CN114069633A - Hybrid intelligent distribution transformer containing high-frequency isolated back-to-back converter - Google Patents
Hybrid intelligent distribution transformer containing high-frequency isolated back-to-back converter Download PDFInfo
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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
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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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- 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
- H01F2027/408—Association with diode or rectifier
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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 mixed type intelligent distribution transformer containing a high-frequency isolation type back-to-back converter, which comprises a high-voltage side main winding connected with a three-phase power supply and a low-voltage side winding used for receiving input voltage and current from the three-phase power supply and inputting the voltage and the current to a three-phase nonlinear load, wherein the high-voltage side main winding and the low-voltage side winding are magnetically coupled through a wound iron core; the power frequency transformer and the power electronic device are deeply integrated, so that the requirements of comprehensive treatment of power quality, flexible regulation and control of power flow and novel source/load centralized management can be met; and the device also has the advantages of low cost and high operational reliability.
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 high-frequency isolation type back-to-back converter.
Background
The power distribution system is used as the link which is the most closely connected with a user in five links of power generation, transmission, transformation, distribution and utilization, is directly oriented to the terminal user, and is an important public infrastructure for serving the livelihood. Under the drive of a double-carbon target, novel sources/loads such as massive wind/light new energy sources and electric automobiles and the like can continuously flow into a medium-low voltage power distribution system. The novel source/load has the characteristics of randomness, volatility, impact, disorder and the like, and a power distribution system faces the power quality problems of power distribution terminals of high/low voltage, harmonic amplification, three-phase imbalance and the like. 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.
Because the novel source/load has the direct current intrinsic property, the construction of the alternating current-direct current flexible power distribution system is an effective solution for realizing high-quality power supply, flexible operation of a power grid and efficient utilization of new energy. 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, power electronic transformers with functions of electric energy quality control, multi-port power conversion, tide flexible regulation and control and the like are widely concerned, and are considered to be effective carriers of urban energy internet electric energy routing in the future. Because the power electronic transformer has the problems of high manufacturing cost, incompatible fault protection, low electric energy conversion efficiency and the like, the power electronic transformer still has no productization reliability and is applied to a power distribution system.
Disclosure of Invention
The invention aims to provide a hybrid intelligent distribution transformer containing a high-frequency isolation type back-to-back converter, which solves the problem that the transformer cannot be applied to a distribution system through commercialization in the prior art.
The invention adopts the technical scheme that the hybrid intelligent distribution transformer comprises a high-voltage side main winding connected with a three-phase power supply and a low-voltage side winding used for receiving input voltage and current from the three-phase power supply and inputting voltage and current to a three-phase nonlinear load, wherein the high-voltage side main winding and the low-voltage side winding are in magnetic reaction coupling through wound iron cores, the output end of the three-phase power supply is connected with the alternating current side of a preceding-stage voltage source converter in series through a filter, the input end of the three-phase nonlinear load is connected with the different phases of the alternating current side of a later-stage voltage source converter, and the direct current side of the preceding-stage voltage source converter and the direct current side of the later-stage voltage source converter are both connected with a low-voltage direct current distribution port.
The invention is also characterized in that:
the low voltage side winding includes three low voltage windings: low-voltage winding Wa1Low voltage winding Wb1Low voltage winding Wc1One end of each low-voltage winding is star-connected to form a node n1, the other end of each low-voltage winding is connected with a different phase of the three-phase nonlinear load, each low-voltage winding and a corresponding phase of the high-voltage winding are magnetically coupled through a wound iron core, and the node n1 is connected with a load neutral line through a lead.
The high-voltage side main winding comprises three high-voltage windings, the three high-voltage windings are connected in an angle mode, each angle formed in the angle mode is connected with one phase of a three-phase power supply through a bypass switch, one end of each bypass switch is connected with the corresponding phase of the preceding-stage voltage source converter, the other end of each bypass switch is connected with the neutral line of the preceding-stage voltage source converter, and any one high-voltage winding connected with the phase A is defined as a high-voltage winding WA1The high-voltage winding connected to the phase B is defined as a high-voltage winding WB1The high-voltage winding connected to the C phase is defined as a high-voltage winding WC1Winding a high voltage WA1Coupling connection of low-voltage winding W by winding iron corea1Winding a high voltage WB1Coupling connection of low-voltage winding W by winding iron coreb1Winding a high voltage WC1Coupling connection of low-voltage winding W by winding iron corec1。
The high-voltage side main winding comprises three high-voltage windings, one ends of the three high-voltage windings are star-connected, the other ends of the three high-voltage windings are respectively connected with one phase of a three-phase power supply through bypass switches, one ends of the bypass switches are connected with the corresponding phase of the preceding-stage voltage source converter through filters, the other ends of the bypass switches are connected with the neutral line of the preceding-stage voltage source converter, and the high-voltage winding connected with the phase A of the three-phase power supply is defined as a high-voltage winding W'A1A high-voltage winding connected to the B phase of a three-phase power supply is defined as a high-voltage winding WB′1A high-voltage winding connected to the C phase of a three-phase power supply is defined as a high-voltage winding WC′1Of the high-voltage winding W'A1Coupling connection of low-voltage winding W by winding iron corea1High voltage winding WB′1Coupling connection of low-voltage winding W by winding iron coreb1High voltage winding WC′1Coupling connection of low-voltage winding W by winding iron corec1。
The filter comprises filter capacitors and filter inductors, wherein each filter inductor is connected between the bypass switch with the same phase and the alternating current side of the preceding-stage voltage source converter, and each filter capacitor is connected between each phase of the alternating current side of the preceding-stage voltage source converter in parallel.
The direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with a separation capacitor in parallel.
The invention has the beneficial effects that:
the power frequency transformer and the power electronic device are deeply fused, and a hybrid distribution transformer with partial power regulation is provided, so that the requirements of comprehensive treatment of electric energy quality, flexible regulation and control of power flow and novel source/load centralized management can be met; a stable and reliable low-voltage direct-current bus is provided to realize plug and play of distributed renewable energy sources, an energy storage system and a novel direct-current load; the hybrid intelligent distribution transformer also has the advantages of low equipment cost, high operation reliability and good popularization prospect.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of a hybrid intelligent distribution transformer including a high-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 with a high-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 diagram of the circuit structure of the H-bridge connected to the A phase in the preceding stage voltage source converter according to the present invention;
FIG. 5 is a schematic diagram of the load side voltage stabilized by regulated modulation in accordance with the present invention;
FIG. 6 is a schematic circuit diagram of a rear stage voltage source converter according to the present invention;
FIG. 7 is a block diagram of a harmonic detection link control strategy for harmonic compensation of a rear-stage voltage source converter in accordance with the present invention;
FIG. 8 is a block diagram of the harmonic compensation link and the control strategy of DC-side voltage stabilization for the harmonic compensation of the post-stage voltage source converter according to the present invention;
FIG. 9 is a SPWM modulation block diagram for the pre-stage voltage source converter transistor IGBT of the present invention;
FIG. 10 is a SPWM modulation block diagram for the back-stage voltage source converter transistor IGBT of the present invention;
FIG. 11 is a schematic diagram of the current waveform on the load side after harmonic compensation of the rear stage voltage source converter in accordance with the present invention;
fig. 12 is a schematic diagram of the dc-side regulated waveform of the post-stage voltage source converter according to the present invention.
In the figure, Vga、Vgb、VgcThe grid-side three-phase voltages A, B, C phase voltages are shown, respectively;
Vsa、Vsb、Vscthe user side three phase voltages A, B, C phase voltages are shown respectively;
iga、igb、igcnet side three phase current A, B, C phase currents are shown, respectively;
isa、isb、iscthe low-side three-phase current A, B, C phase currents are shown respectively;
iLa、iLb、iLcthe three-phase current A, B, C phase currents flowing into the user side are shown, respectively;
ifa、ifb、ifcfundamental components of three-phase current A, B, C flowing into the user side are shown respectively;
iha、ihb、ihcthe harmonic components of the three-phase current A, B, C flowing into the user side are shown separately;
ia2、ib2、ic2the rear-stage voltage source converter output current A, B, C phase currents 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;
La、Lb、Lcrespectively showing the filter inductors of the post-stage voltage source type converter;
Ca、Ca、Carespectively showing the filter capacitors of the post-stage voltage source type converter;
La2、Lb2、Lc2respectively showing the filter inductors of the preceding-stage voltage source type converter;
WA1、WB1、WC1a, B, C three-phase windings on the high-voltage side of the power frequency transformer are respectively shown;
Wa1、Wb1、Wc1a, B, C three-phase windings on the low-voltage side of the power frequency transformer are respectively shown;
Cv1、Cv2showing a preceding stage voltage source converter and a succeeding stage voltage source converter, respectively;
VTn1、VTn2、VTn3、VTn4four insulated gate bipolar transistors forming an H-bridge in a preceding voltage source converter are shown;
Sn1、Sn2、Sn3、Sn4showing 4 insulated gate bipolar transistors forming an LLC primary inverter bridge;
Dn5、Dn6、Dn7、Dn 84 diodes are shown forming an LLC secondary rectifier bridge;
VD1、VD2、VD3、VD4、VD5、VD6、VD7、VD8the 8 insulated gate bipolar transistors in the later stage voltage source converter are shown separately.
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 high-frequency isolation type back-to-back converter, which comprises a high-voltage side main winding connected with a three-phase power supply and used for receiving input voltage and current from the three-phase power supply, and a low-voltage side winding for inputting voltage and current to a three-phase nonlinear load, wherein the high-voltage side main winding and the low-voltage side winding are magnetically coupled through a wound iron core, the output end of the three-phase power supply is connected with the alternating current side of a preceding-stage voltage source converter in series through a filter, the input end of the three-phase nonlinear load is connected with the different phases of the alternating current side of a subsequent-stage voltage source converter, and a port V at the direct current side of the preceding-stage voltage source converter CV1 is provided with a port Vdc1+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-The direct current source load connection device is used for connecting direct current source loads such as photovoltaic, energy storage, automobile charging piles and fans, friendly access of novel source loads is achieved, the direct current side of the preceding-stage voltage source converter and the direct current side of the rear-stage voltage source converter are connected in parallel to separate capacitors, and voltage of the direct current side is stabilized.
The low voltage side winding includes three low voltage windings: low-voltage winding Wa1Low voltage winding Wb1Low voltage winding Wc1One end of each low-voltage winding is star-connected, the other end of each low-voltage winding is connected with one phase of the load, and each low-voltage winding and the corresponding phase of the high-voltage winding are magnetically coupled through the wound iron core.
The first embodiment is as follows:
as shown in fig. 1, the high-voltage side main winding includes three high-voltage windings, the three high-voltage windings form a triangle by angle connection, each angle of the triangle is connected with one phase of the three-phase power supply through a bypass switch, one end of the bypass switch is connected with the corresponding phase of the preceding-stage voltage source converter through a filter, and the other end of the bypass switch is connected with the neutral line of the preceding-stage voltage source converter, so that the on-off time of the alternating-current side of the high-frequency isolated converter can be controlled, and when voltage regulation operation is required, the bypass switch is closed; when the voltage on the network side is stable, the bypass switch is switched off; defining any high-voltage winding connected with phase A as a high-voltage winding WA1The high-voltage winding connected to the phase B is defined as a high-voltage winding WB1The high-voltage winding connected to the C phase is defined as a high-voltage winding WC1Winding a high voltage WA1Coupling connection of low-voltage winding W by winding iron corea1Winding a high voltage WB1Coupling connection of low-voltage winding W by winding iron coreb1Winding a high voltage WC1Coupling connection of low-voltage winding W by winding iron corec1。
Example two:
as shown in fig. 2, the high-voltage side main winding includes three high-voltage windings, one end of each of the three high-voltage windings is star-connected, the other end of each of the three high-voltage windings is connected with one phase of a three-phase power supply through a bypass switch, one end of each of the bypass switches is connected with a corresponding phase of a preceding-stage voltage source converter through a filter, the other end of each of the bypass switches is connected with a neutral line of the preceding-stage voltage source converter, on-off time of an alternating-current side of the high-frequency isolation type converter can be controlled, and when voltage regulation operation is required, the bypass switch is closed; when the voltage on the network side is stable, the bypass switch is switched off; a high-voltage winding connected with A phase of a three-phase power supply is defined as a high-voltage winding W'A1A high-voltage winding connected to the B phase of a three-phase power supply is defined as a high-voltage winding WB′1A high-voltage winding connected to the C phase of a three-phase power supply is defined as a high-voltage winding WC′1Of the high-voltage winding W'A1Coupling connection of low-voltage winding W by winding iron corea1High voltage winding WB′1Coupling connection of low-voltage winding W by winding iron coreb1High voltage winding WC′1Coupling connection of low-voltage winding W by winding iron corec1。
The filter comprises filter capacitors and filter inductors, each filter inductor is connected between the bypass switch with the same phase and the alternating current side of the preceding-stage voltage source converter, and each filter capacitor is connected in parallel to two sides of the bypass switch; the on-off time of the alternating current side of the high-frequency isolation type converter can be controlled, and the bypass switch is switched off when voltage regulation operation is needed; and when the voltage on the network side is stable, the bypass switch is closed.
Each preceding-stage voltage source converter CV1 is a high-frequency isolation converter, adopts a three-phase four-wire system, is connected with a CV1 part of the bypass switches of the A phase, the B phase and the C phase, and comprises n cascaded H bridges, wherein three ports of the A phase, the B phase or the C phase are separated from the alternating current side of the n cascaded H bridges, and six terminals are separated from the three-phase H bridges, namely a phase a1And a1'terminal, B' and B of B phase1'terminal, C phase C' and C1' terminal in which six ports branched from the AC side of the preceding stage voltage source converter CV1 are connected in series with a filter connected to a three-phase power supply, and inductor LseOne end is connected with a capacitor CseOne pole plate and one side of the bypass switch on the A phase, inductor LseThe other end is connected with a of phase A1Terminal, capacitor CseThe other pole plate is connected with a of phase A1'the other side of the terminal and bypass switch, similarly, B' and B of phase B1'terminal, C phase C' and C1The terminals are connected to the B-phase bypass switch and the C-phase bypass switch in the same way; the on-off of the alternating current side of the preceding-stage voltage source converter CV1 is controlled through a bypass switch corresponding to each phase of three-phase power supply, the direct current side of each H bridge is connected with the rectifying end and the voltage stabilizing capacitor C1 of the LLC resonant converter, and the inverting end of each LLC resonant converter is connected with a low-voltage direct current power distribution port.
The rear-stage voltage source converter CV2 is of a three-phase four-wire system structure and comprises an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm and a zero-sequence bridge arm which are connected with a low-voltage direct-current power distribution port, wherein the bridge arm midpoints of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm are respectively connected with a three-phase nonlinear load through inductors, and the bridge arm midpoint of the zero-sequence bridge arm is sequentially connected with an inductor Ln, a resistor Rn and a zero line of a grid-side bus B.
As shown in fig. 6, each of the a-phase bridge arm, the B-phase bridge arm, the C-phase bridge arm, and the zero-sequence bridge arm includes two insulated gate bipolar transistors, an emitter of a first insulated gate bipolar transistor is connected to a collector of a second insulated gate bipolar transistor, the collector of the first insulated gate bipolar transistor is connected to an anode of the low-voltage dc distribution port, an emitter of the second insulated gate bipolar transistor is connected to a cathode of the low-voltage dc distribution port, and an emitter of each first insulated gate bipolar transistor is connected to a corresponding phase of the three-phase nonlinear load through an inductor.
The DC side of the preceding stage voltage source converter and the DC side of the following stage voltage source converter can adopt a separation capacitor (or a single capacitor) to stabilize the DC side voltage, and the DC side port V of the preceding stage voltage source converter CV1dc1+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-The device is used for connecting direct current source loads such as photovoltaic, energy storage, automobile charging piles and fans, and friendly access of novel source loads is achieved.
The control mode of the voltage regulation of the hybrid intelligent distribution transformer adopts independent control of each phase, and A, B, C three phases are not influenced mutually. A. B, C when voltage fluctuation occurs in any phase, each phase control acts independently to collect voltage fluctuation value higher or lower than normal voltage level, and the voltage fluctuation value is eliminated by coupling transformer control to control the voltage within normal level.
The invention relates to a first intelligent distribution transformer and a second intelligent distribution transformer which are constructed by two examples, the control strategies of the first intelligent distribution transformer and the second intelligent distribution transformer are consistent, the first intelligent distribution transformer constructed by the first example of the invention is described in detail, and the structure of the embodiment is shown in figure 1.
The first intelligent distribution transformer mainly comprises a power frequency transformer and a power electronic transformer. In which no modification of the line frequency transformer is required, as shown in the first embodiment of fig. 1, the line frequency transformer comprises a ferromagnetic core and a high-voltage side winding WA1、WB1、WC1Low voltage side main winding Wa1、Wb1、Wc1And the high-voltage side winding and the low-voltage side winding are wound on respective iron cores, wherein the magnetic core material is silicon steel sheets. The power electronic transformer comprises a front stage voltage source type converter CV1 and a rear stage voltage source type converter CV2, which are connected in a back-to-back manner.
High-voltage side winding W of industrial frequency transformer in embodiment of hybrid transformerA1、WB1、WC1By delta connection, the low-voltage side winding Wa1、Wb1、Wc1By YnA type wiring method. Wherein the transformation ratio of the high-voltage side winding to the low-voltage side winding is 14140: 311. The AC output side of the preceding-stage voltage source type converter is connected in series into a high-voltage bus, each phase is connected with a bypass switch, and v is regulatedca、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 high-frequency isolation type transformer is realized when the voltage on the network side fluctuates. For example, if the rated voltage of the network side is 10kV, when the voltage of the network side is stable, the voltage compensation function is not needed, and the bypass switch is in a closed state at this time; when the amplitude fluctuation (sudden rise or sudden drop) of +/-10% of the grid-side voltage occurs in a certain period of time, voltage compensation is needed, the bypass switch is controlled to be switched off, and the reference value of the output voltage of the preceding-stage voltage source converter CV1 when the grid-side voltage fluctuates can be obtained through the voltage compensation control block diagram shown in FIG. 3. Wherein Vga、Vgb、VgcThe three-phase voltages of the voltage source side A, B, C are respectively shown, each phase is independently controlled by a voltage compensation control strategy, and n is the cascade number of an H bridge and a high-frequency isolator LLC in a preceding-stage voltage source converter.
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 of each phase is in steady-state operationThe voltage amplitude is 8164V (if the voltage on the network side fluctuates in a certain period of time, the amplitude will suddenly rise or drop). The phase of each phase voltage can be obtained through a phase-locked loop. When the voltage of the grid side voltage fluctuates, the control system makes the difference between the real-time amplitude of the grid voltage and the rated voltage amplitude of the grid side to obtain the fluctuation quantity of the grid side voltage, and the fluctuation quantity of the grid side voltage is used as the reference voltage v of the output port of the preceding-stage voltage source converter CV1ca、vcb、vcc. 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, and regulating the AC side voltage v of the preceding voltage source converterca、vcb、vccTo realize the user side phase voltage vsa、vsb、vscStabilize at the rated voltage value of 220V.
Preceding stage voltage source converter CV1May be a voltage source converter having a cascaded topology as shown in fig. 4. In this example, the preceding stage voltage source converter CV1The structure of the H-bridge series high-frequency isolator LLC is adopted, the structure adopts a cascade connection mode, the modules can be expanded, cascade connection of a plurality of modules can be designed according to specific use requirements, the stability of output quantity can be improved, and the range of voltage regulation can be improved. Shown in the example given. Preceding stage voltage source converter CV1The high-frequency isolation type direct-current voltage converter comprises A, B, C three-phase bridge arms and a high-frequency isolation type direct-current voltage converter. Taking phase A as an example, multiple sets of H-bridges and high frequency isolators LLC can be selected, wherein each H-bridge contains VTn1、VTn2、VTn3、VTn4( n 1, 2, 3.) four Insulated Gate Bipolar Transistors (IGBTs) and anti-parallel diodes, where VTn1、VTn2Leading arm of the bridge, VTn, forming an H bridge1、VTn2A lag bridge arm forming an H bridge, wherein the DC side of the H bridge is connected with the secondary side of the LLC, the AC side is connected in series with a bus at the high-voltage side, and the AC side is connected in series with the bus at the high-voltage sideA filter inductor L is laterally connectedcaFilter inductor CcaB, carrying out the following steps of; the parameters of the filter inductor and the filter capacitor are respectively 2mH and 1.5uF, and each LLC resonant converter comprises a primary side inverter bridge power switch tube Sn1、Sn2、Sn3、Sn4(ii) a Secondary side rectifier bridge diode Dn1、Dn2、Dn3、Dn4(n＝1、2、3......)，VdcRepresenting the voltage, V, of the primary side input sidedcDenotes the secondary output side voltage. The transformation ratio of the converter T is 1:1, and when the converter T works, energy firstly passes through the front-stage inverter and then passes through the rear-stage rectifier. L ismnThe inductance is the excitation inductance of the transformer, Lrn is the primary resonance inductance of the transformer, and Crn is the primary resonance capacitance of the transformer. Wherein n is 1, 2, 3. Parameters of the excitation inductance, the resonance inductance and the resonance capacitance are respectively 2mH, 150uH and 6.755 uF. The topology of the preceding-stage voltage source converter is not limited to the structure used by the invention, and other structures can be adopted as long as the similar topology capable of realizing the function of the intelligent distribution transformer is adopted.
When the network side voltage fluctuates in high/low voltage, the voltage waveform of the subscriber side with the hybrid solid-state transformer dynamic voltage compensation function is shown in fig. 5, in which the dotted line represents the actual high-voltage side voltage, and the solid line represents the compensated high-voltage side voltage. In the stage of 0s-0.1s, the voltage of the high-voltage side does not fluctuate, and the peak voltage of the grid side is stabilized at 8164V; in the stage of 0.1s-0.2s, the voltage of the network side suddenly rises by 10%, the voltage peak value reaches 8980V, the preceding-stage voltage source converter detects the voltage of the network side suddenly rises and adjusts the compensation voltage V with the output voltage peak value of 816Vca、vcb、vccWhich is connected to the network side voltage Vga、Vgb、VgcCompensating the high-voltage side voltage to a stable voltage 8164V by the same phase, wherein the voltage of the high-voltage side winding is 14140V because the high-voltage side winding adopts a delta connection mode, and the peak voltage of a user side can be stabilized at 311V through a power frequency transformer; the voltage of the network side is recovered to the rated voltage in the stage of 0.2s-0.3s, and the peak voltage of the network side is stabilized at 8164V; 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 output voltage peakCompensation voltage V of 816Vca、vcb、vccWhich is connected to the network side voltage Vga、Vgb、VgcAnd (3) inverting the phase to compensate the high-voltage side voltage back to a stable voltage 8164V, wherein the voltage of the high-voltage side winding is 14140V because the high-voltage side winding adopts a delta connection mode, and the peak voltage of the user side can be stabilized at 311V through the industrial frequency transformer. By reasonably designing the quantity of H bridges and high-frequency isolator LLC cascade modules in the preceding-stage voltage source converter, the fluctuation range of the voltage on the regulation network side of the preceding-stage voltage source converter can be improved, and the reference voltage calculation formula of the compensation voltage of the preceding-stage voltage source converter is as follows:
Vckref＝(Vgkm-Vref)sinθk(k＝a、b、c) (2)
wherein, VgkmIs the amplitude of the voltage on the high-voltage side, VrefIs a reference value when the high-pressure side is stable, and theta represents the angle of the high-pressure side;
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 in FIG. 6, CV2A post-stage voltage source converter for an intelligent distribution transformer is shown. The subsequent voltage source converter may be a voltage source converter having the VSC architecture shown in figure 6. The rear-stage voltage source converter adopts a three-phase four-wire system structure. In this example, the subsequent voltage source converter CV2Comprising a DC side VdcThree-phase bridge arm on alternating current side A, B, C, zero sequence bridge arm and VD1、VD2、VD3、VD4、VD5、VD6、VD7、VD8Eight Insulated Gate Bipolar Transistors (IGBTs) and anti-parallelDiode of which VD4、VD8An A-phase bridge arm of the rear-stage voltage source converter is formed; VD3、VD7A B-phase bridge arm of the rear-stage voltage source converter is formed; VD2、VD6And forming a C-phase bridge arm of the rear-stage voltage source converter. VD1、VD5And a zero sequence bridge arm of the rear-stage voltage source converter is formed and used for providing a passage for the zero sequence component when the load is unbalanced. A. B, C three phases are respectively and correspondingly connected in parallel to the three-phase bus at the load side for harmonic current compensation, reactive compensation and the like. In addition, the left and right sides L of the rear-stage voltage source converterk、Ck、Cdc(k ═ a, b, and c) are connected to the ac side and the dc side of the subsequent voltage source converter, respectively, and to the ac side Lk、CkThe parameters are 2mH and 20uF respectively for filtering. C connected to the DC sidedcThe voltage stabilizing function is realized, and the parameter is 10 mF. 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 detection 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 i through a Low Pass Filter (LPF)pAnd iqThe 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、ifcMaking a difference, namely obtaining the harmonic current iha、ihb、ihcThe harmonic current is calculated by equation 9.
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. While performing d-q axis transformationHarmonic current id、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 an SPWM control block diagram for generating and controlling the leading bridge arm and the lagging bridge arm of the H-bridge constituting the preceding-stage voltage source converter and controlling the on and off of the Insulated Gate Bipolar Transistor (IGBT) of the cascade structure by using the carrier phase shift modulation method. Taking phase a as an example, the leading bridge arm and the lagging bridge arm of the H bridge need to be controlled separately, and the phases of the leading bridge arm and the lagging bridge arm are different by 180 °. Modulated wave daPerforming difference operation with a triangular carrier wave with the frequency of 20kHz, and if the obtained difference value is more than 0, outputting a high level 1 by the selector, otherwise, outputting a low level 0 to form an SPWM pulse waveform for controlling a switching tube of the leading bridge arm; modulated wave daTaking a negative value to obtain-daPerforming difference operation with a triangular carrier wave with the frequency of 20kHz, and if the obtained difference value is more than 0, outputting a high level 1 by the selector, otherwise, outputting a low level 0 to form an SPWM pulse waveform for controlling a switch tube of a lagging bridge arm; in the cascade structure, carrier phase shift control and unipolar control are adopted, and when the triangular carriers of each expansion module in the cascade are mutually different, the angle is 180 degrees/n (n is the number of cascade units, and n is 1, 2 and 3.). Therefore, when other H bridges forming the A-phase voltage source converter are controlled, the triangular carrier wave is only required to be shifted in phase. The switching tube on the primary side of the high-frequency isolator LLC is directly controlled by adopting square waves with the frequency of 5kHz and the phase difference of 180 degrees, wherein Sn1、Sn4At the same time on and off Sn2、Sn3And simultaneously switching on and off.
FIG. 10 shows a SPWM control block diagram for generating Insulated Gate Bipolar Transistors (IGBTs) for controlling the turn-on and turn-off of the three-phase bridge arm and the zero-sequence bridge arm of the rear-stage voltage source converter A, B, C, the control using bipolar modulation, modulating the wave da、db、dcAnd carrying out difference operation with a carrier (the frequency is 20kHz), if the obtained difference value is more than 0, outputting a high level 1 by the Switch selector, otherwise, outputting a low level 0, forming an SPWM pulse wave, and modulating to form an A, B, C three-phase bridge armThe transistor IGBT of (1) is turned on and off. For the transistors forming the zero sequence bridge arm, collecting three-phase current to make difference with actual zero sequence current, then comparing the modulation wave obtained by the PI controller with a carrier wave, if the obtained difference value is more than 0, the Switch selector outputs high level 1, otherwise, low level 0 is output, SPWM pulse wave is formed, and the transistors IGBT forming the zero sequence bridge arm are modulated to be switched on and switched off.
Fig. 11 shows that the low-voltage side winding side current is compensated by adding harmonic wave at 0.1s in the post-stage voltage source converter, and it can be seen that the main harmonic component of the output port current of the low-voltage side winding of the power frequency transformer is eliminated.
Fig. 12 shows the dc-side regulated waveform, which quickly settles to the desired voltage amplitude of 800V when both a voltage surge and a voltage dip occur in the grid-side voltage.
Through the mode, the invention provides a hybrid distribution transformer topology series for comprehensive treatment of electric energy quality and provides a low-voltage direct-current distribution interface, integrates the electric energy quality treatment functions of voltage regulation, harmonic treatment, three-phase load unbalance and the like, 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 (6)
1. The hybrid intelligent distribution transformer is characterized by comprising a high-voltage side main winding connected with a three-phase power supply and a low-voltage side winding used for receiving input voltage and current from the three-phase power supply and inputting the voltage and the current to a three-phase nonlinear load, wherein the high-voltage side main winding and the low-voltage side winding are in magnetic reaction coupling through wound iron cores, the output end of the three-phase power supply is connected with the alternating current side of a preceding-stage voltage source converter in series through a filter, the input end of the three-phase nonlinear load is connected with the different phases of the alternating current side of a later-stage voltage source converter, and the direct current side of the preceding-stage voltage source converter and the direct current side of the later-stage voltage source converter are both connected with a low-voltage direct current distribution port.
2. The high-frequency isolation type according to claim 1Hybrid intelligent distribution transformer of back-to-back converter, its characterized in that, low pressure side winding includes three low-voltage winding: low-voltage winding Wa1Low voltage winding Wb1Low voltage winding Wc1One end of each of the three low-voltage windings is star-connected to form a node n1, the other end of each low-voltage winding is connected with a different phase of the three-phase nonlinear load, each low-voltage winding and a corresponding phase of the high-voltage winding are magnetically coupled through a wound iron core, and the node n1 is connected with a load neutral line through a lead.
3. The hybrid intelligent distribution transformer of claim 2, wherein the high-side main winding comprises three high-voltage windings, the three high-voltage windings are connected by an angle, each angle formed by the angle connection is connected to a phase of a three-phase power supply through a bypass switch, one end of each bypass switch is connected to a corresponding phase of the preceding-stage voltage source converter, the other end of each bypass switch is connected to a neutral line of the preceding-stage voltage source converter, and any one of the high-voltage windings connected to phase a is defined as a high-voltage winding WA1The high-voltage winding connected to the phase B is defined as a high-voltage winding WB1The high-voltage winding connected to the C phase is defined as a high-voltage winding WC1Winding a high voltage WA1Coupling connection of low-voltage winding W by winding iron corea1Winding a high voltage WB1Coupling connection of low-voltage winding W by winding iron coreb1Winding a high voltage WC1Coupling connection of low-voltage winding W by winding iron corec1。
4. The hybrid intelligent distribution transformer of claim 2, wherein the high-voltage main winding comprises three high-voltage windings, one end of each of the three high-voltage windings is star-connected, the other end of each of the three high-voltage windings is connected to one phase of a three-phase power supply through a bypass switch, one end of each of the bypass switches is connected to a corresponding phase of a preceding-stage voltage source converter through a filter, the other end of each of the bypass switches is connected to a neutral line of the preceding-stage voltage source converter, and the high-voltage winding connected to the phase a of the three-phase power supply is defined as a high-voltage winding W'A1High voltage to be connected to phase B of three-phase power supplyThe winding is defined as a high-voltage winding W'B1A high-voltage winding connected to the C phase of the three-phase power supply is defined as a high-voltage winding W'C1W 'of the high-voltage winding'A1Coupling connection of low-voltage winding W by winding iron corea1W 'of the high-voltage winding'B1Coupling connection of low-voltage winding W by winding iron coreb1W 'of the high-voltage winding'C1Coupling connection of low-voltage winding W by winding iron corec1。
5. The hybrid intelligent distribution transformer with the high-frequency isolated back-to-back converter as recited in claim 3 or 4, wherein the filter comprises a filter capacitor and a filter inductor, each filter inductor is connected between the bypass switch of the same phase and the ac side of the preceding voltage source converter, and each filter capacitor is connected in parallel between each phase of the ac side of the preceding voltage source converter.
6. The hybrid intelligent distribution transformer with the high-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 both connected in parallel with a separation capacitor.
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