阅读说明：本技术 一种光伏高压直流串联并网系统 (Photovoltaic high-voltage direct-current series grid-connected system ) 是由 国建鸿 王环 张玉波 黄欣科 王一波 于 2019-09-23 设计创作，主要内容包括：本发明提供一种光伏高压直流串联并网系统,涉及电力系统技术领域。该光伏高压直流串联并网系统将高压交直流变换器放置于第一蒸发器的绝缘冷却介质中；将电感放置于第二蒸发器的绝缘冷却介质中；功率半导体器件与第二蒸发器的外壁面接触；当液态的绝缘冷却介质受热气化转换为气态的绝缘冷却介质后进入冷凝器冷凝为液态的绝缘冷却介质后,再次进入第一蒸发器和第二蒸发器冷却高压交直流变换器、电感和功率半导体器件,本发明的绝缘冷却介质为绝缘冷却液体,直接与DC-DC变换器的发热部件进行热交换,液-气相变过程吸热提高了热交换效率,提高了DC-DC变换器的散热效率。(the invention provides a photovoltaic high-voltage direct-current series grid-connected system, and relates to the technical field of power systems. The photovoltaic high-voltage direct-current series grid-connected system places a high-voltage alternating-current/direct-current converter in an insulating cooling medium of a first evaporator; placing an inductor in the insulating cooling medium of the second evaporator; the power semiconductor device is in contact with the outer wall surface of the second evaporator; when the liquid insulating cooling medium is heated, gasified and converted into the gaseous insulating cooling medium, then the gaseous insulating cooling medium enters the condenser to be condensed into the liquid insulating cooling medium, and then the liquid insulating cooling medium enters the first evaporator and the second evaporator again to cool the high-voltage alternating current-direct current converter, the inductor and the power semiconductor device.)

1. A photovoltaic high-voltage direct-current series grid-connected system is characterized by comprising a direct-current-direct-current converter and a cooling device;

The DC-DC converter includes: a high voltage AC/DC converter and a low voltage DC-AC converter;

the cooling device includes: the system comprises a condenser, a first evaporator, a second evaporator, a gas pipeline, a liquid pipeline and an insulating cooling medium;

The gas outlet of the first evaporator is communicated with the gas inlet of the condenser through the gas pipeline;

The liquid inlet of the first evaporator is communicated with the liquid outlet of the condenser through the liquid pipeline;

The high-pressure liquid port of the first evaporator is communicated with the low-pressure liquid port of the second evaporator through a high-pressure and low-pressure communicating pipe; the low-pressure liquid port of the second evaporator is arranged at the top of the second evaporator;

The high-low pressure communicating pipe is used for communicating an insulating cooling medium in the first evaporator with an insulating cooling medium in the second evaporator, and communicating gas in the second evaporator with gas in the first evaporator;

The first evaporator is filled with the insulating cooling medium; the high-voltage AC-DC converter is placed in the first evaporator and is immersed in the insulating cooling medium;

The second evaporator is placed in the low-voltage DC-AC converter; the second evaporator is filled with the insulating cooling medium;

A low-voltage output lead of the low-voltage DC-AC converter penetrates through the high-low voltage communicating pipe to be electrically connected with a high-frequency high-voltage transformer of the high-voltage AC/DC converter; the high-low pressure communicating pipe is also used for placing the low-pressure output lead;

The inductor of the low-voltage DC-AC converter is placed in the insulating cooling medium of the second evaporator;

The power semiconductor device of the low-voltage DC-AC converter is in contact with the outer wall surface of the second evaporator.

2. The pv hvdc series grid connection system of claim 1, further comprising: a cabinet;

The DC-DC converter and the cooling device are both placed in the cabinet.

3. the pv hvdc series grid connection system of claim 1, wherein the condenser is positioned at a higher level than the first and second evaporators.

4. The photovoltaic high-voltage direct-current series grid-connected system according to claim 1, wherein the second evaporator is a sealed hollow box body, the side walls of the second evaporator are made of insulating materials or metal materials, and at least one side wall is made of metal materials;

and the heating surface of the power semiconductor device of the low-voltage direct current-alternating current converter is in contact with the outer surface of the side wall made of the metal material of the second evaporator.

5. The photovoltaic high-voltage direct-current series grid-connected system according to claim 1, wherein an air inlet of the condenser is formed in the upper half part of the condenser;

The liquid outlet of the condenser is arranged at the bottom of the condenser;

the air outlet of the first evaporator is arranged at the upper half part of the first evaporator;

The liquid inlet of the first evaporator is arranged at the bottom of the first evaporator.

6. The photovoltaic high-voltage direct-current series grid-connected system according to claim 1, wherein the first evaporator is a hollow box body, and the box body is made of an insulating material.

7. The photovoltaic high-voltage direct current series grid-connected system according to claim 1, characterized in that the insulating cooling medium is a fluorocarbon.

8. The photovoltaic high-voltage direct-current series grid-connected system according to claim 1, wherein sectional areas of a high-pressure liquid port of the first evaporator, the high-low pressure communicating pipe and a low-pressure liquid port of the second evaporator are all larger than or equal to 13 square centimeters.

9. The photovoltaic high-voltage direct-current series grid-connected system according to claim 1, wherein the condenser is a rectangular or cylindrical hollow box body, and the box body is made of metal.

10. The photovoltaic high-voltage direct current series grid-connected system of claim 1, wherein the outer surface of the side wall of the first evaporator opposite to the second evaporator is a corrugated surface.

Technical Field

the invention relates to the technical field of power systems, in particular to a photovoltaic high-voltage direct-current series grid-connected system.

Background

with the construction of a high-voltage Direct-current power transmission network and the rapid development of a high-voltage Direct-current power distribution network, a Direct-current grid-connected DC-DC converter (Direct-current-Direct-current converter) is an effective means for solving large-capacity remote transmission of electric energy and large-scale renewable energy collection, and a high-voltage Direct-current (HVDC) line corridor can be fully utilized to realize complementation between multiple energy forms and multiple user types. The grid-connected form of the photovoltaic power generation system which is common at present is mainly integrated into an alternating current power grid. The flexible direct current and traditional direct current transmission in China are rapidly developed, demonstration projects are more and more, and photovoltaic power generation must have the capacity of being connected into a high-voltage direct current transmission network.

the common photovoltaic direct current converters have the problems that the output voltage is low and the voltage cannot be boosted to a high voltage at one time, in order to realize that the output of a photovoltaic system is merged into a high-voltage direct current power grid, the input of a plurality of photovoltaic direct current converters is generally connected with an independent photovoltaic assembly at present, and the output voltage of the system is improved in a series output mode, so that the aim of outputting higher direct current voltage to be connected into the high-voltage direct current power grid is fulfilled. The output of the photovoltaic direct current converter is merged into a direct current transmission line with more than +/-10 KV, +/-30 KV and +/-300 KV levels, and the boosting ratio is up to 20-600 times.

Because the high-power converter has larger heat loss in the operation process, a set of cooling system is required to be equipped for ensuring that the high-power converter has good operation environment. At present, the most common cooling system of the high-power converter adopts a water cooling technology and adopts a forced water circulation structure, a cooling medium needs to adopt deionized water and needs to be provided with a circulating pump, an expansion valve, water deionization treatment equipment and the like, and a separate cabinet body weighing dozens or even hundreds of kilograms is needed for a water treatment and circulation system, so that the volume, the weight and the cost are high. In addition, the common photovoltaic DC converter includes a high voltage Alternating Current (AC) -DC (DC) converter and a low voltage DC-AC converter, and the high voltage AC-DC converter generally includes a high frequency high voltage transformer, a high voltage capacitor, a silicon stack, and other devices for realizing a high voltage AC/DC conversion function; the low-voltage DC-AC converter generally comprises a control circuit board, a low-voltage capacitor, a power semiconductor device, an inductor, a voltage sensor, a current sensor and other devices for realizing the DC-AC conversion function and a protective shell, wherein the heat exchange is carried out between the low-voltage DC-AC converter and the power semiconductor device and the inductor in the high-voltage AC-DC converter and the low-voltage DC-AC converter which mainly need to be cooled in the existing water cooling mode through air, and the existence of an air medium can cause the low heat exchange efficiency. Therefore, the conventional cooling method has a problem of low heat exchange efficiency.

disclosure of Invention

the invention aims to provide a photovoltaic high-voltage direct-current series grid-connected system, which solves the problem of low heat exchange efficiency of the existing cooling mode.

In order to achieve the purpose, the invention provides the following scheme:

A photovoltaic high-voltage direct-current series grid-connected system comprises a direct-current-direct-current converter and a cooling device;

The DC-DC converter includes: a high voltage AC/DC converter and a low voltage DC-AC converter;

the cooling device includes: the system comprises a condenser, a first evaporator, a second evaporator, a gas pipeline, a liquid pipeline and an insulating cooling medium;

the gas outlet of the first evaporator is communicated with the gas inlet of the condenser through the gas pipeline;

The liquid inlet of the first evaporator is communicated with the liquid outlet of the condenser through the liquid pipeline;

The high-pressure liquid port of the first evaporator is communicated with the low-pressure liquid port of the second evaporator through a high-pressure and low-pressure communicating pipe; the low-pressure liquid port of the second evaporator is arranged at the top of the second evaporator;

The high-low pressure communicating pipe is used for communicating an insulating cooling medium in the first evaporator with an insulating cooling medium in the second evaporator, and communicating gas in the second evaporator with gas in the first evaporator;

The first evaporator is filled with the insulating cooling medium; the high-voltage AC-DC converter is placed in the first evaporator and is immersed in the insulating cooling medium;

The second evaporator is placed in the low-voltage DC-AC converter; the second evaporator is filled with the insulating cooling medium;

a low-voltage output lead of the low-voltage DC-AC converter penetrates through the high-low voltage communicating pipe to be electrically connected with a high-frequency high-voltage transformer of the high-voltage AC/DC converter; the high-low pressure communicating pipe is also used for placing the low-pressure output lead;

The inductor of the low-voltage DC-AC converter is placed in the insulating cooling medium of the second evaporator;

the power semiconductor device of the low-voltage DC-AC converter is in contact with the outer wall surface of the second evaporator.

Optionally, the photovoltaic high-voltage direct-current series grid-connected system further includes: a cabinet;

the DC-DC converter and the cooling device are both placed in the cabinet.

optionally, the horizontal position of the condenser is higher than the horizontal positions of the first evaporator and the second evaporator.

Optionally, the second evaporator is a sealed hollow box body, the side walls of the second evaporator are made of an insulating material or a metal material, and at least one side wall is made of a metal material;

and the heating surface of the power semiconductor device of the low-voltage direct current-alternating current converter is in contact with the outer surface of the side wall made of the metal material of the second evaporator.

Optionally, the air inlet of the condenser is arranged at the upper half part of the condenser;

the liquid outlet of the condenser is arranged at the bottom of the condenser;

The air outlet of the first evaporator is arranged at the upper half part of the first evaporator;

The liquid inlet of the first evaporator is arranged at the bottom of the first evaporator.

optionally, the first evaporator is a hollow box body, and the box body is made of an insulating material.

optionally, the insulating cooling medium is a fluorocarbon.

Optionally, cross-sectional areas of the high-pressure liquid port of the first evaporator, the high-low pressure communicating pipe, and the low-pressure liquid port of the second evaporator are all greater than or equal to 13 square centimeters.

Optionally, the condenser is a rectangular or cylindrical hollow box body, and the box body is made of metal.

Optionally, the outer surface of the side wall of the first evaporator opposite to the second evaporator is a corrugated surface.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

The invention provides a photovoltaic high-voltage direct-current series grid-connected system, which is characterized in that a high-voltage alternating-current/direct-current converter is placed in a first evaporator; the first evaporator is filled with insulating cooling medium; placing a second evaporator in the low-voltage DC-AC converter; insulating cooling media are filled in the second evaporator; placing the inductor of the low-voltage DC-AC converter in the insulating cooling medium of the second evaporator; the power semiconductor device of the low-voltage DC-AC converter is contacted with the outer wall surface of the second evaporator; the invention places the high-voltage AC/DC converter in the first evaporator, the inductor in the insulating cooling medium of the second evaporator and the power semiconductor device in contact with the outer wall surface of the second evaporator, when the liquid insulating cooling medium is heated, gasified and converted into the gaseous insulating cooling medium, then the gaseous insulating cooling medium enters the condenser and is condensed into the liquid insulating cooling medium, and then the liquid insulating cooling medium enters the first evaporator and the second evaporator again to cool the high-voltage AC/DC converter, the inductor and the power semiconductor device, the insulating cooling medium of the invention is insulating cooling liquid, and directly exchanges heat with the heating part of the DC-DC converter, the liquid absorbs heat and is gasified, the liquid absorbs heat in the liquid-gas phase change process, the heat exchange is not needed through air, the heat exchange efficiency is improved, the heat dissipation efficiency of the DC-DC converter is improved, and a self-circulation closed structure is formed by utilizing the, auxiliary treatment equipment such as pumps and the like is not needed. In addition, because the insulating cooling liquid has good insulativity, the high-voltage component can be soaked in the insulating cooling liquid, compared with an air cooling mode, the insulating distance can be shortened by more than 8 times, high-density arrangement of heating electric components in a limited space is realized, and the heat dissipation problem caused by high-power-density electric energy conversion can be solved.

drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a structural diagram of a photovoltaic high-voltage direct-current series grid-connected system according to an embodiment of the invention;

FIG. 2 is a sectional view of the A-A' plane of a photovoltaic high-voltage direct-current series grid-connected system according to an embodiment of the invention;

fig. 3 is a structural view of a first evaporator and a second evaporator according to an embodiment of the present invention.

Wherein, 1, high-voltage AC-DC converter; 2. a low voltage DC-AC converter; 3. a condenser; 4. a first evaporator; 5. a second evaporator; 6. a gas conduit; 7. a liquid conduit; 8. high-low pressure communicating pipes; 11. a high-voltage capacitor; 12. stacking silicon; 21. a power semiconductor device; 22. an inductance; 23. a low pressure port; 24. a low voltage output lead; 31. a high voltage high frequency transformer; 32. an air inlet; 33. a liquid outlet; 34. a pressure transmitter; 35. an exhaust joint; 41. an air outlet; 42. a liquid inlet; 43. a high pressure liquid port; 44. a high voltage lead connector; 9. a cabinet; A-A' is a cutting plane.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

in order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

FIG. 1 is a structural diagram of a photovoltaic high-voltage direct-current series grid-connected system according to an embodiment of the invention; FIG. 2 is a sectional view of the A-A' plane of a photovoltaic high-voltage direct-current series grid-connected system according to an embodiment of the invention; fig. 3 is a structural view of a first evaporator and a second evaporator according to an embodiment of the present invention. Referring to fig. 1, 2 and 3, a photovoltaic high voltage dc series grid-connected system includes: a Direct current-Direct current converter (DC-DC converter) and a cooling device.

the DC-DC converter includes: a high voltage AC-DC converter 1 (high voltage Alternating Current (AC) -DC converter, high voltage AC-DC converter) and a low voltage DC-AC converter 2 (low voltage DC-AC converter). The output of the low voltage DC-AC converter 2 is connected to the input of a high voltage high frequency transformer 31 of the high voltage AC-DC converter 1.

Existing high voltage AC-DC converters generally include: the high-voltage high-frequency transformer 31, the high-voltage capacitor 11, the silicon stack 12 and other devices realize a high-voltage alternating current-direct current conversion function; the high voltage in this embodiment means that the withstand voltage level of the device is 1000 volts (V) or more. Low voltage DC-AC converters generally comprise: the direct current-alternating current converter comprises a step-up transformer, a control circuit board, a low-voltage capacitor, a power semiconductor device 21, an inductor 22, a voltage sensor, a current sensor and other devices for realizing the direct current-alternating current conversion function and a protective shell. The low voltage in this embodiment refers to a conventional photovoltaic generation voltage, less than 1 Kilovolt (KV).

The cooling device includes: a condenser 3, a first evaporator 4, a second evaporator 5, a gas pipe 6, a liquid pipe 7 and an insulating cooling medium.

The condenser 3 is a rectangular or cylindrical hollow box body, the box body is made of metal, and the optional metal is stainless steel or aluminum alloy; the horizontal position of the condenser 3 is higher than the horizontal positions of the first evaporator 4 and the second evaporator 5, and the phenomenon that the condensation efficiency of the condenser 3 is affected by excessive liquid insulating cooling medium carried when the gaseous insulating cooling medium ascends into the condenser 3 is prevented. The first evaporator 4 is a sealed hollow box body made of insulating materials. The second evaporator 5 is a sealed hollow box body, the side wall of the second evaporator 5 is made of polymer insulating material or metal material, and at least one side wall is made of metal material.

The insulating cooling medium is fluorocarbon, the insulating property is good, the dielectric strength reaches 22 kilovolts/millimeter (KV/mm), the boiling point is 40-55 ℃ under one standard atmospheric pressure, and the volume resistivity is more than 10⁷omega meter (omega m), good fluidity, and viscosity of 0.4-0.7 square meter per second (mm)²the inductor 22, the high-voltage AC-DC converter and the like can be directly soaked in a liquid insulating cooling medium, the electrified part of an electric element can be directly contacted with the liquid insulating cooling medium, the liquid insulating cooling medium directly absorbs heat generated by the electric element such as the inductor 22 or the high-voltage AC-DC converter and the like, and meanwhile, the best cooling effect can be achieved due to the fact that the thermal resistance of fluorocarbon is low, compared with a water cooling mode, deionization processing equipment is not needed, so that the system is simple in structure, the power density is greatly improved compared with an air cooling mode, the integrated design volume power density is high, the heat dissipation effect is good, and the heating surface temperature of the electric element soaked in the liquid insulating cooling medium can be controlled to be below 65 ℃.

The first evaporator 4 includes: the number of the air outlet 41, the liquid inlet 42 and the high-pressure liquid port 43 can be a plurality. The air outlet 41 of the first evaporator 4 is arranged at the upper half part of the first evaporator 4; the liquid inlet 42 of the first evaporator 4 is provided at the bottom of the first evaporator 4.

The condenser 3 includes: the number of the gas inlet 32 and the liquid outlet 33, and the number of the gas inlet 32 and the liquid outlet 33 may be plural. The air inlet 32 of the condenser 3 is arranged at the upper half part of the condenser 3 and is higher than the liquid outlet 33; the liquid outlet 33 of the condenser 3 is arranged at the bottom of the condenser 3, which is beneficial for the liquid insulating cooling medium to flow back to the first evaporator 4 without forming air blockage. The condenser 3 further includes: the pressure transmitter 34 and the exhaust joint 35, and the number of the pressure transmitter 34 and the exhaust joint 35 may be plural, and the pressure transmitter 34 and the exhaust joint 35 may be provided on the top of the condenser 3. The exhaust joint 35 includes: the pressure transmitter comprises a first exhaust joint and a second exhaust joint, wherein an automatic exhaust valve is arranged on the first exhaust joint, a manual exhaust valve is arranged on the second exhaust joint, and the pressure transmitter 34 is electrically connected with the first exhaust joint. Pressure transmitter 34 is used for detecting the pressure of condenser 3, and when pressure reached the setting value, pressure transmitter 34 transmission signal of telecommunication was for first exhaust joint, reports to the police simultaneously, and automatic exhaust valve on the first exhaust joint is opened automatically and is exhausted, and the staff can open the manual exhaust valve on the second exhaust joint according to alarm information and exhaust, makes condenser 3 keep running in lower pressure, improves the security of photovoltaic high voltage direct current series-wound system.

the gas outlet 41 of the first evaporator 4 communicates with the gas inlet 32 of the condenser 3 through the gas pipe 6, and the gaseous insulating cooling medium in the first evaporator 4 enters the condenser 3 through the gas pipe 6.

the liquid inlet 42 of the first evaporator 4 is communicated with the liquid outlet 33 of the condenser 3 through a liquid pipeline 7, and the liquid-state insulating cooling medium in the condenser 3 enters the first evaporator 4 through the liquid pipeline 7.

the high-pressure liquid port 43 of the first evaporator 4 is communicated with the low-pressure liquid port 23 of the second evaporator 5 through a high-low pressure communicating pipe 8; the number of the high-low pressure communicating pipes 8 is at least one; the low-pressure liquid ports 23 of the second evaporator 5 are arranged at the top of the second evaporator 5, the number of the low-pressure liquid ports 23 is at least one, and the high-pressure liquid ports 43 of the first evaporator 4 are higher than the low-pressure liquid ports 23 of the second evaporator 5 or are parallel to the low-pressure liquid ports 23 of the second evaporator 5.

The high-low pressure communicating pipe 8 is used for communicating the insulating cooling medium in the first evaporator 4 with the insulating cooling medium in the second evaporator 5, and the gas in the second evaporator is communicated with the gas in the first evaporator, wherein the gas refers to the gaseous insulating cooling medium, that is, the high-low pressure communicating pipe 8 is used for communicating the liquid insulating cooling medium in the first evaporator 4 with the liquid insulating cooling medium in the second evaporator 5, and the gaseous insulating cooling medium in the second evaporator 5 with the gaseous insulating cooling medium in the first evaporator 4.

The first evaporator 4 is filled with insulating cooling medium; the high-voltage AC-DC converter 1 is placed in the first evaporator 4 and immersed in an insulating cooling medium, in particular in a liquid state. All components in the high-voltage AC-DC converter 1 are placed in the first evaporator 4 and immersed in the insulating cooling medium, so that the heat dissipation and insulation effects on all components in the high-voltage AC-DC converter 1 are achieved.

The second evaporator 5 is placed inside the low-voltage DC-AC converter 2; the second evaporator 5 is filled with an insulating cooling medium.

A low-voltage output lead 24 of the low-voltage DC-AC converter 2 passes through the high-low voltage communicating pipe 8 and is electrically connected with a high-voltage high-frequency transformer 31 of the high-voltage AC-DC converter 1; the high-low pressure communicating tube 8 is also used for placing a low-pressure output lead 24. The low-voltage output lead 24 penetrates into the first evaporator 4 from the high-low voltage communicating pipe 8 to be electrically connected with the high-voltage high-frequency transformer 31, and electrical connection circuits between the high-voltage AC-DC converter 1 and the low-voltage DC-AC converter 2 are soaked in the insulating cooling medium, so that the length of the electrical connection circuit is effectively shortened under the condition of meeting the requirement of high voltage withstand voltage, the length of the electrical connection circuit is far smaller than the distance of the electrical connection circuit in the air, and the safety is improved.

the inductor 22 of the low-voltage DC-AC converter 2 is placed in the insulating cooling medium of the second evaporator 5, in particular immersed in the liquid insulating cooling medium, and the inductor 22 is in direct contact with the insulating cooling medium for heat exchange. The second evaporator 5 includes: and the number of the sealed electric joints is at least 4, one end of each sealed electric joint is positioned in the second evaporator 5, and the other end of each sealed electric joint is positioned outside the second evaporator 5.

The input of the inductor 22 is electrically connected to the low voltage power supply via a first sealed electrical connection, and the output of the inductor 22 is electrically connected to the input of the power semiconductor device 21 via a second sealed electrical connection. The positive and negative poles of the output of the power semiconductor device 21 are electrically connected to the low-voltage output lead 24 via a third and a fourth sealed electrical connection, respectively.

The power semiconductor device 21 of the low voltage DC-AC converter 2 is in contact with the outer wall surface of the second evaporator 5, and the optional power semiconductor device 21 is fixed to the outer wall surface of the second evaporator 5 by screws. Since the thermal conductivity of the metal material is much higher than that of the non-metal material, the heat generating surface of the power semiconductor device 21 of the preferred low-voltage DC-AC converter 2 is in close contact with the outer surface of the metal sidewall of the second evaporator 5, so that the heat loss of the power semiconductor device 21 exchanges heat with the insulating cooling medium in the second evaporator 5 more effectively through the metal sidewall of the second evaporator 5. The positive and negative poles of the output terminal of the power semiconductor device 21 are electrically connected to the low-voltage output lead 24, and further to the high-voltage high-frequency transformer 31 of the high-voltage AC-DC converter 1, through a third sealed electrical connector and a fourth sealed electrical connector, respectively. In the present embodiment, the power semiconductor device 21 is an Insulated Gate Bipolar Transistor (IGBT). The optional arrangement of the components of the low-voltage DC-AC converter 2, except for the inductor 22 and the power semiconductor device 21, may be arranged outside the second evaporator 5 and around the second evaporator 5, which arrangement may effectively reduce the electrical connection lines between the components of the low-voltage DC-AC converter 2 and reduce the stray capacitance effect.

When the photovoltaic high-voltage direct-current series grid-connected system operates and only one high-low pressure communicating pipe 8 is provided, the liquid or gaseous insulating cooling medium in the first evaporator 4 circulates through the high-low pressure communicating pipe 8 and the liquid or gaseous insulating cooling medium in the second evaporator 5, and the circulating process specifically comprises the following steps: liquid insulating cooling medium flows into the second evaporator 5 from the first evaporator 4 through the high-low pressure communicating pipe 8, absorbs heat in the second evaporator 5 and is gasified to generate gaseous insulating cooling medium, the gaseous insulating cooling medium rises to the top of the second evaporator 5 according to the gravity difference principle of gas and liquid, and enters the high-low pressure communicating pipe 8 through the low-pressure liquid port 23 of the second evaporator 5 and then enters the first evaporator 4. The sectional areas of the high-pressure liquid port 43 of the first evaporator 4, the high-low pressure communicating pipe 8 and the low-pressure liquid port 23 of the second evaporator 5 are all larger than or equal to 13 square centimeters, so that the air blocking phenomenon is avoided, and if the liquid or gaseous insulating cooling medium in the second evaporator 5 cannot normally circulate, the working temperature of the power semiconductor device 21 is high, and the power semiconductor device 21 is damaged.

in the photovoltaic high-voltage direct-current series grid-connected system of the embodiment, the gas outlet 41 of the first evaporator 4 is communicated with the gas inlet 32 of the condenser 3 through the gas pipeline 6, the liquid inlet 42 of the first evaporator 4 is communicated with the liquid outlet 33 of the condenser 3 through the liquid pipeline 7, and the high-pressure liquid port 43 of the first evaporator 4 is communicated with the low-pressure liquid port 23 of the second evaporator 5 through the high-low pressure communicating pipe 8, so as to form a closed loop; the closed loop is filled with low-boiling point insulating cooling liquid. The condensation process is as follows: when the alternating current and direct current are converted, heat generated by the inductor 22, the high-voltage high-frequency transformer 31 and the power semiconductor device 21 exchanges heat with the liquid insulating cooling medium, the liquid insulating cooling medium absorbs heat and is gasified to generate the gaseous insulating cooling medium, the gaseous insulating cooling medium rises along the gas pipeline 6 to enter the condenser 3 to be condensed into the liquid insulating cooling medium according to the gravity difference principle of gas and liquid, and the liquid insulating cooling medium flows back to the first evaporator 4 along the liquid pipeline 7 to achieve the purpose of heat dissipation. The condensation process is circulated repeatedly, and the self-circulation process of the insulating cooling medium is realized. Noise and cost are reduced.

The top or one side wall of the first evaporator 4 is provided with two high-voltage terminal connections 44 with a sealed structure, one end of the high-voltage terminal connection 44 is located inside the first evaporator 4, and the other end of the high-voltage terminal connection 44 is located outside the first evaporator 4. When only one high-voltage AC-DC converter 1 is provided, the positive pole of the output end of the high-voltage AC-DC converter 1 is electrically connected with the negative pole of the power grid through one high-voltage lead connector 44, and the negative pole of the output end of the high-voltage AC-DC converter 1 is electrically connected with the positive pole of the power grid through the other high-voltage lead connector 44; when a plurality of high-voltage AC-DC converters are connected in series, the negative pole of the output end of the first high-voltage AC-DC converter is electrically connected with the positive pole of the power grid through the first high-voltage lead connector of the first high-voltage AC-DC converter, the positive pole of the output end of the first high-voltage AC-DC converter is electrically connected with the first high-voltage lead connector of the second high-voltage AC-DC converter through the second high-voltage lead connector of the first high-voltage AC-DC converter so as to be connected with the negative pole of the output end of the second high-voltage AC-DC converter, and after the high-voltage AC-DC converters are connected in series in sequence, the positive electrode of the output end of the last high-voltage AC-DC converter is electrically connected with the negative electrode of the power grid through a second high-voltage lead connector of the last high-voltage AC-DC converter; when the high-voltage AC-DC converters are connected in parallel, the anode of the output end of each high-voltage AC-DC converter is electrically connected with the cathode of the power grid through one high-voltage lead connector, and the cathode of the output end of each high-voltage AC-DC converter is electrically connected with the anode of the power grid through the other high-voltage lead connector.

the outer surface of the side wall of the first evaporator 4 opposite to the second evaporator 5 is corrugated, and the top or the side wall of the first evaporator 4 with the high-voltage lead connector 44 is also corrugated, so that the creepage distance between high-voltage and low-voltage wires can be effectively increased. Because the insulativity of the insulating cooling medium and the dielectric strength of the insulating cooling medium reach 22KV/mm, the charged components can be directly soaked in the insulating cooling medium, and the dense arrangement of high-voltage devices in a limited space is realized. The high-voltage components and the low-voltage components are respectively arranged in the two evaporators, so that the design of the high-voltage part does not need to consider the insulation distance between the low-voltage components, and the volume power density of the first evaporator is higher and safer. In addition, the outer surface of the side wall of the first evaporator opposite to the second evaporator is provided with a corrugated surface, so that the creepage distance between the first evaporator and the second evaporator can be increased, and the distance between the first evaporator and the second evaporator can be even not more than 100 millimeters (mm). If the creepage distance between the high-voltage outgoing line and the low-voltage DC-AC converter needs to be at least 1.5 meters (m) according to a conventional air insulation method, and the electrical distance needs to be at least 50 centimeters (cm) when the voltage level of 30 Kilovolts (KV) is high, the arrangement distance between the high-voltage AC-DC converter and the low-voltage DC-AC converter can be reduced by adopting the first evaporator and the second evaporator of the embodiment, and the volume power density of the photovoltaic high-voltage direct-current series grid-connected system is improved.

The number of the first evaporator 4, the high-voltage AC-DC converter 1, the second evaporator 5 and the low-voltage DC-AC converter 2 can be multiple, and the number of the first evaporator 4, the number of the high-voltage AC-DC converter 1, the number of the second evaporator 5 and the number of the low-voltage DC-AC converter 2 are all equal.

The first evaporator 4, the high-voltage AC-DC converter 1, the second evaporator 5 and the low-voltage DC-AC converter 2 form a group, the connection relationship between the second evaporator 5 and the low-voltage DC-AC converter 2 in each group and the first evaporator 4 and the high-voltage AC-DC converter 1 is not changed, namely, the high-voltage liquid port 43 of the first evaporator 4 is communicated with the low-voltage liquid port 23 of the second evaporator 5 through the high-low pressure communicating pipe 8.

When the number of the groups is less than or equal to 4, the first evaporators 4 of three groups further comprise a gas inlet 32 and a liquid outlet 33, the gas outlet 41 of the first evaporator 4 of the first group is communicated with the gas inlet 32 of the condenser 3 through a gas pipeline 6, and the liquid inlet 42 of the first evaporator 4 of the first group is communicated with the liquid outlet 33 of the condenser 3 through a liquid pipeline 7; the gas inlet 32 of the first evaporator 4 of the first group is communicated with the gas outlet 41 of the first evaporator 4 of the second group through a pipeline, and the liquid outlet 33 of the first evaporator 4 of the first group is communicated with the liquid inlet 42 of the first evaporator 4 of the second group through a pipeline; the gas inlet 32 of the first evaporator 4 of the second group is communicated with the gas outlet 41 of the first evaporator 4 of the third group through a pipeline, and the liquid outlet 33 of the first evaporator 4 of the second group is communicated with the liquid inlet 42 of the first evaporator 4 of the third group through a pipeline; the air inlet 32 of the first evaporator 4 of the third group is communicated with the air outlet 41 of the first evaporator 4 of the fourth group through a pipeline, and the liquid outlet 33 of the first evaporator 4 of the third group is communicated with the liquid inlet 42 of the first evaporator 4 of the fourth group through a pipeline.

When the number of the groups is more than 4, the gas outlet 41 of the first evaporator 4 of each group is communicated with the gas inlet 32 of the condenser 3 through the gas pipeline 6, and the liquid inlet 42 of the first evaporator 4 of each group is communicated with the liquid outlet 33 of the condenser 3 through the liquid pipeline 7.

Photovoltaic high voltage direct current establishes ties and is incorporated into the power networks system still includes: a cabinet 9.

The dc-dc converter is placed in the cabinet 9. The cooling device can be placed in the cabinet 9 or outside the cabinet 9, preferably, the condenser 3 is fixed on the top of the cabinet 9, that is, the shell of the condenser 3 is coplanar with the cabinet 9, the condenser 3 adopts circulating cooling water or circulating cooling air for refrigeration, and in practical application, the condenser 3 is a heat exchanger.

according to the invention, the high-voltage AC/DC converter is placed in the first evaporator, the inductor is placed in the insulating cooling medium of the second evaporator and the power semiconductor device is contacted with the outer wall surface of the second evaporator, and when the liquid insulating cooling medium is heated, gasified and converted into the gaseous insulating cooling medium, then the gaseous insulating cooling medium enters the condenser and is condensed into the liquid insulating cooling medium, and then the liquid insulating cooling medium enters the first evaporator and the second evaporator again to cool the high-voltage AC/DC converter, the inductor and the power semiconductor device. In addition, because the insulating cooling liquid has good insulativity, the high-voltage component can be soaked in the insulating cooling liquid, compared with an air cooling mode, the insulating distance can be shortened by more than 8 times, high-density arrangement of heating electric components in a limited space is realized, and the heat dissipation problem caused by high-power-density electric energy conversion can be solved. In addition, the operating pressure of the self-circulation closed system is basically near 0 pascal (Pa), namely the cooling device normally works between 0 Pa and 105Pa, the working pressure is low, vacuumizing is not needed, and the working pressure of a water cooling mode is about more than 0.2 Megapascal (MPA), so that the photovoltaic high-voltage direct-current series grid-connected system is simple in structure and low in cost; the heat generated by a plurality of dispersed heating sources can be transmitted and dissipated in a centralized manner, the operation of the totally-enclosed cabinet body of the high-power converter is realized, and the high-power converter can adapt to the severe humid environment conditions such as deserts, seas, ships and the like. According to the invention, the high-voltage AC-DC converter is placed in the first evaporator, the electric elements of the low-voltage DC-AC converter are placed in the second evaporator, and the high-voltage electric elements and the low-voltage electric elements are separately placed, so that the volume of the first evaporator is reduced, meanwhile, the safety coefficient is improved by the insulating material box bodies of the first evaporator and the second evaporator, the creepage distance is increased by effectively utilizing the insulating property and the corrugated surface of the box bodies, and the voltage-resistant grade is improved. Because electrical components such as IGBT belong to the part of easy damage among them at the converter, so place the electrical components of low pressure DC-AC converter alone, reduce the volume weight of second evaporimeter, and whole dismouting when being convenient for maintain reduces maintenance cost, shortens maintenance cycle, and has shortened the dismantlement time compared with the whole technical scheme of placing of current high low pressure, the cost is reduced.

the principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.