CN111541370B - Flexible direct current transmission DC/DC converter for true and false bipolar interconnection - Google Patents
Flexible direct current transmission DC/DC converter for true and false bipolar interconnection Download PDFInfo
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- CN111541370B CN111541370B CN202010437552.4A CN202010437552A CN111541370B CN 111541370 B CN111541370 B CN 111541370B CN 202010437552 A CN202010437552 A CN 202010437552A CN 111541370 B CN111541370 B CN 111541370B
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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
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/125—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M3/135—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
- H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
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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]
Abstract
The invention discloses a flexible direct-current power transmission DC/DC converter for true and false bipolar interconnection, which comprises thyristor strings Tu 1-Tu 4, thyristor strings Tl 1-Tl 4, thyristor strings T1-T2, half-bridge sub-modules SMu-SMuN, half-bridge sub-modules SMl-SMlN and inductors L1-L2, wherein the half-bridge sub-modules SMu-SMuN and SMu-SMuN synchronously realize charging or discharging according to respective corresponding half-bridge sub-module driving signals, so that when power transmission occurs between a direct-current low-voltage side and a direct-current high-voltage side of the DC/DC converter, the energy balance of the converter can be maintained. The invention can continue normal operation without causing complete interruption of transmission power when the true bipolar side needs unipolar independent operation, and has the characteristics of no need of an alternating current transformer, few submodules, low cost and small volume and weight.
Description
Technical Field
The invention belongs to the field of power electronic technology and flexible direct current transmission, relates to a flexible direct current transmission DC/DC converter, and particularly relates to a flexible direct current transmission DC/DC converter for true and false bipolar interconnection.
Background
Networking of flexible direct current transmission is an inevitable trend in the future, and therefore high-voltage large-capacity DC/DC converters are needed to interconnect direct current transmission lines with different voltage levels. Considering the factors of the voltage withstanding level of the power electronic device, the size of the filter, the efficiency of the converter and the like in the prior art, the adoption of the modularized technical route is the only feasible scheme.
CN106160463A proposes a hybrid modular DC/DC converter, which does not need to be configured with an AC transformer and a large-capacity filter, effectively reduces the size and weight of the converter, requires a small number of sub-modules, reduces the cost and improves the efficiency. However, when the DC/DC converter is used for connecting a true bipolar and a pseudo bipolar direct current transmission system, the characteristic that the true bipolar system can operate independently in a single pole cannot be fully utilized, and when one pole of the true bipolar system fails or needs to be overhauled, energy transmission can only be completely stopped, which has certain limitations.
Disclosure of Invention
The invention provides a flexible direct-current transmission DC/DC converter for interconnecting true and false dipoles, aiming at solving the problem that the true bipolar side cannot operate independently in a single pole mode when the existing hybrid modular DC/DC converter is connected with a true bipolar direct-current power grid and a false bipolar direct-current power grid.
The purpose of the invention is realized by the following technical scheme:
the utility model provides a flexible direct current transmission DC/DC converter for bipolar interconnection of authenticity, includes thyristor cluster, anodal half-bridge submodule piece cluster, negative pole half-bridge submodule piece cluster, inductance L1 and inductance L2, wherein:
the thyristor string comprises a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string Tl4, a thyristor string T1 and a thyristor string T2;
the thyristor string Tu1, the thyristor string Tu2, the thyristor string Tu3, the thyristor string Tu4, the thyristor string Tl1, the thyristor string Tl2, the thyristor string Tl3, the thyristor string Tl4, the thyristor string T1 and the thyristor string T2 are identical in circuit structure, and each thyristor string comprises a plurality of thyristors connected in series in the forward direction;
the anode half-bridge submodule string comprises a half-bridge submodule SMu-half-bridge submodule SMuN, the cathode half-bridge submodule string comprises a half-bridge submodule SMl-half-bridge submodule SMlN, the circuit structures of all half-bridge submodules are the same, and for the anode half-bridge submodule string and the cathode half-bridge submodule string, the current output end of the half-bridge submodule in the submodule string is sequentially connected with the current input end of the next half-bridge submodule;
the thyristor string Tu1 and the thyristor string Tu3 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current low-voltage side and the current input end of the half-bridge submodule SMu, and the thyristor string Tu2 and the thyristor string Tu4 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current high-voltage side and the current input end of the half-bridge submodule SMu;
the thyristor string Tl1 and the thyristor string Tl3 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current low-voltage side and the current output end of the half-bridge sub-module SMlN, and the thyristor string Tl2 and the thyristor string Tl4 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current high-voltage side and the current output end of the half-bridge sub-module SMlN;
the current output end of the half-bridge submodule SMuN is connected with the first end of an inductor L1, the second end of the inductor L1 is connected with the first end of an inductor L2, and the second end of the inductor L2 is connected with the current input end of a half-bridge submodule SMl;
the thyristor string T1 and the thyristor string T2 are reversely connected in parallel and are respectively connected with the common end and the grounding end of the inductor L1 and the inductor L2;
the half-bridge submodule SMu-half-bridge submodule SMuN and the half-bridge submodule SMu-half-bridge submodule SMuN synchronously realize charging or discharging according to corresponding half-bridge submodule driving signals, so that when power transmission occurs between a direct current low-voltage side and a direct current high-voltage side of the DC/DC converter, energy balance of the converter can be maintained.
A control method for the flexible direct current transmission DC/DC converter for the authenticity bipolar interconnection comprises the following steps:
step one, when a true bipolar side and a false bipolar side both normally operate, setting on-off states of a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string Tl4, a thyristor string T1 and a thyristor string T2 according to a power transmission direction between a high voltage side and a low voltage side of a DC/DC converter; controlling the charging or discharging states of the half-bridge submodule SMu-half-bridge submodule SMuN and the half-bridge submodule SMl-half-bridge submodule SMlN, so that when the converter performs energy conversion at a direct-current high-voltage side and a direct-current low-voltage side, the internal energy balance of the converter is maintained;
step two, when the true bipolar side needs to operate independently in a single-pole mode due to the reasons of faults, maintenance and the like, the on-off states of the thyristor string Tu1, the thyristor string Tu2, the thyristor string Tu3, the thyristor string Tu4, the thyristor string Tl1, the thyristor string Tl2, the thyristor string Tl3, the thyristor string Tl4, the thyristor string T1 and the thyristor string T2 are set according to the power transmission direction between the high-low voltage sides of the DC/DC converter and the polarity of the pole needing to operate normally in the two poles of the true bipolar side; the energy balance of the converter is realized by controlling the charging or discharging state of the sub-module string corresponding to the pole of the true bipolar side which normally operates, and the sub-module string corresponding to the pole of the true bipolar side which stops operating is always kept in a bypass state.
Compared with the prior art, the invention has the following advantages:
the DC/DC converter can continue to normally operate when a true bipolar side needs unipolar independent operation without causing complete interruption of transmission power, and has the characteristics of no need of an alternating-current transformer, few submodules, low cost and small volume and weight; the method is suitable for realizing interconnection of true and false bipolar direct-current power grids with different voltage levels.
Drawings
Fig. 1 is a schematic circuit diagram of a flexible direct-current transmission DC/DC converter for true-false bipolar interconnection proposed by the present invention;
FIG. 2 is a schematic circuit diagram of a thyristor string;
FIG. 3 is a schematic circuit diagram of a half bridge sub-module;
FIG. 4 is a block diagram of the control principle of the DC/DC converter proposed by the present invention;
FIG. 5 is a schematic diagram of the normal operation of the DC/DC converter according to the present invention;
FIG. 6 is a schematic diagram of the operating principle of the true bipolar side unipolar independent operation of the DC/DC converter proposed by the present invention;
FIG. 7 is a schematic circuit diagram of a three-phase parallel-derived topology of the DC/DC converter according to the present invention;
fig. 8 is a schematic circuit diagram of a DC/DC converter according to the present invention in which the thyristor string is replaced with an IGCT switch string;
fig. 9 is a schematic circuit diagram of a DC/DC converter according to the present invention in which the thyristor string is replaced by an IGBT switching string.
Detailed Description
The technical solutions of the present invention are further described below with reference to the drawings, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
The invention provides a flexible direct current transmission DC/DC converter for true and false bipolar interconnection, which comprises a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string T4, a thyristor string T1, a thyristor string T2, a positive half-bridge sub-module string, a negative half-bridge sub-module string, an inductor L1 and an inductor L2, wherein as shown in figure 1:
the circuit structures of the thyristor string Tu1, the thyristor string Tu2, the thyristor string Tu3, the thyristor string Tu4, the thyristor string Tl1, the thyristor string Tl2, the thyristor string Tl3, the thyristor string Tl4, the thyristor string T1 and the thyristor string T2 are the same, as shown in fig. 2, each thyristor string comprises a plurality of thyristors connected in series in the forward direction;
the positive half-bridge submodule string comprises half-bridge submodules SMu 1-half-bridge submodules SMuN, the negative half-bridge submodule string comprises half-bridge submodules SMl-half-bridge submodules SMlN, as shown in fig. 3, the circuit structures of all half-bridge submodules are the same, and the current output ends of the half-bridge submodules in the submodule strings are sequentially connected with the current input end of the next half-bridge submodule for the positive half-bridge submodule string and the negative half-bridge submodule strings;
the thyristor string Tu1 and the thyristor string Tu3 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current low-voltage side and the current input end of the half-bridge submodule SMu, and the thyristor string Tu2 and the thyristor string Tu4 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current high-voltage side and the current input end of the half-bridge submodule SMu;
the thyristor string Tl1 and the thyristor string Tl3 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current low-voltage side and the current output end of the half-bridge sub-module SMlN, and the thyristor string Tl2 and the thyristor string Tl4 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current high-voltage side and the current output end of the half-bridge sub-module SMlN;
the current output end of the half-bridge submodule SMuN is connected with the first end of an inductor L1, the second end of the inductor L1 is connected with the first end of an inductor L2, and the second end of the inductor L2 is connected with the current input end of a half-bridge submodule SMl;
the thyristor string T1 and the thyristor string T2 are reversely connected in parallel and are respectively connected with the common end and the grounding end of the inductor L1 and the inductor L2;
the half-bridge submodule SMu-half-bridge submodule SMuN and the half-bridge submodule SMu-half-bridge submodule SMuN synchronously realize charging or discharging according to corresponding half-bridge submodule driving signals, so that when power transmission occurs between a direct current low-voltage side and a direct current high-voltage side of the DC/DC converter, energy balance of the converter can be maintained.
As shown in fig. 4, 5 and 6, the control method of the flexible direct current transmission DC/DC converter for the authenticity bipolar interconnection includes the following steps:
step one, when a true bipolar side and a false bipolar side both normally operate, setting on-off states of a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string Tl4, a thyristor string T1 and a thyristor string T2 according to a power transmission direction between high and low voltage sides of a DC/DC converter; controlling the charging or discharging states of the half-bridge submodule SMu-half-bridge submodule SMuN and the half-bridge submodule SMl-half-bridge submodule SMlN, so that when the converter performs energy conversion of a direct current high-voltage side and a direct current low-voltage side, the internal energy balance of the converter is maintained; the specific method comprises the following steps:
(1) When the DC/DC converter transmits power from a direct current low-voltage side to a direct current high-voltage side (P > 0), the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string Tl2 are controlled to be in a switching state, the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string Tl4 are always set to be in a switching-off state, and the thyristor string T1 and the thyristor string T2 are always set to be in a switching-on state;
(2) When the DC/DC converter transmits power from a direct current high-voltage side to a direct current low-voltage side (P < 0), the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string Tl4 are controlled to be in a switching state, the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string Tl2 are always set to be in a switching-off state, and the thyristor string T1 and the thyristor string T2 are always set to be in a switching-on state;
(3) A direct current high-voltage side current reference signal is given out in a constant voltage or constant power control mode; a direct-current low-voltage side current reference signal is given through an energy balance control link, so that the average capacitance voltage of a half-bridge sub-module SMu-a half-bridge sub-module SMuN and a half-bridge sub-module SMl-a half-bridge sub-module SMlN tracks a given value; adding the current reference signals of the direct current high-voltage side and the direct current low-voltage side to obtain a current reference signal of the submodule string, sending the difference between the fed-back submodule string current and the reference signal to a proportional-integral regulator, and then obtaining a voltage reference signal of the submodule string; sending the sub-module string voltage reference signal to a modulation and sub-module balance control link to obtain a driving signal of each sub-module;
step two, when the true bipolar side needs to operate independently in a single pole mode due to the reasons of faults, maintenance and the like, the on-off states of the thyristor string Tu1, the thyristor string Tu2, the thyristor string Tu3, the thyristor string Tu4, the thyristor string Tl1, the thyristor string Tl2, the thyristor string Tl3, the thyristor string T4 and the thyristor string T2 are set according to the power transmission direction between the high-low voltage sides of the DC/DC converter and the polarity of the pole needing to operate normally in the two poles of the true bipolar side; the energy balance of the converter is realized by controlling the charging or discharging state of the sub-module string corresponding to the pole of the true bipolar side which normally operates, and the sub-module string corresponding to the pole of the true bipolar side which stops operating is always kept in a bypass state; the specific method comprises the following steps:
(1) When the positive electrode in the direct-current high-voltage side true bipolar operates independently and the DC/DC converter transmits power to the direct-current high-voltage side from the direct-current low-voltage side (P > 0), the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string T2 are controlled to be in a switching state, and the rest thyristor strings are set to be in a switching-off state all the time;
(2) When the negative electrode in the true bipolar of the direct-current high-voltage side operates independently and the DC/DC converter transmits power to the direct-current high-voltage side from the direct-current low-voltage side (P > 0), the thyristor string Tu1, the thyristor string Tl2 and the thyristor string T1 are controlled to be in a switching-on state, and the rest thyristor strings are set to be in a switching-off state all the time;
(3) When the positive electrode in the direct-current high-voltage side true bipolar electrode operates independently and the DC/DC converter transmits power from the direct-current high-voltage side to the direct-current low-voltage side (P < 0), the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string T1 are controlled to be in a switching-on state, and the rest thyristor strings are set to be in a switching-off state all the time;
(4) When the negative electrode in the true bipolar of the direct-current high-voltage side operates independently and the DC/DC converter transmits power from the direct-current high-voltage side to the direct-current low-voltage side (P < 0), the thyristor string Tu3, the thyristor string Tl4 and the thyristor string T2 are controlled to be in a switching-on state, and the rest thyristor strings are set to be in a switching-off state all the time;
(5) When the positive electrode in the direct-current high-voltage side bipolar operates independently, the half-bridge submodule SMu-half-bridge submodule SMuN normally performs charge and discharge control, and the half-bridge submodule SMl-half-bridge submodule SMlN is always in a bypass state; when the negative electrodes in the direct-current high-voltage side true bipolar electrodes operate independently, the half-bridge sub-module SMl-half-bridge sub-module SMlN normally performs charge and discharge control, and the half-bridge sub-module SMu-half-bridge sub-module SMuN is always in a bypass state.
In practical application, the flexible direct-current transmission DC/DC converter for the true and false bipolar interconnection can obtain continuous direct-current waveforms in a multi-phase parallel operation mode. Fig. 7 is a schematic circuit diagram of a three-phase parallel-derived topology structure of the DC/DC converter according to the present invention.
In the present invention, the thyristor string may also be replaced by an IGCT switch string or an IGBT switch string, as shown in fig. 8 and 9, respectively.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.
Claims (6)
1. The control method for the flexible direct-current transmission DC/DC converter for the authenticity bipolar interconnection is characterized in that the flexible direct-current transmission DC/DC converter comprises a thyristor string, a positive half-bridge sub-module string, a negative half-bridge sub-module string, an inductor L1 and an inductor L2, wherein:
the thyristor string comprises a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string Tl4, a thyristor string T1 and a thyristor string T2;
the anode half-bridge submodule string comprises half-bridge submodules SMu-half-bridge submodules SMuN, the cathode half-bridge submodule string comprises half-bridge submodules SMl-half-bridge submodules SMlN, and for the anode half-bridge submodule string and the cathode half-bridge submodule string, the current output ends of the half-bridge submodules in the submodule strings are sequentially connected with the current input end of the next half-bridge submodule;
the thyristor string Tu1 and the thyristor string Tu3 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current low-voltage side and the current input end of the half-bridge submodule SMu, and the thyristor string Tu2 and the thyristor string Tu4 are reversely connected in parallel and are respectively connected with the positive electrode of the direct-current high-voltage side and the current input end of the half-bridge submodule SMu;
the thyristor string Tl1 and the thyristor string Tl3 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current low-voltage side and the current output end of the half-bridge sub-module SMlN, and the thyristor string Tl2 and the thyristor string Tl4 are reversely connected in parallel and are respectively connected with the negative electrode of the direct-current high-voltage side and the current output end of the half-bridge sub-module SMlN;
the current output end of the half-bridge submodule SMuN is connected with the first end of an inductor L1, the second end of the inductor L1 is connected with the first end of an inductor L2, and the second end of the inductor L2 is connected with the current input end of a half-bridge submodule SMl;
the thyristor string T1 and the thyristor string T2 are reversely connected in parallel and are respectively connected with the common end and the grounding end of the inductor L1 and the inductor L2;
the method comprises the following steps:
step one, when a true bipolar side and a false bipolar side both normally operate, setting on-off states of a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string Tl4, a thyristor string T1 and a thyristor string T2 according to a power transmission direction between a high voltage side and a low voltage side of a DC/DC converter; controlling the charging or discharging states of the half-bridge submodule SMu-half-bridge submodule SMuN and the half-bridge submodule SMl-half-bridge submodule SMlN, and accordingly maintaining the internal energy balance of the converter when the converter performs direct-current high-low voltage side energy conversion;
step two, when the true bipolar side needs monopole independent operation, setting the on-off states of a thyristor string Tu1, a thyristor string Tu2, a thyristor string Tu3, a thyristor string Tu4, a thyristor string Tl1, a thyristor string Tl2, a thyristor string Tl3, a thyristor string T4, a thyristor string T1 and a thyristor string T2 according to the power transmission direction between the high-low voltage sides of the DC/DC converter and the polarity of the pole needing normal operation in the two poles of the true bipolar side; the energy balance of the converter is realized by controlling the charging or discharging state of the sub-module string corresponding to the pole of the true bipolar side which normally operates, and the sub-module string corresponding to the pole of the true bipolar side which stops operating is always kept in a bypass state.
2. The method for controlling the flexible direct current transmission DC/DC converter for the authenticity bipolar interconnection according to claim 1, characterized in that the specific steps of the first step are as follows:
(1) When the DC/DC converter transmits power from a direct-current low-voltage side to a direct-current high-voltage side, the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string Tl2 are controlled to be in a switching state, the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string Tl4 are always set to be in a switching-off state, and the thyristor string T1 and the thyristor string T2 are always set to be in a switching-on state;
(2) When the DC/DC converter transmits power from the direct-current high-voltage side to the direct-current low-voltage side, the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string Tl4 are controlled to be in a switching state, the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string Tl2 are always set to be in a switching-off state, and the thyristor string T1 and the thyristor string T2 are always set to be in a switching-on state;
(3) A direct current high-voltage side current reference signal is given out in a constant voltage or constant power control mode; providing a direct-current low-voltage side current reference signal through an energy balance control link, and enabling average capacitance voltage of a half-bridge sub-module SMu-half-bridge sub-module SMuN and a half-bridge sub-module SMl-half-bridge sub-module SMlN to track a given value; adding the current reference signals of the direct current high-voltage side and the direct current low-voltage side to obtain a current reference signal of the submodule string, sending the difference between the fed-back submodule string current and the reference signal to a proportional-integral regulator, and then obtaining a voltage reference signal of the submodule string; and sending the sub-module string voltage reference signal to a modulation and sub-module balance control link to obtain a driving signal of each sub-module.
3. The control method for the authenticity bipolar interconnected flexible direct current transmission DC/DC converter according to claim 1, characterized in that the second step comprises the following steps:
(1) When the positive electrode in the direct-current high-voltage side true bipolar operates independently and the DC/DC converter transmits power to the direct-current high-voltage side from the direct-current low-voltage side, the thyristor string Tu1, the thyristor string Tl1, the thyristor string Tu2 and the thyristor string T2 are controlled to be in a switching state, and the rest thyristor strings are set to be in a switching-off state all the time;
(2) When the negative electrode in the true bipolar of the direct-current high-voltage side operates independently and the DC/DC converter transmits power to the direct-current high-voltage side from the direct-current low-voltage side, the thyristor string Tu1, the thyristor string Tl2 and the thyristor string T1 are controlled to be in a switching state, and the rest thyristor strings are set to be in a switching-off state all the time;
(3) When the positive electrode in the direct-current high-voltage side true bipolar operates independently and the DC/DC converter transmits power to the direct-current low-voltage side from the direct-current high-voltage side, the thyristor string Tu3, the thyristor string Tl3, the thyristor string Tu4 and the thyristor string T1 are controlled to be in a switching state, and the rest thyristor strings are set to be in a switching-off state all the time;
(4) When the negative electrode in the direct-current high-voltage side true dipole independently operates and the DC/DC converter transmits power to the direct-current low-voltage side from the direct-current high-voltage side, the thyristor string Tu3, the thyristor string Tl4 and the thyristor string T2 are controlled to be in a switching-on state, and the rest thyristor strings are set to be in a switching-off state all the time;
(5) When the positive electrode in the direct-current high-voltage side true bipolar operates independently, the half-bridge sub-module SMu-half-bridge sub-module SMuN normally performs charge and discharge control, and the half-bridge sub-module SMl-half-bridge sub-module SMlN is always in a bypass state; when the negative electrode in the direct-current high-voltage side true bipolar operates independently, the half-bridge sub-module SMl-half-bridge sub-module SMlN normally performs charge and discharge control, and the half-bridge sub-module SMu-half-bridge sub-module SMuN is always in a bypass state.
4. The control method for the flexible direct current/direct current converter for the authenticity bipolar interconnection according to claim 1, wherein the thyristor string Tu1, the thyristor string Tu2, the thyristor string Tu3, the thyristor string Tu4, the thyristor string Tl1, the thyristor string Tl2, the thyristor string Tl3, the thyristor string Tl4, the thyristor string T1 and the thyristor string T2 have the same circuit structure, and each thyristor string includes a plurality of thyristors connected in series in the forward direction.
5. The control method for the authenticity bipolar interconnected flexible direct current transmission DC/DC converter according to claim 1, characterized in that the circuit structures of all half-bridge sub-modules in the positive half-bridge sub-module string and the negative half-bridge sub-module string are the same.
6. The control method for the authenticity bipolar interconnected flexible direct current transmission DC/DC converter according to claim 1, wherein said thyristor string is replaced by an IGCT switch string or an IGBT switch string.
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