Transformer Area Interconnection System Based on DC Coupling and Its Control Method

Abstract

The present invention relates to the technical field of electric power systems, and discloses a DC-coupled substation interconnection system and a control method thereof. The system connects two substations through a DC coupling module, and at least one substation includes photovoltaic power generation equipment and / or energy storage batteries, all of which are connected to the DC bus through a DC / DC converter, and then connected to the low-voltage side of the distribution network through an AC / DC converter. Each substation is equipped with a fast-charging DC charging station, which can be connected to the low-voltage side of the distribution network or the DC bus. The control method includes collecting transformer power and voltage, calculating the average power and maximum power demand of the substation for a continuous preset time, controlling the charging and discharging power of the energy storage battery according to the average power change, and implementing substation power balancing control according to the maximum energy storage capacity of the energy storage battery. The present invention improves energy utilization efficiency and power supply reliability, reduces operating costs, and improves the intelligence level of energy management, with significant economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and discloses a DC-coupled interconnection system for distribution substations and its control method. Background Art

[0002] At present, due to the development of fast charging equipment, the distribution capacity of many distribution substations is insufficient, which restricts the development of many fast charging equipment. This problem is particularly prominent in fast charging stations in highway service areas. When the seasonal or time-of-day load growth in a substation exceeds expectations, the insufficient capacity of low-voltage lines will lead to a decline in voltage quality. In addition, the distribution of distribution transformers fails to keep up with the growth of electricity demand, and the insufficient capacity of transformers easily causes overload and heavy load phenomena, affecting their service life and the stability of output voltage. In some areas, there is also a problem of a relatively large power supply radius in the substation, resulting in a low voltage at the end. For substations with an average low-voltage power supply radius exceeding 0.8 km, the low voltage phenomenon at the end is particularly serious. 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 consumption capacity of the distribution network, it will cause reverse power flow, resulting in voltage increase or even overvoltage, threatening the stability of the power grid. Summary of the Invention

[0003] Aiming at the above-mentioned existing technical deficiencies, the purpose of the present invention is to provide a DC-coupled interconnection system for distribution substations and its control method, so as to solve the problem of relatively low intelligent level of energy management in the existing technology.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions:

[0005] In the first aspect, the present invention provides a DC-coupled interconnection system for distribution substations, including two distribution substations;

[0006] The two distribution substations are DC-coupled through a first DC-DC converter;

[0007] At least one of the two distribution substations includes photovoltaic power generation equipment and / or energy storage batteries;

[0008] The photovoltaic power generation equipment and the energy storage batteries are both connected to the DC bus of the substation where they are located through a DC / DC converter; the DC bus is connected to the low-voltage side of the distribution network through an AC / DC converter;

[0009] A fast charging DC charging station is provided in each distribution substation, and the fast charging DC charging station is connected to the low-voltage side of the distribution network or connected to the DC bus of the substation where it is located.

[0010] Preferably, in a possible implementation manner of the first aspect, the first DC-DC converter has a bidirectional power transmission function and can dynamically adjust according to the difference in power demand between the two distribution substations.

[0011] Preferably, in a possible implementation manner of the first aspect, the fast-charging DC charging station accessing the distribution network includes a DC coupling method and an AC coupling method;

[0012] The DC coupling method is that the fast-charging DC charging station is connected to the DC bus of the corresponding substation area, and then accesses the low-voltage side of the distribution network through the AC / DC converter of the substation area;

[0013] The AC coupling method is that the fast-charging DC charging station directly accesses the low-voltage side of the distribution network.

[0014] Preferably, in a possible implementation manner of the first aspect, the system further includes:

[0015] When a fast-charging DC charging station is newly added to any substation area in the DC coupling mode, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding substation area, 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 area;

[0016] When a fast-charging DC charging station is newly added to any substation area in the AC coupling mode, the newly added fast-charging DC charging station directly accesses the low-voltage side of the distribution network.

[0017] In a second aspect, the present invention provides a method for controlling the interconnection of substation areas based on DC coupling, including:

[0018] Step S100: Collect the power and voltage of the transformer through a metering unit deployed in the substation area transformer;

[0019] Step S200: Calculate the average power of the substation area for a continuous preset time and the maximum demand of the power of the substation area;

[0020] Step S300: Control the charging power and discharging power of the energy storage battery according to the change of the average power of the substation area;

[0021] Step S400: Implement the balanced control of the substation area power according to the maximum energy storage capacity of the energy storage battery.

[0022] Preferably, in a possible implementation manner of the second aspect, the average power calculation process includes:

[0023] Obtain the transformer power acquisition data for a continuous preset time through step S100 to form a power sampling sequence , the average power of the substation area for a continuous preset time is , where , , is the continuous preset time length in minutes, is the sampling frequency.

[0024] Preferably, in a possible implementation manner of the second aspect, the maximum demand of power is the maximum continuous preset-time average power, and the calculation process is .

[0025] Preferably, in a possible implementation manner of the second aspect, the step S300 specifically includes:

[0026] When , control the discharge power of the energy storage battery in this substation area to increase, and the increased value of the discharge power is ;

[0027] When , control the charging power of the energy storage battery in this substation area to increase, and the increased value of the charging power is ;

[0028] where t represents a certain sampling moment, and t + 1 represents the next sampling moment after this sampling moment.

[0029] Preferably, in a possible implementation manner of the second aspect, the step S300 further includes:

[0030] When there is a photovoltaic power generation device in a working state, read the remaining power of all the energy storage batteries in the substation area, and preferentially select this photovoltaic power generation device to charge the energy storage battery in the substation area where it is located. If the remaining power of this energy storage battery is full, charge the energy storage batteries in other substation areas through the DC-DC converter between the substations.

[0031] Preferably, in a possible implementation manner of the second aspect, the step S400 specifically includes:

[0032] When the increased value of power in a certain substation area is greater than the maximum capacity of the energy storage battery in this substation area, control the energy storage battery in this substation area to transfer the differential power of this substation area to the substation area where the increased value of power is less than the maximum capacity of the energy storage battery in the substation area through the DC-DC converter between the substations;

[0033] When the increased values of all substation areas are greater than the maximum capacity of the energy storage battery in the substation area, the DC-DC converter between the substations only acts as isolation and does not perform power transmission.

[0034] The beneficial effects of the present invention are as follows: When the photovoltaic power generation module generates electricity and the remaining power of the energy storage battery is not full, the minimum grid power consumption control method is executed. Through the DC coupling module, direct charging of the energy storage battery by photovoltaic power generation and cross-region charging are realized, reducing the grid power consumption. When the photovoltaic power generation module does not generate electricity and the remaining power of the energy storage battery is not full, the power consumption balance control method between regions and the maximum demand power consumption balance control method are executed. The metering unit collects data and calculates, and adjusts the power of the energy storage battery according to the calculation result to achieve power balance between regions, avoiding energy waste. In addition, the system also has an energy storage module, a charging module, a DC coupling module, etc., realizing flexible interconnection between photovoltaic power generation, energy storage batteries and the grid, improving energy utilization efficiency and power supply reliability. Overall, the present invention reduces the operating cost of highway service areas, improves the intelligent level of energy management, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 This application provides a structural diagram of the DC coupling subsystem of a fast charging station based on a DC coupling inter-region system.

[0037] Figure 2 This application provides a structural diagram of the AC coupling subsystem of a fast charging station based on a DC coupling inter-region system.

[0038] Figure 3 This application provides a flowchart of a DC coupling inter-region control method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0040] Embodiment 1: The present invention provides an inter-region system based on DC coupling, including a first region, a second region, and a first DC-DC converter; the first DC-DC converter is used to realize DC coupling between the DC bus of the first region and the DC bus of the second region.

[0041] The first substation area 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, where:

[0042] 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 are uniformly connected to the distribution network through the first AC / DC converter; the first other load is directly connected to the distribution network.

[0043] The second substation area 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, where:

[0044] The second photovoltaic power generation device and the second energy storage battery are respectively connected to the DC bus through the third DC / DC converter and the fourth DC / DC converter, and then are uniformly connected to the distribution network through the charging station AC / DC converter; the second other load is directly connected to the distribution network.

[0045] When the fast-charging DC charging station in any substation area is connected to the distribution network in a DC coupling manner, this substation 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 substation area is connected to the grid in an AC coupling manner, this substation area also includes a fast-charging DC charging station, and the fast-charging DC charging station is directly connected to the distribution network.

[0046] The first DC-DC converter has a two-way power transmission function and can dynamically adjust according to the power demand difference between the first substation area and the second substation area.

[0047] As Figure 1 shown, both the fast-charging DC charging stations in the first substation area and the second substation area are connected to the distribution network in a DC coupling manner.

[0048] Specifically, in the first substation area 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 device and the first energy storage battery through the DC bus of the first substation area; in the second substation area 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 device and the first energy storage battery through the DC bus of the second substation area.

[0049] As Figure 2 shown, both the fast-charging DC charging stations in the first substation area and the second substation area are connected to the distribution network in an AC coupling manner.

[0050] Specifically, in the first sub-region of the system, the third fast-charging DC charging station is directly connected to the distribution network; in the second sub-region of the system, the fourth fast-charging DC charging station is directly connected to the distribution network.

[0051] In this embodiment, the photovoltaic power generation device is a device that directly converts sunlight into electrical energy using the photovoltaic effect. For example, the first photovoltaic power generation device in the first sub-region and the second photovoltaic power generation device in the second sub-region are both connected to the DC bus through corresponding DC / DC converters. This enables the DC electrical energy generated by the photovoltaic power generation device to be efficiently and safely transmitted to the system and finally connected to the distribution network through an AC / DC converter, realizing the sustainable utilization of energy.

[0052] The energy storage battery is a device for storing electrical energy and can release electrical energy when needed to balance supply and demand. For example, the first energy storage battery in the first sub-region and the second energy storage battery in the second sub-region are also connected to the DC bus through DC / DC converters. In this way, the energy storage battery can store excess electrical energy when the light is sufficient and release electrical energy when the light is insufficient or during peak demand periods, ensuring the stable operation of the system.

[0053] The fast-charging DC charging station is a charging facility designed for fast charging of electric vehicles, etc. For example, the first fast-charging DC charging station and the second fast-charging DC charging station can be directly connected to the DC bus and connected to the distribution network through an AC / DC converter. At the same time, the fast-charging DC charging station can also be directly connected to the distribution network. For example, the third fast-charging DC charging station and the fourth fast-charging DC charging station use AC power supply to provide DC charging services for electric vehicles.

[0054] The DC / DC converter is a device used to convert DC electrical energy from one voltage level to another. DC / DC converters (such as the first DC / DC converter to the fifth DC / DC converter) are applied to the connection between the photovoltaic power generation device, the energy storage battery and the DC bus. It can ensure that devices with different voltage levels can be safely and efficiently connected to the system, realizing the flexible scheduling and distribution of electrical energy.

[0055] The AC / DC converter is a device for converting between AC electrical energy and DC electrical energy. For example, the first AC / DC converter to the fourth AC / DC converter is used to convert the electrical energy on the DC bus into AC electrical energy and finally connect to the distribution network. This enables the system to transmit the DC electrical energy generated by the photovoltaic power generation device and the energy storage battery and the electrical energy provided by the fast-charging DC charging station to the power grid to meet the electricity demand.

[0056] Other loads include lighting loads, domestic electrical loads, and electrical maintenance equipment loads.

[0057] In one embodiment, the system further includes that when a fast-charging DC charging station is newly added to any substation area in a DC coupling manner, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding substation area, 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 area; when a fast-charging DC charging station is newly added to any substation area in an AC coupling manner, the newly added fast-charging DC charging station is directly connected to the low-voltage side of the distribution network.

[0058] Specifically, when a fast-charging DC charging station is newly added in a DC coupling manner, the newly added fast-charging DC charging station is directly connected to the DC bus of the corresponding substation area (such as the first substation area or the second substation area). After connection, the newly added fast-charging DC charging station can be connected to the distribution network through the newly added AC / DC converter of the substation area, realizing two-way power flow and efficient utilization of electric energy.

[0059] At the same time, the newly added fast-charging DC charging station is interconnected with the photovoltaic power generation equipment and energy storage battery of the substation area through the DC bus. This enables the fast-charging DC charging station to directly obtain stable electric energy from the photovoltaic power generation equipment and energy storage battery, reducing the dependence on the power grid.

[0060] When a fast-charging DC charging station is newly added in an AC coupling manner, the newly added fast-charging DC charging station can be directly connected to the distribution network without interconnection through the DC bus. This connection method simplifies the system structure, reduces the construction cost, and at the same time ensures that the newly added charging station can be quickly and flexibly put into operation.

[0061] Embodiment 2: As Figure 3 shown, the present invention provides a method for controlling the interconnection of substation areas based on DC coupling, including:

[0062] Step S100: Collect the power and voltage of the transformer through a metering unit deployed in the substation area transformer.

[0063] Specifically, the metering unit first measures the current and voltage values at the input and output ends of the transformer through the built-in current transformer and voltage transformer. These measured values are converted by an 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 for subsequent data analysis and processing.

[0064] After collecting the original 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 the current and voltage and the corresponding mathematical formula. In this embodiment, the calculation formula for active power is , where I represents the effective value of the current, in amperes, and U represents the effective value of the voltage, in volts; The power factor is the cosine value of the angle between the current and the voltage, which reflects the proportion of the active power in the apparent power.

[0065] In addition, the metering unit also has a data communication function, which can upload the collected power and voltage information to the control system in real time. It supports the system administrator to remotely monitor the operation status of the transformer in the substation area and timely discover and solve potential problems.

[0066] Step S200: Calculate the average power of the substation area for a continuous preset time and the maximum demand of the power of the substation area.

[0067] Specifically, the average power calculation process is to obtain the transformer power acquisition data for a continuous preset time through Step S100 to form a power sampling sequence and , where represents the power sampling sequence of the first substation area for a continuous preset time, represents the power sampling sequence of the second substation area for a continuous preset time. The average power of the first substation area for a continuous preset time is , and the average power of the second substation area for a continuous preset time is , where , , is the length of the continuous preset time in minutes, is the sampling frequency. In this embodiment, the preset time is 15 minutes.

[0068] The maximum demand of the power is the maximum average power of the continuous preset time. The calculation process includes: the maximum demand of the power of the first substation area ; the maximum demand of the power of the second substation area .

[0069] Step S300: Control the charging power and discharging power of the energy storage battery according to the change of the average power of the substation area.

[0070] Specifically, when , control the discharging power of the energy storage battery in the first substation area to increase, and the increased value of the discharging power is ; when , control the charging power of the energy storage battery in the first substation area to increase, and the increased value of the charging power is ; when , control the discharging power of the energy storage battery in the second substation area to increase, and the increased value of the discharging power is ; when , control the charging power of the energy storage battery in the second substation area to increase, and the increased value of the charging power is ; where t represents a certain sampling moment, and t + 1 represents the next sampling moment of this sampling moment.

[0071] In one embodiment, step S300 further includes: reading the remaining power of all the energy storage batteries in the power distribution areas. If the photovoltaic power generation device is in a working state, the photovoltaic power generation device is preferentially selected to charge the energy storage batteries in its own power distribution area. If the remaining power of the energy storage battery is full, the excess power is used to charge the energy storage batteries in another power distribution area through the DC-DC converter between the power distribution areas.

[0072] Specifically, after reading the remaining power of all the energy storage batteries in the power distribution areas, if it is detected that the photovoltaic power generation device is in a working state, the system will preferentially arrange the energy storage batteries in these power distribution areas to be charged. Such a design aims to maximize the utilization of the photovoltaic power generation device, reduce the dependence on the traditional power grid, and also reduce the overall operating cost.

[0073] When the power of the energy storage battery in a certain power distribution area has reached the full state, the system will further judge the power of the energy storage batteries in other power distribution areas. If the power of the energy storage batteries in other power distribution areas is not full, the system will transfer the excess photovoltaic power through the DC-DC converter between the power distribution areas to charge them. Such a design not only avoids the waste of energy, but also realizes the energy sharing and complementarity between the power distribution areas, improving the energy utilization efficiency of the whole system.

[0074] Step S400: Implement the balanced control of the power in the power distribution area according to the maximum energy storage capacity of the energy storage battery.

[0075] Specifically, when the increase value of the first power distribution area is greater than the maximum capacity of the energy storage battery in the first power distribution area, and the increase value of the second power distribution area is less than the maximum capacity of the energy storage battery in the second power distribution area, control the energy storage battery in the first power distribution area to transfer the differential power of the first power distribution area to the second power distribution area through the DC-DC converter between the two power distribution areas;

[0076] When the increase value of the first power distribution area is less than the maximum capacity of the energy storage battery in the first power distribution area, and the increase value of the second power distribution area is greater than the maximum capacity of the energy storage battery in the second power distribution area, control the energy storage battery in the second power distribution area to transfer the differential power of the second power distribution area to the first power distribution area through the DC-DC converter between the two power distribution areas;

[0077] When the increase value of the first power distribution area is greater than the maximum capacity of the first energy storage battery and the increase value of the second power distribution area is also greater than the maximum capacity of the second energy storage battery, the DC-DC converter between the two power distribution areas only acts as isolation and does not perform power transmission.

[0078] 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 equivalent technologies, 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 stations are DC-coupled via a first DC-DC converter, wherein 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; Both areas include photovoltaic power generation equipment and 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; 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 any area adds a fast-charging DC charging station using AC coupling, the newly added fast-charging DC charging station is directly connected to the low-voltage side of the distribution network; The control method of the system includes: Step S100: collecting the current and voltage of the transformer through a metering unit deployed in the transformer of the substation, and calculating the power of the transformer according to the current and voltage of the transformer; Step S200: Calculate the average power of the station area for a preset continuous time. The average power calculation process includes: The transformer power data of the continuous 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; 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; The step S200 also includes calculating the maximum power demand of the substation, where the maximum power demand is the maximum continuous preset time average power. The calculation process is as follows: .

2. 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.

3. The area interconnection system according to claim 1, 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.

4. The area interconnection system according to claim 1, 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 first DC-DC converter between substations.

5. The area interconnection system according to claim 3, 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 first DC-DC converter between the areas, and the power increase value is the increase value of the charging power or discharging power of the energy storage battery; When the added values ​​of all substations are greater than the maximum capacity of the substation energy storage battery, the first DC-DC converter between substations only serves as isolation and does not transmit power.

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