CN102891500A - Parallel control method of three-phase two-level inverter with isolation transformers - Google Patents

Abstract

The invention discloses a parallel control method of a three-phase two-level inverter with isolation transformers. The parallel control method comprises the steps of: (1) connecting each auxiliary inverter with one isolation transformer, to be specific, modulating direct-current into alternating-current power with certain amplitude and frequency by the regulation of the auxiliary inverters, and then carrying out voltage reduction and filtering on the alternating-current by the isolation transformers to supply the power to alternating-current auxiliary loads on a motor train unit for use; (2) sampling the output line current of the auxiliary inverters and the liner voltage of secondary sides of the isolation transformers, calculating active power and passive power under the instantaneous output of the auxiliary inverters and carrying out filtering treatment; (3) generating given voltage amplitude signals and given frequency signals for current-sharing control of the auxiliary inverters by using a drooping characteristic algorithm; and (4) enabling the auxiliary inverters to output three-phase alternating-current power with certain voltage amplitude and frequency by means of voltage closed-loop control and frequency closed-loop control. The parallel control method has the advantages of simple principle, easiness for implementation, capabilities of improving antijamming capability of the system and greatly enhancing system reliability, and simultaneously reducing system hardware cost, and the like.

Description

A kind of three-phase two-level inverter control method for parallel with isolating transformer

Technical field

The present invention is mainly concerned with inverter parallel control design field, refers in particular to a kind of three-phase two-level inverter control method for parallel with isolating transformer.

Background technology

Take the motor train unit auxiliary power supply system as example, as the part of motor train unit auxiliary power supply system, the single-phase or three-phase alternating current that subordinate inverter is mainly used to provide stable exchanges assistant load for air-conditioning unit, ventilation unit, air compressor machine, electric heater, guest room illumination etc.The subordinate inverter of present most vehicles is unit operation, and capacity is larger, and reliability is not high.Therefore, in order to improve the power supply reliability of motor train unit auxiliary power supply system, for auxiliary power supply provides redundant, can be with many subordinate inverter parallel runnings.

Existing inverter parallel control method mainly contains: centralized control formula, principal and subordinate control formula, decentralized control formula and no control interconnections formula.First three plants the common shortcoming of control method is that interconnection line is a lot of between the inversion module, and poor reliability easily is disturbed, and is difficult to expansion, and the control unit computing is complicated.The control of no control interconnection inverter parallel is so that parallel system is simple in structure, and antijamming capability is strong, is easy to expansion.When an inverter broke down, other inverters still can normally move, and continued as auxiliary AC load power supply, and it still can be worked, and had increased the reliability of system.Simultaneously, many inverter parallels have reduced the output capacity requirement of single inverter, and then have alleviated the stress of power device of inverter.But existing no control interconnection inverter parallel control also fails really to realize " no control interconnections ", and control algolithm is very complicated, implements very difficult.

Summary of the invention

The technical problem to be solved in the present invention just is: for the technical problem of prior art existence, the invention provides a kind of principle simple, easily realize, can improve the antijamming capability of system, greatly strengthen the reliability of system, also reduce the three-phase two-level inverter control method for parallel with isolating transformer of system hardware cost simultaneously.

For solving the problems of the technologies described above, the present invention by the following technical solutions:

A kind of three-phase two-level inverter control method for parallel with isolating transformer the steps include:

1. each subordinate inverter links to each other with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, and the assistant load that exchanges of supplying with on the motor train unit through isolating transformer step-down and filtering again uses; The inferior limit of described isolating transformer is connected with bus on the motor train unit by auxiliary contactor;

The line voltage on the output line electric current of the described subordinate inverter of 2. sampling and isolating transformer time limit calculates instantaneous active power of output and the reactive power of described subordinate inverter and carries out the filtering processing;

3. produce the given signal of voltage magnitude and the given signal of frequency of described subordinate inverter sharing control by the droop characteristic algorithm;

4. by voltage close loop control and Frequency servo so that the three-phase alternating current of described subordinate inverter output certain voltage amplitude and frequency.

As a further improvement on the present invention:

2. described step is by the line voltage on isolating transformer time limit is converted former avris, and in former avris estimation subordinate inverter power output, its idiographic flow is:

2.1 amplitude conversion: the amplitude Ud of the line voltage on isolating transformer time limit and the Uq design no-load voltage ratio K by isolating transformer is converted former avris;

2.2 phase place conversion: isolating transformer time sideline voltage U ab and Ubc are carried out phase-locked, obtain time phase theta of sideline voltage; Then, extrapolate the phase difference θ of former sideline voltage according to the design parameter of isolating transformer, obtain the phase place of former sideline voltage

2.3 former sideline voltage is reduced: former sideline voltage magnitude UD, the UQ and the phase place that obtain

Convert three-phase voltage to by coordinate transform;

2.4 the power output of subordinate inverter estimation:

Active-power P=u _ai _a+ u _bi _b+ u _ci _c, i wherein _ai _bi _cBe the former sideline electric current of isolating transformer, u _au _bu _cFormer limit phase voltage for isolating transformer;

Reactive power

I wherein _ai _bi _cBe the former sideline of isolating transformer electric current, u _Abu _Bcu _CaFormer sideline voltage for isolating transformer.

Described step 3. in, the governing equation of droop characteristic algorithm is: the given signal f=f of frequency ₀-mP, the given signal V=V of voltage magnitude ₀-nQ, wherein f ₀And V ₀Be output voltage frequency and the amplitude of subordinate inverter when the zero load.

When carrying out Parallel Control, at the beginning of the startup, subordinate inverter of host computer assigned at random is sent starting command as the main frame inverter and to main frame, the three-phase alternating voltage of stable output after the host-initiated; Close and give bus three-phase alternating voltage behind the auxiliary contactor on this power supply branch road, a collection of dead load that be connected on the bus this moment must be established beginning work by cable immediately, and the three-phase voltage that gathers on bus of other subordinate inverter carries out phase-locked simultaneously; Host computer sends starting command to other subordinate inverter after judging the normal startup of main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, so that the voltage magnitude of its output is basically consistent with busbar voltage with phase place; Close auxiliary contactor on other subordinate inverter branch road is finished the parallel connection output of many subordinate inverter; After this load contactor that in batches closes again drops into loaded work piece.

When the main frame subordinate inverter started, two voltage sensors on auxiliary transformer time limit gathered respectively Uab and the Ubc line instantaneous voltage of three-phase electricity, as the input variable of control algolithm part; Uab becomes two DC voltage component Ud and Uq to three phase sine line voltage transitions with Ubc by coordinate transform; The coordinate transform formula of amplitude principle of invariance is as follows:

$\left[\begin{array}{c}{U}_d\\ U_q\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\θ}& \sin (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \sin (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\\ \cos \mathrm{\θ}& \cos (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \cos (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{U}_{\mathrm{ab}}\\ U_{\mathrm{bc}}\\ U_{\mathrm{ca}}\end{array}\right],$ U _ca＝-(U _ab+U _bc)

Wherein, θ is given frequency f ₀Obtain by integration is cumulative, and it is limited within 0～2 π θ=∫ (f ₀* 2 π) dt;

With

DC voltage component for given wherein makes

Value is for wishing the three-phase voltage amplitude of output; Given

With

Value is carried out respectively the proportional integral regulating error with the Ud and the Uq that calculate by coordinate transform, and adjuster output Vd and two error components of Vq are transformed into rest frame to error component from rotating coordinate system by coordinate transform again:

$\left[\begin{array}{c}{U}_{\mathrm{\α}}\\ U_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{V}_d\\ V_q\end{array}\right]$

The U that obtains _αAnd U _βAs the input of Using dSPACE of SVPWM algorithm, by the break-make of Using dSPACE of SVPWM algorithm output modulating pulse control subordinate inverter switching tube, inversion goes out the voltage of certain amplitude and frequency.

Compared with prior art, the invention has the advantages that:

1, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, principle is simple, easy to operate, easily realize and promote; After application, can improve the antijamming capability of system, greatly strengthen the reliability of system, also reduce the system hardware cost simultaneously.

2, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, be based on the three-phase two-level inverter of isolating transformer (inferior linear filter electric capacity) for the parallel control technology scheme of topology, be applicable to the high voltage large capcity auxiliary system.As the high-power subordinate inverter parallel system of motor train unit, its dc voltage is very high (such as 3500V) often, existing main circuit topology does not have the step-down filtering of isolating transformer, and inverter is difficult to the DC side high voltage directly is modulated into the auxiliary used voltage of AC load of stable suitable vehicle.The present invention adopts isolating transformer just can be controlled at transformer time polygonal voltage within the voltage range that is fit to the load use (such as 380V or 440V etc.) by step-down at an easy rate.

3, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention is because the introducing of isolating transformer causes the output power value estimation of each inverter that variation has occured; For the computational methods of the instantaneous output of inverter, higher than fourier series algorithm real-time among the present invention.It is existing that what all adopt for the estimation of inverter power output is the coefficient of first order of electric current and voltage being obtained respectively Fourier, thus the active power of extrapolating and reactive power.But the algorithm of the coefficient of first order of Fourier is to do integral operation within a primitive period, and that is to say need to be through a voltage or current cycle, and the active power of estimation and reactive power value just can upgrade, and this is influential for real-time control.And the present invention adopts the estimated value of instantaneous active power and reactive power calculating method real-time update power, can satisfy real-time control requirement.

4, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, the high-power auxiliary three-phase inverter parallel system of band isolating transformer (inferior linear filter electric capacity) that adopts is based on jumbo inverter system (such as 300 kilovolt-amperes), therefore the switch of inverter can very high (not being about 800Hz), but the total harmonic distortion of inverter output voltage can be controlled in 5%.The characteristic of high voltage large capcity inverter has determined that the switch control frequency is lower, is about 800Hz, and the total harmonic distortion of inverter output voltage can be controlled in 5%.

5, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, adopt the droop characteristic algorithm of each inverter active power of output and reactive power to regulate output voltage and the frequency of inverter separately given, realize that power output and the output current of each inverter in the parallel system divided equally.This control mode has been broken away from the transmission signal line between each inverter, so that parallel system is simple in structure, antijamming capability is strong, is easy to expand inverter number of units in parallel, realize modularized design fully, the hardware and software design of total each module of parallel system is identical.

Description of drawings

Fig. 1 is the schematic flow sheet of the inventive method.

Fig. 2 is the schematic diagram of the parallel control system of the present invention in concrete application example.

The schematic flow sheet of Fig. 3 when to be the present invention carry out Parallel Control in concrete application example.

Control schematic diagram during Fig. 4 main frame inverter startup that is the present invention in concrete application example.

Fig. 5 is the phasor difference phase place schematic diagram of the present invention in concrete application example.

Fig. 6 is the control schematic diagram of the present invention's three-phase software phase-lock loop (PLL) in concrete application example.

Fig. 7 is the schematic diagram of the present invention's auxiliary change control of subsidiary engine in concrete application example.

Fig. 8 is the present invention converts inferior sideline voltage former limit in concrete application example calculating control schematic diagram.

Fig. 9 is phase place droop characteristic schematic diagram.

Figure 10 is voltage droop characteristic schematic diagram.

Figure 11 is the control schematic diagram of the present invention's main frame inverter droop characteristic in concrete application example.

Figure 12 is the control schematic diagram of the present invention's auxiliary machine inverter droop characteristic in concrete application example.

Embodiment

Below with reference to Figure of description and specific embodiment the present invention is described in further details.

As shown in Figure 1, the three-phase two-level inverter control method for parallel of band isolating transformer of the present invention the steps include:

1, each subordinate inverter links to each other with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, and the assistant load that exchanges of supplying with on the motor train unit through isolating transformer step-down and filtering again uses; The inferior limit of described isolating transformer is connected with bus on the motor train unit by auxiliary contactor.

Referring to Fig. 2, in concrete application example, form the schematic diagram of the high-power subordinate inverter parallel system of motor train unit for the present invention.Have four subordinate inverter (N inverter parallel can be arranged in theory) parallel connection in this example, they are respectively by different four-quadrant circuit output (Ud1～Ud4) power supply, then direct current is modulated into the alternating current with certain amplitude and frequency by the adjusting of subordinate inverter separately, pass through again isolating transformer step-down and filtering, can be for the interchange assistant load on the motor train unit.Isolating transformer time limit is connected with bus by auxiliary contactor, and the auxiliary contactor that closes then can be delivered to alternating current on the bus, disconnects auxiliary contactor and then this road subordinate inverter power supply branch road and bus is separated.Three-phase and single phase alternating current (A.C.) assistant load are arranged on the motor train unit, and their load contactors by separately link to each other with bus, the then load power taking from the bus of load contactor of closing, then load dead electricity of disconnecting consumers contactor.From system schematic, can find out, use method of the present invention after, connect without any rigid line between each subordinate inverter, without any control data transmission, the data of utilization sampling calculating itself are carried out droop characteristic and are controlled fully; That is, mutual without any holding wire between each subordinate inverter power supply branch road, reality is " no control interconnection parallel system ".After the present invention adopted the no control interconnection Parallel Control, subordinate inverter expansion in parallel was convenient, system configuration is simple, but expanded rear control software directly transplanting, need not to revise, and it is highly consistent that hardware-software reaches.

As the high-power subordinate inverter parallel system of motor train unit, its dc voltage is very high (such as 3500V) often.The present invention then is easy to by step-down isolating transformer time polygonal voltage is controlled within the voltage range that is fit to the load use (such as 380V or 440V etc.) by band isolating transformer (inferior linear filter electric capacity) is set.

In preferred embodiment, the present invention can adopt jumbo subordinate inverter (such as 300 kilovolt-amperes) according to actual needs, therefore the switch of subordinate inverter can very high (not being about 800Hz), but the total harmonic distortion of subordinate inverter output voltage can be controlled in 5%.

2, the line voltage on the output line electric current of sampling subordinate inverter and isolating transformer time limit calculates instantaneous active power of output and the reactive power of subordinate inverter and carries out the filtering processing.The present invention adopts the estimated value of instantaneous active power and reactive power calculating method real-time update power, can satisfy real-time control requirement.

3, produce the given signal of voltage magnitude and the given signal of frequency of subordinate inverter sharing control by the droop characteristic algorithm.

4, by voltage close loop control and Frequency servo so that the three-phase alternating current of subordinate inverter output certain voltage amplitude and frequency.

The present invention is in concrete application example, and the flow process when carrying out Parallel Control as shown in Figure 3.At the beginning of the startup, subordinate inverter of host computer assigned at random is sent starting command as the main frame inverter and to main frame, the three-phase alternating voltage of stable output after the host-initiated; Close and give bus three-phase alternating voltage behind the auxiliary contactor on this power supply branch road, a collection of dead load that be connected on the bus this moment must be established beginning work by cable immediately, and the three-phase voltage that gathers on bus of other subordinate inverter carries out phase-locked simultaneously; Host computer sends starting command to other subordinate inverter after judging the normal startup of main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, so that the voltage magnitude of its output is basically consistent with busbar voltage with phase place; Close auxiliary contactor on other subordinate inverter branch road is finished the parallel connection output of many subordinate inverter; After this load contactor that in batches closes again drops into loaded work piece.

As from the foregoing, in concrete application example of the present invention, when carrying out Parallel Control, can be divided into four steps:

One, main frame inverter startup operation.

The separate unit subordinate inverter need to possess the three-phase alternating current of the certain effective value of having of stable output and frequency.After controller receives the starting command that host computer passes down, start working; As shown in Figure 4, be the control schematic diagram of main frame inverter startup.

Two voltage sensors on auxiliary transformer time limit are used for respectively gathering Uab and the Ubc line instantaneous voltage of three-phase electricity, as the input variable of control algolithm part.Uab becomes two DC voltage component Ud and Uq to three phase sine line voltage transitions with Ubc by coordinate transform.

The coordinate transform formula of amplitude principle of invariance is as follows:

$\left[\begin{array}{c}{U}_d\\ U_q\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\θ}& \sin (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \sin (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\\ \cos \mathrm{\θ}& \cos (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \cos (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{U}_{\mathrm{ab}}\\ U_{\mathrm{bc}}\\ U_{\mathrm{ca}}\end{array}\right],$ U _ca＝-(U _ab+U _bc) (1)

Wherein, θ is given frequency f ₀Obtain by integration is cumulative, and it is limited within 0～2 π.Computing formula is as follows:

θ＝∫(f ₀×2π)dt (2)

With

DC voltage component for given wherein makes

Value is for wishing the three-phase voltage amplitude of output, if wish that the output three-phase voltage is 380V, then

Given With Value is carried out respectively PI with the Ud that calculates by coordinate transform and Uq and is regulated (proportional integral regulating error), adjuster output Vd and two error components of Vq, by coordinate transform error component is transformed into rest frame from rotating coordinate system again, formula is as follows:

$\left[\begin{array}{c}{U}_{\mathrm{\α}}\\ U_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{V}_d\\ V_q\end{array}\right]---\left(3\right)$

The U that calculates _αAnd U _βInput as SVPWM (Using dSPACE of SVPWM) algorithm.The seven segmentation space voltage vector asynchronous modulation algorithm that the SVPWM algorithm can adopt engineering to use.

The break-make of SVPWM algorithm output modulating pulse control subordinate inverter switching tube, inversion goes out the voltage of certain amplitude and frequency.Close auxiliary contactor so that bus gets electricly, and the assistant load that fixedly hangs on the bus is started working.

Phase-locked control when two, subsidiary engine starts.

After the main frame stable operation, subsidiary engine begins the three-phase line voltage on the bus is carried out software phlase locking.

Phase-locked for the bus three-phase voltage, phase information that must comprehensive three-phase voltage.As shown in Figure 5: work as busbar voltage

Amplitude when constant,

Q axle component u _SqReflected the d axle with

Phase relation.Work as u _Sq＞0 o'clock, the d axle lagged behind Should increase signal frequency; Work as u _Sq＜0 o'clock, the d axle was leading Should reduce signal frequency; Work as u _Sq=0 o'clock, the d axle with

Homophase.Therefore can be by control u _Sq, make u _Sq=0 realizes homophase between the two.

Therefore, the control of three-phase voltage software phlase locking signal as shown in Figure 6.UAB and UBC are the three-phase line voltage instantaneous value that bus bar side collects, and convert Ud* and Uq* to through following formula (1).By control Uq*=0, make PI regulation output regulating error frequency w _Con, add the natural frequency w of three-phase line voltage _Ff, obtain target frequency w ^*, the θ that is obtained by formula (2) simultaneously forms closed loop as the input of following formula (1) again.Like this, the θ that calculates just is consistent with bus line voltage.

After subsidiary engine receives the starting command that host computer passes down, judge that θ started subsidiary engine at 0 o'clock, guarantee that its output is consistent with the phase place of busbar voltage, finish phase-locked.The control signal of subsidiary engine as shown in Figure 7.

The control technology scheme of subsidiary engine is substantially consistent with main frame, just amplitude and frequency is given is provided by phase-locked loop: used θ is the output phase angle of PLL in the coordinate transform, guarantees that subsidiary engine output line voltage phase place is consistent with the busbar voltage phase place; Voltage magnitude is given as Ud* and the Uq* of PLL output, guarantees that subsidiary engine output line voltage amplitude is consistent with busbar voltage.

Three, the estimation of inverter power output.

Accurately the power output of estimation subordinate inverter is the precondition that the droop control characteristic realizes.

Because must being installed in isolating transformer time limit, the line voltage sensor also is used in real time control to catch filtering voltage waveform afterwards; And because system considers wire laying mode, the output line current sensor can't voltage sensor be installed in the same side of isolating transformer.This has brought certain difficulty with regard to the estimation of giving the subordinate inverter power output.

Therefore, the method that the present invention takes is: time sideline voltage is converted former avris, in the power output of former avris estimation subordinate inverter.As shown in Figure 8, for inferior sideline voltage being converted the calculating control schematic diagram on former limit.

2.1 the amplitude conversion: the amplitude Ud of inferior sideline voltage and Uq (or effective value) convert former limit by the design no-load voltage ratio K of isolating transformer;

2.2 phase place conversion: by above-mentioned software Phase-Lock inferior sideline voltage U ab and Ubc are carried out phase-lockedly, obtain time phase theta of sideline voltage.Then, extrapolate the phase difference θ of former sideline voltage according to the design parameter of isolating transformer, thereby obtain the phase place of former sideline voltage

2.3 former sideline voltage reduction: former sideline voltage magnitude UD, the UQ and the phase place that obtain

Convert three-phase voltage to by coordinate transform.Original edge voltage and electric current have been arranged, and the power output estimation of subordinate inverter can be calculated by Instantaneous Power in Three-phase Circuits is theoretical:

Active-power P=u _ai _a+ u _bi _b+ u _ci _c(4)

Wherein, i _ai _bi _cBe the former sideline of isolating transformer electric current, u _au _bu _cBe the former limit of isolating transformer phase voltage.

Reactive power $Q=\sqrt{1/3}(u_{\mathrm{bc}}{i}_a+u_{\mathrm{ca}}{i}_b+u_{\mathrm{ab}}{i}_c)---\left(5\right)$

Wherein, i _ai _bi _cBe the former sideline of isolating transformer electric current, u _Abu _Bcu _CaBe the former sideline of isolating transformer voltage.

Because auxiliary change output voltage is modulating pulse wave, therefore the harmonic wave of former sideline electric current existence can cause the larger fluctuation of meritorious idle value existence that the former avris of isolating transformer calculates, therefore in preferred embodiment, can also add and commonly usedly on the engineering reduce comparatively real performance number such as single order low-pass filtering and average value filtering scheduling algorithm.

Four, droop control algorithm.

The variation of inverter active power of output mainly is subjected to the impact of output voltage phase place, and the variation of output reactive power is affected by output voltage amplitude mainly.The leading more modules of phase place, the active power of output is larger; The module that amplitude is larger, the reactive power of output is also larger.So the output voltage frequency of control inverter can be controlled active power, the output voltage amplitude of control inverter can be controlled reactive power.Therefore, inverter no control interconnection Parallel Control has just had theoretical support, can adopt the droop characteristic of voltage magnitude and frequency to control, i.e. PQ method, and its governing equation is:

f＝f ₀-mP，V＝V ₀-nQ，

Wherein, f ₀And V ₀Be output voltage frequency and the amplitude of auxiliary change module when zero load.

By phase place droop characteristic shown in Figure 9 and voltage droop characteristic shown in Figure 10 as can be known, when the module active power of output is larger, also will reduce by its phase place of droop control, thereby cause that active power reduces, and reaches active power balance; When the module output reactive power is larger, by sagging algorithm, its amplitude will reduce, and then cause the decline of reactive power, reach reactive balance.

As from the foregoing, P among the present invention in the droop characteristic and Q are performance number and the adjusting of do-it-yourself droop characteristic that each inverter controller calculates oneself, each subordinate inverter is robbed power in sagging adjusting separately, finally reach power stage dynamic equilibrium, thereby realize each subordinate inverter output current-sharing.

As shown in figure 11, be main frame inverter droop characteristic control schematic diagram, the control set-point is that voltage magnitude and frequency are the output of droop characteristic.

As shown in figure 12, be auxiliary machine inverter droop characteristic control schematic diagram, different from main frame is, its with the state that cut-offs of auxiliary contactor as the sign before and after the grid-connected inverters.Before being incorporated into the power networks (or when auxiliary contactor disconnects), the control set-point is voltage magnitude and the frequency of phase-locked loop output; After being incorporated into the power networks (or when auxiliary contactor is closed), the control set-point is voltage magnitude and the frequency of droop characteristic output.

Below only be preferred implementation of the present invention, protection scope of the present invention also not only is confined to above-described embodiment, and all technical schemes that belongs under the thinking of the present invention all belong to protection scope of the present invention.Should be pointed out that for those skilled in the art, the some improvements and modifications not breaking away under the principle of the invention prerequisite should be considered as protection scope of the present invention.

Claims (5)

1. the three-phase two-level inverter control method for parallel with isolating transformer is characterized in that, step is:

1. each subordinate inverter links to each other with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, and the assistant load that exchanges of supplying with on the motor train unit through isolating transformer step-down and filtering again uses; The inferior limit of described isolating transformer is connected with bus on the motor train unit by auxiliary contactor;

The line voltage on the output line electric current of the described subordinate inverter of 2. sampling and isolating transformer time limit calculates instantaneous active power of output and the reactive power of described subordinate inverter and carries out the filtering processing;

3. produce the given signal of voltage magnitude and the given signal of frequency of described subordinate inverter sharing control by the droop characteristic algorithm;

4. by voltage close loop control and Frequency servo so that the three-phase alternating current of described subordinate inverter output certain voltage amplitude and frequency.

2. the three-phase two-level inverter control method for parallel with isolating transformer according to claim 1, it is characterized in that, 2. described step is by the line voltage on isolating transformer time limit is converted former avris, and in former avris estimation subordinate inverter power output, its idiographic flow is:

2.1 amplitude conversion: the amplitude Ud of the line voltage on isolating transformer time limit and the Uq design no-load voltage ratio K by isolating transformer is converted former avris;

2.2 phase place conversion: isolating transformer time sideline voltage U ab and Ubc are carried out phase-locked, obtain time phase theta of sideline voltage; Then, extrapolate the phase difference θ of former sideline voltage according to the design parameter of isolating transformer, obtain the phase place of former sideline voltage

2.3 former sideline voltage is reduced: former sideline voltage magnitude UD, the UQ and the phase place that obtain Convert three-phase voltage to by coordinate transform;

2.4 the power output of subordinate inverter estimation:

Active-power P=u _ai _a+ u _bi _b+ u _ci _c, i wherein _ai _bi _cBe the former sideline electric current of isolating transformer, u _au _bu _cFormer limit phase voltage for isolating transformer;

Reactive power

I wherein _ai _bi _cBe the former sideline of isolating transformer electric current, u _Abu _Bcu _CaFormer sideline voltage for isolating transformer.

3. the three-phase two-level inverter control method for parallel with isolating transformer according to claim 2 is characterized in that, described step 3. in, the governing equation of droop characteristic algorithm is: the given signal f=f of frequency ₀-mP, the given signal V=V of voltage magnitude ₀-nQ, wherein f ₀And V ₀Be output voltage frequency and the amplitude of subordinate inverter when the zero load.

4. the described three-phase two-level inverter control method for parallel with isolating transformer of any one according to claim 1～3, it is characterized in that: when carrying out Parallel Control, at the beginning of the startup, subordinate inverter of host computer assigned at random is sent starting command as the main frame inverter and to main frame, the three-phase alternating voltage of stable output after the host-initiated; Close and give bus three-phase alternating voltage behind the auxiliary contactor on this power supply branch road, a collection of dead load that be connected on the bus this moment must be established beginning work by cable immediately, and the three-phase voltage that gathers on bus of other subordinate inverter carries out phase-locked simultaneously; Host computer sends starting command to other subordinate inverter after judging the normal startup of main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, so that the voltage magnitude of its output is basically consistent with busbar voltage with phase place; Close auxiliary contactor on other subordinate inverter branch road is finished the parallel connection output of many subordinate inverter; After this load contactor that in batches closes again drops into loaded work piece.

5. the three-phase two-level inverter control method for parallel with isolating transformer according to claim 4, it is characterized in that, when the main frame subordinate inverter starts, two voltage sensors on auxiliary transformer time limit gather respectively Uab and the Ubc line instantaneous voltage of three-phase electricity, as the input variable of control algolithm part; Uab becomes two DC voltage component Ud and Uq to three phase sine line voltage transitions with Ubc by coordinate transform; The coordinate transform formula of amplitude principle of invariance is as follows:

$\left[\begin{array}{c}{U}_d\\ U_q\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\θ}& \sin (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \sin (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\\ \cos \mathrm{\θ}& \cos (\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \cos (\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{U}_{\mathrm{ab}}\\ U_{\mathrm{bc}}\\ U_{\mathrm{ca}}\end{array}\right],$ U _ca＝-(U _ab+U _bc)

Wherein, θ is given frequency f ₀Obtain by integration is cumulative, and it is limited within 0～2 π θ=∫ (f ₀* 2 π) dt;

With

DC voltage component for given wherein makes

Value is for wishing the three-phase voltage amplitude of output; Given

With

Value is carried out respectively the proportional integral regulating error with the Ud and the Uq that calculate by coordinate transform, and adjuster output Vd and two error components of Vq are transformed into rest frame to error component from rotating coordinate system by coordinate transform again:

$\left[\begin{array}{c}{U}_{\mathrm{\α}}\\ U_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{V}_d\\ V_q\end{array}\right]$

The U that obtains _αAnd U _βAs the input of Using dSPACE of SVPWM algorithm, by the break-make of Using dSPACE of SVPWM algorithm output modulating pulse control subordinate inverter switching tube, inversion goes out the voltage of certain amplitude and frequency.

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