Power supply guarantee type power grid electric energy regulation and control method and system based on optical storage flexible direct current

Abstract

The invention discloses a power supply protection type power grid electric energy regulation and control method and system based on optical storage flexible direct current, and the method comprises the steps: connecting the head end of a distribution transformer with the middle and rear ends of a line through a dual-port flexible direct current system, and configuring a plug-and-play energy storage / photovoltaic interface at a direct current side; wherein the converter D1 is connected with the head end of the low-voltage side of the distribution transformer, and the converter D2 is arranged in a voltage-sensitive user concentration area; based on the voltage threshold real-time monitoring result, triggering multi-mode operation of the D1-D2 bidirectional converter, including: when the terminal voltage is lower than a low threshold, starting a D1-D2 power supply mode; when the voltage is higher than a high threshold value, switching to a D2-D1 energy storage charging mode; when 50%-90% of voltage sag is detected, double converters are started for combined power supply; through linkage of rapid turn-off of a thyristor switch and an optical storage system, an emergency power supply channel of D2-users is established when a power grid fails. The power supply quality and the power supply reliability of the power distribution network can be improved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of integrated power quality control, and specifically to a power supply-guaranteed power grid control method and system based on photovoltaic storage and flexible direct current. Background Art

[0002] The distribution networks in mountainous areas, lake regions, and other regions across the country have long power supply radii and dispersed residential loads, resulting in low voltage problems for end users during peak load periods. With the advancement of new power system construction, distributed photovoltaics are being connected to the distribution network on a large scale. The centralized power generation during the day cannot be consumed locally, causing it to be fed back to the distribution network, which will cause high voltage problems for users. This will result in high voltage for users in the distribution areas where photovoltaics are connected, and low voltage for users at night. In addition, such areas are frequently affected by severe weather, and the power line failure rate is high. Due to the complex terrain of the line corridors, fault repairs take a long time, and residents experience long power outages, affecting normal production and life. Current power quality management equipment, such as high and low voltage and voltage sags, makes it difficult to address both power supply quality and power supply reliability. Summary of the Invention

[0003] In response to the technical problems existing in the prior art, the present invention provides a power supply-guaranteed grid power control method and system based on photovoltaic storage and flexible direct current to improve the power supply quality and reliability of the distribution network.

[0004] In order to solve the above technical problems, the technical solution proposed by the present invention is: A method for controlling power supply of a power grid based on a photovoltaic storage flexible direct current system comprises the following steps: A dual-port flexible DC system connects the distribution transformer headend with the middle and rear ends of the line, with a plug-and-play energy storage / photovoltaic interface configured on the DC side, forming a scalable multi-port interconnection architecture. The AC / DC converter D1 is connected to the low-voltage headend of the distribution transformer, and the DC / AC converter D2 is deployed in areas where voltage-sensitive users are concentrated. Based on real-time voltage threshold monitoring results, the D1-D2 bidirectional converter triggers multi-mode operation, including: starting the D1-D2 power supply mode when the terminal voltage falls below the low threshold; switching to the D2-D1 energy storage charging mode when the voltage rises above the high threshold; and starting the dual-converter joint power supply when a 50%-90% voltage sag is detected; By quickly shutting down the thyristor switch SCR and linking it with the photovoltaic storage system, an emergency power supply channel for D2-users is established in the event of a grid failure.

[0005] Preferably, by adding the D3 port, a mutual backup architecture is formed with the adjacent distribution transformers, a three-terminal flexible DC system is constructed, and cross-transformer energy transfer in the faulty substation is realized.

[0006] Preferably, the multi-mode operation is specifically implemented including: Establish a voltage threshold hierarchical response mechanism, setting low voltage threshold, high voltage threshold and deep sag threshold; Under normal distribution network conditions, the distribution transformer supplies power to the user loads in the substation area through low-voltage lines. When the flexible DC system converter D2 detects that the terminal voltage is lower than the low-voltage threshold, converters D1 and D2 start to supply power to the end user, increasing the user voltage. When the terminal voltage is higher than the high-voltage threshold, the current flows from converter D2 to converter D1, giving priority to charging the energy storage device. At the same time, the current is directly connected to the head end of the distribution transformer through the flexible DC system to control the user's high voltage, achieving reactive power compensation, high and low voltage, and three-phase imbalance control. When D1 detects a voltage sag in the distribution network with an amplitude greater than the deep sag threshold, converters D1 and D2 supply power to the terminal; when the sag amplitude is lower than 50%, the SCR is quickly shut down, and the photovoltaic storage system supplies power to the terminal through converter D2, ensuring the normal production of sensitive loads at the terminal and reducing user downtime losses.

[0007] Preferably, when a grid fault occurs, the SCR shuts down quickly, and the solar-storage system supplies power to the terminal through the converter D2, ensuring short-term and reliable power supply to low-voltage users. The power supply duration is determined by the configured energy storage system capacity and the effective output of distributed photovoltaics. For the three-port flexible DC system, when the 1# distribution transformer fails and is interrupted, the 2# distribution transformer forms the converter D3-D2 to interconnect and transfer power, achieving highly reliable power supply to low-voltage users.

[0008] Preferably, the energy storage device is connected to the DC line through a DC / DC module, and is first charged through the converter D2 when photovoltaic power generation is high, thereby improving the user's photovoltaic absorption capacity; secondly, it is charged through the converter D2 during low load periods or periods of high voltage.

[0009] The present invention also discloses a control system for realizing the above-mentioned guaranteed power grid power control method based on photovoltaic storage and flexible direct current, comprising a 1# distribution transformer, a thyristor switch SCR, a multi-converter module, an energy storage module, and a distributed photovoltaic module; the multi-converter module comprises an AC / DC converter D1 and a DC / AC converter D2; the AC side of D1 is connected to the output end of the 1# distribution transformer, and the DC side is connected to the energy storage system in two ways and connected to the DC side of the converter D2 through a DC bus; the DC side of the converter D2 is interconnected with the DC bus of the converter D1, the AC side is connected to the load, and the photovoltaic array is directly connected to the DC bus of the converter D2 through a DC cable; another group of photovoltaic arrays is directly connected to the load side AC bus through an inverter; the thyristor switch SCR is connected in series between the 1# distribution transformer and the load.

[0010] Preferably, it also includes an AC / DC converter D3; the AC side of the converter D3 is connected to the output end of the 2# distribution transformer, the DC side is connected to the common DC bus of the converters D1 and D2 through the DC bus, and the AC output end is connected in parallel to the load side.

[0011] Preferably, the thyristor switch SCR comprises a thyristor assembly consisting of a mechanical switch and two anti-parallel thyristors, and the mechanical switch is connected in parallel with the thyristor assembly.

[0012] Compared with the prior art, the advantages of the present invention are: Based on low-voltage flexible direct current technology, the present invention combines energy storage and user photovoltaics to propose a power supply-guaranteed grid power control technology and device based on photovoltaic storage flexible direct current. Low-voltage flexible direct current solves the low voltage and three-phase imbalance management of end users, energy storage solves the local consumption of photovoltaics, and combines with user photovoltaics to realize grid fault power supply and voltage sag prevention and control; in addition, low-voltage flexible direct current can adopt a multi-terminal mode to achieve flexible interconnection and mutual assistance between substations, thereby improving the power supply quality and reliability of the distribution network.

[0013] The present invention is based on a flexible direct current system, plug-and-play energy storage, distributed photovoltaics, and fast switches to construct a power control topology for distribution areas based on flexible direct current with photovoltaic storage. By monitoring user voltage fluctuations and voltage sags, voltage control is achieved through control methods such as low-voltage lines, converters D1-D2, converters D2-D1, and the photovoltaic storage system through converter D2. When the distribution network is interrupted by a fault, the photovoltaic storage system supplies power to the end user through converter D2, thereby ensuring power supply to the distribution network and simultaneously improving power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the power control topology diagram of the distribution area of ​​the PV-storage flexible direct current in the present invention.

[0015] Figure 2 This is a flow chart of the comprehensive control of power quality and power supply guarantee under fault conditions in the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1As shown, an embodiment of the present invention provides a power grid power control system based on photovoltaic storage and flexible direct current, including a 1# distribution transformer, a thyristor switch SCR, a multi-converter module, an energy storage module, and a distributed photovoltaic module; the multi-converter module includes an AC / DC converter D1 and a DC / AC converter D2; the AC side of D1 is connected to the output end of the 1# distribution transformer, and the DC side is connected to the energy storage system in two ways and connected to the DC side of the converter D2 through a DC bus; the DC side of the converter D2 is interconnected with the DC bus of the converter D1, and the AC side is connected to the load, and the photovoltaic array is directly connected to the DC bus of the converter D2 through a DC cable; another group of photovoltaic arrays is directly connected to the load side AC bus through an inverter; the thyristor switch SCR is connected in series between the 1# distribution transformer and the load.

[0018] In addition, it also includes an AC / DC converter D3; the AC side of the converter D3 is connected to the output end of the 2# distribution transformer, the DC side is connected to the common DC bus of the converters D1 and D2 through the DC bus, and the AC output end is connected in parallel to the load side.

[0019] Specifically, the thyristor switch SCR includes a thyristor assembly consisting of a mechanical switch and two anti-parallel thyristors, and the mechanical switch is connected in parallel with the thyristor assembly.

[0020] like Figure 2 As shown, an embodiment of the present invention further provides a control method for a power grid power control system based on the above-mentioned solar-storage flexible direct current system, comprising the following steps: A dual-port flexible DC system connects the distribution transformer headend with the middle and rear ends of the line, with a plug-and-play energy storage / photovoltaic interface configured on the DC side, forming a scalable multi-port interconnection architecture. The AC / DC converter D1 is connected to the low-voltage headend of the distribution transformer, and the DC / AC converter D2 is deployed in areas where voltage-sensitive users are concentrated. Based on real-time voltage threshold monitoring results, the D1-D2 bidirectional converter triggers multi-mode operation, including: starting the D1-D2 power supply mode when the terminal voltage falls below the low threshold; switching to the D2-D1 energy storage charging mode when the voltage rises above the high threshold; and starting the dual-converter joint power supply when a 50%-90% voltage sag is detected; By quickly shutting down the thyristor switch (SCR) and linking it with the solar-storage system, an emergency power supply channel for D2 users is established in the event of a grid failure. By adding the D3 port, a mutual backup architecture is formed with the adjacent distribution transformers, a three-terminal flexible DC system is constructed, and cross-transformer energy transfer in the faulty substation is realized.

[0021] The flexible DC system in a single substation has two ports. One end (AC / DC converter D1) is connected to the head end of the low-voltage line of the distribution transformer, and the other end (DC / AC converter D2) is connected to the middle and rear end of the low-voltage line, close to the low-voltage users. The DC line is equipped with multiple energy storage and distributed photovoltaic plug-and-play interfaces. The number of interfaces is determined by the power load, the capacity of a single energy storage unit, and the number of photovoltaic devices used by nearby users. The user's photovoltaic power generation can be flexibly connected to the distribution network in two ways: local access to the low-voltage AC grid through an inverter, and access to the DC line through a DC / DC module; DC ports can be added to form a multi-port flexible DC interconnection system. For example, one DC port (AC / DC converter D3) can be added to interconnect with another distribution transformer to improve the power supply capacity and reliability of the distribution network. Low-voltage lines can be optionally configured with a fast-switching module, consisting of a thyristor switch (SCR) (two thyristors connected in anti-parallel) and a mechanical switch. The thyristor switch is a power electronic switch that receives control commands from the monitoring module for rapid opening and closing. The mechanical switch primarily serves as a bypass switch during maintenance and overhaul of internal components. In the event of a power outage due to a distribution network fault, the thyristor switch quickly shuts off, allowing the PV-storage flexible DC system to restore power within 5ms.

[0022] When the power grid is operating normally, the power quality of the power grid is comprehensively regulated. That is, under normal distribution network conditions, the distribution transformer supplies power to the user loads in the substation area through low-voltage lines. When the flexible DC system converter D2 detects that the terminal voltage is lower than the low-voltage threshold, converters D1 and D2 start to supply power to the end user, increasing the user voltage. When the terminal voltage is higher than the high-voltage threshold, the current flows from converter D2 to converter D1, giving priority to charging the energy storage equipment. At the same time, the current is directly connected to the head end of the distribution transformer through the flexible DC system to control the high voltage of the user, achieving reactive power compensation, high and low voltage, and three-phase imbalance control. The energy storage device is connected to the DC line through a DC / DC module and is first charged through the converter D2 when the photovoltaic power generation is high, thereby improving the user's photovoltaic absorption capacity; secondly, it is charged through the converter D2 during off-peak load periods or periods of high voltage. When D1 detects a voltage sag of 50%-90% in the distribution network, converters D1 and D2 supply power to the terminal. When the sag is lower than 50%, the SCR shuts down quickly, and the photovoltaic storage system supplies power to the terminal through converter D2, ensuring the normal operation of sensitive loads at the terminal and reducing user downtime losses.

[0023] When a grid fault occurs, the system provides temporary power supply to the distribution network. That is, when a grid fault occurs, the SCR is quickly shut down, and the solar-storage system supplies power to the end users through the converter D2, ensuring short-term and reliable power supply to low-voltage users. The power supply duration is determined by the configured energy storage system capacity and the effective output of the distributed photovoltaic system. For a three-port flexible DC system, when the 1# distribution transformer fails and is interrupted, the 2# distribution transformer can be used to form the converter D3-D2 for interconnected transfer, achieving highly reliable power supply to low-voltage users. The power quality control method under this method is shown in step B.

[0024] Based on low-voltage flexible direct current technology, the present invention combines energy storage and user photovoltaics to propose a power supply-guaranteed grid power control technology and device based on photovoltaic storage flexible direct current. Low-voltage flexible direct current solves the low voltage and three-phase imbalance management of end users, energy storage solves the local consumption of photovoltaics, and combines with user photovoltaics to realize grid fault power supply and voltage sag prevention and control; in addition, low-voltage flexible direct current can adopt a multi-terminal mode to achieve flexible interconnection and mutual assistance between substations, thereby improving the power supply quality and reliability of the distribution network.

[0025] The present invention is based on a flexible direct current system, plug-and-play energy storage, distributed photovoltaics, and fast switches to construct a power control topology for distribution areas based on flexible direct current with photovoltaic storage. By monitoring user voltage fluctuations and voltage sags, voltage control is achieved through control methods such as low-voltage lines, converters D1-D2, converters D2-D1, and the photovoltaic storage system through converter D2. When the distribution network is interrupted by a fault, the photovoltaic storage system supplies power to the end user through converter D2, thereby ensuring power supply to the distribution network and simultaneously improving power quality.

[0026] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for controlling power supply of a guaranteed power grid based on a photovoltaic storage flexible direct current system, characterized in that: The following steps are involved: A dual-port flexible DC system connects the distribution transformer headend with the middle and rear ends of the line, with a plug-and-play energy storage / photovoltaic interface configured on the DC side, forming a scalable multi-port interconnection architecture. The AC / DC converter D1 is connected to the low-voltage headend of the distribution transformer, and the DC / AC converter D2 is deployed in areas where voltage-sensitive users are concentrated. Based on real-time voltage threshold monitoring results, the D1-D2 bidirectional converter triggers multi-mode operation, including: starting the D1-D2 power supply mode when the terminal voltage falls below the low threshold; switching to the D2-D1 energy storage charging mode when the voltage rises above the high threshold; and starting the dual-converter joint power supply when a 50%-90% voltage sag is detected; By quickly shutting down the thyristor switch SCR and linking it with the photovoltaic storage system, an emergency power supply channel for D2-users is established in the event of a grid failure.

2. The method for controlling power supply of a guaranteed power grid based on PV-storage flexible direct current according to claim 1 is characterized in that: By adding the D3 port, a mutual backup architecture is formed with the adjacent distribution transformers, a three-terminal flexible DC system is constructed, and cross-transformer energy transfer in the faulty substation is realized.

3. The method for controlling power supply of a guaranteed power grid based on PV-storage flexible direct current according to claim 1 or 2, characterized in that: The specific implementation of multi-mode operation includes: Establish a voltage threshold hierarchical response mechanism, setting low voltage threshold, high voltage threshold and deep sag threshold; Under normal distribution network conditions, the distribution transformer supplies power to the user loads in the substation area through low-voltage lines. When the flexible DC system converter D2 detects that the terminal voltage is lower than the low-voltage threshold, converters D1 and D2 start to supply power to the end user, increasing the user voltage. When the terminal voltage is higher than the high-voltage threshold, the current flows from converter D2 to converter D1, giving priority to charging the energy storage device. At the same time, the current is directly connected to the head end of the distribution transformer through the flexible DC system to control the user's high voltage, achieving reactive power compensation, high and low voltage, and three-phase imbalance control. When D1 detects a voltage sag in the distribution network with an amplitude greater than the deep sag threshold, converters D1 and D2 supply power to the terminal; when the sag amplitude is lower than 50%, the SCR is quickly shut down, and the photovoltaic storage system supplies power to the terminal through converter D2, ensuring the normal production of sensitive loads at the terminal and reducing user downtime losses.

4. The method for controlling power supply of a guaranteed power grid based on a PV-storage flexible direct current according to claim 1 or 2, characterized in that: When a grid fault occurs, the SCR shuts down quickly, and the solar-storage system supplies power to the end users through converter D2, ensuring short-term and reliable power supply to low-voltage users. The power supply duration is determined by the configured energy storage system capacity and the effective output of distributed photovoltaics. For the three-port flexible DC system, when the 1# distribution transformer fails and is interrupted, the 2# distribution transformer forms the converter D3-D2 to interconnect and transfer power, achieving highly reliable power supply to low-voltage users.

5. The method for controlling power supply of a guaranteed power grid based on PV-storage flexible direct current according to claim 1 or 2, characterized in that: The energy storage device is connected to the DC line through a DC / DC module, and is first charged through the converter D2 when photovoltaic power generation is high, thereby improving the user's photovoltaic absorption capacity; secondly, it is charged through the converter D2 during low load periods or periods of high voltage.

6. A control system for implementing the method for controlling power grid electricity supply based on PV-storage flexible direct current as described in any one of claims 1 to 5, characterized in that: It includes 1# distribution transformer, thyristor switch SCR, multi-converter module, energy storage module, and distributed photovoltaic module; the multi-converter module includes AC / DC converter D1 and DC / AC converter D2; the AC side of D1 is connected to the output end of 1# distribution transformer, and the DC side is connected to the energy storage system in two ways and connected to the DC side of converter D2 through the DC bus; the DC side of converter D2 is interconnected with the DC bus of converter D1, the AC side is connected to the load, and the photovoltaic array is directly connected to the DC bus of converter D2 through a DC cable; another group of photovoltaic arrays is directly connected to the load-side AC bus through an inverter; the thyristor switch SCR is connected in series between 1# distribution transformer and the load.

7. The control system according to claim 6, characterized in that: It also includes an AC / DC converter D3; the AC side of the converter D3 is connected to the output end of the 2# distribution transformer, the DC side is connected to the common DC bus of the converters D1 and D2 through the DC bus, and the AC output end is connected in parallel to the load side.

8. The control system according to claim 6 or 7, characterized in that: The thyristor switch SCR comprises a thyristor assembly consisting of a mechanical switch and two anti-parallel thyristors, and the mechanical switch is connected in parallel with the thyristor assembly.

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