CN103457225B - AC ice melting method based on flow battery - Google Patents

Abstract

The invention discloses an alternating current ice melting method based on a flow battery, which comprises the following steps: connecting the tail end of the transmission line needing to be deiced with a grounding system comprising a resistor and a sixth switching unit; the main control system calculates critical current for preventing the ice coating of the power transmission line needing ice melting; the main control system obtains the required ice melting power; closing the third switch unit, closing the switch unit which is connected with the high-voltage bus and the starting end of the transmission line needing ice melting, and closing the sixth switch unit; the main control system controls the output power of the flow battery power supply system to reach the required ice melting power P; the master control system calculates the time required by ice melting; the master control system judges whether the time required by ice melting is reached, and if so, the sixth switch unit is switched off; according to the invention, the tail end of the power transmission line needing ice melting is connected with the grounding system, and the initial end of the power transmission line needing ice melting adopts the flow battery power supply system combined with the solar power supply system or the wind power supply system as the ice melting alternating current power supply, so that the energy-saving and practical ice melting alternating current power supply is energy-saving and convenient to use.

Description

AC ice melting method based on flow battery

technical field

The invention relates to the technical field of ice melting for power transmission lines, in particular to an AC ice melting method based on a liquid flow battery.

Background technique

China is one of the countries with the most serious icing on transmission lines in the world. Severe icing will lead to a sharp decline in the mechanical and electrical performance of transmission lines, which will lead to icing accidents. There have been icing accidents on transmission lines in Hunan, Hubei, Guizhou, Jiangxi, Yunnan, Sichuan, Henan and Shaanxi provinces in China. Icing accidents have seriously threatened the safe operation of my country's power system and caused huge economic losses.

The main hazards of wire icing are as follows:

1. Overload: The actual weight of the ice-covered conductor exceeds the design value by a lot, which leads to mechanical and electrical accidents on the overhead transmission line;

2. Accidents of non-uniform deicing or uneven icing: uneven icing of adjacent wires or different tensions caused by deicing in different periods will cause the wires and ground wires to slide in the clamp, and in severe cases, the outer aluminum strands of the wires will be online All the clip outlets are broken and the steel core twitches;

3. Insulator string ice flash accident: After the insulator is covered with ice or bridged by ice, the insulation strength decreases, the leakage distance is shortened, and the local surface resistance of the insulator increases when the ice melts, forming a flashover accident. During the development of the flashover, the arc burns the insulator continuously. Cause the insulation strength of the insulator to decrease;

4. Conductor ice-covered galloping accidents: Conductors gallop under the action of wind due to uneven ice-coating. The low-frequency and high-amplitude galloping of ice-coated conductors causes serious accidents such as damage to hardware, broken strands of conductors, phase-to-phase short circuits, tilting or collapse of towers, etc.

Therefore, effective and practical ice-melting methods are of great significance for alleviating the ice and snow attacks on transmission lines in winter. The ice-melting methods in the prior art are mainly various thermal ice-melting methods. The basic principle of the thermal ice-melting method is to pass high Transmit current at normal current density to obtain Joule heat to melt ice. The previous research mainly includes: high current density ice melting adopted by Pohlmsn and LSnders in 1982; Ice and resistive ferromagnetic wires developed by YSsui, YSmSmoto and Fuji in Japan from 1987 to 1990. At present, domestic 220kV and below transmission lines, in addition to adopting measures such as "avoidance, modification, resistance, and prevention" in the design and construction of power lines , for the problem of icing on large-scale transmission lines, the method of thermal ice melting of wires is the most effective method.

Among them, the principle of AC ice-melting technology is to apply AC power to the ice-coated line as a load, and provide ice-melting current to heat the wire to melt the ice. Although it can reduce the investment, it is limited by the capacity of the generator set and the capacity required for ice melting, and most of the cases do not meet the demand; the use of system power as the ice melting power supply is limited, and the system power supply is under the condition of power grid failure and decoupling Power out, unusable.

Contents of the invention

In view of the above problems, the present invention develops an AC ice-melting method based on a liquid flow battery.

Technical means of the present invention is as follows:

An AC ice-melting method based on a liquid flow battery, comprising the steps of:

S1: Connect the end of the power transmission line to be deiced to the grounding system including a resistor and the sixth switch unit; one end of the resistor is grounded, and the other end is connected to the end of the power transmission line to be deiced through the sixth switch unit, and S2 is executed ;

S2: The main control system calculates the critical current I for preventing icing on transmission lines that need to be melted according to the formula I _C ＝(D/ρ)[(t _s -t)(πh+πσεt ³ +2EVWc _w +2EVW _E L _V ] _C , where D is the wire diameter of the transmission line that needs to melt ice, ρ is the resistivity of the wire that needs to melt ice, t _s is the surface temperature of the wire that needs to melt ice, h is the convective heat transfer coefficient, and σ is StefSn- BoltcomSnn constant, ε is the blackness of the conductor of the power transmission line that needs to be ice-melted, E is the capture coefficient of the conductor of the power transmission line that needs to be ice-melted to the supercooled water droplet in the air, V is the average moving speed of the humid air or supercooled water droplet, W is the humidity Moisture content of air or supercooled water droplet, t is the temperature of humid air or supercooled water droplet, c _w is specific heat capacity of water at constant pressure, W _E is the liquid share evaporated on the surface of the wire of the transmission line that needs to melt ice, L _V is the latent heat of vaporization of water, execute S3;

S3: The main control system obtains the required ice-melting power P=I _C ² R according to the calculated critical current I _C and the sum R of the transmission line resistance and the resistor resistance at the current ambient temperature, and executes S4 ;

S4: close the third switch unit, close the switch unit connecting the high-voltage bus and the beginning of the transmission line to be deiced, and close the sixth switch unit, and execute S5;

S5: The main control system controls the output power of the flow battery power supply system to reach the required ice-melting power P; the flow battery power supply system includes a flow battery unit connected in series, an energy storage inverter, a third transformer and a third A switch unit, the output end of the flow battery power supply system is connected to the high-voltage bus; execute S6;

S6: The main control system according to the formula $T=\frac{[c_i(273.15-T_a)+L_f]{\mathrm{\ρ}}_i{R}_i({2R}_0-{\mathrm{\πR}}_i/2)}{{I_C}^2{R}_e}$ Calculate the time T required to melt ice, where ci is the specific heat of ice, T _a is the air temperature, L _F is the latent heat released by solidification of water, ρ _i is the density of ice _, and R ₀ is the ice-covered transmission line to be melted. The average radius of the conductor, R _i is the radius of the conductor when the power transmission line needs to be melted without ice, I _C is the ice melting current, that is, the critical current to prevent the icing of the power transmission line that needs to be melted, and R _e is the unit length of the conductor at zero degrees resistance, execute S7;

S7: The main control system judges whether the time T required for melting ice has been reached, if yes, execute S8, otherwise execute S7;

S8: disconnect the sixth switch unit;

Further, the method further includes the following steps after step S3:

C1: The main control system judges whether the rated power of the flow battery power supply system is greater than or equal to the required ice-melting power P, if yes, execute S4, otherwise execute C2;

C2: The main control system starts a solar power supply system or a wind power generation system; the solar power supply system is composed of a plurality of parallel solar power supply branches; the wind power supply system is composed of a plurality of parallel wind power supply branches; each The solar power supply branch includes a solar power station, a first transformer and a first switch unit; each of the wind power supply branches includes a wind power station, a second transformer and a second switch unit; the output terminal of the solar power supply system and The output end of the wind power supply system is connected to the high-voltage busbar, and C3 is executed;

C3: Close the first switch unit or the second switch unit, close the third switch unit, close the switch unit connecting the high-voltage bus and the beginning of the transmission line to be deiced, and close the sixth switch unit, and execute C4;

C4: The main control system controls the output power of the solar power supply system or wind power generation system combined with the output power of the flow battery power supply system to achieve the required ice-melting power P, and execute S6;

Further, the power transmission line to be melted is a high-voltage power transmission and distribution line, a solar power supply branch or a wind power supply branch;

When the power transmission line to be thawed is a high-voltage power transmission and distribution line, the switch unit connected to the high-voltage bus and the start of the power transmission line to be thawed is the fourth switch unit, and the start of the high-voltage power transmission and distribution line is connected to the high-voltage power transmission line through the fourth switch unit. A bus bar, the end of the high-voltage transmission and distribution line is connected to the public grid through the fifth switch unit;

When the power transmission line to be thawed is a solar power supply branch, the switch unit connecting the high-voltage bus and the beginning of the power line to be thawed is the first switch unit;

When the power transmission line that needs to melt ice is a wind power supply branch, the switch unit that connects the high-voltage bus and the beginning of the power transmission line that needs to melt ice is the second switch unit;

Further, the solar power supply system, wind power supply system, and flow battery power supply system connected to each other through the high-voltage busbar, and the public grid connected to the high-voltage busbar through the high-voltage power transmission and distribution line constitute a grid-connected microgrid system;

Further, when the power transmission line to be thawed is a high-voltage power transmission and distribution line, the following steps are also included before step S1:

disconnecting the first switch unit, the second switch unit, the third switch unit, the fourth switch unit and the fifth switch unit;

Further, when the power transmission line to be thawed is a solar power supply branch, the following steps are also included before step S1:

Disconnect the connection between the first switch unit, the second switch unit, the third switch unit, the fourth switch unit, and the first transformer and the solar power station; the solar power supply branch disconnects the connection of the solar power station as The end of the transmission line that needs to be deiced;

Further, when the power transmission line to be deiced is a wind power supply branch, there are the following steps before step S1:

Disconnect the connection between the first switch unit, the second switch unit, the third switch unit, the fourth switch unit, and the second transformer and the wind power station; the wind power supply branch disconnects the connection of the wind power station as The end of the transmission line that needs to be deiced;

Further, each phase at the end of the power transmission line to be deiced can be connected to the grounding system respectively;

Further, the two-phase or three-phase at the end of the power transmission line that needs to be melted can be short-circuited together and then connected to the grounding system;

Further, a fourth transformer is also arranged between the fourth switch unit and the high-voltage bus; the first switch unit, the second switch unit, the third switch unit, the fourth switch unit, the fifth switch unit and the sixth switch unit The switch unit is a manual switch or a switchgear.

Due to the adoption of the above technical scheme, the AC ice melting method based on the flow battery provided by the present invention, by connecting the end of the power transmission line to be melted to the grounding system, the beginning of the power transmission line to be melted uses the flow battery power supply system as the AC power supply for ice melting , which is energy-saving, practical, and easy to use. It can not only solve the problem in the prior art that using generator sets to provide ice-melting power is limited by the capacity of the generator set and the capacity required for ice-melting, but also avoids the use of system power as the ice-melting power in the event of grid failure and In the case of unloading, the power supply of the system is cut off and cannot be used, which effectively ensures the safety and stability of the transmission line in the cold weather of ice and snow; the main control system is adopted to reasonably control the ice melting current and ice melting time, and the ice melting process is safe and reliable; In addition, the solar power supply system, wind power generation system and flow battery power supply system can be combined to provide ice-melting power. Not only is it convenient for normal power supply when there is no need to melt ice, but also it is beneficial to increase the power of ice melting, thereby prolonging the length of the power transmission line that needs to melt ice to realize ice melting, and has a wide application range.

Description of drawings

Fig. 1, Fig. 2 are the flow charts of method of the present invention;

Fig. 3 is a system block diagram of the method of the present invention.

In the figure: 1. Solar power supply system, 2. Wind power supply system, 3. Flow battery power supply system, 4. Grounding system, 5. Main control system, 6. High-voltage busbar, 7. High-voltage transmission and distribution lines, 8. Four switch units, 9, fifth switch unit, 10, public grid, 11, solar power station, 12, first transformer, 13, first switch unit, 21, second switch unit, 22, second transformer, 23, Wind power station, 31, liquid flow battery unit, 32, energy storage inverter, 33, third transformer, 34, third switch unit, 41, resistor, 42, sixth switch unit, 50, fourth transformer.

detailed description

An AC ice-melting method based on a flow battery as shown in Figure 1, Figure 2 and Figure 3 includes the following steps:

S1: Connect the end of the power transmission line to be thawed with the grounding system 4 including the resistor 41 and the sixth switch unit 42; one end of the resistor 41 is grounded, and the other end is connected to the end of the power transmission line to be thawed through the sixth switch unit 42 connected, execute S2;

S2: The main control system 5 calculates the critical current to prevent icing on transmission lines that need to be melted according to the formula I _C =(D/ρ)[(t _s -t)(πh+πσεt ³ +2EVWc _w +2EVW _E L _V ] I _C , where D is the wire diameter of the power transmission line that needs to melt ice, ρ is the resistivity of the wire that needs to melt ice, t _s is the surface temperature of the wire that needs to melt ice, h is the convective heat transfer coefficient, and σ is StefSn -BoltcomSnn constant, ε is the blackness of the conductor of the power transmission line that needs to be melted, E is the capture coefficient of the conductor of the power transmission line that needs to be melted to the supercooled water droplet in the air, V is the average moving speed of the humid air or the supercooled water droplet, W is Moisture content of humid air or supercooled water droplet, t is the temperature of humid air or supercooled water droplet, cw is the specific heat capacity of water at constant pressure, _{W E} is the liquid share evaporated on the surface of the wire of the transmission line that needs to melt ice, L _V is the latent heat of vaporization of water, execute S3;

S3: The main control system 5 obtains the required ice-melting power P=I _C ² R according to the calculated critical current I _C and the sum R of the resistance of the transmission line to be ice-melted and the resistance of the resistor 41 at the current ambient temperature, Execute S4;

S4: close the third switch unit 34, close the switch unit connecting the high-voltage bus 6 and the beginning of the power transmission line to be deiced, and close the sixth switch unit 42, and execute S5;

S5: The main control system 5 controls the output power of the flow battery power supply system 3 to reach the required ice-melting power P; the flow battery power supply system 3 includes a flow battery unit 31, an energy storage inverter 32, a second Three transformers 33 and a third switch unit 34, the output end of the flow battery power supply system 3 is connected to the high-voltage bus 6; execute S6;

S6: The main control system 5 according to the formula $T=\frac{[c_i(273.15-T_a)+L_f]{\mathrm{\ρ}}_i{R}_i({2R}_0-{\mathrm{\πR}}_i/2)}{{I_C}^2{R}_e}$ Calculate the time T required to melt ice, where ci is the specific heat of ice, T _a is the air temperature, L _F is the latent heat released by solidification of water, ρ _i is the density of ice _, and R ₀ is the ice-covered transmission line to be melted. The average radius of the conductor, R _i is the radius of the conductor when the power transmission line needs to be melted without ice, I _C is the ice melting current, that is, the critical current to prevent the icing of the power transmission line that needs to be melted, and R _e is the unit length of the conductor at zero degrees resistance, execute S7;

S7: The main control system 5 judges whether the time T required for melting ice has been reached, if yes, execute S8, otherwise execute S7;

S8: disconnect the sixth switch unit 42;

Further, the method further includes the following steps after step S3:

C1: The main control system 5 judges whether the rated power of the flow battery power supply system 3 is greater than or equal to the required ice-melting power P, if yes, execute S4, otherwise execute C2;

C2: The main control system 5 starts the solar power supply system 1 or the wind power generation system 2; the solar power supply system 1 is composed of a plurality of parallel solar power supply branches; the wind power supply system 2 is composed of a plurality of parallel wind power supply branches Each of the solar power supply branches includes a solar power station 11, a first transformer 12 and a first switch unit 13; each of the wind power supply branches includes a wind power station 23, a second transformer 22 and a second switch Unit 21; the output end of the solar power supply system 1 and the output end of the wind power supply system 2 are connected to the high-voltage bus 6, and C3 is executed;

C3: close the first switch unit 13 or the second switch unit 21, close the third switch unit 34, close the switch unit connecting the high-voltage bus 6 and the beginning of the power transmission line to be deiced, and close the sixth switch unit 42, and execute C4;

C4: The main control system 5 controls the output power of the solar power supply system 1 or the wind power generation system 2 combined with the output power of the flow battery power supply system 3 to achieve the required ice-melting power P, and execute S6;

Further, the power transmission line that needs to melt ice is a high-voltage transmission and distribution line 7, a solar power supply branch or a wind power supply branch; when the power transmission line that needs to melt ice is a high-voltage transmission and distribution line 7, the high-voltage bus 6 and The switch unit at the beginning of the power transmission line that needs to be melted is the fourth switch unit 8, the beginning of the high-voltage power transmission and distribution line 7 is connected to the high-voltage bus 6 through the fourth switch unit 8, and the end of the high-voltage power transmission and distribution line 7 is connected to the fifth switch unit 9 is connected to the public power grid 10; when the power transmission line that needs to melt ice is a solar power supply branch, the switch unit that connects the high-voltage bus 6 and the beginning of the power transmission line that needs to melt ice is the first switch unit 13; when the power transmission line that needs to melt ice When it is a wind power supply branch, the switch unit connecting the high voltage bus 6 and the beginning of the power transmission line to be melted is the second switch unit 21; further, the solar power supply system 1 and wind power supply system connected to each other through the high voltage bus 6 2 and the liquid flow battery power supply system 3, and the public grid 10 connected to the high-voltage bus 6 through the high-voltage transmission and distribution line 7 constitute a grid-connected micro-grid system; further, when the power transmission line to be melted is a high-voltage transmission and distribution line 7 , before step S1, there are the following steps: disconnect the first switch unit 13, the second switch unit 21, the third switch unit 34, the fourth switch unit 8 and the fifth switch unit 9; When the line is a solar power supply branch, the following steps are also included before step S1: disconnect the first switch unit 13, the second switch unit 21, the third switch unit 34, the fourth switch unit 8, and the first transformer 12 from the solar power generation The connection between stations 11; the solar power supply branch disconnects the connection of the solar power station 11 as the end of the power transmission line that needs to melt ice; further, when the power transmission line that needs to melt ice is a wind power supply branch, before step S1 Have the following steps: disconnect the first switch unit 13, the second switch unit 21, the third switch unit 34, the fourth switch unit 8, and the connection between the second transformer 22 and the wind power station 23; The junction of the wind power station 23 is used as the end of the power transmission line that needs to melt ice; further, each phase of the end of the power transmission line that needs to be melted can be connected to the grounding system 4 respectively; further, the power transmission line that needs to be melted can be connected The two-phase or three-phase at the end of the line are shorted together and then connected to the grounding system 4; further, a fourth transformer 50 is also provided between the fourth switch unit 8 and the high-voltage bus 6; the first switch unit 13. The second switch unit 21 , the third switch unit 34 , the fourth switch unit 8 , the fifth switch unit 9 and the sixth switch unit 42 are manual switches or switch cabinets.

In actual use, the ice-melting range can be any power transmission and distribution line inside or outside the power plant. According to the length of the power transmission line that needs to be ice-melted, the ice-melting transmission line can be segmented to melt ice, and the ice-melting current limit can be calculated. value, the maximum allowable temperature of the conductor under the ambient temperature can also be calculated according to the product of the allowable long-term operating current and the correction coefficient of the ambient temperature at 70°C to obtain the maximum ice-melting current. Taking the LGL-120 conductor as an example, when When the ambient temperature is 25°C, the temperature of the wire is calculated as 70°C, and the long-term allowable current of the wire is 380A. When the ambient temperature is not 25°C, multiply the correction coefficient K _t , where the calculation formula of the correction coefficient is Q ₁ is the maximum temperature of the conductor; Q _e is the current ambient temperature; Q _s is the standard temperature; in addition, the blackness ε of the conductor of the transmission line that needs to be melted is 0.23-0.43 for the new conductor and 0.9 for the old conductor, and the liquid The flow battery power supply system includes a flow battery unit, an energy storage inverter, a third transformer, and a third switch unit connected in series in sequence. The output end of the flow battery power supply system is connected to a high-voltage bus, wherein the flow battery unit includes a flow The battery stack, electrolyte pump and battery management system, etc., the flow battery power supply system, solar power supply system, wind power generation system and public grid constitute a grid-connected microgrid system. The flow battery power supply system includes energy storage inverters. The inverter can store solar energy or wind energy in the flow battery, and the energy stored in the flow battery can also be released to the high-voltage bus through the energy storage inverter. The supporting power supply of the system and the wind power generation system has a wide range of applications. The ice-melting process is controlled according to the ice-melting current and ice-melting time calculated by the main control system, which is safe and reliable; the solar power supply system is supported by multiple parallel solar power supplies. A plurality of solar power supply branches can work at the same time or independently. When the work is stopped, the long power supply branch in ice and snow weather may be covered with ice; the wind power supply system is powered by multiple parallel wind power branch circuit, a plurality of wind power supply branches can work at the same time or can work alone, when the power supply branch is stopped in ice and snow weather, there may be icing phenomenon; each solar power supply branch includes a solar power station , a first transformer and a first switch unit; each of the wind power supply branches includes a wind power station, a second transformer and a second switch unit; If the rated power is less than the ice-melting power, start the solar power supply system or wind power supply system to supplement the power difference between the ice-melting power and the rated power of the flow battery power supply system. The power supply system can store solar energy or wind energy. When melting ice on the solar power supply branch, if the rated power of the flow battery power supply system is less than the ice melting power, the wind power supply system or other solar power supply branches in the solar power supply system can be started. In order to supplement the insufficient part of the ice-melting power, when melting the ice of the wind power supply branch, if the rated power of the liquid flow battery power supply system is less than the ice-melting power, the solar power supply system or other wind power supply in the wind power supply system can be started In order to supplement the insufficient part of the ice-melting power, the main control system can obtain the required ice-melting power P according to the calculated critical current I _C , the sum value R of the transmission line resistance and the resistance of the resistor to be ice-melted at the current ambient temperature =I _C ² R, wherein R is the sum of the resistance values obtained by adding the resistance value of the power transmission line to be deiced and the resistance value of the resistor; the AC deicing method based on the liquid flow battery provided by the present invention, by making the power transmission line to be deiced The end is connected to the grounding system, and the beginning of the transmission line that needs to melt ice uses a flow battery power supply system as the AC power supply for ice melting , which is energy-saving, practical, and easy to use. It can not only solve the problem in the prior art that using generator sets to provide ice-melting power is limited by the capacity of the generator set and the capacity required for ice-melting, but also avoids the use of system power as the ice-melting power in the event of grid failure and In the case of unloading, the power supply of the system is cut off and cannot be used, which effectively ensures the safety and stability of the transmission line in the cold weather of ice and snow; the main control system is adopted to reasonably control the ice melting current and ice melting time, and the ice melting process is safe and reliable; In addition, the solar power supply system, wind power generation system and flow battery power supply system can be combined to provide ice-melting power. Not only is it convenient for normal power supply when there is no need to melt ice, but also it is beneficial to increase the power of ice melting, thereby prolonging the length of the power transmission line that needs to melt ice to realize ice melting, and has a wide application range.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (10)

1. An AC ice-melting method based on liquid flow battery, is characterized in that comprising the steps: S1: Connect the end of the transmission line to be deiced to the grounding system (4) including the resistor (41) and the sixth switch unit (42); one end of the resistor (41) is grounded, and the other end passes through the sixth switch unit (42) Connect to the end of the power transmission line that needs to melt ice, and execute S2; S2: The main control system (5) according to the formula Calculate the critical current I _C to prevent the icing of the transmission line that needs to be thawed, where D is the diameter of the wire of the transmission line that needs to be thawed, ρ is the resistivity of the wire of the transmission line that needs to be thawed, and t _s is the wire of the transmission line that needs to be thawed Surface temperature, h is the convective heat transfer coefficient, σ is the StefSn-BoltcomSnn constant, ε is the blackness of the wire of the power transmission line that needs to melt ice, E is the capture coefficient of the wire of the power transmission line that needs to melt ice to the supercooled water droplets in the air, and V is The moving uniform speed of humid air or supercooled water droplet, W is the moisture content of humid air or supercooled water droplet, t is the temperature of humid air or supercooled water droplet, c _w is the specific heat capacity of water at constant pressure, W _E is the The proportion of liquid evaporated on the surface of the conductor of the transmission line that needs to be deiced, L _V is the latent heat of vaporization of water, and S3 is executed; S3: The main control system (5) obtains the required ice-melting power P=I according to the calculated critical current I _C and the sum R of the resistance of the transmission line to be ice-melted and the resistance of the resistor (41) at the current ambient temperature _C ² R, execute S4; S4: close the third switch unit (34), close the switch unit connected to the high-voltage bus (6) and the beginning of the transmission line to be deiced, and close the sixth switch unit (42), and execute S5; S5: The main control system (5) controls the output power of the flow battery power supply system (3) to reach the required ice-melting power P; the flow battery power supply system (3) includes flow battery units (31), The energy storage inverter (32), the third transformer (33) and the third switch unit (34), the output end of the flow battery power supply system (3) is connected to the high-voltage bus (6); execute S6; S6: The main control system (5) according to the formula $T=\frac{\[c_i(273.15-T_a)+L_f\]{\mathrm{\ρ}}_i{R}_i(2R_0-{\mathrm{\πR}}_i/2)}{{I_C}^2{R}_e}$ Calculate the time T required to melt ice, where ci is the specific heat of ice, T _a is the air temperature, L _F is the latent heat released by solidification of water, ρ _i is the density of ice _, and R ₀ is the ice-covered transmission line to be melted. The average radius of the conductor, R _i is the radius of the conductor when the power transmission line needs to be melted without ice, I _C is the ice melting current, that is, the critical current to prevent the icing of the power transmission line that needs to be melted, and R _e is the unit length of the conductor at zero degrees resistance, execute S7; S7: The main control system (5) judges whether the time T required for ice melting is reached, if yes, execute S8, otherwise execute S7; S8: disconnecting the sixth switch unit (42). 2. A flow battery-based AC ice melting method according to claim 1, characterized in that the method further comprises the following steps after step S3: C1: The main control system (5) judges whether the rated power of the flow battery power supply system (3) is greater than or equal to the required ice-melting power P, if yes, execute S4, otherwise execute C2; C2: The main control system (5) starts the solar power supply system (1) or the wind power generation system (2); the solar power supply system (1) is composed of multiple parallel solar power supply branches; the wind power supply system (2 ) is composed of a plurality of parallel wind power supply branches; each of the solar power supply branches includes a solar power station (11), a first transformer (12) and a first switch unit (13); each of the wind power supply branches The branch circuit includes a wind power station (23), a second transformer (22) and a second switch unit (21); the output end of the solar power supply system (1) and the output end of the wind power supply system (2) are connected to the high voltage busbar (6) , execute C3; C3: Close the first switch unit (13) or the second switch unit (21), close the third switch unit (34), close the switch unit connecting the high-voltage bus (6) and the beginning of the transmission line to be deiced, and close the sixth switch unit (42), execute C4; C4: The main control system (5) controls the output power of the solar power supply system (1) or the wind power generation system (2) combined with the output power of the flow battery power supply system (3) to achieve the required ice-melting power P, and execute S6. 3. An AC ice-melting method based on a flow battery according to claim 2, characterized in that the power transmission line to be melted is a high-voltage power transmission and distribution line (7), a solar power supply branch or a wind power supply branch ; When the power transmission line to be ice-melted is a high-voltage power transmission and distribution line (7), the switch unit connecting the high-voltage busbar (6) and the beginning of the power transmission line to be ice-melted is the fourth switch unit (8), and the high-voltage power transmission and distribution line The beginning of the line (7) is connected to the high-voltage bus (6) through the fourth switch unit (8), and the end of the high-voltage transmission and distribution line (7) is connected to the public power grid (10) through the fifth switch unit (9); When the power transmission line that needs to melt ice is a solar power supply branch, the switch unit that connects the high-voltage bus (6) and the beginning of the power transmission line that needs to melt ice is the first switch unit (13); When the power transmission line that needs to melt ice is a wind power supply branch, the switch unit that connects the high-voltage bus (6) and the beginning of the power transmission line that needs to melt ice is the second switch unit (21). 4. An AC ice melting method based on a liquid flow battery according to claim 3, characterized in that the solar power supply system (1), the wind power supply system (2) and the liquid A flow battery power supply system (3), and a public grid (10) connected to a high-voltage busbar (6) through a high-voltage transmission and distribution line (7) constitute a grid-connected micro-grid system. 5. An AC ice-melting method based on a flow battery according to claim 3, characterized in that when the power transmission line to be ice-melted is a high-voltage power transmission and distribution line (7), the following steps are performed before step S1: The first switch unit (13), the second switch unit (21), the third switch unit (34), the fourth switch unit (8) and the fifth switch unit (9) are disconnected. 6. The AC ice-melting method based on a flow battery according to claim 3, wherein when the power transmission line to be ice-melted is a solar power supply branch, the following steps are performed before step S1: Disconnect between the first switch unit (13), the second switch unit (21), the third switch unit (34), the fourth switch unit (8), and the first transformer (12) and the solar power station (11) connection; the solar power supply branch disconnects the connection of the solar power station (11) as the end of the power transmission line that needs to melt ice. 7. The AC ice-melting method based on a liquid flow battery according to claim 3, characterized in that when the power transmission line to be ice-melted is a wind power supply branch, the following steps are also performed before step S1: Disconnect between the first switch unit (13), the second switch unit (21), the third switch unit (34), the fourth switch unit (8), and the second transformer (22) and the wind power station (23) connection; the wind power supply branch disconnects the connection of the wind power station (23) as the end of the power transmission line that needs to melt ice. 8. The AC ice melting method based on a flow battery according to claim 3, characterized in that each phase at the end of the power transmission line to be ice melted is connected to the grounding system (4) respectively. 9. An AC ice-melting method based on a flow battery according to claim 3, characterized in that two or three phases at the end of the power transmission line to be ice-melted are short-circuited together and then connected to the grounding system (4) . 10. The AC ice-melting method based on a flow battery according to claim 3, characterized in that a fourth transformer (50) is also arranged between the fourth switch unit (8) and the high-voltage bus (6) ; The first switch unit (13), the second switch unit (21), the third switch unit (34), the fourth switch unit (8), the fifth switch unit (9) and the sixth switch unit (42) For manual switch or switchgear.