CN102891500B - Parallel control method of three-phase two-level inverter with isolation transformers - Google Patents
Parallel control method of three-phase two-level inverter with isolation transformers Download PDFInfo
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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
Technical field
The present invention is mainly concerned with inverter parallel and controls design field, refers in particular to a kind of three-phase two-level inverter control method for parallel with isolating transformer.
Background technology
Take motor train unit auxiliary power supply system as example, as a part for 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 current 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 redundancy, can be by 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 between inversion module, interconnection line is a lot, and poor reliability, is easily disturbed, and is difficult to expansion, and control unit computing is complicated.No control interconnection inverter parallel is controlled and is made parallel system simple in structure, and antijamming capability is strong, is easy to expansion.When an inverter breaks down, other inverters still can normally move, and continue as auxiliary AC load power supply, and it still can normally be worked, and have increased the reliability of system.Meanwhile, 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 is controlled and is failed and really realizes " 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 is just: the technical problem existing for prior art, 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 three-phase two-level inverter control method for parallel with isolating transformer, the steps include:
1. each subordinate inverter is connected with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, then the assistant load that exchanges of supplying with in motor train unit through isolating transformer step-down and filtering is used; The inferior limit of described isolating transformer is connected with the bus in 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 filtering processing;
3. by droop characteristic algorithm, produce the given signal of voltage magnitude and the given signal of frequency of described subordinate inverter sharing control;
4. by voltage close loop, control the three-phase alternating current that makes described subordinate inverter output certain voltage amplitude and frequency with Frequency servo.
As a further improvement on the present invention:
2. described step is by the line voltage on isolating transformer time limit is converted to former avris, and in former avris estimation subordinate inverter power output, its idiographic flow is:
2.1 amplitudes conversions: the design no-load voltage ratio K by the amplitude Ud of the line voltage on isolating transformer time limit and Uq by isolating transformer converts former avris;
2.2 phase places conversions: isolating transformer time sideline voltage U ab and Ubc are carried out phase-locked, obtain time phase theta of sideline voltage; Then, according to the design parameter of isolating transformer, extrapolate the phase difference θ of former sideline voltage, obtain the phase place of former sideline voltage
2.3 reduce former sideline voltage: former sideline voltage magnitude UD, the UQ and the phase place that obtain
by coordinate transform, convert three-phase voltage to;
The power output estimation of 2.4 subordinate inverter:
Active-power P=u
ai
a+ u
bi
b+ u
ci
c, i wherein
ai
bi
cfor the former sideline electric current of isolating transformer, u
au
bu
cformer limit phase voltage for isolating transformer;
Reactive power
i wherein
ai
bi
cfor 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
0for output voltage frequency and the amplitude of subordinate inverter when the zero load.
When carrying out Parallel Control, at the beginning of startup, subordinate inverter of host computer assigned at random is as main frame inverter and send starting command to main frame, the three-phase alternating voltage of stable output after host-initiated; After the auxiliary contactor closing on this power supply branch road, three-phase alternating voltage, give bus, be now connected to a collection of dead load on bus immediately electric starting working, the three-phase voltage that other subordinate inverter gathers on bus simultaneously carries out phase-locked; Host computer sends starting command to other subordinate inverter after the normal startup of judgement main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, makes the voltage magnitude of its output substantially consistent with busbar voltage with phase place; The auxiliary contactor closing on other subordinate inverter branch road, completes the parallel connection output of many subordinate inverter; After this load contactor that in batches closes again drops into loaded work piece.
When 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 Uds and Uq by coordinate transform three phase sine line voltage transitions with Ubc; The coordinate transform formula of amplitude principle of invariance is as follows:
Wherein, θ is given frequency f
0by integration, add up and obtain, and within it is limited in to 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 proportional integral regulating error with the Ud and the Uq that calculate by coordinate transform, adjuster output Vd and two error components of Vq, then by coordinate transform, error component is transformed into rest frame from rotating coordinate system:
The U obtaining
αand U
βas the input of Using dSPACE of SVPWM algorithm, by Using dSPACE of SVPWM algorithm output modulating pulse, controlled the break-make of 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 system hardware cost simultaneously.
2, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, be that three-phase two-level inverter based on isolating transformer (inferior linear filter electric capacity) is topological parallel control technology scheme, be applicable to 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 DC side high voltage to be directly modulated into the auxiliary AC load voltage used of stable applicable vehicle.The present invention adopts isolating transformer just can by step-down, transformer time polygonal voltage be controlled within the voltage range that is applicable to load use (such as 380V or 440V etc.) at an easy rate.
3, the three-phase two-level inverter control method for parallel with isolating transformer of the present invention, due to the introducing of isolating transformer, causes the output power value estimation of each inverter that variation has occurred; For the computational methods of the instantaneous output of inverter, higher than fourier series algorithm real-time in the present invention.What the existing estimation for inverter power output all adopted is electric current and voltage to be obtained respectively to the coefficient of first order of 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, 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 controls and have impact for real-time.And the present invention adopts the estimated value of instantaneous active power and reactive power calculating method real-time update power, can meet real-time and 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) adopting 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 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 power output and the output current of each inverter in parallel system and divide equally.This control mode has been broken away from the transmission signal line between each inverter, make parallel system simple in structure, antijamming capability is strong, is easy to expand inverter number of units in parallel, realize modularized design completely, the hardware and software design of total each module of parallel system is identical.
Accompanying drawing explanation
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 present invention's schematic diagram that the auxiliary change of subsidiary engine is controlled in concrete application example.
Fig. 8 is the calculating control schematic diagram that the present invention converts inferior sideline voltage former limit in concrete application example.
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 is connected with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, then the assistant load that exchanges of supplying with in motor train unit through isolating transformer step-down and filtering is used; The inferior limit of described isolating transformer is connected with the bus in motor train unit by auxiliary contactor.
Referring to Fig. 2, for the present invention forms the schematic diagram of the high-power subordinate inverter parallel system of motor train unit in concrete application example.In this example, have four subordinate inverter (can have in theory N inverter parallel) parallel connection, they are respectively by different four-quadrant circuit output (Ud1~Ud4) power supplies, then by the adjusting of subordinate inverter separately, direct current is modulated into the alternating current with certain amplitude and frequency, pass through again isolating transformer step-down and filtering, can be for the interchange assistant load in motor train unit.Isolating transformer time limit is connected with bus by auxiliary contactor, and the auxiliary contactor that closes can be delivered to alternating current on bus, disconnects auxiliary contactor Ze Bagai road subordinate inverter power supply branch road and bus and separates.In motor train unit, have three-phase and single phase alternating current (A.C.) assistant load, they are connected with bus by load contactor separately, the load power taking from bus of load contactor of closing, load dead electricity of disconnecting consumers contactor.From system schematic, can find out, apply after method of the present invention, between each subordinate inverter, without any rigid line, connect, without any control data transmission, the data that utilization sampling itself is calculated are completely carried out droop characteristic control; That is, mutual without any holding wire between each subordinate inverter power supply branch road, reality is " no control interconnection parallel system ".The present invention adopts after no control interconnection Parallel Control, and subordinate inverter expansion in parallel is convenient, system configuration is simple, and after expansion, controlling software can directly transplanting, and without modification, 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 is easy to by step-down, isolating transformer time polygonal voltage is controlled within the voltage range that is applicable to 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 filtering processing.The present invention adopts the estimated value of instantaneous active power and reactive power calculating method real-time update power, can meet real-time and control requirement.
3, by droop characteristic algorithm, produce the given signal of voltage magnitude and the given signal of frequency of subordinate inverter sharing control.
4, by voltage close loop, control and Frequency servo makes 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 startup, subordinate inverter of host computer assigned at random is as main frame inverter and send starting command to main frame, the three-phase alternating voltage of stable output after host-initiated; After the auxiliary contactor closing on this power supply branch road, three-phase alternating voltage, give bus, be now connected to a collection of dead load on bus immediately electric starting working, the three-phase voltage that other subordinate inverter gathers on bus simultaneously carries out phase-locked; Host computer sends starting command to other subordinate inverter after the normal startup of judgement main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, makes the voltage magnitude of its output substantially consistent with busbar voltage with phase place; The auxiliary contactor closing on other subordinate inverter branch road, completes 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.
Separate unit subordinate inverter need to possess the three-phase alternating current of the certain effective value of having of stable output and frequency.When controller receives after 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 Uds and Uq by coordinate transform three phase sine line voltage transitions with Ubc.
The coordinate transform formula of amplitude principle of invariance is as follows:
Wherein, θ is given frequency f
0by integration, add up and obtain, and within it is limited in to 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 output three-phase voltage is 380V,
given
with
value is carried out respectively PI adjusting (proportional integral regulating error) with the Ud and the Uq that calculate by coordinate transform, 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:
The U calculating
αand U
βinput as SVPWM (Using dSPACE of SVPWM) algorithm.SVPWM algorithm can adopt seven segmentation space voltage vector asynchronous modulation algorithm in engineering application.
The break-make of subordinate inverter switching tube is controlled in SVPWM algorithm output modulating pulse, and inversion goes out the voltage of certain amplitude and frequency.It is electric that the auxiliary contactor that closes obtains bus, and the assistant load fixedly hanging on bus is started working.
Phase-locked control when two, subsidiary engine starts.
After main frame stable operation, subsidiary engine starts the three-phase line voltage on bus to carry out software phlase locking.
Phase-locked for 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 d axle with
phase relation.Work as u
sqduring > 0, d axle lags behind
should increase signal frequency; Work as u
sqduring < 0, d axle is leading
should reduce signal frequency; Work as u
sq=0 o'clock, d axle with
homophase.Therefore can be by controlling 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 through above formula (1), convert Ud* and Uq* to.By controlling 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 being obtained by formula (2) forms closed loop as the input of above formula (1) again simultaneously.Like this, the θ calculating is just consistent with bus line voltage.
When subsidiary engine receives after the starting command that host computer passes down, judgement θ starts subsidiary engine at 0 o'clock, guarantees that its output is consistent with the phase place of busbar voltage, completes 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: the output phase angle that in coordinate transform, θ used is PLL, guarantees that subsidiary engine output line voltage phase place is consistent with 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 droop control characteristic realizes.
Because line voltage sensor must be arranged on isolating transformer time limit with the voltage waveform after seizure filtering and for real-time control; And because system considers wire laying mode, output line current sensor cannot voltage sensor be arranged on the same side of isolating transformer.This has just brought certain difficulty to the estimation of subordinate inverter power output.
Therefore, the method that the present invention takes is: time sideline voltage is converted to former avris, in the power output of former avris estimation subordinate inverter.As shown in Figure 8, for inferior sideline voltage being converted to the calculating on former limit, control schematic diagram.
2.1 amplitude conversions: 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 places conversions: 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, according to the design parameter of isolating transformer, extrapolate the phase difference θ of former sideline voltage, 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
by coordinate transform, convert three-phase voltage to.Had original edge voltage and electric current, 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
cfor the former sideline of isolating transformer electric current, u
au
bu
cfor the former limit of isolating transformer phase voltage.
Reactive power
Wherein, i
ai
bi
cfor the former sideline of isolating transformer electric current, u
abu
bcu
cafor the former sideline of isolating transformer voltage.
Because auxiliary change output voltage is modulating pulse wave, therefore the harmonic wave that former sideline electric current exists can cause the meritorious idle value that the former avris of isolating transformer calculates to have larger fluctuation, therefore in preferred embodiment, can also add and conventionally in engineering such as single order low-pass filtering and average value filtering scheduling algorithm, reduce comparatively real performance number.
Four, droop control algorithm.
The variation of inverter active power of output is mainly subject 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.
Phase place droop characteristic and the voltage droop characteristic shown in Figure 10 are as shown in Figure 9 known, when module active power of output is larger, by its phase place of droop control, also will reduce, thereby cause that active power reduces, and reaches active power balance; When 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 in the present invention in droop characteristic and Q are performance number 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, for main frame inverter droop characteristic, control schematic diagram, controlling set-point is the output that voltage magnitude and frequency are droop characteristic.
As shown in figure 12, for auxiliary machine inverter droop characteristic is controlled schematic diagram, different from main frame, it usings the state that cut-offs of auxiliary contactor as the sign before and after grid-connected inverters.Before grid-connected (or when auxiliary contactor disconnects), controlling set-point is voltage magnitude and the frequency of phase-locked loop output; After grid-connected (or when auxiliary contactor is closed), controlling set-point is voltage magnitude and the frequency of droop characteristic output.
Below be only the preferred embodiment of the present invention, protection scope of the present invention is also not only confined to above-described embodiment, and all technical schemes belonging under thinking of the present invention all belong to protection scope of the present invention.It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principles of the present invention, should be considered as protection scope of the present invention.
Claims (4)
1. with a three-phase two-level inverter control method for parallel for isolating transformer, it is characterized in that, step is:
1. each subordinate inverter is connected with an isolating transformer: the adjusting by subordinate inverter is modulated into direct current the alternating current with certain amplitude and frequency, then the assistant load that exchanges of supplying with in motor train unit through isolating transformer step-down and filtering is used; The inferior limit of described isolating transformer is connected with the bus in 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 filtering processing;
3. by droop characteristic algorithm, produce the given signal of voltage magnitude and the given signal of frequency of described subordinate inverter sharing control;
4. by voltage close loop, control the three-phase alternating current that makes described subordinate inverter output certain voltage amplitude and frequency with Frequency servo;
2. described step is by the line voltage on isolating transformer time limit is converted to former avris, and in former avris estimation subordinate inverter power output, its idiographic flow is:
2.1 amplitudes conversions: the design no-load voltage ratio K by the amplitude Ud of the line voltage on isolating transformer time limit and Uq by isolating transformer converts former avris;
2.2 phase places conversions: isolating transformer time sideline voltage U ab and Ubc are carried out phase-locked, obtain time phase theta of sideline voltage; Then, according to the design parameter of isolating transformer, extrapolate the phase difference △ θ of former sideline voltage, obtain the phase place of former sideline voltage
2.3 reduce former sideline voltage: former sideline voltage magnitude UD, the UQ and the phase place that obtain
by coordinate transform, convert three-phase voltage to;
The power output estimation of 2.4 subordinate inverter:
Active-power P=u
ai
a+ u
bi
b+ u
ci
c, i wherein
ai
bi
cfor the former sideline electric current of isolating transformer, u
au
bu
cformer limit phase voltage for isolating transformer;
Reactive power
i wherein
ai
bi
cfor the former sideline of isolating transformer electric current, u
abu
bcu
caformer sideline voltage for isolating transformer.
2. the three-phase two-level inverter control method for parallel with isolating transformer according to claim 1, 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
0for output voltage frequency and the amplitude of subordinate inverter when the zero load.
3. according to the three-phase two-level inverter control method for parallel with isolating transformer described in any one in claim 1~2, it is characterized in that: when carrying out Parallel Control, at the beginning of startup, subordinate inverter of host computer assigned at random is as main frame inverter and send starting command to main frame, the three-phase alternating voltage of stable output after host-initiated; After the auxiliary contactor closing on this power supply branch road, three-phase alternating voltage, give bus, be now connected to a collection of dead load on bus immediately electric starting working, the three-phase voltage that other subordinate inverter gathers on bus simultaneously carries out phase-locked; Host computer sends starting command to other subordinate inverter after the normal startup of judgement main frame, other subordinate inverter is chosen in busbar voltage phase place place at zero point and starts after phase-locked success, makes the voltage magnitude of its output substantially consistent with busbar voltage with phase place; The auxiliary contactor closing on other subordinate inverter branch road, completes the parallel connection output of many subordinate inverter; After this load contactor that in batches closes again drops into loaded work piece.
4. the three-phase two-level inverter control method for parallel with isolating transformer according to claim 3, it is characterized in that, when 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 Uds and Uq by coordinate transform three phase sine line voltage transitions with Ubc; The coordinate transform formula of amplitude principle of invariance is as follows:
Wherein, θ is given frequency f
0by integration, add up and obtain, and within it is limited in to 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 proportional integral regulating error with the Ud and the Uq that calculate by coordinate transform, adjuster output Vd and two error components of Vq, then by coordinate transform, error component is transformed into rest frame from rotating coordinate system:
The U obtaining
αand U
βas the input of Using dSPACE of SVPWM algorithm, by Using dSPACE of SVPWM algorithm output modulating pulse, controlled the break-make of subordinate inverter switching tube, inversion goes out the voltage of certain amplitude and frequency.
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