Two-stage active power distribution network system

Abstract

The invention provides a two-stage active power distribution network system, and belongs to the technical field of electrical engineering and automation, the system comprises a 10kV-level power transformation-photovoltaic-energy storage integrated device and a 400V-level flexible interconnection device, the 10kV-level power transformation-photovoltaic-energy storage integrated device comprises a bidirectional converter ACDC0-1, a bidirectional converter DCDC0-1, a bidirectional converter ACDC0-2, a bidirectional converter DCDC0-2 and a bidirectional converter DCDC0-3, and the 400V-level flexible interconnection device is connected with the 400V-level flexible interconnection device. The 400V-level flexible interconnection device comprises a bidirectional converter ACDCn-1 and a bidirectional converter ACDCn-2, and is used for distributed power generation and energy storage. According to the two-stage active power distribution network system, the power transformation function between a 10kV power distribution line and a 400V power distribution station interval is achieved through the 10kV-stage power transformation-photovoltaic-energy storage integrated device, and active power supply is provided when the 10kV-stage power transformation-photovoltaic-energy storage integrated device is disconnected with a main network; and electric energy management of the power distribution area is realized through the 400V-level flexible interconnection device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrical engineering and automation technology, in particular to a two-stage active power distribution network system. BACKGROUND

[0002] In some remote counties in Xinjiang region, due to the relatively weak power grid infrastructure, there are still problems of unstable connection with the main grid. In order to ensure the reliability of power supply in these areas, distributed power generation systems and energy storage devices need to be configured to flexibly provide necessary energy support for the power distribution network. The introduction of intelligent transformer technology realizes the efficient access of distributed power generation and energy storage resources, which not only can play a role in normal operation of the power grid, but also can maintain the energy supply of the local power grid in the case of disconnection with the main grid, thereby enhancing the resilience and self-sufficiency of the power grid.

[0003] However, with the continuous evolution of the power distribution network system and the large number of access of non-load units such as new energy distributed power generation, the power flow distribution becomes more flexible and uncertain, which brings many challenges to the power quality of the power distribution network, such as current harmonics, voltage fluctuations and drops. Despite this, these changes have indirectly improved the active support capability of the power distribution network, i.e. by flexibly adjusting power generation and load to realize stable control of the power grid. Unfortunately, the traditional transformer technology is not up to the task in this context, and cannot effectively isolate the current harmonics or voltage drops introduced by new energy and power electronic devices, and lacks the necessary power control means. Therefore, developing a flexible interconnection device with flexible power quality management and power control capability has become the key to improving the efficiency and stability of modern power distribution networks.

[0004] Therefore, the present application proposes a two-stage active power distribution network system, which uses a 10kV-level power transformation-photovoltaic-energy storage integrated device and a 400V-level flexible interconnection device to realize the above functions. SUMMARY

[0005] The present application aims to provide a two-stage active power distribution network system, which realizes the power transformation function between 10kV power distribution lines and 400V power distribution areas through a 10kV-level power transformation-photovoltaic-energy storage integrated device, and provides active power supply when disconnected from the main grid; realizes power management in the power distribution area through a 400V-level flexible interconnection device; and at the same time, uses distributed power generation and energy storage in the power distribution network to provide support for the power grid.

[0006] To achieve the above purpose, the present application provides a two-stage active power distribution network system, which comprises a 10kV-level power transformation-photovoltaic-energy storage integrated device and a 400V-level flexible interconnection device,

[0007] 10kV level power transformation-pv- energy storage integrated device includes bidirectional converter ACDC0-1, DCDC0-1, bidirectional converter ACDC0-2, DCDC0-2, DCDC0-3, bidirectional converter ACDC0-1 is connected with 10kV feeder, bidirectional converter ACDC0-2 is connected with 400V feeder, bidirectional converter ACDC0-1 is connected with bidirectional converter ACDC0-2 through DCDC0-1, DCDC0-2 is connected with energy storage system, and DCDC0-3 is connected with photovoltaic power generation;

[0008] The system further comprises a 400V power distribution area, and a 400V level flexible interconnection device is arranged in the 400V power distribution area, wherein the 400V level flexible interconnection device comprises a bidirectional converter ACDCn-1, a bidirectional converter ACDCn-2 and distributed power generation and energy storage, the bidirectional converter ACDCn-1 is connected with the 400V feeder, the bidirectional converter ACDCn-2 is connected with a load of the power distribution area, and the distributed power generation and energy storage are connected to the DC side of the bidirectional converter ACDCn-1 and the bidirectional converter ACDCn-2.

[0009] Preferably, the DCDC0-1 is arranged between the bidirectional converter ACDC0-1 and the bidirectional converter ACDC0-2, and functions as a voltage transformer and an isolator.

[0010] Preferably, when the system is in a normal operation state, the bidirectional converter ACDC0-1, the DCDC0-1 and the bidirectional converter ACDC0-2 jointly constitute a power electronic transformer, so as to realize AC voltage conversion from 10kV to 400V; the bidirectional converter ACDCn-1 establishes DC bus voltage, suppresses current harmonics and isolates faults, and the bidirectional converter ACDCn-2 establishes AC voltage for the load of the power distribution area.

[0011] Preferably, when the system is disconnected from the main grid and the 10kV level power transformation-pv- energy storage integrated device can provide energy supply, the bidirectional converter ACDC0-1 does not work, and the photovoltaic power generation and the energy storage system provide energy for the power distribution area on the 400V feeder through the DCDC0-2, the DCDC0-3, the DCDC0-1 and the bidirectional converter ACDC0-2.

[0012] Preferably, when the system is disconnected from the main grid and the 10kV level power transformation-pv- energy storage integrated device cannot provide energy supply, the 10kV level power transformation-pv- energy storage integrated device does not work; the distributed power generation and energy storage in the 400V level flexible interconnection device provide power supply, the bidirectional converter ACDCn-1 operates in a droop mode, adaptive power distribution is performed between power distribution areas, and the bidirectional converter ACDCn-2 establishes AC voltage for the load of the power distribution area.

[0013] Preferably, when the system provides active support to the power grid, the bidirectional converter ACDC0-1 connected to the 10kV feeder and the bidirectional converter ACDC0-2 connected to the 400V feeder work in the grid-forming mode respectively to provide voltage and frequency support.

[0014] Therefore, the application adopts the above-mentioned two-stage active distribution network system, and the technical effects are as follows:

[0015] 1. Fully utilizing the distributed generation and energy storage in the distribution network: through the collaborative work of the 10kV-level power transformation-photovoltaic-energy storage integrated device and the 400V-level flexible interconnection device, the effective integration and utilization of the distributed generation and energy storage resources are realized.

[0016] 2. Rich power management functions: the 400V-level flexible interconnection device in the system has multiple functions such as current harmonic suppression, fault isolation, and voltage establishment, effectively solving the power quality problems caused by the access of non-load units such as new energy distributed generation to the distribution network.

[0017] 3. Ensuring the power supply of the load in the distribution area when the system is disconnected from the main grid: the distributed generation and energy storage device provides continuous energy supply for the distribution area, ensuring the normal operation of the load.

[0018] 4. Providing active support capability: by adjusting the working mode of the bidirectional converter, the voltage and frequency support are provided, thereby enhancing the stability of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 is a structural schematic diagram of the two-stage active distribution network system of the application;

[0020] Figure 2 FIG. 2 is a voltage waveform schematic diagram of three distribution areas in the first embodiment of the application;

[0021] Figure 3 FIG. 3 is a load voltage waveform schematic diagram when the power grid is single-phase voltage drop in the second embodiment of the application;

[0022] Figure 4 FIG. 4 is a load voltage waveform schematic diagram when the power grid is three-phase voltage drop in the third embodiment of the application;

[0023] Figure 5 FIG. 5 is a current waveform schematic diagram injected into the power grid when the load current is unbalanced in the fourth embodiment of the application. DETAILED DESCRIPTION

[0024] The technical solutions of the application are further described below through the drawings and embodiments.

[0025] Unless otherwise defined, technical terms or scientific terms used in the present application shall have the ordinary meaning as understood by a person having ordinary skill in the art to which the present application pertains.

[0026] Embodiment one

[0027] As Figure 1 shown, the present application provides a two-stage active power distribution network system, including a 10kV level power transformation-photovoltaic- energy storage integrated device and a 400V level flexible interconnection device;

[0028] The 10kV level power transformation-photovoltaic-energy storage integrated device includes a bidirectional converter ACDC0-1, a DCDC0-1 for voltage transformation and isolation, a bidirectional converter ACDC0-2, a DCDC0-2, and a DCDC0-3, the bidirectional converter ACDC0-1 is connected with a 10kV feeder, the bidirectional converter ACDC0-2 is connected with a 400V feeder, the bidirectional converter ACDC0-1 is connected with the bidirectional converter ACDC0-2 through the DCDC0-1, the DCDC0-2 is connected with an energy storage system, and the DCDC0-3 is connected with a photovoltaic power generation.

[0029] The system further includes a plurality of 400V power distribution areas, the 400V power distribution areas are provided with 400V level flexible interconnection devices, the 400V level flexible interconnection devices include a bidirectional converter ACDCn-1, a bidirectional converter ACDCn-2, and distributed power generation and energy storage, the bidirectional converter ACDCn-1 is connected with a 400V feeder, the bidirectional converter ACDCn-2 is connected with a power distribution area load, and the distributed power generation and energy storage are connected at the DC side of the bidirectional converter ACDCn-1 and the bidirectional converter ACDCn-2.

[0030] The two-stage active power distribution network is connected with a main network, the number of power distribution areas is selected as three, and each area normally operates. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder, the DCDC0-1 for voltage transformation and isolation, and the bidirectional converter ACDC0-2 connected with the 400V feeder jointly constitute a power electronic transformer, realize the AC voltage change from 10kV to 400V, and provide an electrical isolation function; the bidirectional converter ACDCn-1 connected with the 400V feeder is responsible for establishing a DC bus voltage, and the bidirectional converter ACDCn-2 connected with the power distribution area load is responsible for establishing an AC voltage for the power distribution area load. The voltages of the three power distribution areas are as shown in Figure 2 , and each area can normally work.

[0031] Embodiment two

[0032] The two-stage active distribution network is connected with the main network, three distribution areas are selected, and single-phase voltage drop occurs in the 400V feeder. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder, the DCDC0-1 for voltage transformation and isolation, and the bidirectional converter ACDC0-2 connected with the 400V feeder together constitute a power electronic transformer, realize the change of 10kV to 400V AC voltage, and provide electrical isolation function; the bidirectional converter ACDCn-1 connected with the 400V feeder is responsible for establishing the DC bus voltage and isolating the voltage drop, and the bidirectional converter ACDCn-2 connected with the distribution area load is responsible for establishing AC voltage for the distribution area load. As shown in Figure 3 , the load voltage waveform can be guaranteed to be normal.

[0033] Example three

[0034] The two-stage active distribution network is connected with the main network, three distribution areas are selected, and three-phase voltage drop occurs in the 400V feeder. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder, the DCDC0-1 for voltage transformation and isolation, and the bidirectional converter ACDC0-2 connected with the 400V feeder together constitute a power electronic transformer, realize the change of 10kV to 400V AC voltage, and provide electrical isolation function; the bidirectional converter ACDCn-1 connected with the 400V feeder is responsible for establishing the DC bus voltage and isolating the voltage drop, and the bidirectional converter ACDCn-2 connected with the distribution area load is responsible for establishing AC voltage for the distribution area load. As shown in Figure 4 , the load voltage waveform can be guaranteed to be normal.

[0035] Example four

[0036] The two-stage active distribution network is connected with the main network, three distribution areas are selected, and the load of the distribution area is unbalanced. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder, the DCDC0-1 for voltage transformation and isolation, and the bidirectional converter ACDC0-2 connected with the 400V feeder together constitute a power electronic transformer, realize the change of 10kV to 400V AC voltage, and provide electrical isolation function; the bidirectional converter ACDCn-1 connected with the 400V feeder is responsible for establishing the DC bus voltage, and the bidirectional converter ACDCn-2 connected with the distribution area load is responsible for establishing AC voltage for the distribution area load and performing current harmonic compensation. As shown in Figure 5 , the three-phase current injected into the power grid can be guaranteed to be symmetrical.

[0037] Example five

[0038] The two-stage active distribution network is disconnected from the main network, and three distribution areas are selected. The photovoltaic and energy storage in the 10kV device can provide energy supply. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder does not work, and the photovoltaic power generation and energy storage system establishes the voltage of the 400V feeder through DCDC0-2, DCDC0-3, DCDC0-1 and bidirectional converter ACDC0-2. The bidirectional converter ACDCn-1 connected with the 400V feeder is responsible for establishing the DC bus voltage, and the bidirectional converter ACDCn-2 connected with the distribution area load is responsible for establishing the AC voltage for the distribution area load. Three distribution areas work normally, and the working conditions of the three distribution areas are the same as those in the implementation example two.

[0039] Example six

[0040] The two-stage active distribution network is disconnected from the main network, and three distribution areas are selected. The photovoltaic and energy storage in the 10kV device cannot provide energy supply, and the distributed power generation and energy storage in the 400V device provide energy supply. At this time, the 10kV device does not work; the bidirectional converter ACDCn-1 connected with the 400V feeder operates in droop mode, and the adaptive power distribution is carried out between the distribution areas; and the bidirectional converter ACDCn-2 connected with the distribution area load is responsible for establishing the AC voltage for the distribution area load.

[0041] Example seven

[0042] The two-stage active distribution network provides voltage and frequency support for the 10kV and 400V feeders, and three distribution areas are selected. At this time, the bidirectional converter ACDC0-1 connected with the 10kV feeder works in the virtual synchronous generator control mode to provide voltage and frequency support for the 10kV feeder; and the bidirectional converter ACDCn-1 connected with the 400V feeder also works in the virtual synchronous generator mode to provide voltage and frequency support for the 400V feeder.

[0043] For the 10kV transformer-pv-energy storage integrated device, in the conventional operation, the bidirectional converter ACDC0-1 connected with the 10kV feeder, the DCDC0-1 for voltage transformation and isolation, and the bidirectional converter ACDC0-2 connected with the 400V feeder together constitute a power electronic transformer, realize the change of 10kV to 400V AC voltage, and provide electrical isolation function, in addition, provide a DC bus for distributed power generation and energy storage, which is convenient for them to access the system; when disconnected from the main network, the bidirectional converter ACDC0-1 connected with the 10kV feeder does not work, and the photovoltaic power generation and energy storage system provides energy for the distribution area on the 400V feeder through DCDC0-2, DCDC0-3, DCDC0-1 and bidirectional converter ACDC0-2.

[0044] For the 400V flexible interconnection device, in the conventional operation, the bi-directional converter ACDCn-1 connected with the 400V feeder is responsible for establishing the DC bus voltage, current harmonic suppression and fault isolation function, and the bi-directional converter ACDCn-2 connected with the distribution area load is responsible for establishing the AC voltage for the distribution area load; in the off-grid operation, if the 10kV transformer-pv-storage integrated device can still provide energy supply, the working mode of the 400V flexible interconnection device does not change, and if the 10kV transformer-pv-storage integrated device cannot provide energy supply, the distributed power generation and storage are responsible for power supply, the bi-directional converter ACDCn-1 connected with the 400V feeder operates in droop mode, and the adaptive power distribution is carried out between each distribution area, and the function of the bi-directional converter ACDCn-2 does not change.

[0045] In addition, if support capability is needed, according to the network to be supported, the bi-directional converter ACDC0-1 connected with the 10kV feeder and the bi-directional converter ACDC0-2 connected with the 400V feeder can respectively work in the network construction mode to provide voltage and frequency support.

[0046] Therefore, the application adopts the above-mentioned two-stage active distribution network system, through the cooperative work of the 10kV transformer-pv-storage integrated device and the 400V flexible interconnection device, not only the power quality problems caused by new energy access, such as current harmonic suppression and voltage fluctuation, are solved, but also the power supply reliability of the distribution area is guaranteed when off the main network, and active support of voltage and frequency is provided, and the stability and self-sufficiency of the power grid are enhanced.

[0047] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A two-stage active power distribution network system, characterized by, The system comprises a 10kV-level power transformation-photovoltaic-energy storage integrated device and a 400V-level flexible interconnection device, The 10kV-level power transformation-photovoltaic-energy storage integrated device comprises a bidirectional converter ACDC0-1, a DC / DC converter DCDC0-1, a bidirectional converter ACDC0-2, a DC / DC converter DCDC0-2, and a DC / DC converter DCDC0-3, the bidirectional converter ACDC0-1 is connected with a 10kV feeder, the bidirectional converter ACDC0-2 is connected with a 400V feeder, the bidirectional converter ACDC0-1 is connected with the bidirectional converter ACDC0-2 through the DC / DC converter DCDC0-1, the DC / DC converter DCDC0-2 is connected with an energy storage system, and the DC / DC converter DCDC0-3 is connected with photovoltaic power generation. The system further comprises a 400V power distribution area, and the 400V power distribution area is provided with a 400V-level flexible interconnection device, the 400V-level flexible interconnection device comprises a bidirectional converter ACDCn-1, a bidirectional converter ACDCn-2, and distributed power generation and energy storage, the bidirectional converter ACDCn-1 is connected with a 400V feeder, the bidirectional converter ACDCn-2 is connected with a power distribution area load, and the distributed power generation and energy storage are connected at the DC side of the bidirectional converter ACDCn-1 and the bidirectional converter ACDCn-2.

2. A two-stage active power distribution network system according to claim 1, characterized in that, The DC / DC converter DCDC0-1 is arranged between the bidirectional converter ACDC0-1 and the bidirectional converter ACDC0-2, and functions as a voltage transformer and an isolator.

3. A two-stage active power distribution network system as claimed in claim 1, wherein, When the system is in normal operation, the bidirectional converter ACDC0-1, the DC / DC converter DCDC0-1, and the bidirectional converter ACDC0-2 jointly constitute a power electronic transformer, and realize AC voltage conversion from 10kV to 400V; the bidirectional converter ACDCn-1 establishes DC bus voltage, suppresses current harmonics, and isolates faults, and the bidirectional converter ACDCn-2 establishes AC voltage for a power distribution area load.

4. The two-stage active power distribution network system of claim 1, wherein, When the system is disconnected from the main grid and the 10kV-level power transformation-photovoltaic-energy storage integrated device can provide energy supply, the bidirectional converter ACDC0-1 does not work, and the photovoltaic power generation and the energy storage system provide energy for a power distribution area on the 400V feeder through the DC / DC converter DCDC0-2, the DC / DC converter DCDC0-3, the DC / DC converter DCDC0-1, and the bidirectional converter ACDC0-2.

5. The two-stage active power distribution network system of claim 1, wherein, When the system is disconnected from the main grid and the 10kV-level power transformation-photovoltaic-energy storage integrated device cannot provide energy supply, the 10kV-level power transformation-photovoltaic-energy storage integrated device does not work; the distributed power generation and energy storage in the 400V-level flexible interconnection device provide power supply, the bidirectional converter ACDCn-1 operates in a droop mode, power distribution areas adaptively distribute power, and the bidirectional converter ACDCn-2 establishes AC voltage for a power distribution area load.

6. A two-stage active power distribution network system as claimed in claim 1, wherein, When the system provides active support for the power grid, the bidirectional converter ACDC0-1 connected with the 10kV feeder and the bidirectional converter ACDC0-2 connected with the 400V feeder respectively operate in a grid-forming mode, and provide voltage and frequency support.

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