CN114156874A - Flexible multi-state switch device, multi-state switching method and alternating current system - Google Patents
Flexible multi-state switch device, multi-state switching method and alternating current system 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
- 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
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0073—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The application provides a flexible multi-state switch device, a multi-state switching method and an alternating current system. The switching device comprises a commutation chain, a first bypass switch, an energy supply unit and an energy acquisition unit, wherein the commutation chain comprises N serially-connected submodules, and N is more than or equal to 1. All the submodules of the commutation chain at high potential are powered by a small number of power supplies at low potential. The application also provides a switching method of each state of the flexible multi-state switch; an alternating current system based on the flexible multi-state switching device is provided, and the alternating current system has the functions of flexible loop closing, voltage regulation and power flow regulation.
Description
Technical Field
The application relates to the technical field of power electronic converter, in particular to a flexible multi-state switch device, a multi-state switching method and an alternating current system.
Background
The flexible multi-state switch improves the operation flexibility of the power system by utilizing the advantage that the power electronic converter is flexible and controllable. At present, the existing flexible multi-state switch device is based on a voltage source converter, adopts a common high-voltage direct-current bus or a submodule direct-current bus technology to connect two-end or multi-end power systems, realizes the loop closing operation and the power flow control function of an alternating-current system, and plays an important role in the safe, stable and flexible operation of a power grid.
In general, when the voltage source converters are connected to the system in parallel, the equipment ports need to bear all the voltage. When the power distribution network is applied, the defects of insufficient voltage resistance of devices, numerous submodules, large occupied area and the like exist.
In another distributed power flow controller, when a voltage source converter is connected into a system in a series connection mode, enough insulation to the ground can be obtained simply by using an insulator, the voltage of a port during working is reduced, and the number of devices is reduced.
However, when the voltage source converter is connected into the system in a series connection mode, two problems exist:
firstly, due to the lack of a stable energy supply unit, the system can only provide reactive power, and the change of the system impedance is utilized to adjust the power flow, so that the system cannot play a role of a flexible switch.
Secondly, the energy-taking problem limits the technical development; the energy extraction in the prior art adopts a line current transformer to extract energy, when the current of a line is small, enough energy cannot be obtained to enable a main control unit to work, and a device connected in series with the line cannot be sensed and monitored, so that the flexibility of system operation is influenced.
Therefore, a flexible multi-state switch device, a multi-state switching method and an alternating current system are needed, which can realize the functions of flexible loop closing, voltage regulation and power flow regulation.
The above information disclosed in this background section is only for enhancement of understanding of the background of the application and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.
Disclosure of Invention
The application provides a flexible multi-state switching device, a multi-state switching method and an alternating current system, which can realize the functions of flexible loop closing, voltage regulation and power flow regulation.
According to an aspect of the application, a flexible multi-state switching device is proposed, the switching device comprising a commutation chain, a first bypass switch, an energy supply unit and an energy extraction unit, wherein:
the commutation chain comprises N submodules, wherein N is an integer greater than or equal to 1; the sub-module comprises a power unit, a direct current capacitor and a main control unit, wherein the direct current end of the power unit is electrically connected with the direct current capacitor; the control module controls the power unit;
the alternating current ends of the power units of each submodule are connected in series;
the first bypass switch is connected with the commutation chain in parallel;
the energy supply unit comprises a rectifying unit and outputs direct current to supply energy to the direct current capacitor of the submodule and/or the main control unit;
the energy obtaining unit comprises P isolation transformers and/or K current transformers, the P isolation transformers comprise M secondary windings, P is larger than or equal to 1 and smaller than or equal to M and smaller than or equal to N, and K is 1 or N; primary windings of the P isolation transformers are connected with an alternating-current power supply, and M secondary windings are connected with M sub-module energy supply units or form M short-circuit rings through lead short-circuit;
a primary winding of the current transformer surrounds an external connection line of the switching device or the short-circuit ring, and a secondary winding of the current transformer is electrically connected with the energy supply unit of the submodule;
and the submodule electrically connected with the isolation transformer or the secondary winding of the current transformer is defined as an energy supply submodule and used for supplying energy to other submodules.
According to some embodiments, the power unit is a full bridge circuit comprising a power semiconductor device;
the alternating current end of the power unit is connected with a sub-module protection bypass switch and/or a thyristor in parallel;
the direct current side of the full-bridge circuit is connected in parallel or is connected with a battery or/and a super capacitor or/and a photovoltaic power generation unit in parallel through a DC/DC converter;
the battery or/and the super capacitor or/and the photovoltaic power generation unit are connected with a contactor or/and a fuse in series.
According to some embodiments, the sub-module protection bypass switch is in an off state before and/or after the switching device is precharged;
and when the sub-module fails, the sub-module protection bypass switch is closed, and mechanical holding or magnetic holding is adopted.
According to some embodiments, the isolation transformer is a multi-stage transformer connected in series stage by stage, and the primary winding is connected with an alternating current power supply;
the short circuit ring is in short circuit with the output end of any one-stage secondary winding of the multi-stage transformer;
the insulation level of the isolation transformer is not lower than the ground insulation level of the flexible multi-state switching device.
According to some embodiments, the switching device further comprises:
the first isolating switch is connected with the converter chain in series;
and a series branch comprising the commutation chain and the first isolating switch is connected with the first bypass switch in parallel.
According to some embodiments, the switching device further comprises:
and the second bypass switch is connected in parallel at two ends of the commutation chain.
According to some embodiments, the second bypass switch is a mechanical switch or a semiconductor device.
According to some embodiments, the switching device further comprises:
the bridge is connected with a nonlinear resistor and/or a thyristor string in parallel and connected with an alternating current end of the commutation chain;
the thyristor string allows bidirectional current to flow and is conducted when the withstand voltage exceeds a device breakdown threshold value.
According to some embodiments, the switching device further comprises a ground nonlinear resistor, one end of the ground nonlinear resistor is connected with the alternating current end of the commutation chain, and the other end of the ground nonlinear resistor is grounded.
According to some embodiments, the switching device comprises the following states:
in an open circuit state, the first bypass switch is switched off, and the first isolating switch is switched off;
in a short-circuit state, the first bypass switch is switched on;
in a pre-charging state, the first isolating switch is switched off, and the second bypass switch is switched on;
in a ready state, the first isolating switch is switched on, the second bypass switch is switched off, and the pre-charging of the current conversion chain is completed;
the flexible connection state, the first bypass switch is switched off, the first partition switch is switched on, the second bypass switch is switched off, the pre-charging of the commutation chain is completed, and the output voltage Uc & ltbeta & gt, the voltage amplitude Uc and the phase angle beta are manually or automatically adjusted.
According to another aspect of the present application, there is provided a multi-state switching method of the flexible multi-state switching device described in the foregoing, including:
the pre-charge state is completed independently;
a precondition of the ready state is that the precharge state is complete;
the open circuit state and the short circuit state are switched mutually, and the first bypass switch is operated to switch on and off;
the open circuit state and the ready state are switched mutually, and the first isolating switch is operated to be switched on and off;
the short circuit state and the ready state are switched mutually, and the first isolating switch is operated to be switched on and off;
and the ready state and the flexible connection state are mutually switched, and the commutation chain is unlocked.
According to some embodiments, the pre-charge state is done independently, including:
breaking the first partition switch;
closing the second bypass switch;
the primary winding alternating current power supply of the isolation transformer is electrified, the direct current capacitor of the energy supply submodule is charged, and the main control unit of the energy supply submodule is started after a starting threshold value is reached;
controlling an alternating current port of the power unit of the energy supply submodule to output direct current voltage to charge the direct current capacitors of other submodules, and starting the main control unit of the submodule after a starting threshold value is reached;
and the alternating current end of the submodule power unit of the cyclic control part outputs zero level, so that the direct current capacitor voltage of all the submodules reaches a rated value.
According to another aspect of the present application, a flexible alternating current system is proposed, comprising a flexible multi-state switching device as defined in any one of the preceding claims, comprising:
the flexible multi-state switching device is connected among different alternating current buses, compensates amplitude or/and phase difference among the connected alternating current buses, and realizes different alternating current bus closed-loop operation or switching operation;
the flexible multi-state switch device is connected in series between a higher-level power supply and a lower-level power supply or a load or a converter, and the power quality or/and the operating characteristics of the lower-level power supply or the load voltage are improved by adjusting the output voltage of the flexible compensation switch;
the power flow distribution of the power transmission line is changed by adjusting the output voltage or impedance of the flexible power flow switch.
According to example embodiments, the present application has one or more of the following benefits:
(1) the application provides a flexible many state switch device to the function of many state switch has been realized to the mode of series connection transverter, has huge advantage in the aspect of equipment cost, volume compared with traditional scheme.
(2) The low potential energy taking problem of the series equipment is solved, the energy supply unit is in an energy taking mode of combination of a line current transformer or an isolation converter, and the device can realize that a single set of energy taking equipment is charged for the whole current conversion chain, so that the reliability is improved, and the investment is saved.
(3) The application adds the partition switch and the multiple bypass switches, provides the multi-state conversion method, meets the safety requirement of series equipment, safely completes the pre-charging process of a current conversion chain under the short-circuit state of the device, and reliably ensures the conversion of multiple states of the device.
(4) The application also provides a pre-charging method, after single submodule gets the energy earlier, becomes the energy supply submodule piece, separates the deciliter of switch and bypass switch through the control, constitutes the energy supply return circuit, and the energy supply submodule piece can charge to other submodule pieces through the energy supply return circuit, realizes the cross between the submodule piece and gets the energy, and the advantage of this kind of mode lies in: on one hand, the cost is reduced, and a one-to-one energy supply loop is not required to be provided for each submodule; on the other hand, the reliability of the device is improved, when more than 1 energy supply sub-modules are configured, because the sub-modules can be charged mutually, when one energy supply sub-module fails or the energy supply sub-module fails, energy can be obtained from other energy supply sub-modules, and multiple redundancy is realized.
(5) The application also provides a power grid system based on the flexible multi-state switching device, the power grid system can realize flexible bus loop closing, voltage sag compensation and tide regulation functions, the function that the flexible multi-state switching device can quickly regulate the amplitude and the phase of output voltage is fully utilized, and the power quality and the operating characteristic of the power grid system are improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
The above and other objects, features and advantages of the present application will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings. The drawings described below are for illustrative purposes only of certain embodiments of the present application and are not intended to limit the present application.
1A-1D illustrate embodiments of an exemplary flexible multi-state switching device;
FIG. 2 illustrates yet another embodiment of an exemplary flexible multi-state switching device;
FIG. 3 illustrates yet another embodiment of an exemplary flexible multi-state switching device;
FIG. 4 illustrates yet another embodiment of an exemplary flexible multi-state switching device;
FIG. 5 illustrates a multi-state switching method of the flexible multi-state switching device of an exemplary embodiment;
FIG. 6 illustrates a flow diagram of a pre-charge state of a flexible multi-state switching device of an exemplary embodiment;
FIG. 7 shows a schematic diagram of a pre-charge current loop of an exemplary embodiment;
FIG. 8 illustrates a schematic diagram of a flexible communication system of an exemplary embodiment;
FIG. 9A illustrates a flexible multi-state switching device voltage relationship vector diagram of an exemplary embodiment;
FIG. 9B illustrates yet another embodiment of an exemplary flexible multi-state switching device voltage relationship vector diagram.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The same reference numerals denote the same or similar parts in the drawings, and thus, a repetitive description thereof will be omitted.
The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the embodiments of the disclosure can be practiced without one or more of the specific details, or with other means, components, materials, devices, etc. In such cases, well-known structures, methods, devices, implementations, materials, or operations are not shown or described in detail.
The flow charts shown in the drawings are merely illustrative and do not necessarily include all of the contents and operations/steps, nor do they necessarily have to be performed in the order described. For example, some operations/steps may be decomposed, and some operations/steps may be combined or partially combined, so that the actual execution sequence may be changed according to the actual situation.
The terms "first," "second," and the like in the description and claims of the present application and in the above-described drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
It will be appreciated by those skilled in the art that the drawings are merely schematic representations of exemplary embodiments, and that the blocks or processes shown in the drawings are not necessarily required to practice the present application and are, therefore, not intended to limit the scope of the present application.
Embodiments of apparatus of the present application are described below that may be used to perform embodiments of the methods of the present application. For details not disclosed in the embodiments of the apparatus of the present application, reference is made to the embodiments of the method of the present application.
Fig. 1A-1D illustrate embodiments of an exemplary flexible multi-state switching device.
As shown in fig. 1A, the flexible multi-state switching device comprises a converter chain 1, an energy supply unit 3, an energy extraction unit 4 and a first bypass switch 6. The current conversion chain 1 comprises N submodules 2, N is more than or equal to 1, each submodule 2 comprises a power unit and a direct current capacitor, the direct current end of each power unit is electrically connected with the direct current capacitor, the alternating current ends of the power units of the submodules 2 are sequentially connected in series, and the two ends of the series connection are defined as the alternating current ends of the current conversion chain; the submodule 2 further comprises a main control unit (not shown in the figure) which controls the operation of the power unit.
According to some embodiments, the power unit may be a full bridge circuit of power semiconductor devices; the alternating current port of the power unit is also connected with the sub-module protection bypass switch and/or the thyristor in parallel. But the application is not limited thereto.
According to some embodiments, the direct current side of the full-bridge circuit is also connected in parallel or connected in parallel with a battery or/and a super capacitor or/and a photovoltaic power generation unit through a DC/DC converter; the battery or/and the super capacitor or/and the photovoltaic power generation unit branch are connected in series with the contactor or/and the fuse.
According to some embodiments, the sub-module protection bypass switch is in an open state before/after pre-charging of the device, is closed when the sub-module fails, and adopts mechanical holding or magnetic holding.
According to an exemplary embodiment, the power supply unit 3 comprises a rectifying unit, which supplies the output direct current to the submodule direct current capacitors and/or to the main control unit, the rectifying unit comprising an uncontrolled or controlled rectifying loop.
According to an exemplary embodiment, the energy extraction unit 4 comprises P isolation transformers with M secondary windings, 1 ≦ P ≦ M ≦ N, K ≦ 1 or K ≦ N, or/and K current transformers.
According to some embodiments, the isolation transformer is a multi-stage transformer connected in series in stages, with the primary side connected to a low voltage ac power source.
According to some embodiments, the isolation transformer has an insulation level not lower than a ground insulation level of the flexible multi-state switching device.
According to some embodiments, the primary sides of the P isolation transformers are connected to an ac power supply, and the M secondary windings are connected to the M sub-module power supply units or short-circuited through wires to form M short-circuit loops.
According to some embodiments, the shorting ring shorts the output of any secondary side of the multi-stage transformer.
According to some embodiments, the primary winding of the current transformer 3 surrounds the external connection line or short-circuit loop of the device, and the secondary side is connected to the sub-module power supply unit.
According to an exemplary embodiment, the submodule connected to the secondary side of the isolation transformer or current transformer is defined as an energizing submodule.
Fig. 1A shows a circuit configuration diagram of an apparatus powered by one isolation transformer and one secondary winding when P ═ M ═ 1.
Fig. 1B shows a circuit configuration diagram of an apparatus powered by one isolation transformer and three secondary windings when P is 1 and M is 3.
Fig. 1C shows a circuit diagram of an apparatus powered by one current transformer when K is 1.
Fig. 1D shows a circuit configuration diagram of an apparatus that is powered by a hybrid of an isolation transformer and a current transformer when K is equal to N.
Fig. 2 illustrates yet another embodiment of an exemplary flexible multi-state switching device.
As shown in fig. 2, the circuit shown in fig. 2 is substantially the same as the circuit shown in fig. 1, except that the flexible multi-state switching device further comprises a first disconnector switch 5 connected in series with the converter chain 1; the first bypass switch 6 is connected in parallel with a series branch consisting of the converter chain 1 and the first cut-off switch 5.
According to some embodiments, the first isolating switch 5 may disconnect the commutation chain from the line, avoiding interference from external voltages when the device is being serviced or performing pre-charging operations.
Fig. 3 illustrates yet another embodiment of an exemplary flexible multi-state switching device.
As shown in fig. 3, the circuit shown in fig. 3 is substantially the same as the circuit shown in fig. 2, except that the flexible multi-state switching device further comprises a second bypass switch 7, the second bypass switch 7 being connected in parallel across the chain 1.
According to some embodiments, the second bypass switch 7 is a mechanical switch or a switch made of a semiconductor device.
According to some embodiments, the second bypass switch 7 may bypass the converter valve, avoiding interference from external voltages when the device is being serviced or performing a pre-charging operation.
According to some embodiments, the flexible multi-state switching device further comprises a series of thyristors and/or a non-linear resistor connected in parallel at the ac end of the commutation chain, the series of thyristors and non-linear resistor providing overvoltage protection. The ground nonlinear resistor provides an overvoltage protection function for the device, and the device is prevented from being damaged due to overvoltage bearing; the thyristor string allows bi-directional current to flow and conducts when the withstand voltage exceeds the device breakdown threshold.
Fig. 4 illustrates yet another embodiment of an exemplary flexible multi-state switching device.
As shown in fig. 4, the circuit shown in fig. 4 is substantially the same as the circuit shown in fig. 3, except that the flexible multi-state switching device further includes a non-linear resistor 8 to ground, wherein one end of the non-linear resistor 8 to ground is connected with the alternating current end of the commutation chain, and the other end is grounded.
Fig. 5 illustrates a multi-state switching method of the flexible multi-state switching device of an exemplary embodiment.
As shown in fig. 5, the multi-states of the flexible multi-state switching device include:
1) in an open circuit state, the first bypass switch 6 is switched off, and the first partition switch 5 is switched off;
2) in the short-circuit state, the first bypass switch 6 is switched on;
3) a pre-charging state: the first isolating switch 5 is switched off, and the second bypass switch 7 is switched on;
4) in a ready state, the first isolating switch 5 is switched on, the second bypass switch 7 is switched off, and the pre-charging of the converter chain is completed;
5) in a flexible connection state, a first bypass switch 6 is switched off, a first isolating switch 5 is switched on, a second bypass switch 7 is switched off, pre-charging of a converter chain is completed, and the voltage Uc & ltbeta & gt is output; the voltage amplitude Uc and the phase angle β can be adjusted manually or automatically.
As shown in fig. 5, the multi-state switching method of the flexible multi-state switching device includes:
1) the precharge state is completed independently, for example, by a process described later with reference to fig. 6;
2) the precondition for the ready state is that the precharge state is complete;
3) the open circuit state and the short circuit state are switched mutually, and the first bypass switch 6 is operated to switch on and off;
4) the open circuit state and the ready state are switched mutually, and the first isolating switch 5 is operated to switch on and off;
5) the short-circuit state and the ready state are switched mutually, and the first isolating switch 5 is operated to switch on and off;
6) the ready state and the flexible connection state are switched with each other, and the commutation chain is unlocked.
FIG. 6 illustrates a flow diagram of a pre-charge state of a flexible multi-state switching device of an exemplary embodiment.
In S601, the first blocking switch is turned off.
At S603, the second bypass switch is turned on.
At S605, the primary ac power source of the isolation transformer is powered on, and the dc capacitor of the power supply sub-module is charged.
According to an exemplary embodiment, the primary side ac power source of the isolation transformer is powered on to charge the dc capacitor of the energy supply submodule, and the main control unit of the energy supply submodule is started after the dc capacitor voltage of the energy supply submodule reaches the start threshold.
And S607, controlling the alternating current port of the power supply sub-module power unit to output direct current voltage to charge direct current capacitors of other sub-modules.
According to an example embodiment, the main control unit controls the alternating current port of the power unit of the energy supply submodule to output direct current voltage to charge direct current capacitors of other submodules. And after the direct current capacitors of other sub-modules reach the starting threshold value, starting the main control unit of the sub-module.
In S609, the ac terminals of the sub-module power units of the cyclic control part output zero level, so that the dc capacitor voltages of all the sub-modules reach the rated value.
According to some embodiments, the zero state of the power unit means that two upper tubes of the full bridge circuit are conducted simultaneously or two lower tubes are conducted simultaneously.
FIG. 7 illustrates a schematic diagram of a pre-charge current loop of an exemplary embodiment.
As shown in fig. 7, a schematic diagram of a pre-charge current loop is shown, and other submodules in a converter chain are charged by an energy supply submodule.
FIG. 8 illustrates a schematic diagram of a flexible communication system of an exemplary embodiment.
The present application further proposes a flexible ac system, which includes a flexible multi-state switching device, as shown in fig. 8, and includes the following forms or combinations:
the bus loop closing flexible alternating current system is characterized in that a flexible multi-state switching device is connected among different alternating current buses, the amplitude or/and phase difference among the connected alternating current buses is compensated, and loop closing operation or switching operation of the different alternating current buses is realized; the flexible multi-state switching device is now in position a in fig. 8.
The flexible alternating current system comprises a voltage compensation flexible alternating current system, a flexible multi-state switch device and a control system, wherein the flexible multi-state switch device is connected in series between a higher-level power supply and a lower-level power supply or a load or a converter; the flexible multi-state switch device is connected in series between the upper power supply and the lower power supply, as shown in the position B1 in FIG. 8; the flexible multi-state switching device is connected in series between the upper power supply and the load or current transformer, as shown at position B2 in fig. 8.
In the power flow adjustment flexible alternating current system, a flexible multi-state switch device is connected in series in a power transmission line, and the power flow distribution of the power transmission line is changed by adjusting the output voltage or impedance of a flexible power flow switch. The flexible multi-state switching device is in position C in fig. 8.
According to some embodiments, the flexible compensation switch and the flexible power flow switch are application states of the flexible multi-state switching device.
FIG. 9A illustrates a flexible multi-state switching device voltage relationship vector diagram of an exemplary embodiment.
Describing the voltage relationship of the flexible multi-state switch device by using a vector diagram, when the voltages at two ends of the device have phase difference, phase compensation can be realized, as shown in fig. 9A, the device is applied to an alternating current bus flexible loop or utilizes a phase-adjusting circuit to transmit power flow, wherein V1 and V2 are voltages of connection points of the flexible multi-state switch and can be voltages of two connected alternating current buses respectively; v δ is the output voltage of the flexible multi-state switching device itself.
FIG. 9B illustrates yet another embodiment of an exemplary flexible multi-state switching device voltage relationship vector diagram.
By adjusting the voltage amplitude to change the voltage on the load side, as shown in fig. 9B, it can be applied to voltage sag compensation or motor soft start.
According to an example embodiment, in fig. 9B, the V δ voltage compensation amplitude is maximized, suitable for application of voltage sag compensation.
It should be clearly understood that this application describes how to make and use particular examples, but the application is not limited to any details of these examples. Rather, these principles can be applied to many other embodiments based on the teachings of the present disclosure.
Furthermore, it should be noted that the above-mentioned figures are only schematic illustrations of the processes involved in the method according to exemplary embodiments of the present application, and are not intended to be limiting. It will be readily understood that the processes shown in the above figures are not intended to indicate or limit the chronological order of the processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, e.g., in multiple modules.
Exemplary embodiments of the present application are specifically illustrated and described above. It is to be understood that the application is not limited to the details of construction, arrangement, or method of implementation described herein; on the contrary, the intention is to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (13)
1. A flexible multi-state switching device, said switching device comprising a commutation chain, a first bypass switch, an energy supply unit and an energy pick-up unit, wherein:
the commutation chain comprises N submodules, wherein N is an integer greater than or equal to 1; the sub-module comprises a power unit, a direct current capacitor and a main control unit, wherein the direct current end of the power unit is electrically connected with the direct current capacitor; the control module controls the power unit;
the alternating current ends of the power units of each submodule are connected in series;
the first bypass switch is connected with the commutation chain in parallel;
the energy supply unit comprises a rectifying unit and outputs direct current to supply energy to the direct current capacitor of the submodule and/or the main control unit;
the energy obtaining unit comprises P isolation transformers and/or K current transformers, the P isolation transformers comprise M secondary windings, P is larger than or equal to 1 and smaller than or equal to M and smaller than or equal to N, and K is 1 or N; primary windings of the P isolation transformers are connected with an alternating-current power supply, and M secondary windings are connected with M sub-module energy supply units or form M short-circuit rings through lead short-circuit;
a primary winding of the current transformer surrounds an external connection line of the switching device or the short-circuit ring, and a secondary winding of the current transformer is electrically connected with the energy supply unit of the submodule;
and the submodule electrically connected with the isolation transformer or the secondary winding of the current transformer is defined as an energy supply submodule and used for supplying energy to other submodules.
2. The switching device according to claim 1, wherein the power unit is a full bridge circuit including power semiconductor devices;
the alternating current end of the power unit is connected with a sub-module protection bypass switch and/or a thyristor in parallel;
the direct current side of the full-bridge circuit is connected in parallel or is connected with a battery or/and a super capacitor or/and a photovoltaic power generation unit in parallel through a DC/DC converter;
the battery or/and the super capacitor or/and the photovoltaic power generation unit are connected with a contactor or/and a fuse in series.
3. The switching device according to claim 2, wherein the sub-module protection bypass switch is in an off-state before and/or after the switching device is precharged;
and when the sub-module fails, the sub-module protection bypass switch is closed, and mechanical holding or magnetic holding is adopted.
4. The switching device according to claim 1, wherein the isolation transformer is a multi-stage transformer connected in series in stages, and the primary winding is connected to an ac power supply;
the short circuit ring is in short circuit with the output end of any one-stage secondary winding of the multi-stage transformer;
the insulation level of the isolation transformer is not lower than the ground insulation level of the flexible multi-state switching device.
5. The switching device according to claim 1, further comprising:
the first isolating switch is connected with the converter chain in series;
and a series branch comprising the commutation chain and the first isolating switch is connected with the first bypass switch in parallel.
6. The switching device according to claim 5, further comprising:
and the second bypass switch is connected in parallel at two ends of the commutation chain.
7. The switching device of claim 6, wherein the second bypass switch is a mechanical switch or a semiconductor device.
8. The switching device according to claim 1, further comprising:
the bridge is connected with a nonlinear resistor and/or a thyristor string in parallel and connected with an alternating current end of the commutation chain;
the thyristor string allows bidirectional current to flow and is conducted when the withstand voltage exceeds a device breakdown threshold value.
9. The switching device according to claim 1, further comprising a non-linear resistor to ground, wherein one end of the non-linear resistor to ground is connected to the AC end of the commutation chain, and the other end of the non-linear resistor to ground is connected to the AC end of the commutation chain.
10. The switching device according to claim 6, characterized in that it comprises the following states:
in an open circuit state, the first bypass switch is switched off, and the first isolating switch is switched off;
in a short-circuit state, the first bypass switch is switched on;
in a pre-charging state, the first isolating switch is switched off, and the second bypass switch is switched on;
in a ready state, the first isolating switch is switched on, the second bypass switch is switched off, and the pre-charging of the current conversion chain is completed;
the flexible connection state, the first bypass switch is switched off, the first partition switch is switched on, the second bypass switch is switched off, the pre-charging of the commutation chain is completed, and the output voltage Uc & ltbeta & gt, the voltage amplitude Uc and the phase angle beta are manually or automatically adjusted.
11. A method of multi-state switching of a flexible multi-state switching device according to claim 10, comprising:
the pre-charge state is completed independently;
a precondition of the ready state is that the precharge state is complete;
the open circuit state and the short circuit state are switched mutually, and the first bypass switch is operated to switch on and off;
the open circuit state and the ready state are switched mutually, and the first isolating switch is operated to be switched on and off;
the short circuit state and the ready state are switched mutually, and the first isolating switch is operated to be switched on and off;
and the ready state and the flexible connection state are mutually switched, and the commutation chain is unlocked.
12. The multi-state switching method of claim 11, wherein the pre-charge state is completed independently, comprising:
breaking the first partition switch;
closing the second bypass switch;
the primary winding alternating current power supply of the isolation transformer is electrified, the direct current capacitor of the energy supply submodule is charged, and the main control unit of the energy supply submodule is started after a starting threshold value is reached;
controlling an alternating current port of the power unit of the energy supply submodule to output direct current voltage to charge the direct current capacitors of other submodules, and starting the main control unit of the submodule after a starting threshold value is reached;
and the alternating current end of the submodule power unit of the cyclic control part outputs zero level, so that the direct current capacitor voltage of all the submodules reaches a rated value.
13. A flexible ac system comprising a flexible multi-state switching device according to any one of claims 1 to 9, comprising:
the flexible multi-state switching device is connected among different alternating current buses, compensates amplitude or/and phase difference among the connected alternating current buses, and realizes different alternating current bus closed-loop operation or switching operation;
the flexible multi-state switch device is connected in series between a higher-level power supply and a lower-level power supply or a load or a converter, and the power quality or/and the operating characteristics of the lower-level power supply or the load voltage are improved by adjusting the output voltage of the flexible compensation switch;
the power flow distribution of the power transmission line is changed by adjusting the output voltage or impedance of the flexible power flow switch.
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