is characterized in that the method for the initial value of described definite switching angle is:

1) takes to confirm the initial value of junior one group switching angle, confirm global optimum according to the majorized function value then according to the method that certain intervals is divided grid;

2) first group of switching angle confirmed, with last optimizing result, as the initial value of optimizing next time, according to described method 1) optimizing of constraint multidimensional is arranged then one by one, all optimized angle;

3) when switching angle more for a long time, the method for taking to produce start angle is at random carried out repeatedly optimizing, and then to each time optimizing result relatively, obtains the result of global optimum.

4. electric railway train traction commutation system according to claim 2 is optimized modulator approach; It is characterized in that; The calculating of described optimal switching angle is optimization aim with the synthetic net side total current harmonic wave minimum of two rectification units; Power device switching angle to rectification unit is carried out the associating optimizing, and step is following:

1) adopt the method for 7 pulse wave unipolarities modulation, promptly in the per quart cycle, switch motion 7 times; Suppose each switching angle sequence arrangement by size, calculate the fourier coefficient of different switching angles, obtain each time voltage harmonic content:

b _n: be the nth harmonic coefficient

$b_n=\frac{{4U}_d}{\mathrm{n\&pi;}}(\cos n{\mathrm{\&alpha;}}_1-\cos {\mathrm{n\&alpha;}}_2+\cos {\mathrm{n\&alpha;}}_3-\cos {\mathrm{n\&alpha;}}_4+\cos {\mathrm{n\&alpha;}}_5-\cos {\mathrm{n\&alpha;}}_6+\cos {\mathrm{n\&alpha;}}_7)---\left(1\right)$

N is a harmonic number, the nth harmonic current i _nThe weighting expression formula be:

$i_n=\frac{u_n}{{\mathrm{nx}}_{\mathrm{\&sigma;}}}=\frac{b_n}{{\mathrm{nx}}_{\mathrm{\&sigma;}}}---\left(2\right)$

u _nBe the voltage harmonic component value that calculates according to formula (1), x _σBe the anti-coefficient of rectifier transformer leakage inductance; Therefore, total harmonic current effective value I _DnFor:

$I_{\mathrm{dn}}=\frac{1}{x_{\mathrm{\&sigma;}}}\sqrt{\underset{n=2}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{u_n}{n}\right)}^2}=\frac{1}{x_{\mathrm{\&sigma;}}}\sqrt{\underset{n=2}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{b_n}{n}\right)}^2}---\left(3\right)$

N is the calculating harmonic number upper limit of setting as required, x _σBe generally constant;

Foundation with the harmonic current be variable weighted optimization parameter WTHD as shown in the formula:

$\mathrm{WTHD}=\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{b_n}{n}\right)}^2}}{u_1}---\left(4\right)$

In the formula, u ₁Be the fundamental voltage coefficient, the total harmonic distortion coefficient of WTHD--weight.

Majorized function func is expressed as:

$\mathrm{func}=\min \left(\mathrm{WTHD}\right)=\min \left(\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{u_n}{n}\right)}^2}}{u_1}\right)=\min \left(\frac{\sqrt{\underset{n=2}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{b_n}{n}\right)}^2}}{b_1}\right)---\left(5\right)$

Promptly ask for the minimum value of weighted optimization criterion (4).

Adopt perunit value, modulation ratio from 0 to 1 is divided into 100 grades, every grade differs 0.01, under every grade of modulation ratio, changes each switching angle, calculates the commutation system harmonic current value under the different switching angles respectively, when total harmonic current hour, obtain the optimum switch angle;

2) the power device switching angle with two rectification units merges optimization, and the Harmonics Calculation formula of setting up first rectification unit 1 and second rectification unit 2 is following:

$\left\{\begin{array}{c}0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<{\mathrm{\&alpha;}}_3<{\mathrm{\&alpha;}}_4<{\mathrm{\&alpha;}}_5<{\mathrm{\&alpha;}}_6<{\mathrm{\&alpha;}}_7<\mathrm{\&pi;}/2\\ 0<{\mathrm{\&alpha;}}_8<{\mathrm{\&alpha;}}_9<{\mathrm{\&alpha;}}_{10}<{\mathrm{\&alpha;}}_{11}<{\mathrm{\&alpha;}}_{12}<{\mathrm{\&alpha;}}_{13}<{\mathrm{\&alpha;}}_{14}<\mathrm{\&pi;}/2\\ b_{1\_1}=\frac{{4U}_d}{\mathrm{\&pi;}}(\cos {\mathrm{\&alpha;}}_1-\cos {\mathrm{\&alpha;}}_2+\cos {\mathrm{\&alpha;}}_3-\cos {\mathrm{\&alpha;}}_4+\cos {\mathrm{\&alpha;}}_5-\cos {\mathrm{\&alpha;}}_6+\cos {\mathrm{\&alpha;}}_7)\\ b_{1\_2}=\frac{{4U}_d}{\mathrm{\&pi;}}({\cos \mathrm{\&alpha;}}_8-\cos {\mathrm{\&alpha;}}_9+\cos {\mathrm{\&alpha;}}_{10}-\cos {\mathrm{\&alpha;}}_{11}+\cos {\mathrm{\&alpha;}}_{12}-\cos {\mathrm{\&alpha;}}_{13}+\cos {\mathrm{\&alpha;}}_{14})\\ b_1=b_{1\_1}+b_{1\_2}\\ b_n=\frac{{4U}_d}{\mathrm{n\&pi;}}(\cos n{\mathrm{\&alpha;}}_1-\cos n{\mathrm{\&alpha;}}_2+\cos n{\mathrm{\&alpha;}}_3-\cos n{\mathrm{\&alpha;}}_4+\cos n{\mathrm{\&alpha;}}_5-\cos n{\mathrm{\&alpha;}}_6+\cos {\mathrm{n\&alpha;}}_7\\ +\cos n{\mathrm{\&alpha;}}_8-\cos n{\mathrm{\&alpha;}}_9+\cos n{\mathrm{\&alpha;}}_{10}-\cos n{\mathrm{\&alpha;}}_{11}+\cos n{\mathrm{\&alpha;}}_{12}-\cos n{\mathrm{\&alpha;}}_{13}+\cos n{\mathrm{\&alpha;}}_{14})\end{array}\right.---\left(6\right)$

In the formula, b _{1_1}Be the first-harmonic content of first rectification unit 1, b _{1_2}Be the first-harmonic content of second rectification unit 2, b ₁Be the first-harmonic content sum of first rectification unit (1) and second rectification unit (2), b _nBe the nth harmonic content sum of two rectification units, α ₁, α ₂, α ₃, α ₄, α ₅, α ₆, α ₇Be the switching angle of first rectification unit (1), α ₈, α ₉, α ₁₀, α ₁₁, α ₁₂, α ₁₃, α ₁₄It is the switching angle of second rectification unit (2).

5. electric railway train traction commutation system according to claim 1 is optimized modulator approach; It is characterized in that; The real-time control method of described pair of closed loop PWM rectification algorithm comprises: outer shroud is controlled DC bus-bar voltage according to set-point; DC bus-bar voltage is carried out outer shroud control, and interior ring carries out closed-loop control according to the definite given electric current of outer shroud output to the current inner loop of rectification unit; And comprise that the compensation of power feedforward link, electric voltage feed forward link compensate; In the pulse generation link, through the power device dead band is caused that wave distortion compensates, when sending into the pulse generation unit; Introduce the pulsewidth compensation tache; And obtain voltage amplitude and phase place according to the closed-loop control link, through the online switching angle that searches, by the trigger impulse of the controller output corresponding power device of single-phase rectifier system; The work of driving rectifier, digital control delayed impact is eliminated in the adjustment compensation.

6. electric railway train traction commutation system according to claim 5 is optimized modulator approach; It is characterized in that: described that switching angle is carried out the method for dead area compensation is following: according to the moment and the mode of switch triggering; In conjunction with current direction and switching tube state; Switching tube is controlled, realized compensation dead time effect.

7. electric railway train traction commutation system according to claim 5 is optimized modulator approach, and it is characterized in that: described modulated process is following: according to given rectification unit output d-c bus voltage value

The d-c bus voltage value U that obtains with actual measurement _DcIt is poor to subtract each other, and sends into the constant voltage controlling unit, and suing for peace divided by the feedforward compensation amount of voltage effective value with power output P afterwards obtains current amplitude i _Sm: measure net side input ac voltage U simultaneously _s, obtain voltage-phase and voltage given amount through phase-locked loop (PLL), multiply each other with current amplitude, divided by 2 obtain rectification unit (1) Current Control link set-point

The rectification unit input current value i that obtains with actual measurement _S1It is poor to subtract each other, and sends into the current tracking controlling unit, and carries out voltage compensation; With voltage on line side value U _sProportionally after the subtraction calculations, obtain the given voltage of rectification Send into the pulse generation unit, inquiry combines the dynamic response demand simultaneously according to the optimal switching angle that calculated off-line obtains; Carry out the pulsewidth compensation, the final synthetic switching angle that obtains power device is through the trigger impulse link; Produce trigger impulse 1, drive rectification unit (1) work.

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