CN115378268A - DAB and bipolar short-circuit fault current limiting method thereof - Google Patents
DAB and bipolar short-circuit fault current limiting method thereof Download PDFInfo
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- CN115378268A CN115378268A CN202210377891.7A CN202210377891A CN115378268A CN 115378268 A CN115378268 A CN 115378268A CN 202210377891 A CN202210377891 A CN 202210377891A CN 115378268 A CN115378268 A CN 115378268A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
- H02H7/1216—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for AC-AC converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
- H02H9/025—Current limitation using field effect transistors
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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
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0009—Devices or circuits for detecting current in a converter
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33573—Full-bridge at primary side of an isolation transformer
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
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- Emergency Protection Circuit Devices (AREA)
Abstract
The invention relates to a DAB (digital audio broadcasting) and a bipolar short-circuit fault current limiting method thereof, which utilize the topological structure and the control mode of the DAB, increase the current limiting inductance on the secondary side of a double-active-bridge high-frequency transformer, increase the IGBT (insulated gate bipolar transistor) element blocking capacitance discharge on a secondary side capacitance branch, and simultaneously cooperate with the reasonable phase shift ratio and the switching frequency of a primary side bridge, can control the outlet current of the DAB to be less than 2 times of the steady-state current, realize that a direct-current power distribution network containing the DAB does not need to lock DAB body power electronic devices after the bipolar short-circuit fault occurs, can provide stable fault information for a protection device, and are favorable for the reliable action of protection. The invention has simple principle, and the improvement on the DAB topology does not lead the volume of the DAB module to be increased obviously; the size of the fault current can be controlled by utilizing the topological structure and the control strategy of the DAB, so that the economy is good; the method is suitable for a direct current distribution network containing DAB, such as a medium-voltage alternating current source, an energy storage device, a photovoltaic and the like, which are connected into the direct current distribution network through the DAB.
Description
Technical Field
The invention relates to the technical field of automatic relay protection of a power system, in particular to DAB and a fault current limiting method aiming at the occurrence of a bipolar short circuit on a low-voltage direct-current side of the DAB.
Background
The development of renewable energy, distributed power generation and other clean energy is more and more concerned in the current academic and industrial circles, and the development is not only an important foundation for the development and transformation of future energy, but also an important component of an energy internet with intelligent power grid management capability in the future. In the composition framework of the energy internet, a power electronic interface technology supporting plug and play of equipment such as energy storage, photovoltaic, direct current load and distributed power generation, reasonable and efficient management and scheduling of electric energy and fault ride-through is a key technology for realizing the energy internet. A device equipped with the above energy management schedule is called an energy router. The core equipment of the energy router is a power electronic transformer with the advantages of electrical isolation, high control freedom, fault isolation and the like, wherein a double-active-bridge direct current converter (DAB) has the advantages of high modularization degree, zero-voltage switching capability, power bidirectional transmission capability, simple phase-shifting control and the like, and the double-active-bridge direct current converter has wide attention when being proposed and is the most suitable core equipment for the power electronic transformer at present.
In recent years, domestic and foreign research on DAB mainly focuses on modeling, control strategy improvement, zero voltage technology and fault ride-through technology of DAB. At present, aiming at the fault current limiting technical research of a low-voltage direct-current power distribution network containing DAB after a bipolar short-circuit fault occurs, most of the low-voltage direct-current power distribution network adopts blocking DAB and a converter station connected with the DAB or primarily limiting fault current and then cooperating with a breaker to act to cut off the fault current. Such a method can cause the non-faulty line to be shut down, which brings great difficulty to the recovery of the power grid after the fault.
Therefore, there is a need in the art for a technical solution for completing fault ride-through rapidly, economically and reliably without blocking the DAB body IGBT element.
Disclosure of Invention
The invention aims to provide DAB and a Bipolar short-circuit fault current-limiting method thereof, which realize the technical scheme of rapidly, economically and reliably completing fault ride-through on the premise of not locking an IGBT (Insulated Gate Bipolar Transistor) element of a DAB body by serially connecting the IGBT element to a secondary side capacitance branch of a DAB high-frequency transformer and switching off the IGBT element after the fault by combining the switching frequency and the shift ratio of a primary side bridge IGBT.
In order to achieve the purpose, the invention provides the following scheme:
a DAB circuit comprising a high frequency transformer;
the high-frequency transformer is connected with the two full-bridge sub-modules; the two full-bridge sub-modules comprise: a primary bridge and a secondary bridge;
the primary side of the high-frequency transformer is provided with an inductor, and the secondary side of the high-frequency transformer is provided with a current-limiting inductor; IGBT elements are connected in parallel at two ends of the current-limiting inductor;
the primary side bridge and the secondary side bridge of the high-frequency transformer are both composed of four IGBT anti-parallel diodes, the primary side and the secondary side are both provided with capacitors for supporting voltage and filtering, and secondary side capacitor branches are connected with IGBT elements in series.
In some embodiments of the present invention, the,
the IGBT element with the secondary side capacitors connected in series comprises two IGBT switching tubes which are connected in parallel in an opposite direction;
and the two IGBT switching tubes are reversely connected in parallel and then are connected in series with the secondary side capacitor.
The invention also provides a fault current limiting method for DAB bipolar short circuit, which comprises the following steps:
acquiring steady-state current of a DAB low-voltage direct-current side outlet;
monitoring a real-time current value of the low-voltage direct-current side outlet, and starting a current limiting mode when the real-time current value reaches a preset multiple of the steady-state current;
turning off the IGBT element with the secondary side capacitor branch circuit connected in series;
connecting a current-limiting inductor of a secondary side of the DAB high-frequency transformer;
and increasing the switching frequency of the IGBT of the primary side bridge, and setting the phase shift ratio of the IGBT of the primary side bridge as a fixed value.
In some embodiments, the steady state current is the DAB low voltage dc side outlet current under normal operating conditions.
In some embodiments, the monitoring a real-time current value of the DAB low-voltage dc side outlet, and when the real-time current value reaches a preset multiple of the steady-state current, starting a current limiting mode specifically includes:
and monitoring the real-time current value of the DAB low-voltage direct-current side outlet, and starting a current limiting mode when the real-time current value reaches 1.85 times of the steady-state current.
In some embodiments, the switching in the current-limiting inductor of the secondary side of the DAB high-frequency transformer specifically includes:
and switching off IGBT elements at two ends of the secondary current-limiting inductor of the high-frequency transformer.
In some embodiments, the increasing the switching frequency of the primary bridge IGBT specifically includes:
the switching frequency of the primary bridge IGBT was adjusted to 20kHz.
In some embodiments, the setting of the primary bridge IGBT as a fixed phase shift specifically includes:
and setting the internal shift ratio of the primary bridge IGBT to be 0.8.
In some embodiments, the peak value of the fault current at the low-voltage DC side outlet can be (1-d) times the original value after setting the step-in ratio to d.
In some embodiments, after the increasing the switching frequency of the primary side bridge IGBT and setting the phase shift ratio of the primary side bridge IGBT to a fixed value, the method further includes:
controlling the protection element to normally act to clear the fault;
and switching the operation mode of the DAB into a normal operation mode.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
when the direct current distribution network that contains DAB after taking place bipolar short circuit fault, needn't block DAB body power electronics, can provide stable fault information for protection device, help the reliable action of protection. The invention has simple principle, and the improvement on the DAB topology does not lead the volume of the DAB module to be increased obviously; the size of the fault current can be controlled by using the topological structure and the control strategy of the DAB, so that the method is good in economy; the method is suitable for a direct current distribution network containing DAB, such as a medium-voltage alternating current source, an energy storage device, a photovoltaic and the like, which are connected into the direct current distribution network through the DAB. Therefore, the method can remarkably improve the bearing capacity of the low-voltage direct-current distribution network to the bipolar short-circuit fault.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. The following drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
FIG. 1 is a schematic diagram of a DAB circuit according to an embodiment of the present invention.
Fig. 2 is a flowchart of a fault current limiting method for a DAB bipolar short circuit according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a fault current loop when the DAB current limiting mode is turned on according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of the on/off states of the switching tubes S1 and S3 when the inward shift ratio provided by the embodiment of the present invention is 0.8.
Fig. 5 is a DAB low voltage dc side outlet current schematic diagram of the non-enabled fault current limiting mode after the fault occurs according to the embodiment of the present invention.
Fig. 6 is a DAB low-voltage dc side outlet current schematic diagram for starting a fault current-limiting mode after a fault occurs according to an embodiment of the present invention.
Fig. 7 is an enlarged schematic diagram of the DAB low-voltage dc-side outlet current for starting the fault current-limiting mode after the fault occurs according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As used in this disclosure and in the claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are inclusive in the plural, unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
Flow charts are used in the present invention to illustrate the operations performed by a system according to embodiments of the present invention. It should be understood that the preceding or following operations are not necessarily performed in the exact order in which they are performed. Rather, the various steps may be processed in reverse order or simultaneously, as desired. Meanwhile, other operations may be added to or removed from these processes.
The current research situation at home and abroad shows that the current fault current limiting technology research aiming at the low-voltage direct-current power distribution network containing DAB after the occurrence of the bipolar short-circuit fault mostly adopts blocking DAB and a converter station connected with the DAB or primarily limiting the fault current and then cooperating with a breaker to remove the fault current. Such a method can cause the non-fault line to be shut down, and great difficulty is brought to the recovery of the power grid after the fault.
Therefore, the invention is urgently needed to provide a fault current limiting method after a bipolar short-circuit fault occurs in a low-voltage direct-current power distribution network containing DAB, fully utilize topological characteristics and a control mode of the DAB, and rapidly, economically and reliably complete fault ride-through on the premise of not locking an IGBT (insulated gate bipolar transistor) element of a DAB body. Meanwhile, the method can realize rapid and stable control of the fault current on the premise of not increasing the volume of the DAB obviously, and can be suitable for scenes that medium-voltage alternating current sources, energy storage devices, photovoltaic devices and the like are connected into a power grid through the DAB.
The invention provides a current limiting method for DAB low-voltage direct current side after a Bipolar short-circuit fault occurs, which utilizes a topological structure and a control mode of DAB, increases current limiting inductance on a secondary side of a double-active-bridge high-frequency transformer, increases an Insulated Gate Bipolar Transistor (IGBT) element on a secondary side capacitance branch to block capacitance discharge, and simultaneously cooperates with a reasonable phase shift ratio and switching frequency of a primary side bridge to control the outlet current of DAB to be less than 2 times of steady-state current, so that a DAB body power electronic device does not need to be locked after the DAB-containing direct current power distribution network has the Bipolar short-circuit fault, stable fault information can be provided for a protection device, and reliable protection action is facilitated. The method is simple in principle, and the improvement on the DAB topology does not increase the volume of a DAB module obviously; the size of the fault current can be controlled by utilizing the topological structure and the control strategy of the DAB, so that the economy is good; the method is suitable for a direct current distribution network containing DAB, such as a medium-voltage alternating current source, an energy storage device, a photovoltaic and the like, which are connected into the direct current distribution network through the DAB. Therefore, the method can remarkably improve the bearing capacity of the low-voltage direct-current distribution network to the bipolar short-circuit fault.
The invention aims to provide DAB and a Bipolar short-circuit fault current-limiting method thereof, which realize the technical scheme of rapidly, economically and reliably completing fault ride-through on the premise of not locking an IGBT (Insulated Gate Bipolar Transistor) element of a DAB body by serially connecting the IGBT element to a secondary side capacitance branch of a DAB high-frequency transformer and switching off the IGBT element after the fault by combining the switching frequency and the shift ratio of a primary side bridge IGBT.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The first embodiment is as follows:
as shown in FIG. 1, the present invention provides a DAB circuit including a high frequency transformer;
the high-frequency transformer is connected with the two full-bridge sub-modules; the two full-bridge sub-modules comprise: a primary bridge and a secondary bridge;
the primary side of the high-frequency transformer is provided with an inductor L t1 The secondary side of the high-frequency transformer is provided with a current-limiting inductor L t2 (ii) a The current-limiting inductor L t2 Both ends are connected with IGBT elements in parallel;
the primary side bridge and the secondary side bridge of the high-frequency transformer are both composed of four IGBT anti-parallel diodes, the primary side and the secondary side are both provided with capacitors for supporting voltage and filtering, and secondary side capacitor branches are connected with IGBT elements in series.
The IGBT element with the secondary side capacitors connected in series comprises two IGBT switching tubes which are reversely connected in parallel;
and the two IGBT switching tubes are reversely connected in parallel and then are connected in series with the secondary side capacitor.
When the circuit works normally, the IGBT element connected in series with the secondary side capacitor branch circuit is always in a conducting state. Starting a current limiting mode when the DAB low-voltage direct-current side outlet current reaches 1.85 times of steady-state current after the fault, and turning off an IGBT element of a secondary side capacitor branch circuit to block the capacitor from discharging; secondary current-limiting inductance L for turn-off high-frequency transformer t2 IGBT element with two parallel ends for accessing secondary side current limitingInductor L t2 . And meanwhile, the shift ratio and the switching frequency of the primary side bridge of the DAB are adjusted, the outlet current of the low-voltage direct-current side is limited to be less than 2 times of the steady-state current in a short time, and the converters connected with the low-voltage direct-current side of the DAB in parallel are prevented from being locked.
The secondary side of the DAB high-frequency transformer is connected with a current-limiting inductor after a fault, for a step-down transformer, the current-limiting effect of the inductor connected with the secondary side is superior to that of the inductor connected with the primary side, an IGBT element is connected in series with a capacitor branch of the secondary side of the DAB after the fault, the capacitor can be switched off to block the capacitor to discharge after the fault, the current-limiting capacitor has a remarkable effect on the fault current limitation and the voltage recovery after the fault is cleared, a DAB primary side bridge-shift comparison is given after the fault, the fault current is reduced to a great extent by the given primary side bridge-shift comparison, and further the control of the low-voltage direct-current side outlet current of the secondary side of the DAB is realized.
Example two:
as shown in fig. 2, an embodiment of the present invention provides a fault current limiting method for a DAB bipolar short circuit, which utilizes a topology structure and a control manner of DAB, increases a current limiting inductance on a secondary side of a dual-active-bridge high-frequency transformer, increases an IGBT element in a secondary side capacitance branch to block capacitance discharge, and simultaneously, controls an outlet current of DAB to be less than 2 times of a steady-state current by matching with a reasonable phase shift ratio and a switching frequency of a primary side bridge, thereby ensuring that an IGBT element of a DAB body cannot be locked after a bipolar short circuit fault occurs on a low-voltage direct-current side of DAB. The method has the advantages that after the bipolar short-circuit fault occurs in the direct-current power distribution network containing the DAB, the DAB body power electronic device does not need to be locked, stable fault information can be provided for the protection device, and the reliable action of protection is facilitated.
The fault current limiting method comprises the following steps:
s1, obtaining steady-state current 1pu of a DAB low-voltage direct-current side outlet;
and the steady-state current is the DAB low-voltage direct-current side outlet current under the normal operation condition.
S2, referring to fig. 2, monitoring a real-time current value i2 of the low-voltage direct-current side outlet, and starting a current limiting mode when the real-time current value reaches a preset multiple of the steady-state current 1pu;
in this embodiment, the preset multiple is set to 1.85, that is, when the real-time current value i2 reaches 1.85 times of the steady-state current 1pu, the current limiting mode is started.
S3, switching off IGBT elements, namely switching tubes Q3 and Q4 shown in figure 1, of the secondary side capacitor branch circuit in series, blocking uncontrollable discharge of the secondary side capacitor C2 and reducing fault current;
s4, limiting inductance L of secondary side of DAB high-frequency transformer t2 Switching-on, i.e. switching-off, secondary current-limiting inductance L of high-frequency transformer t2 IGBT elements at both ends (switching tubes Q1 and Q2 shown in fig. 1).
And S5, improving the switching frequency of the IGBT of the primary side bridge, and setting the phase shift ratio of the IGBT of the primary side bridge as a fixed value.
The switching frequency of the primary side bridge IGBT (S1-S4 in the figure 1) is improved through the controller, and meanwhile, the switching frequency of the primary side bridge IGBT is given, namely the conduction time of S1 and S3 in the figure 1 is different by a certain value, S1 and S4 are conducted in a complementary mode, and S2 and S3 are conducted in a complementary mode. Preventing the primary bridge from shorting. The larger the difference between the conduction time of S1 and the conduction time of S3 is, the shorter the conduction time of the primary side bridge is, the equivalent is that the duty ratio is reduced in the same period, and the limiting effect on the fault current is also generated. Taking the internal shift ratio of the primary side bridge IGBT as 0.8 and the switching frequency of the primary side bridge IGBT as 5kHz as an example, the signal conduction schematic diagram of the primary side bridge IGBT is shown in fig. 4.
The period corresponding to 5kHz is 200 mus, the internal shift ratio is 0.8, S3 lags behind the conduction of the S1 switch by 80 mus, and the current has no path at the moment and is equivalent to the locking of a primary bridge. Since 160 μ s of fault current will be dead-ended in 200 μ s of a cycle, the peak value of the fault current becomes (1-d) times the original value after setting the step-in ratio to d.
The secondary side capacitor C2 is blocked to discharge, and a current-limiting inductor L is connected t2 Meanwhile, after the internal shift ratio and the switching frequency of the primary side bridge IGBTS1-S4 are changed, the DAB low-voltage direct-current side outlet current i2 can be limited below 2 times of steady-state current, so that the IGBT element of the DAB body cannot be locked.
Then, controlling the protection element to normally act to clear the fault; after the fault line is successfully isolated, the operation mode of the DAB can be switched to a normal operation mode, and the whole system recovers normal operation.
As a specific example:
when the DAB circuit shown in the figure 1 is in a normal working mode, IGBT elements Q3 and Q4 of a secondary side capacitor branch circuit are in a conducting state, a secondary side capacitor C2 can be normally charged and discharged, a current-limiting inductor Lt2 connected in series with a secondary side inductor of a DAB high-frequency transformer is not connected, the IGBT elements Q1 and Q2 connected in parallel are in a conducting state, the switching frequency of a primary side bridge IGBTS1-S4 is 5kHz, and the primary side bridge shift ratio is 0. After the fault occurs, the DAB low-voltage direct-current side outlet current i2 quickly rises to 1.85 times of the steady-state current, and the current limiting mode is started. At the moment, IGBT elements Q3 and Q4 of the secondary side capacitor branch are turned off to block the capacitor from discharging; IGBT elements Q1 and Q2 at two ends of a secondary inductor of the high-frequency transformer are turned off, meanwhile, the switching frequency of a primary side bridge IGBTS1-S4 is adjusted to 20kHz, and the given primary side shift ratio is 0.8.
Comparing fig. 5 with fig. 6 and 7, it can be seen that when the fault current reaches 1.85 times the steady-state current, the current limiting mode is started, and the DAB low-voltage dc side outlet current can be controlled below 2 times the rated current in a short time. The method and the device have the advantages that after the double-pole short-circuit fault occurs in the direct-current power distribution network containing the DAB, the DAB body power electronic device does not need to be locked, stable fault information can be provided for the protection device, and the reliable action of protection is facilitated. The method is simple in principle, and the improvement on the DAB topology does not increase the volume of a DAB module obviously; the size of the fault current can be controlled by using the topological structure and the control strategy of the DAB, so that the method is good in economy; the method is suitable for a direct current distribution network containing DAB, such as a medium-voltage alternating current source, an energy storage device, a photovoltaic and the like, which are connected into the direct current distribution network through the DAB. Therefore, the method can remarkably improve the bearing capacity of the low-voltage direct-current distribution network to the bipolar short-circuit fault.
From the simulation results, the fault current limiting method based on the DAB low-voltage direct-current side when the bipolar short circuit occurs can control the fault current to be less than 2 times of the steady-state current after the bipolar short circuit occurs at the DAB low-voltage direct-current side outlet, so that the DAB body cannot be locked, and the reliable action of protection is guaranteed.
The present invention has been described using specific terms to describe embodiments of the invention. Reference to "a first/second embodiment," "an embodiment," and/or "some embodiments" means a feature, structure, or characteristic described in connection with at least one embodiment of the invention. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some of the features, structures, or characteristics of one or more embodiments of the present invention may be combined as suitable.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. It is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the claims and their equivalents.
Claims (10)
1. A DAB-circuit, comprising a high frequency transformer;
the high-frequency transformer is connected with the two full-bridge sub-modules; the two full-bridge sub-modules comprise: a primary bridge and a secondary bridge;
the primary side of the high-frequency transformer is provided with an inductor, and the secondary side of the high-frequency transformer is provided with a current-limiting inductor; IGBT elements are connected in parallel at two ends of the current-limiting inductor;
the primary side bridge and the secondary side bridge of the high-frequency transformer are both composed of four IGBT anti-parallel diodes, the primary side and the secondary side are both provided with capacitors for supporting voltage and filtering, and secondary side capacitor branches are connected with IGBT elements in series.
2. A DAB circuit according to claim 1, characterised in that,
the IGBT element with the secondary side capacitors connected in series comprises two IGBT switching tubes which are connected in parallel in an opposite direction;
and the two IGBT switching tubes are reversely connected in parallel and then are connected in series with the secondary side capacitor.
3. A method of fault current limiting for a DAB bipolar short circuit, the method comprising:
acquiring steady-state current of a DAB low-voltage direct-current side outlet;
monitoring a real-time current value of the low-voltage direct-current side outlet, and starting a current limiting mode when the real-time current value reaches a preset multiple of the steady-state current;
switching off the IGBT element with the secondary side capacitor branch circuit connected in series;
connecting a current-limiting inductor of a secondary side of the DAB high-frequency transformer;
and increasing the switching frequency of the IGBT of the primary side bridge, and setting the phase shift ratio of the IGBT of the primary side bridge as a fixed value.
4. The method of fault current limiting for bipolar shorting of claim 3, wherein the steady state current is a DAB low voltage DC side outlet current under normal operating conditions.
5. The method as claimed in claim 3, wherein the monitoring the real-time current value of the DAB low-voltage dc side outlet, and when the real-time current value reaches a preset multiple of the steady-state current, starting a current limiting mode specifically comprises:
and monitoring the real-time current value of the DAB low-voltage direct-current side outlet, and starting a current limiting mode when the real-time current value reaches 1.85 times of the steady-state current.
6. A method for limiting a fault to a DAB bipolar short circuit according to claim 3, wherein said switching in a current-limiting inductor of a secondary side of a DAB high-frequency transformer specifically comprises:
and switching off IGBT elements at two ends of the secondary current-limiting inductor of the high-frequency transformer.
7. A method for limiting a fault to a DAB bipolar short circuit as claimed in claim 3, wherein said increasing the switching frequency of the primary bridge IGBT comprises:
the switching frequency of the primary bridge IGBT is adjusted to 20kHz.
8. A fault current limiting method for DAB bipolar shorting according to claim 3, wherein the setting of the phase shift ratio of the primary bridge IGBT to a fixed value specifically comprises:
the phase shift ratio of the primary bridge IGBT is set to 0.8.
9. A method of limiting fault current for a DAB bipolar short circuit as claimed in claim 3, wherein the peak value of the fault current at the low voltage dc side outlet can be changed to 1-d times the original value after setting the step-in ratio to d.
10. A method for limiting fault current to a DAB bipolar short circuit as in claim 3, wherein after the increasing the switching frequency of the primary bridge IGBT and setting the phase shift ratio of the primary bridge IGBT to a fixed value, further comprising:
controlling the protection element to normally act to clear the fault;
and switching the operation mode of the DAB into a normal operation mode.
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| CN117639517A (en) * | 2024-01-25 | 2024-03-01 | 广东工业大学 | Fault isolation type medium-voltage direct-current transformer and control strategy thereof |
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| CN117639517A (en) * | 2024-01-25 | 2024-03-01 | 广东工业大学 | Fault isolation type medium-voltage direct-current transformer and control strategy thereof |
| CN117639517B (en) * | 2024-01-25 | 2024-04-26 | 广东工业大学 | Fault isolation type medium-voltage direct-current transformer and control strategy thereof |
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