CN108683351B - Hybrid modulation method, controller and the system of a kind of source Z three-level inverter - Google Patents
Hybrid modulation method, controller and the system of a kind of source Z three-level inverter Download PDFInfo
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- CN108683351B CN108683351B CN201810586830.5A CN201810586830A CN108683351B CN 108683351 B CN108683351 B CN 108683351B CN 201810586830 A CN201810586830 A CN 201810586830A CN 108683351 B CN108683351 B CN 108683351B
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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
- H02M7/487—Neutral point clamped inverters
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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
- H02M1/0048—Circuits or arrangements for reducing losses
- H02M1/0054—Transistor switching losses
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- 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
Abstract
The invention discloses a kind of hybrid modulation method of source Z three-level inverter, controller and systems.Wherein, it is high to solve the problems, such as that the existing source Z three-level inverter eliminates midpoint potential low-frequency oscillation method switching loss for the hybrid modulation method of a kind of source Z three-level inverter of the invention.This method combines zero-sequence component injection and double modulation wave modulator approach, by the way that the clipping factor is set dynamically, different modulation schemes are selected under different condition, carrys out the elimination of coordinated control midpoint potential low-frequency oscillation eventually by hybrid modulation method and boosting exports, while maximizing reduction switching loss.
Description
Technical field
The invention belongs to the hybrid modulation method of power electronics control field more particularly to a kind of source Z three-level inverter,
Controller and system.
Background technique
The source Z three-level inverter combines three-level topology and Z source network structure, remains three-level inverter derailing switch
The advantages such as low, the output waveform quality height of voltage suffered by part, while there is the boost function of Z-source inverter, and control is not required to be added
Dead zone, improves system reliability, and application prospect is extensive.However, uneven this of the midpoint potential of the source Z three-level inverter is asked
There is still a need for solve for topic.
In midpoint potential imbalance problem, the oscillation of midpoint potential three times fundamental frequency is referred to as low-frequency oscillation.Midpoint
The low-frequency oscillation of current potential all has an impact to DC capacitor volume and output waveform quality.To solve this problem, researcher proposes
Virtual vector PWM (Virtual Space Vector PWM, VSVPWM) modulator approach and double modulation wave carrier signal PWM
(double-modulation-wave carrier-based PWM, DMWPWM) modulator approach solves low-frequency oscillation problem.
Wherein, VSVPWM modulator approach is realized by converting virtual vector PWM for traditional 3 level space vector PWM
The control that centering line current is zero, to eliminate the low-frequency oscillation of midpoint potential.DMWPWM modulation strategy substantially with
VSVPWM is identical.But all there is switching frequency height, the high problem of switching loss in above two method.
Therefore, midpoint potential low-frequency oscillation can be completely eliminated by needing one kind, and reduce the modulation of switching loss as far as possible
Method, this has a very big significance the application of the source Z three-level inverter.
Summary of the invention
In order to solve the deficiencies in the prior art, there is provided a kind of source Z three-level inverters for the first object of the present invention
Hybrid modulation method, in conjunction with zero-sequence component injection and double modulation wave modulator approach, by the way that the clipping factor, different items are set dynamically
Different modulation schemes are selected under part, realize the coordinated control of the elimination and boosting output of midpoint potential low-frequency oscillation, while most
Bigization reduces switching loss.
A kind of hybrid modulation method of source Z three-level inverter of the invention, comprising:
Step 1: based on neutral point current average in a switch periods be zero principle and residual voltage offset with
The constraint condition of each phase modulated signal solves residual voltage offset；When more solutions occurs in residual voltage offset, amplitude is chosen
The smallest solution is for optimal solution and as residual voltage offset；
Step 2: according to straight-through duty ratio and three-phase reference voltage, the clipping factor of residual voltage offset is set dynamically；
Step 3: the residual voltage offset after clipping being superimposed on original three-phase modulations signal, straight-through offset is added
Amount, obtains modified three-phase modulations signal, and compared with carrier signal, generates pwm signal and to act on three level of the source Z inverse
Become device；
Step 4: by the residual voltage offset calculated in real time residual voltage compensation limit corresponding with the current clipping factor
Width threshold value comparison, if the former uses injected zero-sequence voltage scheme not above the latter；Otherwise, it is switched to double modulation wave scheme；Most
It is exported eventually by hybrid modulation method come the elimination of coordinated control midpoint potential low-frequency oscillation and boosting, while maximizing reduction and opening
Close loss.
Further, in the step 1, average neutral point current is obtained by average neutral point current model, wherein in
The building process of property point current model are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, the three-phase modulations signal and carrier wave after being changed by mark are believed
Number compare, each phase output state and corresponding action time is obtained, according to the time and three-phase current for being respectively connected to neutral point
Value obtains average neutral point current model.
Further, in the step 2, the size of the amplitude limit value of residual voltage offset according to modulated signal and is led directly to
The change of duty ratio and dynamic change, to guarantee to effectively eliminate midpoint electricity while the boosting output of the source Z three-level inverter
The low-frequency oscillation of position.
Further, in the step 3, the method that straight-through offset is added is based on the straight of same phase carrier wave stacking modulation
Logical insertion, detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, in the Yi Xiangqiao that modulated signal is minimized
Arm is inserted into lower pass-through state.
The second object of the present invention is to provide a kind of hybrid modulation controller of source Z three-level inverter.
A kind of hybrid modulation controller of source Z three-level inverter of the invention, comprising:
Residual voltage offset solves module, is configured as: being based on neutral point current average in a switch periods
Zero principle and the constraint condition of residual voltage offset and each phase modulated signal solve residual voltage offset；Work as zero sequence
When voltage compensation value appearance solves more, the smallest solution of amplitude is chosen for optimal solution and as residual voltage offset；
Module is set dynamically in the clipping factor, is configured as: according to straight-through duty ratio and three-phase reference voltage, dynamic setting
The clipping factor of residual voltage offset；
Three-phase modulations modification of signal module, is configured as: the residual voltage offset after clipping is superimposed to original three
In phase modulated signal, straight-through offset is added, obtains modified three-phase modulations signal, and compared with carrier signal, is produced
Raw pwm signal simultaneously acts on the source Z three-level inverter；
Modulation scheme switching module, is configured as: by the residual voltage offset calculated in real time and the current clipping factor
Corresponding residual voltage compensation limiting threshold compares, if the former uses injected zero-sequence voltage scheme not above the latter；It is no
Then, it is switched to double modulation wave scheme；Eventually by hybrid modulation method come the elimination of coordinated control midpoint potential low-frequency oscillation with
Boosting output, while maximizing reduction switching loss.
Further, it is solved in module in the residual voltage offset, average neutral point current is by average neutral point electricity
Flow model obtains, wherein the building process of neutral point current model are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, the three-phase modulations signal and carrier wave after being changed by mark are believed
Number compare, each phase output state and corresponding action time is obtained, according to the time and three-phase current for being respectively connected to neutral point
Value obtains average neutral point current model.
Further, in clipping factor dynamic setting module, the big rootlet of the amplitude limit value of residual voltage offset
The dynamic change according to the change of modulated signal and straight-through duty ratio, to guarantee the same of the boosting output of the source Z three-level inverter
When effectively eliminate the low-frequency oscillation of midpoint potential.
Further, in the three-phase modulations modification of signal module, the method that straight-through offset is added is based on same phase
The straight-through insertion of carrier wave stacking modulation, detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, in the Yi Xiangqiao that modulated signal is minimized
Arm is inserted into lower pass-through state.
The third object of the present invention is to provide a kind of control system of source Z three-level inverter.
The control system of a kind of source Z three-level inverter of the invention, including the source Z three-level inverter described above
Hybrid modulation controller.
Compared with prior art, the beneficial effects of the present invention are:
(1) present invention is by the precise classification under different situations, by the computational short cut of residual voltage offset, convenient for answering
With；Also pass through the setting of the dynamic slice factor, selects different modulation schemes under different condition, realize midpoint potential low-frequency oscillation
Elimination and boosting output coordinated control, while maximizing reduction switching loss.
(2) present invention solves the problems, such as that existing elimination mid-point voltage low-frequency oscillation scheme switching loss is high, can be complete
The low-frequency oscillation of mid-point voltage is eliminated, and there is lower switching loss compared to the modulation of double modulation wave and VSVPWM modulation,
To improve the efficiency of inverter.
(3) present invention is led for expanding the source Z three-level inverter in new energy such as photovoltaic generating system, power generation systems
Domain application is of great significance.
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 source Z NPC three-level inverter topology figure；
Fig. 2 is three-phase modulations signal and corresponding output state duty ratio of time relational graph each in a cycle；
Fig. 3 is that the pass-through state based on the stacking modulation of same phase carrier wave is inserted into figure；
Fig. 4 (a) is D=0.1, when M=0.9, PF=1, applies dc-link capacitance voltage, three before and after hybrid modulation method
Phase current, phase voltage Uab, Z source network output voltage waveforms；
Fig. 4 (b) is D=0.1, when M=0.9, PF=0.8, apply dc-link capacitance voltage before and after hybrid modulation method,
Three-phase current, phase voltage Uab, Z source network output voltage waveforms；
Fig. 4 (c) is D=0.2, when M=0.9, PF=1, applies dc-link capacitance voltage, three before and after hybrid modulation method
Phase current, phase voltage Uab, Z source network output voltage waveforms；
Fig. 5 (a) is D=0.1, when M=0.9, PF=1, injects VcompThree-phase modulations signal, residual voltage offset
VcompWaveform；
Fig. 5 (b) is D=0.1, when M=0.9, PF=0.8, injects VcompThree-phase modulations signal, residual voltage offset
Vcomp, different schemes switching waveform；
Fig. 5 (c) is D=0.2, when M=0.9, PF=1, injects VcompThree-phase modulations signal, residual voltage offset
Vcomp, different schemes switching waveform；
Fig. 6 (a) is D=0, when M=1, using double modulation wave method and hybrid modulation method under different capacity factor
Device loss comparison diagram；
Fig. 6 (b) is D=0.1, when M=0.8, using double modulation wave method and hybrid modulation method in different capacity factor
Under device loss comparison diagram；
Fig. 6 (c) is D=0.15, when M=0.8, using double modulation wave method and hybrid modulation method in different capacity factor
Under device loss comparison diagram；
Fig. 7 is system control block figure.
Specific embodiment
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.
As background technique is introduced, it is currently used for the side of the source Z three-level inverter mid-point voltage low-frequency oscillation inhibition
Case has that switching loss is high, and to solve this problem, the present invention provides a kind of hybrid modulation side of source Z three-level inverter
Method.
A kind of hybrid modulation method of source Z three-level inverter of the invention, specifically includes the following steps:
Step 1: based on neutral point current average in a switch periods be zero principle and residual voltage offset with
The constraint condition of each phase modulated signal solves residual voltage offset；When more solutions occurs in residual voltage offset, amplitude is chosen
The smallest solution is for optimal solution and as residual voltage offset.
Specifically, average neutral point current is obtained by average neutral point current model, wherein the structure of neutral point current model
Build process are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, the three-phase modulations signal and carrier wave after being changed by mark are believed
Number compare, each phase output state and corresponding action time is obtained, according to the time and three-phase current for being respectively connected to neutral point
Value obtains average neutral point current model.
Fig. 1 is the source Z NPC three-level inverter topology figure.By to three-phase modulations signal Vx *(x=a, b, c) injects V0It mentions
High DC bus-bar voltage utilization rate.Three-phase modulations signal expression, three-phase modulations signal value size sequence expression formula, is added V0
Expression formula and its value size afterwards sorts respectively as shown in formula (1), (2), (3):
Wherein, V0For the zero sequence for being used to improve DC bus-bar voltage utilization rate being calculated by standard three-phase modulations signal
Component, M are modulation degree, Va’、Vb’、Vc' it is plus V0Three-phase modulations signal afterwards.
Fig. 2 is to mark the three-phase modulations signal after changing and corresponding output state duty ratio of time relationship each in a cycle
Figure.If the straight-through time is equal above and below in a switch periods, then the injection of pass-through state will not influence the flat of inverter
Equal current in middle wire.As intermediate voltage value VmidWhen greater than zero, average neutral point current INPIt indicates are as follows:
I in formulamax、ImidAnd IminThe output that respectively there is the modulated signal of maximum value, median and minimum value to correspond to phase
Electric current, dmax、dmid、dminValue is respectively equal to mark the V after changingmax、VmidAnd Vmin。
In order to inhibit midpoint potential low-frequency oscillation, the average neutral point current in a switch periods should be zero.Pass through
A residual voltage offset V is added to each phase original modulation signalscompChange each phase to be connected in a switch periods
The time of neutral point, to realize that median average electric current is zero and does not influence output line voltage.
After injecting residual voltage offset, if Vmid+Vcomp> 0, median average electric current is expressed as (5)；If Vmid+Vcomp≤ 0,
Median average electric current is expressed as (6):
INP=-(Vmax+Vcomp)·Imax-(Vmid+Vcomp)·Imid+(Vmin+Vcomp)·Imin(Vmid+Vcomp> 0) (5)
INP=-(Vmax+Vcomp)·Imax+(Vmid+Vcomp)·Imid+(Vmin+Vcomp)·Imin(Vmid+Vcomp≤0)(6)
The calculation formula of residual voltage offset changes with the variation of modulated signal, compensates here according to residual voltage
The constraint condition of value and each phase modulated signal, is classified as four kinds for all possible situation.
1) situation 1:Vmid> 0 and Vmid≥1+Vmin
In this case, the solution of offset voltage value determines that uniquely median average current formula is provided by formula (5), enables one to open
Closing median average electric current in the period is zero zero sequence compensation voltage V to be calculatedcomp:
2) situation 2:Vmid> 0 and Vmid<1+Vmin
In this case, VcompWhen taking negative value, in fact it could happen that Vmid+Vcomp≤ 0 the case where, that is to say, that the voltage compensation of injection
Value changes the polarity of former modulated signal, so need to select midpoint current formula according to the actual situation.Work as Vmid+VcompWhen > 0,
Median average electric current is provided by formula (5)；Work as Vmid+VcompWhen≤0, median average electric current is provided by formula (6).Enable INP=0, two kinds
V under subcasecompIt can be calculated respectively by following formula:
3) situation 3:Vmid≤ 0 and | Vmid| > 1-Vmax
In this case, median average electric current is provided by (6) formula, and offset voltage value uniquely determines, and calculation formula is such as
Under:
4) situation 4:Vmid≤ 0 and | Vmid|≤1-Vmax
In this case, VcompWhen taking positive value, it may occur however that Vmid+Vcomp> 0 situation, it is similar with situation 2, according to VmidWith
VcompAmplitude and polar difference, median average current formula is likely to occur two kinds of situations, the voltage compensation under different situations
Value can be calculated by following formula respectively:
Calculating process has been divided into four kinds of situations according to the constraint of modulated signal, and different forms can be according to initial modulation
Signal VmidWith modified VmidIt distinguishes.
In situation 1 and 3, the solution of voltage compensation value is unique and determines, however, in situation 2 and 4, when inputting constant
There may be two solutions while meeting the requirements.Once voltage compensation value exists simultaneously two redundancy solutions, in order to minimize zero sequence electricity
Pressure amplitude degree and maximization midpoint potential oscillation elimination ability, choose the lesser solution of amplitude here and are used as optimal solution.Add zero sequence electricity
Modulating wave expression formula such as (11) after pressure value for the source Z three-level inverter PWM generation is shown.
Step 2: according to straight-through duty ratio and three-phase reference voltage, the clipping factor of residual voltage offset is set dynamically.
Specifically, in order to realize that the coordinated control with boosting output is eliminated in oscillation, in conjunction with the value of current straight-through duty ratio
Three-phase modulations signal maximum, minimum value, are set dynamically the clipping factor of residual voltage, including upper clipping and lower limit after changing with mark
Width.
After calculating the optimal residual voltage offset for eliminating midpoint potential low-frequency oscillation, by setting offset voltage clipping
The factor guarantees the normal work of Z-source inverter, does not cause output voltage abnormal while realizing Z-source inverter boosting output function
Become, and reaches the target for effectively eliminating midpoint potential low-frequency oscillation.
In conjunction with the value of straight-through duty ratio, the upper limit magnitude of offset voltage value may be set to 1-T0/Ts-Vmax, offset voltage
The lower limit set of value is -1+T0/Ts-Vmin, the size of amplitude limit value according to the change of modulated signal and straight-through duty ratio and dynamic becomes
Change, to guarantee the low-frequency oscillation that can effectively eliminate midpoint potential while boosting output.Wherein, T0=TU=TL,TUIt is one
Upper straight-through time in switch periods, TLFor the lower straight-through time in a switch periods, TsFor switch periods.
Step 3: the residual voltage offset after clipping being superimposed on original three-phase modulations signal, straight-through offset is added
Amount, obtains modified three-phase modulations signal and compared with carrier signal, generates pwm signal and to act on three level of the source Z inverse
Become device.
In the step 3, the method that straight-through offset is added is the straight-through insertion based on the stacking modulation of same phase carrier wave,
Detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, in the Yi Xiangqiao that modulated signal is minimized
Arm is inserted into lower pass-through state.
Step 4: by the residual voltage offset calculated in real time residual voltage compensation limit corresponding with the current clipping factor
Width threshold value comparison, if the former uses injected zero-sequence voltage scheme not above the latter；Otherwise, it is switched to double modulation wave scheme；Most
It is exported eventually by hybrid modulation method come the elimination of coordinated control midpoint potential low-frequency oscillation and boosting, while maximizing reduction and opening
Close loss.
The clipping factor that residual voltage offset is set according to modulated signal and straight-through duty ratio, calculates when by formula
When the residual voltage offset arrived is more than clipping, the residual voltage value after illustrating clipping cannot be completely eliminated low-frequency oscillation.In terms of
Whether obtained residual voltage offset is more than Rule of judgment that clipping switches as scheme, if not above clipping, using zero
Sequence voltage injecting scheme needs to be switched to double modulation wave scheme if being more than clipping, carries out low frequency vibration using double modulation wave strategy
Swing elimination.Consider that the double modulation wave modulated signal expression formula such as (12) of pass-through state insertion is shown, according to size corresponding relationship pair
ABC three-phase should be arrived, the generation pwm signal compared with carrier wave.System entirety control block diagram is as shown in Figure 7.
Wherein,To be used for the expression formula that double modulation wave is modulated after the modulating wave modification with maximum value,For
For adding the expression formula of upper pass-through state；WithIt is adjusted for what the modulating wave modification with median generated for double
Two new modulated signals of wave modulation processed；For what is modulated after the modulating wave modification with minimum value for double modulation wave
Expression formula,For the expression formula for adding lower pass-through state.
Simulating, verifying and analysis are carried out below:
In order to verify the validity of proposed control method, in MATLAB/Simulink R2014b, the source Z NPC tri- is built
Electrical level inverter and pessimistic concurrency control carry out emulation experiment verifying.Simulation parameter is as shown in table 1.
1 simulation parameter of table
Fig. 4 (a)-Fig. 4 (c) is the simulation result waveform under the conditions of different parameters, by simulation result it is found that mixing applying
After modulator approach, the low-frequency oscillation of DC bus midpoint potential is eliminated, and inverter boost function is normal.By observing Fig. 5
(a) the residual voltage offset under the conditions of-Fig. 5 (c) different parameters and modified three-phase modulations wave are it is found that according to the zero of calculating
Whether sequence voltage offset is more than clipping, i.e., whether the modulating wave after injection residual voltage is more than ± 1, has carried out two schemes
Switching is increased with the reduction of power factor using the ratio of double modulation wave method.
Fig. 6 (a)-Fig. 6 (c) is the switching tube of double modulation wave method and hybrid modulation method loss comparison under different operating conditions,
Lossy data is emulated by PLECS and is obtained.As can be seen from the results, under different operating conditions, hybrid modulation side proposed by the present invention is used
Method, the loss that switching tube generates are substantially reduced compared with using double modulation wave method.
By the above simulation result it is found that eliminating the hybrid modulation method of DC side midpoint potential low-frequency oscillation in the present invention
Low-frequency oscillation can be eliminated, and the loss that switching tube generates is substantially reduced compared with double modulation wave method.
The present invention also provides a kind of hybrid modulation controllers of source Z three-level inverter.
Specifically, the hybrid modulation controller of a kind of source Z three-level inverter of the invention, comprising:
(1) residual voltage offset solves module, is configured as: based on neutral point current average in a switch periods
The constraint condition of the principle for being zero and residual voltage offset and each phase modulated signal solves residual voltage offset；When zero
When the appearance of sequence voltage offset solves more, the smallest solution of amplitude is chosen for optimal solution and as residual voltage offset；
Specifically, it is solved in module in the residual voltage offset, average neutral point current is by average neutral point current
Model obtains, wherein the building process of neutral point current model are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, the three-phase modulations signal and carrier wave after being changed by mark are believed
Number compare, each phase output state and corresponding action time is obtained, according to the time and three-phase current for being respectively connected to neutral point
Value obtains average neutral point current model.
(2) module is set dynamically in the clipping factor, is configured as: according to straight-through duty ratio and three-phase reference voltage, dynamic
The clipping factor of residual voltage offset is set；
Specifically, in clipping factor dynamic setting module, the size of the amplitude limit value of residual voltage offset according to
The change of modulated signal and straight-through duty ratio and dynamic change, thus while guaranteeing the boosting output of the source Z three-level inverter
Effectively eliminate the low-frequency oscillation of midpoint potential.
(3) three-phase modulations modification of signal module, is configured as: the residual voltage offset after clipping being superimposed to original
On three-phase modulations signal, straight-through offset is added, obtains modified three-phase modulations signal；Modified three-phase modulations are believed
Number compared with carrier signal, generates pwm signal and simultaneously act on the source Z three-level inverter.
Specifically, in the three-phase modulations modification of signal module, the method that straight-through offset is added is to be carried based on same phase
The straight-through insertion of wave stacking modulation, detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, in the Yi Xiangqiao that modulated signal is minimized
Arm is inserted into lower pass-through state.
(4) modulation scheme switching module is configured as: by the residual voltage offset calculated in real time and current clipping because
The corresponding residual voltage compensation limiting threshold of son compares, if the former uses injected zero-sequence voltage scheme not above the latter；It is no
Then, it is switched to double modulation wave scheme；Eventually by hybrid modulation method come the elimination of coordinated control midpoint potential low-frequency oscillation with
Boosting output, while maximizing reduction switching loss.
The present invention is by the precise classification under different situations, by the computational short cut of residual voltage offset, convenient for application；Also
By the setting of the dynamic slice factor, different modulation schemes are selected under different condition, realize disappearing for midpoint potential low-frequency oscillation
Except the coordinated control with boosting output, while maximizing reduction switching loss.
The present invention solves the problems, such as that existing elimination mid-point voltage low-frequency oscillation scheme switching loss is high, can completely eliminate
The low-frequency oscillation of mid-point voltage, and there is lower switching loss compared to the modulation of double modulation wave and VSVPWM modulation, thus
Improve the efficiency of inverter.
The present invention is for expanding the source Z three-level inverter in new energy fields such as photovoltaic generating system, power generation systems
Using being of great significance.
The present invention also provides a kind of control systems of source Z three-level inverter.It specifically, should include the source Z described above
The hybrid modulation controller of three-level inverter.
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 (9)
1. a kind of hybrid modulation method of source Z three-level inverter characterized by comprising
Step 1: the principle for being zero based on neutral point current average in a switch periods, in residual voltage offset and each phase tune
Under the constraint condition of signal processed, residual voltage offset is solved；When more solutions occurs in residual voltage offset, it is minimum to choose amplitude
Solution be optimal solution and as residual voltage offset；
Step 2: according to straight-through duty ratio and three-phase reference voltage, the clipping factor of residual voltage offset is set dynamically；
Step 3: the residual voltage offset after clipping is superimposed on original three-phase modulations signal, straight-through offset is added,
Modified three-phase modulations signal is obtained, and compared with carrier signal, generate pwm signal and acts on the source Z tri-level inversion
Device；
Step 4: the residual voltage offset calculated in real time residual voltage corresponding with the current clipping factor is compensated into clipping threshold
Value compares, if the former uses injected zero-sequence voltage scheme not above the latter；Otherwise, it is switched to double modulation wave scheme；It is final logical
It crosses hybrid modulation method and comes the elimination and boosting output of coordinated control midpoint potential low-frequency oscillation, while maximizing reduction switch damage
Consumption.
2. a kind of hybrid modulation method of source Z as described in claim 1 three-level inverter, which is characterized in that in the step
In rapid 1, average neutral point current is obtained by average neutral point current model, wherein the building process of neutral point current model are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, three-phase modulations signal and carrier signal ratio after being changed by mark
Compared with obtaining each phase output state and corresponding action time, according to the time and three-phase electricity flow valuve for being respectively connected to neutral point, obtain
To average neutral point current model.
3. a kind of hybrid modulation method of source Z as described in claim 1 three-level inverter, which is characterized in that in the step
In rapid 2, the size of the amplitude limit value of residual voltage offset dynamic change according to the change of modulated signal and straight-through duty ratio, from
And guarantee the low-frequency oscillation that midpoint potential is effectively eliminated while the boosting output of the source Z three-level inverter.
4. a kind of hybrid modulation method of source Z as described in claim 1 three-level inverter, which is characterized in that in the step
In rapid 3, the method that straight-through offset is added is the straight-through insertion based on the stacking modulation of same phase carrier wave, detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, is inserted in the phase bridge arm that modulated signal is minimized
Enter lower pass-through state.
5. a kind of hybrid modulation controller of source Z three-level inverter characterized by comprising
Residual voltage offset solves module, is configured as: being zero based on neutral point current average in a switch periods
Principle solves residual voltage offset in residual voltage offset under the constraint condition of each phase modulated signal；Work as residual voltage
When offset appearance solves more, the smallest solution of amplitude is chosen for optimal solution and as residual voltage offset；
Module is set dynamically in the clipping factor, is configured as: according to straight-through duty ratio and three-phase reference voltage, zero sequence is set dynamically
The clipping factor of voltage compensation value；
Three-phase modulations modification of signal module, is configured as: the residual voltage offset after clipping is superimposed to original three-phase tune
On signal processed, straight-through offset is added, obtains modified three-phase modulations signal, and compared with carrier signal, generates PWM
Signal simultaneously acts on the source Z three-level inverter；
Modulation scheme switching module, is configured as: the residual voltage offset calculated in real time is opposite with the current clipping factor
The residual voltage compensation limiting threshold answered compares, if the former uses injected zero-sequence voltage scheme not above the latter；Otherwise, it cuts
Change to double modulation wave scheme；Eventually by hybrid modulation method come coordinated control midpoint potential low-frequency oscillation elimination and boosting it is defeated
Out, while reduction switching loss is maximized.
6. a kind of hybrid modulation controller of source Z as claimed in claim 5 three-level inverter, which is characterized in that described
Residual voltage offset solves in module, and average neutral point current is obtained by average neutral point current model, wherein neutral point electricity
The building process of flow model are as follows:
Assuming that three-phase modulations signal value is constant in a switch periods, three-phase modulations signal and carrier signal ratio after being changed by mark
Compared with obtaining each phase output state and corresponding action time, according to the time and three-phase electricity flow valuve for being respectively connected to neutral point, obtain
To average neutral point current model.
7. a kind of hybrid modulation controller of source Z as claimed in claim 5 three-level inverter, which is characterized in that described
The clipping factor is set dynamically in module, and the size of the amplitude limit value of residual voltage offset is according to modulated signal and straight-through duty ratio
Change and dynamic change, to guarantee the low frequency for effectively eliminating midpoint potential while the boosting output of the source Z three-level inverter
Oscillation.
8. a kind of hybrid modulation controller of source Z as claimed in claim 5 three-level inverter, which is characterized in that described
In three-phase modulations modification of signal module, the method that straight-through offset is added is the straight-through insertion based on the stacking modulation of same phase carrier wave,
Its detailed process are as follows:
It is inserted into upper pass-through state in the phase bridge arm that modulated signal is maximized, is inserted in the phase bridge arm that modulated signal is minimized
Enter lower pass-through state.
9. a kind of control system of source Z three-level inverter, which is characterized in that including as described in any one of claim 5-8
The source Z three-level inverter hybrid modulation controller.
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