Hybrid direct-current energy consumption device and control method thereof

Abstract

The invention relates to the technical field of flexible direct-current power transmission, in particular to a hybrid direct-current energy consumption device and a control method thereof, and the device comprises an energy consumption valve which comprises a plurality of submodules connected in series; the centralized energy consumption resistor is connected with the energy consumption valve in series, and the energy consumption valve and the centralized energy consumption resistor which are connected in series are arranged at the two ends of the direct current bus; wherein each sub-module is provided with a battery energy storage unit, and the battery energy storage unit can switch charging and discharging states. The advantages of centralized energy consumption and distributed energy consumption are integrated, and better electrical characteristics and expansibility are achieved. And energy storage is introduced on the basis of energy consumption, so that the system power is balanced more effectively, and the bus voltage is kept stable. The problem that a traditional hybrid direct current energy consumption device is complex in structure and control logic is solved, and the maintenance cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC power transmission, and in particular to a hybrid DC energy dissipation device and its control method. Background Art

[0002] Since the flexible DC power transmission technology can independently adjust the active power and reactive power, realize power transmission to a passive network, and adopts fully controlled devices and PWM (Pulse Width Modulation) technology, which is flexible and variable in control, at present, the flexible DC power transmission technology is mainly used for the transmission of large-scale distributed long-distance offshore wind power.

[0003] When a short-circuit open-phase fault occurs at the receiving-end converter station, the power transmitted by the system to the power grid decreases, and the power generation system cannot respond quickly, resulting in power imbalance in the system. The excess power accumulates on the DC bus, causing the DC voltage to rise.

[0004] The excessively high bus voltage will threaten the system stability and can cause large-area paralysis of the system in severe cases. Adding a DC energy dissipation device on the DC bus side is one of the effective solutions to solve the above problems. When the DC bus voltage rises, the DC energy dissipation device is started to consume the surplus power to reduce the DC bus voltage, thereby maintaining the overall stability of the system. However, as a DC system protection device, the DC energy dissipation device is only put into operation in the case of AC system faults, etc. The number of its annual inputs is limited in actual operation, and the steady-state loss under long-term energization will be unfavorable to the operation economy of the system.

[0005] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The present invention provides a hybrid DC energy dissipation device and its control method, thus effectively solving the problems in the background art.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a hybrid DC energy dissipation device, comprising: An energy dissipation valve, the energy dissipation valve includes a plurality of series-connected sub-modules; A centralized energy dissipation resistor, the centralized energy dissipation resistor is connected in series with the energy dissipation valve, and the series-connected energy dissipation valve and centralized energy dissipation resistor are arranged at both ends of the DC bus; Wherein, each of the sub-modules is provided with a battery energy storage unit, and the battery energy storage unit can switch the charge and discharge states.

[0008] Further, each of the sub-modules includes a half-bridge sub-module, and the half-bridge sub-module includes: Two insulated gate bipolar transistors (IGBTs) that are complementary and conduct in series; A capacitor module connected in parallel to the series branch of the two IGBTs, and the battery energy storage unit is connected in parallel across the two ends of the capacitor module; Wherein, when both of the two IGBTs are turned off, the half-bridge sub-module is in a locked state, and when one of the IGBTs is turned on and the other IGBT is turned off, the half-bridge sub-module is in an inserted or removed state.

[0009] Further, the battery energy storage unit includes: A bidirectional DC / DC converter, which is connected in parallel across the two ends of the capacitor module and includes an upper transistor and a lower transistor connected in series; An inductor and a battery pack, which are connected in series with each other and are connected in parallel across the two ends of the lower transistor.

[0010] Further, the bidirectional DC / DC converter includes a boost mode and a buck mode; in the boost mode, the upper transistor is always turned off and the lower transistor is turned on, and the battery pack discharges to the capacitor module; in the buck mode, the upper transistor is turned on and the lower transistor is always turned off, and the capacitor module charges the battery pack.

[0011] Further, the number of the sub-modules and the resistance value of the centralized energy-consuming resistor are matched with the power level of the system.

[0012] The present invention further includes a control method for a hybrid DC energy-consuming device, which controls the device as described above, and the method includes the following steps: Obtain the surplus power of the system, and according to the surplus power of the system, control the insertion and removal states of the sub-modules of the energy-consuming valve and the charge and discharge states of the battery energy storage unit; According to the condition that the DC bus voltage drops due to the system being disturbed, control the state of the battery energy storage unit in the sub-module to switch the charge and discharge states of the battery energy storage unit.

[0013] Further, the step of controlling the insertion and removal states of the sub-modules of the energy-consuming valve and the charge and discharge states of the battery energy storage unit according to the surplus power of the system includes: When the surplus power of the system is within a preset range, control the battery energy storage unit to be in a charging state so that the energy-consuming power matches the surplus power of the system; When the surplus power of the system exceeds the preset range, control the sub-module of the energy-consuming valve and the battery energy storage unit to consume the surplus power simultaneously, so that the energy-consuming power matches the system surplus power, and the surplus power consumed by the sub-module is greater than the surplus power consumed by the battery energy storage unit. After the sub-module consumes the surplus power, the battery energy storage unit absorbs the remaining surplus power.

[0014] Further, according to the condition of the DC bus voltage drop caused by system disturbance, controlling the state of the battery energy storage unit in the sub-module to switch the charge and discharge state of the battery energy storage unit includes: When the system is disturbed and the DC bus voltage drops, control the battery energy storage unit to discharge to maintain the DC bus voltage.

[0015] The beneficial effects of the present invention are as follows: The present invention combines the advantages of centralized and distributed energy consumption, has better electrical characteristics and expandability. Energy storage is also introduced on the basis of energy consumption to more effectively balance the system power and maintain the stability of the bus voltage. It solves the problems of complex structure and control logic existing in traditional hybrid DC energy-consuming devices and reduces the maintenance cost. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is the topological structure diagram of the hybrid DC energy-consuming device; Figure 2 It is the DC bus voltage diagram under the condition of voltage reduction; Figure 3 It is the DC bus voltage diagram when the surplus power is large under the condition of voltage rise; Figure 4 It is the DC bus voltage diagram when the surplus power is small under the condition of voltage rise. Detailed Embodiments

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0019] Embodiment 1: As Figure 1 shown: A hybrid DC energy-consuming device includes: An energy-consuming valve, and the energy-consuming valve includes a plurality of serially connected sub-modules; A centralized energy-consuming resistor, the centralized energy-consuming resistor is connected in series with an energy-consuming valve, and the series-connected energy-consuming valve and the centralized energy-consuming resistor are arranged at both ends of the DC bus; Among them, each sub-module is provided with a battery energy storage unit, and the battery energy storage unit can switch the charge and discharge states.

[0020] When a fault occurs in the receiving-end converter station and the DC bus voltage rises too high due to excessive power surplus in the transmission line, a centralized resistor can be used to consume most of the surplus power, and the battery energy storage unit in the sub-module absorbs the remaining power; for some small disturbance surplus power that causes a small rise in the DC bus voltage, there is no need to pass through the centralized energy-consuming resistor, and it can be directly absorbed by charging the battery energy storage unit in the sub-module; and when the DC bus voltage is disturbed and decreases, the battery energy storage unit in the sub-module discharges to make up for it, thereby maintaining the stability of the DC bus voltage.

[0021] It combines the advantages of centralized and distributed energy consumption, has better electrical characteristics and expandability. It also introduces energy storage on the basis of energy consumption, which can more effectively balance the system power and maintain the stability of the bus voltage. It solves the problems of complex structure and control logic existing in traditional hybrid DC energy-consuming devices, and reduces the maintenance cost.

[0022] In this embodiment, each sub-module includes a half-bridge sub-module, and the half-bridge sub-module includes: Two insulated gate bipolar transistors IGBTs connected in series and complementary conduction; A capacitor module connected in parallel on the series branch of the two IGBTs, and the battery energy storage unit is connected in parallel at both ends of the capacitor module; Among them, when both IGBTs are turned off, the half-bridge sub-module is in the locked state, and when one IGBT is turned on and the other IGBT is turned off, the half-bridge sub-module is in the input or cut-off state.

[0023] The battery energy storage unit includes: A bidirectional DC / DC converter, the bidirectional DC / DC converter is connected in parallel at both ends of the capacitor module, and includes an upper transistor and a lower transistor connected in series; An inductor and a battery pack, the inductor and the battery pack are connected in series with each other and are connected in parallel at both ends of the lower transistor.

[0024] The bidirectional DC / DC converter includes a boost mode and a buck mode; in the boost mode, the upper transistor is always turned off and the lower transistor is turned on, and the battery pack discharges to the capacitor module; in the buck mode, the upper transistor is turned on and the lower transistor is always turned off, and the capacitor module charges the battery pack.

[0025] As a preference of the above embodiment, the number of sub-modules and the resistance value of the centralized energy-consuming resistor match the power level of the system.

[0026] This embodiment also includes a control method for a hybrid DC energy dissipation device to control the device as described above. The method includes the following steps: Obtain the system surplus power, and control the input and output states of the sub-modules of the energy dissipation valve and the charge and discharge states of the battery energy storage unit according to the system surplus power; According to the condition that the DC bus voltage drops due to system disturbance, control the state of the battery energy storage unit in the sub-module to switch the charge and discharge states of the battery energy storage unit.

[0027] Among them, controlling the input and output states of the sub-modules of the energy dissipation valve and the charge and discharge states of the battery energy storage unit according to the system surplus power includes: When the system surplus power is within the preset range, control the battery energy storage unit to be in the charging state so that the energy dissipation power matches the system surplus power; When the system surplus power exceeds the preset range, control the sub-modules of the energy dissipation valve and the battery energy storage unit to consume the surplus power simultaneously so that the energy dissipation power matches the system surplus power, and the surplus power consumed by the sub-modules is greater than the surplus power consumed by the battery energy storage unit. After the sub-modules consume, the battery energy storage unit absorbs the remaining surplus power.

[0028] As an optimization of the above embodiment, controlling the state of the battery energy storage unit in the sub-module to switch the charge and discharge states of the battery energy storage unit according to the condition that the DC bus voltage drops due to system disturbance includes: When the system disturbance causes the DC bus voltage to drop, control the battery energy storage unit to discharge to maintain the DC bus voltage.

[0029] Embodiment 2: As Figure 1 shown, this embodiment includes a hybrid DC energy dissipation device. The hybrid DC energy dissipation device includes an energy dissipation valve composed of a plurality of sub-modules connected in series and a centralized energy dissipation resistor. Each sub-module in the energy dissipation valve includes a half-bridge sub-module and a battery energy storage unit. The battery pack is connected in parallel to both ends of the capacitor of the half-bridge sub-module through a bidirectional DC / DC converter. Each half-bridge sub-module includes two IGBTs: , , and the two are complementary to conduct. The half-bridge sub-module has three working states: the locked state (the upper tube is turned off, the lower tube is turned off), the removed state (the upper tube is turned off, the lower tube is turned on), and the input state (the upper tube is turned on, the lower tube is turned off). The battery energy storage unit includes a bidirectional DC / DC converter, an energy storage filter inductor L, and a battery 。The battery pack exchanges energy with the sub-module capacitors through a bidirectional DC / DC converter to maintain the stability of the DC bus voltage. The bidirectional DC / DC converter changes the operating states of the switches and to make the converter operate in the Boost mode and the Buck mode. Among them, in the Boost mode, is always turned off, is turned on, and the battery pack discharges to the sub-module capacitors; in the Buck mode, is always turned off, is turned on, and the sub-module capacitors charge the battery pack. When the switch is turned on, S takes the value of 1, and when the switch is turned off, S takes the value of 0.

[0030] The specific steps are as follows: Step 1: Select to establish a smaller system. Adopting a small-capacity system can reduce the number of sub-modules and maximize the simulation speed with larger individual parameters, which is beneficial for the study of principles and feasibility; in this embodiment, the DC bus voltage of the constructed power system is 50 kV. According to the selection of IGBT power devices, the rated operating voltage of the sub-module capacitors is determined to be 12.5 kV. From this, the number N of sub-modules of the DC energy-consuming device can be calculated as 4, and the concentrated energy-consuming resistor is 200 Ω, and the sub-module capacitor is 1 mF; Step 2: Introduce a battery energy storage unit and determine the battery type according to the established power system. The selected lithium battery has a rated voltage of 10 kV and a rated capacity of 1000 Ah; the energy storage filter inductor L is 5 mH; Step 3: Connect the hybrid DC energy-consuming device in parallel at the DC bus; Verification experiment; In the case of configuring the hybrid DC energy-consuming device, a fault is simulated at 0.5 s, and the load resistance is reduced from 200 Ω to 100 Ω. At this time, the load current increases to 50% of the rated current, and the DC bus voltage drops. The device is put into operation at 0.6 s until the fault is eliminated at 2 s. The DC bus voltage of the system is as Figure 2 shown. At 0.5 s, due to the sudden decrease in the load, the DC voltage drops. The device is put into operation at 0.6 s, and the battery discharges, causing the bus voltage to rise and recover at approximately 0.807 s.

[0031] For the case of generating surplus power, verification is also carried out separately.

[0032] First, in the case of large disturbances and large surplus power, a fault is simulated at 0.5 s, and the load resistance is increased from 200 Ω to 400 Ω. At this time, the load current decreases to 50% of the rated current, and the DC bus voltage rises. The device is put into operation at 0.6 s until the fault is eliminated at 2 s. The DC bus voltage of the system is asFigure 3 As shown. At 0.5 s, due to a sudden increase in the load, the DC voltage rises. The device is put into operation at 0.6 s. According to the surplus power, some sub-modules are cut off. The voltage of the cut-off sub-modules is transferred to the centralized energy-consuming resistor, and at the same time, the batteries of the uncut sub-modules are charged, causing the bus voltage to decrease and quickly recover at about 0.622 s.

[0033] When the disturbance is small and the surplus power is small, there is no need to cut off the energy-consuming valve sub-modules, and the surplus power can be directly absorbed by charging the batteries in the sub-modules. A fault is simulated at 0.5 s, and the load resistance is increased from 200 Ω to 220 Ω, causing the DC bus voltage to rise. Energy consumption starts at 0.6 s until the fault is eliminated at 2 s. The DC bus voltage of the system is as Figure 4 As shown. At 0.5 s, due to a sudden increase in the load, the DC voltage rises. Energy consumption starts at 0.6 s and is directly absorbed by charging the batteries in the sub-modules, causing the DC bus voltage to decrease and recover at about 0.742 s.

[0034] This embodiment verifies the feasibility and effectiveness of the proposed hybrid DC energy-consuming device, and the stability of the DC bus voltage is improved.

[0035] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. The meaning of "a plurality" is two or more unless otherwise specifically defined.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0038] Any process or method description represented in the flowchart or described in other ways herein can be understood to represent a module, segment, or portion of code including one or more executable instructions for implementing a specific logical function or process, and the scope of the preferred embodiments of the present invention includes additional implementations, where the functions can be executed in a manner other than shown or discussed, including in a substantially simultaneous manner or in a reverse order according to the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention pertain.

[0039] The logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or in connection with these instruction execution systems, apparatus, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection portion having one or more wirings (electronic device), a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other appropriate processing as necessary, and then stored in a computer memory.

[0040] It should be understood that each part of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one or a combination of the following technologies well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0041] Those of ordinary skill in the art can understand that all or part of the steps carried by the method of the above embodiments can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiments.

[0042] The above-mentioned storage medium can be a read-only memory, a magnetic disk, an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A hybrid DC energy dissipation device, characterized in that, Including: A power-consuming valve, the power-consuming valve includes a plurality of serially-connected sub-modules; A centralized power-consuming resistor, the centralized power-consuming resistor is connected in series with the power-consuming valve, and the serially-connected power-consuming valve and centralized power-consuming resistor are arranged at both ends of the DC bus; Wherein, each of the sub-modules is provided with a battery energy storage unit, and the battery energy storage unit can switch the charge and discharge states.

2. The hybrid DC energy dissipation device according to claim 1, wherein Each of the sub-modules includes a half-bridge sub-module, and the half-bridge sub-module includes: Two insulated gate bipolar transistors IGBTs that are connected in series and conduct complementarily; A capacitor module connected in parallel on the series branch of the two IGBTs, and the battery energy storage unit is connected in parallel at both ends of the capacitor module; Wherein, when both of the two IGBTs are turned off, the half-bridge sub-module is in a locked state, and when one of the IGBTs is turned on and the other IGBT is turned off, the half-bridge sub-module is in an input or cut-off state.

3. The hybrid DC energy dissipation device according to claim 2, wherein The battery energy storage unit includes: A bidirectional DC / DC converter, the bidirectional DC / DC converter is connected in parallel at both ends of the capacitor module, and includes an upper transistor and a lower transistor connected in series; An inductor and a battery pack, the inductor and the battery pack are connected in series with each other and are connected in parallel at both ends of the lower transistor.

4. The hybrid DC energy dissipation device according to claim 3, wherein, The bidirectional DC / DC converter includes a boost mode and a buck mode; in the boost mode, the upper transistor is always turned off and the lower transistor is turned on, and the battery pack discharges to the capacitor module; in the buck mode, the upper transistor is turned on and the lower transistor is always turned off, and the capacitor module charges the battery pack.

5. The hybrid DC energy dissipation device according to claim 1, wherein The number of the sub-modules and the resistance value of the centralized power-consuming resistor match the power level of the system.

6. A control method for a hybrid DC energy dissipation device, characterized in that, Controlling the device according to any one of claims 1 to 5, the method includes the following steps: Obtain the surplus power of the system, and according to the surplus power of the system, control the input and output states of the sub-modules of the power-consuming valve and the charge and discharge states of the battery energy storage unit; According to the condition that the DC bus voltage drops due to the system being disturbed, control the state of the battery energy storage unit in the sub-module to switch the charge and discharge states of the battery energy storage unit.

7. The control method of the hybrid DC energy dissipation device according to claim 6, characterized in that, The controlling the input and output states of the sub-modules of the power-consuming valve and the charge and discharge states of the battery energy storage unit according to the surplus power of the system includes: When the surplus power of the system is within a preset range, control the battery energy storage unit to be in a charging state so that the power consumption matches the surplus power of the system; When the surplus power of the system exceeds the preset range, control the sub-modules of the power-consuming valve and the battery energy storage unit to consume the surplus power simultaneously so that the power consumption matches the surplus power of the system, and the surplus power consumed by the sub-modules is greater than the surplus power consumed by the battery energy storage unit. After the sub-modules consume, the battery energy storage unit absorbs the remaining surplus power.

8. The control method of the hybrid DC energy dissipation device according to claim 6, characterized in that, The controlling the state of the battery energy storage unit in the sub-module to switch the charge and discharge states of the battery energy storage unit according to the condition that the DC bus voltage drops due to the system being disturbed includes: When the system is disturbed and the DC bus voltage drops, control the battery energy storage unit to discharge to maintain the DC bus voltage.

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