CN103023291A - Resonance suppression method based on voltage-type grid-connected inverter - Google Patents

Resonance suppression method based on voltage-type grid-connected inverter Download PDF

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CN103023291A
CN103023291A CN2012103491472A CN201210349147A CN103023291A CN 103023291 A CN103023291 A CN 103023291A CN 2012103491472 A CN2012103491472 A CN 2012103491472A CN 201210349147 A CN201210349147 A CN 201210349147A CN 103023291 A CN103023291 A CN 103023291A
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current
inverter
control
resonance
output current
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张笑天
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Abstract

The invention discloses a simple and practical control method of a grid-connected inverter. Mean current of the inverter is measured by a synchronous sampling method. A series of band-pass filters are combined into a linear controller which is then integrated with duty ratio feedforward to control output current of the inverter, so that the application use of a damping resistor is avoided when an LCL filter is adopted. The grid-connected inverter is simple and reliable in structure, and can not only restrict a possible resonance risk, but also meet the requirements of international standards. Measurement of a harmonic component of the output current in the conventional method is avoided by virtue of the linear controller, so that the distortion of the output current is effectively restricted. By virtue of the combination of the duty ratio feedforward, the tracking accuracy and the dynamic response speed of the output current of the inverter are greatly improved while the stability of the system is not affected. Practical application of the LCL filter in the grid-connected inverter becomes possible by the combination of these methods, and the stability, the validity, the reliability and the practicability of the original grid-connected inverter are greatly improved.

Description

A kind of resonance suppressing method based on voltage controlled grid-connected inverter
Technical field
The present invention relates to the current control method of a kind of voltage source inverter (VSI), be particularly suitable in the microgrid suppressing with the resonance of the combining inverter of LCL filter.
Background technology
When inverter was controlled as current source and is the electrical network transmission of electric energy, the common adoption rate integration of traditional control method (PI) adjuster was controlled output current.This control method needs very large gain to realize enough control precisions.On the other hand, the use of LCL filter has greatly increased the complexity of inverter system, thereby guarantees that Systems balanth is a great problem of combining inverter control.For fear of the appearance of resonance, for choosing of LCL filter parameter and controller parameter strict requirement is arranged also.Satisfy these and require to suppress to have brought difficulty for the harmonic distortion of inverter output current the present domestic very effective solution that also lacks.
At present for being incorporated into the power networks of inverter, main solution is to use a large inductance as filter, by to the control of inductive current to reach the output current that satisfies index request.This method needs a larger filter inductance usually, thereby has greatly increased volume and the cost of system.Yet, because this system configuration is simple, be convenient to design and control, therefore be widely used in the combining inverter.
In recent years, the LCL filter has obtained increasing concern as the output filter of combining inverter.But because the parameter of LCL filter is chosen comparatively complexity, the difficult design of control system easily causes the problems such as resonance, and this class filter is also not yet universal in present home products.Yet, the use of LCL filter can reduce volume and the cost of inverter system largely, improves the quality of output current, reduces electromagnetic interference (EMC), thereby the use of LCL filter has become an important development trend of combining inverter output filter technology.How finding a scheme, can use the LCL filter to reduce the cost of system, can provide high-quality electric current to electrical network again, can also guarantee system stability and suppress resonance, is to control the subject matter that faces with the combining inverter of LCL filter at present.For the control of the LCL filtering type combining inverter output current that suppresses based on resonance, domesticly there is no very simple and effective application example.
Analyze as seen from above-mentioned introduction to prior art, there is no at home the report that the method that resonance is suppressed to combine with Current Control realizes the control of LCL filtering type combining inverter at present.
Summary of the invention
The object of the present invention is to provide a kind of control technology of the LCL filtering type combining inverter that suppresses based on resonance, use simple current control method, can make inverter reach very high output accuracy, can guarantee again Systems balanth and suppress resonance.When there is distortion in line voltage, the distortion of output current can also be suppressed in the very little scope, satisfy the international standard of combining inverter.
The specific implementation of technical scheme of the present invention is to measure the inductive current of inverter side, and single inverter control is become current source, the steps include:
The first step utilizes Hall element to measure the inverter side inductive current of the LCL filter of inverter.The way of this way and domestic most is different.The most domestic way is to measure the grid side electric current of LCL filter, and this method is difficult to the feedback factor of conditioning controller to avoid vibration.And method proposed by the invention is to measure the inductive current of inverter side, and the benefit of doing like this is to be convenient to the design of feedback controller to suppress resonance, so that system has higher robustness;
Second step uses pulse width modulation (PWM) signal as excitation, the synchronous acquisition inductive current.This is because the inductive current of inverter side contains more switching noise and ripple.Adopt digital signal processor to carry out synchronized sampling, will record the mean value of the inductive current of inverter side, these sampled values then can form a smooth sine curve;
The 3rd step, the inductive current of the inverter side that synchronized sampling is obtained carry out the monocycle FEEDBACK CONTROL, effectively simple.The method that the adoption rate controller combines with a series of resonant controller, the band connection frequency of resonant controller are power frequency and each odd harmonic frequencies;
In the 4th step, utilize formula d Ff=v Ref/ V Dc, be converted into duty ratio with reference to voltage and feedover, thus the dynamic response performance of raising system;
The 5th step, the gain of allocation ratio feedback factor and band pass filter.Electric current loop Proportional Feedback coefficient is L/T s/ V Dc/ 2, wherein L is the inverter side inductance, T sBe switching frequency.The gain of resonant controller is decided according to the each harmonic number of times, and along with the rising of harmonic number, the gain of resonant controller reduces one by one, with the product that guarantees the gain of harmonic number and harmonic wave less than stablizing the upper limit;
The 6th step, measure line voltage, utilize phase-locked loop to make instruction current and line voltage synchronous.Because inverter side inductive current and grid side inductive current exist certain difference in magnitude and phase difference, can proofread and correct according to LCL filter side parameter, estimation is the reference signal of required current regulator finally;
The 7th step is with output feedback duty cycle signals and the addition of feedforward duty cycle signals of current regulator, as the driving signal of inversion full-bridge.Adopt bipolarity PWM, obtain the pwm signal of each insulated gate bipolar transistor (IGBT) device in the control inversion full-bridge.
The present invention is by being combined proportional controller, a series of resonant controller to regulate with feedforward controller the inductive current of inverter side, not only so that the control of the output current of inverter has obtained effective control, also effectively suppress the resonance that the use by the LCL filter brings, improved the using value of LCL filtering type inverter system.
Description of drawings
Fig. 1 is the schematic diagram of the converter main circuit that is suitable for of the present invention;
Fig. 2 is control circuit core block diagram;
Fig. 3 is the Laplace domain transfer function model of the grid-connected inverter system that is suitable for of the present invention;
Fig. 4 (a) be among Fig. 3 output current to the gain Bode diagram of instruction current;
Fig. 4 (b) be among Fig. 3 line voltage to the transfer function Bode diagram of output current;
Fig. 5 is the Z domain model of this grid-connected inverter system;
Fig. 6 (a) is the discrete system root locus diagram of the digital control combining inverter of minimum time-delay;
Fig. 6 (b) is the discrete system root locus diagram of the digital control combining inverter of typical case's time-delay;
Fig. 6 (c) is the discrete system root locus diagram of the digital control combining inverter of maximum delay;
Fig. 7 (a) is the Steady Experimental oscillogram of combining inverter full load output current and line voltage;
Fig. 7 (b) is the Steady Experimental oscillogram of combining inverter output current and line voltage during semi-load;
The dynamic experiment oscillogram of output current and line voltage when Fig. 7 (c) is the multiplication of combining inverter current-order;
Fig. 7 (d) is the dynamic experiment oscillogram of combining inverter current-order output current and line voltage when reducing by half;
Embodiment
Accompanying drawing is specific embodiments of the invention;
Below in conjunction with accompanying drawing content of the present invention is described in further detail:
With reference to shown in Figure 1, direct current becomes interchange by the inversion full-bridge, and its output is by inverter side filter inductance L, filter capacitor C and grid side filter inductance L gMains supply.r LAnd r gThe dead resistance that all represents filter inductance, R is the damping resistance with capacitances in series.
With reference to shown in Figure 2, measure line voltage v with Hall element gWith inverter side inductive current i L, as the feedback control signal of inverter.Adopt digital signal processor, carry out digital control to system.Owing to containing a large amount of ripples and switch noise in the inverter side inductive current, adopting the synchronized sampling method to carry out filtering.The sampling time of control electric current makes it synchronous with the peak value of PWM triangular wave, just can realize good filter effect.Feedback controller adopts the monocycle control method: i.e. ratio+the industrial frequency resonance of inductive current+harmonic resonance control, and the controller z territory expression formula that is used for inhibition resonance is:
G c ( z ) = k p ( 1 + Σ h = 1 , odd 9 k h a zh z 2 + b zh z + c zh A zh z 2 + B zh z + C zh )
Its midsplit type represents the digital band-pass filter of certain subharmonic, and its expression formula and parameter are drawn by Bilinear transformation method usually.Proportionality coefficient is chosen and must be satisfied K L＜L/T s/ V Dck pValue be 1, k hValue then determine according to the required harmonic inhibition capability of reality.If need inverter to have stronger restraint at certain subharmonic place, then get larger k hThe important controller of another one is exactly feedforward controller among Fig. 2.Feedfoward control can reduce steady-state error, improves dynamic responding speed, does not affect Systems balanth.Therefore, the feed-forward coefficients of duty ratio is chosen for k Ff=v Ref/ V DcThe inverter side inductor current feedback combines with the duty ratio feedforward, has formed the controller of whole inverter, and this control method can realize the fastest dynamic responding speed.The duty ratio that controller finally calculates generates pwm signal and drives the inversion full-bridge through the modulation of digital signal processor.
Native system does not need to detect output current, and can realize the control to output.Controller adopts reasonably control parameter, so that can suppress resonance effectively.Use such feedback controller, the tracking effect that not only can realize ideal, and can avoid electric energy loss because using damping resistance to bring is for the practical application of LCL filter brings great convenience.The combination of feedforward controller has further improved output accuracy and the response speed of inverter, and the practical value of this control program is increased greatly.
With reference to shown in Figure 3, the figure shows the combining inverter Laplace domain transfer function model that the present invention is suitable for.Because the existence of line voltage, the harmonic components in the electrical network also can produce larger impact to the control effect of combining inverter.To this, the present invention has made corresponding analysis.
Shown in Fig. 4 (a), (b), provided the frequency response analysis result of native system, wherein Fig. 4 (a) is the gain response of reference current to output current, and wherein abscissa represents angular frequency, and ordinate represents respectively amplitude and phase angle; Fig. 4 (b) is the disturbance response of line voltage to output current, and wherein abscissa represents angular frequency, and ordinate represents respectively amplitude and phase angle.
As seen, the control method of native system is simple, only needs the control inductive current, just can make inverter reach very high control precision and harmonic inhibition capability.In the lower scope of frequency, the distortion of line voltage can not cause excessive impact to output current yet.Adopt control method proposed by the invention, can realize comparatively ideal electric current output effect.
With reference to shown in Figure 5, the figure shows this combining inverter z territory transfer function model, be used for the dynamic characteristic of accurate descriptive system.
Shown in Fig. 6 (a), (b), (c), provided the discrete domain root locus diagram based on Fig. 5 system.Wherein Fig. 6 (a) is the discrete system root locus diagram of minimum time-delay (half switch periods) digital control combining inverter; Fig. 6 (b) is the discrete system root locus diagram of typical case's time-delay (switch periods) digital control combining inverter; Fig. 6 (c) is the discrete system root locus diagram of the digital control combining inverter of maximum (one and half switch cycles) time-delay; According to these root locus diagrams, can draw and satisfy the required control parameter of robustness.The dynamic indicator that also can go out system according to the control parameter prediction is such as overshoot, natural hunting angle frequency, rise time and response time etc.
Below provide experimental example:
Experiment is take the combining inverter of a per kilowatt as example.Use common frequency power network to be connected on the output of combining inverter in the experiment.Reference voltage frequency and the synchronized of inverter, main circuit parameter is: L=1.6mH, r L=0.4 Ω, C=10 μ F, R=0, L g=1.6mH, r g=0.4 Ω, measuring circuit adopts the accuracy of precorrection to guarantee that feedback is measured.
With reference to shown in Figure 7, take line voltage as reference, provided the waveform of the output current of combining inverter in the experiment.Fig. 7 (a) is the stable state output current of combining inverter full load and the experimental waveform figure of line voltage, wherein abscissa represents the time, ordinate represents electric current and voltage magnitude, the power factor that draws output current according to spectrum measurement is 98.5%, total harmonic distortion factor (THD) is 2.6%, and the distortion factor that electrical network itself has is 2%; Fig. 7 (b) is the stable state output current of combining inverter during semi-load and the experimental waveform figure of line voltage, wherein abscissa represents the time, ordinate represents electric current and voltage magnitude, the THD that draws output current according to spectrum measurement is 2.9%, all the time less than 5%, can satisfy the THD upper limit of defined in the IEEE1547-2003 standard; The dynamic response experimental waveform figure of output current and line voltage when Fig. 7 (c) doubles for the combining inverter current-order, wherein abscissa represents the time, ordinate represents electric current and voltage magnitude, can find out that control method used in the present invention can be so that the output current that increases in a leap enters stable state in a power frequency period; The dynamic response experimental waveform figure of output current and line voltage when Fig. 7 (d) reduces by half for the combining inverter current-order, wherein abscissa represents the time, ordinate represents electric current and voltage magnitude, can find out that this control method can so that the output current that subtracts that jumps enters stable state in a power frequency period, have very fast dynamic response performance.
From above result as seen, hardware component used in the present invention has seldom been saved system cost and volume greatly.Use controller proposed by the invention, the resonance when at first having solved combining inverter and using the LCL filter suppresses problem, can also avoid the electric energy loss because using damping resistance to bring, for the practical application of LCL filter brings great convenience.The combination of linear controller and feedfoward control has not only improved the tracking accuracy of output current, but also has guaranteed very high power factor, has obtained good output characteristic.In the situation that the line voltage distortion, the harmonic components in the output current also can be effectively suppressed, and can not cause because of the distortion of output voltage harmonic pollution.Applying in a flexible way of control method so that grid-connected inverter system has very fast dynamic responding speed, guaranteed stability, validity and the reliability of whole grid-connected inverter system operation.

Claims (3)

1. control method that suppresses the current-control type combining inverter based on resonance, comprise Current Control, resonance suppresses and phase-locked control, it is characterized in that: the inverter side inductive current of measuring the LCL filter carries out FEEDBACK CONTROL to suppress resonance, and use pulse width modulation (PWM) signal as excitation, the synchronous acquisition inductive current.Adopt digital signal processor to carry out synchronized sampling, will record the mean value of the inductive current of inverter side, the switching noise and the ripple that exist in can the filtering inductive current.The inductive current of the inverter side that synchronized sampling is obtained carry out the monocycle FEEDBACK CONTROL.
2. as claimed in claim 1, a kind of control method that suppresses the current-control type combining inverter based on resonance, it is characterized in that: the method that the adoption rate controller combines with a series of resonant controller is carried out monocycle control, and the band connection frequency of resonant controller is power frequency and each odd harmonic frequencies.Utilize formula d Ff=v Ref/ V Dc, be converted into duty ratio with reference to voltage and feedover.Electric current loop Proportional Feedback coefficient is configured to L/T s/ V Dc/ 2, wherein L is the inverter side inductance, T sBe switching frequency.The gain of resonant controller is decided according to the each harmonic number of times, and along with the rising of harmonic number, the gain of resonant controller reduces one by one, with the product that guarantees the gain of harmonic number and harmonic wave less than stablizing the upper limit.
3. described according to claim 1, a kind of control method that suppresses the current-control type combining inverter based on resonance is characterized in that: utilize phase-locked loop to make instruction current and line voltage synchronous.Because inverter side inductive current and grid side inductive current exist certain difference in magnitude and phase difference, can proofread and correct according to LCL filter side parameter, estimation is the reference signal of required current regulator finally.
CN2012103491472A 2012-09-19 2012-09-19 Resonance suppression method based on voltage-type grid-connected inverter Pending CN103023291A (en)

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CN106329896A (en) * 2015-06-18 2017-01-11 鸿富锦精密工业(武汉)有限公司 DC power supply circuit
CN109687459A (en) * 2018-11-20 2019-04-26 江苏安科瑞电器制造有限公司 It is feedovered based on current forecasting and combines the high speed harmonic current breathing crack method of more PR resonant branch

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103401242A (en) * 2013-07-15 2013-11-20 合肥工业大学 Multi-inverter system resonance restraining device and controlling method thereof
CN103401242B (en) * 2013-07-15 2016-03-09 合肥工业大学 A kind of control method of multi-inverter system resonance restraining device
CN106329896A (en) * 2015-06-18 2017-01-11 鸿富锦精密工业(武汉)有限公司 DC power supply circuit
CN109687459A (en) * 2018-11-20 2019-04-26 江苏安科瑞电器制造有限公司 It is feedovered based on current forecasting and combines the high speed harmonic current breathing crack method of more PR resonant branch
CN109687459B (en) * 2018-11-20 2022-04-29 江苏安科瑞电器制造有限公司 High-speed harmonic current open-close loop control method based on current prediction feedforward combined with multiple PR resonance branches

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Application publication date: 20130403