Dynamic connection device of multi-stage voltage distribution network and control method of dynamic connection device

Abstract

The invention relates to a dynamic connection device of a multistage voltage distribution network and a control method thereof, and the device comprises a medium-voltage modular multilevel converter, one end of which is connected with a first AC power grid, and which is used for converting a first AC output by the first AC power grid into a first DC; one end of the medium voltage-low voltage direct current conversion assembly is connected with the other end of the medium voltage modular multilevel converter, and the medium voltage-low voltage direct current conversion assembly is used for converting the first direct current into second direct current; one end of the low-voltage flexible interconnection assembly is connected with the other end of the medium voltage-low voltage direct current conversion assembly, and the other end of the low-voltage flexible interconnection assembly is connected with a plurality of second alternating current power grids and used for converting the second direct current into the second alternating current. Therefore, the problems of low power density, poor adaptability, low economic benefit and the like in the prior art are solved. The power density of the device is improved, and the adaptability of the system and the economic benefits of products are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a dynamic connection device for a multi-level voltage distribution network and a control method thereof. Background Art

[0002] With the increasing penetration rate of distributed power sources on the source side of the distribution network, and the changing interface properties and load characteristics on the load side, the flexible interconnection technology of medium and low voltage distribution networks has attracted extensive attention from academia and industry. In particular, there are many literatures discussing the networking form, operation characteristics analysis, and demonstration project verification of single-level flexible interconnection systems such as within the substation, between substations, and between medium-voltage lines, in order to achieve dynamic capacity expansion, load rate balancing, power quality improvement, and increase the absorption capacity of distributed power sources in the distribution network.

[0003] However, with the multi-level and large-scale access of the new "source-load-storage" in the distribution network, the operation of the distribution network will become more complex, and the differences in the temporal and spatial characteristics between distribution feeders will become more obvious. Exploring a distribution network form that is more suitable for the multi-level new "source-load-storage" consumption has gradually become a hot topic in the field of distribution technology. The single-level flexible interconnection method commonly used in existing technologies is difficult to meet the distribution network's needs for the new "source-load-storage" consumption and flexible operation, which needs to be solved urgently. Summary of the invention

[0004] The present invention provides a dynamic connection device for a multi-level voltage distribution network and a control method thereof, so as to solve the problems of low power density, poor adaptability and low economic benefit existing in the prior art, improve the power density of the device, and enhance the adaptability of the system and the economic benefit of the product.

[0005] A first aspect of the present invention provides a dynamic connection device for a multi-level voltage distribution network, comprising: a medium voltage modular multilevel converter, one end of the medium voltage modular multilevel converter is connected to a first AC power grid, and is used to convert a first AC power output by the first AC power grid into a first DC power; a medium voltage-low voltage DC conversion component, one end of the medium voltage-low voltage DC conversion component is connected to the other end of the medium voltage modular multilevel converter, and is used to convert the first DC power into a second DC power, wherein the voltage of the second DC power is lower than the voltage of the first DC power; a low voltage flexible interconnection component, one end of the low voltage flexible interconnection component is connected to the other end of the medium voltage-low voltage DC conversion component, and the other end of the low voltage flexible interconnection component is connected to multiple second AC power grids, and is used to convert the second DC power into a second AC power, wherein the voltage of the second AC power is lower than the first AC power.

[0006] Furthermore, in some embodiments, the medium voltage modular multilevel converter adopts a three-phase half-bridge MMC topology structure.

[0007] Further, in some embodiments, the medium voltage-low voltage DC conversion component includes a series high voltage device unit, a DC inductor unit, a low voltage monomer device unit, a low voltage capacitor unit and a low voltage DC bus, wherein the positive electrode of the series high voltage device unit is connected to the positive electrode of the medium voltage modular multilevel converter, and the negative electrode of the series high voltage device unit is connected to the positive electrode of the DC inductor unit; the negative electrode of the DC inductor unit is connected to the negative electrode of the medium voltage modular multilevel converter; the positive electrode of the low voltage monomer device unit is connected to the connection node between the negative electrode of the series high voltage device unit and the positive electrode of the DC inductor unit, the negative electrode of the low voltage monomer device unit is respectively connected to the negative electrode of the low voltage capacitor unit and the negative electrode of the low voltage DC bus, and the positive electrode of the low voltage capacitor unit is respectively connected to the negative electrode of the medium voltage modular multilevel converter and the positive electrode of the low voltage DC bus.

[0008] Furthermore, in some embodiments, the series high-voltage device unit adopts a structure of multiple single devices connected in series. Among them, by connecting multiple sub-modules in series, the modular multi-level converter can achieve multi-level voltage output, thereby improving the flexibility and accuracy of power quality regulation. The structure of multiple single devices connected in series enables the MMC to have a higher voltage level and greater power processing capacity, thereby improving the stability and reliability of the entire back-to-back converter system, and because the sub-modules of the MMC can be controlled independently, when a fault occurs, the faulty sub-module can be quickly isolated to avoid the spread of the fault and ensure the continuous operation of the system.

[0009] Furthermore, in some embodiments, the low voltage flexible interconnection assembly uses a plurality of independent back-to-back two-level voltage source converters.

[0010] Among them, multiple independent back-to-back two-level voltage source converters can adjust the power quality of the power grid, such as voltage stability and harmonic suppression, by controlling the output voltage and current of the converter. Since each converter unit is independent, the system can be expanded or reduced as needed to adapt to different power needs and application scenarios. The back-to-back two-level voltage source converter has a high-efficiency energy conversion capability and can convert one form of electrical energy into another while maintaining efficient energy utilization.

[0011] Furthermore, in some embodiments, the positive poles of all back-to-back two-level voltage source converters are connected to the positive pole of the low-voltage DC bus, and the negative poles of all back-to-back two-level voltage source converters are connected to the negative pole of the low-voltage DC bus.

[0012] The dynamic connection device of the multi-level voltage distribution network provided in the embodiment of the present invention can provide both medium voltage AC ports and medium voltage DC, low voltage DC and multiple low voltage AC ports, and can meet the construction requirements of the dynamic connection device of the multi-level voltage distribution network. It solves the problems of low power density, poor adaptability and low economic benefits existing in the prior art. It improves the power density of the device, improves the adaptability of the system and the economic benefits of the product.

[0013] A second aspect of the present invention provides a control method for a dynamic connection device of a multi-level voltage distribution network, using a dynamic connection device of a multi-level voltage distribution network as described above, wherein the method includes: determining whether a first adjustment demand is received; if the first adjustment demand is received, based on a preset grid-following control strategy, using the medium voltage modular multilevel converter to adjust the reactive power of the first direct current and the first alternating current power grid.

[0014] Furthermore, in some embodiments, the control method of the dynamic connection device of the multi-level voltage distribution network also includes: determining whether a second adjustment demand is received; if the second adjustment demand is received, based on a preset adjustment strategy, the medium voltage-low voltage DC conversion component adjusts the second DC power so that the second DC power is in a preset constant state.

[0015] Furthermore, in some embodiments, the preset adjustment strategy is:

[0016]

[0017] Where D is the on-duty cycle, U dc低 is the low voltage DC voltage, U dc中 is a medium voltage DC voltage.

[0018] Furthermore, in some embodiments, the control method of the dynamic connection device of the multi-level voltage distribution network also includes: determining whether a third adjustment demand is received, wherein the third adjustment demand is issued by an upper-level scheduling system; if the third adjustment demand is received, parsing the third adjustment demand to obtain a control mode and a control instruction value; and controlling the low-voltage flexible interconnection component based on the control mode and the control instruction value.

[0019] The control method of the dynamic connection device of the multi-level voltage distribution network provided by the embodiment of the present invention can provide both medium voltage AC ports and medium voltage DC, low voltage DC and multiple low voltage AC ports, and can meet the construction requirements of the cross-voltage multi-port distribution network flexible interconnection system. It solves the problems of low power density, poor adaptability and low economic benefits existing in the prior art. It improves the power density of the device, improves the adaptability of the system and the economic benefits of the product.

[0020] In summary, the dynamic connection device for a multi-level voltage distribution network according to an embodiment of the present invention has the following advantages:

[0021] (1) The dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention can provide not only a medium voltage AC port, but also a medium voltage DC, a low voltage DC and a plurality of low voltage AC ports, and can meet the construction requirements of a cross-voltage multi-port distribution network flexible interconnection system.

[0022] (2) The dynamic connection device for a multi-level voltage distribution network according to the embodiment of the present invention does not contain a heavy and bulky AC transformer, which significantly improves the power density and compactness of the proposed device.

[0023] (3) The dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention adopts the technology of device series connection to realize the high-voltage switch structure, which significantly reduces the use of power electronic switch monomers and improves the economic benefits of the proposed device.

[0024] (4) The multiple low-voltage AC ports of the dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention are independently controlled and do not need to be communicated to ensure their coordinated control, so the system reliability is high.

[0025] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0027] Figure 1 A block diagram of a dynamic connection device for a multi-level voltage distribution network according to an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of a topological structure of a dynamic connection device of a multi-level voltage distribution network provided according to an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of the structure of a dynamic connection device for a multi-level voltage distribution network according to an embodiment of the present invention;

[0030] Figure 4 A schematic diagram of a strategy for controlling a dynamic connection device of a multi-level voltage distribution network according to a specific embodiment of the present invention;

[0031] Figure 5 A waveform diagram of the working principle of a medium voltage-low voltage DC conversion interface provided according to an embodiment of the present invention;

[0032] Figure 6 It is a flow chart of a control method of a dynamic connection device of a multi-level voltage distribution network proposed according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0034] The following describes the dynamic connection device and control method of the multi-level voltage distribution network of the embodiment of the present invention with reference to the accompanying drawings. In view of the problems of low power density, poor adaptability and low economic benefits in the prior art mentioned in the above background technology, the present invention provides a dynamic connection device of a multi-level voltage distribution network, which can provide both medium voltage AC ports and medium voltage DC, low voltage DC and multiple low voltage AC ports, and can meet the construction requirements of a flexible interconnection system of a cross-voltage multi-port distribution network. It solves the problems of low power density, poor adaptability and low economic benefits in the prior art.

[0035] Specifically, Figure 1 It is a block diagram of a dynamic connection device for a multi-level voltage distribution network according to an embodiment of the present invention.

[0036] like Figure 1 As shown, the dynamic connection device 10 of the multi-level voltage distribution network includes: a medium voltage modular multilevel converter 100, a medium voltage-low voltage direct current conversion component 200 and a low voltage flexible interconnection component 300.

[0037] Among them, the medium voltage modular multilevel converter 100 is connected to the first AC power grid, and is used to convert the first AC power output by the first AC power grid into a first DC power; one end of the medium voltage-low voltage DC conversion component 200 is connected to the other end of the medium voltage modular multilevel converter 100, and is used to convert the first DC power into a second DC power, wherein the voltage of the second DC power is lower than the voltage of the first DC power; one end of the low voltage flexible interconnection component 300 is connected to the other end of the medium voltage-low voltage DC conversion component 200, and the other end of the low voltage flexible interconnection component 300 is connected to multiple second AC power grids, and is used to convert the second DC power into a second AC power, wherein the voltage of the second AC power is lower than the first AC power.

[0038] In some embodiments, a three-phase half-bridge MMC topology structure is adopted for the medium voltage modular multilevel converter 100 .

[0039] Specifically, the three-phase half-bridge MMC topology structure adopted in the embodiment of the present invention completes the connection and power transmission between the dynamic connection device of the multi-level voltage distribution network and the medium-voltage AC power grid. The nominal voltage of existing commercial power electronic switch devices is about 6.5kV, and the actual maximum withstand voltage is about 4kV. Due to the use of the MMC structure, the limitation of insufficient withstand voltage of the power electronic switch devices can be avoided, so that the dynamic connection device of the proposed multi-level voltage distribution network can be connected to the medium-voltage distribution system of 10kV to 35kV.

[0040] Furthermore, in the embodiment of the present invention, the medium voltage modular multilevel converter 100 adopts a conventional grid-following control strategy to control the medium voltage DC voltage U dc中 And its AC side reactive power.

[0041] Furthermore, in some embodiments, Figure 2 As shown, the medium voltage-low voltage DC conversion assembly 200 includes a series connection of high voltage device units Q 串联 (Right now Figure 2 201), DC inductor unit L dc (Right now Figure 2 202), low voltage single device unit Q 单体 (Right now Figure 2 203), a low voltage capacitor unit 204 and a low voltage DC bus 205, wherein a high voltage device unit Q is connected in series 串联 The positive electrode is connected to the positive electrode of the medium voltage modular multilevel converter 100, and the high voltage device unit Q is connected in series 串联 The negative pole of the DC inductor unit L dc The positive pole is connected to the DC inductor unit L dc The negative electrode of the low voltage single device unit Q is connected to the negative electrode of the medium voltage modular multilevel converter 100; 单体 The positive electrode is connected in series with the high voltage device unit Q 串联 The negative pole and DC inductor unit L dc The connection node between the positive electrodes is connected, and the low voltage single device unit Q 单体 The negative electrode is connected to the low voltage capacitor unit U dc低 The negative electrode of the low voltage DC bus 205 is connected to the negative electrode of the low voltage capacitor unit U dc低 The positive pole is connected to the negative pole of the medium voltage modular multilevel converter 100 and the positive pole of the low voltage DC bus 205 respectively.

[0042] Among them, Figure 2 As shown, Figure 2This is a schematic diagram of the topological structure of a dynamic connection device for a multi-level voltage distribution network provided according to an embodiment of the present invention. The medium voltage-low voltage DC conversion component 200 completes the voltage conversion and power transmission of the medium voltage DC and the low voltage DC inside the device, and the medium voltage-low voltage DC conversion component 200 does not include an AC transformer link, which can significantly improve the compactness and power density of the dynamic connection device for the multi-level voltage distribution network.

[0043] Among them, Figure 2 As shown, the series high voltage device unit Q 串联 The structure of multiple single devices connected in series is adopted. The series voltage balancing between each single device is achieved through a voltage balancing circuit and a voltage balancing algorithm. The voltage balancing circuit adopts an active voltage balancing circuit structure of a diode, a unidirectional switch, a resistor and a capacitor. DC inductor unit L dc Can be a separate inductor, low voltage single device unit Q 单体 It can be a separate active voltage balancing circuit composed of a diode, a unidirectional switch, a resistor and a capacitor.

[0044] In some embodiments, the low voltage flexible interconnect assembly 300 uses a plurality of independent back-to-back two-level voltage source converters 301 .

[0045] Furthermore, in some embodiments, the positive poles of all back-to-back two-level voltage source converters 301 are connected to the positive pole of the low-voltage DC bus 205 , and the negative poles of all back-to-back two-level voltage source converters 301 are connected to the negative pole of the low-voltage DC bus 205 .

[0046] Therefore, the dynamic connection device of the multi-level voltage distribution network according to the embodiment of the present invention has the following advantages:

[0047] (1) The dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention can provide not only a medium voltage AC port, but also a medium voltage DC, a low voltage DC and a plurality of low voltage AC ports, and can meet the construction requirements of a cross-voltage multi-port distribution network flexible interconnection system.

[0048] (2) The dynamic connection device for a multi-level voltage distribution network according to the embodiment of the present invention does not contain a heavy and bulky AC transformer, which significantly improves the power density and compactness of the proposed device.

[0049] (3) The dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention adopts the technology of device series connection to realize the high-voltage switch structure, which significantly reduces the use of power electronic switch monomers and improves the economic benefits of the proposed device.

[0050] (4) The multiple low-voltage AC ports of the dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention are independently controlled and do not need to be communicated to ensure their coordinated control, so the system reliability is high.

[0051] In order for those skilled in the art to further understand the dynamic connection device of the multi-level voltage distribution network according to the embodiment of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0052] like Figure 3 As shown, Figure 3 The present invention is a schematic diagram of the structure of a cross-voltage multi-port distribution network flexible interconnection system according to an embodiment of the present invention.

[0053] Specifically, the dynamic connection device 10 of the multi-level voltage distribution network is the core of the cross-voltage multi-port distribution network flexible interconnection system, and the dynamic connection device of the multi-level voltage distribution network should be able to provide a medium voltage AC interface and multiple low voltage AC interfaces, and ensure the stable operation of the entire system.

[0054] Furthermore, if Figure 4 As shown, Figure 4 A strategy diagram of a control method of a dynamic connection device of a multi-level voltage distribution network according to an embodiment of the present invention.

[0055] Specifically, Figure 4 As shown, the control method of the dynamic connection device of the multi-level voltage distribution network of the embodiment of the present invention includes three key points, including: the medium voltage modular multi-level converter 100 adopts a conventional grid-following control strategy, the medium voltage-low voltage DC conversion component 200 controls the low voltage DC voltage U dc低 Maintain constant control and low-voltage flexible interconnection interface using Vf network control or PQ network control.

[0056] Specifically, the medium voltage modular multilevel converter 100 of the embodiment of the present invention can adopt a conventional grid-following control strategy to control the medium voltage DC voltage U dc中 and its AC side reactive power;

[0057] The medium voltage-low voltage DC conversion assembly 200 of the embodiment of the present invention controls the low voltage DC voltage U dc低 Maintain constant, series high voltage device part Q 串联 When the voltage balancing strategy is adopted, it can effectively ensure that each single device is voltage balanced during switching, so that the Q of the series high-voltage device part can be 串联 It is equivalent to a single switch Q that can withstand medium voltage. 串联 , the specific principles are as follows:

[0058] Specifically, due to the voltage balancing switch S in each single device voltage balancing circuit 均压 When not in use, the medium voltage DC bus charges the DC capacitors therein, causing the capacitor voltage to increase. The voltage balancing switch S in each single device voltage balancing circuit 均压During the input period, the resistor in the voltage-equalizing circuit consumes the energy stored in the capacitor, causing the capacitor voltage to drop. Therefore, it is only necessary to set the maximum and minimum values ​​of the capacitor voltage in each single device voltage-equalizing circuit and control the voltage-equalizing switch S 均压 The series connection of high voltage device unit Q 串联 structural design.

[0059] In this embodiment of the present invention, in order to avoid connecting the high voltage device unit Q 串联 During the switching operation, the uneven voltage of each single device causes device damage. Usually, the maximum and minimum values ​​of the capacitor voltage in the voltage equalization circuit of each single device are set to 1.02UC voltage equalization and 0.98UC voltage equalization respectively, where UC voltage equalization is the rated value of the capacitor voltage in the voltage equalization circuit of each single device, which is equal to the quotient of the medium voltage DC voltage value and the number of single devices connected in series.

[0060] Furthermore, after the maximum and minimum values ​​of the capacitor voltage in each single device voltage balancing circuit are known, the embodiment of the present invention can control the voltage balancing switch S when the capacitor voltage in the voltage balancing circuit is greater than its maximum value. 均压 In the input state, the capacitor voltage value is reduced; when the capacitor voltage in the voltage balancing circuit is less than its minimum value, the voltage balancing switch S is controlled 均压 In the non-input state, the capacitor voltage value is increased; thereby, the capacitor voltage value in each single device voltage equalization circuit is always kept between the maximum value and the minimum value, thereby ensuring the series high-voltage device unit Q 串联 The voltage of each single device during switching action.

[0061] Furthermore, due to the series connection of the high voltage device Q 串联 It can be equivalent to a single switch Q that can withstand medium voltage 串联 Although the control of the medium voltage-low voltage DC conversion component 200 in the embodiment of the present invention is slightly different when the power transmission direction is different, the basic principle is similar. The embodiment of the present invention takes the transmission of power from the high voltage side to the low voltage side as an example for analysis.

[0062] Furthermore, the detailed voltage reduction control method of the medium voltage-low voltage DC conversion component of the embodiment of the present invention is as follows: Figure 5 As shown. Among them, Figure 5 (a) is a schematic diagram of the waveform change of the internal power transmission from medium voltage to low voltage in a dynamic connection device of a multi-level voltage distribution network. Figure 5 (b) is a schematic diagram of the waveform change of the internal power transmitted from low voltage to medium voltage in a dynamic connection device of a multi-level voltage distribution network.

[0063] Among them, when the high-voltage device unit Q is connected in series 串联 When conducting, the medium voltage is the DC inductor unit L dc Charging, DC inductor unit Ldc The current increases; when the high voltage device unit Q is connected in series 串联 When turned off, the DC inductor unit L dc Discharge to the low voltage side, DC inductor unit L dc The current decreases. In one cycle, the DC inductor unit L dc The current fluctuations in should be kept balanced, expressed as the following formula:

[0064]

[0065] That is, in each cycle, the DC inductance unit L dc The increase in the medium current should be equal to its decrease in order to ensure the energy balance of the system.

[0066] From formula (1), we can see that D should be:

[0067]

[0068] Therefore, after the medium voltage DC link voltage of the dynamic connection device of the multi-level voltage distribution network proposed in the embodiment of the present invention is determined, it is only necessary to control the series connection of the high voltage device unit Q in each cycle. 串联 The conduction duty ratio D of the single device can effectively control the voltage on the low voltage side. 串联 When the above voltage balancing strategy is adopted, it can effectively ensure that each single device is voltage balanced during the switching action, so that the series high-voltage device part can be connected in series with the high-voltage device unit Q 串联 It is equivalent to a single switch that can withstand medium voltage and connect high voltage device unit Q in series 串联 .

[0069] Furthermore, each low-voltage flexible interconnection interface adopts Vf networking control or PQ following network control, and the control mode and control instruction value come directly from the upper-level scheduling system. There is no need for communication between the low-voltage flexible interconnection interfaces for coordinated control.

[0070] The dynamic connection device of the multi-level voltage distribution network provided in the embodiment of the present invention can provide both medium voltage AC ports and medium voltage DC, low voltage DC and multiple low voltage AC ports, and can meet the construction requirements of a flexible interconnection system for a multi-port distribution network across voltages. It solves the problems of low power density, poor adaptability and low economic benefits existing in the prior art. It improves the power density of the device, and improves the adaptability of the system and the economic benefits of the product.

[0071] Next, a control method for a dynamic connection device of a multi-level voltage distribution network proposed according to an embodiment of the present invention is described with reference to the accompanying drawings.

[0072] Figure 6It is a flow chart of a control method of a dynamic connection device of a multi-level voltage distribution network proposed according to an embodiment of the present invention.

[0073] like Figure 6 As shown, the output pipeline cleaning method includes the following steps:

[0074] In step S401, it is determined whether a first adjustment request is received;

[0075] In step S402, if a first regulation demand is received, based on a preset grid-following control strategy, the reactive power of the first direct current and the first alternating current grid is regulated using a medium voltage modular multilevel converter;

[0076] Furthermore, in some embodiments, the control method of the dynamic connection device of the multi-level voltage distribution network also includes: determining whether a second adjustment demand is received; if the second adjustment demand is received, based on a preset adjustment strategy, the medium voltage-low voltage DC conversion component adjusts the second DC power so that the second DC power is in a preset constant state.

[0077] Furthermore, in some embodiments, the preset adjustment strategy is:

[0078]

[0079] Where D is the on-duty cycle, U dc低 is the low voltage DC voltage, U dc中 is a medium voltage DC voltage.

[0080] Furthermore, in some embodiments, the control method of the dynamic connection device of the multi-level voltage distribution network further includes: determining whether a third adjustment demand is received, wherein the third adjustment demand is issued by the upper scheduling system; if the third adjustment demand is received, parsing the third adjustment demand to obtain a control mode and a control instruction value; and controlling the low-voltage flexible interconnection component based on the control mode and the control instruction value.

[0081] It should be noted that the above description of the embodiment of the dynamic connection device for a multi-level voltage distribution network is also applicable to the control method of the dynamic connection device for a multi-level voltage distribution network of this embodiment, and will not be repeated here.

[0082] The control method of the dynamic connection device of the multi-level voltage distribution network provided by the embodiment of the present invention can provide both medium voltage AC ports and medium voltage DC, low voltage DC and multiple low voltage AC ports, and can meet the construction requirements of the cross-voltage multi-port distribution network flexible interconnection system. It solves the problems of low power density, poor adaptability and low economic benefits existing in the prior art. It improves the power density of the device, improves the adaptability of the system and the economic benefits of the product.

[0083] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction 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 may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0084] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0085] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

[0086] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiment, the N 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, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0087] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

Claims

1. A dynamic connection device for a multi-level voltage distribution network, characterized in that: include: A medium voltage modular multilevel converter, one end of which is connected to a first AC power grid, and is used to convert a first AC power output by the first AC power grid into a first DC power; a medium voltage-low voltage direct current conversion component, one end of which is connected to the other end of the medium voltage modular multilevel converter, and is used to convert the first direct current into a second direct current, wherein the voltage of the second direct current is lower than the voltage of the first direct current; A low-voltage flexible interconnection component, one end of which is connected to the other end of the medium-voltage-low-voltage DC conversion component, and the other end of which is connected to a plurality of second AC power grids, for converting the second DC power into a second AC power, wherein the voltage of the second AC power is lower than that of the first AC power.

2. The dynamic connection device for a multi-level voltage distribution network according to claim 1, characterized in that: The medium voltage modular multi-level converter adopts a three-phase half-bridge MMC topology structure.

3. The dynamic connection device for a multi-level voltage distribution network according to claim 1, characterized in that: The medium voltage-low voltage DC conversion assembly comprises a series high voltage device unit, a DC inductor unit, a low voltage monomer device unit, a low voltage capacitor unit and a low voltage DC bus, wherein the positive electrode of the series high voltage device unit is connected to the positive electrode of the medium voltage modular multi-level converter, and the negative electrode of the series high voltage device unit is connected to the positive electrode of the DC inductor unit; The negative electrode of the DC inductor unit is connected to the negative electrode of the medium voltage modular multi-level converter; The positive electrode of the low-voltage single device unit is connected to the connection node between the negative electrode of the series high-voltage device unit and the positive electrode of the DC inductor unit, and the negative electrode of the low-voltage single device unit is connected to the negative electrode of the low-voltage capacitor unit and the negative electrode of the low-voltage DC bus, respectively. The positive electrode of the low-voltage capacitor unit is connected to the negative electrode of the medium-voltage modular multi-level converter and the positive electrode of the low-voltage DC bus respectively.

4. The dynamic connection device for a multi-level voltage distribution network according to claim 3, characterized in that: The series high-voltage device unit adopts a structure in which a plurality of single devices are connected in series.

5. The dynamic connection device for a multi-level voltage distribution network according to claim 3, characterized in that: The low voltage flexible interconnection assembly adopts a plurality of independent back-to-back two-level voltage source converters.

6. The dynamic connection device for a multi-level voltage distribution network according to claim 5, characterized in that: The positive poles of all the back-to-back two-level voltage source converters are connected to the positive pole of the low-voltage DC bus, and the negative poles of all the back-to-back two-level voltage source converters are connected to the negative pole of the low-voltage DC bus.

7. A control method for a dynamic connection device of a multi-level voltage distribution network, characterized in that: The dynamic connection device of a multi-level voltage distribution network according to any one of claims 1 to 6 is adopted, wherein the method comprises the following steps: determining whether a first adjustment demand is received; If the first regulation demand is received, based on a preset grid-following control strategy, the medium voltage modular multilevel converter is used to regulate the reactive power of the first direct current and the first alternating current grid.

8. The control method of the dynamic connection device of the multi-level voltage distribution network according to claim 7, characterized in that: Also includes: determining whether a second adjustment request is received; If the second regulation demand is received, based on a preset regulation strategy, the medium voltage-low voltage DC conversion component regulates the second DC power so that the second DC power is in a preset constant state.

9. The control method of the dynamic connection device of the multi-level voltage distribution network according to claim 8, characterized in that: The preset adjustment strategy is: Where D is the on-duty cycle, U dc低 is the low voltage DC voltage, U dc中 is a medium voltage DC voltage.

10. The control method of the dynamic connection device of the multi-level voltage distribution network according to claim 7, characterized in that: Also includes: Determining whether a third adjustment requirement is received, wherein the third adjustment requirement is issued by an upper scheduling system; If the third adjustment requirement is received, the third adjustment requirement is parsed to obtain a control mode and a control instruction value; Based on the control mode and the control instruction value, the low voltage flexible interconnection component is controlled.

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