CN110289639A - A kind of cascade connection type current transformer and its control method and application system - Google Patents
A kind of cascade connection type current transformer and its control method and application system Download PDFInfo
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- CN110289639A CN110289639A CN201910695848.3A CN201910695848A CN110289639A CN 110289639 A CN110289639 A CN 110289639A CN 201910695848 A CN201910695848 A CN 201910695848A CN 110289639 A CN110289639 A CN 110289639A
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- 238000006243 chemical reaction Methods 0.000 claims abstract description 110
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- H02J3/383—
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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
- H02M7/493—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 the static converters being arranged for operation in parallel
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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
- 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
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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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
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Abstract
The present invention provides a kind of cascade connection type current transformer and its control method and application system, when cascade connection type current transformer in the standby state when, determine the upper voltage limit and voltage lower limit value of inverter module DC bus in each phase tandem type power conversion circuit of cascade connection type current transformer, periodically obtain the voltage max and voltage minimum of inverter module DC bus in each phase tandem type power conversion circuit, if the voltage max of inverter module DC bus is more than or equal to upper voltage limit in any phase tandem type power conversion circuit, or, voltage minimum is less than or equal to voltage lower limit value, inverter module DC bus corresponding to voltage max in the phase tandem type power conversion circuit is then controlled to discharge, reduce the voltage of corresponding inverter module DC bus, avoid inverter module DC bus-bar voltage seriously unbalanced problem；Also, it is not necessarily to fictitious load in the prior art, therefore avoids the increase of corresponding cost, weight and volume, to improve power density and system effectiveness.
Description
Technical field
The invention belongs to electric power electric transformer technical fields, more specifically, more particularly to a kind of cascade connection type current transformer
And its control method and application system.
Background technique
In recent years, cascade connection type current transformer has obtained the extensive concern of academia and industry.Pass through modular design, grade
Parallel-type inverter system can be directly incorporated into mesohigh power grid, to avoid using heavy and expensive Industrial Frequency Transformer.In addition,
Cascade connection type current transformer system can integrate function abundant, improve power grid friendly, therefore, cascade connection type current transformer system is in new energy
It played an important role in the fields such as source generates electricity by way of merging two or more grid systems, energy internet.
Fig. 1 is a kind of structural schematic diagram of cascade connection type current transformer.The ac output end of its M inverter module is together in series structure
The ac output end access mesohigh of Cheng Yixiang tandem type power conversion circuit, such three-phase tandem type power conversion circuit is handed over
Flow transmission and distribution network.Parameter type selecting is roughly the same when due to modularized design, and each inverter module DC bus-bar voltage should keep flat
Weighing apparatus, however, in practice since the loss of each modular circuit or the imbalance of DC side equivalent load, each inverter module direct current are female
Line voltage is it is possible that serious imbalance, therefore inverter module DC bus-bar voltage may be too high or too low, Jin Eryin
Send out the system failure.
For inverter module DC bus-bar voltage under standby mode, seriously unbalanced problem, prior art are every
The DC side of a inverter module increases fictitious load, the power of each inverter module DC side consumption is balanced, to balance each inversion
Module DC bus-bar voltage.But fictitious load is increased by the DC side in inverter module, to balance each inversion under standby mode
In the technical solution of module DC bus-bar voltage, due to using fictitious load, so that the cost of system, weight and volume are improved,
And it is unfavorable for the raising of power density, reduce system effectiveness.
Summary of the invention
In view of this, the purpose of the present invention is to provide a kind of cascade connection type current transformer and its control method and application system,
For controlling inverter module DC bus corresponding to voltage max when each inverter module DC bus-bar voltage is unbalanced
Electric discharge, keeps the voltage difference in each phase tandem type power conversion circuit between each inverter module DC bus smaller, thus
Solve the problems, such as that inverter module DC bus-bar voltage is seriously unbalanced.
First aspect present invention discloses a kind of control method of cascade connection type current transformer, comprising:
When the cascade connection type current transformer in the standby state when, determine each phase tandem type power of the cascade connection type current transformer
The upper voltage limit and voltage lower limit value of inverter module DC bus in translation circuit；Wherein, the standby mode includes: power grid
It charges to each inverter module DC bus；
Periodically obtain the voltage max and electricity of inverter module DC bus in each phase tandem type power conversion circuit
Press minimum value；
If the voltage max of inverter module DC bus is greater than in tandem type power conversion circuit described in any phase
The phase tandem type function is then controlled or, the voltage minimum is less than or equal to the voltage lower limit value equal to the upper voltage limit
The electric discharge of inverter module DC bus corresponding to voltage max described in rate translation circuit.
Optionally, inverter module direct current in each phase tandem type power conversion circuit of the determination cascade connection type current transformer
The upper voltage limit and voltage lower limit value of bus, comprising:
Obtain the number of inverter module in power grid phase voltage and each phase tandem type power conversion circuit；
It is straight according to the number of inverter module and inverter module in power grid phase voltage, each phase tandem type power conversion circuit
The voltage reference value for flowing bus, is calculated inverter module in each phase tandem type power conversion circuit of the cascade connection type current transformer
The upper voltage limit and voltage lower limit value of DC bus.
Optionally, according to the number of inverter module in power grid phase voltage, each phase tandem type power conversion circuit and inverse
The voltage reference value for becoming module DC bus, is calculated in each phase tandem type power conversion circuit of the cascade connection type current transformer
The upper voltage limit and voltage lower limit value of inverter module DC bus, used calculation formula are as follows:
Udc_ideal=k*U/N, Udc_max_thres=a*Udc_ideal, Udc_min_thres=b*Udc_ideal,；
Wherein, U is power grid phase voltage, and N is the number of inverter module in each phase tandem type power conversion circuit, and k is electricity
Loss factor is pressed, a is upper voltage limit coefficient, and b is lower voltage limit coefficient, Udc_idealFor each phase cascade of the cascade connection type current transformer
The voltage reference value of inverter module DC bus, U in formula power conversion circuitdc_max_thresIt is each for the cascade connection type current transformer
The upper voltage limit of inverter module DC bus, U in phase tandem type power conversion circuitdc_min_thresFor the tandem type unsteady flow
The voltage lower limit value of inverter module DC bus in each phase tandem type power conversion circuit of device.
Optionally, the voltage for periodically obtaining inverter module DC bus in each phase tandem type power conversion circuit
Maximum value and voltage minimum, comprising:
To each phase tandem type power conversion circuit, the voltage of each inverter module DC bus is periodically obtained respectively
Value, then the voltage value of each inverter module DC bus is ranked up, it obtains in the phase tandem type power conversion circuit
The voltage max and voltage minimum of inverter module DC bus.
Optionally, inversion mould corresponding to the voltage max described in described control phase tandem type power conversion circuit
Before the electric discharge of block DC bus, further includes:
Obtain current electric grid voltage.
Optionally, inverter module corresponding to voltage max described in described control phase tandem type power conversion circuit
DC bus electric discharge, comprising:
If the current electric grid voltage is in positive half period, inverter module corresponding to the voltage max is controlled
First switch tube and the 4th switching tube remain open, and control second switch and third switching tube conducting and with particular switch
Frequency work makes grid-connected current by the second switch and the third switching tube to corresponding to the voltage max
The electric discharge of inverter module DC bus；
If the current electric grid voltage is in negative half-cycle, inverter module corresponding to the voltage max is controlled
First switch tube and the 4th switching tube conducting and with the work of particular switch frequency, and control second switch and third switching tube
It remains open, keeps grid-connected current straight to inverter module corresponding to the voltage max through first switch tube and the 4th switching tube
Flow bus discharge；
Wherein, one end of the first switch tube connects with one end of the third switching tube and previous inverter module respectively
It connecing, the other end of the first switch tube is connect with one end of one end of the second switch and dc-link capacitance respectively,
The other end of the second switch is connect with one end of the 4th switching tube and the latter inverter module respectively, and the described 4th
The other end of switching tube is connect with the other end of the other end of the third switching tube and the dc-link capacitance respectively.
Second aspect of the present invention discloses a kind of cascade connection type current transformer, comprising: controller and at least two tandem type power
Translation circuit；The controller is used to execute the control method such as the described in any item cascade connection type current transformers of first aspect；
The exchange side of the tandem type power conversion circuit is connect by filter with power grid；
The DC side of the tandem type power conversion circuit is used to receive the electric energy of DC power supply.
Optionally, the tandem type power conversion circuit, comprising: the cascade H-bridge circuit in multiple exchange sides.
Optionally, the tandem type power conversion circuit, including upper bridge arm and lower bridge arm, the upper bridge arm and lower bridge
For arm about middle point symmetry, the upper bridge arm and the lower bridge arm include: multiple to exchange the cascade H-bridge circuit in side and inductance；
Exchange side of the midpoint of the tandem type power conversion circuit as the tandem type power conversion circuit, by right
The filter and alternating-current switch answered are connect with power grid；
One end of multiple exchange cascade H-bridge circuits in side is connected by the midpoint of the inductance and tandem type power conversion circuit
It connects, other end pole connection corresponding to DC bus.
Third aspect present invention discloses a kind of mesohigh photovoltaic parallel in system, comprising: filter, DC/DC converter, straight
Galvanic electricity source and the described in any item cascade connection type current transformers of second aspect；
The exchange side of the cascade connection type current transformer is connect by filter with mesohigh power grid；
In each phase tandem type power conversion circuit of cascade connection type current transformer the prime of inverter module with pass through the DC/
DC converter is connect with the low-voltage direct bus of the DC power supply.
From above-mentioned technical proposal it is found that in a kind of control method of cascade connection type current transformer provided by the invention, comprising: when
Cascade connection type current transformer in the standby state when, determine inverter module in each phase tandem type power conversion circuit of cascade connection type current transformer
Then the upper voltage limit and voltage lower limit value of DC bus periodically obtain inversion in each phase tandem type power conversion circuit
The voltage max and voltage minimum of module DC bus, if inverter module direct current in any phase tandem type power conversion circuit
The voltage max of bus is more than or equal to upper voltage limit, or, voltage minimum is less than or equal to voltage lower limit value, then controls the phase
Inverter module DC bus corresponding to voltage max discharges in tandem type power conversion circuit, and it is right to reduce voltage max institute
The voltage for the inverter module DC bus answered, to keep each inverter module direct current in each phase tandem type power conversion circuit female
Voltage difference between line is smaller, avoids inverter module DC bus-bar voltage seriously unbalanced problem；Also, it is not necessarily to existing skill
Fictitious load in art, therefore the increase of corresponding cost, weight and volume is avoided, to improve power density and system effectiveness.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is the present invention
Some embodiments for those of ordinary skill in the art without creative efforts, can also basis
These attached drawings obtain other attached drawings.
Fig. 1 is a kind of schematic diagram for cascade connection type current transformer that the prior art provides；
Fig. 2 is the schematic diagram of inverter module in a kind of cascade connection type current transformer of prior art offer；
Fig. 3 is a kind of schematic diagram of cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 4 is the schematic diagram of another cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 5 is a kind of flow chart of the control method of cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 6 is the flow chart of the control method of another cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 7 is the flow chart of the control method of another cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 8 is the flow chart of the control method of another cascade connection type current transformer provided in an embodiment of the present invention；
Fig. 9 is the schematic diagram of inverter module in a kind of cascade connection type current transformer provided in an embodiment of the present invention.
Specific embodiment
In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with the embodiment of the present invention
In attached drawing, technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment is
A part of the embodiment of the present invention, instead of all the embodiments.Based on the embodiments of the present invention, those of ordinary skill in the art
Every other embodiment obtained without making creative work, shall fall within the protection scope of the present invention.
In this application, the terms "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion,
So that the process, method, article or equipment for including a series of elements not only includes those elements, but also including not having
The other element being expressly recited, or further include for elements inherent to such a process, method, article, or device.Do not having
There is the element limited in the case where more limiting by sentence "including a ...", it is not excluded that in the mistake including the element
There is also other identical elements in journey, method, article or equipment.
The application provides a kind of control method of cascade connection type current transformer, and the cascade connection type current transformer is as shown in Figure 1, it is internal every
A inverter module can be all made of H bridge structure as shown in Figure 2, that is, include four switching tubes, respectively first switch tube T1, the
Two switch transistor Ts 2, third switch transistor T 3 and the 4th switch transistor T 4, aforementioned four switching tube are full-controlled switch device.
Specifically, one end of first switch tube T1 is connect with one end of third switch transistor T 3, tie point is as the inversion mould
One connectivity port of block, the other end of first switch tube T1 respectively with one end of second switch T2 and dc-link capacitance
One end connection, the other end of second switch T2 are connect with one end of the 4th switch transistor T 4, and tie point is as the inverter module
Another connectivity port, the other end of the 4th switch transistor T 4 respectively with the other end of third switch transistor T 3 and dc-link capacitance
Other end connection.Mesohigh reactive power compensator can be used as using the cascade connection type current transformer of H bridge structure.Also, this H bridge knot
The cascade connection type current transformer of structure can difference according to the specific application occasions, derive various cascade connection type current transformers.For example, being applied to
Current transformer during the tandem type mesohigh of mesohigh photovoltaic parallel in system occasion is grid-connected, structure are as shown in Figure 3；Example again
Such as, applied to mesohigh frequency control or the MMC (Modular based on full-bridge circuit submodule of flexible DC transmission occasion
Multilevel Converter, Modular multilevel converter), circuit structure is as shown in Figure 4；Certainly other be can also be
Application, such as D.C. high voltage transmission and mesohigh solid-state transformer, this is no longer going to repeat them.
Above-mentioned cascade connection type current transformer is connected by alternating-current switch with power grid.And the working condition packet of the cascade connection type current transformer
It includes: normal operating conditions and standby mode.When cascade connection type current transformer under normal operating conditions when, opening in cascade connection type current transformer
It closes pipe and switch motion is executed according to control strategy, to complete specific energy transmission target, such as reactive compensation, parallel network power generation
Deng；However, when cascade connection type current transformer in the standby state when, cascade connection type current transformer holding is connected with power grid, but does not realize routine
Energy transmission target under operating status, such as reactive compensation, parallel network power generation.
Under ideal conditions, the parameter of each inverter module is roughly the same when due to modularized design, and each inverter module direct current is female
Line voltage should keep balancing.However, in practice, due to the loss of each inverter module or the injustice of DC side equivalent load
Situations such as weighing apparatus, such as all kinds of accessory power supplys, control power supply take electricity from each inverter module DC bus, each inverter module direct current is female
Line voltage is it is possible that serious imbalance, some or certain several inverter module DC bus-bar voltages are too high or too low, in turn
Cause the system failure.
For the serious unbalanced problem of inverter module DC bus-bar voltage under the standby mode, this application provides one
The control method of kind cascade connection type current transformer, applied to the controller of above-mentioned cascade connection type current transformer, referring to Fig. 5, the tandem type unsteady flow
The control method of device specifically includes:
S501, when cascade connection type current transformer in the standby state when, determine that each phase tandem type power of cascade connection type current transformer becomes
Change the upper voltage limit and voltage lower limit value of inverter module DC bus in circuit.
Wherein, standby mode includes: that power grid charges to each inverter module DC bus.Specifically, power grid passes through inversion
The each inverter module DC bus charging of the anti-and diode pair of switching tube in module, alternatively, power grid in inverter module by opening
The body diode for closing pipe charges to each inverter module DC bus, specific diode selection ground practical application scene,
This is not specifically limited.
Determine the upper voltage limit of inverter module DC bus in each phase tandem type power conversion circuit of cascade connection type current transformer
The purpose of value and voltage lower limit value: for the voltage of inverter module DC bus in clearly each phase tandem type power conversion circuit
Control range, wherein using voltage lower limit value as the minimum value of the control reference voltage, using upper voltage limit as the voltage control
The maximum value of range processed.
Specifically, upper voltage limit and voltage lower limit value are and in network voltage, each phase tandem type power conversion circuit
The factors such as pressure-resistant degree and DC side power demands of device are related in the quantity of inverter module, inverter module, upper voltage limit
Value and the size of voltage lower limit value are depending on practical application scene, within the scope of protection of this application.
S502, the voltage max for periodically obtaining inverter module DC bus in each phase tandem type power conversion circuit
And voltage minimum.
Wherein, at interval of specific period, inverter module DC bus in each phase tandem type power conversion circuit is obtained
Voltage max and voltage minimum, the specific period can be 100us, naturally it is also possible to and it is other durations, specific period
Depending on value is according to the specification and application scenarios of actual stage parallel-type inverter, within the scope of protection of this application.
In practical applications, at interval of specific period, each inversion in each phase tandem type power conversion circuit is first obtained
The voltage of module DC bus, then the voltage of each inverter module DC bus is compared, it is straight to obtain each inverter module
Flow the voltage max and voltage minimum in the voltage of bus.
Periodically obtain the voltage max and electricity of inverter module DC bus in each phase tandem type power conversion circuit
The purpose of minimum value: the current voltage state in order to determine each phase tandem type power conversion circuit is pressed, it is every convenient for subsequent determination
The current voltage state of one phase tandem type power conversion circuit in control reference voltage or not in control reference voltage, and
And periodic acquisition pattern, inversion in each phase tandem type power conversion circuit of detection cascade connection type current transformer can be continued
Mould DC bus-bar voltage is realized in conjunction with subsequent step in each phase tandem type power conversion circuit for persistently controlling parallel-type inverter
Inversion mould DC bus-bar voltage.
In practical applications, this step S502 may is that each phase tandem type power conversion circuit, periodically obtain respectively
The voltage value of each inverter module DC bus is obtained, then the voltage value of each inverter module DC bus is ranked up, is obtained
The voltage max and voltage minimum of inverter module DC bus in the phase tandem type power conversion circuit.
Specifically, first obtaining the voltage value U of N number of inverter module DC bus at interval of specific perioddc1、Udc2……
UdcN；N is the number of inverter module DC bus in the phase tandem type power conversion circuit, then by N number of inverter module DC bus
Voltage value Udc1、Udc2……UdcN, it is ranked up by sequence from big to small, it is then that the inverter module for coming first is straight
The voltage value of bus is flowed as voltage max, comes the voltage value of the inverter module DC bus of n-th as voltage minimum
Value.
It is, of course, also possible to be ranked up by sequence from small to large, first inverter module direct current will be then come
The voltage value of bus comes the voltage value of inverter module DC bus of n-th as voltage max as voltage minimum.
If the voltage max of inverter module DC bus is more than or equal in S503, any phase tandem type power conversion circuit
Upper voltage limit then controls voltage in the phase tandem type power conversion circuit or, voltage minimum is less than or equal to voltage lower limit value
The electric discharge of inverter module DC bus corresponding to maximum value.
Voltage max is more than or equal to upper voltage limit, or, it includes three kinds that voltage minimum, which is less than or equal to voltage lower limit value,
Situation.Specifically, the first situation: voltage max is more than or equal to upper voltage limit, and voltage minimum is less than or equal to voltage
Lower limit value, second situation: voltage max is more than or equal to upper voltage limit, and voltage minimum is greater than voltage lower limit value, the
Three kinds of situations: voltage max is less than upper voltage limit, and voltage minimum is less than voltage lower limit value.
Therefore, if inverter module DC bus occurs to appoint in above-mentioned three kinds of situations in any phase tandem type power conversion circuit
It anticipates one kind, then controls inverter module DC bus corresponding to voltage max in the phase tandem type power conversion circuit and discharge.
Control what inverter module DC bus corresponding to voltage max in the phase tandem type power conversion circuit discharged
Purpose is: reducing the voltage of inverter module DC bus corresponding to voltage max, also, each phase tandem type power becomes
It changes only one inverter module (i.e. inverter module corresponding to voltage max) in circuit to be modulated, therefore, in tandem type
In current transformer modulated process, ac-side current is smaller, and cascade connection type current transformer loss is lower.It can be by this control tandem type unsteady flow
The switching tube foundation switching strategy execution switch motion of the corresponding inverter module of voltage max in device, and remaining inverter module
The operating mode that switching tube remains open, the referred to as blend modes of operation of cascade connection type current transformer.
In the present embodiment, the voltage for reducing inverter module DC bus corresponding to voltage max, to make each
Voltage difference in phase tandem type power conversion circuit between each inverter module DC bus is smaller, avoids inverter module direct current
The serious unbalanced problem of busbar voltage；Also, it is not necessarily to fictitious load in the prior art, therefore avoids corresponding cost, weight
With the increase of volume, to improve power density and system effectiveness.
Optionally, it is defined the level involved in embodiments of the present invention Fig. 5 step S501 really each phase grade of parallel-type inverter
The upper voltage limit and voltage lower limit value of inverter module DC bus in connection formula power conversion circuit, referring to Fig. 6, specifically include with
Lower step:
S601, the number for obtaining inverter module in power grid phase voltage and each phase tandem type power conversion circuit.
In the present embodiment, power grid phase voltage can be acquired by voltage acquisition equipment, wherein each phase tandem type power
The number of inverter module is when designing circuit it has been determined that the tandem type unsteady flow of the number of inverter module and use in translation circuit
The practical specification of device is related, does not illustrate one by one herein.
S602, according to the number and inversion of inverter module in power grid phase voltage, each phase tandem type power conversion circuit
The voltage reference value of module DC bus, calculation obtain inverter module in each phase tandem type power conversion circuit of cascade connection type current transformer
The upper voltage limit and voltage lower limit value of DC bus.
The voltage reference value of inverter module DC bus is the voltage in inverter module after the rectification of diode pair network voltage,
Wherein, voltage reference value is related to the number of inverter module in each phase tandem type power conversion circuit to power grid phase voltage, electricity
Pressure reference value is proportional to power grid phase voltage, power grid reference value and inverter module in each phase tandem type power conversion circuit
Number be in inverse relation.
In practical applications, formula calculation formula used by above-mentioned steps S602 are as follows:
Udc_ideal=k*U/N, Udc_max_thres=a*Udc_ideal, Udc_min_thres=b*Udc_ideal。
Wherein, U is power grid phase voltage, and N is the number of inverter module in each phase tandem type power conversion circuit, and k is electricity
Loss factor is pressed, a is upper voltage limit coefficient, and b is lower voltage limit coefficient, Udc_idealFor each phase tandem type function of cascade connection type current transformer
The voltage reference value of inverter module DC bus, U in rate translation circuitdc_max_thresFor each phase tandem type of cascade connection type current transformer
The upper voltage limit of inverter module DC bus, U in power conversion circuitdc_min_thresFor each phase cascade of cascade connection type current transformer
The voltage lower limit value of inverter module DC bus in formula power conversion circuit.
In order to guarantee inverter module device safe operation, upper voltage limit should be less than or equal to inverter module device
Pressure voltage.Specifically, if being greater than the device pressure voltage of inverter module according to the upper voltage limit that voltage limits formula is calculated,
Then using the device pressure voltage of inverter module as the upper voltage limit of inverter module DC bus, if being calculated according to voltage limits formula
Obtained upper voltage limit is less than or equal to the device pressure voltage of inverter module, then the upper voltage limit is female as inverter module direct current
The upper voltage limit of line.
For example, when power grid phase voltage is 311V, each phase tandem type power conversion circuit shares 4 inverter modules, k=
The device pressure voltage of 0.9, a=1.3, b=0.5, inverter module are 75V or 150V, are calculated according to module DC bus-bar voltage
It is as follows to upper voltage limit and voltage lower limit value:
Udc_idea=k*U/N=0.9*311/4=70V；
Udc_max_thres=a*Udc_idea=1.3*Udc_ideal=90V；
Udc_min_thres=b*Udc_ideal=0.5*Udc_ideal=35V.
If the device pressure voltage of inverter module is 75V, upper voltage limit Udc_max_thresFor 75V, voltage lower limit value
Udc_min_thresFor 35V；If the device pressure voltage of inverter module is 150V, upper voltage limit Udc_max_thresFor 90V, under voltage
Limit value Udc_min_thresFor 35V.
In the present embodiment, it depending on the value of any one in k, a and b can be according to practical application scene, does not do herein
It is specific to limit, within the scope of protection of this application.
Optionally, it on the basis of Figures 5 and 6 of the embodiment of the present invention, (is shown by taking Fig. 5 as an example) referring to Fig. 7, in step
Before rapid S503, can with the following steps are included:
S701, current electric grid voltage is obtained.
In practical applications, current electric grid voltage can be obtained by voltage sample equipment.
Wherein, the coil of power station generator rotates in parallel magnetic field, the wave for the voltage that cutting magnetic line comes out
Shape is sine wave, and therefore, the waveform of network voltage is sine wave, and a sinusoidal cycles can be divided into positive half period and negative half period
Phase, that is to say, that current electric grid voltage may be at positive half period, also may be at negative half-cycle.
In practical applications, phase tandem type power conversion of the control involved in Fig. 7 step of embodiment of the present invention S503
Inverter module DC bus corresponding to voltage max discharges in circuit, referring to Fig. 8, specifically includes the following steps:
S801, judge whether current electric grid voltage is in positive half period.
Specifically, judging whether current electric grid voltage is positive voltage, if judging, current electric grid voltage is positive voltage, is sentenced
Settled preceding network voltage is in positive half period, if judging, current electric grid voltage is not positive voltage, determines current electric grid voltage
It is not at positive half period, i.e. current electric grid voltage is in negative half-cycle.
It should be noted that if current electric grid voltage is in positive half period, S802 is thened follow the steps；If current electric grid voltage
It is not at positive half period, i.e. current electric grid voltage is in negative half-cycle, thens follow the steps S803.
The first switch tube of inverter module corresponding to S802, control voltage max and the 4th switching tube remain open,
And control second switch and the conducting of third switching tube and worked with particular switch frequency, make grid-connected current by second switch
It discharges with third switching tube inverter module DC bus corresponding to voltage max.
It should be noted that by being located between inverter module corresponding to power grid firewire and voltage max, and and voltage
The connected inverter module of inverter module corresponding to maximum value is known as previous inverter module；Grid zero line and voltage will be located at most
Between the corresponding inverter module of big value, and the inverter module being connected with inverter module corresponding to voltage max is referred to as latter
A inverter module.
In practical applications, referring to Fig. 9, the conducting dutycycle D of second switch T2 and third switch transistor T 32_3_onMeet 0
< D2_3_on< 1.With the work of particular switch Frequency Synchronization, particular switch frequency can be with for second switch T2 and third switch transistor T 3
It is 500Hz, is also possible to 1000Hz；The value of particular switch frequency is related to practical application, and particular switch frequency is other values
Also within the scope of protection of this application.
The connection relationship of each switching tube in inverter module is as follows see also Fig. 9:
One end of first switch tube T1 is connect with one end of third switch transistor T 3 and previous inverter module respectively, and first opens
The other end for closing pipe T1 is connect with one end of one end of second switch T2 and dc-link capacitance respectively, second switch T2's
The other end is connect with one end of the 4th switch transistor T 4 and the latter inverter module respectively, the other end of the 4th switch transistor T 4 respectively with
The other end of third switch transistor T 3 is connected with the other end of dc-link capacitance.
Be in positive half period in current electric grid voltage, and the second switch T2 of inverter module corresponding to voltage max and
Discharge loop when third switch transistor T 3 is connected, in inverter module corresponding to voltage max are as follows: previous inverter module →
3 → dc-link capacitance of third switch transistor T → second switch T2 → the latter inverter module.
The first switch tube of inverter module corresponding to S803, control voltage max and the 4th switching tube are connected and with spy
Constant switching frequency work, and control second switch and third switching tube remains open, make grid-connected current through first switch tube and
4th switching tube discharges to inverter module DC bus corresponding to voltage max.
In practical applications, referring to Fig. 9, the conducting dutycycle D of the 4th switch transistor T 4 and first switch tube T11_4_onMeet 0
< D1_4_on< 1, the connection relationship of the connection relationship of each switching tube and the inverter module in above-mentioned steps S802 in inverter module
Identical, details are not described herein.
Be in negative half-cycle in current electric grid voltage, and the first switch tube T1 of inverter module corresponding to voltage max and
When 4th switch transistor T 4 is connected, discharge loop in inverter module corresponding to voltage max are as follows: the latter inverter module → the
Four 4 → dc-link capacitances of switch transistor T → first switch tube T1 → previous inverter module.
It should be noted that in step S802 and step S803, in addition to voltage in the phase tandem type power conversion circuit
Other inverter modules outside inverter module corresponding to maximum value do not control, i.e., each switching tube is equal in other inverter modules
It remains open, at this point, inverter module DC bus corresponding to voltage max discharges, other inverter module DC bus fill
Electricity.
In practical applications, it can be in the implementation of step S503 in above-mentioned steps S802 and above-mentioned steps S803 extremely
A few step, the implementation specifically combined can do repeat one by one herein depending on actual conditions, in the guarantor of the application
It protects in range.
The invention discloses a kind of cascade connection type current transformers, comprising: controller and at least two tandem type power conversion circuits.
The exchange side of tandem type power conversion circuit is connect by filter with power grid, tandem type power conversion circuit it is straight
Stream side is used to receive the electric energy of DC power supply.
Controller, for executing the control method of the cascade connection type current transformer as described in above-mentioned any embodiment, with controlled stage
The voltage value of each inverter module DC bus meets preset condition in connection formula power conversion circuit.The specific execution of controller
Process and principle are referring to above-described embodiment, and this is no longer going to repeat them.
In practical applications, above-mentioned tandem type power conversion circuit includes: the cascade H-bridge circuit in multiple exchange sides.It is any
Cascade connection type current transformer including this tandem type power conversion circuit, within the scope of protection of this application, than as shown in Figure 4
: Modular multilevel converter MMC, at this point, being specifically included in the tandem type power conversion circuit: upper bridge arm and lower bridge arm,
About middle point symmetry, upper bridge arm includes: multiple to exchange cascade H-bridge circuit (such as Fig. 4 in side with lower bridge arm for upper bridge arm and lower bridge arm
In inverter module 11) and inductance L.
Exchange side of the midpoint of tandem type power conversion circuit as tandem type power conversion circuit, passes through corresponding filtering
Device RT and alternating-current switch T are connected with the one of mesohigh power grid；One end of multiple exchange cascade inverter modules 11 in side passes through electricity
Sense L is connect with the midpoint of tandem type power conversion circuit, other end pole connection corresponding to DC bus.
Certainly, above-mentioned cascade connection type current transformer is also possible to other current transformers comprising cascade H bridge structure, does not do one herein
One illustrates, within the scope of protection of this application.
The invention discloses a kind of tandem type mesohigh photovoltaic parallel in system, comprising: filter, DC/DC converter and grade
Parallel-type inverter.
The exchange side of cascade connection type current transformer is connect by filter with mesohigh power grid；
In each phase tandem type power conversion circuit of cascade connection type current transformer the prime of inverter module with pass through DC/DC converter
It is connect with the low-voltage direct bus of the DC power supply.
Referring to Fig. 3, the prime of inverter module DC/AC passes through in each phase tandem type power conversion circuit of cascade connection type current transformer
DC/DC converter accesses low-voltage direct bus, and one end of the exchange side of the tandem type power conversion circuit of each phase passes through correspondence
Filter RT be connected with the one of mesohigh power grid, the tandem type power conversion circuit of each phase exchange side the other end connect
Meet mesohigh grid zero line N.
It should be noted that each phase tandem type power conversion electricity of the current transformer in tandem type mesohigh photovoltaic parallel in system
Road can use star-like connection, can also be connected using triangle, specific connection type is related to practical application scene, herein
It does not do and repeats one by one, within the scope of protection of this application.
All the embodiments in this specification are described in a progressive manner, same and similar portion between each embodiment
Dividing may refer to each other, and each embodiment focuses on the differences from other embodiments.Especially for system or
For system embodiment, since it is substantially similar to the method embodiment, so describing fairly simple, related place is referring to method
The part of embodiment illustrates.System and system embodiment described above is only schematical, wherein the conduct
The unit of separate part description may or may not be physically separated, component shown as a unit can be or
Person may not be physical unit, it can and it is in one place, or may be distributed over multiple network units.It can root
According to actual need that some or all of the modules therein is selected to achieve the purpose of the solution of this embodiment.Ordinary skill
Personnel can understand and implement without creative efforts.
Professional further appreciates that, unit described in conjunction with the examples disclosed in the embodiments of the present disclosure
And algorithm steps, can be realized with electronic hardware, computer software, or a combination of the two, in order to clearly demonstrate hardware and
The interchangeability of software generally describes each exemplary composition and step according to function in the above description.These
Function is implemented in hardware or software actually, the specific application and design constraint depending on technical solution.Profession
Technical staff can use different methods to achieve the described function each specific application, but this realization is not answered
Think beyond the scope of this invention.
The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention.
Various modifications to these embodiments will be readily apparent to those skilled in the art, as defined herein
General Principle can be realized in other embodiments without departing from the spirit or scope of the present invention.Therefore, of the invention
It is not intended to be limited to the embodiments shown herein, and is to fit to and the principles and novel features disclosed herein phase one
The widest scope of cause.
Claims (10)
1. a kind of control method of cascade connection type current transformer characterized by comprising
When the cascade connection type current transformer in the standby state when, determine each phase tandem type power conversion of the cascade connection type current transformer
The upper voltage limit and voltage lower limit value of inverter module DC bus in circuit；Wherein, the standby mode includes: power grid to every
A inverter module DC bus charging；
Periodically obtain in each phase tandem type power conversion circuit the voltage max of inverter module DC bus and voltage most
Small value；
If the voltage max of inverter module DC bus is more than or equal in tandem type power conversion circuit described in any phase
The upper voltage limit then controls phase tandem type power change or, the voltage minimum is less than or equal to the voltage lower limit value
Change the electric discharge of inverter module DC bus corresponding to voltage max described in circuit.
2. the control method of cascade connection type current transformer according to claim 1, which is characterized in that the determination tandem type
The upper voltage limit and voltage lower limit value of inverter module DC bus in each phase tandem type power conversion circuit of current transformer, packet
It includes:
Obtain the number of inverter module in power grid phase voltage and each phase tandem type power conversion circuit；
It is female according to the number of inverter module in power grid phase voltage, each phase tandem type power conversion circuit and inverter module direct current
Inverter module direct current in each phase tandem type power conversion circuit of the cascade connection type current transformer is calculated in the voltage reference value of line
The upper voltage limit and voltage lower limit value of bus.
3. the control method of cascade connection type current transformer according to claim 2, which is characterized in that according to power grid phase voltage, often
The number of inverter module and the voltage reference value of inverter module DC bus, calculate in one phase tandem type power conversion circuit
The upper voltage limit and electricity of inverter module DC bus into the cascade connection type current transformer each phase tandem type power conversion circuit
Depress limit value, used calculation formula are as follows:
Udc_ideal=k*U/N, Udc_max_thres=a*Udc_ideal, Udc_min_thres=b*Udc_ideal,；
Wherein, U is power grid phase voltage, and N is the number of inverter module in each phase tandem type power conversion circuit, and k is voltage damage
Coefficient is consumed, a is upper voltage limit coefficient, and b is lower voltage limit coefficient, Udc_idealFor each phase tandem type function of the cascade connection type current transformer
The voltage reference value of inverter module DC bus, U in rate translation circuitdc_max_thresFor each phase grade of the cascade connection type current transformer
The upper voltage limit of inverter module DC bus, U in connection formula power conversion circuitdc_min_thresIt is every for the cascade connection type current transformer
The voltage lower limit value of inverter module DC bus in one phase tandem type power conversion circuit.
4. the control method of cascade connection type current transformer according to claim 1, which is characterized in that the periodically acquisition is each
The voltage max and voltage minimum of inverter module DC bus in phase tandem type power conversion circuit, comprising:
To each phase tandem type power conversion circuit, the voltage value of each inverter module DC bus is periodically obtained respectively, then
The voltage value of each inverter module DC bus is ranked up, inversion mould in the phase tandem type power conversion circuit is obtained
The voltage max and voltage minimum of block DC bus.
5. the control method of cascade connection type current transformer according to claim 1, which is characterized in that in the control, this is mutually cascaded
Before the electric discharge of inverter module DC bus corresponding to voltage max described in formula power conversion circuit, further includes:
Obtain current electric grid voltage.
6. the control method of cascade connection type current transformer according to claim 5, which is characterized in that described control phase tandem type
The electric discharge of inverter module DC bus corresponding to voltage max described in power conversion circuit, comprising:
If the current electric grid voltage is in positive half period, of inverter module corresponding to the voltage max is controlled
One switching tube and the 4th switching tube remain open, and control second switch and third switching tube conducting and with particular switch frequency
Work makes grid-connected current by the second switch and the third switching tube to inversion corresponding to the voltage max
The electric discharge of module DC bus；
If the current electric grid voltage is in negative half-cycle, of inverter module corresponding to the voltage max is controlled
One switching tube and the 4th switching tube are connected and with the work of particular switch frequency, and control second switch and the holding of third switching tube
It disconnects, makes grid-connected current through first switch tube and the 4th switching tube to the mother of inverter module direct current corresponding to the voltage max
Line electric discharge；
Wherein, one end of the first switch tube is connect with one end of the third switching tube and previous inverter module respectively,
The other end of the first switch tube is connect with one end of one end of the second switch and dc-link capacitance respectively, described
The other end of second switch is connect with one end of the 4th switching tube and the latter inverter module respectively, the 4th switch
The other end of pipe is connect with the other end of the other end of the third switching tube and the dc-link capacitance respectively.
7. a kind of cascade connection type current transformer characterized by comprising controller and at least two tandem type power conversion circuits；Institute
Controller is stated for executing the control method such as cascade connection type current transformer described in any one of claims 1 to 6；
The exchange side of the tandem type power conversion circuit is connect by filter with power grid；
The DC side of the tandem type power conversion circuit is used to receive the electric energy of DC power supply.
8. cascade connection type current transformer according to claim 7, which is characterized in that the tandem type power conversion circuit includes:
The cascade H-bridge circuit in multiple exchange sides.
9. cascade connection type current transformer according to claim 7, which is characterized in that the tandem type power conversion circuit, comprising:
About middle point symmetry, the upper bridge arm and the lower bridge arm include: more for upper bridge arm and lower bridge arm, the upper bridge arm and lower bridge arm
The cascade H-bridge circuit in a exchange side and inductance；
Exchange side of the midpoint of the tandem type power conversion circuit as the tandem type power conversion circuit, by corresponding
Filter and alternating-current switch are connect with power grid；
One end of multiple exchange cascade H-bridge circuits in side is connect by the inductance with the midpoint of tandem type power conversion circuit,
Other end pole connection corresponding to DC bus.
10. a kind of tandem type mesohigh photovoltaic parallel in system characterized by comprising filter, DC/DC converter, direct current
Source and the cascade connection type current transformer as described in claim 7 to 9 is any；
The exchange side of the cascade connection type current transformer is connect by filter with mesohigh power grid；
The prime of inverter module becomes with by the DC/DC in each phase tandem type power conversion circuit of cascade connection type current transformer
Parallel operation is connect with the low-voltage direct bus of the DC power supply.
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| CN110867846A (en) * | 2019-10-25 | 2020-03-06 | 中国科学院电工研究所 | Large-scale photovoltaic direct current series connection boosting grid-connected system with power balancer |
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