CN103219745B - Grid-connected inverter control algorithm based on orthogonal sine wave extractor - Google Patents
Grid-connected inverter control algorithm based on orthogonal sine wave extractor Download PDFInfo
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Abstract
The invention discloses a grid-connected inverter control algorithm based on an orthogonal sine wave extractor. The grid-connected inverter control algorithm based on the orthogonal sine wave extractor can be used in control of photovoltaic three-phase grid-connected inverter, a wind-electricity three-phase grid-connected inverter and the like. The invention includes the orthogonal sine wave extractor and a grid-connected inverter current control method based on the orthogonal sine wave extractor. The orthogonal sine wave extractor is achieved through a second order discrete state equation, simultaneously has band-pass filtering and phase shifting action for an input signal and is used for conducting treatment on a sine alternating quantity such as a voltage and a current in grid-connected inverter control. Based on the grid-connected inverter current control method based on the orthogonal sine wave extractor, tracking conducted by three-phase alternating-current feedback on floating which is given by the method is achieved, and the grid-connected inverter control algorithm based on the orthogonal sine wave extractor has strong power grid adaptability, can effectively suppress entry network current harmonics and reduce entry network current total harmonic distortion.
Description
Technical field
The invention belongs to combining inverter control technology field, can be applicable in the grid-connected power generation system such as photovoltaic, wind-powered electricity generation.
Background technology
In recent years, the new forms of energy electric power such as photovoltaic, wind-powered electricity generation network on a large scale, and generation of electricity by new energy accounts for the proportion of gross generation to reach the degree of can not ignore, and continue to rise.If it is not high to enter network electric energy quality, whole electric power system is caused to harmful effect.Stable and the pure new forms of energy that just can make of electric energy of carrying to electrical network really promote the well-being of mankind.Photovoltaic and wind-powered electricity generation etc. generally need be by inverter to electrical network conveying capacities, and this requires inverter to have higher grid adaptability on the one hand, in the situation that Voltage Harmonic is heavier, still can be incorporated into the power networks.On the other hand, the current harmonic content that requires inverter itself to send is low, is unlikely to further to affect electrical network.This just requires combining inverter Current Control to have good performance.
The combining inverter of three-phase full-controlled bridge form has the advantages such as power factor is adjustable, is the general choice of current high-power grid-connected inverting system.This main circuit will be comprised of 6 IGBT and antiparallel diode thereof, and every two IGBT are connected into a bridge.Controller need send control signal to each IGBT, and different drive level duty ratios can make three-phase full-controlled bridge be operated in rectification, inversion, send out idle, inhale the various states such as idle.Although this circuit topology has obtained large-scale application, its control performance need to improve.At present, the current control method of three-phase grid-connected inverter main flow has the proportional plus integral control that adopts under rotating coordinate system and the ratio resonance under rest frame to control two classes.The former utilizes three-phase alternating current amount is the feature of DC quantity under rotating coordinate system, adoption rate integral controller just can be realized the floating of electric current and follow the tracks of, but being each control cycle, its shortcoming needs to be rotated in the forward conversion and reverse rotation conversion, wherein relate to trigonometric function operation, algorithm execution time is longer.The latter can directly realize the floating of of ac is followed the tracks of in rest frame, saved real time rotation conversion, but its major defect is that the effective ratio resonant controller of design is very difficult, traditional method for designing is under continuous domain, to determine after the performances such as filtering bandwidth, discretization is in numerical control system again, discretization process must be brought the phase shift of signal, affects control performance.
The present invention makes up some defects that ratio resonance is controlled, and designs a kind of novel grid-connected inverter current control algolithm.
Summary of the invention
For overcoming above deficiency, the invention provides a kind of parallel network reverse control algolithm based on orthogonal sinusoidal wave extractor.
In order to address the above problem, the present invention by the following technical solutions:
A parallel network reverse control algolithm based on orthogonal sinusoidal wave extractor, is characterized in that including orthogonal sinusoidal wave extractor, and described orthogonal sinusoidal wave extractor is defined as following discrete state equations:
（1）
Wherein
for the Output rusults of orthogonal sinusoidal wave extractor, initial condition can be taken as
,
;
sinusoidal signal angular frequency for to be extracted, is referred to as centre frequency here;
be called forgetting factor, play the effect of controlling filtering bandwidth;
Then utilize orthogonal sinusoidal wave extractor to realize the given calculating of alternating current, under rest frame, realize the floating of current first harmonics component is followed the tracks of, and reduce the content of 3,5,7 subharmonic.
As a kind of improvement, describedly utilize orthogonal sinusoidal wave extractor to realize the given calculating of alternating current to be realized by following steps:
Cosine is
, sine is
, u
α, u
βcorresponding to
, be the Output rusults of orthogonal sinusoidal wave extractor;
for active current given,
for reactive current given.
As a kind of improvement, fundametal compoment in current error between the given calculated value of alternating current and adopted value is controlled, thereby realize the floating of current first harmonics component is followed the tracks of under rest frame, 3,5,7 inferior harmonic components in current error between alternating current set-point and sampled value are controlled simultaneously, reduce by 3, the content of 5,7 inferior harmonic waves, concrete steps are as follows:
U
αfor voltage acquisition value, e
α i(n) be first-harmonic error,
,
,
for inductance;
K
rifor other each harmonic control coefrficient, the method that can adopt ascending examination to add, too large harmonic wave control coefrficient can make system unstable, and being added to 5-10 proportionality coefficient doubly is enough to the harmonic suppression effect that reaches satisfied.
QSE has following two characteristics:
1), orthogonality
If input variable
centered by frequency
sinusoidal signal, in the time of can calculating stable state
equate with input, without any amplitude, change and phase deviation, and
lag behind
90 degree, mutually orthogonal.
2), frequency-selecting
The input of QSE
to the decay of different frequency input signal and phase shift, be different.Can draw amplitude-frequency characteristic and the phase-frequency characteristic of QSE, as shown in Figure 2.As can be seen from Figure, the amplitude characteristic at positive and negative centre frequency place is 1, and phase shift is 0, illustrates that it does not have amplitude attenuation and phase shift to centre frequency.Other frequency is had to very large decay and phase shift, and decentre frequency far decays larger.So
right
there is bandpass filtering effect, there is in other words frequency-selecting.Forgetting factor
play the effect of controlling bandwidth, forgetting factor
more, close to 1, passband is narrower, more approaches 0, and passband is wider.
QSE not only can be by
in centre frequency Sinusoidal retrieval out, and can will be with
the signal of phase lag signal 90 degree also extracts simultaneously, therefore be called orthogonal sinusoidal wave extractor.
Accompanying drawing explanation
Fig. 1 QSE schematic diagram of the present invention.
The amplitude-frequency characteristic of Fig. 2 QSE of the present invention and phase-frequency characteristic.
Fig. 3 three-phase grid-connected inverter system of the present invention.
Fig. 4 parallel network reverse control algolithm block diagram based on QSE of the present invention.
Fig. 5 mains voltage signal extraction effect based on QSE of the present invention.
Fig. 6 Current Control effect based on QSE of the present invention.
Embodiment
Combining inverter current Control Algorithm generally realizes in digital signal processor (DSP).Alternating voltage and electric current are after sensor sample, AD conversion, and the signal being input in digital processing chip is discrete sampling sequence.These discrete sample signals conventionally with fundamental frequency for leading and containing each harmonic.In these signals, extract the component of characteristic frequency, frequency division, is very significant for inverter control.Although the method for traditional Fourier decomposition can realize frequency division effect, the sampled data of needs preservation is many and real-time is bad.The method of bandpass filtering generally, in continuous domain design, has certain error in discretization real process.
It is orthogonal sinusoidal wave extractor (Quadrature Sinewave Extractor, is called for short QSE below) that the present invention directly provides a kind of operator with division function in discrete domain.
The interval of adjacent two sampling instants is called the sampling period.Suppose that the sampling period is T, the
individual sampled signal is
, QSE is defined as following discrete state equations:
（1）
Wherein
for the Output rusults of QSE, initial condition can be taken as
,
;
sinusoidal signal angular frequency for to be extracted, is referred to as centre frequency here;
be called forgetting factor, play the effect of controlling filtering bandwidth.The schematic diagram of QSE as shown in Figure 1.The transfer matrix of this state equation is that the first row of spin matrix is multiplied by forgetting factor.The effect of this spin matrix is to predict current bat according to upper one Output rusults of clapping.The object that is multiplied by forgetting factor is to allow current Output rusults only remember a certain proportion of upper one Output rusults of clapping, and makes current signal upgrade in certain proportion Output rusults.In the sampling period one, fix, it is to need to regulate that the parameter in formula only has forgetting factor.
QSE has following two characteristics:
1), orthogonality
If input variable
centered by frequency
sinusoidal signal, in the time of can calculating stable state
equate with input, without any amplitude, change and phase deviation, and
lag behind
90 degree, mutually orthogonal.
2), frequency-selecting
The input of QSE
to the decay of different frequency input signal and phase shift, be different.Can draw amplitude-frequency characteristic and the phase-frequency characteristic of QSE, as shown in Figure 2.As can be seen from Figure, the amplitude characteristic at positive and negative centre frequency place is 1, and phase shift is 0, illustrates that it does not have amplitude attenuation and phase shift to centre frequency.Other frequency is had to very large decay and phase shift, and decentre frequency far decays larger.So
right
there is bandpass filtering effect, there is in other words frequency-selecting.Forgetting factor
play the effect of controlling bandwidth, forgetting factor
more, close to 1, passband is narrower, more approaches 0, and passband is wider.
QSE not only can be by
in centre frequency Sinusoidal retrieval out, and can will be with
the signal of phase lag signal 90 degree also extracts simultaneously, therefore be called orthogonal sinusoidal wave extractor.
Hardware connection and input/output signal
The hardware topology the present invention is based on as shown in Figure 3, is typical three-phase grid-connected inverting system.Direct current side joint photovoltaic PV cell panel in figure, therefore upper figure is typical grid-connected photovoltaic system.If in wind-powered electricity generation is controlled, the right connects the inverter that Electric Machine Control needs.Three phase network is received in the output of inverter three-phase alternating current to the isolating transformer of 270V through 380V.In inverter, realizing direct current is the three-phase full-controlled bridge that 6 IGBT form to the nucleus module of ac converter.Three-phase full-controlled bridge ac output end and transformer bay need connect the high-frequency harmonic that LC filter modulates with filtering.The direct-flow input end of three-phase full-controlled bridge need fill DC support electric capacity, and what direct current was inputted can measure cushioning effect, stable DC voltage.
Line voltage transducer gathers the line voltage of step down side, and current sensor gathers the electric current on inductance, and direct current voltage sensor gathers the voltage of positive and negative of DC support electric capacity.
These sampled signals, through suitably conditioning, are passed to DSP, and DSP is by these signals, and the control method proposing according to the present invention is processed, the driving signal of 6 IGBT of finally modulation output.
Three-phase current is simple alternating current amount, if directly it is carried out to proportional plus integral control under rest frame, cannot realize floating and follow the tracks of, and this is because integration only has floating follow-up control for DC quantity.Integral element is actually a low pass filter, and it is actually has extracted the DC component in error.If the alternating current component of certain frequency is had to floating follow-up control, need the alternating current component of this frequency in error to extract.And QSE just in time can realize this function, therefore obtain the current Control Algorithm based on QSE.
Parallel network reverse current Control Algorithm based on QSE realizes under rest frame, as shown in Figure 4.Compare with traditional control algolithm, this algorithm utilizes QSE to realize the given calculating of alternating current, the floating tracking of current first harmonics and the inhibition of harmonic wave.Given value of current value is depending on the concrete applied environment of inverter.But generally, the given output of the PI by direct current pressure ring of general active current obtains, the given power factor being needed by electrical network of reactive current determines, if the power factor needing is 1, reactive current is given as 0.Given and the reactive current of active current is given is DC quantity, need to further determine that again alternating current is given according to the phase place of line voltage first-harmonic.
A phase line voltage sampled value is processed through QSE, obtained the voltage signal u of one group of quadrature
αand u
β.Its centre frequency w gets power frequency 100
rad/s, to extract the first-harmonic in line voltage.The phase place cosine of an angle of line voltage is
, sine is
.Obtain the cosine of line voltage first-harmonic and sine value and just can be used for given value of current and calculated, need not calculate angle.Given according to active current
given with reactive current
, and the cosine of line voltage first-harmonic and sine value, from Park conversion, being calculated as follows a, b biphase current is given.
（2）
From formula, can find out given 120 degree of the given a phase current that always lags behind of b phase current, and amplitude equates.Because three-phase current sum is 0, the given sum of three-phase current is also 0, only needs to calculate a here, and b biphase current is given.
Second step: the equational realization of Current Control.
The a of take is example explanation mutually, and the control of b phase is the same.
First, first-harmonic extracts.
The current feedback value that the set-point obtaining according to the first step and current sensor record, calculates current error,
.Frequency in QSE is made as to fundamental frequency, by the programming of (1) formula, gets first output of QSE, obtain first-harmonic error e
α i(n).
Secondly, harmonic wave extracts.
Frequency in QSE is made as to certain subfrequency, 5 subharmonic for example, the centre frequency of QSE is taken as 5 times of fundamental frequencies, by the programming of (1) formula, the e of its output
α 5(n) be 5 order harmonic components in error.Other subharmonic processing method is similar.
Finally, realize Current Control equation.
Overall error is multiplied by proportionality coefficient k
pas proportional.First-harmonic error is multiplied by k
ri, each harmonic error is multiplied by control coefrficient separately as the output of QSE controlling unit.For offsetting the disturbance of line voltage, need in governing equation, add voltage feed-forward control item in addition.Proportional, QSE item and feedforward term are added, as a phase modulation voltage.That is:
（3）
With same step, can calculate b phase modulation voltage, the relation that is then 0 by three-phase voltage sum calculates c phase voltage.
The 3rd step: three-phase voltage modulation.
According to the size of three phase control voltages and direct voltage, can determine the duty ratio of each IGBT.This topology can adopt the modulator approaches such as SVPWM or SPWM to carry out voltage modulated.For example, take duty ratio calculation method that SPWM is modulation algorithm as:
（4）
Wherein
for certain goes up the duty ratio of brachium pontis mutually,
for the voltage on DC support electric capacity.The driving signal of upper and lower two IGBT of each brachium pontis is complementary, and the duty ratio sum of the duty ratio of lower brachium pontis and upper brachium pontis is 1.According to duty ratio, fill in the corresponding register of DSP, DSP exports the driving signal of each brachium pontis IGBT.
Control choosing of parameter
Choosing of forgetting factor: forgetting factor is good wave filtering effect greatly, but the tracking velocity of voltage-phase sudden change is slower.According to mains frequency and harmonic wave situation, by industry standard, line voltage frequency fluctuates within the scope of 50 ± 2.5Hz, gets a=0.99 and can adapt to well electrical network.
Choosing of each control coefrficient: proportionality coefficient k
pwith inductance
size and the time delay of control system etc. relevant, get here
, can obtain dynamic and steady-state behaviour preferably.The method that adopts ascending examination to add of other each harmonic control coefrficient, too large harmonic wave control coefrficient can make system unstable, and being added to 5-10 proportionality coefficient doubly is enough to the harmonic suppression effect that reaches satisfied.
Technique effect of the present invention is as follows:
Line voltage first-harmonic based on QSE and the extraction effect of quadrature lagging signal thereof are as shown in Figure 5.As can be seen from the figure, the component extracting based on QSE is the fundametal compoment of floating voltage always, for the sudden change of line voltage, also has good adaptive capacity.Based on QSE extraction voltage signal, calculate alternating current given, major advantage is that grid adaptability is strong: 1), line voltage balance whether no matter, it always obtains the fundametal compoment of A phase voltage, and the orthogonal signalling of the A phase fundametal compoment that simultaneously obtains lagging behind, by this group amplitude, equate, the signal of phase place mutual deviation 90 degree, as the basis of given value of current, can remain that given value of current is balance; 2),, when line voltage contains harmonic wave, QSE still can extract fundametal compoment wherein exactly, does not have time delay; 3) because QSE has certain bandwidth, can adapt to the occasion that mains frequency has some fluctuations like this.
Parallel network reverse Current Control effect based on QSE as shown in Figure 6.This is 500kw combining inverter, the networking current waveform while sending out 30% rated power, and three-phase current is steadily exported and has been reached first-harmonic floating and follows the tracks of.In left figure, shown current waveform and fft analysis result thereof while not taking harmonic wave to suppress, the first half networking three-phase current, the latter half is the result of a phase fft analysis wherein.From waveform, find out, current sinusoidal degree is bad, and fft analysis is known wherein contains larger 5 times and 7 subharmonic, 5 subharmonic content 22.7dB wherein, and 7 subharmonic 11.7dB, account for first-harmonic ratio approximately 4.5% and 1.3%.After right figure is the harmonic wave inhibition adding based on QSE, the current waveform recording and FFT result thereof.5 subharmonic content 7.4dB wherein, 7 subharmonic-8dB, accounts for first-harmonic ratio and is about 0.8% and 0.1%.Therefore, add after the harmonic wave Restrainable algorithms based on QSE, harmonic wave obviously reduces, and current waveform sine degree improves.
Claims (2)
1. the parallel network reverse control algolithm based on orthogonal sinusoidal wave extractor, is characterized in that including orthogonal sinusoidal wave extractor, and described orthogonal sinusoidal wave extractor is defined as following discrete state equations:
Wherein
for the Output rusults of orthogonal sinusoidal wave extractor, be X(n-1) with respect to X(n) Output rusults of previous moment, be Y(n-1) with respect to Y(n) Output rusults of previous moment, U(n) be n sampled signal, n is natural number, and T is the sampling period, and initial condition can be taken as
,
;
sinusoidal signal angular frequency for to be extracted, is referred to as centre frequency here;
be called forgetting factor, play the effect of controlling filtering bandwidth;
Then utilize orthogonal sinusoidal wave extractor to realize the given calculating of alternating current, under rest frame, realize the floating of current first harmonics component is followed the tracks of, and reduce the content of 3,5,7 subharmonic.
2. the parallel network reverse control algolithm based on orthogonal sinusoidal wave extractor according to claim 1, is characterized in that describedly utilizing orthogonal sinusoidal wave extractor to realize the given calculating of alternating current to be realized by following steps:
Cosine is
, sine is
, u
α, u
βcorresponding to
, be the Output rusults of orthogonal sinusoidal wave extractor;
for active current given,
for reactive current given, i
a *for a phase current is given, i
b *for b phase current given.
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| CN104201720B (en) * | 2014-09-12 | 2016-09-21 | 阳光电源股份有限公司 | The control method of a kind of grid-connected system resonance suppression and device |
| ES2910456T3 (en) | 2014-09-12 | 2022-05-12 | Sungrow Power Supply Co Ltd | Method and device for monitoring and resonance suppression |
| CN105629064B (en) * | 2015-12-30 | 2018-10-02 | 浙江埃菲生能源科技有限公司 | A kind of sine wave low-pass filtering extracting method |
| CN110954749B (en) * | 2019-11-06 | 2021-07-30 | 许继电源有限公司 | Electric automobile wireless charging phase detection circuit for realizing frequency tracking |
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