CN110582186A - A liquid-cooled photovoltaic high-voltage DC series grid-connected system - Google Patents

Abstract

The invention discloses a liquid cooling type photovoltaic high-voltage direct current series grid-connected system, which comprises a DC-DC converter and a cooling device, wherein the cooling device comprises a first cooling device and a second cooling device; the DC-DC converter comprises a low-voltage DC-AC converter, a high-frequency transformer and a high-voltage AC-DC converter; the output end of the low-voltage DC-AC converter is connected with the input end of the high-frequency transformer, and the output end of the high-frequency transformer is connected with the input end of the high-voltage AC-DC converter; the cooling device comprises a condenser, an evaporator, a gas pipeline, a liquid pipeline and insulating cooling liquid; the low-voltage DC-AC converter comprises an inductor, the evaporator is filled with insulating cooling liquid, and the inductor, the high-frequency transformer and the high-voltage AC-DC converter are immersed in the insulating cooling liquid; the condenser is arranged above the evaporator, the air outlet joint of the evaporator is connected with the air inlet joint of the condenser through a gas pipeline, and the liquid outlet joint of the condenser is connected with the liquid inlet joint of the evaporator through a liquid pipeline. The invention enables the high-voltage component to be soaked in the insulating cooling liquid, improves the deployment density of the heating electric component and simultaneously improves the heat dissipation efficiency of the heating electric component.

Description

A liquid-cooled photovoltaic high-voltage DC series grid-connected system

technical field

The invention relates to the technical field of grid-connected photovoltaic power generation systems, in particular to a liquid-cooled photovoltaic high-voltage DC series grid-connected system.

Background technique

With the rapid development of high-voltage direct current transmission network construction and high-voltage direct current distribution network, direct current grid-connected DC-DC converter is an effective means to solve large-capacity long-distance transmission of electric energy and large-scale renewable energy collection, which can make full use of HVDC transmission lines Corridors realize the complementarity between multiple energy forms and multiple user types.

At present, the common grid-connected form of photovoltaic power generation system is mainly integrated into the AC grid. Domestic flexible direct current and traditional direct current transmission are developing rapidly, and there are more and more demonstration projects. Photovoltaic power generation must have the ability to be connected to the high-voltage direct current transmission network. A general photovoltaic high-voltage DC series grid-connected system includes a DC-DC converter, and the DC-DC converter includes a low-voltage DC-AC conversion device, a high-frequency transformer, and a high-voltage AC-DC conversion device. Existing low-voltage DC-AC converters include: low-voltage capacitors, IGBTs, inductors, and other components; existing high-voltage AC-DC converters include: high-voltage capacitors, silicon stacks, and other devices that implement AC-DC conversion functions.

The output voltage of common photovoltaic DC converters is low, and it is difficult to step up to a very high voltage at one time. In order to realize the output of photovoltaic system into the high-voltage DC grid, it is generally adopted to connect multiple photovoltaic DC converters to independent photovoltaic modules. The way of outputting in series increases the output voltage of the system, so as to achieve the purpose of outputting higher DC voltage and connecting to the high-voltage DC grid. The output of the converter is connected to the DC transmission lines above ±10KV, ±30KV, and ±300KV. The boost ratio is as high as 20-600 times. However, the high and low voltages of the entire system are in the same cabinet. Improving equipment power density and higher withstand voltage levels are a pair of contradictions, which brings great difficulties to structural design.

Since the high-power converter has a large heat loss during operation, a cooling system must be equipped to ensure a good operating environment for the converter. At present, the most commonly used cooling technology for converters is air cooling or water cooling. The air cooling method has a simple structure, but the cooling efficiency is low, the volume and noise are large, and it is suitable for low-power equipment. It has been difficult to meet the technical development requirements of more than MW. Water cooling It can meet the current cooling requirements, but the water cooling technology adopts the forced water circulation structure, the cooling medium must be deionized water and must be equipped with circulation pumps, expansion valves, water deionization treatment equipment, etc. Even for a cabinet of hundreds of kilograms, the cost increases due to the larger volume and weight. Moreover, once water leaks, running on high-voltage equipment will bring potential safety hazards. Therefore, the development and selection of new high-efficiency heat dissipation technology to cool the converter equipment is an important measure to ensure the reliability of the device and improve the power volume density.

At the same time, the equipment belongs to high-voltage equipment, and the insulation withstand voltage strength must reach the level above ±10KV, ±30KV, and ±300KV. When the insulation thickness and insulation spacing are large enough, it will affect the miniaturization of the equipment and the heat dissipation design, which brings certain difficulties to the equipment structure design. At present, the insulation of high-voltage components in conventional converters is air-insulated, and the general air compressive strength is 2.5KV/mm. Among them, the main high-voltage components, high-frequency and high-voltage transformers, are dry-type or oil-immersed. The oil-immersed type is relatively viscous and easy to leak, which leads to the accumulation of dirt around the equipment, causing discharge breakdown and affecting the safety of the equipment, and it is necessary to replace the oil value regularly, and the maintenance workload is heavy. The dry-type transformer has a large volume, which is 4-5 times that of the oil cooler, which is not conducive to the miniaturization of the equipment.

Contents of the invention

The purpose of the present invention is to provide a liquid-cooled photovoltaic high-voltage DC series grid-connected system, which allows high-voltage components to be immersed in insulating cooling liquid, increases the deployment density of heat-generating electrical components, and improves the heat dissipation efficiency of heat-generating electrical components.

To achieve the above object, the present invention provides the following scheme:

A liquid-cooled photovoltaic high-voltage DC series grid-connected system, characterized in that the system includes a DC-DC converter and a cooling device; the DC-DC converter includes a low-voltage DC-AC converter, a high-frequency transformer and a high-voltage AC-DC converter;

The output end of the low-voltage DC-AC converter is connected to the input end of the high-frequency transformer, and the output end of the high-frequency transformer is connected to the input end of the high-voltage AC-DC converter;

The cooling device includes a condenser, an evaporator, a gas pipeline, a liquid pipeline, and an insulating cooling liquid; the low-voltage DC-AC converter includes an inductor, and the evaporator is filled with the insulating cooling liquid, and the inductor, The high-frequency transformer and the high-voltage AC-DC converter are immersed in the insulating cooling liquid;

The condenser is placed above the evaporator, the gas outlet joint of the evaporator is connected to the inlet joint of the condenser through the gas pipeline, and the liquid outlet joint of the condenser is connected through the liquid pipeline Connected to the liquid inlet joint of the evaporator.

Optionally, the low-voltage DC-AC converter further includes a power semiconductor device, and the power semiconductor device is in contact with the outer wall of the evaporator.

Optionally, the low-voltage DC-AC converter is immersed in the insulating cooling liquid of the evaporator.

Optionally, the insulating cooling liquid is fluorocarbon.

Optionally, the condenser also includes a pressure transmitter and an exhaust joint, the pressure transmitter is used to detect the pressure of the condenser, the exhaust joint is connected to a valve, and when the pressure reaches a set value , exhaust air through the exhaust joint.

Optionally, the evaporator is a sealed box, the bottom and side surfaces of the evaporator are made of metal materials, the top surface of the evaporator is made of insulating material, and there are two high-voltage lead joints on the top surface, and the high-voltage The lead joint is sealed and connected to the high-voltage lead sleeve, and the high-voltage lead wire at the output end of the DC-DC converter is inserted into the high-voltage lead sleeve through the high-voltage lead joint, and the high-voltage lead sleeve is filled with the insulating cooling liquid .

Optionally, the condenser includes at least one inlet joint and at least one liquid outlet joint, and the inlet joint is located above the liquid outlet joint.

Optionally, the evaporator includes at least one gas outlet joint and at least one liquid inlet joint, and the gas outlet joint is located above the liquid inlet joint.

Optionally, the system further includes a cabinet, and the DC-DC converter and the evaporator are placed in the cabinet.

Optionally, the condenser is refrigerated by circulating cooling water or circulating cold air.

According to the content of the invention provided by the present invention, the present invention discloses the following technical effects: The present invention provides a liquid-cooled photovoltaic high-voltage DC series grid-connected system, including a DC-DC converter and a cooling device, and the low-voltage DC-AC converter The high-voltage inductors, high-frequency transformers and high-voltage AC-DC converters are immersed in the insulating cooling liquid in the evaporator. The high-voltage components are insulated by the insulating cooling liquid, which shortens the insulation distance compared with air, and increases the deployment density of heating electrical components. Moreover, the insulating cooling liquid absorbs the heat of the electrical components and dissipates heat through the evaporator and the condenser, which can centrally transmit and dissipate the heat generated by the scattered heat sources, and improve the heat dissipation efficiency of the heat-generating electrical components.

Description of drawings

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

Fig. 1 is a schematic diagram of the front view of a liquid-cooled photovoltaic high-voltage DC series grid-connected system according to an embodiment of the present invention;

Fig. 2 is a schematic side structure diagram of a liquid-cooled photovoltaic high-voltage DC series grid-connected system according to an embodiment of the present invention;

Fig. 3 is a detailed structural diagram of a DC-DC converter in a liquid-cooled photovoltaic high-voltage DC series grid-connected system according to an embodiment of the present invention;

Description of reference signs: 1-cabinet, 2-condenser, 3-DC-DC converter, 4-gas pipeline, 5-liquid pipeline, 6-high voltage lead bushing, 7-cooling liquid, 21-pressure transformer Transmitter, 22-exhaust valve, 23-intake connector, 24-liquid outlet connector, 31-high frequency transformer, 32-high voltage capacitor, 33-silicon stack, 34-inductor, 35-power semiconductor device, 36-evaporation Device, 41-gas outlet connector, 51-liquid inlet connector, 61-high voltage lead wire connector.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The purpose of the present invention is to provide a liquid-cooled photovoltaic high-voltage DC series grid-connected system, which allows high-voltage components to be immersed in insulating cooling liquid, increases the deployment density of heat-generating electrical components, and improves the heat dissipation efficiency of heat-generating electrical components.

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figures 1-3, the present invention discloses a liquid-cooled photovoltaic high-voltage DC series grid-connected system, including a cabinet 1, a DC-DC converter 3 and a cooling device; the DC-DC converter 3 includes a low-voltage DC-AC converters, high frequency transformers and high voltage AC-DC converters.

The output end of the low-voltage DC-AC converter is connected to the input end of the high-frequency transformer, and the output end of the high-frequency transformer is connected to the input end of the high-voltage AC-DC converter.

Low-voltage DC-AC converters include: low-voltage capacitors, power semiconductor devices, inductors and other components. The high-voltage AC-DC converter includes: a high-voltage capacitor 32 , a silicon stack 33 and other devices that realize the AC-DC conversion function.

The cooling device includes a condenser 2, an evaporator 36, a gas pipeline 4, a liquid pipeline 5 and an insulating cooling liquid 7; the evaporator 36 is filled with the insulating cooling liquid 7, and the inductor 34, a high-frequency transformer and a high-voltage AC-DC converter are immersed In the insulating cooling liquid 7, due to the insulating properties of the insulating cooling liquid 7, the insulating cooling liquid 7 has a compressive strength of 22KV/mm, so that the components with dots can be placed in the insulating cooling liquid 7, and the high-voltage devices in a limited space can be densely packed Arrangement, the insulating cooling liquid 7 can play a cooling role at the same time; other low-voltage DC-AC conversion devices except the inductor 34 are placed on the outer wall of the evaporator 36, and the feature is that the power semiconductor device 35 must be in close contact with the outer wall of the evaporator 36, which is convenient for the power semiconductor The heat exchange between the device 35 and the insulating coolant in the evaporator 36 reduces the operating temperature of the power semiconductor device 35, which is a high-heating component, improves reliability and facilitates the maintenance of vulnerable parts. The power semiconductor device 35 is an insulated gate bipolar type Transistor (Insulated Gate Bipolar Transistor IGBT); Another solution is to place all the low-voltage DC-AC converter, high-frequency transformer and high-voltage AC-DC converter in the evaporator 36, which has a better heat dissipation effect and is easy to realize DC- Modular design of DC converter.

The condenser 2 is placed above the evaporator 36. The purpose of the condenser 2 being higher than the evaporator 36 is to prevent the gas from rising into the condenser 2 and entraining too much liquid to affect the condensation efficiency. The gas outlet joint 41 of the evaporator 36 is connected to the inlet joint 23 of the condenser 2 through the gas pipeline 4, and the liquid outlet joint 24 of the condenser 2 is connected to the liquid inlet joint 51 of the evaporator 36 through the liquid pipeline 5, forming a closed circuit , the circuit is filled with insulating coolant 7 with a low boiling point. When the AC-DC conversion operation is realized, the heat generated by the inductor 34, the high-frequency transformer and the high-voltage AC-DC converter is transferred to the insulating cooling liquid 7, and the insulating cooling liquid 7 absorbs heat and gasifies, relying on the principle of gravity difference between gas and liquid, gasification is generated The gas enters the condenser 2 along the gas pipeline 4 and condenses into a liquid, and then the liquid flows back to the evaporator 36 along the liquid pipeline 5 to achieve the purpose of heat dissipation, and the cycle is repeated, realizing the self-circulation process of the insulating cooling liquid , while reducing noise and cost.

The insulating coolant 7 is a fluorocarbon compound with good insulation and a compressive strength of 22KV/mm. The boiling point at a standard atmospheric pressure is 40-55°C, the volume resistivity is greater than 10 ⁷ Ωm, the fluidity is very good, and the viscosity is 0.4-0.7 mm ² /s, no flash point, inductors, transformers, etc. are directly immersed in liquid, the live parts of electrical components are in direct contact with the liquid, and the cooling liquid directly absorbs the heat generated by electrical components such as inductors, transformers, etc. Cooling effect, compared with the water cooling method, no deionization treatment equipment is required, which makes the system structure simple, compared with the air cooling method, the power density is greatly improved, the integrated design is safe, and the heat dissipation effect is good, and the temperature of the heating surface of the device immersed in it can be controlled below 65 °C .

The evaporator 36 is a sealed box, the bottom and side surfaces of the evaporator 36 are metal materials or insulating materials, the top surface of the evaporator 36 is an insulating material, and there are two high-voltage lead joints 61 with a sealing structure on the top surface. 61 is sealed and connected to the high-voltage lead sleeve 6, the high-voltage lead wire at the output end of the DC-DC converter 3 is inserted into the high-voltage lead sleeve 6 through the high-voltage lead joint, and the two ends of the high-voltage lead wire are sealed and connected to the top surface of the evaporator 36, Utilize the lead joint structure to connect the high-voltage lead bushing 6 with the evaporator 36. The high-voltage lead bushing 6 is filled with an insulating cooling liquid medium 7 for insulation. Since it is sealed externally and does not contact with air, there is no air passage between the evaporators 36. , Effectively shorten the insulation distance between the equipment, so that the high-voltage lead wire connector 61 in the limited space and the evaporator 36 box insulation withstand voltage strength can reach more than 20KV, so that the volume of the equipment cabinet is greatly reduced. The evaporator 36 is made of metal box material. The first purpose is to ensure the strength of the entire equipment. Since the high and low voltage DC-DC conversion devices and transformers and the modular design of the liquid medium are relatively heavy in weight, more than 150KG, the strength of the insulating material under the same thickness cannot be achieved. Another purpose is that the evaporator 36 can be used as the ground of the entire cabinet system by using the metal box material, and multiple DC-DC converters can be densely arranged to increase the power density of the system.

The condenser 2 is a rectangular or cylindrical hollow body made of metal materials such as stainless steel or aluminum alloy. The condenser 2 includes at least one inlet joint 23 and at least one outlet joint 24. The inlet joint 23 is located at the outlet joint 24. above. The condenser 2 also includes a pressure transmitter 21 and 2 exhaust joints, each exhaust joint is provided with an exhaust valve 22, wherein one exhaust valve 22 is used for means exhaust, and the other exhaust valve 22 is used for Automatic exhaust, the pressure transmitter 21 is used to detect the pressure of the condenser 2, when the pressure reaches the set value, exhaust through the exhaust valve 22 on the exhaust joint, so that the condenser can be kept at a lower pressure to improve the operation system security.

At least one gas outlet connector 41 on the upper part of the evaporator 36 communicates with the gas pipeline 4, and at least one liquid inlet connector 51 on the lower part of the evaporator 36 communicates with the liquid pipeline. Return to the evaporator 36 without forming a gas block.

The DC-DC converter 3 and the evaporator 36 are placed in the cabinet 1, and the DC-DC converter 3 and the evaporator 36 correspond one by one, and multiple sets of DC-DC converters 3 and the evaporator 36 can share one condenser 2, one Set of gas management 4 and liquid pipeline 5. The condenser 2 can be placed in the cabinet 1 or outside the cabinet 1 .

The condenser 2 is preferably integrated with the top of the cabinet 1, that is, the shell of the condenser 2 is in the same plane as the cabinet 1, and the condenser 2 is cooled by circulating cooling water or circulating cold air.

The invention provides a liquid-cooled photovoltaic high-voltage DC series grid-connected system, which uses the principle of liquid-gas phase transformation heat to form a self-circulating closed structure, without the need for auxiliary processing equipment such as pumps; the cooling liquid is an insulating cooling liquid, due to the good medium High-voltage components can be immersed in liquid, and the insulation distance is shortened by more than 8 times compared with air, which realizes the high-density deployment of heating electrical components in a limited space, and solves the heat dissipation problem caused by high-power-density electric energy conversion; The operating pressure of the circulating airtight structure is basically around 0Pa, that is, the normal operation of the cooling device is between 0 and 105Pa, the working pressure is relatively low, and no vacuuming is required, while the working pressure of the water cooling method is about 0.2MPA or above, which makes the system simple in structure and low in cost. In addition, the heat generated by many scattered heat sources is transmitted and dissipated in a concentrated manner, realizing the operation of a fully enclosed cabinet of a high-power converter, and adapting to humid and harsh environmental conditions such as deserts, seas, and ships.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; meanwhile, for those of ordinary skill in the art, according to the present invention Thoughts, there will be changes in specific implementation methods and application ranges. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. A liquid-cooled photovoltaic high-voltage DC series grid-connected system, characterized in that the system includes a DC-DC converter and a cooling device; the DC-DC converter includes a low-voltage DC-AC converter and a high-frequency transformer and high voltage AC-DC converters; The output end of the low-voltage DC-AC converter is connected to the input end of the high-frequency transformer, and the output end of the high-frequency transformer is connected to the input end of the high-voltage AC-DC converter; The cooling device includes a condenser, an evaporator, a gas pipeline, a liquid pipeline, and an insulating cooling liquid; the low-voltage DC-AC converter includes an inductor, and the evaporator is filled with the insulating cooling liquid, and the inductor, The high-frequency transformer and the high-voltage AC-DC converter are immersed in the insulating cooling liquid; The condenser is placed above the evaporator, the gas outlet joint of the evaporator is connected to the inlet joint of the condenser through the gas pipeline, and the liquid outlet joint of the condenser is connected through the liquid pipeline Connected to the liquid inlet joint of the evaporator. 2. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the low-voltage DC-AC converter also includes a power semiconductor device, and the power semiconductor device is connected to the outer wall of the evaporator touch. 3. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the low-voltage DC-AC converter is immersed in the insulating cooling liquid of the evaporator. 4. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the insulating cooling liquid is a fluorocarbon compound. 5. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the condenser further includes a pressure transmitter and an exhaust joint, and the pressure transmitter is used to detect the condensation When the pressure reaches the set value, the exhaust will be exhausted through the exhaust joint. 6. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the evaporator is a sealed box, the bottom and side surfaces of the evaporator are made of metal materials, and the top of the evaporator is The surface is made of insulating material, and there are two high-voltage lead joints on the top surface, and the high-voltage lead joints are sealed and connected with the high-voltage lead bushings, and the high-voltage lead wires at the output end of the DC-DC converter are inserted into the high-voltage lead joints through the high-voltage lead joints. In the high-voltage lead bushing, the high-voltage lead bush is filled with the insulating cooling liquid. 7. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the condenser includes at least one inlet joint and at least one outlet joint, and the inlet joint Located above the liquid outlet joint. 8. The liquid-cooled photovoltaic high-voltage DC series grid-connected system according to claim 1, wherein the evaporator includes at least one gas outlet joint and at least one liquid inlet joint, and the gas outlet joint is located at the above the inlet connector. 9. The liquid-cooled photovoltaic high voltage DC series grid-connected system according to claim 1, wherein the system further comprises a cabinet, and the DC-DC converter and the evaporator are placed in the cabinet. 10. The liquid-cooled photovoltaic HVDC series grid-connected system according to claim 1, wherein the condenser is cooled by circulating cooling water or circulating cold air.