Transformer area interconnection system based on direct current coupling and control method thereof

Abstract

The invention relates to the technical field of power systems, and discloses a transformer area interconnection system based on direct current coupling and a control method thereof. The system is connected with two transformer areas through a direct-current coupling module, at least one transformer area comprises photovoltaic power generation equipment and / or an energy storage battery, and the photovoltaic power generation equipment and / or the energy storage battery are connected to a direct-current bus through a DC / DC converter and then connected to the low-voltage side of a power distribution network through an AC / DC converter. Each transformer area is provided with a fast-charging direct-current charging station which can be connected to the low-voltage side of the power distribution network or a direct-current bus. The control method comprises the steps of collecting the power and the voltage of the transformer, calculating the average power and the maximum power demand of the transformer area in continuous preset time, controlling the charging and discharging power of the energy storage battery according to the change of the average power, and implementing the power balance control of the transformer area according to the maximum energy storage capacity of the energy storage battery. The energy utilization efficiency and the power supply reliability are improved, the operation cost is reduced, the intelligent level of energy management is improved, and remarkable economic and social benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of electric power systems and discloses a DC-coupled-based substation interconnection system and a control method thereof. Background Art

[0002] At present, due to the development of fast charging equipment, the distribution capacity of many distribution stations is insufficient, which limits the development of many fast charging equipment, especially in fast charging stations in highway service areas. This problem is more prominent. When the seasonal or periodic growth of the load in the substation exceeds expectations, the insufficient capacity of the low-voltage line will lead to a decline in voltage quality. In addition, the distribution of distribution transformers has failed to keep up with the growth of electricity demand, and the insufficient capacity of transformers is prone to overload and overload, affecting their service life and the stability of output voltage. In some areas, the power supply radius of the substation is too large, resulting in low terminal voltage. The low terminal voltage is particularly serious in the substations with an average low-voltage power supply radius of more than 0.8 kilometers. Such substations account for 85% of the total number of low-voltage substations, which makes the power supply efficiency low. In a distribution network with a high photovoltaic penetration rate, when the output of photovoltaic power exceeds the absorption capacity of the distribution network, it will cause a reverse flow of the current, resulting in a voltage increase or even overvoltage, threatening the stability of the power grid. Summary of the invention

[0003] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a DC-coupled substation interconnection system and a control method thereof to solve the problem of low level of intelligent energy management in the prior art.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a DC-coupled based interconnection system for substations, comprising two substations; The two sections are DC coupled via a first DC-DC converter; At least one of the two areas includes photovoltaic power generation equipment and / or energy storage batteries; Photovoltaic power generation equipment and energy storage batteries are connected to the DC bus of the substation through DC / DC converters; the DC bus is connected to the low-voltage side of the distribution network through AC / DC converters; A fast-charging DC charging station is installed in each substation, which is connected to the low-voltage side of the distribution network or to the DC bus of the substation.

[0005] Preferably, in a possible implementation manner of the first aspect, the first DC-DC converter has a bidirectional power transmission function, and can be dynamically adjusted according to the difference in power demand between the two substations.

[0006] Preferably, in a possible implementation of the first aspect, the fast-charging DC charging station is connected to the distribution network including a DC coupling mode and an AC coupling mode; The DC coupling method is that the fast-charging DC charging station is connected to the DC bus of the substation where it is located, and then connected to the low-voltage side of the distribution network through the AC / DC converter of the substation; The AC coupling method is that the fast charging DC charging station is directly connected to the low-voltage side of the distribution network.

[0007] Preferably, in a possible implementation manner of the first aspect, the system further includes: When a fast-charging DC charging station is added in any substation by DC coupling, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding substation, and the newly added fast-charging DC charging station is connected to the low-voltage side of the distribution network through the AC / DC converter of the substation; When a fast-charging DC charging station is added in any substation using AC coupling, the newly added fast-charging DC charging station is directly connected to the low-voltage side of the distribution network.

[0008] In a second aspect, the present invention provides a DC coupling-based area interconnection control method, comprising: Step S100: collecting the power and voltage of the transformer through a metering unit deployed in the transformer of the substation; Step S200: Calculate the average power of the area for a preset continuous time and the maximum power demand of the area; Step S300: Controlling the charging power and discharging power of the energy storage battery according to the average power change of the station area; Step S400: Implementing balanced control of the power in the substation area according to the maximum energy storage capacity of the energy storage battery.

[0009] Preferably, in a possible implementation manner of the second aspect, the average power calculation process includes: The transformer power acquisition data of the preset time is obtained through step S100 to form a power sampling sequence , the average power of the station area for the continuous preset time is ,in , , is the continuous preset time length in minutes, is the sampling frequency.

[0010] Preferably, in a possible implementation manner of the second aspect, the maximum power demand is the maximum continuous preset time average power, and the calculation process is: .

[0011] Preferably, in a possible implementation manner of the second aspect, step S300 specifically includes: when , control the discharge power of the energy storage battery in this area to increase, and the increase in discharge power is ; when , control the charging power of the energy storage battery in this area to increase, and the charging power increase value is ; Where t represents a certain sampling time, and t+1 represents the next sampling time after the sampling time.

[0012] Preferably, in a possible implementation manner of the second aspect, step S300 further includes: When a photovoltaic power generation device is in working condition, the remaining power of the energy storage batteries in all substations is read, and the photovoltaic power generation device is preferentially selected to charge the energy storage battery in its substation. If the remaining power of the energy storage battery is full, the energy storage batteries in other substations are charged through the DC-DC converter between substations.

[0013] Preferably, in a possible implementation manner of the second aspect, step S400 specifically includes: When the power increase value of a certain area is greater than the maximum capacity of the energy storage battery in the area, the energy storage battery in the area is controlled to transfer the difference power of the area to the area whose power increase value is less than the maximum capacity of the energy storage battery in the area through the DC-DC converter between the stations; When the added value of all substations is greater than the maximum capacity of the substation energy storage battery, the DC-DC converters between substations only serve as isolation and no power transmission is performed.

[0014] The beneficial effects of the present invention are as follows: when the photovoltaic power generation module is generating electricity and the remaining power of the energy storage battery is not full, the minimum power grid power consumption control method is executed, and the direct charging of the energy storage battery by photovoltaic power generation and the charging across substations are realized through the DC coupling module, thereby reducing the power grid power consumption. When the photovoltaic power generation module is not generating electricity and the remaining power of the energy storage battery is not full, the inter-substation power consumption and maximum demand power consumption balancing control method is executed, and data is collected and calculated through the metering unit, and the power of the energy storage battery is adjusted according to the calculation results, so as to achieve power balance between substations and avoid energy waste. In addition, the system also has an energy storage module, a charging module, a DC coupling module, etc., which realizes flexible interconnection between photovoltaic power generation, energy storage batteries and power grids, and improves energy utilization efficiency and power supply reliability. On the whole, the present invention reduces the operating costs of highway service areas, improves the intelligent level of energy management, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A structural diagram of a DC coupling subsystem of a fast charging station based on a DC coupling area interconnection system is provided for this application.

[0017] Figure 2 A structural diagram of an AC coupling subsystem of a fast charging station based on a DC coupling area interconnection system is provided for this application.

[0018] Figure 3 A flow chart of a DC-coupled area interconnection control method is provided for this application. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Embodiment 1: The present invention provides a substation interconnection system based on DC coupling, comprising a first substation, a second substation and a first DC-DC converter; the first DC-DC converter is used to realize DC coupling between the DC bus of the first substation and the DC bus of the second substation.

[0021] The first section includes a first photovoltaic power generation device, a first energy storage battery, a second DC / DC converter, a third DC / DC converter, a first AC / DC converter, and a first other load, wherein: The first photovoltaic power generation device and the first energy storage battery are respectively connected to the DC bus through the first DC / DC converter and the second DC / DC converter, and then connected to the distribution network through the first AC / DC converter; the first other load is directly connected to the distribution network.

[0022] The second section includes a second photovoltaic power generation device, a second energy storage battery, a fourth DC / DC converter, a fifth DC / DC converter, a second AC / DC converter and a second other load, wherein: The second photovoltaic power generation equipment and the second energy storage battery are connected to the DC bus through the third DC / DC converter and the fourth DC / DC converter respectively, and then connected to the distribution network through the charging station AC / DC converter; the second other loads are directly connected to the distribution network.

[0023] When the fast-charging DC charging station in any area is connected to the distribution network by DC coupling, the area also includes a fast-charging DC charging station and a charging station AC / DC converter. The fast-charging DC charging station is directly connected to the DC bus and then connected to the distribution network through the charging station AC / DC converter; when the fast-charging DC charging station in any area is connected to the power grid by AC coupling, the area also includes a fast-charging DC charging station, and the fast-charging DC charging station is directly connected to the distribution network.

[0024] The first DC-DC converter has a bidirectional power transmission function and can be dynamically adjusted according to the difference in power demand between the first area and the second area.

[0025] like Figure 1 As shown, the fast-charging DC charging stations in the first and second areas are both connected to the distribution network using DC coupling.

[0026] Specifically, in the first substation of the system, the first fast-charging DC charging station is directly connected to the DC bus, and then connected to the distribution network through the third AC / DC converter. The first fast-charging DC charging station is interconnected with the first photovoltaic power generation equipment and the first energy storage battery through the DC bus of the first substation; in the second substation of the system, the second fast-charging DC charging station is directly connected to the DC bus, and then connected to the distribution network through the fourth AC / DC converter. The second fast-charging DC charging station is interconnected with the first photovoltaic power generation equipment and the first energy storage battery through the DC bus of the second substation.

[0027] like Figure 2 As shown, the fast-charging DC charging stations in the first and second areas are both connected to the distribution network using AC coupling.

[0028] Specifically, in the first substation of the system, the third fast-charging DC charging station is directly connected to the distribution network; in the second substation of the system, the fourth fast-charging DC charging station is directly connected to the distribution network.

[0029] In this embodiment, the photovoltaic power generation equipment is a device that directly converts sunlight into electrical energy using the photovoltaic effect, such as the first photovoltaic power generation equipment in the first area and the second photovoltaic power generation equipment in the second area, which are both connected to the DC bus through corresponding DC / DC converters. The DC power generated by the photovoltaic power generation equipment is efficiently and safely transmitted to the system, and finally connected to the distribution network through the AC / DC converter to achieve sustainable use of energy.

[0030] Energy storage batteries are devices that store electrical energy and can release electrical energy when needed to balance supply and demand. For example, the first energy storage battery in the first station area and the second energy storage battery in the second station area are also connected to the DC bus through a DC / DC converter. In this way, the energy storage battery can store excess electrical energy when there is sufficient sunlight, and release electrical energy when there is insufficient sunlight or when demand is at a peak, ensuring the stable operation of the system.

[0031] A fast-charging DC charging station is a charging facility designed for fast charging of electric vehicles, such as the first and second fast-charging DC charging stations, which can be directly connected to the DC bus and connected to the distribution network through an AC / DC converter. At the same time, a fast-charging DC charging station can also be directly connected to the distribution network, such as the third and fourth fast-charging DC charging stations, which use AC power supply to provide DC charging services for electric vehicles.

[0032] A DC / DC converter is a device used to convert direct current power from one voltage level to another. DC / DC converters (such as the first DC / DC converter to the fifth DC / DC converter) are used to connect photovoltaic power generation equipment, energy storage batteries and DC buses. It can ensure that equipment of different voltage levels can be safely and efficiently connected to the system, and realize flexible scheduling and distribution of electric energy.

[0033] The AC / DC converter is a device that converts AC power and DC power. For example, the first to fourth AC / DC converters are used to convert the power on the DC bus into AC power and finally connect it to the distribution network. This enables the system to transmit the DC power generated by photovoltaic power generation equipment and energy storage batteries and the power provided by fast-charging DC charging stations to the grid to meet power demand.

[0034] Other loads include lighting loads, household power loads and electrical maintenance equipment loads.

[0035] In one embodiment, the system also includes when any substation adopts DC coupling to add a fast charging DC charging station, the newly added fast charging DC charging station is directly connected to the DC bus of the corresponding substation, and the newly added fast charging DC charging station is connected to the low-voltage side of the distribution network through the AC / DC converter of the substation; when any substation adopts AC coupling to add a fast charging DC charging station, the newly added fast charging DC charging station is directly connected to the low-voltage side of the distribution network.

[0036] Specifically, when a fast-charging DC charging station is added by DC coupling, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding area (such as the first area or the second area). After the connection, the newly added fast-charging DC charging station can be connected to the distribution network through the newly added AC / DC converter in the area, realizing the two-way flow and efficient use of electric energy.

[0037] At the same time, the newly added fast-charging DC charging station is interconnected with the photovoltaic power generation equipment and energy storage batteries in the area through the DC bus, which enables the fast-charging DC charging station to directly obtain stable electricity from the photovoltaic power generation equipment and energy storage batteries, reducing its dependence on the power grid.

[0038] When adding a fast-charging DC charging station using AC coupling, the new fast-charging DC charging station can be directly connected to the distribution network without the need for interconnection through the DC bus. This access method simplifies the system structure, reduces construction costs, and ensures that the new charging station can be put into operation quickly and flexibly.

[0039] Embodiment 2: Figure 3 As shown, the present invention provides a DC coupling-based area interconnection control method, comprising: Step S100: collecting the power and voltage of the transformer through a metering unit deployed in the transformer of the substation.

[0040] Specifically, the metering unit first measures the current and voltage values ​​at the input and output of the transformer through the built-in current transformer and voltage transformer. These measured values ​​are converted by the analog-to-digital converter (ADC) and stored in the local memory of the metering unit. At the same time, the metering unit is also equipped with a clock synchronization module to ensure that the collected data has an accurate timestamp, which is convenient for subsequent data analysis and processing.

[0041] After collecting the raw data of current and voltage, the metering unit uses the built-in power calculation algorithm to calculate the active power of the transformer according to the phase relationship between current and voltage and the corresponding mathematical formula. In this embodiment, the calculation formula of active power is: , where I represents the effective value of current in amperes, and U represents the effective value of voltage in volts; It represents the power factor, which is the cosine value of the angle between current and voltage, and reflects the proportion of active power in apparent power.

[0042] In addition, the metering unit also has data communication function, which can upload the collected power and voltage information to the control system in real time, supporting system administrators to remotely monitor the operating status of transformers in the substation area and promptly discover and solve potential problems.

[0043] Step S200: Calculate the average power of the area for a preset continuous time and the maximum power demand of the area.

[0044] Specifically, the average power calculation process is to obtain transformer power collection data for a preset time continuously through step S100 to form a power sampling sequence and ,in Represents a continuous preset time power sampling sequence for the first station area, represents the continuous preset time power sampling sequence of the second station area, and the average power of the first station area for the continuous preset time is , the average power of the second station area for the continuous preset time is ,in , , is the continuous preset time length in minutes, is the sampling frequency, and the preset time in this embodiment is 15 minutes.

[0045] The maximum power demand is the maximum continuous preset time average power. The calculation process includes: the maximum power demand of the first station area ; Maximum power demand of the second station area .

[0046] Step S300: Controlling the charging power and discharging power of the energy storage battery according to the average power change of the station area.

[0047] Specifically, when , control the discharge power of the energy storage battery in the first station area to increase, and the increase in discharge power is ;when , control the charging power of the energy storage battery in the first area to increase, and the charging power increase value is ;when , control the discharge power of the energy storage battery in the second station area to increase, and the increase in discharge power is ;when , control the charging power of the energy storage battery in the second station area to increase, and the charging power increase value is ; Where t represents a sampling time, and t+1 represents the next sampling time after the sampling time.

[0048] In one embodiment, step S300 also includes: reading the remaining power of all energy storage batteries in all substations; if the photovoltaic power generation equipment is in working condition, the photovoltaic power generation equipment is preferentially selected to charge the energy storage battery in the substation where it is located; if the remaining power of the energy storage battery is full, the energy storage battery in another substation is charged through the DC-DC converter between substations.

[0049] Specifically, after reading the remaining power of all the energy storage batteries in the substation, if it is detected that the photovoltaic power generation equipment is in working condition, the system will give priority to charging the energy storage batteries in these substations. This design aims to maximize the use of photovoltaic power generation equipment, reduce dependence on traditional power grids, and also reduce overall operating costs.

[0050] When the energy storage battery in a certain area has reached full capacity, the system will further determine the power status of the energy storage batteries in other areas. If the energy storage batteries in other areas are not full, the system will transfer the excess photovoltaic power through the DC-DC converter between the stations to charge them. This design not only avoids energy waste, but also realizes energy sharing and complementarity between stations, improving the energy utilization efficiency of the entire system.

[0051] Step S400: Implementing balanced control of the power in the substation area according to the maximum energy storage capacity of the energy storage battery.

[0052] Specifically, when the increase value of the first station is greater than the maximum capacity of the energy storage battery in the first station, and the increase value of the second station is less than the maximum capacity of the energy storage battery in the second station, the energy storage battery in the first station is controlled to transfer the difference power of the first station to the second station through the DC-DC converter between the two stations; When the increase value of the first station area is less than the maximum capacity of the energy storage battery in the first station area, and the increase value of the second station area is greater than the maximum capacity of the energy storage battery in the second station area, the energy storage battery in the second station area is controlled to transfer the difference power of the second station area to the first station area through the DC-DC converter between the two stations; When the increase value of the first station area is greater than the maximum capacity of the first energy storage battery and the increase value of the second station area is also greater than the maximum capacity of the second energy storage battery, the DC-DC converter between the two stations only serves as isolation and does not perform power transmission.

[0053] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A DC-coupled substation interconnection system, characterized in that: It includes two sections; The two sections are DC coupled via a first DC-DC converter; At least one of the two areas includes photovoltaic power generation equipment and / or energy storage batteries; Photovoltaic power generation equipment and energy storage batteries are connected to the DC bus of the substation through DC / DC converters; the DC bus is connected to the low-voltage side of the distribution network through AC / DC converters; A fast-charging DC charging station is installed in each substation, which is connected to the low-voltage side of the distribution network or to the DC bus of the substation.

2. The area interconnection system according to claim 1, characterized in that: The first DC-DC converter has a bidirectional power transmission function and can be dynamically adjusted according to the difference in power demand between the two stations.

3. The area interconnection system according to claim 1, characterized in that: The fast-charging DC charging station is connected to the distribution network in a DC coupling mode and an AC coupling mode; The DC coupling method is that the fast-charging DC charging station is connected to the DC bus of the substation where it is located, and then connected to the low-voltage side of the distribution network through the AC / DC converter of the substation; The AC coupling method is that the fast charging DC charging station is directly connected to the low-voltage side of the distribution network.

4. The area interconnection system according to claim 1, characterized in that: The system further comprises: When a fast-charging DC charging station is added in any substation by DC coupling, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding substation, and the newly added fast-charging DC charging station is connected to the low-voltage side of the distribution network through the AC / DC converter of the substation; When a fast-charging DC charging station is added in any substation using AC coupling, the newly added fast-charging DC charging station is directly connected to the low-voltage side of the distribution network.

5. A DC-coupled area interconnection control method, characterized in that: include: Step S100: collecting the power and voltage of the transformer through a metering unit deployed in the transformer of the substation; Step S200: Calculate the average power of the area for a preset continuous time and the maximum power demand of the area; Step S300: Controlling the charging power and discharging power of the energy storage battery according to the average power change of the station area; Step S400: Implementing balanced control of the power in the substation area according to the maximum energy storage capacity of the energy storage battery.

6. The area interconnection control method according to claim 5, characterized in that: The average power calculation process includes: The transformer power acquisition data of the preset time is obtained through step S100 to form a power sampling sequence , the average power of the station area for the continuous preset time is ,in , , is the continuous preset time length in minutes, is the sampling frequency.

7. The area interconnection control method according to claim 6, characterized in that: The maximum power demand is the maximum continuous preset time average power, and the calculation process is: .

8. The area interconnection control method according to claim 6, characterized in that: The step S300 specifically includes: when , control the discharge power of the energy storage battery in this area to increase, and the increase in discharge power is ; when , control the charging power of the energy storage battery in this area to increase, and the charging power increase value is ; Where t represents a sampling time, and t+1 represents the next sampling time after the sampling time.

9. The method for controlling interconnection of substations according to claim 6, characterized in that: The step S300 further includes: When a photovoltaic power generation device is in working condition, the remaining power of the energy storage batteries in all substations is read, and the photovoltaic power generation device is preferentially selected to charge the energy storage battery in its substation. If the remaining power of the energy storage battery is full, the energy storage batteries in other substations are charged through the DC-DC converter between substations.

10. The area interconnection control method according to claim 8, characterized in that: The step S400 specifically includes: When the power increase value of a certain area is greater than the maximum capacity of the energy storage battery in the area, the energy storage battery in the area is controlled to transfer the difference power of the area to the area whose power increase value is less than the maximum capacity of the energy storage battery in the area through the DC-DC converter between the stations; When the added value of all substations is greater than the maximum capacity of the substation energy storage battery, the DC-DC converters between substations only serve as isolation and no power transmission is performed.

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