Consumption-storage integrated converter for DC power transmission system and control method thereof

Abstract

The present application provides a power consumption and storage integrated converter for a DC power transmission system and a control method thereof, wherein the power consumption and storage integrated converter comprises at least one power consumption submodule and at least one energy storage submodule, wherein the power consumption submodule and the energy storage submodule are connected in series and connected to a DC line, wherein: the energy storage submodule is used to store the surplus power of the DC power transmission system; the energy consumption submodule is used to consume the surplus power; the energy storage submodule and the energy consumption submodule cooperate to support the power grid frequency and power regulation requirements. It can not only solve the DC overvoltage problem when the receiving-end power grid fails, but also reduce the impact of new energy fluctuations on the power grid, and enhance the support of new energy for power grid frequency and power regulation.

Description

Technical Field

[0001] The present application relates to the technical field of direct current transmission of electric power systems, and in particular to a power consumption and storage integrated converter for direct current transmission systems and a control method thereof. Background Art

[0002] Large-scale renewable energy power generation is the key and foundation for achieving dual carbon goals and energy transformation, and is an indispensable part of building my country's modern energy system. The centralized transmission of large-scale wind and solar bases and large offshore wind power can save investment costs and improve transmission efficiency. DC transmission has become one of the main technologies for power transmission of large-scale wind and solar bases and large offshore wind power bases due to its long transmission distance, high transmission capacity, small transmission corridor and low loss.

[0003] With the continuous emergence of large-scale new energy bases, large-scale new energy through direct current transmission has become a development trend of the power grid. When the receiving end power grid of new energy direct current transmission fails, the AC power grid cannot send out the new energy power, resulting in the accumulation of new energy power on the DC side, causing DC overvoltage tripping, affecting system operation and reliability. Therefore, previous offshore wind power flexible direct current projects have solved the DC overvoltage problem by configuring DC energy consumption. For example, patent CN113839409A proposes a modular distributed resistance energy consumption device, and patent CN109873441A proposes a distributed DC energy consumption device, but the energy consumption device cannot store power, which will lead to energy waste.

[0004] In the future, as the proportion of new energy sources gradually increases, in the context of building a new power system, new energy sources will be integrated into the power system using direct current transmission. Since they are all non-synchronous power sources, they do not have the inherent power angle stability capability of synchronous machines, which will inevitably pose a challenge to the power grid. In addition, due to the large volatility of the power of new energy grid-connected, under the condition of limited acceptance of the power system, new energy sources are limited by natural conditions and lack the support for participating in the frequency, power and peak regulation of the power grid. Some scholars and experts have proposed a full direct current energy storage solution, but the full direct current energy storage solution has problems such as large land occupation, high cost, and power surplus after the energy storage equipment is fully stored, causing the system to be shut down.

[0005] Therefore, it is necessary to propose a new solution that can not only solve the DC overvoltage problem when the receiving-end power grid fails, but also reduce the impact of renewable energy fluctuations on the power grid and enhance the support of renewable energy for the frequency and power regulation of the power grid.

[0006] The above information disclosed in the Background section is only for enhancement of understanding of the background of the present application and therefore it may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0007] The present application aims to provide a power consumption and storage integrated converter and a control method thereof for a DC transmission system, which can not only solve the DC overvoltage problem when a receiving-end power grid fails, but also reduce the impact of new energy fluctuations on the power grid and enhance the support of new energy for the frequency and power regulation of the power grid.

[0008] According to one aspect of the present application, a power consumption and storage integrated converter for a direct current transmission system is provided, characterized in that the power consumption and storage integrated converter comprises at least one energy consumption submodule and at least one energy storage submodule, the energy consumption submodule and the energy storage submodule are connected in series and then connected to a direct current line, wherein:

[0009] The energy storage submodule is used to store the surplus power of the DC power transmission system;

[0010] The energy consumption submodule is used to consume the surplus power;

[0011] The energy storage submodule and the energy consumption submodule cooperate to support the frequency and power regulation requirements of the power grid.

[0012] According to some embodiments, the energy consumption submodule includes a DC capacitor branch, a first bypass branch and an energy consumption branch, wherein:

[0013] The DC capacitor branch, the bypass branch and the energy consumption branch are connected in parallel;

[0014] The DC capacitor branch includes a first DC capacitor;

[0015] The first bypass branch includes a first bypass switch and a turn-on thyristor connected in parallel;

[0016] The energy consumption branch includes an energy consumption power unit and an energy consumption circuit connected in series.

[0017] According to some embodiments, the energy dissipation power unit includes a controllable semiconductor and a first diode connected in reverse parallel, and the energy dissipation circuit includes an energy dissipation resistor and a second diode connected in parallel.

[0018] According to some embodiments, the energy consumption submodule further includes a first power unit, wherein:

[0019] The first power unit is connected in parallel with the DC capacitor branch;

[0020] The first power unit includes a first switch module and a second switch module connected in series;

[0021] The second switch module is connected in parallel with the first bypass switch.

[0022] According to some embodiments, the first switch module and the second switch module respectively include a diode, or a turn-off semiconductor and a diode connected in reverse parallel;

[0023] The anode of the turning thyristor is electrically connected to the anode of the diode of the second switch module;

[0024] The cathode of the thyristor is electrically connected to the cathode of the diode of the second switch module.

[0025] According to some embodiments, the energy consumption submodule further includes a first wiring terminal and a second wiring terminal, wherein the first wiring terminal is electrically connected to a cathode of the thyristor, and the second wiring terminal is electrically connected to an anode of the thyristor.

[0026] According to some embodiments, the energy storage submodule comprises a half-bridge submodule and an energy storage unit connected in parallel, wherein:

[0027] The half-bridge submodule includes a second power unit, a second DC capacitor and a second bypass branch, the second power unit and the second DC capacitor are connected in parallel, the second power unit includes a third switch module and a fourth switch module connected in series, the fourth switch module is connected in parallel with the second bypass branch, and the second bypass branch includes a second bypass switch and a thyristor connected in parallel;

[0028] The energy storage unit includes an energy storage element and a DC bypass switch connected in series, the positive electrode of the energy storage element is electrically connected to the positive electrode of the second DC capacitor, and the negative electrode of the energy storage element is electrically connected to the negative electrode of the second DC capacitor.

[0029] According to some embodiments, the third switch module and the fourth switch module respectively include a turn-off semiconductor and a diode connected in reverse parallel;

[0030] The cathode of the diode of the fourth switch module is electrically connected to the cathode of the thyristor of the second bypass branch, and the anode of the diode of the fourth switch module is electrically connected to the anode of the thyristor of the second bypass branch.

[0031] According to some embodiments, the energy storage submodule includes a third terminal and a fourth terminal, the third terminal is electrically connected to the cathode of the thyristor of the second bypass branch, and the fourth terminal is electrically connected to the anode of the thyristor of the second bypass branch.

[0032] According to some embodiments, the energy storage element includes batteries connected in series, cascade batteries, supercapacitors, flywheel energy storage, gas compression energy storage, or any combination thereof.

[0033] According to some embodiments, further comprising:

[0034] When the AC system needs the DC transmission system to provide more power to support the system frequency, switching on the turn-off semiconductor of the third switch module of the energy storage submodule;

[0035] When the AC system requires the DC power transmission system to reduce the injected power or lower the system frequency, the turnable semiconductor of the fourth switch module of the energy storage submodule is controlled or switched by current;

[0036] After the energy of the energy storage submodule exceeds the limit, the energy consumption branch of the energy consumption submodule is put into use to absorb power.

[0037] According to another aspect of the present application, a control method for a power consumption and storage integrated converter for a direct current transmission system is provided, the control method comprising:

[0038] In response to the DC voltage increasing, calculating surplus power;

[0039] Calculating redundant energy according to the surplus power;

[0040] Calculate the maximum energy that the energy storage can absorb;

[0041] Comparing the redundant energy with the maximum energy that can be absorbed by the energy storage to obtain a comparison result;

[0042] Based on the comparison result, the energy storage submodule and / or the energy consumption submodule are put into operation.

[0043] According to some embodiments, calculating the surplus power includes:

[0044] The surplus power is calculated based on the current DC system sending-end transmission power, the actual transmission power of the receiving-end converter station during the fault period, and the losses of the DC cable and the converter station.

[0045] According to some embodiments, calculating redundant energy according to the surplus power includes:

[0046] The redundant energy is calculated according to the surplus power and the system fault ride-through tolerance time.

[0047] According to some embodiments, calculating the maximum energy that can be absorbed by the energy storage includes:

[0048] The maximum energy that can be absorbed by the energy storage is obtained by calculating the charge state of the energy storage unit of the energy storage submodule.

[0049] According to some embodiments, based on the comparison result, putting the energy storage submodule and / or the energy consumption submodule into use includes:

[0050] When the maximum energy that can be absorbed by the energy storage is greater than or equal to the redundant energy, the energy storage submodule is put into use;

[0051] When the maximum energy that can be absorbed by the energy storage is less than the redundant energy, the energy storage submodule and the energy consumption submodule are put into use.

[0052] According to some embodiments, further comprising:

[0053] The power required for energy consumption is calculated according to the redundant energy, the maximum energy that can be absorbed by the energy storage and the system fault ride-through tolerance time, and the number of energy storage submodules invested is calculated according to the power required for energy consumption and the power of one of the energy consumption submodules;

[0054] The number of energy storage submodules put into operation is calculated according to the state of charge control calculation of the energy storage submodule.

[0055] According to some embodiments, further comprising:

[0056] When the AC system needs the DC transmission system to provide more power to support the system frequency, the energy storage submodule is switched on and off through current control.

[0057] The present application provides a power consumption and storage integrated converter for a direct current transmission system and a control method thereof, which is applicable to a large-scale new energy direct current transmission system, and is particularly applicable to an offshore wind power direct current transmission system. The power consumption and storage integrated converter is used to store surplus power in an energy storage submodule, and the energy storage submodule can effectively smooth the inherent fluctuations of new energy and provide the power and frequency support required by the power grid. When the energy storage submodule is fully loaded, the number M of configured energy consumption submodules can meet the single-phase and phase-to-phase fault ride-through requirements, meet the three-phase fault ride-through requirements, and improve the stability of flexible direct current operation.

[0058] The present application provides an integrated energy storage converter for a DC power transmission system and a control method thereof. The integrated energy storage converter can overcome the problem that a pure energy storage converter is expensive and does not have the surplus power consumption capacity after the pure energy storage converter is fully stored, causing the DC system to shut down.

[0059] The present application provides an integrated power consumption and storage converter for a direct current transmission system and a control method thereof. The integrated power consumption and storage converter can effectively smooth out fluctuations in renewable energy, enhance fault ride-through capability, and improve system safety and reliability. At the same time, by combining the advantages of energy storage and energy consumption, it can reduce the cost of offshore wind power and large-scale renewable energy transmission, and promote the grid parity of offshore wind power.

[0060] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] By describing in detail exemplary embodiments thereof with reference to the accompanying drawings, the above and other objects, features and advantages of the present application will become more apparent. The accompanying drawings described below are only some embodiments of the present application, and are not intended to limit the present application.

[0062] Figure 1A schematic diagram showing the composition of a new energy DC transmission system with a power consumption and storage integrated converter according to an exemplary embodiment is shown;

[0063] Figure 2 A schematic diagram of a consumption-storage integrated converter for a DC power transmission system according to an exemplary embodiment is shown;

[0064] Figure 3 A schematic diagram showing an energy consumption submodule in an integrated consumption and storage converter for a direct current transmission system according to an exemplary embodiment;

[0065] Figure 4a Another embodiment of a schematic diagram showing an exemplary energy consumption submodule in an integrated energy consumption and storage converter for a DC power transmission system;

[0066] Figure 4b Another embodiment of a schematic diagram showing an exemplary energy consumption submodule in an integrated energy consumption and storage converter for a DC power transmission system;

[0067] Figure 5 A schematic diagram showing an energy storage submodule in a consumption-storage integrated converter for a direct current transmission system according to an exemplary embodiment;

[0068] Figure 6 A flow chart showing a control method of a power consumption and storage integrated converter for a direct current transmission system according to an exemplary embodiment is shown. DETAILED DESCRIPTION

[0069] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0070] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices, etc. may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0071] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0072] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0073] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of example embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing the present application, and therefore cannot be used to limit the scope of protection of the present application.

[0074] With the continuous emergence of large-scale new energy bases, traditional energy systems and power grids are gradually developing towards new energy systems and new power grids. New energy depends on natural conditions of wind and solar power. Large-scale wind and solar new energy lacks frequency and power support capabilities when transmitted through DC. In order to prevent the system from being shut down due to power surplus when the AC power grid at the receiving end of the DC system fails, the existing offshore wind power DC system is equipped with energy-consuming converters on the DC side to consume surplus power. However, the energy consumed by the energy-consuming converter cannot be stored. At the same time, the energy-consuming system cannot effectively release energy to smooth the inherent fluctuations of new energy. When the AC power grid needs frequency and power support, it is even more difficult to provide additional power to support the system frequency. Therefore, some scholars have proposed the use of a full DC energy storage solution, but the full energy storage solution is expensive; and after the full energy storage energy is fully stored, if there is a power surplus, the DC system will be shut down, reducing the reliability of resisting power grid failures.

[0075] In response to the existing large-scale renewable energy DC transmission problems, this application proposes an integrated power consumption and storage converter for a DC transmission system and a control method thereof. The integrated power consumption and storage converter can effectively shift renewable energy fluctuations, enhance fault ride-through capability, and improve system safety and reliability. At the same time, it combines the advantages of energy storage and energy consumption to reduce the cost of offshore wind power and large-scale renewable energy transmission, and promote offshore wind power grid parity.

[0076] In the following, a consumption-storage integrated converter for a DC power transmission system and a control method thereof are described in detail in conjunction with embodiments.

[0077] Figure 1A schematic diagram showing the composition of a new energy DC transmission system with an integrated power consumption and storage converter according to an exemplary embodiment is shown.

[0078] like Figure 1 As shown, the new energy DC transmission system with integrated power consumption and storage converter includes a wind farm 210, a sending-end DC converter station 211, a receiving-end DC converter station 213, an integrated power consumption and storage converter 212 and a receiving-end power grid 214. The new energy DC transmission system mainly transmits new energy from large-scale wind farms to the receiving-end power grid.

[0079] According to some embodiments, when the receiving-end power grid 214 fails, the power of the wind farm 210 cannot change suddenly, and the sending-end wind farm 210 continues to provide power. However, 214 cannot transmit power due to the AC power grid voltage drop failure, resulting in a power surplus in the DC system. If no measures are taken when there is a power surplus, the DC voltage will rise and trip, causing the DC system to shut down. In order to avoid the shutdown of the DC system, the integrated power consumption and storage converter 212 is put into operation according to the DC voltage and surplus power to consume the surplus power.

[0080] Figure 2 A schematic diagram of a consumption-storage integrated converter for a direct current transmission system according to an exemplary embodiment is shown.

[0081] like Figure 2 As shown, the integrated energy consumption and storage converter includes M energy consumption submodules 201 and N energy storage submodules 203. The M energy consumption submodules 2011-201M and the N energy storage submodules 2031-203N are connected in series and then connected to a DC bus or line.

[0082] During normal operation, the voltage balance of M energy-consuming sub-modules and N energy storage sub-modules is achieved through sequencing control; the frequency and peak regulation of the power grid are supported by controlling the N energy storage sub-modules to smooth out the fluctuation of new energy; the energy storage sub-modules are controlled to consume the stored surplus power, and the remaining surplus power is consumed by the energy-consuming sub-modules to achieve DC system voltage stability; the number of energy-consuming sub-modules M is determined by the fault ride-through requirement, and the number of energy storage sub-modules N is determined by the power grid support requirement.

[0083] According to an exemplary embodiment, the energy consumption submodule 201 includes a DC capacitor branch, a bypass branch, and an energy consumption branch.

[0084] According to an example embodiment, the energy storage submodule 203 includes a power unit, a DC capacitor, a bypass switch, a first DC switch unit, and an energy storage unit.

[0085] Figure 3 A schematic diagram showing an energy consumption submodule in an integrated consumption and storage converter for a direct current transmission system according to an exemplary embodiment is shown.

[0086] like Figure 3As shown, the energy consumption submodule 201 includes a DC capacitor branch, a first bypass branch and an energy consumption branch, and the DC capacitor branch, the first bypass branch and the energy consumption branch are connected in parallel, wherein: the DC capacitor branch includes a first DC capacitor 306; the first bypass branch includes a first bypass switch 307 and a turning thyristor 308, wherein the first bypass switch 307 and the turning thyristor 308 are connected in parallel; the energy consumption branch includes an energy consumption first power unit 305 and an energy consumption circuit 309, the energy consumption first power unit 305 and the energy consumption circuit 309 are connected in series, the energy consumption first power unit 305 includes a controllable semiconductor 301 and a diode 302 connected in reverse parallel, and the energy consumption circuit 309 includes an energy consumption resistor 303 and a diode 304.

[0087] According to an example embodiment, the anode of the diode 302 is connected in series with the cathode of the diode 304 , and the cathode of the diode 304 is electrically connected with the cathode of the thyristor 308 .

[0088] According to an exemplary embodiment, the energy consumption sub-module includes a first terminal X1 and a second terminal X2, which are connected in parallel with the first bypass switch 307, the first terminal X1 is electrically connected to the cathode of the turning thyristor 308, and the second terminal X2 is electrically connected to the anode of the turning thyristor 308, and the first terminal X1 and the second terminal X2 are used to be connected in series with other energy consumption sub-modules.

[0089] According to an exemplary embodiment, the controllable semiconductor 301 of the first power unit of the energy consumption branch is turned on, and the energy consumption resistor 303 is used to consume energy. The power consumption Pch of a single energy consumption submodule is:

[0090] Pch=(Ucmch) 2 / R

[0091] Wherein, Ucmch is the voltage of the energy consumption submodule, and R is the energy consumption resistor 303 .

[0092] Figure 4a Another embodiment of the schematic diagram of an energy-consuming submodule in an exemplary integrated energy-consuming and energy-storage converter for a direct current transmission system is shown.

[0093] like Figure 4a As shown, the energy consumption submodule includes a first power unit, a DC capacitor branch, a first bypass branch and an energy consumption branch.

[0094] According to an exemplary embodiment, the DC capacitor branch includes a first DC capacitor 306; the first bypass branch includes a first bypass switch 307 and a transition thyristor 308, wherein the first bypass switch 307 and the transition thyristor 308 are connected in parallel; the energy consumption branch includes an energy consumption first power unit 305 and an energy consumption circuit 309, the energy consumption first power unit 305 and the energy consumption circuit 309 are connected in series, the energy consumption first power unit 305 includes a controllable semiconductor 301 and a diode 302, and the energy consumption circuit 309 includes an energy consumption resistor 303 and a diode 304; the first power unit includes a first switch module M1 and a second switch module M2, the first switch module M1 and the second switch module M2 are connected in series.

[0095] According to an example embodiment, the anode of the diode 302 is connected in series with the cathode of the diode 304 , and the anode of the diode 304 is electrically connected with the anode of the thyristor 308 .

[0096] According to an exemplary embodiment, the first power unit, the first bypass branch and the energy consumption branch are connected in parallel, and the first bypass switch 307 and the second switch module M2 are connected in parallel.

[0097] According to an exemplary embodiment, the energy consumption sub-module includes a first terminal X1 and a second terminal X2, which are connected in parallel with the first bypass switch 307, the first terminal X1 is electrically connected to the cathode of the turning thyristor 308, and the second terminal X2 is electrically connected to the anode of the turning thyristor 308, and the first terminal X1 and the second terminal X2 are used to be connected in series with other energy consumption sub-modules.

[0098] According to an example embodiment, the first switch module M1 is a diode 309 and the second switch module M2 is a diode 310 .

[0099] According to an example embodiment, the anode of the diode 309 is connected in series with the cathode of the diode 310 , and the anode of the diode 310 is electrically connected to the second connection terminal X2 .

[0100] According to an exemplary embodiment, the controllable semiconductor 301 of the first power unit of the energy consumption branch is turned on, and the energy consumption resistor 303 is used to consume energy. The power consumption Pch of a single energy consumption submodule is:

[0101] Pch=(Ucmch) 2 / R

[0102] Wherein, Ucmch is the voltage of the energy consumption submodule, and R is the energy consumption resistor 303 .

[0103] Figure 4b Another embodiment of the schematic diagram of an energy-consuming submodule in an exemplary integrated energy-consuming and energy-storage converter for a direct current transmission system is shown.

[0104] Figure 4b The circuit shown is Figure 4a The circuits shown are essentially the same, with the following differences: Figure 4b In the embodiment, the first switch module M1 includes a turn-off semiconductor 311 and a diode 309 connected in reverse parallel, and the second switch module M2 includes a turn-off semiconductor 312 and a diode 310 connected in reverse parallel.

[0105] Figure 5 A schematic diagram showing an energy storage submodule in an integrated energy storage converter for a direct current transmission system according to an exemplary embodiment is shown.

[0106] like Figure 5 As shown, the energy storage submodule includes a half-bridge submodule 413 and an energy storage unit 405 connected in parallel; wherein the half-bridge submodule 413 includes a second power unit, a second DC capacitor 406 and a second bypass branch; the second power unit and the second DC capacitor 406 are connected in parallel; the second bypass branch includes a bypass switch 407 and a thyristor 408 connected in parallel.

[0107] According to an example embodiment, the second power unit includes a third switch module M3 and a fourth switch module M4, the third switch module M3 and the fourth switch module M4 are connected in series; the bypass switch 407 is connected in parallel with the fourth switch module M4.

[0108] According to an example embodiment, the first switch module ( M1 ) includes a turn-off semiconductor 411 and a diode 409 connected in reverse parallel, and the fourth switch module M4 includes a turn-off semiconductor 412 and a diode 410 connected in reverse parallel.

[0109] According to an example embodiment, the energy storage submodule includes a third terminal X3 and a fourth terminal X4, which are connected in parallel with the bypass switch 407, the third terminal X3 is electrically connected to the cathode of the turning thyristor 408, and the fourth terminal X4 is electrically connected to the anode of the turning thyristor 408, and the third terminal X3 and the fourth terminal X4 are used to be connected in series with other energy storage submodules.

[0110] According to some embodiments, the energy storage unit 405 includes an energy storage element 401 and a DC bypass switch 402 . The positive electrode of the energy storage element 401 is connected to the DC bypass switch 402 and then to the positive electrode of the second DC capacitor 406 . The negative electrode of the energy storage element 401 is connected to the negative electrode of the second DC capacitor 406 .

[0111] According to some embodiments, the energy storage unit 401 includes batteries connected in series, cascade batteries, supercapacitors, flywheel energy storage, gas compression energy storage, or any combination thereof.

[0112] According to some embodiments, considering the input requirements of passive energy storage elements, the DC bypass switch 402 is connected in parallel with a starting loop, and the starting loop includes a starting resistor 403 and a switch 404 connected in series.

[0113] According to some embodiments, when the second DC capacitor 406 is connected to the energy storage element 401, the switch 404 is first closed to connect the starting resistor 403 in series to prevent the energy storage element 401 from being short-circuited through the capacitor. When the second DC capacitor 406 is fully charged, the DC switch 402 is closed and the switch 404 is opened to cut off the starting resistor 403.

[0114] According to some embodiments, in order to protect the energy storage device, a fuse 414 is added between the second DC capacitor 406 and the energy storage element 401 . When an overcurrent occurs, the fuse 414 blows to protect the energy storage element 401 .

[0115] by Figure 1 For example, when a fault occurs in the receiving end AC grid 214, the input power is determined according to the DC voltage of the DC transmission system and the surplus power of the DC transmission system. Figure 2 The number of energy-consuming submodules and the number of energy-storage submodules in the integrated energy-consuming and energy-storage converter shown consume surplus power.

[0116] Figure 6 A flow chart showing a control method of a power consumption and storage integrated converter for a direct current transmission system according to an exemplary embodiment is shown.

[0117] like Figure 6 As shown, during a fault period, the number of energy-consuming submodules and the number of energy-storage submodules to be put into operation are determined according to the DC voltage of the DC transmission system and the surplus power of the DC transmission system to consume the surplus power.

[0118] S610, the integrated power consumption and storage converter is running.

[0119] According to an example embodiment, a DC power transmission system uses a power consumption and storage integrated converter for operation.

[0120] S620: It is detected that the DC voltage increases.

[0121] According to an example embodiment, it is monitored that a fault occurs in the receiving-end AC power grid and the DC voltage increases.

[0122] S630: Calculate surplus power and redundant energy.

[0123] According to an exemplary embodiment, the surplus power is calculated based on the system fault ride-through tolerance time requirement, the DC voltage, and the power of the transmitting and receiving ends. The surplus power is calculated by:

[0124] Prest=Psend-Pdc-Ploss

[0125] Among them, Prest is the surplus power, Psend is the current DC system sending end transmission power, Pdc is the actual transmission power of the receiving end converter station during the fault period, and Ploss is the DC cable and converter station loss. Generally, Ploss can be set to 0.

[0126] According to an exemplary embodiment, the redundant energy that needs to be stored is calculated based on the calculated surplus power Prest and the system fault ride-through tolerance time Ts:

[0127] Wrest=Prest*Ts

[0128] Wherein, Wrest is the redundant energy.

[0129] According to some embodiments, the system fault ride-through tolerance time Ts is determined by the wind turbine access system ride-through and is at least 625 ms.

[0130] According to an exemplary embodiment, the integrated energy storage converter calculates the state of charge (SOC) of the remaining energy storage units in real time, and calculates the maximum energy Wbat that can be absorbed by the energy storage.

[0131] S640, determining whether the maximum energy Wbat that can be absorbed by the energy storage is greater than or equal to the redundant energy Wrest.

[0132] According to an exemplary embodiment, it is determined whether the energy storage remaining energy Wbat is greater than or equal to the redundant energy Wrest, where the redundant energy is the maximum fault ride-through required energy of the surplus power.

[0133] S650, the energy storage submodule is put into use to absorb surplus power.

[0134] According to an exemplary embodiment, if the maximum energy Wbat that can be absorbed by the energy storage is greater than or equal to the redundant energy Wrest, the energy storage submodule is activated to absorb the surplus power through voltage control.

[0135] S660, the energy storage submodule and the energy consumption submodule are put into use to absorb surplus power.

[0136] According to an exemplary embodiment, if the maximum energy Wbat that can be absorbed by the energy storage is less than the redundant energy Wrest, the excess energy is absorbed by the energy consumption submodule, and the number of energy storage submodules and energy consumption submodules to be put into use needs to be calculated, where:

[0137] The number of energy-consuming submodules put into operation is n = Pch_all / Pch,

[0138] Wherein, Pch is the power of each energy-consuming submodule, Pch_all is the power required to be absorbed by the energy consumption, and Pch_all=(Wrest-Wbat) / Ts.

[0139] The number of energy storage submodules put into use is calculated by the energy storage SOC control, and can be calculated based on the voltage control or current control PI loop.

[0140] S670, exit the integrated power consumption and storage converter.

[0141] According to the exemplary embodiment, the AC fault is cleared, the DC voltage is restored, and the integrated power consumption and storage converter is exited.

[0142] According to some embodiments, the number M of energy-consuming submodules may be configured according to the requirements of system fault ride-through. It is first assumed that the energy storage submodule is in a full capacity state and cannot store energy:

[0143] 1) When the system needs to traverse a single-phase fault and restart, the number of energy-consuming submodules M is greater than or equal to 1 / 3 of the total number of submodules (M+N);

[0144] 2) When the system needs to traverse a phase-to-phase fault and restart, the number of energy-consuming submodules M is greater than or equal to 1 / 2 of the total number of submodules (M+N).

[0145] After the energy consumption sub-modules are determined, the remaining sub-modules can be configured as energy consumption sub-modules or energy storage sub-modules according to system requirements.

[0146] According to some embodiments, a basic control method of a power consumption and storage integrated converter for a DC power transmission system includes: based on the voltage size sorting of module capacitors, the voltage of the energy consumption submodule capacitor and the voltage of the energy storage submodule capacitor are balanced by controlling the switching of power units; based on the voltage size sorting of module capacitors, the state of charge (SOC) of the remaining energy storage units is balanced by switching the power units of the energy storage submodules; based on the voltage size sorting of module capacitors, the voltage balance control of the submodule capacitors is achieved by switching the energy consumption branches of the energy consumption submodules. Among them, the energy storage submodule consumes energy by turning on the turnable semiconductor 411 of the first switch module M1 of the energy storage submodule or turning on the turnable semiconductor 413 of the second switch module M2 of the energy storage submodule.

[0147] The present application provides an integrated power consumption and storage converter for a DC power transmission system that can effectively support the system frequency and power. When the AC system requires the DC power transmission system to provide more power to support the system frequency and power, the first switch module M1 controllable semiconductor device 411 of the energy storage submodule is actively switched through current control to realize energy storage and inject power into the DC power transmission system.

[0148] When the AC system requires the DC system to reduce the injected power to lower the system frequency, the controllable semiconductor device 413 of the second switch module M2 of the energy storage submodule is preferentially switched on to enable the energy storage submodule to absorb power from the DC transmission system, or actively absorb power through SOC current control; after the energy storage submodule absorbs power exceeding its capacity limit, the power semiconductor of the energy-consuming branch of the energy-consuming submodule can be opened to absorb more power.

[0149] The present application provides a power consumption and storage integrated converter for a direct current transmission system and a control method thereof, which can utilize the power consumption and storage integrated converter to store surplus power in the energy storage submodule; when the energy storage submodule is fully loaded, the number M of configured energy consumption submodules can meet the single-phase and phase-to-phase fault ride-through requirements, meet the three-phase fault ride-through requirements, and improve the stability of flexible direct current operation; at the same time, the power consumption and storage integrated converter can effectively smooth out the fluctuation of new energy, enhance the fault ride-through capability, improve the safety and reliability of the system, possess the advantages of energy storage and energy consumption, reduce the cost of offshore wind power and large-scale new energy transmission, and promote the grid parity of offshore wind power.

[0150] It should be clearly understood that the present application describes how to form and use specific examples, but the present application is not limited to any details of these examples. On the contrary, based on the teaching of the content disclosed in the present application, these principles can be applied to many other embodiments.

[0151] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present application, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0152] The exemplary embodiments of the present application are specifically shown and described above. It should be understood that the present application is not limited to the detailed structures, configurations or implementations described herein; on the contrary, the present application is intended to cover various modifications and equivalent configurations included in the spirit and scope of the appended claims.

Claims

1. A power consumption and storage integrated converter for a DC power transmission system, characterized in that: The integrated energy consumption and storage converter comprises at least one energy consumption submodule and at least one energy storage submodule, wherein the energy consumption submodule and the energy storage submodule are connected in series and then connected to a DC line, wherein: The energy storage submodule is used to store the surplus power of the DC power transmission system; The energy consumption submodule is used to consume the surplus power; The energy storage submodule and the energy consumption submodule cooperate to support the frequency and power regulation requirements of the power grid, wherein: When the maximum energy that can be absorbed by the energy storage submodule is greater than or equal to the redundant energy, the energy storage submodule is put into use, wherein the redundant energy can be calculated according to the surplus power; When the maximum energy that can be absorbed by the energy storage submodule is less than the redundant energy, the energy storage submodule and the energy consumption submodule are put into use.

2. The integrated power converter according to claim 1, characterized in that: The energy consumption submodule includes a DC capacitor branch, a first bypass branch and an energy consumption branch, wherein: The DC capacitor branch, the first bypass branch and the energy consumption branch are connected in parallel; The DC capacitor branch includes a first DC capacitor; The first bypass branch includes a first bypass switch and a turn-on thyristor connected in parallel; The energy consumption branch includes an energy consumption power unit and an energy consumption circuit connected in series.

3. The integrated power consumption and storage converter according to claim 2, characterized in that: The energy consumption power unit includes a controllable semiconductor and a first diode connected in reverse parallel, and the energy consumption circuit includes an energy consumption resistor and a second diode connected in parallel.

4. The integrated power consumption and storage converter according to claim 1, characterized in that: The energy consumption submodule includes: a DC capacitor branch, a first bypass branch, an energy consumption branch and a first power unit, wherein: The DC capacitor branch, the energy consumption branch and the first power unit are connected in parallel; The DC capacitor branch includes a first DC capacitor; The first bypass branch includes a first bypass switch and a turn-on thyristor connected in parallel; The energy consumption branch includes an energy consumption power unit and an energy consumption circuit connected in series; The first power unit includes a first switch module and a second switch module connected in series; The second switch module is connected in parallel with the first bypass switch.

5. The integrated power consumption and storage converter according to claim 4, characterized in that: The first switch module and the second switch module respectively include a diode, or a turn-off semiconductor and a diode connected in reverse parallel; The anode of the turning thyristor is electrically connected to the anode of the diode of the second switch module; The cathode of the thyristor is electrically connected to the cathode of the diode of the second switch module.

6. The integrated power consumption and storage converter according to claim 2, characterized in that: The energy consumption submodule further includes a first wiring terminal and a second wiring terminal, wherein the first wiring terminal is electrically connected to the cathode of the turn thyristor, and the second wiring terminal is electrically connected to the anode of the turn thyristor.

7. The integrated power consumption and storage converter according to claim 1, characterized in that: The energy storage submodule comprises a half-bridge submodule and an energy storage unit connected in parallel, wherein: The half-bridge submodule includes a second power unit, a second DC capacitor and a second bypass branch, the second power unit and the second DC capacitor are connected in parallel, the second power unit includes a third switch module and a fourth switch module connected in series, the fourth switch module is connected in parallel with the second bypass branch, and the second bypass branch includes a second bypass switch and a thyristor connected in parallel; The energy storage unit includes an energy storage element and a DC bypass switch connected in series, the positive electrode of the energy storage element is electrically connected to the positive electrode of the second DC capacitor, and the negative electrode of the energy storage element is electrically connected to the negative electrode of the second DC capacitor.

8. The integrated power consumption and storage converter according to claim 7, characterized in that: The third switch module and the fourth switch module respectively include a turn-off semiconductor and a diode connected in reverse parallel; The cathode of the diode of the fourth switch module is electrically connected to the cathode of the thyristor of the second bypass branch, and the anode of the diode of the fourth switch module is electrically connected to the anode of the thyristor of the second bypass branch.

9. The integrated power consumption and storage converter according to claim 7, characterized in that: The energy storage submodule includes a third terminal and a fourth terminal, the third terminal is electrically connected to the cathode of the thyristor of the second bypass branch, and the fourth terminal is electrically connected to the anode of the thyristor of the second bypass branch.

10. The integrated power consumption and storage converter according to claim 7, characterized in that: The energy storage element includes batteries connected in series, cascade batteries, supercapacitors, flywheel energy storage, gas compression energy storage or any combination thereof.

11. The integrated power consumption and storage converter according to claim 8, characterized in that: Also includes: When the AC system needs the DC transmission system to provide more power to support the system frequency, switching on the turn-off semiconductor of the third switch module of the energy storage submodule; When the AC system requires the DC power transmission system to reduce the injected power or lower the system frequency, the turnable semiconductor of the fourth switch module of the energy storage submodule is controlled or switched by current; After the energy of the energy storage submodule exceeds the limit, the energy consumption branch of the energy consumption submodule is put into use to absorb power.

12. A method for controlling a power consumption and storage integrated converter for a DC power transmission system, characterized in that: Used to control the integrated power consumption and storage converter according to any one of claims 1 to 11, the control method comprising: In response to the DC voltage increasing, calculating surplus power; Calculating redundant energy according to the surplus power; Calculate the maximum energy that the energy storage can absorb; Comparing the redundant energy with the maximum energy that can be absorbed by the energy storage to obtain a comparison result; Based on the comparison result, the energy storage submodule and / or the energy consumption submodule are put into operation.

13. The control method according to claim 12, characterized in that: The calculation of surplus power includes: The surplus power is calculated based on the current DC system sending-end transmission power, the actual transmission power of the receiving-end converter station during the fault period, and the losses of the DC cable and the converter station.

14. The control method according to claim 13, characterized in that: The calculating the redundant energy according to the surplus power comprises: The redundant energy is calculated according to the surplus power and the system fault ride-through tolerance time.

15. The control method according to claim 12, characterized in that: The calculation of the maximum energy that the energy storage can absorb includes: The maximum energy that can be absorbed by the energy storage is obtained by calculating the charge state of the energy storage unit of the energy storage submodule.

16. The control method according to claim 14, characterized in that: Based on the comparison result, investing in the energy storage submodule and / or the energy consumption submodule includes: When the maximum energy that can be absorbed by the energy storage is greater than or equal to the redundant energy, the energy storage submodule is put into use; When the maximum energy that can be absorbed by the energy storage is less than the redundant energy, the energy storage submodule and the energy consumption submodule are put into use.

17. The control method according to claim 16, characterized in that: Also includes: The power required for energy consumption is calculated according to the redundant energy, the maximum energy that can be absorbed by the energy storage and the system fault ride-through tolerance time, and the number of energy consumption submodules invested is calculated according to the power required for energy consumption and the power of one energy consumption submodule; The number of the energy storage submodules put into operation is calculated according to the charge state of the energy storage submodule.

18. The control method according to claim 12, characterized in that: Also includes: When the AC system needs the DC transmission system to provide more power to support the system frequency, the energy storage submodule is switched on and off through current control.

Images