CN114093625A - Hybrid intelligent distribution transformer containing power frequency isolated back-to-back converter - Google Patents
Hybrid intelligent distribution transformer containing power frequency isolated back-to-back converter Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/40—Structural association with built-in electric component, e.g. fuse
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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
- H02J3/01—Arrangements for reducing harmonics or ripples
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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
- H02J3/02—Circuit arrangements for ac mains or ac distribution networks using a single network for simultaneous distribution of power at different frequencies; using a single network for simultaneous distribution of ac power and of dc power
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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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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- 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
- Y02E40/40—Arrangements for reducing harmonics
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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 invention discloses a hybrid intelligent distribution transformer containing a power frequency isolation type back-to-back converter, which provides a low-voltage direct-current distribution interface, integrates the functions of voltage regulation, harmonic treatment, three-phase load unbalance and other electric energy quality treatment functions, and simultaneously provides a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and a novel direct-current load, thereby overcoming the problems in the prior art.
Description
Technical Field
The invention belongs to the technical field of power electronic devices in power distribution systems, and particularly relates to a hybrid intelligent distribution transformer containing a power frequency isolated back-to-back converter.
Background
The power quality of the power distribution terminal directly affects the safety of power supply and utilization equipment, the industrial production level and the quality of life of people. Along with energy internet construction, novel source/load ratios of distributed photovoltaic, electric vehicles, battery energy storage and the like in a power distribution network are promoted year by year, so that the problems of power quality of power distribution terminals such as high/low voltage, harmonic amplification, three-phase imbalance and the like are increasingly highlighted. Especially, important loads sensitive to the power quality in a power supply area, such as precision instrument manufacturing enterprises, large-scale data centers and the like, have higher requirements on the power quality.
The power transformer is basic equipment of a power transmission and distribution system, and is widely applied to the fields of industry, agriculture, traffic, urban communities and the like. The traditional power transformer does not have the functions of current harmonic suppression, voltage flexible voltage regulation, direct-current power distribution interface and the like. In recent years, hybrid distribution transformers combining a power conversion device with a power transformer to improve the quality of electric energy have been proposed. The scheme is often carried out respectively or partly integrated together to reactive compensation, harmonic treatment, unbalanced three-phase load scheduling problem at present, and the solution does not have the comprehensiveness, and device integrated level and comprehensive utilization are rateed lowly, do not possess the direct current distribution interface of novel source/load "plug and play" simultaneously yet.
Disclosure of Invention
The invention aims to provide a hybrid intelligent distribution transformer containing a power frequency isolation type back-to-back converter, which can provide a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and novel direct-current loads.
The invention adopts the technical scheme that the hybrid intelligent distribution transformer containing the power frequency isolation type back-to-back converter comprises three high-voltage windings, three high-voltage independent windings, three low-voltage windings and three low-voltage independent windings, wherein each high-voltage independent winding is connected with a bypass switch in parallel, each high-voltage winding is connected with one high-voltage independent winding to form a high-voltage side winding, one end of each high-voltage side winding is connected with a three-phase power supply, the other end of each high-voltage side winding is connected with other high-voltage side windings, one end of each low-voltage winding is star-connected to form a node n1, and the other low-voltage winding is star-connected to form a node n1The ends of the three-phase low-voltage independent windings are respectively connected with a three-phase load, the node n1 is connected with a neutral line of the three-phase load through a lead, one ends of the three low-voltage independent windings are connected in star to form a node n2, the other ends of the three low-voltage independent windings are respectively connected with different phases of a preceding-stage voltage source converter through a filter, and the node n2 is connected with a different phase of the preceding-stage voltage source converter through a filter inductor LseThe three high-voltage windings are respectively in magnetic reaction coupling with three corresponding low-voltage windings through wound iron cores, the three high-voltage independent windings are respectively in magnetic reaction coupling with three corresponding low-voltage independent windings through wound iron cores, the three high-voltage independent windings further comprise a rear-stage voltage source converter, the alternating current side of the rear-stage voltage source converter is connected with a load side bus through an inductor, and the direct current side of the front-stage voltage source converter is connected with the direct current side of the rear-stage voltage source converter and leads out a low-voltage direct-current power distribution port.
The invention is also characterized in that:
the three high-voltage side windings are connected in the following mode: the three high-voltage side windings are sequentially connected end to form a triangle, and each angle of the triangle is respectively connected with one phase of a three-phase power supply;
any high-voltage side winding connected with the phase A of the three-phase power supply is defined as a phase A high-voltage side winding, the high-voltage side winding connected with the phase B of the three-phase power supply is defined as a phase B high-voltage side winding, and the high-voltage side winding connected with the phase C of the three-phase power supply is defined as a phase C high-voltage side winding.
The three high-voltage side windings are connected in the following mode: one ends of the three high-voltage side windings are connected into a node, and the other ends of the three high-voltage side windings are respectively connected with three phases of a three-phase power supply;
the high-voltage side winding connected with the phase A of the three-phase power supply is an phase A high-voltage side winding; the high-voltage side winding connected with the phase B of the three-phase power supply is a phase B high-voltage side winding; and the high-voltage side winding connected with the C phase of the three-phase power supply is a C-phase high-voltage side winding.
The direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are simultaneously separated from the capacitor.
The filter comprises a filter inductor and a filter capacitor, the filter inductor is connected in series between the other end of the low-voltage independent winding and different phases of the preceding-stage voltage source converter, and the filter capacitor is connected in parallel between the different phases of the preceding-stage voltage source converter.
The invention has the beneficial effects that:
the invention relates to a hybrid intelligent distribution transformer containing a power frequency isolated back-to-back converter, which provides a low-voltage direct-current distribution interface, integrates the functions of voltage regulation, harmonic treatment, three-phase load unbalance and other electric energy quality treatment functions, and simultaneously provides a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and a novel direct-current load, thereby overcoming the problems in the prior art.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of a hybrid intelligent distribution transformer including a power frequency isolated back-to-back converter according to the present invention;
FIG. 2 is a schematic structural diagram of a second embodiment of a hybrid intelligent distribution transformer including a power frequency isolated back-to-back converter according to the present invention;
FIG. 3 is a schematic diagram of a voltage regulation control strategy of the preceding stage voltage source converter of the present invention;
FIG. 4 is a schematic circuit diagram of a three-phase four-leg voltage source converter in two voltage source converters according to the present invention;
FIG. 5 is a schematic diagram of the load side voltage during a sudden rise and fall of the grid side voltage;
FIG. 6 is a schematic diagram of a load side voltage stabilized by regulated modulation;
FIG. 7 is a block diagram of the harmonic detection strategy of the back-stage voltage source converter of the present invention;
FIG. 8 is a block diagram of a harmonic compensation link of harmonic compensation of a rear-stage voltage source converter and a control strategy of voltage stabilization at a direct current side;
FIG. 9 shows an SPWM modulation block diagram for a voltage source converter transistor IGBT;
FIG. 10 shows a schematic diagram of a load side current waveform after harmonic compensation of a later stage voltage source converter;
fig. 11 shows a waveform diagram after the dc side of the post-stage voltage source converter is stabilized.
In the figure, Vga、Vgb、VgcRespectively represent grid-side three-phase voltage A, B, C phase voltage;
Vsa、Vsb、Vscrespectively represent the three-phase voltage A, B, C phase voltage of the user side;
vca、vcb、vccshowing the compensation voltage provided by the output port of the pre-stage voltage source type converter;
iga、igb、igcrespectively representing the three-phase current A, B, C phase current on the grid side;
isa、isb、iscrespectively representing A, B, C phase currents of a low-voltage side three-phase current;
iLa、iLb、iLca, B, C phase currents respectively representing three-phase currents flowing into the user side;
ifa、ifb、ifcrespectively representing fundamental components of three-phase current A, B, C flowing to the user side;
iha、ihb、ihcrespectively representing harmonic components of the three-phase current A, B, C flowing to the user side;
ia1、ib1、ic1a, B, C phase currents respectively representing output currents of the preceding-stage voltage-source type converters;
ia2、ib2、ic2a, B, C phase currents of the output current of the rear-stage voltage source type converter are respectively shown;
idref、iqrefa harmonic current reference value of a user side under a d-q coordinate axis;
id2、iq2actual harmonic compensation current of a later-stage voltage source type converter under the d-q coordinate axes;
Lsea、Lseb、Lsecrespectively representing filter inductors of a preceding-stage voltage source type converter;
Csea、Cseb、Csecrespectively representing filter capacitors of a preceding-stage voltage source type converter;
Lsha、Lshb、Lshcrespectively representing the filter inductors of the post-stage voltage source type converter;
WA1、WB1、WC1individual watchThe high-voltage side A, B, C three-phase main winding of the power frequency transformer is shown;
Wa1、Wb1、Wc1respectively representing A, B, C three-phase main windings on the low-voltage side of the power frequency transformer;
WA2、WB2、WC2respectively, representing A, B, C three-phase independent windings on the high-voltage side of the coupling transformer;
Wa2、Wb2、Wc2respectively represent A, B, C three-phase independent windings on the low-voltage side of the coupling transformer;
sa, Sb and Sc respectively represent A, B, C three-phase bypass switches on the high-voltage side of the coupling transformer;
Cv1、Cv2respectively representing a preceding stage voltage source converter and a succeeding stage voltage source converter;
VT1, VT2, VT3, VT4, VT5, VT6, VT7 and VT8 respectively represent 8 insulated gate bipolar transistors in the preceding-stage three-phase four-leg converter;
VD1, VD2, VD3, VD4, VD5, VD6, VD7, and VD8 respectively represent 8 insulated gate bipolar transistors in the rear-stage three-phase four-leg inverter.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a hybrid intelligent distribution transformer containing a power frequency isolation type back-to-back converter, which is characterized by comprising three high-voltage windings WA1、WB1、WC1Three high voltage independent windings WA2、WB2、WC2Three low voltage windings Wa1、Wb1、Wc1Three independent low voltage windings Wa2、Wb2、Wc2Each high-voltage independent winding is connected with a bypass switch in parallel, the on-off time of the coupling transformer can be controlled, and the bypass switch is switched off when voltage regulation operation is needed; when the network side voltage is stable, the bypass switch is closed, each high-voltage winding is connected with a high-voltage independent winding to form a high-voltage side winding, one end of each high-voltage side winding is connected with a three-phase power supply, the other end of each high-voltage side winding is connected with other high-voltage side windings, and one end of each low-voltage winding is connected with a starThe three low-voltage independent windings are connected with one end in star to form a node n1, the other end of the three low-voltage independent windings are respectively connected with a three-phase load, the node n1 is connected with the three-phase load through a lead, one end of each low-voltage independent winding is connected with a node n2 in star, the other end of each low-voltage independent winding is connected with the different phases of the alternating current side of the preceding-stage voltage source converter through a filter inductor, a filter capacitor is connected between the two ends of each low-voltage independent winding, and the node n2 is connected with a three-phase load through a filter inductor LseThe three high-voltage windings are respectively magnetically reacted and coupled with corresponding phases of the three low-voltage windings through wound iron cores to form a power frequency transformer, the three high-voltage independent windings are respectively magnetically reacted and coupled with corresponding phases of the three low-voltage independent windings through wound iron cores to form a coupling transformer, the three-phase power frequency transformer further comprises a rear-stage voltage source converter, the alternating current side of the rear-stage voltage source converter is connected with a three-phase load through an inductor, the direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are simultaneously connected with a separation capacitor in parallel to stabilize the voltage of the direct current side, and the direct current side port V of the front-stage voltage source converter CV1 is connected with a separation capacitor in parallel to stabilize the voltage of the direct current sidedc1+And a DC side port V of a rear-stage voltage source converter CV2dc2+Connected as the positive port V of the low-voltage direct current of the intelligent distribution transformerdc+Front stage voltage source converter CV1 DC side port Vdc1-And a DC side port V of a rear-stage voltage source converter CV2dc2-Connected as a low-voltage DC negative electrode port V of an intelligent distribution transformerdc-And the novel source/load friendly access of photovoltaic, energy storage, automobile charging pile, fan and the like is realized.
The front-stage voltage source converter CV1 and the rear-stage voltage source converter CV2 are both in a three-phase four-wire system.
Example one
As shown in fig. 1, the three high-voltage side windings are connected in the following manner: the three high-voltage side windings are sequentially connected end to form a triangle, and each angle of the triangle is respectively connected with one phase of a three-phase power supply;
wherein, connect arbitrary one high-pressure side winding of three phase power A looks to define as A looks high-pressure side winding, connect the high-pressure side winding of three phase power B looks to define as B looks high-pressure side winding, connect the high-pressure side winding of three phase power C looks to define as C looks high-pressure side winding, specifically do: the high-voltage winding in the A-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load A phase, the high-voltage winding in the B-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load B phase, the high-voltage winding in the C-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load C phase, a high-voltage independent winding in the A-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load A phase, a high-voltage independent winding in the B-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load B phase, and a high-voltage independent winding in the C-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load C phase.
Example two
As shown in fig. 2, the three high-voltage side windings are connected in the following manner: one ends of the three high-voltage side windings are connected into a node, and the other ends of the three high-voltage side windings are respectively connected with three phases of a three-phase power supply;
the high-voltage side winding connected with the phase A of the three-phase power supply is an phase A high-voltage side winding; the high-voltage side winding connected with the phase B of the three-phase power supply is a phase B high-voltage side winding; the high-voltage side winding connected with the C phase of the three-phase power supply is a C phase high-voltage side winding, and the method specifically comprises the following steps: the high-voltage winding in the A-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load A phase, the high-voltage winding in the B-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load B phase, the high-voltage winding in the C-phase high-voltage side winding is coupled and connected with a low-voltage winding of a three-phase load C phase, a high-voltage independent winding in the A-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load A phase, a high-voltage independent winding in the B-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load B phase, and a high-voltage independent winding in the C-phase high-voltage side winding is coupled and connected with a low-voltage independent winding of the three-phase load C phase.
The first and second embodiments of the present invention are two configurations of intelligent distribution transformers, and control strategies for the two intelligent distribution transformers are consistent when the transformer is used, and a first intelligent distribution transformer configured in the first embodiment of the present invention is described in detail below, and an example of the embodiment is shown in fig. 1. The embodiments described below with reference to the drawings are exemplary and are intended to be used for explaining the present invention.
In the present invention, a high-voltage winding W is usedA1High voltage winding WB1High voltage winding WC1Low voltage winding Wa1Lower, lowerPressure winding Wb1Low voltage winding Wc1Forming the power frequency transformer. High voltage independent winding WA2High voltage independent winding WB2High voltage independent winding WC2Low voltage independent winding Wa2Low voltage independent winding Wb2Low voltage independent winding Wc2The high-voltage independent winding and the low-voltage independent winding are wound on respective iron cores to form main windings, the high-voltage independent winding and the low-voltage independent winding are wound on respective iron cores to form independent windings, silicon steel sheets are selected as magnetic core materials, and the bypass switches control the on-off of the high-voltage independent winding of the coupling transformer and are integrated in the power frequency transformer in a unified mode. The power electronic transformer comprises a front-stage voltage source type converter CV1 and a rear-stage voltage source type converter CV2, wherein the two voltage source type converters are connected in a back-to-back mode, and the voltage source type converter adopted in the embodiment is a three-phase four-leg converter.
High-voltage phase winding W of industrial frequency transformerA1、WB1、WC1High-voltage independent winding W of each phase of coupling transformerA2、WB2、WC2After being connected in series, a delta connection mode is adopted, the three-phase high-voltage independent winding is connected with the bypass switches Sa, Sb and Sc in parallel, and the low-voltage winding W of the power frequency transformera1、Wb1、Wc1With low-voltage independent winding W of coupling transformera2、Wb2、Wc2Each using YnA type wiring method. The transformation ratio of the high-voltage winding and the low-voltage winding of the power frequency transformer is 14140:311, and the transformation ratio of the high-voltage independent winding and the low-voltage independent winding of the coupling transformer is 4: 1. Low-voltage independent winding Wa2、Wb2、Wc2Is connected with the preceding-stage voltage source type converter. Wherein v isca、vcb、vccThree-phase compensation voltage supplied to preceding-stage voltage source converter by regulating vca、vcb、vccThe voltage on the load side is controlled to be stabilized at a rated value, so that the dynamic voltage continuous compensation function of the hybrid intelligent distribution transformer is realized when the voltage on the network side fluctuates. For example, if the rated voltage on the grid side is 10kV, when the voltage on the grid side is stable, no power supply is neededVoltage compensation function, wherein the bypass switches Sa, Sb and Sc are in a closed state; when the amplitude fluctuation (sudden rise or sudden drop) of the grid side voltage is +/-10% in a certain time period, voltage compensation is needed, the bypass switches Sa, Sb and Sc are controlled to be switched off, the coupling transformer starts to work, and a reference value of the output voltage of the preceding-stage voltage source type converter CV1 when the grid side voltage fluctuates can be obtained through a voltage compensation control block diagram shown in fig. 3. Wherein Vga、Vgb、VgcThe voltage compensation control strategy respectively represents A, B, C three-phase voltage on the voltage source side, each phase is independently controlled, when A, B, C any phase has voltage fluctuation, each phase is independently controlled to collect voltage fluctuation values higher or lower than the normal voltage level, the voltage fluctuation values are eliminated through the control of the coupling transformer, and the voltage is always controlled within the normal level.
According to the formula (1), A, B, C after the three-phase voltage acquisition signal is delayed by a quarter cycle, the amplitude of each phase voltage can be calculated. In the embodiment, the voltage amplitude of each phase under steady-state operation is 8164V (if the voltage on the network side fluctuates in a certain period of time, the amplitude can suddenly rise or drop). The phase of each phase voltage can be obtained by a phase-locked loop, and the power frequency transformer adopts delta/YnIn the connection mode, the angle difference between the grid side voltage and the load side voltage is 30 °, and when the voltage regulation control is performed, the angle difference needs to be compensated to formula (2) in the modulation wave of the preceding-stage voltage source converter CV 1.
Wherein, VgkmIs the amplitude of the voltage on the high-voltage side, VrefIs a reference value when the high pressure side is stable, and θ represents the angle of the high pressure side.
When the voltage of the network side phase fluctuates, the control system makes the difference between the real-time amplitude of the network voltage and the rated voltage amplitude of the network side to obtain the network sideThe voltage fluctuates and is used as the reference voltage of the output port of the preceding voltage source converter CV 1. The dynamic voltage compensation control strategy adopts double-loop control of a voltage outer loop current inner loop, a PR (Proportional resonant Controller) Controller is adopted by an outer loop to control voltage error, a P Controller (Proportional Controller) Controller is adopted by an inner loop to control current error, and feed-forward compensation is added to realize a wide voltage regulation range and improve the dynamic response characteristic of a closed-loop system. Inputting the error signal into the control side of the preceding voltage source converter, regulating the preceding voltage source converter vca、vcb、vccTo realize the user side phase voltage vsa、vsb、vscStabilize at the rated voltage value of 220V.
Preceding stage voltage source converter CV1And a subsequent voltage source converter CV2May be a voltage source converter having the VSC structure shown in figure 4. The preceding-stage voltage source converter CV1 adopts a three-phase four-wire system structure, CV1Comprises A, B, C and four zero-sequence bridge arms containing VT1、VT2、VT3、VT4、VT5、VT6、VT7、VT8Eight Insulated Gate Bipolar Transistors (IGBTs) and anti-parallel diodes, wherein VT1、VT5A-phase bridge arm, VT, constituting a preceding-stage voltage source converter2、VT6B-phase bridge arm, VT, constituting a preceding-stage voltage source converter3、VT7And a C-phase bridge arm of the preceding-stage voltage source converter is formed. VT4、VT8The zero sequence bridge arm forming the preceding-stage voltage source converter is connected to the neutral point of the low-voltage independent winding, and the problem of three-phase imbalance can be solved through the zero sequence bridge arm. In addition, the preceding stage voltage source converter passes through a filter inductor La1、Lb1、Lc1Filter capacitor Ca1、Cb1、Cc1Connected to low-voltage independent windings Wa2、Wb2、Wc2Wherein the filter parameters are 500uH and 20uF respectively. The front-stage voltage source type converter CV1 and the rear-stage voltage source type converter CV2 are connected in parallel on a low-voltage direct-current bus V with the rated voltage level of 760VdcUpper, DC busCapacitor CdcPlays a role of voltage stabilization, CdcThe parameter (2 mF). The topology of the preceding-stage voltage source converter is not limited to a three-phase four-leg converter, and a voltage source type converter topology structure such as a three-level converter can be adopted as long as the voltage value of the output port can be adjusted.
When the network side voltage fluctuates with high/low voltage, the voltage waveform of the subscriber side with dynamic voltage compensation effect of the hybrid intelligent distribution transformer is shown in fig. 5, wherein the dotted line represents the high-voltage winding voltage and the solid line represents the low-voltage winding voltage. As shown in fig. 6, in the phase of 0.05s-0.1s, the voltage on the network side does not fluctuate, and the peak voltage of the voltage on the user side is stabilized at 311V; when the voltage peak value of 10% of the net side voltage suddenly rises to 8980V in the stage of 0.1s-0.2s, the preceding-stage voltage source converter detects the net side voltage suddenly rises and regulates the voltage V of the independent windingca、vcb、vccThe peak voltage is 353V, which is equal to the grid side voltage Vga、Vgb、VgcIn phase. The independent winding transformation ratio adopted by the embodiment is 1: 4, the peak value of the high-voltage independent winding voltage is 1413V. The peak voltage of the user side is rapidly stabilized from 342V to 311V after 0.01 s; the voltage of the network side is recovered to the rated voltage in the stage of 0.2s-0.3s, the preceding-stage voltage source converter detects the voltage change of the network side and regulates the voltage vv of the independent windingca、vcb、vccAbout 0V; the voltage peak value of the network side voltage drop of 10% is reduced to 7348V in the stage of 0.3s-0.4s, the preceding-stage voltage source converter detects the voltage change of the network side and adjusts the voltage V of the independent windingca、vcb、vccThe peak voltage is 353V, which is equal to the grid side voltage Vga、Vgb、VgcAnd (4) reversing the phase. The independent winding transformation ratio adopted by the embodiment is 1: 4, the peak value of the high-side auxiliary winding voltage is 1413V. The peak voltage on the user side rapidly stabilized from 280V to 311V after 0.01 s. The voltage fluctuation range of the regulation network side of the preceding-stage voltage source converter can be improved by reasonably designing the turn ratio of the independent winding, and the voltage calculation formula of the low-voltage side of the preceding-stage voltage source converter is as follows:
the expression of the control signal for generating the compensation voltage by the preceding-stage voltage source converter is as follows:
as shown by CV in FIG. 42A post-stage voltage source converter for an intelligent distribution transformer is shown. In this example, the subsequent voltage source converter CV2And a three-phase four-wire system structure is adopted to realize the functions of direct current side voltage stabilization, user side harmonic compensation and the like. CV of2Comprising A, B, C and four zero-sequence bridge arms containing VD1、VD2、VD3、VD4、VD5、VD6、VD7、VD8Eight Insulated Gate Bipolar Transistors (IGBT) and anti-parallel diodes, where VD4、VD8Form the A-phase bridge arm of the post-stage voltage source converter, VD3、VD7B-phase bridge arm of the voltage source converter of the rear stage, VD2、VD6Form a C-phase bridge arm of a rear-stage voltage source converter, VD1、VD5And a zero sequence bridge arm of the rear-stage voltage source converter is formed and connected to a neutral line of a three-phase four-wire system user side. Rear-stage voltage source type converter CV2With preceding voltage source converter CV1Common DC bus vdc. Rear-stage voltage source type converter CV2A, B, C three-phase filter inductor L passing through 2mHa2、Lb2、Lc2And then are respectively and correspondingly connected to the three-phase bus at the user side in parallel. Rear stage voltage source converter CV2And functions of harmonic current compensation, reactive compensation and the like are realized.
FIG. 7 shows a block diagram of a harmonic compensation control strategy of a later-stage voltage source converter, wherein a detection link adopts ip-iqAnd (4) a harmonic detection algorithm. Phase and frequency of voltage at network side are tracked by phase-locked loop (PLL), and three-phase current i at user side is acquiredLa、iLb、iLcThrough Clark transformation formula (5), two-phase current i can be obtainedɑAnd iβ. The instantaneous active current i can be calculated by the instantaneous power formula (6)pAnd instantaneous reactive current iqNumerical values. Instantaneous active current ipAnd instantaneous reactive current iqObtaining a DC component by a Low Pass Filter (LPF)
And
the three-phase current fundamental component i can be obtained through Clark inverse transformation formula (8)fa、ifb、ifc. Will adopt the nonlinear current i on the user sideLa、iLb、iLcFundamental component i of three-phase currentfa、ifb、ifcThe difference is shown as formula (9), so that the harmonic current i can be obtainedha、ihb、ihc。
Fig. 8 shows a block diagram of the dc bus voltage stabilization and harmonic current compensation control strategy of the rear-stage voltage source converter CV 2. In order to realize the voltage control on the direct current side and the accurate compensation of harmonic current, the harmonic current i is usedha、ihb、ihcAnd the output current i of the port of the rear-stage voltage source convertera2、ib2、ic2Obtaining a harmonic current reference value i under a d-q coordinate axis by performing park transformationdref、iqrefAnd the actual harmonic compensation current id2、iq2. Wherein the stable DC voltage is related to active current, and the voltage V on the DC side of the sampling quantity is measureddcAdding the value obtained by proportional integral control (PI) after the difference with the desired voltage of 800V to the d-axis reference value i of the harmonic currentdrefAnd in current, the functions of harmonic current compensation and direct-current side voltage stabilization are realized. Harmonic current i when d-q axis conversion is performedd、iqThe coupling quantity exists, and decoupling control is added in the current inner ring, so that accurate compensation of harmonic current is realized. Duty ratio reference value d of current loop outputd、dqObtaining the required duty ratio d through park inverse transformationa、db、dc。
FIG. 9 shows SPWM control block diagram for controlling the on and off of Insulated Gate Bipolar Transistors (IGBT) forming A, B, C three-phase bridge arms, wherein the example adopts a bipolar modulation strategy to obtain a reference modulation wave da、db、dcAnd comparing the signal with a carrier (the frequency is 20kHz), and if the obtained value is more than 0, outputting a high level 1 by the selector, otherwise, outputting a low level 0 to form an SPWM pulse wave and modulating the on and off of a transistor IGBT forming an A, B, C three-phase bridge arm. For the switching tube of the zero-sequence bridge arm, the difference between the sum of three-phase current and the zero-sequence current of the neutral line is collected in the later-stage voltage source transformation, the difference between the sum of three-phase voltage and the zero-sequence voltage of the neutral line is collected in the former-stage voltage source transformation, the modulation wave obtained by the PI controller is compared with the carrier wave, if the obtained difference value is larger than 0, the selector outputs high level 1, otherwise, low level 0 is output, SPWM pulse wave is formed, the IGBT of the modulation bridge arm zero-sequence switching tube is switched on and switched on, and the IGBT of the modulation bridge arm zero-sequence switching tube is switched on and switched on with the PWM pulse waveAnd (6) turning off.
Fig. 10 shows the low-voltage winding side current after the harmonic compensation is added to the post-stage voltage source converter at 0.1s, and it can be seen that the main harmonic component of the current at the output port of the low-voltage winding of the power frequency transformer is eliminated.
Fig. 11 shows the dc-side regulation waveform, which can rapidly stabilize to the desired voltage amplitude of 800V when the grid-side voltage undergoes voltage swell and voltage sag.
Through the mode, the hybrid intelligent distribution transformer with the power frequency isolation type back-to-back converter provided by the invention provides a low-voltage direct-current distribution interface, integrates the functions of voltage regulation, harmonic treatment, three-phase load unbalance and other electric energy quality treatment functions, and simultaneously provides a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and a novel direct-current load, thereby overcoming the problems in the prior art.
Claims (5)
1. The hybrid intelligent distribution transformer is characterized by comprising three high-voltage windings, three high-voltage independent windings, three low-voltage windings and three low-voltage independent windings, wherein each high-voltage independent winding is connected with a bypass switch in parallel, each high-voltage winding is connected with one high-voltage independent winding to form a high-voltage side winding, one end of each high-voltage side winding is connected with a three-phase power supply, the other end of each high-voltage side winding is connected with other high-voltage side windings, one end of each three low-voltage winding is star-connected to form a node n1, the other end of each low-voltage winding is connected with a three-phase load respectively, the node n1 is connected with a three-phase load central line through a lead, one end of each three low-voltage independent winding is star-connected to form a node n2, the other end of each low-voltage side winding is connected with a preceding-stage voltage source converter through a filter respectively, and the node n2 is connected with a preceding-stage voltage source converter through a filter inductor L2 to form different phasesseConnect preceding stage voltage source converter AC side central line, three high-voltage winding carries out the magnetic reaction coupling through winding the iron core with three low-voltage winding corresponding phase respectively, three high-voltage isolated winding respectively with three low-voltage isolated winding corresponding phase carries out the magnetic reaction coupling through winding the iron core, still includes back stage voltage source converter, and back stage voltage source converter AC side passes through inductance connection load side generating line, preceding stage electricityThe direct current side of the voltage source converter is connected with the direct current side of the rear-stage voltage source converter and leads out a low-voltage direct current distribution port.
2. The hybrid intelligent distribution transformer with the power frequency isolated back-to-back converter as recited in claim 1, wherein the three high-voltage side windings are connected in a manner that: the three high-voltage side windings are sequentially connected end to form a triangle, and each angle of the triangle is respectively connected with one phase of a three-phase power supply; any high-voltage side winding connected with the phase A of the three-phase power supply is defined as a phase A high-voltage side winding, the high-voltage side winding connected with the phase B of the three-phase power supply is defined as a phase B high-voltage side winding, and the high-voltage side winding connected with the phase C of the three-phase power supply is defined as a phase C high-voltage side winding.
3. The hybrid intelligent distribution transformer with the power frequency isolated back-to-back converter as recited in claim 1, wherein the three high-voltage side windings are connected in a manner that: one ends of the three high-voltage side windings are connected into a node, and the other ends of the three high-voltage side windings are respectively connected with three phases of a three-phase power supply;
the high-voltage side winding connected with the phase A of the three-phase power supply is an phase A high-voltage side winding; the high-voltage side winding connected with the phase B of the three-phase power supply is a phase B high-voltage side winding; and the high-voltage side winding connected with the C phase of the three-phase power supply is a C-phase high-voltage side winding.
4. The hybrid intelligent distribution transformer with the power frequency isolated back-to-back converter as recited in claim 1, wherein the dc side of the front stage voltage source converter and the dc side of the back stage voltage source converter are simultaneously separated by capacitors.
5. The hybrid intelligent distribution transformer with the power frequency isolated back-to-back converter as recited in claim 1, wherein the filter comprises a filter inductor and a filter capacitor, the filter inductor is connected in series between the other end of the low voltage independent winding and the different phases of the preceding voltage source converter, and the filter capacitor is connected in parallel between the different phases of the preceding voltage source converter.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105119290A (en) * | 2015-07-21 | 2015-12-02 | 河南行知专利服务有限公司 | Power compensation system for uninterrupted power supplies and control method |
| CN107658905A (en) * | 2017-10-31 | 2018-02-02 | 长沙理工大学 | A kind of fault ride-through of power grid system and method based on double-fed fan motor field |
| CN110535334A (en) * | 2019-09-30 | 2019-12-03 | 深圳古瑞瓦特新能源股份有限公司 | Three-phase multiple power frequency isolation type photovoltaic grid-connected inverter |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105119290A (en) * | 2015-07-21 | 2015-12-02 | 河南行知专利服务有限公司 | Power compensation system for uninterrupted power supplies and control method |
| CN107658905A (en) * | 2017-10-31 | 2018-02-02 | 长沙理工大学 | A kind of fault ride-through of power grid system and method based on double-fed fan motor field |
| CN110535334A (en) * | 2019-09-30 | 2019-12-03 | 深圳古瑞瓦特新能源股份有限公司 | Three-phase multiple power frequency isolation type photovoltaic grid-connected inverter |
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