CN108574403B - Non-isolation type photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing method - Google Patents
Non-isolation type photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/123—Suppression of common mode voltage or current
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Abstract
The invention discloses a kind of non-isolation type photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing methods; including three-phase I font three-level inverter and modified LCL filter circuit; the capacitor common end of the modified LCL filter circuit is directly connected at the neutral point of DC side filter capacitor; change the common mode circuit of three-phase I font three-level inverter, inhibits system leakage current.The invention proposes the closed loop control algorithms in common mode circuit, increase PI controller in common mode circuit, realize the inhibition of common mode resonance loop current.The present invention can save the cost, improve system transfer efficiency, have very high practical value.
Description
Technical field
The present invention relates to a kind of non-isolation type photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing methods.
Background technique
In recent years, the rapid growth of photovoltaic power generation is that solution world energy sources shortage and problem of environmental pollution play huge work
With.Photovoltaic DC-to-AC converter is core component in photovoltaic generating system, and direct current is converted to alternating current by it.Three electricity of I font three-phase
Zero diopter volt inverter topology is widely used in mesohigh high-power photovoltaic system.I font three-level topology has lower open
The advantage of pass loss, more preferably output waveform quality and higher energy density and efficiency, makes it be increasingly becoming the market mainstream, obtains
To the attention of various countries scientific research personnel and the extensive use of industry.
But the parasitic capacitance in the non-isolated photovoltaic inverter system in photovoltaic panel unavoidably generates leakage current.Leakage
Electric current will increase the electromagnetic interference of system, and output current wave is made to distort, and bring huge safety hidden to equipment and operator
Suffer from.For this purpose, national standard is made that regulation to the size of leakage current, the electric leakage of the photovoltaic DC-to-AC converter of 10kW and following power grade
Big palpulus is flowed lower than 300mA.
Mainly start at present from change inverter topology and in terms of changing modulation strategy two about the method for reducing leakage current.
On the one hand, change inverter topology reduce leakage current method in, by DC side or exchange side increase switching tube and
Diode changes the common-mode voltage that inverter system generates, and then inhibits leakage current.But this method needs to increase additionally auxiliary
Switching device is helped, this not only adds the costs of system to also increase control difficulty.On the other hand, changing modulation strategy reduction
In the method for leakage current, common method is to abandon partial switch vector (the biggish common mode electricity of these switching vector selectors generation amplitude
Pressure), it is electric by reducing common mode such as reversed (APOD) modulator approach of carrier wave and LMZ (only using big or middle, zero vector) modulator approach
The amplitude of pressure realizes the purpose for inhibiting leakage current.But this method inhibits the ability of leakage current limited, simultaneously because only with
Segment vector carrys out synthesized reference voltage, and the total harmonic distortion factor (THD) of output voltage or current waveform increases.Based on this,
There is document to propose using a kind of improved LCL filter the method for reducing leakage current, the method is hardly increasing cost
Under the premise of controlling and modulating difficulty, leakage current is greatly reduced.But modified LCL filter, change inverter
The common mode leakage current circuit of system, common-mode voltage evoke common mode resonance loop current in improved common mode circuit.Common mode resonance
Loop current makes a series of problems, such as inverter side current oscillation, the increase of system leakage current, system power protection misoperation, this is broken
It is broken the stability of system.
Therefore, not for common mode resonance loop current in I font three-level photovoltaic inverter system and leakage current bring
Benefit influences, and it is significant to study a kind of simple and effective solution.
Summary of the invention
The present invention to solve the above-mentioned problems, propose a kind of non-isolation type photovoltaic DC-to-AC converter common mode resonance loop current and
LCL filter capacitor common end is connected to DC bus by drain current suppressing method, present invention modified LCL filter
Midpoint increases a low-impedance capacitive branch in common mode circuit, changes the circuit structure in common mode circuit, the common mode of high frequency
The high frequency common mode leakage current that voltage evokes flows back to the midpoint of DC bus by this increased low-impedance capacitive branch, thus
Significantly reduce the leakage current for flowing into the earth.
To achieve the goals above, the present invention adopts the following technical scheme:
The first object of the present invention is to provide a kind of photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing system,
Including three-phase I font three-level inverter and modified LCL filter circuit, the capacitor of the modified LCL filter circuit is public
End is directly connected at the neutral point of DC side filter capacitor, changes the common mode circuit of three-phase I font three-level inverter, is inhibited
System leakage current.Modified LCL filter will not change the filtering in differential mode circuit there is no the differential mode circuit for changing system simultaneously
Effect.
Further, the three-phase I font three-level inverter includes three-phase bridge arm, and every phase bridge arm includes upper and lower bridge arm,
The upper and lower bridge arm includes two pole of clamp of two concatenated switching tubes and two connection upper and lower bridge arm switching tube midpoints
Pipe, DC side include two concatenated identical filter capacitors, and a neutral point is formed among two capacitors, every phase bridge arm
The centre of two clamp diodes is connected with neutral point, makes to exchange bridge arm midpoint generation zero potential.
Further, the on state of four switching tubes of every phase bridge arm is different, the electricity that exchange bridge arm midpoint generates
Position is different, generation+Udc/2、-Udc/ 2,0 three kind of level, UdcFor DC side supply voltage.
Preferably, the switching tube is IGBT switching tube.
Further, opening for the switching tube passes through conditioning circuit and driving by the controller in control system with shutdown
Circuit directly controls.
Further, the control system includes protecting circuit, driving circuit, over-sampling modulate circuit and control circuit, and three
The signal of phase I font three-level inverter is connected to controller by over-sampling modulate circuit, and the controller and protection circuit are logical
Letter, realizes overcurrent and overvoltage protection, and controller connects driving circuit, the pwm signal of controller output through overdrive circuit every
From the control electrode that amplification is sent to switching tube, control switch pipe being opened and turning off.
Further, the over-sampling modulate circuit acquisition and the capacitance voltage up and down, the three-phase bridge inverter side that improve DC side
Electric current, three-phase filter capacitor voltage and three-phase power grid voltage value.
Further, three-phase inverter side is exported electric current phase adduction by the common-mode circuit control method based on above system
It is made the difference with reference value, difference passes through common mode loop resonance current controller, obtains for adjusting positive and negative small vector action time
Variable is controlled, realizes the real-time adjustment of the positive and negative small vector action time in seven segmentation modulation algorithms；By changing positive and negative small arrow
Measuring action time reduces amplitude of the common-mode voltage at common mode loop resonance frequency, realizes the inhibition of common mode resonance loop current.
Further, it in common mode circuit, realizes that the controller that common mode resonance loop current inhibits is PI controller, realizes
The zero steady state error control of common mode resonance loop current.Since expectation common mode resonance loop current is eliminated as far as possible, so common mode resonance ring
The reference value of road electric current is set as zero.
It is real by capacitance voltage feed-forward control algorithm based on the capacitance voltage feed forward control method in above system differential mode circuit
When adjust modulating wave, to change amplitude of the bridge arm output voltage at differential mode loop resonance frequency, realize to humorous in differential mode circuit
The inhibition of vibration electric current.
Neutral-point voltage balance method based on above system acquires the difference of DC side or more capacitance voltage, utilizes
The control variable for adjusting positive and negative small vector action time in real time is calculated according to the difference for mid-point voltage controller, changes
Positive and negative small vector action time controls neutral point voltage balance.
Specifically, when upside capacitance voltage is greater than downside capacitance voltage, Ying Zengjia p-type small vector action time；Instantly
When lateral capacitance voltage is greater than upside capacitance voltage, Ying Zengjia N-type small vector action time.
Compared with prior art, the invention has the benefit that
1, it is compared with using traditional LCL filter, modified LCL filter is by changing common mode loop structure, effectively
Inhibit leakage current.Reduce caused by leakage current that electromagnetic interference is big, system stability is poor, the low-quality unfavorable shadow of output waveform
It rings.
2, change main circuit topology by increasing auxiliary switch or diode with tradition and inhibit the comparison of leakage current method,
The method of the present invention is not necessarily to any auxiliary switch or diode, need to only increase a conducting wire.This greatly reduces system at
This, reduces system bulk, simplifies control algolithm and modulation algorithm.
3, the method for leakage current is inhibited to compare by changing modulation algorithm with tradition, the present invention does not abandon any vector,
So that the waveform quality of output voltage and electric current is more excellent, harmonic content is lower, is more advantageous to the volume for reducing filter, reduces system
System cost.
4, the method inhibited with no common mode resonance loop current compares, and the invention proposes a kind of closed loop controls in common mode circuit
Algorithm processed can effectively inhibit common mode resonance loop current, so that inverter output current oscillation is effectively suppressed, export current wave
Shape better quality, the stability and anti-interference of system are stronger.
5, the method for common mode resonance loop current and differential mode loop resonance electric current is inhibited to compare with using passive damping, this hair
It is bright to realize that the resonance current in common mode and differential mode circuit inhibits by closed loop control algorithm.Increase PI controller in common mode circuit,
Inhibit common mode resonance loop current.Capacitance voltage feedforward control is used in differential mode circuit, inhibits differential mode loop resonance electric current.By
Damping resistance is eliminated in this method, so reducing the energy loss of system, this method has saved cost, improves and is
System transfer efficiency, has very high practical value.
Detailed description of the invention
The accompanying drawings constituting a part of this application is used to provide further understanding of the present application, and the application's shows
Meaning property embodiment and its explanation are not constituted an undue limitation on the present application for explaining the application.
Fig. 1 is the I font three-level photovoltaic inverter system construction drawing of modified LCL filter；
Fig. 2 is the common mode equivalent circuit figure of the I font three-level photovoltaic inverter of modified LCL filter；
Fig. 3 is that the bode of modified LCL filter common mode equivalent circuit schemes；
Fig. 4 is the control block diagram of common mode resonance loop current；
Fig. 5 is the differential mode equivalent circuit of the I font three-level photovoltaic inverter based on modified LCL filter；
Fig. 6 is that the bode of modified LCL filter differential mode equivalent circuit schemes；
Fig. 7 is system main-control block diagram；
Fig. 8 is 3 level space vector distribution map；
Fig. 9 is seven segmentation on off sequence figures；
Specific embodiment:
The invention will be further described with embodiment with reference to the accompanying drawing.
It is noted that following detailed description is all illustrative, it is intended to provide further instruction to the application.Unless another
It indicates, all technical and scientific terms used herein has usual with the application person of an ordinary skill in the technical field
The identical meanings of understanding.
It should be noted that term used herein above is merely to describe specific embodiment, and be not intended to restricted root
According to the illustrative embodiments of the application.As used herein, unless the context clearly indicates otherwise, otherwise singular
Also it is intended to include plural form, additionally, it should be understood that, when in the present specification using term "comprising" and/or " packet
Include " when, indicate existing characteristics, step, operation, device, component and/or their combination.
In the present invention, term for example "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", " side ",
The orientation or positional relationship of the instructions such as "bottom" is to be based on the orientation or positional relationship shown in the drawings, only to facilitate describing this hair
Bright each component or component structure relationship and the relative of determination, not refer in particular to either component or element in the present invention, cannot understand
For limitation of the present invention.
In the present invention, term such as " affixed ", " connected ", " connection " be shall be understood in a broad sense, and indicate may be a fixed connection,
It is also possible to be integrally connected or is detachably connected；It can be directly connected, it can also be indirectly connected through an intermediary.For
The related scientific research of this field or technical staff can determine the concrete meaning of above-mentioned term in the present invention as the case may be,
It is not considered as limiting the invention.
In order to effectively inhibit leakage current, the adverse effect of leakage current is reduced, the present invention uses modified LCL filter.It
LCL filter capacitor common end is connected to the midpoint of DC bus, increases a low-impedance capacitor branch in common mode circuit
Road, changes the circuit structure in common mode circuit, and the high frequency common mode leakage current that the common-mode voltage of high frequency evokes is increased by this
Low-impedance capacitive branch flows back to the midpoint of DC bus, to significantly reduce the leakage current for flowing into the earth.
Although leakage current can be effectively reduced in improved LCL filter, common mode resonance loop current can be caused simultaneously, given
System brings adverse effect.In order to effectively inhibit the common mode resonance loop electricity that common-mode voltage evokes in modified LCL filter
Stream, the invention proposes a kind of common mode circuit Closed-loop Control Strategies, realize common mode by increasing PI controller in common mode circuit
The inhibition of resonance loop electric current.The output of PI controller changes the action time of positive and negative small vector in space vector modulation, reduces
Amplitude of the common-mode voltage at resonance frequency in common mode circuit, and then inhibit common mode resonance loop current.
The present invention is under the premise of hardly increasing cost, not increasing control and modulation difficulty, the common mode resonance ring of realization
Effective inhibition of road electric current and leakage current.Present invention improves system output waveform quality, the safety of system and steady is improved
It is qualitative.
To achieve the above object, the present invention adopts the following technical scheme:
Main circuit is three-phase I font three-level inverter, and every phase bridge arm includes four IGBT switching tubes and two clamps two
Pole pipe.DC side is two identical filter capacitor series connection, and a neutral point O is formed among two capacitors, every phase bridge arm
The centre of two clamp diodes is connected with neutral point O, makes to exchange bridge arm midpoint generation zero potential.Obviously, it is opened up in this circuit
In flutterring, the on state of four pipes of every phase is different, and the current potential that exchange bridge arm midpoint generates is also different, and this topology can produce
Raw+Udc/2、-Udc/ 2,0 three kind of level.
In the modified LCL filter circuit, capacitor common end is connected to DC side filter capacitor by a conducting wire
Neutral point O changes the common mode circuit of I font Three-Level Inverter System, effectively inhibits system leakage current.
Opening for switching tube is directly controlled by the controller in control system by conditioning circuit and driving circuit with shutdown；
The modulation strategy and control algolithm of system are realized in controller DSP.
The control system includes protection circuit, driving circuit, over-sampling modulate circuit and control circuit composition.Main circuit
Signal is connected to DSP module by over-sampling modulate circuit, and the signal of main circuit is sent to the operation that DSP carries out control algolithm.DSP
Module and protection circuit communication, realize the overcurrent and overvoltage protection of system.DSP module connects driving circuit, the PWM of DSP output
Signal is sent to the gate pole of IGBT through the isolation amplification of overdrive circuit, controls opening and turning off for IGBT.
The over-sampling modulate circuit, capacitance voltage, three-phase bridge inverter side electric current, three-phase are filtered up and down with conditioning DC side for acquisition
Wave capacitance voltage, three-phase power grid voltage.
The modulation strategy is the seven segmentation dSPACE of SVPWM that positive and negative small vector action time can be changed
(SVPWM)。
The control algolithm of the three level I font inverter topologies based on modified LCL filter includes common-mode circuit
Closed loop control algorithm, differential mode circuit capacitance voltage feed-forward control algorithm and neutral point voltage balance algorithm control algolithm.
The control algolithm of I font three-level inverter based on above-mentioned modified LCL filter, specifically:
Common mode circuit closed loop control algorithm realizes system due to the common mode resonance ring using the introducing of modified LCL filter
The inhibition of road electric current.Three-phase inverter side output electric current phase adduction is made the difference with reference value, difference is by common mode loop resonance electricity
Stream controller obtains the control variable for adjusting positive and negative small vector action time, realizes positive and negative in seven segmentation modulation algorithms
The real-time adjustment of small vector action time.Common-mode voltage is reduced in common mode loop resonance by changing positive and negative small vector action time
Amplitude at frequency realizes the inhibition of common mode resonance loop current.In common mode circuit, realize that common mode resonance loop current inhibits
Controller be PI controller, for realizing the zero steady state error control of common mode resonance loop current, due to it is expected common mode resonance loop
Electric current is eliminated as far as possible, and reference value is set as zero.
The capacitance voltage feed-forward control algorithm in differential mode circuit, realizes the inhibition of differential mode loop resonance electric current.Due to using
Modified LCL filter, there are intrinsic resonance point in differential mode circuit, the pulse voltage of bridge arm output is generated at resonance point
Differential mode resonance current causes the unstable of system.Modulating wave is adjusted in real time by capacitance voltage feed-forward control algorithm, changes bridge arm
Amplitude of the output voltage at differential mode loop resonance frequency realizes the inhibition of resonance current in differential mode circuit.
Neutral-point voltage balance algorithm realizes the balance control of the DC side mid-point voltage of I font three-level inverter
System.The difference of capacitance voltage above and below DC side is obtained by mid-point voltage controller for adjusting positive and negative small vector effect in real time
The control variable of time changes positive and negative small vector action time, realizes the control of neutral point voltage balance.When upside, capacitance voltage is big
When the capacitance voltage of downside, Ying Zengjia p-type small vector action time；Instantly it when lateral capacitance voltage is greater than upside capacitance voltage, answers
Increase N-type small vector action time.
As a kind of exemplary embodiments, as shown in Figure 1, using the three level photovoltaic inversion of I font of modified LCL filter
Device system construction drawing, main circuit are three-phase I font three-level inverter, totally 12 IGBT switching tubes and six clamp diodes；
Filter uses modified LCL filter, and the capacitor common end of this filter is connected in DC bus capacitor by a conducting wire
Point；DC side is two concatenated filter capacitors, and a neutral point O, two pincers of every phase bridge arm are formed among two capacitors
The centre of position diode is connected with neutral point O, and this topology can produce+Udc/2、-Udc/ 2,0 three kind of level.
Fig. 2 is the three level photovoltaic of I font of the modified LCL filter obtained according to kirchhoff circuit equation in Fig. 1
The common mode equivalent circuit figure of inverter.Compared with traditional LC L common mode equivalent circuit, this equivalent circuit increases in common mode circuit
One low-impedance capacitive branch, the branch provide access for the common mode current of high frequency, greatly reduce the electric leakage for flowing into the earth
Stream.Transmission function of the leakage current to common-mode voltage are as follows:
It can be seen that the common mode circuit based on modified LCL filter is a fourth-order system, have more to high-frequency leakage current
Strong damping capacity, this greatly reduces the leakage currents for flowing into the earth.From Fig. 2 and leakage current to the transmission function of common-mode voltage
It can be concluded that there are intrinsic resonance points for filter itself, in resonance due to the design feature of Modified Filter system itself
It will lead to common mode resonance loop current at point.
Fig. 3 is that the bode of modified LCL filter common mode equivalent circuit schemes, and due to the introducing of low-impedance capacitor branch, is made
There are resonance points in common mode equivalent circuit, in practical applications, it will usually in fr1Common mode resonance loop current is generated at frequency,
Inverter output current is caused to vibrate, the current protection of system malfunctions, and system is unstable.Resonance frequency fr1Are as follows:
By resonance frequency fr1Expression formula can be seen that this resonance frequency by circuit parameter L and CfInfluence.Assuming that system
Leakage current can be suppressed to zero, so the mathematical model of common mode resonance loop current are as follows:
It can be seen that ucmFor common mode resonance loop current icmzDriving source, for realize icmzEffective suppression of resonance loop electric current
System, can be by reducing ucmAmplitude at resonance frequency realizes the inhibition of common mode resonance loop current.The present invention passes through altogether
Increase Closed-loop Control Strategy in mould circuit, Closed-loop Control Strategy reduces amplitude of the common-mode voltage at resonance frequency, and then presses down
Common mode resonance loop current processed.
Fig. 4 is the control block diagram that common mode resonance loop current inhibits, and the controller in common mode circuit is PI controller, in order to have
Effect inhibits common mode resonance loop current, and the given value of common mode resonance loop current is set as zero, and common mode resonance loop current is given
The difference of definite value and actual value is sent into PI controller.The output of PI controller passes through for adjusting positive and negative small vector action time
In real time pairs of positive and negative small vector action time in seven segmentation modulation strategies of adjustment, reduce common-mode voltage amplitude at resonance frequency,
And then realize effective inhibition of common mode resonance loop current.For adjusting the control variable of positive and negative small vector action time in real time
Are as follows:
Fig. 5 is the differential mode equivalent circuit of the I font three-level photovoltaic inverter of modified LCL filter；It is filtered using LCL
Device under the premise of realizing identical filter effect, can substantially reduce the volume of filter, reduce system loss, raising system turn
Change efficiency, save the cost.System bridge arm exports electric current to the transmission function of bridge arm output voltage are as follows:
But there are resonance points for LCL filter itself, will lead to the resonance of system output current, differential mode resonance frequency are as follows:
Fig. 6 is the bode figure of the differential mode equivalent circuit of the I font three-level photovoltaic inverter of modified LCL filtering, due to
The reason of this body structure of filter, so that there are resonance spikes for LCL filter, if resonance spikes cannot be effectively suppressed,
System is unstable, causes system oscillation, system crash.Here differential mode loop current resonance is realized using capacitance voltage feedforward control
Inhibition.
Fig. 7 is whole control block diagram of the invention, and control section is controlled by the PI inhibited for common mode resonance loop current
Device, the differential mode controller for the inhibition of differential mode loop resonance, the mid-point voltage for DC side neutral-point voltage balance control
Device is constituted.The controller action can effectively inhibit to leak electricity on the three-phase I font three-level inverter of modified LCL filter
Stream, common mode resonance loop current；Differential mode loop resonance；The fluctuation of DC side mid-point voltage.The algorithm is hardly increasing cost
Under the premise of realize the efficient, stable of system, reliability service.
Fig. 8 is 3 level space vector figure, and each phase bridge arm has tri- kinds of states of P, O, N, so three level of three-phase I font is opened up
27 switching vector selectors are flutterred, long according to the mould of vector, 27 vectors are divided into 4 groups, large, medium and small, zero vector.Wherein big vector point
Cloth outer hexagon apex, totally six；Middle vector is distributed in the midpoint on the side of outer hexagon, and totally six；Small vector at
To appearance, it is divided into positive small vector and negative small vector, is distributed in the apex of interior hexagon, totally 12；Zero vector is distributed in six sides
The midpoint of shape, totally 3.
Fig. 9 is the on off sequence assumed when reference vector is located at 5 region of the big sector I using seven segmentation modulation strategies, is led to
The action time for adjusting positive and negative small vector is spent, realizes different control targets.PI device output in Fig. 4 is used to adjust positive and negative small
The action time of vector reduces amplitude of the common-mode voltage at resonance frequency, and then inhibits common mode resonance loop current.At this time three
The adjustment of phase separation time are as follows:
In order to guarantee the stability of system, dzIt must satisfy following condition
Similarly, when the output of DC side neutral-point voltage balance device is for adjusting the effect of positive and negative small vector in Fig. 7
Between, realize effective control of neutral point voltage balance.The action time of three-phase adjusts again at this time are as follows:
In order to guarantee the stability of system, yzIt must satisfy following condition
Table 1 is seven segmentation switching vector selector tables, and seven section space vector modulation strategies are with negative small vector beginning and end.Using
The modulation of seven section space vectors can effectively improve output waveform quality.Reduce the volume of filter.
The corresponding switching sequence of 1 different sectors of table
The foregoing is merely preferred embodiment of the present application, are not intended to limit this application, for the skill of this field
For art personnel, various changes and changes are possible in this application.Within the spirit and principles of this application, made any to repair
Change, equivalent replacement, improvement etc., should be included within the scope of protection of this application.
Above-mentioned, although the foregoing specific embodiments of the present invention is described with reference to the accompanying drawings, not protects model to the present invention
The limitation enclosed, those skilled in the art should understand that, based on the technical solutions of the present invention, those skilled in the art are not
Need to make the creative labor the various modifications or changes that can be made still within protection scope of the present invention.
Claims (6)
1. the common-mode circuit control method of a kind of photovoltaic DC-to-AC converter common mode resonance loop current and drain current suppressing system, the system
System includes: three-phase I font three-level inverter and modified LCL filter circuit, the capacitor of the modified LCL filter circuit
Common end is directly connected to the neutral point of DC side filter capacitor, changes the common mode circuit of three-phase I font three-level inverter, suppression
System leakage current processed；It is characterized in that: three-phase inverter side output electric current phase adduction is made the difference with reference value, difference is returned by common mode
Road resonance current controller obtains the control variable for adjusting positive and negative small vector action time, realizes seven segmentation modulation algorithms
In positive and negative small vector action time real-time adjustment；Common-mode voltage is reduced in common mode by changing positive and negative small vector action time
Amplitude at loop resonance frequency realizes the inhibition of common mode resonance loop current.
2. the common mode electricity of a kind of photovoltaic DC-to-AC converter common mode resonance loop current as described in claim 1 and drain current suppressing system
Road control method, it is characterized in that: realize that the controller that common mode resonance loop current inhibits is PI controller in common mode circuit,
Realize that the zero steady state error control of common mode resonance loop current, the reference value of common mode resonance loop current are set as zero.
3. the common mode electricity of a kind of photovoltaic DC-to-AC converter common mode resonance loop current as described in claim 1 and drain current suppressing system
Road control method, it is characterized in that: the three-phase I font three-level inverter includes three-phase bridge arm, every phase bridge arm includes upper and lower bridge
Arm, the upper and lower bridge arm include the clamp of two concatenated switching tubes and two connection upper and lower bridge arm switching tube midpoints
Diode, DC side include two concatenated identical filter capacitors, and a neutral point, every phase bridge are formed among two capacitors
The centre of two clamp diodes of arm is connected with neutral point, makes to exchange bridge arm midpoint generation zero potential.
4. the common mode electricity of a kind of photovoltaic DC-to-AC converter common mode resonance loop current as claimed in claim 3 and drain current suppressing system
Road control method, it is characterized in that: the on state of four switching tubes of every phase bridge arm is different, exchange bridge arm midpoint is generated
Current potential is different, and generation+Udc/2 ,-Udc/2,0 three kinds of level, Udc is supply voltage.
5. the common mode electricity of a kind of photovoltaic DC-to-AC converter common mode resonance loop current as claimed in claim 4 and drain current suppressing system
Road control method, opening for the switching tube are straight by conditioning circuit and driving circuit by the controller in control system with shutdown
Control is connect, it is characterized in that: the control system includes protection circuit, driving circuit, over-sampling modulate circuit and control circuit, three-phase
The signal of I font three-level inverter is connected to controller, the controller and protection circuit communication by over-sampling modulate circuit,
Realize that overcurrent and overvoltage protection, controller connect driving circuit, the pwm signal of controller output is put through the isolation of overdrive circuit
It is sent to the gate pole of switching tube greatly, control switch pipe being opened and turning off.
6. the common mode electricity of a kind of photovoltaic DC-to-AC converter common mode resonance loop current as claimed in claim 5 and drain current suppressing system
Road control method, it is characterized in that: over-sampling modulate circuit acquisition and the capacitance voltage up and down, the three-phase bridge inversion that improve DC side
Side electric current, three-phase filter capacitor voltage and three-phase power grid voltage value.
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| CN109302094A (en) * | 2018-10-10 | 2019-02-01 | 山东大学 | Three level parallel inverter of non-isolation type modularization, control method and system |
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| CN109995259B (en) * | 2019-05-17 | 2020-04-21 | 山东大学 | Common-mode voltage suppression method and system of NPC three-level inverter with unbalanced direct current side |
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| CN113179035A (en) * | 2021-05-12 | 2021-07-27 | 太原理工大学 | Non-isolated converter capable of eliminating leakage current and common mode voltage and control method |
| CN113285583B (en) * | 2021-05-26 | 2022-06-03 | 山东大学 | Non-isolated photovoltaic inverter leakage current suppression method and system |
| CN114142715A (en) * | 2021-12-03 | 2022-03-04 | 山东大学 | Common-mode resonance circulating current suppression method and system for high-power parallel inverter |
| CN114244169A (en) * | 2021-12-16 | 2022-03-25 | 山东大学 | Fractional order-based multi-index cooperative control method and system for three-level inverter |
| CN117318454B (en) * | 2023-11-28 | 2024-02-02 | 锦浪科技股份有限公司 | Low-frequency common-mode leakage current suppression method |
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| CN106532701B (en) * | 2016-11-16 | 2019-01-18 | 西安交通大学 | LCL type Active Power Filter-APF and its control method |
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| US11837868B2 (en) | 2021-03-27 | 2023-12-05 | Huawei Digital Power Technologies Co., Ltd. | Photovoltaic system and leakage current control method for photovoltaic system |
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Application publication date: 20180925 Assignee: AOTAI ELECTRIC Co.,Ltd. Assignor: SHANDONG University Contract record no.: X2021980009598 Denomination of invention: Common mode resonant loop current and leakage current suppression method for non isolated photovoltaic inverter Granted publication date: 20190903 License type: Exclusive License Record date: 20210922 |