CN115498648B - Hybrid transformer for active power distribution network and control method thereof - Google Patents

Hybrid transformer for active power distribution network and control method thereof Download PDF

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CN115498648B
CN115498648B CN202211452566.9A CN202211452566A CN115498648B CN 115498648 B CN115498648 B CN 115498648B CN 202211452566 A CN202211452566 A CN 202211452566A CN 115498648 B CN115498648 B CN 115498648B
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voltage
low
phase
hybrid transformer
control
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CN115498648A (en
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徐霄
董安奇
高辉
黎倩婷
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Nanjing University of Posts and Telecommunications
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Nanjing University of Posts and Telecommunications
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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
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
    • 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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion 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
    • H02M5/42—Conversion 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
    • H02M5/44—Conversion 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
    • H02M5/453—Conversion 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
    • H02M5/458—Conversion 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
    • H02M5/4585—Conversion 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • 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
    • Y02E40/30—Reactive power compensation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Ac-Ac Conversion (AREA)

Abstract

The invention belongs to the technical field of transformers, and discloses a hybrid transformer for an active power distribution network and a control method thereof, wherein the hybrid transformer consists of a transformer winding and a power converter; the transformer winding is composed of a high-voltage three-phase winding, a low-voltage three-phase winding and a low-voltage three-phase control winding; the power converter is formed by connecting two fully-controlled silicon carbide current converters in a back-to-back manner, and is respectively connected with the high-voltage and low-voltage three-phase control windings through filter inductors; when the hybrid transformer is used as an active power distribution network distribution transformer, by comparing the size relationship between the new energy grid-connected permeability connected with a feeder line on the low-voltage side of the device and the maximum bearing capacity of the new energy of the power distribution network in the area where the device is located, the low-voltage side can be seamlessly switched between two control strategies of voltage-frequency control and active-reactive control, so that constant-voltage constant-frequency control when the new energy permeability is not high and moisture flow control when the new energy permeability is too high are realized, and the power supply quality of the active power distribution network is improved while the safe grid connection of the new energy is ensured.

Description

Hybrid transformer for active power distribution network and control method thereof
Technical Field
The invention belongs to the technical field of transformers, and particularly relates to a hybrid transformer for an active power distribution network and a control method thereof.
Background
The output of new energy equipment such as photovoltaic equipment, wind power generation equipment and the like has randomness and volatility, and the large-scale access of the new energy equipment to a medium-low voltage distribution network not only brings bidirectional flow of power flow of the distribution network, but also causes the voltage control, the electric energy quality and the reliability of the distribution network to be influenced in different degrees. The traditional distribution transformer reduces the voltage of a high-voltage side to another voltage level by a fixed transformation ratio by means of a high-voltage winding and a low-voltage winding, has the advantages of high efficiency, high reliability, low cost and the like, and has the defects of single function, no voltage dynamic control, active power supply quality adjustment and the like. Therefore, when the problems of voltage out-of-limit, voltage flicker, tidal current feedback, protection misoperation, refusal operation and the like caused by large-scale access of new energy are faced, an independent electric energy quality control device such as a static var generator, a dynamic voltage regulator and the like is usually required to be additionally installed near the traditional distribution transformer, so that the investment cost is increased, and the waste of space resources is also caused. The hybrid transformer combines the advantages of simple structure and high transmission efficiency of the traditional distribution transformer and the advantages of flexible control and quick response of voltage and current of the power electronic converter, and the power quality is controlled while the high-power is transmitted without installing an additional power quality control device.
The existing research aiming at the hybrid transformer focuses on topology improvement, the control target of the hybrid transformer is mainly to maintain the stability of the downstream power supply voltage and the unit power factor, when the hybrid transformer is applied to an active power distribution network, the hybrid transformer is used as a hub for electric energy transmission and conversion between an upstream power grid and downstream new energy equipment, the quality of the power supply voltage is not only ensured not to be influenced by the output of the downstream new energy or load fluctuation from the electric energy quality influence perspective, but also the maximum short-circuit current and the maximum feedback power flow of a system are ensured to be within an allowable range from the power grid safe and reliable operation perspective, so that the large-scale safe access of the new energy equipment is realized, and the existing research aiming at the hybrid transformer does not discuss the feedback power flow out-of-limit scene and the corresponding control method which are possibly encountered when the hybrid transformer is applied to the active power distribution network. The maximum safe access capacity of new energy which can be consumed by a power distribution network in any area is usually expressed by the maximum bearing capacity of the new energy in the area, the value of the safe access capacity is comprehensively influenced by factors such as the load in the area, the distribution condition of the new energy, the running state, the power grid topology and the running condition, and the safe access capacity has time-varying property. When the grid-connected permeability of the new energy of the power distribution network in the target area is monitored to be larger than the maximum bearing capacity of the new energy in the area, the feedback power flow needs to be limited; and when the grid-connected permeability of the new energy of the power distribution network in the target area is less than or equal to the maximum bearing capacity of the new energy in the area, the power supply quality is optimized, and the sensitivity of the grid-connected permeability of the new energy of the power distribution network in the target area to the voltage fluctuation of a superior power grid and the output fluctuation of downstream new energy equipment is reduced. Therefore, how to perform adaptive transformation on the existing hybrid transformer and dynamically monitor the relationship between the grid-connected permeability of the new energy of the target area distribution network and the maximum bearing capacity of the new energy of the area is to provide a comprehensive control method aiming at optimizing the power supply quality at low permeability and aiming at limiting the feedback flow and ensuring the safe access of the new energy at high permeability, which is an urgent problem to be solved.
Disclosure of Invention
In order to solve the technical problems, the invention provides an active power distribution network-oriented hybrid transformer and a control method thereof, which can realize constant-voltage constant-frequency control aiming at optimizing power supply quality when new energy is low in grid-connected permeability and power control aiming at ensuring safe access of new energy when the new energy is too high by combining the seamless switching capacity of a low-voltage side power converter between a voltage-frequency control mode and an active-reactive control mode according to the dynamic change relation between the new energy grid-connected permeability and the maximum bearing capacity of new energy in a target active area power distribution network, and improve the power supply quality of the active power distribution network on the premise of ensuring safe grid-connected of the new energy.
The invention relates to a hybrid transformer for an active power distribution network, wherein the hybrid transformer body comprises a high-voltage three-phase winding (A)W A1 、W B1 、W C1 ) A low-voltage three-phase winding (W a1 、W b1 、W c1 ) A low-voltage three-phase control winding (W a1_con 、W b1_con 、W c1_con ) And a back-to-back power converter, each winding being star-connected and the neutral point being grounded; the corresponding phases of the high-voltage three-phase winding and the low-voltage three-phase winding and the corresponding phases of the high-voltage three-phase winding and the low-voltage three-phase control winding are respectively coupled through magnetic reaction by winding an iron core; the selected turn number position of each phase winding of the high-voltage three-phase winding (n aux ) The three-phase alternating current ports on the other side of the back-to-back power converter are connected with corresponding phase ports of the low-voltage three-phase control winding through the three-phase circuit breaker; the non-grounding port of the high-voltage three-phase winding passes through high voltageAnd the low-voltage three-phase winding is connected with a downstream load and new energy through the low-voltage side bus.
Furthermore, the back-to-back type power converter is formed by connecting two identical full-control type power converters in a back-to-back mode, namely a rectification side full-control type power converter 1 and an inversion side full-control type power converter 2, each full-control type power converter comprises three pairs of bridge arms which are connected in a full-bridge mode, each pair of bridge arms is formed by connecting two silicon carbide metal oxide semiconductor field effect transistors in series, the direct current sides of the two full-control type power converters are coupled through a capacitor bank, the capacitor bank is formed by connecting two capacitors with the same specification in series, the connection point of the capacitor bank is grounded, and the alternating current sides of the two full-control type power converters are connected with a winding leading-out port of a high-voltage three-phase winding and a three-phase port of a three-phase control winding in a series filter inductor mode.
Further, the maximum bearing capacity of the new energy in the area where the hybrid transformer is located at the current moment is determined by three types of power grid safety allowable constraint conditions, namely the maximum short-circuit current allowed by a low-voltage side bus at the current moment, the maximum voltage deviation of each node and the maximum distribution and transformation allowable feedback power, the corresponding total power generation power of the new energy is respectively measured when each type of constraint condition just reaches the boundary value of the constraint condition, the minimum value of the three calculation results is taken as the maximum safe access power of the new energy of the target area power distribution network at the current moment, and the percentage of the minimum value in the current total load power is taken as the maximum bearing capacity of the new energy of the area power distribution network at the current moment;
and the new energy grid-connected permeability of the area where the hybrid transformer is located at the current moment is the percentage of the total new energy generated power to the current total load power at the moment.
Further, the hybrid transformer performs seamless switching between two control strategies of voltage-frequency control and active-reactive control on the low-voltage side of the hybrid transformer according to the magnitude relation between the new energy grid-connected permeability of the power distribution network in the area at any moment and the maximum bearing capacity of the new energy in the area at the current moment, so that power supply voltage regulation when the new energy is low in permeability and back-flow limitation when the new energy is too high are realized, and the method specifically comprises the following steps:
at any moment, when the monitored new energy grid-connected permeability of the distribution network of the area where the hybrid transformer is located is smaller than or equal to the maximum bearing capacity of the new energy of the area measured and calculated at the current moment, the low-voltage side of the hybrid transformer adopts voltage-frequency control to control the voltage amplitude and the frequency of a bus at the low-voltage side to be constant on a set value; when the monitored new energy grid-connected permeability of the power distribution network in the target area is larger than the maximum bearing capacity of the new energy in the area measured and calculated at the current moment, the low-voltage side of the hybrid transformer adopts active-reactive control, the feedback power flow monitored by a low-voltage side bus is controlled on a set value, and the safe access of the new energy in the target area is guaranteed in a mode of limiting the feedback power flow.
Further, the control of the high-voltage side of the hybrid transformer by adopting the reactive-direct current bus voltage specifically comprises the following steps:
a. according to the voltage measurement value of the DC bus of the back-to-back power converteru dc And a reference value
Figure 100002_DEST_PATH_IMAGE001
Calculating the input current of the high-voltage side of the hybrid transformerdReference per unit value of axis component
Figure 100002_DEST_PATH_IMAGE002
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE003
in the formula (I), the compound is shown in the specification,sin order to be the laplacian operator,U dc,b is a reference value of the DC bus voltage of the back-to-back type power converter,k pi andk ii are respectively proportional integral linksiThe scaling factor and the integration factor of (a),ithe value range is [1,6 ]]，GAndTthe gain coefficient and the time constant of a first-order low-pass filtering link are respectively, DBlk is a power converter locking signal, DBlk is 0 when the power converter is locked, otherwise DBlk is 1;
b. according to the change of mixtureMeasurement of reactive power at the high-voltage side of a transformerQ 1 And a reference valueQ 1 * Calculating the input current of the high-voltage side of the hybrid transformerqReference per unit value of axis component
Figure 100002_DEST_PATH_IMAGE004
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE005
in the formula (I), the compound is shown in the specification,S b the reference value of the apparent power of the hybrid transformer is obtained;
c. measuring three-phase current of high-voltage side of hybrid transformeri A1 ,i B1 ,i C1 Performing per unit processing, and then performing Park conversion on the per unit processing to obtain three-phase current measurement valuesd、qPer unit value of each component under axisi d1,pu Andi q1,pu as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE006
in the formula (I), the compound is shown in the specification,I 1,b andθ i1 respectively setting the reference value and the electrical angle of the three-phase current at the high-voltage side of the hybrid transformer;
d. measuring three-phase voltage of high-voltage side of hybrid transformeru A1 ,u B1 ,u C1 Performing per unit processing, and then performing Park transformation to obtain three-phase voltage measurement valuesd、qPer unit value of each component under axisu d1,pu Andu q1,pu as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE007
in the formula (I), the compound is shown in the specification,U 1,b andθ u1 respectively representing a reference value and an electrical angle of a three-phase voltage at the high-voltage side of the hybrid transformer;
e. byi d1,pu 、
Figure 100002_DEST_PATH_IMAGE008
、i q1,pu 、
Figure 100002_DEST_PATH_IMAGE009
、u d1,pu Andu q1,pu the three-phase voltage of the alternating current side of the fully-controlled power converter 1 in the back-to-back converter is obtained after the current inner loop processingd、qReference per unit value of axis component
Figure 100002_DEST_PATH_IMAGE010
And
Figure 100002_DEST_PATH_IMAGE011
then obtained by inverse Park transformationabcCorresponding reference phase voltage under the shaft
Figure 100002_DEST_PATH_IMAGE012
，
Figure 100002_DEST_PATH_IMAGE013
，
Figure 100002_DEST_PATH_IMAGE014
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE015
Figure 100002_DEST_PATH_IMAGE016
in the formula (I), the compound is shown in the specification,L 1,pu is a filter inductor connected in series at the AC side of the fully-controlled power converter 1L 1 The per-unit value of (c) is,w 1 L 1,pu is a filter inductor connected in series at the AC side of the fully-controlled power converter 1L 1 The per-unit value of the inductive reactance,f 1 and
Figure 100002_DEST_PATH_IMAGE017
reference values of the voltage frequency at the alternating current side and the effective value of the line voltage of the full-control power converter 1 respectively;
f. to be provided with
Figure 100002_DEST_PATH_IMAGE018
、
Figure 100002_DEST_PATH_IMAGE019
、
Figure 100002_DEST_PATH_IMAGE020
The reference modulation wave is compared with the high-frequency triangular carrier wave logically, if the reference modulation wave is larger than 0, the three upper bridge arm switches SW of the full-control type power converter 1 are conducted ua1 ,SW ub1 And SW uc1 Output high level, to three lower bridge arm switches SW la1 ,SW lb1 And SW lc1 Outputting a low level; if the current is less than or equal to 0, three upper bridge arm switches SW of the full-control type power converter 1 are conducted ua1 ,SW ub1 And SW uc1 Output low level, to three lower bridge arm switches SW la1 ,SW lb1 And SW lc1 And outputting a high level, thereby forming a pulse wave of sine pulse width modulation and controlling the on-off of six silicon carbide metal-oxide-semiconductor field effect transistors in the fully-controlled power converter 1.
Further, the low-voltage side of the hybrid transformer is seamlessly switched between two control strategies of voltage-frequency control and active-reactive control;
the low-voltage side of the hybrid transformer adopts a voltage-frequency control or active-reactive control mode and is determined by a control signal S _ TM: when S _ TM is 0, the low-voltage side of the hybrid transformer adopts a voltage-frequency control mode; and when the S _ TM is 1, the low-voltage side of the hybrid transformer adopts an active-reactive control mode.
Further, when the low-voltage side of the hybrid transformer is adoptedWhen the voltage-frequency control mode is used, firstly, the amplitude values of the three-phase reference voltage on the low-voltage side of the hybrid transformer are respectively generated
Figure 100002_DEST_PATH_IMAGE021
And phaseθ u2 As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE023
in the formula (I), the compound is shown in the specification,
Figure 100002_DEST_PATH_IMAGE024
andU 2,b respectively a reference per unit value and a reference value of the three-phase voltage at the low-voltage side of the hybrid transformer,
Figure 100002_DEST_PATH_IMAGE026
before switching control modes, three-phase voltage reference phases on the low-voltage side of the hybrid transformer are switched;
then, will
Figure 100002_DEST_PATH_IMAGE027
Andθ u2 inputting the three-phase sine wave generator to generate a three-phase voltage reference waveform of the low-voltage side of the hybrid transformer
Figure 100002_DEST_PATH_IMAGE028
、
Figure 100002_DEST_PATH_IMAGE029
、
Figure 100002_DEST_PATH_IMAGE030
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE031
will be provided with
Figure 594579DEST_PATH_IMAGE028
、
Figure 117964DEST_PATH_IMAGE029
、
Figure 547808DEST_PATH_IMAGE030
Performing per unit processing and then performing Park conversion on the voltage to obtain the three-phase voltage of the low-voltage side of the hybrid transformerd、qReference per unit value for each component under axis
Figure 100002_DEST_PATH_IMAGE032
、
Figure 100002_DEST_PATH_IMAGE033
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE034
synchronously, measuring three-phase voltage of low-voltage side of hybrid transformeru a2 ,u b2 ,u c2 Is subjected to per-unit processing and then is subjected to Park transformation to obtain three-phase voltage measured valuesd、qPer unit value of each component under axisu d2,pu Andu q2,pu as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE035
then, respectively calculateu d2,pu And with
Figure DEST_PATH_IMAGE036
Andu q2,pu and with
Figure 100002_DEST_PATH_IMAGE037
The errors are input into a proportional-integral link respectively, and then the three-phase current of the low-voltage side of the hybrid transformer is obtainedd、qUnder the shaftReference per unit value of each component
Figure 100002_DEST_PATH_IMAGE038
And
Figure 100002_DEST_PATH_IMAGE039
as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE040
measuring three-phase current of low-voltage side of hybrid transformeri a2 ,i b2 ,i c2 Performing per unit processing, and then performing Park conversion on the per unit processing to obtain three-phase current measurement valuesd、qPer unit value of each component under axisi d2,pu Andi q2,pu as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE042
in the formula (I), the compound is shown in the specification,I 2,b andθ i2 respectively setting a reference value and an electrical angle of a three-phase current at the low-voltage side of the hybrid transformer;
will be provided withi d2,pu 、
Figure 100002_DEST_PATH_IMAGE043
、i q2,pu 、
Figure DEST_PATH_IMAGE044
、u d2,pu Andu q2,pu transmitting the voltage to the current inner ring to obtain three-phase voltage of alternating current side of fully-controlled power converter 2 in back-to-back power converterd、qReference per unit value of axis component
Figure 100002_DEST_PATH_IMAGE045
And
Figure 100002_DEST_PATH_IMAGE046
then obtained by inverse Park transformationabcCorresponding reference phase voltage under the shaft
Figure 100002_DEST_PATH_IMAGE047
、
Figure 100002_DEST_PATH_IMAGE048
、
Figure 100002_DEST_PATH_IMAGE049
As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE050
Figure 100002_DEST_PATH_IMAGE052
in the formula (I), the compound is shown in the specification,L 2,pu a filter inductor connected in series at the AC side of the fully-controlled power converter 2L 2 The per-unit value of (c) is,w 2 L 2,pu a filter inductor connected in series at the AC side of the fully-controlled power converter 2L 2 The per-unit value of the inductive reactance,f 2 and
Figure 100002_DEST_PATH_IMAGE053
reference values respectively for the ac side voltage frequency and the line voltage effective value of the fully controlled power converter 2,kdqis a directional coefficient;
finally, to
Figure DEST_PATH_IMAGE054
、
Figure 100002_DEST_PATH_IMAGE055
、
Figure 100002_DEST_PATH_IMAGE056
As a logic comparison of the reference modulated wave with the high-frequency triangular carrier wave,if the output voltage is more than 0, three upper bridge arm switches SW of the full-control type power converter 2 are conducted ua2 ,SW ub2 And SW uc2 Output high level to three lower bridge arm switches SW la2 ,SW lb2 And SW lc2 Outputting a low level; if the current is less than or equal to 0, three upper bridge arm switches SW of the full-control type power converter 2 are conducted ua2 ,SW ub2 And SW uc2 Output low level, to three lower bridge arm switches SW la2 ,SW lb2 And SW lc2 And outputting high level to form pulse wave modulated by sine pulse width to control the on-off of six silicon carbide metal oxide semiconductor field effect transistors in the fully-controlled power converter 2.
Further, when the low-voltage side of the hybrid transformer adopts an active-reactive control mode, the active power of the low-voltage side of the hybrid transformer is firstly calculated respectivelyP 2 And reactive powerQ 2 As shown in the following formula:
Figure 100002_DEST_PATH_IMAGE057
will be provided withP 2 、Q 2 And corresponding reference value
Figure 100002_DEST_PATH_IMAGE058
、
Figure 100002_DEST_PATH_IMAGE059
Is subjected to per-unit processing to obtainP 2,pu 、Q 2,pu 、
Figure 100002_DEST_PATH_IMAGE060
、
Figure 100002_DEST_PATH_IMAGE061
Respectively calculate
Figure 98088DEST_PATH_IMAGE060
AndP 2,pu and
Figure 100002_DEST_PATH_IMAGE062
and withQ 2,pu The difference values are subjected to low-pass filtering respectively and then transmitted to a proportional integral link, so that the three-phase current of the low-voltage side of the hybrid transformer is obtaineddqReference per unit value of each component under axis
Figure 100002_DEST_PATH_IMAGE063
And
Figure 100002_DEST_PATH_IMAGE064
as shown in the following formula:
Figure 100002_DEST_PATH_IMAGE065
the current inner loop in the power control mode is completely consistent with the current inner loop in the voltage-frequency control mode; finally, the product is processedi d2,pu 、
Figure 451840DEST_PATH_IMAGE063
、i q2,pu 、
Figure 100002_DEST_PATH_IMAGE066
、u d2,pu Andu q2,pu and pulse signals for controlling the on-off of six silicon carbide gold oxygen half field effect transistors in the full-control power converter 2 are obtained after current inner loop processing.
The invention has the beneficial effects that: the invention provides an active power distribution network-oriented hybrid transformer and a control method thereof, aiming at the problem that a traditional hybrid transformer with the main purpose of maintaining stable power supply voltage is difficult to actively control the back-transmission power flow of an active power distribution network.
Drawings
Fig. 1 is a topological diagram of a hybrid transformer facing an active power distribution network according to the present invention;
fig. 2 is a topology diagram of a back-to-back power converter in the proposed hybrid transformer;
FIG. 3 is a flow chart of reactive-DC bus voltage control for the high side of the proposed hybrid transformer;
fig. 4 is a schematic diagram of the sinusoidal pulse width modulation adopted by the fully-controlled power converter 1 in the proposed hybrid transformer;
fig. 5 is a flow chart and a schematic diagram of a switching method of a corresponding control outer loop in the voltage-frequency control and active-reactive control adopted by the low-voltage side of the hybrid transformer;
FIG. 6 is a flow chart of a current control inner loop shared by voltage-frequency control and active-reactive control for the low voltage side of the proposed hybrid transformer;
fig. 7 is a schematic diagram of the sinusoidal pulse width modulation adopted by the fully-controlled power converter 2 in the proposed hybrid transformer;
fig. 8 is a schematic diagram of a low-voltage active distribution network connected to a hybrid transformer;
fig. 9 is a diagram of changes in active power and reactive power at the low-voltage side in the test scenario 1;
FIG. 10 is a graph showing the voltage per unit value variation of the high-voltage side and low-voltage side buses under test scenario 1;
fig. 11 is a graph of active power and reactive power changes at the low-voltage side in the test scenario 2;
FIG. 12 is a graph showing the voltage per unit value variation of the high-voltage side and low-voltage side buses under the test scenario 2;
fig. 13 is a graph of active power and reactive power changes at the low-voltage side in the test scenario 3;
fig. 14 is a graph of the voltage per unit value of the high-voltage side and the low-voltage side bus under the test scenario 3.
Detailed Description
In order that the present invention may be more readily and clearly understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings.
The invention provides a topological structure diagram of a hybrid transformer for an active power distribution network, as shown in fig. 1, the hybrid transformer body comprises: a high-voltage three-phase winding (W A1 、W B1 、W C1 ) A low-voltage three-phase winding (W a1 、W b1 、W c1 ) A low-voltage three-phase control winding (W a1_con 、W b1_con 、W c1_con ) And a back-to-back power converter, wherein each winding is connected in a star connection mode and the neutral point is grounded, the high-voltage winding and the low-voltage winding and the high-voltage winding and the low-voltage control winding are respectively coupled in a magnetic reaction mode by winding an iron core, and the low-voltage winding and the low-voltage control winding of the hybrid transformer correspond to phase coils: (W a1 AndW a1_con ,W b1 andW b1_con ,W c1 andW c1_con ) Are connected in parallel and have completely consistent specification parameters.
Position of assigned turns of left side ac port and high voltage winding of back-to-back power converter: (n aux ) The lead-out ports are connected, and the right-side alternating current port is connected with the non-grounding port of the low-voltage control winding correspondingly; three-phase circuit breakerK 1 、K 2 When the back-to-back power converter fails or needs manual maintenance, the back-to-back power converter is separated from the connection with the high-voltage winding and the low-voltage control winding, and the rest windings can still be usedStep-down is performed in the manner of a conventional distribution transformer; switching on and off the high frequency pulse signal from the controller for 6 silicon carbide MOSFETs in a back-to-back type power converter: (G VSC1 、G VSC2 ) Determining that the input signal of the controller is three-phase voltage measured by the high-voltage side bus and the low-voltage side (u A1 、u B1 、u C1 、u a2 、u b2 、u c2 ) Three-phase current (A), (B)i A1 、i B1 、i C1 、i a2 、i b2 、i c2 ) DC bus voltageu dc Circuit breakerK 1 、K 2 And a low-side mode switching control signal S _ TM.
The back-to-back power converter is formed by connecting two identical full-control power converters (a full-control power converter 1 and a full-control power converter 2) in a back-to-back manner, as shown in fig. 2, each converter consists of three pairs of bridge arms and is connected in a full-bridge manner, each pair of bridge arms is formed by connecting two silicon carbide Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in series, and the on-off state of each pair of bridge arms is controlled by a pulse signal (A) sent by a controllerG VSC1 AndG VSC2 ) Controlling; the DC sides of the two converters are coupled by a capacitor bank consisting of two capacitors (C) of the same sizeC dc1 、C dc2 ) Is formed in a series connection mode, and the connection point of the two is grounded; the AC sides of the full-control power converter 1 and the full-control power converter 2 are respectively connected with a filter inductor in seriesL 1 AndL 2 and then a three-phase cross flow connection port is led out.
The high-voltage side of the hybrid transformer adopts reactive-direct current bus voltage control and is realized by a fully-controlled power converter 1 in a back-to-back power converter, and the control aim is to control the reactive power of the high-voltage sideQ 1 And DC bus of back-to-back power converterLine voltageu dc Constant at the corresponding reference value
Figure 100002_DEST_PATH_IMAGE067
And
Figure 100002_DEST_PATH_IMAGE068
the control flow is shown in fig. 3, and specifically includes:
a. calculating the detected DC bus voltageu dc And its reference value
Figure 100002_DEST_PATH_IMAGE069
The difference value is transmitted to a proportional-integral link, and the output result is subjected to low-pass filtering to obtain the three-phase current of the high-voltage side of the hybrid transformerdThe reference per unit value of the axis component,
Figure DEST_PATH_IMAGE070
as shown in the following formula:
Figure DEST_PATH_IMAGE071
in the formula (I), the compound is shown in the specification,U dc,b is a reference value of the direct current bus voltage,k pi andk ii are respectively proportional integral linksiThe scaling factor and the integration factor of (a),ithe value range is [1,6 ]]，GAndTthe gain coefficient and the time constant of a first-order low-pass filtering link are respectively, DBlk is a power converter locking signal, DBlk is 0 when the power converter is locked, otherwise DBlk is 1;
b. calculating reactive power of high-voltage side of hybrid transformerQ 1 And its reference value
Figure DEST_PATH_IMAGE072
The difference value is transmitted to a proportional-integral link, and then low-pass filtering is carried out to obtain the input current of the high-voltage sideqThe reference value after the axis component is unified,
Figure DEST_PATH_IMAGE073
as shown in the following formula:
Figure DEST_PATH_IMAGE074
in the formula (I), the compound is shown in the specification,S 1,b the reference value is the apparent power of the hybrid transformer;
c. to three-phase voltage at high-voltage side of hybrid transformeru A1 ,u B1 ,u C1 And three-phase currenti A1 ,i B1 ,i C1 After per unit processing, park conversion is respectively carried out to obtain three-phase voltage and currentdqPer unit value of each component under axisu d1,pu 、u q1,pu 、i d1,pu Andi q1,pu as shown in the following formula:
Figure DEST_PATH_IMAGE075
，
in the formula (I), the compound is shown in the specification,U 1,b andI 1,b reference values of three-phase voltage and three-phase current at the high-voltage side of the hybrid transformer are respectively,θ u1 andθ i1 the electrical angles of the three-phase voltage and the three-phase current on the high-voltage side of the hybrid transformer are respectively;
d. a step of subjecting the product obtained in the step a to the step ci d1,pu 、
Figure DEST_PATH_IMAGE076
、i q1,pu 、
Figure DEST_PATH_IMAGE077
、u d1,pu Andu q1,pu the voltage is transmitted to a current inner ring controlled by the voltage of a reactive-direct current bus and is processed by the inner ring to obtain three-phase voltage of the alternating current side of the full-control power converter 1d、qReference per unit value of axis component
Figure DEST_PATH_IMAGE078
And
Figure DEST_PATH_IMAGE079
as shown in the following formula:
Figure DEST_PATH_IMAGE080
in the formula (I), the compound is shown in the specification,k p3 andk i3 respectively are a proportional coefficient and an integral coefficient of a proportional-integral link,w 1 L 1,pu is a filter inductor connected in series at the AC side of the fully-controlled power converter 1L 1 Per unit value of inductive reactance of
Figure DEST_PATH_IMAGE081
，f 1 And
Figure DEST_PATH_IMAGE082
reference values of the voltage frequency at the alternating current side and the effective value of the line voltage of the full-control power converter 1 respectively;
then through Park inverse transformation
Figure DEST_PATH_IMAGE083
And
Figure DEST_PATH_IMAGE084
converting the dq axis to the abc axis to obtain a reference waveform of the three-phase voltage at the AC side of the fully-controlled power converter 1
Figure DEST_PATH_IMAGE085
、
Figure DEST_PATH_IMAGE086
、
Figure DEST_PATH_IMAGE087
As shown in the following formula:
Figure DEST_PATH_IMAGE088
；
e. finally, in order to
Figure 656163DEST_PATH_IMAGE085
、
Figure 804379DEST_PATH_IMAGE086
、
Figure 533301DEST_PATH_IMAGE087
As a reference modulation wave and a high-frequency triangular wave as a carrier wave, performing sinusoidal pulse width modulation to obtain pulse control signals of six silicon carbide MOSFET switching devices of the fully-controlled power converter 1, as shown in fig. 4, specifically: at any time point, if the reference modulation wave is larger than the triangular wave, the three upper bridge arm switches SW of the full-control power converter 1 are switched ua1 ,SW ub1 And SW uc1 Output high level, to three lower bridge arm switches SW la1 ,SW lb1 And SW lc1 Output low level, otherwise to SW ua1 ,SW ub1 And SW uc1 Output low level, to SW la1 ,SW lb1 And SW lc1 And outputting a high level.
The low-voltage side of the hybrid transformer adopts two control strategies of voltage-frequency control and active-reactive control, the control objects are six silicon carbide MOSFETs in a fully-controlled power converter 2, the six silicon carbide MOSFETs can be seamlessly switched according to the value of a mode switching control signal S _ TM, when the value of the S _ TM is 0, the low-voltage side adopts voltage-frequency control, and when the value of the S _ TM is 1, the low-voltage side adopts active-reactive control; the value of the S _ TM depends on the size relationship between the new energy grid-connected permeability and the maximum bearing capacity of the new energy in the area of the distribution network where the hybrid transformer is located at any time, if the former is smaller than or equal to the latter, the S _ TM takes a value of 0, otherwise, the S _ TM takes a value of 1; the new energy grid-connected permeability at any time is defined as the percentage of the total new energy generating power in the area at any time point to the current total load power; the method for defining the maximum bearing capacity of the new energy of the regional power distribution network at any time comprises the following steps: the method comprises the steps of firstly, measuring and calculating the corresponding total power generation power of the new energy when short-circuit current of a low-voltage side bus, the maximum voltage deviation of a node and the backward power flow allowed by distribution transformer at any time point respectively reach the maximum boundary value allowed by each new energy, taking the minimum value of three calculation results as the maximum safe access capacity of the new energy of a target area power distribution network at the time, and then converting the minimum value into the percentage of the total load power at present and taking the percentage as the maximum bearing capacity of the new energy of the area at the present time.
Two control strategies of voltage-frequency control and active-reactive control adopted by the low-voltage side of the hybrid transformer share one current control inner ring, and a control outer ring is changed according to different control targets; wherein the control target of the voltage-frequency control is to maintain the voltage of the low-voltage side of the hybrid transformeru a2 、u b2 、u c2 And frequencyf 2 At its corresponding reference value
Figure DEST_PATH_IMAGE089
The control target of active-reactive power control is to maintain the active power of the low-voltage side of the hybrid transformerP 2 And reactive powerQ 2 At its corresponding reference value
Figure DEST_PATH_IMAGE090
。
The voltage-frequency control adopted by the low-voltage side of the hybrid transformer of the invention has the control outer ring as shown in fig. 5, and specifically comprises the following steps:
a. firstly, generating the amplitude of the reference phase voltage at the low-voltage side of the hybrid transformer
Figure DEST_PATH_IMAGE091
And phaseθ u2 The three-phase sine wave generator is combined to generate a three-phase voltage reference waveform on the low-voltage side of the hybrid transformer
Figure DEST_PATH_IMAGE092
、
Figure DEST_PATH_IMAGE093
、
Figure DEST_PATH_IMAGE094
Performing per-unit conversion on the voltage and the voltage, and then performing Park conversion to obtain the three-phase voltage of the low-voltage side of the hybrid transformerd、qReference per unit value of the corresponding component under axis
Figure DEST_PATH_IMAGE095
、
Figure DEST_PATH_IMAGE096
As shown in the following formula:
Figure DEST_PATH_IMAGE097
Figure DEST_PATH_IMAGE098
in the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE099
andU 2,b the per unit reference value and the reference value of the three-phase voltage at the low-voltage side of the hybrid transformer are respectively,
Figure DEST_PATH_IMAGE101
before switching control modes, the reference phase of the three-phase voltage at the low-voltage side of the hybrid transformer is switched;
b. separately detectingu d2,pu 、u q2,pu With corresponding reference values
Figure DEST_PATH_IMAGE102
、
Figure DEST_PATH_IMAGE103
The respective errors are respectively input into a proportional-integral link to obtain the three-phase current of the low-voltage side of the hybrid transformerdqReference per unit value for each component under axis
Figure DEST_PATH_IMAGE104
And
Figure DEST_PATH_IMAGE105
as shown in the following formula:
Figure DEST_PATH_IMAGE107
。
the active-reactive control adopted by the low-voltage side of the hybrid transformer of the invention has the control outer ring as shown in fig. 5, and specifically comprises the following steps: three-phase voltage obtained according to detection of low-voltage side of hybrid transformeru a2 、u b2 、u c2 And three-phase currenti a2 、i b2 、i c2 Calculating active power of low-voltage side of hybrid transformerP 2 And reactive powerQ 2 Then it is made per unitP 2,pu 、Q 2,pu CalculatingP 2,pu 、Q 2,pu Corresponding reference value thereof
Figure DEST_PATH_IMAGE108
、
Figure DEST_PATH_IMAGE109
The respective errors are respectively filtered and then transmitted to a proportional-integral link to obtain three-phase current of the low-voltage side of the hybrid transformerd、qReference per unit value of axis component
Figure DEST_PATH_IMAGE110
And
Figure DEST_PATH_IMAGE111
as shown in the following formula:
Figure DEST_PATH_IMAGE112
Figure DEST_PATH_IMAGE113
the current inner loop control shared by the voltage-frequency control and the active-reactive control at the low-voltage side of the hybrid transformer is shown in fig. 6, and specifically comprises the following steps:
a. detecting three-phase current on low-voltage side of hybrid transformeri a2 ,i b2 ,i c2 And per-unit processing is carried out on the data, and then Park transformation is carried out to obtaini a2 ,i b2 ,i c2 In thatd、qPer unit value of each component under axisi d2,pu Andi q2,pu as shown in the following formula:
Figure DEST_PATH_IMAGE114
in the formula (I), the compound is shown in the specification,I 2,b andθ i2 respectively setting a reference value and an electrical angle of a three-phase current at the low-voltage side of the hybrid transformer;
b. will control the outer loop to obtain
Figure DEST_PATH_IMAGE115
、
Figure DEST_PATH_IMAGE116
Associationi d2,pu 、i q2,pu 、u d2,pu Andu q2,pu the three-phase voltage is transmitted to the current inner ring together to obtain the three-phase voltage of the AC side of the full-control power converter 2d、qReference per unit value of axis component
Figure DEST_PATH_IMAGE117
And
Figure DEST_PATH_IMAGE118
then through Park inverse transformation
Figure 694391DEST_PATH_IMAGE117
And
Figure 192368DEST_PATH_IMAGE118
fromdqShaft conversion toabcShaft, obtainingabcPer unit value of reference phase voltage under axis
Figure DEST_PATH_IMAGE119
、
Figure DEST_PATH_IMAGE120
、
Figure DEST_PATH_IMAGE121
As shown in the following formula:
Figure DEST_PATH_IMAGE122
Figure DEST_PATH_IMAGE052A
in the formula (I), the compound is shown in the specification,kdqwhich is a directional coefficient, when S _ TM is 0,kdqwhen-1,S _TMis 1,kdqthe number of the carbon atoms is 1,w 2 L 2,pu a filter inductor connected in series at the AC side of the fully-controlled power converter 2L 2 Per unit value of the inductive reactance of
Figure DEST_PATH_IMAGE123
，f 2 And
Figure DEST_PATH_IMAGE124
reference values of the effective values of the alternating-current side voltage frequency and the line voltage of the full-control power converter 2 are respectively;
c. finally, in order to
Figure 449168DEST_PATH_IMAGE119
、
Figure 665386DEST_PATH_IMAGE120
、
Figure 610208DEST_PATH_IMAGE121
As a reference modulation wave and a high-frequency triangular wave as a carrier wave, performing sinusoidal pulse width modulation to obtain pulse control signals of six silicon carbide MOSFET switching devices of the fully-controlled power converter 2, as shown in fig. 7, specifically: at any time point, if the reference modulation wave is larger than the triangular wave, the three upper bridge arm switches SW of the full-control power converter 2 are switched ua2 ,SW ub2 And SW uc2 Output high level, to three lower bridge arm switches SW la2 ,SW lb2 And SW lc2 Output low level, otherwise to SW ua2 ,SW ub2 And SW uc2 Output low level, to SW la2 ,SW lb2 And SW lc2 And outputting a high level.
Experimental verification
In order to make the present invention more understandable to those skilled in the art, a specific simulation example is listed below.
The method is characterized in that a low-voltage active power distribution network connected with a hybrid transformer is taken as an example, a corresponding simulation model is established in PSCAD, a single line diagram of the simulation model is shown in FIG. 8, a high-voltage side of the hybrid transformer is connected with an 11kV bus and is connected with a superior power grid through a line 1, a low-voltage side of the hybrid transformer is connected with a 400V bus and is connected with a load and a new energy station through a line 2, the superior power grid is represented by a three-phase controllable voltage source module, a switch K is used for switching between two simulation scenes of a passive power distribution network and an active power distribution network, the load power of a downstream low-voltage side is constant at 150kW, and the new energy station adopts an equivalent model based on the controllable voltage source module.
The basic circuit parameters of the hybrid transformer simulation model in fig. 8 are as follows: the rated line voltage of the high-voltage three-phase winding is 11kV, the rated line voltage of the low-voltage three-phase winding is 400V, the rated line voltage of the low-voltage three-phase control winding is 400V, a tap is led out from each phase of the high-voltage three-phase winding, and the number of turns obtained by the tap and the total turn ratio are 4:11, the rated value of the line voltage connected to the left side of the back-to-back power converter is 400V, and the right side of the back-to-back power converter is directly connected with the low-voltage three-phase control winding, so that the rated value of the output line voltage is 400V, and the inductance of the back-to-back power converter isL 1 、L 2 Are all 0.4mH, capacitanceC dc1 、C dc2 All are 750uF, the reference value of the direct current bus voltage is 800V, and the switching frequency of the silicon carbide MOSFET is 16kHz.
In order to verify the proposed hybrid transformer and control method, three different typical test scenarios are proposed, and the simulation equipment of each test scenario is as follows:
test scenario 1: control mode dynamic switching test when new energy grid connection permeability is changed
In simulation time 0 to 2s, a switch K is kept closed to simulate an active power distribution network, when simulation 0S starts, the output of a new energy station is 300kW, the corresponding grid-connected permeability is 200% and is larger than the maximum bearing capacity 33% of new energy of the power distribution network in the time period, the output of the new energy station needs to be reduced, and therefore active-reactive control (a mode switching control signal S _ TM = 1) is adopted on the low-voltage side of the hybrid transformer in the time period, specifically: the grid-connected permeability is reduced to 167% by reducing the output of the new energy station within 0 to 1s, and the reference values of active power and reactive power of the low-voltage side of the hybrid transformer are correspondingly reduced
Figure DEST_PATH_IMAGE125
,
Figure DEST_PATH_IMAGE126
Setting the power as-100 kW (the power is negative and represents the reverse delivery of the tidal current), further reducing the new energy grid-connected permeability to 33% within the simulation time of 1 to 2s at 0kVAr, and correspondingly reducing the new energy grid-connected permeability to the maximum value
Figure 775741DEST_PATH_IMAGE125
,
Figure 718289DEST_PATH_IMAGE126
Set to 100kW; when the switch K is disconnected at the simulation time of 2S, the new energy station is disconnected, the active power distribution network is changed into a passive power distribution network, the active-reactive control of the low-voltage side of the hybrid transformer is switched to be voltage-frequency control (S _ TM is changed from 1 to 0), the switch K is closed again when the simulation time reaches 4S, the new energy station is switched into the power distribution network again, the voltage-frequency control of the low-voltage side of the hybrid transformer is switched to be active-reactive control, and new energy is converted into active-reactive controlThe grid-connected permeability is stabilized on the maximum bearing capacity of the new energy of the distribution network in the area; active power of low-voltage side of hybrid transformer in test sceneP 2 Reactive powerQ 2 The curve is shown in FIG. 9, the amplitude per unit value of the three-phase line voltage measured at the high-voltage side and the low-voltage side of the hybrid transformer: (U 1,pu AndU 2,pu ) As shown in fig. 10, simulation results show that the hybrid transformer can dynamically switch the control mode according to the change of the new energy grid-connected permeability.
Test scenario 2: the amplitude of the low-voltage side power supply voltage can be dynamically adjusted within a certain range
In the simulation time of 0 to 1s, switchingKKeeping closed, setting a simulation scene the same as that of the test scene 1, adopting active-reactive control (S _ TM = 1) at the low-voltage side of the hybrid transformer, disconnecting a simulation time 1S switch K, disconnecting a new energy station, converting an active power distribution network into a passive power distribution network, switching the active-reactive control at the low-voltage side of the hybrid transformer into voltage-frequency control (S _ TM is changed from 1 to 0), and then maintaining the per-unit value of input voltage at the high-voltage sideU 1,pu The per unit value of the low-voltage side power supply voltage is referenced within 1 to 2s, 2 to 3s and 3 to 4s under 1pu
Figure DEST_PATH_IMAGE127
The low-voltage side of the hybrid transformer is obtained through simulation with 1pu, 1.1pu and 1.2pu being respectively setP 2 、Q 2 The curves are as shown in figure 11 of the drawings,U 1,pu andU 2,pu the curve is shown in fig. 12, and the simulation result shows that the amplitude of the low-voltage side supply voltage can be controlled by the hybrid transformer to be adjustable within a certain range.
Test scenario 3: maintaining constant power supply voltage at low-voltage side of lower reaches when voltage of upper-level power grid fluctuates
In the simulation time of 0 to 1s, switchingKKeeping closed, setting a simulation scene the same as a test scene 1, adopting active-reactive control (S _ TM = 1) at the low-voltage side of the hybrid transformer, disconnecting a simulation time 1S switch K, disconnecting a new energy station, converting an active power distribution network into a passive power distribution network, and switching the active-reactive control at the low-voltage side of the hybrid transformer to be the passive power distribution networkVoltage-frequency control (S _ TM is changed from 1 to 0), and then per unit value of high-voltage side input voltage is controlled within 1 to 2s, 2 to 3s and 3 to 4sU 1,pu The low-side supply voltage reference per unit value is set to 1pu, 1.05pu and 1.1pu respectively
Figure DEST_PATH_IMAGE128
Respectively setting the voltage of the low-voltage side of the hybrid transformer to be 1pu all the time, and obtaining the low-voltage side of the hybrid transformer through the hybrid transformerP 2 、Q 2 The curves are as shown in figure 11 of the drawings,U 1,pu andU 2,pu the curve is shown in fig. 12, and the simulation result shows that the hybrid transformer can maintain the downstream power supply voltage constant at the set value when the upper grid voltage fluctuates.
By the mode, the invention provides the hybrid transformer facing the active power distribution network and the control method thereof, and the low-voltage side of the hybrid transformer can be seamlessly switched between two control strategies of voltage-frequency control and active-reactive control by dynamically monitoring the magnitude relation between the new energy grid-connected permeability of the area power distribution network and the maximum bearing capacity of the new energy of the area, so that constant-voltage constant-frequency control when the new energy permeability is not high and power control when the new energy permeability is greater than the maximum bearing capacity of the area power distribution network are realized, and the power supply quality of the active power distribution network is improved while the safe grid connection of the new energy is ensured.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all equivalent variations made by using the contents of the present specification and the drawings are within the protection scope of the present invention.

Claims (6)

1. A control method for a hybrid transformer facing an active power distribution network is characterized in that the hybrid transformer comprises a high-voltage three-phase winding, a low-voltage three-phase control winding and a back-to-back type power converter, wherein the windings are in star connection and neutral points of the windings are grounded; the corresponding phases of the high-voltage three-phase winding and the low-voltage three-phase winding and the corresponding phases of the high-voltage three-phase winding and the low-voltage three-phase control winding are respectively coupled through magnetic reaction by winding iron cores;
the selected number of turns of each phase winding of the high-voltage three-phase winding is respectively led out of a port and is connected with a three-phase alternating current port on one side of the back-to-back type power converter through a three-phase circuit breaker, and a three-phase alternating current port on the other side of the back-to-back type power converter is also connected with a corresponding phase port of the low-voltage three-phase control winding through the three-phase circuit breaker;
the non-grounding port of the high-voltage three-phase winding is connected with a superior power grid through a high-voltage side bus, and the low-voltage three-phase winding is connected with a downstream load and new energy through a low-voltage side bus;
the hybrid transformer carries out seamless switching of the low-voltage side of the hybrid transformer between two sets of control strategies of voltage-frequency control and active-reactive control according to the magnitude relation between the new energy grid-connected permeability of the power distribution network in the area at any moment and the maximum bearing capacity of the new energy in the area at the current moment, realizes power supply voltage regulation when the new energy is low in permeability and feedback power flow limitation when the new energy is too high, and specifically comprises the following steps:
at any moment, when the monitored new energy grid-connected permeability of the distribution network of the area where the hybrid transformer is located is smaller than or equal to the maximum bearing capacity of the new energy of the area measured and calculated at the current moment, the low-voltage side of the hybrid transformer adopts voltage-frequency control to control the voltage amplitude and the frequency of a bus at the low-voltage side to be constant on a set value; when the monitored new energy grid-connected permeability of the power distribution network in the target area is greater than the maximum bearing capacity of the new energy in the area obtained by measurement and calculation at the current moment, the low-voltage side of the hybrid transformer adopts active-reactive control, the feedback power flow monitored by a low-voltage side bus is controlled on a set value, and the safe access of the new energy in the target area is guaranteed in a mode of limiting the feedback power flow;
the maximum bearing capacity of the new energy in the area where the hybrid transformer is located at the current moment is determined by three types of power grid safety allowable constraint conditions, namely the maximum short-circuit current allowed by a low-voltage side bus at the current moment, the maximum voltage deviation of each node and the maximum allowable feedback power of the hybrid transformer, the corresponding total power generation power of the new energy is respectively measured and calculated when each constraint condition just reaches the boundary value of the constraint condition, the minimum value of the three calculation results is taken as the maximum safety access power of the new energy of the target area power distribution network at the current moment, and the percentage of the minimum value in the current total load power is taken as the maximum bearing capacity of the new energy of the area power distribution network at the current moment;
and the new energy grid-connected permeability of the area where the hybrid transformer is located at the current moment is the percentage of the total new energy generated power to the current total load power at the moment.
2. The method for controlling the hybrid transformer for the active power distribution network according to claim 1, wherein the reactive-direct current bus voltage control adopted on the high-voltage side of the hybrid transformer is specifically as follows:
a. according to the voltage measurement value of the DC bus of the back-to-back power converteru dc And reference value
Figure DEST_PATH_IMAGE001
Calculating the input current of the high-voltage side of the hybrid transformerdReference per unit value for the axis component->
Figure DEST_PATH_IMAGE002
As shown in the following formula:
Figure DEST_PATH_IMAGE003
in the formula (I), the compound is shown in the specification,sin order to be the laplacian operator,U dc,b is a reference value of the DC bus voltage of the back-to-back type power converter,k pi andk ii are respectively proportional integral linksiThe scaling factor and the integration factor of (a),ithe value range is [1,6 ]]，GAndTthe gain coefficient and the time constant of a first-order low-pass filtering link are respectively, DBlk is a power converter locking signal, DBlk is 0 when the power converter is locked, otherwise DBlk is 1;
b. according to the reactive power measurement value of the high-voltage side of the hybrid transformerQ 1 And a reference valueQ 1 * Computing blendingHigh-voltage side input current of transformerqReference per unit value of axis component
Figure DEST_PATH_IMAGE004
As shown in the following formula:
Figure DEST_PATH_IMAGE005
in the formula (I), the compound is shown in the specification,S b the reference value is the apparent power of the hybrid transformer;
c. measuring three-phase current of high-voltage side of hybrid transformeri A1 ,i B1 ,i C1 Performing per unit processing, and then performing Park conversion on the per unit processing to obtain three-phase current measurement valuesd、qPer unit value of each component under axisi d1,pu Andi q1,pu as shown in the following formula:
Figure DEST_PATH_IMAGE006
in the formula (I), the compound is shown in the specification,I 1,b andθ i1 respectively indicating the reference value and the electrical angle of the three-phase current at the high-voltage side of the hybrid transformer;
d. measuring three-phase voltage of high-voltage side of hybrid transformeru A1 ,u B1 ,u C1 Performing per unit processing, and then performing Park transformation to obtain three-phase voltage measurement valuesd、qPer unit value of each component under axisu d1,pu Andu q1,pu as shown in the following formula:
Figure DEST_PATH_IMAGE007
in the formula (I), the compound is shown in the specification,U 1,b andθ u1 respectively three phases at the high-voltage side of the hybrid transformerA reference value and an electrical angle of the phase voltage;
e. byi d1,pu 、
Figure DEST_PATH_IMAGE008
、i q1,pu 、/>
Figure DEST_PATH_IMAGE009
、u d1,pu Andu q1,pu the three-phase voltage of the alternating current side of the fully-controlled power converter 1 in the back-to-back power converter is obtained after the current inner loop processingd、qReference per value for an axis component &>
Figure DEST_PATH_IMAGE010
And &>
Figure DEST_PATH_IMAGE011
Then obtained by inverse Park transformationabcThe corresponding reference phase voltage under the shaft->
Figure DEST_PATH_IMAGE012
，/>
Figure DEST_PATH_IMAGE013
，/>
Figure DEST_PATH_IMAGE014
As shown in the following formula:
Figure DEST_PATH_IMAGE015
/>
Figure DEST_PATH_IMAGE016
in the formula (I), the compound is shown in the specification,L 1,pu is a filter inductor connected in series at the AC side of the fully-controlled power converter 1L 1 The per-unit value of (c) is,w 1 L 1,pu is a filter inductor connected in series at the AC side of the fully-controlled power converter 1L 1 The per-unit value of the inductive reactance,f 1 and
Figure DEST_PATH_IMAGE017
reference values of the voltage frequency at the alternating current side and the effective value of the line voltage of the full-control power converter 1 respectively;w 1 the voltage angular frequency of the alternating current side of the fully-controlled power converter 1;
f. to be provided with
Figure DEST_PATH_IMAGE018
、/>
Figure DEST_PATH_IMAGE019
、/>
Figure DEST_PATH_IMAGE020
The reference modulation wave is compared with the high-frequency triangular carrier wave logically, if the reference modulation wave is larger than 0, the three upper bridge arm switches SW of the full-control type power converter 1 are conducted ua1 ,SW ub1 And SW uc1 Output high level, to three lower bridge arm switches SW la1 ,SW lb1 And SW lc1 Outputting a low level; if the current is less than or equal to 0, three upper bridge arm switches SW of the full-control type power converter 1 are conducted ua1 ,SW ub1 And SW uc1 Output low level, to three lower bridge arm switches SW la1 ,SW lb1 And SW lc1 And outputting a high level, thereby forming a pulse wave of sine pulse width modulation and controlling the on-off of six silicon carbide metal-oxide-semiconductor field effect transistors in the fully-controlled power converter 1.
3. The control method for the hybrid transformer oriented to the active power distribution network of claim 1, wherein the low-voltage side of the hybrid transformer is seamlessly switched between two control strategies of voltage-frequency control and active-reactive control;
the low-voltage side of the hybrid transformer adopts a voltage-frequency control mode or an active-reactive control mode and is determined by a control signal S _ TM: when S _ TM is 0, the low-voltage side of the hybrid transformer adopts a voltage-frequency control mode; and when the S _ TM is 1, the low-voltage side of the hybrid transformer adopts an active-reactive control mode.
4. The method as claimed in claim 3, wherein when the low-voltage side of the hybrid transformer adopts the voltage-frequency control mode, the amplitudes of the three-phase reference voltages on the low-voltage side of the hybrid transformer are first generated respectively
Figure DEST_PATH_IMAGE021
And phaseθ u2 As shown in the following formula:
Figure DEST_PATH_IMAGE023
in the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE024
andU 2,b a reference per unit value and a reference value, which are the three-phase voltage at the low-voltage side of the hybrid transformer respectively>
Figure DEST_PATH_IMAGE026
Before switching control modes, three-phase voltage reference phases on the low-voltage side of the hybrid transformer are switched;sis Laplace operator;
then, will
Figure DEST_PATH_IMAGE027
Andθ u2 is input into a three-phase sine wave generator to generate a three-phase voltage reference waveform ^ on the low-voltage side of the hybrid transformer>
Figure DEST_PATH_IMAGE028
、/>
Figure DEST_PATH_IMAGE029
、/>
Figure DEST_PATH_IMAGE030
As shown in the following formula: />
Figure DEST_PATH_IMAGE031
Will be provided with
Figure DEST_PATH_IMAGE032
、/>
Figure DEST_PATH_IMAGE033
、/>
Figure 747235DEST_PATH_IMAGE030
Performing per-unit processing, and performing Park conversion on the per-unit processing to obtain the three-phase voltage of the low-voltage side of the hybrid transformerd、qReference per unit value for each component under the axis->
Figure DEST_PATH_IMAGE034
、/>
Figure DEST_PATH_IMAGE035
As shown in the following formula:
Figure DEST_PATH_IMAGE037
synchronously, measuring three-phase voltage of low-voltage side of hybrid transformeru a2 ,u b2 ,u c2 Performing per unit processing, and then performing Park transformation to obtain three-phase voltage measurement valuesd、qPer unit value of each component under axisu d2,pu Andu q2,pu as shown in the following formula:
Figure DEST_PATH_IMAGE038
then, respectively calculateu d2,pu And
Figure DEST_PATH_IMAGE039
andu q2,pu and/or>
Figure DEST_PATH_IMAGE040
The errors are input into a proportional-integral link respectively, and then the three-phase current of the low-voltage side of the hybrid transformer is obtainedd、qReference per unit value for each component under the axis->
Figure DEST_PATH_IMAGE041
And
Figure DEST_PATH_IMAGE042
as shown in the following formula:
Figure DEST_PATH_IMAGE043
in the formula (I), the compound is shown in the specification,k pi andk ii are respectively proportional integral linksiThe scaling factor and the integration factor of (a),ithe value range is [1,6 ]]DBlk is a power converter locking signal, DBlk is 0 when the power converter is locked, otherwise DBlk is 1;
measuring three-phase current of low-voltage side of hybrid transformeri a2 ,i b2 ,i c2 Performing per unit processing, and then performing Park conversion on the per unit processing to obtain three-phase current measurement valuesd、qPer unit value of each component under axisi d2,pu Andi q2,pu as shown in the following formula:
Figure DEST_PATH_IMAGE045
in the formula (I), the compound is shown in the specification,I 2,b andθ i2 respectively setting a reference value and an electrical angle of a three-phase current at the low-voltage side of the hybrid transformer;
will be provided withi d2,pu 、
Figure DEST_PATH_IMAGE046
、i q2,pu 、/>
Figure DEST_PATH_IMAGE047
、u d2,pu Andu q2,pu transmitted to the current inner ring to obtain three-phase voltage of the alternating current side of the fully-controlled power converter 2 in the back-to-back power converterd、qReference per unit value for the axis component->
Figure DEST_PATH_IMAGE048
And &>
Figure DEST_PATH_IMAGE049
Then obtained by inverse Park transformationabcThe corresponding reference phase voltage under the shaft->
Figure DEST_PATH_IMAGE050
、/>
Figure DEST_PATH_IMAGE051
、/>
Figure DEST_PATH_IMAGE052
As shown in the following formula:
Figure DEST_PATH_IMAGE053
Figure DEST_PATH_IMAGE055
in the formula (I), the compound is shown in the specification,L 2,pu a filter inductor connected in series at the AC side of the fully-controlled power converter 2L 2 The per-unit value of (c) is,w 2 L 2,pu a filter inductor connected in series at the AC side of the fully-controlled power converter 2L 2 The per-unit value of the inductive reactance,f 2 and
Figure DEST_PATH_IMAGE056
reference values respectively for the ac side voltage frequency and the line voltage effective value of the fully controlled power converter 2,kdqis a directional coefficient;w 2 the voltage angular frequency of the alternating current side of the fully-controlled power converter 2 is obtained;S b the reference value of the apparent power of the hybrid transformer is obtained;
finally, to
Figure DEST_PATH_IMAGE057
、/>
Figure DEST_PATH_IMAGE058
、/>
Figure DEST_PATH_IMAGE059
The reference modulation wave is logically compared with the high-frequency triangular carrier wave, if the reference modulation wave is larger than 0, the three upper bridge arm switches SW of the full-control type power converter 2 are switched ua2 ,SW ub2 And SW uc2 Output high level, to three lower bridge arm switches SW la2 ,SW lb2 And SW lc2 Outputting a low level; if the voltage is less than or equal to 0, three upper bridge arm switches SW of the full-control type power converter 2 are switched ua2 ,SW ub2 And SW uc2 Output low level, to three lower bridge arm switches SW la2 ,SW lb2 And SW lc2 And outputting high level to form pulse wave modulated by sine pulse width to control the on-off of six silicon carbide metal oxide semiconductor field effect transistors in the fully-controlled power converter 2.
5. A noodle as claimed in claim 4A control method for a hybrid transformer to an active distribution network is characterized in that when the low-voltage side of the hybrid transformer adopts an active-reactive control mode, the active power of the low-voltage side of the hybrid transformer is firstly calculated respectivelyP 2 And reactive powerQ 2 As shown in the following formula:
Figure DEST_PATH_IMAGE060
will be provided withP 2 、Q 2 And corresponding reference value
Figure DEST_PATH_IMAGE061
、/>
Figure DEST_PATH_IMAGE062
Is subjected to per unit treatment to obtainP 2,pu 、Q 2,pu 、/>
Figure DEST_PATH_IMAGE063
、/>
Figure DEST_PATH_IMAGE064
Respectively calculate
Figure 54588DEST_PATH_IMAGE063
AndP 2,pu and->
Figure DEST_PATH_IMAGE065
AndQ 2,pu the difference values are subjected to low-pass filtering respectively and then transmitted to a proportional integral link, so that the three-phase current of the low-voltage side of the hybrid transformer is obtaineddqReference per unit value for each component under the axis->
Figure DEST_PATH_IMAGE066
And &>
Figure DEST_PATH_IMAGE067
As shown in the following formula:
Figure DEST_PATH_IMAGE068
S b the reference value of the apparent power of the hybrid transformer is obtained;GandTrespectively is a gain coefficient and a time constant of a first-order low-pass filtering link;
the current inner loop of the active-reactive control mode is completely consistent with the current inner loop of the voltage-frequency control mode; finally, the product is processedi d2,pu 、
Figure 772008DEST_PATH_IMAGE066
、i q2,pu 、/>
Figure DEST_PATH_IMAGE069
、u d2,pu Andu q2,pu and pulse signals for controlling the on-off of six silicon carbide gold oxygen half field effect transistors in the full-control power converter 2 are obtained after current inner loop processing.
6. The method as claimed in claim 1, wherein the back-to-back power converters are connected in a back-to-back manner by two identical fully-controlled power converters, each fully-controlled power converter comprises three pairs of legs connected in a full-bridge manner, each pair of legs is formed by two silicon carbide mosfets connected in series, the dc sides of the two fully-controlled power converters are coupled by a capacitor bank, the capacitor bank is formed by two capacitors with the same specification connected in series and the connection point thereof is grounded, and the ac sides of the two fully-controlled power converters are connected in series with the winding outlet of the high-voltage three-phase winding and the three-phase port of the low-voltage three-phase control winding respectively in the form of series filter inductors.
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