CN109067193A - A kind of cascade connection type electric power electric transformer and its imbalance compensation control method - Google Patents

A kind of cascade connection type electric power electric transformer and its imbalance compensation control method Download PDF

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CN109067193A
CN109067193A CN201810939314.6A CN201810939314A CN109067193A CN 109067193 A CN109067193 A CN 109067193A CN 201810939314 A CN201810939314 A CN 201810939314A CN 109067193 A CN109067193 A CN 109067193A
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voltage
current
phase
transformer
control
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CN109067193B (en
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曲正伟
姚云枭
王云静
郭蕊
孟令楠
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Nanjing Yanzhan Technology Co.,Ltd.
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Yanshan University
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS 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
    • H02M5/00Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26Arrangements for eliminating or reducing asymmetry in polyphase networks
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50Arrangements for eliminating or reducing asymmetry in polyphase networks

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Inverter Devices (AREA)

Abstract

The present invention provides a kind of imbalance compensation control method of cascade connection type electric power electric transformer, including control assembly and transformer, and transformer is made of input rectifying grade, isolation level and output inverse cascade.Wherein input stage is the Cascade H bridge rectifier that three-phase star connects, and isolation level is multiple independent double active bridge current transformers, and output stage is Single-phase PWM Inverter.Control method of the invention includes input rectifying stage layered control unit, isolation level voltage close loop control unit and output inverse cascade constant pressure and sharing control unit, the hierarchical control unit of input stage is divided into top level control unit and lower layer's control unit again, wherein top level control unit inhibits three parts to form by coordinate transform, positive sequence decoupling control and negative-sequence current, and lower layer's control unit is Pressure and Control in phase.Using control method provided by the invention, negative-sequence current compensation problem of the PET in voltage on line side and threephase load imbalance can be solved simultaneously, to promote the application of electric power electric transformer in practice in engineering.

Description

A kind of cascade connection type electric power electric transformer and its imbalance compensation control method
Technical field
The invention belongs to electric power electric transformer technical fields, and in particular to a kind of cascade connection type electric power electric transformer is not Balanced compensated control method.
Background technique
Electric power electric transformer (Power Electronic Transformer, PET), also known as solid-state transformer (Solid State Transformer, SST), it is a kind of power transformation that traditional Industrial Frequency Transformer is substituted in the electric system of power electronics Device, other than being able to achieve traditional transformation and isolation, also have both reactive compensation, harmonics restraint, power bi-directional transmission and The function of multi output power supply.
In recent years, with the continuous development of PET technology, in mesohigh power distribution network application more and more attention has been paid to.And In high pressure applications, since the resistance to voltage levels of device for power switching are limited, frequently with modularization or cascade structure to improve The input voltage that electric power electric transformer can be born.Wherein the more extensive two kinds of topologys of application are that U.S.'s future is renewable respectively Electric energy transmission and management project (Future Renewable Electric Energy Delivery and Management, FREEDM) use based on Cascade H bridge rectifier single-phase PET topology and the Chinese Academy of Sciences develop it is how electric based on modularization The three-phase PET topology of flat inverter (Modular Multilevel Converter, MMC).Both topologys are in ideal power grid With the various functions that can realize PET under the operating condition of three phase symmetry load well, but in practical power distribution network, due to system Often there is the operating condition of asymmetrical three-phase in the investment of failure or extensive single-phase load, voltage on line side and output lateral load, If can not compensate to above-mentioned imbalance, PET can inject negative-sequence current to power grid, pollute to bulk power grid, together When each phase high voltage direct current capacitor voltage as caused by negative-sequence current it is unbalanced, the switching device of input stage can be made due to excessively electric It presses and damages.Therefore, the Compensation Strategies studied under three-phase imbalance have very PET in the popularization of engineering in practice Important meaning.
Realize that PET can solve the compensation of unbalanced load in terms of topology and controlling unit two, but from topology Improved method often will increase the complexity of circuit, usually also need matched control strategy, and cost can also increase therewith, In comparison, the method compensated from controlling unit is more practical.Conventional compensation method is real using symmetrical component method The separation of existing positive and negative order components, is then respectively controlled under respective rotating coordinate system, this method not can avoid positive and negative Sequence separates bring detection delay, and dynamic response is poor, and control system is more complex.There are also one kind to be based on injected zero-sequence voltage Compensation method, this method needs to calculate the amplitude and phase angle of offset voltage in real time according to the voltage fluctuation of DC side, so that mending The residual voltage sine repaid is poor, is easy to pollute to net side harmonic, and what is compensated is limited in scope.
Summary of the invention
In order to overcome the drawbacks of the prior art, the present invention provides a kind of imbalance compensation of cascade connection type electric power electric transformer Control system and method can solve negative-sequence current compensation problem of the PET in voltage on line side and threephase load imbalance simultaneously, from And promote the application of electric power electric transformer in practice in engineering.
Specifically, the present invention provides a kind of cascade connection type electric power electric transformer comprising transformer and control assembly, institute State transformer include input rectifying grade, isolation level and output inverse cascade,
The input rectifying grade is made of the single-phase cascade type H bridge rectifier of three star-like connections;The isolation level is more A independent double active bridge current transformers, the output end of each double active bridge current transformers are connected in parallel, and constitute low-voltage direct bus; The output inverse cascade is Single-phase PWM Inverter;
Input rectifying grade, isolation level and output inverse cascade are all made of single-phase H bridge current transformer and are controlled, single-phase H bridging Switching device in stream device is all made of powerful IGBT;
The control assembly includes input rectifying stage layered control unit, isolation level control unit and output inverse cascade control The hierarchical control unit of unit processed, input stage is divided into top level control unit and lower layer's control unit again, in top level control unit A depression of order Generalized Integrator is embedded in inhibit the negative-sequence current of net side and realize the control of net side power using positive sequence decoupling control The decoupling of system and total DC voltage are constant;Lower layer's control unit of the input rectifying grade is for overcoming circuit parameter and opening Closing influences caused by delay, maintains the electric voltage equalization between every mutually each submodule, and the isolation level is real using closed loop PI controller The low-voltage direct busbar voltage of existing each submodule is constant, and the output inverse cascade uses the control method of voltage and current double closed-loop Maintain output voltage constant.
Preferably, double active bridge current transformers of the isolation level include primary side H bridge current transformer, high frequency transformer and pair side H Bridge current transformer, configured with single phase-shifted pulse width modulation unit, single phase shift between the primary side H bridge current transformer and secondary side H bridge current transformer Pwm unit utilizes single phase-shifted pulse width modulation (Single Phase Shift-Pulse Width Modulation, SPS- PWM two-way flow of the power in isolation level current transformer) is realized.
Preferably, PR controller subject to the controller of the output inverse cascade.
Preferably, using inductor filter after three of the input rectifying grade single-phase Cascade H bridge rectifier star-like connections It is connected with AC network or AC load.
Preferably, the output end of the input stage H bridge rectifier is connected with the input terminal of DAB primary side H bridge current transformer; The primary side of the output termination high frequency transformer of DAB primary side H bridge current transformer, the secondary H bridging stream when connecting DAB pair of high frequency transformer The input terminal of device;The output end of DAB pair side H bridge current transformer is connected with the input terminal of output stage Single-phase PWM Inverter;Output stage The output end of Single-phase PWM Inverter connects low-voltage alternating-current power grid or AC load by filter.
Preferably, the present invention also provides a kind of imbalance compensation control method of cascade connection type electric power electric transformer, packets It includes:
S1, input stage hierarchical control unit be divided into top level control unit and lower layer's control unit, wherein top level control list Member inhibits three parts to form by coordinate transform, positive sequence decoupling control and negative-sequence current.
Coordinate transform: the three-phase voltage e of net sideabcActive voltage component e is obtained after dq coordinate transformdWith idle electricity Press component eq;The three-phase current i of net sideabcWatt current measured value i is obtained after dq coordinate transformsdIt is measured with reactive current Value isq, watt current measured value isdWith reactive current measured value isqRespectively by a trapper to obtain respective positive sequence Component, watt current isdPositive-sequence component beReactive current isqPositive-sequence component be
Positive sequence decoupling: the high voltage direct current capacitor average voltage U of all modules is acquireddc_ave, and and reference valueMake Difference obtains the reference value of watt current using a pi regulatorSimultaneously by the reference value of reactive currentIt is set as 0, for realizing the unity power factor correction of net side, the watt current reference value that will be previously obtainedIt is referred to reactive current ValueActive voltage reference signal is obtained by a decoupling controller with after respective positive-sequence component measured value work difference respectively usdWith reactive voltage reference signal usq
Negative-sequence current inhibits: watt current reference value isd *With watt current measured value isdIt is wide by a depression of order after work difference Adopted integrator obtains the thermal compensation signal u of active voltagedcom;Reactive current reference value isq *With reactive current measured value isqAfter making difference The thermal compensation signal u of reactive voltage is obtained by a depression of order Generalized Integratorqcom
By the thermal compensation signal u of active voltagedcomSubtract reference signal usdAnd the feed-forward voltage e with net sidedIt is added, idle electricity The thermal compensation signal u of pressureqcomSubtract the reference signal u obtained from the output of positive sequence decoupling controlsqAnd the feed-forward voltage e with net sideq It is added, finally obtains the modulated voltage signal of input stage by dq inverse transformation respectively
S2, input rectifying grade lower layer's control unit be phase in Pressure and Control, specifically: acquisition xth phase (x ∈ a, b, C }) the DC capacitor voltage U of internal each submoduledc_x_1,...,Udc_x_N, and the DC capacitor average voltage with xth phase Udc_x_aveIt is poor to make, and is multiplied after a proportional controller with the sign function of watt current, finally obtains with by top level control Modulation voltage reference signalIt is first multiplied and is added again, finally obtain the modulation voltage u of each submodulexm1,uxm1,...uxmN
The low-voltage direct busbar voltage that S3, isolation level adjust each submodule using closed-loop control is constant, and uses SPS-PWM Two-way flow of the modulation technology power in isolation level current transformer, the control method of N number of submodule is all the same, x-th of son The low-voltage direct capacitor voltage measuring value U of module (x=1,2 .., N)dc_LxWith low-voltage direct busbar voltage reference value Udc_L *Make After difference, the phase-shift control angle of each DAB current transformer is obtained by pi regulatorEach DAB current transformer is controlled respectively Flow of power;
S4, output stage closed-loop control: in output stage control, the measured value u of inverse cascade output voltagexIt is electric with output first The reference value u of pressurex *It is poor to make, and then believes again divided by the output current reference that N obtains each submodule by a quasi- PR controller Number ix *, in this, as the input of current inner loop, respectively with the output current measurement value i of each submodulex_1,ix_2,...,ix_NMake Difference finally obtains the modulated voltage signal u of each submodule by a quasi- PR controllerx_1,ux_2,...,ux_N
Preferably, modulation voltage reference signal of the input stage rectifier under α β shafting can indicate are as follows:
U in formulaαAnd U *β* the modulation voltage reference signal under α β shafting, E are indicatedd,EqFor the active and nothing of power grid electromotive force Function component,WithIndicate the active and reactive voltage of PI controller output, ω1The angular frequency of power grid is indicated, when t is indicated Between, I2d,I2qFor two frequency multiplication of negative phase-sequence is active and the amplitude of reactive component,For the initial phase angle of negative sequence component;
UαAnd U *β* only contain fundamental positive sequence and negative sequence component in, wherein positive-sequence component is used for the power of control system transmission, Negative sequence component is used to inhibit the negative-sequence current of net side.
Preferably, the trapper frequency in step S1 is 100HZ.
Compared with prior art, the present invention has the advantage that
1, disclosed by the invention that control strategy is assisted based on depression of order Generalized Integrator, cascade connection type PET reply can be improved not The ability of balance condition makes PET still be able to achieve the power transmission of high quality when net side and load-side three-phase imbalance occur.
2, the compensation method based on ROGI adjuster that the present invention uses can effectively inhibit the net side under uneven operating condition Negative-sequence current, with it is traditional based on double dq shaftings divide sequence compensation method compared with, possess in response speed and compensation effect bright Aobvious advantage.
3, imbalance compensation control method disclosed by the invention only works in three-phase imbalance, will not influence PET and exists Normal operation under the conditions of voltage and load balance.
4, unbalance control scheme disclosed by the invention can make PET when voltage on line side is seriously asymmetric, still maintain The high power quality of alternating current-direct current output, this makes PET be provided with certain fault ride-through capacity.
5, imbalance compensation control strategy disclosed by the invention, suitable for the application of any voltage class and any The cascade connection type PET of number of modules, can also be extended in the PET of three-phase four-wire system.
Detailed description of the invention
Fig. 1 is the cascade connection type electric power electric transformer main circuit topological structure schematic diagram that the present invention uses.
Fig. 2 is the existing point sequence imbalance compensation control principle drawing based on double dq shaftings.
Fig. 3 is the input stage top level control schematic diagram proposed by the present invention based on the auxiliary control of ROGI adjuster.
Fig. 4 is Pressure and Control schematic diagram in the input rectifying grade lower layer phase of the invention used.
Fig. 5 is the voltage close loop control principle drawing for the isolation level that the present invention uses.
Fig. 6 is the output stage Single-phase PWM Inverter voltage and current double closed-loop control based on quasi- PR controller that the present invention uses Schematic diagram processed.
Fig. 7 is simulation waveform when asymmetrical three-phase occurs in voltage on line side.
Fig. 8 is simulation waveform when threephase load power occurs uneven.
Current on line side simulation waveform when Fig. 9 is point sequence compensating controller using double dq shaftings.
Figure 10 is current on line side simulation waveform when being compensated using unbalance control scheme of the invention.
Figure 11 is using the compensated net side A phase voltage of control program and current waveform figure of the invention.
Figure 12 is simulation waveform when serious asymmetrical three-phase occurs in voltage on line side.
Figure 13 is using the unbalance control scheme of the invention input compensation in voltage on line side serious asymmetrical three-phase Current on line side simulation waveform.
Specific embodiment
Below with reference to the attached drawing exemplary embodiment that the present invention will be described in detail, feature and aspect.It is identical attached in attached drawing Icon note indicates element functionally identical or similar.Although the various aspects of embodiment are shown in the attached drawings, unless special It does not point out, it is not necessary to attached drawing drawn to scale.
The invention discloses it is a kind of based on depression of order Generalized Integrator auxiliary control cascade connection type PET imbalance compensation strategy, By one ROGI adjuster of insertion in the decoupling control link of positive dq shafting, positive-negative sequence current is uniformly controlled, Link is separated with positive-negative sequence due to not needing instruction current calculating, so that the control of input stage has obtained apparent simplification.
A kind of typical PET is topological as shown in Figure 1, including three rectification, isolation, inversion parts.Wherein rectification stage is by three The single-phase cascade type H bridge rectifier of a star-like connection forms, and carries out switch control using phase-shifting carrier wave modulation (CPS-PWM) technology System.Isolation level is multiple independent double active bridge (DualActive Bridge, DAB) current transformers;Output stage is that single-phase PWM is inverse Become device.It is connected using inductor filter with utility network after three single-phase rectification stage star-like connections.The output end of DAB can be simultaneously It is linked to together, constitutes low-voltage direct bus, supply distributed generation resource, energy storage device and DC load access.And inverter is defeated Outlet can both connect low-voltage alternating-current power grid, can also connect AC load.
When the threephase load imbalance of ac output end, the electric current of each phase transimission power is different, can make the three of net side There is negative sequence component in phase current, pollutes to power grid.Part document is separated using a kind of as shown in Figure 2 based on positive-negative sequence Double dq shaftings under unbalance control strategy, although can effectively inhibit the negative-sequence current of net side, control system is more complex, And not can avoid positive-negative sequence separation bring compensation delay, the dynamic property of controller is poor.
And the control strategy that this patent proposes, it is by being embedded in a ROGI adjuster in decoupling control link to inhibit The negative-sequence current of net side is not only adapted to voltage on line side and loads asymmetric operating condition, but also can obtain high electric energy matter The alternating current-direct current of amount exports, and is a kind of simple and practical compensation method.Below with reference to the mathematical model of PET input stage to this paper not Balanced compensated strategy is analyzed.
Such as Fig. 1, a kind of typical cascade connection type PET input stage topology, every phase is made of N number of cascaded H-bridges rectification module, three-phase Star-like connection between input, and do not include zero sequence electricity without the neutral conductor between net side power supply and output end load, therefore in system Stream.
When net side and load-side occur uneven, the supply voltage of net side can be indicated are as follows:
In formula, ea,eb,ecFor the instantaneous electromotive force of net side;Ep,En,EzFor positive and negative, zero-sequence component the width of voltage on line side Value;Be positive the phase angles of negative zero order components.
If be not controlled to the imbalance of system, negative sequence component will occur in the input current of net side, may be expressed as:
In formula, LacFor the filter inductance of net side;Ra,Rb,RcFor the equivalent series resistance of rectification output end, it is for characterizing The switching loss of system is compared with the power that the AC load of output stage consumes, and often can be ignored.
Dq transformation, expression formula of the available three-phase bridge arm input terminal electric current under dq shafting are carried out to formula (3)
By decoupling control, active and reactive current control device can be indicated are as follows:
In formula, ia,ib,icFor the three-phase transient current of net side;Ip,InFor the amplitude of net side positive-negative sequence current;θpnFor The first phase of positive-negative sequence current.
The input current of Cascade H bridge rectifier can indicate are as follows:
When system occurs uneven, the negative sequence component of current on line side will appear 2 harmonics under dq shafting, at this time Active and reactive current may be expressed as:
I in formula1d,i1qFor active and reactive current DC component, I2d,I2qFor the amplitude of two harmonic of negative phase-sequence,For The initial phase angle of negative sequence component.
Non differential regulation can not be carried out to the negative sequence component of 2 frequencys multiplication only with PI controller, therefore decouples control in positive sequence herein A ROGI adjuster is embedded on the basis of system, for inhibiting the negative-sequence current of net side.The hierarchical control of input stage includes upper Layer control and lower layer's control, for top level control block diagram as shown in figure 3, comprising coordinate transform, positive sequence decoupling and negative-sequence current inhibit three A part.
The purpose of coordinate transform is in order to which voltage and current to be transformed into dq shafting, conveniently to the active and idle of net side Electric current is respectively controlled.Such as Fig. 3, eabcAnd iabcThe three-phase voltage and electric current for respectively indicating net side, after dq coordinate transform To respective active and reactive component (esd,esq),(isd,isq)。isdAnd isqAlso respectively by a 100Hz trapper to Obtain respective positive-sequence component
Positive sequence decouples link for realizing active and reactive current control device decoupling.Such as Fig. 3,Indicate high straightening The reference value of capacitance voltage is flowed,Indicate the high voltage direct current capacitor average voltage of all modules, the two is made to pass through after difference The reference value of one PI controller watt currentThe reference value of reactive currentIt is set as 0, for realizing the list of net side Position PFC.isd *And isq *Respectively with respective positive-sequence component measured valueIt is obtained after making difference by decoupling control Active and reactive voltage reference signal usdAnd usq.Here s is the abbreviation of source, and source refers to power supply, that is, power grid, Therefore the electric current that target electric current under s just refers to grid side is taken, similarly L is the abbreviation of load, takes target electric current under L and just refers to The electric current of load-side.
It includes active and idle two parts that negative-sequence current, which inhibits link, and the control of the two is just the same, with watt current For, reference value id *Measured value idThe thermal compensation signal u of active voltage is obtained by a ROGI adjuster after work differencedcom
The compensation term u of active voltage and reactive voltagedcomAnd uqcomReference signal u is individually subtractedsdAnd usq, then it is electric with net side Press edAnd eqIt is added, finally obtains the modulated voltage signal of input stage by dq inverse transformation.Since this method does not need positive-negative sequence point From link, divides sequence compensation method based on double dq shaftings relative to such as Fig. 2, enormously simplify the complexity of control unit.
Lower layer's control of input stage maintains every mutually each submodule for overcoming influence caused by circuit parameter and switching delay Electric voltage equalization between block, control block diagram are as shown in Figure 4.Acquire the DC capacitor of xth phase (x ∈ { a, b, c }) internal each submodule Voltage Udc_x_1,...,Udc_x_N, and the DC capacitor average voltage U with xth phasedc_x_aveIt is poor to make, by a proportional controller Be multiplied afterwards with the sign function of watt current, finally with the modulation voltage reference signal that is obtained by master controlFirst be multiplied phase again Add, finally obtains the modulation voltage u of each submodulexm1,uxm1,...uxmN
The isolation level DAB current transformer is used for the Power Exchange of input stage and output stage.It is of the present invention such as Fig. 5 Isolation level voltage close loop control principle drawing.It is constant using each submodule low-voltage direct busbar voltage of closed loop PI control and regulation, and And the two-way flow using SPS-PWM modulation technology power in isolation level current transformer.In figure, Udc_L *It is low-voltage direct mother The reference signal of line, Udc_LxIt is the low-voltage direct capacitor voltage measuring value of x-th of submodule, wherein x=1,2 ..., N.Measurement Value Udc_LxWith reference value Udc_L *The phase-shift control angle of each DAB current transformer is obtained after PI is controlledIt controls respectively The flow of power of each DAB.
It is the output stage Single-phase PWM Inverter voltage and current double closed-loop of the present invention based on quasi- PR controller such as Fig. 6 Control principle drawing, in figure, ux *And uxThe respectively reference value and measured value of inverse cascade output voltage, ix *Indicate each submodule output The reference value of electric current, ix_1,ix_2,...,ix_NRespectively indicate the output current measurement of each mutually N number of submodule, ux_1,ux_2,..., ux_NIt is the modulated voltage signal of N number of shunt chopper.The control method of three-phase is identical, by taking U phase as an example, in output stage control In system, it is poor that the measured value of inverse cascade output voltage is made with reference value first, obtains every height divided by N using after quasi- PR controller The output current reference signal of module, as the input of current inner loop, then respectively with the output current measurement of each submodule It is poor that value is made, and finally obtains the modulated voltage signal of each submodule by quasi- PR controller.Herein, why controlled using quasi- PR Device processed rather than PI controller are that PR control is more preferable to the DAZ gene effect of AC signal because subject to, and uses voltage electricity The control method of stream two close cycles can make output voltage constant and the stream of each submodule in parallel.
Below with reference to the transmission function of ROGI adjuster, to cascade connection type PET imbalance compensation controlling party disclosed by the invention The principle of method is analyzed.
The transmission function of ROGI adjuster is respectively as shown in formula (7)
The transmission function of ROGI only has-j ωrOne pole, therefore work as ωrWhen=2 π * 100rad/s, controller only- Gain is maximum at 100Hz, and the gain at other frequencies is almost 0, therefore ROGI can not influence forward-order current component Under the premise of, negative sequence component is adjusted.
Negative-sequence current controller based on ROGI, output can be expressed as
In formulaWithThe active and reactive voltage compensation rate of controller output is respectively indicated,Indicate Laplace Inverse transformation, * indicate convolution algorithm.
With the increase of time t, the exponential term of Section 2 can be quicklyd increase in formula (8), and value will be considerably beyond first item. Therefore formula (8) can be with Approximate Equivalent are as follows:
It is controlled by positive sequence decoupling control and negative-sequence current, reference voltage signal can be under dq shafting for input stage rectifier It indicates are as follows:
Dq inverse transformation is carried out to formula (10), expression formula of the reference voltage signal under α β shafting can be obtained are as follows:
U in formulaαAnd U *β* the modulation voltage reference signal under α β shafting is indicated.
Only contain fundamental positive sequence and negative phase-sequence in the modulated signal of input stage Cascade H bridge rectifier it can be seen from formula (11) Component, wherein positive-sequence component is used for the power of control system transmission, and negative sequence component is used to inhibit the negative-sequence current of net side.
In actual operation, the fluctuation range that mains frequency allows is -2.5~+1.5Hz, if directlying adopt ROGI adjusting Device, when mains frequency fluctuates, the robustness of controller is poor, it is therefore desirable to introduce cutoff frequency ωc, to improve control The gain bandwidth range of device.ROGI adjuster at this time becomes depression of order quasi-resonance adjuster (Reduced order quasi- Resonant, ROQR), shown in transmission function such as formula (12).
In order to verify the present invention, it is imitative that three-phase cascade PET identical with Fig. 1 topology has been built based on Matlab/Simulink True mode.Its main simulation parameter is as follows:
Rated capacity: 2MVA
Net side line voltage: 10kV (virtual value)
Cascade module number: 3
Three-phase nominal load power: 360kW
Simulation process is as follows: before 0.45s, voltage on line side three-phase symmetrical, threephase load is 360kW.Net after 0.45s There is slight asymmetry in side voltage, and the load of U phase remains unchanged, and bearing power decline 20%, the W phase load power of V phase becomes Originally 50%.It is put under double dq shaftings respectively in 0.45s and divides sequence compensating controller and imbalance compensation proposed by the present invention Scheme, the effect of comparison negative-sequence current compensation.Fig. 7-Figure 13 gives simulation result of the invention.
It is voltage on line side variation simulation waveform of the invention such as Fig. 7, before 0.45s, voltage on line side three-phase symmetrical, Occur after 0.45s slight asymmetric.
It is threephase load changed power simulation waveform of the invention such as Fig. 8.Before 0.45s, threephase load power is 1: The variation of the ratio between back loading of 1:1,0.45s is 1:0.8:0.5.
Fig. 9 and Figure 10 respectively shows point sequence compensation control and unbalance control scheme of the invention based on double dq shaftings Compensation effect.Can intuitively it find out from comparison of wave shape, when using compensation scheme of the invention, after approximately passing through 0.04 second The electric current of net side just restores balance, and divides sequence compensating controller using double dq shaftings, when need to pass through very long response in 0.15 second Between, and compensated current on line side still remains slight asymmetry.
The reason of causing the above results not can avoid positive-negative sequence point when essentially consisting in use point sequence compensating three-phase unbalance From the detection delay in bring a quarter period, and coordinate transform excessive in control program and complicated instruction calculate shadow The precision of compensation is rung.And unbalance control scheme of the invention is used, instruction current calculating, which is avoided, with positive-negative sequence separates ring Section, substantially increases the response speed of imbalance compensation controller.
Such as Figure 11, be using the compensated A phase voltage of unbalance control scheme and current simulations waveform of the invention, can be with Compensated PET work is found out in unity power factor state, and the power quality of output is high.
It is simulation waveform when voltage on line side occurs serious asymmetric such as Figure 12, before 0.45s, voltage on line side three is opposite Claim, it is original 70% that A phase voltage, which is fallen, after 0.45s.
It is using the unbalance control scheme of the invention input compensation in voltage on line side serious asymmetrical three-phase such as Figure 13 Current on line side simulation waveform.Simulation result shows when network voltage occurs seriously to fall, using controlling party of the invention Method remains to so that current on line side keeps three-phase symmetrical, this explanation can not only using the three-phase PET of ROGI adjuster auxiliary control Unbalanced load is compensated, also there is certain fault ride-through capacity.
Finally, it should be noted that above-described embodiments are merely to illustrate the technical scheme, rather than to it Limitation;Although the present invention is described in detail referring to the foregoing embodiments, those skilled in the art should understand that: It can still modify to technical solution documented by previous embodiment, or to part of or all technical features into Row equivalent replacement;And these modifications or substitutions, it does not separate the essence of the corresponding technical solution various embodiments of the present invention technical side The range of case.

Claims (8)

1. a kind of imbalance compensation control method of cascade connection type electric power electric transformer, which is characterized in that it include transformer with And control assembly, the transformer include input rectifying grade, isolation level and output inverse cascade,
The input rectifying grade is made of the single-phase cascade type H bridge rectifier of three star-like connections;The isolation level is multiple only The output end of vertical double active bridge current transformers, each double active bridge current transformers is connected in parallel, and constitutes low-voltage direct bus;It is described Output inverse cascade is Single-phase PWM Inverter;
Input rectifying grade, isolation level and output inverse cascade are all made of single-phase H bridge current transformer and are controlled, single-phase H bridge current transformer In switching device be all made of powerful IGBT;
The control assembly includes that input rectifying stage layered control unit, isolation level control unit and output inverse cascade control are single The hierarchical control unit of member, input stage is divided into top level control unit and lower layer's control unit again, is embedded in top level control unit One depression of order Generalized Integrator is to inhibit the negative-sequence current of net side and realize net side power control using positive sequence decoupling control Decoupling and total DC voltage are constant;Lower layer's control unit of the input rectifying grade is for overcoming circuit parameter and switch to prolong It is influenced caused by late, maintains the electric voltage equalization between every mutually each submodule, the isolation level is realized each using closed loop PI controller The low-voltage direct busbar voltage of a submodule is constant, and the output inverse cascade is maintained using the control method of voltage and current double closed-loop Output voltage is constant.
2. cascade connection type electric power electric transformer according to claim 1, it is characterised in that: double active bridges of the isolation level Current transformer includes primary side H bridge current transformer, high frequency transformer and pair side H bridge current transformer, the primary side H bridge current transformer and secondary side H bridge Configured with single phase-shifted pulse width modulation unit between current transformer, for realizing two-way flow of the power in isolation level current transformer.
3. cascade connection type electric power electric transformer according to claim 1, it is characterised in that: the control of the output inverse cascade PR controller subject to device.
4. cascade connection type electric power electric transformer according to claim 1, it is characterised in that: three of the input rectifying grade It is connected using inductor filter with AC network or AC load after single-phase Cascade H bridge rectifier star-like connection.
5. cascade connection type electric power electric transformer according to claim 1, it is characterised in that: the input stage H bridge rectification The output end of device is connected with the input terminal of DAB primary side H bridge current transformer;The output of DAB primary side H bridge current transformer terminates high frequency transformation The primary side of device, the input terminal of the secondary H bridge current transformer when connecting DAB pair of high frequency transformer;The output of DAB pair side H bridge current transformer End is connected with the input terminal of output stage Single-phase PWM Inverter;The output end of output stage Single-phase PWM Inverter is connected by filter Connect low-voltage alternating-current power grid or AC load.
6. a kind of imbalance compensation control method of cascade connection type electric power electric transformer, it is characterised in that: comprising:
S1, input stage hierarchical control unit be divided into top level control unit and lower layer's control unit, wherein top level control unit by Coordinate transform, positive sequence decoupling control and negative-sequence current inhibit three parts composition;
Coordinate transform: the three-phase voltage e of net sideabcActive voltage component e is obtained after dq coordinate transformdAnd reactive voltage component eq;The three-phase current i of net sideabcWatt current measured value i is obtained after dq coordinate transformsdWith reactive current measured value isq, have Function current measurement value isdWith reactive current measured value isqHave respectively by a trapper to obtain respective positive-sequence component Function electric current isdPositive-sequence component beReactive current isqPositive-sequence component be
Positive sequence decoupling: the high voltage direct current capacitor average voltage U of all modules is acquireddc_ave, and and reference valueIt is poor to make, then The reference value of watt current is obtained by a pi regulatorSimultaneously by the reference value of reactive currentIt is set as 0, is used In the unity power factor correction for realizing net side, the watt current reference value that will be previously obtainedWith reactive current reference valueActive voltage reference signal u is obtained by a decoupling controller with after respective positive-sequence component measured value work difference respectivelysd With reactive voltage reference signal usq
Negative-sequence current inhibits: watt current reference value isd *With watt current measured value isdBy a depression of order Generalized Product after work difference Device is divided to obtain the thermal compensation signal u of active voltagedcom;Reactive current reference value isq *With reactive current measured value isqMake difference after by One depression of order Generalized Integrator obtains the thermal compensation signal u of reactive voltageqcom
By the thermal compensation signal u of active voltagedcomSubtract reference signal usdAnd the feed-forward voltage e with net sidedIt is added, reactive voltage Thermal compensation signal uqcomSubtract the reference signal u obtained from the output of positive sequence decoupling controlsqAnd the feed-forward voltage e with net sideqIt is added, Finally the modulated voltage signal of input stage is obtained by dq inverse transformation respectively
S2, input rectifying grade lower layer's control unit be phase in Pressure and Control, specifically: acquisition xth phase (x ∈ { a, b, c }) in The DC capacitor voltage U of each submodule in portiondc_x_1,...,Udc_x_N, and the DC capacitor average voltage U with xth phasedc_x_aveMake Difference is multiplied after a proportional controller with the sign function of watt current, finally with obtained by top level control modulation electricity Pressure reference signalIt is first multiplied and is added again, finally obtain the modulation voltage u of each submodulexm1,uxm1,...uxmN
The low-voltage direct busbar voltage that S3, isolation level adjust each submodule using closed-loop control is constant, and is modulated using SPS-PWM Technology realizes two-way flow of the power in isolation level current transformer, and the control method of N number of submodule is all the same, x-th of submodule The low-voltage direct capacitor voltage measuring value U of (x=1,2 .., N)dc_LxWith low-voltage direct busbar voltage reference value Udc_L *After making difference, The phase-shift control angle of each DAB current transformer is obtained by pi regulatorThe power of each DAB current transformer is controlled respectively Flowing;
S4, output stage closed-loop control: in output stage control, the measured value u of inverse cascade output voltagexFirst with output voltage Reference value ux *It is poor to make, and then obtains the output current reference signal of each submodule divided by N again by a quasi- PR controller ix *, in this, as the input of current inner loop, respectively with the output current measurement value i of each submodulex_1,ix_2,...,ix_NMake Difference finally obtains the modulated voltage signal u of each submodule by a quasi- PR controllerx_1,ux_2,...,ux_N
7. the imbalance compensation control method of cascade connection type electric power electric transformer according to claim 6, it is characterised in that: Modulation voltage reference signal of the input stage rectifier under α β shafting can indicate are as follows:
U in formulaα*And Uβ*Indicate the modulation voltage reference signal under α β shafting, Ed,EqIt is active and idle point of power grid electromotive force Amount,WithIndicate the active and reactive voltage of PI controller output, ω1Indicate that the angular frequency of power grid, t indicate time, I2d, I2qFor two frequency multiplication of negative phase-sequence is active and the amplitude of reactive component,For the initial phase angle of negative sequence component;
Uα*And Uβ*In only contain fundamental positive sequence and negative sequence component, wherein positive-sequence component be used for control system transmission power, negative phase-sequence Component is used to inhibit the negative-sequence current of net side.
8. the imbalance compensation control method of cascade connection type electric power electric transformer according to claim 6, it is characterised in that: Trapper frequency in step S1 is 100HZ.
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