CN105703392B - Combined type unified power flow controller - Google Patents
Combined type unified power flow controller Download PDFInfo
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- CN105703392B CN105703392B CN201610128541.1A CN201610128541A CN105703392B CN 105703392 B CN105703392 B CN 105703392B CN 201610128541 A CN201610128541 A CN 201610128541A CN 105703392 B CN105703392 B CN 105703392B
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in 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
- Y02E40/30—Reactive power compensation
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- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention provides a combined unified power flow controller, which comprises a reactor unit, a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer, wherein both ends of the reactor unit and the capacitor unit are connected with a switching device in parallel; the reactor unit, the capacitor unit and the first converter are connected in series and then connected in parallel with one side winding of the series transformer, and the other side winding of the series transformer is connected with the power transmission line; the first converter is connected with a parallel transformer through a second converter, and the other end of the parallel transformer is connected into the power transmission line. Compared with the prior art, the invention provides a combined unified power flow controller, by putting in different reactor capacities or capacitor capacities, different steady-state operation working points can be obtained, so that the combined unified power flow controller realizes dynamic adjustment while carrying out hierarchical adjustment, and has a larger dynamic adjustment range.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a combined unified power flow controller.
Background
With the vigorous development of the power system, the problems of large-scale access of new energy, increasingly complex grid structure, uneven tide distribution, insufficient voltage supporting capability and the like bring new challenges to the safe and stable operation of the power grid. The power supply bottleneck appears in partial areas, and the load development needs can not be met. From the practical situation of the power grid, uneven power flow distribution is an important factor for limiting the transmission capacity of the power grid. The traditional power grid lacks an effective tide adjusting means, the system operation condition is improved by adopting a novel FACTS (Flexible Alternative Current Transmis System) device, and the improvement of the power grid conveying capacity is a realistic and ideal choice.
The unified power flow controller (Unified Power Flow Controller, UPFC) is used as the representative of 3 rd generation FACTS equipment, is the most comprehensive-function FACTS device so far, and can respectively or simultaneously realize multiple basic functions such as parallel compensation, series compensation, phase shifting, terminal voltage regulation and the like. UPFC can realize tide regulation in the aspect of power system stability, reasonably control active power and reactive power, improve the transmission capacity of a circuit and realize optimized operation; in the dynamic aspect, the voltage of the access point can be dynamically supported through rapid reactive throughput, so that the voltage stability of the system is improved; and the damping of the system can be improved, and the stability of the power angle can be improved.
The conventional unified power flow controller has flexible and excellent control function, but is popularized and used in a power system and does not have the advantages of capacity and price. The traditional capacitor and the reactor can be used as line series compensation, but the flexibility and the action speed can not meet the requirement of accurate adjustment. The unified power flow controller needs a more flexible functional configuration and needs to combine series compensation with the unified power flow controller.
Disclosure of Invention
In order to meet the needs of the prior art, the invention provides a combined unified power flow controller.
The technical scheme of the invention is as follows:
the unified power flow controller comprises a reactor unit, a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the reactor unit, the capacitor unit and the first converter are connected in series and then connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the reactor unit comprises a reactor or a plurality of reactors connected in series, and a first switching device is connected in parallel with the reactor; the capacitor unit comprises a capacitor or a capacitor group formed by connecting a plurality of capacitors in series and parallel, and the capacitor is connected with a second switching device in parallel.
The invention provides further the preferred embodiments are:
the first switching device, the second switching device and the third switching device adopt mechanical switches or power electronic switches;
the power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
Further preferred embodiments provided by the present invention are:
the first switching device, the second switching device and the third switching device adopt mechanical switches or power electronic switches;
the power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
Further preferred embodiments provided by the present invention are:
the first switching device, the second switching device and the third switching device comprise a mechanical switch and a power electronic switch which are connected in parallel;
the power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
Further preferred embodiments provided by the present invention are:
the first switching device, the second switching device and the third switching device comprise a mechanical switch and a power electronic switch which are connected in parallel;
the power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
Further preferred embodiments provided by the present invention are:
the converters comprise at least one of a two-level converter, a three-level converter, a modularized multi-level converter, an H-bridge cascading converter, a diode clamping converter and a flying capacitor converter.
Further preferred embodiments provided by the present invention are:
when the first switching device is closed, the second switching device and the third switching device are opened, the unified power flow controller works in a capacitive compensation mode; the capacitor unit provides a steady-state operation point with forward offset, and the converter provides a dynamic operation range; adjusting the steady-state operation operating point by adjusting the capacitance value or the series and parallel numbers of the capacitors in the capacitor unit;
when the second switching device is closed and the first switching device and the third switching device are opened, the unified power flow controller works in an inductive compensation mode; the reactor unit provides a steady-state operation point of reverse offset, and the converter provides a dynamic operation range; the steady-state operation working point is adjusted by adjusting the reactance value or the series quantity of the reactors in the reactor unit;
when the first switching device and the second switching device are closed and the third switching device is opened, the unified power flow controller works in a dynamic regulation mode; the converter provides a dynamic working range; and continuously adjusting the steady-state operation point to be in a capacitive operation area or an inductive operation area by adjusting the converter.
Further preferred embodiments provided by the present invention are: the unified power flow controller comprises a fixed capacitive offset structure and a fixed inductive offset structure.
Further preferred embodiments provided by the present invention are:
when the unified power flow controller is of a fixed capacity offset structure: the power supply comprises a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the capacitor unit is connected in series with the first converter, and then is connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the capacitor unit comprises a capacitor or a capacitor group formed by connecting a plurality of capacitors in series and parallel, and the capacitor is connected with a second switching device in parallel.
Further preferred embodiments provided by the present invention are:
when the unified power flow controller is of a fixed inductive offset structure: the power supply comprises a reactor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the reactor unit is connected in series with the first converter, then is connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the reactor unit comprises a reactor or a plurality of reactors connected in series, and the reactor is connected with a first switching device in parallel.
In contrast to the closest prior art technique, the beneficial effects of the invention are as follows:
1. according to the combined unified power flow controller provided by the invention, different steady-state operation working points can be obtained by inputting different reactor capacities or capacitor capacities, and capacitive or inductive bidirectional compensation is realized, so that the combined unified power flow controller realizes dynamic adjustment while carrying out hierarchical adjustment, and has a larger dynamic adjustment range; the problem that the conventional unified power flow controller cannot be continuously and rapidly adjusted in a large range is solved, the transmission capacity of a circuit can be greatly improved or reduced, the power or voltage oscillation of the circuit is damped, and the cost of the device is reduced.
2. The combined unified power flow controller provided by the invention can reduce the capacity of a voltage source converter and reduce the insulation level of a reactor and a capacitor. The equivalent capacitive reactance of the power transmission line can be adjusted in a grading manner through the first switching device and the second switching device, and the steady-state control is focused; the converters can provide continuous, fast, bi-directional regulation capability, focusing on dynamic control.
Drawings
Fig. 1: the embodiment of the invention discloses a combined unified power flow controller structure schematic diagram;
fig. 2: another combined unified power flow controller structure schematic diagram in the embodiment of the invention
Fig. 3: the equivalent impedance range of the current converter in the embodiment of the invention is shown in a schematic diagram;
fig. 4: the embodiment of the invention provides an equivalent circuit diagram for capacitive compensation;
fig. 5: an impedance compensation domain schematic diagram of capacitive compensation in the embodiment of the invention;
fig. 6: in the embodiment of the invention, a schematic diagram of a device side compensation range in capacitive compensation is provided;
fig. 7: an equivalent circuit diagram of inductive compensation in the embodiment of the invention;
fig. 8: an impedance compensation domain schematic diagram of inductive compensation in the embodiment of the invention;
fig. 9: schematic diagram of device side compensation range in inductive compensation in the embodiment of the invention;
fig. 10: the embodiment of the invention provides a dynamic compensation equivalent circuit diagram;
wherein, 101: a reactor unit; 102: a capacitor unit; 103: a first inverter; 104: a series transformer; 105: a second inverter; 106: and a parallel transformer.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The following describes a combined unified power flow controller provided by the embodiment of the invention with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a combined unified power flow controller according to an embodiment of the present invention, as shown in the drawing, where the combined unified power flow controller in this embodiment includes:
a reactor unit 101, a capacitor unit 102, a first converter 103, a series transformer 104, a second converter 105, and a shunt transformer 106. Wherein,
after the reactor unit 101, the capacitor unit 102 and the converter 103 are connected in series, the reactor unit is connected in parallel with one side winding of the series transformer 104, the other side winding of the series transformer 104 is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding and is used for switching the series transformer 104.
The first converter 103 is connected to a shunt transformer 106 via a second converter 105, and the other end of the shunt transformer 106 is connected to the transmission line.
The reactor unit 101 includes one reactor or a plurality of reactors connected in series, and a first switching device for switching the reactor is connected in parallel to the reactor.
The capacitor unit 102 comprises a capacitor or a plurality of capacitors connected in series, and a second switching device is connected in parallel to the capacitor, and the second switching device is used for switching the capacitor.
The first converter 103 and the second converter 105 each include at least one of a two-level converter, a three-level converter, a modular multilevel converter, an H-bridge cascade converter, a diode clamp converter, and a flying capacitor converter.
The first switching device, the second switching device and the third switching device in the embodiment of the present invention each include a plurality of preferred embodiments, and each of the preferred embodiments is specifically described below:
example 1
In this embodiment, the first switching device, the second switching device and the third switching device are mechanical switches or power electronic switches. The power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
Example two
In this embodiment, the first switching device, the second switching device and the third switching device are mechanical switches or power electronic switches. The power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
Example III
The first switching means, the second switching means and the third switching means in this embodiment comprise a mechanical switch and a power electronic switch connected in parallel. The power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
Example IV
The first switching means, the second switching means and the third switching means in this embodiment comprise a mechanical switch and a power electronic switch connected in parallel. The power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
Fig. 2 is a schematic structural diagram of a combined unified power flow controller according to a preferred embodiment of the present invention, where the reactor unit 101 includes a reactor L connected in parallel with a first switching device as shown in the drawing; the capacitor unit 102 comprises a capacitor C connected in parallel with the second switching means; the first converter 103 and the second converter 105 are converter VSCs; the series transformer unit 104 comprises a series transformer Tse connected in parallel with the third switching means, the parallel transformer unit 105 being connected to the system. Wherein,
in this embodiment, the reactor L, the capacitor C and the converter VSC are connected in series and then connected in parallel to two ends of one side winding of the series transformer Tse, and the other side winding of the series transformer Tse is connected to the transmission line between the system 1 and the system 2.
The unified power flow controller comprises a fixed capacitive offset structure and a fixed inductive offset structure. Wherein,
1. fixed volumetric deflection structure:
the unified power flow controller in the embodiment comprises a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer; after the capacitor unit is connected with the first converter in series, the capacitor unit is connected with one side winding of a series transformer in parallel, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected with the other side winding of the series transformer in parallel; the first converter is connected with a parallel transformer through a second converter, and the other end of the parallel transformer is connected into a power transmission line; the capacitor unit comprises a capacitor or a capacitor group formed by connecting a plurality of capacitors in series and parallel, and the capacitor is connected with a second switching device in parallel.
2. Fixed perceptual offset structure:
the unified power flow controller in the embodiment comprises a reactor unit, a first converter, a second converter, a series transformer and a parallel transformer; after the reactor unit is connected in series with the first converter, the reactor unit is connected in parallel with one side winding of a series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding of the series transformer; the first converter is connected with a parallel transformer through a second converter, and the other end of the parallel transformer is connected into a power transmission line; the reactor unit comprises a reactor or a plurality of reactors connected in series, and a first switching device is connected in parallel with the reactor.
Fig. 3 is a schematic diagram of an equivalent impedance range of a first converter 103 according to an embodiment of the present invention, where the converter unit 103 in this embodiment can obtain the equivalent impedance range of the converter within a circle with Zinv as a radius and the reactance value range is [ -Xinv, +xinv by adjusting the relation between the output voltage and the amplitude and phase angle of the current flowing through the transmission line]If the capacitive compensation is set to positive compensation and the inductive compensation is set to negative compensation, the capacitive compensation range is [0, +X ] as shown in FIG. 3 inv ]The inductive compensation range is [ -X inv ，0]。
FIG. 4 is a circuit diagram showing the equivalent circuit during capacitive compensation of a combined unified power flow controller according to an embodiment of the present invention, wherein the transformation ratio of the series transformer is set to be k 1, and the capacitance reactance of the capacitor is set to be X c The first switching means is closed, and the second switching means and the third switching means are opened, the unified power flow controller operates in a capacitive compensation mode. Capacitor unit 102 provides a forward-offset steady-state operating point and inverter 103 provides a dynamic operating range; the steady-state operating point is adjusted by adjusting the capacitance value or the number of series-parallel connections of the capacitors in the capacitor unit 102.
FIG. 5 shows a combined type of the embodiment of the present invention unified power flow controller during capacitive compensationAs shown in the diagram of the impedance compensation range of the converter 103, the equivalent impedance range of the first converter 103 in this embodiment is shown as Z inv Within a circle of radius, the reactance range is [ -X inv ，+X inv ]。
Fig. 6 is a schematic diagram of a compensation range of a combined unified power flow controller on a device side during capacitive compensation according to an embodiment of the present invention, where the compensation range of the combined unified power flow controller on the device side is shown as X c As the center of a circle, Z inv Is an impedance circle of radius. Different steady-state operation working points can be obtained by inputting different reactor capacities, so that the combined unified power flow controller realizes dynamic adjustment while carrying out hierarchical adjustment, and has a larger dynamic adjustment range.
FIG. 7 is a schematic diagram of an equivalent circuit diagram of a combined unified power flow controller during inductive compensation according to an embodiment of the present invention, wherein the transformation ratio of the series transformer is set to be k 1, and the capacitive reactance of the reactor is set to be X L And when the second switching device is closed and the first switching device and the third switching device are opened, the unified power flow controller works in the inductive compensation mode. Reactor unit 101 provides a steady state operating point of reverse offset, and inverter 103 provides a dynamic operating range; the steady-state operation point is adjusted by adjusting the reactance value or the number of series-parallel connections of the reactors in the reactor unit 101.
Fig. 8 is a schematic diagram of an impedance compensation range of the converter 103 during inductive compensation of the combined unified power flow controller according to an embodiment of the present invention, where the equivalent impedance range of the converter 103 is shown as Z inv Within a circle of radius, the reactance range is [ -X inv ，+X inv ]。
Fig. 9 is a schematic diagram of a compensation range of a combined unified power flow controller at a device side during inductive compensation according to an embodiment of the present invention, where the compensation range of the combined unified power flow controller at the device side is represented by-X L As the center of a circle, Z inv Is an impedance circle of radius. Different steady-state operation working points can be obtained by inputting different reactor capacities, so that the combined unified power flow controller adjusts in a grading mannerThe dynamic adjustment is realized at the same time, and the dynamic adjustment range is larger.
Fig. 10 is an equivalent circuit diagram of the combined unified power flow controller in the embodiment of the present invention when the dynamic compensation is performed, as shown in the drawing, and in the embodiment, when the first switching device and the second switching device are closed and the third switching device is opened, the unified power flow controller operates in a dynamic regulation mode. The first converter 103 provides a dynamic operating range; by adjusting the first converter 103, the steady state operating point is continuously adjusted to be in the capacitive operating region or in the inductive operating region. The maximum sensitivity compensation of the combined unified power flow controller at the device side in the embodiment is-X L -Z inv Maximum capacitive compensation is X c +Z inv . By putting in a combined unified power flow controller, dynamic adjustment from capacitive impedance compensation to inductive impedance compensation can be achieved.
The following describes the working procedure of the combined unified power flow controller in the embodiment of the present invention:
1. combined unified power flow controller unaccessed system
Before the combined unified power flow controller is accessed into the system, the first switch device, the second switch device and the third switch device are all in a closed state, and the whole combined unified power flow controller is in a bypass state without affecting the running state of the system.
2. Combined unified power flow controller access system
And the combined unified power flow controller determines an impedance value to be compensated according to the upper layer scheduling instruction and the actual operation condition. When the impedance of the long-distance power transmission line is large, the power transmission line needs to operate in a capacitive compensation mode to compensate the impedance of the power transmission line, so that the transmission loss is reduced. When the power transmission line is overloaded due to short circuit fault or load increase, tripping of parallel lines and the like, the power transmission line needs to operate in an inductive impedance compensation mode to limit the amplitude of the circuit. When the combined unified power flow controller is used for improving system damping and restraining system oscillation, the combined unified power flow controller operates in a dynamic compensation mode.
And selecting an operation mode with a steady-state operation point closest to the compensation impedance in the capacitive compensation mode, the inductive compensation mode and the dynamic adjustment mode according to the impedance value to be compensated, and meeting the requirement of dynamic adjustment as much as possible. When switching between different operation modes, care needs to be taken when switching between the corresponding reactor unit 101, capacitor unit 102 or first converter 103, and when each unit is switched, the switching device is disconnected at the zero crossing point of the current, so that overvoltage is avoided. When each unit is thrown out, the switching device is thrown in a voltage zero crossing point, so that current impact is avoided, and impact-free switching of a compensation mode is realized.
The protection measures of the combined unified power flow controller in the embodiment of the invention mainly comprise:
1. in the event of a fault on the system side, for example a single-phase earth fault in the line or a line overcurrent, the second switching device needs to be closed to protect the first converter 103, and the operation of the first converter 103 is exited.
2. In the event of a fault inside the first converter 103, it is necessary to latch the switching device trigger pulse of the first converter 103 and close the second switching device, exiting the operation of the first converter 103.
Those skilled in the art will appreciate that implementing all or part of the above-described methods in accordance with the embodiments may be accomplished by way of a computer program stored on a computer readable storage medium, which when executed may comprise the steps of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only memory (ROM), a random access memory (Random Access Memory, RAM), or the like. Meanwhile, the invention does not refer to equipment such as lightning arresters, gaps and the like for protecting capacitors, series transformers, converters and switching devices thereof, and does not refer to equipment design, manufacture and engineering practice. In practical engineering implementation, there are many isolation switches, circuit breakers, current measurement devices and voltage measurement devices which are not labeled in the drawings of the embodiment, and these devices are not present when the engineering is not actually implemented.
According to the embodiment of the invention, the combined unified power flow controller can obtain different steady-state operation working points by inputting different reactor capacities or capacitor capacities, so that the combined unified power flow controller realizes dynamic adjustment while carrying out hierarchical adjustment, and has a larger dynamic adjustment range. Solves the problem that the existing unified power flow controller can not be continuously and quickly regulated in a large range, the circuit transmission capacity can be greatly improved or reduced, the circuit power or voltage oscillation is damped, and the device cost is reduced.
It should be noted that the case of connecting the inductor and the capacitor in series is not limited to the structure shown in the embodiment, and any case of adding or subtracting the inductor and the capacitor to realize a wide series compensation is within the scope of the present invention. It is within the scope of the invention that the parallel side of the unified power flow control may be connected to the bus of the present line as well as to other lines. .
It should be noted that the case of connecting the inductor and the capacitor in series is not limited to the structure shown in the embodiment, and any case of adding or subtracting the inductor and the capacitor to realize a wide series compensation is within the scope of the present invention. It is within the scope of the invention that the parallel side of the unified power flow control may be connected to the bus of the present line as well as to other lines.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (9)
1. A combined unified power flow controller, characterized in that the unified power flow controller comprises a reactor unit, a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the reactor unit, the capacitor unit and the first converter are connected in series and then connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the reactor unit comprises a reactor or a plurality of reactors connected in series, and a first switching device is connected in parallel with the reactor; the capacitor unit comprises a capacitor or a capacitor group formed by connecting a plurality of capacitors in series and parallel, and a second switching device is connected to the capacitor in parallel;
when the first switching device is closed, the second switching device and the third switching device are opened, the unified power flow controller works in a capacitive compensation mode; the capacitor unit provides a steady-state operation point with forward offset, and the first converter provides a dynamic operation range; adjusting the steady-state operation operating point by adjusting the capacitance value or the series and parallel numbers of the capacitors in the capacitor unit; the compensation range of the unified power flow controller at the device side is represented by X c As the center of a circle, Z inv An impedance circle with a radius;
when the second switching device is closed and the first switching device and the third switching device are opened, the unified power flow controller works in a inductive compensation mode; the reactor unit provides a steady-state operation point which is offset reversely, and the first converter provides a dynamic operation range; the steady-state operation working point is adjusted by adjusting the reactance value or the series quantity of the reactors in the reactor unit; the compensation range of the unified power flow controller at the device side is represented by-X L As the center of a circle, Z inv An impedance circle with a radius;
when the first switching device and the second switching device are closed and the third switching device is opened, the unified power flow controller works in a dynamic regulation mode; the first converter provides a dynamic working range; continuously adjusting the steady-state operation point to be in a capacitive operation area or an inductive operation area by adjusting the converter; the maximum sensitivity compensation of the unified power flow controller at the device side is-X L -Z inv Maximum capacitive compensation is X c +Z inv 。
2. A combined unified power flow controller according to claim 1 wherein,
the first switching device, the second switching device and the third switching device adopt mechanical switches or power electronic switches;
the power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
3. A combined unified power flow controller according to claim 1 wherein,
the first switching device, the second switching device and the third switching device adopt mechanical switches or power electronic switches;
the power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
4. A combined unified power flow controller according to claim 1 wherein,
the first switching device, the second switching device and the third switching device comprise a mechanical switch and a power electronic switch which are connected in parallel;
the power electronic switch comprises a half-control type power electronic device which is connected in parallel in an inverse mode, and the half-control type power electronic device adopts a thyristor; the mechanical switch is a disconnecting switch or a circuit breaker.
5. A combined unified power flow controller according to claim 1 wherein,
the first switching device, the second switching device and the third switching device comprise a mechanical switch and a power electronic switch which are connected in parallel;
the power electronic switch comprises an anti-parallel full-control power electronic device, wherein the full-control power electronic device adopts any one of IGBT, GTO, IGCT and SIC; the mechanical switch is a disconnecting switch or a circuit breaker.
6. A combined unified power flow controller according to claim 1 wherein,
the converters comprise at least one converter among a two-level converter, a three-level converter, a modularized multi-level converter, an H-bridge cascading converter, a diode clamping converter and a flying capacitor converter.
7. The combined unified power flow controller of claim 1 wherein the unified power flow controller comprises a fixed capacitive offset structure and a fixed inductive offset structure.
8. A combined unified power flow controller according to claim 7 wherein,
when the unified power flow controller is of a fixed capacity offset structure: the device comprises a capacitor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the capacitor unit is connected in series with the first converter, and then is connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the capacitor unit comprises a capacitor or a capacitor group formed by connecting a plurality of capacitors in series and parallel, and the capacitor is connected with a second switching device in parallel.
9. A combined unified power flow controller according to claim 7 wherein,
when the unified power flow controller is of a fixed inductive offset structure: the device comprises a reactor unit, a first converter, a second converter, a series transformer and a parallel transformer;
the reactor unit is connected in series with the first converter, then is connected in parallel with one side winding of the series transformer, the other side winding of the series transformer is connected with a power transmission line, and a third switching device is connected in parallel with the other side winding;
the first converter is connected with the parallel transformer through the second converter, and the other end of the parallel transformer is connected into a power transmission line;
the reactor unit comprises a reactor or a plurality of reactors connected in series, and a first switching device is connected in parallel with the reactor.
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