CN206712478U - A kind of distributed photovoltaic power generation grid-connected system - Google Patents

Abstract

The utility model discloses a distributed photovoltaic power generation grid-connected system, which includes a plurality of photovoltaic power generation grid-connected systems. The photovoltaic power generation grid-connected system includes a photovoltaic module string composed of a plurality of series connected photovoltaic The grid-connected system also includes a DC combiner box, a string inverter and an AC distribution box. The photovoltaic module string is connected to the DC combiner box through a DC line, and the string inverter is connected between the DC combiner box and the AC distribution box. , The AC distribution box is connected to the 220-volt or 380-volt power grid through the AC line. The utility model can accurately disconnect the connection with the power grid side, and transfer to the off-grid operation state, and has high safety and reliability, simple structure and strong expansion ability.

Description

A distributed photovoltaic power generation grid-connected system

technical field

The utility model relates to the technical field of photovoltaic power generation grid connection, in particular to a distributed photovoltaic power generation grid connection system.

Background technique

Distributed photovoltaic power plants are mainly used to solve the user's electricity consumption problem nearby, and realize the compensation and delivery of power supply balance through grid connection. Generally, the capacity of a single power plant is small, and it is usually incorporated into the low-voltage distribution network. After the distributed photovoltaic power generation is connected to the distribution network, the current distribution structure of power access to the power grid has been changed. The distribution network has changed from a pure load radiation structure to a multi-port multi-directional power flow structure. The connection and grid connection of a large number of power generation equipment, It is bound to bring safety risks to normal power grid operation, maintenance and overhaul. Most of the existing photovoltaic grid-connected power generation systems have technical problems such as low safety, complex structure, and poor expansion ability.

Utility model content

The technical problem to be solved by the utility model is to provide a distributed photovoltaic power generation grid-connected system, which can accurately disconnect its connection with the grid side and switch to an off-grid operation state, with high safety and reliability. , Simple structure and strong expansion ability.

In order to solve the problems of the technologies described above, the technical solution adopted by the utility model is:

A distributed photovoltaic power generation grid-connected system, including a plurality of photovoltaic power generation grid-connected systems, the photovoltaic power generation grid-connected system includes a photovoltaic module string composed of a plurality of series-connected photovoltaic modules for photovoltaic power generation, the photovoltaic power generation grid-connected system also includes DC combiner box, string inverter and AC distribution box, the photovoltaic module string is connected to the DC combiner box through a DC line, the string inverter is connected between the DC combiner box and the AC distribution box, and the AC distribution box Connect to the 220V or 380V power grid through the AC line; the DC combiner box includes a DC circuit breaker and the first intelligent power distribution device, the DC circuit breaker is connected in series to the input circuit of the DC combiner box, and the first intelligent power distribution device is connected in parallel to the DC combiner box The input circuit of the first intelligent power distribution device is used to monitor the input circuit of the DC combiner box; the AC distribution box includes a metering device, the second intelligent power distribution device and an AC circuit breaker, and the metering device is connected to the input circuit of the AC power distribution box Above, the AC circuit breaker is connected in series to the input circuit of the AC distribution box, the second intelligent power distribution device is connected in parallel to the input circuit of the AC distribution box, and the second intelligent power distribution device is used to monitor the input circuit of the AC distribution box.

Further, when the capacity of the photovoltaic module strings in the grid-connected photovoltaic power generation system is 8 kilowatts or less, the grid-connected photovoltaic power generation system is connected to a 220-volt power grid.

Further, when the capacity of the photovoltaic module string in the grid-connected photovoltaic power generation system is between 8 kW and 400 kW, the grid-connected photovoltaic power generation system is connected to a 380-volt grid.

Further, the number of photovoltaic modules≤the maximum DC input voltage of the string inverter/the preset low-temperature open-circuit voltage of a photovoltaic module under working conditions.

Further, the minimum value of the maximum power tracking voltage of the string inverter / the preset high temperature working voltage of a photovoltaic module under working conditions ≤ the number ≤ the maximum value of the maximum power tracking voltage of the string inverter / A preset low-temperature operating voltage for a PV module under operating conditions.

Further, a lightning protection device is provided inside the DC combiner box.

Further, the input circuit of the DC combiner box is provided with an overcurrent protection device.

Further, the input circuit of the DC combiner box is provided with an anti-backflow protection device.

Further, the output circuit of the DC combiner box is provided with an isolation protection device.

Further, the AC distribution box is provided with a lightning protection device, the input circuit of the AC distribution box is provided with an overcurrent protection device, and the output circuit of the AC distribution box is provided with an isolation protection device.

The beneficial effects of adopting the above technical solution are: the utility model provides a distributed photovoltaic power generation grid-connected system, which can ensure that the distributed photovoltaic power generation system can accurately disconnect from the grid side when a permanent fault occurs on the grid side , into the off-grid operation state, which solves the problem that the distributed photovoltaic power generation system cannot be off-grid and may endanger the safety of distribution network operation and maintenance personnel; at the same time, it can ensure that the distributed photovoltaic power generation The grid status waits for the system to return to normal, which solves the problem that the distributed photovoltaic power generation system is frequently disconnected from the grid when there is a voltage disturbance on the grid side, which affects the distributed photovoltaic power generation. The utility model has the advantages of high safety and reliability, simple structure and strong expandability.

Description of drawings

Fig. 1 is the electrical schematic diagram of the grid-connected system of photovoltaic power generation in the utility model embodiment;

Fig. 2 is a circuit diagram of the grid-connected system of photovoltaic power generation connected to the 220-volt power grid in the embodiment of the utility model;

Fig. 3 is a circuit diagram of a grid-connected photovoltaic power generation system connected to a 380-volt grid in an embodiment of the utility model.

detailed description

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.

As shown in FIG. 1 , it is an embodiment of a distributed photovoltaic power generation grid-connected system of the present invention, which includes multiple photovoltaic power generation grid-connected systems. The photovoltaic power generation grid-connected system includes a photovoltaic module string composed of multiple photovoltaic modules connected in series for photovoltaic power generation. The grid-connected photovoltaic power generation system also includes a DC combiner box, a string inverter and an AC distribution box. The photovoltaic module string is connected to the DC combiner box through a DC line, and the string inverter is connected to the DC combiner box and the AC distribution box Between them, the AC distribution box is connected to the 220V or 380V power grid through the AC line; the DC combiner box includes a DC circuit breaker (QF1) and the first intelligent power distribution device (SPD1), and the DC circuit breaker (QF1) is connected in series to the DC bus The input circuit of the DC combiner box, the first intelligent power distribution device (SPD1) is connected in parallel to the input circuit of the DC combiner box, and the first intelligent power distribution device (SPD1) is used to monitor the input circuit of the DC combiner box; the AC power distribution box includes a metering device ( FM), the second intelligent power distribution device (SPD2) and AC circuit breaker (QF2), the metering device (FM) is connected to the input circuit of the AC distribution box, and the AC circuit breaker (QF2) is connected in series to the input of the AC distribution box circuit, the second intelligent power distribution device (SPD2) is connected in parallel to the input circuit of the AC power distribution box, and the second intelligent power distribution device (SPD2) is used to monitor the input circuit of the AC power distribution box.

After the distributed photovoltaic power generation grid-connected system is connected, the allowable deviation of the supply voltage is:

1) The allowable deviation of the three-phase power supply voltage of 10kV and below is ±7% of the rated voltage.

2) The allowable deviation of 220V single-phase power supply voltage is +7% and -10% of the rated voltage.

To add a photovoltaic power generation grid-connected system to an existing building, a structural and electrical safety review of the building must be carried out to meet the safety requirements of the building structure and electrical.

The photovoltaic power generation grid-connected system installed on the roof of a residential building should be in a position where people may touch or approach, and should be designed with anti-shock warning signs and corresponding electrical safety protection measures.

In the utility model, the string inverter is selected as the grid-connected inverter.

The selection of grid-connected inverters should also follow the following principles:

1. Grid-connected inverters should have automatic operation and stop functions, maximum power tracking control functions and anti-islanding functions;

2. The countercurrent grid-connected inverter should have the function of automatic voltage adjustment;

3. Grid-connected inverters without power frequency isolation transformers should have DC detection function;

4. Grid-connected inverters without isolation transformers should have a DC grounding detection function;

5. The grid-connected inverter should have a grid-connected protection device, and have the same voltage, phase number, phase, frequency and wiring method as the power system;

6. The selection of grid-connected inverters should meet the requirements of high efficiency, energy saving and environmental protection.

In the utility model, the design of the DC circuit should follow the following principles:

1. The withstand voltage level should be 1.25 times higher than the maximum output voltage of the photovoltaic array;

2. The rated current carrying capacity should be higher than the setting value of the short-circuit protection device, and the setting value of the short-circuit protection device should be higher than 1.25 times the nominal short-circuit current of the photovoltaic array;

3. Line loss should be controlled within 2%. The rated capacity of the string inverter should be determined according to the installed capacity of the photovoltaic power generation grid-connected system, and the number of inverters should be determined according to the installed capacity of the photovoltaic power generation grid-connected system and the rated capacity of a single inverter.

Photovoltaic power generation grid-connected systems should be provided with isolating switches between the power supply load and the grid-connected inverter and between the shared grid and the load. The isolating switch should have an obvious disconnection point indication and zero-off function.

An isolation device should be installed between the photovoltaic power grid-connected system and the public grid. The photovoltaic power grid-connected system should be equipped with a low-voltage switch box (cabinet) for grid-connected at the grid-connected place, and should be equipped with special signs and "warning" and "dual power supply" prompt words and symbols.

The grid-connected low-voltage switch box (cabinet) for the grid-connected photovoltaic power generation system shall be equipped with a manual isolating switch and an automatic circuit breaker, and the circuit breaker shall be a mechanical switch with a visible breakpoint; Electronic switches shall not be used.

The isolating switch and circuit breaker between the photovoltaic power generation grid-connected system and the public grid should have the function of breaking zero, and the phase line and neutral line should be able to break and close at the same time.

The isolating switch shall meet the following requirements:

1. The separation distance between disconnected contacts shall be visible or clearly marked with "closed" and "disconnected" states;

2. The isolator should be able to prevent accidental closing;

3. There should be locking measures to prevent accidental disconnection of isolating appliances.

Isolation appliances should use the following appliances:

1. Single-stage or multi-stage isolator, isolating switch or isolating plug;

2. Plugs and sockets;

3. Connecting piece;

4. There is no need to remove the special terminal of the wire;

5. Fuse;

6. Switches and circuit breakers with isolation function.

Photovoltaic power generation grid-connected system should have automatic detection function and grid-connected cut-off protection function, and should meet the following requirements:

1. Photovoltaic power generation grid-connected systems should be installed with grid protection devices, and should comply with the relevant provisions of the current national standard "Photovoltaic (PV) System Grid Interface Characteristics" GB/T20046;

2. When the power quality of the public grid exceeds the limit, the photovoltaic power generation grid-connected system should automatically disconnect from the public grid. Within 5 minutes after the quality of the public grid returns to normal, the photovoltaic power generation grid-connected system must not supply power to the grid.

3. Select miniature or molded case circuit breakers, select the breaking capacity of the equipment according to the level of short-circuit current, and leave a certain margin. The circuit breaker should have the ability to reverse the connection between the power supply end and the load end.

4. When the centralized grid-connected mode is adopted, the circuit breaker at the grid-connected point should have short-circuit instantaneous, long-delay protection functions, shunt tripping, and undervoltage tripping functions. When a short-circuit fault occurs on the line, the line protection can act quickly and instantaneously Trip the circuit breaker to meet the requirements of fast and reliable fault removal when the whole line is faulty. The circuit breaker should also have auxiliary contacts that reflect the operating status of the faulty machine.

220V and 380V voltage levels are not equipped with anti-islanding detection and safety automatic devices, and inverters with anti-islanding capabilities are used. The inverter must have the ability to quickly monitor islands and disconnect from the grid immediately after detecting islands.

The electric energy metering device and communication of photovoltaic power generation grid-connected system shall comply with the following regulations:

1. The grid-connected system of photovoltaic power generation should be configured and installed with special electric energy metering devices on the power generation side and the gateway metering point respectively.

2. The metering device on the power generation side is used to measure all the power generated by the photovoltaic power generation grid-connected system, and the grid will settle and subsidize the electricity fee based on this. Power returned to the grid.

3. The electric energy metering device should use the wireless method to transmit the power generation information to the monitoring center or connect to the existing centralized reading system to realize the remote transmission of electric quantity information.

4. The electric energy metering device shall comply with the relevant provisions of the current national standard "Technical Regulations for the Design of Electrical Measurement and Electric Energy Metering Devices" DL/T 5137 and "Technical Regulations for Electric Energy Metering Devices" DL/T 448.

Further, when the capacity of the photovoltaic module strings in the grid-connected photovoltaic power generation system is 8 kilowatts or less, the grid-connected photovoltaic power generation system is connected to a 220-volt power grid.

Further, when the capacity of the photovoltaic module string in the grid-connected photovoltaic power generation system is between 8 kW and 400 kW, the grid-connected photovoltaic power generation system is connected to a 380-volt grid.

The utility model is suitable for the design of installing a small-capacity household photovoltaic power generation system on the roof of a new or existing residential building. The photovoltaic power generation system operates in the "spontaneous self-use, and the surplus is connected to the Internet", including the following three types:

a) Each user is scattered and grid-connected, and the total installed capacity of a single grid-connected point does not exceed 8kW. 220V single-phase is connected to the user's power supply inlet box. The string inverter should choose a string inverter with AC 220V single-phase output. device, the specific circuit is shown in Figure 2.

b) The centralized grid connection of each user, the total installed capacity of a single grid connection point does not exceed 400kW, and the 380V three-phase is centrally connected to the low-voltage side of the user's distribution transformer. The string inverter should choose the AC 380V three-phase output string inverter Transformer, the specific circuit shown in Figure 3.

c) Some users are connected to the grid in a) and b) ways, and the remaining users are connected to the grid at 10kV.

Further, the number of photovoltaic modules≤the maximum DC input voltage of the string inverter/the preset low-temperature open-circuit voltage of a photovoltaic module under working conditions.

The number of photovoltaic modules satisfies the following formula:

Among them, N is the number of photovoltaic modules,

Kv is the open circuit voltage temperature coefficient of the photovoltaic module,

t is the preset low temperature (°C) under the working conditions of the photovoltaic module,

Voc is the open circuit voltage (V) of the photovoltaic module,

Vdcmax is the maximum DC input voltage (V) of the string inverter.

Further, the minimum value of the maximum power tracking voltage of the string inverter / the preset high temperature working voltage of a photovoltaic module under working conditions ≤ the number ≤ the maximum value of the maximum power tracking voltage of the string inverter / A preset low-temperature operating voltage for a PV module under operating conditions.

The number of photovoltaic modules satisfies the following formula:

Among them, Kv' is the operating voltage temperature coefficient of the photovoltaic module,

t’ is the preset high temperature (°C) under the working conditions of the photovoltaic module,

Vpm is the operating voltage of the photovoltaic module (V),

Vmpptmax is the maximum power tracking voltage maximum value (V) of the string inverter,

Vmpptmin is the minimum value (V) of the maximum power tracking electric voltage of the string inverter.

According to the rated DC voltage of the string inverter, the maximum power tracking control range, the maximum output operating voltage of the photovoltaic module and its temperature coefficient, determine the number of photovoltaic modules connected in series, and the maximum open circuit voltage of the photovoltaic module string under the local extreme temperature It should be lower than the design voltage of the DC side of the string inverter, and the variation range of the maximum power working voltage of the photovoltaic module string should be within the maximum power tracking voltage range of the string inverter.

Further, a lightning protection device is provided inside the DC combiner box.

Further, the input circuit of the DC combiner box is provided with an overcurrent protection device.

Further, the input circuit of the DC combiner box is provided with an anti-backflow protection device.

Further, the output circuit of the DC combiner box is provided with an isolation protection device.

Further, the AC distribution box is provided with a lightning protection device, the input circuit of the AC distribution box is provided with an overcurrent protection device, and the output circuit of the AC distribution box is provided with an isolation protection device.

The following is a further description of the above-mentioned distributed photovoltaic power generation grid-connected system combined with the working principle: the DC current generated by the photovoltaic module string enters the DC combiner box through the DC line, and the DC combiner box monitors, controls and protects the DC current. The DC current output by the box is converted into AC current by the string inverter and sent to the AC distribution box. The AC distribution box monitors, controls and protects the AC current, and the AC current output by the AC distribution box is sent into the power grid.

Claims (10)

1. A distributed photovoltaic power generation grid-connected system, comprising a plurality of photovoltaic power generation grid-connected systems, said photovoltaic power generation grid-connected system comprising a photovoltaic module string composed of a plurality of series-connected photovoltaic modules for photovoltaic power generation, characterized in that : The photovoltaic power generation grid-connected system also includes a DC combiner box, a string inverter and an AC distribution box, the photovoltaic module string is connected to the DC combiner box through a DC line, and the string inverter is connected to the DC combiner box. Between the DC combiner box and the AC distribution box, the AC distribution box is connected to a 220-volt or 380-volt power grid through an AC line; the DC combiner box includes a DC circuit breaker (QF1) and a first intelligent A power distribution device (SPD1), the DC circuit breaker (QF1) is connected in series to the input circuit of the DC combiner box, the first intelligent power distribution device (SPD1) is connected in parallel to the input circuit of the DC combiner box, the The first intelligent power distribution device (SPD1) is used to monitor the input circuit of the DC combiner box; the AC power distribution box includes a metering device (FM), a second intelligent power distribution device (SPD2) and an AC circuit breaker (QF2) , the metering device (FM) is connected to the input circuit of the AC distribution box, the AC circuit breaker (QF2) is connected in series to the input circuit of the AC distribution box, and the second intelligent power distribution device ( SPD2) is connected in parallel to the input circuit of the AC distribution box, and the second intelligent power distribution device (SPD2) is used to monitor the input circuit of the AC distribution box. 2. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: when the capacity of the photovoltaic module string in the photovoltaic power generation grid-connected system is 8 kW or less, the photovoltaic power generation grid-connected The system is connected to the 220-volt grid. 3. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: when the capacity of the photovoltaic module string in the photovoltaic power generation grid-connected system is between 8 kW and 400 kW, the photovoltaic The grid-connected power generation system is connected to the 380-volt grid. 4. A distributed photovoltaic power generation grid-connected system according to any one of claims 1 to 3, characterized in that: the number of the photovoltaic modules ≤ the maximum DC input voltage of the string inverter/ A preset low-temperature open-circuit voltage of the photovoltaic module under working conditions. 5. A distributed photovoltaic power generation grid-connected system according to claim 4, characterized in that: the minimum value of the maximum power tracking voltage of the string inverter/the minimum value of a photovoltaic module under working conditions The preset high-temperature working voltage≤the number≤the maximum value of the maximum power tracking voltage of the string inverter/the preset low-temperature working voltage of one photovoltaic module under working conditions. 6. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: said DC combiner box is provided with a lightning protection device. 7. A distributed photovoltaic power grid-connected system according to claim 1, characterized in that: the input circuit of the DC combiner box is provided with an overcurrent protection device. 8. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: the input circuit of the DC combiner box is provided with an anti-backflow protection device. 9. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: the output circuit of the DC combiner box is provided with an isolation protection device. 10. A distributed photovoltaic power generation grid-connected system according to claim 1, characterized in that: the AC distribution box is provided with a lightning protection device, and the input circuit of the AC distribution box is provided with an overcurrent Protection device, the output circuit of the AC distribution box is provided with an isolation protection device.